Feman Tooling Co.,Limited
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Causes of Weld Marks of Plastic Products in Injection Molding

Injection moulding die makers own many new injection technology, but weld marks still occur during injection molding.

The weld lines of plastic products are caused by the incomplete fusion of the fused resins from different directions during the injection process. The two streams of resins at the fusion point do not mix with each other. The lower the temperature, the more obvious the melt marks are and the lower the strength is. Conversely, the higher the temperature, the stronger the bonding force. The bonding of the fusion joint also depends on the pressure applied there. The lower the holding pressure is, the worse the fusion and the lower the strength will be. The weld mark is the confluence point of the resins or the end of the resin flow. If a vent is not well set in the weld line of plastic products to exhaust gas, the appearance and strength of fusion will be damaged.


1. Increase resin temperature, injection molding mold temperature, injection pressure and speed.

2. Highlight air exhaust of parting surface. Adding inserts and ejector pins to weld lines is also conducive to air exhaust.

3. Choose a reasonable position for glue feeding, and it is best to do the flow analysis before the moulding of plastic products.

4. Increase the spills, and cut it off after cooling and forming.

5. Thicken and shorten the runner gating system to improve injection molding.

6. Rough texture is a good option for wool products, which is also beneficial to improve the weld mark problem.

The technology is developing and the technology is improving. There is no need to list all of them. Advanced technology is waiting for the injection moulding die makers

to study!

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