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In This Issue:

• Up Front: Air Intake Neglect Means Lubrication Disaster

• Book Bits: How Oxidation Changes Oil

• Today's Tip: Water Contamination and Viscosity

• Q & A: Understanding Particle Count Reports
  

Up Front

Air Intake Neglect Means Lubrication Disaster

A major bus operator in Zimbabwe, Africa was short of maintenance funds. To solve the problem, he considered sacrificing air intake systems maintenance because he thought its impact on overall maintenance costs was negligible.

When he encountered huge maintenance costs as a result of engine seizures, he blamed it on the poor quality of oil he was using.

Random oil samples from his fleet unveiled a serious problem. Oil was heavily congested with dust and wear metals well before it was due to be changed.

Further investigations - including that of storage, craftsmen, bus drivers and physical air intake inspection - concluded the following:

• Air filters were not being changed or even blown. - Air intake hoses had holes and missing clips.

• Buses had no power due to clogged air filters. Drivers had to by-pass filters, meaning direct intake of dusty air into the engine.

• Maintenance schedules were haphazard and overextended without basis for their effectiveness.

Although the cost of refurbishing the air intake systems was high, the bus company is now experiencing extended engine life and reduced maintenance costs. (Submitted by Edwin Chamanga, Lubrication Engineer, Mobil Oil Zimbabwe. Thanks Edwin!)

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Book Bits

How Oxidation Changes Oil

From "Proactive Maintenance for Mechanical Systems":

Once the oxidation process occurs, five major changes in the oil result in the following:

1. Color becomes darker - changes from transparent or translucent in color to some degree of discoloration toward the point of complete opacity.

2. Odor becomes pungent and acetic due to the presence of excessive organic petroleum acid and similar products of oxidation.

3. Acidity increases - changes from a neutralization number from 0.06 to 0.12 KOH mg/g to well above 2.0 can occur.

4. Viscosity increases - the viscosity of an oil frequently may double or triple due to oxidation. Oxidative thickening is capable of producing fluids that have the consistency of molasses-like sludge under high operating temperature conditions.

5. Insolubles precipitate (sludging occurs) - after an induction period, the deterioration of an oil gradually accelerates until the formation of organic acids or deposition of sludge completely destroys the oil.

More information about "Proactive Maintenance for Mechanical Systems".

Today's Tip

• It's important to understand what can happen to the viscosity of an industrial lubricant, such as hydraulic or gear oil, when it is contaminated with water. A common misconception is that the water will reduce the viscosity of the lubricant. In fact, if an excessive amount of water is "whipped" into the oil in such a way that it forms a stable emulsion, the viscosity can increase, sometimes dramatically so. The oil/water emulsion will not lubricate as well as clean, dry oil. Not only that, but the viscometrics of an emulsion are different than that of oil, so that other problems such as poor valve response or high pressure drops across filters can occur. (Submitted by Larry Cote, Reliability Specialist, DOFASCO Inc. Thanks Larry!)

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Q & A

Understanding Particle Count Reports

"What is the difference between the NAS and ISO standards for classifying fluid cleanliness via particle counting? How can I convert NAS based cleanliness limits to conform to the ISO standard?" - Charlie Bryant, Reliability Engineer, A.K. Steel/Siemens

There is actually no fully accurate way to convert limits between the 1964 NAS 1638 and ISO 4406:99 standards. The NAS standard assumes a fixed particle size distribution for the determination of a cleanliness class, whereas the ISO standard recognizes that actual particle size distributions depend upon the process that produces the particles.

The latest revisions of the NAS standard indicate that it should not be used with automatic particle counters but rather microscopic particle counts. It refers users to a newer standard, AS4059 (now in revision D). AS4059 addressed this issue while remaining true to the "feel" of NAS 1638. The size distribution issue is significant because certain size ranges tend to be of greater interest in certain systems. Look for Mike Day's article on NAS 1638 in the Nov/Dec issue of Practicing Oil Analysis magazine.

It is possible to roughly convert NAS limits to conform to ISO 4406:99. Assume the NAS size distribution is valid (which it may not be for filtered systems that remove most of the larger particles). Assume also that the 5 to 15 micron range is the common trigger for determining the NAS value. The following may then be used to convert limits:

Adam Davis, Technical Consultant, Noria Corporation

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