Abstract:
Provided is an arc furnace, including: a furnace body having a bottomed cylindrical shape; a furnace lid that openably closes an opening of the furnace body; an electrode that is provided at the furnace lid and melts a metal material supplied into the furnace body by electric discharge; a tilting floor that is tiltable within a plane substantially perpendicular to the tilting floor; and a rotation mechanism that is provided on the tilting floor inward from an outer circumference of the furnace body to support a bottom wall of the furnace body, and rotates the furnace body around a cylinder axis thereof.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an arc furnace, and particularly relates to an arc furnace that enables uniform melting. 
     BACKGROUND OF THE INVENTION 
     In an arc furnace, in particular, a three-phase arc furnace, there has been the problem that the metal material in the furnace is not melted uniformly. That is, while melting of the metal material quickly advances in the hot spot near each of the three electrodes, the metal material tends to remain unmelted in the cold spot distant from each of the electrodes. Therefore, there have been the problems that electric power more than necessary to melt the metal material in the cold spots is required, and that the furnace wall lining is damaged due to excessive supply of electric power in the hot spot. Consequently, Patent Document 1 proposes the arc furnace that enables uniform melting by making a bottomed cylindrical furnace body rotatable around a cylinder axis thereof, and replacing the hot spots and the cold spots. 
     [Patent Document 1] JP-A-S60-122886 
     SUMMARY OF THE INVENTION 
     However, in the above described conventional arc furnace, there has been the problem that the entire arc furnace increases in size to outside since the rack and the pinion, the speed reducer, the electric motor and the like for rotating the furnace body are provided at an outside of the circumference of the furnace body. Further, the conventional arc furnace also has the problem that the operation efficiency is low because the furnace is incapable of tilting pouring. 
     Consequently, the present invention is to solve the problems as above, and has an object to provide an arc furnace that realizes improvement in operation efficiency by avoiding increase in size of an entire furnace, and enabling tilting pouring, while enabling uniform melting of a material. 
     In order to attain the above described object, the present invention provides an arc furnace, including: a furnace body ( 1 ) having a bottomed cylindrical shape; a furnace lid ( 2 ) that openably closes an opening of the furnace body ( 1 ); an electrode ( 3 ) that is provided at the furnace lid ( 2 ) and melts a metal material supplied into the furnace body ( 1 ) by electric discharge; a tilting floor ( 5 ) that is tiltable within a plane substantially perpendicular to the tilting floor; and a rotation mechanism ( 4 ) that is provided on the tilting floor ( 5 ) inward from an outer circumference of the furnace body ( 1 ) to support a bottom wall ( 11 ) of the furnace body ( 1 ), and rotates the furnace body ( 1 ) around a cylinder axis thereof. 
     The arc furnace of the present invention has the structure in which the rotation mechanism is provided on the tilting floor and the furnace body is mounted thereon. Therefore, tilting pouring is enabled, and operation efficiency is improved. Further, since the rotation mechanism is provided on the tilting floor inward from the outer circumference of the furnace body, nothing protrudes outward of the furnace body, and the size of the entire furnace is prevented from increasing outward. The furnace body is rotated around the cylinder axis by the rotation mechanism, whereby the positions of the hot spots and the cold spots are replaced with one another, and uniform melting of the material is achieved. 
     Moreover, in the arc furnace of the present invention, it is preferable that the rotation mechanism ( 4 ) includes: a ring body ( 41 ) that is provided at an outer circumferential portion of the bottom wall ( 11 ) of the furnace body ( 1 ), and has a connecting portion ( 42 ) formed on an inner circumferential surface of the furnace body; a bearing member ( 8 ) that is provided at a necessary part of a bottom surface of the ring body ( 41 ) to support the ring body ( 41 ) rotatably around a center thereof; and a drive mechanism ( 92 ,  93 ,  95 ) that is provided on the tilting floor ( 5 ) inward of the ring body ( 41 ) and has an output portion connected to the connecting portion ( 42 ). 
     According to the present invention, the furnace body is rotatably supported by the bearing member with the compact structure, and the ring body with the connecting portion formed on the inner circumferential surface of the furnace body is connected to the drive mechanism and is rotationally driven, whereby the furnace body can be reliably rotated. 
     Furthermore, it is preferable that stopper mechanisms ( 961 ,  963 ,  964 ) are provided at the ring body ( 41 ) side and the tilting floor ( 5 ) side, and are fitted to each other to restrict rotation of the ring body ( 41 ) when the ring body ( 41 ) is in a predetermined rotation position. 
     According to the present invention, rotation of the furnace body is restricted by the stopper mechanisms, for example, in a state in which the furnace body directly confronts the tapping yard, whereby a reliable tapping operation is enabled. 
     The reference signs in the parentheses show the correspondence with the specific means described in embodiments that will be described later. 
