A gate structure for preventing shrinkage printing

Abstract

The present invention provides a gate structure for preventing shrinkage, which is formed by a cavity between a movable mold and a fixed mold, and includes: a first cold runner, a second cold runner, a third cold runner and a fourth cold runner extending in sequence, wherein the first cold runner and the third cold runner extend approximately in a horizontal direction, and the second cold runner and the fourth cold runner extend approximately in a vertical direction relative to each other, thereby forming an inverted "J"-shaped structure, wherein a gate section whose height dimension is reduced relative to both the second cold runner and the third cold runner is provided between the second cold runner and the third cold runner; wherein the molten material flows in from the first cold runner, flows through the second cold runner, the gate section, and the third cold runner in sequence, and then flows out from the fourth cold runner and enters a mold cavity for product molding. The present invention is further confirmed by analysis software that the gate structure provided according to the present invention can effectively solve the problem of shrinkage on the product appearance surface at the front end of the gate, thereby ensuring a good product appearance and improving product quality.

Description

Technical Field

[0001] The invention relates to injection molding technology, and more particularly to an anti-shrinkage gate structure. Background Art

[0002] In the automotive industry, exterior decorative plastic parts usually have very high quality requirements. Except for the snap-on position, the rest are all exterior surfaces. When the molten resin after filling the mold cools and solidifies from the outer surface, when the volume shrinkage cannot be compensated, the resin on the surface of the molded product will be stretched due to the volume shrinkage of the internal molten resin, resulting in a dent in the product. This shrinkage dent produced during the cooling process of plastic injection molding is called shrinkage.

[0003] According to the shrinkage characteristics of the material, the higher the temperature area, the greater the volume shrinkage rate of the product, the more likely it is to shrink, or the greater the shrinkage difference between adjacent areas of the product, the more likely this area is to shrink. Generally, gate shrinkage occurs within a radius of 20mm at the front end of the gate. The standard for measuring shrinkage can be judged from the value of the analysis result of the analysis software MOLDFLOW. Theoretically, when the maximum volume shrinkage rate is <5%, or the difference between adjacent volume shrinkage rates within a 10mm area is <2%, the risk of shrinkage is small. In fact, this measurement value may still cause shrinkage, and the smaller the better.

[0004] For products with the same wall thickness, the gate area is the last area where the molten material stops flowing during the entire molding cycle, and it is also the area with the highest temperature. Therefore, the shrinkage at the front end of the gate is also the largest. As the gate freezes, the conventional gate cannot solve the shrinkage at the front end of the gate because the balance between feeding and over-feeding cannot be guaranteed.

[0005] Ordinary gates cannot avoid shrinkage at the front end of the gate, and shrinkage generally occurs within a 20mm radius of the front end of the gate. Common solutions are to increase the gate width and add inserts. However, due to the constraints of the product structure, it is often impossible to increase the gate width. At this time, the only solution is to add inserts to make the distance from the gate to the appearance surface > 20mm, forcing the shrinkage to appear on the insert, and then trim the insert to ensure that there is no shrinkage on the appearance surface. However, from the actual effect, although the insert solution has a certain optimization effect on shrinkage and a certain reduction effect on shrinkage, it still cannot solve the shrinkage problem at the front end of the gate. Summary of the invention

[0006] The purpose of the present invention is to provide a gate structure for preventing shrinkage, so as to solve the problem that the prior art cannot effectively solve the shrinkage on the appearance surface of the product at the front end of the gate.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] Provided is a gate structure for preventing shrinkage printing, which is formed by a cavity between a movable mold and a fixed mold. The gate structure comprises: a first cold runner, a second cold runner, a third cold runner and a fourth cold runner extending in sequence, wherein the first cold runner and the third cold runner extend approximately in a horizontal direction, and the second cold runner and the fourth cold runner extend approximately in a vertical direction relative to each other, thereby forming an inverted "J"-shaped structure, wherein a gate section whose height dimension is reduced relative to both the second cold runner and the third cold runner is provided between the second cold runner and the third cold runner; wherein the molten material flows in from the first cold runner, flows through the second cold runner, the gate section and the third cold runner in sequence, then flows out from the fourth cold runner and enters a mold cavity for product molding.

