Ferrography

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Ferrography is a method of oil analysis used to inspect the severity and mechanisms of wear in machinery. This is achieved by separating ferrous debris from lubricating oil by use of a magnetic field with an instrument called a ferrograph, the result is then examined with microscopy. A trained analyst can then diagnose faults or predict failures.

Contents

Ferrography is related to tribology, which is the study of friction between interacting surfaces. Since the advent of ferrography in the 1970s it has been used in many industrial settings as a form of predictive maintenance.

History

Ferrography was pioneered in the 1970s by the late Vernon C. Westcott [1] , sponsored by the Advance Research Projects Agency of the United States Department of Defense [2] At the time, the methods used to gauge wear; spectroscopic analysis and ferromagnetic chip detectors, could only provide warning of imminent failure, after the wear had already reached the severity, where preventative maintenance alone would not be an effective control to prevent catastrophic failure. [1] The military reached out to Westcott to find a way to solve this problem and from that Westcott developed the first ferrograph. The ferrograph saw its first practical use, by the British during the Falklands War, where it was used to inspect the condition of helicopter transmissions. [3]

In 1975, Westcott filed a patent that outlined the principles of multiple varieties of ferrography, including microscopic analysis of wear and a quantitative method of on-line ferrography. [1]

In 2009 a new method of visual on-line ferrography was published by a group of researchers from Xi'an Jiaotong University, Theory of Lubrication and Bearing Institute. [4] This is significant as it allows images of wear debris to be obtained during regular machine operation.

Purpose & Uses

Ferrography is a staple in failure prevention maintenance. Continuous monitoring of the lubricating oil allows a change from expensive and often unnecessary preplanned maintenance to more cost-effective failure prevention. [5] Ferrography is unique because it can deliver information about enclosed parts as lubricating oil circulates through these areas and is still accessible. Rinsing vital components with particle-free lubricant and analyzing the output can offer a detailed report of machine wear without disassembling anything.

Since its initial application in the military, ferrography has been found to be helpful in [6]

Further applications

Applying the idea of ferrography in other fields, techniques have been found to analyze wear outside of lubricating oil and of particles that do not carry magnetic properties. These uses have been found in processing grease samples, gas emissions; and in examining wear on arthritic joints. [6] In arthritic joints, residue from bone-on-bone contact can be found in fluid near the joint and analyzed using direct-reading ferrography which can give information regarding rate of decline in the joint. As of November 2016, minimal information is available regarding further uses of ferrography.

Types

Analytical ferrography

Analytical ferrography works through magnetic separation of contaminant particles and a professional analysis of the particles. A sample of the machine's lubricating oil is taken and diluted, then run across a glass slide. This glass slide is then placed on a magnetic cylinder that attracts the contaminants. Non-magnetic contaminants remain distributed across the slide from the wash. These contaminants are then washed, to remove excess oil, heated to 600 °F for two minutes, and the slide is analyzed under a microscope. [7] After analysis, the particles will be ranked according to size. Particles over 30 microns in size are considered "abnormal" and indicate severe wear. [7]

Particles are divided into six categories, with an additional five subcategories under ferrous wear: [8]

Being able to identify different particles can prove to be invaluable because the prominence of certain particles can point to specific locations of wear. Furthermore, the presence of particles that do not make contact with the lubricating oil can uncover contamination. This kind of analysis required a trained professional and can be prohibitively expensive for smaller operations.

Direct-reading method

Direct-reading ferrography is a more mathematical approach to ferrography. Essentially, the buildup on the glass slide is measured by shining a light across the slide. The blockage of the light by the buildup of particles is then used, over time, to calculate an average. An increase in blockage indicates higher amounts of machine wear. [9] This method is less expensive, as expert analysis is not required, and can be automated. However, once an issue is identified, less information is available to diagnose the problem.

