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  • 1.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Essel, Emmanuel Kwame
    Fabricius, John
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Reiterated homogenization applied in hydrodynamic lubrication2008Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, nr 7, s. 827-841Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work is devoted to studying the combined effect that arises due to surface texture and surface roughness in hydrodynamic lubrication. An effective approach in tackling this problem is by using the theory of reiterated homogenization with three scales. In the numerical analysis of such problems, a very fine mesh is needed, suggesting some type of averaging. To this end, a general class of problems is studied that, e.g. includes the incompressible Reynolds problem in both artesian and cylindrical coordinate forms. To demonstrate the effectiveness of the method several numerical results are presented that clearly show the convergence of the deterministic solutions towards the homogenized solution.Moreover, the convergence of the friction force and the load carrying capacity of the lubricant film is also addressed in this paper. In conclusion, reiterated homogenization is a feasible mathematical tool that facilitates the analysis of this type of problem.

  • 2.
    Armada, Sergio
    et al.
    Department of Corrosion and Tribology SINTEF, Materials and Chemistry, Trondheim.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Special issue: Selected papers from the 15th Nordic Symposium on Tribology2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 809-Artikkel i tidsskrift (Annet vitenskapelig)
  • 3.
    Avan, Evan Y.
    et al.
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Spencer, Andrew
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dwyer-Joyce, Rob S.
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Experimental and numerical investigations of oil film formation and friction in a piston ring–liner contact2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 2, s. 126-140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The piston ring–cylinder liner contact is a major source of the total parasitic losses in an internal combustion engine. The lubrication process of this contact highly influences the amount of friction, oil consumption and wear that occurs. In this work, a reciprocating test rig combined with an ultrasonic film thickness measurement system was developed and then used for tribological investigation of the piston ring–cylinder liner contact under idealised cold conditions. A special piston ring and cylinder liner holder were designed and five sensors were glued on to the back side of the liner specimen. Ultrasonic reflections captured by the sensors, used to obtain the film thickness, and friction were continuously recorded as the piston ring section reciprocated over the liner. Several experiments were performed at different speed and load conditions. Furthermore, a numerical model has been developed to predict film thickness and friction in all lubrication regimes. The experimentally measured film thickness and friction were compared with the output from the numerical model and good correlation was found. The parameters affecting the accuracy of the ultrasound measurements and numerical simulations of film thickness and friction are then discussed.

  • 4. Baart, Pieter
    et al.
    Lugt, Piet
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Review of the lubrication, sealing, and pumping mechanisms in oil- and grease-lubricated radial lip seals2009Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, nr 3, s. 347-358Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radial lip seals are successfully used since the 1940s to seal lubricated systems. Despite extensive experimental and theoretical research in the field, it is still not fully clear how these seals function. Experimental studies, found in the public literature, show that the relatively high surface roughness of the seal lip is very important for good and reliable performance. In addition, the pressure distribution under the lip seems to be a critical factor. Six fundamental hypotheses are presented on the lubrication, pumping, and sealing mechanisms to explain the working principles of these seals. It is generally accepted that lubrication results from micro-elastohydrodynamic film build up between the rough seal surface and the shaft. Non-symmetrical tangential deformations of the lip surface are observed during experiments and assumed to act like spiral groove bearings that generate a pumping action and lubricant film. Another hypothesis suggests that the lubricant will behave non-Newtonian under the very high shear rates experienced in operating conditions. This will reduce friction because of shear-thinning and enhances sealing. Macroscopic aids, like hydrodynamic pumping aids and engineered asperity patterns on the shaft, do improve seal performance. Almost all public literature discusses oil-lubricated radial lip seals while many seals are grease lubricated, especially in certain technical fields. Due to the non-Newtonian behaviour of grease, the lubrication, sealing, and pumping mechanisms are assumed to differ from the oil-lubricated seals. Lower friction and improved protection against contamination are measured, and it is expected that the interest in grease lubrication will rapidly grow in future.

  • 5.
    Berglund, Kim
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Larsson, Roland
    Lubricant ageing effects on the friction characteristics of wet clutches2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 7, s. 639-647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The friction characteristics and performance of wet clutches have been investigated by several authors. Studies have also been made to understand the frictional performance during the service life of the clutch system. However, most lifetime studies have been conducted for systems with paper-based friction material so that systems using sintered bronze friction material remain largely unexplored. To study the friction performance of how these systems can vary over time, the friction characteristics for a clutch system using lubricants aged in three different ways were compared. The effects on friction characteristics resulting from oxidation of the lubricant, reduced additive concentration, and ageing under real operating conditions in a wet clutch test rig were studied. The oxidation effects on friction characteristics were examined using a modified waterless turbine oil oxidation stability test on a fully formulated lubricant. Five oxidation time periods from 48 to 408 h were investigated. For each period of oxidation, a friction performance test was run using a pin-on-disc machine. The ageing carried out in a wet clutch test rig is a standard test of a wet clutch systems manufacturer which is used in order to verify that an oil-friction disc combination will last the full service life of the specific application. This test gives a realistic ageing process similar to that in a wet clutch in a field test. Under boundary-lubricated conditions, additives are vital to the performance of wet clutches. Therefore, the effect of reducing the additive concentration in the oil was also studied, in the range of 10 to 100 per cent of the original additive package used in the fully formulated wet clutch lubricant. Results showed that a general friction increase can be observed for oxidation, additive reduction, and test rig ageing. It was also concluded that different methods of simulating the wet clutch ageing process differ and cannot be directly correlated with each other

  • 6.
    Björling, Marcus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Berglund, Kim
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Spencer, Andrew
    Dynamics, Acoustics and Tribology, Engine Dynamics, Scania, Scania Technical Centre.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The effect of ageing on elastohydrodynamic friction in heavy-duty diesel engine oils2017Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 231, nr 6, s. 708-715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To further improve the efficiency of machine components found in automotive engine systems it is important to understand the friction generation in these components. Modelling and simulation of these components are crucial parts of the development process. Accurate simulation of the friction generated in these machine components is, amongst other things, dependent on realistic lubricant rheology and lubricant properties, where especially the latter may change during ageing of the lubricant. Many modern heavy-duty diesel engines are in operation for several hundred hours before the engine oil is changed. In this work, two engine oils, one 10 W-30 and one 5 W-20, have been aged in full heavy-duty diesel engine bench tests for 400 and 470 hours respectively. This roughly corresponds to the amount of ageing these oils are subjected to between oil drains in field conditions. The aged oils were subjected to a number of oil analyses showing, among other things, a maximum increase in oil viscosity of 12.9% for the 5 W-20 oil and 5.5% for the 10 W-30 oil, which is most likely primarily an effect of evaporation and oxidation. The aged oils were tested in a ball-on-disc test rig under elastohydrodynamic conditions where friction was measured and the performance was compared to fresh samples of the same oils. The results show that there is almost no difference in elastohydrodynamic friction when comparing the aged oils with the fresh oils. These results indicate that it is not necessary to include oil ageing in numerical elastohydrodynamic friction models as long as the oil is changed before the ageing has reached a critical level

