Abstract:
Provided are an agitation device, a melting apparatus, and a melting method which achieve good melting efficiency without contaminating molten metal. The agitation device is provided with a traveling magnetic field generating unit which is disposed outside a charging tank for storing molten metal and generates, inside the charging tank, a magnetic field that travels downward along the rear sidewall of the charging tank, whereby a flow of the molten metal that rotates longitudinally about an axis approximately parallel to the surface of the molten metal is produced in the molten metal. By charging aluminum cutting chips into the molten metal in which the flow is produced, the aluminum cutting chips move with the flow of the molten metal, get into the molten metal roughly in the position where a downward flow of the molten metal is produced, and are immersed in the molten metal, and thus the melting of the aluminum cutting chips is accelerated.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to an agitation device in which a melted matter (for example, cutting chips of nonferrous metal such as aluminum or magnesium) is introduced to molten metal and the molten metal is agitated, a melting apparatus having such agitation device, and a melting method in which a melted matter is introduced to molten metal and the molten metal is agitated so as to melt the melted matter. 
       BACKGROUND ART  
       [0002]    There are conventional arts as methods for melting cutting chips of nonferrous metal such as aluminum or magnesium by introducing them to molten metal and agitating the molten metal: (1) a method in which the cutting chips floating on the liquid surface of the molten metal are pushed with an implement such as a stick so as to soak them compulsorily to the molten metal; and (2) a method in which a propeller agitator is inserted into the molten metal through the liquid surface of the molten metal so as to agitate the molten metal. 
         [0003]    However, in the methods (1) and (2), the implement and a propeller touch the molten metal with high temperature, whereby the implement and the propeller are worn. Therefore, it is necessary to exchange the implement and the propeller frequently, whereby the maintenance is troublesome. 
         [0004]    In the methods (1) and (2), components of the broken implement or propeller may be mixed with the molten metal, thereby reducing the quality of the molten metal (the components may pollute the molten metal). 
         [0005]    In addition to the above-mentioned methods, as a method in which cutting chips of aluminum are introduced to molten metal and the molten metal is agitated so as to melt the cutting chips, methods described in the Patent Literatures 1, 2 and 3 are known. 
         [0006]    In the methods described in the Patent Literatures 1, 2 and 3, an inner space of a reverberatory furnace is partitioned into four chambers, a melting chamber, an open well part, a vortex generating chamber and a molten metal passage and these parts are communicated with each other so as to form a circulating passage of molten metal. An electromagnetic agitator constructed by an induction coil is arranged at the bottom of the molten metal passage and electromagnetic force is made act on the molten metal in the molten metal passage so as to circulate the molten metal in the molten metal passage, the melting chamber, the open well part, the vortex generating chamber, the molten metal passage, . . . in this order. 
         [0007]    An opening (orifice) is formed at the bottom of the vortex generating chamber and the vortex generating chamber is communicated with the molten metal passage through this opening. When molten metal moving from the vortex generating chamber to the molten metal passage passes through the opening, a vortex is generated in the liquid surface of the molten metal in the vortex generating chamber. The aluminium metal cutting chips are rolled up by the vortex so as to melt the aluminium metal cutting chips. 
         [0008]    However, in the methods described in the Patent Literatures 1, 2 and 3, the electromagnetic agitator generates electromagnetic force enough large for circulating the whole molten metal in the reverberatory furnace, whereby it is necessary to supply large electric power to the electromagnetic agitator. 
         [0009]    Generally, when the aluminium metal cutting chips are introduced to the vortex generated in the liquid surface, the aluminium metal cutting chips float on the liquid surface of the molten metal and are not rolled up by the molten metal successfully, whereby the cutting chips are hardly melted. 
         [0010]    Especially, the aluminium metal cutting chip has large surface area and the surface thereof is formed therein with an oxide layer having high melting point by temperature rise, whereby the aluminium metal cutting chip can hardly be melted. When the aluminium metal cutting chips float and retain in the liquid surface of the molten metal, the oxidization (combustion) of the aluminium metal cutting chips is advanced, in its turn yield of recycling by melting the aluminium metal cutting chips is reduced. 
         [0011]    In the methods described in the Patent Literatures 1, 2 and 3, the molten metal moves to the molten metal passage passes through the opening formed in the bottom of the vortex generating chamber, whereby the aluminium metal cutting chips can finally be rolled up by the molten metal compulsorily. However, for generating strong vortex, it is necessary to make the sectional area of the opening of the bottom of the vortex generating chamber small to some degree. When a large quantity of the aluminium metal cutting chips are introduced to the molten metal at once, the unmelted aluminium metal cutting chips rush in the opening and clog the opening. Therefore, the processing speed (melting amount per unit time) of the aluminium metal cutting chips cannot be made very large. 
       Citation List 
     Patent Literature 
       [0012]    [PTL 1] JP 2-179834 A 
         [0013]    [PTL 2] JP 2-219978 A 
         [0014]    [PTL 3] JP 2-232323 A 
       SUMMARY OF INVENTION  
     Technical Problem 
       [0015]    The present invention is provided in consideration of the above-mentioned conditions so as to provide an agitation device, a melting apparatus and z melting method each of which does not pollute molten metal and has high melting efficiency. 
       Solution to Problem 
       [0016]    The above-mentioned problems are solved by the following solutions according to the present invention. 
         [0017]    An agitation device according to the first aspect of the present invention, which agitates molten metal to which a melted matter is introduced so as to promote melting of the melted matter, comprises a traveling magnetic field generating unit which is arranged outside a melting tank in which the molten metal is stored and generates a first magnetic field traveling downward along a sidewall of the melting tank. 
         [0018]    In the embodiment of the present invention, preferably, the traveling magnetic field generating unit generates a second magnetic field traveling upward along the sidewall of the melting tank in the melting tank at a position spaced at a predetermined distance away from the first magnetic field. 
         [0019]    In the preferable embodiment of the present invention, the traveling magnetic field generating unit comprises a permanent magnet facing the sidewall of the melting tank, a support member supporting the permanent magnet, and a motor rotatively driving the support member. 
         [0020]    Furthermore, preferably, the motor comprises a rotational shaft arranged at a predetermined distance below a liquid surface of the molten metal. 
         [0021]    In another embodiment of the present invention, preferably, the traveling magnetic field generating unit comprises a liquid surface position detection device detecting the position of the liquid surface of the molten metal, a vertical moving device vertically movably supporting the motor, and a controller transmitting a signal to the vertical moving device for moving vertically the motor on the basis of the position of the liquid surface of the molten metal detected by the liquid surface position detection device so as to control the relative position of the motor about the liquid surface of the molten metal in the vertical direction. 
         [0022]    Furthermore, preferably, the controller transmits a signal to the vertical moving device for moving vertically the motor so as to hold the position of the rotational shaft of the motor lower than the liquid surface of the molten metal for a predetermined distance. 
         [0023]    In another embodiment of the present invention, preferably, the traveling magnetic field generating unit comprises a plurality of electromagnetic coils arranged along the sidewall of the melting tank, and an electric power supply device supplying electric power to the electromagnetic coils in order. 
         [0024]    Preferably, the embodiment of the present invention comprises a first molten metal straightening member is provided which is arranged in the melting tank at a corresponding position to the first magnetic field traveling downward along the sidewall of the melting tank, and has a first molten metal straightening surface perpendicular to the sidewall of the melting tank and the horizontal plane. 
         [0025]    Especially, preferably, the first molten metal straightening surface comprises a recess at the center thereof. 
         [0026]    The preferable embodiment of the present invention comprises a second molten metal straightening member which is arranged in the melting tank positioned at the opposite side to the traveling magnetic field generating unit through the sidewall of the melting tank, and has a second molten metal straightening surface in parallel to the sidewall of the melting tank. 
         [0027]    A melting apparatus according to the second aspect of the present invention for melting a melted matter by introducing the melted matter to molten metal stored in a melting tank comprises the agitation device according to the first aspect of the present invention. 
         [0028]    A melting method according to the third aspect of the present invention comprises an introducing process in which a melted matter is introduced to molten metal stored in a melting tank, and an agitating process in which a first magnetic field traveling downward along the sidewall of the melting tank is generated in the melting tank so as to agitate the molten metal. 
         [0029]    In the embodiment of the present invention, preferably, in the agitating process, a second magnetic field is generated which travels upward along the sidewall of the melting tank in the melting tank spaced at a position away from the first magnetic field. 
         [0030]    In the preferable embodiment of the present invention, the agitating process further comprises, a process of preparing a traveling magnetic field generating unit arranged outside the melting tank which comprises a permanent magnet facing the sidewall of the melting tank, a support member supporting the permanent magnet, and a motor rotatively driving the support member, and a process of generating the first magnetic field traveling downward along the sidewall of the melting tank. 
         [0031]    In another embodiment of the present invention, preferably, the agitating process further comprises a process of preparing a traveling magnetic field generating unit arranged outside the melting tank which comprises a plurality of electromagnetic coils arranged along the sidewall of the melting tank, and an electric power supply device supplying electric power to the electromagnetic coils in order, and a process of generating the first magnetic field traveling downward along the sidewall of the melting tank. 
         [0032]    In the embodiment of the present invention, preferably, the agitating process further comprises a process of arranging a first molten metal straightening member in the melting tank at a corresponding position to the first magnetic field traveling downward along the sidewall of the melting tank, the first molten metal straightening member including a first molten metal straightening surface perpendicular to the sidewall of the melting tank and the horizontal plane. 
         [0033]    Furthermore, preferably, the first molten metal straightening surface comprises a recess at the center thereof. 
         [0034]    In the embodiment of the present invention, preferably, the agitating process further comprises a process of arranging a second molten metal straightening member in the melting tank, positioned at the opposite side to the traveling magnetic field generating unit through the sidewall of the melting tank, the second molten metal straightening member including a second molten metal straightening surface in parallel to the sidewall of the melting tank. 
         [0035]    An agitation device according to the fourth aspect of the present invention for melting a melted matter by introducing the melted matter to molten metal stored in a melting tank, comprises a traveling magnetic field generating unit which is arranged outside a melting tank in which the molten metal is stored and generates a magnetic field traveling downward along a sidewall of the melting tank, and an introduced/suspended matter partition member arranged inside the melting tank and dividing a space inside the melting tank into two spaces communicated with each other at lower portions thereof, wherein one of the two spaces divided by the introduced/suspended matter partition member closer to the traveling magnetic field generating unit is employed as a charging/melting chamber which is a space for introducing the melted matter to the molten metal in the melting tank, and the other one of the two spaces divided by the introduced/suspended matter partition member further from the traveling magnetic field generating unit is employed as a suspended matter recovery chamber which is a space for recovering a suspended matter generated by melting of the melted matter. 
         [0036]    Preferably, the embodiment of the present invention further comprises a suspended matter/molten metal partition member arranged inside the melting tank and dividing a part further from the traveling magnetic field generating unit than the introduced/suspended matter partition member in the space inside the melting tank into two spaces communicated with each other at lower portions thereof, wherein one of the two spaces divided by the suspended matter/molten metal partition member closer to the traveling magnetic field generating unit is employed as the suspended matter recovery chamber, and the other one of the two spaces divided by the suspended matter/molten metal partition member further from the traveling magnetic field generating unit is employed as a molten metal recovery chamber which is a space for recovering the molten metal from the melting chamber. 
         [0037]    A melting apparatus according to the fifth aspect of the present invention for melting a melted matter by introducing the melted matter to molten metal stored in a melting chamber comprises the agitation device according to the fourth aspect of the present invention. 
         [0038]    A melting apparatus according to the sixth aspect of the present invention comprises a melting tank having an outside plate constructed by metal material and a fireproof member covering the outside plate, and a traveling magnetic field generating unit which is arranged outside the outside plate of the melting tank and generates a magnetic field traveling along the outside plate in the melting tank so as to agitate the molten metal stored in the melting tank, wherein the melted matter is introduced to the molten metal stored in the melting chamber so as to melt the melted matter, wherein the traveling magnetic field generating unit comprises a permanent magnet facing the sidewall of the melting tank, a support member supporting the permanent magnet, and a motor rotatively driving the support member centering on a rotational shaft perpendicular to an outer plate surface of the outside plate, wherein a resistance band which has larger electric resistance than the metal material constructing the outside plate is formed at a part of the outside plate of the melting tank facing the permanent magnet, wherein the middle part of the resistance band is arranged at a position in the outside plate of the melting tank facing the rotational shaft, and wherein an end of the resistance band is arranged at a position far from the position in the outside plate of the melting tank facing the rotational shaft. 
         [0039]    In the embodiment of the present invention, preferably, a north pole and a south pole of the permanent magnet are arranged at positions whose phases are shifted mutually for 180° centering on the rotational shaft when viewed from the axial direction of the rotational shaft. 
         [0040]    In the preferable embodiment of the present invention, the resistance band is a slot formed in the outside plate of the melting tank. 
         [0041]    In the embodiment of the present invention, preferably, an auxiliary resistance band which has larger electric resistance than the metal material constructing the outside plate of the melting tank and is arranged separately from the resistance band is formed at a part of the outside plate of the melting tank facing the permanent magnet. 
         [0042]    In the embodiment of the present invention, preferably, the auxiliary resistance band is a slot formed in the outside plate of the melting tank. 
         [0043]    In a melting method according to the seventh aspect of the present invention using a melting apparatus which introduces a melted matter to a molten metal stored in a melting chamber for melting the melted matter, in which the melting apparatus comprises a melting tank, which has an outside plate constructed by metal material and a fireproof member covering the outside plate, and a traveling magnetic field generating unit which is arranged outside the outside plate of the melting tank and generates a magnetic field traveling along the outside plate in the melting tank so as to agitate the molten metal stored in the melting tank and introducing the melted matter to the molten metal stored in the melting chamber so as to melt the melted matter, wherein the traveling magnetic field generating unit comprises a permanent magnet facing the sidewall of the melting tank, a support member supporting the permanent magnet, and a motor rotatively driving the support member centering on a rotational shaft perpendicular to an outer plate surface of the outside plate, wherein a resistance band which has larger electric resistance than the metal material constructing the outside plate is formed at a part of the outside plate of the melting tank facing the permanent magnet, wherein the middle part of the resistance band is arranged at a position in the outside plate of the melting tank facing the rotational shaft, and wherein an end of the resistance band is arranged at a position far from the position in the outside plate of the melting tank facing the rotational shaft. 
         [0044]    In the embodiment of the present invention, preferably, a north pole and a south pole of the permanent magnet are arranged at positions whose phases are shifted mutually for 180° centering on the rotational shaft when viewed from the axial direction of the rotational shaft. 
         [0045]    In the embodiment of the present invention, preferably, the resistance band is a slot formed in the outside plate of the melting tank. 
         [0046]    In another embodiment of the present invention, preferably, an auxiliary resistance band which has larger electric resistance than the metal material constructing the outside plate of the melting tank and is arranged separately from the resistance band is formed at a part of the outside plate of the melting tank facing the permanent magnet. 
         [0047]    Especially, preferably, the auxiliary resistance band is a slot formed in the outside plate of the melting tank. 
       Advantageous Effects of Invention 
       [0048]    The present invention does not pollute molten metal and brings high melting efficiency. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0049]      FIG. 1  is a sectional side view of a first embodiment of a melting apparatus and an agitation device according to the present invention. 
           [0050]      FIG. 2  is a plan view of the first embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0051]      FIG. 3  is a rear view of the first embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0052]      FIG. 4  is a plan view of flowing of molten metal in the first embodiment of the melting apparatus according to the present invention. 
           [0053]      FIG. 5  is a rear view of flowing of molten metal in the first embodiment of the melting apparatus according to the present invention. 
           [0054]      FIG. 6  is a plan view of another embodiment of a first molten metal straightening member according to the present invention. 
           [0055]      FIG. 7  is a sectional side view of a second embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0056]      FIG. 8  is a rear view of the second embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0057]      FIG. 9  is a flow chart of an embodiment of a melting method according to the present invention. 
           [0058]      FIG. 10  is a drawing of an embodiment of change of arrangement of a traveling magnetic field generating unit in the first embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0059]      FIG. 11  is a sectional side view of a third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0060]      FIG. 12  is a plan view of flowing of melted matters in the third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0061]      FIG. 13  is a sectional side view of flowing of the melted matters in the third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0062]      FIG. 14  is a plan view of flowing of suspended matters in the third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0063]      FIG. 15  is a side view of flowing of the suspended matters in the third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0064]      FIG. 16  is a plan view of another mode of the third embodiment of the melting apparatus and the agitation device according to the present invention. 
           [0065]      FIG. 17  is a sectional side view of an embodiment of an agitation device having a suspended matter /molten metal partition member. 
           [0066]      FIG. 18  is a plan view of an embodiment of an agitation device having an introduced/suspended matter partition member. 
           [0067]      FIG. 19  is a plan view of an embodiment of an agitation device having a flux injection device and a suspended matter recovery device. 
           [0068]      FIG. 20  is a sectional side view of a fourth embodiment of the melting apparatus according to the present invention. 
           [0069]      FIG. 21  is a plan view of the fourth embodiment of the melting apparatus according to the present invention. 
           [0070]      FIG. 22  is a front view of arrangement of permanent magnets in the fourth embodiment of the melting apparatus according to the present invention. 
           [0071]      FIG. 23  is a plan view of a magnetic field and an induced current in the fourth embodiment of the melting apparatus according to the present invention. 
           [0072]      FIG. 24  is a perspective view of a charging tank and a traveling magnetic field generating unit in the fourth embodiment of the melting apparatus according to the present invention. 
