| 1. |
- Almqvist, Andreas, et al.
(författare)
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Simulation of piston ring : cylinder liner lubrication considering layered fluid films
- 2009
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 28:3-4, s. 44-58
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Tidskriftsartikel (refereegranskat)abstract
- During the operation of hydrodynamically lubricated devices a fully formulated lubricant has the ability to form layers at the surfaces. A friction modifier's task is to adjust the interaction between lubricant and the surface so that friction is lowered. An antiwear additive creates a protective layer on the surface and this definitely influence the performance of the lubricated device. To gain fundamental understanding, models that address the modified liquid - solid interaction due to the formation of layers, but also models that may be used to study the effects of layers already formed on the contacting surfaces are required. In this paper, two non-Newtonian lubricant rheology models that may be used to simulate reacted layers resembling those created by lubricant additives are adopted for the simulation of the piston ring - cylinder liner lubrication problem. The possibility of layer to layer interaction, which is likely to occur in the convex conjunction between the ring and the liner, is considered and this extends the models found in the literature. The effects induced by this type of layering are studied by using a modified Reynolds' equation where the coefficients have been corrected with factors that accounts for the layer properties. This enables, effectively, studies of layers resembling those created by lubricant additives during the operation of the lubricated conjunction between a piston ring and a cylinder liner.
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| 2. |
- Almqvist, Andreas, et al.
(författare)
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The homogenization process of the time dependent Reynolds equation describing compressible liquid flow
- 2007
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 26:4, s. 30-44
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Tidskriftsartikel (refereegranskat)abstract
- To increase the hydrodynamic performance in different machine elements during lubrication, e.g. journal bearings and thrust bearings, it is important to understand the influence of surface roughness. In this connection one encounters different approaches commonly based on some form of the Reynolds equation. They may generally be divided into deterministic- and averaging- techniques. The former regards all surface roughness information and provides a detailed understanding of the local effects that arise. The latter method is suitable when investigating how the surface roughness affects performance of the machine element as a whole. Homogenization is a rigorous mathematical concept that when applied to a certain problem may be thought of as an averaging technique also providing information about local effects. In this work the compressible time dependent Reynolds equation is homogenized. Related problems have recently been analyzed by homogenization techniques under various assumptions. In the present paper the compressibility is modeled assuming a constant lubricant bulk modulus. The formal method of multiple scale expansion is used to derive a so-called homogenized equation and a numerical solution method to solve both the deterministic problem and the homogenized problem is implemented. The numerical results clearly show that the solution of the homogenized equation is a suitable approximation to the solution of the deterministic problem. It is also demonstrated that for small values of the roughness wavelength, the homogenization technique is superior, since the solution of the deterministic problem requires an extremely fine discretization mesh. More over, the solution of the time dependent homogenized problem may in some cases be reduced to solve a stationary problem that facilitates the solution process and interpretation of results.
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| 3. |
- Andre, Benny, et al.
(författare)
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Nanoindentation on micro pillars for determination of intrinsic hardness and residual stress in coatings deposited on complex geometries
- 2012
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Ingår i: Tribologia. - 0780-2285. ; 31:1-2, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- In this work a procedure to assess the local residual stress in coatings deposited on complex substrate geometries is described. A focused ion beam (FIB) is used to mill structures small enough to relax from residual stress. Nanoindentation is used to measure the change in mechanical properties, most importantly the hardness, in relaxed coating and in as-deposited coating. This change is then related to the residual stress in the coating. This relationship can then be used to calculate the residual stresses, at other positions or at other components, from changes in hardness as measured as before. The procedure is demonstrated on two different PVD coatings; one TiN coating and one nanocomposite TiNiC coating. On a large high speed steel substrate the TiN was measured to a hardness of 28 GPa using conventional techniques. Using this procedure, this could be divided into 23 GPa of intrinsic hardness and an extra 5 GPa induced by the known compressive residual stress of 3.9 GPa. When the same coating was deposited on a thin wire the full procedure allowed the residual stress to be determined to 3.5 GPa in compression.
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| 4. |
- Bodin, Anders
(författare)
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Tracked vehicles - the influence of design parameters on the tractive performance in deep snow
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:3, s. 6-12
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Tidskriftsartikel (refereegranskat)abstract
- A new tracked vehicle has been developed for studying the influence of different vehicle parameters on mobility in soft terrain, particularly on muskegs and in deep snow. The vehicle is skid steered with a hydrostatic transmission, driven by a five-cylinder diesel engine. The vehicle makes it possible to vary several design parameters in the field, and it is equipped with transducers to measure the vehicle trust, track motion resistance, belly resistance, drawbar pull, the trim angle of the vehicle and the slip between the tracks and snow.
