Abstract:
Provided is a knife holder ( 10 ) for use with an underwater cutting pelletizing device which includes a die plate ( 40 ) and the knife holder ( 10 ). The die plate ( 40 ) includes an annular projected portion ( 52 ) and a plurality of die holes ( 51 ) having an opening on the projected portion ( 52 ). The knife holder ( 10 ) holds a plurality of knives ( 30 ) which slide on the surface of the projected portion ( 52 ) to thereby cut melt resin, which has been pushed through each of the die holes ( 51 ), into resin pellets in cooling water. The knife holder ( 10 ) can reduce the deflection of the knife ( 30 ) and thereby the gap that appears between the sliding plane thereof and the die plate projected portion ( 52 ). The knife holder ( 10 ) includes a knife holder body ( 11 ) and a plurality of rib portions ( 12 ). The knife holder body ( 11 ) has an outer circumference end ( 11   a ) which is located inside the inner circumference end of the projected portion ( 52 ) of the die plate ( 40 ) in the radial direction. The rib portions ( 12 ) are provided at respective multiple positions that are arranged in the circumferential direction of the outer circumference end ( 11   a ); are projected radially outwardly from the outer circumference end ( 11   a ) to extend outwardly past the inner circumference end of the projected portion ( 52 ); and have a front face located above the die plate and have the knife ( 30 ) secured thereto with the back face of the knife ( 30 ) facing the front face.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to knife holders provided in underwater cutting pelletizing devices that manufacture thermoplastic resin pellets. 
       BACKGROUND ART 
       [0002]    Devices such as that disclosed in Japanese Utility Model Laid-Open No. H7-40112 (a first conventional example) are known as conventional underwater cutting pelletizing devices.  FIG. 5  is a side cross-sectional view illustrating an underwater cutting pelletizing device provided with a knife holder for an underwater cutting pelletizing device according to the stated first conventional example,  FIG. 6  is a perspective view of a projected portion of a die plate and a knife in the stated pelletizing device,  FIG. 7  is a rear view of the knife and a knife holder that holds the knife, and  FIG. 8  is a cross-sectional view illustrating the knife holder, the knife, and the die plate illustrated in  FIG. 5 . 
         [0003]    As shown in  FIG. 5 , this underwater cutting pelletizing device includes: a die plate  1 , attached to the leading end portion of an extrusion barrel in a mixer/extruder, that has a die portion  2  (see  FIG. 8 ) in which a plurality of die holes  2   a  are formed; a water chamber  6  that forms a water compartment that is filled with cooling water and in which the cooling water (warm water, at approximately 60° C.) circulates; a rotating shaft  7  that protrudes into the water chamber  6 ; a knife driving unit that rotates the rotating shaft  7 ; a knife holder  8  anchored to the leading end portion of the rotating shaft  7 ; and a plurality of knives (cutter knives)  9  held by the knife holder  8  so as to face to the die portion  2 . 
         [0004]    The die plate  1  has a circular plate shape (disk shape) that is thick overall. To be more specific, as shown in  FIGS. 7 and 8 , the die plate  1  includes the die portion  2  that has a circular ring shape, an outer circumference portion  4  that has a circular ring shape and that is disposed on the outside of the die portion  2 , and a center portion  5  that has a disk shape and that is disposed on the inside of the die portion  2 . The plurality of die holes  2   a,  for extruding a thermoplastic resin supplied to the mixer/extruder and mixed by a screw thereof into strands, are formed in an inner portion of the die portion  2 . A hardened layer (for example, a TiC hardened layer) is formed on the entire surface of the die portion  2 , and as a result, a projected portion  3  that projects further toward the knives  9  than the other portions is formed. 
         [0005]    The knives  9  are pressed against the surface of the projected portion  3  and rotationally driven integrally with the rotating shaft  7  along the surface of the projected portion  3  (see  FIG. 6 ), and as a result, the strand-shaped thermoplastic resin that has been extruded from the plurality of die holes  2   a  is cut into pellets by the knives  9 . This realizes underwater pelletizing for thermoplastic resin. 
         [0006]    The knives  9  have rectangle shapes that extend in one direction when viewed from the front (or the rear) as shown in  FIG. 7 ; and as shown in  FIG. 6 , each of the knives  9  has a sliding surface  9   a  that rotates while it is pressed against the projected portion  3  of the die plate  1  so as to slide along the surface of the projected portion  3 , and a cutting face  9   b  that forms a face angle of the knife. In this example, four knives  9  are supported by one end on the front face of the knife holder  8  (that is, the surface that faces the die plate  1 ) with a circular plate-shape by using bolts to tighten the base end portions of the knives (that is, one end portion of each knife) onto an outer circumference area of the holder in positions arranged at equal intervals in the circumferential direction. 
