Friday, March 17, 2017

ELEMENT IDENTIFICATION AND EMISSION SPECTRA

The energy levels in atoms and ions are the key to the production and detection of light. Energy levels or "shells"exist for electrons in atoms and molecules. The colors of dyes and other compounds results from electron jumps between these shells or levels. The colors of fireworks result from jumps of electrons from one shell to another. Observations of light emitted by the elements is also evidence for the existence of shells, subshsells and energy levels. The kinds of light that interact with atoms indicate the energy differences between shells and energy levels in the quantum theory model of the atom. Typically the valence electrons are the ones involved in these jumps.
Atoms have two kinds of states; a ground state and an excited state. The ground state is the state in which the electrons in the atom are in their lowest energy levels possible (atoms naturally are in the ground state). This means the electrons have the lowest possible values for "n" the principal quantum number.
Specific quantized amounts of energy are needed to excite an electron in an atom and produce an excited state. The animation shows the opposite of excitation. It shows how the excited hydrogen atom with an electron in the n = 3 shell can release energy. If the electron in hydrogen only drops to the n = 2 shell the energy matches a pulse of red light.
Note the size of the electron cloud in the excited atom changes when the electron moves from shell to shell. The size of the atom decreases in volume when the electron goes from the n=3 shell to the n = 2 shell. On average the electrons are closer to the nucleus for lower values of "n". The electron cloud is related to the most probable distance between the nucleus and the electron. The most probable distance increases with increasing "n" value. The excited electron is still "in" the atom even in an excited state. The valence electron will only escape the atom if the electron is given an amount of energy equal to the ionization energy for that atom

Friday, February 27, 2015

Sources of Wear Metals in Lube Oil Analysis

Sources of Wear Metals in Lube Oil Analysis

Iron (Fe)
Iron is the most common of the wear metals, present in some form in virtually all equipment. Its widespread presence means that there are many sources of wear particles. Because of this knowledge, the metallurgy of the component allows the analyst to distinguish the source of the wear debris , e.g. cast Iron bolts Vs Stainless steel lube oil piping.

Equipment
Wear Metal Sources
Engines
Most common of the wear metals. Engines : cylinder liners, piston Ring, valve train, crankshaft ,rocker arms, spring gears , lock washers, nuts  , pins, connecting rods engine blocks oil pump.
Bearings
Rolling element Bearings; rollers (tungsten alloyed steel), raceways and cages, journal bearings journal shaft.
Gears
Bull gears, Pinions , case hardened teeth  locking pins
Transmission
Gears, bearings, brake bands, clutch, shift spools, pumps power take off
Hydraulic system
Pump, motor, vanes, pump housing ,cylinder bores and rods servo valves, piston
Compressors
Rotary Screw lobes, vanes connecting rods, rocker arm bearings, cylinders, housing, shaft, roller bearings.
Turbines
Reduction  gear, shaft bearings piping ,case.

COPPER
Widely used as an alloying element , copper is prized because of its material properties – very ductile, and excellent thermal and electrical conductivity. It is heavy used in bearing systems, as well as heat exchangers.

Equipment
Wear Metal Source
Engines
Valve train bushing , wrist pin bushings , cam bushing , oil cooler core, thrust washers, governor, connecting rods bearings, valve gear, train thrust buttons
Bearing
Rolling  element Bearings : alloyed element in cages, journal bearings Journal bearing pads, slinger rings , locking key
Gears
Bushing , thrust washers
Transmission
Clutches , steering discs, bearing
Hydraulic  system
Pump thrust plate, bushing , cylinder gland guides, pump pistons , oil coolers
Heat Exchangers
Cooler tubes , baffles , plates
Compressor
Bearings , cylinder guides , wear plates, thrust washers , bearings , oil pump , oil coolers thermostats , separator filters
Turbines
Bearing , Piping , cooler

TIN (Sn)
Tin is used an alloying element with copper and lead for sacrificial bearing liners.

Equipment
Wear metal Source
Engines
Valve train bushing , wrist pin bushing , cam bushing , oil cooler core, thrust washers , governor , connecting rods bearings , valve gear train thrust buttons
Bearing
Rolling element bearing : alloyed element in cages , Journal Bearings : Journal bearing pads
Gears
Bushing
Transmissions
Clutches, steering , disc, bearing
Hydraulic System
Pump thrust plates, bushings, can be residue from catalyst in some oils
Compressive
Bearings, Separator filter
Turbines
Bearing , Piping , coolers

Aluminium (Al)
Aluminium is valued in equipment because of it high strength to weight ration, and excellent corrosion resistance, alloyed with other elements improves its wear and temperature resistance. It is widely specified for equipment manufacturing now a day.

