JP4323211B2 - Molding material supply device in injection molding machine - Google Patents

Description

[0001]
[Industrial application fields]
In the present invention, a sheet-shaped or columnar-shaped molding material that is larger than a pellet is charged into a hopper, and during the molding cycle, a pressing force is applied to the molding material from above to pressurize the molding material. The present invention relates to an improvement of a molding material supply apparatus in an injection molding machine of a type.
[0002]
[Prior art]
In general, there are various plastic materials for molding by injection molding machines. These are broadly divided into thermoplastic materials such as PE and PET (polyethylene, polyethylene terephthalate), and thermosetting materials such as melanin and urea resin. And it can be divided into materials close to thermosetting such as silicon rubber and BMC (Bulk Modulus Compound).
[0003]
The thermoplastic molding material is processed into a pellet shape in advance, and is put into a hopper of an injection molding machine as a pellet. The thermosetting molding material is in powder form. However, rubber-based molding materials such as BMC and silicon rubber are supplied to the market as a molding material in the form of a sheet or a cylinder / cylindrical shape having an outer diameter substantially equal to the inner diameter of the hopper. The applicant of the present application has already proposed an apparatus for efficiently supplying and switching a sheet-shaped or cylindrical molding material into the hopper.
[0004]
[Patent Document 1]
Japanese Utility Model Publication No. 7-53956 Name of device "Raw material supply device"
[0005]
Such BMC and rubber-based molding materials (hereinafter simply referred to as molding materials) are vulcanized in the production stage, and also contain a large amount of volatile components, so that they deteriorate during storage and transportation, that is, volatile components are contained in the materials. Great care is taken not to be exposed to the open air to be preserved. (For example, when injection molding is performed using the molding material having a reduced amount of volatile components, white turbidity appears in the molded product and the molding quality is impaired.)
[0006]
In addition, attention is paid to the operating conditions during the metering process so that the molding material is subjected to excessive shearing and heating by the injection screw in the barrel of the injection molding machine and its effective volatile components are not dissipated.
[0007]
In addition, unlike pellets, this molding material cannot be dropped and supplied from the hopper through the barrel opening to the inside of the barrel due to its own weight, so the upper end surface portion of the molding material is pressed downward in the hopper to remove the molding material. A pushing means for pushing into the barrel opening is required. The pressing of the molding material by the pushing means is usually performed in a metering step, that is, the injection molding screw until the plasticized molding material is sent to the barrel tip while rotating the injection screw and stays in the barrel, and the retention amount reaches a predetermined amount. Is continued during the process of retreating depending on the amount of residence.
[0008]
FIG. 6 shows a configuration of the above-described injection molding machine for molding material as viewed from the injection device side.
[0009]
In FIG. 6, a support base 10 is placed on a base BS arranged on the injection device side of the injection molding machine. The support base 10 is provided with a barrel support portion 12 through which a barrel 14 through which the injection screw 16 is rotatably inserted and retracted is penetrated and fixed by a fastening means 12A. Further, a band heater 18 is disposed on the left outer peripheral portion of the barrel 14 so as to heat the barrel 14.
[0010]
Reference numeral 20 denotes an injection nozzle, which is attached to the left end portion of a nozzle support 24 attached to the left end portion of the barrel 14. Reference numeral 16 </ b> A is a shaft portion of the injection screw 16.
[0011]
A hopper 26 for supplying a molding material to the groove portion of the injection screw 16 through the barrel 14 is disposed on the barrel 14 at the barrel support portion 12. Furthermore, a guide 22 is disposed at the upper end of the barrel support 12. On this guide 22, a hydraulic cylinder 32 provided with a pressure sensor 32A at the upper end, and a rod lower end of the cylinder 32 are attached to the molding material in the hopper 26, and a pressing force is applied downward from the upper opening of the hopper 26 to the molding material. In order to generate it, a pushing device PSD having a pushing piston 30 is provided. Reference numeral S is a sensor that detects the position of the piston 30 in the vertical direction.
[0012]
That is, as shown in the drawing, the pushing device PSD further includes a frame body 25 slidably mounted on the guide 22 in a direction perpendicular to the drawing sheet, a cylinder mounting plate 28 fixed to the top of the frame body 25, and not shown. Has a drive unit that moves the frame body 25 along the guide 22.
