Ch 27

Quartz

A hard, crystalline mineral made of silica.

Emery

A mixture of alumina and magnetite, a natural abrasive used on coated paper and cloth.

Corundum

A type of abrasive, natural Ai2O3.

Attrition

Abrasive wear action of the grits resulting in dulled edges, grit flattening and wheel glazing.

Aluminum Oxide

Ai2O3 most widely used artificial abrasive.

Coated Abrasive

Being used increasingly in finishing both metal and nonmetal products; made by gluing abrasive grains onto a cloth or paper backing; available in sheets, rolls, endless belts, and disks of various sizes.

Resinoid Bond

Common type of bonding material for grinding wheels. Because plastics can be compounded to have a wide range of properties, such wheels can be obtained to cover a variety of work conditions.

Cylindrical Grinding

Commonly used for producing external cylindrical surfaces. A grinding wheel rotates on an axis parallel with the work piece, and traverses along the length of the workpiece.

Crush Dressing

Consists of forcing a hard roll having the same contour as the part to be ground against the grinding wheel while it is revolving- usually quite slowly.

G ratio

Grinding ratio; defined as the cubic inches of stock removed divided by the cubic inches of wheel lost.

Silicon carbide

Grits or grains irregular in shape whose crystals are very hard, friable, and rather brittle.

Diamond

Hardest of all materials. Those that are used for abrasives are either natural, off-color stones that are not suitable for gems, or mall, synthetic stones that are produced specifically for abrasive purposes.

Centerless Grinding

Makes it possible to grind both external and internal cylindrical surfaces without requiring the workpiece to be mounted between centers or in a chuck.

Abrasive Machining

Material removal process that involves the interaction of abrasive grits with the workpiece at high cutting speeds and shallow penetration depths.

Garnet

Off-colored stones; used for abrasives.

Friability

Refers to the fracture of the grits and is the opposite of toughness.

Truing

Restores the original shape.

Silicate Bond

Silicate wheels used silicate of soda (waterglass) as the bond material. These wheels are more brittle and not so strong as vitrified wheels, the abrasive grains are released more readily. are useful in grinding tools when heat must be kept to a minimum.

Grade

The bond strength which controls the fracturing of the grits.

Creep Feed Grinding

The work is fed very slowly past the wheel and the total downfeed or depth is accomplished in a single pass.

Surface grinding

These machines are primarily used to grind flat surfaces

Vitrified bond

This bond is composed of clays and other ceramic substances. The abrasive particles are mixed with the wet clays so that each grain is coated.

CBN

This material is not found in nature. Extremely hard, registering at 4700 on knoop scale. Second hardest substance created by nature. High thermal resistance.

Honing

This process is a stock-removal process that uses fine abrasive stones to remove very small amounts of metal.

Lapping

This process is an abrasive surface-finishing process wherein fine abrasive particles are charged (caused to become embedded) into a soft material, called a lap.

Shellac Bond

This type of bond on wheels is made by mixing the abrasive grains with shellac in a heated mixture. Used primarily for strong, thin wheels having some elasticity. Produces a high polish.

Snagging

Type of rough manual grinding that is done to remove fins, gates, risers, and rough spots from castings or flash from forgoings, preparatory to further machining.

Rubber Bond

Used to produce wheels that can operate at high speeds but must have a considerable degree of flexibility so as to resist side thrust.

Dressing

When a wheel is cleaned and sharpened.

Grinding

Wherein the abrasives are bonded together into a wheel; the most common abrasive machining process.