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Viscosity Index: The Complete Guide to Understanding & Improving Lubricants 2025 Home Wiki Viscosity Index: The Complete Guide to Understanding & Improving Lubricants 2025 Viscosity Index: The Complete Guide to Understanding & Improving Lubricants 2025 TriboNet December, 5 2025 ASTM D2270 standard calculating viscosity index oil viscosity chart viscosity formula viscosity index viscosity index calculator viscosity index formula viscosity temperature relations Table of Contents Temperature – Viscosity Relation Temperature – Viscosity Calculator Oil Viscosity Index Definition Viscosity Index Formula Viscosity Index Calculator Classification of Viscosity Indexes of Oils Video Explaining Viscosity Index About the Author References Temperature – Viscosity Relation Viscosity Index is a measure of a lubricating oil’s resistant to flow. It is well-known from Hydrodynamic Lubrication Theory that viscosity plays a central role in the lubrication regime encountered in the machine element – the higher is the viscosity, the thicker is the oil film that separates the surfaces from touching each other. However, it is also known that temperature impacts the viscosity. Temperature-viscosity characteristics of lubricating oils and/or greases is one of the important determinant for lubricants performances in mechanical systems. Sustainability of lubricating film between contacting bodies in mechanical systems is often critical owing to the highly sensitive nature of lubricants temperature-viscosity relationship. Oil viscosity often declines rapidly with respect to rise in temperature. Loss in lubricants viscosity may lead to severe performance issues of mechanical systems in industry and transportation applications. In tribology systems (e.g. gears, bearings, engines), temperature rise due to friction induced heating is inevitable. Another major source of heat is the high temperature operating environment (e.g. steam/gas turbines). On the other hand, viscosity of lubricant can also be critical for the performance of applications at sub-zero atmospheres. In such cases, lubricants get thicker and add up resistance to the movement of elements. Thereby, neither a thick nor a thin lubricant can be the suitable choice that an engineer can make during the selection of lubricant. An attention to the temperature-viscosity characteristics of lubricants is therefore of practical importance for ensuring the lubricants desirable performance in any particular system. Over the years, attempts have been made to develop empirical relationships to describe the lubricants temperature-viscosity behaviors. Reynolds have pioneered in this direction and prescribed an exponential fit to describe the declining trend of viscosity with respect to temperature. The equation appears to be as simple as: where is dynamic viscosity, and are empirical constants. This equation appears to be simple and can be easily implemented in mathematical models but owing to its highly conservative functionality (i.e. to follow only an exponential curve), it may work well only over a limited temperature range for a limited range of products. Another notable equation was developed by Walther in 1928: where is kinematic viscosity, and , , , and are empirical constants. Interestingly, this equation forms the basis of ASTM chart (D341) for viscosity-temperature relationship, and the most general form of this relationship is: ; ; Where Z is a transcendental function of kinematic viscosity in cST , T is temperature in Kelvin scale, A and B are constants. The equation looks unsatisfactory to any math-sophisticated readers; nevertheless, it works well for a large class of petroleum oils over a wide range of temperature to . For further reads, refer to Wright [1969]. Another model was proposed by Vogel: , where x, y, and z are empirical constants. This model proves to be more useful in engineering calculations and predictive numerical models. Despite of the development in temperature-viscosity characteristics in empirical terms, some of which are useful for engineering calculations; nevertheless, they often appear to be less useful as a quick guidance for practitioners. The reason behind such ambiguity lies in the need of huge experimental data in order to reliably fit each of these equations. In simple terms, empirical relationships do not satisfy the need of a readymade metric for viscosity-temperature characteristics for a common user of lubricants. Temperature – Viscosity Calculator Here is a simple calculator that can be used to calculate dynamic viscosity of an oil at operating temperature, if the dynamic viscosities at 2 other temperatures are known (typically the viscosities at 40 °C and 100 °C are taken from the data sheet as reference points, but any two temperatures and viscosities can be used). Operational viscosity Temperature T1, [ºC] Dynamic Viscosity µ [mPa·s] at T1 Temperature T2 [ºC] Dynamic Viscosity µ [mPa·s] at T2 Operating Temperature, [ºC] Viscosity at Operating Temperature by Reynolds equation [mPa·s] Viscosity at Operating Temperature by Vogel equation [mPa·s] As a rule of thumb, the viscosity of a machine oil fall about 25% with every 10ºC temperature increase. The Reynolds interpolation function is accurate in the vicinity of the reference points. The Vogel equation is most accurate over the whole range. Oil Viscosity Index Definition Dan and Davis in 1929 introduced a term, viscosity index to compare the oils temperature-viscosity relationships in relative to each other. In early days of industrial lubrication, it was realized that lubricants made from Pennsylvania crude oil is less sensitive to temperature as compared to the lubricants from Golf Coast oil while they both have same kinematic viscosity at 100 . Therefore, these two categories were initially designated as reference oils where former group was assigned a viscosity index of 100 and the latter group as 0 (as demonstrated in the illustration below). Since then, this index has been largely popularized and proven to be highly useful for a range of professionals from manufacturer to a common user of lubricants. According the ASTM standard, viscosity index is: —an arbitrary number used to characterize the variation of the kinematic viscosity of a petroleum product with temperature. Mathematically, viscosity index represents a relative measure of a lubricants temperature-viscosity behavior with respect to two reference oils. The index is estimated with the help of kinematic viscosity measured at two temperature points; therefore, unlike the empirical relationships, the index does not necessarily tell about the path that lubricants kinematic viscosity follows with respect to temperature. The illustration below shows a representation of the viscosity index. Viscosity Index Formula A stepwise procedure to estimate viscosity index, VI, may be outlined as below: Measure kinematic viscosity of the unknown oil at C and C. Get the look-up chart (ASTM D2270-86) of kinematic viscosity (for the information purposes only, the old chart is available here). Identify two reference oils whose kinematic viscosity at C coincides with the kinematic viscosity of the unknown oil (from the look-up chart of ASTM standard). Pick-up the kinematic viscosity of two identified reference oils at C In reference to illustration above, now a, b, and c are known. Use the following formula to calculate viscosity index, . Figure: Graphical Representation for VI estimation It is important to mention here that a higher VI means the oils kinematic viscosity is less sensitive to temperature; therefore, the lubricant is likely to perform better over a wide range of temperature. On the other hand, in case of low VI, the viscosity of the lubricant may decline rapidly with respect to increase in temperature. Usually, synthetic oil based lubricants and multi-grade oils exhibit higher VI as compared to mineral oil based lubricants. Interestingly, the VI may go above 100 in case the value of in above figure appears in between and . Usually, in industrial lubricant market, mineral oil based lubricants exhibit VI around 100; whereas, VI of synthetic oil based lubricant may go up to 150. It is important to know that a lubricants VI can be improved with selective additives in the lubricant formulation. High molecular weight polymers which are soluble such as polymethaacrylates above molecular weight of 10000 has found to be suitable for arresting viscosity declination with respect to temperature rise. These polymer additives are commonly being used for viscosity index improvement in multi-grade oils. In the process of lubricant selection, the VI of lubricants should not be ignored since optimum viscosity requirement of any system is often not precisely well known and machinery operating parameters such as load, speed, and temperature are likely to fluctuate. Low VI oil may be chosen when operating parameters of the machineries are almost constant (e.g. household applications); whereas, in a situation of highly fluctuating load and operating parameters (e.g. excavators, automobiles), high VI oil should be preferred. However, high VI oils incur high operational cost which in turn lead to a debate among industry professionals on the lubricants cost-VI trade-offs! Overall, the importance of understanding of the temperature-viscosity relationship is well recognized in industrial lubrication practices. While empirical relationships are useful for mathematical calculations and engineering design, viscosity index has been internationally accepted and popularized as a highly useful metric to determine the temperature-viscosity behavior of lubricants for practical purposes. Viscosity Index Calculator Here is a simple calculator to get the VI based on the kinematic viscosity values: Viscosity Index (VI) Calculator Kinematic viscosity 40°C [cSt or mm^2/s] Kinematic viscosity 100°C [cSt or mm^2/s] Viscosity Index VI [ -] Classification of Viscosity Indexes of Oils Viscosity index Classification Under 35 Low 35-80 Medium 80-110 High Over 110 Very High Video Explaining Viscosity Index About the Author Sandip Panda (sa***********@***il.com) (https://www.linkedin.com/in/sandip-panda-phd-iit-kharagpur-89907162/) References ASTM D341-03, 2003, Standard Practice for Viscosity-Temperature Charts for Liquid Petroleum Products, ASTM International, West Conshohocken, PA, 2017,;astm.org Wright, A., 1969, An Improved Viscosity-Temperature Chart for Hydrocarbons, Journal of Materials, 4(1), pp. 19–27. Stachowiak, G. W. and Batchelor, W., 2000, Engineering Tribology (Second Edition), Butterworth-Heinemann, United Kingdom. Robinson, J. et al, Probing the molecular design of hyper-branched aryl polyesters towards lubricant applications, https://doi.org/10.1038/srep18624. TriboNet Administration of the project --> 1 Comment Sathyan Tivakaran says: 25.05.2023 at 15:32 Thanks Sir. Very good report and useful. Best regards. Log in to Reply Leave a Reply Cancel reply You must be logged in to post a comment. Login using social account This site uses Akismet to reduce spam. Learn how your comment data is processed.
