Lubricants

Lubricants type of between liquid, semi-solid and solid lubricants. To reduce friction and wear, lubricant must provide a good slippery surface. They

This section we can see different type between liquid, semi-solid and solid lubricants.

General Characteristics

To reduce friction and wear, lubricant must provide a good slippery surface. They must be able to get between the moving surfaces and fill in the surface roughness. In addition, the lubricant must stay between the surfaces. That means the lubricant must have the right consistency for the job. It must be thick enough to keep the surfaces lubricated and not run off, yet it can't be so thick that it causes problems itself.

Lubricants must keep their characteristics under a range of operating conditions. As rotating equipment works, there will be some heat generated. Heavy equipment causes pressures between the moving surfaces that change with the work load and with time. The speed of rotation can change as well as the flow of material being pumped. All these have an effect on the conditions of the moving surfaces. The right lubricant must be selected for each set of operating conditions.

Lubricants control contamination in one of two ways. In a flowing system the lubricant carries the contamination away from the moving surfaces. This flowing lubricant must then be replaced by other clean lubricant. That means the lubricant must be able to flow and be replaced by more of the same clean lubricant. Lubricants can also be used to protect moving surfaces from dirt by forming a barrier between the dirt and the surfaces. Lubricants are used to protect surfaces from oxidation or other corrosion. Lubricants can do this only if the lubricant itself doesn’t cause oxidation or corrosion.

Specific Characteristics

Equipment manufacturers determine the best type of lubricant for each piece of equipment they design. It’s up to you to follow those specifications when you lubricate the equipment. That means the right kind of materials and the right kind of lubricating procedures. To be sure you follow the specifications properly, you’ll need to know some terms describing specific lubricant characteristics. Those terms are: viscosity, viscosity index, pour point, flash point, and fire point.

Viscosity is the measure of a fluid’s resistance :o flow. In other words, viscosity is fluid friction. The thicker the fluid, the higher its viscosity. A lubricant's viscosity is affected by two physical conditions: temperature and pressure. The higher the temperature of the lubricant the lower its viscosity - the lubricant thins as temperature increases. Viscosity increases with an increase in pressure. As the load increases on bearing surfaces, the viscosity increases and works to keep the surfaces separated by the lubricant.

Viscosity Index. Viscosity Index is the measure of a lubricant’s change in viscosity because of a change in temperature. If viscosity changes by a large amount as the temperature changes, the viscosity index is small. If the viscosity changes a small amount with changing temperature, the lubricant has a high viscosity index.

Pour Point. Pour Point is the lowest temperature at which a lubricant will flow. Below that temperature the lubricant thickens so much that it doesn’t flow by its own weight. Pour point is particularly important if the equipment must run in very cold weather.

Flash Point. Flash Point is important when lubricants are working in higher temperatures. The chemicals in most lubricants will vaporize when they are heated to a high enough temperature. The higher the temperature, the more vapor given off. When enough vapor is given off so that it could ignite and burn, the flash point has been reached.

Fire Point. If the lubricant is heated above the flash point, enough vapor will be released to burn continuously. That’s called the fire point. A serious fire hazard exists when lubricants are heated above the flash point or fire point. If the equipment is being operated under heavy loads in a warm area, a lubricant with a high flash point will usually be specified.

Forms of Lubricants

Lubricants exist in three forms: liquid (oils), semisolid (greases), and solid (graphite).Most of the lubricants you’ll be using are liquids.

Oils. There are many different oils used in a typical production facility: turbine oils, steam cylinder oils, gear oils, automotive oils, heat transfer oils, metal cutting oils, and others. Each oil is specified because its physical characteristics are right for the job to be done. Some oils need to circulate through a closed lubricating system and are often used both to lubricate and transfer hydraulic pressure. General purpose lubricants sometimes have an additive to enable the oil to work under pressure. As an example, this type of oil is used to lubricate gears. When sensitive equipment such as measuring instruments need to be lubricated, a low viscosity oil called spindle oil is used. This oil can also be used to lubricate bearings on small shafts that are turning at a high rate of speed. In some cases, the fluid being pumped or circulated can be the lubricant itself.

