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BONDED
ABRASIVES
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GRINDING CONTACT AREA
The contact area affects the selection of wheel grade and structure. Large contact areas, as on segmental
grinders, generally produce low grinding pressures and require soft grade, open structure wheels. Induced
porosity wheels are most efficient for grinding very large contact areas.
Conversely, small contact areas, as on cylindrical grinding machines, require harder grade
and/or closer structure wheels.
The size of workpiece can also affect the grinding contact area. In general, the larger the workpiece, relative
to the grinding wheel diameter, the larger the contact area, requiring softer grade wheels.
GRINDING FLUID
Dry grinding with vitrified wheels require wheels one or two grades softer than when wet grinding.
SEVERITY OF THE GRINDING OPERATION
This can affect the choice of abrasive type, grade and even bond type. Where the wheel is subjected to shock
loads, as in fettling operations, a resinoid bond should be used. In general, the more severe the grinding operation,
the harder the grade of wheel required and the tougher the abrasive that can be used. Severity of grinding
operation can be due to heavy infeeds, high work speeds and traverse rates or intermittent grinding contact.
The latter is usually due to workpiece geometry, resulting in a dressing action on the wheel.
GRINDING WHEEL DRESSING & TRUING
Truing and dressing of grinding wheels are often considered to be the same thing, since they are frequently
performed as one operation. Truing is performed to ensure concentricity and introduce any profile that
may be required on the wheel face. Dressing conditions the wheel surface to give the desired cutting action.
EFFECT ON GRINDING ACTION
Speed
Increased
Decreased
Wheel Speed *
Harder
Softer
Work Speed
Softer
Harder
Traverse Speed
Softer
Harder
Infeed Rate
Softer
Harder
* The maximum peripheral speed (m/s) specified for the wheel must never be exceeded.
STOCK TO BE REMOVED & SURFACE FINISH
This affects the choice of abrasive size and bond type.
High stock removal rates, as in fettling operations, require coarse grit wheels, typically 12 to 24 mesh.
Fine finishes and tight limits on finished workpiece geometry require finer grit sizes.
Final surface finish is often achieved by ‘spark out’. No further infeed is applied and the wheel is allowed to grind
until the majority of the grinding sparks cease.
THE GRINDING MACHINE
The type of machine can effectively define the grinding contact area and the ease with which grinding fluid
can be applied to the grinding zone.
The power available on the machine governs the stock removal rate. The greater the power available, the harder
the grade of wheel that is required for efficient operation.
Any deterioration in the condition of machine bearings and slideways will lead to vibration and, consequently,
premature wheel breakdown. This can, in part, be overcome by using a harder grade wheel and/or a tougher
abrasive but the only effective solution is to maintain the machine as recommended by the machine manufacturer.
SPEEDS & FEEDS
The effect of speeds and feeds on grinding action and, hence, the selection of wheel, can best be summarised
in the following table: