JP2001129855A - Structure of gas injection part in mold for gas injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always stably perform expected gas injection molding by preventing the leakage of gas from a gas injection part in a mold for gas injection molding. SOLUTION: The outer peripheral surface of a gas injection nozzle 6 is bent in the axial direction of the nozzle by forming a stepped part 15 or recessed and projected parts 16, 17 to the outer peripheral surface of the gas injection nozzle 6 protruded into the molding cavity 1 of a mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection part structure of a mold in gas injection molding in which high-pressure nitrogen gas is injected after injection of a thermoplastic resin into a molding cavity.

[0002]

2. Description of the Related Art As is well known, gas injection molding (also referred to as gas-assisted injection molding) is performed by injecting a thermoplastic resin into a molding cavity (cavity) of a mold followed by high-pressure nitrogen gas. Injection molding is an injection molding method in which the pressure in the molding cavity is maintained, the molded product is made hollow, the occurrence of warpage, sink marks and the like of the molded product is prevented, and the weight of the molded product is reduced.

Conventionally, in the gas injection molding, there are a method of injecting a gas from a resin injection nozzle of an injection molding machine and a method of injecting a gas from a gas injection nozzle separately provided in a mold. FIG. 9 is a longitudinal sectional view of a mold showing the latter method. In the figure, reference numeral 1 denotes a molding cavity (cavity) formed by a fixed mold 2 and a movable mold 3; A boss forming portion having a truncated conical shape, and a gas injection nozzle 6 fixed so that the front end faces the boss forming portion. In the gas injection nozzle, as shown in FIG. 10, a conventional gas injection portion is enlarged, and a cylindrical core pin 9 is arranged so that a ventilation gap 8 is provided in a cylindrical sleeve 7. The nitrogen gas G is injected into the molding cavity 1 through the ventilation gap 8. R indicates the resin injected into the molding cavity 1 prior to the injection of the gas G.

By the way, in such a structure of the conventional gas injection portion, the nitrogen gas G injected into the molding cavity 1 is formed as shown in FIG.
As shown in FIG. 1, a gap g with the resin may be formed along the outer peripheral surface of the sleeve 7 due to the high pressure, and may leak out. As a result, it is difficult to control the gas pressure in the molded product, and the injected gas does not reach the end of the molding cavity. For example, sink marks are generated in the molded product, and quality cannot be maintained. there were.

In order to prevent this, conventionally, the boss forming portion 5 is used.
The height h of the boss was raised as high as about 6 to 8 mm. However, depending on the molded product, the boss may have to be cut after molding because the appearance is impaired or the shape is restricted. The cost may be high, and even if the protruding portion is protruded high, sufficient leakage cannot be prevented. In addition, when gas is supplied to compensate for the gas leakage, the gas consumption increases, and it takes time to inject the gas, so that there is a problem that the operation rate is reduced and productivity is deteriorated.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention is to prevent the above-described gas leakage from the gas injection portion and to always perform the desired gas injection molding stably.

[0007]

For this purpose, the gas injection part structure in the gas injection molding die according to the present invention has a step or irregularities formed on the outer peripheral surface of a gas injection nozzle projecting into the molding cavity of the die. By doing so, the outer peripheral surface of the nozzle is bent in the axial direction.
Further, the gas injection part structure in the gas injection molding die of the present invention is such that a diameter-increasing step is formed on the outer peripheral surface of the gas injection nozzle, and the step surface of the diameter-increasing step forms a molding surface of the molding cavity. The nozzle is set in a mold.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a gas injection portion in a gas injection molding die according to the present invention, wherein 1 is a molding cavity (cavity) formed by a fixed mold 2 and a movable mold 3 and 5 is extended into the molding cavity. The frusto-conical boss forming portion 6 is a gas injection nozzle fixed so that the front end faces into the molding cavity. The gas injection nozzle 6 is provided with a cylindrical sleeve 7 on a mounting substrate 11 fixed by bolts 10 on the outer surface of the movable mold 3 and 0.03
A cylindrical core pin 9 is inserted so as to have a ventilation gap 8 of about 0.1 mm, the core pin 9 is fixed by a spiral lid 12, and an air supply passage 13 communicating with the ventilation gap 8 is attached to a mounting substrate 11. The nitrogen gas G can be injected into the molding cavity 1 from the air supply port 14 at a high pressure of several hundred atmospheres. R indicates the resin injected into the molding cavity 1 prior to the injection of the nitrogen gas G.

