Methods of Applying Solid Lubricants

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There are several methods for applying solid lubricants.

Powdered solids. The oldest and simplest methods of applying solid lubricants are noted as follows:

(a) Burnishing: Burnishing is a rubbing process used to apply a thin film of dry powdered solid lubricant such as graphite, MoS2 , etc., to a metal surface. This process produces a highly polished surface that is effective where lubrication requirements and wear-life are not stringent, where clearance requirements must be maintained, and where wear debris from the lubricant must be minimized. Surface roughness of the metal substrate and particle size of the powder are critical to ensure good application.

(b) Hand rubbing: Hand rubbing is a procedure for loosely applying a thin coating of solid lubricant.

(c) Dusting: Powder is applied without any attempt to evenly spread the lubricant. This method results in a loose and uneven application that is generally unsatisfactory.

(d) Tumbling:. Parts to be lubricated are tumbled in a powdered lubricant. Although adhesion is not very good, the method is satisfactory for noncritical parts such as small threaded fasteners and rivets.

(e) Dispersions: Dispersions are mixtures of solid lubricant in grease or fluid lubricants. The most common solids used are graphite, MoS2 , PTFE, and Teflon. The grease or fluid provides normal lubrication while the solid lubricant increases lubricity and provides extreme pressure protection. Addition of MoS2 to lubricating oils can increase load-carrying capacity, reduce wear, and increase life in roller bearings, and has also been found to reduce wear and friction in automotive applications. However, caution must be exercised when using these solids with greases and lubricating fluids. Grease and oil may prevent good adhesion of the solid to the protected surface. Detergent additives in some oils can also inhibit the wear-reducing ability of MoS2 and graphite, and some antiwear additives may actually increase wear. Solid lubricants can also affect the oxidation stability of oils and greases. Consequently, the concentration of oxidation inhibitors required must be carefully examined and controlled. Aerosol sprays are frequently used to apply solid lubricant in a volatile carrier or in an air-drying organic resin. However, this method should be limited to short-term uses or to light- or moderate-duty applications where thick films are not necessary. Specifications for solid lubricant dispersions are not included in this manual.  Before using dispersions, users should become familiar with their applications and should obtain information in addition to that provided in this manual. The information should be based on real-world experiences with similar or comparable applications.

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