Greases. Greases are used when the lubricant needs to stay in place for a longer time or when the operating temperature may be too high for oil. Greases are made from a liquid, usually oil, and some thickening agent, usually a form of soap. The soap acts as a reservoir for the oil.

There are several different types of thickeners used, including: sodium, calcium, lithium, and sometimes borium. The type specified will depend on the application, based on the need to resist water, operate under high temperatures or pressures, or work under varying speeds. The melting point or drop point of a grease is another important physical property. This is the temperature at which the grease turns to a liquid. If the grease liquefies, it will tend to flow away from the area where lubrication is needed and not do its job.

The stiffness or consistency of a grease is also important. If a grease is too stiff, it may be too hard to get into small areas. Too much stiffness may also cause excessive operating resistance and can be just as bad as the friction the grease is designed to overcome.

Solids. Solid lubricants are used in special applications, such as extremely high temperatures. Typical examples of solid lubricants are graphite and molybdenum disulfide. They can occur as a dry powder or suspended in water or oil. Solid lubricants are often used to coat the threads of nuts and bolts used at high temperatures. Solid lubricants are sometimes used as additives in petroleum lubricants. Solid lubricants should never be used in roller or ball bearings. A solid lubricant in this application would act like an abrasive and cause bearing wear.

Additives

Although the lubricants used today, especially the synthetic oils, are better than the fats and oils that were used years ago, they still cannot meet the requirements of modern equipment by themselves. Other chemicals, called additives, are used to improve the basic properties of a lubricant. They can help increase the life of the lubricant and make it work better under special conditions.

Some of the more common types of additives are :

Oxidation Inhibitors. These additives minimize the formation of varnish and sludge on metal parts by decreasing the amount of oxygen combining with the oil. The additive is usually oxidized instead of the oil.
Corrosion Inhibitors. The purpose of these additives is to form a protective film on metal surfaces and keep corrosive materials away from the surfaces.
Extreme Pressure Agents. The purpose of these additives is to reduce friction and wear and to prevent galling and seizing under extreme pressure conditions. Under extreme pressure, a chemical reaction causes the additive to leave a film on the metal surfaces. If pressure builds up so that the oil film is forced out from between the surfaces, the additive film keeps the surfaces from welding together.
Detergents. Detergents are added to lubricants to keep metal surfaces clean and prevent deposits.
Pour Point Depressors. The purpose of this additive is to lower the pour point of the oil. This helps the equipment operate at lower temperatures. That’s particularly important if the equipment must work outside in cold weather.
Foam Inhibitors. These additives are used to prevent foam or bubbles from building up in the oil. They're used in situations where the oil is subjected to a lot of churning action.
Viscosity Index Improvers. These additives reduce the rate-of-change of viscosity with temperature. They work by increasing the viscosity more at higher temperatures.
Emulsion Breakers. An emulsion is a mixture of oil and water that’s hard to separate. Water mixed with the oil reduces the effectiveness of the lubricant. Emulsion breaker additives make it easier to separate the water from the oil and keep emulsions from forming.

NEVER MIX DIFFERENT LUBRICANTS
The additives in one lubricant may not be compatible with the additives in another. When adding lubricant to a partially filled system, be sure to use the same type of lubricant - the one that’s right for that system.

• [accordion]
• 1. Lubricants
• 
• 2. Refining Used Lubricating Oils
• 3. Practical Lubrication for Industrial
• 4. Encyclopedia of Lubricants and Lubrication
• 5. Lubrication Tactics for Industries Made Easy (2020)
• 6. Design Aspects of Used Lubricating Oil Re-Refining
• 7. ASM_HANDBOOK_Vol_18,_Friction,_Lubrication,_and_Wear_Technology
• 8. IADC Vol-2 03 Lubrication