Calculating Bearing Requirements for Oil Lubricants:
V = A x T
V = volume in terms of lube-oil replacement rate in cubic inches per hour (in³/hr)
A = bearing surface area in square inches (in²) (sized differently based on bearing type)
T = film thickness….generally .001 inch….but it may vary based on oil type and application
Calculating Bearing Requirements for Grease Lubricants:
V = A x T
V = volume in terms of lube-grease replacement as cubic inches per four hour (in³/4 hrs)
A = bearing surface area in square inches (in²) (sized differently based on bearing type)
T = film thickness….generally .002 inch….but it may vary based on grease type and application
Metric Conversion Note:
Quite often requirements are expressed in metric terms. To convert to metric, calculate volume requirements as noted above and simply multiply by 16.39 to convert to cubic centimeters per hour (cc³/hr) for oil or cubic centimeters per four hours (cc³/4 hrs) for grease.
Common Bearing Types: (Necessary to know for calculating areas)
- Plain bearings: Area (in²) = 3.14 x shaft diameter (ins) x length of bearing (ins)
- Slides, gibs and ways: Area (in²) = area of the largest contact surface
- Anti-friction bearings: Area (in²) = shaft diameter squared x number of rows
Gears: Area (in²) = 3.14 x pitch diameter of gears (ins) x width of gear (ins)
Sizing Example: Plain bearing with 6 inch shaft and 6 inch long bearing surface using oil
Area (in²) = 3.14 x 6 (ins) x 6 (ins) = 113.04 in²
Volume (in³/hr) = 113.04 (in²) x .001 (in) = .113 (in³/hr)
Should this need to be converted to metric, the requirement for this single bearing application would be 1.85 cubic centimeters per hour. .113 (in³/hr) x 16.39 = 1.85 (cc³/hr)
Total Machine Lube Requirement:
Each and every bearing or lube point on a machine would be calculated in this fashion and when done, the replacement rates for all points would be added together to determine the total system lubrication requirement.
Note: This information is provided as a quick reference resource and is not intended to serve as a substitute for qualified engineering assistance. While every effort has been made to ensure the accuracy of this information, errors can occur. As such, neither Flodraulic, any of its affiliated companies nor its employees will assume any liability for damage, injury or misapplication as result of using this reference guide.