Calender Design Features

Taking the example of a three-roll calendering machine, the successful calendering operation is ensured by the following basic features. 

The rolls should be of close grained chilled cast iron. The surface of the rolls must be ground to a perfectly true diameter free from pinholes and should be highly polished to assist the production of first quality defect- free sheeting with a high degree of surface finish. 

The frames of the machine should be sturdy and made of closely grained cast iron of heavy design, free of blowholes which usually form during casting, to withstand the load exerted by the rubber stock. 

The top and the bottom rolls should be adjustable to keep the nip distance for taking out sheets of precise and uniform thickness. The central roll is fixed. 

When the rubber stock is passed through the rolls, the pressure between them causes deflection which results in parallel openings or nips between the rolls as shown in figure 13.2. 

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These media are described as two-sided, with an upper slick surface for filtration being produced by a sateen weave. This surface is fiuther modified by calendering. Another important feature of this design is that ultrafines are not retained by the cloth, being released downstream by the underside fiumel-shaped pores. A published industrial report [Technical Textiles International, 1992] refers to success with this type of cloth (monofilament polyester, calendered to screen size 30 pm) in high- pressure variable chamber pressing of dyestuff hydroxides, stearates, etc. 

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