JPS6013622Y2 - injection mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection mold, and particularly to an injection mold in which at least a portion of the side surface of the core is knurled.

Weld lines, gas burns, etc. on plastic external parts such as knobs used in audio equipment such as radios and stereos significantly deteriorate not only the appearance but also the value of the set and destroy the value of the product.

A detailed investigation of the filling of molding material into the mold and the occurrence of weld lines revealed the following.

During the resin filling process, due to differences in the thickness (gap) of the resin flow path, filling may be partially delayed or proceed too far, resulting in unevenness on the filling tip line.

In the entire process until filling is completed, for example, the first
As shown in the figure, when the flow front lines 101 are connected while leaving an unfilled portion 100, a ξ weld line 102 is always generated.

As a means to prevent the occurrence of weld lines, increasing the temperature of the resin material and the temperature of the mold, and increasing the injection speed and injection pressure of the resin material are carried out.

However, this would rather emphasize the reweld line that caused the gas burn.

Slowing the injection speed of the resin material may prevent gas burns, but will further accentuate the weld lines.

The part where air is forced into the cavity (unfilled part 1)
It is also possible to bush a pin into the cavity or core of 00) to allow air to escape from the gap between the pin and the mold, but this is not practical as the gap gets clogged during molding and the air removal effect is lost.

An object of the present invention is to provide an injection mold having a structure that can reduce the occurrence of weld lines.

The present invention will be described in detail below based on examples.

As shown in FIGS. 2a and 2b, the mold 1 of the present invention has a knurling 111 carved in at least a portion of the side surface 110 of the core portion 11 thereof.

The knurling 111 may be carved at a pitch of 0.5 mm using a cutting tool having a tip angle of 120°, for example.

It is important that the bottom tip of the knurl is sharp.

If the tip is not sharp or the tip angle is extremely large, the resin material may fill up to the tip, which is not preferable.

As shown in FIG. 3, in the process of filling the cavity 2 with the molten resin material 3, the molten resin material 3 does not completely fill the knurling 111, and there is a gap 112 between them.
exists.

Air 4 in the cavity space, which is forced in by the intrusion of the molten resin material 3 into the cavity space 2, flows out of the cavity through this gap 112.

Since the air flows out, it is possible to increase the injection speed, and as a result, the occurrence of weld lines can be reduced.

Fortunately, resin flowing along the knurled side 111 tends to lag somewhat behind the non-knurled side 113 due to its flow resistance.

Therefore, the air 4 is rather trapped in the molten resin material on the knurl 111 side, and as a result, the air flows out from the gap 112 more easily.

Note that the knurling 111 can eventually be pressurized and completely filled with the resin material.

In this way, an approximately cylindrical or cup-shaped injection molded product, such as a knob used in audio equipment, can be obtained with reduced weld lines.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram explaining how weld lines occur in injection molding using a conventional mold, Fig. 2a is a front cross-sectional view of an embodiment of the mold of the present invention, and Fig. 2 is a main FIG. 3 is a perspective view of one embodiment of the core portion of the mold according to the invention, and FIG. 3 is an explanatory plan view illustrating the flow state of the molten resin material within the cavity space thereof. 1... Injection mold of the present invention, 2...
・Cavity, 3...Resin material, 4...
・Cavity space air, 11...Core part, 1
10...Core side, 111...Knurling, 113...Non-knurling side.

Claims (1)

[Scope of utility model registration request] It has a cavity space for obtaining a substantially cylindrical or cup-shaped injection molded product, and a knurling is carved on at least a part of the side surface of the core that forms the inner surface of the molded product and forms the cavity space. Mold for injection molding.