Getting misty
Building a successful total productive maintenance program with oil-mist lubrication

by Todd Kierstead

In order for an effective total productive maintenance (TPM) program to thrive, target equipment must be returned to and maintained in like-new condition.

Effective lubrication is essential to maximizing the life of rotating equipment such as pumps, motors, gear boxes and other moving equipment.

At a recent lubrication workshop, Drew Troyer of Noria Corporation said, "Industry rides on an oil film of about 10 microns."

One of the best methods by which that thin film is successfully created is oil-mist lubrication.

What is it?
Oil-mist lubrication is the process of distributing liquid oil in a moving air stream and delivering it directly to the surfaces to be lubricated.  The oil is atomized into the air, forming oil droplets 1 to 3 microns in size.  The resulting mist has the appearance of fog.

Turbulence created by the moving equipment causes these small droplets to coalesce into larger droplets, which then condense on the surfaces to be lubricated.

At the point of lubrication, the oil-mist is "wet out" on the rotating surfaces.  Small, precise quantities of lubricant are delivered to the moving surfaces, creating that thin film necessary to prevent metal-to-metal wear.

Compared to traditional wet sump lubrication, oil-mist offers substantial benefits.  These include reduced oil consumption, reduced bearing failures, lower bearing temperatures and continuous, controlled lubrication.

How is it applied?
Oil-mist has the versatility to be applied to bearings, gears, chains, and slides and ways.  The key to successfully applying oil-mist is the simple use of an appropriate application fitting to ensure that the proper quantity of oil is delivered to the rotating equipment.

The three major types of application fittings are mist, condensing and spray.

Mist fittings simply control the flow into a bearing housing or gearbox where the mist will condense on the rotating components.

Condensing fittings convert the oil-mist to liquid oil, which can be
applied to plain bearings.

Spray fittings convert the mist to larger particles by increasing the turbulence in the air stream.  Spray type fittings are used on gears, chains, and slides and ways.

How does this reduce bearing failure?
Oil-mist delivers a continuous flow of contamination-free oil to extend bearing life by reducing wear and preventing corrosion.

A positive pressure prevents contaminants, such as water or airborne particles, from entering the bearing housing.  This reduces corrosion and particle-induced wear.   Friction is also reduced since the bearing no longer is forced to push through the liquid oil in the sump.  Reduced friction lowers the overall bearing temperature by 40 to 50 degrees F (8 to 12 degrees C).

Who relies on oil-mist lubing?
Oil refineries around the world use oil-mist to lubricate thousands of pumps.  One oil refinery's internal study found bearing failures were reduced 11.5 percent (from 16.8 percent down to 5.3 percent) through such a lubrication system.

This automatic lubrication technology allows a greater focus on preventive maintenance techniques, such as vibration analysis and oil analysis, to predict and determine root causes of equipment failure.

Oil-mist lubrication is also applied to rolling mills and high-speed paper-making equipment, and has been successfully implemented on high-speed spindles and machine tools.

What about stray mist?
Not all of the oil-mist applied to a moving part is condensed and used to lubricate.  A small percentage exits the bearing housing as stray mist.

The Occupational Safety and Health Administration (OSHA) set a limit of 5 milligrams per cubic meter of oil-mist exposure.  This limit is mainly targeted at machine shops where CNC machines can send large quantities of oil-mist into the environment.

Not all oils are mistable.  Mist oils contain special additives which improve the atomization of the oil and maximize its ability to condense on rotating surfaces.  Using a true mist oil reduces the overall stray mist and maximizes the amount of oil available for lubrication.

What type of equipment is available?
Oil-mist systems are specially engineered for each unique application.  It is essential to know what type of equipment is to be lubricated and the size and number of the bearings to receive oil-mist lubrication.  The oil-mist generator is then sized to meet the requirements of the equipment.

Two examples are oil-mist systems designed to lubricate five to 20 points.  Oil reservoir capacities are one pint and one gallon.  The larger the reservoir, the longer the refill interval.

An oil-mist system designed for a hazardous location has the capability to lubricate the hundreds of points typically found in a petrochemical plant.

Conclusions
What are the important points to remember?
-- Effective lubrication is a vital component of a successful total productive maintenance program.
-- Oil-mist installation can reduce bearing failures by as much as 90 percent.
-- Oil-mist systems have few moving parts to maintain and require little attention.
-- Oil-mist systems allow greater focus on critical areas such as vibration and oil analysis, which can help predict equipment failures and improve uptime.

Todd Kierstead is a product manager for Alemite Corporation, a manufacturer of oil-mist lubrication systems.

This article appeared in the April/May 2000 issue of MRO Today magazine.  Copyright, 2000.

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