A friction test is conducted in a WAM ball on disc test rig. The output from the test is friction coefficient versus entrainment speed and slide-to-roll ratio presented as a 3D friction map. A number of parameters are varied while studying the friction coefficient; surface roughness, base oil viscosity and EP additive package. Entrainment speed, slide to roll ratio and oil temperature are also varied. The results show that the mapping is efficient in showing the different types of friction that may occur in an EHL contact. The results also show that the friction behaviour can be strongly influenced by changing surface roughness as well as base oil viscosity, EP additive content and operating temperature.
A friction test is conducted in a Wedeven Associates Machine ball-on-disc test rig. The output from the test, friction coefficient versus entrainment speed and slide-to-roll ratio (SRR), is presented as a three-dimensional friction map. A number of parameters are varied while studying the friction coefficient; surface roughness, base oil viscosity, base oil type, and extreme pressure (EP) additive package. Entrainment speed, SRR, and oil temperature are also varied. The results show that the mapping is efficient in showing the different types of friction that may occur in an elasto-hydrodynamic lubrication contact. The results also show that the friction behaviour can be strongly influenced by changing surface roughness as well as base oil viscosity, base oil type, EP additive content, and operating temperature.
Increased awareness of environmental problems has stressed the importance of switching from traditional lubricants to more environmentally friendly alternatives. Different investigations with standard test methods indicate that such a switch is possible without loss of lubricating power. The question arises if the statement above is true for industrial lubricating conditions, without laboratory cleanliness. This paper presents a study of friction and wear in a two grooved journal bearing at different shaft speeds, oil temperatures and contamination levels. A number of tests have been conducted combined with a theoretical analysis of film thickness and lubricating regime. The aim was to investigate whether an environmentally adapted rape seed-synthetic ester oil could replace a traditional mineral oil in a full scale application. The results show that the rape seed-synthetic ester oil gives significantly lower values of wear regardless of the operating conditions and there is also a tendency of lower values of frictional torque compared with the mineral oil. Mainly operating in the mixed lubrication regime, no signs of impending bearing failure have been registered, even though a large amount of silica particles added to the oil gave higher wear values than with uncontaminated oil.
This paper presents studies of the contact between a soft rubber specimen and glass counterface using the Digital Speckle Correlation method, which provides information of displacements and structural similarities between recorded images. The setup is designed with a real contact and changes in the contact can be varied. Microscopic images using laser light illumination for different displacements are recorded and correlated. The results show that the contact area can be identified both for dry and lubricated contacts. The method can be applied on different geometries, surface roughness and lubricants. Influences of scars and contaminations, e.g. wear particles, may also be analysed.
There has been a growing usage of high strength steels, particularly in automobile applications mainly as structural parts in view of their light weight and high strength properties. These materials are also being considered for dynamic applications. However, the understanding of their tribological behaviour vis-a-vis their hot forming and also as tribological materials is highly inadequate. The present work thus aims at creating new knowledge about the tribological characteristics of high strength steels and bridging this existing gap. High temperature tribological studies on different tool steels (with and without surface treatment) sliding against high strength boron steel (with and without coating) and studies on self-mated hardened high strength boron steel under dry reciprocating sliding conditions have been conducted. High temperature tribological studies keeping in view the hot metal forming aspects were conducted by using an SRV machine whereas a two-disc machine was employed for investigating their fundamental friction and wear behaviour. The results from the high temperature studies indicate that the friction is dependent on temperature since a reduced friction level was observed with increasing temperature. The wear of the tool steels increased with increasing temperature and nitriding of the tool steels provided better protection against severe wear. The results from the study on self-mated hardened high strength boron steel showed that sliding speed has a marginal effect on friction whereas the effect of contact pressure is more pronounced (decreasing friction with increased contact pressure). The specific wear rate decreased with increased sliding speed.
When using the inverse hydrodynamic theory to calculate leakage flow and frictional force in an elastomeric seal contact, the pressure distribution is a necessary input. Up till now, assumed or measured pressure distributions usually have been used. One of the authors has earlier presented a semiempirical method for calculating the pressure distribution in an O-ring seal contact. The new calculation method, presented in this paper, is a generalization and an improvement of this earlier work. The method presented is mainly analytical and is based on calculations of the boundary strains in the contact zone and a model of the material behavior, which is based on the pressure dependence of the material compressibility. A computer program has been developed and two test examples are treated. A comparison with experiments is made.
