The shrikange of the plastic injection moldings is key problems, especially for large plastic visual parts, which have high requirment on the surface. Therefore, various techniques have been developed to minimize shrinkage, improve product quality.
The positions easily shrinked are the thinck wall section, the adjacent ribs or protrusions, because the cooling rate is much slower than the surrounding area of the thicker regions. Different cooling rates lead to depression formed at the connecting surface, namely the familiar contraction marks. This deficiency severely limit precision plastic mold design and molded products, especially large thick-walled products such as televisions and monitors slant cabinet shell. In fact, this type of requirement for household electrical appliances must eliminate shrinakge marks on the strict product.
Reasons for the formation mark may have one or more, including the processing methods, part geometry, material selection, and mold design. Where the geometry and material selection is usually determined by customers, and not easy to change. But there is still a lot other factors that may affect the contraction. Cooling channel design, gate type, gate size, etc. For example, a small gate as tubular gate cooling much faster than the cone of the gate. The gate prematurely cooling will reduce the cavity filling time, thereby the risk of shrinkage mark will be higher . resetting the processing conditions is one way to solve the shrinkage problem. The filling pressure and time significantly affect shrinkage. After the filling member, the excess material continues to fill the cavity to compensate for shrinkage of the material. Filling phase is too short will cause contraction intensified, ultimately will produce more or larger contraction marks. This approach may not be able to shrink marks itself reduced to a satisfactory level, but it can be improved by adjusting the fill molding conditions . Another method is to modify mold after trial and reveiw, there is a simple solution is to modify the conventional core hole, but it is not suitable for all of the material. In addition, the gas-assisted method is also worth a try.
In past, JOINTUS experienced many kinds of these problems, and finally get the solution. We did manufacture many visual plastic injection parts for Household appliance, telecommunications. For T1, we did meet the serious shrinkage mark on the surface, we tried to move the gate position, resetting the molding parameters, etc.
The below is the plastic injection telecommunication covers, pannels, cases we made, high visual requirement.