What is mist lubrication?
Answer:
*Oil mist lubrication is used on literally thousands of pumps and electric motors in the U.S. petrochemical industry. This lubrication method has been demonstrated to reduce rolling element bearing failures by as much as 90%, thus offering significant technical and economic advantages over other lubrication systems.
*Oil Mist is a centralized system in which the energy of compressed gas, usually air taken from the plant supply, is used to atomize oil. Oil is then conveyed by the air in a low pressure distribution system to multiple points of lubricant application.
The compressed air is passed through a venturi. Oil, siphoned from a reservoir by the air flow, is atomized into a fine spray. Baffles downstream from the venturi nozzle causing the larger oil particles to coalesce and return to the reservoir. The remaining air-oil-mixture is Oil Mist. Oil Mist contains oil particles (droplets) averaging about 1-1/2 microns in diameter (.00006 inches), which can be conveyed through distribution piping (mist manifold), at velocities up to 24 feet per second, to application fittings (mist fittings which meter oil to bearing housings). Air-borne oil particles are then "wetted out" by impinging upon bearing surfaces rotating at sufficient speed to cause adherence and the formation of larger drop sizes. Because there are no moving parts in the basis Oil Mist generator system, and because the system pressure is very low (manifold pressures from 5 to 40 inches of water), it is a reliable lubrication method. Also, the system can be interlocked with machine operation or an alarm system to ensure proper functioning. Note that, even when malfunctions occur, most bearings will operate for hours on an existing film of lubricant.
*Advantages Of Oil Mist
This system is ideal in that a metered amount of oil (approaching optimum) can be provided to the bearing for proper lubricity. Lubricant friction itself is virtually eliminated. Keep in mind that grease is used only as a "carrier" for those oils within it which provide lubricity. Other than that, it is an impediment to rotation, causes frictional heat, can carry and recycle abrasive particles to the bearing, and doesn’t guarantee good dispersion (i.e., coating of all surfaces of the bearing at all times to prevent corrosion).
The oil mist provides a flushing action with fresh, clean lubricant and acts in a slight manner as a bearing coolant. The carrier air used to distribute the oil provides additional benefits in that it maintains bearing housings under slight positive pressure and the "outward" air flow prevents the entrance of contaminants. Where mist systems run continuously - and when motors are inoperative - problems with condensation reaching bearing surfaces are eliminated.
Maintenance "human factor" problems are reduced: Over-greasing, lack of replenishment of the proper grease and the right amount at the right time.
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