Hydraulic cylinder seal performance is studied experimentally and theoretically. The seal performance is discussed in terms of friction force and oil leakage, which are due to the oil film build-up in the seal contact. The theoretical analysis is based both on calculated and measured contact pressure distributions. The compressibility of seal materials is determined experimentally, and it is shown that the compressibility is a pressure dependent material property. A method for calculation of the contact pressure distribution for a seal with an arbitrary cross-section is proposed, based on geometrical considerations and the experimentally determined compressibility. The pressure calculations are verified experimentally. Theoretically calculated oil film thicknesses in a seal contact are compared with measured film thicknesses. The increase of film thickness with increasing sliding velocity shows a good agreement between theory and experiment. The oil film is thicker in the experiments due to the surface roughness of the seal. A complete theoretical analysis of the seal performance is developed to be used as a design tool.
A comparison has been carried out between one mineral based hydraulic oil and three environmentally adapted hydraulic oils. Two of these are semi-synthetic oils, i.e. mixtures of vegetable base oil and synthetic esters, and the last is based on synthetic esters only. Technical properties such as viscosity, pour point etc., and chemical properties such as phosphorus and sulphur content etc. were documented using standard test methods. The lubricant capability properties were determined through measurements of the capability of each oil to build a film in an elastohydrodynamic contact. The oil film thickness is important to avoid wear and failure and to guarantee separation of surfaces. The results show that at 40°C the environmentally adapted oils give a thicker film than the mineral oil. At 80°C there is no significant difference between the different types of oil in their capability to build a lubricating film. The maximum shear strength was measured and these results are presented with the constant of proportionality γ, from the theoretical model τ approximately equals γp, which is valid at very high pressures. The measurements were carried out at contact pressures in the range 5-7 GPa. The results show that all environmentally adapted oils give a lower γ value than the mineral oil, which is an advantage since a low shear strength results in lower friction in highly loaded contacts. Measurements of toxicity to aquatic organisms (Daphnia magna) show very large differences between the tested oils, and this implies that a change from a mineral oil to an environmentally adapted oil can give important environmental advantages.
Nine different types of commercial lubricants have been tested in an apparatus which can produce squeeze and sliding motion simultaneously. It is found that lubricants with the same viscosity show big differences in lubricant capability in terms of wear and oil film collapse, and that these differences are due to the additives
The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel.Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results.Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased.
The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength boron steel. Reducing the wear of rails and wheels and controlling the frictional behaviour in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic etc. The cost of the rail material when replacing a section of the rail is just a small portion of the total cost. Planning, disturbance of traffic and loss of income during the maintenance are some of the larger parts of the total costs. Likewise, the large difference in frictional behaviour in the wheel/rail contact of materials used today creates huge problems. Friction at the rail head needs to be high enough to withstand the traction force when accelerating and braking while the friction at the gauge corner should be low to save energy and give good steering capability of the train. The low friction at the gauge face can be achieved by using rail lubrication but the controlled friction at the rail head at different temperatures and other weather conditions is still a problem. In order to reduce the total costs it is therefore crucial to reduce the time for replacing the rail and increasing the service life of the rail. The ReRail rail cap has the potential to do both.There are almost no results published regarding the tribological properties of Boron steel in contact with other metallic materials for mechanical engineering applications. Therefore, the aim of this work has been to investigate the tribological properties of boron steel in contact with Blue Light wheel steel under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro hardness indenter, light microscope and SEM/EDS were used to analyse the results.Results from the experiments show that the friction coefficient in tests with boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased.
In this study, base fluid parameters for elastohydrodynamic lubrication (EHL) and friction analyses have been determined experimentally. The viscosity at atmospheric pressure, η0, the pressure-viscosity index, α and the EHL friction coefficient, γ, are important parameters in EHL theory and they are crucial in the selection of efficient lubricants for different applications. This investigation focuses on three important lubrication mechanisms: The capability of forming a separating lubricants film, the friction generated in a lubricated contact, and the height of pressure peaks, such as the outlet pressure spike and pressure ripple caused by surface roughness. The influence of different lubricant parameters on these three mechanism is discussed. The value of α is measured in a Couette high-pressure viscometer, and the value of γ is obtained from a jumping-ball device. Other parameters discussed are temperature-viscosity coefficient, β, bulk modulus, BO, thermal conductivity at atmospheric pressure, λO, and heat capacity unit volume, ρCpO. A comparison between traditional mineral base oils and environmentally adapted oil based on rapeseed oil and synthetic esters contributes to the further understanding of the performance of these new materials in lubrication applications. It is shown that rapeseed oil and synthetic esters have good lubricating properties and are, in most cases, better than mineral oils.
