Mounting rolling bearings
Hot mounting Fig. 35
The requisite difference in temperature between
the bearing ring and shaft or housing depends
on the degree of interference and the diameter
of the bearing seat.
When heating bearings, temperature control
is essential:
Do not heat open bearings to more than
120 °C (250 °F).
Do not heat sealed bearings above 80 °C
(175 °F) because of their grease fill and/or
seal material.
For housings, a moderate increase in tempera-
ture, from 20 up to 50 °C (35 up to 90 °F), is
normally sufficient, since the degree of interfer-
Fig. 36
ence is seldom large.
Once a bearing has been heated, the objective
is to get that bearing in place, up against its
shoulder as quickly as possible and keep it there
until the bearing has cooled. To do this, SKF rec-
ommends using the SKF Bearing handling tool
and lifting tackle, especially when mounting
medium-size and large bearings († figs. 7 to 9
on page 50).
CAUTION: When mounting a bearing, never
strike it directly with any hard object such as a
steel hammer or a chisel, and never apply the
mounting force through the rolling elements.
To heat a bearing or housing to the proper tem-
perature quickly and safely, SKF offers a wide
assortment of heaters. The following is a listing
of available heating techniques and their typical Electric hot plates
uses. An electric hot plate († fig. 36) can be used to
heat small bearings or small housings. To pro-
CAUTION: Never heat a bearing using an open vide uniform heating, the bearings must be
flame († fig. 35)! turned over a number of times.
The SKF Electric hot plate is a thermostatic-
ally controlled heating device with an adjustable
temperature range of 50 to 200 °C
(120 to 390 °F).
CAUTION: Sealed bearings should never con-
tact the heating plate directly. Place a ring be-
tween the plate and bearing.
68
Hot mounting
Induction heaters Fig. 37
SKF recommends using an electric induction
heater († fig. 37) to heat rolling bearings.
Induction heaters heat bearings evenly within
a relatively short time and are particularly safe 2
because the heater and yoke never get hot.
Induction heaters will magnetize a bearing.
Therefore, it is important to demagnetize the
bearing prior to installation. All SKF induction
heaters have an automatic demagnetizing
device. They are available in several sizes for
heating bearings with a bore diameter from
20 mm and upwards.
Operating instructions are supplied with the
induction heaters.
Aluminium heating rings
Aluminium heating rings († fig. 38), originally Fig. 38
developed for dismounting the inner rings of
NU, NJ and NUP cylindrical roller bearings, can
also be used for mounting.
SKF aluminium heating rings are available for
bearing sizes 204 to 252, 304 to 340 and 406
to 430.
Operating instructions are supplied with the
rings.
69
Mounting rolling bearings
Heating cabinets Fig. 39
Heating cabinets are typically used when a
larger number of small bearings or a number of
bearings of different sizes as well as small hous-
ings have to be heated.
Suitable heating cabinets are equipped with
an adjustable thermostat and fan († fig. 39).
The fan circulates the heated air to maintain an
even temperature throughout the cabinet.
Infrared radiators
Infrared radiators provide a clean, safe and very
simple way to heat small, thin-walled housings.
The infrared radiator, encased in a screw cap is
placed in the housing bore and switched on. It
normally takes only a few minutes to sufficiently
heat the housing, because the interference fit
Fig. 40
between the housing bore and bearing is rarely
tight († fig. 40). After heating, switch off the
radiator, remove it from the housing bore and
quickly push the cold bearing into position.
70
Hot mounting
Heating panels Oil baths
Flexible heating panels are an excellent and safe Years ago, oil baths were a popular way to heat
solution for heating housings without compli- bearings and small housings. Today, this method
cated installations. They are made from several is no longer recommended due to economic, en-
flexible materials and available in a number of vironmental and safety reasons. However, 2
types and sizes († fig. 41). sometimes there is no alternative.
Heating panels suit individual heating needs, When heating a bearing in an oil bath, some
e.g. they can be used to cover the housing or basic rules must be followed. Only use clean oil
placed in the housing bore or as a flat bottom with a flashpoint above 250 °C (480 °F) and a
heater. clean receptacle with an adjustable thermostat.
Furthermore, the bearings or bearing rings
should never make direct contact with the re-
ceptacle. After heating the bearing and before
pushing the bearing into position on the shaft,
allow the oil adhering to the bearing to drip off
and then wipe clean the outside of the bearing.
WA R NING
Do not place large heavy bearings on the
heating panels as this could create an elec-
trical hazard and may damage the heating
elements.
Fig. 41
71
