Why do melt lines appear on the surface of extruded profiles, and what are the methods to eliminate them?

Why do melt lines appear on the surface of extruded profiles, and what are the methods to eliminate them?

The main reasons for the appearance of weld marks on the surface of profiles are: 

① Inconsistent material flow velocity inside the die; 
② Insufficient header pressure; 
③ The die shaping section is too short; 
④ The material flow at the inlet of the machine head is too small; 
⑤ The formula has excessive external lubricity; 
⑥ Poor material flowability; 
⑦ The melt temperature at the parting line is too low; 
⑧ Extrusion speed is too fast. 


The main solutions are: 

① Ensure uniform material flow within the die; 
② Increase the head pressure; 
③ Increase the length of the head section shaping zone; 
④ Place the material reservoir behind the mold core support; 
⑤ Increase the resin flow channel at the die inlet; 
⑥ Reduce the external lubricity of the mixture; 
⑦ Use materials with good fluidity; 
Increase the barrel temperature and lower the die temperature. 
⑨ Reduce the extrusion speed.
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