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
|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|
|color||—||natural / black||black||grey||yellow|
moisture absorbtion at 23°C / 50% rF
|max. moisture absorbtion||Gew.-%||8.5||6.8||6.4||7.5|
|modulus of elasticity||MPa||1500||8000||7000||3500|
|max. static surface pressure (20°C)||MPa||20||100||80||60|
|max. temperature (long-term)||°C||80||130||120||90|
|max. temperature (short-term)||°C||120||190||180||170|
|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|
|specific volume resistance||Ωcm||>1013||>105||>1012||>1013|
|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.