Roll Stack and Calendering Processes

Sometimes, especially In sheet applications, the plastic is extruded, either horizontally or vertically, onto one roll in a three-roll stack of polishing rolls, rather than onto a chill roll. The roll stack is designed to exert pressure, and to impart desired surface characteristics to the sheet-either smooth or textured. The gap between the rolls helps in controlling the sheet thickness. The rolls are temperature-controlled, often with circulating hot oil, and the plastic next travels through a cooling section consisting of a number of smaller rolls in a frame. 

Calendering can also be used to produce film and sheet with desired thicknesses and surface textures. In this process, the polymer melt is squeezed between pairs of co-rotating high precision rollers, followed by a series of chilling rolls. Very tight tolerances in film or sheet thickness can be attained. PVC sheet is usually made in this manner. 

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