CN1171756A - Valve gate type injection molding method and apparatus thereof - Google Patents

Abstract

A valve pin of a valve for injecting a molten resin is inserted into a cavity formed in a die, and then the molten resin is injected and filled through a gate into a space formed between the valve pin and the cavity. Then the molten resin is cooled and solidified to provide injection moldings.

Description

Valve gate injection molding method and device

The present invention relates to the improvement of valve gate injection molding method and device. The molten plastic and other synthetic resins are injected into a closed mould, and then the mold is opened to take out the cooled and solidified molded product to obtain the desired molded product.

Various injection molding methods and devices have been proposed as existing injection molding methods and devices for producing relatively precise molded articles from synthetic resins such as plastics.

In particular, in the injection molding method and apparatus described above, in recent years, a so-called valve gate injection molding method and apparatus have been provided in order to reduce the molding cycle of molded products.

The valve gate injection molding method and device are composed of a valve temporarily storing pre-pressed molten resin, and a freely movable valve pin arranged in the valve, through which the gate formed in the mold is opened. , quickly fill the mold cavity with pre-pressed molten resin, and after filling the resin, plug the gate through the valve pin.

If such a valve gate injection molding method and device are used, since the molten resin in the valve is pre-compressed during the time when the mold is opened and the molded product is taken out, the useless time required for compression before the injection of the molten resin is reduced, so It has the effect of shortening the forming cycle of molded products.

18 is a schematic cross-sectional view of main parts of the above-mentioned conventional valve gate injection molding apparatus 1, showing the valve gate injection molding apparatus 1 for molding cylindrical moldings such as rollers with bearing holes formed in the center.

This valve gate injection molding device 1 is composed of an upper mold 2 configured with a valve body not shown in the figure, and a lower film 4 forming a cylindrical cavity 3, wherein, in the mold 2, the A truncated cone-shaped first hole 5 is formed at a position corresponding to the upper end 3a of the 3, and the inner peripheral surface of the lower end is a gate 6 for filling molten resin into the cavity 3. In addition, in the above-mentioned upper mold 2, a second hole 7 with a truncated cone shape in cross-section that is connected to the upper edge of the first hole 5 and has a larger diameter than the first hole 4 is formed. In the center, it is opposite to the gate 6. A valve pin 8 of a valve not shown in the figure is arranged freely movable in the vertical direction.

The structure of the valve pin 8 is that its front end forms a cylindrical shape, and its diameter L is substantially consistent with the diameter M of the gate 6; when the valve pin 8 descends to the position of the gate 6, the gate 6 is blocked, and the valve pin 8 rises When reaching the position shown in the figure, the gate 6 is open.

In addition, in the center of the cavity 3 formed in the lower mold 4, a cylindrical core 9 is arranged to form a central hole of a cylindrical molded product molded by filled molten resin, and a cylindrical core 9 is embedded around the core 9. The ejector pin 10 that is inserted into the cavity 3 to take out the molded product, and the arrangement of the ejector pin 10 can move up and down freely on the core 9 .

The operation of the valve gate injection molding apparatus 1 described above will be described below.

As shown in FIG. 19, the same parts as in FIG. 18 are denoted by the same symbols, the gate 6 is in an open state according to the position of the valve pin 8 receding upward, so as shown by the arrow A, injection is made into the cavity 3 through the gate 6. Fill with molten resin compressed in the valve not shown in the figure.

In this way, the molten resin is injected into the cavity 3 through the gate 6. When the filling is completed, as shown by the arrow C in FIG. 20, the valve pin 8 descends and stops at the gate 6, thereby blocking the gate 6 and blocking The molten resin B is injected into the cavity 3 (so-called gate cutting).

Then, the molten resin B filled in the cavity is solidified by cooling the molten resin B by cooling means not shown in the figure.

In this way, after the molten resin B in the cavity 3 is solidified, the upper mold 2 is separated from the lower mold 4, and the mold is opened. As shown in FIG. 21, the molten resin B in the cavity 3 of the lower mold 4 is solidified, leaving a The shape of the cavity 3 is corresponding to the shape of the cylinder forming the molded product 11 .

Also, when the ejector pin 10 is raised from the position of the ejector pin 10 shown in Figure 21, the ejector pin 10 rises along the core 9, and at the same time, the cylindrical molded product 11 receives the ejector pin 10 on its lower side. Brace, one side is taken out by the cavity 3 of lower mold 4 as shown in Figure 22.