         [0007]    The dimension of the outer diameter of the knife holder  8  is set so that, as shown in  FIGS. 7 and 8 , a holder outer circumference end  8   a  is positioned further inward of an inside circumference end  3   b  of the projected portion  3  in the die plate  1 . The reason for this is that, if the outer diameter dimension of the knife holder  8  is increased so that the outer circumference end  8   a  of the knife holder  8  is located further outside than the inside circumference end  3   b  of the projected portion  3 , the projected portion  3  will be covered by the knife holder  8  from above when the knives  9  rotate, and as a result, it is highly likely that the resin pellets cut by the knives  9  will become caught in the gap between the projected portion  3  and the front face of the knife holder  8 , which in turn can result in a breakdown in the shape of the resin pellets. 
         [0008]    As described earlier, each of the knives  9  is pushed against the projected portion  3  while being supported on one end by the knife holder  8 ; accordingly, although the sliding surfaces  9   a  of the knives  9  make contact with the surface of the projected portion  3  at a position of the knives  9  that is near the knife holder  8 , the knives  9  experience more warping toward the free ends of the knives  9  away from the knife holder  8 , and thus the gap between the sliding surfaces  9   a  and the projected portion  3  increases. This inhibits the manufacture of resin pellets having a good cylindrical shape, and may result in tail pellets in which strand-shape entities of approximately 2-3 mm stick to the cut surface, fines, which are strand-shaped entities shredded from the tail pellets, and so on. 
         [0009]    A knife holder for an underwater cutting pelletizing device capable of suppressing such warping in knives is proposed in Japanese Patent Application Laid-Open No. H11-165316 (a second conventional example).  FIG. 9  is a front view illustrating a knife holder  100  for an underwater cutting pelletizing device according to the second conventional example. This knife holder  100  holds four knives  200 , and includes: a circular plate portion  103  that is rotationally driven along with a rotating shaft, an inner holder portion  101  and an outer holder portion  102  that protrude from the circular plate portion  103  and rotate integrally with the circular plate portion  103 , and four ribs  104 . The inner holder portion  101  has a circular shape with a small diameter, and an attachment portion  200   a,  to which one end of each of the knives  200  is attached, is anchored thereto with a bolt. The outer holder portion  102  has a circular ring shape with an inner diameter that is larger than the diameter of the inner holder portion  101 , and an attachment portion  200   b,  on which the other end of each of the knives  200  is provided, is anchored thereto with a bolt. Each of the ribs  104  connects the inner holder portion  101  and the outer holder portion  102  in the radial direction thereof. 
         [0010]    In this manner, with the knife holder  100 , the attachment portion  200   a  on one end of each of the knives  200  is attached to the inner holder portion  101 , and the attachment portion  200   b  on the other end is attached to the outer holder portion  102 , respectively; and as a result, each of the knives  200  is supported on both ends and warping in the knives  200  is reduced, which in turn makes it possible to reduce the gaps between the projected portion of the die plate and the sliding surfaces of the knives. 
         [0011]    However, with the knife holder  100  according to the second conventional example, there is a risk of resin pellets that have been cut accumulating in a space formed between the ribs  104  and the knives  200 , or making contact with the ribs  104  which are rotating at a high speed to be deformed as a result. 
       CITATION LIST 
     Patent Document 
       [0012]    Patent Document 1: Japanese Utility Model Laid-Open No. H7-40112
 
Patent Document 2: Japanese Patent Application Laid-Open No. H11-165316
 
       SUMMARY OF INVENTION 
       [0013]    It is an object of the present invention to provide a knife holder that holds a knife used in an underwater cutting pelletizing device and is capable of reducing a gap between a sliding surface of the knife and a projected portion of a die plate in the pelletizing device by reducing warping of the knife, so as to enable the manufacture of resin pellets having a favorable shape. 
