Product Guide for Design Engineers - Quadrant

Technical Specifi cation of General Engineering Plastics
Fig. 36: Limiting PV-Values for Cylindrical Sleeve Bearings [*]
0,5
0,4
HIGHER IS BETTER
sliding velocity = 0.1 m/s
sliding velocity = 1 m/s
Limiting PV-value [MPa.m/s]
0,3
0,2
0,1
0
Ertalon ® 6 SA
Ertalon ® 66 SA
Ertalon ® 4.6
Ertalon ® 66-GF30
Nylatron ® GS
Ertalon ® 6 PLA
Ertalon ® 6 XAU+
Ertalon ® LFX
Nylatron ® MC901
Nylatron ® GSM
Nylatron ® NSM
Nylatron ® 703 XL
Ertacetal ® C
Ertacetal ® H
Ertacetal ® H-TF
Ertalyte ®
Ertalyte ® TX
TIVAR ® 1000
PV-Values
[*] The limiting PV-values given in the graph refer to properly designed plastics-metals combinations with excellent heat dissipation
characteristics that operate continuously and without lubrication in a normal air environment of about 23 °C [e.g. a steel shaft rotating in a
thin walled plastics bushing with a length to I.D. ratio of max. 1]. Obviously, higher pv-values can be allowed in case of intermittent or
lubricated operation.
In many plastic bearing systems [sleeve-, slide bearings and thrust washers] it is the maximum occurring bearing temperature - which can
be assessed by means of the so-called PV-value - that sets a limit to the load capacity.
The PV-value is the product of the average bearing pressure P [MPa] and the relative velocity V [m/s] between the sliding partners. For a
given construction, this pressure-velocity rating determines the quantity of heat generated by friction and therefore the bearing temperature.
In order to obtain the longest possible and trouble free bearing life [without unallowable deformation, excessive wear or even melting], the
bearing temperature and hence the PV-value should not exceed a certain limit. This limiting PV-value is often reported as one unique
material property value although it varies e.g. as a function of speed and above all depends very much on the heat evacuation possibilities
of the bearing system at hand. Consequently, published limiting PV-values can only give the designer a rough idea about the pressurevelocity
capability of a plastics material. It is therefore often recommended to run a practical test under real operating conditions to assess
the fi nal suitability of a chosen plastics material for the given application.
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