What are the differences in the process when producing UPVC pipes by directly extruding PVC granules and powder?

What are the differences in the process when producing UPVC pipes by directly extruding PVC granules and powder?

When manufacturing UPVC pipes, if PVC pellets are used as raw materials, single-screw extruders are usually selected for production. However, when directly using PVC powder for production, conical twin-screw extruders are generally preferred. The differences in the process flow and process control are as follows: 
The process flow for producing pipes with PVC powder: 
PVC powder sieving → raw material weighing and metering → high-speed thermal mixing → cold mixing → extrusion molding by twin-screw extruder → shaping → cooling → traction → cutting → inspection and storage 
The process flow for molding with PVC granules is as follows: 
PVC pellets → extrusion molding by single-screw extruder → shaping → cooling → traction → cutting → inspection and warehousing
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