Wear mechanisms of the cutting tools are well investigated worldwide. Usually researchers use the cutting process itself, turning by single point cutting, as their investigation method, which includes turning a metal cylinder with a pre-selected work-material and predetermined cutting conditions. Thereafter the tool worn surface is examined by scanning electron microscopy in order to characterize the tool wear mechanisms and tool failure. However, this may be the most appropriate way to investigate the wear mechanisms which occur during machining since it simulates the real operation. Metal cutting involves extreme conditions such as high temperature and high-pressure and the different condition results in different wear modes on the insert’s surface. The wear modes are overlapping and the transition boarder between them are not sharp making it difficult to obtain a detailed information of wear mechanisms. Because of these reasons many researchers try to refine the machining to a single condition e.g; high pressure, at the laboratory level in order to characterize the wear mechanisms and to get a more detailed information. In this thesis the wear tests of the cutting tool are performed by using a slider-on-flat-surface (SOFS) wear tester. SOFS involves a normal load, which applies to the sample and a tangential force that enables the sliding of the sample against a counterface. To enable conducting the wear tests in SOFS a newly design of tool holder was prepared. The wear tests were performed at different contact conditions and the stainless steel EN 1.4310 was used as the counterface material. After the tools were tested, the worn surface of the tool was examined by optical light microscopy and scanning electron microscopy in order to identify the wear rate and wear mechanisms. At low load the dominating wear mechanism was adhesive wear. The adhesive wear was induced by material pick-up during sliding i.e. material from the counterface was transferred to the insert’s surface. Further sliding results in delamination of the insert surface and removal of a part of the coatings material. At high load the dominating wear mechanism was a combination of severe adhesive wear and fracture of the coating material. The fracture of the coating material occurred because of overloading. Coating defects promote crack formation under high load and these cracks propagate through the coating during sliding movement and result in microchipping of the coating material. This procedure does not simulate the metal cutting but it still gives an understanding of the behavior of the coating material when it is exposed to a high mechanical stress.

Mechanical components operating at elevated temperatures can be identified in the aerospace industry as well as in metal forming. Hot stamping is a metal forming technique utilized for manufacturing high strength lightweight components for the automotive industry. Three types of Ni-based hardfacings doped with solid lubricants were manufactured using laser cladding. An additional hardfacing was also manufactured using the Ni-based alloy only as a reference. Solid lubricants added were Ag+WS2, WS2 and Cu+MoS2. These hardfacings were manufactured and tribologically evaluated for potential application in hot stamping tooling. Direct diode laser was used for the cladding process. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization of the microstructure after deposition. Tribological testing was done using a reciprocating pin-on-disk tribometer under dry sliding conditions at temperatures in the range between RT and 600°C. Bearing steel ball and a flat pin made of the same material were used as counterbodies. Wear volume loss was measured using a 3D optical interferometer. For identification of the wear mechanisms SEM/EDS techniqueswere used. Formation of a lubricious CrxSy phase was detected after deposition, additionally encapsulation of silver particles by CrxSy was also observed. Reduction of friction coefficient was observed for every self-lubricating hardfacing compared to the reference. Lowest friction coefficient (0.23-0.3) was observed when the testing temperature was set to 400°C using a pin-on-flat configuration. Lowest wear rate was observed at 400°C, with the coating containing Ag and WS2 having a specific wear rate of 3.04 · 10−5mm3/Nm. The lubricity of the self-lubricating hardfacings was attributed to the CrxSy phase observed on the worn surface. At low to moderate temperatures abrasive wear is the main wear mechanism. At the highest testing temperature, oxidative wear was dominant.

