JP5482081B2 - Injection molding method and injection molding apparatus - Google Patents

Description

  The present invention relates to an injection molding method and an injection molding apparatus for injecting synthetic resin into a permanent magnet housing hole formed in a rotor core for a motor, for example.

  A plurality of accommodation holes are formed in the rotor core along the circumferential direction, and permanent magnets are accommodated in the accommodation holes. And in order to fix the said permanent magnet and seal the clearance gap between the internal peripheral surface of an accommodation hole, and the outer peripheral surface of a permanent magnet, it is synthetic resin as a sealing material between an accommodation hole and a permanent magnet. Is filled by injection.

  A technique for sealing with such a synthetic resin is disclosed in Patent Document 1, for example. In the prior art of Patent Document 1, the rotor core is held between the upper mold and the lower mold, and a thermosetting synthetic resin is inserted into a plurality of pots formed in the upper mold. Then, while the synthetic resin is heated and melted in the pot, the plunger is press-fitted between the inner peripheral surface of the accommodation hole and the outer peripheral surface of the permanent magnet through the upper mold gate. By curing the synthetic resin, the permanent magnet is fixed in a sealed state in the accommodation hole of the rotor core.

  However, in this conventional apparatus, a thermosetting synthetic resin is used as a sealing material. For this reason, the synthetic resin is easily cured in the pot, and once cured, it cannot be injected and discarded. For this reason, there was a problem that the yield of the synthetic resin material was bad and the material cost was high.

  In order to cope with such a problem, it is also conceivable to use a thermoplastic synthetic resin as a sealing material. In this method, since the synthetic resin material can be held in a molten state in the mold, unlike the case where a thermosetting synthetic resin is used, the above-described problems due to thermosetting do not occur. However, in this method, even if a draft angle is formed in the sprue or runner of the mold, the synthetic resin portion solidified in the sprue and runner portions remains on the mold side when the mold is opened after injection molding and is removed. It ’s difficult. For this reason, every time injection molding is completed, there is often a need to remove the sprue and runner synthetic resin portions from the tip of the nozzle, resulting in a problem of reduced productivity.

  Further, when a thermoplastic synthetic resin is used, it is unavoidable that slag hardened at the tip of the nozzle is injected at the initial stage of injection of the synthetic resin material. For this reason, as in Patent Document 2, a slag reservoir called a cold slag well for accommodating the slag is generally provided in a part of the sprue.

JP 2007-68356 A JP 2003-39495 A

However, in the case of the conventional technique such as Patent Document 2, since a small chamber-like slag reservoir is provided in a part of the sprue, the hardened synthetic resin part in the sprue cannot be pulled out from the product part side. . For this reason, it is necessary to comprise a shaping | molding die so that the part of a sprue may be divided into 2 along the extension direction, and the structure of a shaping | molding die becomes complicated. In addition, since it is necessary to provide a slag reservoir part in the middle of the sprue in the mold, the sprue becomes long, and thus the amount of the synthetic resin to be discarded increases, and it is difficult to improve the yield as described above.

  The present invention has been made paying attention to such problems existing in the prior art. An object of the present invention is to provide an injection molding method and an injection molding apparatus that can improve the yield of the synthetic resin material, further simplify the structure of the mold, and improve the productivity.

  In order to achieve the above object, the invention of the injection molding method is formed on the outer shell from the runner formed between the mold and the outer shell by joining the die to the end face of the outer shell. In the injection molding method of injecting synthetic resin into the space, the slag of synthetic resin at the initial injection is stored in the slag reservoir formed in the mold so as to open to the end face side of the outer shell body, and when the mold is opened The synthetic resin portion formed in the runner and the slag reservoir is held on the end surface of the outer shell.

In the injection molding method, wherein space is provided in plural, to fill the synthetic resin into the space through a plurality of runners from the mold one sprue, storing the slag slag reservoir section provided in each runner It is desirable.

