molding flow line

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Injection Molding defect:molding flow line

Solving molding flow line problems
Definition
A flow mark or halo, is a surface defect in which circular ripples or wavelets appear near the gate. Ripples, a similar defect, appear as small fingerprint-like waves near the edge or at the end of the flow.molding flow line

Causes
Material freezing near the gate
Low melt and mold temperature and low ram speed can result in cold material entering the cavity. The partly solidified material takes on the form of the flow pattern.

where:
a = normal fountain flow with no ripples
b = flow causing ripples(R)
Insufficient material compensation
Early gate freeze-off or low packing pressure may not pack the cavity properly. The material near the gate then freezes while maintaining the form of the flow pattern.molding flow line

Remedies
Optimize the cold well
Design the cold well in the runner system to trap the cold material during the filling phase. The proper length of the cold well is usually equal to that of the runner diameter.
Optimize the runner system design
Restrictive runner system design can result in premature gate freeze-off. It can however, increase shear heating for better melt flow.
Increase mold & melt temperature
Optimize packing pressure

Solving one problem can often introduce other problems to the injection molding process. Each option hence requires consideration of all relevant aspects of the mold design specification.


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