Using such an existing valve gate injection molding apparatus 1, as shown in the enlarged view of FIG. 23, a roller-shaped molded product 11 having a bearing hole formed in the center is produced.

In addition, as shown in FIG. 24, when the undercut C is formed on the upper edge of the bearing hole 11a of the molded product 11, machining is performed after forming.

However, if the above-mentioned existing valve gate injection molding method and device 1 are used to manufacture a molded product 11 with a bearing hole formed in the center, a cylindrical core 9 for forming the bearing hole 11a must be arranged in the lower mold 4 , so there are many mold parts and the structure is complex, which becomes the main reason for increasing the production cost of the entire valve gate injection molding device.

Also, if the above-mentioned existing valve gate injection molding method and device 1 are used, as shown in FIG. Since the molten resin is filled by injection, insufficient pressure of the molten resin filled in the cavity 3 often occurs. Therefore, the molded product 11 molded by the conventional valve gate injection molding method and apparatus 1, as shown in FIG. The deformed portion D, that is, produces a defect, and becomes the main cause of the dimensional defect of the molded product.

In addition, molded products having defects have to be trimmed in size after post-processing, and thus the manufacturing cost of molded products has become extremely difficult.

Therefore, in view of the above problems, it is an object of the present invention to provide a valve gate injection molding method and device for reducing all device parts.

Next, while reducing the number of parts in the entire device, the present invention also aims to provide a valve gate injection molding method and device for preventing dimensional defects such as "defects" in molded products.

The valve pin of the valve for injecting molten resin is inserted into the cavity formed in the mold of the present invention, and then the space formed between the pin valve and the cavity is injected and filled with molten resin through the gate, thereby obtaining a molded product.

When such a valve gate injection molding method and device are used, the valve pin inserted into the cavity forms a hole in the molded article filled with molten resin in the space formed between the valve pin and the cavity. Therefore, in order to A hole is formed in the center of a molded product in the past, and it is not necessary to arrange a core, one of the mold parts, in the cavity of the mold. Therefore, the number of components of the valve gate injection molding apparatus can be reduced.

Secondly, the valve pin of valve among the present invention is made up of the large-diameter part of opening and closing the mold gate and the small-diameter part in the cavity formed in the insert mold, inserts the small-diameter part of valve pin into the cavity formed in the mold, and then Through the gate, inject and fill the molten resin into the space formed between the small diameter part of the valve pin and the cavity, and at the same time cut off the gate through the large diameter part of the valve pin, and then let the large diameter part enter to the valve pin The molten resin injected and filled between the small diameter part and the cavity is pressurized to obtain a molded product.

When such a valve gate injection molding method and device are used, holes are formed in the molded product formed by filling the space formed between the small diameter portion of the valve pin and the cavity through the small diameter portion of the valve pin inserted into the cavity. , Therefore, in order to form a hole in a molded product as in the past, it is not necessary to provide a core, one of the mold parts, in the cavity of the mold. Therefore, the parts of the valve gate injection molding device can be reduced, and at the same time, after the gate is cut off by the large diameter part of the valve pin, the large diameter part enters the cavity side and pressurizes the molten resin in the cavity, so as much as possible It can effectively prevent the occurrence of defective parts such as defects in the thick part of the molded product.

The following is a brief description of the accompanying drawings.

Fig. 1 is a schematic cross-sectional view of a valve gate injection molding device implementing the valve gate injection molding method of the present invention.

Fig. 2 is a schematic cross-sectional view of a valve gate injection molding device showing a state in which a valve pin moves downward.

Fig. 3 is an enlarged cross-sectional view of a main part of Fig. 1 .

Fig. 4 is a schematic sectional view showing the operation of the valve gate injection molding device of the present invention.

Fig. 5 is a schematic cross-sectional view showing the operation of the valve gate injection molding device of the present invention.

Fig. 6 is a schematic sectional view showing the operation of the valve gate injection molding apparatus according to the present invention.

Fig. 7 is a schematic sectional view showing the operation of the valve gate injection molding apparatus according to the present invention.

Fig. 8 is a schematic sectional view showing the operation of the valve gate injection molding apparatus according to the present invention.

Fig. 9 is a cross-sectional view of a molded product molded by a valve gate injection molding apparatus according to the present invention.

