MOUNTING AND FITTING (continued) _____________________________________________________________________
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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 (see preload
section on pages 31-32).
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|
| 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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