Hydrostatic Bearings: Principles, Design, and Applications 2025 Home Wiki Hydrostatic Bearings: Principles, Design, and Applications 2025 Hydrostatic Bearings: Principles, Design, and Applications 2025 Michal Michalec December, 5 2025 bearing full film hydrostatic hydrostatic bearings pressure Introduction to Hydrostatic Bearing Hydrostatic bearings are a particular type of bearings that work on the principle of separating sliding surfaces using pressurized fluid: air, oil or any other type of lubricant. This is in contrast with hydrodynamic bearings, where the separation of the sliding surfaces occurs naturally due to relative motion of the surfaces and their geometry. One of the most important drawbacks of hydrodynamic bearings is that in order for the oil film to form, the surfaces must be moving, but also have a “curved” geometry. The principles of hydrodynamic lubrication are discussed in another article. Lubrication in Hydrostatic Bearing For the hydrostatic bearings, the separating lubricant film is introduced into a contact by an external pressure, thus a good lubrication can be provided independently of the speed or geometry. Hydrostatic bearings can be divided into two main parts – the pad (often referred as the hydrostatic bearing itself), and the hydraulic circle. The bearing pad contains a recess groove (or several grooves in case of multi-recess pad types), ensuring there is sufficient area to lift the bearing load. The pressurized fluid flows into the recess through the inlet hole (see Figure 1). The hydraulic circuit must be able to withstand the pressures generated during the lifting phase. The fluid pressure profile in the recess area is constant and it gradually decreases, at the outlets, to the outside pressure (usually atmospheric pressure). Figure 1 Scheme of the open-type hydrostatic bearing pad and fluid pressure distribution (reprinted from [2] under licence CC BY 3.0). Hydrostatic lubrication is beneficial due to the lack of contact between the sliding surfaces, which are fully separated by a thick lubricating film (usually 1-100 µm). Therefore, little or no wear is present, and the coefficient of friction is generally very low (depending on the speed, lubricant properties, and bearing geometry). High stiffness and vibration damping result thanks to the fluid film,. Moreover, no stick-slip effect occurs during normal working conditions, thus a very precise motion can be achieved. A continuous pressurized fluid (e.g. oil) feed is required during operation to achieve proper function. This leads to higher energy requirements, but also significantly higher initial costs related to hydraulic system. Hydraulic system Hydraulic circuit consists of an oil tank, filter, pump, and safety elements. Measuring devices, such as flowmeters and pressure sensors, provide information about the inlet flow to the bearing and fluid pressure in the hydraulic aggregate, respectively. If necessary, a cooler is added to stabilize the lubricant temperature. In case of an unexpected shut down or a hydraulic fluid supply failure, a safety element is usually included (especially for large bearings). Usually a hydraulic accumulator is used which is able to supply the required system pressure until bearing stops. For multi-pad or multi-recess bearings, restrictors are used to compensate eccentric or asymmetrical loading, pad misalignment, or dynamic loading. Thus, a constant film thickness is guaranteed. Figure 2 Full scheme of the hydraulic circuit and cross section of two hydrostatic pads of a large multi-pad hydrostatic bearing (reprinted from [2] under licence CC BY 3.0). Hydrostatic bearings are used in a wide range of applications – from small spindles and guideways (millimetres) to large-scale turntables, machining centres, space telescopes, and antennas, etc.. The methodology of hydrostatic bearing design is well described in the book by Bassani and Piccigallo [1]. The design of such bearings of large-scale was further extended in an article by Michalec et al. [2]. The calculation is based on the fluid mechanics principles. For simple bearing pads (e.g., circular, square, rectangular), analytical equations can be used for a rapid calculation and design. The hydrostatic bearing design begins with pad size determination to withstand acting loads. The minimum recess area can be obtained using eqn.: (1) ; where W is the applied load, and pr is the recess pressure. Subsequently, the required flow can be determined. For a circular recess following equation can be used. (2) ; where h is film thickness, µ is dynamic viscosity, and r1 and r2 are recess and pad radius, respectively. Other important parameters can be supplied pressure, friction and pressure losses, or stiffness and damping. Some non-basic geometries (e.g. four-recess pads – Figure 3) can be calculated using coefficients, as described in the book Applied Tribology: Bearing Design and Lubrication by Khonsari and Booser [3]. The non-derived shapes can be obtained using experimental modelling or electric field analogy plotting [4]. For more complex shapes, numerical simulations are appropriate and widely used. Figure 3 Example of four-recess hydrostatic linear pad (own gallery). The review publication by Liu et al. [5] indicates that research on hydrostatic bearings is growing, this might be a result of the latest developments in hydraulics control and manufacturing precision. The latest research is aimed at numerical simulations of the lubricant flow in the pad, possibly combined with FSI (Fluid-Structure interaction) methods to gain insight into the deformation of the solid bodies during operation. This is related with manufacturing and precise assembling of bearing solid bodies, which influences the bearing performance. When it comes to large dimensions hydrostatic bearings, i.e. bearings over 10 meters in diameter, manufacturing, transportation, and assembly further increases the complexity of the component. In the near future, major developments on hydraulic circuit optimization and feedback control according to online diagnostics of the lubricating film layer are expected. References [1] R. BASSANI and B. PICCIGALLO. Hydrostatic Lubrication. 22, Elsevier B.V., 1992. ISBN 10: 044488498X. [2] M. MICAHLEC, P. SVOBODA, I. KŘUPKA and M. HARTL. A review of the design and optimization of large-scale hydrostatic bearing systems, Engineering Science and Technology, an International Journal. Volume 24, Issue 4, 2021. Pages 936-958. ISSN 2215-0986, DOI: 10.1016/j.jestch.2021.01.010. [3] M. M. KHONSARI and R. E. BOOSER. Applied Tribology: Bearing Design and Lubrication. Chichester, UK: John Wiley & Sons, Ltd, 2017. ISBN 9781118700280. DOI: 10.1002/9781118700280 [4] A. M. LOEB. The Determination of the Characteristics of Hydrostatic Bearings through the use of the Electric Analog Field Plotter, A S L E Transactions, 217-224, 1958. DOI: 10.1080/05698195808972333 [5] Z.F. LIU, Y. M. WANG, L. G. CAI, Y. S. ZHAO, Q. CHENG and X. M. DONG. A review of hydrostatic bearing system: Researches and applications. Advances in Mechanical Engineering. 2017, 9 (10).ISSN 1687-8132. DOI: 10.1177%2F1687814017730536 Michal Michalec M. Michalec is a PhD student and junior researcher at Brno University of Technology in Czechia. During his studies he gained insignt into tribology and machine design. He is currently working on projects related to large-scale hydrostatic bearing design and development. --> 3 Comments Meghna Choudhary says: 09.03.2023 at 15:07 Well explained Cleared my doubt!! Log in to Reply Sir says: 20.05.2023 at 12:03 Thanksss Log in to Reply Kevin says: 15.06.2023 at 23:16 Contact me at hy*************@***il.com Mr. Scheid about design Log in to Reply Leave a Reply Cancel reply You must be logged in to post a comment. Login using social account This site uses Akismet to reduce spam. Learn how your comment data is processed.
Engine Bearing Home Wiki Engine Bearing Engine Bearing TriboNet December, 5 2025 engine bearings engine main bearing main bearing Table of Contents What is an Engine Bearing How Engine Bearings Work — Principle & Design Why Engine Bearings Remain Critical in Modern Engines Conclusion What is an Engine Bearing An engine bearing is a specially designed bearing used inside internal-combustion engines to support rotating components — most notably the crankshaft. In common piston engines, the “main bearings” cradle the crankshaft inside the engine block (the crankcase), allowing it to rotate smoothly while withstanding the mechanical forces produced by piston operation. The internal combustion engine (piston engine) currently is still the most common engine used in automotive indutstry, even though the electric vehicles using electric vehicles are getting rapidly popular. Combustion engines contain several bearings and the one that allows the crankshaft to rotate is named as main bearing or engine bearing. The figure above shows the location of an engine bearing in a four cylinders combustion engine. Bearing is a device that is used to reduce friction between moving parts of machine elements to provide movement in a desired way with minimum power losses. Development of bearings is one of the most revolutionary steps in the development of human made machines. First concept of a bearing was described by Leonardo da Vinci. The main functions of bearings are: Reducing friction Supporting parts of the machine or machine elements Bearing radial or thrust laods The function of the main engine bearings is to support crankshaft and allowing rotation during the engine operation. Main bearings are mounted in the crankcase. How Engine Bearings Work — Principle & Design Engine bearings (especially for crankshafts) typically use journal bearing design: two semi-cylindrical shell halves (upper and lower shells) that together surround the crankshaft journal. At rest, the shaft might contact the bearing shell directly, but once the engine starts and oil is pumped through the system, the crankshaft begins to rotate and the oil is forced into the narrow gap — creating a hydrodynamic oil film. This film lifts and separates the journal from the bearing surface, enabling the crankshaft to “float” and rotate with minimal friction — often described as a “wedge” effect. This oil film does more than reduce friction — it also acts as the primary medium for heat removal, protecting both bearing and crankshaft from thermal stress. If lubrication fails (for instance due to low oil pressure, contamination, or oil breakdown), the protective film collapses, leading to metal-to-metal contact, rapid wear (scoring, scuffing), overheating, and possible catastrophic failure. Additionally, engine bearings are designed with layered materials: a strong backing (often steel) to provide structural support, with a softer overlay (e.g. a friction-reducing alloy) that provides a conformable, embeddable surface. This layered construction helps protect against surface imperfections in the crankshaft journal and allows the bearing to accommodate debris (small particles) by embedding them without catastrophic damage. Some bearings also incorporate features like oil grooves or eccentric wall design (to promote oil flow and heat dissipation), helping carry away heat and flush out contaminants — essential for bearing longevity under harsh engine conditions. Why Engine Bearings Remain Critical in Modern Engines Even as the automotive industry gradually shifts toward electrification, internal-combustion engines remain widespread globally — especially in legacy vehicles, heavy-duty machinery, industrial engines, and many hybrid powertrains. The reliability and lifetime of these engines depend heavily on the quality of their internals — and engine bearings are among the most critical. Moreover, modern engines are increasingly pushed for higher performance, greater efficiency, and tighter tolerances — placing even more demand on bearings to deliver low friction, high load capacity, excellent lubrication compatibility, and long-term durability. Advances in materials, coatings, and lubrication technology continue to make bearings more reliable, but their proper selection, installation, and maintenance remain fundamental. Conclusion The engine bearing is a small yet vital component — a true “unsung hero” — that enables smooth rotation, reduces friction, supports heavy loads, maintains alignment, and ensures longevity of the engine’s rotating assembly. Understanding how bearings work, how they’re built, and what conditions they require is essential for engine designers, mechanics, or anyone interested in engine performance and reliability. By combining proper design (material, geometry, lubrication channels), precise machining, and diligent maintenance (oil quality, cleanliness, correct tolerances), engine bearings can maintain engine health for hundreds of thousands of miles — but neglect just one factor, and the consequences can be severe. TriboNet Administration of the project -->
