Industrial greases

A grease is an oil held in place

A grease has three components: the base oil, which does the actual lubricating; the thickener, which holds it at the lubrication point; and the additives. The practical consequence is that a grease's most important property is not the NLGI grade — which describes consistency only — but the base oil viscosity, chosen exactly as you would choose an oil, on speed and load. The thickener decides the rest: lithium is versatile and cheap; lithium complex raises the working temperature; calcium sulphonate resists water remarkably well and has EP capability of its own without additives; polyurea is the standard for electric motors and sealed-for-life bearings; bentonite has no dropping point, so it goes to high temperatures, but does not recover after cooling.

How to read a grease datasheet

The base classification comes from DIN 51502 and ISO 6743-9, and the code on the pack says more than the trade name: the leading letter gives the type (K for rolling bearings), followed by additive class and temperature range. NLGI 2 is the default grade for rolling bearings, NLGI 1 for centralised systems, NLGI 00 and 000 for gearboxes on semi-fluid grease, NLGI 3 where extra sealing is needed. EP capability, checked by the Timken or four-ball test, matters under shock loading; molybdenum disulphide is added where motion is oscillating, as on pins and bushings. For speed, the practical reference is the n·dm speed factor, and for food environments the same greases exist in NSF H1 registered versions.

Common greasing mistakes

More bearings are ruined by wrong greasing than by bad grease:

Mixing incompatible thickeners — lithium on top of polyurea, for instance. The mix can soften until it runs out, or harden until it blocks.
Choosing on NLGI rather than on base oil viscosity. A "universal" NLGI 2 with too thin a base oil will not hold a film on a slow, heavily loaded bearing.
Overgreasing. A bearing filled beyond roughly a third of its free volume heats up through internal friction and pushes grease out past the seals.
Greasing with the machine stopped and unloaded where the grease has to reach the bushing under movement — on pins, timing matters.
Ordinary grease where there is water washing. Without water resistance, the bearing is bare after the first rain or the first hose-down.