Engine downsizing, improving fuel efficiency while satisfying the environmental legislations are one of the main driving forces in developing new solutions for passenger cars.Engine main bearings, are journal bearings which support the crankshaft and operate principally in full film lubrication. Defining the optimum design parameters of the bearings which can provide low friction and high durability for automobiles represents a multi-variable problem.Being the supporters of the main shaft driven by the internal combustion engine, main bearings are subjected to strenuous operating conditions. These include high loads and pressures amongst others. The trend in lubricant selection for these components is shifting towards choosing engine oils with lower viscosity to further reduce fuel consumption. Simultaneously with the shift in oil, new solutions for controlling the geometry and the topography on the micro-scale are becoming available. Three main bearing top layers plated on a conventional aluminum alloy containing tin and silicon were selected for the study. The top layers, one bismuth based and two newly developed polymer based, were investigated for their frictional and wear performance.In order to study experimentally the influence of different design parameters on bearing performance a test rig and a methodology was developed. The selected engine main bearings were tested in lubricated condition with two oils having different viscosity. Pre - and post test analysis of the shaft surface roughness was performed using white light interferometry. The wear performance of the bearings was measured both as mass loss and surface topography.The results suggest that the developed test rig can be used to simulate close to running condition testing. The measurement method and set up shows good consistency at a load of 2000 N, but indicates inconsistency in set up at 500 N.It is found that the newly developed engine main bearing top layers have promising frictional and wear performance, providing a reduction in friction by up to 20%.

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Babbitt has long been used as the lining material in hydrodynamic sliding bearings. However, with the new operating conditions imposed on hydro-electric power plants due to grid frequency regulation, the power plants undergo more frequent starts and stops which increases the need for an alternative material with better friction characteristics at start-up compared to conventionally used white-metal (Babbitt). Polytetrafluoroethylene (PTFE) based materials have potential to provide significant improvements in hydrodynamic sliding bearings through their compliant and breakaway characteristics under loading. However, while pure PTFE can provide excellent performance, it is somewhat limited in extreme loading situations. This study is therefore aimed at investigating the tribological characteristics at the initiation of sliding (breakaway friction) of several polytetrafluoroethylene (PTFE) based materials including virgin PTFE, PTFE filled with 25% black glass, PTFE filled with 40% bronze, PTFE filled with 25% carbon, and PTFE filled with 20% glass fibre and 5% Molybdenum disulphide, as well as standard Babbitt material in lubricated sliding contact with a steel counter-face. Experiments were carried out using a reciprocating tribo-meter in the block on plate configuration with the specific goal of determining the friction characteristics at breakaway under various conditions. Apparent contact pressures of 1 to 8 MPa were applied with oil temperature levels of 25° to 85°C.Bronze- and carbon-filled PTFE and virgin PTFE were found to provide generally lower and more stable breakaway friction over the course of testing than the other materials. Breakaway friction tests after an extended stop under loading showed a maximum change in breakaway friction of 0.07 for bronze filled, carbon filled, and virgin PTFE whereas Babbitt produced an increase of 0.32 in the first cycle after the extended stop, reaching the friction level of more than three times of those of PTFE based composites. Breakaway friction for the four tested materials after an extended stop returned to the pre-stop values after 1 stroke. The effect of materials on the steel counter face was also examined using an optical profilometer finding that only glass filled composites (black glass filled PTFE, and glass fiber and MoS2 filled PTFE) produced significant polishing of the steel surface under high loads. No measurable polishing was detected for other tested materials. / <p>Validerat; 20110224 (anonymous)</p>

Demanding applications, as well as the push to eliminate the need for fossil-fuel based lubricants, create the need for the development of high-performance polymers. Polyphenylene Sulfide (PPS) is an example of a high-performance polymer and has a high service temperature, good dimensional stability, and excellent chemical resistance. However, it has a low impact strength and is very brittle in neat form. Another high-performance polymer, Polytetrafluoroethylene (PTFE), provides low friction in dry sliding conditions and can deposit polymer transfer films onto the counterface but exhibits high wear rates in neat form. To take advantage of the desirable characteristics of both polymers, PPS/PTFE-based composites were produced through the Injection Molding process. The individual disadvantages of these polymers were further improved by incorporating the following fillers: SCF, GO and CNT. The tribological performance under dry sliding conditions and two different loads were investigated as well as the microhardness and degree of crystallinity of the materials. The DSC results showed that the incorporation of reinforcements did not significantly alter the total degree of crystallinity in the material. PPS/PTFE and the composites have significantly lower specific wear rates and coefficient of friction values compared to neat PPS and PTFE. The composites have higher microhardness and friction coefficient values (60N and 100N) compared to PPS/PTFE. For both loads, composites SCFCNT, 5SCF and 10SCF had the lowest specific wear rates recorded where a synergistic effect between SCF and CNT has been observed. The filler loading content did not affect the friction performance of the composites in both loads. However, for composites with SCF as the only reinforcement, the increase in wt% content of SCF increased the specific wear rate at 60N and decreased the specific wear rate at 100N. SEM images of the pin surfaces show that the governing wear mechanisms in the polymer blend and composites are abrasive and adhesive wear. The reduction of the specific wear rate values is also accompanied by the improvement in the uniformity of the observed transfer film formation.

