JPH0269215A - Mold for molding annular plastic - Google Patents

Abstract

PURPOSE:To make the characteristic of an annular molded item uniform by preventing resin from flowing in the opposite direction over all the circumference of the item by a structure wherein the thickness of a filmy gate, through which the resin poured in an annular runner surrounding the outer circumferential part of an annular cavity is introduced in the cavity, is made the thinnest near the pouring part of resin to the runner and gradually thicker to the intermediate part between the pouring part to the farthest part from the pouring part and further gradually thinner again from the intermediate part to the farther part. CONSTITUTION:The thickness of a filmy gate 6, which interposes between an annular runner 4 and an annular cavity 3 and through which thermoplastic resin poured in the annular runner 4 is introduced in the cavity 3, is varied in response to the position, through which the runner 4 and a resin pouring runner 5. The thickness of the gate is the thinnest at t1, which is the nearest to a resin inlet, and becomes gradually thicker in proportion to the increase of the distance from t1. Let the inlet and the farthest part from the inlet be 0 deg. and 180 deg. in a circle with center at the central part of an annulus. The thickness of the gate is the thickest near 140 deg. or at t4 and further becomes gradually thinner from t4 to the farthest part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold for molding ring-shaped plastics by injection molding, and particularly to a mold that can prevent welding within a molded product.

[Conventional technology]

Generally, ring-shaped molded products are often manufactured by plastic injection molding in consideration of productivity, etc., but the predominant gate methods are either bottle point gates or side gates. However, in such a gate method, welds occur when the resin that flows out faces each other within the cavity, resulting in major problems such as insufficient strength, poor appearance, and poor shape accuracy.

Conventionally, as an example of a method for solving such problems, there has been a method for manufacturing a ring-shaped plastic magnet disclosed in Japanese Unexamined Patent Publication No. 58-213410.

In Fig. 7, (l) is a mold made of, for example, an iron-aluminum alloy, (2) is a plate made of a thin steel plate), and (2a) is a die formed by drawing the plate (2). The flange portion (3) is a ring-shaped cavity in which the molded product is formed, and is configured to encompass the flange portion (2a) of the plate. (7) is a resin retaining portion provided near the center of each gate in the same number as the number of bin gates and side gates at a position above or below the outer periphery of the ring-shaped cavity (3). This retaining part is provided to completely absorb the weld.
As shown in the figure, from the direction of arrows E and F, material 2 in a molten state, for example, a thermoplastic resin material and a molecular formula MO-nP, 203
(However, M is B or S, and n is 5 to 6) The mixed material with the isotropic magnetic powder flows and passes through the two passages (7a) after merging at the stop (just before the force). , the weld caused by the flow of the material is absorbed by the conical shape g (7b) of the retaining part, and there is no weld in the mixture part in the cavity (3), that is, the ring-shaped plastic molded product, and the magnetic powder is distributed. This force is cut off after molding, and multiple N and S poles are alternately magnetized on the outer circumferential surface of the molded product, making it possible to create a plastic that can be used as a high-precision rotating magnetic sensor. This means that a magnet can be obtained.

Note that (8) is an injection port for the molding material, and (9) is a passage for the injected material to the cavity (3).

[Problem to be solved by the invention]

In the conventional manufacturing method for ring-shaped plastic molded products as described above, the occurrence of welds cannot be sufficiently suppressed.2 For example, in the case of plastic magnets, the material is a mixture of a thermoplastic resin material and anisotropic magnetic powder. When fully used, the magnetic powder becomes abnormally oriented at the position where the molten materials meet, and the magnetic properties change at this position after magnetization, resulting in noise generation. In addition, abnormal orientation occurs not only in plastic magnets but also in the molding of ring-shaped plastic molded products using mixtures of short fibers and other materials with anisotropic shapes and thermoplastic resin materials.

There is a problem that variations in characteristics occur.

The present invention solves all of the above problems.

This can cause welds to occur around the entire circumference of the ring-shaped molded product. The opposite flows of resin are worthless.

The overall purpose is to provide a mold that allows a ring-shaped plastic molded product with uniform properties to be obtained.

[Means to solve the problem]

The ring-shaped plastic molding die according to the present invention has a ring-shaped cavity in which a molded product is made of cedar bark.

A ring-shaped runner is disposed on the outer periphery of the cavity to surround the cavity, and a film-shaped gate is provided between the runner and the cavity to introduce the thermoplastic resin injected into the launch into the cavity. The thickness of the film-like gate is made thinner near the thermoplastic resin injection part of the launch, and gradually thickens from this position to the middle part between the injection part and the part farthest from there, and further from the middle part to the middle part. It is made thinner again toward the farthest part.

[Effect]

In the present invention, the resin injected into the runner completely flows to surround the cavity, and after filling the launch, it begins to flow in the inner circumferential direction through the film gate. .

Since it changes depending on the distance from the resin injection port,
The resin flows out from the gate uniformly, and the entire circumference of the cavity is filled with resin at the same time, suppressing the occurrence of welds within the cavity.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
FIG. 2 shows a mold according to an embodiment in which the present invention is applied to a ring-shaped plastic magnet.

