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The influence factors of injection molding process

by:CSSSLD     2021-02-03
The influencing factors of thermoplastic plastic molding shrinkage is as follows: plastic varieties of thermoplastic plastic molding process because there are crystal taxiing on volume change, internal stress is strong, frozen inside the plastic residual stress is large, molecular orientation factors such as the gender is strong, so compared with thermosetting plastic shrinkage is bigger, wide range of shrinkage and clear direction, also after molding shrinkage, shrinkage rate after annealing or wet processing generally are larger than the thermosetting plastic.

plastic feature forming molten material and cavity surface contact with the outer cooling form low density solid shell immediately. Due to the thermal conductivity of the plastic is poor, the inner plastic shrinkage of high density solid layer, formed by the slow cooling. So the wall thickness, slow cooling, high density layer thickness contraction. In addition, the presence of insert and insert layout and quantity are directly affect the direction of material flow, density distribution and the shrink resistance and so on, so the characteristics of the plastic parts had a greater influence on the size and direction of contraction.

inlet form, size, distribution of these factors directly affect the direction of material flow, density distribution, pressure feeding function and forming time. Direct inlet, the inlet cross section ( Especially section thicker) Were not narrowing but big direction, inlet width and length of short little direction. From the inlet near or parallel to the direction of material flow of contraction.

the molding condition of high temperature, molten material slow cooling, high density, high shrinkage, especially for crystalline materials with high crystallinity, volume change is big, so the shrinkage is bigger. Mould and plastic parts inside and outside cooling temperature distribution and density uniformity, also directly affect the shrinkage of each part size and direction. In addition, keep the pressure and time is influence on shrinkage, pressure, time will shrink but direction.

high injection pressure, viscosity of molten material difference is small, small interlayer shear stress, elastic rebound after demoulding is big, so the contract can be just the right amount of reduced, high temperature, shrinkage, but the direction is small. When molding accordingly adjust the mold temperature, pressure, injection rate and the cooling time and other factors also can change the plastic shrinkage appropriately. Mold design according to the scope of all kinds of plastic shrinkage, wall thickness and shape, feed port, size and distribution of the form according to the experience to determine the shrinkage rate of plastic pieces of each part, and then to calculate the cavity size.
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