1.9 Lubrication and
Surface Finishes
Rolling contact bearings have to be lubricated in addition to having
exceedingly good surface finishes.
The life of a rolling element bearing depends to a large extent on the
smoothness of the contacting surfaces – the balls, rollers, and races. Typical
surface roughness dimensions for production bearings are as follows:
These are in terms of microinches or millionths of an inch, usually
written min.
The unit of measurement of the surface roughness is rms which stands
for "root-mean-square height". This value is obtained by drawing a diamond point
instrument over the surface with a magnified readout. These measurements are taken at
equidistant points on the profile, squaring these values, adding them, dividing the sum by
the number of readings taken and taking the square root of this average.
There are calibrated specimens available and surface roughness can be
established by comparison to the specimen.
Surface finishes of bearings vary considerably from manufacturer to
manufacturer. They are usually not given specifically for each product.
As far as lubrication is concerned, in general, the application
environment will usually dictate the proper lube required. Today’s lubrication
selection has varied greatly over the past few years. Modern methods of mixing,
compounding and blending various additives and bases has become a very exact science, a
far cry from late 1940 when almost all lubricants were a refined petroleum product.
Operational conditions such as temperature, loads, speed, environment
and torque available, will determine what type should be used – oil, grease or dry
films. Oil fluid is the base lubricant for nearly all bearings, whereas grease is an oil
that has been thickened. The use of lubrication will reduce friction and wear, prevent
corrosion or oxidation and help to prevent heat buildup within the bearing. Other benefits
that result from proper lubrication are quietness, lower torque and extended life.
Lubrication selection is very important to good bearing performance. The following tables
of lubrications shown are the most widely used by bearing users today. Due to the constant
change of product demand and scientific technology, we recommend that a QBC engineer be
consulted if you cannot locate a suitable lubrication in the following charts.
Unless otherwise specified by the customer, QBC will supply bearings
with an oil lubrication meeting military specifications (MIL-L-6085A) or grease meeting
(MIL-G-23827A).
The numbering system developed by QBC incorporates a lubrication code. This gives the
user an opportunity to specify the lubricant required as per Table 1-10. In case the code
numbers
 
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