Grinding wheel

All machining operations are potentially dangerous - lack of understanding or undue care have resulted in many accidents. The use of grinding wheels, also known as abrasive wheels, which are described fully at the end of this chapter, is potentially one of the most dangerous for two reasons. 

Sharpness and trueness of the face can be achieved by dressing with an industrial diamond. The diamond, held in a suitable holder, is positioned on the chuck under the grinding wheel. The wheel is then lowered until it touches the diamond, whereupon the diamond is moved across the surface of the wheel using the crosstraverse movement. Fig. 10.7. The wheel is then lowered a little and the operation is repeated until all the worn grains have been torn out and fresh ones exposed and the face is flat and true. 

It is impossible to produce good-quality work on any grinding machine if the wheel Is out of balance, thus setting up vibrations through the spindle. 

When the wheel Is mounted correctly and the periphery has been dressed, the collet assembly is removed from the spindle. The balance masses are then removed. A balancing arbor is inserted in the bore. The balancing arbor has a taper identical to that on the spindle and has equal size parallel diameters at each end. Fig. 10.9(a). This assembly is placed on a balancing stand. Fig. 10.9(b), which has previously been set leveL The wheel is allowed to roll on the knife edges and is left until it comes to rest, which it will do with the heaviest portion at the bottom 

Due to the fragile nature of a grinding wheel and the high speeds at which It runs, it is possible for a wheel to burst. Under the regulations, all grinding wheels must be adequately guarded and the guard be fitted at all times before the wheel is run. 

A 300 mm diameter wheel is run at about 2000 rev/min, giving a speed at the diameter of almost 1900 m/min. Compare this with a piece of steel of the same diameter being cut with a high-speed-steel cutting tool on a lathe at 30 m/min. 

The Provision and Use of Work Equipment Regulations 1998 (PUWER) require, amongst other things, that all machinery is suitable for its intended use and is properly maintained, and that employees, including those using, mounting and managing the operation of abrasive wheels, are fully informed and properly trained in their use. 

A grinding wheel is made up of a large number of tiny teeth. The teeth are formed by the tiny 

The diamond can be single point or multi-point and by varying the depth of cut and the traverse rate of dressing, different wheel surfaces and hence different cutting actions can be achieved. The size of diamond used is important and is 

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Very small synthetic diamonds have been made industrially by subjecting graphite to pressures in the range 5.5-b.9 GN m , at temperatures between 1500 and 2700 K. The diamonds produced are very small but competitive with natural diamonds for use in industrial cutting and grinding wheels. 

Grinding glass Grinding wheel Grinding wheels... 

Useful thermosetting resins are obtained by interaction of furfural with phenol. The reaction occurs under both acidic and basic catalysis. Other large uses of furfural together with phenol are in the manufacture of resin-bonded grinding wheels and coated abrasives (5). 

Advances ia grinding wheels, abrasive belts, and the grinding process have been controlled primarily by the development of abrasives and to a lesser extent by advances ia bonding and manufactufing methods. Without abrasives, modem iadustrial production would be impossible. The U.S. Government alone has over 300,000 tons of abrasives ia its strategic National Defense Stockpile (4). 

Corundum. Comndum [1302-75-5] (see Aluminum compounds) is a naturally occurring massive crystalline mineral composed of aluminum oxide. It is an impure form of the gems mby and sapphke. Prior to 1900 comndum was an important abrasive for the production of grinding wheels. Today it is mainly employed as a loose abrasive for grinding and polishing optical lenses. Almost all the world s supply of comndum now comes from Africa, primarily from Zimbabwe. 

Coated abrasive products, once limited to sandpaper in woodworking shops, are versatile and efficient industrial tools. Machines ranging from portable Sanders to giant slab conditioners and roU grinders utili2e coated abrasives. Abrasive belt machines now perform many of the operations that were once the exclusive province of grinding wheels. 

Fig. 3. Standard wheel markings recommended and approved by the Standards Committee of The Grinding Wheel Institute.

Bonded abrasive products are made as wheels, disks, cylinders, sticks, blocks, and segments, all of which are defined n.yiSyi-B74.2-1974, "USA Standard Specifications for Shapes and Sizes of Grinding Wheels." This bulletin is sponsored by the Grinding Wheel Institute it is obtainable from most wheel manufacturers. 

M. F. Cokie, The Saga of the Abrasive Industry Grinding Wheel Institute and Abrasive Grain Association, Cleveland, Ohio, 1951, p. 2. 

W. E. Schleicher, The Grinding Wheel, 3rd ed.. The Grinding Wheel Institute, Cleveland, Ohio, 1976. 

Fluorotitanic acid is used as a metal surface cleaning agent, as a catalyst, and as an aluminum finishing solvent (see Metal surface treatments). Fluorotitanates are used in abrasive grinding wheels and for incorporating titanium into aluminum aHoys (see Abrasives Aluminumand aluminum alloys). 

Hexafluorozirconic acid is used ia metal finishing and cleaning of metal surfaces, whereas the fluorozirconates are used in the manufacture of abrasive grinding wheels, in aluminum metallurgy, ceramics industry, glass manufacturing, in electrolytic cells, in the preparation of fluxes, and as a fire retardant (see Abrasives Metal surface treati nts). 

Workers in the metals treatment industry are exposed to fumes, dusts, and mists containing metals and metal compounds, as well as to various chemicals from sources such as grinding wheels and lubricants. Exposure can be by inhalation, ingestion, or skin contact. Historically, metal toxicology was concerned with overt effects such as abdominal coHc from lead toxicity. Because of the occupational health and safety standards of the 1990s such effects are rare. Subtie, chronic, or long-term effects of metals treatment exposure are under study. An index to safety precautions for various metal treatment processes is available (6). As additional information is gained, standards are adjusted. 

Pulpstones. Improvements have been made in the composition and speed of the grinding wheel, in methods of feeding the wood and pressing it against the stone, in control of power to the stones, and in the size and capacity of the units. The first pulpstones were manufactured from quarried sandstone, but have been replaced by carbide and alumina embedded in a softer ceramic matrix, in which the harder grit particles project from the surface of the wheel (see Abrasives). The abrasive segments ate made up of three basic manufactured abrasive siUcon carbide, aluminum oxide, or a modified aluminum oxide. Synthetic stones have the mechanical strength to operate at peripheral surface speeds of about 1200—1400 m /min (3900 to 4600 ft/min) under conditions that consume 0.37—3.7 MJ/s (500—5000 hp) pet stone. 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

Uses. Apphcations for boron carbide relate either to its hardness or its high neutron absorptivity ( B isotope). Hot-pressed boron carbide finds use as wear parts, sandblast no22les, seals, and ceramic armor plates but in spite of its hardness, it finds Httie use as an abrasive. However, this property makes it particulady usehil for dressing grinding wheels. 

Grinding Wheel Institute data sheets, Cleveland, Ohio, 1990. 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Design and Operation The pan crusher (Fig. 20-30) consists of one or more grinding wheels or mullers revolving in a pan the pan may remain stationaty and the mullers be driven, or the pan may be driven while the iTuillers revolve by friction. The mullers are made of tough alloys such as Ni-Hard. Iron scrapers or plows at a proper angle feed the material under the mullers. 

This enormous hardness is exploited in grinding wheels which are made from small particles of a high-performance engineering ceramic (Table 15.3) bonded with an adhesive or a cement. In design with ceramics it is never necessary to consider plastic collapse of the component fracture always intervenes first. The reasons for this are as follows. 

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