[0013]
The drive unit moves the piston 30 and the frame body 25 during the operation of supplying a molding material from the upper opening of the hopper 26 or the operation of cleaning, mounting, disassembling the hopper 26 itself, and the opening of the hopper 26. A space is secured above the section.
[0014]
A guide 34 is disposed on the upper right side of the support 10, and a rotation transmission device 42 that applies a rotational force to the shaft portion 16 </ b> A of the injection screw 26 via the engaging portion 36 is mounted on the guide 34. . The engaging portion 36 is configured such that movement of the injection screw 16 in the axial direction is restricted by a nut 42B and only rotation can be transmitted.
[0015]
A measuring servo motor 38 is disposed above the rotation transmission device 42 via a support 40. Therefore, the rotation of the servo motor 38 is transmitted to the lower rotation transmission device 42 via the pulley and timing belt inside the cover 42A, and further applied to the shaft portion 16A of the injection screw 16 via the engagement portion 36.
[0016]
The rotation transmission device 42 is arranged on the guide 34 so as to be slidable in the X direction. Although not shown, an injection cylinder for moving the rotation transmission device 42 and the injection screw 16 in the X direction is arranged in parallel with the injection screw 16 on the barrel support portion 12, and the piston rod end portion of each cylinder rotates. It is fixed to the transmission device 42.
[0017]
Reference numeral 10A is a so-called nozzle touch drive cylinder for bringing the left end of the injection nozzle 20 into contact with a resin introduction portion of a mold disposed on the mold clamping mechanism side, and the piston rod right end is the support base. 10 is attached.
[0018]
However, in the molded product by the injection molding machine described above, there is still a problem that plasticization non-uniformity exists in terms of molding quality, and the density of the molding material is generated in the molded product.
[0019]
Various causes are involved in the cause, and as one of them, as shown in FIG. 7, when the remaining amount of the molding material MT in the hopper 26 decreases and approaches the stroke limit SL of the piston 30, molding is performed. It is necessary to raise the piston 30 in the Y direction via the rod RD for replenishing material. In that case, the molding material MT in contact with the lower surface of the piston 30 rises together with the piston 30 without leaving the lower surface of the piston 30.
[0020]
That is, outside air enters through a gap between the hopper 26 and the outer peripheral surface of the piston 30 and enters between the lower surface of the piston 30 and the upper surface of the molding material MT until the negative pressure is eliminated and the two are easily separated. A phenomenon occurs in which the molding material MT in the groove is drawn into the hopper from the lower end opening of the hopper 26 and this drawing is finally transmitted to the molded product being molded.
[0021]
When such a phenomenon occurs, the molding material MT that has been supplied from the hopper 26 into the barrel 14 is returned to the hopper side again, which causes the above-mentioned non-uniform plasticization and the density of the molding material in the molded product. It becomes. Further, in the molding of BMC or the like, the cooling time generally takes as long as 2 minutes or more. Therefore, the molding material is charged into the hopper 26 by using this time. This means that the above phenomenon occurs every time the molding material MT is introduced.
[0022]
[Problems to be solved by the invention]
The present inventor believes that by preventing the occurrence of the above-described phenomenon, one of the causes of the above-mentioned non-uniform plasticization and the density of the molding material in the molded product can be surely removed. When pulling up the piston 30, the inventors have focused on the fact that the pull-in phenomenon can be prevented by preventing a negative pressure state from occurring between the lower surface of the piston 30 and the upper surface of the molding material MT.
[0023]
Accordingly, an object of the present invention is to supply a molding material that does not cause a pull-in phenomenon of the molding material in the barrel when the piston in the hopper is pulled up to replenish the BMC or rubber-based molding material during the molding operation of the injection molding machine. To provide an apparatus.
[0024]
[Means for Solving the Problems]
In order to achieve the above object, a molding material supply apparatus according to the present invention comprises:
A barrel in which an injection nozzle is mounted at the tip and an injection screw is inserted into the inside so as to be able to rotate and advance, a hopper disposed at a molding material supply port position at the rear of the barrel, and the molding material previously charged in the hopper are the same. A molding material supply apparatus in an injection molding machine having a pressing means for pressing into the barrel through a hopper bottom opening, wherein the pressing means is
A piston that presses the upper surface of the molding material charged in the hopper, a rod fixedly coupled to the piston, and a piston drive unit that moves the piston in the hopper axial direction via the rod;
A gas passage for communicating between both end faces of the piston and a valve body that shuts off and conducts the passage;
Valve body drive means for driving the valve body so as to cause the gas passage to conduct in response to the piston lifting operation of the piston driving portion when replenishing the molding material to the hopper, and when the piston is lifted, It is configured to prevent the generation of negative pressure.