The influence of surface roughness in a rail/wheel contact has been a concern for railway owners since the introduction of ‘rail grinding' as a maintenance strategy. Presently, there are no well-defined guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish scientific guidelines regarding the surface topographies for the rails and wheels in order to minimize grinding costs/time and to improve rail/wheel performance. This study is aimed at investigating the influence of surface topographies of wheels and rails on running-in behaviour, wear, friction, and the resultant surface damage through experimental simulation in the laboratory. A two-disc rolling/sliding test machine has been used in this experimental work. Two different roughness values were produced on both the rail and wheel test specimens. A design of experiment approach has been used to conduct experiments and to analyse the results. The results show that the surface roughness values of the specimens in some material pairs do influence wear, friction, and resulting surface damage.
Baldos II originates as an entry for the 2009 Shell Eco-marathon competition. It is built in cooperation between students from different fields of study, such as Mechanical Engineering, Industrial Design Engineering and Computer Science from Luleå University of Technology, Sweden. The car has been designed to meet the requirements set by Swedish authorities for legal street use. This includes wind screen wiper, 3-point seat belt, proper lighting, reverse gear and twin electric engines. Baldos II is tested and found to be Sweden's most fuel efficient car approved for street use.The internal combustion engine in the serial hybrid drive train is modified from an ordinary gasoline engine to run on pure ethanol. The fuel consumption of the vehicle corresponds to 0.065 litres ordinary gasoline/10 km, which results in a CO2 emission of 12 g/km. The car is design for one person only, and has room for a luggage in the size of an ordinary cabin bag. With full tank the total weight is 220 kg, and the total length is 2650 mm. The light weight has been achieve thorough an advanced monocoque chassis manufactured of carbon fiber sandwich construction.According to safety regulations the car is equipped with dual circuit hydraulic disc brakes. Today, the Team Baldos aims for defining a higher standard for street vehicles in Sweden.
Experiments are conducted to compare the performance of fresh and aged samples of three oils in a boundary lubricated contact. These oils are Oil A (a commercially available unsaturated synthetic ester based hydraulic fluid (ISOVG32)), Oil B (a mineral based turbine oil (ISOVG68), and Oil C (a saturated synthetic ester based lubricating fluid (ISOVG46)). Tests are performed using a tin-bronze on steel contact in a pin-on-disc apparatus. Results from these tests provide data relating to friction and wear and their coupling to the aging of the fluids. No evidence of any significant deterioration of lubricant performance is observed for any of the fluids tested. This is an abstract of a paper presented at the 15th International Colloquium Tribology - Automotive and Industrial Lubrication (Ostfildern, Germany 1/17-19/2006).
This paper presents the influence of aging the nitrile rubber, the most popular seal material, in various base fluids on sliding friction and abrasive wear. The lubricants used are synthetic esters, natural esters, different types of mineral base oils, poly-*-olefins and very high viscosity index oils. Friction has been studied for two directions of motion with respect to lay on the elastomer sample by using the SRV Optimol test machine. These findings show that as compared to all other lubricant formulations, ageing the elastomer in polyol ester leads to the maximum reduction of friction coefficient especially in perpendicular sliding to the initial lay on the surface. The abrasive wear studies were carried out by using a two-body abrasive wear tester against dry and lubricated elastomer. It was interesting to note that two-body abrasive wear of elastomeric material was higher during rubbing in presence of the fluids as compared to that in dry condition. Further, aging the elastomer in these base fluids especially in ester base fluids, results in more abrasive wear.