[0009] Preferably, the height dimension of the third cold runner is 1.8 to 2.2 times the height dimension of the fourth cold runner, and most preferably, the height dimension of the third cold runner is twice the height dimension of the fourth cold runner.

[0010] The heights of the first cold runner and the second cold runner are comparable, and most preferably are equal.

[0011] The widths of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner are all equal.

[0012] Preferably, the widths of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner are all 20 to 30 mm.

[0013] Preferably, the height dimensions of the first cold runner and the second cold runner are 4-5 mm, the height dimension of the third cold runner is 4 mm, and the height dimension of the fourth cold runner is 2 mm.

[0014] Preferably, the length of the first cold runner is 45-50 mm, the length of the second cold runner is 25-30 mm, the length of the third cold runner is 10 mm, and the length of the fourth cold runner is 20-25 mm.

[0015] Preferably, the angle between the second cold runner and the third cold runner is 115° to 120°, and the angle between the third cold runner and the fourth cold runner is 95° to 100°.

[0016] Preferably, an angle transition section is provided between the first cold runner and the second cold runner. It should be understood that no angle transition section may be provided between the first cold runner and the second cold runner.

[0017] The total length of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner is less than 120 mm.

[0018] The gate structure provided by the present invention is composed of a first cold runner, a second cold runner, a third cold runner and a fourth cold runner extending in sequence. In particular, compared with the insert gate in the prior art, a fourth cold runner basically perpendicular to the third cold runner is added, thereby forming a structure similar to an inverted "J" shape.

[0019] Furthermore, the present invention provides a gate structure with optimized performance by optimizing the angles, height dimensions, and length dimensions of the first cold runner, the second cold runner, the third cold runner, and the fourth cold runner, respectively.

[0020] Finally, the present invention further confirms through analysis software that the gate structure provided by the present invention can effectively solve the problem of shrinkage on the appearance of the product at the front end of the gate, ensuring a good appearance of the product and improving the product quality. Such a gate structure provided by the present invention is particularly suitable for injection molding of polypropylene products, but it should be understood that it is not limited to polypropylene, and can also be used for injection molding of any other similar plastic products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a gate structure provided according to a preferred embodiment of the present invention;

[0022] Figure 2 It is a gate design diagram on a bumper product, wherein 1-1 is the gate of the present invention, and the remaining gates 2-2 are common gates;

[0023] Figure 3 It is an enlarged schematic diagram of the details printed on the exterior surface of the bumper product at the front end of the gate;

[0024] Figure 4 This is a schematic diagram of analyzing the front end shrinkage of the gate from a temperature perspective using MLODFLOW analysis software;

[0025] Figure 5 This is a schematic diagram of analyzing the shrinkage of the gate front end from the perspective of volume shrinkage using MLODFLOW analysis software;

[0026] Figure 6 , 7 ,8 The schematic diagrams of BLOCK gate, ordinary gate and insert gate are analyzed from the perspective of volume shrinkage using MLODFLOW analysis software. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific examples. It should be understood that the following examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0028] like Figure 1As shown, a gate structure 1-1 for preventing shrinkage printing, also known as a BLOCK gate, is provided according to a preferred embodiment of the present invention. This gate structure 1-1 is a flat runner formed by the cavity between the moving mold and the fixed mold and is used for the flow of molten injection molding material before it enters the mold cavity. By providing such a structural design, the present invention can greatly reduce the shrinkage printing problem on the product appearance surface, and the details are as follows.

