Plastic is to point to in the process of plastic melt processing internal stress due to the orientation of macromolecule chain and cooling contraction of factors such as an inner stress.

The essence of the internal stress of macromolecular chains in the process of the molten form conformation, the imbalance of the imbalance conformation during cooling and solidification cant immediately return to adapted to the environmental conditions of equilibrium conformation, the imbalance of conformation in a reversible high elastic deformation, high elastic deformation and freeze at ordinary times in the form of potential energy stored in the plastic products, under appropriate conditions, this forced the stability of the unstable conformation to the freedom of conformational conversion of potential energy into kinetic energy and release. When forces and mutual entanglement between the macromolecular chain force bear the kinetic energy, internal stress balance is destroyed, the plastic products can produce stress cracking and buckling deformation phenomenon.

Almost all plastic products will exist in different degrees internal stress, especially the internal stress of plastic injection products is more apparent. The existence of internal stress not only make the plastic products in the process of storage and use of stress cracking and buckling deformation, also affects the mechanical properties of plastic products, optical properties, electrical properties and the appearance quality, etc.

So we must find out the causes of internal stress and the stress relief method, maximum reduce internal stress of the plastic products, and make the residual internal stress on plastic products as evenly as possible, avoid to produce stress concentration and improve plastic products, such as mechanical and thermal properties.