Most grinding fluids are applied in high-volume, lowvelocity flood streams (Figure L-66) by the machine coolant pump.
It is important to apply grinding fluid at the right place (Figure L-68). This is usually at the immediate vicinity of the contact area. One of the greatest difficulties in both surface and cylindrical grinding is “grinding dry with fluid.” The Figure L-68 A specially designed nozzle like this helps to keep the fanlike effect of the rapidly rotating wheel from blowing coolant away from the wheel–work interface (Courtesy of MAG
Industrial Automation Systems, LLC).explanation for this is that on some heat-sensitive steels, inadequate grinding fluid application can result in the development of grinding cracks from having the high-temperature line contact with the grinding wheel quenched an instant later
with the grinding fluid. The hot metal at the contact point tries to flow, but the abrupt quench arrests the flow, putting the metal into such stress that cracking often results. This type of grinding crack is parallel to the grinding wheel axis. Unless you have full flowing contact with the grinding fluid, it is sometimes better to shut off the fluid to avoid damaging a sensitive workpiece. One good way to ensure better fluid flow
is to use a dummy block of the same height ahead of the workpiece, to keep the fluid flowing over the workpiece. If the finish ground workpiece shows the appearance of a ramping down on the exit side of the grinding, another dummy block can be used in the exit side to prevent this problem by maintaining fluid contact with the workpiece.
There is also another good way to prevent these problems. Because vitrified wheels are porous, it is possible to apply grinding fluid through an open L-structured wheel (Figure L-69). Grinding fluid is fed to a circular channel and then passes through holes in the channel into the wheel.
Centrifugal force causes the grinding fluid to spray outward.
This method is effective in getting the fluid into the contact area. However, this method of application requires fluid filtration down to the 3- to 5-m range (120–200 millionths of an inch) to keep the pores in the wheel open.
Also, the wheel guards must be kept clean to avoid having swarf wash back onto the work.
Air/mist coolant is another application method (Figure L-70).
Grinding fluid combined with air under pressure sprays a small volume of grinding fluid between the wheel and the workpiece. Mist systems use much less liquid coolant volume and need no coolant return systems. The rapidly evaporating mist provides cooling in the contact
area. The view of the workpiece is clearer than in flood applications. Active ventilation of the mist is essential, for health reasons, when using mist coolant.