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| 5. |
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| 6. |
- Ekerfors, L.
(författare)
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Screw-Nut Transmission
- 1984
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 3:3, s. 35-41
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Gerth, Julia, et al.
(författare)
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Survey of damage mechanisms on PVD coated HSS hobs used in Swedish gear manufacturing industry
- 2011
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Ingår i: Tribologia. - 0780-2285. ; 30:1-2, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- Gear hobbing is widely used for production of cylindrical gears in the Swedish transmission industry. The hob, usually consisting of a homogenous HSS (High Speed Steel) body coated with a ceramic PVD (Physical Vapour Deposition) coating, is designed for regrinding and recoating several times without affecting its cutting geometries. Efficient usage of the tool, considering production costs and gear quality, requires reconditioning before wear starts to affect the gear quality negatively and certainly before tool wear renders reconditioning impossible. Hobs of today generally lack in reliability, making it difficult to judge when they have to be taken out for reconditioning. This work presents a survey of wear as observed on today’s state of the art hobs used by Swedish gear manufactures. It aims to identify damage mechanisms and the common problems in order to enable future production of more reliable hobs. The tools were temporarily borrowed from the production and the analyses were made non-destructively using optical microscopes. This was complemented by destructive cross-sectional analysis on two of the hobs. Wear was most commonly located on the rake faces and the cutting edges of the cutting teeth. It mainly propagates by discrete fractures which appear to originate at local defects in the coating or at the interface. High intrinsic stress in the coating likely promotes coating spallation and accelerates the wear of the cutting edge.
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| 8. |
- Glavatskih, Sergei, et al.
(författare)
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Hydrodynamic thrust bearing experimental apparatus for testing environmentally adapted oils
- 1998
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 17:2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- There are indications that some environmentally friendly oils provide performance advantages in hydrodynamic bearings compared to mineral oils. To verify and to quantify the advantages of the synthetic oils in hydrodynamic lubrication in terms of operating film thickness, bearing power loss and operating temperature, a test rig for laboratory experiments has been designed and manufactured. At the first stage of the project temperature and pressure distributions, power loss and oil film thickness for ISO VG46 and VG68 mineral and synthetic oils will be measured at different loads and rotational speeds. At the next stage several other lubricants will be tested. Among them rape seed oil and pine tree oil can be mentioned.
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| 9. |
- Hogmark, Sture, et al.
(författare)
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On adhesion in tribological contacts-Causes and consequences
- 2007
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Ingår i: Tribologia. - 0780-2285. ; 26:1, s. 3-16
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Tidskriftsartikel (refereegranskat)abstract
- This paper is focused to the metallurgical consequences of severe adhesive wear of metallicmaterials. Early examples from the late 70:ies from sliding wear tests of different steels areshown together with some high-resolution TEM micrographs of a cemented carbide cutting tooledge, prepared by using a Focused Ion Beam.Irrespective of sliding conditions, severe metallic wear of the adhesive type results in a surfacelayer, the structure of which is totally different from that of the original bulk material. Theoutermost surface layer displays a nano-crystalline structure followed by a textured layer inwhich the original grains are heavily deformed. For carbon steels, the nano-crystalline layeroften represents untempered martensite.During the wear process, oxide fragments and wear particles from the counter-material may alsobe mixed into the surface layer.The consequence for all metallic materials is that severe wear generates a hard superficial layer.For carbon steels, the hardness of the outermost layer may well exceed 1000 HV. The hardeningmechanisms are well known to a metallurgist and consist of grain refinement, deformationhardening through dislocation generation and tangling, solute hardening (martensite in carbonsteels) and second phase or particle strengthening through intermixing.Consequently, the wear process generates a surface layer on metallic materials that has a muchhigher wear resistance than the original material. This was also demonstrated in one of theexperiments.