Wear: Essential Insights to Prevent Costly Mechanical Failures Home Wiki Wear: Essential Insights to Prevent Costly Mechanical Failures Wear: Essential Insights to Prevent Costly Mechanical Failures Pranay Kumar December, 5 2025 mechanical wear wear classification wear meaning wear mechanisms wear modes wear of materials wear types what is wear Table of Contents What is Wear: Factors affecting Wear: Wear mechanisms: Wear Reduction Methods: References: What is Wear: Wear is defined as surface damage of one or all solid surfaces in contact subject to relative motion. Wear might have different patterns corresponding to various wear mechanisms. A surface can be subject to more than one wear mechanism simultaneously such as it can have adhesive and corrosive wear or abrasive and fatigue wear or a combination of several of these. The process of wear can change continuously in time or with changes in operational conditions. Wear is usually accelerated by frictional heating by means of chemical and mechanical interactions. Factors affecting Wear: The key factors influencing wear are temperature, sliding speed, hardness, modulus of elasticity, load, and composition of material. The wear resistance is influenced by the contact temperature [1]. Since the hardness and yield strength;diminish as the temperature rises [2] abrasive wear would increase. The yield strength and hardness for;most of the;materials diminishes as the temperature rises. At elevated temperatures the;dislocation movement in metals causes a drop in yield strength, making plastic deformation simpler. The wear rate is substantially influenced by the normal load. ; With an increase in the;load applied, the shear force and frictional thrust rise as well, speeding up the wear rate [3]. In the range of 0 to 2.5 m/s sliding speed, the rate of abrasive wear increased marginally. Frictional heating [8] may be to blame for the increase in wear. We cannot generalise that the increase in sliding speed would definitely increase wear as it also depends on the load being applied on the surfaces, presence of lubricant and the surface roughness of the contacting bodies. The elastic modulus is an indicator of the material’s resistance to deformation under load, with a larger number indicating more stiffness [4]. The materials’ composition also has a significant impact on wear behaviour for example in composites, it’s mechanical behaviour can be affected based on the concentration of inorganic fillers [5]. The presence of organic matrix which is responsible for low resistance to wear can be reduced by the introduction of this inorganic fillers [18]. Fig-1 Factors affecting Wear [5] Wear mechanisms: Many researchers have attempted to classify the wear mechanisms [6-8] and few classification schemes are available in the literature [9]. Mechanisms of wear according to Ludema [10] are “the succession of events whereby atoms, products of chemical conversion, fragments are induced to leave the system (perhaps after some circulation) and are identified in a manner that embodies or immediately suggests solutions”. There is a wide range of terms (for instance adhesive, abrasive, fretting, surface fatigue, corrosion, erosion) available for the description of wear mechanisms [10, 11], but at least four groups can be distinguished [12]: 3.1 Adhesive wear: Adhesive wear is the undesired movement and adhesion of wear debris and material compounds from one surface to another that occurs in frictional contact between surfaces. When the atomic forces between the materials in contacting surfaces under relative pressure are greater than the inherent material properties of each surface, adhesive wear develops. [19] 3.2 Abrasive Wear: When a hard, rough surface glides across a smooth surface, abrasive wear develops. [13] It is defined by ASTM International as material loss caused by hard particles;that are pressed against and slide over a solid surface. [14] The abrasive wear mode is dictated by the type of contact and there’re two types of abrasive wear namely two-body and three-body wear. When;hard particles remove material from one surface, this is known as two-body wear. When particles are not restricted and are allowed to roll and glide along a surface, three-body wear develops. 3.3 Corrosive wear: Corrosive wear is indeed an indirect wear mechanism that occurs when a sliding surface is exposed to a corrosive medium and the sliding movement continuously eliminates the preventive corrosion product. As a result, the new surface is exposed to additional corrosive damage. Since this removes corrosive products and the passive protective layer faster than surfaces without any relative motion, corrosion wear could be regarded an accelerated process for corrosion. [20] 3.4 Surface fatigue: Surface fatigue occurs due to the;growth and formation of;cracks. It;is a kind of basic material fatigue in which the material;surface;weakens as a result of cyclic loads. Fig-2 Wear Mechanisms [15] Wear Reduction Methods: We all understand that wear can only be mitigated, not prevented. We can minimize wear, but we won’t be able to eradicate it. Many strategies have been devised to minimize wear, as detailed below. [16] 4.1 Prevention of Overloading: Overloading should be avoided since it causes lubricants to break down and puts an excess force on the worn surface. 4.2 Maintain a Proper Clearance: When the clearance between the surfaces is too small, a lubricating oil layer cannot be applied to the worn surface, resulting in metal-on-metal contact. If there is more space between the surfaces, motion is lost. Due to the sheer absence of lubrication, the machine’s parts wear down quickly, making it loud and vibrating. 4.3 Better Lubrication: Lubrication produces a lubricant film in the space between the contacting;surfaces, which improves its;smoothness;and avoids material contact. Improper lubrication leads to wear of surfaces. 4.4 Improving the Surface Finishing: Various sorts of straight or circular lays are formed when parts are passed through the machining process, that cannot;be seen with the human eye. Because of the good surface, a line contact rather than a point contact is created, which is advantageous in processes. Good surface finish uniformly distributes load rather than maintaining asperity contacts leading to reduction of wear. 4.5 High Surface Hardness: In compared to soft surfaces, hard surfaces wear down faster. Heat treatment is used to enhance the surface hardness of the shaft, bearing, and guide way, which reduces wear. 4.6 Proper Surface Treatment: Mechanical wear can be minimized by applying a hard coating of metal, such as chromium or galvanic, on the surface. As a result, it may be argued that if a hard layer is applied to the surface of a wear-resistant metal, the part’s wear can be minimized. 4.7 Protection of Surface Against the Ingress of Dirt, Dust and Metal Particles: If debris, dirt, or metal particles get inside the bearings, they get crushed much more. If the particles are tougher than the surface of the part, the surface will wear down and gets;damaged. 4.8 Proper Atmosphere: Dust, debris, moisture, dangerous chemical vapour;are all present in the atmosphere, affecting machining operations and reducing their service life. Several other techniques for wear reduction include proper maintenance, varying clearance adjustments over time, good planning, integration of preventive maintenance, controlling the preventive maintenance tasks, selection of appropriate;material for the component, reducing sliding pairs with the replacement of rolling pairs, and using a fully automated maintenance facility [17]. References: ;Rymuza , “Tribology of Polymers”, Archives of; Civil and Mechanical Engineering, Vol. VII, No. (4), pp. 177- 184,(2007). ASM International, ASM Handbook Volume 18, “Friction, Lubrication, and Wear Technology”, American Society for Metals, Metals Park, Ohio, pp. 341-347, (1992). Nuruzzaman, D.M., Chowdhury, M.A., and Rahaman, M.L. “Effect of Duration of Rubbing and Normal Load on Friction Coefficient for Polymer and Composite Materials”, Industrial Lubrication and Tribology, Vol. 63, pp. 320 – 326, (2011). Lu H., Lee Y., OguriM, Powers J., “Properties of a Dental Resin Composite with a Spherical Inorganic Filler”, Operative Dentistry, Vol.31, No. 6, pp.734-740, (2006). , Meshref & A., Mazen & A., and & Y., Ali. (2020). WEAR BEHAVIOR OF HYBRID COMPOSITE REINFORCED WITH TITANIUM DIOXIDE NANOPARTICLES. 39. 89-101. 10.21608/jaet.2020.75738. Blau, P.J. Friction and Wear Transitions of Materials. New Jersey: Noues Publications, 1989. Knowels, G.D. Mechanisms of Wear Particle Formation and Detachment. Vancouver: The University of British Columbia, 1994. Ludema, K. A Textbook in Tribology. Ann Arbor: CRC Press, 1996. Bhushan, B. Principles and Applicaion of Tribology. New York: A Wiley-Interscience Publication, 1999. Wear Patterns and Laws of Wear – A Review. Zmitrowicz, A. 2006, Journal of Theoretical and Applied Mechanics, pp. 219-253. van Drogen, M. The Transition to Adhesive Wear of Lubricated Concentrated Contacts. Enschede: University of Twente, 2005. Classification of Wear Mechanisms/Models. Kato, K. 2002, Journal of Engineering Tribology, pp. 349-355. Rabinowicz, E. (1995). Friction and Wear of Materials. New York, John Wiley and Sons. Standard Terminology Relating to Wear and Erosion, Annual Book of Standards, Vol 03.02, ASTM, 1987, p 243-250 Tsujimoto, Akimasa & Barkmeier, Wayne & Erickson, Robert & Nojiri, Kie & Nagura, Yuko & Takamizawa, Toshiki & Latta, Mark & Miazaki, Masashi & Fischer, Nicholas. (2017). Wear of resin composites: Current insights into underlying mechanisms, evaluation methods and influential factors. Japanese Dental Science Review. 54. 10.1016/j.jdsr.2017.11.002. K. Dodiya, J. P. Parmar, A Study of Various Wear Mechanism and its Reduction Method, International Journal for Innovative Research in Science & Technology, Volume 2, Issue 09, February 2016, ISSN (online): 2349-6010. Book of Plant maintenance and safety by K.K.Patel. Aljosa I., Tijana L., Larisa B., Marko V., Influence of Light-Curing Mode on the Mechanical Properties of Dental Resin Nanocomposites, Procedia Engineering, Vol. 69, pp. 921–930, (2014). “Adhesive Wear.” Wikipedia, 16 September 2021, https://en.wikipedia.org/wiki/Wear#Adhesive_wear “Tribocorrosion.” Wikipedia, 14 June 2020, https://en.wikipedia.org/wiki/Tribocorrosion Pranay Kumar I'm an Erasmus Mundus Scholarship recipient in the field of Tribology of Surfaces and Interfaces. The masters program takes place in four different universities namely University of Leeds (UK), University of Ljubljana (Slovenia), University of Coimbra (Portugal) and Lulea Technical University (Sweden). -->