Nästan alla maskiner och fordon behöver smörjning i någon form. Cellulosatorkar tillverkade av Andritz AB är inte något undantag. Dessa maskiner innehåller en mängd olika komponenter som är i behov av smörjning. För Andritz som har kunder över hela världen uppstår ett problem när dessa kunder söker alternativ till de smörjmedel som Andritz i första hand rekommenderar. Detta arbete har till syfte att kunna ge olika alternativ på smörjmedel oberoende från vilken tillverkare. I arbetet har en lista tagits fram med alternativa smörjmedel från olika smörjmedelstillverkare. Arbetet innefattar även de kritiska faktorer hos smörjmedel som måste uppfyllas för att de ska kunna ersätta varandra. En livstidsanalys, eftersmörjningsintervall och initial fettfyllning för hårt belastade rullager i en av Andritz cellulosatork ingår även i arbetet.

Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue. This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (A–C). Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface. The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination. / QC 20111123

While there has been substantial body of work in the field of journal bearing research, much of it is today theoretical or simulated due to today’s computing power. Scania produces experimental data from motor testing, but these are expensive and time consuming. Furthermore there is a difficulty in keeping a sufficiently controlled environment, which at times makes it hard to draw conclusions from testing results. They therefore wish to develop a test-rig which can evaluate friction and wear in journal bearings. This thesis is a continuation of a project in the course Advanced Machine Design given at KTH Royal Institute of Technology. During this thesis the test-rig has been manufactured, built, and evaluated. Furthermore software for the test-rig was developed. Information on journal bearings, risk assessment and signal noise handling were sought. Mechanical development was done with Autodesk Inventor, while Matlab was used for software development. Factorial design was utilised when designing tests and compared to a simple theoretical model. Test results showed promising results for Stribeck curve-producing tests, with good resemblance to known frictional values and trends. Furthermore the test-rig showed good repeatability for replicated tests and produced wear on the bearing shells used. During a prolonged test, the shaft and support-bearings were damaged and requires servicing to be in an operational state. The test-rig requires to be further verified, but the tests that were carried out showed valuable and reliable information on wear and frictional values. Keywords: journal bearing, hydrodynamic lubrication, wear, start-stop, test-rig / Även om en betydande mängd forskning inom glidlager och fullfilmslager har genomförts så är med dagens datorkapacitet en stor del av resultaten numera teoretiska eller simulerade. Medan Scania producerar experimentella resultat, så är dessa dyra och tidskrävande. Vidare är det ibland svårt att hålla en tillräckligt kontrollerad miljö för att dra slutsatser från proverna. Med en dedikerad testrigg som kan tillförlitliga resultat tas fram billigare och snabbare. Detta examensarbete är en fortsättning av kursen Avancerad Maskinkonstruktion som ges vid Kungliga Tekniska Högskolan. Under detta examensarbete har testriggen tillverkats, byggts och utvärderats. Vidare har programvara för testriggen utvecklats. Informationssökning gjordes på glidlager, fullfilmslager, riskbedömning och signalbrushantering. Mekanisk utveckling har gjorts i Autodesk Inventor, medan Matlab användes för mjukvaruutveckling. Faktorial design har nyttjats vid utformningen av tester. Resultaten jämfördes med en enkel teoretisk modell. Testresultaten visade lovade resultat för Stribeck kurva-producerande tester, med god likhet till kända friktionsvärden och trender. Testriggen visade god reproducerbarhet vid replikerade tester. Testriggen producerar slitage på samtliga testade lagerytor. Under ett längre test så har axel och stödlager skadats, varför service behövs för att testriggen skall vara i brukbart skick. Testriggen kräver ytterligare verifiering, men resultaten från de prov som genomförts visar att test-riggen ger värdefull och tillförlitlig information om slitage och friktion kunna utrönas. Nyckelord: glidlager, hydrodynamisk smörjfilm, nötning, start-stop, testrigg

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