Technological features and characteristics of thermoplastics – thermoplastic, te
Thermoplastic varieties that many, even the same species, and because attachment ratio of resin to different molecules and their use and process characteristics are different.
Addition, in order to change the characteristics of the original species, common copolymerization, crosslinking and other chemical polymerization of the resin in the original structure into a certain percentage of the amount of dissimilar monomer or polymer resin equivalent to changing the original resin structure into a new use and technological characteristics of the modified species. For example, ABS Shall be imported in polystyrene molecules of acrylonitrile, butadiene monomers such as heterogeneous became modified copolymer, also known as modified polystyrene, with polystyrene is superior than the use of process characteristics. As the thermoplastic variety, performance, complexity, even if the same type of plastic is also only used for injection or extrusion, and therefore some of this chapter introduces a variety of thermoplastic injection.
One process characteristic (A) shrinkage Thermoplastic molding shrinkage in the form and calculation mentioned above, affect the thermoplastic molding shrinkage of the following factors:
1, plastic forming process of thermoplastic varieties there as crystallization from the volume change of form, which should be strong, frozen in plastic residual stress within the large, strong molecular orientation and other factors, therefore, compared with thermoset the greater shrinkage, shrinkage rate range, clear direction, while the shrinkage after forming, annealing, or humidity generally shrink after treatment than thermosetting plastics large.
2, plastic material and financial characteristics of forming the outer cavity surface contact immediately the formation of low-density solid-state cooling shell. Because of poor thermal conductivity of plastics, so that the inner plastic parts formed by the slow contraction of a large cooling high-density solid layer. Therefore, wall thickness, cooling slowly, while high-density thick shrink large. In addition, with or without inserts and insert the layout, the number of directly affected the direction of material flow, density, size distribution and shrinkage resistance, so the characteristics of plastic parts on the contraction of the size, orientation influenced
3, the feed port form, size, distribution of these factors directly affect the material flow direction, density distribution, the role of packing and forming feeding time. Direct inlet, inlet section (in particular, thick section) is small but directional large contraction, inlet width and the shorter the direction of small. From the inlet or near parallel to the direction of the feed stream large contraction.
4, forming conditions Mold High temperature melting material cooled slowly, high density, shrink large, particularly for crystalline materials due to high crystallinity, the volume changes, so a greater contraction. Plastic mold temperature distribution and internal and external cooling and density uniformity in the direct impact on the part of the shrinkage of the size and direction. Also, keep up the pressure and time have a greater impact on systolic pressure, while long contraction of small but great direction. High injection pressure, melt viscosity material difference is small, the shear stress between layers of small, elastic rebound after stripping big, it can also be appropriate to reduce shrinkage, high temperature material, shrink large, but little direction. Therefore, adjustments in the forming mold temperature, pressure, injection speed and the cooling time and other factors may also be appropriate to change the contraction of plastic parts.
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