# 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.