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  MOUNTING AND FITTING  

RELATIVE THERMAL EXPANSION


The effects of relative thermal expansions of different mating materials must also be taken into account when calculating final radial play values for an interference-fit assembly that will be used over an extended temperature range. Thermal effects must also be considered in a preloaded bearing assembly.

MATERIAL
LINEAR EXPANSION COEFFICIENT
ppm/oC
ppm/oF
Bearing Materials
DR/ES1
10
6
400 series stainless
10
6
52100 chrome steel

12

7

Other Materials
300 series stainless
16
9
Aluminum
23
13
Brass
19
11
Bronze
18
10
Copper
16
9
Invar
1
0.6
Iron
12
7
Lead
29
16
Nickel
13
7
Magnesium
8
4
Titanium
9
5
ABS
72
40
ABS (glass reinforced)
31
17
Delrin / Acetal
85
48
Epoxy
54
30
Epoxy (glass reinforced)
36
20
Nylon
81
45
Nylon (glass reinforced)
23
13
Polycarbonate
65
36
Polycarbonate (glass reinforced)
22
12


Example: SR144 bearing pressed on .125 inch aluminum shaft is used at 200°F
Initial interference at 70°F = .0004
Relative expansion of shaft at 200°F = .125 x (13 - 6) x 130 x 10-6 = .0001
Interference at 200°F = .0005
SR144 inner ring thickness .018 inch, therefore interference factor fp = .4
Reduction of radial play at 200°F = .0005 x fp = .0002






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