In the figure, (4) is a ring-shaped runner arranged around the outer periphery of the cavity (3), and a resin injection launch (5) is connected to this ring-shaped runner (4). has been done. (6) is a film-shaped (band-shaped) gate that is interposed between the ring-shaped launch (4) and the ring-shaped cavity (3) and introduces the thermoplastic resin injected into the ring-shaped launch (4) into the cavity (3). can be.

The thickness of this gate (6) changes depending on the position where the runner (4) and the resin injection launch (5) are connected, that is, the distance from the resin injection port. Figure 3 shows the change in the thickness of this gate, and shows the lower half of Figure 2, cut along the gate, when fully expanded. What is the thickness of the gate?

The thinnest at tl closest to the resin injection port (0,311+11
From this position, it gradually becomes thicker as it moves away from the injection port.

Assuming that the center of the ring is the center, the injection port 1o' is 180', and the deepest point is 180', the thickest point (
, 3,7s+m, and gradually thinner from this position to the farthest part, +5 = 0.6t! It is M.

In other words, the thickness of the gate is tl from the thinner to the thicker.
The order is +2, +3, +5, +4.

In addition, in this example, the outer diameter of the ring-shaped cavity 3) is 60 mm.
．． The diameter of the ring-shaped lunch (4) is 5 degrees, and the cavity (3)
The distance between the gate and the runner (4), that is, the width of the gate (6) is 1
, 5 as.

Next, the operation of the above embodiment will be explained. Molten resin is injected at higher speeds and under higher pressure than an injection molding machine.

As shown in FIG. 2, the water branches along the C runner (5) and flows in the direction of the arrow and the direction of the arrow B, and merges at the convex part of the injection port.

After the ring-shaped runner (4) has been completely filled.

Goo) +6) ', filling of the resin into the cavity (3) forming the molded part (3) is started.

If the thickness of the gate (61) is uniform over the entire circumference, the resin will preferentially flow out from the gate near the injection port where pressure is easily applied. Because it changes depending on distance.

The amount of resin flowing toward the inner circumference becomes uniform over the entire circumference of the gate (6). Figure 4 shows the flow of resin inside the cavity (3). The resin that has passed through the gate flows simultaneously over the entire circumference of the cavity only in the height direction of the ring as shown by arrows C and D. The occurrence of welds due to circumferential flow is prevented.

In the above embodiment, the resin injection runner (5), that is, the resin injection port, is provided at only one location, but it may be provided at multiple locations.

FIGS. 5 and 6 show the arrangement of the main parts and the change in the thickness of the film-like gate between the resin injection launches in the case where resin injection ports are provided at three locations. In this example, the specific value of the gate thickness is not illustrated, but tl(+
2(+5(+5(+4) relationship is the same as in the above embodiment.

In the above embodiment, the present invention was applied to a plastic magnet, but for example, it may be mixed with short fibers such as glass, and even if it is a plastic molded product that is not mixed with anything, it can be used in the weld part. This can prevent the strength from weakening.

〔Effect of the invention〕

As described above, according to the present invention, there is a ring-shaped cavity in which a molded product is formed, and a cavity on the outer periphery of this cavity. a ring-shaped launch arranged to surround the runner, and a film-shaped gate interposed between the runner and the cavity for introducing the thermoplastic resin injected into the runner into the cavity; the thickness of the film-shaped gate; is thinnest near the thermoplastic resin injection part of the runner, and gradually thickens from this position to the middle part between the injection part and the fastest part, and further from the middle part to the farthest part. By making it thin again, welding is less likely to occur inside the molded product.

This has the effect of suppressing variations in characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a ring-shaped plastic mold according to one embodiment of the present invention, and FIG. 2 is an explanatory view showing the arrangement of the main parts of the mold shown in FIG. Figure 3 is an explanatory diagram showing how the thickness of the film-like gate changes when the lower part of Figure 2 is cut along the gate and expanded, and Figure 4 is the inside of the cavity of Figure 1. FIG. 5 is an explanatory diagram showing the arrangement of the main parts of a ring-shaped plastic mold according to another embodiment of the present invention, and FIG. 6 is an explanatory diagram showing the flow of resin in FIG. 5. FIG. 7 is an explanatory diagram showing how the thickness of the film-like gate changes between launches. FIG. 7 is a sectional view showing a conventional ring-shaped plastic mold, and FIG. 8 is a partially cutaway perspective view of the main part of the mold shown in FIG. 7, showing how the resin flows. (2) is the mold, (2) is the play), +3) is the cavity, (4) is the ring-shaped launch, (5) is the launch for resin injection, (6) is the film-shaped launch), (7) is the resin retention part. Further, arrows A-F indicate the flow of resin during molding. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A ring-shaped cavity in which a molded product is formed, a ring-shaped runner arranged around the outer periphery of this cavity, and a ring-shaped runner interposed between this runner and the above-mentioned cavity, in which the thermoplastic resin injected into the above-mentioned runner is A film-like gate is provided to be introduced into the cavity, and the thickness of the film-like gate is made thinnest in the vicinity of the thermoplastic resin injection part of the runner, and from this position, the thickness of the film-like gate is made thinnest in the vicinity of the thermoplastic resin injection part of the runner, and from this position, the thickness of the film-like gate is made thinner in the vicinity of the thermoplastic resin injection part of the runner. A ring-shaped plastic mold that is gradually thickened toward the middle part and then thinned again from the middle part to the farthest part.