239 / 306
BONDED
ABRASIVES
239
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 m/s). 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.
SAFE WORKING PRACTICES
PERSONAL PROTECTION
Safety goggles, ear defenders, safety gloves, dust masks and, if grinding conditions are severe, additional face
protection. Leather aprons and safety shoes must be worn.
PERSONAL PROTECTION
Mouth
Protection
Wear
Gloves
Eye
Protection
Ear
Protection
Read
Instruction
Damaged
Wheel
Dry
Wet