Lubricants And Lubrications Flashcards
Why is lubrication necessary?
It is needed where friction is a problem and must be reduced as much as possible. Unwanted friction causes machine parts to wear out resulting in costly repairs.
What is a lubricant?
Any substance that reduces friction by creating a slippery film between two surfaces.
What is static friction?
The force that must be overcome to start one surface sliding over another.
Whats the primary purpose of lubricants?
The primary purpose is to reduce friction. Lubrication is merely a means of separating moving surfaces by providing a film for the surfaces to slide on.
What is dampening shock?
One of the six basic purposes of a lubrication. Thats is, a lubricant can help to absorb the metal to metal impacts that occur with mechanical motion. A lubricant converts mechanical impact into fluid motion in an effort to equalize pressure.
Whats a common way to cool oil in many systems?
Circulate the oil through an oil cooler. The oil cooler may simply have metal fins to radiate heat into the air, it could have a very complex counter flow heat exchanger.
What is a thin skin of grease sometimes called a scab or clot?
It is the small portion that is exposed to the air. It oxidizes just a bit and hardens a lil bit to seal the grease in place and keep dirt from entering the bearing.
What are the three origins of lubricants?
They come from animals, vegetables, or a mineral.
What is distallation?
When vapors pass through a condenser, the heat removal causes them to condense. That is, vapors cool off and become liquid again.
What are hydrocarbons?
Compounds made from molecules of approximately 85% carbon and 15% hydrogen.
What are the important properties of lubricating oils?
They are
Viscosity-thickness of the fluid low #=thin high #=thick greatly affected by temperature. Also resistance to flow.
Viscosity index- measure of rate of change of viscosity of an oil as the temp. changes. Ex. Oil operated at wide range of temp. or constantly switching temp. = high VI.
Flash point - point in temp of lubricants that is just before it will flash over to flame.
Fire point- point at which a lubricants vapor will constantly burn.
Pour point -the temp at which a lubricant will no longer flow. Operate in cold weather= low pour point
Oxidation resistance- ability to repel oxygen from the air when its exposed. Oil thickens and acids are formed that can corrode bearings made from certain materials.
Resistance to emulsification- emulsification is the process of stabilizing water oil/water mixtures in preparation for removal.
Aside from SAE (society of automotive engineers) what rating system applies to industrial lubricants in the US.
Saybolt seconds universal or SSU or sometimes SUS. Oil is heated in a tank, allowed to drain a certain amount within a given amount of time to fill a flask. The ratings are how many seconds it takes to fill the flask. 50 sec. = 50 SSU
When should greases be used instead of oils as a lubricant?
Greases are chosen when the frequent lubricant is not feasible or where an oil would easily leak,
What is the dropping point or melting point of a grease?
The point at which the greases changes form from a semicolon to a liquid, usually through heating of the grease.
Whats a grease made up of?
Usually a mineral oil thickened up with chemical compounds called soaps. Gives the grease its operating characteristics.
What’s an anti-foam agent?
It is an additive to lubricants that is made up of silcone polymers. They prevent the formation of bubbles or foam.they break the air bubbles that circulation in a lubrication system.
What is an extreme pressure or film strength additive?
Assist the oil in protecting metal surfaces from very high loads. Often found in gear lubricants, also cushion the shock that often occurs. Chemical reaction causes reaction with metal, creating a film of solid lubricant powder. It bears the extreme pressures better than the lubricant
