Gears Lubrication General

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Energy is transmitted from a power source to a terminal point, through gears that change speeds, directions, and torque. Gear lubricants are formulated and applied to prevent premature component failure, assure reliable operation, reduce operating cost, and increase service life. The important objectives accomplished by these lubricants include: reduction of friction and wear, corrosion prevention, reduction of operating noise, improvement in heat transfer, and removal of foreign or wear particles from the critical contact areas of the gear tooth surfaces.

Gears vary greatly in their design and in their lubrication requirements. Proper lubrication is important to prevent premature wear of gear tooth surfaces. When selecting a lubricant for any gear application the following issues must be considered: type and materials of gear; operating conditions, including rolling or sliding speed, type of steady load, and temperature; method of lubricant application; environment; and type of service. Enclosed gears -- those encased in an oil-tight housing -- usually require an oil with various additives, depending on the operating conditions. Rust, oxidation, and foam inhibitors are common. Extreme pressure (EP) additives are also used when loads are severe.

Worm gears are special because the action between the worm and the mating bull gear is sliding rather than the rolling action common in most gears. The sliding action allows fluid film lubrication to take place. Another significant difference is that worm gears are usually made of dissimilar materials, which reduces the chance of galling and reduces friction. EP additives usually are not required for worm gears and may actually be detrimental to a bronze worm gear. Lubrication can be improved by oiliness additives.

In open gear applications, the lubricant must resist being thrown off by centrifugal force or being scraped off by the action of the gear teeth. A highly adhesive lubricant is required for most open gear applications. Most open gear lubricants are heavy oils, asphalt-based compounds, or soft greases. Depending on the service conditions, oxidation inhibitors or EP additives may be added. Caution must be exercised when using adhesive lubricants because they may attract and retain dust and dirt, which can act as abrasives. To minimize damage, gears should be periodically cleaned.

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