Cold runner unit and cold runner forming method

Abstract

To ensure that sufficient injection pressure is transmitted to the cavity during molten resin injection while suppressing the amount of solidified resin generated within the cold runner.SOLUTION: A cold runner unit for forming a cold runner that feeds molten resin into a cavity of an injection molding die, comprising a first runner plate and a second runner plate that are superimposed on each other to form the cold runner between them, at least a portion of the cold runner is formed by a main runner groove provided on the cold runner forming surface of the first runner plate facing the second runner plate, and a sub-runner groove provided on the cold runner forming surface of the second runner plate facing the first runner plate side, corresponding to the main runner groove, for adjusting the injection pressure transmissibility of the molten resin, the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow direction of the cold runner are smaller than those of the main runner groove.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cold runner unit and a method for forming a cold runner. [Background technology]

[0002] Among injection molding molds, in the case of cold runner molds and semi-hot runner molds that combine hot runners and cold runners, the molten resin supplied to the mold sprue from the nozzle of the molding machine passes through the cold runner and is injected into the cavity through the cavity gate. After the resin injected into the cavity cools and solidifies, the mold is opened and the molded part is removed from the cavity and becomes a finished product. At this time, the solidified resin remaining in the cold runner is also removed from the mold.

[0003] The solidified resin removed from the cold runner is discarded as waste and does not contribute to the formation of products. Therefore, there is a need to reduce the amount of solidified resin remaining in the cold runner and suppress the amount of resin consumption. Patent Document 1 proposes forming a cold runner so that the cross-sectional area in the direction perpendicular to the flow path gradually decreases toward the cavity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-077174 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 is effective for a relatively short cold runner that extends from a hot runner to a cavity gate in the same direction as the hot runner axis (the mold opening / closing direction). However, most molds with cold runners, particularly multi-cavity molds, supply molten resin from a sprue or hot runner to multiple cavities via the cold runner section. Therefore, the cold runner does not have a linear shape that extends only in the mold opening / closing direction, but rather has a complex shape that extends in a direction perpendicular to the mold opening / closing direction. It is difficult to apply the technology disclosed in Patent Document 1 to molds with cold runners of this shape.

[0006] One possible solution to this problem is to reduce the cross-sectional area of the cold runner in the direction perpendicular to the flow path, but if the cold runner is made too thin, the injection pressure of the molten resin from the molding machine will not be transmitted sufficiently to the cavity, resulting in insufficient filling of the cavity and problems such as sink marks on the molded product.

[0007] The present invention has been made in consideration of the above problems, and aims to suppress the amount of solidified resin generated in the cold runner while transmitting sufficient injection pressure to the cavity when injecting molten resin. [Means for solving the problem]

[0008] Increasing the cross-sectional area of the cold runner in the flow direction is one way to facilitate the transmission of the injection pressure of the resin to the cavity. However, simply increasing the cross-sectional area of the cold runner increases the volume of the cold runner, although it improves the transmission of the injection pressure of the molten resin. This increases the amount of solidified resin remaining in the cold runner, resulting in increased resin consumption. Therefore, in this invention, by adding a structure to the cold runner that contributes to improving the injection pressure of the molten resin, the amount of solidified resin that occurs in the cold runner is reduced without increasing the cross-sectional area of the cold runner more than necessary.

[0009] That is, the cold runner unit according to the present invention is a cold runner unit that forms a cold runner for feeding molten resin into the cavity of an injection molding die, and comprises first and second runner plates that are superimposed on each other to form the cold runner therebetween, at least a portion of which is formed by a main runner groove provided on the cold runner-forming surface of the first runner plate that faces the second runner plate, and a sub-runner groove for adjusting the injection pressure transmittance of the molten resin that is provided in correspondence with the main runner groove on the cold runner-forming surface of the second runner plate that faces the first runner plate, and the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow path direction of the cold runner are smaller than those of the main runner groove.