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| 10. |
- Holgerson, Mikael
(författare)
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Wet clutch engagement characteristics
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:3, s. 4-5
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Tidskriftsartikel (refereegranskat)abstract
- A wet clutch test rig has been built to examine the characteristics of engagements of wet clutch plates. Results show that the drive torque has a major effect on the engagement and should therefore be taken into consideration when investigating wet clutch characteristics. Furthermore, it was found that the temperature rise is approximately a linear function of the developed energy, and that the friction coefficient is mainly independent of the operating conditions
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| 11. |
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| 12. |
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| 13. |
- Jacobson, Bo
(författare)
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Rolling contact and EHD
- 1985
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 4:1, s. 1-22
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Tidskriftsartikel (refereegranskat)
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| 14. |
- Jolkin, Alexei
(författare)
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EHL investigations using a hybrid technique - an experimental and numerical approach
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:4, s. 3-
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid experimental and numerical method for investigation of film thickness and pressure distribution in an EHL conjunction is presented. The hybrid technique combines experimental study and advanced numerical calculations. Optical interferometry and image analysis are employed for the determination of high-resolution film thickness maps. A numerical algorithm is used for the reconstruction of the pressure distribution in a circular EHL contact from 3D film thickness map by solving the film thickness equation.
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| 15. |
- Jonsson, Ulf J., et al.
(författare)
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Elastohydrodynamic lubrication properties of polyol ester lubricants-R134a mixtures
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:1, s. 31-37
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Tidskriftsartikel (refereegranskat)abstract
- A falling ball viscometer which can be pressurized up to 34 MPa was designed to measure the viscosity and pressure-viscosity of oil-refrigerant mixtures. Eight different polyolesters mixed with R-134a were evaluated. The results show that the degree of branching has a large impact on the pressure-viscosity coefficient. An empirical model which can be used to predict the pressure-viscosity coefficient was developed based on viscosity and the amount of branched acids in the lubricant.
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| 16. |
- Jonsson, Ulf J., et al.
(författare)
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Lubrication limits of rolling element bearings in refrigeration compressors
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:1, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Traditional methods for life calculations for rolling element bearings have shown limitations when used for bearings in refrigeration applications and there is a need for design data that can be used in the selection of bearings and the design of the lubrication systems. A bearing test apparatus has been designed to test axial and radial rolling element bearings under conditions similar to those to be found in full-scale refrigeration compressors. Four angular contact ball bearings have been tested using two different lubricants. Three tests were made to study the influence of refrigerant concentration. The fourth test aimed at comparing the influence of lubricant structure on bearing wear rate. SEM-images of the tested bearings showed that the contact surface between the ball and race was chemically attacked in bearings operating with a refrigerant dilution of 23% R-134a. The lubricant that was formulated with shorter acids gave the highest wear rate. A new toroidal roller bearing, CARB(TM), was tested with and without a cage separating the rollers in an ammonia-mineral oil environment. It was found that the bearing can only be used in ammonia compressors if it is fitted with a cage separating the rollers.Four angular contact ball bearings were tested using two different lubricants. Three tests were made to study the influence of refrigerant concentration, and the fourth test was aimed at comparing the influence of lubricant structure on bearing wear rate. Scanning electron microscopic images of the tested bearings showed that the contact surface between the ball and race was chemically attacked in bearings operating with a refrigerant dilution of 23% R-134a. The lubricant that was formulated with shorter acids gave the highest wear rate.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Larsson-Kråik, Per-Olof, et al.
(författare)
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A new high-pressure viscometer
- 1997
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 16:3, s. 31-48
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Tidskriftsartikel (refereegranskat)
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| 21. |
- Lind, Jonna, et al.
(författare)
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Friction and wear studies of some PEEK materials
- 2015
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Ingår i: Tribologia - Finnish Journal of Tribology. - : Helsinki University of Technology. - 0780-2285. ; 33:2, s. 20-28
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Tidskriftsartikel (refereegranskat)
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| 22. |
- Lind, Jonna, 1984-, et al.
(författare)
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Friction and wear studies of some PEEK materials
- 2015
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Ingår i: Tribologia - Finnish Journal of Tribology. - 0780-2285. ; 33:2, s. 20-28
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Tidskriftsartikel (refereegranskat)abstract
- The friction and wear behavior of several types of PEEK polymers and composites were studied. The influence of carbon fiber, lubricant and thermally conductive fillers were evaluated, as well as the effects of contact load and temperature. The tests were done using a reciprocating ball-on-disc set-up. The materials were tested under the load of 5 N and 15 N, at room temperature, 80 °C, 120 °C and 150 °C. The difference between the materials was substantial, with a friction coefficient varying between 0.03 and 0.3 for the different materials at 120 °C. PEEK with carbon fiber filler showed an improvement in both friction and wear compared to unfilled PEEK. When adding lubricant, PTFE, to the composite the friction and wear were improved even more. PEEK with thermally conductive filler on the other hand had both highest friction and wear. Increasing the temperature slightly decreased both friction and wear for most of the PEEK materials. At 150 °C, only the composite with PTFE lubricant had a low friction and wear.
