Bearing Regrease Quantity and Interval

The 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 at 1,800 rpm horizontal takes 14.9 g every 900 hours, about five weeks of continuous running; put the same bearing on a vertical shaft in a hot room and it is roughly 225 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.

grease_grams = 0.005 x od_mm x width_mm; base_interval_hr = 14,000,000 / (rpm x sqrt(bore_mm)) - 4 x bore_mm; corrected_interval_hr = base x correction_factor.

Grease 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.

Both relations are published maintenance practice applied to the bearing's own dimensions and speed; no manufacturer's interval chart is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: od_mm, width_mm, bore_mm, rpm, correction_factor, duty_hours_per_day, 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