JPH0211151Y2 - - Google Patents

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) This invention relates to an injection mold for molding rubber-like elastic bodies such as various rubbers or soft plastics, and particularly relates to the gate structure thereof. It is.

(Prior Art) Conventionally, injection molds for injection molding rubber-like elastic bodies such as various rubbers or soft plastics have a sprue 31 and a sprue 31 of the mold shown in FIG. A ring gate portion 34 with a bag 33 was formed between the cavity 32 and the ring gate portion 34 .

However, with this method, when the shape of the molded product is long, such as when molding a bellows hose for an automobile, etc., it is necessary to create a structure that supports both ends of the core 35 in order to prevent the core 35 from bending. . In this case, the ring gate part 34 cannot be attached to the bag 33, so a method must be used in which the material is injected from the side of the ring gate part 34, as shown in FIG. In this case, the injected material is divided into two parts and goes around to the opposite side of the ring gate part 34, and at the same time flows into the material injection side of the cavity 32, so that the material is separated on the side opposite to the injection direction of the cavity 32. It took a considerable amount of time for them to join together. For this reason,
Welds may occur on the opposite side to the material injection side due to hardening of the material. As a means to suppress the occurrence of this weld, the gate portion 34
It is conceivable to lengthen the gate, but this method is not very effective and increases the remaining part of the gate of the molded product, which is not desirable.

(Problems to be Solved by the Invention) Therefore, the present invention attempts to solve the problem that welds occur in molded products during molding.

Structure of the invention (means for solving the problem) Therefore, in order to solve the above problems, the present invention provides a fixed type, a movable type, and a double type for forming a rubber-like elastic body such as rubber or soft plastic. A mold for injection molding consisting of a core whose both ends are supported by the mold, and the mold has an annular sprue gap that communicates with the sprue space when the mold is clamped, and an annular constriction part in the sprue gap. An annular gate part that communicates with the gate part through the gate part, and an annular product cavity part that communicates with the gate part through an annular stress concentration part that tapers in diameter with increasing distance from the gate part. are being taken.

(Function) After the injected material is once focused at the constriction part,
The material passes through the gate portion, is concentrated again at the stress concentration portion, and is filled into the cavity, so that the same material preferentially flows around the entire circumference of the annular gate portion before flowing into the cavity. Therefore, welding is less likely to occur in the part of the molded product on the side 180° opposite to the material injection side of the cavity.

(Example) Hereinafter, an example in which this invention is embodied in a mold for injection molding a boot for a CVJ joint of an automobile (hereinafter referred to as a boot) will be described with reference to FIGS. 1 to 3.

A fixed platen 1 is provided on the upper part of the mold, and a through hole 2 through which an injection nozzle (not shown) passes is bored in the center of the fixed platen 1. A fixed mold 3 is attached to the lower surface of the fixed platen 1, and a boot forming groove 4 is recessed in the mold joint surface of the fixed mold 3.
Further, a step-shaped mounting recess 5 is provided at a position adjacent to the boot molding groove 4 of the fixed mold 3.
A fixed injection member 6 is fitted into the bolt 7.
It is tightened and fixed by. The fixed side injection member 6 includes a nozzle abutting part 8 and a sprue 9 that extends in a tapered shape from the bottom surface of the abutting part 8 toward the mold joining surface.
is drilled.

At the lower end of the opening of the sprue 9, a sprue base 10 is provided which forms an arcuate shape together with a sprue base 16 of a movable injection member 15, which will be described later. Further, a gate groove 22 is formed between the sprue base 10 and the boot molding groove 4, and when the molds are matched, an annular space is formed by a movable gate groove 23, which will be described later. ing.

In addition, the gate groove 22 and the sprue base 10
A first convex portion 24 having a half circumference and projecting in a rectangular cross section is formed between the gate groove 22 and the boot forming groove 4, and a second convex portion having a half circumference and projecting in a trapezoidal cross section is formed between the gate groove 22 and the boot forming groove 4. A portion 25 is formed.

Further, a movable mold 12 is attached to the upper surface of the movable platen 11, and a boot molding groove 13 and a gate are provided on the mold joint surface of the movable mold 12 so as to face the boot molding groove 4 and the gate groove 22. A mounting recess 14 having a stepped shape at a position adjacent to the groove 23 and the molded groove 13
A movable injection member 15 is fitted into the movable injection member 15 and fixed by tightening with a bolt 7. Also,
Between the gate groove 23 and the sprue base 16 and between the gate groove 23 and the boot molding groove 13, there are a first protrusion 26 and a second protrusion half a circumference opposite to the first protrusion 24 and the second protrusion 25. A portion 27 is formed respectively.

The core 17 for forming the hollow part of the molded product is inserted into the boot molding groove 4 and the boot molding groove 13 during mold matching.
It is located in the center of the Further, since the core 17 has a long overall length, both ends are supported by both the movable mold 12 and the fixed mold 3 during shaping, thereby preventing the central portion of the core 17 from bending. A molded product (boot) is provided between the boot molding groove 4 and the boot molding groove 13 and the core 17.
A product cavity 18 is formed for molding both sprue bases 10, 16 and the core 1.
7, an annular sprue gap 19 is formed. A similarly annular gate portion 21 is formed between the sprue gap 19 and the product cavity portion 18.