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| 23. |
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| 24. |
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| 25. |
- Lundberg, Jan
(författare)
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Vattenbaserade hydraulvätskors obliteration
- 1984
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Ingår i: Tribologia : Finnish Journal of Tribology. - Luleå : Luleå tekniska universitet. - 0780-2285. ; 3:4, s. 1-24
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Tidskriftsartikel (refereegranskat)
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| 26. |
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| 27. |
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| 28. |
- Mäki, Rikard
(författare)
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Wet clutch tribology : friction characteristics in all-wheel drive differentials
- 2003
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 22:3, s. 5-16
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Tidskriftsartikel (refereegranskat)abstract
- In recent past several electronically controlled automotive transmission systems, where wet clutches are used as intelligent differentials, have emerged on the market. These applications generally impose high stresses on the transmission fluids. The fluids must retain the desired frictional characteristics at different torque levels during its lifetime in an environment where the ambient and system temperatures vary in a wide temperature range. This paper deals with friction characteristics of transmission fluids for wet clutches in all-wheel drive systems, and summarizes a recent licentiate thesis on the subject. The all-wheel drive system, featuring a wet multi-plate clutch with a sintered bronze based friction material, is described. Test equipment designed in order to determine the frictional characteristics of transmission fluids are described. This equipment can also be used to measure the actual temperature experienced by the fluid in the contact zone using an infrared temperature measurement method. Results show the influence of several operating parameters on the frictional behaviour of the clutch. Temperature is shown to have significant influence on the friction characteristics of transmission fluids. The friction decreases with increasing temperature, and it is therefore necessary to measure the correct temperature in the clutch to obtain realistic values of friction. The friction-velocity relationship is a good indicator of the fluid's ability to suppress friction induced vibrations. It is, however, important to measure the friction-velocity relationship at constant temperature, or compensate the relationship accordingly. The influence of clutch disc pressure on friction is quite moderate, as compared to the influence of temperature and sliding velocity. The influence of different oil additives on friction has also been investigated. These additives have considerable influence on friction, and this must be considered when formulating new transmission fluids.
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| 29. |
- Pettersson, Anders, et al.
(författare)
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Running-in studies of a hydraulic rotator
- 2007
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 26:3, s. 3-8
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 30. |
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| 31. |
- Rebeggiani, Sabina, 1980-, et al.
(författare)
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Empirical Evaluation of Spin-on-Glass-Layers on Steel Surfaces by Wear Tests
- 2014
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Ingår i: Tribologia Finnish Journal of Tribology. - Helsinki, Finland : Helsinki University of Technology. - 0780-2285. ; 32:1, s. 19-24
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Tidskriftsartikel (refereegranskat)abstract
- Dies and moulds with high precision surfaces are being used in various branches, e.g. in the plastic industry where the surface finish are conventionally performed by manual polishers. With ever increasing demands of shorter lead times and reduced costs, efforts have been made to automate this finishing process. This paper presents an empirical study performed to test durability properties of SOG (spin-on-glass)-layers on steel surfaces. The results showed that the thin coating last longer than the thicker ones, and that the harder coatings withstood wear significantly better than the steel reference samples thus motivating further investigations.
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| 32. |
- Sannellappanavar, G., et al.
(författare)
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Towards real time automated early gear failure detection
- 2022
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Ingår i: Tribologia. - : The Finnish Society for Tribology. - 0780-2285 .- 1797-2531. ; 39:3-4, s. 42-44
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Tidskriftsartikel (refereegranskat)abstract
- The ability to stop a gear fatigue test before catastrophic failure has many advantages. However, today, a wide-ly accepted approach is not available. This case study applies a vibration-based condition monitoring methodologyto detect early gear failures. The gear studied takes part in an all-wheel-drive drivetrain system. Vibration signalsfrom four run-to-failure fatigue tests at two constant torque-speed combinations were used as input to time-synchronous averaging and autoregression model generation. The applied methodology shows promising resultsfor early failure detection, and the process is feasible for implementation in an automated environment. Real timeanalysis is also possible since the autoregression model generates a healthy state TSA signal during the early tes-ting stages. However, the time to failure detection varies with operating conditions, with low sensitivity at high-speed and low-torque conditions.
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| 33. |
- Tuomas, Roger, et al.
