MOUNTING AND FITTING (continued) _____________________________________________________________________
|
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).
|
|
| 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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