What is the internal stress generated by plastic products during injection molding

The so-called stress refers to the force on the object per unit area, which emphasizes the internal force of the object. Generally, when an object is subjected to external force, its internal stress will be generated against the external force; when the object is not subjected to external force, the internal stress is called internal stress, which is caused by uneven plastic deformation of various parts inside the object. produced. According to the range of internal stress,
It can be divided into three categories:
(1) The first type of internal stress (macro internal stress), that is, the internal stress in the macro range caused by uneven deformation of various parts of the material;
(B) The second type of internal stress (microscopic internal stress), that is, the grains or sub-grains produced by uneven deformation between each grain or sub-grain of the object (in nature, most solid materials are crystals) Internal stress between grains;
(3) The third type of internal stress (lattice distortion stress), that is, the internal stress caused by lattice distortion that causes some atoms in the crystal to deviate from its equilibrium position, it is the most important internal stress in deformed objects (damaged objects) stress. Plastic internal stress refers to a kind of internal stress that is generated due to factors such as the orientation of macromolecular chains and cooling shrinkage during plastic melt processing. The essence of the internal stress is the unbalanced conformation formed by the macromolecular chain during the melt processing. This unbalanced conformation cannot be immediately restored to the equilibrium conformation that is suitable for the environmental conditions during cooling and solidification. The essence of this unbalanced conformation is one A kind of reversible hyperelastic deformation, and frozen hyperelastic deformation is stored in plastic products in the form of potential energy when it is flat. Under suitable conditions, this forced and unstable conformation will transform into a free and stable conformation. Transform into kinetic energy and release. When the acting force and entanglement force between the macromolecular chains cannot bear such kinetic energy, the internal stress balance will be destroyed, and plastic products will produce stress cracking and warpage deformation.

Almost all plastic products have internal stress to varying degrees, especially the internal stress of plastic injection products is more obvious. The existence of internal stress not only causes plastic products to warp and crack during storage and use, but also affects the mechanical properties, optical properties, electrical properties, and appearance quality of plastic products. Therefore, it is necessary to find out the cause of internal stress and the method of eliminating internal stress, to minimize the internal stress of plastic products, and to distribute the residual internal stress as evenly as possible on the plastic products to avoid the occurrence of stress concentration, thus Improve the mechanical properties of plastic products such as 1 thermal.