the brasses, which require a soft wheel in order to prevent clogging or
glazing of the wheel with particles of metal.
Bonds.—The three bonds commonly employed in the order of their
importance are: the vitrified, the silicate, and the elastic. The first is
composed of clays, properly a pure grade of kaolin. The wheels are
moulded and subjected to a prolonged heat to partially fuse the bond. The
wheels are of a reddish-brown colour, are very porous and free-cutting,
and are not affected by water, oils,
or temperature, and the bond is hard.
SECTIONAL ELEV. THRO.
AXJS Of ROTATION.
Fig. 31. — Edge Wheel mounted per-
manently on Flanges for accurate Replace-
ment and Wheel-changing on Mandrel
Fig. 32.—Cup Wheel Mounting, with Safety
But the risks of cracking do not permit of making these wheels beyond about
30 in. diameter. These are suitable for general grinding. For the silicate
bond the silicate of soda is chiefly used. The process is less prolonged than
that for vitrified wheels, and larger sizes can be manufactured. These are
not used much for cylindrical grinding; their function is that of wet grinding
of tools. The elastic wheels are mostly bonded with shellac. Vulcanite
wheels are bonded with vulcanized rubber. Both can be made very thin,
and be run in water. Vulcanite wheels can be used with oil or caustic
soda; elastic wheels cannot. These are made thin for cutting off materials,
for grinding saws, and sharpening cutters.
Wheel Shapes and Mountings.—Fig 30 shows an edge wheel, used
for cylindrical grinding, with one method of mounting. The flanges are