[0010] A cold runner forming method according to the present invention is a method for forming a cold runner for feeding molten resin into a cavity of an injection molding die, comprising: a preparation step of preparing first and second runner plates to be superimposed on each other to form the cold runner therebetween; a first formation step of forming a main runner groove on the cold runner forming surface of the first runner plate facing the second runner plate at a position where the cold runner will be formed; and a second formation step of forming sub-runner grooves for adjusting the injection pressure transmission of molten resin in at least a part of the position where the cold runner will be formed on the cold runner forming surface of the second runner plate facing the first runner plate, wherein in the second formation step, the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow direction of the cold runner are made smaller than those of the main runner groove. [Effects of the Invention]

[0011] According to the cold runner unit of the present invention, the cold runner has a portion formed by the main runner grooves provided in the first runner plate and the sub-runner grooves provided in the second runner plate for adjusting the injection pressure transmission of the molten resin, so that the proportion of resin with a high melting point that contributes to the injection pressure transmission is increased, compared to a case in which only the main runner grooves have the same cross-sectional area, thereby improving the injection transmission of the molten resin. Therefore, when the molten resin is injected, sufficient injection pressure can be transmitted to the cavity while suppressing the amount of solidified resin generated in the cold runner without increasing the cross-sectional area of the cold runner more than necessary.

[0012] According to the cold runner forming method of the present invention, a main runner groove is formed in the first runner plate at the cold runner formation position, and a sub-runner groove for adjusting the injection pressure transmission of molten resin is formed in at least a portion of the cold runner formation position in the second runner plate, so that when molten resin is injected, sufficient injection pressure can be transmitted to the cavity while suppressing the amount of solidified resin generated in the cold runner without increasing the cross-sectional area of the cold runner more than necessary. Moreover, the injection pressure of molten resin transmitted to the cavity can be adjusted by adjusting only the size of the sub-runner groove, without changing the size of the main runner groove. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view showing an embodiment of a cold runner unit in a direction parallel to the flow path direction of the cold runner. [Figure 2] FIG. 2 is a cross-sectional view of the cold runner unit of the embodiment taken along a direction perpendicular to the flow path direction of the cold runner. [Figure 3] FIG. 10 is a cross-sectional view taken along a line perpendicular to the flow path direction of the cold runner, showing an example in which the size of the sub-runner groove is changed in the embodiment; [Figure 4] 10 is a cross-sectional view in a direction perpendicular to the flow path direction of the cold runner, showing an example of a structure in which the cold runner is formed only by grooves in a first runner plate. FIG. [Figure 5] FIG. 2 is a cross-sectional view in a direction perpendicular to the flow path direction of the cold runner, showing an example of the structure when the cold runner has a full round shape. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cold runner unit and a method for forming a cold runner according to the present invention will now be described with reference to the drawings.

[0015] FIG. 1 shows a cross section in a direction parallel to the flow path direction of a cold runner 10 in a section where a structure for adjusting the injection pressure of molten resin of a cold runner unit 1 is formed.

[0016] As shown in Fig. 1, a cold runner unit 1, which is the main part of a cold runner mold (and a semi-hot runner mold), comprises a first runner plate 2 and a second runner plate 4. The first runner plate 2 and the second runner plate 4 are overlapped when the mold is closed, and a cold runner 10 is formed between the surfaces 2a and 4a (each of which is referred to as a cold runner forming surface) that come into close contact with each other. When the cold runner unit 1 is opened after resin has been filled into the cavity and solidified, the first runner plate 2 and the second runner plate 4 are also opened in the mold opening / closing direction in the figure (the vertical direction in the figure), and the resin that has solidified in the cold runner 10 is also removed.

[0017] A main runner groove 6 forming a main part of a cold runner 10 is provided at a cold runner forming position on a cold runner forming surface 2a (upper surface in the figure) of the first runner plate 2 facing the second runner plate 4. A sub-runner groove 8 for adjusting the injection pressure of the molten resin is provided at a cold runner forming position on a cold runner forming surface 4a (lower surface in the figure) of the second runner plate 4 facing the first runner plate 2.

[0018] FIG. 2 shows a cross section of the cold runner unit 1 of FIG. 1 taken along a line XX in a direction perpendicular to the flow path direction of the cold runner 10. In FIG.

[0019] 2, the cross-sectional shape of the main runner groove 6 formed in the first runner plate 2 in a direction perpendicular to the flow path direction of the cold runner 10 is a substantially U-shape widening toward the cold runner forming surface 2a. The cross-sectional shape of the main runner groove 6 may also be a substantially trapezoidal or arc-shaped shape widening toward the cold runner forming surface 2a.

[0020] The main runner groove 6 is the main part of the cold runner 10, and by making the cross-sectional shape of this main runner groove 6 an approximately U-shape, approximately trapezoidal shape, or approximately arc shape that widens toward the cold runner forming surface 2a, it becomes easier to release the solidified resin from the cold runner 10 when removing it, and the resin utilization efficiency is improved compared to when the cross-sectional shape is a perfect semicircular shape.