Hydrodynamic Lubrication: How It Ensures High Performance and Reliability 2025 Home Wiki Hydrodynamic Lubrication: How It Ensures High Performance and Reliability 2025 Hydrodynamic Lubrication: How It Ensures High Performance and Reliability 2025 Manoj Rajankunte Mahadeshwara December, 4 2025 definition hydrodynamic bearing hydrodynamic lubrication hydrodynamic lubrication theory hydrodynamic theory theory of hydrodynamic lubrication what is wiki wikipedia Definition of Hydrodynamic Lubrication (HL) Hydrodynamic lubrication is a term that defines a situation in which two rubbing surfaces are separated by a thin film of a lubricant. This situation is often beneficial and lubrication is used to reduce friction and/or wear of rubbing solids with the aid of liquid (or semi-solid) lubricant. For a vast majority of the surfaces encountered in nature and used in industry, the source of friction is the imperfections of the surfaces. Even mirror shining surfaces are composed of hills and valleys – surface roughness. The goal of hydrodynamic lubrication is to add a proper lubricant, so that it penetrates into the contact zone between rubbing solids and creates a thin liquid film, as shown in the figure below. This film separates the surfaces from direct contact and it in general reduces friction and consequently wear (but not always), since friction within the lubricant is less than between the directly contacting solids. The theory is developed within a field known as tribology. Lubricant is a substance which is used to control (more often to reduce) friction and wear of the surfaces in a contact of the bodies in relative motion. Depending on its nature, lubricants are also used to eliminate heat and wear debris, supply additives into the contact, transmit power, protect, seal. A lubricant can be in liquid (oil, water, etc.), solid (graphite, graphene, molybdenum disulfide), gaseous (air) or even semisolid (grease) forms. Most of the lubricants contain additives (5-30%) to improve their performance. Read further about the lubricant definition here. Lubricant Film (From: Lubrication for Industry, by Ken Bannister, Industrial Press) History of lubrication theory goes more than a century back to 1886 when O. Reynolds published famous equation of thin fluid film flow in the narrow gap between two solids (Reynolds 1886). This equation carries his name and forms a foundation of the lubrication theory. Derivation of Reynolds equation and possible solution methods are given here. It differs from elastohydrodynamic lubrication theory (EHL) due to negligible elastic deformation of the surfaces. Absence of the elastic deformations simplifies the problem as compared to EHL theory, but allows one to construct some important analytical solutions as will be shown further. Solutions of Reynolds Equation First solutions of lubrication theory were obtained by Reynolds himself and can be found in the original work. One of the most important analytical solutions of the HL theory (of the most interest in tribology field) was obtained by Martin in 1916. The solution considers a relative motion of cylinder on flat plane, as shown in figure below. Following system of equations is considered: (1) ; where are film thickness, pressure, viscosity and average sliding speed correspondingly ( ). here is the normal load (per unit length). There are two unknowns, pressure and the approach with two equations to determine them. Martin’s solution states following: (2) ; This solution immediately shows the major relations within the HL theory (but they also remain qualitatively true in elastohydrodynamic theory as well). The sliding speed has to be higher to generate a thicker film. The same is true for viscosity: higher viscosity leads to a thicker lubricant film. It should be noted, that it is typically desired to have a sufficiently thick lubricant film, so that the surface are completely separated to reduce wear. At the same time, it is clear, that the friction (lubricated) will increase with the increase of both, sliding speed and viscosity. This in turn leads to energy losses. Therefore, there will be a trade-off between the wear performance and the optimization of energy losses. Currently, continuous efforts are undertaken to reduce the energy losses and to move towards a sustainable society and at the same time increase the reliability of tribological devices. According to the discussion above it is clear that there is a contradiction between the wear performance and the energetic performance. Therefore, classical lubrication theory has reached its fundamental limit in the energy losses reduction and new theories have to be developed. From that standpoint, solid lubricants, such as graphene or diamond like carbon are promising materials to reduce friction further and reach a so-called superlubricity regime. See this video for further information regarding hydrodynamic lubrication principles: Manoj Rajankunte Mahadeshwara I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students. -->
Stylus Profilometer: The Ultimate Tool for Accurate Surface Topography 2025 Home Wiki Stylus Profilometer: The Ultimate Tool for Accurate Surface Topography 2025 Stylus Profilometer: The Ultimate Tool for Accurate Surface Topography 2025 Manoj Rajankunte Mahadeshwara December, 4 2025 profilometer roughness measurement stylus profilometer stylus tip Surface characterization Introduction of the Stylus profilometer Analyzing the material’s surface characteristics with precision is very important for mechanical component parts and there are various techniques that are sophisticated and precise. There are various 2D and 3D surface profilometers and optical measurements are mostly used because of their non-destructive and non-contact methods of surface analysis. However, in many industries and in case of the highly reflective materials the conventional method of stylus profilometry is applied [1]. Fig-1 shows the stylus profilometer by RES surface engineering. Fig-1 Stylus profilometer by RES surface engineering [2]. Definition of Stylus profilometer A stylus profilometer is a contact-based profilometer that brings its stylus tip into direct contact with the measuring surface and traces the desired path to determine the topography of the surface. This is one of the early profilometry techniques that was developed during surface characterization research. A stylus profilometer is mostly used in measuring the step heights and the sample feature sizes that have been patterned on the surface [3]. The schematic diagram of the stylus profilometer is shown in Fig. 2. Fig-2 Schematic diagram of stylus profilometer [4]. Working principle of the Stylus profilometer The working principle of the stylus profilometer is to analyse the surface topography using a probe that moves physically along the surface to acquire the surface characteristics, such as height. This analysis will be supported by the mechanical feedback loop that monitors the force at which the probe moves over the surface of the sample. The arm of the stylus is controlled by the feedback system at a specific amount of torque known as a set point. The changes in the z direction made during the tracing of the stylus probe over the surface are measured which reconstructs the surface. The stylus profilometer works with the feedback system which physically touches the surface, and the probe is very sensitive toward the surface which might cause the destruction to the cantilever tip [5]. In Fig-3 basic elements of the stylus, profilometer are shown. Fig-3 Basic elements of the stylus profilometer [6]. Measurement consideration of the Stylus profilometer The most important part of the stylus profilometer is the cantilever tip because this tip makes physical contact with the measuring surface. The dimensions of this tip are very important to be considered where the radius of the stylus tip should be very small with low contact pressure. The materials used in this stylus tip are diamond and sapphire and the shape of the tip is usually a ballpoint tip with a conical shape. The measurement data from this stylus profilometer is very reliable as they make the contact based measurements. Fig-4 Stylus tip of the profilometer [7]. Advantages and disadvantages of the Stylus profilometer The stylus profilometer is a contact-based and destructive technique for analyzing the topographical characteristics of the material surface. The major advantage of this technique is its capability of long-distance measurement and clear wave profile of the surface roughness. The disadvantages of this method involve the physical contact of the stylus tip over the surface which leads to stylus wear. The measuring pressure maintained to trace the surface can cause scratches on the samples, however, this technique is unable to measure the topography of the viscous samples. The measurement is very time-consuming and is limited to the radius of the stylus tip. The sample preparation is one of the important steps that has to be considered during this technique where the samples might be cut and processed for tracing the detectors. The initial positioning of the stylus tip over the surface is another difficult task. Research on Stylus profilometer The stylus profilometer is a traditional method that uses physical contact over the surface for the topographical analysis, there are various researchers who have studied the performance using various calibration techniques. Kyung Joong Kim et.al., studied a new calibration technique for a stylus profilometer using multiple delta layer films [8]. The stylus profilometer technique determines the very accurate wave profile of the surface hence it is mostly used in medical applications. Massimiliano Merloa et.al. studied the tribological characteristics of the hip femoral head affected by metallic debris and found that the surface roughness of the femoral head was the influencing factor [9]. Reference: [1] Lee, D.H. and Cho, N.G., 2012. Assessment of surface profile data acquired by a stylus profilometer. Measurement science and technology, 23(10), p.105601. [2] remchem.com/resources/roughness-measurement-tips/ [3] https://lnf-wiki.eecs.umich.edu/wiki/Stylus_profilometry [4] Lee, D.H. and Cho, N.G., 2012. Assessment of surface profile data acquired by a stylus profilometer. Measurement science and technology, 23(10), p.105601. [5] https://www.nanoscience.com/techniques/optical-profilometry/stylus/ [6] https://australiasurfacemetrologylab.org/new-page [7] https://www.keyence.eu/ss/products/microscope/roughness/equipment/line_01.jsp [8] Kim, K.J., Jung, C.S. and Hong, T.E., 2007. A new method for the calibration of the vertical scale of a stylus profilometer using multiple delta-layer films. Measurement Science and Technology, 18(9), p.2750. [9] Merola, M., Ruggiero, A., De Mattia, J.S. and Affatato, S., 2016. On the tribological behavior of retrieved hip femoral heads affected by metallic debris. A comparative investigation by stylus and optical profilometer for a new roughness measurement protocol. Measurement, 90, pp.365-371. ; Manoj Rajankunte Mahadeshwara I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students. -->
Viscosity Index : Definition, Important Calculator (2025) Home Wiki Viscosity Index : Definition, Important Calculator (2025) Viscosity Index : Definition, Important Calculator (2025) Riya Veluri October, 21 2025 ASTM D2270 ASTM D567 VI viscosity index viscosity index calculator Table of Contents What is viscosity index? Calculate Viscosity Index ASTM D2270 and ISO 2909: ASTM D567 Method for Calculation of Viscosity Index from Viscosity at 100ºF and 210ºF. Viscosity Index Calculator VI modifiers: Classification: References: What is viscosity index? The;viscosity index;(VI) is an arbitrary, unitless measure of a fluid’s viscosity change relative to a temperature change. We can say that the it is the dimensionless number that shows how the temperature change can affect viscosity of an oil (engine oil and automatic gear oils, and power-steering fluids). The higher the VI, the smaller the change in fluid viscosity for a given change in temperature and vice versa. Thus, a fluid with a low viscosity index will experience a relatively large swing in viscosity as temperature changes. High-VI liquids, in contrast, are less affected by temperature changes. Viscosity Index was measured by a scale of 0 to 100; however, modern science of lubrication has led to the development of oils with very high VI. The best oils with the highest VI are stable and do not vary greatly in viscosity over a wide temperature range. In turn, this means consistent, high performance in the machine. Calculate Viscosity Index Standard ASTM D2270 Calculates Viscosity Index by Measuring the Kinetic Viscosity of Liquids at 40° and 100°C and ASTM D567 Method for Calculating Viscosity Index from Viscosity at 100ºF and 210ºF. Normally, all things being equal, highly refined mineral oils with few contaminants have high VIs and Synthetic oils generally have a higher VI than mineral oils. Below you will find a simple VI calculator. ASTM D2270 and ISO 2909: Oil viscosity (see ASTM D445) usually decreases with increasing temperature. If this reduction is significant, the system may not be sufficiently lubricated over the entire operating temperature range. The viscosity index describes this change – a high viscosity index indicates a slight viscosity change with increase in temperature compared to a low viscosity index. The standard covers procedures for calculating the viscosity index of petroleum products, such as lubricating oils, and related materials by their kinetic viscosities at 40°C and 100°C. The standard does not apply to petroleum products with a kinematic viscosity less than 2.0 mm2/s at 100 °C. This practice applies to that petroleum or lubricating products whose kinetic viscosity is between 2mm2/s and 70 mm2/s at 100°C. Equations are already provided for calculation of viscosity