  • 7.
    Björling, Marcus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Kassfeldt, Elisabet
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Elastohydrodynamic lubrication friction mapping: The influence of lubricant, roughness, speed, and slide-to-roll ratio2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 7, s. 671-681Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 8.
    Burkhart, Christoph
    et al.
    Institute of Machine Elements, Gears & Transmissions (MEGT), University of Kaiserslautern.
    Johansson, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Uukonsari, Jan
    R&D, Vattenfall AB.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Performance of lubricating oils for wind turbine gear boxes and bearings2018Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 1, s. 62-72Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the friction and wear properties of six different new and used wind turbine gear oils (ISO VG 320), with different base oil formulations and additives packages, were investigated. For that purpose, a four-ball tribometer and an Optimol SRV were used. Moreover, the lubricants extreme pressure properties were also evaluated, using the same four-ball tribometer. The study also includes a characterization of the lubricants. The main objective was to compare the new and used gear oils in order to identify performance differences and predict oil change intervals. The results indicate that a use of 3 to 4 years is within the lifetime of the lubricant.

  • 9. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Computational fluid dynamics analysis of a journal bearing with surface texturing2008Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, nr 2, s. 97-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analysis of a lubricated conformal contact is carried out to study the effect of surface texture on bearing friction and load carrying capacity using computational fluid dynamics. The work focuses on a journal bearing with several dimples. Two- and three-dimensional bearing geometries are considered. The full Navier-Stokes equations are solved under steady-state conditions with a multi-phase flow cavitation model.The coefficient of friction can be reduced if a texture of suitable geometry is introduced. This can be achieved either in the region of maximum hydrodynamic pressure for a bearing with high eccentricity ratio or just downstream of the maximum film for a bearing with low eccentricity ratio. An additional pressure build-up produced as a result of the surface texture has been shown at low eccentricity ratios.

  • 10. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Inertia effects in textured hydrodynamic contacts2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 8, s. 751-756Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A flow analysis is carried out for a parallel textured slider to investigate the role of fluid inertia. Numerical simulations are performed for a laminar, two-dimensional, steady and isothermal flow. Stokes solutions are compared with Navier-Stokes solutions at the same Reynolds number. A range of texture depths is analysed. It is shown that there is an optimum value of texture depth that provides maximum load-carrying capacity. It is also shown that there is a critical depth value. Inertia has a negative effect on the load-carrying capacity for depths higher than the critical value, whereas it has a positive effect for lower depths. For a given texture depth, these effects are amplified as the Reynolds number increases. The global effect of inertia is positive when a realistic configuration of a parallel textured slider with a fore-region is considered.

  • 11.
    Eriksson, Patrik
    et al.
    Luleå tekniska universitet.
    Wikström, Victoria
    SKF Göteborg.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Grease passing through an elastohydrodynamic contact under pure rolling conditions2000Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, nr 4, s. 309-316Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using optical interferometry in a standard ball-and-disc apparatus and a high-speed video camera with light enhancer, thickener particles entering a grease-lubricated elastohydrodynamic (EHD) contact were traced as they passed through the contact in pure rolling. In previous studies, it has not been possible to track specific particles but, due to the short exposure time and high recording rates used here, sharp images of a passing particle could be captured. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex respectively were studied and for a freshly lubricated track it could be documented that the lithium complex thickener causes fewer, but larger, particles to pass the contact. The influence of the base oil bleeding on film formation is also discussed in the paper

  • 12. Eriksson, Patrik
    et al.
    Wikström, Victoria
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Grease soap particles passing through an elastohydrodynamic contact under side slip conditions2000Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, nr 4, s. 317-325Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used. Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.

  • 13.
    Fatima, Nowshir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Minami, Ichiro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Degradation Mechanism of Automatic Transmission Fluid by Water as a Contaminant2015Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 229, nr 1, s. 74-85Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The degradation mechanism of water contaminated Automatic Transmission Fluids (ATF) was experimentally investigated. Water contaminated ATF was tribotested in a full-scale wet clutch test rig to monitor the friction durability during clutch ageing, and was also statically aged in oven to evaluate the interaction of ATF with water. The bulk properties and chemical nature of the ATF were analysed using viscosity measurements, Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). It was shown that water presence in the ATF can increase the mean friction coefficient over a short time period, though in the long term perspective there is a higher loss of mean friction. Phase separation of the water-in-oil emulsion by centrifugation at 20000 rpm made it possible to examine the water phase using infrared 2spectroscopy. The spectroscopic analysis revealed the hydrophilic nature of certain ATF constituents, although the impact of water on the bulk properties like lubricant viscosity and thermal stability was insignificant. The analysis of the tribotests showed that the friction increase for water contamination was a short-term effect and likely due to the interaction between polar surface active additives and water. Even though no significant change has been found for thermal degradation or in bulk properties of the lubricant, the initially changed action of the water soluble additives and generation of high friction resulted in a total deterioration of the clutch performance during long term use.

  • 14.
    Gebretsadik, Daniel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Seizure behaviour of Pb-free engine bearing materials under dry condition2018Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 2, s. 106-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Due to new environmental regulations, Pb-free engine bearing materials are becoming more common and there is a need for studying their tribological performance. Under severe operating conditions, failure due to seizure can occur in engine bearings. In this work, seizure behaviour of different multi-layered engine bearing materials has been studied by using a block-on-ring test setup under dry condition. These materials included Al–Sn-based lining with no overlay, bronze lining with polyamide-imide-based overlay containing MoS2 and graphite, bronze lining with two overlays of Al–Sn-based and polyamide-imide-based material, bronze-based lining with Sn-based overlay and bismuth (Bi)-containing bronze with Sn-based overlay. The tests were performed by gradually increasing the load at a specific time interval and in a stepwise manner and at a constant speed under unidirectional dry sliding conditions. The test materials, counter surfaces and the wear debris were analysed using SEM with a view to understand the seizure mechanisms. Bronze-based lining with a polyamide-imide-based overlay containing MoS2 and graphite does not exhibit seizure up to a load of 475 N. For Al–Sn-based lining without overlay, seizure occurs at a relatively lower load of 125 N. The Al–Sn-based lining with no overlay shows higher friction and the polyamide-imide-based overlay containing MoS2 and graphite shows lower friction during the seizure test. In most cases, there is material transfer onto the test ring counter surface. Material transfer onto the counter surface either due to severe adhesion or wear debris adhered and smeared on it. Al–Sn-based lining and an exposed Al–Sn-based overlay show severe adhesion that causes seizure. On the other hand, exposed Pb containing lining and Bi containing lining seize due to mechanical interlocking caused by the adhered wear debris on both surfaces.

