Slide bearings - fitting instructions

SKIFFY bearings are manufactured to comply with DIN h6-H7 fitting. This means that the diameter of the hole into which the bearing is fitted is the same or larger than the stated size, and the shaft diameter is smaller than or the same as the stated bearing diameter. With this fitting, the bearing should sit firmly in the bearing housing, while there shouldn't be a tight fit between the bearing and shaft. After all, the shaft must be able to rotate in the bearing, but the bearing must not rotate in its housing.

In order to achieve this fit, the properties of the plastic are taken into consideration and the bearings are made slightly larger than the size stated in the catalogue. The outer diameter is larger so that it fits firmly in the housing (interference fit). The inner diameter is a little larger so that there won't be a tight fit between shaft and bearing when the nylon has absorbed water (clearance fit). Nylon always absorbs water, even from the air. This is necessary for its proper resilience and strength, and in doing so it expands a little.

When fitting, some force will be required to press the bearing into its housing. The bearing should then sit firmly in its housing. The bearing as a whole is then compressed, so the inner diameter is smaller. Only then, AFTER FITTING, does the bearing have the correct size. It has an interference fit in the housing and 1% bearing clearance in the shaft diameter.

Physical properties chart




material 02 42 43 47
PA-66 PA-66 CF PTFE PA-66 GF PTFE PA-66 AF PTFE
series 008 / 008-1 / 103 008-2 / 103-1 008-3 / 103-2 008-4 / 103-3
General properties          
density g/cm3 1.14 1.31 1.40 1.23
color natural / black black grey yellow

moisture absorbtion at 23°C / 50% rF

Gew.-% 2.3 2.0 1.9 2.1
max. moisture absorbtion Gew.-% 8.5 6.8 6.4 7.5
Mechanical properties          
modulus of elasticity MPa 1500 8000 7000 3500
max. static surface pressure (20°C) MPa 20 100 80 60
tensile strenght MPa 60 160 150 90
Thermal properties          
relaxation temperature °C 70 90 80 70
max. temperature (long-term) °C 80 130 120 90
max. temperature (short-term) °C 120 190 180 170
min. temperature °C -40 -40 -40 -40
thermal conductivity W/m x K 0.24 0.6 0.23 0.24
coefficient of thermal expansion at 23°C K-1 x 10-5 10 12 9 9
Electrical properties          
specific volume resistance Ωcm >1013 >105 >1012 >1013
surface resistance Ω >1013 >104 >1012 >1012
Tribological properties          
coefficient of friction against steel (dynamic) 0.12 - 0.25 0.10 - 0.25 0.08 - 0.20 0.08 - 0.18
max. surface speed rotation m/s 0.9 0.9 0.9 1.5
max. specific load x surface speed (dry) MPa x m/s 0.08 0.35 0.30 0.22

All information is given in good faith but without warranty.
1) The performance of plastic bearings depends on interactions between load, lubrication, surface roughness, surface speed and temperature in specific applications.

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