JPS58122835A - Mold for injection molding - Google Patents

Abstract

PURPOSE:To completely prevent the occurrence of sink and warping by a method in which an ejector pin is matched with the face of molds again at the completion of injection, and resin trapped at the tip of the ejector pin is pushed into the cavity. CONSTITUTION:When injection molding is made and a gata 9 is sealed up by resin cooled, the pressure of the resin becomes a fixed one. At the stage, the inside of the cavity is gradually cooled and the molten resin is also cooled, whereupon the volume of the resin begins to shrink but an ejector pin 11 is pushed back again by the force of a spring 14 to become matched with the mold face 3a. Accordingly, the resin trapped inbetween the ejector pin 11 and a through hole 3b formed in a movable side mold plate is again pushed back to the cavity 3. Thus, compensation is made for the shrinkage of molten resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection mold, and particularly to an injection mold that can prevent phenomena such as sink marks caused by resin shrinkage.

In general, in an injection mold, after the heated plasticized resin is filled into the cavity, the molded product contracts due to the internal contraction of the resin filled in the cavity as the resin is cooled and solidified. The resin is replenished until the gate is sealed.

In order to make it easier to replenish this resin, it would be better to increase the thickness (size) of the gate, but considering the appearance of the molded product and the post-finishing (gate cutting) of the gate, the size of the gate should be increased. Especially in thick injection molded products, even after the gate is sealed, the cooling and assimilation of the resin inside the cavity is not yet completed, resulting in volumetric shrinkage inside the mold, which can lead to sinkage. As a result, many defective products such as warping or sink marks occur, and the precision of molded products decreases, making it extremely difficult to mold thick injection molded products. Ta.

The present invention provides an injection mold that prevents the occurrence of sink marks and warpage during molding as described above.

That is, in the present invention, the ejector bin is retracted by the injection molding pressure during resin molding, and when the injection is completed, that is, the pressure inside the mold has decreased, the ejector bin is brought into alignment with the mold surface again by the biasing pressure. The resin accumulated at the tip of the bottle is forced into the cavity to compensate for shrinkage, thereby achieving the above object.

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

FIG. 1 shows a cross section of a main part of an injection mold according to the present invention. In FIG. 5
A movable side mold plate attached via the two mold plates 1,
A cavity 6 of the required molded product shape is formed on the parting surface of 3.
is formed, and communicates with a runner 8 and a gate 9 formed on the above-mentioned parting surface via a sprue 7 formed through the fixed side mounting plate 2 and the mold plate 1. The movable side template 3 is penetrated through the insertion hole 3b formed therein, and its tip is inserted into the mold surface 3a of the movable side template 3.
An ejector bin 11 is provided whose rear end is held by the first ejector plate 10. The rear end surface of this ejector bin 11 has 7 langes 1.
1a is provided, and when both mold plates 1 and 3 are clamped,
The flange 11 of the first ejector plate 10 is
a is engaged so that the tip of the ejector bin 11 is aligned with the mold surface 3a of the movable mold 3.

Further, a second ejector plate 12 is stacked on the rear end surface of the first ejector plate 10, and the second ejector plate 12 is located on the rear end surface of the seven flange 11a and accommodates the second ejector plate 12. A void 12a is formed for this purpose. . fP An adjustment screw 13 is screwed into this gap 12a, with its tip head 13a facing the rear end surface of the flange 11a, and
A compression coil spring 14 is interposed between the adjustment screw 13 and the flange 11a, and presses the rear end surface of the seven flange 11a, thereby urging the tip of the ejector bin 11 to always align with the mold surface 3a. .