On-line visual ferrography

On-line visual ferrography (OLVF) allows for images of wear debris to be acquired during routine operation of machinery. It requires attaching an electromagnet, a way to vary the oil flow rate and an image sensor into the oil circuit of the compartment whose oil is being monitored. The ferrous particles in the oil are then deposited in a similar way to using a bench-top ferrograph. Relative wear debris concentration, particle coverage area and images of debris can be obtained from this method. [4]

Limitations

While ferrography is an effective tool for wear analysis, it does come with several limitations. Ferrography is a very expensive procedure because of the specialized and sophisticated instruments required. [6] Ferrography stands out among oil analysis methods because of the magnetic element involved. This allows for a more detailed report that similar methods cannot produce. Additionally, for the qualitative approach which is analytical ferrography, experts are needed to make sense of the raw output. [9] Furthermore, ferrography cannot solve problems, only bring attention to them. These issues then need to be dealt with on their own.

See also

Related Research Articles

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

<span class="mw-page-title-main">Motor oil</span> Lubricant used for lubrication of internal combustion engines

Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, detergents, dispersants, and, for multi-grade oils, viscosity index improvers. The main function of motor oil is to reduce friction and wear on moving parts and to clean the engine from sludge and varnish (detergents). It also neutralizes acids that originate from fuel and from oxidation of the lubricant (detergents), improves the sealing of piston rings, and cools the engine by carrying heat away from moving parts.

<span class="mw-page-title-main">Bearing (mechanical)</span> Mechanism to constrain relative movement to the desired motion and reduce friction

A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts.

<span class="mw-page-title-main">Wear</span> Damaging, gradual removal or deformation of material at solid surfaces

Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical or chemical. The study of wear and related processes is referred to as tribology.

Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is highly interdisciplinary, drawing on many academic fields, including physics, chemistry, materials science, mathematics, biology and engineering. People who work in the field of tribology are referred to as tribologists.

<span class="mw-page-title-main">Roller chain</span> Type of chain drive

Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire- and tube-drawing machines, printing presses, cars, motorcycles, and bicycles. It consists of a series of short cylindrical rollers held together by side links. It is driven by a toothed wheel called a sprocket. It is a simple, reliable, and efficient means of power transmission.

<span class="mw-page-title-main">Rolling-element bearing</span> Bearing which carries a load with rolling elements placed between two grooved rings

In mechanical engineering, a rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing rolling elements between two concentric, grooved rings called races. The relative motion of the races causes the rolling elements to roll with very little rolling resistance and with little sliding.

<span class="mw-page-title-main">False brinelling</span>

False brinelling is a bearing damage caused by fretting, with or without corrosion, that causes imprints that look similar to brinelling, but are caused by a different mechanism. False brinelling may occur in bearings which act under small oscillations or vibrations.

<span class="mw-page-title-main">Galling</span> Form of wear caused by adhesion between sliding surfaces

Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.

Oil analysis (OA) is the laboratory analysis of a lubricant's properties, suspended contaminants, and wear debris. OA is performed during routine predictive maintenance to provide meaningful and accurate information on lubricant and machine condition. By tracking oil analysis sample results over the life of a particular machine, trends can be established which can help eliminate costly repairs. The study of wear in machinery is called tribology. Tribologists often perform or interpret oil analysis data.

Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequently broken again by the small movement. This breaking causes wear debris to be formed.

Condition monitoring is the process of monitoring a parameter of condition in machinery, in order to identify a significant change which is indicative of a developing fault. It is a major component of predictive maintenance. The use of condition monitoring allows maintenance to be scheduled, or other actions to be taken to prevent consequential damages and avoid its consequences. Condition monitoring has a unique benefit in that conditions that would shorten normal lifespan can be addressed before they develop into a major failure. Condition monitoring techniques are normally used on rotating equipment, auxiliary systems and other machinery like belt-driven equipment,, while periodic inspection using non-destructive testing (NDT) techniques and fit for service (FFS) evaluation are used for static plant equipment such as steam boilers, piping and heat exchangers.

<span class="mw-page-title-main">Predictive maintenance</span> Method to predict when equipment should be maintained

Predictive maintenance techniques are designed to help determine the condition of in-service equipment in order to estimate when maintenance should be performed. This approach promises cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted. Thus, it is regarded as condition-based maintenance carried out as suggested by estimations of the degradation state of an item.

