THE AMERICAN WELDER Fig. 4 — Consider the upfront wheel costs and those related to downtime and changeover when selecting the best cutting wheel for the job. Keep in mind that product cost also typically increases along with durability and cut rate. 1) Aluminum Oxide Aluminum oxide wheels utilize softer bonds that are less resistant to heat, resulting in a cut that is fast, smooth, and easy-to-control. However, they are by far the least durable of the three grains. Aluminum oxide wheels are the most economical and have a high initial cut rate, but the tradeoff is shorter product life. As a result, aluminum oxide wheels are ideal for cutting milder alloys, such as carbon steels. White aluminum oxide wheels provide increased durability and cut rate, while maintaining a lower cost of use. 2) Zirconia Alumina Zirconia alumina is a harder, tougher grain that is more resistant to heat than aluminum oxide. Zirconia alumina grains also maintain sharpness longer than an aluminum oxide grain. As a result, zirconia alumina wheels cut faster throughout the cutting process. Their increased toughness makes them more resistant to heat and allows for harder bonds, resulting in longer wheel life. Zirconia alumina cutting wheels provide an excellent overall value as they do not need to be replaced as often, reducing product changeover while also minimizing costly operator downtime. 3) Ceramic Alumina Ceramic alumina grains are designed to self-sharpen and are also more durable, making them the most expensive choice. Ceramic grains are manufactured with thousands of fracture points designed to fracture and chip during use so they self-sharpen — rather than dull — throughout the cutting process. As a result, ceramic alumina wheels maintain their sharpness and cut rate for roughly 75% of their lifespan before an operator feels a decrease in cutting performance. Calculating Costs When selecting the best cutting wheel for the job, it’s important to consider not only the upfront wheel cost, but also the costs associated with downtime and changeover — Fig. 4. In many applications, selecting a zirconia alumina or ceramic alumina cutting wheel provides a lower overall cost of use because operators can perform significantly more work with the same wheel and spend much less time changing wheels to finish a job. When given the opportunity to do a time study, it is often a surprise to the line leader or foreman to see how much time their operators spend changing wheels and walking to the tool crib for replacements. One such study found that a single cutting wheel changeover took more than 30 min, given that each operator had to walk to the tool crib, sign out another wheel, wait for the wheel, return to their cell, and then change the wheel before continuing the job. This loss of productivity can be staggering to any business. In cases like this, there is a significant benefit to selecting a higher quality, more durable product. The individual wheel cost more than pays for itself through minimized downtime and reduced overall consumable use. 88 WELDING JOURNAL / DECEMBER 2016
Welding Journal | December 2016
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