Choosing the Right Grease, Not Just "Grease"

Specifying lubrication is engineering, not an afterthought. The wrong grease - too thin, too viscous, or wrong thickener - causes more bearing failures than almost any other single cause. The choice is driven by speed, temperature, load and the bearing's internal geometry.

NLGI Grade and Thickener

Grease consistency is rated on the NLGI scale: most rolling bearings use NLGI 2 (general duty) or NLGI 1/1.5 for colder climates and central-lubrication systems; NLGI 3 is used where a stiffer consistency is needed to stay in place. The thickener (lithium, complex lithium, polyurea, calcium sulphonate) sets drop point, water resistance and compatibility.

Base-Oil Viscosity and the κ Ratio

The base oil - not the thickener - does the actual film-forming. Its viscosity must suit the bearing size and speed. The key metric is the viscosity ratio κ = (actual viscosity at operating temperature) / (minimum required viscosity from the bearing's speed × mean diameter, n×dm). For long life κ should be ≥ 1 (ideally 1.5-2 for contaminated or moisture-rich duty). If κ < 1 the film is too thin and wear accelerates.

Speed Factor n×dm

The speed factor n×dm (rpm × mean diameter in mm) summarises a bearing's speed demand. High n×dm needs low-viscosity base oil and sometimes oil (mist, jet, or oil-air) instead of grease, because churning grease at high speed generates heat. Grease is normally limited to lower n×dm ranges; above that, oil lubrication is preferred.

Fill Quantity and Over-Greasing

The fill is not "more is better". A common rule of thumb fills the free space to roughly G = 0.005 × D × B (D = outside diameter, B = width, in cm³). Over-greasing is a leading cause of bearing failure: the churning grease heats up, the thickener breaks down, and seals can blow out. For high-speed or continuous-duty bearings, periodic re-lubrication with the right interval matters more than a one-time over-fill.

Extreme-Pressure Additives and Sealing

Where shock or boundary lubrication occurs, an EP (extreme pressure) additive package helps. Sealed (2RS / ZZ) bearings arrive pre-greased for life in moderate duty; for harsher or hotter duty, choose the correct grease grade and re-lubrication interval rather than relying on the factory fill.

How KMK Bearing Applies This

At KMK Bearing (SINO BEARINGS, KMK brand) these principles guide every order we manufacture in Chengdu, China. Our in-house process chain - forging, heat treatment, precision grinding, superfinishing and cleanroom assembly - is built to the standards described above, whether the part is a standard catalog bearing or a custom-engineered solution.

• 20+ years of precision bearing manufacturing
• Materials from chrome steel to 17-4PH stainless steel and full ceramic (ZrO2, Si3N4)
• In-house heat treatment and metrology to P4/P2 (ABEC 7/9) precision
• Custom designs and low-MOQ prototyping from drawings or samples

Discuss your application with kevin@sinoti.com or browse our bearing catalog.

SINO BEARINGS (KMK) - Perfect Quality -- Great Service -- Customized.

Source: SINO BEARINGS