           [0073]      FIG. 25  is a rear view of flowing of the induced current in the fourth embodiment of the melting apparatus according to the present invention. 
           [0074]      FIG. 26  is a rear view of arrangement of slots formed in an outside plate according to comparing example and the present invention. 
           [0075]      FIG. 27  is a diagram of increase of temperature at the center of the outside plate according to the comparing example and the present invention. 
           [0076]      FIG. 28  is a diagram of relation between distance from the center of the outside plate and increase of temperature according to the comparing example and the present invention. 
           [0077]      FIG. 29  is a diagram of relation between the increase of temperature at the center and elapsed time of the outside plate of temperature according to the comparing example and the present invention. 
           [0078]      FIG. 30  is a diagram of power consumption of a motor rotatively driving the permanent magnets according to the comparing example and the present invention. 
           [0079]      FIG. 31  is a drawing of another embodiment of a resistance band according to the present invention. 
           [0080]      FIG. 32  is a sectional perspective view of the outside plate in which reinforcing ribs are formed. 
           [0081]      FIG. 33  is a drawing of another embodiment of arrangement of the permanent magnets. 
           [0082]      FIG. 34  is a drawing of flowing of the induced current induced on an outside plate in which any resistance slot and auxiliary resistance slot are not formed. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0083]    Explanation will be given on a melting furnace  100  which is a first embodiment of a melting apparatus according to the present invention referring to  FIGS. 1 to 6 . 
         [0084]    For convenience, hereinafter, “vertical direction” is defined on the basis of the direction of gravity (the direction of gravity is defined as the downward), “longitudinal direction” is defined as the direction perpendicular to the vertical direction, “lateral direction” is defined as the direction perpendicular to the vertical direction and the longitudinal direction, and these directions are employed in the explanation. 
         [0085]    As shown in  FIG. 1 , the melting furnace  100  generates molten metal  3  by melting aluminum cutting chips  2  and has a main body  10 , a charging tank  20  and an agitation device  150 . 
         [0086]    The aluminum cutting chips  2  are an embodiment of melted matter according to the present invention and is an object melted by the melting furnace  100 . The aluminum cutting chips  2  include aluminum alloy. The aluminum cutting chips  2  are hair-like shaped (long and narrow shaped) and the length of each of the aluminum cutting chips  2  is about 1 mm to 10 cm. 
         [0087]    The aluminum cutting chips  2  are generated by cuttingly processing members of aluminum (for example, an engine block). 
         [0088]    The material constituting the melted matter according to the present invention is not limited to aluminum alloy constituting the aluminum cutting chips  2 . 
         [0089]    As the material constituting the melted matter according to the present invention, various metal materials can be employed such as native aluminum, aluminum alloy, native magnesium, magnesium alloy, native titanium and titanium alloy. 
         [0090]    Among the above materials, each of native aluminum, aluminum alloy, native magnesium and magnesium alloy is non-magnetic at solid state, has comparatively lower melting point than the other metal materials, has comparatively smaller specific gravity and is floaty on the surface of the molten metal, and tends to be formed thereon with an oxide layer having high melting point. Accordingly, the agitation device, the melting apparatus and the melting method are preferably adopted to these materials. 
         [0091]    The shape of the melted matter according to the present invention is not limited to that of the aluminum cutting chips  2 . For example, the melted matter according to the present invention may alternatively be the other shape, such as spherical or massive. 
         [0092]    The size of the melted matter according to the present invention is not limited to that of the aluminum cutting chips  2 . For example, the melted matter according to the present invention includes a matter whose size is less than 1 mm such as impalpable powder of aluminum alloy and a matter whose size is more than 10 cm such as cut pieces of parts of aluminum alloy. 
         [0093]    The molten metal  3  is liquid obtained by melting the aluminum cutting chips  2 . 
         [0094]    The molten metal according to the present invention only should be liquid of substantially the same material (in the case of alloy, substantially the same components) as the melted matter. Namely, molten metal charged with the melted matter at the time of starting the melting (initial molten metal) may alternatively be generated by a method different from the method melting the melted matter (for example, the method of melting an ingot including substantially the same material as the melted matter). 
         [0095]    The main body  10  holds the temperature of the molten metal  3  higher than solidifying temperature. 
         [0096]    The main body  10  has a structure  11 , a fireproof thermal insulating member  12  and a burner  13 . 
         [0097]    The structure  11  is a substantially rectangular box-like member. 
         [0098]    The fireproof thermal insulating member  12  is constructed by ceramics or the like and is fixed to the inner peripheral surface of the structure  11  so as to cover the inner peripheral surface of the structure  11 . 
         [0099]    A holding chamber  14  is formed I side the structure  11  as a space surrounded by the fireproof thermal insulating member  12 , and a communication passage  15  is formed in the lower portion of the rear surface of the structure  11 . The molten metal  3  is stored in the lower half of the holding chamber  14 . 
         [0100]    The burner  13  is provided in the upper portion of the inner peripheral surface of the structure  11  and heats air in the holding chamber  14 , in its turn the molten metal  3  stored in the lower half of the holding chamber  14  (the molten metal  3  touching the air). 
         [0101]    In this embodiment, the molten metal  3  is heated by the burner  13 . However, the present invention is not limited thereto and the molten metal  3  may alternatively be heated by the other heat source (for example, an electric heater). 
         [0102]    The charging tank  20  is a part of the melting furnace  100  through which the aluminum cutting chips  2  is introduced. 
         [0103]    The charging tank  20  is fixed to the rear end of the main body  10 . The charging tank  20  has a bottom floor  21  and a sidewall  22 . 
         [0104]    The bottom floor  21  is a part of the charging tank  20  which is a plate-like part substantially rectangular when viewed in plan and is extended rearward from the rear end of the structure  11 . 
         [0105]    The sidewall  22  is a part of the charging tank  20  which is a plate-like part and is standingly provided along the left end, rear end and right end of the bottom floor  21 . The left and right front ends of the sidewall  22  are respectively extended to the left and right ends of the rear surface of the structure  11 . 
         [0106]    A charging chamber  23  is formed in the charging tank  20  as a space surrounded by the bottom floor  21 , the sidewall  22  and the rear surface of the structure  11 . The molten metal  3  is stored in the lower half of the charging chamber  23 . 
         [0107]    The holding chamber  14  is communicated with the charging chamber  23  through the communication passage  15 , and the molten metal  3  can moves between the holding chamber  14  and the charging chamber  23  through the communication passage  15 . 
         [0108]    The upper surface of the charging tank  20  is opened and the aluminum cutting chips  2  is introduced through the opening into the charging chamber  23  (in more detail, introduced through a part surrounded by a first molten metal straightening member  170  and a second molten metal straightening member  189  discussed later and the sidewall  22  when viewed in plan). The aluminum cutting chips  2  is introduced into the charging chamber  23  touch the molten metal  3  stored in the lower half of the charging chamber  23  and heated, and then melted when the temperature thereof becomes higher than the melting point. 
         [0109]    In this embodiment, the molten metal  3  is stored in the part constructed by combining the rear surface of the structure  11 , whose inner peripheral surface is covered by the fireproof thermal insulating member  12 , with the charging tank  20 . Therefore, each of “the rear surface of the structure  11  whose inner peripheral surface is covered by the fireproof thermal insulating member  12 ” and “the charging tank  20 ” is an embodiment of the melting tank according to the present invention. 
         [0110]    The agitation device  150  is an embodiment of the agitation device according to the present invention and agitates the molten metal  3  to which the aluminum cutting chips  2  are introduced (the molten metal  3  stored in the lower half of the charging chamber  23 ) so as to promote melting of the aluminum cutting chips  2 . 
         [0111]    As shown in  FIGS. 1 ,  2  and  3 , the agitation device  150  has a traveling magnetic field generating unit  160 , the first molten metal straightening member  170  and the second molten metal straightening member  180 . 
         [0112]    The traveling magnetic field generating unit  160  is an embodiment of the traveling magnetic field generating unit according to the present invention and generates (α) a magnetic field traveling downward along the sidewall  22  of the rear side and (β) a magnetic field traveling upward along the sidewall  22  of the rear side in the charging tank  20 . 
         [0113]    As shown in  FIG. 1 , the traveling magnetic field generating unit  160  is arranged outside the charging tank  20  (in this embodiment, behind the charging tank  20 ). 
         [0114]    The traveling magnetic field generating unit  160  has two permanent magnets  161 , a support member  162 , a motor  163 , a liquid surface position detection device  164 , a vertical moving device  165  and a controller  166 . 
         [0115]    The permanent magnets  161  are an embodiment of the permanent magnets according to the present invention and face the sidewall  22  of the rear side as shown in  FIGS. 1 and 2 . 
         [0116]    “Permanent magnet” means an object which maintains its magnetism for a comparative long period without supply of magnetic field or current from the outside. 
         [0117]    As the permanent magnets according to the present invention, concretely, alnico magnet, KS-steel, MK-steel, ferrite magnet, samarium-cobalt magnet, or neodymium magnet may be employed. 
         [0118]    In this embodiment, for generating strong magnetic power, the permanent magnets  161  are constructed by the neodymium magnet. 
         [0119]    In this embodiment, the traveling magnetic field generating unit  160  has the two permanent magnets  161 . However, the present invention is not limited thereto and the number of the permanent magnets provided in the traveling magnetic field generating unit according to the present invention may be one or the plural. 
         [0120]    The support member  162  is an embodiment of the support member according to the present invention and supports the permanent magnets  161 . 
         [0121]    In this embodiment, the support member  162  is substantially discoid and is arranged so that the surface thereof is in parallel to the sidewall  22  of the rear side. On the surface of the support member  162  facing the sidewall  22  of the rear side, the permanent magnets  161  are fixed to positions symmetrical about the center of the surface. 
         [0122]    The motor  163  is an embodiment of the motor according to the present invention and rotatively drives the support member  162 , in its turn the permanent magnets  161  fixed to the support member  162 . 
         [0123]    A rotational shaft  163   a  of the motor  163  is fixed to the support member  162 . The axis of the rotational shaft  163   a  is coaxial to the center line of the support member  162  (the line passing through the centers of the pair of surfaces of the support member  162 ). 
         [0124]    In this embodiment, the motor  163  is an electric motor. However, motor according to the present invention is not limited thereto and may alternatively be a motor rotatively driven by fluid pressure (for example, hydraulic motor or pneumatical motor). 
         [0125]    By supplying electric power to the motor  163 , the rotational shaft  163   a , the support member  162  fixed to the rotational shaft  163   a  and the permanent magnets  161  fixed to the support member  162  are integrally rotated (in this embodiment, the permanent magnets  161  are rotated counterclockwise when viewed in rear). 
         [0126]    As a result, as shown in  FIG. 3 , on the sidewall  22  of the rear side, the magnetic field traveling substantially downward along the sidewall  22  of the rear side is generated in the part facing the left half of the support member  162 , and the magnetic field traveling substantially upward along the sidewall  22  of the rear side is generated in the part of the inside of the charging tank  20  corresponding to the part facing the right half of the support member  162  (that is, the position away from the magnetic field traveling downward for a predetermined distance). 
         [0127]    When the magnetic field traveling substantially downward along the sidewall  22  is generated inside the charging tank  20 , in the molten metal  3  stored in the charging tank  20 , the substantially downward flowing of the molten metal  3  (molten metal flowing) is generated at the part on which the magnetic field acts. 
         [0128]    When the magnetic field traveling substantially upward along the sidewall  22  is generated inside the charging tank  20 , in the molten metal  3  stored in the charging tank  20 , the substantially upward flowing of the molten metal  3  (molten metal flowing) is generated at the part on which the magnetic field acts. 
         [0129]    As a result, in the molten metal  3 , flowing of the molten metal  3  (molten metal flowing) is generated which circulates centering on the axis substantially in parallel to the liquid surface of the molten metal  3  (in this embodiment, the rotational shaft  163   a  of the motor  163 ). 
         [0130]    When the aluminum cutting chips  2  are introduced to the molten metal  3  in which the flowing is generated, the aluminum cutting chips  2  are moved on the flowing of the molten metal  3  (molten metal flowing) and dive into the inside of the molten metal  3  (soaked in the molten metal  3 ) at the position as which the substantially downward flowing of the molten metal  3  (molten metal flowing) is generated, and then melted by the heat of the molten metal  3 . 
         [0131]    When the aluminum cutting chips  2  are melted, the temperature of the molten metal  3  in the vicinity of the molten aluminum cutting chips  2  is reduced. However, the molten metal  3  is agitated by the flowing of the molten metal  3  (molten metal flowing) so that the temperature of the molten metal  3  is held substantially equally. 
         [0132]    Furthermore, by generating the substantially upward flowing of the molten metal  3  (molten metal flowing), the molten metal  3  with comparative high temperature is moved to the vicinity of the liquid surface of the molten metal  3  to which the aluminum cutting chips  2  are introduced. Accordingly, when a large quantity of the aluminum cutting chips  2  are introduced continuously to the molten metal  3 , the aluminum cutting chips  2  can be melted efficiently. 
         [0133]    The liquid surface position detection device  164  is an embodiment of the liquid surface position detection device according to the present invention and detects the position of liquid surface of the molten metal  3 . 
         [0134]    As shown in  FIG. 1 , the liquid surface position detection device  164  is arranged above the charging tank  20 , in its turn above the liquid surface of the molten metal  3  stored in the charging chamber  23 , transmits (irradiates) a supersonic wave to the liquid surface of the molten metal  3 , receives the supersonic wave reflected on the liquid surface of the molten metal  3 , and calculates the distance between the liquid surface position detection device  164  and the liquid surface of the molten metal  3  on the basis of the speed of the supersonic wave and the time from the transmission of the supersonic wave toward the liquid surface of the molten metal  3  to the receipt thereof, thereby detecting the position (height) of the liquid surface of the molten metal  3 . 
         [0135]    The liquid surface position detection device according to the present invention is not limited to the construction such as the liquid surface position detection device  164  in this embodiment in which the position of the liquid surface of the molten metal is detected by employing the supersonic wave, and the position of the liquid surface of the molten metal may alternatively be detected by another method. 
         [0136]    The vertical moving device  165  is an embodiment of the vertical moving device according to the present invention and supports the motor  163  movably vertically. 
         [0137]    As shown in  FIG. 1 , the vertical moving device  165  has a base member  165   a , a stay member  165   b , a top member  165   c , a ball screw  165   d , a servomotor  165   e  and a slide member  165   f.    
         [0138]    The base member  165   a  is a plate-like member forming the lower portion of the vertical moving device  165 . The base member  165   a  is fixed to a floor surface, a ground surface or another structure. 
         [0139]    The stay member  165   b  is a substantially cylindrical member. One of ends (lower end) of the stay member  165   b  is fixed to the base member  165   a . The lengthwise direction of the stay member  165   b  is in agreement with the vertical direction. 
         [0140]    The top member  165   c  is a plate-like member forming the upper portion of the vertical moving device  165 . The top member  165   c  is fixed to the other end (upper end) of the stay member  165   b.    
         [0141]    The ball screw  165   d  is a substantially cylindrical member whose outer peripheral surface is formed therein with a male screw. The upper and lower ends of the ball screw  165   d  are rotatably pivotally supported respectively by the top member  165   c  and the base member  165   a.    
         [0142]    The servomotor  165   e  is an electric motor that the rotational direction and the rotational amount (rotational angle) of the rotational shaft thereof can be regulated. The servomotor  165   e  is fixed to the top member  165   c . The rotational shaft of the servomotor  165   e  is fixed to the upper end of the ball screw  165   d.    
         [0143]    The slide member  165   f  is a plate-like member. A through hole is formed in the slide member  165   f  and penetrates the upper and lower surfaces thereof. The stay member  165   b  is slidably inserted into the through hole. A tapped hole is formed in the slide member  165   f  and penetrates the upper and lower surfaces thereof. The ball screw  165   d  is screwed into the tapped hole. 
         [0144]    The motor  163  is fixed to the upper surface of the slide member  165   f.    
         [0145]    When electric power is supplied to the servomotor  165   e , the rotational shaft of the servomotor  165   e  and the ball screw  165   d  are rotated integrally, and the slide member  165   f  to which the ball screw  165   d  is screwed is moved (slid) vertically along the stay member  165   b.    
         [0146]    By regulating the rotational direction and the rotational amount (rotational angle) of the rotational shaft of the servomotor  165   e , the vertical movement amount of the combination of the slide member  165   f , the motor  163 , the support member  162  and the permanent magnets  161  can be regulated. 
         [0147]    The controller  166  is an embodiment of the controller according to the present invention and transmits a signal so as to make the motor  163  move vertically (hereinafter, referred to as “control signal”) to the vertical moving device  165  on the basis of the position of the liquid surface of the molten metal  3  detected by the liquid surface position detection device  164 , thereby controlling the relational position of the motor  163  about the liquid surface of the molten metal  3  in the vertical direction. 
         [0148]    The controller  166  can store various programs and the like therein, expand the programs, perform predetermined operations on the basis of the programs, store the results of the operations, and output the results of the operations. 
         [0149]    Substantially, the controller  166  may be constructed by connecting CPU (Central Processing Unit), ROM (Read-Only Memory), RAM (Random Access Memory) and HDD (Hard Disk Drive) to each other through a bus, or may alternatively be constructed by a one-chip LSI (Large Scale Integration). 
         [0150]    In this embodiment, the controller  166  is for exclusive use. However, the controller  166  may alternatively be constructed by a personal computer or work station on the market in which programs are suitably stored. 
         [0151]    The controller  166  is connected to the liquid surface position detection device  164  so as to obtain the information (signal) about the position of the liquid surface of the molten metal  3  detected by the liquid surface position detection device  164 . 