         [0014]    A knife holder provided by the present invention is used as a knife holder for an underwater cutting pelletizing device, the underwater cutting pelletizing device including a rotating shaft; a die plate that is anchored to the rotating shaft and has a ring-shaped projected portion that projects further in a direction parallel to the rotating shaft than the other portions, in which a plurality of die holes are formed in the projected portion and a melt resin is extruded from each of the die holes; and the knife holder that holds a plurality of knives that slide along a surface of the projected portion and cut the melt resin extruded from each of the die holes within a cooling water in order to create resin pellets. This knife holder includes: a knife holder body having an outer circumference end positioned further inward in the radial direction of an inner circumference end of the projected portion of the die plate; and a plurality of rib portions, each of which is provided in a respective plurality of positions arranged in the circumferential direction of the outer circumference end of the knife holder body, that protrude outward in the radial direction from the outer circumference end and extend further outward of the inner circumference end of the projected portion, and to which the knives are anchored in a state in which back faces of the knives face front faces of the rib portions that face the die plate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    [ FIG. 1 ] A rear view of a knife holder for an underwater cutting pelletizing device according to an embodiment of the present invention. 
           [0016]    [ FIG. 2 ] A rear view illustrating the knife holder for the underwater cutting pelletizing device shown in  FIG. 1  in a state in which knives are mounted thereon. 
           [0017]    [ FIG. 3 ] A cross-sectional view of the elements shown in  FIG. 2 . 
           [0018]    [ FIG. 4 ] A cross-sectional view taken along the IV-IV line shown in  FIG. 3 . 
           [0019]    [ FIG. 5 ] A side cross-sectional view illustrating an underwater cutting pelletizing device provided with a knife holder for an underwater cutting pelletizing device according to a first conventional example. 
           [0020]    [ FIG. 6 ] A perspective view of a projected portion of a die plate and knives shown in  FIG. 5 . 
           [0021]    [ FIG. 7 ] A rear view of the knife holder and knives shown in  FIG. 5 . 
           [0022]    [ FIG. 8 ] A cross-sectional view of the knife holder, knives, and die plate shown in  FIG. 5 . 
           [0023]    [ FIG. 9 ] A front view illustrating a knife holder for an underwater cutting pelletizing device according to a second conventional example. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is a rear view of a knife holder for an underwater cutting pelletizing device according to an embodiment of the present invention,  FIG. 2  is a rear view illustrating the knife holder for the underwater cutting pelletizing device shown in  FIG. 1  in a state in which knives are mounted thereon, and  FIG. 3  is a cross-sectional view of the elements shown in  FIG. 2 . 
         [0025]    The underwater cutting pelletizing device illustrated in  FIGS. 1 through 3  includes: a knife holder  10  for an underwater cutting pelletizing device (also called simply a “knife holder” hereinafter), a plurality of knives  30  held by the knife holder  10 , a rotating shaft  20 , and a die plate  40  having a circular plate shape. 
         [0026]    The die plate  40  is configured by a die portion  50  having a circular ring shape, an outer circumference portion  60  that has a circular ring shape and is disposed on the outer side of the die portion  50 , and a center portion  70  that has a circular plate shape or a circular ring shape and that is disposed on the inner side of the die portion  50 . A plurality of bolt holes are provided in the outer circumference portion  60  and the center portion  70 , respectively, and the die plate  40  is anchored to a die holder by bolts that are inserted through the respective bolt holes. As shown in  FIG. 3 , a plurality of die holes  51  are formed in the die portion  50 , extending in the thickness direction thereof. A hardened layer (for example, a TiC hardened layer) is formed on a surface of the die portion  50 , which forms, across the entire surface of the die portion  50 , a projected portion  52  that projects further toward the knives  30  than the other surface than the die portion  50 , or in other words, a surface of the outer circumference portion  60  and a surface of the center portion  70 ; and the die holes  51  are provided in this projected portion  52 . The surface of the projected portion  52  configures a sliding surface, which is a plane along which the knives  30  are capable of sliding. 
         [0027]    The knife holder  10  includes a knife holder body  11  configured by, for example, stainless steel, and a plurality of rib portions  12  configured by, for example, stainless steel; and in this embodiment, four rib portions  12  are provided. 
         [0028]    The knife holder body  11  is anchored to a leading end portion of the rotating shaft  20 , has a circular plate shape or a disk shape having a circular outer circumference end  11   a,  and has an outer diameter of a size that positions the outer circumference end  11   a  further inside than an inner circumference end  52   b  of the projected portion  52 . The knives  30  are held by the knife holder  10  so that base end portions of the knives  30  are positioned further inward of the outer circumference end  11   a  of the knife holder body  11 , when viewed in the radial direction. In other words, the outer circumference end  11   a  of the knife holder body  11  is positioned further outward of the base ends of the knives  30 , when viewed in the radial direction. 
