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Factors that affect the shrinkage of injection molding
Release time:
2017-02-15 8:41:31 |
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Shrinkage is in the injection molding process to consider an important factor in the impact of injection molding shrinkage factors are the following:
Plastic varieties of thermoplastic molding process due to the presence of crystallization from the volume changes, strong internal stress, frozen in the plastic parts of the residual stress, molecular orientation and other factors, and therefore compared with the thermosetting plastic shrinkage , The shrinkage range is wide, the direction is obvious, the other shrinkage after shrinkage, annealing or humidity treatment after the shrinkage is generally larger than thermosetting plastics.
Plastic parts of the shape of the melt and the cavity surface contact with the outer layer immediately cooled to form a low-density solid-state shell.As the plastic thermal conductivity is poor, so that the inner part of the plastic slowly cooled to form a large high-density solid layer shrinkage, Cooling, slow, high-density layer of the shrinkage is also large.In addition, whether the insert and insert layout, the number of direct impact on the direction of the material, density distribution and shrinkage resistance size, so the characteristics of plastic parts shrinkage, Greater impact.
Size, size and distribution of these factors directly affect the direction of the material, the density distribution, the role of pressure filling and forming time. Direct feed port, the inlet cross section is large (especially thick cross section) is narrow but the direction Large, the width of the feed and the length of the short direction of the small direction from the feed near or parallel to the direction of the material is contraction.
Molding conditions Mold temperature is high, the molten material slows down, the density is high, the shrinkage is large, especially for the crystallization material because of the high crystallinity, the volume change is big, so the shrinkage is bigger. The mold temperature distribution is related to the internal and external cooling and density uniformity of the plastic parts , Directly affect the size of each part of the amount of shrinkage and direction.In addition, to maintain the pressure and time on the contraction also a greater impact, the pressure is long, but the shrinkage is small but the direction of large injection pressure, melt viscosity difference is small, The interlayer shear stress is small, the elasticity after stripping is large, so the shrinkage can also be reduced appropriately, the material temperature is high, the shrinkage is large, but the direction is small, so the mold temperature, pressure, injection speed and Cooling time and other factors can also be appropriate to change the plastic shrinkage. |
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