  • 15.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Laboratory research facility for testing hydrodynamic thrust bearings2002Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 216, nr 2, s. 105-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A research facility has been designed and manufactured to study performance characteristics of industrial hydrodynamic thrust bearings. The facility includes a test rig containing two identical tilting pad thrust bearings operating against separate collars. A shaft supported by two journal bearings is driven by a 143 kW variable-speed d.c. motor. The bearings are tested in a balanced pair to accommodate the substantial axial force generated by hydraulic cylinders. Bearing instrumentation encompasses a distribution of thermocouples, pressure transducers and oilfilm thickness sensors of eddy current type. Two piezoelectric transducers for pressure profile measurements and three thermistors are mounted in one of the shaft collars. Additional instrumentation includes thermocouples, pressure sensors, flowmeters, a load cell and inductive sensors. Signals from all sensors are logged by a personal computer-based high-speed data acquisition system that acquires the measured data, conditions them and presents the results on line. Power losses are obtained by monitoring bearing friction torque and by the calorimetric technique. A detailed description of the research facility is provided together with some representative results of equalizing tilting pad thrust bearing performance obtained for the steady state and transient operating conditions

  • 16.
    Glavatskih, Sergei
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Decamillo, S.
    Kingsbury.
    Influence of oil viscosity grade on thrust pad bearing operation2004Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 218, nr 5, s. 401-412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of oil viscosity grade on the performance of tilting pad thrust bearings is examined in a wide range of shaft speeds and specific bearing loads. Data being discussed were obtained in tests carried out with 228 mm outer diameter (o.d.) and 267 mm o.d. bearings lubricated with ISO VG32 and ISO VG68 mineral oils in a fully flooded mode. In a low-speed range (below 40 m/s), the performance of the 228 mm bearing is analysed in terms of pad and collar temperatures, power loss and oil film thickness. Pad temperature and power loss are employed in the analyses of the 267 mm o. d. bearing operated at high sliding speeds of up to 115 m/s. The results show that there is a significant effect of oil viscosity grade on bearing main operating parameters. The substitution of ISO VG32 oil for ISO VG68 oil results in considerably reduced pad temperatures, lower power loss and thinner oil film thickness. However, no measurable difference in power loss was observed after the onset of turbulence. The influence of oil viscosity grade on pad temperature pattern is analysed. The thermal effect of oil viscosity grade on pad temperature pattern and power loss is also compared with the effect of offset pivot.

  • 17.
    Glavatskih, Sergei
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Special issue on NORDTRIB: The Nordic Symposium on Tribology 2010: Guest editorial2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 7, s. 563-564Artikkel i tidsskrift (Annet vitenskapelig)
  • 18.
    Golchin, Arash
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Nguyen, Tan Dat
    Department of Mechanical Construction and Production, Ghent University.
    Baets, Patrick De
    Department of Mechanical Construction and Production, Ghent University.
    Glavatskih, Sergei
    Division of Machine Design, School of Industrial Engineering and Management, Royal Institute of Technology.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effect of shaft roughness and pressure on friction of polymer bearings in water2014Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, nr 4, s. 371-381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the frictional behavior of selected commercially available unfilled polymers, namely, polyether ether ketone, polytetrafluoroethylene, polyethylene terephthalate, and ultra-high molecular weight polyethylene against an Inconel shaft was investigated using a journal bearing test configuration in water-lubricated sliding contact. Dynamic friction curves were obtained for various shaft roughness values and polymer combinations. The results showed a significant influence of shaft surface roughness on running-in and steady state friction in water-lubricated conditions. Contact angle measurements revealed a significant increase in wettability of Inconel counterfaces. The X-ray photoelectron spectroscopy (XPS) analysis of the surfaces suggests formation of a reaction layer on worn Inconel surfaces when sliding against the polymers. The influences of counter surface roughness and load on frictional response of polymers were studied through intermittent tests by obtaining dynamic and breakaway friction maps for different polymer materials, shaft roughness values, and pressure combinations. In general, a trend of decreasing friction was obtained with increasing contact pressure; however, the materials’ frictional responses to variations in counter surface roughness were different. These results indicate that although a reduced counter surface roughness may be beneficial for dynamic friction of polymers in all lubrication regimes, it can adversely affect the materials’ breakaway friction response.

  • 19.
    Golchin, Arash
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Simmons, Gregory F
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Glavatskih, Sergei
    Machine Design, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Tribological behaviour of polymeric materials in water-lubricated contacts2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 811-825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims at investigating the tribological behaviour of several unfilled polymer materials sliding against 316L stainless steel in distilled water. The tests were carried out in a unidirectional pin-on-disc configuration with an initial apparent contact pressure of 5 MPa at room temperature. The worn surfaces were examined using scanning electron microscopy and energy dispersive spectroscopy techniques and the wear mechanisms were discussed. These studies indicate the occurrence of tribocorrosion of stainless steel during sliding against polypropylene. It is inferred that the frictional behaviour of the polymers is determined by both their wettability and solubility in water, where generally an increased hydrophobicity and relative energy difference with regard to water results in lower friction. The results from friction and wear tests show overall superior tribological performance of ultrahigh molecular weight polyethylene compared with the other polymeric materials in water.

  • 20.
    Gustafsson, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Olov
    Measuring lubricant film thickness with image analysis1994Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 208, s. 199-205Artikkel i tidsskrift (Fagfellevurdert)
  • 21. Hardell, Jens
    et al.
    Pelcastre, Leonardo
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    High-temperature friction and wear characteristics of hardened ultra-high-strength boron steel2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 10, s. 1139-1151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The usage of ultra-high-strength boron steel (UHSS) in automotive industry has increased rapidly in the recent past. Forming of UHSS components is performed at elevated temperatures, which also offers the possibility of hardening through quenching directly after forming. However, the influence of hardening on friction and wear during relative sliding between the tool and the workpiece is unclear. Therefore, the friction and wear characteristics at elevated temperatures of hardened and unhardened UHSS and tool steel pairs are investigated in this study. The results show that both friction and wear at all the investigated temperatures are affected by hardening of the UHSS. For uncoated UHSS, the hardening resulted in lower friction and the tool wear increased at low temperatures, but was not affected at elevated temperatures. This was attributed to the higher hardness after hardening combined with the presence of an oxide scale on the UHSS after heating and quenching. For Al-Si-coated UHSS, the hardening reduced friction and tool steel wear at elevated temperatures, and also reduced the wear of the Al-Si-coated high-strength steel at low temperature mainly owing to the formation of an intermetallic layer on the Al-Si-coated UHSS surface after exposure to elevated temperatures.

