التحاليل المستخدمة لقياس جودة زيوت التزليق والزيوت المعدنية(luberication oil analysis

Spectroscopy

Spectrographic metals analysis is usually the 'heart' of most oil analysis programs.

Using either a Rotrode Emission Spectrometer or an Inductively Coupled Plasma Spectrometer (ICP), 20 or more metals can be simultaneously determined.

The metals analyzed for include wear, additive, and contaminant metals and are reported in parts per million (ppm).

MRT Laboratories uses a Rotating Disk Emission Spectrometer.

The instrument is quick and easy to operate and is accurate within acceptable limits.

The Rotrode Spectrometer has a particle size detection limitation of between 3µ and 10µ (depending on the particular metal in question and the amount of surface oxidation on the particle surface) compared to the .5µ - 2µ limitation of the ICP.

Results of the Rotrode Spectrometer are accurate to about 1 or 2 ppm.

Results of the ICP are accurate to .1 ppm.

The advantage of the Rotrode Spectrometer is that no dilution of the sample is required, while the advantage of the ICP is its accuracy.

With proper sample preparation, an ICP can measure in the 10's of parts per billion (ppb).

Particle size limitations of an ICP are even more sever than a Rotrode Spectrometer because the sample and particles have to be nebulized.

If measuring very low concentrations, the diluent (usually diesel fuel) has to be at least as clean.

For routine lube oil analysis, accuracy below the 1 ppm level is not required.

The results are very trendable from sample to sample if the sampling interval doesn't exceed every three months and proper sampling procedures are adhered to.

موضوع: Viscosity/Viscosity Index السبت فبراير 09, 2013 2:26 pm

Viscosity/Viscosity Index

Viscosity is defined as a measurement of resistance to flow and is a KEY physical property of lubricants.

Industrial lubricating oils are generally measured at 40° C and results are reported as centiStokes (cSt).

Engine Oils are most often measured at 100° C.

Most industrial lubricating oils are classified by their viscosity.

For example, an ISO Viscosity Grade 32 (ISO VG) will have a viscosity of 32 cSt @ 40° C, ± 10%.

Engine oils are classified by their Society of Automotive Engineers (SAE) grade.

SAE 20 or SAE 30 for example.

Engine oils often have additives that give them multi-grade characteristics, such as SAE 10W40.

This refers to the oil that has the viscosity characteristics of an SAE 10 oil when it is cold, and the viscosity characteristics of a SAE 40 weight oil in normal temperatures.

Viscosity of oils is inversely proportional to temperature.

Viscosity is determined by measuring the time it takes for a liquid to flow between two sensors on a glass tube immersed in a constant temperature bath.

The fluid is allowed to reach bath temperature (usually 40 deg C) before the analysis is performed. The tube is calibrated using NIST Traceable viscosity standards.

Viscosity increases are normally a result of lubricant oxidation and degradation or contamination with a higher grade oil.

Viscosity decreases are almost always a result of contamination, either with fuel in the case of engine oils, or product in the case of industrial oils.

Viscosity Index is a calculated number that indicates the rate of viscosity change as the lubricant is heated.

The less the change, the higher the Viscosity Index number.

The lubricant's viscosity is determined at two different temperatures, usually 40° C and 100° C, and using an API formula, the Viscosity Index is calculated.

Viscosity indexes of 95 to 105 are normal for most industrial mineral oils.

Severely hydro-cracked base stock and PolyAlphaOlefin (PAO) synthetic base stock have much higher viscosity indexes, usually in the 120's to 140's.

Diester synthetic base stock on the other hand has a low Viscosity Index, around 76.

موضوع: Neutralization Number السبت فبراير 09, 2013 2:36 pm

Neutralization Number

As lubricants degrade from oxidation they form a number of acids.

These acids are corrosive to Babbitt, yellow metals, carbon steel, cast iron, and if left uncorrected for a period of time will begin a corrosion process and possibly eventual bearing failure.

While small increases in the Total Acid Number (TAN) usually indicate oxidation and lubricant degradation, contaminants with acidic constituents can also be a factor.

Monitoring the oil's Total Acid Number should be an important part of your lubricant maintenance program.

Generally when a lubricant's acid number reaches a condemning limit, replacement or sweetening is your best option.

Total Acid Number (TAN) is the standard neutralization number test for industrial lubricating oils.

It is performed by titrating a solution of oil and diluent with an alcohol/potassium hydroxide (KOH) solution, a base, until all the acids present are neutralized.

