GUIDES

How to Buy the Right Metalworking Abrasive

An abrasive in metalworking is any material used to shape, grind, or cut metal. Minerals, or mineral-like substances, are used to create abrasives. For the process to be successful, an abrasive must be a harder substance than the material upon which it is being applied. Materials that are used as abrasives are either hard minerals or synthetic compositions, made to be identical to minerals, yet are not naturally occurring.

Metalworking is quite simply the process of working with various types of metals to create specific parts for assembly of various pieces, or for large-scale structures. The evolution of the process of metalworking has evolved from producing tools from smelting to modern metalworking processes such as forming, cutting, or joining.

Why Abrasives Are Significant to Metalworking

Abrasive materials (most often minerals) are used extensively in metalworking in a variety of domestic and industrial applications to alter the metal either by cutting, shaping, or finishing. Abrasives are also used in more finite manners such as tool repair and pipe threading. The shape, size, and nature of the metal and the finish desired will influence the type of abrasive to be used. An abrasive that is too coarse or too hard could leave scratches or cause other lasting damages to the metal.

The following table details some basic abrasive materials and the jobs for which they are best suited.

Abrasive

Description

Uses

Aluminum Oxide

Synthetic material derived from bauxite; most commonly used abrasive because of toughness and versatility.

Smoothing metal and metal welds, removing rust.

Ceramic

Industrial aluminum oxide; very rugged abrasive.

Heavy metal removal.

Emery

Natural mineral that combines aluminum oxide and iron oxide; a cloth-backed abrasive with a medium to coarse grit.

Metal polishing.

Garnet

Natural inexpensive abrasive used on lightweight papers in medium and fine grit.

Light-duty metal smoothing; small hand-sanding jobs.

Silicon Carbide

Combination of synthetic and natural materials. Used on waterproof paper so water can be used as a cutting lubricant. A fine to ultrafine abrasive.

Smoothing nonferrous metals, which are metals that don't contain large amounts of iron, including aluminium, copper, titanium, zinc, gold, silver, and platinum, and many others.

Zirconia Alumina

Synthetic, industrial grade abrasive comprised of zirconium oxide and aluminum oxide.

Medium metal removal and weld smoothing.

Sanding

Abrasive discs are miniscule abrasive grains adhered to the back of cloth, fiber, film, paper, or non-woven material. The discs are mounted onto machines such as sanders and grinders, which are used in the sanding, grinding, or polishing of any number of metal surfaces. Abrasive discs are most commonly used for sanding, removing surface materials, and fixing other imperfections. Abrasive sanding discs are composed of aluminum oxide, silicon carbide, or a range of superabrasives of extreme hardness such as diamond and CBN (cubic boron nitride).

Grinding

Grinding is an abrasive process that uses a grinding wheel to cut metal. Machines used for grinding include hand-cranked grindstones, such as those used to sharpen knives; handheld power tools, such as angle grinders and die grinders; industrial grinders; and bench grinders.

Each grain of the abrasive material acts as a single cutting edge. Grinding is one of the most common forms of abrasive machining.

Grinding Wheel

Used in grinding machines for abrasive machining operations and in abrasive cutting, grinding wheels are typically made from various coarse particles bonded together. The five characteristics that are significant in the composition of a cutting wheel are: material, grain size, wheel grade, grain spacing, and bond type. There is no standard among manufacturers of grinding wheels, however there are certain pieces of information that have to be included in the label. For example, a label might contain the following specification: A60-I10-VS.

Material

The first letter listed in the specification refers to the material of the actual abrasive. This abrasive material changes depending on what is being cut. This category is also referred to as grit type. In the example above, the grinding wheel is composed of Aluminum Oxide. Other examples of abrasive materials are listed below.

  • A - Aluminum Oxide
  • C - Silicon Carbide
  • D, MD, SD - Diamond
  • B - Cubic Boron Nitride

Grain Size

The sizes of the grains range from coarsest (8) to finest (600). Larger or coarser grains will allow for better, faster cutting, and the finer grains are for finishing work or work that requires precision. In the example above, the grain size is 60.

Wheel Grade

The grade from soft (A) to hard (Z) determines how tightly the abrasives are bonded to the wheel. Wheel speed, flow of the coolant, grinding depth, and feed rates are affected by the grade of the wheel. In the example above, the wheel grade is I. A soft grade is preferred for harder materials and a harder grade is preferred for softer materials.

Grain Spacing

The spacing of the grain refers to the structure the most dense (1) to the least dense (16). Density of a grinding wheel refers to the ratio of the bond of the abrasive and air space. A wheel that is less dense will cut freely and take deeper cuts with less coolant required. In the example provided, the grain spacing is 10.

Wheel Bond

The bond measures how the wheel holds the abrasives and affects the finish, coolant, and wheel speed. The following are the various types of wheel bonds:

  • Vitrified (V)
  • Resinoid (B)
  • Silicate (S)
  • Rubber (R)
  • Metal (M)
  • Oxychloride (O)

Wheel Types

A variety of grinding wheels serve different purposes. The following table includes details about each type of wheel:

Wheel Type

Description

Straight Wheel

Most common type of wheel that is found on bench or pedestal grinders. Used for cylindrical, centerless, and surface grinding.