  • 22.
    Isaksson, Patrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Nilsson, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The influence of surface roughness on friction in a flexible hybrid bearing2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr J10, s. 975-985Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of surface roughness on friction in all lubrication regimes is studied for a flexible hybrid bearing of a radial piston hydraulic motor. The effect is studied by performing experiments in a specially designed test rig and numerical simulations of the real measured surface topographies of the bearings. The simulations are performed with a two-scale model where surface roughness is treated on a local asperity level by homogenized flow factors and a global scale where the bearing structure is included. Three bearings with different surface topographies are included in the study and both experimentally measured and simulated friction are analysed for each of them. Comparison of friction predicted by the model and experimentally measured friction is performed and it reveals that the model is a valuable tool for analysing the effect of surface roughness in this type of bearing

  • 23.
    Larsson, Roland
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Andersson, Ove
    Umeå university.
    Lubricant thermal conductivity and heat capacity under high pressure2000Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, nr 4, s. 337-342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal conductivity λ and the heat capacity per unit volume, ρcp, have been measured for a number of common lubricating oils. The oils tested were paraffinic and naphthenic mineral oils and a 50/50 blend of these. Polyα-olefin, polyglycol, Santotrac, ester and rapeseed oils have also been tested. The measurements, using the transient hot-wire method, were carried out under isothermal conditions over a pressure range from atmospheric to 1.1 GPa and at two temperatures, 295 and 380 K (22 and 107°C respectively). The temperature had only a marginal effect on thermal conductivity; however, the thermal conductivity was doubled as the pressure was increased to 1 GPa. The heat capacity per unit volume was influenced by both the pressure and the temperature. Some of the lubricants solidified as the pressure increased and the transition from a fluid to a solid state could be detected in the measurements of ρcp,The relationship between the thermodynamic properties and the pressure and temperature are described by two empirical equations. These equations can be used in thermal elastohydrodynamic analyses.

  • 24.
    Larsson, Roland
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson-Kråik, Per-Olof
    Eriksson, Erland
    Sjöberg, Martin
    Luleå University of Technology.
    Höglund, Erik
    Lubricant properties for input to hydrodynamic and elastohydrodynamic lubrication2000Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, nr 1, s. 17-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The properties of a number of common lubricants have been measured, namely the viscosity, elastohydrodynamic lubrication (EHL) friction coefficient, density, thermal conductivity and heat capacity per unit volume. These properties have been measured within relatively broad pressure and temperature ranges. The lubricants tested were naphthenic and paraffinic mineral oils, blends of these, polyalphaolefins and a polyglycol. Physical--empirical expressions have been developed upon the basis of the measurement results and a number of lubricant constants, or lubricant parameters, have been determined for each lubricant. These expressions can be used in engineering computational tools for lubrication analysis. The use of such analyses is expected to increase into the new millennium and it is thus important to provide reliable and relevant input data

  • 25.
    Larsson, Roland
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Special issue on tribology research in Scandinavia: Guest editorial2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr J10, s. 973-974Artikkel i tidsskrift (Annet vitenskapelig)
  • 26.
    Lingesten, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The influence of repeated high-energy engagements on the permeability of a paper-based wet clutch friction material2017Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 231, nr 12, s. 1574-1582Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behavior of a wet clutch during engagement is of great importance to the durability of the clutch and the drivability of a vehicle. While many different factors influence the engagement behavior, the focus of this paper is to investigate only one factor, the permeability of the wet clutch friction material. Two test cells for measuring the permeability of friction material mounted on clutch discs have been developed. The test cells were then used to examine the effect of clutch material ageing through clutch engagement on the permeability of the material. The tests were performed on full size friction discs including the steel core prior and subsequent to testing in a wet clutch engagement test rig. The ability of the friction material to allow for oil flow both through the sliding surface layer and the bulk of the material was measured. The results indicate that repeated clutch engagements will increase the bulk permeability. However, the repeated engagements will decrease the ability to pass fluid through the friction material sliding surface. This contradictory behavior could be explained by a combination of an increase in pore size through repeated compression and the surface glaze clogging of the friction interface surface pores.

  • 27. Lord, John
    et al.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effects of slide-roll ratio and lubricant properties on elastohydrodynamic lubrication film thickness and traction2001Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 215, nr 3, s. 301-308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With tribology research aimed at decreasing energy consumption, two factors are inherently in focus: lubricant film thickness and traction. These factors are effectively decoupled and depend on lubricant properties which are sometimes contradictory - favourable for one factor and disadvantageous for the other. The film thickness ought to be maximized to reduce the number of asperities in contact and thus wear, whilst the traction should be minimized in order to reduce energy losses. In this experimental investigation the tested lubricants were investigated to see whether they possess beneficial properties for forming thick lubricant films under severe operating conditions while maintaining low traction forces. This is done by experimentally studying the film thickness reduction due to thermal and rheological effects for a fully flooded electrohydrodynamic lubrication (EHL) contact. The base oils tested were a naphthenic mineral VG150, a synthetic poly-α-olefin VG68 and a synthetic ester VG46. It was found that the synthetic ester maintained a relatively thicker lubricant film during sliding than the poly-α-olefin and mineral oil. The film thickness reduction for the mineral oil was greater than for the poly-α-olefin.