Further, in the injection molding method, the outer shell is a cylindrical iron core, the space is a housing hole for housing a permanent magnet, and the synthetic resin is used as an inner peripheral surface of the housing hole and the permanent magnet. It is preferable to fill the space between the outer peripheral surface and the outer peripheral surface.

  In order to achieve the above object, in the invention of the injection molding apparatus, the first mold holding the outer shell body and the end face of the outer shell body can be contacted and separated by being opened and closed with respect to the first mold. The second mold is provided with a runner that opens on the end face side of the outer shell body, and the second mold sprues the space formed in the outer shell body when the mold is closed. In the injection molding apparatus configured to inject the synthetic resin through the runner, the second mold has a slag reservoir opening on the end surface side of the outer shell body branched from the runner, and the runner and the mold are opened when the mold is opened. A holding means for holding the synthetic resin portion formed in the slag reservoir portion on the end face of the outer shell is provided.

In the above configuration, the outer shell body is a cylindrical iron core, and the second mold includes a plurality of runners and slag reservoirs in annular regions corresponding to the end surfaces of the outer shell body, respectively. Is preferably provided .
In the above configuration, a plurality of runners may be extended from one sprue.

The said structure WHEREIN: While forming a bending part in the intermediate part of the said runner, it is good to branch the said slag reservoir part from the bending part.
The said structure WHEREIN: It is good to arrange | position the said slag reservoir part on the straight line rather than a runner with respect to a sprue.

In the above-described configuration, it is preferable that the holding unit includes a holding member that can protrude and retract from the opening / closing surface of the second mold and a biasing member that biases the holding member in the protruding direction.
In the above configuration, the holding means may be provided at a position corresponding to the slag reservoir so as to hold the slag in the slag reservoir.

Further, in the above configuration, it is desirable that the holding means is provided at a position between adjacent slag reservoirs.
Therefore, in this invention, when the synthetic resin is injected into the outer shell space from the nozzle through the runner in the mold closed state, the synthetic resin slag at the initial injection is guided to the slag reservoir through the runner. It is stored. Subsequently, the synthetic resin from which the slag has been removed is injected into the space. Accordingly, it is possible to prevent the slag of the synthetic resin at the initial injection from being introduced into the space, and to improve the quality of the molded product. And in this invention, the synthetic resin part formed in the runner and the slag reservoir part is hold | maintained at the end surface of an outer shell body at the time of the mold opening after injection molding. Therefore, since slag can be stored and removed in the slag reservoir, a thermoplastic resin can be used as a synthetic resin without any problem. In addition, since the runner and the slag reservoir are arranged at a position facing the outer shell, the sprue can be brought close to the outer shell to shorten the runner. Therefore, the synthetic resin in the runner and the slag reservoir can be reduced. Therefore, the yield of the synthetic resin material can be improved. Moreover, it is possible to prevent the synthetic resin portion of the runner and the slag reservoir portion from remaining on the mold side, and it is possible to omit a complicated operation of removing the synthetic resin portion from the tip of the nozzle. Moreover, since the synthetic resin part of a runner and a slag reservoir part is hold | maintained at the outer shell body side, in order to take out a synthetic resin part, the complicated structure which divides | segments a type | mold into 2 is unnecessary.

  As described above, according to the present invention, the yield of the synthetic resin material can be improved, the structure of the mold can be simplified, and the productivity can be improved.

Sectional drawing which shows one Embodiment of the injection molding apparatus which actualized this invention. The top view of the iron core used for injection molding of the injection molding apparatus of FIG. The partial enlarged plan view which shows the state after the injection molding with respect to the iron core of FIG. The fragmentary sectional view which shows the state at the time of shaping | molding of the injection molding apparatus shown as a cross section in the 4-4 line | wire of FIG. The perspective view which expands and shows the holding member of the injection molding apparatus of FIG. The fragmentary sectional view which shows the operation state of the process in which the type | mold of an injection molding apparatus is open | released from the state shown in FIG. FIG. 7 is a partial cross-sectional view showing a state in which the mold opening operation has progressed from the state of FIG. 6. The perspective view of the iron core which shows the state which injection molding was completed.

