Patent Publication Number: US-10307767-B2

Title: Rotary drum-type magnetic separator

Description:
RELATED APPLICATIONS 
     Priority is claimed to Japanese Patent Application No. 2014-202824, filed Oct. 1, 2014, and International Patent Application No. PCT/JP2015/075807, the entire content of each of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     Certain embodiment of the present invention relates to a rotary drum-type magnetic separator which recovers a metal component from sludge included in a coolant liquid. 
     Description of Related Art 
     In polishing, cutting, or the like of a metal material, particularly, a magnetic material represented by a steel material, sludge-shaped cut chips, chips, or the like discharged along with a coolant liquid are separated from a liquid to be recovered. Since the cut chips, the chips, or the like have various shapes, various magnetic separation (recovery) devices are developed from the viewpoint of recovery efficiency. 
     For example, since the chips are powdery, the chips are easily collected and are likely to contain a liquid. Accordingly, a magnetic separation device which favorably separates the liquid of the sludge is required. For example,  FIG. 1  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing a configuration of a rotary drum-type magnetic separator of the related art. 
     As shown in  FIG. 1 , in the rotary drum-type magnetic separator of the related art, a liquid reservoir portion  2  which stores a coolant liquid is provided inside a box-shaped main body  1 . In addition, a rotary drum  3  is pivotally supported in an approximately horizontal direction in the vicinity of a center portion of the main body  1  so as to divide the liquid reservoir portion  2  into two. The rotary drum  3  is a cylindrical body formed of a nonmagnetic material such as stainless steel, and inner tube  5  in which a plurality of magnets  4 ,  4 , . . . are disposed in a predetermined arrangement on the outer peripheral surface is coaxially fixed to the inner portion of an outer tube  9 . In the plurality of magnets  4 ,  4 , . . . , in order to magnetically attach cut chips, chips, or the like included in the coolant liquid, magnetic poles are disposed to generate a predetermined magnetic flux on the outer peripheral surface of the rotary drum  3 . 
     In the example of  FIG. 1 , the plurality of magnets  4 ,  4 , . . . are disposed from a portion in which the rotary drum  3  is immersed into the liquid reservoir portion  2  to a top portion, that is, on the inner tube  5  corresponding to a portion equivalent to approximately ¾ of the outer periphery of the rotary drum  3 . In a portion corresponding to the approximately remaining ¼, the magnets  4 ,  4 , . . . are not disposed on the inner tube  5  and a magnetic force does not act on the portion. 
     The cut chips, the chips, or the like, which are magnetically attached to the outer peripheral surface of the outer tube  9  on the bottom portion of liquid reservoir portion  2  by the magnetic forces of the magnets  4 ,  4 , . . . , are transported to the top portion of the rotary drum  3  according to the rotation of the outer tube  9 , magnetization forces generated by the magnetic forces of the magnets  4 ,  4 , . . . are released at the time point at which the cut chips, the chips, or the like pass through the top portion, and the cut chips, the chips, or the like are scrapped off by a scraper  7  abutting on the rotary drum  3  so as to be recovered. A squeezing roller  6  in which an elastic body such as rubber is disposed on the surface is provided in the vicinity of the top portion of the rotary drum  3  and abuts on the outer peripheral surface of the outer tube  9  of the rotary drum  3  by predetermined pressing. The magnetically attached sludge passes through a portion between the outer tube  9  and the squeezing roller  6 , a liquid of the sludge is squeezed out, and the cut chips, the chips, or the like are separated and recovered at the time point at which the sludge passes through the top portion of the rotary drum  3 , that is, a position at which the magnetic force of the magnet  4  is not applied. 
     In the above-described rotary drum-type magnetic separator of the related art, it is possible to purify the coolant liquid up to a certain level. However, recently, it is required to perform purification to be the coolant liquid having high cleanness. Meanwhile, for example, in the related art, a plurality of magnetic separation devices are disposed in multiple stages so as to provide a coolant liquid having higher cleanness. 
     Moreover, in the related art, a purifying device is disclosed, which includes a first rotary drum in which a plurality of magnets are disposed on the outer peripheral surface, and a second rotary drum which is disposed so as to be close to the first rotary drum and in which a plurality of magnets are disposed on an outer peripheral surface to which suspended solid matters adsorbed to the first rotary drum and transported therefrom are delivered. 
