The flow velocity is stable at low-speed filling, the product size is relatively stable, the fluctuation is small, the internal stress of the product is low, and the internal and external stress of the product tends to be consistent (for example, a polycarbonate part is immersed in carbon tetrachloride, which is molded by high-speed injection molding Parts have a tendency to crack, low speed does not crack).
Under relatively slow filling conditions, the temperature difference of the material flow, especially the temperature difference between the material before and after the gate, helps to avoid the occurrence of shrinkage holes and depressions. However, due to the longer mold filling time, it is easy to make the parts delaminated. And the combination of poor welding marks not only affects the appearance, but also greatly reduces the mechanical strength.
During high-speed injection, the material flow rate is fast. When the high-speed mold filling is successful, the melt rapidly fills the cavity, the material temperature drops less, the viscosity decreases less, and lower injection pressure can be used. It is a kind of hot material charge. Modal potential. High-speed filling can improve the glossiness and smoothness of the parts, eliminate the phenomenon of seam lines and delamination phenomenon, shrink small depressions, uniform color, and ensure that the larger part of the parts can be full.
However, it is easy to produce products that cause blisters or yellowing of parts, or even burn the lens, or cause difficulty in demoulding, or the phenomenon of uneven mold filling. For high-viscosity plastics, it may cause melt fracture and cause clouding on the surface of parts. .
High-speed high-pressure injection can be considered in the following situations:
High plastic viscosity, fast cooling, long process parts can not fully fill all corners of the cavity with low pressure and slow speed;
If the wall thickness is too thin, the molten material reaches the thin wall where it can easily condense and remain. A high-speed injection must be used to allow the molten material to be consumed immediately before entering the cavity.
Glass fiber-reinforced plastics, or plastics containing a relatively large amount of filler materials, must have high-speed, high-pressure injections in order to obtain smooth, uniform parts because of poor fluidity.
For high-precision products, thick-walled parts, parts with large wall thickness changes, and parts with thick flanges and ribs, it is best to use multi-level injections, such as secondary, tertiary, quaternary, or even five.