Equipment
Wear metal Sources
Engines
Engine blocks, pistons, blowers, oil pump bushings, Cabushing , Oil coolers
Bearing
Rolling element bearing : alloyed element in cages, locking key
Gears
Bushing , thrust washers, grease contamination
Transmission
Bushings, clutches
Hydraulic system
Cylinder glands pump, motor pistons , oil coolers, aluminium complex grease contaminant.
Heat exchanges
Cooler tubes, baffles, plate
Compressor
Housing ,bearing, cylinder  guides, wear plate, thrust washers, bearing , oil pump , oil coolers
Turbines
Bearing , piping coolers EHC systems, residue from synthetic media

Chrome (Cr)
Chrome is used as an engineering material for its great hardness and corrosion resistance. It is found in many systems operating under harsh conditions.

Equipment
Wear metal Sources
Engines
Rings, liners, exhaust valves , zinc chromate from cooling system inhibitor
Bearings
Rolling element bearing: alloyed /coated element in rollers, tappers
Gears
Bearing , shaft coatings, some special gears are chrome plate
Transmissions
Bearing, water treatment
Hydraulic system
Cylinder liners , rods , spools
Heat exchangers
Cooler tubes , baffles , plates
Compressors
Housing bearings, cylinder guides , wear plates , thrust washers, bearing , oil pump , oil coolers
Turbines
Shaft coating bearing

 Lead (Pb)
A soft metal used for sacrificial wear surfaces such as journal bearings .lead based babbits are widely used.

Equipment
Wear Metal Sources
Engines
Main bearings, connecting rod bearings. Lead can be present as a contaminant from gasoline improver , anti - knock
Bearings
Rolling element bearing : alloyed element in cages, journal bearing : major alloying element in babbit bearings , alloying element
Gears
Bearing , can also be red lead paint flakes from gear case walls
Hydraulic System
Bearing
Compressor
Bearings
Turbines
Bearing

Silicon (Si)
Silicon is the most common contaminant found in lube oil analysis. Abundant in all areas send is a very hard crystalline material, and very abrasive to metal components.

Equipment
Wear metal source
Engines
Engines blocks , ingested dirt from breathers, external source , can also be from defoamant additive in lubricant.
Bearings
Rolling element bearings: alloyed element with aluminium an cages
Gears
Bushings, thrust washer, silicone sealant , defoamant  additive
Transmissions
Brake shoes , clutch plates ingested dirt
Hydraulic system
Elastomeric seals pump , motor pistons, oil coolers
Heat exchanger
Coolers tubes, baffles , plates
Compressors
Ingested dirt, silicon sealant , bearings , cooler
Turbines
Ingested dirt, silicone sealant  defoamant additive



Silver (Ag)
Silver has exceptional thermal conductivity, and is an excellent bearing plate material , providing minimum friction . It is susceptive to corrosive attack by zinc – based additives,and so railroads ensure that they receive zinc free oil if they run EMD locomotives, Silver is used more outside of the US in general industrial equipment

Equipment
Wear metal source
Engines
Valves, valve liner , cylinder liner bearings
Bearings
 Rolling element bearings : alloyed element in rollersa , raes
Gears
Alloying element for tool steel gears
Hydraulic system
Bearings, servo valve plating pumps
Compressor
Bearings
Turbines
Bearings, shaft , reduction gears

Metallic additives

Several other elements are detected with oil analysis. The major elements found are listed here:

Element
Possible Sources
Sodium
Corrosion, inhibitor additive, also indicates coolant leak into oil, can be road salt, sea water, ingested dirt.
Boron
Corrosion inhibitor additive, anti wear/antioxidant additive ,can indicate coolant leak , grease contamination
Magnesium
Detergent/dispersant additive can also be alloying element in steel
Calcium
Detergent/dispersant additive, alkaline , reserve additive, for high sulphur fuelled engines , can be grease contamination
Molybdenum
Solid /liquid anti wear additive, alloy in bearing and piston
Barium
Corrosion inhibitors , detergents ,rust inhibitor
Zinc
Anti wear, corrosion inhibitors , anti – oxidants , alloying element for bearings , thrust washer galvanized cases
Phosphorus
Anti wear , corrosion inhibitors, anti – oxidants additive , EP additive


                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

Friday, February 20, 2015

RDE Atomic Emission Spectrometer for Lube oil Analysis

Rotrode type Atomic Emission Spectrometer for lube Oil Analysis:

Introduction

For the past forty years or so, spectrometric analysis of used oil samples has been applied as a machine health monitoring technique (the terms condition monitoring and predictive maintenance are more commonly used today). Spectrometric analysis determines the elemental concentration of various wear metals, contaminants, and additives present in a used oil sample. Results are usually reported in ppm (parts per million). Commercial oil analysis laboratories report on as many as 32 different elements.Atomic emission spectroscopy was relied on to provide an insight into abnormal wear rates, even though the technique was known to have decreasing sensitivity as particle size increased.

