Patent Publication Number: US-2018043591-A1

Title: Sprue bush and bush component thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2016/086345, filed on Dec. 7, 2016, now pending, herein incorporated by reference. Further, this application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-036549, filed on Feb. 29, 2016, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a sprue bush that is attached to a mold used to mold synthetic resin, and a bush component attached thereto. 
     BACKGROUND ART 
     In an example of a synthetic resin molding process implemented when injection-molding synthetic resin, a pair of molds are closed such that a cavity is formed therebetween, and molten synthetic resin is injected into the cavity. A sprue bush is a member having a flow passage (a sprue) through which synthetic resin injected from an injection molding machine is injected into the molds, and the sprue bush is attached interchangeably to the mold on the side where the synthetic resin is injected. An injection nozzle of the injection molding machine is then brought into direct contact with a nozzle contact surface of the sprue bush, whereupon the synthetic resin is injected. During the injection molding, the high-temperature, molten resin material is injected into the cavity through the sprue of the sprue bush and a runner provided in the molds, and by advancing a mold release timing, a molding cycle time can be shortened, leading to enhancement in productivity. However, when the molds are released before the resin in a sprue inlet portion hardens, stringing occurs. When, as a result, a string is trapped in a mold, problems such as variation in the shape of the mold and deterioration of the quality of a molded article occur. 
     In response to the problem of stringing, as described above, it has been proposed that stringing may be prevented by implementing heat diffusion in the sprue bush serving as the resin flow passage. More specifically, providing a partition plate that bisects a flow passage cross-section (an opening in the nozzle contact surface) in a resin injection port of the sprue bush (Patent Document 1), forming the opening (the flow passage cross-section) in a shape other than a circular shape, such as a six-pronged fork shape (Patent Document 2), forming the entire sprue bush from a high thermal conductivity member made of copper alloy, copper, aluminum alloy, aluminum, or the like (Patent Document 3), and embedding a high thermal conductivity member in a sprue bush main body as a component thereof (Patent Document 4) have been disclosed. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: Japanese Laid-open Patent Publication No. 2001-246649 
         Patent Document 2: Japanese Laid-open Patent Publication No. 2008-247014 
         Patent Document 3: Japanese Laid-open Patent Publication No. 2007-083462 
         Patent Document 4: Japanese Laid-open Patent Publication No. 2014-046537 
       
    
     SUMMARY OF INVENTION 
     Problems to be Solved by the Invention 
     However, in the method of Patent Document 1, the sprue cross-section through which the resin flows is obstructed by the partition plate, and therefore the fluidity of the resin deteriorates. It is therefore needed to take measures such as increasing the injection pressure, increasing the temperature of the resin in order to reduce the viscosity thereof, and reducing the cross-section of the partition plate, but as a result of these measures, deterioration of and damage to the partition plate are more likely to occur. Moreover, when a resin blockage occurs in the sprue bush, an operation to remove the resin is complicated, and therefore the partition plate may be damaged while removing the resin, leading to an increase in the frequency with which the partition plate or the entire sprue bush has to be exchanged for a new one. 
     It is known that by employing the method of Patent Document 2, a greater stringing suppression effect than that obtained with a circular cross-section can be realized, but under present circumstances, when even greater yield is needed, the effect is insufficient. 
     In the method of Patent Document 3, a high thermal conductivity member typically exhibits lower strength and wear resistance than a conventional sprue bush material, and therefore the resin flow passage may deteriorate due to wear and deformation. When the resin flow passage deteriorates, molding conditions vary, and components have to be replaced more frequently. 
     Furthermore, in the method of Patent Document 4, preparing and combining a plurality of metal members having different thermal conductivity values may lead to an increase in manufacturing cost. 
     Hence, in consideration of the problems described above, an object of the present invention is to provide a novel sprue bush with which stringing can be prevented without the use of a partition plate or a high thermal conductivity member, and a bush component forming the sprue bush. 
