Any grinding wheel has it of some use wear requirements, reach a certain degree of wear of grinding wheel must be replaced with new. In order to save material, Super wear is required, this is a very unsafe and illegal behavior. General provisions, when diameter 10MM diameter of grinding wheel wear than chucks should be replaced when the new wheel.
From the Treasury brought out a new grinding wheel of grinding wheel is not necessarily qualified, even from manufacturers buying new wheels are not necessarily qualified for the grinding wheel. Any wheel it must be valid, duration of use, it is a qualified wheel over validity of use, not necessarily qualified for the grinding wheel. Rules "wheel should be used within the validity period, resin and rubber bond wheel storage must be approved by the Rotary test after one year, candidates may use".
In the course of using, if you find cracks on wheels local, you should immediately stop using, replace the new wheel to avoid wheel crushing injury accident.