     SUMMARY 
     According to an embodiment of the present invention, there is provided a rotary drum-type magnetic separator which separates magnetic substances from a used coolant liquid, including: a first rotary drum on which a plurality of magnets are disposed; a second rotary drum on which a plurality of magnets are disposed and which is provided before the first rotary drum in a direction in which the used coolant liquid flows such that the magnetic substances are adsorbed to each other so as to be getting larger by magnetizing the magnetic substances in the used coolant liquid using the second drum; a scraper which scrapes off the magnetic substances attached to the second rotary drum; and a bottom member which forms a flow path below the first rotary drum, in which the magnetic substances are introduced to the first rotary drum along a flow of the used coolant liquid in a state where sizes of the magnetic substances scrapped off by the scraper are increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing a configuration of a rotary drum-type magnetic separator of the related art. 
         FIG. 2  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing a configuration of a rotary drum-type magnetic separator according to an embodiment of the present invention. 
         FIG. 3  is an exemplary view showing a distribution of a magnetic flux density of a second rotary drum of the rotary drum-type magnetic separator according to the embodiment of the present invention. 
         FIGS. 4A and 4B  are schematic sectional views taken along a surface orthogonal to a rotary shaft of the second rotary drum showing a disposition example of a plurality of magnets of the second rotary drum according to the embodiment of the present invention. 
         FIGS. 5A and 5B  are schematic sectional views taken along a surface orthogonal to the rotary shaft of the second rotary drum showing another disposition example of the plurality of magnets of the second rotary drum according to the embodiment of the present invention. 
         FIG. 6  is a graph showing variation in recovery rates of magnetic sludge which is an unnecessary object. 
         FIG. 7  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing another configuration of the rotary drum-type magnetic separator according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     However, as disclosed in the related art, in the method of disposing the magnetic separation devices in multiple stages, it is necessary to provide a plurality of magnetic separation devices, which is not a realistic solution from the viewpoint of a manufacturing cost. 
     Moreover, in the related art, sizes of suspended solid matters which are finally recovered can be classified by magnitudes of magnetic forces of magnets mounted on a second rotary drum. However, since the sizes of suspended solid matters which are recovered from a coolant liquid are the same as those in the past, the total amount of the suspended solid matters in the circulating coolant liquid is not changed, and there is a problem that it is not possible to improve cleanness of the coolant liquid. 
     It is desirable to provide a rotary drum-type magnetic separator in which cleanness of a circulating coolant liquid can be improved by a simple structure. 
     In a rotary drum-type magnetic separator according to an embodiment of the present invention, the separator includes a second rotary drum on which a plurality of magnets are disposed and which is provided before a first rotary drum in a direction in which a used coolant liquid flows such that magnetic substances are adsorbed to each other so as to be getting larger by magnetizing the magnetic substances in the used coolant liquid using the second drum, the scraper which scrapes off the magnetic substances attached to the second rotary drum, and a bottom member which forms a flow path below the first rotary drum, in which the magnetic substances are introduced to the first rotary drum along a flow of the used coolant liquid in a state where the sizes of the magnetic substances scrapped off by the scraper are increased. Accordingly, magnetic substances adsorbed by the second rotary drum are attracted to each other by being magnetized, fine particles are collected, and the size per grain increases. Therefore, since the magnetic substances are introduced to the first rotary drum in which the state where the magnetic substances are particles of which the sizes are increased, it is possible to more reliably recover the magnetic substances by the first rotary drum, and it is possible to further improve cleanness of the coolant liquid. 
     In addition, in the rotary drum-type magnetic separator, the second rotary drum may include an outer tube and an inner tube, and the outer tube may be fixed and the inner tube on which a plurality of magnets are disposed may rotate inside the outer tube. 
     In this configuration, since the second rotary drum includes the outer tube and the inner tube, and the outer tube is fixed and the inner tube on which the plurality of magnets are disposed can rotate inside the outer tube, it is possible to more reliably recover the magnetic substances by the first rotary drum, and it is possible to further improve cleanness of the coolant liquid. 
     Moreover, in the rotary drum-type magnetic separator, the second rotary drum may include an outer tube and an inner tube, and the inner tube on which a plurality of magnets are disposed may be fixed and the outer tube may rotate outside the inner tube. 
