Polyurethane roll covers

Polyurethane roll covers were introduced to the paper industry at the end of the 1980s. The outstanding mechanical and dynamical properties make polyurethane the most suitable material for soft elastomeric covers in press positions. Depending on paper quahty and press design, high open surfaces up to 45 % with grooves, blind drilled holes or suction holes, as well as combinations thereof are used. An example of surface design is shown in Fig. 5.11. 

In fast running machines the dynamic heat build up in the cover limits the application of elastomeric materials. Polyurethane polymers, based on special formulations with excellent dynamic properties, ensure good performance in these applications with minimal heat build up. An example of such an application is the substitution of grooved steel rolls by elastomeric covers in shoe presses. 

Another method for manufacturing polyurethane covers is the moldless rotational casting process (Fig. 6.12). Here the reacting polyurethane mixture is cast as a spiral on the rotating roll, the fast reaction of the polyurethane mixture prevents the material dripping off the roll. Layers of different hardness can be applied easily with this method. 

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