What are the causes and solutions for uneven edges when extruding sheet materials?

What are the causes and solutions for uneven edges when extruding sheet materials?

There is too much leftover material between the calender rolls. The die lip opening should be adjusted appropriately and the traction speed increased. 
② Unstable extrusion. The screw speed should be appropriately reduced and the raw materials should be further pre-dried. 
③ The rollers are improperly installed with significant assembly errors. The positions of the rollers should be appropriately adjusted. The installation eccentricity of the three rollers must not exceed 0.025mm. 
④ The temperature at the die head is too low or it is blocked. The mold temperature should be appropriately increased and the die head should be cleaned. 
⑤ The pressure of the calender roller is insufficient. The gap between the rollers should be appropriately reduced. 
⑥ The extrusion temperature is out of control. It is necessary to check whether the temperature control thermocouple is damaged and adjust the temperature according to the process requirements to meet the molding conditions.