Precautions to be taken before mounting a grinding wheel:
In the interest of satisfactory operation and safety, it is important that grinding wheels are mounted correctly on the machine and before mounting they should be examined for any defects.
1. The wheel should be first examined for any flaw or crack which, under stresses set up due to high speed of rotation, might lead to fracture of the wheel, thus causing serious accident.
For testing this, the wheel is supported with the fingers in the bore and struck lightly with a piece of wood. If any crack is present, it can be judged by the sound produced. The sound of vitrified and silicate wheels gives a clear, bell like ring when struck.
2. Wheel Balance:
Out-of balance and out-of-round wheels result in vibrations and poor surface finish, faster wheel breakdown and sometimes even cause injury to the operator. For this the wheel is mounted at the centre of a perfectly straight and round spindle, the assembly is then rested on level knife-edge ways.
The test should be carried out after turning up the wheel face and mounting it on its spindle. If there is any unbalance, wheel will come to rest with its heavy side underneath. Error is rectified by cutting some of the lead from heavy side of bush.
Other way is to adjust the position of the slotted weights provided in the rim of the flange. These adjustable segments can be fixed round a circle at any position by tightening the screws. Best results are achieved by dynamically balancing the wheel.
3. The sides of the wheel and the flanges which clamp the wheel should be flat and bear evenly all the around.
4. The lead bushing should be an easy fit and no force be used.
5. The back, fixed flange should be keyed, shrunk or otherwise fixed to the spindle in order to transmit the power from the spindle to the wheel.
6. Both flanges must be relieved so that they only bear on the wheel at their rim.
On no account must one of them or both should touch the sides or the wheel anywhere else. Blotting paper or rubber washer should be used between the flanges and the wheel.
7. Both flanges should be of the same size, the diameter being preferably equal to one-half the diameter of the grinding wheel. If they are not equal in diameter, then bending stresses will be induced.
8. The nut should be tightened only just enough to hold the wheel. The undue tightness is unnecessary and not desirable.
9. When wheel is mounted for the first time it should be made to run idle for some time.
10. Safety guard should always be used, so that in case of accident operator is not injured.
11. The cut type wheel is usually inclined by a little amount so that arc of contact is decreased and also the lay is unidirectional and does not cross each other. Thus when two surface rub, jamming effect is also not observed.
12. The wheel speed chosen should be proper.
13. If possible, some proper lubricant should be used in grinding operation and while grinding cast iron job, dust collector should also be operated.