         [0152]    The controller  166  is connected to the vertical moving device  165 , in more detail the servomotor  165   e  so as to obtain the information (signal) about the rotational amount (rotational angle) of the servomotor  165   e , in its turn the position (height) of the rotational shaft  163   a  of the motor  163  from the servomotor  165   e.    
         [0153]    The controller  166  can transmits the signal which commands the rotational direction, the rotational speed and the rotational amount (rotational angle) of the rotational shaft of the servomotor  165   e  (corresponding to the control signal) to the servomotor  165   e.    
         [0154]    On the basis of “the information about the position of the liquid surface of the molten metal  3 ” detected by the liquid surface position detection device  164  and “the information about the position of the rotational shaft  163   a  of the motor  163 ” obtained from the servomotor  165   e , the controller  166  calculates the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 . 
         [0155]    The controller  166  previously stores therein “tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” and compares “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” with “the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ”. 
         [0156]    As the result of the comparison, when “the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is included in “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” (“the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is not less than the lower limit and not more than the upper limit of “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ”), the controller  166  does not transmit the control signal to the servomotor  165   e  so as to hold the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0157]    As the result of the comparison, when “the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is not included in “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” (“the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is less than the lower limit or more than the upper limit of “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ”), the controller  166  transmits the control signal to the servomotor  165   e  so as to regulate the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0158]    More concretely, when “the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is less than the lower limit of “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ”, the controller  166  transmits the control signal to the servomotor  165   e  so as to raise the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0159]    The servomotor  165   e  receiving the control signal rotatively drives so as to raise the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0160]    When “the calculated result of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is more than the upper limit of “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ”, the controller  166  transmits the control signal to the servomotor  165   e  so as to fall the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0161]    The servomotor  165   e  receiving the control signal rotatively drives so as to fall the position (height) of the rotational shaft  163   a  of the motor  163 . 
         [0162]    In this embodiment, the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ″ is determined so that the position of the rotational shaft  163   a  of the motor  163  is lower than the liquid surface of the molten metal  3  for a predetermined distance. In other words, the controller  166  transmits the control signal to the servomotor  165   e  so as to hold the position of the rotational shaft  163   a  of the motor  163  lower than the liquid surface of the molten metal  3  detected by the liquid surface position detection device  164  for a predetermined distance. 
         [0163]    According to the construction, in the case that the position (height) of the liquid surface of the molten metal  3  is changed by changing the amount (volume) of the molten metal  3  stored in the melting furnace  100  (for example, in the case that the molten metal  3  of a predetermined amount is taken out from the melting furnace  100 ), in the locus of the traveling magnetic field, most of “the part in which the traveling direction of the magnetic field is substantially downward” and the part in which the traveling direction of the magnetic field is substantially upward” faces the side surface of the molten metal  3  stored in the charging tank  20 , whereby the traveling magnetic field can act on the molten metal  3  more efficiently. 
         [0164]    The concrete value of “the tolerance of the relative position of the rotational shaft  163   a  of the motor  163  about the liquid surface of the molten metal  3 ” is set in consideration of various elements such as the components (material) of the molten metal  3  (the aluminum cutting chips  2 ), the temperature of the molten metal  3 , the amount (volume) of the molten metal  3 , the shape of the charging tank  20  (the shape of the charging chamber  23 ), the magnetic power of the permanent magnets  161  and the rotational speed of the motor  163  (the rotational speed of the permanent magnets  161 ) synthetically. 
         [0165]    The first molten metal straightening member  170  is an embodiment of the first molten metal straightening member according to the present invention and straightens the flowing of the molten metal  3  so as to promote the melting of the aluminum cutting chips  2 . 
         [0166]    In this embodiment, the first molten metal straightening member  170  is a plate-like member at least the surface thereof is constructed by refractory material such as ceramic and has a first molten metal straightening surface  171 . The inside of the first molten metal straightening member  170  may be constructed by heat-resistant material such as metal. 
         [0167]    The first molten metal straightening member  170  is arranged inside the charging tank  20  (inside the charging chamber  23 ) and at the position corresponding to “the magnetic field traveling substantially downward along the sidewall  22  of the charging tank  20 ” generated by the traveling magnetic field generating unit  160  (in this embodiment, the position inside the charging tank  20  slightly left from the magnetic field traveling substantially downward), and the rear end of the first molten metal straightening member  170  is fixed to the sidewall  22  of the rear side of the charging tank  20 . 
         [0168]    The upper end of the first molten metal straightening member  170  fixed to the sidewall  22  of the rear side of the charging tank  20  is arranged above the liquid surface of the molten metal  3 , and a gap of predetermined size is formed between the lower end of the first molten metal straightening member  170  and the bottom floor  21  of the charging tank  20 . Therefore, the molten metal  3  positioned at the left of the first molten metal straightening member  170  and the molten metal  3  positioned at the right of the first molten metal straightening member  170  when viewed in plan are communicated with each other through the gap formed between the lower end of the first molten metal straightening member  170  and the bottom floor  21  of the charging tank  20  (the molten metal can move mutually). 
         [0169]    The first molten metal straightening surface  171  of the first molten metal straightening member  170  arranged in the charging tank  20  is directed rightward and is substantially perpendicular to the sidewall  22  of the charging tank  20  and the horizontal plane. 
         [0170]    As shown in  FIGS. 4 and 5 , the flowing of the molten metal  3  generated by the traveling magnetic fields (the magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20  and the magnetic field traveling substantially upward along the sidewall  22  of the rear side of the charging tank  20 ) is substantially leftward (strictly, leftward and forward) in the vicinity of the liquid surface of the molten metal  3 , and when the flowing reaches the first molten metal straightening surface  171  of the first molten metal straightening member  170 , the direction is revised downward along the first molten metal straightening surface  171 . 
         [0171]    Namely, by arranging the first molten metal straightening member  170 , the flowing in the vicinity of the liquid surface of the molten metal  3  can be changed from substantially leftward to substantially downward. 
         [0172]    Therefore, in comparison of the case that the first molten metal straightening member  170  is not arranged, the downward flowing of the molten metal  3  can be generated more strongly. 
         [0173]    The center of the first molten metal straightening surface  171  is hollow when viewed in plan. This shape of the first molten metal straightening surface  171  brings below merits. 
         [0174]    Namely, strictly, the flowing of the molten metal  3  in the vicinity of the liquid surface of the molten metal  3  is not leftward completely, that is, not in parallel to the sidewall  22  of the rear side when viewed in plan and is along the direction going away gradually from the sidewall  22  of the rear side (in this embodiment, leftward and forward). 
         [0175]    By forming the first molten metal straightening surface  171  so that the center thereof is hollow when viewed in plan, the flowing of the molten metal  3  in the vicinity of the liquid surface of the molten metal  3  can be changed downward while revising the flowing close to the sidewall  22  of the rear side of the charging tank  20  when viewed in plan, whereby the downward flowing of the molten metal  3  can be generated more strongly. 
         [0176]    The second molten metal straightening member  180  is an embodiment of the second molten metal straightening member according to the present invention, and straightens the flowing of the molten metal  3  so as to promote the melting of the aluminum cutting chips  2 . 
         [0177]    In this embodiment, the second molten metal straightening member  180  is a plate-like member at least the surface thereof is constructed by refractory material such as ceramic and has a second molten metal straightening surface  181 . The inside of the second molten metal straightening member  180  may be constructed by heat-resistant material such as metal. 
         [0178]    The second molten metal straightening member  180  is arranged inside the charging tank  20  (inside the charging chamber  23 ) and at the position opposite to the traveling magnetic field generating unit  160  about the sidewall  22  of the rear side of the charging tank  20 . The left end of the second molten metal straightening member  180  is fixed to the front end of the first molten metal straightening member  170 , and the right end of the second molten metal straightening member  180  is fixed to the sidewall  22  of the right side of the charging tank  20 . 
         [0179]    The upper end of the second molten metal straightening member  180  fixed to the sidewall  22  of the right side of the charging tank  20  is arranged above the liquid surface of the molten metal  3 , and a gap of predetermined size is formed between the lower end of the second molten metal straightening member  180  and the bottom floor  21  of the charging tank  20 . Therefore, the molten metal  3  positioned at the front of the second molten metal straightening member  180  and the molten metal  3  positioned at the rear of the second molten metal straightening member  180  when viewed in plan are communicated with each other through the gap formed between the lower end of the second molten metal straightening member  180  and the bottom floor  21  of the charging tank  20  (the molten metal can move mutually). 
         [0180]    The second molten metal straightening surface  181  of the second molten metal straightening member  180  arranged in the charging tank  20  is directed rearward (faces the sidewall  22  of the rear side of the charging tank  20 ) and is substantially in parallel to the sidewall  22  of the rear side of the charging tank  20 . 
         [0181]    As shown in  FIGS. 4 and 5 , the flowing of the molten metal  3  generated by the traveling magnetic fields (the magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20  and the magnetic field traveling substantially upward along the sidewall  22  of the rear side of the charging tank  20 ) is substantially leftward and forward in the vicinity of the liquid surface of the molten metal  3 , and when the flowing reaches the second molten metal straightening surface  181  of the second molten metal straightening member  180 , the direction is revised leftward along the second molten metal straightening surface  181  (in parallel to the sidewall  22  of the rear side when viewed in plan). 
         [0182]    Therefore, in comparison of the case that the second molten metal straightening member  180  is not arranged, the leftward flowing of the molten metal  3  can be generated more strongly, in its turn the downward flowing of the molten metal  3  can be generated more strongly. 
         [0183]    As mentioned above, the agitation device  150  agitates the molten metal  3  to which the aluminum cutting chips  2  is introduced so as to promote the melting of the aluminum cutting chips  2  and has the traveling magnetic field generating unit  160  which is arranged outside the charging tank  20  and generates the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20 . 
         [0184]    According to the construction, the aluminum cutting chips  2  introduced to the molten metal  3  ride on the downward flowing of the molten metal  3  (molten metal flowing) generated by the magnetic field traveling downward along the sidewall  22  of the rear side and are soaked in the molten metal  3 , whereby the melting of the aluminum cutting chips  2  can be promoted (the aluminum cutting chips  2  can be melted efficiently). 
         [0185]    The agitation device  150  can be added to an existing melting device without large-scale remodeling, thereby being adoptable easily to the existing melting device. 
         [0186]    In this embodiment, the traveling magnetic field generating unit  160  is arranged to face the sidewall  22  of the rear side of the charging tank  20 . However, the agitation device according to the present invention is not limited thereto. 
         [0187]    For example, as shown in  FIG. 10 , the traveling magnetic field generating unit  160  may alternatively be arranged to face the sidewall  22  of the left side of the charging tank  20 , or may alternatively be arranged to face the sidewall  22  of the right side of the charging tank  20  (not shown). 
         [0188]    In addition to the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20 , the traveling magnetic field generating unit  160  of the agitation device  150  generates the magnetic field traveling upward along the sidewall  22  of the rear side of the charging tank  20  at the position far from the magnetic field traveling downward for the predetermined distance in the charging tank  20 . 
         [0189]    According to the construction, the molten metal  3  of comparative high temperature can be supplied to the vicinity of the liquid surface of the molten metal  3  to which the aluminum cutting chips  2  is introduced, whereby the melting of the aluminum cutting chips  2  can be promoted (the aluminum cutting chips  2  can be melted efficiently). 
         [0190]    The traveling magnetic field generating unit  160  of the agitation device  150  has the permanent magnets  161  facing the sidewall  22  of the rear side of the charging tank  20 , the support member  162  supporting the permanent magnets  161 , and the motor  163  rotatively driving the support member  162 . 
         [0191]    According to the construction, the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20  can be generated by the construction which is easy and has small power consumption. 
         [0192]    The traveling magnetic field generating unit  160  of the agitation device  150  has the liquid surface position detection device  164  detecting the position of the liquid surface of the molten metal  3 , the vertical moving device  165  vertically movably supporting the motor  163 , and the controller  166  transmitting the signal to the vertical moving device  165  for moving vertically the motor  163  on the basis of the position of the liquid surface of the molten metal  3  detected by the liquid surface position detection device  164  so as to control the relative position of the motor  163  about the liquid surface of the molten metal  3  in the vertical direction. 
         [0193]    According to the construction, the magnetic field traveling corresponding to the position of the liquid surface of the molten metal  3  can act on the molten metal  3  more efficiently. 
         [0194]    The controller  166  of the traveling magnetic field generating unit  160  of the agitation device  150  transmits the signal to the vertical moving device  165  for moving vertically the motor  163  so as to hold the position of the rotational shaft  163   a  of the motor  163  lower than the liquid surface of the molten metal  3  for the predetermined distance. 
         [0195]    According to the construction, in the case that the position (height) of the liquid surface of the molten metal  3  is changed, most of “the part in which the traveling direction of the magnetic field is substantially downward” and the part in which the traveling direction of the magnetic field is substantially upward” faces the side surface of the molten metal  3  stored in the charging tank  20 , whereby the traveling magnetic field can act on the molten metal  3  more efficiently. 
         [0196]    In this embodiment, the traveling magnetic field generating unit  160  has the liquid surface position detection device  164 , the vertical moving device  165  and the controller  166 . However, in the case that the position (height) of the liquid surface of the molten metal  3  is not changed substantially (there is no change or the change amount is negligibly small) in the construction of the melting furnace  100  or in the application of the melting furnace  100 , the liquid surface position detection device  164 , the vertical moving device  165  and the controller  166  may be omitted. 
         [0197]    In the case that the liquid surface position detection device  164 , the vertical moving device  165  and the controller  166  are omitted, for making the traveling magnetic field act on the molten metal  3  more efficiently, the motor  163  is preferably fixed so as to arrange the rotational shaft  163   a  of the motor  163  at the position lower than the liquid surface of the molten metal  3  for the predetermined distance. 
         [0198]    The agitation device  150  has the first molten metal straightening member  170  which is arranged at the position inside the charging tank  20  and corresponding to the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20  generated by the traveling magnetic field generating unit  160  and has the first molten metal straightening surface  171  perpendicular to the sidewall  22  of the rear side of the charging tank  20  and the horizontal plane. 
         [0199]    According to the construction, the downward flowing of the molten metal  3  can be generated more strongly, in its turn the melting of the aluminum cutting chips  2  can be promoted (the aluminum cutting chips  2  can be melted efficiently). 
         [0200]    The center of the first molten metal straightening surface  171  of the first molten metal straightening member  170  of the agitation device  150  is hollow when viewed in plan. 
         [0201]    According to the construction, the flowing of the molten metal  3  in the vicinity of the liquid surface of the molten metal  3  can be changed downward while revising the flowing close to the sidewall  22  of the rear side of the charging tank  20  when viewed in plan, whereby the downward flowing of the molten metal  3  can be generated more strongly. 
         [0202]    In this embodiment, the first molten metal straightening surface  171  is constructed as a curved surface. However, the shape of the first molten metal straightening surface according to the present invention is not limited thereto. 
         [0203]    For example, as the first molten metal straightening surface  171  shown in  FIGS. 6(   a ) and ( b ), the first molten metal straightening surface may alternatively be “the combination of a plurality of flat surfaces”. Otherwise, as the first molten metal straightening surface  171  shown in  FIG. 6(   c ), the first molten metal straightening surface may alternatively be “the combination of a plurality of flat surfaces and curved surfaces”. 
         [0204]    The agitation device  150  has the second molten metal straightening member  180  which is arranged at the position inside the charging tank  20  and is opposite to the traveling magnetic field generating unit  160  about the sidewall  22  of the rear side of the charging tank  20  and has the second molten metal straightening surface  181  in parallel to the sidewall  22  of the rear side of the charging tank  20 . 
         [0205]    According to the construction, the leftward flow (the flow in parallel to the sidewall  22  of the rear side of the charging tank  20  when viewed in plan) of the molten metal  3  can be generated more strongly, in its turn the downward flowing of the molten metal  3  can be generated more strongly. 
         [0206]    In this embodiment, the agitation device  150  has the first molten metal straightening member  170  and the second molten metal straightening member  180 . However, for example according to the shape of the charging tank  20 , one or both of the first molten metal straightening member  170  and the second molten metal straightening member  180  may alternatively be omitted. 
         [0207]    In this embodiment, when the charging tank  20  is small in the lateral direction, the sidewall  22  of the right and left sides of the charging tank  20  can function similarly to the first molten metal straightening member  170 , whereby the first molten metal straightening member  170  can be omitted. 
         [0208]    In this embodiment, when the charging tank  20  is small in the longitudinal direction, the rear surface of the structure  11  of the main body  10  can function similarly to the second molten metal straightening member  180 , whereby the second molten metal straightening member  180  can be omitted. 
         [0209]    As shown in  FIG. 3 , by shaping the corners of the bottom floor  21  and the sidewall  22  round, the upward flow of the molten metal  3  can be promoted. 
         [0210]    In this embodiment, the first molten metal straightening member  170  and the second molten metal straightening member  180  are fixed to the charging tank  20 . However, the members may alternatively be moved vertically corresponding to the position (height) of the liquid surface of the molten metal  3 . 
         [0211]    The melting furnace  100  is the melting apparatus for melting the aluminum cutting chips  2  by introducing the aluminum cutting chips  2  to the molten metal  3  stored in the charging tank  20  and has the agitation device  150 . 
         [0212]    According to the construction, the aluminum cutting chips  2  introduced to the molten metal  3  ride on the downward flowing of the molten metal  3  (molten metal flowing) generated by the magnetic field traveling downward along the sidewall  22  of the rear side and are soaked in the molten metal  3 , whereby the aluminum cutting chips  2  can be melted efficiently. 
