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Anti-scuff
Table of Contents
Physical & Chemical Properties
Anti-scuff additives are those that prevent scuffing. Scuffing is defined as damage caused by solid-phase welding between sliding surfaces. Anti-scuff additives reduce scuffing by forming thick films of high melting point metal salts on the surface which prevent metal to metal contact which, when extensive, may cause scuffing. The mechanical properties of the films, such as melting point, shear strength, ductility, and adhesion to the metal surface determine the effectiveness. Common anti-scuff additives are sulfur or phosphorous compounds more chemically active than anti-wear additives. A common gear oil anti-scuff additive is a mixture of an organic sulfur compound and an organic phosphorous compound usually identified as S/P. Excessive chemical activity of anti-scuff additives creates a danger of corrosive wear. For example, an active sulfur compound may reduce the risk of scuffing of steel gear teeth, but severely tarnish any corrodible metal.
Microscopically, the scuffed surface appears irregular, torn, with plastic deformation, and shows evidence of melting. The definitive test of scuffing is the evidence of metal transfer. Anti-scuffing properties of oils are also measured on lubricant testers run under severe conditions. Usually load, oil temperature, speed, or combinations are increased until scuffing occurs. Scuffing is usually accompanied by high f, such as between 0.2 and 0.5, and possible localized heat, oil smoking, and noise. Wear fragments in the oil are usually large metallic particles.
Note: There is some overlapping of anti-wear and anti-scuff performance. That is, some additives have good anti-wear properties and can prevent scuffing to a limited degree. Following are some components of oil or additives that affect lubrication under boundary lubrication conditions.
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