     As described above, according to the arc furnace of the present invention, improvement in the operation efficiency can be realized by avoiding increase in size of the entire furnace and enabling tilting pouring while enabling uniform melting of a material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall vertical sectional view of an arc furnace in a first embodiment of the present invention; 
         FIG. 2  is an overall perspective view of a rotation mechanism; 
         FIG. 3  is an overall plan view of the rotation mechanism; 
         FIG. 4  is a sectional view taken along a line IV-IV of  FIG. 3 ; 
         FIG. 5  is a sectional view taken along a line V-V of  FIG. 3 ; 
         FIGS. 6A to 6F  are schematic horizontal sectional views of a furnace body showing operation steps of the arc furnace; 
         FIG. 7  is a plan view of a half part of a rotation mechanism in a second embodiment of the present invention; and 
         FIG. 8  is a sectional view taken along a line VIII-VIII of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Note that embodiments that will be described hereinafter are only examples, and various design improvements that are made by a person skilled in the art within the range without departing from the gist of the present invention are also included in the range of the present invention. 
     First Embodiment 
       FIG. 1  shows a sectional view of an arc furnace including a structure of the present invention. The arc furnace includes a furnace body  1  having a bottomed cylindrical shape that opens upward. An opening thereof is closed by a furnace lid  2  that is separated upward and capable of being turned and opened. Three (only two are illustrated) electrodes  3  are penetrated through the furnace lid  2  and inserted into the furnace body  1  located under the furnace lid  2 . A bottom wall  11  of the furnace body  1  bends downward in a convex shape, and the bottom wall  11  is supported by a rotation mechanism  4 , which will be described later. The rotation mechanism  4  is provided on a tilting floor  5 . The tilting floor  5  configures a top surface of a tilting body  6 . The tilting body  6  has a bottom surface bent downward in a convex shape, and a vertex thereof is located on a horizontal base stand  7 . 
     An upper end of a drive cylinder  62  that is placed in a vertical direction is rotatably connected to a bracket  61  that is provided at one end of the tilting body  6 . A lower end of the drive cylinder  62  is rotatably connected to a bracket that is installed on a floor surface (not illustrated in  FIG. 1 ). Thereby, when the drive cylinder  62  is extended upward, the tilting body  6  rolls on the base stand  7 , and the tilting floor  5  inclines downward in a right direction in  FIG. 1 . With this, the furnace body  1  which is supported on the tilting floor  5  also inclines downward in a right direction in  FIG. 1 , and tapping of molten steel in the furnace body  1  is enabled. When the drive cylinder  62  is contracted, the tilting floor  5  inclines downward in a left direction in  FIG. 1 , whereby discharge of slag can be performed. 
       FIG. 2  shows an overall perspective view of the rotation mechanism  4 .  FIG. 3  shows an overall plan view of the rotation mechanism  4 . The rotation mechanism  4  has a circular-ring-shaped support frame  41  that includes a number of upright walls, and is a ring body. The furnace body  1  ( FIG. 1 ) is placed on and fixed to a top surface of the support frame  41 . A ring-shaped gear body  42  is fixed to a whole circumference on a bottom surface of an inner circumferential portion of the support frame  41  (see  FIG. 4 ). Note that the gear body  42  does not always have to be provided on the whole circumference, but may be provided only at a necessary part. 
     In the gear body  42 , tooth profiles that are connecting portions are formed on the whole circumference of the inner circumference. Further, an outer circumference intermediate portion of the gear body  42  protrudes outward by forming a rectangular section to configure an inner ring portion  81  of a bearing member  8 . An outer ring portion  82  with a U-shaped section is placed to wrap the inner ring portion  81 , and a roller bearing  83  is interposed between a concave surface of the outer ring portion  82  and top and bottom surfaces and an outer peripheral edge surface of the inner ring portion  81 . The outer ring portion  82  has a bottom surface fixed to a tilting floor  5  ( FIG. 1 ) side. Note that the tooth profiles of the gear body  42  may be formed only at a necessary portion. Further, the connecting portions do not have to be always the tooth profiles of the gear body  42 . 
     By the structure as described above, the support frame  41  is supported by the bearing member  8  to be rotatable in a plane parallel with the tilting floor  5  around a ring center thereof. Thereby, the furnace body  1  ( FIG. 1 ) supported by the rotation mechanism  4  having the circular-ring-shaped support frame  41  is rotatable around a cylinder axis thereof. 
     Gear boxes  91  ( FIG. 3 ) are provided in radially symmetrical positions on the tilting floor  5  at an inner side of the ring of the support frame  41 , and gear bodies are placed inside thereof.  FIG. 4  shows the details. In  FIG. 4 , a hydraulic motor  92  including the drive mechanism, in a vertical posture is provided at the tilting floor  5  side, and a gear body  93  is fitted to an output shaft thereof. The gear body  93  is engaged with a gear body  95  that is rotatably supported by a shaft body  94  vertically provided at the tilting floor  5  side, and the gear body  95  is engaged with the tooth profiles of the above described ring-shaped gear body  42 . 
     Thereby, when the hydraulic motor  92  is rotated in forward and reverse directions, the support frame  41  is rotated in forward and reverse directions via the gear bodies  93 ,  95  and  42 . In the present embodiment, by the hydraulic motor  92 , the support frame  41 , namely, the furnace body  1  can be rotated in a range (a chain line of  FIG. 3 ) of 50° in a counterclockwise direction from an original position shown in  FIG. 3  in which a tapping port of the furnace body  1  directly confronts a tapping yard. 