Cylinder or Wheel Ring

Provide a long, wide surface and do not have center mounting support. Used only in vertical or horizontal spindle grinders and are used for producing flat surfaces.

Tapered Wheel

A straight wheel tapers outward toward the wheel's center. The tapered wheel is stronger than a straight wheel, and is typically used for grinding thread and gear teeth.

Straight Cup

For use in tool and cutter grinders, providing an additional radial grinding surface

Dish Cup

A shallow "cup-style" grinding wheel. The thinness of the shape allows for grinding in slots and crevices. Used primarily in cutter grinding and jig grinding.

Saucer Wheel

Special wheel used to maintain saw blades or other milling cutters.

Cutoff Wheel, or Parting Wheel

Shelf-sharpening wheel that is thin and has radial fibres. Typically used in the construction industry.

Steel Abrasives

Steel abrasives are particles of steel used as an abrasive or for peening metal (working a metal surface to improve material properties). These abrasives are available in both shot and grit, which apply to various industrial uses. Steel shot refers to the spherical grains of molten steel in different sizes and hardness. Steel grit refers to steel grains with very sharp edges.

Industrial applications of steel abrasives in metalworking include cleaning, surface preparation, and shot peening. Both shot and git are used in cleaning, or the removal of loose materials from metal surfaces. Surface preparation also incorporates shot or grit to clean or creating a rougher exterior. Shot peening is the repeated impact of shot on the metal surface to improve durability. Steel abrasives are most commonly used in the automotive industry, construction and metallurgy.

Other Abrasive Machining Processes

Abrasive machining applies various abrasive particles to a metal working surface so that each particle is cutting away a small bit of material for a different purpose. Aside from grinding and sanding, there are other abrasive machining processes, which are presented in more detail below.

Honing

The honing of metal involves scrubbing an abrasive stone along a controlled path. Honing is typically used to improve the form of a metal surface or the surface texture. Industrial uses include finishing of cylinders for internal combustion engines, air-bearing spindles, and gears. In everyday uses, honing steel is used to hone knives, which is a fine sharpening process, as opposed to abrasive-stone knife sharpening.

Buffing or Brushing

Buffing, or brushing, is a finishing process for smoothing a metal surface with a loose abrasive applied to the working wheel. Mirrored bright finishes are the result of buffing.

Abrasive Sawing

Abrasive sawing is using abrasion to cut an item. Diamond materials are often used as the abrasive. In metalworking, abrasive saws are are used in machine shops to cut metal parts.

Polishing

This is process of creating a smooth, and often shiny, surface by continuously rubbing the metal surface with a very fine abrasive. Polishing with a fine abrasive removes material on a molecular level. The process produces a flat surface free of defects of the metal's microstructure. Silicon-based pads or even a diamond solution can be used for polishing.

Lapping

Lapping is an abrasive machining process by which two surfaces are rubbed together with an abrasive between them. The more brittle materials (such as glass) are rubbed against a surface such as iron. The abrasives in between these surfaces remove materials from both the glass and the iron (this lapping process is very similar to grinding).

How to Buy Metalworking Abrasives

Working with metal abrasives is far more difficult than finding a vast selection for purchase. An online community such as eBay offers a variety of metalworking supplies and equipment for both personal and industrial use. To get started, visit the Business & Industrial section of eBay. From there, select Manufacturing & Metalworking, which will lead you to Metalworking Tooling . Abrasives can be found under Cutting Tools & Consumables.

If you are unable to find the exact abrasive to fit your needs by perusing categorized listings, you may want to try a specific search. Entering keywords such as "aluminum oxide grinding wheel" will lead you to the specific abrasives that fit the criteria. Should you still have trouble finding a specific abrasive, you can save your search and select the option of being emailed once your product becomes available.

When you have located a listing for your abrasive, be sure to review all of the details provided by the seller. The listing should include the manufacturer, the sizes, and specifications of the abrasives. Remember to figure delivery costs into your budget. Check on the seller's return policy before agreeing to purchase. Should the abrasive not meet specifications once it arrives, it's best to have the option to return it to the seller. Should you have any questions about the abrasives, you can always contact the seller by clicking the "Ask a Question" link on the listing to make sure you are getting the product that you need.

Remember when making a purchase to select a top-rated seller and make sure all questions have been addressed before agreeing to purchase the item. Purchases made within eBay, with an approved eBay payment method such as PayPal, are easier to track, and are covered by the eBay Buyer Protection program, which enables consumers to recover lost funds should there be a problem with the transaction.

Conclusion

Metalworking abrasives are segmented by type, purpose, abrasive material, and how the abrasive mineral is bonded to its backing. Whether cutting or polishing, metalworkers can speed up the process by shopping in a place where the vast number of abrasives, from coarse to fine, are available with the click of a button. An online auction and shopping company such as eBay enables the buyer to easily peruse a variety of options that fit myriad needs and budget restrictions before deciding on a purchase.