JPH10100202A - Runner structure of mold for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten vulcanization time in a cavity of a molding material. SOLUTION: In a mold for injection molding wherein a sprue 1 and a plurality of gates 3 are connected with runners 4 and each linear distance from the sprue 1 to a gate 3 is long or short, a detour part 4a is provided on the runner 4 extending between the sprue 1 and the gate 3 with the shortest linear distance to make extending length of each runner 4 approximately equal mutually.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin,
Thermosetting resin, rubber, a runner structure suitable for use in an injection mold such as a rubber-like elastic material, particularly, a molding material, which enables rapid supply to each of a plurality of cavities, The temperature of the molding material in the cavity and the supply amount in the cavity are sufficiently equalized to effectively reduce the processing time in the cavity such as vulcanization.

[0002]

2. Description of the Related Art In injection molding, it is preferable to increase the number of molds per surface as much as possible in order to increase productivity and reduce manufacturing costs. Therefore, for example, when six rubber molded products are manufactured on one surface, conventionally, as shown in FIG. 6, a primary runner R is provided between one sprue S and six gates G. Are extended or branched at right angles, so that the total extension distance of each runner R from the sprue S to each gate G is substantially equal to each other. .

[0003] In this structure, since the extending distances of the primary runners R are substantially equal to each other, the flow resistance of the rubber as a molding material to the runners R is substantially equal in any of the runners R. In particular, runner R
Has a branch, the average temperature of the rubber injected into each cavity C through each gate G has a relatively large temperature difference between the cavities C, In the cavity C to be injected, the injection temperature is high and the injection amount is large. On the other hand, in the cavity C to be injected at a low temperature, the injection amount is small, and there is a disadvantage that the filling is insufficient and the quality and performance of the molded product are deteriorated. In addition, since the vulcanization time of the rubber injected into the cavity is set based on the rubber with a low average temperature, the vulcanization time is too long for the rubber in the cavity with a high average temperature, resulting in burning, etc. There is also a problem that defects occur.

[0004] These facts are to increase the injection pressure of the rubber to increase the injection speed in order to further increase the productivity by shortening the vulcanization time, thereby causing self-heating of the rubber, particularly, Heat generation was promoted in the vicinity of the peripheral wall of the flow path, and as a result, the temperature difference between the outer peripheral surface of the injected rubber and the vicinity and the central portion became particularly significant.

[0005] That is, in consideration of self-heating when rubber is injected from the injection nozzle, the runner R
Injection rubber immediately after flowing into the runner has the highest temperature in the vicinity of the runner peripheral wall and the lowest temperature in the center of the runner, as shown by the arrow X in FIG. As shown, the injection rubber is the first runner R.
After passing through the branch portion, the temperature distribution becomes high especially near the sprue side peripheral wall portion of each runner R, while it becomes low temperature in all other portions as shown by the arrow Y. , And after it passes the second branch,
As shown by the arrow Z, one of the runners R shows almost the same temperature distribution as the portion shown by the arrow Y, but the other runner R
Then, a low temperature distribution without a high-temperature portion will be exhibited. Therefore, after passing through the second branch portion, one cavity has, for example, about 10 to 20 ° C. as compared with the other cavity. In the cavity into which the high-temperature injection rubber is injected and the high-temperature injection rubber is injected, the inflow speed and the inflow amount of the rubber are both higher than those of the other cavity. This is due to non-uniformity, which is particularly remarkable in rubber having a higher viscosity than resin.

In order to solve the above-mentioned problems, a runner R is linearly extended between the sprue S and each gate G, as shown in FIG. Removed radial runner structures have been proposed.

[0007]

However, in such a proposed technique, in order to absorb the difference in the flow resistance of the injection rubber caused by the unevenness of the extension distance of each runner R, the extension distance is reduced. The cross-sectional area of the short runner R is set to be small, and the cross-sectional area of the runner R having a long extension distance is set to be large. If it does,
Usually, there is another problem that the injection rubber is burned in one of the runners.

That is, the optimum short injection speed of the rubber is largely different between the thin and short runner R and the thick and long runner R.
In the former case, if injection is performed at a relatively low pressure and self-heating is not suppressed, self-heating within the runner will cause burns in the injection rubber, while in the latter case, the injection rubber will be high. Unless the rubber is injected with pressure and passed through the runner R quickly, burned rubber is generated in a portion of the rubber self-generated by the injection nozzle or the like where the flow velocity is low, such as a portion attached to the runner wall.

Therefore, in order to inject rubber so that no burn occurs in any of the runners R, it is necessary to set injection conditions for low-temperature injection, and the vulcanization time becomes longer. was there.