[0025]
In that case, the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to the upper surface of the child piston and the child piston slidably accommodated in the recess. The valve body driving means is attached to the upper surface of the piston, and is coupled to the through rod and allows the child piston to be passed through the through rod. The cylinder unit can be moved downward from the recess.
[0026]
In this case, the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to a child piston and a top surface of the child piston that are slidably accommodated in the recess. The rod is slidably penetrated to the upper end surface side of the piston and is provided with a rod provided with a stopper member at the end thereof, and the valve body driving means is housed in the recess and covers the upper surface of the child piston. It can be constituted by a spring that is pressed downward.
[0027]
Furthermore, the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to a child piston slidably received in the recess and an upper surface of the child piston. The valve body slidably penetrates the piston up to its upper end surface side and is provided with a rod provided with a stopper member at its end, and the valve body driving means has a lower end abutting on the stopper member and its upper end is The spring may be in contact with a position restricting member provided at a position spaced apart from the piston upper end surface by a predetermined distance.
[0028]
Further, in this case, the lower end of the gas passage is opened on the lower surface of the piston, and the valve body has a child piston and a child piston whose upper surface is in contact with the lower surface of the piston and seals the lower end opening of the gas passage. And a rod that slidably penetrates the piston to its upper end surface side and that is coupled to a movement amount regulating means for regulating the downward movement amount of the piston.
[0029]
In this case, the side surface shape of the child piston can be configured to have an inclination that narrows downward.
[0030]
In that case, the said valve body drive means can also be comprised with the compressed gas supply apparatus connected to the said gas channel upper end opening part.
[0031]
Furthermore, the lower end of the gas passage is opened in a concave portion having a divergent inclined side surface formed in the lower surface of the piston, and the valve body is slidably accommodated in the concave portion having the divergent inclined side surface. It is comprised by the movement amount control means couple | bonded with the upper surface of a child piston and the same child piston, and regulates the downward movement amount, The said valve body drive means is comprised with the compressed gas supply apparatus connected to the said gas path upper end opening part. Can do.
[0032]
[Action]
The gas passage for communicating the both end surfaces of the piston constituting the pushing means for the molding material thrown into the hopper and the valve body that blocks and conducts the passage, and the piston at the time of replenishing the molding material to the hopper And the valve body driving means for driving the valve body so that the gas passage is conducted in response to the pulling operation of the cylinder, and prevents the generation of negative pressure on the lower surface side of the piston in the hopper when the piston is pulled up. . Therefore, the pull-in phenomenon of the molding material in the barrel does not occur when the piston in the hopper is pulled up to replenish BMC or rubber-based molding material during the molding operation of the injection molding machine.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples based on the embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5.
[0034]
FIG. 1 shows a first embodiment of the present invention. FIG. 1A shows a state in which the molding material MT in the hopper HP decreases due to the progress of the molding operation, and the molding material MT is replenished via the rod RD. The state immediately before pulling up the piston PS upward Y is shown. FIG. 5B shows a state where the piston PS is being pulled up.
[0035]
In FIG. 1A, a cylinder 50 is attached to the upper end surface of the piston PS by a flange 52. A recess RC (see FIG. 1A) is formed in the lower end surface of the piston PS, and the gas passage 54 is formed through the flange 52 and the piston PS, and the lower end thereof opens into the recess RC. . Further, a child piston 58 is slidably accommodated in the recess RC, and a rod 56 is coupled to the upper surface of the child piston 58, and an upper end portion thereof is coupled to the piston rod of the cylinder 50. Here, the rod 56 and the child piston 58 constitute a valve body in the present invention, and the cylinder 50 constitutes a valve body driving means in the present invention.
