Lubrication is the single most controllable factor in gear life. Study after study puts lubrication-related failures — scoring, pitting, scuffing and accelerated wear — at well over half of all gear breakdowns, and most of those are preventable. A good lubrication programme does not need to be complicated, but it does need to be consistent: the right oil, the right level, the right change interval, and a routine that catches contamination before it damages the teeth.
The first choice is the lubricant itself. Most industrial gears run on mineral-based gear oils with an extreme-pressure (EP) additive package, typically ISO VG 150 to VG 460 depending on speed and load. Synthetic oils — polyalphaolefin (PAO) or polyglycol (PG) — are worth the extra cost where operating temperatures exceed 80 °C, where wide temperature swings are expected, or where a long oil life is needed to reduce downtime. The viscosity must match the pitch-line speed: too thin and the oil film collapses under load, causing metal-to-metal contact; too thick and churning losses overheat the oil and waste energy. A common starting point is ISO VG 220 for medium-speed industrial gearboxes, adjusted up or down by one grade based on the actual speed and load.
Lubrication method matters as much as the oil. Splash lubrication — where the gear dips into an oil sump and throws oil onto the meshing teeth — is the simplest and most common method for enclosed gearboxes running at moderate speeds. For high-speed gears or large units, forced-circulation lubrication delivers filtered, cooled oil directly to the mesh, which is essential where heat generation is high. Open gears and slow-moving slewing drives are usually lubricated with adhesive gear greases or spray-on compounds that cling to the tooth surface instead of dripping off. Whatever the method, the oil level must sit between the minimum and maximum marks on the sight glass: too low starves the mesh, too high causes overheating from churning.
A maintenance routine built around three checks catches most problems early. The daily check is visual: oil level, oil colour and any signs of leakage. The monthly check adds temperature — a sudden rise of more than 10 °C above normal operating temperature almost always signals a problem, whether it is a failing bearing, an overloaded gear or oil that has lost its viscosity. The quarterly or semi-annual check is oil analysis: measuring viscosity, acid number and water content, and examining a wear-particle sample under a microscope. Iron particles with a shiny, spherical shape point to fatigue pitting; sharp, irregular particles indicate abrasive wear from contamination; copper particles suggest bearing wear. Oil analysis turns maintenance from guesswork into a scheduled, evidence-based process.
The most common lubrication mistakes are also the most avoidable. Mixing incompatible oils — especially mineral with polyglycol — causes the additive packages to react and the oil to thicken or separate, destroying its lubricating properties. Water contamination, even at levels below 200 ppm, dramatically reduces fatigue life by promoting hydrogen embrittlement at the tooth surface. Running the gearbox too hot breaks down the EP additives and oxidises the base oil, turning what was a good lubricant into an abrasive sludge. And topping up with the wrong viscosity — perhaps because the correct oil is not on the shelf — is a short cut that almost always ends in premature wear.
At our factory we manufacture gears to the accuracy and surface finish that make proper lubrication effective, and we can advise on lubricant selection, oil-analysis intervals and failure diagnosis for gearboxes already in service. Send us your gear type, speed, load and operating temperature, and we will recommend the lubricant grade, method and maintenance schedule that gives the longest service life — rather than waiting for a failure to tell you something was wrong.