1. Basics of the calendering process

1.1 Process description

The calendering process is based on the high-temperature flow of a viscoelastic thermoplastic material between at least two driven cylinders. In fact, experience shows that calendering PVC with four cylinders is the only way to properly control the quality of films or sheets. In a four-roll calender (Figure 1 ), the molten plastic mass from the gel mixer passes from one roll to the next through three increasingly narrow gaps, causing a reflux before each gap, along with a widening of the sheet. These refluxes form what are known as beads. Only the first bead, called the feed bead, is limited in width by material guides. Beads 2 and 3 have a free width and a cylindrical...