The results are reported as milligrams of potassium-hydroxide per gram of sample, or mg/Gm

Strong Acid Number (SAN) is similar to TAN, except the 'strong' acids are first extracted from the lubricant.

That extract is then titrated with KOH and the SAN reported as mg/gm.

Total Base Number (TBN) is a standard test for engine lubricants.

It is a measurement of the amount of protection in the lubricant remaining to neutralize acids formed as a result of combustion.

A solution of oil and diluent is titrated with an alcohol/Hydrochloric Acid (HCl) solution until all the alkaline or base constituents in the oil are neutralized.

Results are reported as milligrams of HCl per gram of sample, or mg/gm.

Most lubricating oils have a baseline Acid Number as a result of additives.

R&O (rust and oxidation) industrial oils generally have a baseline in the 0.03 to 0.06 mg/gm range.

AW (anti-wear) and EP (extreme pressure) industrial oils will have much higher baselines because of the additional additives that give them their AW or EP qualities.

Baselines for these lubricants can be over 1.0 mg/gm.

Karl Fischer Water Titration

Water is the most common contaminant found in lubricating oils.

It is also one of the most damaging to bearings and other lubricated components.

It causes corrosion to metal surfaces, lubricant degradation, and poor lubrication.

Water can be present in three forms in lubricating oils:

Dissolved:

There is a limited amount of solubility of water in oil which is very temperature dependant. At 120° F, about 100 ppm of water can be dissolved in oil.

Dissolved water is not harmful nor does it affect the appearance or performance of the lubricant.

Emulsified:

Water and oil can form tight bonds that are difficult to break.

This form of water in oil is what causes oil to become milky and is the most harmful.

Oil will begin to become 'milky' at about 150 - 300 ppm, depending on the base stock and additive in the lubricant.

Free Water:

These are free water droplets, often suspended in the lubricant due to surface tension.

This form of water in oil is also very harmful to lubricated parts, but is also the easiest to separate.

Often free water is routinely drained from sumps and reservoirs.

The ability of the oil to separate from the water is an important characteristic of the lubricant in many applications, such as steam turbines and centrifugal compressors.

The Karl Fischer Water Titration is the only suitable test for determining how much moisture is present in a lubricant at levels less than 500 parts per million (0.05%).

Depending on the procedure used, accurate results can be obtained down to the 4 or 5 parts per million (ppm) level.

Karl Fischer Water Titrations will determine the total amount of water present, regardless of the form it is in.

A portion of the sample is injected into a reaction vessel that contains an electrolyte which reacts with water molecules.

The reaction produces a charge across a measuring electrode.

The change in the electrical charge across the electrode is directly proportional to the amount of water that reacted with the electrolyte.

Results are reported as ppm water.

Moisture in gases, semi-solids, and even ground solids can be accurately measured. Different sample methodology can be employed depending on the amount of accuracy required.

موضوع: Flash Point السبت فبراير 09, 2013 2:55 pm

Flash Point

The Flash Point of an industrial lubricant is an important test to determine if light-end hydrocarbons are getting into the oil through seal leaks or other means.

It is an effective way to monitor seal performance in light end hydro-carbon compressors.

Low Flash Points pose a safety hazard in the event of component failure than can generate heat above the flash point of the oil, such as bearing failure.

The Flash Point of most ISO VG 32 R&O mineral oils are in the 370 - 390° F range.

Generally, the more viscous and the more additives in the oil, the higher the Flash Point.

A typical automotive or diesel engine oil will have a Flash Point in the 425 to 460° F range.

The test is conducted by slowly heating a sample of lubricant.

Directly above the sample container is an ignition source, either an open flame or spark source.

As the sample heats, the light-ends boil off and form flammable gasses.

When there is enough gas built-up to be ignited by the ignition source, the gases will flash.

The temperature at which the oil was heated to when this occurs is called the Flash Point. It is reported in degrees F or degrees C.

If you continue to heat the sample after the flash point has been reached, eventually the oil will sustain a flame.

This is known as the Fire Point and again reported as Degrees C. or F.

The Fire Point is generally 10 or 20 degrees F above the Flash Point.

If you remove the ignition source and heat the lubricant, eventually it will auto-ignite.

This is called, you guessed it, the auto-ignition point.

These are generally in the 750 to over 1000 degrees F. range.

موضوع: Direct Read Ferrography السبت فبراير 09, 2013 3:02 pm

Direct Read Ferrography

This test is particularly useful for gearbox and reciprocating equipment samples.

Usually, 1 ml of sample is mixed one to one with a diluent.

