MACHINERY LUBRICATION- INDIA NOVEMBER-DECEMBER 2019 | Page 17

MLI
Comparisons of Operating Temperature Ranges for Different Lubricant Base Stocks
GROUP I
POOR
MODERATE
GROUP II & GROUP III
BEST
POOR
MODERATE
BEST
OXIDATION AND THERMAL STABILITY
LOW VOLATILITY
HYDROLYTIC STABILITY
ADDITIVE SOLUBILITY
BIODEGRADABILITY
LOW-TEMPERATURE BEHAVIOR
HIGH VISCOSITY INDEX
SEAL COMPATIBILITY
LOW COST
MAXIMUM OPERATING TEMPERATURE
200 ° F 93 °C
resistance, as well as the dropping point
that it imparts to the grease. It is
recommended to use a grease below its
dropping point to ensure the lubricant
stays in place. See the sidebar on page
30 for a few simple rules to help
determine the maximum operating
temperature based on a grease’s
dropping point.
High-temperature
Operation
A lubricant’s operating temperature will
depend on several factors, such as the
heat produced in and around the
machine. Heat may also be generated
as a result of normal or abnormal
conditions. Normal or expected
conditions would include the machine’s
environment (production process and
climate conditions), mechanical work
realized by the machine, the combustion
action in internal combustion machines
and the internal fluid friction of the
lubricant. Abnormal conditions would
consist of an unusual mechanical issue,
excessive loads or speeds, lubricant
viscosity that is too low or high, and a
deficient insulating material.
MAXIMUM OPERATING TEMPERATURE
250 ° F 121 °C
Reasons for Choosing a
High-temperature Lubricant
Before beginning the lubricant selection
process, it is important to consider the reason
a high-temperature lubricant is desired or
required. For instance, it may be a requirement
of the original equipment manufacturer
(OEM). This means a particular brand or lubri-
cant type has been tested by the OEM with
approved results. In many cases, this is a
condition for warranty, so it is advisable to use
the recommended lubricant type. Also, always
verify the operating conditions to ensure they
are consistent with what is expected by the
OEM.
Another reason a high-temperature
lubricant might be chosen is because of
an abnormal machine condition.
However, while a better performing
lubricant may help mitigate the
problem, it is more imperative to
POLYALPHAOLEFIN (SYNTHETIC)
POOR
MODERATE
BEST
OXIDATION AND THERMAL STABILITY
LOW VOLATILITY
HYDROLYTIC STABILITY
ADDITIVE SOLUBILITY
BIODEGRADABILITY
LOW-TEMPERATURE BEHAVIOR
HIGH VISCOSITY INDEX
SEAL COMPATIBILITY
LOW COST
MAXIMUM OPERATING TEMPERATURE (CONTINUOUS)
270 ° F 132 °C
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