JPH065929U - Injection mold - Google Patents

Abstract

(57) [Summary] [Purpose] While taking advantage of the characteristics of pinpoint gates, it is possible to prevent the occurrence of defects that were likely to occur at the gate exit portion of molded products, and to significantly increase the strength. A mold for injection molding is provided. [Structure] The length between the sprue 21 and the inlet of the gate to the cavity 23 (corresponding to the gate land cutting portion 27) is approximately 10 mm to 30 mm, and the diameter of the inlet to the cavity 23 is approximately 2.5 to. An injection-molding die provided with a pin-point gate-type gate land 22 having a diverging slope of 6.0 mm.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 TECHNICAL FIELD The present invention relates to an injection molding die, and more specifically, to an injection molding used to form a molded product having a male and female mold surface and injecting a molten synthetic resin material between them. For molds.

[0002]

[Prior art]

 This type of injection molding die is used, for example, to mold a synthetic resin material into a certain shape, and has excellent thermal conductivity and is made of a metallic material of sufficient thickness. It is composed of a mold (cavity mold) and a male mold (core mold), and a synthetic resin material heated and melted is injected from a gate into a cavity formed between these molds. After the injection, the mold on the movable side is moved after cooling and the molded product having a predetermined shape is taken out.

FIG. 4 shows an example of such an injection molding die for synthetic resin. This example shows a mold for forming the base of an office chair. Here, 1 is a cavity mold, 2 and 3 are core molds, and of the core molds 2 and 3, 2 is a core mold fixed to the cavity mold 1 and 3 is a movable core mold. Further, in this example, a sprue bush 5 having a sprue hole (hereinafter referred to as a sprue) 4 is attached to the fixed core mold 2 in consideration of the position of the protruding portion of the molded product.

By the way, such an injection molding die is generally provided with a heating or cooling means for adjusting the temperature of the die surface of the core die and the cavity die. For example, a heater is built in the die. Alternatively, a liquid passage for circulating a liquid medium is formed, and a heating or cooling medium is circulated in the liquid passage. In FIG. 4, 6 and 7 are liquid passages for circulating such liquid, 8 is an annular liquid passage communicating with the liquid passages 6, 7, and the liquid medium is from the liquid passage 6 to the annular liquid passage 8. After being guided, it is again guided to the outside of the mold via the liquid passage 7. Further, 9 is an O-ring for sealing provided between the sprue bush 5 and the fixed core mold 2, and 10 is an O-ring for sealing between the fixed core mold 2 and the cavity mold 1. .

Thus, the weld synthetic resin material injected into the sprue 4 by the nozzle (not shown) passes through the runner 11 and the gate 12 to form a cavity space between the cavity mold 1 and the core molds 2 and 3 (hereinafter referred to as “cavity space”). Is referred to as a cavity (13), where it is cooled and solidified and taken out after the mold is disassembled.

As described above, the gate 12 forms an inlet portion from the runner 11 to the cavity 13, and its position, shape and size have a great influence on the quality of the molded product. Further, it controls the flow direction and flow rate of the resin with which the cavity 13 is filled, and at the same time functions to retain the resin pressure in the cavity 13 until the molded product is solidified.

Therefore, for example, if the cross-sectional area of the gate 12 is increased, the flow to the cavity 13 is facilitated, but it takes time to remove the gate when finishing the molded product, and conversely, if the cross-sectional area is reduced, While the inflow resistance to 13 increases and the gate sealing time becomes shorter, it is easier to clean up. If the number of molded products is large, it is possible to improve the balance of the inflow of each cavity by changing the gate size to correspond to it.

There are two types of gates, a direct gate that is directly connected to the cavity from the sprue and a limiting gate that is not directly connected to the cavity. Known are pinpoint gates with small pore sizes that are often used for good molding materials. However, the direct gate (unlimited gate) has the advantage that the mold structure is relatively simple and the pressure loss is small, but on the other hand, it takes a long time to solidify in the sprue, and residual stress tends to remain, resulting in a product. The major drawback is that cracks tend to occur.

Furthermore, in the case of a side gate, the land (parallel portion of the gate) tends to be too long in order to facilitate gate cutting, which deteriorates moldability. Due to the solidification, the holding pressure becomes insufficient and bubbles and sinks are likely to occur. On the other hand, in the case of a pinpoint gate, its diameter is as small as 0.3 to 1.5 mm, and the resistance of the gate is inevitably higher than that of a side gate. It has been. (0.8 to 1.2 mm) However, in the case of a pinpoint gate, after the gate is removed, it is inconspicuous, the post-finishing is easy, and it is suitable for multi-cavity molding. For example, as shown in Fig. 4. In the case of a large-sized molded product, it is possible to provide a plurality of pinpoint gates and inject resin from them, which is advantageous in that a molded product with less distortion or deformation can be obtained.

