Grinding Operations: Real Wheel Productivity and Cost

Job shops as well as production-manufacturing operations will find that the abrasive products outfitted to their hand-held power tools can play a crucial role in increasing productivity. Often viewed as a negligible expense, abrasives comprise on average less than 2 percent of the total cost of a fabricating operation. However, most shops fail to realize that 10 to 15 percent of their labor is consumed in metal-fabrication and finishing operations. So, rather than simply considering the direct cost on the distributor’s product invoice, a more accurate measure of productivity would be to look at the true total process cost, or the total work to be performed with abrasives.

The abrasive grain is a cutting tool, and the type and quality of the grain can determine the true value of the performance of an abrasive tool. Performance grains deliver benefits such as higher stock-removal rates, increased product life, reduced metallurgical damage and less wear and tear on grinding machines. And, these grains are ergonomically friendly. All of these factors work to minimize the total cost of the grinding process. The most-competitive production operations evaluate these factors when making their purchasing decisions.

Breaking Down the Grains

Abrasive grains can be made by several manufacturing methods. Some are made in large ingots in furnaces, crushed and then sorted by grit size and shape to be used in abrasive tools such as grinding or cutting wheels and sanding products. Other grains are manufactured using molding technology, which produces precision-shaped grains that offer a more uniform structure and size.

Precision-shaped grains can be made into different shapes and sizes depending on the market needs. They generally cut quickly and perform well in precision metal-removal applications requiring tight tolerances and fine scratch patterns. However, it is important to consider the application at hand, as some characteristics of precision-shaped grains—such as bond quality, grain orientation, grain hardness and friability—can make them less effective for rough grinding jobs.

Wheel manufacturers often expend considerable effort to develop a proprietary mixture of grains that will provide optimal performance. For example, in certain grinding- and cutting-wheel lines, Norton offers a proprietary blend of ceramic-alumina and zirconia-alumina grains. These proprietary grains microfracture as they break down, continuously exposing new cutting surfaces—essentially self-sharpening. Compared to the grains on more traditional grinding wheels, these fresh cutting points provide a faster cut rate, higher rate of metal removal and longer wheel life, as the grains can be completely utilized through the microfracturing process. So, rather than prematurely expelling rounded or worn aluminum-oxide grains at only a fraction of their life, microstructure grains such as ceramic alumina and zirconia alumina work together to cut cooler, allowing the wheel to hold onto the grain longer to extend wheel life.