10 is a schematic cross-sectional view showing another embodiment of a valve gate injection molding apparatus for implementing the valve gate injection molding method of the present invention.

Fig. 11 is a schematic sectional view showing the operation of another embodiment.

Fig. 12 is a schematic sectional view showing the operation of another embodiment.

Fig. 13 is a schematic sectional view showing the operation of another embodiment.

Fig. 14 is a schematic sectional view showing the operation of another embodiment.

Fig. 15 is a schematic sectional view showing the operation of another embodiment.

Fig. 16 is a schematic sectional view showing the operation of another embodiment.

Fig. 17 is a sectional view of a molded product molded by another embodiment.

Fig. 18 is a schematic sectional view of main parts of a conventional valve gate injection molding apparatus for carrying out a conventional valve gate injection molding method.

Fig. 19 is a schematic sectional view showing the operation of a conventional valve gate injection molding apparatus.

Fig. 20 is a schematic sectional view showing the operation of a conventional valve gate injection molding apparatus.

Fig. 21 is a schematic sectional view showing the operation of a conventional valve gate injection molding apparatus.

Fig. 22 is a schematic sectional view showing the operation of a conventional valve gate injection molding apparatus.

Fig. 23 is a schematic cross-sectional view showing the operation of a conventional valve gate injection molding device.

Fig. 24 is a schematic cross-sectional view showing the operation of a conventional valve gate injection molding device.

Fig. 25 is a view showing a state where a defect occurs in a molded product molded by a conventional valve gate injection molding apparatus.

An embodiment of the valve gate injection molding method and device of the present invention will be described in detail below.

FIG. 1 is a schematic cross-sectional view of a valve gate injection molding device 20 used for implementing the valve gate injection molding method of the present invention.

The valve gate injection molding device 20 (hereinafter referred to as the device) is composed of an upper film 21 and a lower mold 22, and a valve 23 for injecting molten resin is arranged in the upper mold 21.

The valve 23 consists of a valve pin 24 that opens and closes a gate described later, a valve body 25 that keeps the valve pin 24 free to lift, and a guide sleeve 26 that is arranged on the valve body 25 to make the valve pin 24 to give The air piston 27 that lifts at a fixed distance is formed.

In addition, a flow channel 28 for guiding pre-pressurized and heated molten resin is formed in the valve body 25 , and its lower part reaches a nozzle portion 29 formed at the front end of the valve body 25 .

Also, the above-mentioned valve pin 24 is formed by opening and closing the nozzle hole 29a formed in the nozzle part 29 and opening and closing the large diameter part 24a of the gate 30 formed in the lower part thereof, and formed at the lower end. The small diameter portion 24b is formed.

In addition, a cylindrical cavity 31 is formed in the lower mold 22, and the small-diameter portion 24b of the valve pin 24 is inserted in the center thereof, and the lower end of the small-diameter portion 24b is inserted into the center portion of the push rod 32 formed. Inside the guide hole 32a.

If according to the structure of the above-mentioned valve 23, when the air piston 27 moves, the valve pin 24 promptly performs the following movements respectively: as shown in Figure 1, the valve pin 24 is moved upwards, and the nozzle hole 29a and the gate 30 are expanded by its small diameter portion 24b. , move to the injection position of injection molten resin to mold cavity 31; And shown in Fig. 2 that the same part as Fig. 1 is represented by the same symbol, make valve pin 24 move down, block nozzle hole 29a and the nozzle hole 29a by its large-diameter portion 24a The gate 30 is moved to a gate cutting position for cutting off injection of the molten resin into the cavity 31 .

The valve gate injection molding method of the present invention using the above-mentioned valve gate injection molding apparatus 20 will be described below, and the structure of the valve gate injection molding apparatus 20 of the present invention will be described in detail.

3 is an enlarged cross-sectional view of the main part of the valve gate injection molding device 20 shown in FIG. 30, and the part of the valve pin 24 inserted into the gate 30 and the cavity 31 respectively. The nozzle portion 29 shown in FIG. 1 is omitted in this figure.

The position of the valve pin 24 shown in FIG. 3 corresponds to the position of the valve pin 24 shown in FIG. 1, and its small-diameter portion 24b is inserted into the center of the cavity 31 through the center of the gate 30, especially, its lower end It is inserted into the guide hole 32a formed in the center of the ejector pin 32 from which the molded product is taken out. In addition, symbol 33 in FIG. 3 indicates a cooling channel formed in the center of the valve pin 24 along the axial direction to guide the cooling medium, and the cooling channel 33 guides and supplies cooling medium such as nitrogen.