     Means for Solving the Problems 
     A sprue bush attached to a mold used to mold synthetic resin, the sprue bush comprising a sprue bush main body that has a flow passage, through which synthetic resin injected from an injection molding nozzle flows, and a recessed portion formed in a surface of the sprue bush main body on a synthetic resin injection port side thereof, and a bush component that is embedded in the recessed portion, the bush component including a nozzle contact surface that is contacted by the injection molding nozzle, a through hole that extends from an opening in the nozzle contact surface and communicates with the flow passage in the sprue bush main body so as to form the flow passage for the synthetic resin, and a plurality of ribs that extend radially outward from a peripheral surface of the through hole. 
     Further, a bush component forming the sprue bush according to the present invention is used in a sprue bush configured to include: a sprue bush main body that has a flow passage, through which synthetic resin injected from an injection molding nozzle flows, and a recessed portion formed in a surface of the sprue bush main body on a synthetic resin injection port side thereof; and the bush component, which is embedded in the recessed portion, this bush component including: a nozzle contact surface that is contacted by the injection molding nozzle; a through hole that extends from an opening in the nozzle contact surface and communicates with the flow passage in the sprue bush main body so as to form the flow passage for the synthetic resin; and a plurality of ribs that extend radially outward from an inner peripheral surface of the through hole. 
     Advantageous Effects of the Invention 
     According to the present invention, the nozzle contact surface of the bush component is supported by the ribs, and spaces are provided between the ribs. Therefore, the plurality of radial ribs act as heat radiation fins such that the heat of the resin in the vicinity of the opening in the nozzle contact surface is radiated effectively to the spaces between the ribs. Moreover, the nozzle contact surface is reduced in thickness, thereby enhancing the effect of radiating heat from the nozzle contact surface. Hence, the vicinity of the opening is cooled with greater efficiency such that the temperature of the resin in the vicinity of the opening decreases earlier, and as a result, the occurrence of stringing is suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A-1E  are views illustrating configurations of a sprue bush according to a first embodiment of the present invention. 
         FIGS. 2A-2F  are views illustrating configurations of the bush component  20  according to the first embodiment. 
         FIGS. 3A-3F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment. 
         FIGS. 4A-4F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment. 
         FIGS. 5A-5F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment. 
         FIGS. 6A-6F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment. 
         FIGS. 7A-7F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment. 
         FIGS. 8A-8E  are views illustrating configurations of a sprue bush according to a second embodiment of the present invention. 
         FIGS. 9A-9F  are views illustrating configurations of the bush component  20  according to the second embodiment. 
         FIGS. 10A-10F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment. 
         FIGS. 11A-11F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment. 
         FIGS. 12A-12F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment. 
         FIGS. 13A-13F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment. 
         FIGS. 14A-14F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment. 
         FIGS. 15A-15D  are views illustrating further modified examples of the configuration of the bush component  20  according to an embodiment of the present invention. 
         FIG. 16  is a sectional view illustrating a condition in which an injection molding nozzle  30  contacts the nozzle contact surface of the bush component  20  illustrated in  FIGS. 15A-15D . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the figures. However, the technical scope of the present invention is not limited to these embodiments. 
       FIGS. 1A-1E  are views illustrating configurations of a sprue bush according to a first embodiment of the present invention, wherein  FIG. 1A  is an external perspective view,  FIG. 1B  is a sectional view,  FIG. 1C  is a sectional perspective view,  FIG. 1D  is a side view, and  FIG. 1E  is a top view. The sprue bush according to the first embodiment is configured to include a sprue bush main body  10 , and a bush component  20  that is attached to the sprue bush main body  10 . 
     The sprue bush main body  10  is formed from a steel material having a sufficient hardness to satisfy performance necessities such as wear resistance and durability, and is formed by coaxially integrating a disc-shaped head  10   a  and a columnar shaft  10   b  having a smaller diameter than the head  10   a . A sprue (a flow passage)  11  through which molten resin injected from an injection nozzle (not illustrated) flows is formed in an axial center that extends from the head  10   a  to the shaft  10   b . Further, a pair of screw holes  12  are provided in the head  10   a , and the sprue bush main body  10  is attached fixedly to a mold by fixing screws through the screw holes  12 . Furthermore, a recessed portion  13  having a columnar shape, for example, is formed in a central portion of the head  10   a  of the sprue bush main body  10 , and the bush component  20  is embedded in the recessed portion  13 . 
