Calculation example

Two paired PTFE composite bushings are to be used in the linkage of a locking system for the door of a tramway car.
Which bushings can be used under the given operating conditions and which basic rating life can be achieved?
Design data: 
  • pin diameter d = 20 mm 
  • surface roughness of the pin Ra = 0,4 μm
Operational data: 
  • radial load at the linkage: 
    • during closing 0,8 kN per bushing 
    • after locking the closed door the static load mounts to 15 kN per bushing 
  • half angle of oscillation b = 90° (fig. 1)
  • frequency of oscillation f = 10 min–1 
  • operating temperature t = 30 °C
Based on the design characteristics, two PTFE composite bushings PCM 202325 E are chosen, having a basic dynamic load rating C = 39 kN each.

As a first check that the bearing size is suitable (diagram 1), the specific bearing load p based on the specific load factor K = 80 for PTFE composite is calculated using

p = K F/C
= 80 x 0,8/39 = 1,64 N/mm2


The sliding velocity is calculated using

v = 5,82 x 10–7 d b f
= 5,82 x 10–7 x 20 x90 x 10 = 0,01 m/s

These values are within range I of the pv diagram for PTFE composite bearings (diagram 1).

Furthermore the factors are applied as follows:

  • load factor c1 = 1,3 (diagram 2)
  • speed factor c2 = 1 (diagram 3)
  • temperature factor c3 = 1 (diagram 4)
  • surface roughness factor c4 = 0,6 (diagram 5)
  • factor for the type of load c5 = 1,5 (as the load is rotating)
  • exponent n = 1 (PTFE composite material) 
  • pv value = 0,025 to be applied as
    product pv = 1,64 x 0,1 = 0,0164, which is less than the limiting value of 0,025 for PTFE composite material

Using the material and bearing type factor KM = 480 for PTFE composite bushings, the basic rating life for the chosen bushings can be calculated from


Gh = c1 c2 c3 c4 c5 KM/(p v)n
Gh = 1,3 x 1 x 1 x 0,6 x 1,5 x 480/0,0251 = 22 500 operating hours

With a frequency f = 10 min–1, the working cycles amount to approximately 13,5 millions.
The static load of 15 kN lies within the dynamic load rating of C = 39 kN and far below the static load rating of C0 = 120 kN.
Thus, the chosen bushings meet the requirements.
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