Support
Continued from page 61
CLEANING BEARINGS
From time to time, you may wish to clean bearings for
further use.
Except:
• Do not clean new bearings that you have taken from
unopened and undamaged factory packaging.
• Do not clean (except by surface wiping) any bearing with
integral shields or seals.
Cold cleaning: Wash in clean, white spirits or paraffin. Dry the
bearing and protect it against rust by applying oil or grease
immediately after drying.
Hot cleaning: Heat some thin, clean oil in a clean container
over a hotplate to 120°C maximum. The oil selected must have
a flashpoint of at least 250°C. Use a thermometer to determine
the temperature of the oil. Use clean, long-nose pliers to hold the
bearing in the oil. (This method is very effective.)
Dry immediately after cleaning, using a clean and lint-free
cloth. Do not use cotton wool. Apply grease only at the last
minute, immediately before you close up the bearing housing.
Whenever you apply force, always
apply it through a sleeve or similar
means to the ring that is being
moved. Never transmit force
through the balls.
FITTING OF BEARINGS – TIPS
Never transmit force through the rolling elements. Whenever you
apply force, always apply it through a sleeve or similar means to
the ring that is being moved. Never transmit force through the
balls. In other words, never apply pressure to one ring in order to
move the other. This is true whether a press, pulley, or hammer
and sleeve arrangement is being used.
The solution is not always as easy as is shown here.
Sometimes special tools or spacers are required, and often you
will have to do some thinking.
Never directly strike a bearing’s rings, cage, or rolling
elements. Apart from direct damage to the bearing, metal
chips could fly off and remain in the bearing. These will do
great harm.
Before starting to fit any bearing, confirm that it is the correct
size for the job. That includes any prefix or suffix that appears with
the basic number.
Ensure that the bearing is entering squarely onto the shaft as
you start to fit it.
www.hvacronline.co.za
COLD MOUNTING
Bearings of up to 55mm may be cold mounted onto a shaft. A
one-piece capped tool (sleeve or drift) should be used between
the hammer and the bearing. Check carefully that there is no
loose dirt or half-chipped pieces of metal on this tool. Use a
standard steel hammer. Soft-headed hammers tend to have
breaking fragments fly off. These could enter the bearing, which
is to be avoided. Do not hit a bearing directly with a hammer, as
this will cause damage to the bearing and may cause splinters of
metal to fly off at high speed, causing damage and possible injury.
PRESS MOUNTING
When cold mounting is being performed, it is always better
to mount a bearing using a hydraulic press, if one is available.
Bearings for a shaft size of up to 100mm may be mounted in
this way. Follow safe working practices/procedures when using
a press.
HOT MOUNTING (OIL BATH)
Cold mounting may only be performed on bearings of up to
100mm in diameter. Hot mounting is necessary for larger sizes.
Hot mounting entails heating the bearing, which expands,
allowing the bearing to simply be slid into the correct position on
a shaft. As it cools, the bearing will shrink and tighten on the shaft.
Sealed bearings, which are factory lubricated for life, may not be
fitted by using any heating technique.
The oil bath must have a thermostat controlling the maximum
temperature.
Procedure:
• Heat the bearing up to 110°C in order to fit it to the shaft.
Never heat any bearing to a temperature over 125°C. The oil
bath may contain an immersion heater, or it may be heated
over a hot plate.
• The oil bath must have a wire mesh to support the bearing
clear of the bottom and sides, and well clear of the
immersion element.
• The heated oil must freely flow around all parts of the
bearing to ensure uniform heating. Under no circumstances
allow the bearing to touch the heat source.
• Never be tempted to heat a bearing that is to be installed
with a flame. This is totally unacceptable.
• Do not leave a bearing unattended while it is being heated
in an oil bath.
HEATING USING AN INDUCTION HEATER
An alternative heating method that does not involve hot oil, is
an induction heater. This uses the principles of a transformer
to induce a group of eddy currents within the metal of the
bearing. This process will heat the bearing uniformly from within.
RACA Journal I January 2019
63