         [0213]    In this embodiment, the agitation device  150  is arranged behind the charging tank  20 . However, the agitation device  150  may alternatively be arranged at the left or right of the charging tank  20 . 
         [0214]    Explanation will be given on a melting furnace  200  which is a second embodiment of the melting apparatus according to the present invention referring to  FIGS. 7 and 8 . 
         [0215]    In below explanation, for convenience, the construction of the melting furnace  200  which is the same as the construction of the melting furnace  100  shown in  FIG. 1  is designated by the same reference numeral and description thereof is omitted. 
         [0216]    As shown in  FIG. 7 , the melting furnace  200  has the main body  10 , the charging tank  20  and an agitation device  250 . 
         [0217]    The agitation device  250  is a second embodiment of the agitation device according to the present invention and agitates the molten metal  3  to which the aluminum cutting chips  2  are introduced (the molten metal  3  stored in the lower half of the charging chamber  23 ) so as to promote melting of the aluminum cutting chips  2 . 
         [0218]    As shown in  FIGS. 7 and 8 , the agitation device  250  has a traveling magnetic field generating unit  260 , a first molten metal straightening member  270  and a second molten metal straightening member  280 . 
         [0219]    The traveling magnetic field generating unit  260  is an embodiment of the traveling magnetic field generating unit according to the present invention and generates (α) a magnetic field traveling downward along the sidewall  22  of the rear side and (β) a magnetic field traveling upward along the sidewall  22  of the rear side in the charging tank  20 . 
         [0220]    The traveling magnetic field generating unit  260  has electromagnetic coils  261  and an electric power supply device  262 . 
         [0221]    The electromagnetic coils  261  are an embodiment of the plurality of coils according to the present invention and generate magnetic fields therearound by electric power supply. 
         [0222]    The electromagnetic coils  261  are arranged substantially ring-like along the sidewall  22  of the rear side of the charging tank  20 . 
         [0223]    The electric power supply device  262  is an embodiment of the electric power supply device according to the present invention and supplies electric power to the electromagnetic coils  261  in order (in this embodiment, in counterclockwise order when viewed in rear). 
         [0224]    When the electric power supply device  262  supplies the electric power to the electromagnetic coils  261  in counterclockwise order when viewed in rear, the electromagnetic coils  261  to which the electric power is supplied are excited in order. 
         [0225]    As a result, the magnetic field traveling substantially ring-like along the sidewall  22  of the rear side of the charging tank  20  (similarly to the arrangement of the electromagnetic coils  261 ) is generated inside the charging tank  20 . The left half of the magnetic field when viewed in rear forms a magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20 , and the right half thereof when viewed in rear forms a magnetic field traveling substantially upward along the sidewall  22  of the rear side of the charging tank  20 . 
         [0226]    The construction of the first molten metal straightening member  270  and the second molten metal straightening member  280  is substantially the same as the construction of the first molten metal straightening member  170  and the second molten metal straightening member  180  shown in  FIG. 1 , and then explanation thereof is omitted. 
         [0227]    As mentioned above, the agitation device  250  of the melting furnace  200  has the electromagnetic coils  261  arranged along the sidewall  22  of the rear side of the charging tank  20  and the electric power supply device  262  supplying electric power to the electromagnetic coils  261  in order. 
         [0228]    According to the construction, the magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20  can be generated. 
         [0229]    Since the arrangement of the electromagnetic coils  261  can be changed suitably, the shape of locus of the traveling magnetic field is not limited to the circle and may be various shapes such as a straight line and an oval. 
         [0230]    Explanation will be given on an embodiment of melting method according to the present invention referring to  FIG. 9 . 
         [0231]    The embodiment of melting method according to the present invention is for melting the aluminum cutting chips  2  with the melting furnace  100  (see  FIG. 1 ) and has an introducing process S 1100  and an agitating process S 1200 . 
         [0232]    In the introducing process S 1100 , the aluminum cutting chips  2  are introduced to the molten metal  3  stored in the charging tank  20 . 
         [0233]    When the introducing process S 1100  is finished, the operation is shifted to the agitating process S 1200 . 
         [0234]    In the agitating process S 1200 , the magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20  is generated in the charging tank  20  so as to agitate the molten metal  3 . 
         [0235]    In the agitating process S 1200 , when electric power is supplied to the motor  163 , the rotational shaft  163   a , the support member  162  fixed to the rotational shaft  163   a  and the permanent magnets  161  fixed to the support member  162  are integrally rotated. By the rotation of the permanent magnets  161 , in the charging tank  20 , the magnetic field traveling substantially downward along the sidewall  22  of the rear side and the magnetic field traveling substantially upward along the sidewall  22  of the rear side and separated from the downward traveling magnetic field for a predetermined distance are generated. By acting the magnetic fields on the molten metal  3 , the substantially downward flowing of the molten metal  3  is generated. The aluminum cutting chips  2  introduced to the molten metal  3  in the introducing process S 1100  are moved on the flowing of the molten metal  3  (molten metal flowing) and dive into the inside of the molten metal  3  (soaked in the molten metal  3 ), and then melted by the heat of the molten metal  3 . 
         [0236]    As mentioned above, the embodiment of melting method according to the present invention has the introducing process S 1100  in which the aluminum cutting chips  2  are introduced to the molten metal  3  stored in the charging tank  20  and the agitating process S 1200  in which the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20  is generated in the charging tank  20  so as to agitate the molten metal  3 . 
         [0237]    According to the construction, the aluminum cutting chips  2  introduced to the molten metal  3  are moved on the flowing of the molten metal  3  generated by the magnetic field traveling substantially downward along the sidewall  22  (molten metal flowing) and soaked in the molten metal  3 , whereby the aluminum cutting chips  2  can be melted efficiently. 
         [0238]    In the embodiment of melting method according to the present invention, in the agitating process S 1200 , in the charging tank  20 , the magnetic field is generated which travels substantially upward along the sidewall  22  of the rear side of the charging tank  20  and is separated from the magnetic field traveling substantially downward along the sidewall  22  of the rear side of the charging tank  20  for the predetermined distance. 
         [0239]    According to the construction, the molten metal  3  of comparative high temperature can be supplied to the vicinity of the liquid surface of the molten metal  3  to which the aluminum cutting chips  2  is introduced, whereby the aluminum cutting chips  2  can be melted efficiently. 
         [0240]    In the embodiment of melting method according to the present invention, in the agitating process S 1200 , the traveling magnetic field generating unit  160  is employed which has the permanent magnets  161  facing the sidewall  22  of the rear side of the charging tank  20 , the support member  162  supporting the permanent magnets  161  and the motor  163  rotatively driving the support member  162  and is arranged outside the charging tank  20 , thereby generating the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20 . 
         [0241]    According to the construction, the magnetic field traveling downward along the sidewall  22  of the charging tank  20  can be generated by the construction which is easy and has small power consumption. 
         [0242]    In the melting method according to the present invention, the equipment for generating the magnetic field traveling downward along the sidewall of the charging tank is not limited to the traveling magnetic field generating unit  160  in this embodiment, and such equipment as the traveling magnetic field generating unit  260  shown in  FIGS. 7 and 8  may alternatively be employed. 
         [0243]    In the embodiment of melting method according to the present invention, in the agitating process S 1200 , the first molten metal straightening member  170 , which has the first molten metal straightening surface  171  perpendicular to the sidewall  22  of the rear side of the charging tank  20  and the horizontal plane, is arranged at the position inside the charging tank  20  and corresponding to the magnetic field traveling downward along the sidewall  22  of the rear side of the charging tank  20 . 
         [0244]    According to the construction, the downward flowing of the molten metal  3  can be generated more strongly, in its turn the aluminum cutting chips  2  can be melted efficiently. 
         [0245]    In the embodiment of melting method according to the present invention, in the agitating process S 1200 , the center of the first molten metal straightening surface  171  of the first molten metal straightening member  170  arranged inside the charging tank  20  is hollow when viewed in plan. 
         [0246]    According to the construction, the flowing of the molten metal  3  in the vicinity of the liquid surface of the molten metal  3  can be changed downward while revising the flowing close to the sidewall  22  of the rear side of the charging tank  20  when viewed in plan, whereby the downward flowing of the molten metal  3  can be generated more strongly. 
         [0247]    In the embodiment of melting method according to the present invention, in the agitating process S 1200 , the second molten metal straightening member  180 , which has the second molten metal straightening surface  181  in parallel to the sidewall  22  of the rear side of the charging tank  20 , is arranged at the position inside the charging tank  20  and is opposite to the traveling magnetic field generating unit  160  about the sidewall  22  of the rear side of the charging tank  20 . 
         [0248]    According to the construction, the leftward flow (the flow in parallel to the sidewall  22  of the rear side of the charging tank  20  when viewed in plan) of the molten metal  3  can be generated more strongly, in its turn the downward flowing of the molten metal  3  can be generated more strongly. 
         [0249]    In this embodiment, when the introducing process S 1100  is finished, the operation is shifted to the agitating process S 1200 . However, the present invention is not limited thereto. 
         [0250]    Namely, the introducing process and the agitating process may alternatively be parallel (may alternatively be performed simultaneously). 
         [0251]    Explanation will be given on a melting furnace  300  which is a third embodiment of the melting apparatus according to the present invention referring to  FIGS. 11 to 15 . 
         [0252]    In below explanation, for convenience, the construction of the melting furnace  300  which is fundamentally the same as the construction of the melting furnace  100  shown in  FIG. 1  is designated by the same reference numeral and description thereof is omitted. 
         [0253]    As shown in  FIG. 11 , the melting furnace  300  has the main body  10 , the charging tank  20  and an agitation device  350 . 
         [0254]    The agitation device  350  is a third embodiment of the agitation device according to the present invention and agitates the molten metal  3  to which the aluminum cutting chips  2  are introduced (the molten metal  3  stored in the lower half of the charging chamber  23 ) so as to promote melting of the aluminum cutting chips  2 . 
         [0255]    As shown in  FIG. 11 , the agitation device  350  has a traveling magnetic field generating unit  360  and an introduced/suspended matter partition member  370 . 
         [0256]    The traveling magnetic field generating unit  360  is an embodiment of the traveling magnetic field generating unit according to the present invention and generates (α) a magnetic field traveling downward along the sidewall  22  of the rear side and (β) a magnetic field traveling upward along the sidewall  22  of the rear side in the charging tank  20 . 
         [0257]    As shown in  FIG. 11 , the traveling magnetic field generating unit  360  is arranged outside the charging tank  20  (in this embodiment, behind the charging tank  20 ). 
         [0258]    The traveling magnetic field generating unit  360  has two permanent magnets  361 , a support member  362 , a motor  363  having a rotational shaft  363   a , and a fixing member  364 . 
         [0259]    In the members constituting the traveling magnetic field generating unit  360 , the permanent magnets  361 , the support member  362  and the motor  363  having the rotational shaft  363   a  respectively have fundamentally the same construction as the permanent magnets  161 , the support member  162  and the motor  163  having the rotational shaft  163   a  in  FIG. 1 , therefore description thereof is omitted. 
         [0260]    The fixing member  364  fixes the motor  363  to a predetermined position of the charging tank  20 . 
         [0261]    The fixing member  364  is fixed to a structure or the like (not shown). 
         [0262]    The introduced/suspended matter partition member  370  shown in  FIGS. 11 ,  12  and  13  is an embodiment of the introduced/suspended matter partition member according to the present invention. 
         [0263]    The introduced/suspended matter partition member  370  is a plate-like member at least the surface thereof is constructed by refractory material such as ceramic. The inside of the introduced/suspended matter partition member  370  may be constructed by heat-resistant material such as metal. 
         [0264]    The introduced/suspended matter partition member  370  is arranged inside the charging tank  20  (inside the charging chamber  23 ). In more detail, the introduced/suspended matter partition member  370  is arranged at the position opposite to the traveling magnetic field generating unit  360  about the sidewall  22  of the rear side of the charging tank  20 . 
         [0265]    As shown in  FIG. 12 , the left end of the introduced/suspended matter partition member  370  is fixed to the middle portion in the longitudinal direction of the sidewall  22  of the left side of the charging tank  20 , and the right end of the introduced/suspended matter partition member  370  is fixed to the middle portion in the longitudinal direction of the sidewall  22  of the right side of the charging tank  20 . 
         [0266]    As a result, the introduced/suspended matter partition member  370  divides (partitions) the inner space of the charging tank  20  into two spaces, a charging/melting chamber  24  and a suspended matter recovery chamber  25 . 
         [0267]    The charging/melting chamber  24  is one of the spaces divided by the introduced/suspended matter partition member  370  closer to the traveling magnetic field generating unit  360 . 
         [0268]    The charging/melting chamber  24  is a space for introducing the aluminum cutting chips  2  to the molten metal  3 . The aluminum cutting chips  2  are introduced to the molten metal  3  through the part of the liquid surface of the molten metal  3  corresponding to the charging/melting chamber  24 . 
         [0269]    The suspended matter recovery chamber  25  is the other one of the spaces divided by the introduced/suspended matter partition member  370  further from the traveling magnetic field generating unit  360 , and is a space provided just at the intermediate between the charging/melting chamber  24  and the holding chamber  14  in the melting tank (intermediate chamber). 
         [0270]    The suspended matter recovery chamber  25  is a space for recovering slag  4  (see  FIGS. 14 and 15 ) generated by the melting of the aluminum cutting chips  2  (introduction of the aluminum cutting chips  2  to the molten metal  3  for melting the aluminum cutting chips  2 ). 
         [0271]    The slag  4  is various kinds of contaminants, oxides of adhering matters to the aluminum cutting chips  2  (oil, paints, combustibles and the like), oxides of the surfaces of the aluminum cutting chips  2 , non-metallic inclusions, or mixture (aggregate) thereof, and has smaller density (strictly, bulk density) than the molten metal  3  so as to float on the molten metal  3 . The slag  4  is an embodiment of the suspended matters according to the present invention. 
         [0272]    As shown in  FIGS. 11 and 13 , the upper end of the introduced/suspended matter partition member  370  is arranged at the position higher than the liquid surface of the molten metal  3 . 
         [0273]    A gap of predetermined size (L 1  in  FIG. 13 ) is formed between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20 , and the charging/melting chamber  24  and the suspended matter recovery chamber  25  are communicated with each other through the lower portion of the space. 
         [0274]    The introduced/suspended matter partition member  370  regulates the travel of the molten metal  3  mutually between the charging/melting chamber  24  and the suspended matter recovery chamber  25  in the part near the liquid surface thereof (the part close to the liquid surface of the molten metal  3 ) (the molten metal  3  cannot travel mutually between the charging/melting chamber  24  and the suspended matter recovery chamber  25  in the part near the liquid surface thereof). 
         [0275]    The introduced/suspended matter partition member  370  permits the travel of the molten metal  3  mutually between the charging/melting chamber  24  and the suspended matter recovery chamber  25  (through the gap between the introduced/suspended matter partition member  370  and the bottom floor  21 ) in the part far from the liquid surface thereof (the part close to the bottom floor  21 ). 
         [0276]    The part forming the rear surface of the structure  11  is arranged inside the melting tank in this embodiment (the combination of the structure  11  and the charging tank  20 ). 
         [0277]    The part forming the rear surface of the structure  11  is arranged at the position further from the traveling magnetic field generating unit  360  than the introduced/suspended matter partition member  370 . 
         [0278]    The part forming the rear surface of the structure  11  partitions (divides) “the part further from the traveling magnetic field generating unit  360  than the introduced/suspended matter partition member  370  in the inner space of the melting tank in this embodiment” into two spaces, the suspended matter recovery chamber  25  and the holding chamber  14 . 
         [0279]    The lower portion of the lower end of the part forming the rear surface of the structure  11  (the lower portion of the rear surface of the structure  11 ) is formed therein with the communication passage  15 , and the suspended matter recovery chamber  25  and the holding chamber  14  are communicated with each other through the lower portion of the space. 
         [0280]    The suspended matter recovery chamber  25  is one of the two spaces partitioned by the part forming the rear surface of the structure  11  as a border closer to the traveling magnetic field generating unit  360 . 
         [0281]    In this embodiment, the holding chamber  14  is the other one of the two spaces partitioned by the part forming the rear surface of the structure  11  further from the traveling magnetic field generating unit  360 , and the molten metal  3  is taken out (recovered) from the holding chamber  14 . 
         [0282]    Therefore, the holding chamber  14  corresponds to an embodiment of the molten metal recovery chamber according to the present invention, and the part forming the rear surface of the structure  11  corresponds to an embodiment of the suspended matter/molten metal partition member according to the present invention. 
         [0283]    Explanation will be given on the behavior of the aluminum cutting chips  2  in the case that the aluminum cutting chips  2  is introduced to the liquid surface of the molten metal  3  in the charging/melting chamber  24  referring to  FIGS. 12 and 13 . 
         [0284]    By supplying electric power to the motor  363  of the traveling magnetic field generating unit  360 , the support member  362  (in its turn, the permanent magnets  361 ) is rotated counterclockwise when viewed in rear. 
         [0285]    Therefore, similarly to the melting furnace  100  shown in  FIG. 1 , the magnetic field traveling counterclockwise when viewed in rear is generated inside the charging tank  20  (the charging/melting chamber  24  and the suspended matter recovery chamber  25 ), and “helical flowing which is counterclockwise when viewed in rear” is generated in the molten metal  3  along the magnetic field. 
         [0286]    The aluminum cutting chips  2  introduced to the liquid surface of the molten metal  3  in the charging/melting chamber  24  are rolled up into the molten metal  3  along the flowing in the molten metal  3 . 