[0029] Refer to Figure 1 , this gate structure 1-1 includes: a first cold runner 1, a second cold runner 2, a third cold runner 3, and a fourth cold runner 4 that extend in sequence. Among them, the first cold runner 1 and the third cold runner 3 extend substantially in the horizontal direction, and the second cold runner 2 and the fourth cold runner 4 extend substantially in the vertical direction relative to each other, thus forming a structure similar to an inverted "几" shape as shown in Figure 1 . There is a gate section 5 between the second cold runner 2 and the third cold runner 3, and the height dimension of the gate section 5 is reduced relative to both the second cold runner 2 and the third cold runner 3; among them, the molten material flows in from the inlet of the first cold runner 1 (the leftmost end in the figure), flows through the second cold runner 2, the gate section 5, and the third cold runner 3 in sequence, and then flows out from the outlet of the fourth cold runner 4 (the top rightmost end in the figure) and enters the mold cavity for product molding.

[0030] According to a preferred embodiment of the present invention, the height dimension T3 of the third cold runner 3 is 1.8 to 2.2 times the height dimension T4 of the fourth cold runner 4. Most preferably, the height dimension T3 of the third cold runner 3 is twice the height dimension T4 of the fourth cold runner 4.

[0031] Also preferably, the height dimension T1 of the first cold runner 1 is equal to the height dimension T2 of the second cold runner 2.

[0032] It should be known that the width dimensions W of the first cold runner 1, the second cold runner 2, the gate section 5, the third cold runner 3, and the fourth cold runner 4 should be equal.

[0033] According to this preferred embodiment, the width dimensions W of the first cold runner 1, the second cold runner 2, the gate section 5, the third cold runner 3, and the fourth cold runner 4 are all 20 to 30 mm.

[0034] According to a preferred embodiment of the present invention, the height dimensions of the first cold runner 1 and the second cold runner 2 are 4 to 5 mm, the height dimension of the third cold runner 3 is 4 mm, and the height dimension of the fourth cold runner 4 is 2 mm.

[0035] According to this preferred embodiment, the length dimension of the first cold runner is 45 to 50 mm, the length dimension of the second cold runner is 25 to 30 mm, the length dimension of the third cold runner is 10 mm, and the length dimension of the fourth cold runner is 20 to 25 mm.

[0036] According to the preferred embodiment, the angle B between the second cold runner 2 and the third cold runner 3 is 115° to 120°, and the angle A between the third cold runner 3 and the fourth cold runner 4 is 95° to 100°.

[0037] The first cold runner 1 and the second cold runner 2 can be Figure 1 Although the angle transition section F is provided as shown in FIG. 1 , it should be understood that the angle transition between the first cold runner 1 and the second cold runner 2 may not be provided.

[0038] The total length of the first cold runner 1, the second cold runner 2, the gate segment 5, the third cold runner 3 and the fourth cold runner 4 is preferably less than 120 mm.

[0039] Figure 2 This is a gate design diagram for a bumper product, where 1-1 is the BLOCK gate of the present invention, and the remaining gates 2-2 are designed as ordinary gates. Figure 3 It can be seen that the BLOCK gate 1-1 of the present invention can effectively solve the shrinkage S of the visible surface at the front end of the gate. The BLOCK gate can solve the cause of shrinkage, which can be clearly seen from the result trend values ​​of temperature and volume shrinkage rate of the mold flow analysis of the following analysis software MOLDFLOW.

[0040] It should be understood that the disadvantage of the present invention is that the loss of injection pressure at the gate is relatively large compared with ordinary gates, but it will not affect the pressure required for product molding. This pressure loss factor does not need to be considered when designing the BLOCK gate.

[0041] Figure 4 This is an analysis of the reasons why the front end of the gate is prone to shrinkage from the temperature perspective of the MLODFLOW analysis software. 5-3 is the temperature scale, red represents the highest temperature, blue represents the lowest temperature, and the colors on the product correspond to the temperatures on the temperature scale. In the figure, the temperature at the front end of the gate is the highest, and the farther away from the gate, the lower the temperature, and the temperature gradually decreases from 5-1 to 5-2. According to the shrinkage characteristics of the material: the higher the temperature, the greater the shrinkage, and the more likely it is to cause shrinkage. Therefore, from Figure 4 It can be seen that the front end of the gate is more likely to cause shrinkage than other areas. Regardless of whether it is a conventional gate or a BLOCK gate, all gates follow this principle.