[0036]
As shown in FIG. 1B, when the piston 50 is pulled up and the cylinder 50 is driven, and the child piston 58 comes out of the recess RC, the air on the upper end surface side of the piston PS has been in a negative pressure state until then. The piston PS enters the space on the lower end surface side through the gas passage 54. In this example, it is possible to shorten the time during which the negative pressure state is maintained by driving the child piston 58 before the piston PS is pulled up.
[0037]
FIG. 2 shows an embodiment in which a spring 64 is used as the valve body driving means. In FIG. 1A, the spring 64 is compressed by a molding material MT through a child piston 66 as a valve body. In this example, the upper end portion 60A of the rod 60 integrally coupled to the child piston 66 functions as a stopper when the spring 64 is extended to some extent, as shown in FIG. In this state, as in FIG. 1B, the air on the upper end surface side of the piston PS enters through the gas passage 62, and the negative pressure state on the lower end surface side of the piston PS is eliminated.
[0038]
The embodiment shown in FIG. 3 is a case where a spring as valve body driving means is arranged on the upper end surface side of the piston PS. In FIG. 5A, a recess RC is formed on the lower end surface of the piston PS, and a child piston 78 as a valve body is accommodated in the recess RC. A rod 76 slidably passing through the piston PS and projecting toward the upper end surface of the piston PS is integrally coupled to the upper surface of the child piston 78. Reference numeral 74 is a stopper member for the rod 76 and the child piston 78, and a spring 72 is disposed on the upper surface thereof. Reference numeral 70 denotes a hollow spring housing case having a lower end fixed to the upper end surface of the piston PS. The upper end of the spring 72 is in contact with the inner surface of the top portion of the case 70. Further, the shaft portion of the rod 76 extending above the stopper member 74 passes through the top portion of the case and the shaft center thereof is guided. Further, the lower end side of the gas passage 77 is open to the side surface of the recess RC.
[0039]
In FIG. 3A, the lower surface of the child piston 78 is pushed up in the recess RC by contact with the molding material MT, and therefore the spring 72 is in a compressed state. In this state, as shown in FIG. 5B, when the piston PS is pulled up, the spring 72 is extended at the same time, and when the upper surface of the child piston 78 reaches a position lower than the lower end surface of the piston PS, the gas passage of the piston PS as shown in the figure. The air enters the hopper HP through 77 and the negative pressure state is eliminated.
[0040]
FIG. 4 shows still another embodiment. As shown in FIG. 4A, in this example, the recess RC as shown in FIGS. 1 to 3 is not formed on the lower end surface of the piston PS. Instead, the upper surface of the child piston 88 as a valve body abuts on the lower end surface of the piston PS and seals the lower end opening of the gas passage 82. A rod 80 extending upward from the center of the upper surface of the child piston 88 and penetrating the piston PS is provided. Reference numeral 86 generally indicates a connecting portion with the upper portion of the rod 80. The connecting portion 86 accommodates the cylinder unit 50 in FIG. 1A and the spring 72 and the stopper member 74 in FIG. 3A. This corresponds to the case 70.
[0041]
Further, the coupling portion 86 can be simply configured like the stopper member 60A of FIG. As shown in FIG. 6B, the upper surface of the piston PS releases the sealed state of the gas passage 82 by pulling up the piston PS and simultaneously pushing down the child piston 88. The side is in a communicating state, and the generation of negative pressure can be eliminated more quickly than in the case of FIGS. In FIG. 4A, the bottom and side surfaces of the child piston 88 are in contact with the molding material MT, and when the holding force for maintaining this contact state is large to some extent, the above-described coupling portion 86 is only a stopper member. But you can. Further, by forming the side surface shape of the child piston 88 into a taper shape that becomes narrower toward the bottom, the molding material MT in the vicinity is expanded during the downward operation, and the sealing surface enters the molding material MT. There is an effect to protect from.
[0042]
Further, in FIG. 4A, reference numeral 84 indicates a compressed gas supply device. It is also possible to prevent the above-described negative pressure state from occurring from the beginning by connecting the gas passage 82 to the compressed gas supply device 84 through a pipe.
[0043]
FIG. 5 shows an embodiment in which the compressed gas supply device 84 is used not only for preventing the generation of negative pressure but also as a valve body driving means. In FIG. 5, a recess 90 having an inclined side surface that widens toward the bottom is formed at the lower end surface of the piston PS, and a child piston 92 as a valve element is accommodated in the recess 90. A bolt 96 is screwed and fixed at the center of the upper surface of the child piston 92. The head of the bolt 96 is accommodated in a stepped hole formed in the piston PS, and the lower end surface of the bolt head contacts the step to function as a stopper.
