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Finishing via Non-Woven Abrasives

Saturday, April 01, 2017
 

A part isn’t finished until it’s finished. Post-process deburring, cleaning and other finishing tasks deliver a final part with ideal surface quality. Abrasive products, such as bonded and coated abrasives, often get the call to remove part stock during production. But for final surface finishing, non-woven abrasives are ideal.

Non-woven abrasives, using abrasive-grain-embedded nylon fibers bonded together, offer durability and the ability to conform to a workpiece. This helps make the finishing process easier and less time-consuming. With these products, the nylon web features uniformly dispersed abrasive grain, so as wearing occurs, the grain is constantly replenished. Another plus: Non-woven abrasives are waterproof and can be washed. They will not rust, and with open-mesh construction, they will bounce back to shape easily and repeatedly, bringing long life.

These types of abrasives have fulfilled an important role in grinding applications, bringing capabilities unmatched by other grinding products, chiefly due to the relatively gentle nature of the nylon fibers and their abrasive grains. Non-woven abrasives work on a range of metals, including aluminum, brass, copper, nickel, chrome plate, stainless steel and titanium, and nonmetals.

Types of Non-Woven Products

These products can come in many forms. Non-woven grinding wheels can be classified as follows:

  • Flap wheels consist of sheets of non-woven material mounted around a center hub, ideal when conformability to a surface or a long-line brushed finish is required.
  • Convolute wheels are made by wrapping non-woven material around a center core and bonding together the layers. These wheels can easily be shaped to match preformed parts.
  • Unified wheels are formed by compressing multiple layers of non-woven web material and bonding them together to form a wheel. They find use for general-purpose cleaning and deburring.

Non-woven abrasives, using abrasive-grain-embedded nylon fibers bonded together, offer durability and the capability to conform to a workpiece. With these products, the nylon web features uniformly dispersed abrasive grain, so as wearing occurs, the grain is constantly replenished. Another plus: Non-woven abrasives are waterproof, and can bounce back to shape easily and repeatedly.
Non-woven abrasives exist in other forms besides wheels. Fabricators use arbor-hole non-woven discs with high-speed grinders, with extra-coarse grit often used to remove surface rust and residue, corrosion, light weld splatter and other surface contaminants. Spacers allow multiple discs to form a wide grinding wheel to provide sharp edge radiusing or deburring of decorative-finished parts. Portable grinders employ right-angle non-woven discs for various applications including cleaning, deburring, blending and finishing, as well as for removal of oxidation and coatings.

Non-woven hand pads often are specified in wet applications as a replacement for steel wool due to rust issues. Also, non-wovens come in rolls of various widths, then cut for hand sanding or other sanding applications. Non-woven belts, alternatives to coated abrasive belts, can be used for cleaning, buffing and polishing. The belts conform readily to workpieces, thus minimizing gouging and producing a more consistent finish.

Meaning Behind the Specs.

Grit refers to the size of abrasive grains in the nylon web. Non-woven abrasives feature various grit sizes, from coarse—50 to 80 grit, often used for general cleaning—to micro-fine—1000 to 1200 grit, suitable for light scuffing and blending. Lower numbers mean larger grains. Grit material may be silicon carbide or aluminum oxide. A sharper grit, aluminum oxide cuts quickly and imparts finer scratch patterns on the majority of surfaces. On the other hand, aluminum oxide is more durable and finishes more aggressively on hardened steels while producing less discoloration on aluminum.

Density concerns the amount of bonding agents and abrasive grain compressed into the product. While softer densities offer improved conformability to work surfaces and less tendency to burn a workpiece, harder densities in general cut faster, last longer and provide finer finishes.

Non-woven convolute wheels, made by wrapping non-woven material around a center core and bonding together the layers, can easily be shaped to match preformed parts.
Manufacturers of non-wovens create fiber sizes and bonding agents based on the intended application, with both affecting the operational characteristics of a product. The industry continues efforts to evolve non-woven technology, especially related to bonding agents. As grinding and finishing operations generate significant heat, some resins can break down, causing marks or stains on parts. While okay for grinding operations such as deburring, finishing requirements demand improved surface quality, which then adds time and cost to the finishing process. Improvements in bonding agents include new resin systems that can deliver stain-free finishing with equal or improved product life. That means lower costs and less downtime due to rework or added finishing steps. Improved bonding systems are important in certain aerospace and automotive markets where heavy-element trace contaminants can be an issue.

Much of the information above is contained in typical specification listings for non-woven abrasive products. For example, you may see the following specification:

8 A/O MED, where

8 = density, which can range from 2 (open/most conformable) to 9 (densest/most durable)

A/O = the abrasive used (A or A/O refers to aluminum oxide)

MED = grit size (medium, 100 to 150 grit)

What’s Best for My Application?

The right non-woven abrasive product depends on the particular application, with all of the above and more taken into account. But even with selection of the right products for a particular job, day-to-day operations may lead to confusion, as non-woven abrasive products have tended toward a similar look regardless of grit size and material. That is being addressed. For example, a recent innovation has brought color coding to non-woven convolute wheels, differentiating application groupings as well as grit material. The result is simplified selection and day-to-day use. MF

Information for this article supplied by Norton | St. Gobain Abrasives, Worcester, MA; tel. 254/918-2313, www.nortonabrasives.com.

 

See also: Norton Abrasives

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