[0042] Figure 5 This is to analyze the reason why the front end of the gate is prone to shrinkage from the perspective of volume shrinkage of MLODFLOW analysis software. 40 is the volume shrinkage scale, red represents the largest shrinkage, and it gradually decreases downwards. The colors on the product correspond to the shrinkage of 40. In the figure, the volume shrinkage of the 30 area is the highest at the front end of the gate, and the shrinkage of other areas is lower than that of the front end of the gate. Therefore, the shrinkage at the front end of the gate is the most serious, and all shapes of gates follow this principle.

[0043] Figure 6 , Figure 7 , Figure 8 Experiments were conducted on BLOCK gates, ordinary gates, and insert gates from the perspective of volume shrinkage using MLODFLOW analysis software to analyze why BLOCK gates can solve shrinkage problems. Figure 6 , Figure 7 , Figure 8 In the figure, E, F, G, H, and I are the same points on the product. The volume shrinkage of each point using the BLOCK gate, ordinary gate, and insert gate is calculated by the software. It can be seen that the maximum volume shrinkage at the front end of the gate is: BLOCK = 2.66, insert = 4.03, ordinary = 6.62. The BLOCK gate has the smallest volume shrinkage, so it can effectively solve the shrinkage problem. The maximum difference in volume shrinkage between adjacent areas at the front end of the gate is: BLOCK = 0.37, insert = 1.75, ordinary = 1.14. The difference in volume shrinkage between adjacent BLOCK gates is the smallest, and there is a risk of shrinkage.

[0044] Table 1

[0045] Points on the product BLOCK Volume Shrinkage Insert volume shrinkage Normal volume shrinkage E 1.90 2.28 2.10 F 2.20 2.28 2.72 G 2.57 4.03 4.48 H 2.66 3.14 5.78 I 2.65 2.82 6.62

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0047] In addition, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0048] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiments of the present invention can also be modified in various ways. All simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A gate structure for preventing shrinkage printing, formed by a cavity between a movable mold and a fixed mold, characterized in that: The gate structure includes: a first cold runner, a second cold runner, a third cold runner and a fourth cold runner extending in sequence, the first cold runner and the third cold runner extend in a horizontal direction, the second cold runner and the fourth cold runner extend in a vertical direction relative to each other, thereby forming an inverted "J"-shaped structure, and a gate section with a height dimension reduced relative to the second cold runner and the third cold runner is provided between the second cold runner and the third cold runner; wherein, the molten material flows in from the first cold runner, flows through the second cold runner, the gate section, and the third cold runner in sequence, and then flows out from the fourth cold runner to enter the mold cavity for product molding.

2. The gate structure according to claim 1, characterized in that: The height dimension of the third cold runner is 1.8 to 2.2 times the height dimension of the fourth cold runner.

3. The gate structure according to claim 1, characterized in that: The first cold runner and the second cold runner have similar heights.

4. The gate structure according to claim 1, characterized in that: The widths of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner are all equal.

5. The gate structure according to claim 4, characterized in that: The widths of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner are all 20 to 30 mm.

6. The gate structure according to claim 1, characterized in that: The height dimensions of the first cold runner and the second cold runner are 4-5 mm, the height dimension of the third cold runner is 4 mm, the height dimension of the fourth cold runner is 2 mm, and the height dimension of the gate section is 1.5-1.8 mm.

7. The gate structure according to claim 1, characterized in that: The length of the first cold runner is 45-50 mm, the length of the second cold runner is 25-30 mm, the length of the third cold runner is 10 mm, and the length of the fourth cold runner is 20-25 mm.

8. The gate structure according to claim 1, characterized in that: The included angle between the second cold runner and the third cold runner is 115° to 120°, and the included angle between the third cold runner and the fourth cold runner is 95° to 100°.

9. The gate structure according to claim 1, characterized in that: An angle transition section is provided between the first cold runner and the second cold runner.

10. The gate structure according to claim 1, characterized in that: The total length of the first cold runner, the second cold runner, the gate section, the third cold runner and the fourth cold runner is less than 120 mm.

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