JPH0976273A - Hollow product-molding tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow product-molding tool not to generate a useless thick part. SOLUTION: Resin material in a molten fluid state is introduced into a cavity 1a in a tool from a resin gate 2, pressurized gas is injected into the resin material from a gas injection hole 3, and the resin material is made thin while the resin material is being pressed against an inner surface of the tool by gas pressure. A movable core 6 is arranged at a tip part of the resin flowing in the cavity 1a, and the movable core 6 is connected to a constant load generator 8 via a joint shaft 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for molding hollow articles, and more particularly to a mold for forming pipes and ducts for circulating gas and liquid used in an engine room, a resonator for silencing, etc. in the automobile industry. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow product molding die, which is applicable to, in other general industrial fields, pipes, ducts, handles, shafts, suction ports of pumps, hollowing of casings having thick portions, and the like.

[0002]

2. Description of the Related Art A gas assist injection molding method, for example, is known as a method of manufacturing a hollow tube or a hollow curved tube having a complicated shape used for an automobile engine or the like from a resin material. This gas-assisted injection molding method refers to "injecting a resin material in a molten and fluid state into a cavity in a mold, then injecting a pressurized gas into this resin material, and directing the resin material toward the inner surface of the mold by gas pressure. And pressing to reduce the wall thickness to produce a tubular body having a predetermined shape. ”

When a tubular hollow article P having a shape as shown in FIG. 3A is formed by this gas assisted injection molding method, a cavity 1 is provided in a mold as shown in FIG. When a molten resin material is injected from the resin gate 2 into the cavity 1 and an inert gas is injected from the gas injection port 3 when the resin injected from the resin gate 2 reaches several tens% of the internal volume of the cavity 1. Since the injected inert gas flows selectively in a portion where the melt viscosity of the resin is low, a hollow portion 4 is formed in the center of the tubular molded product, and the inert gas fills the cavity while further stretching the resin material. I do. Then, when the resin is solidified after a predetermined cooling time, the gas held at a constant pressure is discharged from the injection port 3 to the outside of the mold.

[0004] Thereafter, necessary machining is performed on the tubular molded product taken out of the mold to obtain a tubular hollow product having a shape as shown in FIG.

[0005]

However, in the conventional gas-assisted injection molding method, pipe-shaped products in which the ratio (L / D) of the length (L) to the inner diameter (D) of the molded product is 10 or more are compared. Good, but L / D is 2
When a hollow molded product having a relatively small size of 6 is attempted to be molded, as shown in FIG. 3 (b), the resin previously injected into the cavity remains at the flow front end portion and is thicker than the radial direction. The part 5 is formed at the tip. As a result of the formation of such a thick wall portion, "the extra resin material is required, which leads to an increase in material cost.
The time required for solidification increases. Since the shrinkage rate of the resin locally increases, the dimensions are not stable, and sink marks, warps, etc. are likely to occur. Since there are few hollow parts, the amount of machining is large and the machining becomes complicated. And so on.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is L /
An object of the present invention is to provide a hollow product molding die that does not generate an unnecessary thick portion even when D is relatively small.

[0007]

In order to achieve the above object, the present invention is to inject a pressurized gas into a resin material in a molten and fluid state introduced into a cavity in a mold, and press the resin material by a gas pressure. In a hollow product molding die for obtaining a hollow product by pressing it toward the inner surface of a mold to obtain a hollow product, a movable core is arranged at the tip of a resin flowing in a cavity, and the movable core is used as a constant load generator. It is characterized by being connected.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, L / D is 4 to
In the mold for molding the hollow molded article of No. 5, the movable core 6 is arranged at the tip of the fluidized resin where the thick wall portion is easily formed, and the movable core 6 is provided with the constant load generating device 8 via the joint shaft 7.
Connect to The constant load generator is movable while the movable core 6 operates in the direction of the arrow (between the A position and the B position) while opposing the resin pressure and the gas pressure with a resistance of an appropriate amount. The method is not particularly limited as long as it functions so as not to hinder the smooth operation of the expression core 6.
For example, a spring, a damper, a hydraulic cylinder, an air cylinder or the like can be used. FIG. 1 shows an example in which the constant load generating device 8 is a hydraulic cylinder and the joint shaft 7 is moved by hydraulic pressure.

