JPH10193404A - Mold for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the loss of material, the curing occurrence at the runner, and clogging of the gate, and thus lessen the occurrence of nonconforming articles by setting a secondary nozzle to be in contact with the cavity and be open and closed by a needle valve in an injection mold used for millable rubber. SOLUTION: There is provided a secondary nozzle 6 having a needle valve 5 in the gate 4 for introducing material to a cavity 3 defined between a movable mold 1 and a stationary mold 2, and a gate core 7 of the secondary nozzle 6 foundation is cooled outside thereof by a coolant such as water so as to preclude the cross-linking of material from preceding in the interior of the secondary nozzle. Besides, opening and closing operation is conducted by controlling a shut-off pin 8 connected to the needle valve 5 via the action of a hydraulic cylinder 9. Herein, an air cylinder may be employed for such hydraulic cylinder. For example, millable rubber heated to about 60 deg.C at an injection pressure of 20-100kg/cm<2> is introduced into the cavity via the gate 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an injection mold suitable for a millable rubber.

[0002]

2. Description of the Related Art A kneadable crosslinkable rubber composition, that is, a kneadable crosslinkable rubber composition that can obtain fluidity when heated in a solid state at room temperature and hardens when the crosslink temperature is reached, is used for packing of various connectors, It is used as a raw material for forming grommets and plug caps.

FIG. 5 shows a model diagram of a conventionally used injection mold for a millable type rubber. The raw material of the millable type rubber is heated so as to have an appropriate fluidity, and is supplied from a nozzle (not shown) of the injection molding machine to the fixed mounting plate 5 shown in FIG.
The cavity 58 is filled from the sprue bush portion provided in the first through the sprue 53 of the runner plate 52, through the runner 56 and the gate 57 formed by the fixed mold 54 and the movable mold 55.

The fixed mold 54 and the movable mold 55 are heated during molding by a built-in cartridge heater 59,
The cross-linking reaction of the millable type rubber inside the cavity 58 proceeds. The product obtained by curing as a result of the crosslinking reaction is taken out by opening the movable mold together with the portion cured by the runner 56 and the gate 57.

The movable mold 54 and the runner plate 52
Between the movable mold 54 and the runner plate 52 to prevent the transfer of heat, and the runner plate 52 has a cooling mechanism 61 so that the heat insulating plate cannot be completely shut off and the runner plate Remove the heat transferred to 52,
The cross-linking reaction of the millable type rubber in the spool is prevented from proceeding, thereby preventing the occurrence of clogging in the runners and gates and the deterioration of product quality.

[0006] Such a mold has the following disadvantages. That is, since the millable type rubber present in the runner 56 and the gate 57 at the time of molding undergoes a crosslinking reaction,
The material is wasted, and it is necessary to remove the hardened material in this part when opening the mold. However, if this removal is to be automated, the equipment cost will increase, and if it is to be removed manually, the labor cost will be increased. Is required. Further, heat is also conducted to the sprue in the runner plate 52, so that the cross-linking reaction of the raw material existing in this portion proceeds, so-called "mamako" is generated, which causes gate clogging,
This will increase the reject rate.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks, that is, it prevents waste of raw materials, occurrence of curing in a runner and gate clogging, and excellent injection with less occurrence of defective products. An object of the present invention is to provide a mold for molding.

[0008]

According to a first aspect of the present invention, there is provided a mold for injection molding used for performing injection molding using a millable rubber as a raw material. And a secondary nozzle which is in contact with the cavity and is opened and closed by a needle valve.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a secondary nozzle is a nozzle connected to a runner for introducing a millable type rubber injected into a mold from a nozzle (primary nozzle) of an injection molding machine into a cavity. It is necessary that this secondary nozzle is in direct contact with the cavity formed during mold clamping. If there is a distance between the cavity and the secondary nozzle, the millable type rubber is cured at that portion, so that the effects of the present invention cannot be obtained. The secondary nozzle needs to have a needle valve. In other words, if there is no needle valve, uncured millable rubber will stay at the nozzle outlet (gate),
The effect of the present invention cannot be obtained.

