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Causes of overflow during injection mold processing

Release time:2021-07-09

Overflow, also known as flash and overflow, usually occurs at the opening and closing position of the mold. For example, the parting surface of the mold, the gap of the insert and the hole of the ejector rod. If the overflow cannot be eliminated in time, it will lead to local collapse of the injection mold, and even permanent damage will be formed in serious cases. In addition, the overflow of insert gap and ejector pin hole will also lead to waste products stuck on the mold, affecting the demoulding process. So why does the injection mold overflow in the processing process? How to deal with the overflow phenomenon? The following editor will answer for you.

1、 Equipment

1. The improper installation and adjustment of the mold closing of the injection molding machine or the uneven elbow mechanism will cause the mold to not reach the due parallelism, presenting the phenomenon that one side of the mold is tightly closed and the other side is not tightly connected, which is easy to show overflow during the injection process.

2. There is a problem with the parallelism of the injection molding machine itself, and the uneven force distribution of the pull rod will also lead to the failure of the mold to close tightly and form a material overflow condition.

3. The injection molding machine has serious wear of the check ring, too much wear of the screw, lack of the set injection volume of the barrel, too small buffer pad and other conditions, which are likely to cause material overflow, so the operator must stop repairing or changing parts in time.

II. Mold

1. Poor accuracy of mold parting surface

The movable template (such as the middle plate) is deformed and warped, there are foreign objects on the parting surface, and there are prominent skid marks and burrs on the periphery of the mold frame. These conditions will lead to the overflow of the injection mold.

2. Unreasonable mold design

(1) If the opening position of the mold cavity is too biased, the mold will have excessive unilateral tension during the injection process, resulting in overflow.

(2) Polyethylene, polypropylene and other plastic materials have good mobility, and their viscosity in the molten state is low, so it is easy to enter the gap of the mold. Therefore, when manufacturing high-precision molds, operators should try to feed in the thick part of the mold, so as to avoid overflow and affect the integrity of the mold products.

(3) The poor matching accuracy of the sliding core of the mold or the offset between the fixed core and the cavity device will also lead to the appearance of the overflow condition.

(4) As for the multi cavity mold, the designer should pay attention to the reasonable design of the runner and gate, otherwise it will lead to uneven filling force and overflow.

3、 Process aspect

1. Under the action of high pressure and high speed, the tension of the mold will increase, causing overflow, so the operator needs to adjust the injection speed and injection time according to the thickness of the mold product. The filling of thin products should be high-speed and fast, while for thick products, low-speed filling should be used.

2. Some operators often choose to inject more molten material in order to avoid the depression of the injection mold, but doing so will certainly solve the problem, but it will lead to overflow. Therefore, when we encounter this situation, we should deal with it by extending the injection time or pressure holding time.

The above is about the analysis of the reasons for the overflow of injection mold. The editor mainly introduces the equipment, mold and process, and hopes to help you.

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