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Silicon carbide (green silicon carbide or carburundum) is an invaluable abrasive material with only diamond, cubic boron nitride and cemented carbide having comparable hardness levels.

Cutting through soft materials such as glass, ceramics and nonferrous metals with ease, aluminum oxide abrasives are notoriously brittle and short-lived.

Abrasive Grit

An abrasive grit of a grinding wheel is what does the cutting, with its size depending on what material needs grinding. Finer grits provide more precision or fine work, while coarser ones are designed for heavy stock removal or rough grinding.

A grinding wheel’s abrasive grit is classified by its hardness, which is determined by the strength of the bond that holds together its grains. A harder grade means stronger bonds that provide increased resistance against forces that try to pry loose the grains and increase longevity of life for this abrasive material.

Aluminum oxide abrasive grains offer fast and aggressive cutting action; however, their durability or long-term use is less. They’re commonly used for grinding steel and iron; soft nonferrous materials with lower tensile strengths or ductility are also appropriate applications.

Black silicon carbide (Carborundum) offers similar hardness and durability as aluminum oxide, but with greater long-term utility. Often used to grind hard metals such as cast iron and stainless steel, and it may even come bonded in resin, rubber, or shellac bonds with slower cutting rates suitable for detail work on softer alloys.

Bond

Bond is what holds together abrasive grains, determining its strength, hardness and wear resistance. Each type of abrasive material requires specific bonding materials for optimal performance; additionally, different grit sizes offer aggressive material removal while higher grit sizes produce finer surface finishes.

Regular (black) silicon carbide, commonly referred to as SIC, is ideal for grinding ceramics and nonmetallic materials as well as refinishing wood. Its sharp abrasive grains make cutting glass, medium density fiberboard, soft metals and soft ceramics easy; however, their brittle nature precludes its use with harder metals such as masonry.

Strong bonds tend to extend wheel life. Furthermore, stronger bonds enable sharp abrasive grains to fracture more readily – providing superior cutting rates as older grains wear down and reveal sharp new ones. Letters N, R and S indicate the strength of bond on wheels with higher numbers denoting stronger ties.

Faithfull vitrified silicon carbide wheels use premium grade oil-resistant chemical rubber for long-term lapidary use. Each wheel comes equipped with a 1″ arbor hole and is available in either black or green to suit a range of tasks from removing glaze drips, smoothing warped pots and leveling kiln shelf posts/furniture levels to heavy material removal (40 grit) or smoothing (80 grit).

Grade

Silicon carbide grinding wheels’ grades denote the strength of their bond that holds together their abrasive grains, with harder grades capable of grinding harder materials while softer grades work best with soft ones. Grit size also plays an integral part, with lower grit numbers producing aggressive stock removal while higher ones create finer surface finishes.

There are various bond materials used in grinding wheels. The three most prevalent are vitrified, resin and rubber bonds; each offers unique advantages; for instance, vitrified bonds are ideal for grinding ceramics, glass and non-ferrous metal workpieces as well as carbide. They also can withstand higher temperatures while operating at faster speeds than aluminum oxide wheels.

Softer resinoid bonds may be ideal for applications requiring slower stock removal or superior finish, such as brass and copper grinding. By employing organic substances to diffuse heat generated during grinding, this bond allows greater speeds of operation while softening heat generated when grinding brass and copper alloys. Furthermore, its use makes this type of bond suitable for grinding die and tool steel cast iron alloys hard alloys while polishing semiconductors ceramics and ferrous metals as well.

Pores

A grinding wheel with an increased pore volume allows more water and coolant to flow freely through its abrasive grains, thus reducing heat generation during cutting. Furthermore, this provides spaces between particles so they can move and separate freely – thus helping avoid microscopic welds between abrasive particles which lead to vibration issues and minimize vibration levels.

Pores in silicon carbide wheels are created through both natural spacing of abrasive grains and by hollow ceramic materials such as Zeeland Industries’ Z-Light (mullite/fused Si02) hollow spheres, which act to induce pores during firing and prevent excessive oxidation that could otherwise lead to excessive bond component degradation and prevent proper chip clearance.

At one time, achieving a nano metric surface finish on hard brittle material required a series of costly lapping processes that were both time consuming and expensive. Today, however, ELID pre-dressing has proven an efficient means for cutting down or completely eliminating this finishing step, saving both time and money in the process.

Manufacturers blend abrasive grit, bond and hollow ceramic spheres with powdered dextrin binder, liquid animal glue (47% solids) and ethylene glycol as a humectant in a 76.2 cm (30 inch) verticle spindle mixer to create wheels using pressures ranging from 100 to 5000 pounds per square inch (psi). Gauge blocks may be added between face plates to limit movement and maintain uniform thickness for their wheels.