index for products like petroleum with kinematic viscosity above 70mm2/s at 100 °C. Values stated in SI units are considered standard. No other units are there for measurement in this standard. The values stated in SI units are to be regarded as the standard. For user reference, 1 mm2/s = 10-6m;2/s = 1 cSt. ASTM D567 Method for Calculation of Viscosity Index from Viscosity at 100ºF and 210ºF. The viscosity of oil usually decreases as the temperature increases. Viscosity index means that it measures the change in viscosity with temperature – a high viscosity index indicates a small viscosity change of a petroleum product with changes in temperature. This is the method that determines the viscosity index of lubricating oils. This method is considered obsolete by ASTM and replaced by ASTM D2270. Viscosity Index Calculator Here we are discussing the rule of calculating the viscosity Index. L = kinematic viscosity of an oil at 40 °C of 0 viscosity index having the same kinematic viscosity at 100 °C as the oil whose viscosity index needs to be calculated, mm2 /s, Y = kinematic viscosity at 100 °C of the petroleum product whose viscosity index needs to be calculated, mm2 /s. H = kinematic viscosity of an oil at 40 °C of 100 viscosity index having the same kinematic viscosity at 100 °C as the oil whose viscosity index needs to be calculated, mm2 /s. U = kinematic viscosity at 40 °C of the lubricant or petroleum product whose viscosity index needs to be calculated, mm2 /s. The viscosity index can be calculated using the following formula: ASTM D2270 table to get the L & H values for the calculations. Here is a simple VI calculator to calculate viscosity index from the temperatures at 40°C and 100°C: Viscosity Index (VI) Calculator Kinematic viscosity 40°C [cSt or mm^2/s] Kinematic viscosity 100°C [cSt or mm^2/s] Viscosity Index VI [ -] This calculator allows calculating kinematic viscosity at 100°C from the known VI and kinematic viscosity of the oil at 40°C: Kinematic Viscosity @ 100ºC Calculator Viscosity Index VI [-] Kinematic viscosity 40°C [cSt] Calculated Value [cSt] This calculator allows calculating kinematic viscosity at 40°C from the known VI and kinematic viscosity of the oil at 100°C: Kinematic Viscosity @ 40ºC Calculator Viscosity Index VI [-] Kinematic viscosity 100°C [cSt] Calculated Value [cSt] The common equation used to calculate the viscosity by interpolation between two reference points is with the Ubbelohde-Walther equation, which is adopted in ASTM D341. Here is a simple calculator to interpolate viscosity: Kinematic viscosity interpolation ASTM D341 Temperature and viscosity T1, v1 [ 0C ] 0C ]" id="fieldname2_4" name="fieldname2_4" step="1" class="field digits small" type="number" value="40" style=""> Temperature and viscosity T2, v2 [ 0C ] 0C ]" id="fieldname3_4" name="fieldname3_4" step="1" class="field digits small" type="number" value="100" style=""> Temperature and viscosity T3, v3 [ 0C ] 0C ]" id="fieldname4_4" name="fieldname4_4" step="1" class="field digits small" type="number" value="60" style=""> Kinematic Viscosity at T1, [cSt or mm^2/s] Kinematic Viscosity at T2, [cSt or mm^2/s] Kinematic Viscosity at T3, [cSt or mm^2/s] ; VI modifiers: VI modifiers are normally used in multi-grade engine oils, gear oils and automatic transmission fluids, power steering fluids, hydraulic fluids and greases. Widely used materials are, for example, olefin copolymers (OCP), polyalkyl methacrylates (PAMA), poly isobutylene (PIB), styrene block polymers, methylmethacrylate (MMA), polybutadiene rubber (PBR), cis-polyisoprene. (of a synthetic rubber), polyvinyl palmitate, polyvinyl caprylate, copolymers of vinyl palmitate with vinyl acetate, and various other materials used as viscosity index modifiers in a variety of petroleum oils. Below is the table of viscosity indexes of different petroleum products & fluids for ref: Oil / fluid types VI Mineral oil 95 – 105 Multi-grade oil 140 – 200 PAO oil 135 – 160 Ester 140 – 190 Vegetable oil 195 – 210 Glycol 200 – 220 Silicone oil 205 – 400 Classification: The VI scale was established by the Society of Automotive Engineers (SAE). The arbitrarily chosen temperatures for reference are 100 and 210 °F (38 and 99 °C). The scale was initially interpolated between 0 for naphthenic Texas Gulf crude and 100 for paraffinic Pennsylvania crude. Since the scale’s inception, better oils have also been produced, making VI over 100 (see below). VI-improving additives and high-quality base oils are widely used nowadays, allowing VI to be achieved over a value of 100. The viscosity index of synthetic oils ranges from 80 to over 400. Normally when we are talking about the synthetic oils, then there are normally two types of synthetic oil available for widely used in different critical & high temperature applications. PAO Based synthetic Oil (Polyalphaolefin) PAG based synthetic oil (Polyalkylene Glycol). Study shows that PAO based synthetic oils have better viscosity index compare to Group – i, group – ii or group – iii oils (Without addition of any index significantly better than PAO-based lubricants of the same viscosity grade. VI Classification Under 35 Low 35 to 80 Medium 80 to 110 High Above 110 Very high Conclusions: The viscosity index is an essential parameter indicating the flow properties related to the temperature of the oil. Selection of oil for a specific application without considering its VI, e.g. cause premature wear and costly machinery damage. As we have already discussed that normally in synthetic oil, Viscosity index is greater than the any kind of mineral oil. So, In critical applications or high temperature applications synthetic oil or grease is preferred rather than mineral oil based lubricants. References: BLAIR, G. Viscosity of Liquids and Colloidal Solutions.;Nature;156,;147–148 (1945). https://doi.org/10.1038/156147a0 http://ppapco.ir/wp-content/uploads/2019/07/ASTM-D2270-2016.pdf https://wiki.anton-paar.com/en/viscosity-index/ https://en.wikipedia.org/wiki/Viscosity_index Riya Veluri The article is written by Riya Veluri, an editorial team member of Industrial Lubricants. After her graduation, Riya works as a website developer & SEO specialist in Lubrication & Tribology Industry & writes technical articles on Lubricants, Lubrication, Reliability & sustainability. --> 4 Comments Bryan Miller says: 16.08.2022 at 21:24 Is there a way to calculate the Viscosity at -40C for Dexron 75W-90 pour point is -57C Log in to Reply TriboNet says: 18.08.2022 at 22:20 Hello Bryan! You can use the Ubbelohde-Walther calculator. To use it you would need viscosity at 2 different temperatures. I hope this helps! Log in to Reply Chris says: 23.10.2023 at 13:57 Hi there! Great article but it didn’t explain what’s the difference (if any) between ASTM D2270 and ISO 2909, as we could see on many engine oil manufacturers technical sheets. Could you please explain that? Best of luck and keep up the good work you are doing! Chris Log in to Reply CHRISHAN says: 21.01.2024 at 11:24 Hi, Could you please tell me PAG base oil is good for a slow RPM gearbox that is lubricated by splash lubrication? Log in to Reply Leave a Reply Cancel reply You must be logged in to post a comment. Login using social account This site uses Akismet to reduce spam. Learn how your comment data is processed.
Types of Lubrication Systems – Complete Guide and its Benefits (2025) Home Wiki Types of Lubrication Systems – Complete Guide and its Benefits (2025) Types of Lubrication Systems – Complete Guide and its Benefits (2025) Riya Veluri October, 21 2025 Dry Sump Lubrication System Grease Lubrication System lubricant Lubrication system Oil Lubrication System Progressive Lubrication systems Wet Sump Lubrication Table of Contents Introduction to Types of Lubrication system Types of Lubrication system:;Lubricants and Friction What are the types of lubrication system? Types of lubrication systems Benefits of using types of lubrication systems Introduction to Types of Lubrication system There are many types of lubrication systems used across mechanical systems and industrial machinery. From traditional oil and grease systems to modern approaches like MQL (Minimum Quantity Lubrication), each system offers unique benefits and trade-offs. In this guide, we explore each type in detail, explain how they work, and help you choose the right system for your application. Types of Lubrication system:;Lubricants and Friction Lubricants act to reduce friction. Now, this makes it easier to keep machines running smoothly, and it cuts down on the amount of heat and wears caused by friction. A machine’s moving parts generally experience three types of friction. Sliding Friction Rolling Friction Fluid Friction Sliding friction occurs when two surfaces in contact slide past each other. This type of friction offers the most resistance to motion. So machinery is usually built to minimize or eliminate it. Building a machine to minimize sliding friction is to place rolling elements between the moving surfaces. This is the principle behind rolling contact bearings. Rolling contact bearings experience rolling friction that is considerably less severe than sliding friction. Still, they must be properly lubricated to reduce heat and wear. The useful life of a rolling contact bearing or anti-friction bearing would be drastically shortened if the bearing were operated dry. Another way to build a machine to reduce friction is to separate two sliding surfaces by a lubricant film. As long as the surfaces do not touch, sliding friction is eliminated. There’s still some fluid friction within the lubricant, but it’s much less than sliding friction. Fluid friction is the resistance to motion within a fluid, and it’s not as obvious as other types of friction. Lubricants are made from one of four groups of materials or medium. Animal Vegetable Mineral Synthetic Originally animal and vegetable lubricants were the most widely used. Still, they’ve been almost completely replaced by mineral and synthetic types. But whatever lubricant you use, to get maximum benefits from lubricants we need to use a proper lubrication system. What are the types of lubrication system? An automatic lubrication system, also known as a centralized lubrication system, is defined as a controlled and precise amount of a specific lubricant that is delivered to a specific location at a specific time when the machine is running. Reasons for using the types of lubrication system The study says that in plant maintenance, lubrication cost is approx. 3% of the total cost of maintenance budget, but lubrication-related activities could reach up to 40% of the total maintenance budget. If one needs to achieve optimum reliability & maximum benefits from the Lubrication system, the following factors must be considered. The Right Lubricant The proper lubricants selection for proper application is vital to get maximum benefits from the lubrication system. Normally right lubricants selection can depend on four factors of applications. Speed Ambiance Load Temperature Right Quantity Neither less quantity of grease is good nor high quantity. An increase qty of grease can increase temperature & friction inside the bearing & can decrease the efficiency or lifetime of bearing lead to failure. Only measured lubricant qty reached to lubrication point so, no wastage of lubricants hence lubrication cost reduce. At Right Time Lubricants will effectively reduce friction & wear if supplied at the right timing with proper re-lubrication interval. At Right Point Grease or oil should reach the right point where friction & wear is high. If it does not reach the friction point, then it will be of no use. Types of lubrication systems Different types of lubrication systems have been designed and developed over the years based on the specific requirements of the instrument and the different industrial sectors. We are talking about the most popular and beneficial lubricant systems used by different plants in different industrial sectors. Oil Lubrication System The oil lubrication system is also known as the loss lubrication system. In this system, oil or liquid grease produces a thin oil film that protects the parts. It is renewed at regular intervals by an automatic lubrication system with an electric oil pump. The main systems used in oil lubrication are single-line systems and 33V systems. Splash Lubrication System In these types of lubrication systems, the lubricating oil accumulates in an oil sump. Most small four-stroke petrol engines use splash lubrication. On horizontal