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Factors influencing the internal quality of injection molding products

May 12, 2017

1. Internal stress

(1) Internal stress generation

In the injection molding products, the local stress state is different, the deformation degree of the product will be determined by the stress distribution. If the product is cooled, there is a temperature gradient, then this kind of stress will develop, so this kind of force is called "molding stress."

(2) The relationship between internal stress and product quality

The existence of internal stresses in the products can seriously affect the mechanical properties and use properties of the products. Due to the existence and distribution of internal stresses in products, products in the use of cracks occurred in the process of use of glass temperature, the following frequent irregular deformation or warping, but also caused the surface of the product "pan-white", turbidity, optical performance deterioration.

2. Impact strength

The impact strength of injection molding products showed more prominent anisotropy. The impact strength is related to the structure, gate and location, number, distribution and arrangement of the products in addition to the molecular structure and molding process conditions of polymers. This is because the impact strength is mainly determined by the stress of the process of polymer processing (orientation stresses, temperature stresses, deformation-induced stresses).

3. Product Shrinkage

(1) Shrinkage process

The shrinkage of injection molding products in the molding process can be divided into 3 phases.

The first stage is the pressure-preserving stage before the gate solidification. The shrinkage of the product depends largely on the degree of compensation of the melt. Due to the low temperature of the mould, the melt temperature is decreasing continuously, and the melt density and viscosity are continually increasing. Therefore, the compensation capacity of the melt depends mainly on the size of the pressure-preserving and the time that is transmitted in the mould.

The second stage is from the gate solidification to the cooling phase of demoulding. This stage no melt into the mold cavity, the weight of the product will not change, but the density or volume of the products will change.

The third phase is the contraction from the start of demoulding to the use phase. This belongs to the free contracting.

(2) The control of shrinkage

① Injection Molding Process

② Materials

③ in the mould

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