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Causes of overflow in injection mold processing

Release time:2021-12-27

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, the hole of the ejector rod and so on. If the overflow cannot be removed in time, part of the injection mold will collapse and even cause permanent damage. In addition, the overflow of insert gap and ejector pin hole will also cause the finished product to be stuck on the mold, affecting the demoulding process. Then, why does overflow occur in injection mold processing? How to solve the overflow phenomenon?

1、 Equipment

1. Improper adjustment of the clamping device of the injection molding machine or uneven elbow bar mechanism will lead to the mold not reaching the required parallelism. One side of the mold is tightly closed, and the other side is not tightly connected, which is easy to cause overflow during injection molding.

2. The injection molding machine itself has the problem of parallelism, and the uneven force distribution on the pull rod will also cause the mold to be unable to close tightly, resulting in overflow.

3. The injection molding machine has problems such as serious wear of the check ring, excessive wear of the screw, insufficient injection volume of the barrel setting, and too small buffer pad, all of which may cause overflow, so the staff must repair or replace the parts in time.

2、 Mold aspect

1. Poor accuracy of mold parting surface

The deformation and warpage of the movable template (such as the middle plate), foreign matters on the parting surface, and protruding prying burrs around the mold frame will all lead to the overflow of the injection mold.

2. Unreasonable mold design

(1) If the opening position of the mold cavity is too far away, the unilateral tension of the mold will be too large during the injection process, resulting in overflow.

(2) Polyethylene, polypropylene and other plastic materials have good fluidity, low viscosity in the molten state, and are easy to enter the gap of the mold. Therefore, when manufacturing high-precision molds, staff should feed as many thick parts of the mold as possible to prevent overflow and affect the integrity of mold products.

(3) The poor fitting accuracy of the sliding core of the mold or the deviation of the installation position between the fixed core and the cavity will also lead to flash.

(4) For multi cavity mold, designers should pay attention to the reasonable design of gate and shunt channel, otherwise it will lead to uneven force on the filling mold and flash.

3、 Technical aspects

1. Under the action of high pressure and high speed, the tension of the mold will increase and cause flash, so the staff need to adjust the injection speed and injection time according to the thickness of the mold product. For thin products, mold filling should be high-speed and fast, while for thick products, mold filling should be low-speed.

2. Some workers often choose to inject more molten material to prevent the injection mold from sunken, but this may not solve the problem, but will lead to flash. Therefore, when we encounter this situation, we should deal with it by extending the injection time or pressure holding time.

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