What is Calendering of Polymers?
Polymer Calendering is a polymer molding method in which the heated polymer is passed between the two rollers that apply heat & pressure and force the polymer into a sheet.
This plastic sheet can be further passed through other rollers for extra surface works like embossing, surface finish, adding gloss, etc.
Calendering is generally used for manufacturing PVC sheets as well as sheets of other polymers.
Polymer calendering is also used to give finishing work to the already manufactured plastic sheets.
By this technique, the flat, smooth, and glossy surface can be achieved on a polymer surface.
The surface becomes more lustrous when the degree of heat and pressure is increased during the calendering of polymers.
The molten polymer or heated polymer is fed to the calendar rolls from the Banbury mixer or from a large extruder.
Also in the Calendering operation, large forces are generated between the two rollers. These large forces tend to cause rollers to bend slightly.
Due to the bending of rollers, the thickness of polymer sheet may not be uniform on its entire length.
To avoid this roll deflection, the compensation is provided by crown rolls having larger diameter in the middle than at the ends.
The installation of calendars requires high costs. But it is more beneficial for manufacturing superior products at large scales.
The principle of calendering is similar to the principle of hot rolling of steels, but here the material is polymer instead of steel.
Calendering of polymers: Image from Public domain, via Wikimedia Commons