Section 13. qxd

acting hard;
reducing the wheel speed or increasing the work
speed or the depth of cut causes the wheel to 
act softer.
If the wheel
breaks down too rapidly, reversing this procedure will make the wheel
act harder. Harder wheels are generally recommended for soft work
materials, and vice versa.
A variety of 
bond
types are used in grinding wheels; these are generally
categorized as 
organic 
and
inorganic.
Organic bonds are materials such as
resin, rubber, shellac, and other similar bonding agents. Inorganic mate-
rials are glass, clay, porcelain, sodium silicate, magnesium oxychloride,
and metal. The most common bond type is the vitrified bond which is
composed of clay, glass, porcelain, or related ceramic materials. This type
of bond is brittle and produces wheels that are rigid, porous, and resistant
to oil and water. The most flexible bond is rubber which is used in mak-
ing very thin, flexible wheels. Wheels subjected to bending strains should
be made with organic bonds. In selecting a bonding agent, attention
should be paid to its sensitivity to temperature, stresses, and grinding flu-
ids, particularly over a period of time. The term 
reinforced
as applied to
grinding wheels indicates a class of organic wheels which contain one or
more layers of strengthening fabric or filament, such as fiberglass. This
term does not cover wheels with reinforcing elements such as steel rings,
steel cup backs, or wire or tape winding. Fiberglass and filament rein-
forcing increases the ability of wheels to withstand operational forces
when cracked.
The 
structure
of a wheel is important in two aspects: It supplies a
clearance for the chip, and it determines the number of cutting points on
the wheel.
Section_13.qxd 10/05/06 10:32 Page 13-66

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