The present invention has been made as a result of studying to solve all these problems, and an object of the present invention is to solve the problem of the average temperature of the molding material injected into each of the plurality of cavities. By eliminating the possibility of insufficient filling of the molding material into a specific cavity and a decrease in the quality, performance, etc. of a specific molded product, the required vulcanization time for the molding material in each cavity can be reduced by making them approximately equal. Evenly and evenly
Prevent the occurrence of product defects such as burns, and increase the injection pressure and, consequently, the self-heating value as necessary under the equalized runner cross-sectional area, as required for the heat treatment time such as vulcanization. An object of the present invention is to provide a runner structure of an injection mold that can be shortened.

[0011]

According to the present invention, there is provided a runner structure for an injection molding die, in which a sprue communicating with an injection nozzle and a plurality of gates communicating with a cavity are formed by a primary runner or primary and secondary runners. In the multi-cavity injection molding die, each of which has a straight line distance from the sprue to the gate having a long and a short distance, at least the primary runner extending between the sprue and the gate having the shortest linear distance is connected. By providing a detour portion, the extension lengths of the primary runners are made substantially equal to each other.

In this runner structure, even if the runners consist of both primary and secondary runners, each secondary runner usually has substantially the same length, so that Since the extending length of each runner from the sprue to each gate can be made substantially equal, the molding material can be substantially introduced into the respective cavities without making the cross-sectional area of the runner large or small. Injection can be performed under the same conditions, so that the average temperature of the molding material in each cavity is almost equal, and there is a possibility that a specific cavity is insufficiently filled with the molding material, and the quality, performance, etc. of a specific molded product are deteriorated. And ensure that the required vulcanization time for the molding material in each cavity is uniform enough to cause defects such as burning on the product. It can be effectively prevented.

In addition, since the cross-sectional area of each runner can be made a constant area as required, the molding material is made to flow at high speed under an injection pressure that is increased in accordance with the desired shortening of the vulcanization time. However, the molding material does not suffer from burning in the runner.

Preferably, the primary runners extend without branching, so that the average temperature of the molding material injected into the respective cavities is made uniform and the average temperature is still sufficiently high. . In other words,
If attention is paid only to the equalization of the average temperature, as is apparent from FIG. 7, even if there is one branch in the runner, the average temperature of the molding material in each cavity is made uniform. However, in this case, since the absolute amount of the high-temperature molding material flowing into each cavity is reduced, the average temperature of the molding material must be reduced, and an increase in the required vulcanization time is inevitable. Becomes

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing one embodiment of the present invention with respect to a runner structure in a case where six molded products are taken on one surface of a molding die, and this is one sprue communicating with an injection nozzle (not shown). 1 and
Each of the six gates 3 communicating with the cavity 2 is connected by a respective runner 4 having a required cross-sectional area and consisting of only a primary runner.

Here, according to the cavity arrangement shown in the figure, the linear distance from the sprue 1 to each gate 3 is particularly short in the two cavities 2 located in the center of the figure, and the other four For each of the cavities 2, a runner 4 is provided extending radially from the sprue 1 to the gate 3, while the four cavities 2 are substantially equal. For the two cavities 2 located, the runner 4
Is extended from the sprue 1 to the gate 3 by detouring in such a shape that the "U-shape" is joined in the opposite direction to each other,
The extension length of the runner 4 including such a detour portion 4a is made substantially equal to that of the runner 4 extending radially.

Here, the runner 4 having the detour 4a
Tends to be somewhat greater than that of the radial runner 4 due to the presence of the detours 4a, so that the extension length of the runner 4 having the detours 4a By making it somewhat shorter than that of the runners 4, it is also possible to make the flow resistance of both runners 4 substantially equal.

In such a runner structure, the cross-sectional areas of the respective runners 4 are equal to each other and their extending lengths are substantially equal to each other. As a result, the flow resistance exerted by the respective runners 4 on the molding material is increased. Are also substantially equal, so that the average temperature of the respective molding material supplied from the sprue 1 through the respective runners 4 into the cavity 2 can be sufficiently equalized, and as a result, the molding material can be introduced into the cavity. Insufficient filling is effectively prevented, and the molding material in each cavity is reliably vulcanized with the expected short vulcanization time without the risk of burning. become.

Furthermore, since the cross-sectional area and the extending length of each runner 4 can be made substantially equal, the injection pressure can be increased as required and self-heating can be achieved as expected. The required vulcanization time can be further reduced without the risk of burning or the like occurring in the runner.

Furthermore, since none of the illustrated runners 4 has any branches, as described above, the average temperature of the molding material can be equalized and the average temperature can be increased. This can also result in a reduction in vulcanization time.

FIG. 2 is a diagram showing another embodiment of the present invention. This is because the linear distance from the sprue 1 to the gate 3 in each of the four cavities 2 located at the center of the figure among the eight cavities 2 is larger than the similar linear distance in the other four cavities. This is an embodiment for a short case, in which case, with respect to four cavities 2 located at the center of the figure,
An arcuate curved portion 4a is provided in the vicinity of the gate 3 and the runner portion excluding the curved portion 4a is extended radially from the sprue 1 and the remaining four cavities 2a are formed. 1, runners 4 extending radially from the sprue 1 to the respective gates 3 are provided, and the lengths of the runners 4 are set to the respective runners having the detour portions 4a. It is almost equal to that of 4.