  Hereinafter, an embodiment of an injection molding method and an injection molding apparatus embodying the present invention will be described with reference to the drawings. In this embodiment, the invention is embodied in an injection molding method and an injection molding apparatus in which a thermoplastic synthetic resin (for example, Poniphenylene Sulfide: PPS) is injected into a housing hole of a rotor core for a motor.

  As shown in FIG. 1, the injection molding apparatus of this embodiment is disposed so as to be openable and closable in the vertical direction via a plurality of guide rods 13 above a lower first mold 11 and the first mold 11. The second mold 12 is provided. The first mold 11 includes a mounting table 15 on the upper surface, and a cylindrical rotor core 14 as an outer shell is mounted on the mounting table 15. On the mounting table 15, an outer periphery support portion 15 a that supports the outer periphery of the rotor core 14 and an inner periphery support portion 15 b that supports the inner periphery are provided.

  The rotor core 14 is configured by laminating a large number of core pieces 14c shown in FIG. The rotor core 14 is alternately formed with a plurality of housing holes 14 a and 14 b having different directions as spaces on the same circumference, and these housing holes 14 a and 14 b extend in the axial direction of the rotor core 14. . And the rod-shaped permanent magnet 16 which makes a cross-sectional square shape is inserted in each accommodation hole 14a, 14b.

  As shown in FIG. 1, the nozzles 17 are respectively mounted on the plurality of mounting holes 17 b formed in the second mold 12 at predetermined intervals on the same circumference (see FIGS. 2 and 3). Yes. Each nozzle 17 is disposed so as to correspond to the upper surface of the rotor core 14 at a central position between each pair of adjacent housing holes 14a and 14b in a state where the rotor core 14 is held on the first mold 11. ing. A base 18 is disposed at the center of the upper surface of the second mold 12, and an injection device (not shown) is connected to the upper end of the base 18, and the lower end of the base 18 is connected to the upper end of each nozzle 17 via the manifold 19. It is connected to.

  When the first mold 11 and the second mold 12 are closed, the thermoplastic synthetic resin R in a heated and melted state is distributed from the injection device to the nozzles 17 via the caps 18 through the manifolds 19. As shown in FIG. 4, a heater 17 a is incorporated in each nozzle 17, and a heater (not shown) is also incorporated in the manifold 19. The synthetic resin R to be distributed is held in a heat-melted state by these heaters 17a.

  As shown in FIG. 4, a plurality of tapered sprues that communicate with the lower ends of the nozzles 17 and that open downwardly open at the bottom of the second mold 12 toward the opening / closing surface 12 a. 20 is formed. A cylindrical portion 20 a is formed at the upper end of the sprue 20. As shown in FIGS. 3 and 4, the opening / closing surface 12 a of the second mold 12 is located between each pair of adjacent accommodation holes 14 a, 14 b on the rotor core 14 and the lower end of each sprue 20. A plurality of runners 21 are formed in a state opened to the opening / closing surface 12a side. Accordingly, a pair of runners 21 are extended in the opposite directions from the lower end of the sprue 20. A bent portion 21 a is formed at an intermediate portion in the extending direction of each runner 21.

  In the closed state of the first mold 11 and the second mold 12, the lower surface of the second mold 12 is joined to the upper end surface of the rotor core 14, and the lower surface openings of the sprues 20 and runners 21 are the rotor core. 14 is closed by the top surface. Therefore, the rotor core 14 constitutes a part of each sprue 20 and runner 21. In this state, the synthetic resin R distributed to each nozzle 17 is injected into each accommodation hole 14 a of the rotor core 14 through each sprue 20 and runner 21. By this injection, the synthetic resin R is filled as a sealing material between the inner peripheral surface of each accommodation hole 14a and the outer peripheral surface of the permanent magnet 16 and the position of the upper end surface of the permanent magnet 16, and the permanent magnet 16 is accommodated in the accommodation hole. 14a is fixed in a sealed state.

