The molding processability of polyethylene PE. It should be known that PE is a crystalline raw material with very little hygroscopicity, not exceeding 0.01%, so no drying treatment is performed before processing. PE molecular chain has good flexibility, small force between bonds, low melt viscosity and good fluidity, so it does not need too high pressure during molding. The shrinkage rate of polyethylene is wide, the shrinkage value is large, and the directionality is obvious. The shrinkage rate of LDPE is about 1.22%, and the shrinkage rate of HDPE is about 1.5%. Therefore, it is easy to deform and warp, and the cooling condition of the injection mold has a great influence on the shrinkage. Therefore, the mold temperature of the injection mold should be controlled to keep the cooling uniform and stable.

 

The crystallization ability of PE is high, and the temperature of the mold has a great influence on the crystallization condition of the plastic parts. If the mold temperature is high, the melt will cool slowly, the crystallinity of the plastic part will be high, and the strength will be high. The melting point of PE is not high, but the specific heat capacity is large, so it still needs to consume more heat when plasticizing, so the plasticizing device is required to have a large heating power in order to improve production efficiency. The softening temperature range of PE is small, and the melt is easy to oxidize, so the melt and oxygen should be avoided as much as possible during the molding process, so as not to reduce the quality of plastic parts. PE parts are soft and easy to demold, so when the plastic parts have shallow grooves, they can be demolded strongly.

 

The non-Newtonian property of PE melt is not obvious, the change of shear rate has little influence on viscosity, and the influence of temperature on PE melt viscosity is also little. The cooling rate of PE melt is slow, so it is fully cooled. The injection mold should have a better cooling system. If the PE melt is fed directly from the feed port during injection, it is easy to increase the stress and cause uneven search and obvious increase in directionality. Therefore, attention should be paid to the selection of the feed port parameters. The molding temperature of PE is relatively wide. In the flowing state, a little temperature fluctuation has no effect on the molding of injection molded parts. PE has good thermal stability, generally there is no obvious decomposition phenomenon below 300 degrees, and it has no effect on the quality.