How to reduce the shrinkage of plastics processing
Shrink plastic processors are facing the clear plastic box enemy, especially for high surface quality requirements of large plastic products, shrinkage is a chronic illness. Therefore, various techniques have been developed to minimize shrinkage, improve product quality.
????????Thick injection molded plastic parts in position, such clamshell packaging as the ribs or protrusions formed at positions near the shrinkage is more serious than that, this is due to the thicker area of ??the cooling rate is much slower than the surrounding area. Cooling rate causes depression formed at the connecting surface, is the familiar shrinkage marks. This deficiency severely limits the design and molding of plastic products, especially large thick-walled products such as televisions packaging design and monitors slant cabinet shell. In fact, for household electrical appliances demanding products in this category must eliminate sink marks and surface quality for toys and some other less demanding products allow the presence of scar contraction.
????????????????Another method is to modify the mold, there is a simple solution is to modify the conventional core hole, but did not expect this method is suitable for all resins. In addition, the gas-assisted method is also worth a try.
???????????????Causes the formation of sink marks may have one or more, including the processing methods, part geometry, material selection and die design. Including geometry and material selection is usually determined by the raw material suppliers, and less easy plastic package to change. plastic case However, there is still a lot of mold makers mold design on factors that may affect the contraction. Cooling flow channel design, the type of gate, gate size may produce a variety of effects. For example, if a small gate gate than the conical tubular gate cooling much faster. Premature cooling will reduce the gate cavity fill time, thereby increasing the plastic box probability generating sink marks. For molding workers, adjusting the processing conditions is to solve the problem in a way contraction. Filling pressure and time significantly affect shrinkage. Member filled, the excess material continues to fill the cavity in the shrinkage compensation material. Filling phase is too short will cause contractions intensified, eventually will produce more or larger shrinkage marks. This plastic trays method may not be able to shrink scar itself reduced to a satisfactory level, but the molding conditions have improved worker can adjust the fill shrinkage marks….