JPH03219930A - Reactive injection mold for v-ribbed belt - Google Patents

Abstract

PURPOSE:To obtain a V-ribbed belt which is free from a weld defect and has few bubble, by a method wherein a sprue is arranged at the central position of the top of an inner mold and a runner extending to the whole of the top of the inner mold the sprue and communicating with a cavity from the whole fringe of the top is formed. CONSTITUTION:Deaeration of a cavity 15 is performed sufficiently through an exhaust port 29 by actuating a vacuum pump 30 and a molding material in a mixing head 26 is cast into a cavity 15 from a sprue 24 through a runner 25. In this instance, since the molding material is caused to flow into the central part of the top of an inner mold 12 through a sprue 24 and the same is expanded away radially to the whole of the top of the inner mold 12 in a horizontal part of the runner 25, generation of a weld part can be avoided. Since a vacuum drawing is performed, irrespective of a fact that a form of the cavity 15 is in a complicated form with an annular groove 16 and projected line 17, dragging-in of gas is little on the way while the molding materials are being filled away into the cavity 15, the molding material is filled sufficiently into the cavity 15 and a V-ribbed belt free from a weld defect is obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to (1) a reaction injection mold for ribbed belts;

(Prior Art) A V-ribbed belt having a plurality of V-ribs extending over the entire circumference of the belt in the belt circumferential direction is generally known. When molding this V-ribbed belt using a reaction injection molding material such as fast-curing urethane, a mold a shown in FIG. 3 is used.

That is, this mold a has a cylindrical outer mold C having a large number of annular grooves for forming V ribs on the inner circumferential surface and whose axis is perpendicular;
It is provided with an inner mold e that forms a cavity d for molding the V-ribbed belt between the outer mold C and a top lid f and a bottom lid g.

An injection port communicating with the cavity d is formed at one location on the outer periphery of the upper lid f, and an exhaust port i is formed at the lower end of the outer mold C.

(Problems to be Solved by the Invention) In the case of the mold a, there is a problem in that it tends to cause weld defects. That is, when the molding material injected from the injection port reaches the cavity d, the flow is divided into two directions, clockwise and counterclockwise, in the circumferential direction, collides on the opposite side of the injection port, and forms a fused portion, i.e. A weld portion will be formed. Therefore, if the molding material injected into the cavity d entrains gas, this gas tends to concentrate in the weld part, or the outer mold C has many annular grooves and the molding material itself Because it cures quickly, the flow of the molding material within the cavity d is poor, resulting in gas concentrated in the welt portion not being removed from the mold and remaining in the molded product. In some cases, there is also a problem in that the molding material that is split into two parts hardens before reaching the weld part.

To deal with this, measures have been taken such as deaerating the inside of the cavity d from the exhaust port i, increasing the discharge speed of the molding material, and increasing the temperature of the molding material to lower its viscosity. It is difficult to improve defects, especially when the discharge speed of the molding material is increased, gas becomes more likely to be drawn into the molding material, and raising the temperature of the molding material also causes it to harden faster. .

Moreover, the above can be said similarly even when the positions of the molding material injection port and the exhaust port i are reversed, and the molding material is injected into the cavity d from below.

Therefore, the present invention aims to provide a reaction injection mold for V-ribbed belts that does not cause the above-mentioned problem of weld defects.

(Means for Solving the Problems) The present invention solves these problems by providing a method in which the molding material spreads radially from the center of the upper surface of the inner mold and flows uniformly over the entire cavity. It is intended to do so.

That is, a specific means for this purpose is a mold for molding a V-ribbed belt having a plurality of V ribs extending over the entire circumference of the belt in the circumferential direction of the belt using a reaction injection molding material. It is equipped with a cylindrical outer mold having an annular groove for forming ribs and a vertical axis, and an inner mold forming a cavity for forming a V-ribbed belt between the outer mold and the inner mold. A sprue that guides the molding material from the mixing head is provided at the center of the top surface, and a runner that extends from the sprue over the entire top surface of the inner mold and communicates with the cavity from the entire periphery of the top surface.

(Function) In the above reaction injection mold, the molding material spreads radially over the entire upper surface of the inner mold from the sprue located at the center of the upper surface of the inner mold, and flows from the entire periphery of the upper surface of the inner mold into the cavity for molding the V-ribbed belt. There will be an influx. Therefore, the flow of the molding material does not split into two parts, no welds occur, and there is little gas entrainment while the molding material is being filled into the cavity, and of course there is no local concentration of gas. This problem does not arise.

(Effects of the Invention) Therefore, according to the present invention, a sprue is arranged at the center of the upper surface of the inner mold, and a runner is formed that spreads from the sprue over the entire upper surface of the inner mold and communicates with the cavity from the entire periphery of this upper surface. Therefore, it is possible to obtain a ribbed belt with no weld defects and less air bubbles.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a reaction injection mold 1 for a V-ribbed belt. This mold 1 is a V-lid belt 2 shown in FIG.
It is for molding.

First, the V-lid belt 2 will be described. This is provided with a plurality of ribs 3 extending in the belt circumferential direction over the entire circumference of the belt on the inner peripheral side thereof and arranged in parallel in the belt width direction. Further, on the outer peripheral surface of the V-lid belt 2, a large number of grooves 4 extending in the belt width direction are formed at predetermined intervals over the entire circumference of the belt. 5 is a tensile cord.

