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What is the phenomenon of wire drawing on the injection molded parts of automobiles, and how to eliminate it?

Update:17-05-2022
Summary:There are usually the following reasons for the wire drawing phenomenon on the i...
There are usually the following reasons for the wire drawing phenomenon on the injection molded parts of automobiles:
1. Insufficient return stroke of screw
2. Improper nozzle temperature setting
3. There is a gap in the nozzle
4. The nozzle and the mold runner are not aligned, resulting in serious deviation
5. Improper cooling time setting
Drawing solution:
1. In terms of injection molding process: a/Reduce the injection rate (the purpose is to allow the rubber elastomer component in the melt to have more time to achieve elastic recovery, and to avoid the formation of sudden mold expansion and cause pressure fluctuations and the flow rate of the flow front Variety).
b/Increase the plastic processing temperature and mold temperature (the purpose is to reduce the thickness of the plastic frozen layer, reduce the flow resistance, and improve the replication effect of the melt and the mold surface).
2. Mold structure:
a/ To expand the thickness and width of the gate section and the diameter of the runner, the gate thickness must reach 0.8-0.9 times the wall thickness of the part (the purpose is to reduce the resistance in the runner, thereby reducing the mold expansion effect);
b/Increase the number of gates and reduce the flow length ratio as much as possible (in the process of adjusting the machine, we found that there is no tiger skin pattern near the gate, and the tiger skin pattern will be obvious after a certain distance);
c/ Try to use straight gates, side gates and fan gates with gradually enlarged size and cross-sectional area, and avoid using latent gates and point gates with gradually reduced cross-sectional area. In practice, it is found that latent gates and point gates may be very Small side gates are easy to produce tiger skin pattern);
d/ The exhaust of the mold should be as good as possible, which can achieve high-speed injection and avoid stagnation at the front of the flow caused by trapped air, resulting in appearance quality defects;
3. In terms of plastic materials:
a/Reduce the content of rubber elastomer components (however, due to the high impact strength required for the use of many auto parts, this cannot be achieved in many cases);
b/ Improve the fluidity of the material (in practice, it is found that as long as the melting index of the material reaches 25g/10min or more, the tiger skin pattern can be effectively improved);
c/ The use of materials with a wider molecular weight distribution can effectively reduce the occurrence of tiger skin patterns.
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