According to such a stop position of the valve pin 24, the small-diameter portion 24b of the valve pin 24 is located at the center of the gate 30 having a diameter larger than the valve pin 24. Therefore, the gate 30 is in an expanded state, that is, on the inner periphery of the gate 30. An annular gap is formed between the surface and the outer peripheral surface of the small-diameter portion 24b of the valve pin, and molten resin can be injected and filled into the cavity 30 through the annular gap.

In addition, the above-mentioned gate 30 is formed by a cylindrical hole 30a having the same diameter. When the large-diameter portion 24a of the valve pin 24 is inserted into the upper edge 30b of the gate 30, the gate 30 is in a blocked state. It is maintained until the large-diameter portion 24a reaches the cylindrical hole 30a and its lower edge 30c.

In the above-mentioned position where the valve pin 24 shown in FIG. 3 is stopped, when the molten resin heated and melted is guided to the valve hole 29a through the runner 28 shown in FIG. As shown, the molten resin is injected and filled into the cavity 31 through the gap between the small-diameter portion 24b of the valve pin 24 and the gate 30 .

In this way, after the molten resin is filled in the cavity 31, the piston 27 shown in FIG. 1 is operated, and when the valve pin 24 is moved downward, as shown in FIG. The large-diameter portion 24a is inserted into the upper edge 30b of the gate 30 to block the injection of the molten resin into the cavity 31 (the gate is cut off). In addition, the small diameter 24b of the valve pin 24 is inserted into the guide hole 32a of the plunger 32 in its original state.

According to the position of the valve pin 24 shown in FIG. 5, since the upper edge 30b of the gate 30 is blocked (the gate is cut off) by the large-diameter portion 24a, the molten resin cannot flow into the cavity 31 after that, and the injected The molten resin B is filled in the cavity 31, and the part of the gate 30 formed by the cylindrical hole 30a with the same diameter (that is, the part formed between the inner peripheral surface of the hole 30a and the outer peripheral surface of the small diameter part 24b within the space part).

If from the position of the valve pin 24 shown in FIG. 5, the valve pin 24 is further moved downward by the piston 27 shown in FIG. As shown in FIG. 6 , when reaching the lower edge 30c of the gate 30, the molten resin B filled in the part of the gate 30, that is, between the inner peripheral surface of the hole 30a and the outer peripheral surface of the small-diameter portion 24b shown in FIG. The cavity 31 is refilled with the molten resin B partially filled in the space formed between them, and for this reason, the molten resin B previously filled in the cavity 31 is pressurized again.

Then, a cooling medium such as nitrogen is supplied through the cooling channel 33 for guiding the cooling medium formed along the axis of the valve pin 24 to cool and solidify the molten resin B filled in the cavity 31 .

Secondly, the upper film 21 shown in Figure 6 is separated from the lower film 22 up and down, and when the mold is opened, then as shown in Figure 7, the mold cavity 31 of the lower mold 22 is left with a solidified mold corresponding to the shape of the mold cavity 31. The cylindrical molded product 40 molded by the molten resin B.

Thereafter, by the position of the ejector pin 32 shown in FIG. 7, when the ejector pin 32 is raised along the cavity 31, as shown in FIG. While moving the molded product 40 upward, the molded product 40 can be taken out from the cavity 31 of the lower mold 22 for demoulding.

When such a valve gate injection molding apparatus 20 of the present invention is used, as shown in FIG. 9 , the small diameter portion 24b of the valve pin 24 can be used to form a roller molded product 40 in which a bearing hole is formed in the center.

Therefore, when using the valve gate injection molding device 20 described above, in the molded article 40 molded by the molten resin filled in the space formed between the valve pin 24 and the cavity 31 , the small diameter of the valve pin inserted into the cavity 31 Therefore, in order to form a hole in the center of the existing molded product, it is not necessary to arrange a core, one of the mold parts, in the mold cavity, so the number of parts of the valve gate injection molding device can be reduced.

In addition, according to the molded product 40 molded by the above-mentioned valve gate injection molding device 20, as shown in FIGS. The side that enters the cavity 31 presses the molten resin B in the cavity 31. Therefore, the part D of the wall thickness of the molded product 40 shown in FIG. Defective parts, therefore, can be made into injection molded products with extremely high dimensional accuracy.