[0021] The cross-sectional shape of the sub-runner grooves 8 formed in the second runner plate 4 in a direction perpendicular to the flow path direction of the cold runner 10 is a substantially arc shape widening toward the cold runner forming surface 4a. The cross-sectional shape of the sub-runner grooves 8 may also be a substantially U-shape or a substantially trapezoidal shape widening toward the cold runner forming surface 4a.

[0022] The opening width B of the sub-runner groove 8 on the cold runner forming surface 4a is smaller than the opening width A of the main runner groove 6 on the cold runner forming surface 2a. Furthermore, the cross-sectional area of the sub-runner groove 8 in a direction perpendicular to the flow path direction of the cold runner 10 is smaller than the cross-sectional area of the main runner groove 6. The sub-runner grooves 8 are provided so that the molten resin flowing inside them comes into contact with the molten resin flowing in the center of the main runner groove 6, and preferably the sub-runner groove 8 is located in the center of the main runner groove 8.

[0023] As described above, the opening width and cross-sectional area of the sub-runner grooves 8 are smaller than those of the main runners 6. The molten resin flowing in the sub-runner grooves 8 is sufficiently exposed to the heat of the molten resin flowing in the main runner grooves 6. This ensures that the molten state of the resin in the sub-runner grooves 8 is maintained at a sufficiently uniform level. This prevents the formation of wasteful resin stagnation in the sub-runner grooves 8, which does not contribute to the transfer of the injection pressure of the molten resin. Therefore, the provision of the sub-runner grooves 8 efficiently contributes to improving the transfer of the injection pressure of the molten resin to the cavity. In other words, the cold runner according to the present invention, which includes sub-runner grooves in addition to the main runner grooves, has a higher proportion of resin with a high melting point that contributes to the transfer of injection pressure, compared to a cold runner with only the main runner grooves, assuming the same cross-sectional area. This improves the injection transferability of the molten resin. The injection pressure of the molten resin into the cavity can be adjusted simply by changing the opening width and cross-sectional area of the sub-runner grooves 8 at the required locations, as shown in FIG. 3 .

[0024] For comparison, an example in which the cold runner is formed only by the runner grooves 12 provided in the first runner plate 2 is shown in FIG.

[0025] As shown in Figure 4, when the cold runner is formed only with a runner groove 12 provided in one runner plate 2, the overall cross-sectional area of the runner groove 12 must be further increased to improve the injection pressure of the molten resin. However, increasing the cross-sectional area of the runner groove 12 also increases the cross-sectional area of the corner-neighboring portion 12b, which is farther from the center portion 12a of the groove 12. Because the amount of molten resin in the corner-neighboring portion 12b is small, the mold temperature does not rise easily and the temperature is lower than that of the center portion 12a. As a result, the fluidity of the molten resin in the corner-neighboring portion 12b deteriorates, making it less likely to contribute to the transmission of the injection pressure of the molten resin to the cavity. Therefore, even if the cross-sectional area of the corner-neighboring portion 12b is increased, the overall volume of the cold runner increases, increasing the amount of wasted solidified resin removed from the cold runner after mold opening, while making little contribution to improving the injection pressure of the molten resin into the cavity. Furthermore, the increased overall volume of the cold runner also increases the cooling time required to solidify the molten resin, resulting in problems such as a shortened molding cycle.

[0026] Furthermore, when the fluidity of the molten resin is taken into consideration, it is also possible, and this is commonly done, to use a full-round (circular cross section) cold runner, as shown in Figure 5. In such a circular cross section cold runner, the wall surface of the cold runner is uniformly heated by the high-temperature molten resin, which means that the resin fluidity within the cold runner is good and the injection pressure of the molten resin is transmitted to the cavity with excellent efficiency.

[0027] However, a cold runner with a circular cross section like the one described above requires the provision of runner grooves 14 and 16 with uniformly sized semicircular cross sections on the first runner plate 2 and the second runner plate 4, respectively. In the case of a multi-cavity mold in which the cold runner is complex and long, variations in the distance between each cavity and the sprue can cause variations in the resin injection pressure delivered to each cavity. Even if the design ensures that the distances to each cavity are the same, differences in the injection pressure delivered to each cavity can occur depending on the cavity's location. In such cases, to ensure uniform injection pressure delivered to each cavity, the cross-sectional area of the cold runner must be adjusted depending on the distance between each cavity and the sprue and the cavity's location.