This solution is then gravity flowed through a glass tube that is nestled over a strong magnet at a slight upward angle to the flow direction.

Two light paths are located along the base of the glass tube, spaced about 1/4 inch apart.

The magnet will pull out of suspension ferromagnetic particles and deposit them along the bottom of the glass tube in both light paths.

Larger, more ferromagnetic particles (generally from 0.1 to over 300 microns) will be pulled out first and are 'measured' in the first light path.

Smaller, less ferromagnetic particles (generally considered to be 0.1 to about 5 microns) will be deposited along the initial third of the glass tube, and are measured in the second light path.

( The measurement actually consists of how much attenuation of transmitted light is measured at the beginning of the sample flow against the transmitted light at the end of the sample flow due to the build up of particles in the light paths.

The first light path measure the Ferro Direct Read Large (FDRL) because most of the large ferromagnetic particles will be deposited in this light path, and the second light path will measure the Ferro Direct Read Small (FDRS) because few of the larger ferromagnetic particles will be deposited in this light path.

The values obtained are converted into empirical numbers that range from 0.0 to 180.0. Some laboratories will provide higher numbers by using dilution methods with small sample volumes.

The relation between the FDRS and FDRL is sometimes indicative of the type of problem that exists.

If the FDRL/FDRS is greater than 2.0, this may indicate a higher than normal number of large particles and as such, a more severe wear situation.

The sum of the FDRS and FDRL is also an indication of how much wear is occurring. These numbers are usually very trendable over time for a given sample point.

One important variable is non-ferromagnetic particles that gravity alone pulls out of suspension.

Particles such as sand, fibers, lacquer particles, and even water droplets will be 'seen' in the light paths and reported in the "Ferro Direct Read" results.

This variable limits the reliability of using the FDRL/FDRS relationship and the sum of the FDRS and FDRL in determining the amount and severity of wear.

MRT Laboratories uses this test as a back-up to Emission Spectroscopy.

the Rotrode Emission Spectrometer can only 'see' particles up to about 10 microns.

Many wear modes will create numerous large particles that may be missed by the Emission Spectrometer.

Just as important, contaminants such as sand, fibers, and lacquer particles will not be 'seen' by the emission spectrometer, but will be 'seen' the the Direct Read Ferrography test.

The Direct Read Ferrography test will not indicate what the particles are, but that can be determined microscopically.

Particle Count Analysis (ISO 4406)

Maintaining lubricant cleanliness is KEY to increasing component life, increasing lubricant life, and reducing costly routine maintenance.

Clean, dry lubricants will improve machine performance and longevity.

Small particles in the lubricant, those at or near clearances, cause abrasion wear.

Large particles can cause fatigue wear.

Particles in the lubricant will increase lubricant degradation rates.

Particles in hydraulic control systems will degrade hydraulic functions or even cause performance failures.

Particles in other hydraulic systems will cause abrasion wear and hydraulic leaks.

In extreme cases, particles can partially clog oil ports and result in lubricant starvation to vital machine components.

Excessive particles in your turbine, compressor, pump, blower, motor, or other equipment lubricants or hydraulic oils are indicative of a problem that $1 worth of medicine may prevent $100 worth of cure.

You can see why it is so essential to monitor the cleanliness of you lubricants either with Direct Read Ferrography in the case of gear boxes and reciprocating equipment or Particle Counts in the case of most other equipment.

This test is performed using an automatic laser light particle counting instrument.

A laser light beam is shown through a constant flow rate stream of oil.

As particles entrained in the oil pass through the light beam, the attenuation of the transmitted light as seen by a sensor is measured versus time.

Using the flow rate and the attenuation versus time curve, particle size can be determined and counted using an algorithm.

The algorithm is unique to each brand or model of instrument and is usually proprietary.

The number of counts for given size ranges are then classified according to an ISO 4406 Standard.

Originally the results were reported as classes of > 5 microns and > 15 microns. Later, the > 2 micron size class was added to account for silt laden samples.

As technology and calibration techniques improved, a new standard for calibrating automatic laser particle counters was established, ISO 11171 and a new classification Standard was developed, ISO 4406.1999.

The new standard using the new calibration standard reports the results in classes of > 4, > 6>, and > 14 microns. (See ISO 4406 chart)

The new standards have not yet been universally adopted.

MRT Laboratories can provide Particle Counts in either standard.

While a particle Count Analysis will not indicate what the particles are, it will indicate the need for further analysis, usually microscopic particle analysis to determine not only what the particles are, but help determine where they came from, how to clean up the lubricant, and how to prevent them from re-occurring.

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