Contraction of production mainly due to the following:
1. thermal expansion and contraction of the plastic. When the plastic molding, you need raw material melt plastic, melting temperature reaches 200~300du, thermal expansion of plastic raw materials, plastic mold cooling process, the temperature decreases, it is bound to shrink in size.
2. changes in chemical structure. Such as thermosetting plastic molding process, the resin molecule is made up of linear structure into body structure, and size structure of quality than the quality of the linear structure of the volume size, the total volume is less, so the shrinkage phenomena.
3. the residual stress. Plastic mold in the shape, due to the shear effect of molding pressure, anisotropy, additive mixture inhomogeneity and the effect of mold temperature,
Residual stress of the plastic mold after forming, which will gradually become smaller and redistribution of residual stress, which results in the formation of plastic mold shrinkage, this contraction after contraction is generally called.
4. gate section. Different molds, inhabited sections of its size, large size gate helps to improve the cavity pressure and extension of gate closure, easy to melt into the cavity of the more,
Thus the larger the density of plastic parts, and thereby reduce the shrinkage, while increases the shrinkage.