<span class="mw-page-title-main">Oil filter</span> Filter designed to remove contaminants from oil

An oil filter is a filter designed to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles, powered aircraft, railway locomotives, ships and boats, and static engines such as generators and pumps. Other vehicle hydraulic systems, such as those in automatic transmissions and power steering, are often equipped with an oil filter. Gas turbine engines, such as those on jet aircraft, also require the use of oil filters. Oil filters are used in many different types of hydraulic machinery. The oil industry itself employs filters for oil production, oil pumping, and oil recycling. Modern engine oil filters tend to be "full-flow" (inline) or "bypass".

Oil additives are chemical compounds that improve the lubricant performance of base oil. The manufacturer of many different oils can utilize the same base stock for each formulation and can choose different additives for each specific application. Additives comprise up to 5% by weight of some oils.

Dry lubricants or solid lubricants are materials that, despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium.

<span class="mw-page-title-main">Oil pump (internal combustion engine)</span> Internal combustion engine part that circulates engine oil under pressure

The oil pump is an internal combustion engine part that circulates engine oil under pressure to the rotating bearings, the sliding pistons and the camshaft of the engine. This lubricates the bearings, allows the use of higher-capacity fluid bearings and also assists in cooling the engine.

<span class="mw-page-title-main">Tribocorrosion</span> Material degradation due to corrosion and wear.

Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. The name tribocorrosion expresses the underlying disciplines of tribology and corrosion. Tribology is concerned with the study of friction, lubrication and wear and corrosion is concerned with the chemical and electrochemical interactions between a material, normally a metal, and its environment. As a field of research tribocorrosion is relatively new, but tribocorrosion phenomena have been around ever since machines and installations are being used.

Extreme tribology refers to tribological situations under extreme operating conditions which can be related to high loads and/or temperatures, or severe environments. Also, they may be related to high transitory contact conditions, or to situations with near-impossible monitoring and maintenance opportunities. In general, extreme conditions can typically be categorized as involving abnormally high or excessive exposure to e.g. cold, heat, pressure, vacuum, voltage, corrosive chemicals, vibration, or dust. The extreme conditions should include any device or system requiring a lubricant operating under any of the following conditions:

Workplace exposure monitoring is the monitoring of substances in a workplace that are chemical or biological hazards. It is performed in the context of workplace exposure assessment and risk assessment. Exposure monitoring analyzes hazardous substances in the air or on surfaces of a workplace, and is complementary to biomonitoring, which instead analyzes toxicants or their effects within workers.

References

  1. 1 2 3 USpatent 4047814,Vernon C. Westcott,"METHOD AND APPARATUS FOR SEGREGATING PARTICULATE MATTER",published 1977-09-13,issued 1977-09-13, assigned to Trans-Sonics, Incorporated, Inc.
  2. ↑ Westcott, Vernon C. (31 December 1975). Progress in the Development and Utilization of Ferrography. Defense Technical Information Center (Technical report). Archived from the original on 3 June 2023. Retrieved 3 June 2023.
  3. ↑ "A Tribute to Vernon C. Westcott, Inventor of the Ferrograph" . Retrieved 2016-10-23.
  4. 1 2 Wu, T.; Mao, J.; Wang, J.; Wu, J.; Xie, Y. (2009). "A New On-Line Visual Ferrograph". Tribology Transactions. 52 (5): 623–631. doi:10.1080/10402000902825762 – via Taylor & Francis Online.
  5. ↑ "Ferrography". Tribology International. 9.
  6. 1 2 3 "Ferrography—then and now". Tribology International. 38.
  7. 1 2 "Analytical Ferrography - Make It Work For You" . Retrieved 2016-10-25.
  8. ↑ "Analytical Ferrography - Methods, Benefits and Applications". AZoM.com. 2013-04-23. Retrieved 2016-10-23.
  9. 1 2 "WearCheck FYI - Direct-Reading and Analytical Ferrography". wearcheck.com. Retrieved 2016-10-24.
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