leave the Compound exposed to the air, as it will become dry and hard.
- On hot days place sealed bars in cold water for a few minutes before using.
- In addition, store unopened bars of Compound in a cool place to prevent softening and
deterioration.
Cement bonded wheels will withstand higher temperatures both in drying and use, can be dried more
rapidly, and withstand the great frictional heat caused by high polishing speeds. Although most cements
are formulated for fast, tough, coarse polishing, they have been used successfully for fine polishing.
More recently cements are being formulated which have some of the desired flexibility found in hide
glues. As such cements and adhesives are, in the main, proprietary mixtures, it is best to follow the
manufactures recommendation in each case rather than attempt to set general rules to cover all if them.
ABRASIVES:
The abrasive most widely used in polishing metals is fused aluminum oxide. The grain is normally heat
treated to give it good capillarity and in addition many types are etched or coated to improve the
adhesion to the bond used. Fused aluminum oxide is sharp, hard, fast cutting and long wearing.
Another abrasive used is silicon carbide, which fractures when dull to present new sharp cutting edges,
and for this reason is selected in certain specialized operations. Silicon carbide grain, however, is more
difficult to bond firmly to the wheel; its scope is limited. Before the advent of the electric furnace
abrasives, Turkish emery, a natural compound of the iron oxides, was the standard polishing grain. The
edges of Turkish emery tend to wear smooth without fracturing, and although this property decreases
the spread of cut.
It is sometimes desirable for fine polishing operations, particularly in the cutlery field.
LUBRICATION:
Lubrication of the cutting face of a polishing wheel, with oil or grease, is desirable in a number of cases
to prevent gouging when a fine polished surface is required. It is also used to minimize frictional heat
when polishing some of the softer metals, particularly aluminum. The most popular method of lubricating
is by a tallow grease mixture applied by friction from a bar to the rotating polishing wheel.
Special bar lubricants are now available, which have the unique feature of freeing abraded metals,
particularly the softer nonferrous type, and prevent them from loading at the face of the polishing wheel.
Where polishing wheels can be lubricated automatically, spray-able liquid lubricants are now available
in formulations, which are easier to clean.