         [0029]    The knife holder body  11  has a front face that is a surface facing the die plate  40 , and rib attachment grooves  11   b  to which the rib portions  12  are attached are formed in this front face. Each of the rib attachment grooves  11   b  is provided in a respective plurality of positions in an outer circumference area of the knife holder body  11 , which are arranged at equal intervals in the circumferential direction; and in this embodiment, four rib attachment grooves  11   b  are provided. 
         [0030]    The rib portions  12  have rectangular shapes when viewed from the front or the rear, as shown in  FIG. 1 . As shown in  FIG. 3 , a leading end portion, or in other words, a portion on an outer side of the knife holder  10  in the radial direction thereof, of each of the rib portions  12 , has the same thickness as that of the knife holder body  11 , whereas a base end portion, or in other words, a portion on an inner side of the knife holder  10  in the radial direction thereof, of each of the rib portions  12 , has an attachment portion  12   a  having a thickness that has been reduced to the same dimension as the groove depth of the rib attachment grooves  11   b.  Each of the attachment portions  12   a  has a shape that enables fitting into the corresponding rib attachment groove  11   b,  and when fitted therein, is anchored in a removable state to the knife holder body  11  using a bolt  13 . Each of the rib portions  12  has a length such that, in the attached state, protrudes further outward of the outer circumference end  11   a  of the knife holder body  11  in the radial direction, and extends to a position that is further outward of the inner circumference end  52   b  of the projected portion  52 ; and in this embodiment, this position is between the inner circumference end  52   b  and an outer circumference end  52   a  of the projected portion  52 . 
         [0031]    The knives  30  are anchored to the knife holder body  11  or the rib portions  12 , in a state in which the back faces of the knives  30  are positioned on the front face of the knife holder body  11  or the rib portions  12 . In the present embodiment, each of the knives  30  is anchored to a corresponding rib portion  12  using a bolt  31 . 
         [0032]      FIG. 4  is a cross-sectional view taken along the IV-IV line shown in  FIG. 3 . Each of the knives  30  has a rectangular shape that extends in one direction when viewed from the front or the rear, and as shown in  FIG. 4 , has a sliding surface  30   a  that is pressed against and slides upon the projected portion  52  of the die portion  50 , and a cutting face  30   b  that forms a face angle of the knife. As shown in  FIG. 4 , each of the rib portions  12  has a sloped surface  12   b  having the same angle of slope as an angle of slope of the cutting face  30   b  of the corresponding knife  30  thereof so as to be continuous with the cutting face  30   b.  In addition, it is preferable for each of the rib portions  12  to have a width that is less than or equal to a width W of the back face of the corresponding knife  30 , and in this embodiment, as shown in  FIG. 4 , the maximum width dimension of the rib portion  12  matches the dimension of the back face width W of the knife  30 . Here, the “back face” of the knife  30  refers to the surface that corresponds to a portion that is continuous with the cutting face  30   b  of the knife  30  at the following end of the rotational direction, as shown in  FIG. 4 ; and the width W of the back face, meanwhile, refers to the dimension of the back face in the longitudinal direction of the knife  30 . 
         [0033]    In addition, in this embodiment, the knives  30  are anchored to the rib portions  12  in a state extending along the direction in which the corresponding rib portions  12  extend from the knife holder body  11 . This makes it possible for each of the rib portions  12  to efficiently support the corresponding knife  30  with a small surface area. 
         [0034]    In this manner, the knife holder  10  for the underwater cutting pelletizing device according to the present embodiment includes the knife holder body  11  and the plurality of rib portions  12  to which the knives  30  are respectively anchored; in which the knife holder body  11  has the outer circumference end  11   a  located further inward of the inner circumference end  52   b  of the projected portion  52  of the die plate  40 , and each of the rib portions  12  is provided in a respective plurality of positions arranged at equal intervals in the circumferential direction of the outer circumference end  11   a  of the knife holder body  11  and protrude outward in the radial direction from the outer circumference end  11   a  so as to extend further outward of the inner circumference end  52   b  of the projected portion  52 . In other words, the back faces of the knives  30  are anchored to the rib portions  12  in tight contact with the front face of the rib portions  12 . Accordingly, the knife holder  10  can reduce the gap between the sliding surfaces  30   a  of the knives  30  and the projected portion  52  of the die plate  40  compared to the conventional knife holder by reducing warping of the knives  30 , though the knives  30  are supported on one end; and accordingly, it is possible to manufacture resin pellets having a favorable shape without tail pellets, fines, and so on. 
