Wear Debris Analysis
As a supplement to oil analysis, ALS Tribology Division offers wear debris analysis services. There are several analysis methods available.
Analytical FerrographyAnalytical Ferrography utilizes a skilled analyst examining a prepared ferrogram slide with a computer-aided microscope to identify the composition of the material present in a used lubricating oil sample.
Wear material and other debris suspended in a lubricant is deposited and separated onto a ferrogram slide maker. The sample is diluted to improve particle separation onto the ferrogram slide. Magnetic separation of wear material from the lubricating fluid attracts ferrous particles out of the oil onto the ferrogram slide maker. Though the method is biased to ferrous material, other nonferrous wear particle and contaminants are also captured and identified. The slide is examined under a microscope to distinguish composition, morphology, particle size, and relative concentration of the ferrous and non-ferrous wear particles. Treatment of the ferrogram with heating and chemicals will further distinguish identification of the metallurgical composition of the wear material.
The skilled analyst performs the analytical ferrography to provide a root cause for wear mechanisms based on the morphology and composition of the particles. The analyst will report material composition and wear morphology that will include, but is not limited to:
- Ferrous wear particles
- High alloy steel
- Low alloy steel
- Dark metallic oxides and cast iron
- Red oxides (rust)
- White nonferrous metal particles
- Yellow metals wear particles
- Contaminants, dirt (silica), fibers and other particulates
- Fatigue wear
- Sliding wear
- Cutting wear - abrasive wear
- Adhesive wear
- Corrosive wear
Filter Patch Test (FPT, filtergram or patch test)A common method for making a detailed determination of wear occurrence, especially for non-ferrous materials, is to employ a Filter Patch Test examination using a microscope for wear particle analysis. A measured portion of used oil is filtered through a filter patch. Trapped wear particles and debris are then visually examined microscopically for a qualitative report. Observation will generally be accompanied by a photo of the filtered wear material on a test report. The debris is assessed and the particles graded. The FPT can tell us a number of things:
- Is there abnormal wear taking place?
- Is the wear ferrous or non-ferrous?
- Is there any evidence of abrasive contaminants e.g. dirt?
LaserNet FinesSome of our ALS Tribology laboratories employ Lasernet Fines instrumentation, which was developed by Lockheed Martin with the Naval Research Laboratory for military application. Using direct digital imaging Lasernet Fines, test results classify particles larger than 20 micron into cutting wear, severe sliding wear, fatigue wear, and nonmetallic material. The analysis economically combines features of particle count determination with quantifying wear particle classification for industrial, gear and drivetrain components without subjective interpretation.
The test data complements other wear analysis techniques by using laser imaging and advanced image processing software to identify and measure:
- Type of wear mechanism
- Rate and severity of wear processes
- Wear particle size distribution
- Particulate contamination and oil cleanliness
Data Reported Wear mode statistics for particles >20 um, which include:
- Cutting wear, size range number/ml, mean size (um), maximum size (um)
- Severe sliding wear, size range number/ml, mean size (um), maximum size (um)
- Fatigue wear, size range number/ml l, mean size (um), maximum size (um)
- Nonmetallic particles, size range number/ml, mean size (um), maximum size (um)
Particle counting and industry cleanliness codes include:
- Particle ISO Cleanliness Rating for >4, >6, >14 micron
- Maximum Particle Size
- Mean Particle Size
Particle Quantifier Index (PQI)The Particle Quantifier is a magnetometer that measures the mass of ferrous wear debris in a sample and displays this as a PQ Index. Test results are quantitated as a relative number of ferrous material within a sample; this can then be trended for useful wear monitoring. PQI is a simple, cost-effective test that can easily be incorporated into routine trending analysis.
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