[0010]

[Problems to be solved by the device]

 However, the conventional pinpoint gate as described above has an advantage over other types of gates, but on the other hand, residual stress is likely to remain on the gate exit side, that is, the cavity side, which causes a problem in strength. It becomes the starting point of cracks when a high load is applied. In addition, when the gate is cut later, there is a risk of biting into the molded product side and microcracks on the cut surface, which causes cracking due to high load.

It has been considered that such a problem is caused by the following reasons.

1. The pinpoint gate solidifies first because it is the thinnest of the sprue, runner and gate. Therefore, at the pinpoint gate, even if the movement of the resin becomes dull and the gate begins to solidify, the resin at the gate part moves slightly and it is presumed that unmelt (semi-solidified resin) enters the molded product. . At that time, the inside of the molded product is still in a molten state, but solidification is proceeding from the skin layer. Therefore, all of the unmelt does not remelt. This unmelted resin receives a large amount of internal pressure from the injection molding machine when the resin is injected, so that it becomes an internal strain and is contained in the unmelted inner part. Therefore, if the strain is not dispersed by remelting, the strain remains at the gate exit portion of the molded product. This is called residual strain (stress), and if excessive stress is applied to this part, it is highly likely that it will become a crack starting point, and the strength will be significantly reduced.

2. Due to its structure, the pinpoint gate is torn off at the same time when the molded product is solidified and the mold is opened, so there is a high possibility that micro-cracks will occur in the gate cut surface of the molded product and bite into it. Therefore, similarly to the above, if excessive stress is applied to this portion, it is highly likely that it will become a crack starting point, and the strength will be significantly reduced.

In addition, the pinpoint gates that have been adopted so far are that, for one thing, gate cutting work using a nipper or the like, which is troublesome for side gates and direct gates, is required. At the same time, gate cutting is also performed automatically, making automation easy. The other is functional parts such as the engine cylinder head cover, which is easy to ensure flatness. In particular, in the case of a pinpoint gate that uses a three-piece mold, it was easy to install the gate at most places on the molded product, and it was easy to add multiple points, so it was sometimes said that countermeasures against warpage would be easy. .

However, recently, in a molded article using such a multi-point pinpoint gate, the heat cycle test conditions are becoming stricter due to the need for quality improvement, and it is particularly necessary to increase the strength of the gate portion. Is happening.

The object of the present invention is to focus on the problems related to the conventional injection molding die as described above, and to solve the problems, while taking advantage of the advantages of the pinpoint gate, it also affects the strength of the molded product. It is an object of the present invention to provide an injection-molding die that is free from the risk of cracking that would cause the occurrence of a crack and that has a strength that can withstand the recent heat cycle test conditions.

[0017]

[Means for Solving the Problems]

 In order to achieve such an object, the present invention provides an injection molding die capable of directly injecting a molten synthetic resin material into a cavity from a sprue through a runner and / or a gate. A pinpoint gate type gate land having a length of about 10 mm to 30 mm and a diverging gradient of about 2.5 mm to 6.0 mm at the gate injection opening to the cavity was provided between the inlet and the inlet. It is characterized by.

[0018]

[Action]

 According to the present invention, the sprue-side entrance portion of the gate land is formed into a pinpoint gate type having a small diameter of 0.3 to 2.5 mm by the above-described setting, and further toward the cavity entrance side. Since it is formed with an appropriate diverging slope and length, it is automatically cut at the sprue-side inlet of the gate land that is formed with a small diameter when the mold is separated, and the gate is solidified when the molten synthetic resin is solidified. Since residual stress is concentrated on the land, factors that affect the strength such as residual stress do not enter the molded product itself, and even if the gate land is later cut from the molded product, the cut part affects the strength. There is no such element.

[0019]

【Example】

 Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. Here, 21 is a sprue for receiving a molten molding resin material from a nozzle (not shown), 22 is a gate land formed in a tapered shape of the pin point gate according to the present invention, and 23 is a key for forming a molding 24. The cavity 25 is located on the pinpoint gate inlet side of the gate land 22 and has a small diameter (d ₁ : 0.3 to 2.5 mm in this example) and is cut when the upper and lower molds 26A and 26B are separated. The sprue cut portion 27 is formed on the cavity 23 side of the gate land 22 and has a diameter d ₂ of 2.5 to 6.0 mm in this example. The land cutting portion 27 is mechanically separated from the molded product 24 by a nipper or the like at the time of finishing the molding after the mold separation. In this example, the length 1 of the gate land 22 is set to 10 to 30 mm, but the reason for having such a length will be described later.

In the injection molding die having the pinpoint gate thus formed, the molded product 24 is cut by the thin sprue cutting portion 25 by the operation of separating the upper and lower molds 26A and 26B. In this case, the high residual stress generated during the solidification process is concentrated in the gate lands 22 that are long and thick, and thus do not penetrate into the molded product 24 as in the conventional case. . Therefore, even if the gate land cutting portion 27 mechanically cuts the portion of the gate land 22 from the molded product 24 after that, micro-cracks are generated in the cut surface, or the cut surface bites into the molded product 24 side and is cut off. The strength of this cut portion of the molded product 24 is sufficiently ensured without being damaged.

