TECHNICAL INFORMATION 154 / NORTON WINTER PRECISION TECHNOLOGY TOOL GRINDING BONDS To meet the challenges of the wide diversity of grinding applications, it is inevitable that a wide range of bond systems is required. Bonds are categorised according to the fundamental material type used, and many variations exist within each type. RESIN BONDS Phenolic and polyimide resins are used as bonds, to which fillers are added in addition to the abrasive grit. Grinding wheels with resin bond occupy the lower section of the bond hardness scale. They are considered soft, fast, and coolgrinding, yielding only low grinding forces and allowing a wide range of adjustment. SINTERED METAL BONDS Most metal bonds are based on bronze, although harder systems may be based on steel or even hardmetal. Sintered bronze bonds are relatively soft and at their softest can overlap the hardest resin bonds. Steel and hardmetal bonds are more wear resistant, so therefore act harder and grip the abrasive grains more strongly, leading to longer tool life, although the abrasive can sometimes appear blunt. Metal bonded grinding wheels generally grind more slowly, in most applications acting harder, and more grinding heat is developed than in resin bonded wheels. However, metal bonds can also readily dissipate heat, which also impacts the grinding process. Metal bonds are ideal for grinding wheels with sharp edge profiles, and for machining abrasive materials that would otherwise wear the bond. Furthermore, metal bonds are shock-resistant, and are suitable for very aggressive operating conditions. Metal bonds are mostly used in wet grinding. Special variants are crushable, brittle metal bonds that can be dressed on the machine in a special crushing process. These bonds are especially useful in creep feed grinding. ELECTROPLATED BONDS In this bond system, the metal bond is deposited electrolytically onto a bronze or steel body. The grit is tenaciously achored by the bond, and grain tips can protrude from the bond layer by 30 - 50 % of the grain diameter. This leads to a grinding layer with a very high material-removal-rate capability. However, only the outermost grain layer acts in this way, which is why these tools are mainly designed in single-layer versions. Such single layer bond systems are suitable for profiled wheel bodies of all kinds; profile accuracy is dependent on the grit size specified. VITRIFIED BONDS Vitrified bonds are based on fusible glasses combined with fillers and the abrasive grains. While resin and metal bonds are generally fully dense, vitrified bonds are usually produced with a defined porosity, and are available in different hardness levels. This variation in porosity and hardness is analogous to the vitrified bonds of conventional grinding wheels. The main features of vitrified bonds are: • Good dressability and profileability • Free-cutting due to the porosity and self sharpening behaviour • Fluid availability, due to porosity, in the grinding zone allows cool grinding at low grinding forces • High cutting speeds and material removal rates are possible. GLOSSARY For your reference: a short explanation of grinding terms GLOSSARY
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