     In this configuration, since the second rotary drum includes the outer tube and the inner tube, and the inner tube on which the plurality of magnets are disposed is fixed and the outer tube can rotate outside the inner tube, it is possible to more reliably recover the magnetic substances by the first rotary drum, and it is possible to further improve cleanness of the coolant liquid. 
     Moreover, in the rotary drum-type magnetic separator, the second rotary drum may include an outer tube and an inner tube, and the inner tube on which a plurality of magnets are disposed and the outer tube may rotate with respect to each other. 
     In this configuration, since the second rotary drum includes the outer tube and the inner tube, and the inner tube on which the plurality of magnets are disposed and the outer tube can rotate with respect to each other, it is possible to more reliably recover the magnetic substances by the first rotary drum, and it is possible to further improve cleanness of the coolant liquid. 
     Moreover, in the rotary drum-type magnetic separator, the scraper may be inclined to descend toward the first rotary drum side from the second rotary drum side. 
     In this configuration, since the scraper is inclined to descend toward the first rotary drum side from the second rotary drum side, magnetic substances which are attracted (are adsorbed) to each other on the peripheral surface of the second rotary drum and in which the sizes increases are easily separated from the second rotary drum, and it is possible to reliably introduce magnetic substances to the first rotary drum in the state where the sizes are increased. 
     In addition, in the rotary drum-type magnetic separator, the second rotary drum may include a strong magnetic portion which has a stronger magnetic force than those of the surroundings and a weak magnetic portion which has a weaker magnetic force than those of the surroundings. 
     In this configuration, since the second rotary drum includes the strong magnetic portion which has a stronger magnetic force than those of the surroundings and the weak magnetic portion which has a weaker magnetic force than those of the surroundings, the magnetic substances magnetically attached by the strong magnetic portion can be separated by the weak magnetic portion, and it is possible to more reliably introduce the magnetic substances in which the sizes per grain are increased to the first rotary drum. 
     Moreover, in the rotary drum-type magnetic separator, a plurality of sets of magnets in which two magnets having polarities different from each other are formed as one set may be mounted on the inner tube of the second rotary drum. 
     In this configuration, since a plurality of sets of magnets in which two magnets having polarities different from each other are formed as one set are mounted on the inner tube of the second rotary drum, it is possible to form a stronger magnetic portion or a weaker magnetic portion by devising the disposition of the magnets such as disposing two sets of adjacent magnets such that the polarities are opposite to each other, and it is possible to more reliably introduce the magnetic substances in which the sizes per grain are increased to the first rotary drum. 
     In addition, in the rotary drum-type magnetic separator, in one set of magnets mounted on the inner tube of the second rotary drum, a thickness of one magnet may be thicker than a thickness of the other magnet. 
     In this configuration, since in one set of magnets mounted on the inner tube of the second rotary drum, the thickness of one magnet is thicker than the thickness of the other magnet, it is possible to form a stronger magnetic portion or a weaker magnetic portion, and it is possible to more reliably introduce the magnetic substances in which the sizes per grain are increased to the first rotary drum. 
     Moreover, in the rotary drum-type magnetic separator, in a case where even magnet sets are mounted on the inner tube of the second rotary drum, polarities of one set of magnets adjacent to each other may be opposite to each other. 
     In this configuration, in the case where even magnet sets are mounted on the inner tube of the second rotary drum, since polarities of one set of magnets adjacent to each other are opposite to each other, it is possible to reliably form the weak magnetic portion in which the magnetic force is relatively weak between the magnets of each set, and it is possible to more reliably introduce the magnetic substances in which the sizes per grain are increased to the first rotary drum. 
     According to an embodiment of the present invention, magnetic substances adsorbed by the second rotary drum are attracted to each other by being magnetized, fine particles are collected, and the size per grain increases. Therefore, since the magnetic substances are introduced to the first rotary drum in the state where the magnetic substances become large particles, it is possible to more reliably recover the magnetic substances is by the first rotary drum, and it is possible to further improve cleanness of the coolant liquid. 
     Hereinafter, the present invention will be described in detail based on the drawings showing the embodiment.  FIG. 2  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing a configuration of a rotary drum-type magnetic separator according to an embodiment of the present invention. 
     As shown in  FIG. 2 , in the rotary drum-type magnetic separator according to the present embodiment, a liquid reservoir portion  12  which stores a coolant liquid is provided inside a box-shaped main body  10 , and a used coolant liquid in which sludge including cut chips, chips, or the like after polishing or cutting is mixed is charged into the liquid reservoir portion  12  from a charge port  20 . 