In a portion adjacent to both ends of the gate portion 21, an annular constricted portion 28 with a reduced diameter is formed between the first convex portions 24, 26 and the center core 17, and the second convex portion 25, A stress concentration portion 29, which is also reduced in diameter, is formed between the core 17 and the stress concentration portion 29. The diameter of the constricted portion 28 is reduced to approximately half the product wall thickness, and the stress concentration portion 29 is tapered in diameter as it moves away from the gate portion 21, that is, toward the product cavity portion 18. It is narrowest at the end on the product cavity 18 side.

Next, the operation of the injection mold configured as above will be explained.

First, the core 17 is placed inside the movable mold 12 and the fixed mold 3 and the molds are clamped, and the injection nozzle is brought into contact with the nozzle contact portion 8 to inject the rubber material. After filling the sprue gap 19, the rubber material is injected into the product cavity 18 through the constriction section 28, gate section 21 and stress concentration section 29, and is vulcanized and hardened to form a molded product (boot).

At this time, the rubber material is once focused by the constriction part 28, passes through the gate part 21, and is focused again by the stress concentration 29, so that it preferentially rotates 180 degrees to the opposite side of the sprue 9 of the gate part 21. Since the rubber is injected into the product cavity 18 after filling, no welds due to rubber vulcanization occur in the molded part on the opposite side of the sprue 9 by 180 degrees. At this time, the molded product is still integrated with the rubber that has hardened within the constricted portion 28, gate portion 21, and stress concentration portion 29, as well as the rubber that has hardened within the sprue 9 and the sprue gap 19.

After removing the molded product from the mold, if you hold the molded product with one hand and pull on the sprue part of the molded product with the other hand, stress will be concentrated in the stress concentrated area and it will easily be cut from that part. .

Therefore, according to this embodiment, the injected rubber material is once converged at the constriction section 28, passes through the gate section 21, and is converged again at the stress concentration section 29, so that the flow of the material is caused to flow through the gate section 21. sprue 9
It flows preferentially to the opposite side of 180 degrees and then flows into the cavity 18. Therefore, welds due to vulcanization of the rubber do not occur in the molded part on the side 180° opposite to the sprue 9.

Further, since the gate portion 21 itself does not need to be formed long, the remaining gate portion of the molded product does not increase and the yield deteriorates. Further, the stress concentration portion 29 allows the product portion and the remaining portion of the molded product gate to be easily cut with bare hands.

Furthermore, the stress concentration section 29 and the converging section 28 can reduce the amount of rubber material required for molding the remaining part of the gate of the molded product, so that the yield of the rubber material can be improved.

Furthermore, since the injection members 6 and 15 are removably fixed to the molds 3 and 12 by the bolts 7, the parts can be taken out from the molds 3 and 12 independently during cleaning and maintenance of the gate part 21, resulting in improved efficiency. Can be cleaned or replaced.

Note that the present invention is not limited to the above embodiments, and may be embodied as follows, for example.

(1) The depth of the groove of the constricted portion 28 is different from that of this embodiment.
It may be partially changed. In this case, the aperture part 28
should be less than half of the product wall thickness.

(2) The distance between the narrowed portion 28 and the stress concentration portion 29 is not limited to that in the embodiment described above, and may be provided within the gate portion 21. However, the effect of preventing welding is high when this interval is made as far as possible.

(3) In addition to the CVJ boots of this embodiment, the present invention can be applied to molded products such as cylinder boots, rack and pinion boots, and boots other than automobiles.

Effects of the invention As detailed above, the present invention adjusts the flow of material injected into the product cavity, making it possible to prevent welds from occurring in the molded product due to material hardening, and to make the gate part longer. Since there is no need to form a layer, it is possible to reduce the material yield, which is an excellent effect.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing an injection mold embodying the present invention, Fig. 2 is a front sectional view of Fig. 1,
FIG. 3 is a side sectional view showing this injection mold with the mold opened. FIG. 4 is a sectional view showing a mold having a conventional ring gate structure with a bag, and FIG. 5 is a sectional view showing a mold without a conventional ring gate structure. Gate part...21, stress concentration part...29, sprue...9, product cavity part...18, constriction part...28, sprue gap...19.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. Injection molding tool for forming a rubber-like elastic body such as rubber or soft plastic, consisting of a fixed mold, a movable mold, and a core whose ends are supported by both molds. The mold includes an annular sprue gap 19 communicating with the sprue 9 space during mold clamping, an annular gate part 21 communicating with the sprue gap 19 via an annular constriction part 28, and the gate. An injection mold characterized in that a part 21 is formed with an annular product cavity part 18 that communicates with the part 21 through an annular stress concentration part 29 that tapers in diameter as it moves away from the gate part 12. . 2. Utility model registration claim 1, characterized in that the diameter of the constricted portion 28 is reduced to half the product wall thickness.
The injection mold described in Section 1.