JPS5824262B2 - plastic mold equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic molding device, and aims to reduce gate residue and improve molding accuracy.

Fig. 4 shows a gear a molded using a conventional molding device, and shows a chevron-shaped gate remaining b at the gate position.
was occurring.

In the case of a gear, etc., the gate must be provided on the upper or lower surface of the gear, so the remaining gate b protrudes from the upper or lower surface of the gear as shown.

The protruding height h of the remaining gate b varies depending on the material used, and is generally relatively small for hard plastics such as polycarbonate and polyacetal, and is relatively small for soft plastics such as polybutylene terephthalate and polyester elastomer. In the case of plastic, the height h also increases because the gate is difficult to cut.

For this reason, in the case of plastic molded gears, it is necessary to design a large gap between the gears. Especially in the field of watches, where the gap is required to be as small as possible, when plastic molding is used, The remaining portion of the gate b was one of the obstacles to making the movement thinner.

In addition, in order to improve the release of the molded product from the mold, it has been well known that the mold is made of a material with good thermal conductivity, but this increases the heat shrinkage (sink mark) of the molded product and reduces molding accuracy. However, there was also the drawback that the life of the mold was shortened.

The present invention is characterized in that, in order to reduce the remaining gate size and improve molding accuracy, heat is locally taken away from the vicinity of the gate, which is exposed to the highest temperature. An example implemented in a plastic mold device will be described.

In Figure 1, the stationary mold l is mold 11°12.13
The movable mold l'' is composed of molds 21, 22, 2.
3 and 24.

The movable structure between the stationary mold l and the movable mold υ and the movable structure of both relative to the fixed side receiving plate (not shown) are conventional and well-known structures, so explanations and illustrations thereof will be omitted.

The movable side mold υ is attached to the movable side receiving plate 30,
A cavity 4 having a desired part shape is formed in both molds υ.

A runner U is formed in the mold, and a gate 60 communicating with the cavity 0 is provided at the tip thereof.

A rod-shaped member is inserted into the mold υ in a positional relationship corresponding to the gate 60.

In this example, the rod-shaped member 70 has a conical pointed projection 71 formed at its tip, and this pointed projection is connected to the gate 60.
are closely facing.

The shape of the tip of the rod-shaped member 70, that is, the sharp protrusion 71, and the height relative to the gate 60 must be designed so as not to impede the flow of resin from the gate 60.

Further, the rod-shaped member 70 is made of a material having better thermal conductivity than the mold material, such as a copper alloy or copper.

Furthermore, the rear end portion of the rod-shaped member 70 is exposed to the outside air through an opening 31 formed in the movable side receiving plate 30 in this example.

Next, the operation of this device will be explained.

The resin injected from the molding machine passes through the runner 50 and gate 60.
Cavity 0 is filled through the.

When the resin filling is completed, "cavity formation", gate 60
The well-known mold opening is performed after the resin in the runners begins to solidify and after an appropriate period of time has elapsed after the filling of the resin is completed, that is, when the resin has almost completely solidified.

At this time, the molded product (
In other words, gear a) is separated from the runner section.

By the way, since the gate 60 is filled with high-temperature resin and is necessarily located deep in the mold apparatus, this portion has a higher temperature than other portions.

Therefore, in a mold device having a conventional configuration, the solidification speed of the resin in the gate 60 portion is slow, and when the gate is separated by opening the mold, the resin in the gate 60 is elongated, as shown in FIG. The height h of the remaining gate b had increased.

According to the mold apparatus shown in the first figure according to the present invention, the rod-shaped member 70 provided in the movable mold 20 so as to face the gate 60 locally removes heat from the gate 0 section, and the heat is removed from the outside. is released.

For this reason, the solidification of the resin inside the gate 60 after resin filling progresses rapidly, and the gate can be easily cut when the mold is opened.

That is, as shown in FIG. 2, the remaining gate b' becomes very small and hardly protrudes from the upper surface of the gear a.

In addition, the heat balance of the entire mold is improved by locally removing heat from the vicinity of the gate, which is exposed to the highest temperature.

FIG. 3 shows another embodiment of a rod-shaped member 70, in which a well-known heat pipe 72 is loaded.

As is well known, the heat pipe 72 has an extremely good heat transfer coefficient, so that even if the rod-shaped member 70 is thin, a sufficient heat dissipation cooling effect can be obtained.

Further, the shape of the tip of the rod-like member 70 is not limited to the above-mentioned embodiment, but the tip only needs to be in a shape that can locally absorb heat from the vicinity of the gate 60, or in a position facing the gate 60.

According to the mold device configured as described above, since heat radiation can be locally cooled only in the vicinity of the gate, not only can the influence of heat shrinkage on the dimensional accuracy of the molded product be minimized, but also the remaining gate area can be greatly reduced. If the gears used in watches are formed using this device, the gaps between the gears can be reduced, and the movement can therefore be made even thinner.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of an embodiment of the plastic molding device according to the present invention, FIG. 2 is a sectional view of a gear formed using the same device, and FIG. 3 is another embodiment of a rod-shaped member. FIG. 4 is a cross-sectional view of a gear formed by a conventional plastic molding device. S...Fixed side mold, υ...Movable side mold, 30...Movable side receiving plate, raw''...Cavity, 50... ... Runner, 60 ... Gate, 70 ... Rod member, 71 ... Protrusion, 72 ... Heat pipe.

Claims (1)

[Scope of Claims] 1. A plastic molding device in which a cavity of a desired shape is formed by a fixed mold and a movable mold, and a gate and a runner communicating with the cavity are formed in the fixed mold. , a rod-shaped member having a higher thermal conductivity than the mold is embedded in the movable mold at a position facing the gate, and a tip end of the rod-shaped member is closely opposed to the gate with a gap from the opposite side of the gate. A plastic molding device that is characterized by: 2. The plastic molding die device according to claim 1, wherein the rod-shaped member has a sharp protrusion at its distal end that faces closely to the gate. 3. The plastic molding device according to claim 1 or 2, wherein the other end of the rod-shaped member is exposed to the outside air. 4. The plastic mold device according to claim 1, 2, or 3, wherein the rod-shaped member has a heat pipe built therein.