Choosing a Silicon Carbide Abrasive Wheel

When selecting a silicon carbide abrasive wheel, various factors must be taken into account, including material type, grit size and severity of grinding.

Grain types that can be used include ceramic alumina, zirconia alumina, green silicon carbide and aluminum oxide. Each offers distinct performance characteristics: Alumina is suitable for steel and iron applications while green silicon carbide should be considered when working with non-ferrous materials or hard brittle workpieces.

Hardness

Silicon carbide is harder and brittler than aluminum oxide, making it ideal for grinding hard low-tensile strength materials like cast iron and non-metallic metals. Additionally, it may be used to grind fiberglass, medium density fiberboard and some plastics; however, this material may not work as effectively for hardwoods and other high-tensile strength materials.

Hardness of a silicon carbide wheel refers to its bond, which connects its abrasive grains together. Grain hardness determines how much stock is removed from a workpiece in an amount of time; harder abrasives tend to be more resilient and last longer than soft ones.

Green (or black) silicon carbide is an affordable abrasive made by heating sand and petroleum coke together to form synthetic silica, then firing it in electric resistance furnaces. The sharp yet friable grains make green (or black) silicon carbide suitable for grinding hard nonmetallic workpieces like glass, ceramics and alloys; however, for tougher materials requiring diamond angles (ie: tough metal alloys) they cannot provide enough aggressiveness.

An effective grinding wheel specification provides valuable information. To begin with, this section of the specification lists abrasive grain size followed by grit size and then grade/hardness rating which relates to bond strength.

Bond Strength

An essential aspect of any abrasive wheel is its bond strength. This bond connects its grains together and provides support as they cut, with grade being its indicator. See wheel specifications sheet for details about this feature.

Grit size of an abrasive is another crucial consideration. Larger grit sizes such as those used in sandpaper can help rough materials down and remove larger pieces of metal while smaller grit sizes tend to provide smooth finishes and are better for finishing applications.

Porosity and grain spacing are also critical considerations, as softer abrasives with larger gaps between grains offer greater efficiency for clearing metal chips from grinding, while denser grades of abrasives work best with harder materials.

Green silicon carbide is a synthetic material with hardness rivalling diamond, making it the ideal material for cutting glass, quartz, ceramics, titanium zirconium uranium fused silica and fused silica. Black silicon carbide differs slightly in purity; its higher hardness/brittleness make it suitable for applications involving higher temperatures/harsher environments – including sandblasting surface treatment grinding optical glass carbide alloys bearing steel as well as high temperature sandblasting applications/hard environments as sandblasting, surface treatment/grinding optical glasses/carbide alloys/refractory products.

Area of Contact

The area of contact on a wheel determines the severity of grinding, which affects its size, grade and structure. Grit size, grade and structure will differ according to this factor; generally speaking wheels with higher grain density produce greater impacts that result in rougher finishes than open structure wheels; for this reason a coarser grit would be suitable for soft, pliable materials that require fast material removal with greater pressure whereas finer grits are recommended when dealing with hard, brittle materials that must be ground with little or no pressure applied on their surface.

Aluminum oxide works well on non-ferrous metals like rubber and stone but does not work effectively on cast iron and other steels with low tensile strength. Silicon carbide features razor-sharp grains which make short work of cutting through cast iron as well as non-ferrous metals; however, its hard grains do not work so well with wood or extremely tough materials.

Speed of the wheel should also be taken into consideration, since as its speed increases so does force per particle and bond breakdown more rapidly. Every 1000 SFPM an increase in wheel speed causes one grade softer acting abrasives/bond to come into contact. This information may assist in troubleshooting specifications or finding suitable grit/grade combinations.

Severity of Grinding

The severity of a grinding operation – including shock loads, heavy in-feeds and high work and traverse rates – determines wheel selection; this in turn impacts on grit size, grade and type of bond chosen by the operator. Furthermore, depending on its application coolant should also be applied; using it helps slow down grinding operations while simultaneously reducing heat production while prolonging abrasive life spans.

Abrasive grains like aluminum oxide, zirconia alumina or silicon carbide are embedded within an elastic matrix called the bond to hold them together and allow for their easy shaping into wheels. The bond may be inorganic like clay, glass or porcelain or organic like shellac rubber or synthetic resin depending on what abrasives have been chosen as they will impact on strength and durability of an abrasive wheel.

The nature of a grinding application dictates an abrasive grit size; coarse-grit wheels should only be used for more intense operations such as snagging, while medium and soft grade wheels are more appropriate for applications like commercial or precision grinding. Bond and type/grade of the abrasive used also depend on what material it’s being ground on: aluminum oxide is ideal for steels while silicon carbide performs best on nonferrous metals and low-tensile strength irons – leaving fresh cutting edges exposed when its fractured through wearout providing superior cut rates over time.