The only time I have seen a semi fluid grease used in a gearbox was a service type that included an operating environment that was quite hot. In a steel mill for instance it is not unusual to see specialized machinery in an environment that could approach process temperatures. These temperatures are often 250ºF to 300ºF (120ºC to 150ºC). At normal room temperature these greases are semi-solid but at the operating temperatures become liquid. Do some research by looking up "drop point".

semifluid greases are often used in (small) gearboxes that are not oiltight and where the loading is such that heat dissipation is not much of a issue.

the semifluid grease has a composition just like other greases: a thickener, a basefluid and often some additives.

the term "semifluid" is somewhat misleading - although the "semifluid grease" has a high penetration value it is nonetheless a grease which means that the flow properties differ substantially from a "real" fluid.

quote:

Originally posted by darwinred:
Hello guys,
anybody can give me an advice what is the difference of oil and semi fluid grease to be use in gearboxes, I only experience using oil not in semi fluid in the gearbox.

Best regards,
Darwinred

Semi-fluid means an oil with soap thickener that results in a fluid between grease and oil. There is a wide range of properties between grease and oil so it's hard to generalize much.

Semi-fluids are helpful when the lubricant must flow more than grease but oil leaks too much.

There is another kind of lubricant I've seen called semi-fluid - this was a food grade gear oil with a highly viscous EP additive package. The EP additives were formulated for performance but the semi-fluid properties were a side effect. When operated in a drive that did not fully churn the oil, the thicker EP additives would collect in the quiet part of the sump and make full oil changes very difficult.