Oil Mist Lubrication System

An oil mist lubrication system is a widely used bearing lubrication. A centralized lubrication system generates and automatically delivers the lubricant to machinery bearings to keep them lubricated for making moving parts reliable. The fine mixture of oil and air that is generated is called oil mist. Oil-mist lubrication ensures a high standard of lubrication as and when required and prevents the ingress of contaminants to the bearing housing.

Various Types of Lubrication

• Splash Lubrication
• Grease Lubrication
• Forced Lubrication
• Solid Lubrication
• Mist Lubrication

Oil Mist System is a means of generating and transporting a finely dispersed oil mist from a central location to individual bearing housings.

• The oil mist system uses compressed air to atomize oil into micron-size particles which can be effectively moved to lubrication points up to 600 feet (180 meters) through Pipes & Tubes
• One Oil Mist system can provide lubrication to 60 pumps and their drivers with approximate oil consumption of one gallon (3.8L) of oil per 24 hours.

Typical Oil Mist System

Refer to Fig. 1 which shows a typical oil mist lubrication system used for industrial applications.

Types of Oil Mist Lubrication Systems

The oil mist lubrication system can be categorized into the following types.

• Open Loop System (Fig. 2)
• Closed-Loop System (Fig. 2)
• Dry Sump (Pure Mist-Fig. 3)
• Wet Sump (Purge Mist-Fig. 3)

Pure & Purge Mist Lubrication

Pure Mist Lubrication System-

• The bearing is lubricated by oil mist, not oil.
• Bearings can run 10-15 degC cooler with pure mist as compared to sump lubrication.
• The bearing housing is pressurized by continuous oil mist flow, then external contaminants (dust, moisture…) are excluded.
• Centrally controlled hence attention to oil level is not required individually.

Purge Mist Lubrication System-

• The bearing is lubricated by oil, not oil mist.
• The bearing housing is pressurized by continuous oil mist flow, then external contaminants (dust, moisture…) are excluded.
• Here mist purges the bearing housing and provides partial fresh Makeup oil.
• Oil levels must be checked and maintained for each piece of equipment.

Fig. 3 below shows typical pure and purge mist lubrication systems.

Components of Oil-Mist Lubrication Systems

The major components of the oil-mist lubrication system are listed below:

• Oil mist generator- the heart of the oil mist lubrication system, compressed air is passed through a venturi or vortex to produce the oil-mist mixture.
• Oil mist cabinet-Stainless steel cabinet.
• Reclassifiers- Controls the mist flow to applicable points. Bearing type, shaft speed, and diameter dictate the sizing of reclassifiers.
• Air- Clean and Dry air free from toxic, corrosive, and flammable elements.
• Air Filter at the air inlet.
• Air regulator to control supply air pressure
• Air Pre-Heater-For cold climates to maintain the air temperature

While selecting the oil for an oil-mist lubrication system, the following factors need to be considered:

• Oil Viscosity at the operating temperature
• Pour point
• Surface tension
• Solidification tendency of the oil at low ambient temperatures

How does oil mist Lubrication lubricates the bearing?

The following figure (Fig. 4) shows the working of the oil-mist lubrication system to enhance bearing life.

Mist Lubrication Suitability

• Rolling element and sliding contact bearings can be lubricated with Oil Mist either Pure or Purge type.
• Oil mist is used to lubricate rolling element bearings of all types. Ball & Roller bearings are generally applied with Pure Mist Lubrication.
• When sliding contact bearings are used, oil mist alone does not provide complete lubrication & hence, an oil level is maintained in the bearing housing and is called Purge Mist Lubrication.

Advantages of Oil Mist Lubrication System

Oil mist lubrication system offers various advantages over the other lubrication systems as listed below

• Prevent the dust/moisture ingress into bearing housing, due to the pressurized system
• Increased Bearing Life
• Lower friction and thus reduced bearing temperatures
• Reduced maintenance, reduced handling, and spillage.
• As the bearings operate in a thin film of oil, so less power is required.
• Reduced Oil consumption (40% less & 50% of it can be recovered)
• More environmentally friendly than the conventional lubrication system.
• As the oil on the bearings is always new, it provides better lubricant properties.
• In technical papers released by end-users and bearing manufacturers, as well as in university research, bearings lubricated with oil mist have a longer life than bearings lubricated with oil sump or grease. Users report from a 50% to 90% reduction in lubrication-related bearing failures.
• Finally, it is economic to use.

Disadvantages of Oil Mist Lubrication System

Even though mist lubrication systems have various advantages and reduce maintenance and operating problems, still there are a few disadvantages of this system such as

• Relay on Instrument Air System
• LSC is the single vendor of the Oil Mist System for Hydrocarbon Processing Industries
• An oil mist system is almost trouble-free but it cannot be installed and forgotten. Systems should be checked daily for correct air and oil temperature, oil level, and mist header pressure along with other weekly and monthly maintenance programs.
• The oil-mist lubrication system involves environmental hazards. OSHA requirement states that a person shall not be exposed to more than five milligrams of oil per cubic meter of air in an eight-hour period.
• The performance of the oil mist lubrication system is sensitive to temperature.