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Reshaping metal grinding

New engineered abrasives and bond resin for grinding discs encourage fabricators to rethink finishing activities

Figure 1
Operating a hand-held grinder can be an exhausting chore for a fabricator, especially if swarf buildup is occurring on the abrasive disc.

Metal fabricators don’t give much thought to the abrasives they use as part of their metal finishing operations, but maybe they should take a closer look.

In a recently released white paper, Saint-Gobain Abrasives suggested the average cost of abrasives for large metal fabricators was less than 2 percent of overall manufacturing expenditures. Meanwhile, for those same metal fabricators, grinding and finishing activities accounted for 10 to 15 percent of manufacturing labor costs. Fabricating companies have a real opportunity to reduce labor costs associated with grinding and finishing; they just need to consider the latest abrasive grain developments, according to Saint-Gobain Abrasives.

More specifically, the company is talking about its new Norton Quantum 3 abrasive. The abrasive discs have a proprietary grain shape that is designed to boost cutting performance and a resin bond structure that breaks down in a controlled manner, contributing to a long life. The work on the grain and resin combination also led to another benefit, according to Debbie Gaspich, director of product management, thin wheels and construction products—North America, Saint-Gobain Abrasives.

“In this particular product, what we were able to really attain is another axis of performance, which is a good comfort and feel during grinding performance,” she said. Because of the abrasive grains’ consistent shape, they don’t jump or vibrate as much as other abrasive grains, according to Gaspich.

To fully understand how this new grain and resin bond combination works, it might be helpful to review abrasive grain development over the years. Prior to mid to late 1970s, aluminum-oxide discs were the abrasive of choice for metal fabricators. The aluminum oxide’s blocky-shaped grain is strong, but tends to dull rapidly. Later in that same decade, zirconia-alumina grains emerged. They are harder and sharper than aluminum-oxide grains, and when used, they fracture in a much more controlled manner, maintaining a sharp cutting edge. They are believed to last three times longer than similar aluminum-oxide discs.

In the 1990s the doped alumina sol-gel process was used to create ceramic-alumina abrasives. These discs soon emerged as the preferred choice for fabricators looking for high-performance abrasives that demonstrated long-life characteristics. Key to this development was an abrasive grain that demonstrated controlled fracturing on the microscopic level. When this microfracturing occurs, a sharp cutting edge remains for nearly the lifetime of the disc.

The Quantum 3 product is part of this ceramic-alumina heritage. It is part of the latest wave of abrasives that were engineered to deliver specifically shaped grains.

Its grain has a rounder shape than other abrasives, some of which have a pyramid structure, Gaspich said. The roundish shape of the grains makes them more receptive to receiving the resin bond.

“Bonds actually control the grinding process,” Gaspich said. “What you need to do is ensure that you have an even coat around the abrasive grain. The more even the coat, the more even the spacing of the grains in the grinding wheel. Then you have a more even breakdown mode during grinding.”

Gaspich said abrasive discs that have non-round-shaped grains don’t have smooth resin coverage.

Figure 2
Norton’s Quantum 3 ceramic-alumina abrasive discs are designed to offer fabricators more aggressive cutting action and longer lifespans than traditional aluminum-oxide discs.

“You can imagine that if you were to get a large clump of something in one area, like a lot of bond or a lot of grain, the hand tool is going to vibrate more and throw off your ability to have a nice, smooth grind,” she added. “The more that you can get a homogenous mix of bond coating the abrasive grain, the better the performance.”

These “nonoptimal bond technologies,” as Gaspich described them, can result in the abrasive disc retaining the grain too long or not long enough. In the first scenario, the fractured grains are retained in the wheel, and swarf buildup occurs, resulting in slower cutting and the operator of the hand-held grinder having to exert more effort to force the cut (see Figure 1). In the second scenario, the fractured grain is released too quickly, which translates into a fast cut, but a short life for the abrasive wheel.

Gaspich said that the new ceramic-alumina abrasive technology (see Figure 2) has the right “homogenous” distribution of grain within the wheel and better adhesion of the grain to the bonding materials. The result, she said, is a smooth-handling disc that delivers the cutting performance expected of top-tier abrasives and a long operating life.

The abrasive disc makeup also has less than 0.1 percent iron, sulfur, or chlorine content, making it suitable to use with stainless steel and exotic metals. It won’t introduce contaminants that could lead to rust.

Gaspich said early feedback from fabricators has been positive.

“We have been getting a lot of feedback that says this wheel doesn’t grab, and it’s smooth right to the hub—the inside of the wheel,” she said. Typically as an abrasive wheel gets smaller, the disc loses some cutting power, and it tends to be harder to control.

With some metal fabricators dealing with labor rates up to $24 per hour, they might be forced to look more critically at a shop floor task that has been ignored far too long. Longer-lasting and higher-performing abrasive discs hold the promise of reducing downtime associated with changing out discs and reducing operator fatigue.

A few minutes of uptime doesn’t seem like much, but when those minutes are added up over a shift and a year, they result in a big number. It should be big enough to catch the attention of fabrication shop managers.

Saint-Gobain Abrasives, 254-918-2313, www.nortonindustrial.com

About the Author
The Fabricator

Dan Davis

Editor-in-Chief

2135 Point Blvd.

Elgin, IL 60123

815-227-8281

Dan Davis is editor-in-chief of The Fabricator, the industry's most widely circulated metal fabricating magazine, and its sister publications, The Tube & Pipe Journal and The Welder. He has been with the publications since April 2002.