  As shown in FIGS. 3 and 4, a plurality of slag reservoirs 22 are opened on the opening / closing surface 12 a side of the opening / closing surface 12 a of the second mold 12 so as to branch from the bent portions 21 a of the runners 21. Is formed. Therefore, the slag reservoir 22 is also closed by the upper surface of the rotor core 14 in the second mold 12 closed state, and the rotor core 14 constitutes a part of the slag reservoir 22. The slag reservoir 22 is branched from the bent portion 21 a without being bent, and is formed to extend substantially linearly along the circumferential direction of the rotor core 14. The slag reservoir 22, the runner 21, and the sprue 20 are disposed so as to correspond to an annular region on the inner peripheral side of the accommodation hole 14 a of the rotor core 14.

  As shown in FIGS. 3 and 6, the second mold 12 is provided with a plurality of holding mechanisms 23 as a plurality of holding means so as to be positioned between each pair of adjacent slag reservoirs 22. When the first mold 11 and the second mold 12 are opened, the synthetic resin portion Ra formed in the sprue 20, the runner 21, and the slag reservoir portion 22 is formed by the holding mechanism 23 on the end surface of the rotor core 14. And is held by the end surface. That is, as shown in FIGS. 4 and 5, in each holding mechanism 23, an accommodation recess 24 is formed in the opening / closing surface 12 a of the second mold 12. A holding member 25 is housed in the housing recess 24 so as to be able to protrude and retract from the opening / closing surface 12 a of the second mold 12. Protrusions 25 a are formed on both upper sides of the holding member 25, and the protrusions 25 a engage with the upper ends or lower ends of the restricting portions 24 a provided on the inner surfaces on both sides of the housing recess 24, thereby Alternatively, the protruding position is restricted. A spring 26 as an urging member for urging the holding member 25 in the protruding direction is interposed between the inner top portion of the housing recess 24 and the holding member 25.

  On both sides of the lower portion of the holding member 25, a pair of groove portions 25b corresponding to the slag reservoir portion 22 and forming a part thereof are formed. As shown in FIG. 4, when the first mold 11 and the second mold 12 are closed, the holding member 25 is accommodated against the urging force of the spring 26 by contact with the upper end surface of the rotor core 14. It is immersed in the recess 24. In this immersed state, each of the groove portions 25b is disposed at a position where a part of the tip of the pair of adjacent slag reservoir portions 22 is formed.

  When the slag of the synthetic resin R is introduced into the slag reservoir 22 at the initial stage of injection, the slag is dammed up by the groove portion 25 b and stored in the slag reservoir 22. As shown in FIG. 6, when the first mold 11 and the second mold 12 are opened, the holding member 25 is held at the upper surface position of the rotor core 14 by the biasing force of the spring 26 when the first mold 11 and the second mold 12 are opened. Is done. As a result, the holding member 25 protrudes from the opening / closing surface 12 a of the second mold 12. For this reason, the tip of the synthetic resin portion Ra formed in the pair of adjacent slag reservoirs 22 is pressed downward by the both side groove portions 25 b of the holding member 25. As a result, the synthetic resin portion Ra formed in the sprue 20 is separated from the lower end of the nozzle 17, and the synthetic resin portion Ra in the sprue 20, the runner 21 and the slag reservoir portion 22 is pressed against the upper end surface of the rotor core 14. And is held on the upper end surface.