       FIGS. 2A-2F  are views illustrating configurations of the bush component  20  according to the first embodiment, wherein  FIG. 2A  is an external perspective view,  FIG. 2B  is a side view,  FIG. 2C  is a top view,  FIG. 2D  is a bottom view,  FIG. 2E  is an A-A sectional view of  FIG. 2D , and  FIG. 2F  is a B-B sectional view of  FIG. 2D . 
     The bush component  20 , similarly to the sprue bush main body  10 , is formed from a steel material having a predetermined hardness, and the type of steel material may be identical or different to that of the sprue bush main body  10 . The bush component  20  is shaped to fit into the recessed portion  13 , and is configured to include a nozzle contact surface  21  that is contacted by the injection molding nozzle, a through hole  22  that extends from an opening  21   a  in a bottom center of the nozzle contact surface  21  and communicates with the sprue  11  of the sprue bush main body  10  so as to form a synthetic resin flow passage (a sprue), and a plurality of ribs  23  that extend radially outward from a pipe-shaped portion  22   a  forming the through hole  22 . In the example of  FIG. 2 , the opening  21   a  is circular and the through hole  22  has a circular cross-section. The bush component  20  can be manufactured using an existing processing technique such as cutting or electrical discharge machining. 
     The ribs  23  are rectangular thin plate portions, and are provided to extend from the pipe-shaped portion  22   a  at equal intervals in a circumferential direction. In the example of  FIG. 2 , six ribs  23  are formed. An axial direction length of the ribs  23  is determined such that an upper end side of each rib  23  is joined to a rear surface of the nozzle contact surface  21  and a lower end side of each rib  23  contacts a bottom of the recessed portion  13  of the head  10   a  (when the bush component  20  is embedded in the recessed portion  13 ). Further, a radial direction length of the ribs  23  is determined such that each rib  23  contacts a peripheral surface of the recessed portion  13  of the head  10   a  (when the bush component  20  is embedded in the recessed portion  13 ). 
     The nozzle contact surface  21  of the bush component  20  is a depressed curved surface that curves in a circular shape, and is formed at a substantially identical diameter to a tip end shape of the injection molding nozzle. The opening  21   a  connected to the through hole  22  is formed in the bottom center of the nozzle contact surface  21 . Further, a flange  21   b  is formed on an outer periphery of the nozzle contact surface  21 , and the ribs  23  extend to the flange  21   b.    
     The bush component  20  is press-fitted into the recessed portion  13  in the head  10   a  of the sprue bush main body  10 , whereupon the entire periphery of the flange  21   b  is laser-welded, for example, so as to be joined and fixed integrally to the head  10   a  of the sprue bush main body  10 . At this time, the flange  21   b  of the nozzle contact surface  21  is flush with a front surface of the head  10   a  (see  FIG. 1B  and so on), whereby the nozzle contact surface  21  is supported by the ribs  23  and spaces provided between the ribs  23  are formed directly below the nozzle contact surface  21 . 
     By providing a configuration in which the nozzle contact surface  21  of the bush component  20  is supported by the ribs  23  and spaces are formed between the ribs  23 , the plurality of radial ribs  23  act as heat radiation fins such that the heat of the resin in the vicinity of the opening  21   a  in the nozzle contact surface  21  is radiated effectively to the spaces between the ribs  23 . Moreover, the nozzle contact surface  21  can be reduced in thickness, thereby enhancing the effect of radiating heat from the nozzle contact surface  21 . Hence, the vicinity of the opening  21   a  is cooled with greater efficiency such that the temperature of the resin in the vicinity of the opening  21   a  decreases earlier, and as a result, the occurrence of stringing is suppressed. Furthermore, by providing the radially disposed ribs  23  as a structure for supporting the nozzle contact surface  21 , sufficient strength can be secured in the nozzle contact surface  21 , which is contacted by the injection molding nozzle, while reducing the thickness of the nozzle contact surface  21 , and therefore deterioration of the nozzle contact surface  21  can be suppressed. As a result, the durability of the sprue bush can be maintained. 