crankshaft engines, a dipper on the bottom of the connecting rod scoops up oil from the oil sump for the bearings. When the engine runs, the dipper dips in the oil once in every crankshaft revolution and causes the oil to splash on the cylinder walls. Recirculating Oil System The purpose of oil recirculation is to supply lubrication and provide cooling to bearings and gears. An electric pump ensures that an appropriate lubricant pressure is available in the mainline, where the oil flow is also measured and regulated. Air-Oil Lubrication System This system consists of a controlled air-oil stream utilized to cool and carry small quantities of air-oil particles to the lubrication points. It is suitable for large machines in heavy industry and machine tools. Air Oil lubrication system is the optimal solution for economical and reliable lubrication of bearings. The bearings have a longer service life, and thus high production availability is attained. Grease Lubrication System In this system, the greasing pumps provide a proper amount of grease to the lubrication points. The main systems used for grease lubrication are Dual Line and Progressive systems. Dual Line Lubrication Systems The dual-line system has a modular design that allows easy configuration and expansion of the system. It is suitable for industries with large machines and many lubrication points. SKF has developed a Dual Line Lubrication system. These flexible systems are simple to design and can be reduced easily by removing metering devices or extended by installing additional metering devices. You can know more about the Dual Line Lubrication system by watching the video. Progressive Lubrication systems For small to medium-sized machines that require continuous lubrication, a progressive lubrication system will best suit them. Progressive systems provide uninterrupted lubrication as long as the pump is turned on. Once the pump is turned off, the pistons of the progressive metering device will stop at their current position. When the pump starts supplying lubricant again, the pistons will move to where they were left. MQL (Minimum Quantity Lubrication) System & Near Dry Machining An innovative new technology that replaces traditional and pure oil-liquid systems in a machining environment. A controlled compressed air flow carries minimal cutting oil in an “aerosol” format to the cutting surface by external or internal (through equipment lubrication). MQL is a little bit bigger of an umbrella than near dry machining. MQL can be applied to multiple manufacturing operations like sheet metal forming operations, blanking, forming, cutting, etc. Near dry machining is more specific to machining operations such as mills, drills, turning operations, and tapping. Wet Sump Lubrication System In wet sump lubrication systems, the oil is transported to different engine parts with the help of a sump strainer, and the oil pressure is about 4 to 5 kg / cm2. After lubrication, the oil is again taken to the oil sump. In this case, the oil is present in the samp. Therefore, it is called a wet sump lubrication system. The advantage of the wet sump system is its simplicity. And machine parts are near where the lubrication will be applied through lubricating oil, there are not many parts required, and it is relatively safe to make in the car. Dry Sump Lubrication System A dry-sump lubrication system is particularly used in racing cars, and it has additional components to the wet-sump lubrication system. These components include an oil tank with a breather tank. Furthermore, the dry-sump lubrication has a cyclone separator and a multi-stage pump. Check out the video to know more about the Dry Sump Lubrication system. So, we have covered different types of lubrication systems used in different applications to achieve the maximum benefit of lubrication. Except achieving max benefit, there are multiple benefits are there of the automatic lubrication system. Benefits of using types of lubrication systems Easy access: All important components of the machine can be oiled, regardless of criticality and location. This ensures safe machine operation and reduces the risk of undefined lubricating components by maintenance personnel. Increase the machine’s efficiency: In a centralized lubrication system, lubrication occurs when the machine is running so that the lubricant is distributed evenly across all friction points and increases the efficiency of the overall machine performance, less breakdown, less downtime, and replacement cost. Reduced energy consumption: In centralized or automatic lubrication, the system as lubricant reaches the friction point at the right time, in the right amount so low friction, energy consumption is lower, and overall machine operation cost is lower. Cleanliness: Lubricant contamination with the effect of foreign particles carries the overall performance and life. Avoiding grease contamination in manual lubrication systems can be a challenge for every maintenance person. However, through an automatic lubrication system, we can avoid contamination of lubricants and achieve cleanliness. In an automatic lubrication system, an automatic lubricant can provide an uninterrupted and accurate flow of fresh and clean lubricant at the lubrication points. Reference: [1] https://onlinelibrary.wiley.com/doi/abs/10.1002/9783527645565.ch20 [2] https://www.academia.edu/download/121935517/Maintenance_4_25p_merged.pdf Riya Veluri The article is written by Riya Veluri, an editorial team member of Industrial Lubricants. After her graduation, Riya works as a website developer & SEO specialist in Lubrication & Tribology Industry & writes technical articles on Lubricants, Lubrication, Reliability & sustainability. -->
Pour Point Definition & Testing Standards: Complete Guide 2025 Home Wiki Pour Point Definition & Testing Standards: Complete Guide 2025 Pour Point Definition & Testing Standards: Complete Guide 2025 Riya Veluri October, 21 2025 ASTm standard for pour point common values for pour point measurement tools measuring pour point pour point definition pour point depressant pour point table Table of Contents Pour point definition How to Measure Pour Point of Lubricants? What is Pour Point Depressant? Pour Point of Various Lubricants and Oils Pour point definition The pour point is the lowest temperature at which oil flows in a specified lab test. Specifically, the pour point is 3℃ (5℉) above the temperature at which the oil shows no movement when a lab sample container is held horizontally for 5 seconds. Pour point is an indication of the cold temperature properties of oil. But we should not select a lubricant product based solely on its pour point. The cloud point is also a very important factor for choosing any lubricant for any application. Cloud point is approximately the low temperature at which the oil becomes cloudy due to the formation of wax crystals within the oil. ASTM D97 (ISO 3016 or IP 15) covers the standard methods to measure the pour point of petroleum products. In addition, several methods are used to determine cloud points, including ASTM D5772. How to Measure Pour Point of Lubricants? The Seta Cloud and Pour Point Bath give the required cold bath to liquid to take them to the necessary stage. It utilizes the current and with the help of conditioners and couples present in them. They cool the fluids up. They hold four test positions. They can supply the temperature range from 9°C to -69°C. The equipment identifies the minimum safe operating temperature. The bath accommodates four jackets and a steel cover, and a drain tap. Methods of pour point : These are the most common methods that are used to determine the pour point of a product: D97 – Pour Point of Petroleum Products D5853 – Pour Point of Crude Oils; D5949 – Pour Point of Petroleum Products (Automatic Pressure Pulsing Method) Measuring the pour point of petroleum products Manual method: ASTM D97, Standard Test Method for Pour Point of Crude Oils. The specimen is cooled inside a cooling bath to allow the formation of paraffin wax crystals. At about 9 °C above the expected pour point, and for every subsequent 3 °C, the test jar is removed and tilted to check for surface movement. When the specimen does not flow when tilted, the jar is held horizontally for 5 sec. If it does not flow, 3 °C is added to the corresponding temperature, resulting in the pour point temperature. Automatic method: ASTM D5949, Standard Test Method for Pour Point of Petroleum Products (Automatic Pressure Pulsing Method) is an alternative to the manual test procedure. It uses automatic apparatus, and yields pour point results in a format similar to the manual method (ASTM D97) when reporting at a 3 °C. Under ASTM D5949, the test sample is heated and then cooled by a Peltier device at a rate of 1.5±0.1 °C/min. At either 1 °C or 3 °C intervals, a pressurized pulse of compressed gas is imparted onto the sample’s surface. Multiple optical detectors continuously monitor the sample for movement. The lowest temperature at which motion is detected on the sample surface is the pour point. Test Objective/Summary Applications Typical results High/Low Pour Point ( ASTM D97 – 96a) 1) This is the test to determine the lowest temp at which oil will flow under the influence of gravity. 2) The oil sample is placed in a beaker along with a thermometer, sealed with a cork, heated to 46℃ (115℉), and then progressively cooled. The jar is removed at progressive 3℃ (5℉) intervals & tilted to determine fluidity. 3) The pour point is 3℃ (5℉) above the temperature at which the oil shows no movement when a lab sample container is held horizontally for 5 seconds. All lubricants exposed to cold start or cold operating temperatures. -10℃ or -32℃. Low is better What is Pour Point Depressant? Pour ​​point depressant is an additive (polymer) that allows oils and lubricants to flow at very low temperatures without the heavy wax formation at these cold temperatures and enables the oil to remain pumpable (flowable). They are typically used in paraffinic base oils in applications where extremely low machine startup temperature conditions are possible. Most paraffinic motor oils use pour point depressors. Pour Point Depressants work as modifiers & modify the interface between the crystallized wax and the oil. Pour Point of Various Lubricants and Oils Pour points for Crude oils range from 32 °C to below −57 °C (90 °F to below −70 °F). Some typical values of Pour Point are provided below in the table: Liquid Pour Point Multi-grade engine oil -35 Deg. C Monograde engine oil -23 Deg. C Turbine Oil -18 Deg. C Synthetic Polyol ester -32 Deg. C Castor Oil -33 Deg. C Coconut Oil 21 Deg. C Groundnut Oil 3 Deg. C Mustard Oil -18 Deg. C Sunflower Oil -18 Deg. C Olive Oil -9 Deg. C Kerosene -69 Deg. C Table: Typical Pour Point Values for Oils Typical properties of commonly used classes of synthetic lubricants (oils). Lubricants Thermal stability, (◦C) Specific gravity at 20◦C Flash point (◦C) Pour point (◦C) Mineral oils 135 0.86 105 −57 Diesters 210 0.9 230 −60 Neopentyl polyol esters 230 0.96 250 −62 Phosphate esters 240 1.09 180 −57 Silicate esters 250 0.89 185 −65 Disiloxanes 230 0.93 200 −70 Silicones Phenyl methyl 280 1.03 260 −70 Fluoro 260 1.2 290 −50 Polyphenyl ethers 4P-3E 430 1.18 240 −7 5P-4E 430 290 +4 Perfluoropolyethers Fomblin YR 370 1.92 none −30 Fomblin Z-25 370 1.87 none −67 Adapted from PRINCIPLES AND APPLICATIONS OF TRIBOLOGY, Bharat Bhushan, 2013 Due to the presence of high molecular weight components, such as wax, asphaltene, and resin, heavy and extra-heavy crude oils usually have higher pouring points. The pour point of the liquid can be improved by using depressants like polymethacrylates, alkylated wax fennel, alkylated wax naphthalene, etc. References Pour Point - Wikipedia PRINCIPLES AND APPLICATIONS OF TRIBOLOGY, Bharat Bhushan, 2013 Riya Veluri The article is written by Riya Veluri, an editorial team member of Industrial Lubricants. After her graduation, Riya works as a website developer & SEO specialist in Lubrication & Tribology Industry & writes technical articles on Lubricants, Lubrication, Reliability & sustainability. --> 2 Comments Dattatray J. Gharge says: 14.04.2023 at 12:38 very good information , easy to understand . Log in to Reply Vijay Painter says: 23.10.2023 at 07:43 nice information provided. Thanks. Log in to Reply Leave a Reply Cancel reply You must be logged in to post a comment. Login using social account This site uses Akismet to reduce spam. Learn how your comment data is processed.