If the present invention is applied to a mold having a multi-point pinpoint gate for a large-sized molded product which requires strength, the molded product 24 has been generated so far in the vicinity of the cut surface. Surface defects such as winning flow marks (traces of the flow of molding material) are collected on the gate land 22 side and do not occur on the molded product 24 side, and high quality can be maintained.

In order to further confirm the results of the present invention, the inventors of the present invention, as shown in FIGS. 2A to 2C, have a mold 6- having a conventional pinpoint gate 2-0. 0 (A), the die 6-R (B) having an improved type point gate 2-R in which the diameter of the cavity side outlet of the pin point gate is expanded from 2 mm to 9 mm, and the pin point gate 22 according to the present invention. Molds 26 (C) having the above were prepared respectively. Then, as shown in (A) of FIG. 3, test pieces A1 to A4 having dimensions shown in (B) of FIG. 3 were prepared from molded articles (engine rocker covers) molded by these molds. As a result of tensile strength, elongation at break and heat cycle test using these test pieces, the results shown in Table 1 below were obtained.

[0024]

[Table 1]

Further, regarding the conventional form ((A) of FIG. 2) and the form of the present invention ((C) of FIG. 2), the condition of −30 ° C. to 150 ° C., 12 hr / 1 cycle As a result of the heat cycle test conducted in the conventional form (A), a crack was generated across the gate land cut portion in 26 to 30 cycles, while in the case of the form of the present invention (C), 46 Similar cracks were generated in the cycle, and it was confirmed that the device according to the present invention was more durable.

Furthermore, regarding the piece (3 inches × 5 inches, thickness 3.2 mm) according to the embodiment of the present invention, 100 ° C., 125 ° C., 150 ° C. and −30 ° C. to 150 ° C. (12 hr / 1 cycle) As a result of measuring the amount of post-shrinkage under the conditions described above, the post-shrinkage was completed under each temperature condition of 100 ° C to 150 ° C for about 10 hours, and in the case of the cycle pattern, the post-shrinkage was almost completed with 2 cycles. It was confirmed that the elongation limit of the material (3.0% at-40 ° C) was as low as 0.2% or less at 150 ° C.

From the above experimental results, it is clear that the gate land length of about 5 mm is insufficient. From this point, it is desirable that the gate land length is 10 mm or more. Further, the diameter d ₂ at the gate land cutting portion should be 6.0 mm or less in consideration of workability of cutting with a nipper or the like. Further, if the draft angle is 3.5 ° on one side, one sprue cut portion diameter d ₁ is generally 0.3 to 2 in the case of a pinpoint gate. When the pressure is suppressed to 5 mm, the length 1 of the gate land is in the range of 10 to 30 mm due to the relationship with d ₂ .

[0028]

[Effect of device]

 As described above, according to the present invention, the length between the sprue and the gate injection port into the cavity is approximately 10 mm to 30 mm, and the diameter of the gate injection port into the cavity is approximately 30 mm to 30 mm. Since a pin point gate type gate land having a diverging slope of approximately 2.5 to 6.0 mm is provided, the sprue cut portion that is finely formed is automatically connected and disconnected when the mold is opened, which is a feature of the pin point gate. It is possible to concentrate the residual stress on the gate land remaining on the molded product side, and prevent such residual stress from entering the molded product side. Therefore, even if such a gate land is cut from a molded product with a nipper or the like at the gate land cut portion, a defect due to residual stress does not occur on the molded product side, and sufficient strength can be maintained. .

In particular, in the case of a large-sized molded product provided with a multi-point pinpoint gate, it is possible to contribute to the production of a resin molded product in which the strength that can sufficiently withstand the heat cycle test is guaranteed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration example of a pinpoint gate according to the present invention together with dimensions of its applicable range.

FIG. 2 is a cross-sectional view showing a configuration of an embodiment (C) of the present invention set for a strength comparison test, a conventional example (A) and an improved example (B) thereof.

FIG. 3 is a perspective view (A) showing a test piece sampling point from a molded product for strength comparison at a gate land cut portion according to the forms of FIGS. 2 (A), (B) and (C) and the test piece. It is explanatory drawing by the top view (B) which shows the dimension of.

FIG. 4 is a cross-sectional view showing a configuration example of a mold for a large-sized molded product according to a conventional example.

[Explanation of symbols]

21 sprue 22 gate land 23 cavity 24 molded product 25 sprue cut part 26A, 26B mold 27 gate land cut part A1 to A4 test piece d ₁ sprue cut part diameter d ₂ gate land cut part l gate land length

Claims (1)

[Scope of utility model registration request] 1. An injection molding die capable of directly injecting a molten synthetic resin material into a cavity from a sprue via a runner and / or a gate, wherein a long length is provided between the sprue and an inlet of the gate to the cavity. Is about 10 mm to 30 mm, and the diameter at the gate injection port into the cavity is about 2.5 to 6.0 mm.
An injection-molding die, which is provided with a pin-point gate-type gate land having a slope that spreads toward the end.