Grinding and polishing tools - joke Technology GmbH - #6

Text version of the page

93 2 i 6000 4700 2800 2480 2050 1800 Tel. +49 (0) 22 04 / 8 39-0 • Fax +49 (0) 22 04 / 8 39-61 • info@joke.de 2. Grinding and polishing tools Grinding and polishing tools Basic principles In theoretic definitions, abrasives are all hard material grains, which are used to achieve stock removal. These are usually applied bound in grinding tools. A differentiation is made between natural grains such as quartz, corundum, emery, garnet and natural diamond and synthetic grains such as corundum, silicon carbide, chromium oxide, cubic boron nitride (CBN) and diamonds. Corundum (aluminium oxide AI2O3) The most widely used abrasive is classed according to its hardness and toughness: Regular aluminium oxide: consists of approx. 95% AI2O3 predominantly from non-alloy and low alloyed steels as well as cast steel and grey cast iron. Special fused aluminium oxide: Thanks to a 99.9% AI2O3 very hard and heat resistant up to 2,000 °C. Very suitable for tough unhardened steels of more than 60 HRC (tool steel), for working with glass and all steels that require cool grinding. Semi corundum: Mixture of the above. For steels with high hardness and toughness, which are not heat-sensitive. Silicon carbide Silicon carbide can be differentiated by its hard and sharp crystals. It is heat-resistant up to approx. 1,370 °C. An abrasive grain generally only consists of one or a few crystals. This material is harder and more brittle than corundum. Silicon carbide is mainly used on non-ferrous metals, rust-free steels, ceramic and mineral materials such as carbonaceous steels. It is also used for dressing grinding tools. Boron nitride (CBN) Boron nitride is the second-toughest known material after diamond. It is only suitable as an abrasive in its cubic crystal shape (CBN). It is produced synthetically from natural reserves of hexagonal crystalline boron nitride and is usually bound in resin or ceramic. It has a heat resistance of approx. 1,300 °C, from approx. 730 °C, it becomes even harder than diamond! It is used predominantly for grinding tough unhardened steels such as high-speed steel as well as hot- and cold -work steel. Not suitable for soft steels, tungsten carbides, non-ferrous metals, chrome and nickel coatings as well as non-metals. Diamond The diamonds used in modern technology are almost exclusively synthetic. The hardness and geometries for specific applications achieved are superior to those of natural diamonds. Even as the hardest known material, diamonds are only heat-resistant up to 800 °C and their scope of application is therefore somewhat limited. Diamond tools are mainly used for precision grinding on tungsten carbide, grey cast iron, glass, ceramic, porcelain, fire-proof stones, germanium, graphite, cutting ceramics, silicon, rubber, non-ferrous heavy metal, cementite alloys, nickel and chrome alloys, ball bearing steel, tool steels with high carbon and low vanadium content. Abrasive hardness according to Knoop Diamond Cubic boron nitride (CBN) Boron carbide Silicon carbide Corundum Zirconium aluminium oxide manual grinding