What shortens the lubrication interval
Four factors determine how often a grease-lubricated rolling bearing must be relubricated: the dn value (bore diameter × speed—higher values mean more frictional heat), the load (ratio of the bearing load P to the dynamic load rating C), the temperature (the grease service life is roughly halved for every 15 °C increase above 70 °C), and the environment (contamination and moisture further shorten service life).
The approximation formula
Here, n is the speed (rpm), d is the bore diameter (mm), k_f is the bearing type factor (10 for deep groove ball bearings, 5 for cylindrical roller/needle bearings, 1 for single-start roller/tapered roller/thrust bearings), and f_T, f_L, f_U are the correction factors for temperature, load, and environment—the closer the value is to 1.0, the more favorable the conditions. Source of the formula: Rolling bearing manufacturer’s catalog (guideline value). It provides reference values for maintenance planning; the relubrication charts from bearing and grease manufacturers are binding (and vary by manufacturer).
Mnemonic
Worked Example: Rolling Bearing in an Electric Motor
A 6309 deep groove ball bearing (d = 45 mm) is operating at n = 1,800 min⁻¹, under a light load (≈ 6% of the dynamic load rating), in a clean environment, with a bearing temperature of approximately 85 °C.
t_grund = 10 × (14,000,000 / (1,800 × 6.71) − 4 × 45) = 10 × (1,159 − 180) ≈ 9,790 h
t_f = 9,790 × f_T(0.5) × f_L(1.0) × f_U(1.0) ≈ 4,900 operating hours
At 8 hours/day, 5 days/week (≈ 2,080 hours/year), this corresponds to approximately 2.4 Jahre calendar time. Practical recommendation from the guide: Nevertheless, relubricate at least every 2 years as part of major maintenance and visually inspect the grease during every inspection—grease ages due to oxidation even when the equipment is not in use.
Knowledge check
Answer all three questions, then click "Check". From 2 of 3 correct answers, the unit counts as completed. You can retry at any time.
This feature needs JavaScript. You can still read the learning content without JavaScript.