[0044]
Accordingly, when compressed gas PG is supplied from the compressed gas supply device 84 to the gas passage 94, the gas pressure acts on the upper surface of the child piston 92 in the recess 90, and the child piston 92 reaches the position indicated by the alternate long and short dash line. At the same time, the distance L is pushed down. In the meantime, a gap is formed between the concave portion 90 having the inclined side surface and the child piston 92, and the compressed gas acts to separate the lower end surface of the piston PS from the molding material MT. If the lifting operation of the piston PS is performed in such a state, the generation of the negative pressure is almost eliminated, and the power of the lifting operation of the piston PS can be saved because of the compressed gas.
[0045]
In the above description of the embodiment, the contact state between the lower end surface of the piston PS and the molding material MT is easily separated by eliminating the negative pressure in the hopper, but depending on the molding material, the negative pressure may be eliminated. In some cases, the contact state with the lower end surface may be maintained as it is. In such a case, the contact state may be mechanically interrupted by rotating the piston PS. Further, the lower end surface of the piston PS may be formed of a material having relatively good separability such as Teflon (registered trademark).
[0046]
The preferred embodiments of the present invention have been described above with reference to the drawings, but the present invention is naturally not limited to these disclosures.
[0047]
【The invention's effect】
The molding material supply device according to the present invention comprises:
A barrel in which an injection nozzle is mounted at the tip and an injection screw is inserted into the inside so as to be able to rotate and advance, a hopper disposed at a molding material supply port position at the rear of the barrel, and the molding material previously charged in the hopper are the same. A molding material supply apparatus in an injection molding machine having a pressing means for pressing into the barrel through a hopper bottom opening, wherein the pressing means is
A piston that presses the upper surface of the molding material charged in the hopper, a rod fixedly coupled to the piston, and a piston drive unit that moves the piston in the hopper axial direction via the rod;
A gas passage for communicating the both end face sides of the piston and a valve body for blocking and conducting the passage;
Since the valve body driving means is configured to drive the valve body so that the gas passage is conducted in response to the piston pulling-up operation of the piston driving portion when the molding material is replenished to the hopper, the piston It is possible to prevent the generation of negative pressure on the lower surface side of the piston in the hopper at the time of pulling up, and therefore, there is an effect that the plasticization non-uniformity and the density of the molding material in the molded product do not occur at the time of lifting the piston. .
[Brief description of the drawings]
FIGS. 1A and 1B are sectional views of a piston showing an embodiment of the present invention, in which FIG. 1A shows a gas passage cut-off state immediately before a piston pulling operation, and FIG. 1B shows a gas passage conduction state during the pulling operation;
FIGS. 2A and 2B are cross-sectional views of a piston showing another embodiment of the present invention, wherein FIG. 2A shows a gas passage cut-off state immediately before the piston pulling operation, and FIG. 2B shows a gas passage conduction state during the pulling operation. .
3A and 3B are sectional views of a piston showing still another embodiment of the present invention, in which FIG. 3A shows a gas passage shut-off state immediately before the piston pulling operation, and FIG. 3B shows a gas passage conduction state during the pulling operation. Show.
FIG. 4 is a cross-sectional view of a piston showing another embodiment of the present invention in which no recess is formed on the lower surface of the piston, wherein (a) shows a gas passage blocking state immediately before the piston pulling operation, and (b) is during the pulling operation. The gas passage conduction state is shown.
FIG. 5 is a piston cross-sectional view showing still another embodiment of the present invention in which the valve body is driven with compressed gas.
FIG. 6 is a front view of an injection device of an injection molding machine for molding BMC or rubber-based material.
