Cast polyurethan elastomers, is the ease with which blocks of different sizes can be manufactured. The tooling costs are very low and due to the simplicity of shape they can be quickly made. Coupled with this is the suitability of most types of polyurethane, in particular the harder grade, for many machining operations, as already discussed in the next article. This enable in certain cases different designs to be turned out quickly fo evaluation and choice of optimum design.
Apart from blocks there is a considerable call for sheeting in various thicknesses for a wide variety of applications. Sheets are usually manufactured in a cast grade in a centrifuge. This method limits the length and width obtainable, and the largest sheets available aer of the order of 15 x 3 ft with thicknesses from 0.030 to 0.50 inches. Longer sheets can noe be made by peeling from a cylindrical block, although the thickness is limited in such cases to around 1/8 inch.
Larger sheets can also be calendered using either the millable or thermoplastic grades and the blown film extrusion of the latter materials gives very thin sheeting in long lengths. Polyurethane sheets are also available with a pressure sensitive adhesive and a non-stick removable backing paper.
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