  • 28. Marklund, Olov
    et al.
    Gustafsson, Lennart
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Correction for pressure dependence of the refractive index in measurements of lubricant film thickness with image analysis1999Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 213, nr 2, s. 109-126Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The lubricant film thickness between contacting bodies may be determined from interferograms by image analysis. Look-up tables employed in the analysis are obtained from calibration interferograms of contacts of bodies of known shape. Calibration and measurement interferograms are, however, obtained under different pressure conditions and, since the refractive index of lubricants is pressure dependent, the use of look-up tables can introduce significant errors (in the range of 10 per cent). In this paper it is shown that a straightforward correction for this error is available. In an iterative procedure the uncorrected film thickness is first determined through looking up tables. This allows the pressure distribution over the contact to be calculated and a corrected refractive index may then be obtained. The corrected refractive index in turn allows a corrected film thickness to be calculated. This procedure can be followed iteratively. After two iterations the corrections have been found to be of the same order as the resolution yielded by the method, as has been implemented

  • 29. Marklund, Olov
    et al.
    Gustafsson, Lennart
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Interferometry-based measurements of oil-film thickness2001Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 215, nr 3, s. 243-259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurement of the thickness of thin lubricant films separating rotating surfaces in elastohydrodynamic experiments presents some challenging problems. The nature of the experimental apparatus inhibits the use of most commonly applied interferometric phase measurement methods. Also the absolute thickness of the separating film must be determined, as opposed to relative distances that would be sufficient in most other measurement scenarios where interferometry methods are used. In this paper, computer-based analysis of interferograms recorded using an elastohydrodynamic lubrication Fitzeu interferometer (a so-called ball-and-disc apparatus) is discussed, the main objective being to extract the absolute oil-film thickness. Intensity based methods (most importantly, calibration look-up procedures where colour parameters from recorded dynamic interferograms are compared with table values corresponding to known film thicknesses, but also a phase measurement approach based on multi-channel interferometry using trichromatic light) are described. A discussion regarding compensation for measurement errors due to the pressure dependence of the refractive index of the lubricant is also included

  • 30.
    Marklund, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Wet clutch under limited slip conditions: simplified testing and simulation2007Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 221, nr 5, s. 545-551Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When designing new wet clutch systems, simulations and laboratory tests are important to obtain a functional system. An engineering tool is here developed to simulate wet clutches working under boundary lubrication conditions. Boundary lubrication friction is measured by a pin-on-disc test, and cooling oil flow is simulated by solving the Reynolds equation. Depending on the generated heat, the temperature in the clutch pack changes during engagement, affecting the transferred torque. With the developed method it is possible to easily and quickly investigate the behaviour of wet clutches with a variety of friction materials and groove patterns. The model is validated in a wet clutch test rig and the predicted torque agrees well with experimental data.

  • 31. Marklund, Pär
    et al.
    Sahlin, Fredrik
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Modelling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions2009Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, nr 8, s. 1129-1141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wet clutches are frequently used in the drive trains of many modern vehicles. The behaviour of the clutches influences the behaviour of the whole drive train and therefore of the whole vehicle. The design of the clutch is very important because it operates in cooperation with the other parts of the drive train. The clutch also often has to work in the lubricant present in the transmission. To optimize the clutch for an application, properties such as disc geometry, materials, friction disc surface, and engagement axial force can be varied when designing the clutch. Today, the design process involves much testing, which is expensive and time consuming. There are no good hand-book solutions or engineering tools available, hence the designer has to be very experienced and often use trial and error methods in order to end up with a working clutch for an application.A simulation model is developed in this article, which in combination with a simple measurement technique for measuring the boundary lubrication friction coefficient is used to estimate temperature and torque transfer for a wet clutch working under limited slip conditions. The developed simulation model can be used as a design tool for wet clutches. The approach developed in this article can be used to investigate torque behaviour for wet clutches that have not been designed and is, therefore, suitable to use when optimizing the performance of a new clutch. The model includes fluid dynamics, contact mechanics, and temperature computations in the fluid film between the friction disc and the separator disc. Temperature computations in the clutch discs are also included in the model. The fluid dynamics calculations use homogenized flow factors to enable simulations of flow on a coarser grid and still include all surface roughness effects. The temperature distribution in the film in the sliding interface is approximated as a polynomial of the second order. The heat transfer in the grooves of the friction discs is solved by means of an equilibrium equation that includes radial cooling flow effects because of centrifugal flows. The temperature in the friction disc and separator disc is obtained from the solution of the full three-dimensional energy equation in polar cylindrical coordinates.The model is validated by measurements made in a test rig and good agreement between measurements and simulations is obtained, both with regard to temperature and transfered torque.The use of this model can reduce the time needed to develop a limited slip wet clutch application since the systematic way of finding the optimal clutch design will be more efficient than the often used Edisonian trial and error approach.

  • 32. Mccarthy, Donald
    et al.
    Glavatskikh, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Sherrington, I.
    University of Central Lancashire, Jost Institute for Tribotechnology, Department of Technology.
    Oil-film thickness and temperature measurements in PTFE and babbitt faced tilting-pad thrust bearings2005Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 219, nr 3, s. 179-185Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of pad facing material on hydrodynamic lubrication in tilting-pad thrust bearings is investigated in terms of pad and oil-film temperatures and thicknesses. Two tilting-pad thrust bearings are examined: one with babbitt pad facing, the other with a layer of PTFE-based composite material. Frictional torque, pad, collar, and oil-film temperatures and thicknesses are all monitored by means of a comprehensive array of sensors mounted in the bearing and shaft. A considerably smaller range of temperature is seen in the steel backing immediately below the surface material for the PTFE faced pads. Oil-film temperatures measured at the mid-point on the pad trailing edge show no significant difference between the two bearings. Oil-film thicknesses in the two bearings are seen to differ. At the leading edge, oil-film thickness is thinner for the PTFE pad than for babbitt. However, at the trailing edge the PTFE pad has the thicker film.

  • 33.
    Minami, Ichiro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Inada, Taketo
    Department of Chemical Engineering, Iwate University.
    Okada, Yu
    Department of Chemical Engineering, Iwate University.
    Tribological properties of halogen-free ionic liquids2012Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 226, nr 11, s. 891-902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tribological properties of halogen-free ionic liquids, tricyanomethanide [C(CN)3−] salt, tetracyanoborate [B(CN)4−] salts, and N-alkylimidazole-trialkylborane complexes were evaluated by laboratory tribo-testing of steel–steel contact under boundary conditions. Tricyanomethanide salt is composed of hydrogen, carbon, and nitrogen. The other two types of liquids are composed of hydrogen, boron, carbon, and nitrogen. They are free of halogens and heavier elements that are components of common ionic liquids, such as fluorine, phosphorus, and sulphur. As expected, the halogen-free ionic liquids exhibited low corrosion properties to steel. When evaluated as neat liquid, these halogen-free ionic liquids provided less tribological properties in comparison with a reference, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. Tributylmethylphosphonium dimethylphosphate was examined as a prototype tribo-improving additive. It improved the wear-preventing properties and friction reducing properties of tetracyanoborate salts by 10–25% and 20–30% at a concentration of 10 mM (620 ppm of phosphorus), respectively. The additive performances for tricyanomethanide salt and the imidazole-trialkylborane complexes were not uniform under these conditions. Boron oxide and iron oxides were found by surface analysis of rubbed surfaces with tetracyanoborate salts.