Next, an injection molding method for injecting synthetic resin into the accommodation hole 14a of the rotor core 14 in the injection molding apparatus configured as described above will be described.
Now, at the time of this injection molding, outside the first mold 11, the rotor core 14 is placed on the mounting table 15 removed from the first mold 11, and in this state, each housing hole of the rotor core 14 is accommodated. A permanent magnet 16 is inserted into 14a. Then, the mounting table 15 is set together with the rotor core 14 on the first mold 11 in the mold open state, and the rotor core 14 is held on the first mold 11. Thereafter, when the first mold 11 and the second mold 12 are closed, the opening / closing surface 12a of the second mold 12 is joined to the upper end surface of the rotor core 14, as shown in FIG. At this time, as shown in FIG. 4, the holding member 25 of each holding mechanism 23 is immersed in the housing recess 24 against the urging force of the spring 26 due to contact with the upper end surface of the rotor core 14.

  In this state, the thermoplastic synthetic resin R in a heated and melted state is injected from the nozzles 17 through the sprues 20 and the runners 21 into the receiving holes 14 a of the rotor core 14. At the initial stage of injection, the slag of the synthetic resin R is guided to the slag reservoir 22 that branches linearly from the bent portion 21 a of the runner 21 and is stored in the slag reservoir 22. When the synthetic resin containing slag is filled in the slag reservoir 22, the synthetic resin R not containing slag passes through the runner 21 between the inner peripheral surface of each accommodation hole 14 a and the outer peripheral surface of the permanent magnet 16. The permanent magnet 16 is fixed in the accommodation hole 14a using the synthetic resin R as a sealing material.

  Then, when the first mold 11 and the second mold 12 are opened after the synthetic resin R injected into the accommodation hole 14a is solidified, as shown in FIG. The holding member 25 of each holding mechanism 23 is protruded from the opening / closing surface 12a of the second mold 12 by the biasing force of the spring 26, and maintains the position where it is joined to the upper end surface of the rotor core 14. Therefore, the synthetic resin portion Ra formed in the pair of adjacent slag reservoirs 22 is simultaneously pressed against the upper surface of the rotor core 14 by the holding member 25, and the tip of the synthetic resin portion Ra in the sprue 20 is connected to the nozzle 17. It is separated from the lower end of. Therefore, as shown in FIG. 7, when the mold opening of the first mold 11 and the second mold 12 proceeds, the synthetic resin portion Ra integrated in the sprue 20, the runner 21, and the slag reservoir portion 22 becomes the rotor core 14. It is held on the end face of.

  Therefore, when the rotor core 14 is removed from the first mold 11 together with the mounting table 15 after the first mold 11 and the second mold 12 are opened, as shown in FIG. A plurality of synthetic resin portions Ra formed in the sprue 20, the runner 21, and the slag reservoir portion 22 are projected. These synthetic resin portions Ra are removed from the upper end surface of the rotor core 14 in a subsequent process.

Therefore, according to this embodiment, the following effects can be obtained.
(1) In this embodiment, when the synthetic resin R is injected from the nozzle 17 into the accommodation hole 14a of the rotor core 14 through the runner 21 in the mold closed state, the slag of the synthetic resin R at the initial injection is The slag reservoir 22 branched from the runner 21 is guided and stored. For this reason, synthetic resin excluding slag is injected into the accommodation hole 14a. Therefore, it is possible to prevent the slag, which is a deteriorated synthetic resin R at the initial injection, from being introduced into the housing hole 14a of the rotor core 14, and to avoid the possibility of causing a deterioration in the quality of the molded product. It is possible to improve the quality of the sealing material. As described above, since the slag can be appropriately treated, a thermoplastic resin can be used as the synthetic resin R, and unlike the case where a thermosetting resin is used, the yield of the material can be improved.

  (2) In this embodiment, the runner 21 and the slag reservoir 22 are formed on the surface to be joined to the rotor core 14 of the first mold 11. Therefore, the sprue 20 can be disposed close to the rotor core 14, and as a result, the sprue 20 is shortened and the synthetic resin portion Ra in the sprue 20 is also small, and the material yield can be improved as described above. .