         [0287]    The aluminum cutting chips  2  rolled up into the molten metal  3  are moved forward in the molten metal  3  in the charging/melting chamber  24  while rotated counterclockwise when viewed in rear and is melted. 
         [0288]    The unmelted aluminum cutting chips  2  are moved from the charging/melting chamber  24  through the gap between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  to the suspended matter recovery chamber  25 . 
         [0289]    The longer the distance from the permanent magnets  361  is, the weaker the magnetic field traveling counterclockwise when viewed in rear in the molten metal  3  is. 
         [0290]    The charging/melting chamber  24  and the suspended matter recovery chamber  25  are divided by the introduced/suspended matter partition member  370  at the part near the liquid surface of the molten metal  3  so that “the helical flowing which is counterclockwise when viewed in rear” generated in the molten metal  3  in the charging/melting chamber  24  is intercepted to some extent by the introduced/suspended matter partition member  370 . 
         [0291]    Accordingly, “the helical flowing which is counterclockwise when viewed in rear” generated in the molten metal  3  in the suspended matter recovery chamber  25  is weaker than “the helical flowing which is counterclockwise when viewed in rear” generated in the molten metal  3  in the charging/melting chamber  24  and is a substantially forward gradual flowing which is helical to some extent. 
         [0292]    The density of the unmelted aluminum cutting chips  2  is substantially the same as the density of the molten metal  3 , whereby the buoyancy applied to the unmelted aluminum cutting chips  2  by the molten metal  3  substantially balances with the gravity applied to the unmelted aluminum cutting chips  2  (weight). 
         [0293]    Therefore, the unmelted aluminum cutting chips  2  moved through the gap between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  to the inside of the suspended matter recovery chamber  25  is not raised widely by the buoyancy and is moved forward gradually and is melted. 
         [0294]    Then, the unmelted aluminum cutting chips  2  is moved from the suspended matter recovery chamber  25  through the communication passage  15  to the holding chamber  14 . 
         [0295]    The distance of the holding chamber  14  from the permanent magnets  361  is longer than that of the suspended matter recovery chamber  25 , whereby “the helical flowing which is counterclockwise when viewed in rear” is hardly generated in the molten metal  3  in the holding chamber  14 . 
         [0296]    The part of the aluminum cutting chips  2  introduced to the liquid surface of the molten metal  3  in the charging/melting chamber  24  which are not melted and moved to the holding chamber  14  is heated by the molten metal  3  in the holding chamber  14  so as to melted anyway. 
         [0297]    Accordingly, the aluminum cutting chips  2  introduced to the liquid surface of the molten metal  3  in the charging/melting chamber  24  are melted during the movement along “the helical flowing which is counterclockwise when viewed in rear” generated in the molten metal  3  by the traveling magnetic field generating unit  360 . 
         [0298]    The aluminum cutting chips  2  are moved to the liquid surface of the molten metal  3  in the charging/melting chamber  24 , the lower portion of the molten metal  3  in the charging/melting chamber  24 , the lower portion of the molten metal  3  in the suspended matter recovery chamber  25 , and the holding chamber  14  in this order and not moved to the vicinity of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25 . 
         [0299]    Explanation will be given on the behavior of the slag  4  generated by introducing the aluminum cutting chips  2  to the liquid surface of the molten metal  3  in the charging/melting chamber  24  referring to  FIGS. 14 and 15 . 
         [0300]    The slag  4  generated by introducing the aluminum cutting chips  2  to the liquid surface of the molten metal  3  in the charging/melting chamber  24  is rolled up to the inside of the molten metal  3  along the flowing of the molten metal  3 . 
         [0301]    The slag  4  rolled up to the inside of the molten metal  3  is moved forward in the molten metal  3  in the charging/melting chamber  24  while rotated counterclockwise when viewed in rear. 
         [0302]    Then, the slag  4  is moved from the charging/melting chamber  24  through the gap between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  to the suspended matter recovery chamber  25 . 
         [0303]    The slag  4  has smaller density (strictly, bulk density) than the molten metal  3 , whereby the buoyancy applied to the slag  4  by the molten metal  3  is larger than the gravity applied to the slag  4  (weight). 
         [0304]    Therefore, the slag  4  moved through the gap between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  to the suspended matter recovery chamber  25  is separated from the flowing generated in the molten metal  3  in the suspended matter recovery chamber  25  (substantially forward gradual flowing which is helical to some extent) and is raised to the left half of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25  by the buoyancy. 
         [0305]    When the slag  4  is raised to the liquid surface of the molten metal  3 , the buoyancy applied to the slag  4  by the molten metal  3  balances with the gravity applied to the slag  4  (weight). 
         [0306]    Accordingly, the slag  4  raised to the left half of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25  is gradually moved to the left end of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25  along the flowing generated in the molten metal  3  in the suspended matter recovery chamber  25  while floating on the liquid surface of the molten metal  3  and then retained (see  FIG. 14 ). 
         [0307]    Accordingly, the slag  4  generated by introducing the aluminum cutting chips  2  to the liquid surface of the molten metal  3  in the charging/melting chamber  24  is separated from the aluminum cutting chips  2  and collected at the specific position in the melting tank (in this embodiment, “the left end of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25 ”). The collected slag  4  is recovered (taken out to the outside) manually or automatically. 
         [0308]    As a concrete embodiment of the method for recovering manually the slag  4 , an operator may scratch off (ladle out) the slag  4  with a tool like a ladle. As a concrete embodiment of the method for recovering automatically the slag  4 , a device may be employed which ladle out the slag  4  from the vicinity of the liquid surface of the molten metal  3 . 
         [0309]    As mentioned above, the agitation device  350 , which agitates the molten metal  3  to which the aluminum cutting chips  2  are introduced so as to promote melting of the aluminum cutting chips  2 , has the traveling magnetic field generating unit  360  which is arranged outside the melting tank (in this embodiment, outside the charging tank  20 ) and generates the magnetic field traveling downward along the sidewall of the melting tank (in this embodiment, the sidewall  22  of the rear side in the charging tank  20 ) inside the melting tank, and the introduced/suspended matter partition member  370  which is arranged inside the melting tank (in this embodiment, inside the charging tank  20 ) and divides the space inside the melting tank into the two spaces communicated with each other at the lower portions thereof (the charging/melting chamber  24  and the suspended matter recovery chamber  25 ). One of the two spaces divided by the introduced/suspended matter partition member  370  closer to the traveling magnetic field generating unit  360  (in this embodiment, the rear half space of the charging tank  20 ) is employed as the charging/melting chamber  24  which is the space for introducing the aluminum cutting chips  2  to the molten metal  3  in the melting tank. The other one of the two spaces divided by the introduced/suspended matter partition member  370  further from the traveling magnetic field generating unit  360  (in this embodiment, the front half space of the charging tank  20 ) is employed as the suspended matter recovery chamber  25  which is the space for recovering the slag  4  generated by the melting of the aluminum cutting chips  2 . 
         [0310]    Explanation will be given on the merits of the above-mentioned construction of the agitation device  350  (the melting furnace  300  having the agitation device  350  constructed as the above) in comparison with the conventional arts, the scrap melting promotion device described in the Japanese Patent Laid Open Gazette Hei. 5-255770 (hereinafter, referred to as “conventional art (A)”) and the melting processing device described in the Japanese Patent Laid Open Gazette Hei. 6-49553 (hereinafter, referred to as “conventional art (B)”). 
         [0311]    The device of the conventional art (A) is provided in an open well part of a melting furnace (a part of a melting tank opened upward) and mainly has a rotating blade rotated centering on a vertical shaft, a casing covering the rotating blade, and a chute through which aluminum scrap is introduced to a gap between the rotating blade and the inner peripheral surface of the casing. An opening through which molten metal can be sucked is formed in the lower surface of the casing. An opening through which the molten metal can flow out is formed in the side surface of the casing. The chute is connected to the upper surface of the casing. 
         [0312]    The aluminum scrap introduced to the chute falls to the gap between the rotating blade and the inner peripheral surface of the casing, and is agitated by the rotating blade while soaked in the molten metal. As a result, the aluminum scrap is moved through the opening formed in the side surface of the casing to the inside of the melting furnace while melted. 
         [0313]    However, in the conventional art (A), the rotating blade generates strong flowing of the molten metal in the melting tank from the open well part to the inside of the main furnace. Therefore, suspended matters are moved on the flowing to the inside of the main furnace, whereby the suspended matters is mixed with the molten metal in the main furnace so that the quality of the molten metal in the main furnace is worsened. 
         [0314]    When the state that the suspended matters is mixed with the molten metal in the main furnace is held for a long period, self continuous oxidation reaction is caused by the heat of the suspended matters themselves, whereby surrounding clean molten metal may be oxidized so as to generate electric ashes (new suspended matters). 
         [0315]    For solving such a problem, a method is conceivable that a door is provided between the open well part and the main furnace and a cycle of below three processes (a1) to (a3) is repeated.
       (a1) The door is closed and the rotating blade is rotated so as to melt the aluminum scrap.   (a2) The suspended matters floating on the liquid surface of the molten metal in the open well part are recovered.   (a3) The door is opened and the molten metal in the open well part is mixed with the molten metal in the inside of the main furnace.       
 
         [0319]    However, in the method, the melting of the aluminum scrap cannot be performed simultaneously with the heating of the molten metal in the main furnace (the processes are performed as batch operation) and the reduction of the molten metal in the open well part caused by introducing the aluminum scrap to the molten metal reduces the melting speed, whereby the productivity (melting amount per unit time) is reduced. 
         [0320]    When the door is opened, the heat in the main furnace is emitted to the outside, whereby the energy cost is increased. 
         [0321]    In the case that the door is made thick so as to prevent the emission of the heat, the weight of the door is increased, whereby the device is enlarged, the cost of equipment is increased, and energy consumption required for opening and closing of the door is increased. 
         [0322]    Furthermore, in the construction of the conventional art (A), the suspended matters are distributed over the whole open well part in the process (a2) so that the recovery of the suspended matters is complicated (time and labor required for the recovery of the suspended matters are increased), whereby the productivity is reduced. 
         [0323]    In the conventional art (B), a tip tool (stick member) is soaked to molten metal from an open well part of a melting furnace and the tip tool is moved longitudinally and vertically (moved locomotively), thereby agitating the molten metal. 
         [0324]    However, in the conventional art (B), the tip tool (stick member) knocks suspended matters so as to crush them finely while soaking them to the molten metal, whereby fine suspended matters are mixed uniformly with the molten metal and the quality of the molten metal is reduced (the concentration of the suspended matters mixed as foreign matters with the molten metal is increased). 
         [0325]    For solving such a problem, the method similar to the method mentioned in the explanation of the conventional art (A) is conceivable. However, in this case, problems similar to that of the conventional art (A) (reduction of the productivity, enlargement of the device, increase of the cost of equipment, increase of the energy consumption required for opening and closing of the door, complexity of the recovery of the suspended matters) are caused. 
         [0326]    To the contrarily, in the agitation device  350 , the slag  4  can be corrected to the certain position in the suspended matter recovery chamber  25  (the left end of the liquid surface of the molten metal  3  in the charging tank  20 ) and recovered, whereby the recovery of the slag  4  is easy (it is not necessary to perform the recovery of the slag  4  over the whole liquid surface of the molten metal  3  in the charging tank  20 ). 
         [0327]    In the agitation device  350 , the slag  4  can be prevented from being mixed with the molten metal in the holding chamber  14 , thereby increasing the quality of the molten metal in the holding chamber  14 . 
         [0328]    In the agitation device  350 , it is not necessary to provide a door partitioning the charging tank  20  (open well part) and the main body  10  (main furnace), whereby the agitation device  350  can be established easily to the existing melting furnace and the cost of equipment at the time of the providing can be suppressed. 
         [0329]    In the agitation device  350 , the work that the aluminum cutting chips  2  are introduced to the molten metal  3  and melted (the molten metal  3  is agitated), the work that the slag  4  is recovered, and the work that the molten metal in the charging tank  20  is mixed with the molten metal in the main body  10  (the molten metal in the holding chamber  14 ) are performed respectively at the different positions (the charging/melting chamber  24 , the suspended matter recovery chamber  25  and the holding chamber  14 ). Accordingly, these works can be performed simultaneously in parallel, whereby the continuous operation can be performed so as to improve the productivity. 
         [0330]    In this embodiment, the introduced/suspended matter partition member  370  is plate like and the plate surface of the introduced/suspended matter partition member  370  is perpendicular to the axis of the rotational shaft  363   a  of the motor  363  of the traveling magnetic field generating unit  360 , that is, the macro advancing direction of flowing of the molten metal  3  generated by the traveling magnetic field generating unit  360  (the longitudinal direction). However, the present invention is not limited thereto. 
         [0331]    Namely, when the slag  4  can be recovered to the suspended matter recovery chamber  25 , the plate surface of the suspended matter recovery chamber  25  may be slanted slightly from the perpendicular to the macro advancing direction of flowing of the molten metal  3  generated by the traveling magnetic field generating unit  360 . 
         [0332]    In this embodiment, the part constituting the rear surface of the structure  11  corresponds to an embodiment of the suspended matter/molten metal partition member according to the present invention. However, the present invention is not limited thereto. 
         [0333]    For example, as shown in  FIGS. 16 and 17 , a suspended matter/molten metal partition member  380  may alternatively be provided which is arranged inside the melting tank (in  FIGS. 16 and 17 , inside the charging tank  20 ) and further from the traveling magnetic field generating unit  360  than the introduced/suspended matter partition member  370 . 
         [0334]    The suspended matter/molten metal partition member  380  divides the part of the space inside the melting tank further from the traveling magnetic field generating unit  360  than the introduced/suspended matter partition member  370  into two spaces communicated with each other at lower portions thereof. 
         [0335]    In the embodiment shown in  FIGS. 16 and 17 , the suspended matter recovery chamber  25  is one of the two spaces divided by the suspended matter/molten metal partition member  380  closer to the traveling magnetic field generating unit  360 . 
         [0336]    The holding chamber  14  is the other one of the two spaces divided by the suspended matter/molten metal partition member  380  further from the traveling magnetic field generating unit  360 , and serves as a “molten metal recovery chamber” which is a space for recovering the molten metal  3  from the melting tank. 
         [0337]    In the embodiment shown in  FIGS. 16 and 17 , the combination of the part of the inside of the charging tank  20  further from the traveling magnetic field generating unit  360  than the suspended matter/molten metal partition member  380  and the holding chamber  14  corresponds the molten metal recovery chamber. 
         [0338]    Similarly to the introduced/suspended matter partition member  370 , the suspended matter/molten metal partition member  380  shown in  FIGS. 16 and 17  is a plate-like member at least the surface thereof is constructed by refractory material such as ceramic. 
         [0339]    Preferably, a gap L 1  between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  and a height L 2  of the communication passage  15  (see  FIG. 13 ), or the gap L 1  between the lower end of the introduced/suspended matter partition member  370  and the bottom floor  21  of the charging tank  20  and a gap L 3  between the lower end of the suspended matter/molten metal partition member  380  and the bottom floor  21  of the charging tank  20  (see  FIG. 17 ) are set appropriately in synthetic consideration of various elements shown below. 
         [0340]    Namely, for preventing the slag  4  from moving into the holding chamber  14  so as to collect efficiently the slag  4  to the suspended matter recovery chamber  25 , preferably, the gap L 1  and the height L 2  (otherwise, the gap L 1  and the gap L 3 ) are set as small as possible. 
         [0341]    For making the movement of the molten metal  3  between the charging/melting chamber  24  and the suspended matter recovery chamber  25  and between the suspended matter recovery chamber  25  and the holding chamber  14  so as to keep the temperature of the molten metal  3  uniform, or for preventing the unmelted aluminum cutting chips  2  from being caught in the movement passage between the charging/melting chamber  24  and the suspended matter recovery chamber  25  or between the suspended matter recovery chamber  25  and the holding chamber  14 , preferably, the gap L 1  and the height L 2  (otherwise, the gap L 1  and the gap L 3 ) are set large. 
         [0342]    It may alternatively be constructed that the introduced/suspended matter partition member  370  (and the suspended matter/molten metal partition member  380 ) is fixed movably vertically about the sidewall  22  of the right and left sides of the charging tank  20  so as to make the gap L 1  (and the gap L 3 ) changeable (regulatable). 
         [0343]    As shown in  FIG. 18 , it may alternatively be constructed that the introduced/suspended matter partition member  370  is a (plate-like) member L-like shaped when viewed in plan constructed by a first plate member  371  and a second plate member  372  so that the suspended matter recovery chamber  25  is L-like shaped when viewed in plan constructed by a main chamber  25   a  and an auxiliary chamber  25   b  connected to one of ends of the main chamber  25   a . Accordingly, the slag  4  floating on the liquid surface of the molten metal  3  in the main chamber  25   a  of the suspended matter recovery chamber  25  rides on the flowing in the vicinity of the liquid surface of the molten metal  3  and is moved leftward in the main chamber  25   a  and then collected to the auxiliary chamber  25   b  after the rearward binding (the flowing of the liquid surface of the molten metal  3  in the main chamber  25   a  is moved from the other end of the main chamber  25   a  to the one of ends of the main chamber  25   a  (the end connected to the auxiliary chamber  25   b )). 
         [0344]    According to the construction, the suspended matter recovery chamber  25  can set larger, whereby the slag  4  can be collected easily. 
         [0345]    The auxiliary chamber  25   b  to which the slag  4  is collected is arranged further from the holding chamber  14  than the main chamber  25   a , whereby the slag  4  can be prevented from being mixed with the molten metal  3  in the holding chamber  14 , in its turn the quality of the molten metal  3  in the holding chamber  14  is improved. 
