## Cookies on the SKF website

We use cookies to ensure that we give you the best experience on our websites and web applications. By continuing without changing your browser settings, we assume you give your consent to receive cookies. However, you can change your browser cookie setting at any time.

# 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:
• 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.