  (3) In this embodiment, when the mold is opened after injection molding, the synthetic resin portion Ra formed in the runner 21 and the slag reservoir 22 is formed by the action of the holding mechanism 23 accompanying the mold opening operation. 14 is held on the end face. For this reason, it is possible to prevent the synthetic resin portion Ra of the runner 21 and the slag reservoir portion 22 from remaining at the tip portion of the nozzle 17. Therefore, it is not necessary to perform a complicated operation of separating the synthetic resin portion Ra such as the runner 21 from the tip portion of the nozzle 17 every time injection molding is completed, and productivity can be improved. Further, when the synthetic resin portion Ra is peeled off from the rotor core 14 together with the mold opening, the upper surface of the sealing portion is scratched at the joint portion between the synthetic resin portion Ra and the permanent magnet 16 sealing portion, or the sealing portion There is a possibility that small protrusions may remain on the upper surface of the substrate. In such a case, the rotor core 14 is likely to be a defective product. However, in this embodiment, since the synthetic resin portion Ra is held on the upper surface of the rotor core 14 and the synthetic resin portion Ra can be removed by, for example, grinding in a subsequent process, there is almost no possibility of becoming a defective product. Further, since the synthetic resin portion Ra is held by the holding member 25, the synthetic resin portion Ra is appropriately separated between the upper end of the sprue 20 and the tip of the nozzle 17. That is, a cylindrical portion 20a is formed at the upper end of the sprue 20 to absorb the error in the vertical position of the nozzle 17, but this cylindrical portion 20a is worn and deformed into an undercut shape due to multiple injections. There are things to do. In such a case, the synthetic resin portion in the sprue 20 is unlikely to be detached from the tip portion of the nozzle 17, but in this embodiment, the synthetic resin portion Ra is pressed against the upper end surface of the rotor core 14 by the holding member 25. Therefore, such a fear can be avoided in advance.

  (4) In this embodiment, a bent portion 21a is formed at an intermediate position in the extending direction of the runner 21, and a slag reservoir portion 22 is formed so as to branch linearly from the bent portion 21a. In other words, the slag reservoir 22 is positioned almost on a straight line starting from the sprue 20, and the runner 21 bends to reach the accommodation hole 14a. For this reason, when the slag of the synthetic resin R at the initial stage of injection is supplied from the nozzle 17 into the runner 21, the synthetic resin containing the slag is first stored in the slag reservoir portion 22, and then the undegraded synthetic resin is accommodated. The holes 14a are filled. Therefore, it can avoid that slag is guide | induced in the accommodation hole 14a, a high quality sealing part can be formed, and a high quality rotor core 14 can be obtained by extension.

  (5) In this embodiment, the holding member 25 of the holding mechanism 23 is protruded from the opening / closing surface 12a of the second mold 12 by the spring 26 when the holding member 25 opens the mold. For this reason, an actuator for operating the holding member 25 is unnecessary, and the configuration is simple.

  (6) In this embodiment, the nozzle 17 is provided in the 2nd type | mold 12 so that it may be located between a pair of adjacent accommodation holes 14a. A runner 21 is provided between the nozzle 17 and the accommodation hole 14a. Accordingly, the number of nozzles 17 can be made smaller than the number of the accommodation holes 14a, and the configuration can be simplified.

  (7) In this embodiment, the slag reservoir 22 is branched from the runner 21, and the adjacent slag reservoirs 22 are formed so as to extend in directions approaching each other. A holding mechanism 23 is disposed on the second mold 12 so as to be positioned between a pair of adjacent slag reservoirs 22. Therefore, a plurality of holding mechanisms 23 can be arranged in the second mold 12 without interfering with the nozzles 17 and a pair of adjacent slag reservoirs 22 can be pressed and held simultaneously by one holding mechanism 23. Thus, the structure can be simplified.

(Example of change)
In addition, the said embodiment can also be changed and actualized as follows.
-The holding member 25 of the holding mechanism 23 for holding the slag is configured to hold a portion other than the tip of the slag.

