Page 53 - IGUS Bearing

iglidur | Technical data
®
pv value and coefficient of friction

For plain bearings, the product is given a new value Lubrication Lubrication Correction factor Depending on whether an application is starting from a
depending on the pressure [p] and the surface speed [v].The Although iglidur plain bearings are designed for dry Dry operation 1.0 stationary position or the movement is in progress and
®
pv value can be considered a measure of the frictional heat operation, they are quite compatible with standard oils During installation 1.3 needs to be maintained, a distinction is made between
and can be used as an analytical tool to answer questions and greases. A single lubrication during the installation Continuous, grease 2.0 a static coefficient of friction and a dynamic coefficient of
concerning the proper application of a plain bearing. For this improves the start-up behaviour and the coefficient of Continuous, water 4.0 friction.
purpose the actual pv value is compared with a permitted friction, thus reducing the frictional heat. Due to this effect, Continuous, oil 5.0
pv value calculable for the height. The permitted pv value the permissible loads for plain bearings can be increased Coefficient of friction and surfaces
depends on the shaft material, the ambient temperature by lubrication. Table 02 shows the correction factors for Table 02: Correction of the tolerated pv value by Shown here is the relationship between coefficient of friction
and the service time. pv value using lubrication. means of lubrication and surface finish of shaft materials. It is clearly shown that
Material Thermal conductivity [W/m · k] the amount of friction is composed of different factors.
Correction factor Steel 46 If the shaft is too rough, abrasion levels play an important
The permissible pv value can be increased in practical 8 Aluminium 204 role. Small areas of unevenness that can interlock with each
operation if the bearing temperature never reaches the 7 Grey cast iron 58 other must be worn off the surface.
maximum limit because of the short operating time. Tests 6 304 stainless steel 16 When the surfaces are too smooth, however, higher
have shown that this is true for operating times below 5 Ceramics 1.4 adhesion results, i.e. the surfaces stick to each other.
10 minutes. It is known that a longer dwell time makes a 4 Polymer 0.24 Higher forces are necessary to overcome the adhesion,
greater contribution to re-cooling. An important qualifier 3 which results from an increased coefficient of friction.
here is the ratio of the operating time and dwell times. The Correction factor 2 Table 03: Heat conductivity values of shaft or housing Stick-slip can be the result of a large difference between
1
different curves of diagram 09 represent different ratios (3x materials static and dynamic friction and of a higher adhesive tendency
means that the dwell time is three times longer than the 0 of mating surfaces. Stick-slip also occurs due to intermittent
operating time). 0 1 2 3 4 5 6 7 8 9 Coefficient of friction running behaviour and can result in loud squeaking. Over
Duty cycle [min]
iglidur plain bearings are self-lubricating with the addition and over again, it is observed that these noises do not occur
®
4 times 3 times 2 times 1 time
of solid lubricants. The solid lubricants lower the coefficient or can be eliminated with rough shafts. Thus for applications
Diagram 09: Correction factor for p · v
of friction of the plain bearings and thus increase the wear that have a great potential for stick-slip - slow movements,
resistance. The coefficient of friction μ is proportional to the large resonance of the housing - attention must be paid to
normal force and describes which force is needed to move the optimal surface finish of the shafts.
a body in relation to another.

pv value

+
pv = ( [K1 · π · k · ∆T ] [K2 · π · s · ∆T ] ) -3

· 10
perm. µ · s µ · b1 · 2
In these equations:
K1, K2 = Constant for heat dissipation (K1 = 0.5, K2 = 0.042)
s = Bearing wall thickness mm
b1 = Bearing length mm
μ = Coefficient of friction
s = Thermal conductivity of the shaft
k = Thermal conductivity of the bearing
∆T = (T - T )
a u
T = Ambient temperature [°C]
u
T = Max. application temperature [°C]
a

ASEAN 09/2023 ASEAN 09/2023 Picture 05: More cost-effective products - a crucial component: the largest test laboratory in the industry.

2
3,800m laboratory, over 12,000 tests and two billion test strokes a year.
50 Online tools and more information u www.igus-asean.com/iglidur 3D CAD files, prices and delivery times online u www.igus-asean.com/iglidur 51