In a mold having such a structure, molten resin corresponding to 20 to 40% of the volume of the cavity 1a is passed through a nozzle of an injection molding machine (not shown), a runner 9 and a cavity of a resin gate 2. After injecting into 1a, when the inert gas (N ₂ gas) pressurized to 30 to 150 kg / cm ² is injected from the gas inlet 3, the resin previously entered into the cavity 1a is expanded by the gas pressure. The hollow portion 4a is formed. When the resin flow front end reaches the movable core 6, the movable core 6 starts to retreat due to the resin pressure and the gas pressure (FIG. 1 shows the movable core 6 moved to the terminal position). When the gas is further supplied from the gas injection port 3, the resin flow front end is thinly stretched along the inner surface of the mold while following the movement of the movable core 6, as if the cavity volume was expanded. Finally, in the resin reservoir 10 as well, as in the case of the other uniform hollow portion 4a
It is possible to obtain a thin-walled pipe-shaped molded product having a substantially uniform thickness as a whole.

FIG. 2 shows another embodiment, similar to the above,
A molten resin corresponding to 20 to 40% of the volume of the cavity 1 in FIG. 2A is injected from the resin gate 2 into the cavity 1 and then pressurized from the gas inlet 3 to 30 to 150 kg / cm ² inert When the gas (N ₂ gas) is injected, the resin is thinly stretched while forming the hollow portion 4, the movable core 6 is pressed by the flow front end portion of the resin and moves to the left, and further the gas is injected from the gas injection port 3. 2b in the end,
As shown in (3), a thin pipe-shaped molded product having a uniform hollow portion in the resin reservoir portion 10 as well as other portions and having a substantially uniform thickness as a whole could be obtained.

The resin used in the present invention is a resin called thermoplastic engineering plastic,
For example, polyacetal, polycarbonate, polyamide, polyphenylene sulfide, a simple substance of resin such as polyester and a blend or alloy thereof,
For example, those reinforced with glass fiber or carbon fiber.

As is clear from the above description, the mold of the present invention has the movable core in the portion where the thick portion is formed by the conventional molding method, and the movable core expands the cavity volume. Since it performs the same function as described above, it is possible to mold a tubular product with an almost uniform thickness as a whole without producing a locally thickened portion. Hollow products can be obtained.

[0013]

Since the present invention is configured as described above, the following effects can be obtained. Since the inside of the resin reservoir is hollow and a hollow product having a substantially uniform thickness as a whole can be obtained, an extra resin material is not required and the cooling / solidifying time can be shortened.

Sinks, warps and the like are less likely to occur. After molding, a hollow product can be obtained simply by removing the resin reservoir, which reduces the number of machining steps.

[Brief description of drawings]

FIG. 1 is a side sectional view of an embodiment of a hollow product molding die of the present invention.

FIG. 2 (a) is a side sectional view showing a state before the movable core of another embodiment of the hollow article molding die of the present invention is operated,
FIG. 2B is a side sectional view showing a state when the movable core moves to the terminal end in FIG. 2A.

FIG. 3A is a sectional view of one embodiment of a hollow molded product.
FIG. 3B is a diagram illustrating a method of forming the hollow article.

[Explanation of symbols]

 1, 1a ... Cavity 2 ... Resin gate 3 ... Gas injection port 4, 4a ... Hollow part 5 ... Thick part 6 ... Movable core 7 ... Joint shaft 8 ... Constant load generator 9 ... Runner 10 ... Resin pool P ... Tubular hollow product

Claims (1)

[Claims] 1. A hollow product is obtained by injecting a pressurized gas into a resin material in a molten and fluid state introduced into a cavity in a mold and thinning the resin material while pressing the resin material toward the inner surface of the mold by gas pressure. In the obtained hollow product molding die, a movable core is arranged at the tip of a resin flowing in the cavity, and the movable core is connected to a constant load generating device.