Archard Wear Equation: Importance and Formula (2025) Home Wiki Archard Wear Equation: Importance and Formula (2025) Archard Wear Equation: Importance and Formula (2025) Manoj Rajankunte Mahadeshwara October, 21 2025 archard equation wear coefficient wear equation wear model wear volume formula Introduction to Archard wear equation The Archard wear equation is a fundamental empirical model in tribology that relates wear volume to load, sliding distance, and material hardness. The importance of wear losses leads to considerable effort in establishing theories and predictive models of wear. Meng and Ludema; [1] have identified 182 equations for different types of wear. Among them were empirical relations, contact mechanics-based approaches, such as Archard wear model, and equations based on material failure mechanisms, which were found to get more popular recently according to authors. In this review, empirical equations won’t be considered, as they are applicable for very specific range of parameters. No unified fundamental theory of wear was established so far, and as a consequence, there is no unique wear model, applicable in all cases. Archard wear equation Derivation One of the most famous and frequently used wear equations was developed by Holm and Archard in 1953[2]. The Archard wear equation model considers adhesive wear and assumes the sliding spherical asperities to deform fully plastically in contact. The area of contact then is circular with the contact area equal to , where is the radius. The mean contact pressure in this case equal to hardness of the softer material, and thus, . After the asperity slides a distance of , it is released from the contact and there is a probability , that debris will form. It is assumed, that if debris is formed, it is formed as a hemisphere with the radius , having a volume of . Then the wear volume per sliding distance; ; is , and hence, as , . Introducing , the total wear volume for a sliding distance , equals to . The coefficient ;is known as a wear coefficient and is frequently used to compare the material wear resistance[2,3]. Most of the times, it is estimated experimentally. Although the Archard’s equation was developed for the adhesive wear, it is widely used for modeling of abrasive, fretting and other types of wear[4]. It should be noted that Archard wear equation is often applied on a local level. For that, the Archard equation is first formally divided by the area : (1) ; h = k *P_c/H*s \end{eqnarray*} " title="Rendered by QuickLaTeX.com" data-src="https://quicklatex.com/cache3/7c/ql_3221f18a274f582325609d585785867c_l3.png"> h = k *P_c/H*s \end{eqnarray*} " title="Rendered by QuickLaTeX.com" data-eio="l"> where are the local wear depth and contact pressures. Further, this equation is differentiated in time and the equation takes the following form: (2) ; \frac{\partial h}{\partial t} = k *P_c/H*v \end{eqnarray*} " title="Rendered by QuickLaTeX.com" data-src="https://quicklatex.com/cache3/72/ql_0b8f38db42dbbc21e5d9ddb0b336d272_l3.png"> \frac{\partial h}{\partial t} = k *P_c/H*v \end{eqnarray*} " title="Rendered by QuickLaTeX.com" data-eio="l"> where is the sliding speed. This equation can be used to calculate wear locally if the contact pressure is known and is also applied to track the evolution of the surface roughness in rough contacts. This approach was implemented in Tribology Simulator (a stand-alone free to download software). A chart linking the specific wear coefficients and friction is given below: Friction coefficients and specific or volumetric wear rate map of tribological materials, [5] References [1] Expressing Wear Rate in Sliding Contacts Based on Dissipated Energy. Huq, M.,Z., Celis, J.-P. s.l. : Wear, 2002, Vol. 252. [2] Wear Patterns and Laws of Wear – A Review. Zmitrowicz, A. 2006, Journal of Theoretical and Applied Mechanics, pp. 219-253. [3] Classification of Wear Mechanisms/Models. Kato, K. 2002, Journal of Engineering Tribology, pp. 349-355. [4] On the Correlation Between Wear and Entropy in Dry Sliding Contact. Aghdam, A.,B., Khonsari, M.,M. s.l. : Wear, 2011, Vol. 270. [5] Achieving Ultralow Wear with Stable Nanocrystalline Metals, John F. Curry et al.,https://doi.org/10.1002/adma.201802026 Manoj Rajankunte Mahadeshwara I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students. -->
Spalling Damage: 3 Main Types, Causes & Prevention Guide Home Wiki Spalling Damage: 3 Main Types, Causes & Prevention Guide Spalling Damage: 3 Main Types, Causes & Prevention Guide ankitkumar September, 28 2025 Bearings Crack fatigue Flaking Hertzian Stress Pitting Spalling Stress Concentration Table of Contents Bearing Failure Modes Definition of Spalling Damage 3 Modes of Spalling Damage Pitting vs. Spalling Damage – Key Differences Causes of Spalling Damage Bearing Failure Modes Spalling damage is a common cause of bearing failure and occurs when cracks form in the running surfaces, causing flakes of material to detach. This progressive fatigue phenomenon impacts bearing performance, increases vibration, and signals the end of service life if left unaddressed. Understanding the modes of spalling damage, their causes, and prevention strategies is crucial to extending bearing life. Bearing damage, and ultimately, failure, can be caused by a variety of conditions, including improper mounting, poor lubrication, and overloading, to name a few. The mode of damage — what actually happened to the bearing as a result of detrimental conditions — is characterized by visible features, such as discoloration, wear marks, or pitting, on the rolling element and raceway surfaces. However, different modes of damage can produce visually similar results, although their causes and long-term effects may not be the same. This is why it’s important to understand the operating conditions when investigating bearing damage, as they can provide additional clues regarding the root cause of the damage. In this article , we will focus on the surface/subsurface initiated fatigue phenomena called spalling. The ISO standard 15243:2017, Rolling bearings – damage and failures – terms, characteristics, and causes, classifies failure modes for rolling bearings made of standard bearing steels. The standard defines six primary damage/failure modes, along with various sub-modes (Fig.1). Figure 1 :- Modes of damage/failure for rolling bearings according to ISO 15243. Image credit: SKF Definition of Spalling Damage Spalling damage is the result of surface or subsurface fatigue, which causes fractures to form in the running surfaces. When the rolling elements travel over these cracks, pieces, or flakes, of material break away. (Spalling is also referred to as “flaking,” “peeling,” or “pitting.”) In the ISO damage/failure modes, spalling occurs in the category of “Fatigue,” under both “Subsurface-initiated fatigue,” and “Surface initiated fatigue.” Spalling damage is progressive (Fig.2) and can indicate that a bearing has reached the end of its fatigue life. In general , Spalling is the pitting or flaking away of bearing material. Figure 2 :- Spalling in Ball bearings This primarily occurs on the races and rolling elements. The many types of primary damage referenced throughout this guide may eventually deteriorate into a secondary spalling damage mode. 3 Modes of Spalling Damage Three distinct modes classified are stated below : 1. Geometric stress concentration (GSC) spalling.:- The causes include misalignment, deflection or edge loading that initiates high stress at localized regions of the bearing. GSC occurs at the extreme edges of the race/roller paths, or it can also be the result of shaft or housing machining errors. 2. Point surface origin (PSO) spalling :- Very high and localized stress generates this type of damage. The spalling is typically from nicks, dents, debris, etching and hard-particle contamination in the bearing. It’s the most common type of spalling damage and often appears as arrowhead-shaped spalls, propagating in the direction of rotation. 3. Inclusion origin (IO) spalling .:- This damage, in the form of elliptically shaped spalls, occurs when there’s bearing material fatigue at localized areas of sub-surface, non-metallic inclusions following millions of load cycles. Due to improvements in bearing steel cleanliness in recent decades, encountering this type of spalling is unlikely. Figure 3 :- These images show representative rolling-element fatigue failure of an inner race (left) and ball (right) from 120-millimeter-bore ball bearings made of AISI M-50 steel. The failure manifests itself as a spall that is limited to the width of the running track and the depth of the maximum shearing stress below the contact surface. The spall can be of surface or subsurface origin. A spall originating at the surface usually begins as a crack at a surface defect or at a debris dent that propagates into a crack network to form spalling damage. A crack that begins at a stress riser, such as a hard inclusion below the running track in the region of the maximum shearing stress, also propagates into a crack network to form a spall. Fatigue failures that originate below the contacting surface are referred to as classical rolling-element fatigue. Failure by classical rolling-element fatigue is analogous to death caused by old age in humans. Spalling damage can occur on the inner ring, outer ring, or balls. This type of failure is progressive and once initiated will spread as a result of further operation. It will always be accompanied by a marked increase in vibration, indicating an abnormality. The remedy is to replace the bearing or consider redesigning to use a bearing having a greater calculated fatigue life. Figure 4 :- Moderately spalled area of bearing Image Credits :- Schaeffler.com Pitting vs. Spalling Damage – Key Differences Even when operating correctly, rolling element bearings will eventually fail as a result of a surface fatigue phenomenon. It starts after some variable time of service as embryonic particles that are liberated from the surface of a race or rolling element in the load zone. Surface fatigue leaves craters that act as stress concentration sites. Subsequent contacts at those sites cause progression of the spalling process. The duration of satisfactory performance depends largely on the durability of bearing surfaces. Generally, there are three types of surface contact damage that can occur under proper operational conditions: surface distress, fatigue pitting, and fatigue spalling. Other surface damage can occur due to improper mounting or improper operating conditions. Surface distress appears as a smooth surface resulting from plastic deformation in the asperity dimension. This plastic deformation causes a thin work-hardened surface layer (typically less than 10 µm). Pitting appears as shallow craters at contact surfaces with a depth of, at most, the thickness of the work-hardened layer (approximately l0 µm), as shown in Figure 5. Figure 5 :- Pitting and Spalling Spalling damage leaves deeper cavities at contact surfaces with a depth of 20 µm to 100 µm as shown in Figure 2. It must be noted here that no common definitions have been established to distinguish spalling from pitting in the literature. In most of the literature, spalling and pitting have been used indiscriminately, and in some other literature, spalling and pitting were used to designate different severities of surface contact fatigue. For instance, Tallian defined “spalling” as macroscale contact fatigue caused by fatigue crack propagation and reserved “pitting” as surface damage caused by sources other than crack propagation. One of the reasons for the confusing definitions is probably due to the fact that the physical causes of pitting and spalling damage have not yet been established. To discuss spalling and pitting on a common ground, the following discussion rests on the definitions according to the phenomena as described in the foregoing; that is, pitting is the formation of shallow craters by surface-defect fatigue, and spalling is the formation of deeper cavities by subsurface-defect fatigue. Figure 6 shows an example of advanced fatigue wear. The shaft in this tapered roller bearing was approximately 200 mm in diameter and some of the advanced spalling from multiple sites is 30 mm across. Figure 6:- Well-developed Fatigue Spalls on Bearing Inner Race Figure 7 shows a large single spall some 250 µm across. Initial spall particles are typically 30 µm to 50 µm, but it is common for several particles to be generated from individual spall sites. Note at the sharper crater wall (near the top edge of the spall in this micrograph) there are several cracks associated with the spall. Figure 7. Typical Spall Crater (Scale Bar = 400 µm) Though both spalling and pitting are the common forms of surface contact fatigue, spalling results in more rapid deterioration of surface durability when compared to pitting. Spalling damage often induces early failure by severe secondary damage. It has been repeatedly reported as the more destructive surface failure mode for gear contacts. Such secondary damage can result in roller or race breakage, initiated from a severe spall on the contact surface, as well as friction- or heat-induced surface seizure, or complete spalling over all of the contact surfaces. Causes of Spalling Damage Way’s hypothesis postulated that lubricating oil in a surface crack was trapped when the approaching contact reached the surface opening and pinched the crack closed. As a result, the crack tip was extended by the hydraulic pressure of the oil sealed between the crack surfaces. Subsequent work by Keer and Bryant found that the dominant mechanism for surface-breaking crack growth was Mode II (shear) propagation which contradicts Way’s assumption of Mode I (tension) crack propagation. Bower performed a fracture-mechanics analysis of crack propagation in the presence of lubricating oil. His results do not appear to support Way’s hypothesis, either. Furthermore, the experimental results obtained by Cheng and others showed that the surface crack growth was very slow. According to Ding and Kuhnell, surface crack growth can only be in Mode II and can result only in shallow craters. To better understand spalling/pitting mechanisms, many researchers have also studied the behavior of subsurface cracks under contact loads. Fleming and Suh used fracture mechanics methods to analyze the propagation of