         [0346]    As shown in  FIG. 19 , the agitation device  350  may alternatively have a flux injection device  391  and a suspended matter recovery device  392 . 
         [0347]    The flux injection device  391  supplies flux to the molten metal  3 . 
         [0348]    Herein, the “flux” means material which acts on impurities and the like in the molten metal  3  so as to generate the slag  4 . 
         [0349]    In the embodiment shown in  FIG. 19 , the flux injection device  391  supplies the flux to the right end of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25  so as to separate and remove the slag  4  suspended in the molten metal  3  (reduce the mixed concentration of impurities and foreign matters). 
         [0350]    The slag  4  can be separated from the aluminum content rolled up in the slag  4 , thereby improving melting yield (amount of the aluminum which can be recovered). 
         [0351]    The suspended matter recovery device  392  recovers the slag  4  floating on the liquid surface of the molten metal  3 . 
         [0352]    In the embodiment shown in  FIG. 19 , the suspended matter recovery device  392  has a jig  392   a  which ladles the slag  4  and the jig  392   a  is arranged at the left end of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25 , that is, the position at which the slag  4  is collected finally. 
         [0353]    According to the construction, the suspended matter recovery device  392  is not necessary to scan the whole liquid surface of the molten metal  3  in the charging tank  20  so as to recover the slag  4  and can recover the slag  4  only by ladling the slag  4  at the certain position (in the embodiment shown in  FIG. 19 , the left end of the liquid surface of the molten metal  3  in the suspended matter recovery chamber  25 ), thereby simplifying the construction of the suspended matter recovery device  392 . 
         [0354]    At the time of recovery work of the slag  4 , the suspended matter recovery device  392  does not interfere with the other units constituting the agitation device  350  or the other members constituting the melting furnace  300 , whereby the recovery work of the slag  4  can be performed continuously so as to improve the quality of the molten metal  3  and to reduce labor for the recovery work of the slag  4 . 
         [0355]    Explanation will be given on a melting furnace  400  which is a fourth embodiment of the melting apparatus according to the present invention and a melting method of the aluminum cutting chips  2  with the melting furnace  400  referring to  FIGS. 20 to 34 . 
         [0356]    As shown in  FIG. 20 , the melting furnace  400  generates the molten metal  3  by melting the aluminum cutting chips  2  and has the main body  10 , the charging tank  20 , a traveling magnetic field generating unit  460  and a traveling magnetic field generating unit  470 . 
         [0357]    The main body  10  holds the temperature of the molten metal  3  higher than solidifying temperature. 
         [0358]    The main body  10  has the structure  11 , the fireproof thermal insulating member  12  and the burner  13 . 
         [0359]    The structure  11  is an embodiment of the outside plate according to the present invention, and is a substantially rectangular box-like member formed by combining plate-like members constructed by metal material (for example, steel plates). 
         [0360]    The fireproof thermal insulating member  12  is constructed by ceramics or the like and is fixed to the inner peripheral surface of the structure  11  so as to cover the inner peripheral surface of the structure  11  (the inner plate surfaces of the plate-like members constituting the structure  11 ). 
         [0361]    The holding chamber  14  is formed I side the structure  11  as a space surrounded by the fireproof thermal insulating member  12 , and the communication passage  15  is formed in the lower portion of the rear surface of the structure  11 . The molten metal  3  is stored in the lower half of the holding chamber  14 . 
         [0362]    The burner  13  is provided in the upper portion of the inner peripheral surface of the structure  11  and heats air in the holding chamber  14 , in its turn the molten metal  3  stored in the lower half of the holding chamber  14  (the molten metal  3  touching the air). 
         [0363]    The charging tank  20  is a part of the melting furnace  400  through which the aluminum cutting chips  2  is introduced. 
         [0364]    The charging tank  20  is fixed to the rear end of the main body  10 . The charging tank  20  has the bottom floor  21  and the sidewall  22 . 
         [0365]    The bottom floor  21  is a part of the charging tank  20  which is a plate-like part substantially rectangular when viewed in plan and is extended rearward from the rear end of the structure  11 . 
         [0366]    In this embodiment, the bottom floor  21  has an outside plate  21   a  and a fireproof member  21   b.    
         [0367]    The outside plate  21   a  is an embodiment of the outside plate according to the present invention, and constitutes the outer half (in this embodiment, lower half) of the bottom floor  21 . In this embodiment, the outside plate  21   a  is a plate-like member constructed by metal material (for example, a steel plate). 
         [0368]    The fireproof member  21   b  is constructed by ceramics or the like and is fixed to the inner plate surface (in this embodiment, upper plate surface) of the outside plate  21   a  so as to cover the inner plate surface of the outside plate  21   a.    
         [0369]    The sidewall  22  is a part of the charging tank  20  which is a plate-like part and is standingly provided along the left end, rear end and right end of the bottom floor  21 . The left and right front ends of the sidewall  22  are respectively extended to the left and right ends of the rear surface of the structure  11 . 
         [0370]    In this embodiment, the sidewall  22  has an outside plate  22   a  and a fireproof member  22   b.    
         [0371]    The outside plate  22   a  is an embodiment of the outside plate according to the present invention, and constitutes the outer half (in the case of the part of the sidewall  22  standingly provided along the rear end of the bottom floor  21 , rear half) of the bottom floor  22 . In this embodiment, the outside plate  22   a  is a plate-like member constructed by metal material (for example, a steel plate). 
         [0372]    The fireproof member  22   b  is constructed by ceramics or the like and is fixed to the inner plate surface (in the case of the part of the sidewall  22  standingly provided along the rear end of the bottom floor  21 , front plate surface) of the outside plate  22   a  so as to cover the inner plate surface of the outside plate  22   a.    
         [0373]    A charging chamber  23  is formed in the charging tank  20  as a space surrounded by the bottom floor  21 , the sidewall  22  and the rear surface of the structure  11 . The molten metal  3  is stored in the lower half of the charging chamber  23 . 
         [0374]    The holding chamber  14  is communicated with the charging chamber  23  through the communication passage  15 , and the molten metal  3  can moves between the holding chamber  14  and the charging chamber  23  through the communication passage  15 . 
         [0375]    The upper surface of the charging tank  20  is opened and the aluminum cutting chips  2  is introduced through the opening into the charging chamber  23 . The aluminum cutting chips  2  is introduced into the charging chamber  23  touch the molten metal  3  stored in the lower half of the charging chamber  23  and heated, and then melted when the temperature thereof becomes higher than the melting point. 
         [0376]    In this embodiment, the molten metal  3  is stored in the part constructed by combining the rear surface of the structure  11 , whose inner peripheral surface is covered by the fireproof thermal insulating member  12 , with the charging tank  20 . Therefore, each of “the rear surface of the structure  11  whose inner peripheral surface is covered by the fireproof thermal insulating member  12 ” and “the charging tank  20 ” is an embodiment of the melting tank according to the present invention. 
         [0377]    The traveling magnetic field generating unit  460  is an embodiment of the traveling magnetic field generating unit according to the present invention and generates a magnetic field traveling along the sidewall  22  of the rear side (the outside plate  22   a  of the rear side) in the charging tank  20  so as to agitate the molten metal  3  to which the aluminum cutting chips  2  are introduced (the molten metal  3  stored in the lower half of the charging chamber  23 ), in its turn, melting of the aluminum cutting chips  2  is promoted. 
         [0378]    As shown in  FIG. 20 , the traveling magnetic field generating unit  460  is arranged outside the charging tank  20 , in mode detail behind the charging tank  20 . 
         [0379]    The traveling magnetic field generating unit  460  has permanent magnets  461   a  and  461   b , a support member  462 , a motor  463  and a fixing member  464 . 
         [0380]    The permanent magnets  461   a  and  461   b  are an embodiment of the permanent magnets according to the present invention and face the sidewall  22  of the rear side (the outer plate surface of the outside plate  22   a  of the rear side) as shown in  FIGS. 20 and 21 . 
         [0381]    In this embodiment, for generating strong magnetic power, the permanent magnets  461   a  and  461   b  are constructed by the neodymium magnet. 
         [0382]    In this embodiment, the traveling magnetic field generating unit  460  has the two permanent magnets  461   a  and  461   b . However, the present invention is not limited thereto and the number of the permanent magnets provided in the traveling magnetic field generating unit according to the present invention may be one or the plural. 
         [0383]    The support member  462  is an embodiment of the support member according to the present invention and supports the permanent magnets  461   a  and  461   b.    
         [0384]    The support member  462  is substantially discoid. The permanent magnets  461   a  and  461   b  are fixed to the discoid surface of the support member  462  facing the sidewall  22  of the rear side. 
         [0385]    The motor  463  is an embodiment of the motor according to the present invention and rotatively drives the support member  462 , in its turn the permanent magnets  461   a  and  461   b  fixed to the support member  462 . 
         [0386]    A rotational shaft  463   a  of the motor  463  is an embodiment of the rotational shaft according to the present invention and fixed to the support member  462 . The axis of the rotational shaft  463   a  is coaxial to the center line of the support member  462  (the line passing through the centers of the pair of surfaces of the support member  462 ). 
         [0387]    In this embodiment, the motor  463  is an electric motor. However, motor according to the present invention is not limited thereto and may alternatively be a motor rotatively driven by fluid pressure (for example, hydraulic motor or pneumatical motor). 
         [0388]    The fixing member  464  fixes the motor  463  to a position behind the charging tank  20 . The fixing member  464  is fixed to a structure or the like (not shown). 
         [0389]    When the motor  463  is fixed to the fixing member  464 , the rotational shaft  463   a  of the motor  463  is perpendicular to the sidewall  22  of the rear side (the outer plate surface of the outside plate  22   a  of the rear side). When the motor  463  is fixed to the fixing member  464 , the discoid surface of the support member  462  is in parallel to the sidewall  22  of the rear side (the outer plate surface of the outside plate  22   a  of the rear side). 
         [0390]    By supplying electric power to the motor  463 , the rotational shaft  463   a , the support member  462  fixed to the rotational shaft  463   a  and the permanent magnets  461   a  and  461   b  fixed to the support member  462  are integrally rotated centering on the rotational shaft  463   a  (in this embodiment, the permanent magnets  461   a  and  461   b  are rotated counterclockwise when viewed in rear). 
         [0391]    As a result, on the sidewall  22  of the rear side, the magnetic field traveling substantially downward along the sidewall  22  of the rear side is generated in the part facing the left half of the support member  462 , and the magnetic field traveling substantially upward along the sidewall  22  of the rear side is generated in the part of the inside of the charging tank  20  corresponding to the part facing the right half of the support member  462  (that is, the position away from the magnetic field traveling downward for a predetermined distance). In other words, the magnetic field traveling counterclockwise when viewed in rear is generated at the part of the inside of the charging tank  20  facing the permanent magnets  461   a  and  461   b.    
         [0392]    When the magnetic field traveling substantially downward along the sidewall  22  is generated inside the charging tank  20 , in the molten metal  3  stored in the charging tank  20 , the substantially downward flowing of the molten metal  3  (molten metal flowing) is generated at the part on which the magnetic field acts. 
         [0393]    When the magnetic field traveling substantially upward along the sidewall  22  is generated inside the charging tank  20 , in the molten metal  3  stored in the charging tank  20 , the substantially upward flowing of the molten metal  3  (molten metal flowing) is generated at the part on which the magnetic field acts. 
         [0394]    As a result, in the molten metal  3 , flowing of the molten metal  3  (molten metal flowing) is generated which circulates centering on the axis substantially in parallel to the liquid surface of the molten metal  3  (in this embodiment, the rotational shaft  463   a  of the motor  463 ). 
         [0395]    When the aluminum cutting chips  2  are introduced to the molten metal  3  in which the flowing is generated, the aluminum cutting chips  2  are moved on the flowing of the molten metal  3  (molten metal flowing) and dive into the inside of the molten metal  3  (soaked in the molten metal  3 ) at the position as which the substantially downward flowing of the molten metal  3  (molten metal flowing) is generated, and then melted by the heat of the molten metal  3 . 
         [0396]    When the aluminum cutting chips  2  are melted, the temperature of the molten metal  3  in the vicinity of the molten aluminum cutting chips  2  is reduced. However, the molten metal  3  is agitated by the flowing of the molten metal  3  (molten metal flowing) so that the temperature of the molten metal  3  is held substantially equally. 
         [0397]    Furthermore, by generating the substantially upward flowing of the molten metal  3  (molten metal flowing), the molten metal  3  with comparative high temperature is moved to the vicinity of the liquid surface of the molten metal  3  to which the aluminum cutting chips  2  are introduced. Accordingly, when a large quantity of the aluminum cutting chips  2  are introduced continuously to the molten metal  3 , the aluminum cutting chips  2  can be melted efficiently. 
         [0398]    The traveling magnetic field generating unit  470  generates a magnetic field traveling along the plate-like member constituting the lower surface of the structure  11  in the main body  10  so as to agitate the molten metal  3  stored in the lower half of the holding chamber  14 , thereby making the temperature of the molten metal  3  uniform. 
         [0399]    As shown in  FIG. 20 , the traveling magnetic field generating unit  470  is arranged outside the main body  10 , in more detail below the main body  10 . 
         [0400]    The traveling magnetic field generating unit  470  has permanent magnets  471   a  and  471   b , a support member  472 , a motor  473  and a fixing member  474 . 
         [0401]    The permanent magnets  471   a  and  471   b  face the plate-like member constituting the lower surface of the structure  11 . 
         [0402]    In this embodiment, for generating strong magnetic power, the permanent magnets  471   a  and  471   b  are constructed by the neodymium magnet. 
         [0403]    The support member  472  supports the permanent magnets  471   a  and  471   b.    
         [0404]    The support member  472  is substantially discoid. The permanent magnets  471   a  and  471   b  are fixed to the discoid surface of the support member  472  facing the plate-like member constituting the lower surface of the structure  11 . 
         [0405]    The motor  473  is rotatively drives the support member  472 , in its turn the permanent magnets  471   a  and  471   b  fixed to the support member  472 . 
         [0406]    A rotational shaft  473   a  of the motor  473  is fixed to the support member  472 . The axis of the rotational shaft  473   a  is coaxial to the center line of the support member  472  (the line passing through the centers of the pair of surfaces of the support member  472 ). 
         [0407]    The fixing member  474  fixes the motor  473  to a position below the plate-like member constituting the lower surface of the structure  11 . The fixing member  474  is fixed to a structure or the like (not shown). 
         [0408]    When the motor  473  is fixed to the fixing member  474 , the rotational shaft  473   a  of the motor  473  is perpendicular to the lower surface of the plate-like member constituting the lower surface of the structure  11 . When the motor  473  is fixed to the fixing member  474 , the discoid surface of the support member  472  is in parallel to the lower surface of the plate-like member constituting the lower surface of the structure  11 . 
         [0409]    By supplying electric power to the motor  473 , the rotational shaft  473   a , the support member  472  fixed to the rotational shaft  473   a  and the permanent magnets  471   a  and  471   b  fixed to the support member  472  are integrally rotated centering on the rotational shaft  473   a  (in this embodiment, the permanent magnets  471   a  and  471   b  are rotated counterclockwise when viewed in rear). 
         [0410]    As a result, the magnetic field traveling counterclockwise when viewed in rear is generated at the part of the inside of the main body  10  facing the permanent magnets  471   a  and  471   b . In the molten metal  3 , flowing of the molten metal  3  (molten metal flowing) is generated which circulates centering on the axis substantially in parallel to the liquid surface of the molten metal  3  (in this embodiment, the rotational shaft  473   a  of the motor  473 ). 
         [0411]    Therefore, the molten metal  3  is agitated in the main body  10  (the holding chamber  14 ) and the part of the molten metal  3  heated by the burner  13  is mixed with the other part thereof, thereby making the temperature of the molten metal  3  uniform. 
         [0412]    Explanation will be given on the arrangement of the permanent magnets  461   a  and  461   b  fixed to the support member  462 , the polarity of the permanent magnets  461   a  and  461   b , and an induced current C caused on the outside plate  22   a  of the rear side by the rotation of the permanent magnets  461   a  and  461   b  referring to  FIGS. 20 to 22 . 
         [0413]    As shown in  FIGS. 20 to 22 , the permanent magnets  461   a  and  461   b  are arranged on the discoid surface of the support member  462  facing the sidewall  22  of the rear side (the outer plate surface of the outside plate  22   a  of the rear side) at the positions equidistant from the center of the discoid surface. 
         [0414]    As shown in  FIG. 22 , the front surface of the permanent magnet  461   a  (the surface facing the outer plate surface of the outside plate  22   a ) is magnetized as the north pole, and the rear surface of the permanent magnet  461   a  (the surface touching the discoid surface of the support member  462 ) is magnetized as the south pole. 
         [0415]    The front surface of the permanent magnet  461   b  (the surface facing the outer plate surface of the outside plate  22   a ) is magnetized as the south pole, and the rear surface of the permanent magnet  461   b  (the surface touching the discoid surface of the support member  462 ) is magnetized as the north pole. 
         [0416]    Therefore, the north pole of the permanent magnet  461   a  and the south pole of the permanent magnet  461   b  are arranged at the positions whose phases are shifted mutually for 180° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a  (in this embodiment, the longitudinal direction). 
         [0417]    As shown in  FIG. 23 , around the permanent magnets  461   a  and  461   b , a magnetic field traveling from the north pole of the front surface of the permanent magnet  461   a  to the south pole of the front surface of the permanent magnet  461   b  and a magnetic field traveling from the north pole of the rear surface of the permanent magnet  461   b  to the south pole of the rear surface of the permanent magnet  461   a  are formed (see black arrows in  FIG. 23 ). 
