Understanding Today's Machine Coolants - Engine Builder Magazine
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Understanding Today’s Machine Coolants


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Many types of grinding and honing operations require the use of a "process fluid" for cooling and lubrication. Remanufacturing procedures such as crankshaft grinding and surface grinding generate a tremendous amount of heat and require a fluid primarily for cooling. Heat control is absolutely essential for a good finish and accurate tolerances. Use of a coolant also helps prolong the life of the grinding wheel.

With honing, the situation is a little different. Some type of process fluid is also required, but primarily to lubricate the honing stones as they cut the cylinder bore. Lubrication reduces friction so less rotational force and pressure are needed to hone the cylinder, and it allows the abrasives to cut more cleanly. The fluid also provides cooling, but heat buildup is less of a factor in honing because the rate at which the stones travel across the metal in surface feet per minute (sfpm) is only about 85 to 150 sfpm, compared to 5,000 to 6,000 sfpm for crankshaft grinding.


The ability of a fluid to provide lubrication is especially important when honing with superabrasives such as polycrystaline diamond (PCD) and cubic boron nitride (CBN). Superabrasives are much harder and longer lived than traditional vitrified abrasives such as aluminum oxide and silicon carbide, but the superabrasive particles are duller and have more rounded edges. This requires a stronger metal bond to hold and support the superabrasive particles, as well as more force to hone a cylinder bore. Because of this, superabrasives typically generate more heat than vitrified abrasives. So to limit bore distortion, a superabrasive honing fluid must also provide cooling as well as lubrication.


A third function that a coolant provides is to rinse away metal and abrasive particles from the work surface. Removing debris keeps the pores in grinding wheels and honing stones open so the abrasive doesn

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