  • 34. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Influence of counterface topography on sliding friction and wear of some elastomers under dry sliding conditions2008Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, nr 5, s. 667-673Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, the friction and wear behaviour of acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), acrylate rubber (ACM), and fluoroelastomer (FKM) against steel surfaces under unidirectional dry sliding conditions have been studied. The influence of surface roughness of the steel counterface on friction and wear was studied using a block-on-ring test configuration. At low load, the friction coefficient decreased after a running-in period and the wear was insignificant, especially for the ACM and FKM. The running-in time in terms of achieving a stable dry friction for the different elastomers, from longest to shortest, is in the order HNBR, NBR, FKM, and ACM, with an exception in case of FKM sliding against a smooth steel counterface. At higher contact pressure, powdery worn particles on the ACM and a decrease in friction coefficient were observed, but for FKM and HNBR, worn particles with roll shapes were produced. The worn particles of FKM were significantly larger than those of the other tested materials, and a considerably higher wear in FKM was observed.

  • 35.
    Nilsson, Daniel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Isaksson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effects of area ratio and nature of surfaces on scuffing in lubricated contacts2009Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, nr 3, s. 445-455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heavily loaded moving machine components encounter severe tribological problems. Typical examples include piston and cylinder contacts in a hydraulic motor. Piston and cylinder bore contacts invariably operate in boundary lubrication regime and the risk for seizure of these contacts is high particularly when lubricated with low-viscosity lubricants. The piston assembly in a radial piston hydraulic motor has conformal (area) contact. In this work, these contacts have been simulated in the laboratory by using a thrust washer test configuration. The influence of area ratio, nature of contacting surfaces, and speed on scuffing has been investigated by using a factorial design of experiments approach. The influence of area ratio on wear at lower speed has also been studied. The results have revealed that the surface power, or μpv-value, at scuffing varies by 3-4 times when the area ratio was increased from 8 to 72 per cent. The running-in wear tests have shown that running-in of the upper and lower specimens also varies with the area ratio. During the first 30 s the upper specimen is polished with low area ratio, whereas the lower specimen is polished with high area ratio. The surface temperature was estimated by using finite-element calculation and it was found to be similar prior to scuffing for both 8 and 72 per cent area ratios at 1.7 m/s sliding speed. The comparison of the results with the actual motor tests shows that an area ratio of 24 per cent seems to simulate the piston-cylinder contact better.

  • 36.
    Pelcastre, Leonardo
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Investigations into the occurrence of galling during hot forming of Al-Si-coated high-strength steel2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 6, s. 487-498Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Galling is a severe form of adhesive wear associated with both cold and hot metal forming operations. In hot sheet metal forming of Al-Si-coated ultrahigh-strength steel (UHSS), transfer occurs from the coated UHSS to the tool surface. This leads to poor quality of produced parts, damage of expensive tooling, and increased downtime for maintenance of the tools. This study thus aims at identifying the salient mechanism(s), which give rise to initiation/occurrence of galling at elevated temperatures. This has been accomplished by analysing actual hot forming tools and through systematic parametric tribological investigations in the laboratory. The analysis of the actual tools has shown that the transferred layer consists of Al, Si, and Fe. The structure of the transferred materials is composed of sintered/compacted wear particles. The parametric study has shown that galling is dependent on the operating conditions. A strong relationship between the contact pressure and material transfer has been observed. The severity of galling is lower for smoother surfaces at low contact pressure. However, at high contact pressure, the influence of roughness under these conditions is insignificant. It has also been observed that hard-tool steel substrates reduce the severity of galling, particularly, at high contact pressure.

  • 37.
    Ràfols, Francesc Pérez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Van Riet, Egbert J.
    Shell Global Solutions International BV, Innovation, Research and Development, Rijswijk, The Netherlands.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On the loading and unloading of metal-to-metal seals: A two-scale stochastic approach2018Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 12, s. 1525-1537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During operation, the mating surfaces of a metal-to-metal seal typically undergo significant plastic deformation, which in turn can have beneficial effect on its performance. In previous studies, it has, for instance, been shown that plastic deformation can provide for better sealing during unloading. Those studies did, however, only consider flow through unrealistically small domains. Therefore, it is possible that this might be a size effect, which would not be apparent in a real situation with a much larger domain. In this paper, we develop a model which can handle real-sized seal domains at the same time as fine details of the surface topography. More precisely, we construct a two-scale model, in which the global scale represents the seal domain and where the influence of the fine details at the local scale are represented by a stochastic element. By means of this stochastic two-scale model, we show that the beneficial effect associated with the plastic deformation persists also when real-sized seal domains are considered.

  • 38.
    Sahlin, Fredrik
    et al.
    Siemens Industrial Turbomachinery AB.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Lugt, Piet
    SKF Engineering & Research Center, Nieuwegein.
    Marklund, Pär
    A mixed lubrication model incorporating measured surface topography: Part 1: theory of flow factors2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 4, s. 335-351Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mixed lubrication model that permits real three-dimensional surface topography as input is developed. The theory of computing flow factors within the model is presented, and with a following paper (Part 2) the method of measuring and adapting the surface roughness, and model validation through flow measurements and application to a bearing is shown. A contact mechanics model is used to calculate the elastoplastic displacement of a periodic topography signal. A method based on homogenization is used to calculate flow factors for all lubrication regimes. The flow factors are compared with the Patir and Cheng method. Results indicate that the two methods compare well for longitudinal roughness lay, but differ significantly for a cross-patterned surface roughness due to the more complete flow description of the current model.

  • 39.
    Sahlin, Fredrik
    et al.
    Siemens Industrial Turbomachinery AB.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Almqvist, Andreas
    Lugt, Piet
    SKF Engineering & Research Center, Nieuwegein.
    A mixed lubrication model incorporating measured surface topography: Part 2: roughness treatment, model validation, and simulation2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 4, s. 353-365Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mixed lubrication flow factor model that permits real three-dimensional surface topography as input has been developed. Part 1 gives the theory of computing flow factors within the model. In this article, a method of adapting the measured surface topography signal to suit the numerical models is developed and presented in detail. The mixed lubrication model is validated through flow measurements for three different rough surface test specimens. Simulation of a hydrodynamic bearing was conducted and the results are presented in terms of pressure distributions and Stribeck curves covering all lubrication regimes. The results indicate that the model may be an efficient and accurate engineering design and research tool for tribological devices operating in all lubrication regimes.

