Image Credit: Norton Abrasives

What are Abrasive Files?

Abrasive files are small sticks or stones made of bonded abrasives or superabrasive coatings for deburring, finishing, lapping, and polishing in hard to reach places and recesses. They are used to remove surface materials such as metal, ceramics, glass, plastics, and paint .

When selecting an abrasive file, it is important to consider its grain or stone type, physical design, coarseness, cross section shape, and bond type. This selection guide is designed to help buyers with this process.

Grain or Stone Type

The grain or stone type of an abrasive file has a large impact on its performance characteristics. Common abrasive materials include aluminum oxide, Arkansas stone, silicon carbide, and India stone.

  • Aluminum oxide is the most common industrial mineral in use today. It is an angular, durable blasting abrasive that can be recycled many times. It offers longevity and hardness at a low cost. It is also very light, providing many more particles per pound than metallic media.Fused aluminum oxide is produced synthetically by melting bauxite and additive in an arc furnaceto form a fused aluminum oxide ingots, whichare later crushed and sized. The various types of fused aluminum oxides are distinguished by the levels of chemical impurities remaining in the fused mineral. Variations include white (high purity), brown or regular (titanium oxide modified),and pink (chromium oxide additions). Titanium oxide additions can toughen the abrasive and enable heat treating processes, which change brown aluminum oxide to a blue colored grain as TiO2 precipitates form. Aluminum oxide can produce a wide variety of ceramic and stone abrasives using various modifiers and processes.
  • Arkansas stone, known as novaculite, isa natural stone product that is quarried from mines in the state of Arkansas. It is used in sharpening and polishing applications. Genuine natural hard Arkansas oilstone is accepted as the finest abrasive stone in existence for quality metal sharpening.
  • Cubic boron nitride (CBN) is a superabrasive grain with hardness second to diamond and a cubic crystal structure.CBN provides superior grinding performance on carbon and alloy steel.CBN is produced synthetically in a high-temperature, high-pressure process incorporating an anvil press. This process is similar to synthetic diamond production.
  • Diamond is a synthetic superabrasive produced synthetically in a high-temperature, high-pressure process anvil press.Diamond is s superabrasive grain with the highestknown hardness and a cubic crystal structure.Diamond is usedfor grinding nonferrous metals, ceramics, glass, stone,and building materials.Diamond is not useful in grinding steel or ferrous alloys, however,because carbonand diamond readily dissolve or react with iron.Diamond pastes areuseful inferrous polishing or lapping applications where heat and reactivity are not a factor.Like silicon carbide (SiC),diamond is susceptible to oxidation at higher temperatures.
  • India stone isa tough, hardaluminum-oxide or ceramic stone product.
  • Silicon carbide (SiC)is a synthetic abrasive that was first developed in the late 1800s.It isharder than aluminum oxide, but more friable than grains of fused aluminum oxide. Typically, silicon carbide is used with nonferrousmaterials such as brass, aluminum,or titanium.The high solubility of carbon and silicon in iron would cause silicon carbide to react withan iron base alloyandresult inpoor grinding performance. Levels and types of impurities distinguish the green and black forms of silicon carbide.SiC's sharp and easily fractured abrasive grains are used for abrading other non-metals in such as stone, glass, wood,and leather.Like diamond, silicon carbideis susceptible to oxidation at higher temperatures.
  • Waterstone is a soft sharpening stone that is used with water. Waterstones may require more frequent resurfacing.

Physical Design

It is important to consider an abrasive file's physical design specifications when selecting products. These specifications include length, width or outer diameter (OD), grain size, and grading system.

Length and width or outer diameter are important for selecting a file that is usable and fits the given application. For example, when deburring an object in a tight region of space that is hard to reach, a long and narrow file would be especially suitable.

Grain size applies to products using abrasive grains held in a matrix or bonded to a surface such as coated abrasives, MSL superabrasives, vitrified grinding wheels, dressing sticks, honing stones or grit dressers. Grit sizes are based on ANSI, FEPA, JIS or proprietary grading system standards.  Grading system standards define a grit size through specified upper and lower limits at certain points in the size distribution.

Grading systems are used as ways to standardize different classes of abrasive files. For example, micron graded files are those that have a very fine grain specified to micron size ranges.

Coarseness

Coarseness relates to grain type in that it determines what an abrasive file is designed to do. For example, finishing files tend to be much finer than grains for sharpening.

  • Coarse or extra coarse abrasive products are designed or suitable for rough or initial sharpening of the cutting edges of knives, blades, or other cutting tools.
  • Medium coarse abrasive products are used for medium sharpening or deburring.Deburring is the removal of burrs or sharp edges from machining, casting, or other manufacturing processes.
  • Fine grained abrasive products are used forstoning or intermediate finishing between medium sharpening and final honing.
  • Extra fine grained abrasive products are designed for honing or imparting the proper surface finish to a part's surface. Honing, lapping, super finishingand polishing are all considered finishing operations.
  • Flat surfaces are designed or suitable for Blanchard, surface, or creep-feed grinding applications.

Cross Section Shape

Cross section shape is an important abrasive file property, as it determines how it fits or applies itself to the system it is working with. Cross sections can be rectangular, round, square, triangular, half round, flat, oval, diamond, or knife shaped.

Bond Type

Bonded abrasives consist of an abrasive material bonded to or within a matrix or binder. Bonding allows abrasive material that cannot be utilized in its natural form to be made into shapes suitable for various processes and systems, such as grinding wheels. Differentiating between a bonded or non-bonded abrasive and between bond types is important in abrasive file selection, as different types will behave and perform differently.

  • Non-bonding or mineral stone abrasives are products in their natural form that do not have a bonding system.
  • Metal bonded abrasives have a metal bond between the abrasive grainsand a metal substrate. Metal bond systemsare used mainly for superabrasive or tungsten carbide grit products.There are three main types: sintered, MSL, and electroplated. Sintered metal bond systems are used when a thicker layer of superabrasive is required.Metal single layer (MSL) wheels consists of a specialized braze layer that forms a single layerofsuperabrasive and bond.The electroplated bond system is used to produce fine-grit superabrasive products.
  • Resin or resinoid abrasives use a resin or resinoidbond system between the abrasive grains.
  • Rubber bonded abrasive products use a rubber or elastomerbond system between the abrasive grains.
  • Vitrified abrasive products use a vitrified or glass bond system between the abrasive grains.

References

Kramer Industries, Inc. - Abrasive Blasting Media