# Bearing Friction

### Plain Bearing Friction

More Details on plain bearing friction are available on the links below

Plain Bearing Friction

Plain bearings can be linear, journal and thrust.   They can be hydrostatically, or hydrodynamically lubricated or operated dry.  These different modes of operation can all result in very different friction factors.  The coefficient of friction for plain bearings relates to the type of bearing,the speed of rotation, the load, the amount and viscosity of the lubrication, the friction of the seals, etc etc.  The friction factors provided are approximate and are only suitable for assessment of relative values

It is very important to note that determination of reasonably accurate friction factors for lubricated plain bearings is very complicated.   Serious design should include reference to bearing suppliers and/or reputable reference documents

Journal Bearings

The bearing friction torque Mr = P . f . (D/2)

 Mr = Friction Torque (Nmm) P = Radial Force (N) f = coefficient of friction of rolling bearing D = Diameter of the bore of the bearing (Shaft diameter) (mm)
Linear Bearings

The bearing friction Force Fa = P . f

 Fa =Friction Force against direction of movement (N) P = Perpendicular Force on bearing surface (N) f = coefficient of friction of rolling bearing
Rotating Thrust Bearing

The bearing friction torque Mr = P . f .( Do + Di )/ 4

 Mr = Friction Torque (Nmm) P = Axial Force on bearing surface (N) f = coefficient of friction of bearing Do Outside Diameter of Thrust Bearing (mm) Di Inside Diameter of Thrust Bearing (mm)

Approximate values for f are listed below;

 Hydrodynamic Thick Film (Mineral Grease) velocity 1 m/s ..f = 0,0002 to 0,0075 Hydrodynamic Thick Film (Mineral Grease)velocity 2,5 m/s ..f = 0,0027 to 0,015 Hydrodynamic Thick Film (Mineral Oil) velocity 1 m/s ..f = 0,0012 to 0,0040 Hydrodynamic Thick Film (Mineral Oil)velocity 2,5 m/s ..f = 0,0020 to 0,007 Mixed Film (Boundary + Hydrodynamic ).. f = 0,02 to 0,08 Thin Film ...f = 0,08 to 0,14 Dry (Bearing = PTFE /Lead based - surface = steel ) ...f = 0,02 to 0,3- Very dependent on the operating conditions Dry (Bearing = PTFE /Plastic based- surface = steel ) ...f = 0,1 to 0,3 Dry (Bearing = Metal - Surface = Steel) ...f = 0,2 to 0,4

More accurate values for bearing friction are found in the suppliers technical literature..(see links below)