It is desirable that the base of the secondary nozzle be cooled. By this cooling, the needle valve can be indirectly cooled and the millable rubber inside the secondary nozzle can also be cooled, so that the hardening of the rubber inside the secondary nozzle can be completely prevented.

A specific example of the embodiment of the injection mold according to the present invention will be described with reference to the drawings. That is, FIG. 1 is a model diagram showing a cross section of an example of the injection mold according to the present invention. A needle valve 5 is provided at a gate 4 for introducing a raw material into a cavity 3 formed by the movable mold 1 and the fixed mold 2.
Is provided, and the gate core 7 at the base of the secondary nozzle 6 is cooled from the outside with a refrigerant (water in this example) to prevent the progress of the crosslinking reaction of the raw material inside the secondary nozzle. The opening and closing of the secondary nozzle 6 is performed by controlling a shut-off pin 8 connected to the needle valve 5 by a hydraulic cylinder 9. Note that a pneumatic cylinder may be used instead of the hydraulic cylinder.

The molding method using this mold will be described in detail with reference to FIGS. First, the needle valve 5 connected to the shut-off pin 8 is retracted to the rear of the nozzle by controlling the hydraulic cylinder 9, and at the same time, the injection pressure 20 to
The millable type rubber 11 heated to about 60 ° C. at 100 kg / cm ² is introduced into the cavity via the gate 4 (see FIG. 2). At this time, the needle valve 5
Is indirectly cooled by the refrigerant.

Thereafter, the hydraulic cylinder 9 is controlled again to return the needle valve 5 and the gate section 4 is closed. At this time, the millable type rubber in the cavity is heated to 150 to 190 ° C. by the heaters incorporated in the movable mold 1 and the fixed mold 2 and hardened after 120 to 240 seconds to form the product 12 (see FIG. 3). At this time, since the temperature of the needle valve 5 is lowered as described above, the heat of the mold is less likely to be transmitted to the millable rubber inside the nozzle portion 6, and the crosslinking reaction of these rubbers in the nozzle portion 6 proceeds. As a result, obstacles such as clogging of the gate and deterioration of product quality are prevented.

Next, the movable mold 1 moves and is opened.
The product 12 is removed from the fixed mold by a product removal mechanism (not shown) (see FIG. 4). As described above, since there is no runner in the portion to be heated, no cured product is generated inside the runner, so that the removal step is not required and the raw material is not wasted.

[0015]

The use of the injection mold according to the present invention can prevent inadvertent curing of the raw material millable rubber,
It is possible to prevent a decrease in productivity and a decrease in quality due to the gate clogging. Further, since no hardening occurs in the runner portion, waste of raw materials or labor and equipment for removing the hardened product are not required.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a cross section of an example of an injection mold according to the present invention.

FIG. 2 is a model diagram showing a first step (at the time of material injection) of a molding method using the mold of FIG.

FIG. 3 is a model diagram showing a second step (at the time of crosslinking) of a molding method using the mold of FIG. 1;

FIG. 4 is a model diagram showing a third step (at the time of product removal) of a molding method using the mold of FIG. 1;

FIG. 5 is a model diagram showing a cross section of a conventional millable type rubber injection mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Movable type 2 Fixed type 3 Cavity 4 Gate part 5 Needle valve 6 Secondary nozzle 7 Gate core 8 Shut-off pin 9 Hydraulic cylinder 10 Runner part 11 Millable type rubber 12 Product

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Motohisa Murakami 206-1 Nunobikihara, Haibara-cho, Haibara-gun, Shizuoka Prefecture Yazaki Parts Co., Ltd.

Claims (2)

[Claims] 1. An injection mold for use in injection molding using a millable rubber as a raw material, comprising a secondary nozzle which is in contact with a cavity and is opened and closed by a needle valve. Type. 2. The injection mold according to claim 1, wherein a base of the secondary nozzle is cooled.