In the gas injection nozzle 6 according to the present invention, the step 15 is formed on the outer peripheral surface of the sleeve 7 by rapidly increasing the outer diameter from the middle toward the base. Therefore, the outer peripheral surface of the nozzle is bent in the axial direction as shown in FIG.
Even when a gap g is formed between the resin and the resin along the outer peripheral surface to flow outward, the step portion 15 prevents the outflow. The height of the step 15 is desirably 0.5 mm or more to prevent gas outflow.

In another embodiment of the present invention shown in FIG. 2, a ring-shaped convex portion 16 having a height of 0.1 to 0.2 mm is formed on the outer peripheral surface of the sleeve 7 to form the outer peripheral surface of the nozzle. Is bent in the axial direction, and FIG.
In the embodiment shown in (1), the cross-sectional shape of the convex portion 16 is made wedge-shaped to facilitate mold opening. In addition, the embodiment shown in FIG.
By forming a ring-shaped concave portion 17 of about 0.2 mm, the outer peripheral surface of the nozzle is also bent in the axial direction. By forming such irregularities and bending the outer peripheral surface of the nozzle in the axial direction, the outflow of nitrogen gas can be prevented. In the embodiment shown in FIG. 5, the outer peripheral surface of the sleeve 7 is formed as a rough surface (uneven surface) so that the nitrogen gas is prevented from going straight and its outflow is prevented. The nozzle may be formed so as to be tapered toward the front end so as not to hinder the mold opening due to the formation of such irregularities.

On the other hand, the embodiment shown in FIG. 6 is the one described in claim 2 of the present application, and the gas injection nozzle 6
An enlarged diameter step 18 is formed on the outer peripheral surface of the sleeve 7, and the nozzle 6 is set in such a manner that the step surface 19 of the enlarged diameter step forms the molding surface of the molding cavity 1 (the end surface of the boss forming portion 5). It is set by type. This also makes it possible to prevent the nitrogen gas from going straight and preventing leakage. In addition, as shown in FIG. 7, by forming the step surface 19 of the enlarged diameter step portion 18 in a tapered shape toward the base direction, the nitrogen gas can be more effectively prevented from going straight.

Further, in the embodiment of the present invention shown in FIG. 8, a gas injection having a step 15 shown in FIG. In this case, a sufficient thickness is ensured by projecting the gas injection nozzle 6 from the rib forming base portion 22 of the molding cavity 1, and in this case, the boss is dared as in the above embodiment. It is not necessary to provide a formation part.

By providing the step portion 15 on the outer periphery of the gas injection nozzle 6 as in the above embodiment and further providing multiple irregularities and rough surfaces, it is possible to reliably prevent gas leakage as a synergistic effect. .

[0014]

As described above, according to the gas injection portion structure in the gas injection molding die according to the present invention, the nitrogen gas injected into the molding cavity can be prevented from leaking along the outer peripheral surface of the nozzle. In addition, the pressure of the injected gas can be easily controlled, and the quality of the molded product can be improved by improving the circumference of the injected gas. In addition, the gas consumption can be suppressed, the molding time can be shortened, and the productivity can be improved. In addition, there are various beneficial effects, such as eliminating the need for forming a high boss for gas injection in a molded product as in the related art.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a gas injection portion in a gas injection molding die according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 6 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 7 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of a gas injection section showing another embodiment of the present invention.

FIG. 9 is a longitudinal sectional view of a conventional gas injection molding die.

FIG. 10 is a longitudinal sectional view of a gas injection portion of a conventional gas injection molding die.

FIG. 11 is a longitudinal sectional view showing a pattern of gas leakage in the gas injection section of FIG. 10;

[Explanation of symbols]

 Reference Signs List 1 Molding cavity 2 Fixed mold 3 Movable mold 5 Boss forming part 6 Gas injection nozzle 7 Sleeve 8 Vent gap 9 Core pin 14 Air supply port 15 Step part 16 Convex part 17 Concave part 18 Large diameter step part 19 Step surface 22 Rib forming base G Nitrogen gas R resin

Claims (2)

[Claims] 1. An outer peripheral surface of a gas injection nozzle protruding into a molding cavity of a mold is formed with steps or irregularities so that the outer peripheral surface of the nozzle is bent in the axial direction. Of the gas injection part in the mold for gas injection molding. 2. A gas injection nozzle, wherein an enlarged diameter step is formed on an outer peripheral surface of the gas injection nozzle, and the nozzle is set in a mold such that a step surface of the enlarged diameter step forms a molding surface of a molding cavity. The gas injection part structure in the gas injection molding die characterized by the above.