OIL MIST LUBRICATION
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28-09-2010, 05:40 PM
History Of Oil Mist Lubrication 1 (Autosaved).docx.doc (Size: 128.5 KB / Downloads: 112)
The Oil Mist principle was developed by a bearing manufacturer in Europe during the 1930s. The problem that nurtured this development was the inability to satisfactorily lubricate high-speed spindle bearings on grinders and similar equipment. In 1948, oil mist was brought to the United States in the steel industry. Since'the late 1950% oil mist has been servicing rotating equipment 'in the refining industry. The first use of oil mist in the petrochemical industry was in the Gulf Coast due to the high humidity and condensation resulting in bearing failures. The speed of these bearing was too high for grease lubrication, and liquid oil generated too much heat through fluid friction, necessitating an expensive recirculating system. Continuous thin-film lubrication with Oil Mist provided a solution. The purging and slight cooling effects of the carrier air gave additional benefits. The Oil Mist generator resulted later from this development and used a small amount of air to produce a dense concentration of small oil particles. About 97% of these particles could be transmitted to the bearings without condensing in the piping, regardless of the distance of the bearings from the Oil Mist generator itself.
In 1958, air heaters were developed because it was discovered that, by heating the air used to generate Oil Mist, oils of just about any viscosity could be atomized. Many applications, subject to extremes in ambient temperature, use air heaters to ensure a constant oil/air ratio regardless of the oil viscosity. Today Oil Mist is still used to lubricate high speed spindles in grinders. Included in the increasing range of Oil Mist applications are systems applied to all types of other machine tools, web and sheet processing equipment, belt and chain conveyors rolling mills, vibrators, crushers, centrifuges, kilns, pulverizers, ball mills, dryers and liquid processing pumps.
Oil Mist is an aerosol with an appearance of smoke or fog. Oil Mist systems are made up of several simple but effective components, which can supply the proper lubrication for electric motor bearings. The main components of an Oil Mist system are the generator head or venturi, reclassifiers, vents and drains. Passing high velocity air over an orifice that pulls oil into an air stream creates the oil mist.
Later the technology was extended in a limited fashion to the petrochemical industry. Initial applications were for process pump lubrication. A great deal of caution was exercised with the new technology and while progress was made, it was slow. Experience in recent years has shown that many of the early concerns were not really applicable and that oil mist lubrication is a very efficient and reliable method for attaining optimum bearing life.
WHAT IS AN OIL MIST SYSTEM AND HOW DOES IT WORK?
Oil mist is formed of oil particles from 1.0-3.0 microns suspended in an air current, consisting of 1 part oil to 200,000 parts air. This mixture is not a volatile organic compound (VOC); therefore there is no risk of explosion or combustion. There are two main oil mist applications, pure mist for lubrication and purge mist for preservation. The equipment and its operating conditions determine the type of mist application that should be used. Due to its advantages, whenever possible, pure mist is recommended to lubricate rotating equipment.
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.