       FIGS. 3A-3F to 7A-7F  are views illustrating modified examples of the configuration of the bush component  20  according to the first embodiment, wherein each figure. A in  FIGS. 3 to 7  is an external perspective view, each figure B in  FIGS. 3 to 7  is a side view, each figure C in  FIGS. 3 to 7  is a top view, each figure D in  FIGS. 3 to 7  is a bottom view, each figure E in  FIGS. 3 to 7  is an A-A sectional view of each figure D in  FIGS. 3 to 7 , and each figure F in  FIGS. 3 to 7  is a B-B sectional view of each figure D in  FIGS. 3 to 7 . 
       FIGS. 3A-3F  illustrate examples in which the number of ribs  23  is six and the through hole  22  has a six-pronged fork-shaped cross-section.  FIGS. 4A-4F  illustrate examples in which the number of ribs  23  is eight and the through hole  22  has a circular cross-section.  FIGS. 5A-5F  illustrate examples in which the number of ribs  23  is eight and the through hole  22  has a six-pronged fork-shaped cross-section.  FIGS. 6A-6F  illustrate examples in which the number of ribs  23  is twelve and the through hole  22  has a circular cross-section.  FIGS. 7A-7F  illustrate examples in which the number of ribs  23  is twelve and the through hole  22  has a six-pronged fork-shaped cross-section. The number of ribs  23  is not limited to the above examples, and another number, such as three or four, for example, may be employed, the number of ribs  23  being determined as a design matter in consideration of the thickness of the ribs  23  and the strength needed to support the thin nozzle contact surface  21 . Further, as regards the sectional shape of the through hole  22 , by employing a shape having a greater stringing prevention effect than a circular cross-section, such as a six-pronged fork shape, the stringing prevention effect can be enhanced. The sectional shape is not limited to a circular or six-pronged fork shape, and various other shapes, such as a star shape, for example, may be employed. 
       FIGS. 8A-8E  are views illustrating configurations of a sprue bush according to a second embodiment of the present invention, and  FIGS. 9A-9F  are views illustrating configurations of the bush component  20  according to the second embodiment. More specifically,  FIG. 8A  is an external perspective view of the sprue bush,  FIG. 8B  is a sectional view,  FIG. 8C  is a sectional perspective view,  FIG. 8D  is a side view, and  FIG. 8E  is a top view. Further,  FIG. 9A  is an external perspective view of the bush component  20 ,  FIG. 9B  is a side view,  FIG. 9C  is a top view,  FIG. 9D  is a bottom view,  FIG. 9E  is an A-A sectional view of  FIG. 9D , and  FIG. 9F  is a B-B sectional view of  FIG. 9D . 
     The sprue bush according to the second embodiment is a modified example of the sprue bush according to the first embodiment, and therefore modified parts will be described mainly below, while parts that are not described specifically are assumed to be configured identically to the sprue bush according to the first embodiment. 
     In the sprue bush according to the second embodiment, a ring-shaped portion (a part of the head surrounding the peripheral surface of the recessed portion  13 )  10   a - 1  forming the peripheral surface of the recessed portion  13  in the head  10   a  of the sprue bush main body  10  is configured as a separate component that can be detached from the sprue bush main body  10 . The ring-shaped portion  10   a - 1  forms an outside part constituting an outer side of a side face of the recessed portion  13  of the head  10   a , and serves as a part of the head  10   a  that is obtained by partially dividing the head  10   a  along a perpendicular plane to the axial direction. A height of the ring-shaped portion  10   a - 1  is set to match a height (a depth) of the recessed portion  13 . 
     The ring-shaped portion  10   a - 1  includes a pair of screw holes  12 - 1  that are aligned with the screw holes  12  in the head  10   a , and using screw fastenings, the ring-shaped portion  10   a - 1  is integrated with the head  10   a  of the sprue bush main body  10 , thereby realizing the sprue bush main body  10  and forming the recessed portion  13  of the head  10   a . The bush component  20  is fitted into a central hole in the ring-shaped portion  10   a - 1 , which corresponds to the recessed portion  13  of the head  10   a . Preferably, a collar  23   a  is provided on each of the ribs  23  of the bush component  20  to ensure that the bush component  20  does not fall out of the ring-shaped portion  10   a - 1 , and a step portion on which the collar  23   a  catch is provided on a peripheral surface of the central hole of the ring-shaped portion  10   a - 1 . The bush component  20  is attached to the sprue bush main body  10  by placing the bush component  20  on the head  10   a  of the sprue bush main body  10  in a condition where the ring-shaped portion  10   a - 1  is not attached, and then screwing the ring-shaped portion  10   a - 1  to the sprue bush main body  10  so that the bush component  20  is housed in the central hole of the ring-shaped portion  10   a - 1 . As a result, the bush component  20  is embedded fixedly in the recessed portion  13  of the sprue bush main body  10 . 