  -Instead of the structure which hold | maintains slag as the holding member 25 of the holding mechanism 23, it is comprised so that the synthetic resin part Ra of the part of the runner 21 may be hold | maintained. When configured in this manner, the synthetic resin portion Ra of the slag reservoir portion 22 is integral with the synthetic resin portion Ra of the runner 21 portion, so that the entire synthetic resin portion Ra is placed on the rotor core 14 as described above. Can be held on the end face.

-Use an outer shell other than the rotor core 14, such as a motor stator core.
The three or more runners 21 are extended from the sprue 20 so that the synthetic resin is simultaneously injected into the three or more accommodation holes 14a.

  DESCRIPTION OF SYMBOLS 11 ... 1st type | mold, 12 ... 2nd type | mold, 12a ... Opening-and-closing surface, 14 ... Rotor core, 14a ... Accommodating hole, 14b ... Accommodating hole, 16 ... Permanent magnet, 17 ... Nozzle, 20 ... Sprue, 21 ... Runner, 21a ... bent portion, 22 ... slag reservoir, 23 ... holding mechanism as holding means, 25 ... holding member, 26 ... spring as urging member, R ... synthetic resin, Ra ... synthetic resin portion.

Claims (11)

In an injection molding method in which a mold is joined to an end face of an outer shell body, and a synthetic resin is injected into a space formed in the outer shell body from a runner formed between the mold and the outer shell body.
Synthetic resin formed in the runner and slag reservoir at the time of mold opening is stored in the slag reservoir formed in the mold so as to open to the end face side of the outer shell body. An injection molding method characterized in that a portion is held on the end face of the outer shell. Claims wherein the space is provided with a plurality, to fill the synthetic resin into the space through a plurality of runners from the mold one sprue, characterized by storing the slag slag reservoir section provided in each runner Item 2. The injection molding method according to Item 1. The outer shell is a cylindrical iron core, and the space is a housing hole for housing a permanent magnet, and the synthetic resin is filled between the inner circumferential surface of the housing hole and the outer circumferential surface of the permanent magnet. The injection molding method according to claim 1 or 2, wherein: A first mold for holding the outer shell, and a second mold corresponding to an end face of the outer shell by being opened and closed with respect to the first mold, the outer shell being provided in the second mold In an injection molding apparatus provided with a runner that opens to the end face side of the body, and injects synthetic resin from the second mold sprue through the runner into the space formed in the outer shell when the mold is closed ,
In the second mold, a slag reservoir opening to the end surface side of the outer shell body is branched from the runner, and a synthetic resin portion formed in the runner and the slag reservoir portion when the mold is opened includes an end surface of the outer shell body. An injection molding apparatus characterized in that a holding means for holding is provided. The outer shell is a cylindrical iron core,
5. The injection molding according to claim 4, wherein the second mold is provided with a plurality of the runners and slag reservoirs in annular regions corresponding to the end face of the outer shell so as to be able to contact and separate. apparatus. The injection molding apparatus according to claim 4 or 5, wherein a plurality of runners are extended from one sprue. The injection molding apparatus according to any one of claims 4 to 6, wherein a bent portion is formed at an intermediate portion of the runner and the slag reservoir portion is branched from the bent portion. The injection molding apparatus according to claim 7, wherein the slag reservoir is disposed on a line that is more straight than the runner with respect to the sprue. The said holding | maintenance means consists of the holding member which can be projected / recessed from the opening / closing surface of a 2nd type | mold, and the urging member which urges | biases the holding member to a protrusion direction. The injection molding apparatus according to one item. The injection molding apparatus according to claim 9, wherein the holding means is provided at a position corresponding to the slag reservoir so as to hold the slag in the slag reservoir. The injection molding apparatus according to claim 10, wherein the holding means is provided at a position between adjacent slag reservoirs.

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