The mold 1 is made up of an outer mold 11, an inner mold 12, a top lid 13, and a bottom lid 14. The outer mold 11 and the inner mold 12 form a cavity 15 for molding the V-ribbed belt between the inner and outer peripheral surfaces of each other. That is, the outer mold 11
has a cylindrical shape with its axis vertical, and has a large number of V-shaped annular grooves 16 for forming the V-ribs 3 on its inner peripheral surface.
are arranged closely in the axial direction. The inner mold 12 has a cylindrical shape with its axis vertical and its upper end closed, and has a large number of axially extending protrusions 17 spaced apart in the circumferential direction on its outer circumferential surface for winding the tensile cord 5. It is formed by In this case, the protrusions 17 form grooves 4 on the outer peripheral surface of the V-rubbed belt 2.

Then, the upper lid 13 is attached to the peripheral edge of the disc-shaped base 21.
An annular wall 23 is formed which projects downward and whose tip abuts against the upper end of the outer mold 11 via a sealing member.

A sprue 24 is formed at the center of the disk-shaped base 21, and a runner 25 is formed between the inner mold 12 and the upper lid 13 from the sprue 24 to the cavity 15.

That is, the sprue 24 has an upper end connected to a mixing head 26 for molding material, and extends toward the center of the upper surface of the inner mold 12. The runner 25 also connects the upper surface of the inner mold 12 and the disc-shaped base 21 of the upper lid 13.
A horizontal portion formed between the lower end of the sprue 25, and therefore extending from the center of the upper surface of the inner mold 12 over the entire upper surface, and between the outer circumferential surface of the upper end of the inner mold 12 and the annular wall 23 of the upper lid 13. The upper surface of the inner mold 12 has a vertical portion extending from one edge of the entire periphery to the cavity. Also,
A disk 27 having a sprue hole in the center is fitted into the center of the upper lid 13, and a plurality of rods 28 whose tips abut against the upper surface of the inner mold 12 are attached to the lower surface of the disk 27 around the sprue hole. They are provided at predetermined intervals in the direction. This rod 28 is used to facilitate mixing of the molding material and to make it easier for the molding material to spread evenly over the entire upper surface of the inner mold 12.

Further, an exhaust port 29 communicating with the cavity 15 is formed at the lower end of the outer mold 11, and in the embodiment, a vacuum pump 30 is connected to this exhaust port 29.

Next, a mode of injection molding of the V-rubbed belt 2 using the mold 1 will be explained.

■ After assembling the outer mold 11 and the inner mold 12 with the tensile cord 5 wrapped around the outer circumferential surface using the top lid 13 and the bottom lid 14, the mixing head 26 is connected to the sprue 24, while the exhaust port 29 is evacuated. Connect the pump 30.

(2) Operate the vacuum pump 30 to sufficiently evacuate the cavity 15 from the exhaust port 29 (bring it to a vacuum state).

(2) Inject the molding material (fast-curing urethane) for the mixing head 26 from the sprue 24 through the runner 25 into the cavity 15.

In this case, the molding material flows into the center of the upper surface of the inner mold 12 from the sprue 24 and spreads radially over the entire upper surface of the inner mold 12 at the horizontal part of the runner 25, so that the molding material is divided into two large parts. It is possible to avoid a collision situation, that is, the occurrence of a weld portion. In addition, although the shape of the cavity 15 is complicated by the annular groove 16 and the protrusion 17 due to the vacuum being applied, the molding material is still being filled into the cavity 15. The molding material is sufficiently filled in the cavity 15, with less gas being entrained, and of course, without local concentration of gas.

(2) After the molding material has hardened, the molded product is cut out, and the molded product is cut into rings with a predetermined width to obtain a plurality of V-rubbed belts 2.

Therefore, according to the mold 1, a V-rubbed belt 2 with few air bubbles and no weld defects can be obtained.

Incidentally, in the above embodiment, evacuation is performed from the exhaust port, but evacuation is not necessarily required.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a longitudinal sectional view of a reaction injection mold, FIG. 2 is a perspective view of a V-ribbed belt partially cut away, and FIG. 3 is a longitudinal sectional view of a conventional mold. It is a front view. 1... Mold 2... V-ribbed belt 3... V-rib 11... Outer mold 12... Inner mold 13... ... Top lid 14 ... Bottom cover 15 ... Cavity 16 ... Annular groove 24 ... Sprue 25 ... Runner 26 ...・Mixing helad

Claims (1)

[Claims] (1) A mold for molding a V-ribbed belt having a plurality of V-ribs extending over the entire circumference of the belt in the circumferential direction of the belt using a reaction injection molding material, the mold having a large number of annular grooves for molding V-ribs on the inner peripheral surface. It is equipped with a cylindrical outer mold with a vertical axis and an inner mold forming a cavity for molding the V-ribbed belt between the outer mold and the mixing head at the center of the upper surface of the inner mold. A reaction injection molding mold for a V-ribbed belt, comprising: a sprue that guides a molding material; and a runner that extends from the sprue over the entire upper surface of the inner mold and communicates with the cavity from the entire periphery of the upper surface.