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Five influential factors of injection mold shrinkage
by：CSSSLD
2021-01-23
Whatever injection molding processing products, it cannot leave the injection mold, but the injection mold with time can appear the phenomenon of contraction, then affect the injection mold what are causes of contraction.
1, plastic heat bilges cold shrink
in the plastic molding, need plastic raw materials melting, melting temperature of 200 ~ 300 degrees at this moment, plastic raw material thermal expansion, and in the process of injection mold cooling, the temperature is reduced, the volume of it is bound to happen.
2, plastic chemical structure changes
as thermosetting plastic in the process of forming, resin molecules by the linear structure into a shape structure, quality and size of the structure of the volume is larger than the volume of a linear structure quality, its total volume smaller, thus causing shrinkage phenomenon.
3, residual stress change
when injection mold molding, due to the effect of shearing force by the pressure molding, anisotropy, additives mixed inhomogeneity and the influence of mold temperature
there are residual stress in injection mold after molding, the residual stress will gradually become smaller and redistribution, the result form the plastic mold to shrink, the generally called after contraction.
4, gate section size
different injection moulds, the jiaokou section size, large size gate will help improve the cavity pressure and to extend the time of gate closed, facilitate more melt into the cavity
5, plastic varieties
in general, crystalline plastics, such as PP, PA, etc. , than the crystal type of plastic, such as PC, PS, ABS show larger contraction after demoulding and wider range of contraction.
crystalline plastics shrinkage big reason: the plastic melt when the influence of the thermal expansion coefficient and crystal structure formation of cohesion function.
the above 5 points is the cause of injection mold shrinkage, so for injection molding processing plant, in the production of injection molding products, be sure to check quality of injection mold
1, plastic heat bilges cold shrink
in the plastic molding, need plastic raw materials melting, melting temperature of 200 ~ 300 degrees at this moment, plastic raw material thermal expansion, and in the process of injection mold cooling, the temperature is reduced, the volume of it is bound to happen.
2, plastic chemical structure changes
as thermosetting plastic in the process of forming, resin molecules by the linear structure into a shape structure, quality and size of the structure of the volume is larger than the volume of a linear structure quality, its total volume smaller, thus causing shrinkage phenomenon.
3, residual stress change
when injection mold molding, due to the effect of shearing force by the pressure molding, anisotropy, additives mixed inhomogeneity and the influence of mold temperature
there are residual stress in injection mold after molding, the residual stress will gradually become smaller and redistribution, the result form the plastic mold to shrink, the generally called after contraction.
4, gate section size
different injection moulds, the jiaokou section size, large size gate will help improve the cavity pressure and to extend the time of gate closed, facilitate more melt into the cavity
5, plastic varieties
in general, crystalline plastics, such as PP, PA, etc. , than the crystal type of plastic, such as PC, PS, ABS show larger contraction after demoulding and wider range of contraction.
crystalline plastics shrinkage big reason: the plastic melt when the influence of the thermal expansion coefficient and crystal structure formation of cohesion function.
the above 5 points is the cause of injection mold shrinkage, so for injection molding processing plant, in the production of injection molding products, be sure to check quality of injection mold
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