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Modern engineering ceramics are being used in increasing volumes throughout manufacturing industry. They offer a range of interesting and often valuable properties are difficult or indeed impossible to achieve with other materials. The nature of these materials, particularly the combination of hardness and stiffness, makes them ideally suited to the production of high precision balls.
Three materials have attracted particular attention for ball manufacture:
Combining hardness and toughness with low mass, silicon nitride offers significant advantages in high-speed bearing applications, and for these reasons it is finding increasing application in arduous bearing applications such as machine tool spindles and vacuum pumps.
Increasing use and production volumes have dramatically considerably reduced the once astronomic cost of the material so that silicon nitride balls can offer extremely cost-effective solutions to common industrial problems.
Alumina is used in 2 forms for ball production:
Alumina balls range in colour from almost white to a creamy yellow colour. The material is very hard, but less tough than either silicon nitride or alumina. Structurally, the balls perform well, but are prone to localised surface damage, which ultimately promotes failure. Alumina balls are widely used medical applications, particularly for replacement hip joints, and in valves and pumps for aggressive chemical environments.
Single crystal alumina is widely use for contact point for measuring equipment, and in this application it provides good wear resistance at an effective price. Sapphire balls are clear, perhaps with a blue tint, and are far less common than ruby which range in colour from almost clear to dark red. Balls are often supplied with drilled holes for mounting purposes.
Zirconia in its partially stabilised form offers a number of useful properties. It can withstand very high temperatures without deterioration, it has a similar rate of thermal expansion to steel, it has a high toughness, and it is relatively inexpensive. It does have a tendency to porosity, and this can prompt failure in some circumstances, and tends to make it unsuitable for high-stress applications. However, it is widely used in pumps and valves for aggressive environments, and for measurement standards.
Balls shapes are made in other ceramic materials, usually for very specific applications. Cubic Zirconia balls are used as lenses in some specialised fibre optic systems, but they are not generally available. Silicon carbide is interesting for some applications, particularly its conductive forms, but its inherently low toughness makes ball production difficult and consequently expensive.