iglidur® - p x v value and lubrication

Table 01: Thermal conductivity coefficients of shaft and housing materials

Material	Thermal conductivity [W/m x k]
Steel	46
Aluminium	204
Grey cast iron	58
304 stainless steel	16
Ceramics	1.4
Polymer	0.24

p x v value

The product of the specific load [p] and the surface speed [v] is of particular importance for plain bearings. The p x v value can be regarded as a measure of the frictional heat and can therefore be used as an analytical means of answering the question of the suitability of a plain bearing. For this purpose, the actual p x v value is compared with a permissible p x v value that can be calculated in terms of height. The permissible p x v value depends on the material of the running partners, the ambient heat and the duty cycle.

permissible p x v value:

In these equations:
K1, K2	Constant for heat dissipation (K1 = 0.5, K2 = 0.042)
Øs	Bearing wall thickness in mm
b1	Bearing length [mm]
μ	Coefficient of friction
λs	Thermal conductivity of the shaft
λk	Thermal conductivity of the bearing
ΔT	(T_a - T_u)
T_u	Ambient temperature
T_a	Max. Application temperature

Correction factor

The permissible p x v value can be increased in intermittent operation if the bearing temperature does not reach the maximum at all due to the short switch-on times. Tests have shown that this is the case with switch-on times of less than 10 minutes. The shorter the switch-on time, the lower the maximum storage temperature reached.
An important factor here is the ratio of duty cycle and pauses. It is obvious that long pauses contribute more to re-cooling. The different curves in diagram 09 represent the different ratios (3 times means that the pause lasts 3 times longer than the switch-on time).

Lubrication	Correction factor
Dry operation	1
During installation	1.3
Continuous, grease	2
Continuous, water	4
Continuous, oil	5

lubrication

Although iglidur®® bearings are designed for dry operation, they are well compatible with common oils and greases. A single lubrication during assembly improves the running-in behaviour and the coefficient of friction and thus reduces the resulting frictional heat. This effect allows the permissible load for plain bearings to be increased by lubrication. Numerous results from lubricated applications are available from tests. Please contact us if required. Table 03 shows the correction factor for the p x v value when lubricants are used.