Lubrication - The Silent Component of MachineryWritten by Thomas Yoon
The function of a lubrication medium is:
1. To form a film between moving bearing components so that metal to metal contact is prevented. 2. To reduce friction and eliminate wear 3. To protect against corrosion 4. To seal against impurities like dust, dirt, water.
In order for oil film to be formed between moving bearing components, film must be sufficiently thick even under heavy load, high temperatures or vibrations.
Some sleeve bearings that has very heavy loads, like in crosshead bearings of diesel engines, usually have provisions for injecting pressurized oil to float shafts. This method is called hydrostatic lubrication.
However, most common method of lubrication for sleeve bearings is by hydrodynamic method. When two surfaces of a bearing and shaft move rapidly relative to one another, oil is carried along shaft to fill gap between shaft and bearing. When moving components become completely separated by a cohesive film of lubricant, hydrodynamic lubrication occurs. Hydrodynamic lubrication prevents wear in moving parts, as there is no metallic contact between them. The bearing metals can last for a long time.
During starting time, rotating shaft does not have sufficient speed to pick up lubricant. The film separating moving surfaces is very thin - with only thickness of a molecule. This is a condition called boundary-layer lubrication. With this condition, friction losses increases, producing heat, which raises temperature of lubricant, thereby reducing its viscosity so that load-carrying capacity of film is even lower. In worst case conditions, surfaces can even seize together.
Additives that Improve Lubrication OilsWritten by Thomas Yoon
Mechanical machines need lubrication. No machines can run for long without lubrication of its moving parts. At best, moving parts may wear out faster. At worst, entire machines can seize up and develop cracks. In severe conditions, heat built up can even cause explosions and loss of lives.
So lubrication is no small matter in machine operation.
Lubrication oil can last for a very long time in normal machine operation. By determining properties of lubrication oil, many machine operators will be able to know whether oil can still be used.
Some of important properties to watch for when buying or replacing lubrication oil is as follows:
Viscosity Viscosity Index Pour Point Oxidation Resistance Flash Point, Fire Point Alkalinity Additives
Some of additives that are put into lubrication oil include following:
Anti Oxidant - Amines, Phenols Corrosion Inhibitor Detergent and Dispersant - Ca, Ba, Compounds, Soaps Alkalinity - Ca, Ba Hydroxides Anti Bacterial - Biocides Oiliness or Wetting Agents - fatty oils, chlorinated wax Extreme Pressure Agents - organic compounds of Cl, S, P (for hydraulic, gear oil) Pour Point Depressant - Organic polymers (alkyl naphthalene) (for steering gear, refrigerator) Anti foam - Silicones Viscosity Index Improvers - organic polymers Emulsifying Agent - Polar Compounds (emulsifying but do not lose lubricating property)