FIG. 7 is an enlarged cross-sectional view of a hopper bottom opening for explaining a pull-in phenomenon that occurs when a molding material is supplied to the hopper.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Support stand 12 Barrel support part 14 Barrel 16 Injection screw 18 Band heater 20 Injection nozzle 22 Guide 24 Nozzle support body 25 Frame body 26 Hopper 28 Cylinder mounting plate 30 Piston 32 Cylinder 34 Guide 36 Engagement part 38 Servo motor 40 Support base 42 Rotation transmission device 50 Cylinder unit 52 Flange 54, 62, 77, 82, 94 Gas passage 56, 60, 76, 80 Rod 58, 66, 78, 88, 92 Sub piston 60A, 74, 96 Stopper member 64, 72 Spring 84 Compressed gas supply device 86 Joint part HP Hopper PS Piston RC Concave part RD Rod

Claims (11)

A barrel in which an injection nozzle is mounted at the tip and an injection screw is inserted into the inside so as to be able to rotate and advance, a hopper disposed at a molding material supply port position at the rear of the barrel, and the molding material previously put in the hopper are the same. A molding material supply apparatus in an injection molding machine having a pressing means for pressing into the barrel through a hopper bottom opening, wherein the pressing means is
A piston that presses the upper surface of the molding material charged in the hopper, a rod fixedly coupled to the piston, and a piston drive unit that moves the piston in the hopper axial direction via the rod;
A gas passage for communicating the both end face sides of the piston and a valve body for blocking and conducting the passage;
Valve body drive means for driving the valve body so that the gas passage is conducted in response to the piston lifting operation of the piston driving portion when replenishing the molding material to the hopper, and when the piston is lifted, A molding material supply apparatus in an injection molding machine, wherein the generation of negative pressure is prevented on the lower surface of the piston. 2. The lower end of the gas passage according to claim 1, wherein the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to a child piston that is slidably accommodated in the recess and an upper surface of the child piston. The valve body driving means is attached to the upper surface of the piston and is coupled to the penetrating rod and the child through the penetrating rod. A molding material supply device in an injection molding machine, comprising a cylinder unit that moves a piston downward from the recess. 2. The lower end of the gas passage according to claim 1, wherein the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to a child piston that is slidably accommodated in the recess and an upper surface of the child piston. And a rod that slidably penetrates through the piston to its upper end surface side and is provided with a stopper member at its end, and the valve body driving means is housed in the recess and is located on the upper surface of the child piston. A molding material supply device in an injection molding machine, characterized in that it is constituted by a spring that presses down. 2. The lower end of the gas passage according to claim 1, wherein the lower end of the gas passage is opened in a recess formed in the lower surface of the piston, and the valve body is coupled to a child piston that is slidably accommodated in the recess and an upper surface of the child piston. The valve body slidably penetrates through the piston to the upper end surface side and has a stopper member provided at the end thereof. The valve body driving means has a lower end abutting on the stopper member and an upper end thereof. The part is constituted by a spring in contact with a position regulating member provided at a position spaced apart from the upper end surface of the piston by a predetermined distance. The lower end of the gas passage according to claim 1, wherein the lower end of the gas passage is opened to the lower surface of the piston, and the valve body has an upper surface abutting against the lower surface of the piston and a child piston and the same for sealing the lower end opening of the gas passage. An injection molding comprising: a rod coupled to an upper surface of a piston and slidably penetrating through the piston to the upper end surface side and coupled to a movement amount regulating means for regulating a downward movement amount thereof. Molding material supply device in the machine. 6. The molding material supply device in an injection molding machine according to claim 5, wherein the side shape of the child piston has an inclination that becomes narrower downward. 7. A molding material supply apparatus in an injection molding machine according to claim 5, wherein the valve body driving means is a cylinder unit coupled to the upper end portion of the rod. 7. The molding material supply device in an injection molding machine according to claim 5, wherein the valve body driving means has a spring that presses the upper end of the rod downward. 7. The molding material supply device in an injection molding machine according to claim 5, wherein the valve body driving means is a compressed gas supply device connected to the gas passage upper end opening. 2. The lower end of the gas passage according to claim 1, wherein the lower end of the gas passage is opened in a concave portion having a diverging inclined side surface formed on the lower surface of the piston, and the valve body is slidably accommodated in the concave portion having the diverging inclined side surface. The valve body driving means is a compressed gas supply device connected to the upper end opening of the gas passage. The valve body driving means is connected to the upper end portion of the gas passage. The molding material supply apparatus in the injection molding machine characterized by the above-mentioned. 11. The molding material supply apparatus in an injection molding machine according to claim 1, wherein the pushing means further comprises a rotating means for rotating the piston by a predetermined amount.

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