Analytical ferrography is a powerful lubricant analysis tool used to analyze the wear particles present in lubricating fluids. By identifying and quantifying the size, shape, and composition of the particles, analysts can gain a better understanding of the wear process taking place in machinery. You can use this information to improve machine performance and extend component life. But, to do so, it is helpful to have a deeper understanding of how analytical ferrography works and its benefits.
What is Analytical Ferrography?
In addition to being a useful technique for identifying the underlying causes of machine component failure, analytical ferrography also can predict potential equipment breakdowns. Analytical ferrography produces digital images of the actual particles present through a qualitative study instead of a quantitative one. The ferrous particles are then placed on slides for microscopic examination after being captured by strong magnets. The analyst examines particles for their metallic or non-metallic nature, heat-treated alloy, form, size, color, and source (if possible).
Analytical Ferrography vs. Direct Reading Ferrography
When you implement a lubricant analysis program, you may see that your lab offers two different ferrography options: Direct reading ferrography and analytical ferrography. Most in the industry agree that analytical ferrography is the more effective diagnostic tool of the two.
Direct reading ferrography uses magnets to separate wear particles and uses an optical method to count the number of large and small particles in your sample. This can help you understand the wear rate and its intensity and severity. It is possible to set baselines for machine wear and track trends using this method. Then, if the direct reading ferrography results suddenly increase, you can order a thorough analytical ferrography test.
Analytical ferrography more precisely identifies the cause and particular kind of wear by extracting, categorizing, and visually analyzing wear particles. Through the use of an optical microscope, this test can ascertain a particle’s size, concentration, color, form, and composition. All of this information is highly valuable to diagnose equipment and lubrication issues.
What Does Analytical Ferrography Tell You?
The objective of analytical ferrography is to prevent the accelerated wear that frequently precedes equipment failure by identifying the amount, size, and shape of wear particles by microscopic examination. Physical and chemical testing in addition to analytical ferrography can assist in detecting:
- The onset of abnormal wear
- Causes of wear and failure
- Which components are breaking down
- Remaining usability of lubricants
Lubricant particle contamination carries crucial information about the condition of machine parts. With analytical ferrography, you get to basically take a look inside your machine thanks to the following particle information:
- Concentration
- Shape
- Composition
- Size Distribution
The Exciting History of Analytical Ferrography
U.S. military aircraft were failing due to rolling element bearing fatigue in the late 1960s. To find wear particles in the lubricant at the time, the military used spectroscopic and ferromagnetic chip detectors. Both microscopic particles and the beginning of large particles, which can both signal serious wear, were not picked up by either of these systems. The airplane was already in danger of failing catastrophically when the particles were found.
The first ferrograph for used oil analysis was created when military officials contacted Vernon C. Westcott to develop the new technology. Both analytical and direct reading ferrography were created by Westcott and his colleagues. The trick was to develop a non-intrusive ferrography that examines the particles without shutting down the machinery to look for signs of mechanical wear.
Disadvantages of Analytical Ferrography
The testing process is tedious and requires the expertise of a qualified analyst. As a result, analytical ferrography has substantial costs that are higher than other oil analysis tests. However, the majority feel that the advantages greatly outweigh the expense. After understanding what analytical ferrography can reveal, it is a must-have whenever you notice excessive wear.
How Does it Work: General Particle Identification
After heating the slide for two minutes at 600ºF, the analyst divides the particles into six categories according to composition. The categories are as follows:
White Nonferrous Particles
Both before and after heat treatment of the slide, nonferrous particles appear as bright white particles. Larger particles get collected against chains of ferrous particles as they deposit randomly across the slide surface. In most cases, the chains of ferrous particles serve as filters, catching contaminants, copper particles, and babbitts.
Copper Particles
Before and after heat treatment, copper particles usually appear bright yellow, but their surface may change to verdigris. Furthermore, bigger particles will sit at the entrance point of the slide and gradually get smaller as the slide proceeds toward its exit point.
Babbitt Particles
Babbitt particles consisting of tin and lead, are gray and occasionally have speckling before being heated. These particles are still predominantly gray after heating, but with some blue and red spots on the surface. Additionally, these particles tend to become smaller after being heated. Again, these nonferrous particles don’t form chains with the ferrous particles; rather, they show up on the slide at random.
Contaminants
Typically, contaminants like dirt and other particulates do not alter in appearance as a result of heat treatment. They can resemble white crystals and can be recognized by the transmitted light source because they are slightly translucent. On the slide, contaminants occur at random and often by chains of iron particles.
Fibers
Fibers found in oil samples are usually from filters or outside contamination. They show up as long strings that allow light to pass through. In most cases, they do not change in appearance after being heated. These particles can sometimes act as filters, collecting other particles. While they can appear anywhere on the ferrogram, it tends to be towards the exit end where they wash out.
How Does it Work: Ferrous Particle Identification
In some cases, large ferrous particles will clump together at the entry end of the slide. Microscopes use reflected light to identify ferrous particles, as they completely block light transmission. These five categories identify the various ferrous particles:
- High Alloy Steel – On the slide, the particles are found in chains and are gray-white both before and after heating. Position on the slide serves as a defining characteristic in the differentiation between high alloy and white nonferrous. It is most likely high alloy if it is white and in a chain. Otherwise, it is white nonferrous. Ferrograms with high alloy content are uncommon.
- Low Alloy Steel – These also appear in chains and initially have a grayish-white appearance before changing color when heated. They typically appear as blue particles after being heated, though they can also be pink or red.
- Dark Metallic Oxides – Before and after heat treatment, these deposits form chains and are dark gray to black. The level of oxidation can be determined by how dark it is.
- Cast Iron – Particles have a gray appearance before heating and a pale yellow appearance after heating. They mix in with the other ferrous particles on the slide.
- Red Oxides or Rust – Analysts quickly identify red oxides using polarized light. They can occasionally be discovered in chains with other ferrous particles or randomly deposited on the slide surface. A significant buildup of tiny red oxides on the slide’s exit end indicates corrosive wear. Typically, the analyst sees it as a “beach” of red sand.
The analyst first classifies the particle’s composition, and then, using a micrometer scale on the microscope assesses the particle’s size. Any particles over 30 microns warrant a severe or abnormal rating worthy of further inspection and corrective action.
Why Particle Shape Matters
Another crucial indicator of a particle’s origin is frequently its shape. Laminar particles are evidence of crushing or rolling typically in bearings, high-pressure locations, or areas with lateral contact. Additionally, surface striations are a sign of sliding wear often found where metal surfaces scrape. If the particle has a curved form like drill shavings, it signals cutting wear. Cutting wear is due to abrasive contaminants present in the machine. Lastly, spherical particles generally come from bearing fatigue cracks. An increase of spheres in your sample is a sign of spalling.
A Vital Component of Lubricant Analysis
One of the best diagnostic tools for oil analysis today is analytical ferrography. It offers a fantastic return on your oil analysis investment when properly executed. The fact that it is somewhat expensive and generally misunderstood as having little value, however, prevents it from being included in many oil analysis programs. A qualified analyst can depict the type, severity, and underlying cause of abnormal wear by analyzing the size, shape, color, magnetic light effects, and surface detail of wear particles. Maintenance can take appropriate corrective action with the use of this information. The prompt and accurate prediction of abnormal or critical machine wear is a massive benefit of analytical ferrography to help you avoid catastrophic equipment failure.
