GRWs product catalouge

Limiting Speeds
The maximum speed for a ball bearing in
operation is limited by various mechanical and
kinematic criteria. Narrow tolerances of
bearings and surrounding parts, special
measures regarding lubrication and type of
lubricant as well as special retainer materials
and designs generally have a beneficial effect
on the speed limit. The characteristical values
for speed given in the tables only apply to
specially set reference conditions. They
therefore only give an indication of the
relative speed suitability of the ball bearing.
Ask our technical support for more
information if operating conditions are
different.
The Kinematically Permissable
Speed n zul
The “kinematically permissable speed n zul ”
applies to ball bearings with contact seals
which do not have a thermal reference
speed n υr defined in the standard. It takes
into consideration the special conditions
resulting from the wiping contact between
ball bearing inner ring and seals. In principle
the same conditions as for the thermal
reference speed n υr otherwise apply.
The Thermal Reference Speed n υr
The reference conditions have been selected
in DIN 732-1 so that the “thermal reference
speed n υr ” is identical for both types of
lubrication: oil and grease. The essential
operating conditions are:
• Reference temperature of the ball bearing
on stationary outer ring 70 °C
• Reference temperature of the ball bearing
environment 20 °C
• Reference loading P r of the ball bearing 5%
of the static radial load rating C or
• Oil lubrication as oil bath lubrication with a
conventional mineral oil without EP
additives, with a kinematic viscosity of
12 mm 2 /s at 70°C
•Grease lubrication with a standard lithium
soap grease with a mineral base oil without
EP additives. The kinematic viscosity of the
base oil is 22 mm 2 /s at 70 °C. The grease
quantity is approx. 30% of the free space in
the ball bearing.
• Ball bearings with standard designs, i.e. with
standard accuracy, with standard radial play,
with non-contact closures.
• Ball bearing installed on a horizontal shaft
with a stationary outer ring and installation
dimensions and tolerances which do not
reduce bearing radial clearance.
The Permissable Thermal
Operating Speed n υ
The speed at which the average ball bearing
temperature reaches the permissable value in
real operating conditions is called the
“permissable thermal operating speed n υ “. It is
calculated from the thermal reference speed by
multiplying it with the factor “speed ratio f n ”
according to DIN 732-2: n υ = f n · n υr
Following the standard we use diagrams which
make calculating this factor far easier. The
different torque effects of oil and grease
lubrication are taken into consideration.
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