  • 40.
    Schnabel, Stephan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Golling, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The influence of contact time and event frequency on acoustic emission signals2017Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 231, nr 10, s. 1341-1349Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of acoustic emissions (AE) of rotating machine elements is often performed under a constant speed. There are few investigations on speed and contact time dependency of acoustic emission signals, even though some investigations have reported difficulties at elevated rotational speeds. Simplified experiments are, therefore, presented in this article to increase the understanding of the time dependency of acoustic emission signals. Hertzian impacts and tensile tests are used to study contact time, the time duration of an event and offset time, the time between events and accordingly the event frequency. The results of these model experiments indicate an indirect quadratic proportionality of acoustic emission amplitudes and contact time (umax∝1/(tc2)">u max ∝1/(t 2 c ) umax∝1/(tc2) ), as well as a proportional relationship between the root mean square and event frequency (RMS∝fevent∝1/toffset">RMS∝f event ∝1/t offset  RMS∝fevent∝1/toffset ). The relationship between contact time and the root mean square of acoustic emission signals is strongly dependent on the damping of the system

  • 41.
    Schnabel, Stephan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Study of the short-term effect of Fe3O4 particles in rolling element bearings: Observation of vibration, friction and change of surface topography of contaminated angular contact ball bearings2014Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, nr 10, s. 1063-1070Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The harsh environment rolling element bearings are exposed to in iron-mining industries is replicated in a laboratory scale in this work. Bearings (SKF 7204BEP) were tested both with and without magnetite oxide (Fe3O4) contamination. In order to study the interaction between contaminants and extreme pressure additives, the rolling element bearings were lubricated with two different greases: Grease without extreme pressure and grease containing sulphur-based extreme pressure additives. Further, the effect of the contamination–additive interaction on rolling bearing performance and monitoring signals (vibration and acoustic emission) was investigated. The obtained results indicate an advantage of extreme pressure additive in case of the investigated operating conditions. Furthermore, the use of extreme pressure additives decreased wear, surface roughness, vibration and acoustic emission for both test durations of 24 h and 168 h. The decrease of the acoustic emissions and the surface roughness parameter Rq in case of the tests with a duration of 168 h as high as 70% and 60%, respectively using extreme pressure additives in comparison with the plain grease was observed. The major cause for this reduction seems to be the interaction between contaminants and extreme pressure additives.

  • 42. Simmons, Gregory F
    et al.
    Cha, Matthew
    Machine Design, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Steady state and dynamic characteristics for guide bearings of a hydro-electric unit2014Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, nr 8, s. 836-848Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experiments are conducted using a 10-MW Kaplan hydropower machine which is outfitted with an extensive array of sensors to determine oil film thickness, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all journal bearings are compared to a commercial rotor dynamics model and results for the central journal bearing are compared to a multi-physics model to provide insight into the machine's steady state and dynamic characteristics and their variations during normal operation.

  • 43.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A numerical model to investigate the effect of honing angle on the hydrodynamic lubrication between a combustion engine piston ring and cylinder liner2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 7, s. 683-689Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A numerical model has been developed to investigate the effect of cylinder liner honing angle on hydrodynamic lubrication between piston ring and cylinder liner. The Reynolds equation was solved in 2D with periodic boundary conditions. An artificial surface texture was generated, based on a real surface measured with white light interferometry. Cavitation was modelled with the Vijayaraghavan and Keith algorithm. Honing angles between 25° and 75° were investigated to find the effect of honing angle on film thickness.

  • 44.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A semi-deterministic texture-roughness model of the piston ring-cylinder liner contact2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 6, s. 325-333Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many simulations already exist to model the piston ring-cylinder liner contact; however, very few models have been used to investigate the optimum surface texture. An axisymmetric, time-dependent two-dimensional semi-deterministic texture-roughness model of the piston ring to cylinder liner contact with periodic boundary conditions and mass preserving global cavitation has been developed. The cylinder liner texture, generated by honing, was considered deterministically on the global scale, after an investigation comparing deterministic and homogenized solutions. The surface texture of a real cylinder liner was measured with white light interferometry and an algorithm developed to generate an artificial periodic texture representative of the real surface. The effect of cylinder liner plateau roughness has been incorporated on the local scale by homogenization of the Reynolds equation and calculation of flow factors from real surface topography. Using the homogenization technique to incorporate the effect of surface roughness leads to a more efficient solution than mesh refinement of the deterministic problem as the roughness does not need to be resolved on the global solution domain, allowing for significantly less degrees of freedom in the global problem. The lubricant boundary pressures have been calculated using results from a numerical ring-pack model and the lubricant viscosity has been adjusted based on the cylinder liner wall temperature. It was found from the result of a comparison between deterministic and homogenized solutions that surface texture should be modelled on the global and not on the averaged roughness scale as is the case with many previous investigations.

  • 45.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Avan, Emin Yusuf
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dwyer-Joyce, Rob S
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    An experimental and numerical investigation of frictional losses and film thickness for four cylinder liner variants for a heavy duty diesel engine2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 12, s. 1319-1333Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The piston ring pack is the single greatest contributor to mechanical losses in a heavy duty diesel engine, accounting for 1.1–6.8% of the total losses. Therefore, the piston ring-cylinder liner contact is potentially the most rewarding area to study when attempting to reduce mechanical losses in a heavy duty diesel engine. In this work, four different heavy duty diesel engine cylinder liner variants have been tested to evaluate the lubricating conditions that occur when a section of top compression ring is reciprocated against them in a lubricated environment. Two of the cylinder liners were traditional grey cast iron and plateau honed with different honing angles, one had ANS Triboconditioning® applied and the last was plasma sprayed with a stainless steel and ceramic coating, then honed. An experimental test rig was used where friction and film thickness was recorded, by means of an ultrasonic technique. A numerical model was also developed to calculate the friction and film thickness. Comparisons are made between the simulation and experiment, and the four cylinder liner variants are also evaluated. It was found that both simulation and experiment could differentiate between all surfaces and the results from the model and experiment also correlated well with each other. A lower plateau average surface roughness, as exhibited by the ANS Triboconditioning® and plasma liners, led to a significant reduction in friction.