Particle Size Limitation of Spectrometers
What is not widely appreciated is that spectroscopy is more-or-less blind to the larger particles in an oil sample, precisely those particles which are more indicative of an abnormal wear mode. Most severe wear modes such as spalling, severe sliding wear, and cutting wear generate large particles which go undetected by spectroscopy. Large contaminant particles are also missed by spectroscopy. The particle size at which spectrometers begin to lose their detection ability depends on a number of factors including spectrometer make and type, but it is generally agreed that spectrometers lose their ability to detect particles in the 1 to 10 micrometer range. For purposes of this note, particles larger than 10 micrometers will be called large.

SPECTROMETERS MEASURE ONLY VERY SMALL PARTICLES AND DISSOLVED MATERIAL IN OIL

Consequently, spectrometer readings increase steadily between oil changes because, unlike large particles, small particles and dissolved material are not captured by filters, nor do they settle out easily in piping or tanks.

Traditional Methods of Determining Large Particles

Acid Digestion Method

Acid digestion methods have been developed whereby the particles in an oil sample are filtered and then dissolved using such acids as hydrochloric, nitric, and hydrofluoric. The resultant sample is then processed very carefully in a specially prepared spectrometer. This expensive and hazardous method has proven too costly for regular use in predictive maintenance.

Microwave Digestion Method

Microwave digestion methods are in use developed whereby the particles in an oil sample are collected and then dissolved with microwaves in a specially designed autoclave. The resultant sample is then processed very carefully in a specially prepared spectrometer. This method does provide a total concentration of elements in the sample, but it is expensive and time consuming. Like the acid digestion method, you do not know the ratio of large and small particles in the original sample.

Rotrode Filter Spectroscopy

RFS (Rotrode Filter Spectroscopy) was developed to provide an improved spectroscopic method for analysis of used oils for condition monitoring/predictive maintenance without the particle size or metal-type limitations of previous combined spectrochemical and DR ferrographic techniques.
This patented method uses a rotating disc electrode spectometer, known as an RDE spectometer, already in use in many military and commercial laboratories which perform spectrographic oil analysis

Method

·         In the RDE spectrometer, a graphite carbon disc is pressed onto the end of a shaft which rotates causing the disc to rotate.
·         In the normal use of this spectrometer, a quantity of oil is poured from the sample bottle into the sample bottle cap and positioned so that the bottom of the rotating disc passes through the oil.
·         A spark gap is formed between the top of the rotating carbon disc and the tip of the carbon rod electrode.
·         An electric discharge across the gap vaporizes the oil which has adhered to the rotating disc. The light emitted contains wavelengths characteristic of the elements in the oil sample.
·         The spectrometer optics and electronics quantify these wavelengths and report in ppm of up to 20 elements in 30 or 40 seconds. The carbon discs are known as rotrodes.
  
Preparation Station

The rotrodes are porous/Graphite carbon discs and this characteristic makes them ideal filters. A fixture has been designed to to clamp the discs so that oil can be drawn through the outer circumference of the discs when a vacuum is applied to the inside (hub) of the discs. The particles in the oil are captured by the surface of the rotrode. The oil is then washed away with solvent, the disc is allowed to dry, and the particles are left adhered to the rim of the rotrode in just the right position to be vaporized and detected when the rotrode is "zapped" in the RDE spectrometer. The sensitivity of the method is excellent. A multi-station fixture is used so a number of samples can be filtered at once. The procedure is fast and economical to perform. It is an ideal screening test for analytical ferrography.


Advantages of Technique

·         The technique has several advantages which make it a powerful predictor of equipment failure. Most abnormal wear modes cause a significant increase in concentration and size of wear particles. Using porous graphite rotrodes as a filtering media, large particles are captured and subjected to RDE (Rotating Disk Emission) Spectroscopy to obtain a multi-elemental analysis. These captured coarse particles are measured essentially independently of fine and dissolved particle contaminants in the sample. Removal of the used oil from the spectroscopic analysis reduces the energy required to vaporize the sample. This, in effect presents a more concentrated particle sample to the plasma produced during the RDE spectroscopy, and lead to greater sensitivity of the instrument.
·         By combining such large particle results with conventional RDE analysis of the dissolved and fine particles in the oil sample, a complete wear analysis picture for a machine of interest can be obtained. After seven years of applying this new technology in our lab, we and our customers are convinced of its powerful diagnostic capability.
·         Rotrode Filter Spectroscopy is fast and efficient, and is used as a standard screening test for every oil sample entering the lab.
·         The large particle data will flag abnormal wear modes at a very early stage, indicating when an analytical ferrogram should be made, and be of great benefit in defining the metallurgy of the wear particles.
·         The data is also excellent for contamination analysis as it will give elemental composition of large contaminant particles( such as silicon). The nice feature of this is that you may determine whether the element is sourced from an addtive package (such as a silicone polymer for defoaming) or a contaminant(sand/dirt particles)