         [0418]    Therefore, when the support member  462  in which the permanent magnets  461   a  and  461   b  are arranged is rotated, on the basis of the right-handed screw rule, the induced current C is caused on the outside plate  22   a  of the rear side which is metal material arranged in a space surrounded by the permanent magnets  461   a  and  461   b.    
         [0419]    As shown in  FIG. 34 , in the case that the outside plate  22   a  of the rear side is a plate-like member formed by simple metal material, when the support member  462  in which the permanent magnets  461   a  and  461   b  are arranged is rotated, the induced current C flows in the outside plate  22   a  of the rear side along the direction in parallel to the plate surface of the outside plate  22   a  and perpendicular to a line  30  linking the permanent magnets  461   a  and  461   b  with each other, whereby the outside plate  22   a  is heated by the electric resistance of the outside plate  22   a  and the temperature of the outside plate  22   a  is raised. 
         [0420]    As shown in  FIG. 34(   a ) and ( b ), the flowing direction of the induced current C is changed following the rotation of the support member  462  in which the permanent magnets  461   a  and  461   b  are arranged. However, at the position in the outside plate  22   a  of the rear side between the permanent magnets  461   a  and  461   b , that is, the position facing the rotational center of the support member  462  (the rotational shaft  463   a ) (hereinafter, referred to as “center position of the outside plate  22   a” ), the induced current C always flow. 
         [0421]    Therefore, the calorific value at the center position of the outside plate  22   a  is higher than that of the circumference, and the temperature at the center position of the outside plate  22   a  is higher than that of the circumference. 
         [0422]    As shown in  FIGS. 24 and 25 , in this embodiment, a resistance slot  481  and auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed in the part facing the permanent magnets  461   a  and  461   b  in the outer plate surface of the outside plate  22   a  of the rear side (more strictly, the part in the outer plate surface of the outside plate  22   a  of the rear side surrounded by the rotational locus of the permanent magnets  461   a  and  461   b  when viewed along the axial direction of the rotational shaft  463   a  which corresponds to the part surrounded by an alternate long and two short dashes line in  FIG. 25 ). Accordingly, “calorification of the outside plate  22   a  of the rear side caused by the induced current C always flowing (being concentrated) at the center of the outside plate  22   a  (abnormal overheat)” is reduced. 
         [0423]    Explanation will be given on the detailed construction of the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  referring to  FIGS. 24 and 25 . 
         [0424]    The resistance slot  481  is an embodiment of the resistance band according to the present invention. 
         [0425]    In this embodiment, the resistance slot  481  penetrates the outside plate  22   a  of the rear side from the inner plate surface (front plate surface) to the outer plate surface (rear plate surface). 
         [0426]    The part of the outside plate  22   a  at which the resistance slot  481  is formed is substantially hollow and the resistance slot  481  is normally filled with air. 
         [0427]    Therefore, the electric resistance of the resistance slot  481  (more strictly, the part of the outside plate  22   a  at which the resistance slot  481  is formed) is larger than the electric resistance of the other part of the outside plate  22   a  (the part of the outside plate  22   a  at which the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are not formed) constructed by metal material. 
         [0428]    As shown in  FIG. 25 , the middle part of the resistance slot  481  (in this embodiment, the center of the resistance slot  481 ) is arranged at the center of the outside plate  22   a.    
         [0429]    Both of the ends of the resistance slot  481  are arranged at the positions far from the center of the outside plate  22   a  (in this embodiment, the left and right ends of the part of the outer plate surface of the outside plate  22   a  of the rear side surrounded by the rotational locus of the permanent magnets  461   a  and  461   b  when viewed along the axial direction of the rotational shaft  463   a ). 
         [0430]    Therefore, in this embodiment, the resistance slot  481  is extended laterally while passing through the center of the outside plate  22   a.    
         [0431]    As shown in  FIG. 25 , the resistance slot  481  has no break in the middle, that is, the resistance slot  481  is continuous from the left end via the center to the right end. 
         [0432]    The auxiliary resistance slots  482 ,  483 ,  484  and  485  are an embodiment of the resistance band according to the present invention. 
         [0433]    In this embodiment, each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  penetrates the outside plate  22   a  of the rear side from the inner plate surface (front plate surface) to the outer plate surface (rear plate surface). 
         [0434]    The part of the outside plate  22   a  at which the resistance slot  481  is formed is substantially hollow and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are normally filled with air. 
         [0435]    Therefore, the electric resistance of each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  (more strictly, the part of the outside plate  22   a  at which each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  is formed) is larger than the electric resistance of the other part of the outside plate  22   a  (the part of the outside plate  22   a  at which the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are not formed) constructed by metal material. 
         [0436]    As shown in  FIG. 25 , the auxiliary resistance slot  482  is formed at the position upper than the auxiliary resistance slot  482  for a predetermined distance in the part of the outside plate  22   a  of the rear side facing the permanent magnets  461   a  and  461   b.    
         [0437]    The auxiliary resistance slot  483  is formed at the position upper than the resistance slot  481  for a predetermined distance in the part of the outside plate  22   a  of the rear side facing the permanent magnets  461   a  and  461   b.    
         [0438]    The auxiliary resistance slot  484  is formed at the position lower than the resistance slot  481  for a predetermined distance in the part of the outside plate  22   a  of the rear side facing the permanent magnets  461   a  and  461   b.    
         [0439]    The auxiliary resistance slot  485  is formed at the position lower than the auxiliary resistance slot  484  for a predetermined distance in the part of the outside plate  22   a  of the rear side facing the permanent magnets  461   a  and  461   b.    
         [0440]    In this embodiment, each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  is extended laterally and separated from the resistance slot  481  (the auxiliary resistance slots  482 ,  483 ,  484  and  485  are not connected to each other). 
         [0441]    Explanation will be given on the principle of reducing calorification of the outside plate  22   a  of the rear side (abnormal overheat) by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  referring to  FIG. 25 . 
         [0442]    The part of the outside plate  22   a  of the rear side facing the permanent magnets  461   a  and  461   b  is divided by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  into six parts, “the part above the auxiliary resistance slot  483 ”, “the part between the auxiliary resistance slot  483  and the auxiliary resistance slot  482 ”, “the part between the auxiliary resistance slot  482  and the resistance slot  481 ”, “the part between the resistance slot  481  and the auxiliary resistance slot  484 ”, “the part between the auxiliary resistance slot  484  and the auxiliary resistance slot  485 ”, and “the part below the auxiliary resistance slot  485 ”. 
         [0443]    The resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  have larger electric resistance than the metal material constituting the outside plate  22   a  of the rear side, whereby the flowing of current across the six adjacent parts is obstructed (otherwise, the current value across the adjacent parts is reduced). 
         [0444]    Therefore, when the support member  462  in which the permanent magnets  461   a  and  461   b  are arranged is rotated while facing the outside plate  22   a  of the rear side in which the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed as shown in  FIG. 25 , the induced current C is caused at each of the parts divided by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485 . Accordingly, the current value of each induced current C is smaller than that of the case that the induced current C flows continuously in the part surrounded by the rotational locus of the permanent magnets  461   a  and  461   b  from one of ends to the other end via the center of the outside plate  22   a  (see  FIG. 34 ). 
         [0445]    The resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  obstruct the current flowing across the adjacent parts, whereby the induced current C caused in each of the part divided by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  and flowing toward the center of the outside plate  22   a  changes its direction at the time of reaching the vicinity of the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485 , and then flows along the lengthwise direction of the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  (in this embodiment, the lateral direction). 
         [0446]    Accordingly, the induced current C is prevented from being concentrated at the center of the outside plate  22   a , whereby the calorification at the center of the outside plate  22   a  is reduced. 
         [0447]    Explanation will be given on results of experiment showing the fact that the calorification of the outside plate  22   a  of the rear side (abnormal overheat) is reduced by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  referring to  FIGS. 26 to 30 . 
         [0448]    As shown in  FIG. 26(   a ) to ( e ), at the time of performing the experiment, five kinds of the outside plates  22   a  which are different in the mode of the slots (number, length, arrangement and the like of the slots) are prepared. 
         [0449]    In the outside plate surface of the outside plate  22   a  shown in  FIG. 26(   a ), any slot is not formed in the part facing the permanent magnets  461   a  and  461   b  (the part surrounded by an alternate long and two short dashes line in  FIG. 26(   a )). 
         [0450]    In the outside plate surface of the outside plate  22   a  shown in  FIG. 26(   b ), a plurality of slots  486 , a plurality of slots  487 , a plurality of slots  488  and a plurality of slots  489  are formed in the part facing the permanent magnets  461   a  and  461   b  (the part surrounded by an alternate long and two short dashes line in  FIG. 26(   b )). 
         [0451]    The slots  486  are arranged on a circle centering on the center of the outside plate  22   a  at predetermined intervals. Each of the slots  486  is independent (the adjacent slots  486  are not connected to each other). 
         [0452]    The slots  487  are arranged on a circle, centering on the center of the outside plate  22   a  and having larger diameter than the circle corresponding to the slots  486 , at predetermined intervals. Each of the slots  487  is independent. 
         [0453]    The slots  488  are arranged on a circle, centering on the center of the outside plate  22   a  and having larger diameter than the circle corresponding to the slots  487 , at predetermined intervals. Each of the slots  488  is independent. 
         [0454]    The slots  489  are arranged on a circle, centering on the center of the outside plate  22   a  and having larger diameter than the circle corresponding to the slots  488 , at predetermined intervals. Each of the slots  489  is independent. 
         [0455]    In the outside plate surface of the outside plate  22   a  shown in  FIG. 26(   c ), two slots  490  and  491  are formed in the part facing the permanent magnets  461   a  and  461   b  (the part surrounded by an alternate long and two short dashes line in  FIG. 26(   c )). 
         [0456]    The slots  490  and  491  are extended laterally and are arranged for a predetermined interval about the center of the outside plate  22   a.    
         [0457]    In the outside plate surface of the outside plate  22   a  shown in  FIG. 26(   d ), the resistance slot  481  is formed in the part facing the permanent magnets  461   a  and  461   b  (the part surrounded by an alternate long and two short dashes line in  FIG. 26(   d )). 
         [0458]    In the outside plate surface of the outside plate  22   a  shown in  FIG. 26(   e ), the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed in the part facing the permanent magnets  461   a  and  461   b  (the part surrounded by an alternate long and two short dashes line in  FIG. 26(   e )). 
         [0459]    The resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  shown in  FIG. 26(   e ) correspond to the melting furnace  400  shown in  FIGS. 20 to 25  (the fourth embodiment of the melting apparatus according to the present invention). 
         [0460]    (a), (b) and (c) of  FIG. 26  correspond to “comparative embodiments (embodiments which are not modes for carrying out the present invention)”. (d) and (e) of  FIG. 26  correspond to “modes for carrying out the present invention”. 
         [0461]    The outside plate  22   a  of the inside of the charging tank  20  of the melting furnace  400  shown in  FIGS. 20 to 25  is exchanged with the outside plates  22   a  shown in  FIG. 26(   a ) to ( e ) in order, and the temperature of each of the outside plates  22   a  at the time of melting the aluminum cutting chips  2  is measured. 
         [0462]    In more detail, temperature sensors (thermocouples) are arranged at five positions between the center of each of the outside plates  22   a  shown in (a) and (e) of  FIG. 26  and the upper end of the part facing the permanent magnets  461   a  and  461   b  (see (i) to (v) in (a) and (e) of  FIG. 26 ) so as to measure the temperature of each of the outside plates  22   a.    
         [0463]    A temperature sensor (thermocouple) is arranged at the center of each of the outside plates  22   a  shown in (b), (c) and (d) of  FIG. 26  (see (i) in (b), (c) and (d) of  FIG. 26 ) so as to measure the temperature of each of the outside plates  22   a.    
         [0464]      FIG. 27  shows the temperature rise of the center of the outside plates  22   a  shown in  FIG. 26(   a ) to ( e ). Herein, “the temperature rise of the center of the outside plate  22   a ” is the reminder of the measured value of the temperature of the center of the outside plate  22   a  at the time of starting the measurement (at the time at which the rotation of the support member  462  in which the permanent magnets  461   a  and  461   b  are arranged is started) (T1) and the measured value of the temperature of the center of the outside plate  22   a  at the time of temperature saturation (at the time at which the temperature of the outside plate  22   a  becomes uniform) (T2)(=T2−T1). 
         [0465]    As shown in  FIG. 27 , the temperature rise of the center of each of the outside plates  22   a  in  FIGS. 26(   d ) and ( e ) which corresponds to the mode for carrying out the present invention is smaller than the temperature rise of the center of each of the outside plates  22   a  in  FIGS. 26(   a ), ( b ) and ( c ) which corresponds to the comparative embodiment. 
         [0466]    Accordingly, each of the resistance slot  481  and the combination of the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  reduces the temperature rise of the center of the outside plate  22   a.    
         [0467]    As shown in  FIG. 27 , the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   b ) is slightly smaller than the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   a ). 
         [0468]    Accordingly, the slot (resistance slot) different from the resistance slot  481  can reduce slightly the temperature rise of the center of the outside plate  22   a.    
         [0469]    However, the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   c ) is considerably larger than the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   a ). 
         [0470]    The slots  490  and  491  substantially correspond to the resistance slot  481  in which the slot at the part corresponding to the center of the outside plate  22   a  is omitted (the resistance slot  481  divided into two at the middle part). 
         [0471]    In the case of the slots  490  and  491 , in addition to the induced current flowing toward the center of the outside plate  22   a  straight, the induced current flowing at the position far from said induced current changes its direction so as to reach the center of the outside plate  22   a  and flows through the part between the slots  490  and  491  to the other side of the two parts divided by the slots  490  and  491 , whereby the induced current (the current value of the induced current) flowing at the center of the outside plate  22   a  is increased contrary. 
         [0472]    By comparing the temperature rise of the center of each of the outside plate  22   a  in (a), (c) and (d) in  FIG. 26 , it is found that the construction of arranging the middle part of the resistance slot  481  at the center of the outside plate  22   a  and of forming the resistance slot  481  continuously (not dividing the resistance slot  481 ) is effective for reducing the temperature rise of the center of the outside plate  22   a.    
         [0473]    As shown in  FIG. 27 , the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   e ) is further smaller than the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   d ). 
         [0474]    Accordingly, the combination of the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  is effective for reducing the temperature rise of the center of the outside plate  22   a.    
         [0475]      FIG. 28  shows the temperature rise of the center of the outside plate  22   a  at the positions (i) to (v) in each of (a) to (e) in  FIG. 26 . 
         [0476]    As shown in  FIG. 28 , in the case of the outside plate  22   a  corresponding to  FIG. 26(   a ), the temperature rise at the center (i) of the outside plate  22   a  is large, and the temperature rise becomes smaller with distance from the center (i) of the outside plate  22   a.    
         [0477]    On the other hand, in the case of the outside plate  22   a  corresponding to  FIG. 26(   e ), the temperature rise at each of the positions (i) to (v) is substantially uniform. 
         [0478]    Accordingly, by combining the resistance slot  481  with the auxiliary resistance slots  482 ,  483 ,  484  and  485 , the induced current is prevented from concentrating at the center of the outside plate  22   a , in its turn the temperature rise at the center of the outside plate  22   a  is suppressed. 
         [0479]    As shown in  FIG. 28 , the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   e ) is entirely smaller than the temperature rise of the center of the outside plate  22   a  in  FIG. 26(   a ). 
         [0480]    Accordingly, by combining the resistance slot  481  with the auxiliary resistance slots  482 ,  483 ,  484  and  485 , the induced current is caused in each of the part divided by the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485 , whereby each induced current (the current value of each induced current) is small. 
         [0481]      FIG. 28  shows the rise amplitude of the temperature at the positions (i) of the outside plates  22   a  of (a) and (e) in  FIG. 26 . 
         [0482]    Herein, “the rise amplitude of the temperature of the outside plate  22   a”  is the reminder of the temperature of the center of the outside plate  22   a  at the time of starting the measurement (T3) and the temperature of the center of the outside plate  22   a  at the elapsed time (T4)(=T4−T3). 
         [0483]    As shown in  FIG. 29 , the rise amplitude of the temperature at the position (i) of the outside plate  22   a  of (e) is smaller than the rise amplitude of the temperature at the position (i) of the outside plate  22   a  of (a). 
         [0484]    The time required for making uniform the rise amplitude of the temperature at the position (i) of the outside plate  22   a  of (e) is shorter than the time required for making uniform the rise amplitude of the temperature at the position (i) of the outside plate  22   a  of (a). 
         [0485]      FIG. 30  shows the comparison of the power consumption for rotatively driving the motor  463  of the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   a ) with the power consumption for rotatively driving the motor  463  of the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   e ). 
         [0486]    The rotational speed of the motor  463  the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   a ) is the same as the rotational speed of the motor  463  the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   e ). 
         [0487]    As shown in  FIG. 30 , the power consumption for rotatively driving the motor  463  of the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   e ) is smaller about 30 percent than the power consumption for rotatively driving the motor  463  of the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   a ). 
         [0488]    A part of the power consumption for rotatively driving the motor  463  is employed for causing the induced current in the outside plate  22   a . Accordingly, when the induced current (the current value of each induced current) caused in the outside plate  22   a  of  FIG. 26(   e ) becomes smaller than the induced current (the current value of each induced current) caused in the outside plate  22   a  of  FIG. 26(   a ), the power consumption for rotatively driving the motor  463  of the melting furnace  400  having the outside plate  22   a  corresponding to  FIG. 26(   e ) is supposable to become small. 