(författare)
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Influence of molecular structure on the lubrication properties of four different esters
- 2000
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Ingår i: Tribologia. - 0780-2285. ; 19:4, s. 3-8
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Tidskriftsartikel (refereegranskat)abstract
- The lack of published data on the chemical structures of lubricants makes it almost impossible to investigate the influence of structure on lubrication properties. In this investigation, the lubricating properties of three esters with known chemical structure have been investigated and compared with a commercial ester. The lubrication properties that were expected to be dependent on chemical structure such as film thickness and traction, viscosity and friction coefficients were compared by experiment. To measure the film thickness a Ball and Disc Apparatus was used, the traction coefficient was measured in a Jumping Ball Apparatus, the viscosity in a rotational cylindrical viscometer and the friction coefficient in a reciprocating friction and wear test apparatus. The results showed that molecular length has a significant influence on lubrication properties, with longer molecules giving the highest viscosity and greatest film thickness. The length of the molecule did not influence the coefficients of friction, but the traction coefficient, Υ, decreased with increasing molecular length.
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| 34. |
- Ukonsaari, Jan, et al.
(författare)
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Tribological studies on an eal lubricated bearing bronze - Steel pair under reciprocating sliding conditions
- 2008
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Ingår i: Tribologia. - 0780-2285. ; 27:1, s. 3-18
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Tidskriftsartikel (refereegranskat)abstract
- Boundary lubricated journal bearings are found in various applications involving oscillatory sliding conditions. Environmental adaptation of hydraulic systems includes the introduction of synthetic esters. These new environmentally adapted lubricants (EALs) have shown very good boundary lubrication performance but also condition sensitivity. This study examines an oil lubricated bronze pin on hardened steel configuration in a reciprocating friction and wear test machine. Three synthetic esters were tested with a 1 mm stroke length. Results were compared with those for a mineral oil. The tribological performance with synthetic ester lubricant can, under certain conditions, be very good. SEM-EDS and XRD surface sensitive studies indicate the formation of a soft, copper enriched outer contact layer. The layer's nature and contact mechanisms clearly affect the performance of the different lubricants.
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| 35. |
- Ukonsaari, Jan, et al.
(författare)
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Tribological study of boundary lubricated TiN-bronze bearing under slow intermittent motion using an environmentally adapted synthetic ester
- 2008
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 27:1, s. 19-33
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Tidskriftsartikel (refereegranskat)abstract
- Lubricated journal bearings operating at moderate temperatures under conditions of slow intermittent or oscillating motion are important components in many items of machinery. In this application, choosing a suitable lubricant is critical to prolonging the lifetime of the component. The choice of lubricant is often dependent on the material pairing between the bearing and shaft. In parallel with growing concern about the environment, the development of environmentally adapted lubricants (EALs), such as synthetic esters, is gradually gaining pace. Studies have shown the ability of synthetic esters to reduce friction and wear under boundary lubricated conditions, especially with low alloyed bronzes on hardened steel. This study deals with the investigation of three different shaft materials, i.e. hardened, DLC-coated or normal steel, for use with a tin-bronze journal bearing lubricated with a synthetic ester. Experiments using the journal bearing show encouraging friction and wear results with the synthetic ester lubricant in comparison to tests with a mineral oil under the same operating conditions. (16 refs.)
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| 36. |
- Åström, H.
(författare)
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Irregular film thickness fluctuations in elastohydrodynamic lubrication of a point contact lubricated with lubricating grease
- 1992
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 11:4, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- In this research, a grease-lubricated EHD point contact involving a steel ball and sapphire disc has been investigated to clarify the influence of different types of lithium grease on the lubricating film shape. The contact diameter was 0.66 mm, the maximum Hertzian pressure was 1.2 GPa and the rolling speed was 55 mm/s. The conclusions can be summarized as follows. Formations of soap thickener, approx 20 mu m in diameter in the bulk grease, enter the contact area, where they deform and cause local film thickness disturbances with a diameter of 100-200 mu m and a height of 0.1 mu m above the central film thickness. The soap thickener structure that passes the contact area breaks and forms an irregular layer on the surfaces. If the grease supply is stopped, and the contact is starved, lumps of soap thickener fibres left on the surfaces will still cause irregular film thickness fluctuations that might help to separate the surfaces. The frequency of the local disturbances depends mainly on the soap thickener content and the manufacturing process. Greases manufactured to be "quiet-running" in a rolling element bearing are more homogeneous in the soap thickener structure, and therefore cause fewer local deformations in the contact area, meaning reduced noise.
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| 37. |
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