The aging behavior of synthetic lubricants, in particular environmentally adapted lubricants esters, in comparison to mineral base oils, is studied. V Three fully commercially formulated lubricants were subjected to an oxidation process using a modified dry-Waterless Turbine Oil Oxidation Stability Test. The oils were: Oil A (hydraulic unsaturated ester with antioxidants and corrosion inhibitors), Oil B (turbine mineral oil with antioxidants and corrosion inhibitors), and Oil C (turbine saturated ester oil with antioxidants and corrosion inhibitors). This is an abstract of a paper presented at the 15th International Colloquium Tribology - Automotive and Industrial Lubrication (Ostfildern, Germany 1/17-19/2006).
The running-in properties of a hydraulic rotator of vane type for angular positioning of crane tools has been studied. The sliding contact between the vane nose and the stator ring was studied in detail. A pin-on-disc configuration tribometer was used for the tribotests. The pin was made out of a slice from a real vane and the disc was manufactured of the same material and with the same machining process as the real stator ring. Collected data included friction, wear and electric contact resistance. A new method was used to enable measurements of changes in surface topography at a specific location during the test. The results show that the relocation method is useful for monitoring small changes in surface topography under running-in, but the most significant parameter for detection of running-in for this application is electric contact resistance. Significant changes in friction and contact resistance were observed during the running-in period. The main reason for the changes is the build-up of a non-conducting tribofilm. The change in surface topography alone is too small to change the lubricating regime. The tribofilm is formed after a short distance but can not grow until the steepest asperities have been worn off. The results show that the plane milled surface has better running-in properties than the turned surface
Five different anti-wear additives, suitable to formulate environmentally adapted hydraulic fluids, were tested. The used base fluid was a saturated, environmentally adapted synthetic complex ester. The tested materials were steel-steel and bronze-steel. A modified Falex pin and a vee-block tester were used for the tribotests. XPS was used to characterize the surfaces. It was found that the new types of more polar additives work better than the traditional ones, though they can give selective transfer of cupper to the steel pin. To use this type of additives in fully formulated products more investigations have to be performed.
Five different anti-wear additives, suitable for the formulation of environmentally adapted hydraulic fluids were tested, both commercially available and newly developed. The used base fluid was a high performance saturated complex ester. The formulated fluids' performance was evaluated through the use of an assembled pin & vee block in a modified Falex wear tester according to wear and frictional behaviour. The combinations of tested materials were steel-steel and bronze-steel tribopairs. The friction, wear scar volume and visual appearance both inside and outside the wear scar were studied. Some of the tested combinations gave unwanted performance, such as high friction, large wear and etching damages, whereas others gave good performance. It was found that the new additives showed promising results for formulation of environmentally adapted lubricants based on saturated complex esters. Further investigations will look closer at the chemical composition of the formed tribofilms with the use of surface sensitive analysis technology.
The film formation capabilities of six environmentally adapted ester based fluids have been investigated using optical interferometry in a Ball and Disc apparatus. A mineral oil was used as a reference. The properties and molecular structure for the tested base fluids are well known from earlier investigations. The fluids were tested at three different slide/roll ratios of 0, 0.6, and 1.2. The film formation capability was compared to the molecular structure and other properties. It was found that some of the fluids maintain a superior lubricating film at high slide/roll ratios than others, because of their molecular properties. A high level of carboxylate groups in the ester molecule gives high thermal conductivity and heat capacity, which promotes heat transportation out of the contact and this also maintain separation
The lubricating performance of environmentally adapted hydraulic fluids in boundary lubrication situations has been examined and compared to that of a conventional mineral oil based hydraulic fluid. The oils tested were all fully formulated hydraulic oils with the same ISO viscosity grade. Oil A was a conventional mineral oil whilst oils B and C were mixtures of rape seed and synthetic ester oils; oil C containing a significantly higher amount of synthetic ester than oil B. Oil D was a pure synthetic ester based hydraulic fluid. The ability of the test oils to reduce friction and wear was investigated in a Plint and Partner High Frequency Friction Machine (TE 77B). In all the tests the contact geometry was of the cylinder-plate type and the contact surfaces were of roller bearing steel. The sliding friction force was measured at different oscillating sliding speeds, contact pressures and temperatures. The wear tests were performed at constant load, speed and temperature. Multifactor analysis showed that the main factors affecting the coefficient of friction at the contact were oil type, temperature, sliding speed and load. The coefficient of friction decreased with increasing sliding speed and load and increased with increasing temperature. The environmentally adapted hydraulic fluids were seen to give lower friction compared to the conventional mineral oil based hydraulic fluid. Further analysis of variance showed that combined interaction effects exists, but at much lower order of magnitude than the main effects. A comparison between friction measurements in elasto-hydrodynamic lubrication and boundary lubrication showed that the environmentally adapted hydraulic fluids gave lower friction under both lubricating conditions. This implies low shear stress and minimal temperature rise in concentrated contacts, which increase life of both hydraulic equipment and fluid. The wear tests indicated that the environmentally adapted hydraulic fluids resulted in higher wear rate than the mineral oil based hydraulic fluid. This is thought to be a result of the competition between the polar molecules of the environmentally adapted base oils and the anti-wear (AW) and extreme pressure (EP) additives, in covering metal surfaces. The superior lubricity of the environmentally adapted hydraulic fluids seems not to be sufficient to replace the use of AW and/or EP additives in a fully formulated product. When choosing EP or AW additives for a non mineral oil based product, the interference between base oil molecules and additive molecules must be considered.