         [0489]    As mentioned above, the melting furnace  400  has the charging tank  20  which has the outside plate  22   a  constructed by metal material and the fireproof member  22   b  covering the outside plate  22   a , and the traveling magnetic field generating unit  460  which is arranged outside the outside plate  22   a  of the charging tank  20  and generates the magnetic field traveling along the outside plate  22   a  so as to agitate the molten metal  3  stored in the charging tank  20 . The aluminum cutting chips  2  are introduced to the molten metal  3  stored in the charging tank  20  so as to melt the aluminum cutting chips  2 . The traveling magnetic field generating unit  460  has the permanent magnets  461   a  and  461   b  facing the outside plate  22   a  of the charging tank  20 , the rotation of the support member  462  supporting the permanent magnets  461   a  and  461   b , and the motor  463  rotatively driving the rotation of the support member  462  centering on the rotational shaft  463   a  perpendicular to the outer plate surface of the outside plate  22   a . The resistance slot  481  which has larger electric resistance than the metal material constructing the outside plate  22   a  of the charging tank  20  is formed at the part of the outside plate  22   a  of the charging tank  20  facing the permanent magnets  461   a  and  461   b . The middle part of the resistance slot  481  is arranged at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a . Both ends of the resistance slot  481  is arranged at the positions far from the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a  (in this embodiment, the left and right ends of the part of the outside plate  22   a  of the charging tank  20  facing the permanent magnets  461   a  and  461   b ). 
         [0490]    The north pole of the permanent magnet  461   a  and the south pole of the permanent magnet  461   b  are arranged at the positions whose phases are shifted mutually for 180° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a.    
         [0491]    According to the construction, the induced current C caused in the outside plate  22   a  can be prevented from being concentrated at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , in its turn the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a  can be reduced. 
         [0492]    The rotational speed of the motor  463  can be increased by the suppression of the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , in its turn the melting efficiency of the aluminum cutting chips  2  (the weight of the aluminum cutting chips  2  which can be melted per unit time) can be increased. 
         [0493]    Furthermore, by reducing the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , deformation of the outside plate  22   a  can be prevented and any cooling equipment or the like for preventing the deformation of the outside plate  22   a  is not necessary to be provided (see the Japanese Patent Laid Open Gazette 2008-164249). 
         [0494]    Moreover, the induced current C caused in the outside plate  22   a  can be made small, in its turn the energy required for agitating the molten metal  3  (in this embodiment, the power consumption of the motor  463 ) can be made small. By making the energy small, the cost for melting the aluminum cutting chips  2  can be reduced. 
         [0495]    In the melting furnace  400 , the resistance slot  481  which is a slot formed in the outside plate  22   a  of the charging tank  20  is employed as a resistance band. 
         [0496]    The construction brings below merits. 
         [0497]    Namely, the resistance slot  481  can be formed easily by cutting the outside plate  22   a  of the charging tank  20 , thereby being adoptable easily to an existing melting apparatus and the like. 
         [0498]    The inside of the resistance slot  481  is substantially hollow so that the resistance slot  481  can buff the distortion caused by the expansion of the outside plate  22   a  by temperature rise, whereby deformation of the outside plate  22   a  can be prevented. 
         [0499]    The auxiliary resistance slots  482 ,  483 ,  484  and  485  which have larger electric resistance than the metal material constructing the outside plate  22   a  of the charging tank  20  and are arranged separately from the resistance slot  481  are formed at the part in the outside plate  22   a  of the inside of the charging tank  20  of the melting furnace  400  facing the permanent magnets  461   a  and  461   b.    
         [0500]    According to the construction, the induced current C caused in the outside plate  22   a  can be made further small and can be prevented from being concentrated at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a.    
         [0501]    In the melting furnace  400 , the auxiliary resistance slots  482 ,  483 ,  484  and  485  which are slots formed in the outside plate  22   a  of the charging tank  20  are employed as auxiliary resistance bands. 
         [0502]    The construction brings below merits. 
         [0503]    Namely, the auxiliary resistance slots  482 ,  483 ,  484  and  485  can be formed easily by cutting the outside plate  22   a  of the charging tank  20 , thereby being adoptable easily to an existing melting apparatus and the like. 
         [0504]    The inside of each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  is substantially hollow so that the auxiliary resistance slots  482 ,  483 ,  484  and  485  can buff the distortion caused by the expansion of the outside plate  22   a  by temperature rise, whereby deformation of the outside plate  22   a  can be prevented. 
         [0505]    As mentioned above, the melting method of the aluminum cutting chips  2  with the melting furnace  400  employs the melting furnace  400  which has the charging tank  20  which has the outside plate  22   a  constructed by metal material and the fireproof member  22   b  covering the outside plate  22   a , and the traveling magnetic field generating unit  460  which is arranged outside the outside plate  22   a  of the charging tank  20  and generates the magnetic field traveling along the outside plate  22   a  so as to agitate the molten metal  3  stored in the charging tank  20 , and in which the aluminum cutting chips  2  are introduced to the molten metal  3  stored in the charging tank  20  so as to melt the aluminum cutting chips  2 . The traveling magnetic field generating unit  460  has the permanent magnets  461   a  and  461   b  facing the outside plate  22   a  of the charging tank  20 , the rotation of the support member  462  supporting the permanent magnets  461   a  and  461   b , and the motor  463  rotatively driving the rotation of the support member  462  centering on the rotational shaft  463   a  perpendicular to the outer plate surface of the outside plate  22   a . The resistance slot  481  which has larger electric resistance than the metal material constructing the outside plate  22   a  of the charging tank  20  is formed at the part of the outside plate  22   a  of the charging tank  20  facing the permanent magnets  461   a  and  461   b . The middle part of the resistance slot  481  is arranged at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a . Both ends of the resistance slot  481  is arranged at the positions far from the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a  (in this embodiment, the left and right ends of the part of the outside plate  22   a  of the charging tank  20  facing the permanent magnets  461   a  and  461   b ). The north pole of the permanent magnet  461   a  and the south pole of the permanent magnet  461   b  are arranged at the positions whose phases are shifted mutually for  180 ° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a.    
         [0506]    According to the construction, the induced current C caused in the outside plate  22   a  can be prevented from being concentrated at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , in its turn the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a  can be reduced. 
         [0507]    The rotational speed of the motor  463  can be increased by the suppression of the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , in its turn the melting efficiency of the aluminum cutting chips  2  (the weight of the aluminum cutting chips  2  which can be melted per unit time) can be increased. 
         [0508]    Furthermore, by reducing the temperature rise at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a , deformation of the outside plate  22   a  can be prevented and any cooling equipment or the like for preventing the deformation of the outside plate  22   a  is not necessary to be provided (see the Japanese Patent Laid Open Gazette 2008-164249). 
         [0509]    Moreover, the induced current C caused in the outside plate  22   a  can be made small, in its turn the energy required for agitating the molten metal  3  (in this embodiment, the power consumption of the motor  463 ) can be made small. By making the energy small, the cost for melting the aluminum cutting chips  2  can be reduced. 
         [0510]    In the melting method of the aluminum cutting chips  2  with the melting furnace  400 , the resistance slot  481  which is a slot formed in the outside plate  22   a  of the charging tank  20  is employed as a resistance band. 
         [0511]    The construction brings below merits. 
         [0512]    Namely, the resistance slot  481  can be formed easily by cutting the outside plate  22   a  of the charging tank  20 , thereby being adoptable easily to an existing melting apparatus and the like. 
         [0513]    The inside of the resistance slot  481  is substantially hollow so that the resistance slot  481  can buff the distortion caused by the expansion of the outside plate  22   a  by temperature rise, whereby deformation of the outside plate  22   a  can be prevented. 
         [0514]    The auxiliary resistance slots  482 ,  483 ,  484  and  485  which have larger electric resistance than the metal material constructing the outside plate  22   a  of the charging tank  20  and are arranged separately from the resistance slot  481  are formed at the part in the outside plate  22   a  of the inside of the charging tank  20  of the melting furnace  400  facing the permanent magnets  461   a  and  461   b.    
         [0515]    According to the construction, the induced current C caused in the outside plate  22   a  can be made further small and can be prevented from being concentrated at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a.    
         [0516]    In the melting method of the aluminum cutting chips  2  with the melting furnace  400 , the auxiliary resistance slots  482 ,  483 ,  484  and  485  which are slots formed in the outside plate  22   a  of the charging tank  20  are employed as auxiliary resistance bands. 
         [0517]    The construction brings below merits. 
         [0518]    Namely, the auxiliary resistance slots  482 ,  483 ,  484  and  485  can be formed easily by cutting the outside plate  22   a  of the charging tank  20 , thereby being adoptable easily to an existing melting apparatus and the like. 
         [0519]    The inside of each of the auxiliary resistance slots  482 ,  483 ,  484  and  485  is substantially hollow so that the auxiliary resistance slots  482 ,  483 ,  484  and  485  can buff the distortion caused by the expansion of the outside plate  22   a  by temperature rise, whereby deformation of the outside plate  22   a  can be prevented. 
         [0520]    In this embodiment, the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed as the resistance band and auxiliary resistance bands. The width, length, number and the like of these slots can be changed suitably in consideration of (1) intensity of the outside plate  22   a  as a structure, (2) processability (easiness of forming) of these slots, (3) agitating ability (permeability of the magnetic field to the inside of the outside plate  22   a  of the charging tank  20 ) and the like. 
         [0521]    In this embodiment, the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed as the resistance band and auxiliary resistance bands. However, the resistance band and auxiliary resistance bands according to the present invention are not limited thereto. 
         [0522]    As another embodiment of the resistance band and auxiliary resistance bands according to the present invention, there are given the case that heat procession (for example, welding) or surface treatment (for example, shot peening) is performed at a predetermined part of the outside plate and the structure as the metal material (grain size of crystal, distribution of deposited object, dislocation density and the like) so as to make the electric resistance of the processed part larger than that of the part around it, the case that material of difference kind (including metal and nonmetal) with larger electric resistance than that of the metal material constructing the outside plate is implanted at a predetermined part of the outside plate, the case that the thickness of the outside plate is changed at every part so as to change the electric resistance at every part, and the like. 
         [0523]    In this embodiment, the resistance slot  481  is extended laterally while passing through the center of the outside plate  22   a . However, the resistance band according to the present invention is not limited thereto. 
         [0524]    For example, as a resistance slot  492  shown in  FIG. 31(   a ), the resistance slot may alternatively be extended vertically while passing through the center of the outside plate  22   a  (the position facing the rotational center of the support member  462  (the rotational shaft  463   a )). 
         [0525]    As a resistance slot  493  shown in  FIG. 31(   b ), the resistance slot may alternatively be bent at the center of the outside plate  22   a.    
         [0526]    As a resistance slot  494  shown in  FIG. 31(   c ), the resistance slot may alternatively pass through the center of the outside plate  22   a  and is bent at the position other than the center of the outside plate  22   a.    
         [0527]    As a resistance slot  495  shown in  FIG. 31(   d ), the resistance slot may alternatively be extended to three different directions from the center of the outside plate  22   a.    
         [0528]    As a resistance slot  496  shown in  FIG. 31(   e ), the resistance slot may alternatively be extended to four different directions from the center of the outside plate  22   a  (otherwise, two slots crosses at the center of the outside plate  22   a ). 
         [0529]    As a resistance slot  497  shown in  FIG. 31(   f ), the resistance slot may alternatively be extended to six different directions from the center of the outside plate  22   a  (otherwise, three slots crosses at the center of the outside plate  22   a ). 
         [0530]    Each of the slots shown in  FIG. 31(   a ) to ( f ) (the resistance slots  492 ,  493 ,  494 ,  495 ,  496  and  497 ) satisfies the conditions that the middle part of the slot is arranged at the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a  and that both ends of the slot is arranged at the positions far from the position in the outside plate  22   a  of the charging tank  20  facing the rotational shaft  463   a.    
         [0531]    As shown in  FIG. 32 , the outside plate  22   a  may alternatively be formed therein with reinforcing ribs  22   c.    
         [0532]    According to the construction, in the case that the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed in the outside plate  22   a , the intensity of the outside plate  22   a  can be held. 
         [0533]    In this embodiment, the two permanent magnets  461   a  and  461   b  are supported by the support member  462 . However, the number and arrangement of the permanent magnet according to the present invention is not limited thereto. 
         [0534]    For example, as shown in  FIG. 33(   a ), it may alternatively be constructed that one permanent magnet  465  in which one of ends thereof is magnetized as the north pole and the other end thereof is magnetized as the south pole is fixed to the support member  462  so that the rotational center of the support member  462  (the position corresponding to the rotational shaft  463   a ) is arranged between the one of ends (north pole) and the other end (south pole) when viewed along the axial direction of the rotational shaft  463   a.    
         [0535]    In this case, the north pole of the permanent magnet  465  and the south pole of the permanent magnet  465  are arranged at the positions whose phases are shifted mutually for 180° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a  (in this embodiment, along the longitudinal direction). 
         [0536]    As shown in  FIG. 33(   b ), it may alternatively be constructed that permanent magnets  466   a ,  466   b ,  466   c  and  466   d  are fixed to the positions whose distance from the center of the discoid surface of the support member  462  facing the outside plate  22   a  is uniform and whose phases are shifted mutually for 90°. 
         [0537]    In this case, the front surface of the permanent magnet  466   a  is magnetized as the north pole and the rear surface of the permanent magnet  466   a  is magnetized as the south pole. The front surface of the permanent magnet  466   b  is magnetized as the north pole and the rear surface of the permanent magnet  466   a  is magnetized as the south pole. The front surface of the permanent magnet  466   c  is magnetized as the south pole and the rear surface of the permanent magnet  466   a  is magnetized as the north pole. The front surface of the permanent magnet  466   d  is magnetized as the south pole and the rear surface of the permanent magnet  466   a  is magnetized as the notch pole. 
         [0538]    Accordingly, the north pole of the permanent magnet  466   a  and the south pole of the permanent magnet  466   c  are arranged at the positions whose phases are shifted mutually for 180° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a.    
         [0539]    The north pole of the permanent magnet  466   b  and the south pole of the permanent magnet  466   d  are arranged at the positions whose phases are shifted mutually for 180° centering on the rotational shaft  463   a  when viewed from the axial direction of the rotational shaft  463   a.    
         [0540]    In the case shown in  FIGS. 33(   a ) and ( b ), on the basis of the right-handed screw rule, the induced current passing through the center of the outside plate  22   a  is caused on the outside plate  22   a  facing the support member  462 . 
         [0541]    In this embodiment, the resistance slot  481  and the auxiliary resistance slots  482 ,  483 ,  484  and  485  are formed in the outside plate  22   a  o the rear side facing the traveling magnetic field generating unit  460 . However, similar resistance slot (resistance band) and auxiliary resistance slots (auxiliary resistance bands) may alternatively be formed in the plate member constituting the lower surface of the structure  11  facing the traveling magnetic field generating unit  470 . 
         [0542]    In this case, the induced current caused in the plate member constituting the lower surface of the structure  11  by the rotation of the permanent magnets  471   a  and  471   b  of the traveling magnetic field generating unit  470  is prevented from concentrating at the position facing the rotational shaft  473   a , in its turn the temperature rise at the position facing the rotational shaft  473   a  in the plate member constituting the lower surface of the structure  11  is suppressed. 
         [0543]    The traveling magnetic field generating units  460  and  470  in this embodiment generate the traveling magnetic field with the permanent magnets. However, in an electromagnetic traveling magnetic field generating unit, in the case that a magnetic field travels circularly centering on a predetermined center point and reversed polarity appears about the center point, by forming a resistance slot and auxiliary resistance slots similar to the embodiment in an outside plate facing the electromagnetic traveling magnetic field generating unit, an induced current caused in the outside plate can be prevented from concentrating at a position in the outside plate facing the center point. 
         [0544]    In each of the Japanese Patent Laid Open Gazette Hei. 7-126766 and the Japanese Patent Laid Open Gazette Hei. 7-28957, a unit is disclosed in which a melted matter housed in a metal crucible is melted by flowing an alternating current with high frequency in a high-frequency induction coil wound on the outer peripheral surface of the crucible, and the effect is disclosed that an eddy current generated in the crucible is suppressed by forming a plurality of vertical slits in the crucible. However, this disclosure is widely different from the present invention. 
         [0545]    The purpose of the present invention is to suppress the induced current caused by the magnetic field traveling and rotating centering on the axis perpendicular to the outside plate and is different from the disclosure at all in the shape of the object in which the induced current is caused and the mode of generation of the magnetic field, in its turn the behavior of the caused induced current (the flow direction and the change of the mode). 
         [0546]    In the Japanese Patent Laid Open Gazette Hei. 6-176916, the effect is disclosed that a layer having high electric resistance is formed on a surface of a magnetic adjusting plate so as to suppress an eddy current generated in the surface of the magnetic adjusting plate. However, this disclosure is widely different from the present invention. 
         [0547]    In the present invention, parts having high electric resistance (resistance band and auxiliary resistance bands) and parts having low electric resistance (the other parts) are formed in the outside plate in which the induced current is caused and the direction of flowing of the induced current is changed with the parts having high electric resistance so as to prevent the induced current from concentrating at the local position (the center of the outside plate), and the mechanism and the purpose thereof is different from the disclosure. 
       REFERENCE SIGNS LIST  
       [0000]    
       
           2  aluminum cutting chip (melted matter) 
           3  molten metal 
           10  main body (a part of melting tank) 
           20  charging tank (a part of melting tank) 
           22  sidewall 
           150  agitation device (first embodiment) 
           160  traveling magnetic field generating unit (first embodiment)