  • 46.
    Suarez, Aldara Naveira
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Tomala, A.
    Institut für Angewandte Physik, Vienna University of Technology.
    Grahn, Mattias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Zaccheddu, M.
    SKF Engineering & Research Center, Nieuwegein.
    Pasaribu, R.
    SKF Engineering & Research Center, Nieuwegein.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The influence of base oil polarity and slide-roll ratio on additive-derived reaction layer formation2011Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 7, s. 565-576Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Functional additives, particularly extreme-pressure and antiwear additives, in formulated oil will compete to adsorb and form a protective layer in tribological contacts. The thickness of the layer is determined by the equilibrium between the formation and removal processes. In this article, the interactions between additives and base oil molecules and operating conditions influence friction and wear are studied. One polar (ester oil) and one non-polar (poly-α-olefin) commercial base oil blended with zinc dialkyl dithiophosphates were studied. The tribological performance was evaluated using a ball-on-disc test rig under mixed rolling-sliding conditions in the boundary lubrication regime. An adapted in situ interferometry technique was used to monitor the additive-derived reaction layer formation. The properties of the additive-derived reaction layers were studied using surface analysis techniques, X-ray photoelectron spectroscopy and atomic force microscopy. A thicker layer was formed when the additive is blended in the nonpolar oil. This observation suggests that base oil polarity determines the transport of additives to the surface, thereby controlling the maximum reaction layer thickness, friction and wear, as well as the morphology of the additive-derived reaction layer. However, the reaction layer chemical composition is not strongly influenced by the base oil polarity. Among the operating conditions, shear was identified as a fundamental parameter for the activation of additives on rubbing steel surfaces and the properties of the derived reaction layer.

  • 47.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Isaksson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Spencer, Andrew
    Scania CV AB, Södertälje.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The effect of three-dimensional deformations of a cylinder liner on the tribological performance of a piston ring–cylinder liner system2014Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, nr 10, s. 1080-1087Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes a numerical simulation model for prediction of the tribological effects of an oil control ring running against an out-of-round cylinder liner in a heavy duty diesel engine. The model considers the full three-dimensional geometry of the oil control ring and includes the effect of both surface roughness and global deformation. Results that test the model’s ability to do this under stationary conditions are presented. Furthermore, stationary results for prediction of the friction reduction possible by reduced ring tension in combination with reduced out-of-roundness are given. The model predicts the friction for the oil control ring at mid-stroke to be 78% larger in an out-of-round cylinder liner compared to a perfectly cylindrical one.

  • 48.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Texture-induced effects causing reduction of friction in mixed lubrication for twin land oil control rings2018Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 2, s. 166-178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Piston rings are responsible for a major part of the frictional losses in a heavy-duty diesel engine. Such losses can be reduced by applying texture, such as dimples, on the cylinder liner surface. This paper investigates the effect of such texture on the friction between a land of the oil control ring and a textured cylinder liner via numerical simulation. A simulation model considering inertia and mixed lubrication together with a mass-conserving cavitation model is developed. The model is used to determine the dimple parameters that yield the lowest amount of friction for a specific oil control ring of a heavy-duty diesel engine

  • 49.
    Vuorinen, Esa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Heino, V.
    Tampere University of Technology, Department of Materials Science.
    Ojala, N.
    Tampere University of Technology, Department of Materials Science.
    Haiko, O.
    University of Oulu, Faculty of Technology, Materials Engineering.
    Hedayati, Ali
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Erosive-abrasive wear behavior of carbide-free bainitic and boron steels compared in simulated field conditions2018Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 1, s. 3-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wear resistance of carbide-free bainitic microstructures have recently shown to be excellent in sliding, sliding-rolling, and erosive-abrasive wear. Boron steels are often an economically favorable alternative for similar applications. In this study, the erosive-abrasive wear performance of the carbide-free bainitic and boron steels with different heat treatments was studied in mining-related conditions. The aim was to compare these steels and to study the microstructural features affecting wear rates. The mining-related condition was simulated with an application oriented wear test method utilizing dry abrasive bed of 8–10 mm granite particles. Different wear mechanisms were found; in boron steels, micro-cutting and micro-ploughing were dominating mechanisms, while in the carbide-free bainitic steels, also impact craters with thin platelets were observed. Moreover, the carbide-free bainitic steels had better wear performance, which can be explained by the different microstructure. The carbide-free bainitic steels had fine ferritic-austenitic microstructure, whereas in boron steels microstructure was martensitic. The level of retained austenite was quite high in the carbide-free bainitic steels and that was one of the factors improving the wear performance of these steels. The hardness gradients with orientation of the deformation zone on the wear surfaces were one of the main affecting factors as well. Smoother work hardened hardness profiles were considered beneficial in these erosive-abrasive wear conditions.

  • 50.
    Wang, Zhou
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Grahn, Mattias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Antzutkin, Oleg
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Temperature-dependent changes of physicochemical and tribological properties of acrylonitrile-butadiene rubber elastomer upon ageing in hexadecane and diethylene glycol dibutyl ether2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 826-836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Acrylonitrile-butadiene rubber elastomers are widely used in seal and tire industries. Physiochemical, surface and tribological properties of acrylonitrile-butadiene rubber exposed to a lubricant in a sealed mechanical contact may gradually change, in particular, at elevated temperatures. In this study, industrial-grade acrylonitrile-butadiene rubber elastomers were aged in two model non-additivated base oils, namely non-polar hexadecane and polar diethylene glycol dibutyl ether at both ambient (298 K) and elevated (398 K) temperatures from 1 to 168 h. Mass changes of acrylonitrile-butadiene rubber before and after ageing indicated that acrylonitrile-butadiene rubber had distinct ageing dynamics in different model base oils and at different temperatures. For acrylonitrile-butadiene rubber aged in nonpolar hexadecane, the rate of weight loss of the rubber was larger at 398 K compared to that at 298 K. On the contrary, distinct weight-gaining (swelling) dynamics were observed for acrylonitrile-butadiene rubber aged in polar diethylene glycol dibutyl ether at 298 and 398 K. Based on Fourier transform infrared spectroscopy, liquid and solid-state nuclear magnetic resonance spectroscopy and energy dispersive spectroscopy analyses, it was found that aldehydes and sulfur- and zinc-containing compounds were leached out from acrylonitrile-butadiene rubber aged in both hexadecane and diethylene glycol dibutyl ether. The results of tribological studies showed that the non-aged acrylonitrile-butadiene rubber has a good wear-resistance. Acrylonitrile-butadiene rubber samples had a very similar surface topography before and after tribo-tests. However, the worn surfaces of acrylonitrile-butadiene rubber samples were characterized by fine scoring (abrasion) marks after ageing in both model base oils. This has been attributed to changes in the steel–rubber contact environment during the sliding process and degradation of mechanical properties of acrylonitrile-butadiene rubber after ageing. For one acrylonitrile-butadiene rubber sample (after ageing in hexadecane at 398 K), very stable friction in the steel–rubber contact was observed.

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