Free reverse: reverse the non-circular cross-section member, the original cross-sectional plane not remain flat, resulting in warpage, that member in torque effect, each point along the rod axis direction displacement cross-section. If the reverse axial displacement without any constraints freely sectional warping, called free reverse. The free torsion, warping each section of the same longitudinal fibers remain straight line and length remains the same, only the shear stress on the cross section, no longitudinal normal stress. Constraints twist: As the conditions or external force supporting manner sectional warping torsion member is constrained, called constraint reversed. When restrained torsion, bending deformation member, the section will have a vertical normal stress, called warping normal stress. It also must produce and maintain a balance of warping normal stress warping shear stress.
Warpage (warpage) is not in accordance with the shape of the design of plastic parts molding, but the occurrence of twisted surfaces, plastic parts to warp guide due to uneven shrinkage shaping member. If all the plastic parts with uniform shrinkage, plastic deformation will not warp, but will only reduce the size; however, due to molecular chain / fiber regiospecifically, mold cooling, plastic parts design, mold design and molding conditions and other factors the interaction, to be able to achieve low shrinkage or even contraction is a very complex task. The reason plastic parts due to uneven shrinkage and warping, shrinkage change include: plastic internal temperature uniform. When the plastic solidifies flesh along the direction of the pressure difference and the cooling rate differences. Plastic has not fully cooled to top out, or the top of the pin deformation, improper undercut deep, push-up, stripping slope and other factors may cause inappropriate plastic warping. Plastic flesh changes lead to differences in cooling rate. Plastic parts having a curved or asymmetric geometry. Plastic materials, no added fillers difference. The flow direction and perpendicular to the flow direction of the molecular chains / fibers with directional differences, resulting in differential shrinkage. Holding pressure difference (for example, over the gate packing, packing away from the gate but insufficient).
Plastic filler material is added or not, will result in differences in contraction. When the plastic parts with a contraction difference, its flesh direction of flow generating unequal to shrink, internal stresses caused by plastic parts may cause warping. Since the reinforcing fiber heat-shrinkable plastic parts will be small and the modulus increases, so add fiber thermoplastics can inhibit the contraction, which add fiber along the direction of arrangement (usually flow direction) of the shrinkage ratio of the lateral contraction. Similarly, thermoplastics particulate filler added is much smaller than the non-additive plastic shrinkage rate. On the other hand, if no added filler material plastic parts with a high degree of molecular chain with isotropic, anisotropic contraction was, it has a relatively large shrinkage in the direction of the molecular chain arrangement. Self-reinforcing structure of the liquid crystal polymer with a tight regular arrangement, which tends to anisotropic shrink.