Those working with tribology often have a background in mechanical engineering, while people working with lubricant development have a chemistry/chemical engineering background. This means they have a tradition of approaching problems in different ways. Today’s product development puts higher demands on timing and quality, requiring collaboration between people with different backgrounds. However, they can lack understanding of each other’s challenges as well as a common language, and so this book aims to bridge the gap between these two areas.Lubricants: Introduction to Properties and Performance provides an easy to understand overview of tribology and lubricant chemistry. The first part of the book is theoretical and provides an introduction to tribological contact, friction, wear and lubrication, as well as the basic concepts regarding properties and the most commonly made analyses on lubricants. Base fluids and their properties and common additives used in lubricants are also covered. The second part of the book is hands-on and introduces the reader to the actual formulations and the evaluation of their performance. Different applications and their corresponding lubricant formulations are considered and tribological test methods are discussed. Finally used oil characterisation and surface characterisation are covered which give the reader an introduction to different methods of characterising used oils and surfaces, respectively.
This paper describes a new test-rig designed for investigating wear and friction in a conformal conjunction such as journal bearing. Tests have been carried out with this rig to investigate the possibility of replacing mineral oil based lubricants used in turbines in hydro-electric with new more environmentally adapted synthetic ester based lubricants, with or without additives. The lubrication regime under test is boundary lubrication in a highly loaded sliding contact subjected to an intermittent motion. Temperature and linear wear (displacement) have been monitored. The test results show no significant difference in wear rates or levels between the mineral and synthetic esters. The synthetic esters are characterised by higher friction coefficients than mineral oil; especially after running in where the mineral oil lubricated bearings show a decrease in friction. This running in behaviour was only observed when mineral oil was used. The predictable behaviour of the esters indicates that there is a strong possibility to replace mineral oils with more environmentally adapted lubricants
Different compositions of bronze materials are used for sliding bearings in various applications including those involving oscillatory motion and moderate temperatures. The compatibility of new environmentally adapted synthetic esters with different contacting surface materials helps ensure good tribological performance. The present work deals with tribological studies on oscillatory journal bearings manufactured using three different compositions of bronze materials lubricated with EALs under boundary lubricated conditions. Under certain operating conditions, alloying constituents from the bronze-bearing material dissolute into the synthetic ester lubricant, thereby leading to the formation of a copper enriched bearing surface layer. Tin-bronze with synthetic ester lubricant showed more stable friction values and roughly ten times better wear results than harder aluminium- and manganese-bronze as well as outperforming the mineral oil under the same conditions
Different compositions of bronze materials are used for sliding bearings in various applications including those involving oscillatory motion and moderate temperatures. The compatibility of new environmentally adapted synthetic esters with different contacting surface materials is important to ensure good tribological performance. The present work deals with tribological studies on oscillatory journal bearings manufactured with three different compositions of bronze materials lubricated with EALs under boundary lubricated conditions. Under certain operating conditions, dissolution of alloying constituents from the bronze bearing material dissolute into the synthetic ester lubricant occur leading to the formation of a copper enriched bearing surface layer. Tin-bronze with synthetic ester lubricant showed more stable friction values and roughly ten times better wear results than the harder aluminium- and manganese-bronze and also outperformed the mineral oil under the same conditions.