       FIGS. 10A-10F to 14A-14F  are views illustrating modified examples of the configuration of the bush component  20  according to the second embodiment, wherein  FIGS. 10A, 11A, 12A, 13A and 14A  are external perspective views,  FIGS. 10B, 11B, 12B, 13B and 14B  are side views,  FIGS. 10C, 11C, 12C, 13C and 14C  are top views,  FIGS. 10D, 11D, 12D, 13D and 14D  are bottom views,  FIGS. 10E, 11E, 12E, 13E and 14E  are A-A sectional views of  FIGS. 10D, 11D, 12D, 13D and 14D  respectively, and  FIGS. 10F, 11F, 12F, 13F and 14F  are B-B sectional views of  FIGS. 10D, 11D, 12D, 13D and 14D  respectively. 
     The modified examples of the configuration of the bush component  20  according to the second embodiment, illustrated in  FIGS. 10A-10F to 14A-14F , are identical to the modified examples of the configuration of the bush component  20  according to the first embodiment, illustrated in  FIGS. 3A-3F to 7A-7F , except that the ribs  23  are provided with the collar  23   a .  FIGS. 10A-10F  illustrate examples in which the number of ribs  23  is six and the through hole  22  has a six-pronged fork-shaped cross-section.  FIGS. 11A-11F  illustrate examples in which the number of ribs  23  is eight and the through hole  22  has a circular cross-section.  FIGS. 12A-12F  illustrate examples in which the number of ribs  23  is eight and the through hole  22  has a six-pronged fork-shaped cross-section.  FIGS. 13A-13F  illustrate examples in which the number of ribs  23  is twelve and the through hole  22  has a circular cross-section.  FIGS. 14A-14F  illustrate examples in which the number of ribs  23  is twelve and the through hole  22  has a six-pronged fork-shaped cross-section. 
       FIGS. 15A-15D  are views illustrating further modified examples of the configuration of the bush component  20  according to an embodiment of the present invention.  FIG. 15A  is a sectional perspective view,  FIG. 15B  is a sectional view,  FIG. 15C  is a top view (illustrating half of a surface), and  FIG. 15D  is a partial side view. In this further modified example of the configuration of the bush component  20 , the respective bush components  20  of the first and second embodiments are configured such that the nozzle contact surface  21 , which is constituted by a depressed surface that curves in a circular shape, is formed to include a plurality of concentric circle-shaped concavo-convex surfaces. 
       FIG. 16  is a sectional view illustrating a condition in which an injection molding nozzle  30  contacts the nozzle contact surface of the bush component  20  illustrated in  FIGS. 15A-15D . The injection molding nozzle  30  contacts convex portions of the concentric circle-shaped concavo-convex surfaces formed on the nozzle contact surface  21  so as to be supported by the ring-shaped lines or strip-form surfaces forming the convex portions of the concavo-convex surfaces, while ring-shaped spaces are formed between concave portions of the concentric circle-shaped concavo-convex surfaces and the injection molding nozzle  30 . These ring-shaped spaces serve as heat radiation spaces from which heat is radiated from the nozzle contact surface  21 . Hence, heat dissipation from the nozzle contact surface  21  is promoted, leading to enhancement in the cooling effect in the vicinity of the opening  21   a , and as a result, the temperature of the resin in the vicinity of the opening  21   a  decreases earlier, thereby contributing to the prevention of stringing. 
