Sheet extrusion shrinkage problem is the most important influencing factor related to shrinkage: plastic type, cost fluctuation must also be considered; high cooling rate will reduce processing shrinkage; high mold release temperature will produce more than lower mold release temperature Shrinkage; high drafting is equivalent to low shrinkage in most cases; the production conditions of the formed sheet are granulated by different extruders, or the same extruder has different processing parameters, and the produced formed sheet is likely to be produced. There are different shrinkage behaviors; the molded product of the male mold has a smaller shrinkage than the molded product of the female mold; under the same conditions, the shrinkage of the shrinkage rate of the molded article vacuum-molded with the same sheet is 10%. Note: The measurement site or method of measurement of the article in which the shrinkage assay is to be performed should be selected to ensure that no deformation occurs during the test and that product tolerances less than 10% of the shrinkage value are not possible. 4. The orientation shrinkage test of the formed sheet also gives information about the orientation of the macromolecules in the shaped material and article. If the material is highly oriented, such as in the direction of extrusion, this will create wrinkles that should not be present (Figure 3-5). For multi-cavity molds with equal longitudinal and lateral distances, the wrinkles in the extrusion direction are much more pronounced than in the transverse direction (Fig. 3-5a). Figure 3-5 Forming material a. Parts of a single cavity mold; b. Wrinkles produced by orientation of a multi-cavity mold. For vacuum forming, drafting produces another orientation of macromolecules. Figure 3-6 is an article that is vacuum molded from high impact polystyrene, which is easily torn into strips in the radial direction. The strips themselves are very strong in the radial direction because of the high degree of orientation during vacuum forming, which greatly reduces the strength in the direction perpendicular to the drafting, so that tearing tends to occur in a direction parallel to the drafting (see Figure 3). -7).