Although gearbox sludge isn't a desirable condition, it's all too often a common symptom found in many gearbox reservoirs. A gearbox is a simple self-contained mechanical device that allows power to be transmitted from a driven-input shaft connected through a series of gears to an output shaft, which allows it to turn at a different speed. The shaft bearings and gears require constant lubrication, and with few exceptions, are almost always oil lubricated.

Larger gearboxes usually employ a dual-lubrication system in which the reservoir is filled with oil to a determined level. This will ensure partial coverage of lower mating gear teeth. At speed, these gears use surface tension on their teeth to "pick up" lubricant and transfer to other gears and bearings through meshing—and by "flinging and splashing" the lubricant in all directions within the sealed reservoir. This "splash" method is often complemented with a pressure-lubricated delivery system. It uses an internal gear-driven pump that picks up lubricant from the reservoir and delivers oil under pressure to bearings and gears difficult to service with traditional "splash" lubrication.

Significant sludge present in a reservoir is usually indicative of a failed lubricant that's difficult to pump under pressure, and likely with no or little protective additive package, will cause a premature failure of bearings and gears.

One way sludge is caused is through the mixing of different specification lubricating oils during oil "top-ups" or oil changes. The solution? Attach a label to the reservoir clearly indicating the correct lubricant manufacturer, product name, and viscosity to be used, and indicate the same information on the preventive maintenance (PM) work order.

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For more information on implementing asset maintenance management programs, contact Ken Bannister of Engtech Industries at: (519) 469-9173 or by email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .