Polishing

Polishing operations use abrasives that are mounted on prepared shaped wheels or on belts that provide a resilient backing. The stainless steel to be polished may be in either a smooth rolled or a previously ground condition. For the smooth rolled condition, the starting grit size should be selected in a range of 150 to 220. For the ground condition, the initial grit should be coarse enough to remove or smooth out any residual cutting lines or other surface imperfections left from grinding. In either instance, the treatment with the initial grit should be continued until a clean, uniform, blemish-free surface texture is obtained. The initial grit size to use on a preground surface may be set at about 20 numbers finer than the last grit used in grinding and may be changed, if necessary, after inspection. A tallow lubricant may be used to reduce the sharpness of cutting. With broad-belt grinding of stainless steel sheet, the use of a lubricant or coolant is mandatory.

After completion of the initial stage of polishing, wheels or belts are changed to provide finer grits. The step-up in fineness is usually by 30 to 40 numbers. Each succeeding treatment is continued until all residual marks of the preceding cut are removed. Grease in stick form is applied to wheels carrying abrasives of 150 mesh and finer. Aluminum oxide buffing compounds and powdered pumice are preferred for use with abrasives of 200 mesh and finer grit size.

Polishing speeds are generally somewhat higher than those used in grinding. A typical speed for a coated-wheel operation is 38 m/s (7500 sfm).

The same precautions that must be observed in the grinding of stainless steel are equally applicable to polishing:

• Avoidance of iron or other contamination

• Care of wheels and belts when not in use

• Restriction of the use of wheels and belts to stainless steel only

• Avoidance of excessive pressure while polishing

• Operation at proper speeds

• Avoidance of localized heat buildup because of dwelling at one spot

• Removal of loose cuttings and bits of abrasive from work surfaces before changing from one grit size to another

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