         [0035]    In addition, the rib portions  12  according to this embodiment have the sloped surfaces  12   b  having the same angle of slope as an angle of slope of the cutting faces  30   b  of the knives  30  so as to be continuous with the cutting faces  30   b,  and the maximum width dimension of the rib portions  12  is less than or equal to the dimension of the back face width W of the knives  30 ; and accordingly, the resin pellets cut by the knives  30  are not interfered with by the rib portions  12  and do not accumulate, so that the cut resin pellets are smoothly transported from the water chamber of the underwater cutting pelletizing device to the next stage by PCW (pellet cooling water). 
         [0036]    In the aforementioned embodiment, the rib portions  12  protrude outward in the radial direction from the outer circumference end  11   a  of the knife holder body  11  and have a length that extends to the vicinity of a central area between the inner circumference end  52   b  and the outer circumference end  52   a  of the projected portion  52 ; however, the rib portions  12  may have a length that extends to a position of the outer circumference end  52   a  of the projected portion  52 , or to a position further outward in the radial direction therefrom. The rib portions  12  that have such a length can support the knives  30  across a wider region, which makes it possible to further reduce warping of the knives  30 . 
         [0037]    In the aforementioned embodiment, the knife holder body  11  and the rib portions  12  are separate members that are tightened onto each other using bolts, but may be formed as an integral component using a shaving process or welding. 
         [0038]    As described thus far, the present invention provides a holder that holds a knife used in an underwater cutting pelletizing device and is capable of reducing a gap between a sliding surface of the knife and a projected portion of a die plate in the pelletizing device by reducing warping of the knife, so as to enable the manufacture of resin pellets having a favorable shape. 
         [0039]    Specifically, the present invention provides a knife holder for an underwater cutting pelletizing device, the underwater cutting pelletizing device including a rotating shaft; a die plate that is anchored to the rotating shaft and has a ring-shaped projected portion that projects further in a direction parallel to the rotating shaft than the other portions, in which a plurality of die holes are formed in the projected portion and a melt resin is extruded from each of the die holes; and the knife holder that holds a plurality of knives that slide along a surface of the projected portion and cut the melt resin extruded from each of the die holes within a cooling water in order to create resin pellets. This knife holder includes: a knife holder body having an outer circumference end positioned further inward in the radial direction of an inner circumference end of the projected portion of the die plate; and a plurality of rib portions, each of which is provided in a respective plurality of positions arranged in the circumferential direction (preferably, at equal intervals) of the outer circumference end of the knife holder body, that protrude outward in the radial direction from the outer circumference end and extend further outward of the inner circumference end of the projected portion, and to which the knives are anchored in a state in which back faces of the knives face front faces of the rib portions that face the die plate. 
         [0040]    This knife holder can reduce a gap between the sliding surfaces of the knives and the surface of the projected portion of the die plate compared to the conventional knife holder by reducing warping of the knives, though each of the knives is supported on one end; and accordingly, it is possible to manufacture resin pellets having a favorable shape without tail pellets, fines, and so on. 
         [0041]    It is further preferable for each of the rib portions to have a sloped surface having the same angle of slope as an angle of slope of a cutting face of the corresponding knife thereof so as to be continuous with the cutting face, and for the rib portions to have a width dimension that is less than or equal to the width of the back faces of the knives. The rib portions having such a shape do not interfere with the resin pellets cut by the knives and do not cause the resin pellets to accumulate, so as to permit the cut resin pellets to be smoothly transported from the water chamber of the underwater cutting pelletizing device to the next stage by PCW (pellet cooling water). 
         [0042]    It is further preferable for the rib portions to protrude outward in the radial direction from the outer circumference end of the knife holder body and to have a length that extends to a position of the outer circumference end of the projected portion or to a position that is further outward in the radial direction therefrom. The rib portions that have such a length can support the knives across a longer region, which makes it possible to further reduce warping of the knives. 
         [0043]    It is further preferable for the knife corresponding to each of the rib portions to be anchored to the rib portion in a state extending along the direction in which the rib portion extends from the knife holder body. This makes it possible for each of the rib portions to efficiently support the corresponding knife with a small surface area.