Coated Abrasives / 43 www.nortonabrasives.com ABRASIVE GRAIN DISTRIBUTION There are two types of abrasive grain coverage on the backing: • O penly spaced distribution where between 30% and 60% of the backing is covered leaving large spaces between each abrasive grain. It is used in operations where the grinding swarf would otherwise ‘load’ or clog the surface, reducing cutting efficiency and shortening the coated abrasive life • C losely packed grain distribution is where the grain completely covers the backing. The greater number of abrading points in a given area leads to faster stock removal. It is recommended where loading is not a problem and where smoother surface finishes are desired OPEN COAT (1/3 LESS GRAIN THAN CLOSED) CLOSED COAT ABRASIVE GRAIN TYPES In order to provide even further resistance to loading, some open coat paper products are given a special surface treatment of zinc stearate after the sizing operation. Such products are ideal for sanding between sealer coats on furniture, sanding after primer coats on automobiles, removing varnish from wood, and numerous other operations where conventional abrasive products fail prematurely due to loading. Norton’s trademark for products utilising this treatment is No-Fil. SPECIAL COATED SURFACE TREATMENT NO-FIL TREATMENT GRAIN TYPE BOND / TOUGHNESS STRUCTURE PROPERTIES / WEAR PROPERTIES SILICONE CARBIDE (SIC) Very hard / less tough Crystalline Sharp-edged, brittle, highly friable / micro wear ALUMINIUM OXIDE Hard / tough Crystalline, irregular Wedge-shaped, block grain, even wear ZIRCONIA ALUMINA Hard / very tough Crystalline, even Wedge-shaped, block, drop formed grit / micro wear, self-sharpening CERAMIC ALUMINIUM OXIDE Hard / very tough Micro crystalline Sharp-edged, pointed grit / micro wear, self-sharpening COATED ABRASIVES
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