According to the molecular structure of the resin in pet, pet can be divided into two categories: crystalline pet and amorphous (also called amorphous) pet. The main difference between the crystalline pet and the amorphous pet is whether the resin molecules can form a certain degree of regular alignment from the molten state to the condensation. If a certain degree of regular arrangement can be formed, it is referred to as a crystalline form, and otherwise it is referred to as an amorphous form.
Crystalline pet and amorphous pet not only have significant differences in mechanical properties, but also have a large difference in shrinkage when changing from viscous flow to glass. The shrinkage of crystalline pet is usually 210 times that of amorphous pet. . At the same time, for crystalline pets, if the cooling rate of each part is inconsistent during cooling, the crystallinity of each part in the product will be different, and the difference in crystallinity will cause internal stress in the product, which will cause deformation of the product. Even cracking. Therefore, for crystalline pets, the cooling system design of the mold is an important aspect related to the degree of deformation of the Pet Bottle Preform.
In addition to the resin, some fillers are usually added to improve the mechanical, electrical, optical and thermal properties of pet. These fillers form molecular orientation during shear injection due to shear flow, and are analyzed by Moldflow software. Fiber orientation distribution. The orientation causes a significant difference in the shrinkage of the article in different directions. For example, for a 30 glass fiber reinforced PA66, the shrinkage rate is 0.4 in the flow direction and 1.1 in the direction perpendicular to the flow direction, and the difference in shrinkage in the different directions causes internal stress in the article. Therefore, for glass fiber reinforced pet products, the non-uniform orientation of the filler is often the main cause of deformation of the product. In production practice, in order to improve or eliminate the deformation of the resulting product, measures such as changing the position of the gate and adjusting the injection speed are generally employed. It can be seen that there are five major factors affecting the deformation of injection products, namely: forming raw materials, forming methods, product design, Pet Bottle Mould design and injection molding process conditions.