According to this, the respective runners 4 also have the same cross-sectional area and substantially the same length, and none of the runners 4 has any branches. The same operation and effect as those of the runner structure described with reference to FIG.

FIG. 3 is a view showing still another embodiment of the present invention, in which one sprue and two gates provided for each cavity are separated from the primary runner and the secondary runner. Are connected by different runners.

In this case, two pairs of gates 3a and 3b are provided for each cavity 2 and both gates 3a and 3b are connected linearly. Center and sprue 1
Are connected by the primary runner 4c, so that the sprue 1
The molding material injected into the respective primary runners 4c through the secondary runner 4b and the pair of gates 3a, 3b can be filled into the respective cavities 2.

The secondary runner 4b in this case controls the introduction of the molding material into one cavity 2. Therefore, the branch flow of the primary runner for guiding the molding material to different cavities. It is different from a road.

As shown in the figure, eight cavities 2
Of the four cavities 2 located in the center of the figure
Therefore, the linear distance from the sprue 1 to the gates 3a and 3b, more directly, from the sprue 1 to the center of the secondary runner 4b is shorter than the similar linear distance in the other four cavities 2. The primary runners 4c for the cavities 2 in their central part are provided with detours 4a located near the secondary runners 4b, and under the action of the detours 4a, the extension of their respective primary runners 4c. Length of stay,
The length of the other primary runners 4c extending radially for the other four cavities 2 is substantially equal to the extension length.

Also in the runner structure thus configured, the cross-sectional areas of the primary and secondary runners can be made uniform to each other, and the sprue 1 extends to the respective gates 3a and 3b. The lengths of the respective runners 4 can be made substantially equal, and, in addition, since none of the primary runners 4c has a branch, the same operational effects as those of the respective runner structures described above can be obtained.

Although the present invention has been described with reference to the case where rubber is used as a molding material, the runner structure of the present invention can provide the same effect as that of rubber when used for molding a thermosetting resin. On the other hand, when used for molding a thermoplastic resin, the average temperature in the cavity is made uniform and stable, and the reduction in molding accuracy due to the difference in the amount of heat shrinkage among the cavities is sufficiently reduced. Can be prevented.

In addition, in the runner structure, by forming the detour portion of the primary runner in a curved shape, it is possible to effectively prevent the molding material from staying in the runner and, of course, to reduce the molding material in the primary runner. Temperature distribution and flow velocity distribution
It can be made sufficiently uniform throughout it. In other words, if the primary runner is provided with a sharply bent corner, burns due to the stagnation of the molding material at the corner are inevitable, and the stagnation and the flow in the runner are unavoidable. The flow velocity distribution and the temperature distribution downstream of the corners are greatly disturbed by the inertia force of the molding material, and especially when the molding material is injected into the cavity via the secondary runner, However, there is a disadvantage that a large temperature difference occurs in the molding material passing through the gate.

[0030]

EXAMPLE A square engine mount as shown in FIG. 4 (natural rubber 170 g /
In manufacturing the individual pieces, a defect of the product is caused in each of the case where the runner structure of the present invention shown in FIG. 3 is used and the case where the conventional runner structure shown in a schematic diagram in FIG. 5 is used. A comparison of the shortest vulcanization time without the elimination showed that the required vulcanization time was reduced to less than half, compared to 7 minutes for the conventional structure and 3 minutes for the runner structure of the present invention.

[0031]

As described above, according to the present invention, the cross-sectional area of each runner is made sufficiently uniform, and at the same time, the extending length of each runner can be made substantially equal. Insufficient filling, the occurrence of product defects such as burning of the molding material in the specific cavity, and the occurrence of burning of the molding material in the runner are effectively prevented, and the heat treatment time such as vulcanization is expected. Can be shortened as follows.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing still another embodiment of the present invention.

FIG. 4 is a side view illustrating a molded article.

FIG. 5 is a schematic diagram illustrating a conventional runner structure.

FIG. 6 is a diagram showing another conventional structure.

FIG. 7 is a diagram showing a temperature distribution of a molding material in a runner.

FIG. 8 is a view showing still another conventional structure.

[Explanation of symbols]

 Reference Signs List 1 sprue 2 cavity 3, 3a, 3b gate 4 runner 4a detour 4b secondary runner 4c primary runner

Claims (2)

[Claims] A primary runner or a sprue communicating with an injection nozzle and a plurality of gates communicating with a cavity.
A multi-cavity injection molding die connected by primary and secondary runners, each of which has a long and short linear distance from the sprue to the gate, and at least the sprue and the gate having the shortest linear distance. A runner structure of an injection molding die in which a detour portion is provided in a primary runner extending between the primary runners so that extension lengths of the primary runners are substantially equal to each other. 2. The runner structure of an injection mold according to claim 1, wherein said primary runner extends without branching.