6. Common manufacturing faults. Causes and remedies

Some extrusion faults are linked to the extrusion unit or pulling unit and are common to all extrusion lines.

However, the main causes are as follows:

• insufficient plasticization in the extruder (presence of infondus, inhomogeneity, etc.);

• polymer degradation due to too long a residence time and too high a temperature for PVC (polyvinyl chloride) in particular (poor mechanical properties, black spots, etc.);

• flow instability due to extruder operation (irregular tube dimensions);

• extrusion instability leading to sharkskin-type defects in HDPE (high-density polyethylene) or extrudate rupture in LDPE (low-density polyethylene).

The table 3...