What causes the uneven surface and poor gloss of the sheet during the sheet extrusion process? How can it be solved?

What causes the uneven surface and poor gloss of the sheet during the sheet extrusion process? How can it be solved?

The main reasons are as follows:
① The temperature at the die head is too low;
② The surface of the calender roll is not smooth;
③ The temperature of the calender roll is too low;
④ The surface finish of the die lip is too poor;
⑤ The straight section of the die lip is too short;
⑥ The raw material is not fully dried and has a high moisture content;
⑦ The pressure of the compressed air is insufficient, and the calender roll cannot be pressed tightly.
The main solutions are:
① The temperature at the die head should be appropriately increased; 
② The surface of the calendering roller should be cleaned or re-polished. 
③ The temperature of the roller body should be appropriately increased. 
④ The die lips should be reground to improve the surface finish. 
⑤ The length of the straight part of the die should be increased. 
⑥ The raw materials should be thoroughly dried. 
⑦ Slightly increase the pressure of the compressed air and raise the pressure of the calender rolls.
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