DODGE
ENGINEERING
B20-19
Plummer Blocks
Sleeve Bearings
SLEEVOIL
Take-Up Frames
Engineering
Part Number Index
Keyword Index
Expansion of Shafting
Provision should be made to permit the free movement of
shafting endwise due to temperature changes. One bearing
should serve as an anchor bearing to locate the shaft endwise.
All other bearings should permit the shaft to move freely
endwise.
The anchor bearing is often located near an important wheel. On
long shafts it should preferably be located near the center of the
shaft to keep the expansion of the two ends to a minimum. If the
anchor bearing is babbitted it should be fitted with collars. If it is
an anti-friction bearing it should be of the non-expansion type,
which is the designation of DODGE roller and ball bearings for
use as anchor bearings.
All bearings on the shafting other than the anchor bearing
should permit the shaft to move freely endwise. If babbitted
there should be no thrust collars. If anti-friction these bearings
should be of the expansion type.
Several shafts firmly fastened together expand as if one
continuous shaft. An example of this is line shafting with flange
couplings. If the expansion is considered excessive a long line
shaft may be split into two or more sections, the sections being
connected with expansion couplings.
Amount of Expansion to be provided for-
The amount of shaft expansion is given in Table 25 below.
For example, with a 100°F temperature rise on a 150 ft. line
shaft with the anchor bearing located 70 ft. from one end and
80 ft. from the other end the ends will move .529” and .605”
respectively away from the anchor bearing. The structure
supporting the bearings may also expand depending on heat
exposure. Several cases follow:
Case 1
- Bearings supported on steel structures, where the
shaft and structure are exposed to the same temperatures, will
expand at the same rate. Expansion allowance is usually not
required. If the shaft is exposed to a higher temperature than the
support, allowances should be made. For example, if the shaft
temperature is expected to change 80°, and the temperature of
the structure 60°, the resulting movement between shafting and
support ends will be equivalent to a 20° change.
Case 2
- For bearings supported on wood, brick, or concrete
walls, or on piers with foundations in the ground, the amount
of expansion is usually considered negligible. Therefore, the full
amount of shafting expansion as calculated in Table 25 below,
may be accommodated.
Case 3
- Certain structural designs have built-in flexibility.
Where this is the case, expansion type bearings are not
necessary.
Case 4
- Short shafts with only two bearings are usually
designed without compensation for expansion, if temperature
variations are not excessive.
Advice on Expansion Problems-
DODGE power transmission engineers will gladly make
recommendations concerning shaft expansion problems and the
use of suitable bearings.
Table 25:
Linear Expansion of Steel Shafting
Base on Expansion In Inches = 0.0000063 x 12 x Length in Feet x Temp. Increase in Degrees Fahrenheit
Length
(Feet)
Temperature Increase-Degrees F.
Length
Temperature Increase-Degrees F.
20˚
40˚
60˚
80˚
100˚
(Feet)
20˚
40˚
60˚
80˚
100˚
1
.0015
.0030
.0045
.0060
.0075
40
.060
.121
.181
.242
.302
2
.0030
.0060
.0091
.0121
.0151
45
.068
.136
.204
.272
.340
3
.0045
.0091
.0136
.0181
.0227
50
.076
.151
.227
.302
.378
4
.0060
.0121
.0181
.0242
.0302
55
.083
.166
.249
.333
.416
5
.0076
.0151
.0227
.0302
.0378
60
.091
.181
.272
.363
.454
6
.0091
.0181
.0272
.0363
.0454
65
.098
.197
.295
.393
.491
7
.0106
.0212
.0318
.0423
.0529
70
.106
.212
.317
.423
.529
8
.0121
.0242
.0363
.0484
.0605
75
.113
.227
.340
.454
.567
9
.0136
.0272
.0408
.0544
.0680
80
.121
.242
.363
.484
.605
10
.0151
.0302
.0454
.0605
.0756
85
.129
.257
.386
.514
.643
12
.0181
.0363
.0544
.0726
.0907
90
.136
.272
.408
.544
.680
14
.0212
.0423
.0635
.0847
.1058
95
.144
.287
.431
.575
.718
16
.024
.048
.073
.097
.121
100
.151
.302
.454
.605
.756
18
.027
.054
.082
.109
.136
110
.166
.333
.499
.665
.832
20
.030
.060
.091
.121
.151
120
.181
.363
.544
.726
.907
25
.038
.076
.113
.151
.189
130
.197
.393
.590
.786
.983
30
.045
.091
.136
.181
.227
140
.212
.423
.635
.847
1.058
35
.053
.106
.158
.212
.265
150
.227
.454
.680
.907
1.134