Brochure

Mtd. Ball
Bearings
G-249
®
Mounted Ball Bearing Engineering Section
Sealmaster Gold Expansion Bearings:
Expansion bearings allow for linear shaft expansion or
contraction caused by temperature variations. Without this
expansion capability, bearings may be subjected to exces-
sive thrust loads and misalignment which could damage the
bearing, mounting surfaces, and frameworks. Sealmaster
offers two types of expansion (oat) bearings:
1. In Sealmaster Gold mounted units where the bearing
is installed into an AR ring then into a housing assembly
as shown on page G-29. This design allows the bearing
to move axially in the housing assembly. Table 4 below
shows the allowable expansion by size.
2. In Sealmaster Cylindrical O.D. bearings (ER style) and
some Sealmaster Gold mounted units expansion is
achieved by utilizing a special half-dog & wire and
keyway in the shaft by specifying a “HIY” sufx. The
bearing then oats along the shaft. Table 5 shows the
shaft slot dimensions required.
Notes:
•Before installation, make certain proper expansion
is accounted for. Expansion units should be placed in
a location where relative movement between the
bearing insert and the housing can be tolerated.
•When using an expansion bearing, always use a
xed bearing as the second support bearing.
•Half-dog setscrew and lock wire systems are not
recommended for high speed or vibration applications.
Application Engineering can be contacted for specics.
Only one half-dog setscrew should be used in this
arrangement. No other setscrew should be installed.
The half-dog setscrew’s nub is engaged within
the shaft slot, but not tightened into the shaft.
When shafting is heated, it grows longer. This growth in
shaft length is particularly problematic when shafts are long
and temperature differentials are large.
The difference in linear expansion between the shaft (shaft
length between bearing centers) and the bearing mounting
structure must be taken in consideration in high tempera-
ture applications. For example, in the case where the shaft,
bearings and bearing support structure are all in a heated
environment, the effect of thermal expansion on the bear-
ings can be insignicant (assuming that all components are
made of steel).
The shaft expansion concern arises when the shaft is in a
heated environment but the bearings and bearing support
structure are not. In this case the slot length in the shaft
should be machined so as to accommodate the amount of
linear shaft expansion.
Calculate the minimum slot length (
r L) as follows:
r L = α • X r TEMP
sys
Where:
r L = differential linear expansion (inches)
α = coefcient of thermal expansion (inch/inch/°F)
(α = 7x10
-6
inch/inch/°F for most carbon steel shafting)
(α = 1x10
-5
inch/inch/°F for most stainless steel shafting)
X = length of shaft (inches)
r TEMP
sys
= operating shaft temperature (°F) - installed shaft
temperature (°F)
B
r L
SM Gold Table 5
Bore Sizes Slot Width (C)
Min. Slot
Depth (B)
1/2 Dog
Point Dia. (P)
inch inch inch inch
1/2 to 1/4R 13/64 3/32 5/32
1 1/4 to 1 3/4 9/32 3/32 13/64
1 7/8 to 2 7/16 21/64 1/8 1/4
2 /12 to 3 7/16 21/64 1/8 19/64
3 15/16 to 4 33/64 3/16 15/32
r L is calculated below
SM Gold Table 4
Bore Diameter
Expansion
(inch)
Standard Duty Medium Duty
1/2 - 1 N/A 3/32
1 3/16 - 1 3/4 15/16 - 1 1/2 1/8
1 15/16 - 2 15/16 1 11/16 - 2 11/16 3/16
3 - 3 7/16 2 15/16 - 3 3/16 1/4
3 1/2 - 4 3 7/16 - 4 9/32
5 4 7/16 - 4 15/16 7/16
AR Ring