JPH0724878A - Injection mold - Google Patents

Abstract

(57) [Summary] [Structure] Above the cavity 1 of the injection mold, a runner 2 is provided along the cavity 1 through which a molten resin is injected through a resin injection path 3, and a film gate 4 is provided. The runner 2 and the cavity 1 are communicated with each other via. The shape of the film gate 4 was made to gradually increase as the cross-sectional area along the resin flow direction in the film gate 4 moved away from the resin injection path 3, and the flow path resistance to the resin flow was reduced. [Effect] The resin does not spread to the end portion 1b of the cavity 1 and no deformation occurs. Further, since it is not necessary to increase the resin injection pressure from the resin injection passage 3 into the runner 2, a weld line does not occur near the central portion 1a of the cavity 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold for injecting a molten resin from a film gate into a cavity.

[0002]

2. Description of the Related Art For example, when a relatively large molded product such as a resin bumper for an automobile having a relatively small thickness in the longitudinal direction is injection-molded, an injection mold is used. If the resin is injected into the cavity from one place, the resin is not sufficiently filled up to the end of the cavity and a deformation occurs. If the resin is injected from a plurality of places, a weld line is formed on the bumper surface. Therefore, a runner is provided along the cavity, the runner and the cavity are connected by a substantially slit-shaped film gate, the resin is injected into the cavity from the film gate in a film shape, and the entire area of the cavity is filled with the resin. Things are known, for example, from Japanese Utility Model Publication No. 5-3291.

[0003]

SUMMARY OF THE INVENTION In the above conventional one,
In some cases, the film gate cannot be provided over the entire length of the cavity due to the restriction of the shape of the injection molded product and the improvement of the yield of the resin material. In this case, the resin injected from the end of the film gate must move to the end of the cavity. However, the pressure of the resin injected into the runner through the resin injection path drops while flowing toward the end inside the runner, and the injection pressure of the resin decreases when the resin is injected from the end of the film gate. However, it may not reach the end of the cavity and deform may occur. On the other hand, if the injection pressure from the resin injection path to the runner is increased, the injection pressure from the end of the film gate can be increased, but the injection pressure from the central part of the film gate near the resin injection port increases. Then, the flow of the resin in the cavity may be disturbed and a weld line may be generated.

Therefore, in view of the above problems, the present invention provides an injection molding die capable of reliably reaching the resin to the end of the cavity without increasing the resin injection pressure to the runner. To aim.

[0005]

In order to achieve the above object, the present invention provides a cavity of an injection molding die and a runner which is provided along the cavity and in which a molten resin is injected through a resin injection passage. In the injection molding die provided with a film gate serving as a resin passage from the runner to the cavity, the cross-sectional area of the film gate perpendicular to the longitudinal direction is gradually increased along the runner as the distance from the resin injection passage increases. And

[0006]

Function: The cross-sectional area of the film gate along the resin flow method is increased to reduce the pressure loss as the distance from the resin injection path increases, and the injection pressure at the end of the film gate where the decrease in injection pressure becomes a problem The injection pressure in the part is increased without increasing it to allow the resin to reach the end of the cavity.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes a cavity of a mold for injection molding a bumper for an automobile, and a runner 2 is provided above the cavity 1 along the cavity 1. A molten resin is injected into the runner 2 from an injection molding machine (not shown) through a resin injection path 3. The resin injection path 3 opens at the center of the runner 2, and a slit-shaped film gate 4 is provided on the lower surface of the runner 2 over the entire length of the runner 2, and the runner 2 and the cavity 1 are connected via the film gate 4. Are communicated.

The shape of the film gate 4 will be described with reference to FIG. 2. In order to increase the injection speed of the resin into the cavity 1 of the film gate 4, the slit width of the opening 41 on the cavity 1 side is set to the runner 2 side. Is narrower than the slit width of the opening 42. In this embodiment, the opening 41 is continuously widened from the central portion 41a toward both end portions 41b, and the cross-sectional area along the resin flow direction in the film gate 4 is increased as the distance from the resin injection path 3 increases. The flow path resistance was gradually increased. As a result, the injection pressure from both end portions 41b rises, and the resin does not spread to the end portion 1b of the cavity 1 and no deformation occurs. Further, since the resin injection pressure from the resin injection passage 3 into the runner 2 may be kept as it is, the injection pressure from the central portion 41a of the opening 41 does not rise more than necessary, and the injection pressure is close to the central portion 1a of the cavity 1. Weld line does not occur.

The present invention is not limited to that shown in FIG. 2, but as shown in FIG. 3, the opening 42 on the runner 2 side of the film gate 4 is formed from the central portion 42a to both end portions 42b.
The opening width may be gradually increased toward, or, as shown in FIG.
42, from the central portions 41a and 42a to both end portions 4
The opening width may be gradually increased toward 1b and 42b.

By the way, in each of the above-described embodiments, the shape of the runner 2 has a constant cross-sectional shape perpendicular to the longitudinal direction.
As shown in FIG. 5, the runner 2 has a central portion 2a and both end portions 2b.
Alternatively, the cross-sectional shape may be reduced toward. With this structure, as the resin flows through the runner 2 to both ends 2b, the flow path is narrowed to increase its speed, and the both ends 41 of the opening 41 of the film gate are increased.
The injection speed from b can be further increased.

[0011]

As is apparent from the above description, the present invention can increase the injection pressure from both ends of the film gate without increasing the resin injection pressure from the resin injection passage to the runner. It is possible to prevent deformation at both ends of the cavity without forming a weld line in the central portion of the cavity.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a part to which the present invention is applied.

FIG. 2 is a sectional view taken along the line II-II showing the configuration of the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a second embodiment.

FIG. 4 is a diagram showing a configuration of a third embodiment.

FIG. 5 is a diagram showing a configuration of a fourth embodiment.

[Explanation of symbols]

 1 cavity 2 runner 3 resin injection path 4 film gate

Claims (1)

[Claims] 1. A film serving as a resin passage from the runner to the cavity, which connects a cavity of an injection molding die and a runner provided along the cavity and injecting a molten resin through a resin injection passage. An injection molding die having a gate, wherein a cross-sectional area of a film gate at a right angle in a longitudinal direction is gradually increased along a runner as the distance from the resin injection path increases.