subsurface cracks parallel to the contact surface. Their results showed that the stress intensity factors (SIFs) for Mode I and Mode II were quite low. Kaneta and others studied the growth mechanism of subsurface cracks by numerically analyzing the behavior of a three-dimensional subsurface crack parallel to the contact surface. They concluded that the propagation of subsurface cracks is mainly by Mode II. More recently, Ding and others studied the behavior of subsurface cracks beneath the pitch line of a gear tooth, focusing on developing a fundamental understanding of the mechanisms of spalling in gears. Using the finite element method, the potential modes of crack propagation and failure were analyzed and the values of the stress intensity factors (SIFs) of the subsurface cracks were below the critical SIF, Kc. Consequently, ligament collapse at crack tips was hypothesized as the cause of spalling from subsurface cracks. Elastic-plastic finite element analysis was also performed to further evaluate the hypothesis as the failure mechanism of spalling in gears. According to Ding and Kuhnell, subsurface spalling by crack propagation mechanisms would be too slow. Stress intensity factors for both Mode I and Mode II never exceed the critical stress intensity of crack failure in their study. Therefore, spalling is not caused by crack propagation of subsurface cracks. Ding and others calculated the mean stress, sm, in a ligament region between the crack tip and the contact surface, and concluded that spalling results from ligament collapse at subsurface crack tips. The angles between the direction of the maximum shear stress and the crack line were 33 degrees at the trailing tip and 53 degrees at the leading tip of the subsurface crack. Therefore, a spall cavity should have a shallow wall at an angle of approximately 33 degrees at the trailing end and a steep wall of 53 degrees at the leading end of rolling direction. This finding was supported by the results of the experimental evidence as were the spall depth predictions. Figure 8 provides sectioned micrographs of three spall sites. Figure 8 :- Sectioned Micrographs of Spalling on Gear Teeth Surfaces Near Pitch Line Figure 8a shows a spall site with the material of the potential spall particle(s) still attached. Figure 8b is a spall which has progressed and a number of spall particles have detached. Figure 8c is a cross-section of a spall from which the particle(s) have been liberated. Note the cracks at the steep walls of Figure 8b, Figure 8c and Figure 7. These indicate the readiness for the spalling to continue on subsequent contacts at these sites. References https://www.tribonet.org/wiki/surface-fatigue/ https://www.linearmotiontips.com/whats-the-difference-between-brinelling-spalling-fretting/ https://www.pitandquarry.com/determining-types-of-bearing-damage/ https://www.machinerylubrication.com/Read/664/wear-bearings-gears/ Keer, L. M., and Bryant, M. D. (April 1, 1983). “A Pitting Model for Rolling Contact Fatigue.” ASME. J. of Lubrication Tech. April 1983; 105(2): 198–205. https://doi.org/10.1115/1.3254565 Way, S. (February 17, 2021). “Pitting Due to Rolling Contact.” ASME. J. Appl. Mech. June 1935; 2(2): A49–A58. https://doi.org/10.1115/1.4008607 Ding, Y. and Kuhnell B.T. “The Physical Cause of Spalling in Gears.” Machine Condition Monitoring, The Research Bulletin of the Centre for Machine Condition Monitoring, Vol. 9. Monash University, 1997. Lyu, Y., Bergseth, E. & Olofsson, U. Open System Tribology and Influence of Weather Condition.;Sci Rep;6,;32455 (2016). https://doi.org/10.1038/srep32455 BRUNTON, J., FIELD, J. & THOMAS, G. Deformation of Solids By the Impact of Liquids, and its Relation to Rain Damage in Aircraft and Missiles, to Blade Erosion in Steam Turbines, and to Cavitation Erosion.;Nature;207,;925–926 (1965). https://doi.org/10.1038/207925a0 ankitkumar Ankit works in the Mechanical Maintenance Division of Hot Strip Mill, Jindal Stainless in India. He has keen interest in HVAC , Hot Rolling Machinery & Equipment, and Industrial Hydraulics. -->
Elastohydrodynamic Lubrication: Theory, Types & Practical Guide Home Wiki Elastohydrodynamic Lubrication: Theory, Types & Practical Guide Elastohydrodynamic Lubrication: Theory, Types & Practical Guide Manoj Rajankunte Mahadeshwara September, 28 2025 calculate central film thickness definition EHD ehd meaning EHL elastohydrodynamic history lubrication minimum film thickness theory what is wiki wikipedia Table of Contents What is Elastohydrodynamic Lubrication (EHL)? History of Elastohydrodynamic Lubrication Theory & Equations of Elastohydrodynamic Lubrication Film Thickness in Elastohydrodynamic Lubrication Central and minimum film thickness: Online EHL film thickness calculator What is Elastohydrodynamic Lubrication (EHL)? Elastohydrodynamic lubrication (EHL) describes a lubrication regime where high pressure causes significant elastic deformation of the contacting surfaces, deeply affecting the shape and thickness of the lubricating film. EHL is essential in many machine elements like rolling bearings, gears, and cams to reduce friction and wear. This article explains the fundamentals of elastohydrodynamic lubrication, its theory, how film thickness is measured, and where it applies in engineering practice. Elastohydrodynamic Lubrication – or EHL – is a lubrication regime (a type of hydrodynamic lubrication (HL)) in which significant elastic deformation of the surfaces takes place and it considerably alters the shape and thickness of the lubricant film in the contact. The term underlies the importance of the elastic deflection of the bodies in contact in the development of the total lubricant film. EHL, the same way as HL, is used to decrease friction and wear in tribological contacts. It is achieved by the development of a thin lubricant film between rubbing surfaces, which separates them and decreases friction. EHL has characteristic features, such as constant film thickness and almost Hertzian contact pressure profile within the Hertzian contact area, as shown in the figure below. These features have been extensively used in construction of approximate solutions of EHL theory. Fig. 1. Hertz Contact Pressure Vs. Elastohydrodynamic Pressure. History of Elastohydrodynamic Lubrication Classical Hydrodynamic Lubrication (HL) theory assumes the bodies to be rigid. In 1916 Martin obtained a closed form solution of the Reynolds equation for a film thickness and pressure in a cylinder and plane geometry assuming rigid surfaces and isoviscous lubricant. But comparison with experimental data revealed significant discrepancy with the model predictions. Divergence of experimental and theoretical results leaded researchers to the conclusion that elastic distortion and pressure-viscosity effect play a significant role in lubrication. In 1949, Grubin obtained a first solution (approximate) for elasto-hydrodynamic lubrication problem assuming a cylinder on flat geometry. He was the first to include both elastic deformation and piezoviscous behavior of the lubricant into theoretical solution. Although his solution is only approximate, his analysis is quite accurate under certain conditions and it was recognized as a big step forward in EHL theory (since then the term EHL has been used). Moreover, Grubin’s assumptions are widely used in the modern tribology to build various approximate solutions under highly loaded contacts [1]. The derivation, Matlab code and detailed analysis of Grubin solution is considered here. Petrushevich (Petrusevich 1951) was actually first to obtain the exact solution of the line contact EHL problem by solving the corresponding equations numerically. He was also the first to observe a pressure spike at the outlet of the contact – a characteristic feature of EHL (see the figure above). For this reason the feature is sometimes referred to as “Petrushevich” spike. Obtained in 1951, his solution was first solution of combined elastic distortion, fluid flow and pressure-viscosity dependency equations. It should be emphasized, that the occurrence of the pressure spike is closely related to the variance of viscosity with pressure along with elastic properties of materials and relative speed. In 1959 Dowson and Higginson computed series of numerical solutions of EHL line contact problem for a range and obtained a regression formula for a minimum film thickness. Further information on the development of the EHL theory can be found in [2]. Theory & Equations of Elastohydrodynamic Lubrication A classical EHL system of equations consists of the system of Reynolds equation, film thickness and load balance equations: (1) ; where are hydrodynamic film thickness, pressure, viscosity, and and represent the velocity of the bearing surfaces. Variables represent the approach, macroscale geometry, elastic distortion of the surfaces and microscale geometry (surface roughness) correspondingly. This system of equations can be solved assuming appropriate boundary conditions to obtain unknown hydrodynamic pressure and film thickness in the contact. Typically, parameter is unknown (although sometimes it can be specified), therefore the last integral equation is needed to get the closed system of equations. is the normal load applied to the contact. The system of equations; shown above can be solved analytically in certain cases, however, in general it has to be solved using numerical methods. The problem in solving the Reynolds equation comes from the film thickness equation, when the elastic deflection of the surfaces is not negligible. For a 2-D case, this term can be calculated from the following equation: (2) ; where is the reduced elastic modulus. This equation is the analytical solution of the theory of elasticity equations for a semi-infinite body subjected to normal pressure (for the details of the derivation refer to [3]). The most robust and fast way (in terms of iterations at least) to solve EHL system is to use a fully coupled approach and Newton’s scheme. However, since the elastic distortion equation is given in the integral form, the Jacobian of the system is full which increases the demands in memory enormously. In addition, solution of the equations with full Jacobian is computationally significantly more intense compared to diagonally banded cases. Therefore, researchers worked hard to develop alternative solution methods. The two most common methods for solving EHL systems numerically are the Multilevel-Multigrid and Differential Deflection techniques. The former uses multiple grids and specific integration of the film thickness equation to build an iterative solver [5]. The latter solves a fully coupled system of equations, however, instead of using the original integral form of the film thickness equation, it considered the 2-nd derivative of it [4,6]. It turns out that the use of the derivative equation allows to construct a banded Jacobian and improve the efficiency of coupled approach significantly. Recently, a so called full system approach was proposed [7]. In this case, a Finite Element Methods are used to calculate both Reynolds and elasticity equations in a coupled manner. This method is computationally more demanding since the subsurface volume has to be discretized to calculate elastic distortions (the fully coupled approach based on differential deflection is faster than the FEM based full system technique). Nevertheless, the approach has the advantage of flexibility since it can be developed using commercial software such as COMSOL. A Matlab code for the solution of EHL system for the case of a cylinder-on-disk can be found here or for the cases of high pressures here. A fully coupled approach based on differential deflection technique was utilized. Newtons scheme was employed. Film Thickness in Elastohydrodynamic Lubrication Since the film thickness controls the separation of the rubbing surfaces and consequently friction, researchers developed several ways to measure the hydrodynamic film in the contact. One of the most frequently used techniques is based on optical interferometry. The instrument measures the lubricant film thickness in the contact formed between a steel ball and a rotating glass disc covered by a specific layer. T he lubricant film thickness at any point in the image can be accurately calculated by measuring the wavelength of light at that point. Film thicknesses down to 1 nm can be measured by this approach. You can see the measurement of the film in the video below (at first the disk is stationary and later on stats the motion): Central and minimum film thickness: Online EHL film thickness calculator As it can be clearly seen from the Fig.1, the lubricant film thickness is more or less constant in the whole contact zone (where the pressure is large), except for the small area at the outlet, where the film thickness drops to its minimum value. Since the pressurized area is typically the most important for failure analysis, in practice engineers use only central film thickness and the minimum film thickness to describe the lubrication state (see this article for more details). An online film thickness calculator is available on tribonet for line and elliptical (point) contacts. The calculators allow calculating central and minimum film thicknesses using various equations. Exact equations are described on the calculator’s page. Here is the calculator for elliptical contact: <span data-mce-type="bookmark" style="width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span><span data-mce-type="bookmark" style="width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span> References [1] Ertel – Grubin methods in elastohydrodynamic lubrication – a review, G. E. Morales-Espejel and A. W. Wemekamp. [2] A Review of Elasto-Hydrodynamic Lubrication Theory, P. M. Lugt and G. E. Morales-Espejel. [3] Theory of Elasticity, Timoshenko, S.P., Goodier, J.N., 1970. [4] LUBRICATION AND WEAR AT METAL/HDPE CONTACTS , A. Akchurin [5] Multi-Level Methods in Lubrication, C.H. Venner, A. Lubrecht. [6] Evaluation of Deflection in Semi-Infinite Bodies by a Differential Method, Evans, H.P. Hughes, T.G. [7] A Full-system Finite Element Approach to Elastohydrodynamic Lubrication Problems: Application to Ultra-low-viscosity Fluids. PhD thesis, Habchi, W. Manoj Rajankunte Mahadeshwara I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students. -->
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