JPS6019519A - Degassing in injection molding machine - Google Patents

Abstract

PURPOSE:To obtain a molded piece excellent in surface state and dimensional precision by a method wherein a looped runner part enclosing the entire circumference of the mold cavity and forming the intermediate portion of the runner is provided on the dividing surface of the mold and gas in the mold cavity is exhausted smoothly as the runner is charged with resin. CONSTITUTION:The fixed mold 12 and the movable mold 14 are provided at the closed position to provide the mold cavity 15 and simultaneously degassing is started by the vacuum pump 24 in the mold cavity 15. Under this state, the looped runner 20 enclosing the entire circumference of the mold cavity 15 is charged with molten resin, resin is supplied to the mold cavity 15 through the runner 17 and when the runner 25 is charged with molten resin, the dividing surface 16 between the mold cavity 15 and the external space is interrupted completely by said resin. Therefore, the suction force of the vacuum pump 24 acts effectively on the mold cavity 15, the air in the mold cavity 15, the volatile gas in the resin are absorbed and exhausted efficiently externally from the degassing passage 22.

Description

[Detailed description of the invention] The present invention relates to a method for degassing an injection molding machine.

In injection molding of synthetic resins, when a mold cavity is filled with molten resin, it is necessary to exhaust the air inside the mold cavity and the volatile gas of the resin to the outside using a gas vent pin inserted into the mold.

For example, in the case of injection molding of a molded product such as a gate ball, which requires constant surface condition and dimensional accuracy over the entire surface, there may be traces of degassing pins on the surface of the molded product. As a degassing method that does not cause this, a method is adopted in which degassing is performed from the dividing surface of a pair of molds that form a mold cavity.

However, when increasing the mold clamping accuracy of the dividing surface of the mold in order to improve the surface condition and dimensional accuracy of the molded product, gas venting from the dividing surface cannot be performed smoothly, and the molded product is exposed to gas bubbles. Curling defects occur frequently, and as a result, it becomes difficult to improve the surface condition and dimensional accuracy.

An object of the present invention is to provide a method for venting gas from an injection molding machine, which enables smooth venting of gas from the inside of a mold cavity, and which makes it possible to obtain a molded product with good surface condition and dimensional accuracy. do.

In order to achieve the above object, the method for degassing an injection molding machine according to the present invention includes forming a part of an annular runner that surrounds the entire circumference of the mold cavity and constitutes the middle part of the runner on the dividing surface of the mold, The runner is partially filled with molten resin, and the gas in the mold cavity is sucked out and discharged to the outside.

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a fixed mold 12 is fixed to a fixed part 11 of an injection molding machine, and a movable mold 14 is fixed to a movable part 13 of the injection molding machine.
is fixed. Both molds 12 and 14 are moved toward and away from each other between an open position (not shown) and a closed position shown in FIG. 1, so that a mold cavity 15 having a spherical shape, for example, can be formed in the closed position.

The mold cavity 15 also includes a fixed mold 12 and a runner 1 formed on a dividing surface 16 between the fixed mold 12 and the movable mold 14.
7, it is possible to fill with molten resin. Hot water path 1
7 is constituted by a continuous inflow part 18 formed in the fixed mold 12, a connection part 19 formed in the dividing surface 16, a runner part 20, and an outflow part 21. The runner part 20 has an annular shape that surrounds the entire periphery of the mold cavity 15, and constitutes an intermediate portion of the runner 17. Note that the outflow portion 21 of the runner 17 communicates with the mold cavity 15 at two positions in the diametrical direction of the mold cavity 15 through pin gates with minute diameters.

Further, in the mold cavity 15, there is provided a movable mold 14, a degassing passage 22 formed on the dividing surface 16 between the fixed mold 12 and the movable mold 14, and a suction pipe 23 connected to the degassing passage 22. The suction part 24 of the vacuum pump 24 is communicated through the suction part 24 of the vacuum pump 24. As shown in FIG. 2, the degassing passage 22 is provided through small-diameter openings as shown in FIG. It communicates with the mold cavity 15.

Next, the operation of the above embodiment will be explained.

The fixed mold 12 and the movable mold 14 are set to the closed position and the mold cavity 15 is formed, and at the same time, the vacuum pump 24 starts degassing the mold cavity 15.

Here, the vacuum pump 24 may be operated continuously even before both molds 12 and 14 are closed. In the above state, the molten resin flows into the mold cavity 1 through the runner 17.
When the runner portion 25 is filled with the molten resin, the dividing surface 16 between the mold cavity 15 and the external space is completely blocked by the filled resin. Therefore, the suction force of the vacuum pump 24 is effectively applied to the mold cavity 15.
The air inside the mold cavity 15 and the volatile gas of the resin are efficiently sucked and discharged from the gas vent passage 22 to the outside.

That is, according to the embodiment described above, even when the dividing surfaces 16 of both molds 12° 14 are clamped with high precision, it is possible to smoothly vent gas in the mold cavity 15, and the molded product is free from gas. It becomes possible to stably obtain molded products with good surface gloss, high dimensional accuracy, and reduced weld lines in a short molding cycle without causing blistering defects.

In addition, in the above embodiment, the case where the communication between the outflow part 21 of the runner 17 and the mold cavity 15 and the communication between the degassing passage 22 and the mold cavity 15 are formed at the dividing surface 16 has been described. . However, the above-mentioned communication is not necessarily performed at the dividing plane, but may be performed at any position relative to the mold cavity.

As described above, in the method for degassing an injection molding machine according to the present invention, a part of the annular runner constituting the intermediate part of the runner that surrounds the entire circumference of the mold cavity is formed on the dividing surface of both molds, and The runner is partially filled with molten resin, and the gas in the mold cavity is sucked out and discharged to the outside. therefore,
It is possible to smoothly vent gas from inside the mold cavity, and it is possible to obtain a molded product with good surface condition and dimensional accuracy in a short molding cycle.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway piping system diagram showing an embodiment of the present invention, Fig. 2 is a view taken along the line ■-■ in Fig. 1, and Fig. 3 shows the main parts of Fig. 1. FIG. 3 is an enlarged cross-sectional view. 12. Fixed mold 514-movable mold, 15 mold cavity, 16.
...Divided surface, 17 - Runway, 20 - Part of runner, 22 - Gas vent passage. Patent applicant: Sekisui Chemical Co., Ltd. Representative: Motoi Fujinuma

Claims (1)

[Claims] (1) In a degassing method for an injection molding machine in which a mold cavity formed by a pair of molds is filled with molten resin through a runner, a runner is placed on the dividing surface of both molds, surrounding the entire periphery of the mold cavity. An injection molding machine, characterized in that a part of the annular runner forming the middle part of the mold cavity is formed, and gas in the mold cavity is sucked and discharged to the outside while the part of the runner is filled with molten resin. How to release gas.