Calculation of the frictional torque

The following determination of the frictional torque M_r is based on theoretical and practical insights. The frictional torque is influenced by the rolling friction coefficients, the rolling elements, distance holders, seals, load distribution and the load.

Other influencing factors include, among others

• Deviation including the angular deflection of the upper and lower companion structure.
• The lipid filling and type of lipid.
• The lubrication of the seal lips and the seal preload.
• The bearing's change in clearance through installation.

Of course, the calculated frictional torque is subject to certain fluctuations, which can be used around ± 25%. Non-installed, unloaded bearings have their own frictional torque which is not taken into account in the formula. It is important to note this when using the formula.

1. Start-up frictional torque M_r

Ball-bearing supported rings

M_r = µ/2 (4.4 · M_k + F_a ·D_L + 2.2 · F_r · D_L · 1.73) [kNm]

Roller-bearing slewing rings

M_r = µ/2 (4.1 · M_k + F_a ·D_L + 2.05 · F_r · D_L) [kNm]

2. Standard performance P_Ste.

P_Ste. = M_r · ω · η^-1 [kNm · s^-1]

P_Ste. = (M_r · n) / (9.55 · η) [kW]

rothe erde® bearings with reduced rotational resistance are available as special editions. For such applications, contacting us is essential.

For the whole torque required for the drive, the acceleration performance of all individual masses as a product must be formed, with the square of their centre of gravity distances from the rotational axis. The wind power which could attack, as well as the inclined positions of different components must also be taken into consideration.

Symbols used

F_a = axial load [kN]

F_r = radial load [kN]

M_k = resulting tilting torque [kNm]

D_L = bearing circumference-Ø [m]

µ = coefficient of friction

ω = angular velocity

ω = (π · n) / 30 [s^-1]

n = rotational speed of the slewing bearing [min^-1]

η = efficiency of the drive

Different coefficients of friction

µ = 0.008 for KD 210 series range (model 13 and 21, normal bearings)

= 0.006 for KD 210 series range (model 110)

= 0.004 for KD 320 series range

= 0.006 for KD 600 series range

= 0.003 for KD 700 series range

= 0.004 for KD 800 series range

= 0.003 for RD 900 series range

For precision bearings, clearance-free and pre-loaded bearings, please request frictional torques from us.