If a grinding wheel is too HARD the following may result :
- Wheel surface will glaze up requiring frequent dressing for it to work, the dressing operation will reduce the life of the wheel.
- The free cutting ability of the wheel will suffer. This will heat up the workpiece and grinding wheel, which could cause cracking of carbide and damage to the wheel surface (pullout of diamonds).
- Stock removal speed will decrease
Causes for wheel acting HARD :
- Concentration too high
- Grit size too large (finer grit sizes act softer)
- Incorrect bond chosen i.e. wet bond used dry
- Peripheral wheel speed too high.
If a grinding wheel is too soft or too free cutting the following may result :
- Aggressive grinding may dislodge diamond grit before it has been used to its optimum.
- Increased stock removal rate may result in disproportionate wheel wear
Causes for wheel acting SOFT :
- Concentration too low
- Grit size too fine, size should be chosen as large as possible to achieve an acceptable finish
- Incorrect bond chosen
- Peripheral wheel speed too low
Other factors which affect wheel wear :
- Stability or rigidity of grinder / grinding wheel - any vibration could result in hammering action at the grinding face
- Worn shaft bearings have the same result as above
- Too much infeed per pass as recommended for grit size causes pullout of diamonds
- In the case of diamond wheels, the presence of steel causes erosion of the bond and graphitization of the diamonds
- In the case of CBN wheels, steel which is not sufficiently hard will erode the bond.