| Lubrication
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Functional properties of grease:
Advantages of Grease:
(1) Functions as a sealant to minimize
leakage and to keep out contaminants. Because of its
consistency, grease acts as a sealant to prevent lubricant
leakage and also to prevent entrance of corrosive
contaminants and foreign materials. It also acts to keep
deteriorated seals effective (whereas an oil would simply
seep away).
(2) Easier to contain than oil. Oil
lubrication can require an expensive system of circulating
equipment and complex retention devices. In comparison,
grease, by virtue of its rigidity, is easily confined with
simplified, less costly retention devices.
(3) Holds solid lubricants in suspension.
Finely ground solid lubricants, such as molybdenum disulfide
(moly) and graphite, are mixed with grease in high
temperature service (over 315C [599 F]) or in extreme
high-pressure applications. Grease holds solids in
suspension while solids will settle out of oils.
(4) Fluid level does not have to be
controlled and monitored.
Notable disadvantages of grease:
(1) Poor cooling. Due to its consistency,
grease cannot dissipate heat by convection like a
circulating oil.
(2) Resistance to motion. Grease has more
resistance to motion at start-up than oil, so it is not
appropriate for low torque/high speed operation.
(3) More difficult to handle than oil for
dispensing, draining, and refilling. Also, exact amounts of
lubricant cannot be as easily metered.
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