Page 493 - NORTON cutting-off and grinding wheels - industrial

TECHNICALINFORMATION
493
TECHNICAL INFORMATION
TRAINING OF OPERATORS
Grinding operators should be trained in the safe use
of each machine they operate.
SPEEDS
No abrasive wheel should be operated at a speed in
excess of the maximum permissible speed marked
on the wheel in RPM when the wheel is new and
full size. It is permissible, however, to increase
the spindle speed of the machine beyond the RPM
stated on the wheel provided the increase is in
proportion to the reduction in diameter and that the
original peripheral speed is not exceeded (quoted on
the wheel in metres/sec). In high production areas
it is now normal for machines to have constant
peripheral speed spindles. This is an electronic
device that automatically increases the spindle
speed of the machine as the wheel diameter wears
down and prevents most of the reduction in wheel
performance that is experienced when the wheel
becomes smaller.
COOLANTS
The strength of resin bonded grinding wheels can
be reduced by coolants. The concentration and
alkalinity of coolants should be regularly checked
and a pH value of 8 should not be exceeded.
Prolonged immersion of a stationary wheel in
coolant can produce an out of balance condition.
Coolant should be shut off before stopping a wet
grinding wheel, and the wheel allowed to run free
until all the coolant has been spun out.
WORK RESTS
Work rests should be kept adjusted as close as
possible (gap between wheel and work rest should
not exceed 3mm) to the wheel and maintained in
good condition.
TRUING & DRESSING
Re-dressing of wheels that have become malformed
and out of truth in off-hand operations must only
be performed by a competent person.
If an out of balance condition, due to the wheel
wearing excessively out-of-round, cannot be
corrected by truing, the wheel should be removed
from the machine. Wheels should be dressed
regularly to avoid loading
SIDE GRINDING
Side grinding should only be performed with wheels
designed for this purpose (straight cups etc.).
Grinding on the flat sides of wheels designed for
peripheral grinding may be dangerous and cause a
wheel breakage. This does not preclude their use
for certain precision applications such as shoulder
and form grinding, where it is recognised that
a limited amount of side grinding is performed;
however, in these operations the operator has
control of the pressure through the hand wheels
of the machine whereas with bench grinding and
off-hand machines the pressure is uncontrolled.
Extreme caution should be exercised not to use
excessive pressure.
As a general guide, do not use a straight wheel
which has a thickness of less than 10% of the wheel
diameter for side grinding.
ORGANIC CUTTING˜OFF WHEELS
‘Non-reinforced’ cutting-off wheels should never be
used:
• On a portable grinding machine
• On any machine where the workpiece is fed into
the wheel by hand
Cutting-off wheels should only be mounted on
machines designed for their use.
Cutting-off wheels should be inspected for warping
before use. Warped wheels should not be used.
When grinding, twisting or the exertion of any
pressure on the side of the wheel should be avoided.
Workpieces should be rigidly supported and firmly
clamped wherever possible.
STOPPING WHEELS
Wheels should not be brought to rest by applying
pressure to the periphery or face of the wheel.
SAFE WORKING PRACTICES
PERSONAL PROTECTION
Safety goggles, ear defenders, safety gloves, dust masks and, if conditions are severe, additional face
protection. Leather aprons and safety shoes must be worn.
Mouth
Protection
Wear
Gloves
Eye
Protection
Ear
Protection
Read
Instructions
Damaged
Wheel
Dry Wet