Therefore, the molten resin injected from the injection molding head (not shown) passes through the sprue 7, runner 8, and gate 9 and is filled into the cavity 6. Due to this injection pressure, the ejector bin 11 is moved under the biasing pressure of the spring 14. This ejector bin 11 retreats against the
This means that a surplus of molten resin corresponding to the volume d formed between the tip end of the hole 3b and the insertion hole 3b is taken in. Injection is carried out in this way, and when the gate 9 is sealed by cooling the resin, the resin pressure remains constant, and at this stage, the inside of the cavity is gradually cooled and melted.
l! @4 The cooling of the fat and the volumetric contraction begin along with this, but at this stage the ejector bin 11 is closed to the spring 1.
The resin accumulated between the ejector bin 11 and the insertion hole 3b formed in the movable mold plate is pushed back into the cavity 3 again by the urging pressure of 4. This compensates for the shrinkage of the molten resin.

The spring pressure of the coil spring 14 is lower than the injection pressure of the molten resin to be injected, but higher than the pressure inside the cavity after the gate is sealed, that is, the pressure inside the cavity at a stage where the resin has not yet been completely cooled and solidified. The distance between the tip head 13a of the adjustment screw 13 and the rear end of the 7 flange 11a of the ejector bin 11 is set to be equal to the volume d taking into account the shrinkage of the resin supplied into the cavity. It is set to be.

Further, FIG. 3 shows another embodiment of the present invention, and the same parts as above are given the same reference numerals and the explanation thereof will be omitted.

A flange 20a is formed at the rear end of the ejector bin 20 to engage with the first rainbow J-type plate 10 and restrict its protruding position, and the second ejector plate 12' is mounted on the movable side. It is provided exposed at the rear of the plate 4. And this ejector plate 12-
A hydraulic cylinder 21 is embedded in the flange 20a so as to face the rear end surface of the flange 20a, and its plunger 21a is in opposing contact with the rear end surface of the seven flange 20a.

Therefore, in this example, the ejector bin 20 is moved backward by the injection pressure against the hydraulic pressure of the hydraulic cylinder 21, and the excess resin is taken in between the tip of the ejector bin 20 and its insertion hole. Goo 1 - After being cut, the mold surface 3 is cut again by driving the hydraulic cylinder 21.
It protrudes above a, thereby compensating for the shrinkage of the resin.

In each of the above embodiments, even if the shape of the molded product is complex and it is difficult to apply holding pressure at a position away from the gate part, if the setting position of the ejector bin is provided in accordance with the position, this can be done. It can be highly effective in preventing sink marks and warping in areas where it is difficult to apply pressure.

As explained above with reference to the embodiments, the injection mold according to the present invention is constructed as described above so that the ejector bin is retracted by an amount corresponding to the volumetric shrinkage of the resin, and the excess resin is removed from the cavity. This system is designed to compensate for shrinkage by moving the ejector bin forward, which not only prevents sink marks and warpage, especially in thick-walled molded products, but also improves molding accuracy. There is no need to increase the size of the gate, and the subsequent gate cutting process is simplified, and the appearance can be improved accordingly.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part of an injection molding die according to the present invention, FIG. FIG. 7 is a cross-sectional view of a main part of a mold showing another example. 1...Fixed side template 3...Movable side template 11.20...Ejector bin 10...
・First ejector plate 14...Compression coil spring 21...Hydraulic cylinder Patent applicant Tateishi Electric Co., Ltd. Fig. I No. 2X No.

Claims (1)

[Claims] (1) A stationary mold plate, a movable mold plate, a cavity formed on the parting surface of both mold plates, and a cavity formed on the parting surface of both mold plates, and a cavity formed on the parting surface of both mold plates, passing through the movable mold plate and aligning its tip with the mold surface. In an injection mold comprising an ejector bin that protrudes into the cavity when the mold is opened, the ejector bin is slidably held at the rear of the ejector bin, and
A first ejector plate that restricts the protruding position of the ejector bin when both mold plates are engaged; A second ejector plate is provided in the gap between the second ejector plate, and the ejector bin is always urged toward the mold surface side, and is compressively deformed by the injection molding pressure during resin molding. An injection molding mold, characterized in that it is provided with a biasing means for recessing the ejector bin from the mold surface and compressing and recovering the ejector bin after injection to urge the ejector bin to conform to the mold surface.