     In order to divide the liquid reservoir portion  12  into two, a first rotary drum  13  is pivotally supported in the vicinity of a center portion of the main body  10  so as to be rotatable in an approximately horizontal direction. The first rotary drum  13  is a cylindrical body formed of a nonmagnetic material such as stainless steel, and inner tube  15  in which a plurality of magnets  14 ,  14 , . . . are disposed in a predetermined arrangement on the outer peripheral surface is fixed to the inner portion of an outer tube  19  so as to be coaxial to the outer tube  19 . In the plurality of magnets  14 ,  14 , . . . , in order to magnetically attach cut chips, chips, or the like which are magnetic substances included in the used coolant liquid, polarities are disposed to generate a predetermined magnetic flux on the outer peripheral surface of the outer tube  19 . In addition, as shown in  FIG. 2 , adjacent magnets  14  and  14  are disposed such that the polarities are opposite to each other, and specifically, the magnets  14  are alternately disposed on the outer peripheral surface of the inner tube  15  such that the outer peripheral surface is the magnet of “N” pole, the outer peripheral surface is the magnet of “S” pole, . . . . 
     In  FIG. 2 , the plurality of magnets  14 ,  14 , . . . are disposed from a portion in which the first rotary drum  13  is immersed into the liquid reservoir portion  12  to a top portion, that is, on the inner tube  15  corresponding to a portion equivalent to approximately ¾ of the outer periphery of the first rotary drum  13 . In a portion corresponding to the approximately remaining ¼, the magnets  14 ,  14 , . . . are not disposed on the inner tube  15  and a magnetic force does not act on the portion. 
     The cut chips, the chips, or the like, which are the magnetic substances and magnetically attached to the outer peripheral surface of the outer tube  19  of the first rotary drum  13  on the bottom portion of liquid reservoir portion  12  by the magnetic forces of the plurality of magnets  14 ,  14 , . . . , are transported to the top portion of the first rotary drum  13  according to the rotation of the outer tube  19 , the cut chips, the chips, or the like are released from magnetization forces generated by the plurality of magnets  14 ,  14 , . . . at the time point at which the cut chips, the chips, or the like pass through the top portion, and the cut chips, the chips, or the like are scrapped off by a scraper  17  abutting on the outer tube  19  so as to be recovered. A squeezing roller  16  in which an elastic body such as rubber is disposed on the surface is provided in the vicinity of the top portion of the first rotary drum  13  and abuts on the outer peripheral surface of the outer tube  19  of the first rotary drum  13  by predetermined pressing. The magnetically attached sludge including the cut chips, chips, or the like passes through a portion between the outer tube  19  and the squeezing roller  16 , a liquid of the sludge is squeezed out, and the cut chips, the chips, or the like are separated and recovered at the time point at which the sludge passes through the top portion of the first rotary drum  13 , that is, a position at which the magnetic force of the magnet  14  is not applied. 
     As an elastic body which is used in an abutment surface of the squeezing roller  16  with respect to the outer peripheral surface of the first rotary drum  13 , an elastic body such as CR (chloroprene) based rubber or NBR (nitrile) based rubber is mainly used. However, for example, an uncrosslinked polyurethane material containing polyester polyol as a main component may be used. 
     In the present embodiment, in addition to the first rotary drum  13 , a second rotary drum  21  having a smaller diameter than that of the first rotary drum  13  is disposed before the first rotary drum  13  in a direction in which the used coolant liquid flows. That is, first, after the cut chips or the chips which are magnetic substances are adsorbed by the second rotary drum  21 , and the cut chips, the chips collected by the first rotary drum  13  are adsorbed again. 
     Similarly to the first rotary drum  13 , the second rotary drum  21 , the second rotary drum  21  is a cylindrical body formed of a nonmagnetic material such as stainless steel, and inner tube  25  in which a plurality of magnets  24 ,  24 , . . . are disposed in a predetermined arrangement on the outer peripheral surface is fixed to the inner portion of an outer tube  29  so as to be rotatable coaxially with the outer tube  29 . In the plurality of magnets  24 ,  24 , . . . , in order to magnetically attach cut chips, chips, or the like which are magnetic substances included in the used coolant liquid, polarities are disposed to generate a predetermined magnetic flux on the outer peripheral surface of the outer tube  29 . In addition, each of “N” and “S” shown in  FIG. 2  indicates a polarity of the surface side opposite to the outer peripheral surface side of the outer tube  29  of the magnet  24 . 
