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True Grit: Understanding the construction and application of non-woven abrasives helps distributors and end users find a truly consistent finish

Source: Industrial Distribution, November 2003

By Mike Miller, Sales Manager, Superior Abrasives, Inc.

Non-woven abrasives are a fast growing, innovative segment of an otherwise mature abrasives industry. New products and new manufacturers enter the field almost monthly, offering a plethora of choices for distributors and end users.

A non-woven abrasive is a material with a needled or extruded substrate impregnated with resins and abrasive grain. Coated abrasives, on the other hand, have a cloth or paper backing with resins and abrasive grain applied to one surface.

Non-woven abrasives are either scrim backed (surface conditioning) or non-scrim backed (finishing or open web). Scrim backed or surface conditioning materials are manufactured by needling synthetic fibers into a woven base of monofilament threads known as the scrim. This forms a fuzzy textured substrate on one side onto which a slurry of resins and abrasive grain are deposited. The three-dimensional texture of the substrate dictates the three-dimensional nature of the abrasive surface. Surface conditioning material is similar to coated abrasives in that the abrasive grain is only on one side of the material. The material must therefore be used flat, grain side down, as in various types and sizes of discs or in belts. The uncoated side is fuzzy and acts as the "hook" in a "hook and loop" fastening system that will attach to a large double hook-type backing pad.

Surface conditioning discs are available from ¾- to 4 in. in diameter with quick-change-style fastening systems for use with small-angle head die grinders. They are used on nearly all metals for gasket, paint, rust, scale, and oxidation removal, weld blending, and for satin and decorative finishes.

Low-stretch, scrim-backed material is made with high strength, low-stretch polymers, such as polyesters, in the scrim to make the material strong and stable enough to make excellent belts. Surface conditioning belts are widely used in all types of belt machines including hand held file belts, backstand, bench stand, stroke sanders and wide belt machines. The three-dimensional nature of the abrasive surface allows this material to follow gentle contours and surface variations easily. The cushion of the non-woven substrate produces a more forgiving, consistent finish. Surface conditioning belts are ideal for light deburring, paint, coating, and rust removal, removal of small surface blemishes, weld blending, gasket removal, decorative finishing, and other jobs requiring light stock removal.

Surface conditioning materials are available with aluminum oxide grain in coarse (60-80) grit through very fine (180-240) grit and with silicon carbide grain in ultra fine (320-400) grit. Normally surface conditioning material is color coded by grit with brown or tan for coarse, maroon for medium, blue for very fine, and grey for ultra fine. Some surface conditioning materials have ceramic grain mixed in to extend the life and increase the aggressiveness of the product.

Understanding non-scrim

Non-scrim open web/surface finishing material is distinguished by the absence of the woven base or scrim for lateral strength. It is more homo-genous than scrim-backed material with resin and abrasive grain distributed evenly throughout. This material relies on resins and its non-woven nylon substrate to give it the necessary structural integrity. Surface finishing material consists of nylon or polyester fibers needled together to form an open spongy mesh, which is dipped into a mixture of resins and abrasive grain. After the resins are cured, the result is a lightweight and flexible abrasive material that is relatively less aggressive, less tear resistant, more non-loading, and more forgiving than scrim-backed material, while being very flexible and surprisingly long wearing.

Since the abrasive grain adheres to the fibers throughout the thickness of the material, these products may be used either flat or on edge. Finishing material is converted into many useful shapes and forms, including discs, hand pads, rolls, flap wheels, mounted disc wheels, and interleaved with coated abrasives on flap wheels.

Finishing materials

Finishing material is available in several strengths/densities. Heavy-duty material has the lowest tensile strength: it is possible to tear it by hand. Heavy-duty material is used in hand finishing applications and for discs and wheels where maximum conformance with lower aggressiveness is needed. It is widely used in mold polishing and cleaning, decorative finishing, light deburring, industrial cleaning and light rust and oxidation removal.

High-strength material is the next strongest finishing material available. It usually cannot be torn by hand and is slightly more aggressive and stiff than heavy-duty material. High-strength material will withstand more abrasion and sharper edges than heavy-duty material. It is extremely useful when cleaning weld spatter, light deburring and edge finishing where heavy-duty material would be rapidly degraded.

A third density of finishing material, heavy cut, is just becoming available. This material is coated with extra abrasive grain and resins to produce a very dense, more rigid, and more aggressive material. The cutting action is between high-strength material and surface conditioning material. It is very useful in deburing, weld blending, and finishing applications on most metals.

Extra coarse stripping material is another form of non-woven abrasive. This material consists of an extremely open non-woven substrate impregnated with extra coarse silicon carbide grain and very tough resins that impart extra rigidity to the material. The silicon carbide grain is very hard and sharp, yet breaks down quickly, constantly exposing new grain. This material is ideal for removing paint, rust, coatings, and other oxidation from various metals. It is homogeneous throughout its thickness, is usually black in color and can be used flat or on edge. It is an excellent substitute for wire wheels.

For more information on the application of non-woven abrasives, contact Superior Abrasives at (800) 235-9123 or visit www.superiorabrasives.com.

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