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The proper delivery of coolant (grinding fluid) into the grinding zone is of utmost importance. Adequate volume and pressure are not sufficient if the coolant jet's velocity is either too high or too low. The exit velocity of the coolant jet should be roughly equal to the grinding wheel's surface speed. This will ensure that the wheel will transport coolant into the grinding zone. Equal velocity fluid delivery will be achieved if the coolant jet "clings" to a 30 to 40° section of the grinding wheel's periphery (according to H. W. Ott).
The only coolant that can actualy enter the grinding zone irrespective of pump pressure, is that which the grinding wheel can effectively transport into the arc of contact as illustrated below. If we only had standard wheels, their pumping capacity would be inadequate to prevent burning. For example a standard structure 80 grit 0, 500 by 12-mm (20 by 1/2-inch) wide wheel can transport 0.9-litre/min (0.25-US gal/min) at 35-m/s (7,000 sfpm). Depending on the pump volume and pressure, open structure wheels with interlinked porosity can transport up to 20 times this amount.
