Matters needing attention in plastic raw materials

1. Shrinkage rate

In the molding of plastics, thermoplastic plastics still have volume changes caused by crystallization, strong internal stress, large residual stresses frozen in plastic parts, and strong molecular orientation. Compared with thermosetting plastics, shrinkage rate is larger. The rate range is wide, the directionality is obvious, and the annealing or humidity control treatment is usually larger than that of thermosetting plastics.

2. Crystallinity

Thermoplastics are classified into crystalline plastics and non-crystalline plastics according to whether they crystallize during condensation. The crystallization phenomenon is a phenomenon in which the molecules move independently from the molten state to the condensation state, completely in a disordered state, and the molecules stop moving freely, press a slightly fixed position, and have a tendency to make the molecular arrangement a regular model. .

3. Liquidity

The fluidity of various plastics also changes due to various molding factors, and the main influencing factors are as follows:

①Higher material temperature increases fluidity, but different plastics have their own differences.

② As the processing pressure of precision injection molding increases, the molten material is greatly affected by shearing, and the fluidity also increases, especially PE and POM are more sensitive. Therefore, the injection pressure should be adjusted to control the fluidity during the molding process.

③Injection mold structure, pouring system form, size, layout, cooling system design, melt flow resistance and other factors directly affect the actual fluidity of the melt in the cavity. Anything that causes the melt to lower the temperature and increase the flow resistance The liquidity is reduced.