     Further, the bush component  20  illustrated in  FIGS. 15A-15D  is provided with a ring-shaped rib  24  in addition to the radially extending ribs  23  described above. The ring-shaped rib  24  serves as the outer periphery of the pipe-shaped portion  22   a  forming the through hole  22 , and is provided to intersect the radial ribs  23 . The ring-shaped rib  24 , similarly to the radial ribs  23 , is configured such that an upper end thereof is joined to the rear surface of the nozzle contact surface  21  and a lower end thereof contacts the bottom of the recessed portion  13 . The ring-shaped rib  24 , together with the ribs  23 , provides the strength needed to support the nozzle contact surface  21 , and the position and dimensions thereof are determined together with the number (the intervals between), thickness, and so on of the ribs  23  as design matters in consideration of the strength. 
     The shape of the nozzle contact surface  21  illustrated in  FIGS. 15A-15D  is not limited to being applied to the nozzle contact surface of the bush component  20  according to the embodiments of the present invention, described above, and may also be applied to a nozzle contact surface of an integrated sprue bush in which the sprue bush main body and the bush component are not separated. More specifically, in a sprue bush that is attached to a mold used to mold synthetic resin and includes a nozzle contact surface that is contacted by an injection molding nozzle and a flow passage extending from an opening in the nozzle contact surface, through which synthetic resin injected from the injection molding nozzle flows, the nozzle contact surface is a depressed surface that curves in a circular shape and is formed with a plurality of concavo-convex surfaces. 
     The concavo-convex surfaces provided on the nozzle contact surface  21  are not limited to the concentric circle-shaped surface shape illustrated in  FIGS. 15A-15D and 16 , and the concavo-convex surfaces may take any form as long as spaces where the injection molding nozzle and the nozzle contact surface  21  do not contact each other are formed between a plurality of contacting parts on a contact surface between the injection molding nozzle and the nozzle contact surface  21 . For example, projections and recesses may be formed to extend radially in the circumferential direction, or concavo-convex surfaces may be formed by providing projections intermittently over the entire surface of the nozzle contact surface  21 . The concavo-convex surfaces formed as a plurality of concentric circle-shaped steps, illustrated in  FIGS. 15 and 16 , are useful for positioning the injection molding nozzle reliably. Moreover, the concavo-convex surfaces can be machined comparatively easily, and exhibit a superior heat radiation effect. 
     In a further embodiment of the sprue bush according to the present invention, the sprue bush constituted by the sprue bush main body and the bush component is formed integrally as a single component, rather than by combining these two components. The sprue bush having the above configuration, in which a hollow region is formed in the interior thereof, can be formed integrally using a so-called stereolithography technique. More specifically, a sprue bush that is attached to a mold used to mold synthetic resin includes a nozzle contact surface that is contacted by an injection molding nozzle, and a flow passage extending from an opening in the nozzle contact surface, through which synthetic resin injected from the injection molding nozzle flows, wherein a hollow region surrounding the flow passage is formed in an interior region on a rear surface side of the nozzle contact surface, and a plurality of ribs are provided to extend radially outward from an inner peripheral surface of the through hole. Even more specifically, a sprue bush that is attached to a mold used to mold synthetic resin is formed by coaxially integrating a disc-shaped head and a columnar shaft having a smaller diameter than the head, a flow passage through which synthetic resin injected from an injection molding nozzle flows being formed in an axial center that extends from the head to the shaft, the head including a nozzle contact surface that is contacted by an injection molding nozzle and includes an opening into the flow passage, a hollow region formed in the interior of the head on a rear surface side of the nozzle contact surface so as to surround the flow passage in a ring shape, and a plurality of ribs extending radially toward the hollow region from a peripheral surface of the flow passage. 
     The present invention is not limited to the embodiments described above, and needless to mention includes design modifications within a scope not departing from the spirit of the present invention, these design modifications including various modifications and amendments that could be arrived at by a person having common knowledge in the field of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           10  Sprue bush main body 
           10   a  Head 
           10   a - 1  Ring-shaped portion 
           10   b  Shaft 
           11  Sprue 
           12  Screw hole 
           13  Recessed portion 
           20  Bush component 
           21  Nozzle contact surface 
           21   a  Opening 
           21   b  Flange 
           22  Through hole (part of the sprue) 
           22   a  Pipe-shaped portion 
           23  Rib 
           23   a  Collar 
           24  Ring-shaped rib 
           30  Injection molding nozzle