Also, in the above-mentioned embodiment, as shown in FIG. 3, the upper end of the valve pin 24 is formed in the large diameter portion 24a, and the lower end is formed in the small diameter portion 24b, so that the small diameter portion 24b penetrates into the cavity 31, and the molded product The center of 40 forms hole 41 (Fig. 9), but, the present invention is not limited to above-mentioned embodiment, also can form the upper end of valve pin 24 in small diameter part 24b, and form its lower end in large diameter part 24a, and make this large diameter The diameter portion 24a penetrates into the cavity 31 to form a hole in the center of the molded product.

FIG. 10 is a schematic cross-sectional view showing main parts of another embodiment of the above-mentioned valve gate injection molding apparatus 20, and the same parts as in FIG. 3 are denoted by the same reference numerals.

The valve gate injection molding apparatus 20 of this embodiment, as shown in FIG. The large-diameter portion 24a penetrates into the cavity 31 . Also, the symbol 50 in FIG. 10 is a push rod, and the upper center of the push rod 50 is formed with a protrusion 51 for determining the position, and the protrusion 51 is inserted into the recess 52 formed at the center of the lower end of the valve pin 24. , to determine the position of the valve pin 24 in the cavity 31 .

According to such a stop position of the valve pin 24, the small-diameter portion 24b of the valve pin 24 is located at the center of the gate 30 having a diameter larger than the valve pin 24, so the gate 30 becomes an expanded state, that is, the inner peripheral surface of the gate 30 and the The annular gap is formed between the outer peripheral surfaces of the small-diameter portion 24b of the valve pin, and the molten resin can be injected into the cavity 30 through the annular gap.

When the molten resin is guided to the gate 30 at the stop position of the valve pin 24 shown in FIG. , is injected into the cavity 31, as shown in FIG. 12, so that the cavity 31 is filled.

In this way, after the molten resin is filled in the cavity 31, a cooling medium such as nitrogen is sent through the cooling passage 33 formed along the axial center of the valve pin 24 to guide the cooling medium, and the molten resin B filled in the cooling cavity 31 is cooled. After the degree of solidification, if the valve pin 24 is moved upward, as shown in FIG. 13 with the same parts as in FIG. The injection of the molten resin into the cavity 31 is blocked (gate cut).

Also, as shown in Figure 14, after the large-diameter portion 24a of the valve pin 24 is completely released from the cavity 31, the upper film 21 and the lower film 22 are separated in the vertical direction, and when the mold is opened, as shown in Figure 15, the lower film A cylindrical molded product 60 formed of solidified molten resin B corresponding to the shape of the cavity 31 remains in the cavity of the cavity 22 .

Thereafter, by the position of the ejector pin 50 shown in FIG. 15, when the ejector pin 50 is raised along the cavity 31, as shown in FIG. While moving the molded product 60 upward, the molded product 60 is taken out from the mold 31 of the lower die 22 and removed from the mold.

When such a valve gate injection molding apparatus 20 of the present invention is used, as shown in FIG. 17 , a roller molded product 60 in which a bearing hole is formed at the center can be produced by the large diameter portion 24a of the valve pin 24 .

Therefore, using the valve gate injection molding apparatus 20 of another embodiment described above, in the molded article 60 molded by the molten resin filled in the space formed between the valve pin 24 and the cavity 31 , the valve inserted in the cavity 31 The large-diameter portion 24a of the pin forms a hole. Therefore, in order to form a hole in the center of an existing molded product, one of the cores of the mold does not need to be provided in the cavity of the mold, so the parts of the valve gate injection molding device can be reduced.

In the above, only the roller molded products 40 and 60 with the bearing hole formed in the center were given as examples of the molded products molded by the valve gate injection molding method and apparatus of the present invention, but as examples by the valve gate injection molding method and apparatus of the present invention Of course, the molded products of the device molding are not limited to the roller molded products 40, 60, and all injection molded products with a hole formed in the center, such as compact disks (CDs), gears, floppy disk cases, and magnetic disks of cassette tapes, etc. are molded from synthetic resin. moldings.