     A stopper mechanism  96  is placed in an intermediate position in a circumferential direction of the support frame  41 , between both the gear boxes  91 .  FIG. 5  shows details of the stopper mechanism  96 . In  FIG. 5 , the support frame  41  is provided with a sheath member  961  toward an inside. The sheath member  961  is a cylindrical body, and an inner circumference of a half part thereof at the inner side is formed into a tapered shape that gradually expands inward. At the tilting floor  5  side, a plug member  964  that is linearly advanced and retreated in inward and outward directions by a drive cylinder  963  is provided on a stand  962 . The plug member  964  is formed into a circular-column body in which a distal end portion located at an outer side gradually reduces in diameter in a distal end direction, and a rear end of the plug member  964  is connected to a rod  965  of the drive cylinder  963 . 
     When the support frame  41  is in the original position, the sheath member  961  directly confronts the plug member  964 , as shown in  FIG. 5 , whereas when the plug member  964  is advanced by the drive cylinder  963 , the plug member  964  advances into the sheath member  961 , and the distal end portion in the tapered shape of the plug member  964  is fitted into the half part in the tapered shape of the sheath member  961 . Thereby, rotation of the support frame  41 , namely, the furnace body  1  is reliably restricted, and tapping tilt or slag discharging tilt of the furnace body  1  by the tilting body  6  can be performed in this state. 
     Steps in the case of performing melting of a metal material (scrap) in the arc furnace as above will be described hereinafter with reference to  FIGS. 6A to 6F . Note that in  FIGS. 6A to 6F , shaded parts in the furnace body  1  show unmelted scrap, and hollow parts show melted scrap. Further, reference sign  12  designates the tapping port, and reference sign  13  designates a slag discharge port. In  FIGS. 6A and 6B , each show a first melting time period, in which the scrap in the furnace body  1  is melted by arc discharge (hollow arrows) from the three electrodes  3 . In this stage, extreme nonuniformity of melting does not occur yet ( FIG. 6B ). In  FIGS. 6C and 6D , each show a second melting time period, in which after the furnace lid  2  is opened and the furnace body  1  is rotated by 50° from the original position in advance (the black arrow in  FIG. 6C ), scrap is additionally charged ( FIG. 6C ). 
     When the furnace lid  2  is closed in the above state and the scrap in the furnace body  1  is melted by arc discharge from the three electrodes  3 , hot spots at three spots and cold spots at three spots are alternately generated in the circumferential direction of the furnace body  1  and the scrap is melted non-uniformly ( FIG. 6D ). Thus, in the next oxidation heat increase time period, the furnace lid is separated upward, the furnace body  1  is returned to the original position again to rotate (the black arrow of  FIG. 6E ), and unmelted scrap is moved to the hot spots. When the furnace lid  2  is closed in this state and discharge from the electrodes  3  is restarted, electric power is effectively supplied to the unmelted scrap, quick melting advances, and the entire scrap is melted uniformly ( FIG. 6F ). 
     Second Embodiment 
       FIGS. 7 and 8  show another example of the rotation mechanism in the present invention. In the present embodiment, a plurality of hydraulic motors  10  and drive rollers  101  fixed to output shafts thereof are provided at intervals on a stand  102  provided on the tilting floor  5  side below the support frame  41  along a whole circumference ( FIG. 7  shows only a half of the circumference) of the ring of the support frame  41 . The drive roller  101  has a tapered shape that expands in diameter toward an outer side (a right side in  FIG. 8 ) of the support frame  41 , and a ring-shaped spacer body  411  that is provided on a whole circumference of the bottom surface of the inner circumferential portion of the support frame  41  is placed on the drive rollers  101 . 
     The spacer body  411  has a bottom surface formed into an inclined surface along the outer circumference of the drive rollers  101 , and supports the support frame  41  parallel with the tilting floor  5  in a state in which the spacer body  411  is placed on the drive rollers  101 . Due to such a structure, when the respective hydraulic motors  10  are synchronously rotated, the support frame  41 , namely, the furnace body  1  that is placed on the drive roller  101  is rotated around a cylinder axis thereof. More durability can be expected from the present structure against the dust environment of a site. 
     This application is based on Japanese patent application No. 2013-180757 filed Aug. 31, 2013, the entire contents thereof being hereby incorporated by reference. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
       1 : Furnace body 
       11 : Bottom wall 
       2 : Furnace lid 
       3 : Electrode 
       4 : Rotation mechanism 
       41 : Support frame (ring body) 
       42 : Gear body (connecting portion) 
       5 : Tilting floor 
       6 : Tilting body 
       92 : Hydraulic motor (drive mechanism) 
       93 : Gear body (drive mechanism) 
       95 : Gear body (drive mechanism) 
       961 : Sheath member (stopper mechanism) 
       963 : Drive cylinder (stopper mechanism) 
       964 : Plug member (stopper mechanism)