The most practical scheme to reduce the shrinkage

2022-07-22
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Practical shrinkage reduction scheme for plastic parts

shrinkage (shrinkage) is a big problem for precision plastic mold products of large household appliances with high surface quality requirements. This is a big enemy faced by plastic mold processors. Therefore, people have developed various technologies that can store the experimental results in the computer to minimize shrinkage and improve the dimensional stability and appearance of products

in the thicker position of plastic mold parts, such as rib (commonly known as bone position), the shrinkage is more serious than that in the adjacent position, because the cooling speed of the thicker area is much slower than that of the surrounding area. Different cooling rates lead to the formation of depressions at the joint surface, which is known as shrinkage marks. There may be one or more reasons for the formation of shrinkage marks, including processing method, part geometry, material selection, mold design, etc. the geometry and material selection are usually determined by the raw material supplier and are not easy to change. Mold manufacturers also have many factors about mold design that may affect shrinkage. Cooling channel design, gate type and gate size may have a variety of effects. For example, a small gate, such as a tubular gate, cools much faster than a conical gate, and I am excited about the gate. Premature cooling at the gate will reduce the filling time in the cavity, thus increasing the probability of shrinkage marks

for injection molding workers, adjusting the injection molding process is a way to solve the shrinkage problem. The injection pressure and time also affect the shrinkage. After the parts are filled, the excess material continues to fill the cavity to compensate for the shrinkage of the material. Too short injection time will lead to increased shrinkage and eventually produce more or larger shrinkage marks. This method itself may not be able to reduce the shrinkage marks to a satisfactory level, but the molding workers can adjust the filling conditions to improve the shrinkage marks, including hydraulic universal testing machine and electronic universal testing machine

in addition to the above methods, modifying the mold is the simplest solution to damage the wire. You can try to modify the conventional core hole. This method may not be applicable to all resins, and the gas assisted method can also improve this situation to some extent. In addition, it is also a method to change the plastic with the shrinkage rate of the composite mold. Glass fiber reinforcement, mineral filling and other materials are conducive to reducing the molding shrinkage. Changing the plastic with different materials will have different shrinkage rates

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