     In  FIG. 2 , the entire second rotary drum  21  is immersed into the liquid reservoir portion  12 . In addition, the plurality of magnets  24 ,  24 , . . . are disposed on the inner tube  25 . The cut chips, the chips, or the like, which are magnetic substances magnetically attached to the outer peripheral surface of the outer tube  29  of the second rotary drum  21  on the bottom portion of liquid reservoir portion  12  by the magnetic forces of the plurality of magnets  24 ,  24 , . . . , move on the outer peripheral surface of the outer tube  29  according to the rotation of the inner tube  25 , pass through the top portion of the second rotary drum  21 , and are scrapped off by a scraper  27  abutting on the outer tube  29 . The scraper  27  is connected to a bottom member  30  which forms a flow path below the first rotary drum  13  and introduces scraped unnecessary objects (magnetic substances) to the first rotary drum  13 . 
     Here, the plurality of magnets  24 ,  24 , . . . are disposed such that the magnetic poles alternate with each other and a magnetic flux emitted from the outer peripheral surface of the outer tube  29  is discontinuous.  FIG. 3  is an exemplary view showing a distribution of a magnetic flux density of the second rotary drum  21  of the rotary drum-type magnetic separator according to the embodiment of the present invention. In  FIG. 3 , “sparse” and “dense” respectively indicate a portion having a large magnetic flux density and a portion having a small magnetic flux density. 
     As shown in  FIG. 3 , in the plurality of magnets  24 ,  24 , . . . , a magnet group  241  in which two magnets  24  and  24  are formed as one set is disposed on the outer peripheral surface of the inner tube  25 , and magnetic poles on the outer peripheral surface side are disposed to alternate with each other such as a case where the N pole, the S pole, the N pole, the S pole, . . . are sequentially arranged. According to this disposition, in the front surface of the magnet group  241  and a gap portion between the magnet groups  241  and  241 , there is a difference in magnetic flux densities of magnetic fluxes emitted from the outer peripheral surface of the outer tube  29 . For example, a strong magnetic portion in which the magnetic flux density is large, that is, the magnetic force is strong, and a weak magnetic portion in which the magnetic flux density is small, that is, the magnetic force is weak are generated. 
     Moreover, in the strong magnetic portion, cut chips, chips, or the like magnetized on the surface of the outer tube  29  are easily adsorbed, and even when the chips, chips, or the like are fine particles, these are attracted to each other so as be easily increased. Meanwhile, in the weak magnetic portions, the chips, chips, or the like are easily separated from the surface of the outer tube  29 . Accordingly, at the time point at which the weak magnetic portion reaches the scraper  27  according to the rotation of the inner tube  25 , unnecessary objects (magnetic substances) such as relatively large cut chips or chips are easily separated and are introduced to the first rotary drum  13  along the flow of the used coolant liquid in a state in which the size per grain is increased. 
     The disposition of the plurality of magnets  24 ,  24 , . . . in the second rotary drum  21  of the rotary drum-type magnetic separator according to the present embodiment is not particularly limited to this.  FIGS. 4A and 4B  are schematic sectional views taken along a surface orthogonal to a rotary shaft of the second rotary drum  21  showing a disposition example of the plurality of magnets  24 ,  24 , . . . of the second rotary drum  21  according to the embodiment of the present invention. 
     In the example of  FIG. 4A , three magnet groups  241  in which two magnets  24  and  24  are formed as one set are disposed, and in the example of  FIG. 4B , four magnet groups  241  are disposed. In a case where odd magnet groups  241  are disposed as shown in  FIG. 4A , since the weak magnetic portion is formed between the adjacent magnet groups  241  and  241 , even when polarities of the adjacent magnet groups  241  are disposed to be opposite to each other, a portion in which the magnets  24  and  24  having polarities different from each other face each other is generated. 
     Meanwhile, in a case where even magnet groups  241  are disposed as shown in  FIG. 4B , since the weak magnetic portion is formed between the adjacent magnet groups  241  and  241 , even when polarities of the adjacent magnet groups  241  are disposed to be opposite to each other, a portion in which the magnets  24  and  24  having polarities different from each other face each other is not generated. That is, since the strong magnetic portions and the weak magnetic portions are generated at equal intervals on the peripheral surface of the second rotary drum  21 , it is possible to introduce the unnecessary object (magnetic substance) having a constant size to the first rotary drum  13 . 