As described above, the valve gate injection molding method and apparatus according to the present invention are suitable for producing molded articles made of synthetic resins that require precision molding performance.

claims

Amendments pursuant to Article 19 of the Treaty

1. A valve gate injection molding method, through the gate, the molten resin is injected into the mold cavity by the valve that retains the molten resin such as pre-pressed plastic, and the molten resin injected in the cavity is cooled, Solidify, obtain the molded article of synthetic resin, it is characterized in that, at least comprise following operation:

a valve pin arranged in the valve to control the injection amount of the molten resin injected by the valve, a process consisting of opening and closing the large-diameter portion of the gate and the small-diameter portion inserted into the cavity, and

inserting the small diameter portion of the valve pin into the cavity, and

injecting and filling molten resin into a space formed between the small diameter portion of the valve pin and the cavity through the gate, and

After the gate is cut off by the large-diameter portion of the valve pin, the large-diameter portion enters the cavity, and the molten resin is injected between the small-diameter portion of the valve pin and the cavity to apply pressure.

2. A valve-type gate injection molding device, through the gate, the molten resin is injected into the mold cavity by the valve that retains the molten resin such as pre-pressed plastic, and the molten resin injected into the cavity is cooled, Solidify, obtain the molded product of synthetic resin, it is characterized in that:

The valve pin arranged in the valve to control the injection amount of the molten resin injected by the valve is composed of a large-diameter part that opens and closes the gate and a small-diameter part that can be inserted into the cavity and extends. After the small-diameter portion of the valve pin is inserted into the cavity, the mold filled with molten resin is injected into the space formed between the small-diameter portion of the valve pin inserted into the cavity and the cavity through the gate. At the same time, the gate is cut off by the large-diameter portion of the valve pin, and then the large-diameter portion enters the cavity, and the molten resin injected between the small-diameter portion of the valve pin and the cavity is pressurized. .

Claims (4)

1. valve gate injection moulding method, pass through cast gate, by the valve injecting molten resin in mold cavity that retains through the molten resins such as plastics of precompressed, the molten resin of injecting in described die cavity is through cooling, curing, obtain the moulding product of synthetic resin, it is characterized in that, comprise following operation at least:

Be provided in the described valve, control is by the valve pin of this valve injection molten resin injection volume, insert described die cavity operation and

By described cast gate, the operation of the described molten resin of injection molding process in the formed space between described valve pin and described die cavity.

2. valve gate injection moulding method, pass through cast gate, by the valve injecting molten resin in mold cavity that retains through the molten resins such as plastics of precompressed, the molten resin of injecting in described die cavity is through cooling, curing, obtain the moulding product of synthetic resin, it is characterized in that, comprise following operation at least:

Be provided in the described valve, control is by the valve pin of this valve injection molten resin injection volume, by open, close the large-diameter portion of described cast gate and operation that the minor diameter part that inserts in described die cavity constitutes and

In described die cavity, insert described valve pin minor diameter part operation and

By described cast gate, between the minor diameter part of described valve pin and inner chamber in the formed space operation of injection molding process molten resin and

Large-diameter portion by described valve pin makes large-diameter portion enter described die cavity one side after cutting off cast gate again, the stressed operation of molten resin of injection molding process between the minor diameter part of described valve pin and die cavity.

3. valve gate Coinjection molding apparatus, by cast gate, by the valve injecting molten resin in mold cavity that retains through the molten resins such as plastics of precompressed, the molten resin of injecting in described die cavity is through cooling, curing, obtain the moulding product of synthetic resin, it is characterized in that:

Be provided in the described valve, control is by the valve pin of this valve injection molten resin injection volume, extend in the mode that can insert described die cavity, by described cast gate, between valve pin that in this die cavity, inserts and the described die cavity in the formed space, the injection molding process molten resin.

4. valve gate Coinjection molding apparatus, by cast gate, by the valve injecting molten resin in mold cavity that retains through the molten resins such as plastics of precompressed, the molten resin of injecting in described die cavity is through cooling, curing, obtain the moulding product of synthetic resin, it is characterized in that:

Be provided in the described valve, control is by the valve pin of this valve injection molten resin injection volume, by unlatching, close the large-diameter portion of described cast gate and can insert described die cavity and the minor diameter part that extends constitutes, after the minor diameter part with described valve pin inserts described die cavity, by described cast gate, between the minor diameter part of the described valve pin in inserting this die cavity and the die cavity in the formed space, in the time of the injection molding process molten resin, large-diameter portion by described valve pin cuts off cast gate, after this make described large-diameter portion enter described die cavity one side again, the molten resin plus-pressure of injection molding process between the minor diameter part of described valve pin and die cavity.

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