Bearing Regrease Quantity and Interval
How much grease a bearing takes and how often, which are two numbers commonly wrong in the field in opposite directions.
Example
You enter
- Bearing outside diameter (mm) 110
- Bearing width (mm) 27
- Bearing bore (mm) 50
- Operating speed (rpm) 1800
- Correction factor (1.0 base; 0.5 vertical or hot, 0.25 both) 1
- Operating hours per day 24
- Bearing type (interval factor K) ball
You get
- Grease quantity 14.9 g
- Base interval 8,999 hours
- Corrected interval 8,999 hours
Checked against published worked examples from: Reliability Solutions (reliabilitysolutions.net).
Details, formula, and sources
ScopeThe quantity is proportional to the bearing's outside diameter times its width -- essentially to the free volume inside it -- and it comes out much smaller than people expect: a 110 mm by 27 mm bearing takes about 15 grams, not a cartridge. Over-greasing is not the conservative choice it feels like, because excess grease is churned by the rolling elements, it heats, and it either bleeds out or cooks into a varnish that starves the bearing. A great many lubrication failures are over-lubrication. The interval falls with both speed and bore, and the base relation applies to a horizontal, moderately loaded bearing at normal temperature; the correction factor cuts it hard from there. Roughly halve it for every fifteen degrees Celsius above about 70 C, halve it again for a vertical shaft, and cut it substantially for heavy load, contamination, or vibration -- so two identical bearings in different service can have intervals a factor of ten apart. A 6310 ball bearing at 1,800 rpm horizontal takes 14.9 g about every 9,000 hours (the relation times the ball-bearing factor 10), about a year of continuous running; put the same bearing on a vertical shaft in a hot room and it is roughly 2,250 hours, and a schedule built on the base number would be four times too slow. A planning figure; the bearing manufacturer's own relubrication chart, the grease's specification, and a condition-monitoring program govern.
Formula or tablegrease_grams = 0.005 x od_mm x width_mm; base_interval_hr = K x (14,000,000 / (rpm x sqrt(bore_mm)) - 4 x bore_mm) with the bearing-type factor K = 10 radial ball, 5 cylindrical / needle roller, 1 spherical / tapered roller (SKF; STLE TLT April 2009 Fig. 7-8); corrected_interval_hr = base x correction_factor.
Source and editionGrease quantity from the bearing's free volume and the standard relubrication-interval relation for a horizontal, moderately loaded bearing at normal temperature, by name -- published bearing-maintenance practice, cited and not reproduced. The correction factor for temperature, orientation, load, and contamination is entered. The bearing manufacturer's own relubrication chart and a condition-monitoring program govern.
Free accessBoth relations are published maintenance practice applied to the bearing's own dimensions and speed; no manufacturer's interval chart is reproduced.
What governsEstimate. AHJ and licensed professional govern.
API field namesod_mm, width_mm, bore_mm, rpm, correction_factor, duty_hours_per_day, bearing_type, grease_grams, base_interval_hr, corrected_interval_hr
- Quantity 0.005 x OD x width in grams from millimetres -- the free volume, and much less than people expectbearing maintenance practice
- Base interval conditions horizontal shaft, moderate load, normal temperature; the correction factor only ever shortens itbearing maintenance practice
- Over-greasing excess grease churns, heats, and either bleeds or varnishes; many lubrication failures are over-lubricationbearing maintenance practice