Machinery's Handbook, 31st Edition
ABRASIVE CUTTING
1335
Table 2. Guide to the Selection and Application of Contact Wheels
Hardness and Density
Surface Material Cog-tooth Rubber Standard serrated Rubber
Purposes
Wheel Action
Comments
70 to 90 durometer
For cutting down projections on castings and weld beads. For smoothing projections and face defects. Same as for standard serrated wheels but preferred for soft nonferrous metals.
Roughing Fast cutting, allows long belt life. Roughing Leaves rough- to medium-ground surface.
40 to 50 durometer, medium density
Flexibility of rubber allows entry into contours. Medium polishing, light removal. Plain wheel face allows controlled penetration of abrasive grain. Softer wheels give better finishes. Hard wheels can remove metal, but not as quickly as cog-tooth rubber wheels. Softer wheels polish well. Uniform polishing. Avoids abrasive pattern on work. Adjusts to contours. Can be performed for contours.
X-shaped serra tions
Roughing and polishing Roughing and polishing Roughing and polishing
20 to 50 durometer
Rubber
20 to 70 durometer
Plain face Rubber
For large or small flat faces.
About nine densities from very hard to very soft Soft, medium, and hard
Com pressed canvas Solid sectional canvas Buff section canvas Sponge rubber inserts Fingers of canvas attached to hub Rubber segments
Flat
Good for medium-range grinding and polishing. A low-cost wheel with uniform density at the face. Handles all types of polishing. Can be widened or narrowed by adding or removing sections. Low cost. Has replaceable segments. Polishes and blends contours. Segments allow density changes.
flexible
Flat
Polishing
flexible
Flat
Contour polishing
For fine polishing and finishing. Uniform polishing and finishing. Polishes and blends contours.
Soft
flexible
5 to 10 durometer, soft
Flat
Polishing
flexible
Flexible
Soft
Polishing Uniform polishing and finishing.
For polishing and finishing.
For portable machines. Uses replaceable segments that save on wheel costs and allow density changes.
Roughing and polishing Roughing and polishing
Grinds or polishes depending on density and hardness of inserts.
Flat
Varies in hardness
flexible
Air pressure controls hardness
Flat
Inflated rubber
Uniform finishing.
Adjusts to contours.
flexible
The types of abrasives available in cut-off wheels are: Aluminum oxide, for cutting steel and most other metals; silicon carbide, for cutting non-metallic materials such as carbon, tile, slate, ceramics, etc.; and diamond, for cutting cemented carbides. The method of denoting abrasive type, grain size, grade, structure and bond type by using a system of markings is the same as for grinding wheels (see page 1282). Maximum wheel speeds given in the ANSI Standard “Safety Requirements for The Use, Care, and Protection of Abrasive Wheels” (ANSI B7.1-2017) range from 9500 to 14,200 sfpm (2896–4328 m/min) for organic bonded cut-off wheels larger than 16 inches (40.6 cm) in diameter and from 9500 to 16,000 sfpm (2896–4877 m/min) for organic bonded cut-off wheels 16 inches in diameter and smaller. Maximum wheel speeds specified by the manufacturer should never be exceeded even though they may be lower than those given in the B7.1 Standard. There are four basic types of abrasive cutting machines: Chop-stroke, oscillating stroke, horizontal stroke and work rotating. Each of these four types may be designed for dry cut ting or for wet cutting (includes submerged cutting). The accompanying table based upon information made available by The Carborundum Co. gives some of the probable causes of cutting off difficulties that might be experienced when using abrasive cut-off wheels.
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