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bearings
Bearings – fitting instructions
The Skiffy bearings are made to conform to 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 spindle 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 should be a little play between the bearing and spindle. After all, the spindle 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 advantage of 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 will still be play between spindle
and bearing when the nylon has absorbed water. Nylon will always absorb water, even from air. This is
necessary for its proper resilience and strength, and in doing so its 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 it 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 inner
bearing play is then 1% of the spindle diameter, as stated in the catalogue.
Material Table 1)
General properties
Density
Colour
Moisture absorption at 23ºC/50% rF
Max moisture absorption
Mechanical properties
Modules of elasticity
Max. static surface pressure (20ºC)
Tensile strength
Thermal properties
Relaxatie temperature
Max. temperature (long-term)
Max. temperature (short-term)
Min. temperature
Thermal conductivity
Coefficient of thermal expansion at 23ºC
Electrical properties
Specific volume resistance
Surface resistance
Tribological properties
Coefficient of friction against steel (dynamic)
Max. surface speed rotated
p x v value max. (dry)
Unit
008/103
008-2/103-1
008-3/103-2
008-4/103-3
g/cm3
Gew %
Gew %
1.14
black
2.3
8.5
1.31
black
2.0
6.8
1.40
grey
1.9
6.4
1.23
yellow
2.1
7.5
MPa
MPa
MPa
1500
20
60
8000
100
160
7000
80
150
3500
60
90
ºc
ºc
ºc
ºc
W/m x K
K-1 x 10-5
70
80
150
-40
0.24
10
90
130
190
-40
0.60
12
80
120
180
-40
0.23
9
70
90
170
-40
0.24
9
Ωcm
Ω
>1013
>1013
>105
>104
>1012
>1012
>1013
>1012
m/s
MPa x m/s
0.12-0.25
0.9
0.08
0.10-0.25
0.9
0.35
0.08-0.20
0.9
0.30
0.08-0.18
1.5
0.22
All information is given in good faith but without warranty.
1) The performance of plastic bearings depends of the interactions between load, lubrication, surface roughness, surface speed and temperature in specific applications.
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Skiffy_Catalogus_EX_66_index.indd 62
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16-01-13 13:33