Progressive Distributor - Know the code when selling bonded abrasive wheels

Know the code when selling bonded abrasive wheels

by Bill Hawkins

When probing for information on the plant floor or elsewhere, an abrasives sales veteran often asks this question: “What’s your biggest problem?”

Solve that problem and win the sale. Seems simple enough. Except that the wide range of materials to be cut or abraded barely exceeds the assortment of abrasive wheels on the market. Even by asking the right questions and listening carefully to the answers, salespeople may have problems matching a customer with the appropriate wheel, unless they have the product knowledge to hone in on the right type of wheel for the job. Recommend a wheel on the fly and you risk wearing down your customer base with a mismatched selection.

Fortunately, the abrasives industry wisely established a standard color-coding and identification system to better guide users (and sellers). General-purpose metal grinding or cutting wheels bear a red banner on the label, and concrete/masonry, green. The aluminum color is an appropriate gray; stainless steel, blue; ductile iron, orange; pipeliner, yellow; and asphalt, black.

But, this is only the beginning. The American National Standards Institute (ANSI) system also covers the primary grains used to make the wheel, the size of the abrasive grain, the hardness of the bond and the type of bond used. Knowing how these factors affect abrasive performance can help distributor salespeople narrow the options before recommending a wheel.

When matching a wheel to the job, some information on how a wheel is made and works might help with the decision. Grains and liquid resins are mixed thoroughly, and then layered together with fiberglass before molding and heating. As the wheel spins in use and contacts material (such as angle iron), exposed grains begin to cut away the metal. The grains themselves fracture continuously to expose new cutting points, while the iron wears away the resin bond to successively uncover fresh grain. This continues until no more grains remain, or the job is finished.

Grain size governs the scratch pattern and, ultimately, how much and how quickly material is removed from a work surface. Grain sizes are expressed by a grit number, with smaller values indicating larger grit. For most purposes, common classifications are coarse (16, 20, 24), medium (30, 36,46, 60), fine (100, 120, 180) and very fine (220, 240, 280).

Sharpness, friability (fracture characteristic) and hardness vary considerably by grain types. There is no single ideal, only appropriate compromise. Particles with exceptional hardness may last longer, but the inherent rigidity makes fine finish work more difficult. Soft grains cut more freely, with even finish, but erode quickly. As a rule of thumb, soft grains cut more quickly than hard grains. One reason: Softer grains fracture more readily, each time exposing fresh cutting surfaces.

Aluminum oxide, silicon carbide and aluminum zirconia are commonly used abrasive grains. These differ in terms of grain size, sharpness, friability and hardness. Virgin (non-recycled) grains are more reliable but more expensive than filler grains.

Aluminum Oxide (A)
Aluminum oxide, the most popular of abrasive grains, excels in grinding high-tensile materials, such as ferrous metals and carbon steel, alloy steels and cold-rolled steel. This brown-tone workhorse is remarkable for high-speed penetration of tough materials without excessive fracturing and shedding.

Silicon Carbide (C)
Commonly black, sometimes green, silicon carbide is hard and sharp, superior to other grains in its ability to penetrate and cut faster under light pressure. However, it does not last as long as aluminum oxide. Silicon carbide is ideal for working on non-ferrous metals such as aluminum, brass, bronze, magnesium and titanium, and also for non-metallic materials such as rubber, glass, plastics, fibrous wood and other soft materials. Concrete and masonry grinding and cutting are also common applications for silicon carbide wheels.

Aluminum Zirconia (Z)
A molten mix of zirconium and aluminum oxides, aluminum zirconia has a microcrystalline structure. The result: longer life than the latter, with improved friability. Sharp, hard and extremely tough, aluminum zirconia produces superior performance on a wide variety of materials of both high- and low-tensile strength under high grinding pressures. Materials include carbon steel; stainless steel; tough bronzes; a wide variety of stainless steel and exotic alloys; gray, malleable, ductile and nodular cast iron; aluminum; titanium and others.

Abrasive wheels vary in hardness, depending on the bond used. Hard wheels last longer, but at the expense of fast or clean cutting. Conversely, soft wheels are shorter lived, but cut fast and smooth. In general, use soft wheels for hard material and vice versa. The ratings range from A (softest) to Z (hardest).

Wheels are often reinforced by fiberglass for extra strength at high revolutions (RPM) and for rigidity in withstanding lateral pressure. Under the standard marking system, each wheel carries a warning with maximum allowable RPM — in general, the smaller diameter, the higher tolerance.

Fiber resin wheels are relatively inexpensive to produce, reflected in a consumer price that averages around $1.25 each with backing pad. In contrast, another disc type — the flap disc — typically carries a retail price of around $9 each. Yet, during the past three years, flap discs have grabbed market share at an accelerating rate.

The reason is life-cycle cost. Not only can a single flap disc outlast 15 fiber resin discs, but grind and finish as much as three times faster. Added to these productivity gains is the time savings gained from fewer disc changeovers.

A flap disc is constructed from overlapping segments of cloth-backed sandpaper mounted on a fiberglass backing. Zirconia grit is common for work on materials such as steel, sheet metal, aluminum and cast iron. Typical applications range from slag removal to such metal finishing tasks as deburring, edge blending and chamfering.

Fiber resin wheels have been around for generations. Flap discs, in contrast, were introduced from Europe about five years ago. Add to the novelty the price differential and many purchasing agents have been reluctant to allow users an opportunity to experiment with these newer discs.

Despite all the information available from disc manufacturers, customers too often mismatch grits or grains to the job — or, now, overlook the value of newer products. When it comes to selling abrasives, everyone would agree there’s no substitute to learning the customer’s grinding, cutting or finishing process firsthand before recommending a product. Visiting the factory floor, seeing the process, talking with the customer and asking the right questions will indicate what the customer is trying to accomplish. However, simply knowing what a customer wants to achieve is only half the equation. Helping customers choose the appropriate product to fulfill that need is the answer and the formula for a long-term sales relationship. Be prepared by knowing how the abrasive material and structure are designed to perform for a given application.

Bill Hawkins is accessories product manager for DeWalt, which manufactures and markets industrial power tools and accessories. For more information on the full line of DeWalt products, contact DeWalt Industrial Tool Co. at 701 E. Joppa Road, Baltimore, MD 21286; phone (800) 4-DEWALT or visit www.DEWALT.com for a virtual tool tour.