Page 15 - Industrial Technology EXTRA 19th July 2021

are used. Lubricating oils were traditionally refined as well when the machinery is running and the
from petroleum but today, there are a wide range of ambient temperature of the bearing increases.
synthetic oils, silicon oils and fluorinated When choosing a lubricant, the entire range of
compounds available to choose from. Grease, on temperatures at which the machinery will function
the other hand, is a semi-solid or solid lubricant and should be considered. Naturally, it is helpful if the
is simply an oil combined with a thickener and may lubricant consistency does not change too
include anti-wear, extreme pressure or antioxidant dramatically over its temperature range.
additives. The pour point of oil describes the lowest
Regardless of whether you use an oil or grease, temperature at which the oil will flow. When the
low temperatures can dramatically affect the temperature drops below the pour point, the oil will
effectiveness of a lubricant. Operating in reduced partially or completely solidify. This will either
temperatures results in higher viscosity, which can dramatically increase the bearing’s rolling resistance
restrict lubrication flow within bearings. Too high a or stop it from rotating altogether. When
viscosity can cause excessive friction and, in turn, establishing low temperature limits for greases, the
damage both the bearing and the machinery. pour point of the base oil is an important
consideration.
Temperature ranges The thickener in a grease acts as a sponge to
Lubricants have different optimum temperature ensure that oil stays securely inside the bearing by
ranges. While some low temperature lubricants may releasing and re-absorbing oil, allowing a lubricating
operate at sub-zero temperatures, they may not fare film to form at friction points. At temperatures near

July 2021 • INDUSTRIAL TECHNOLOGY EXTRA • p15