The plastic mold processing factory analyzes the precau […]
The plastic mold processing factory analyzes the precautions during the injection molding process:
1. Overburden, pay attention to the residual material between the mold and the gap between the mold surface during the molding process;
2. Lack of material. If the aluminum liquid is not filled in the injection molding machine, the shape of the plastic part will be incomplete and incomplete;
3. Welding marks, when the aluminum material is shunted in the mold, it cannot be integrated with each other, which will cause a fusion mark;
4. The surface is turbid, and attention should be paid to avoid cracks appearing when the plastic parts are exposed to high temperature or exposed to temperature changes, which will damage the plastic parts;
5. Wave flow marks, pay attention to avoid the melt in the mold cavity due to improper flow forming unevenness, thereby affecting the aesthetics of the plastic parts.
Injection molding process of polyethylene PE
PE is a crystalline raw material with extremely low hygroscopicity, no more than 0.01%, so there is no need for drying before processing. PE molecular chain has good flexibility, small force between bonds, low melt viscosity, and excellent fluidity. Therefore, thin-walled and long-process products can be formed without too high pressure during molding.
The shrinkage rate of PE 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 mold cooling conditions have a great influence on shrinkage. Therefore, the mold temperature should be controlled to maintain uniform and stable cooling.
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. High mold temperature, slow melt cooling, high crystallinity of plastic parts, and high strength.
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 larger heating power in order to improve production efficiency.
The softening temperature range of PE is small and the melt is easy to oxidize. Therefore, contact between 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 nature of PE melt is not obvious, the change of shear rate has little effect on viscosity, and the effect of temperature on PE melt viscosity is also less.
The cooling rate of PE melt is slow, so it must be cooled sufficiently. The 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 feed port parameters.
The molding temperature of PE is relatively wide. In the flowing state, a little temperature fluctuation has no effect on injection molding.
PE has good thermal stability, generally there is no obvious decomposition phenomenon below 300 degrees, and it has no effect on quality.