[0028] Even in such cases, with a full-round type cold runner, it is necessary to perform modification processing to enlarge the runner grooves of the first runner plate 2 and the second runner plate 4 while maintaining the size uniform, which is not an easy task.

[0029] Furthermore, in a full-round cold runner, it is possible to adjust the injection pressure by increasing the cross-sectional area of the runner groove on only one of the runner plates. However, doing so will result in areas near the corners, such as 12b in Figure 4, where the resin flow is poor, in runner grooves with an increased cross-sectional area, and will also tend to produce resin that does not contribute to improving the transferability of the molten resin, so it cannot be said that this will efficiently improve the transferability of the injection pressure.

[0030] As in this embodiment, cold runner 10 is formed from main runner grooves 6 and sub-runner grooves 8 that have smaller opening widths and cross-sectional areas than main runner grooves 6, and by adjusting the cross-sectional area of sub-runner grooves 8 as needed, it is possible to efficiently improve the transferability of the injection pressure of the molten resin without unnecessarily increasing the volume of cold runner 10. In particular, by making the cross-sectional shape of main runner grooves 6 approximately U-shaped or approximately trapezoidal and the cross-sectional shape of sub-runner grooves 8 approximately arc-shaped, there is an advantage in that it is easy to improve the efficiency of transfer of injection pressure by sub-runner grooves 8 while facilitating release of solidified resin when the mold is opened.

[0031] Taking the above into consideration, the method for forming a cold runner that ensures the injection pressure of molten resin into the cavity while suppressing an increase in volume is as follows.

[0032] [Step 1: Prepare the runner plate] Two runner plates (first and second runner plates) are prepared, which are overlapped with each other when the mold is closed to form a cold runner therebetween.

[0033] [Step 2: Forming the main runner groove] A main runner groove having a substantially U-shaped or substantially trapezoidal cross section is formed on the cold runner forming surface of one (the first runner plate) of the two prepared runner plates. Here, the cross-sectional area of the cold runner is empirically determined based on the shape and size of the molded product, the number of products per mold, the type of resin, etc., but it is preferable that the cross-sectional area of the main runner groove be designed to be the empirically determined minimum value of the cross-sectional area of the cold runner or smaller.

[0034] [Step 3: Forming sub-runner grooves] A test molding is performed using a mold equipped with a cold runner consisting only of a main runner groove using two runner plates. During the test molding, areas where defects such as sink marks have occurred due to insufficient filling of the molten resin and where the injection pressure needs to be improved are identified. Sub-runner grooves with a cross-sectional shape that is approximately arc-shaped are formed on the cold runner forming surface of the other of the two runner plates (the second runner plate) in areas where the injection pressure needs to be improved. Test molding is then performed to check for the occurrence of sink marks and other defects, and additional processing such as adding sub-runner grooves or increasing the cross-sectional area is performed as necessary.

[0035] If the cross-sectional area of the main runner groove is designed to be smaller than the empirically determined minimum value of the cross-sectional area of the cold runner, sub-runner grooves large enough to supplement the cross-sectional area of the main runner groove may be formed before test molding is performed. In this case, too, test molding can be performed to identify areas where the injection pressure needs to be increased, and additional processing such as enlarging the cross-sectional area of the sub-runner groove can be performed as necessary.

[0036] With the above-described cold runner formation method, even if it is necessary to improve the transferability of injection pressure, there is no need to perform additional processing on the main runner grooves; only processing such as adding or enlarging sub-runner grooves is required. Because there is very little variation in the degree of resin melting within the sub-runner grooves, it is unlikely that waste resin will be generated that does not contribute to the transferability of injection pressure to the molten resin, and it is possible to suppress the increase in solidified resin within the cold runner that becomes waste material after the mold is opened.

[0037] The first runner plate 2 and the second runner plate 4 may be plates dedicated to forming cold runners, or may be partial mold plates configured in a nested manner, or may be used in combination with mold plates for other purposes.

[0038] The above-described embodiments are merely examples of the cold runner unit and the method for forming a cold runner according to the present invention. The cold runner unit and the method for forming a cold runner according to the present invention are as follows.

[0039] One embodiment of the cold runner unit according to the present invention is a cold runner unit that forms a cold runner for feeding molten resin into a cavity of an injection molding die, The cold runner includes first and second runner plates that are superimposed on each other to form the cold runner therebetween, and at least a portion of the cold runner is formed by a main runner groove provided on the cold runner forming surface of the first runner plate facing the second runner plate, and a sub-runner groove for adjusting the injection pressure transmittance of molten resin that is provided in correspondence with the main runner groove on the cold runner forming surface of the second runner plate facing the first runner plate, and the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow path direction of the cold runner are smaller than those of the main runner groove.

