Why do the surfaces of extruded profiles have weld marks when extruding? What are the solutions to eliminate these marks?

Why do the surfaces of extruded profiles have weld marks when extruding? What are the solutions to eliminate these marks?

The main reasons for the appearance of weld marks on the profile surface are: 
①The material flow rate within the mold is inconsistent. 
② Insufficient pressure at the engine head; 
③ The length of the mold setting section is insufficient; 
④ The material flow at the inlet of the machine head is too small; 
⑤ The formulation has excessive lubricity. 
⑥ The material is too viscous. 
⑦ The melt temperature at the material distribution ribs is too low; 
⑧ The extrusion speed is too fast. 
The solutions mainly include: 
①Make the material flow inside the die uniform. 
② Increase the pressure at the engine head; 
③ Increase the length of the nose section for final shaping; 
④ Set up a material pool behind the mold core support. 
⑤ Increase the resin flow channel at the inlet of the machine head; 
⑥ Reduce the external lubricity of the mixture; 
⑦ Use materials with good fluidity; 
⑧ Increase the temperature of the machine body and reduce the temperature of the die cavity; 
⑨ Reduce the extrusion speed.
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