Plastic extrusion processing is a very common industrial processing method. During the processing, many environmental operation factors are often encountered. The plastic processing shrinkage problem is one of the common problems in plastic processing, so it should be processed during processing. How to deal with this problem? For plastic products with high surface quality, shrinkage is a tricky problem. Therefore, with the continuous improvement of plastic processing technology, it is imperative to greatly reduce the shrinkage of plastic processing and improve product quality.
In thicker plastic injection molded plastic parts, such as ribs or protrusions, the shrinkage is more severe than the adjacent position, because the thicker areas are cooled much more slowly than the surrounding area. The difference in cooling rate causes a depression at the joint surface, which is a familiar shrinkage mark. Such defects severely limit the design and molding of plastic products, especially large thick-walled products such as the beveled casing and display casing of television sets. In fact, for the demanding products such as household appliances, the shrinkage marks must be eliminated, and for products such as toys, which have low surface quality requirements, plastic processing shrinkage marks are allowed.
There may be one or more reasons for forming plastic processing shrink marks, including processing methods, component geometries, material selection, and mold design. The geometry and material selection are usually determined by the raw material supplier and are not easily changed. But mold manufacturers still have a lot of factors about mold design that may affect the shrinkage of plastic processing. Cooling runner design, gate type, gate size can have multiple effects. For example, small gates such as tubular gates cool much faster than tapered gates. Premature cooling at the gate reduces the fill time in the cavity, which increases the chance of shrink marks. For molding workers, adjusting the processing conditions is one way to solve the shrinkage problem of plastic processing. Filling pressure and time significantly affect shrinkage. After the part is filled, the excess material continues to fill the cavity to compensate for the shrinkage of the material. Too short a filling phase will result in increased shrinkage and eventually more or larger shrinkage marks. This method of solving the plastic processing shrinkage itself may not reduce the shrinkage marks to a satisfactory level, but the molder can adjust the filling conditions to improve the shrinkage marks. There is more than one problem in the processing of plastic extrusions, but each problem cannot be ignored. In the process of processing, every problem is solved properly, so that high-quality products can be produced.