[0040] In a first aspect of the above embodiment of the cold runner unit, the cross section of the main runner groove perpendicular to the flow path direction of the cold runner is generally U-shaped or generally trapezoidal.

[0041] In a second aspect of the above embodiment of the cold runner unit, the cross section of the sub-runner groove perpendicular to the flow path direction of the cold runner is substantially arc-shaped.

[0042] In a third aspect of the above embodiment of the cold runner unit, the sub-runner groove is located in the center of the main runner groove.

[0043] One embodiment of a cold runner forming method according to the present invention is a method for forming a cold runner for feeding molten resin into a cavity of an injection molding die, the method comprising the steps of: providing first and second runner plates to be superimposed on one another to form the cold runner therebetween; a first forming step of forming a main runner groove at a cold runner forming position on a cold runner forming surface of the first runner plate facing the second runner plate; a second forming step of forming a sub-runner groove for adjusting the transferability of injection pressure of a molten resin in at least a part of a cold runner forming position on a cold runner forming surface of the second runner plate facing the first runner plate, In the second forming step, the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow path direction of the cold runner are made smaller than those of the main runner groove.

[0044] In a first aspect of the above embodiment of the cold runner forming method, in the first forming step, the cross section of the main runner groove perpendicular to the flow path direction of the cold runner is formed into a substantially U-shape or a substantially trapezoidal shape.

[0045] In a second aspect of the above embodiment of the cold runner forming method, in the second forming step, the cold runner has a cross section perpendicular to the flow path direction that is formed into a substantially arc shape.

[0046] In a third aspect of the above embodiment of the cold runner forming method, in the second forming step, the sub-runner groove is formed so as to be located at a center portion of the main runner groove. [Explanation of symbols]

[0047] 1 Cold runner unit 2 First runner plate 4 Second runner plate 2a, 4a Cold runner forming surface 6 Main runner groove 8 Sub-runner groove 10 Cold Runner

Claims

1. A cold runner unit that forms a cold runner for feeding molten resin into a cavity of an injection molding die, a cold runner unit comprising: first and second runner plates superimposed on each other to form the cold runner therebetween; at least a portion of the cold runner being formed by a main runner groove provided on a cold runner-forming surface of the first runner plate facing the second runner plate; and sub-runner grooves for adjusting injection pressure transferability of molten resin, the sub-runner grooves being provided in the cold runner-forming surface of the second runner plate facing the first runner plate to correspond to the main runner grooves, the sub-runner grooves having smaller opening widths and smaller cross-sectional areas perpendicular to a flow path direction of the cold runner than the main runner grooves.

2. 2. The cold runner unit according to claim 1, wherein a cross section of the main runner groove perpendicular to a flow path direction of the cold runner is substantially U-shaped or substantially trapezoidal.

3. 2. The cold runner unit according to claim 1, wherein the cross section of the sub-runner groove perpendicular to the flow path direction of the cold runner is substantially arc-shaped.

4. The cold runner unit according to claim 1 , wherein the sub-runner groove is located in a central portion of the main runner groove.

5. 1. A method for forming a cold runner for delivering molten resin to a cavity of an injection mold, comprising: providing first and second runner plates to be superimposed on one another to form the cold runner therebetween; a first forming step of forming a main runner groove at a cold runner forming position on a cold runner forming surface of the first runner plate facing the second runner plate; a second forming step of forming a sub-runner groove for adjusting the transferability of injection pressure of a molten resin in at least a part of a forming position of a cold runner on a cold runner forming surface of the second runner plate facing the first runner plate, In the second forming step, the opening width of the sub-runner groove and the cross-sectional area perpendicular to the flow path direction of the cold runner are made smaller than those of the main runner groove.

6. 6. The cold runner forming method according to claim 5, wherein in the first forming step, the cross section of the main runner groove perpendicular to the flow path direction of the cold runner is formed into a substantially U-shape or a substantially trapezoidal shape.

7. 6. The method for forming a cold runner according to claim 5, wherein in the second forming step, the cross section of the cold runner perpendicular to the flow path direction is formed into a substantially arc shape.

8. 6. The cold runner forming method according to claim 5, wherein in the second forming step, the sub-runner groove is formed so as to be located at a center portion of the main runner groove.

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