     Moreover, in one magnet group  241  which is mounted on the inner tube  25  of the second rotary drum  21 , the thickness of one magnet  24  may be thicker than the thickness of the other magnet  24 . Accordingly, the magnetic flux density is proportional to the thickness of the magnet  24 , and in the magnet group  241 , the strong magnetic portion and the weak magnetic portion are generated. 
       FIGS. 5A and 5B  are schematic sectional views taken along a surface orthogonal to the rotary shaft of the second rotary drum  21  showing another disposition example of a plurality of magnets  24   a ,  24   b , . . . of the second rotary drum  21  according to the embodiment of the present invention. In the example of  FIG. 5A , three magnet groups  241  in which two magnets  24   a  and  24   b  are formed as one set are disposed, and in the example of  FIG. 5B , four magnet groups  241  are disposed. 
     As shown in  FIGS. 5A and 5B , in the present embodiment, in two magnets  24   a  and  24   b  for each magnet group  241 , the thickness of one magnet  24   a  which reaches the scraper  27  earlier in the rotation direction of the second rotary drum is thicker than the thickness of the adjacent other magnet  24   b . Accordingly, since the strong magnetic portion and the weak magnetic portion are generated in the magnet group  241 , unnecessary objects (magnetic substances) are more reliably attracted to each other, and it is possible to introduce the unnecessary objects (magnetic substances) in which the sizes per grain are increased to the first rotary drum  13 . 
       FIG. 6  is a graph showing variation in recovery rates of magnetic sludge which is the unnecessary object. In  FIG. 6 , (a) shows the recovery rate of the unnecessary object such as the magnetic sludge in the rotary drum-type magnetic separator of the related art. 
     Meanwhile, (b) shows the recovery rate of the unnecessary object such as the magnetic sludge in a case where the second rotary drum  21  is provided in the rotary drum-type magnetic separator of the related art. As can be seen by comparing (a) and (b) in  FIG. 6 , it is obvious that the recovery rate of (b) is higher than that of (a). 
     Here, the scraper  27  is not limited to the case shown in  FIG. 2  of being provided in the horizontal direction. For example, since it is enough for the scraper  27  to be connected to the bottom member forming the flow path below the first rotary drum  13 , the scraper  27  may be inclined so as to descend toward the first rotary drum  13  from the second rotary drum  21  side. 
       FIG. 7  is a sectional view taken along a surface orthogonal to a rotary shaft of a rotary drum showing another configuration of the rotary drum-type magnetic separator according to the embodiment of the present invention. As shown in  FIG. 7 , in the rotary drum-type magnetic separator according to the present embodiment, the scraper  27  abutting on the outer tube  29  of the second rotary drum  21  is provided to be inclined from the second rotary drum  21  side to the first rotary drum  13  side. 
     Accordingly, the unnecessary objects attached to the second rotary drum  21  which are scraped off by the scraper  27  easily move with the flow toward the first rotary drum  13  side along the inclination and can be more reliably recovered by the first rotary drum  13 . 
     As described above, according to the present embodiment, the unnecessary objects (magnetic substances) adsorbed by the second rotary drum  21  are attracted to each other by being magnetized, fine particles are collected, and the size per grain increases. Accordingly, since the unnecessary objects become large particles and are introduced to the first rotary drum  13 , it is possible to more reliably recover the unnecessary objects by the first rotary drum  13 , and it is possible to further improve cleanness of the coolant liquid. 
     Moreover, various modifications may be applied to the embodiment within a scope which does not depart from the gist of the present invention. For example, a modification of the disposition with respect to the magnets  24  of the second rotary drum  21 , a modification with respect to the inclination angle of the scraper  27 , or the like may be added. 
     Moreover, the above-described embodiment discloses the configuration in which the outer tube  29  of the second rotary drum  21  is fixed and the inner tube  25  on which the plurality of magnets  24  are disposed can rotate inside the outer tube  29 . However, the present invention is not limited to this. For example, a configuration in which the inner tube  25  on which the plurality of magnets  24  are disposed is fixed and the outer tube  29  can rotate outside the inner tube  25  may be realized, or a configuration in which the inner tube  25  on which the plurality of magnets  24  are disposed and the outer tube  29  can rotate with respect to each other may be realized. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.