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In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a sort of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, the overall aim was to gain knowledge of the influence of tool steel microstructure on galling initiation under sliding conditions. It was discovered that material transfer and tool steel damage caused by sheet material flow creating wear-induced galling initiation sites occurred in the early stage of galling. The galling resistance was higher for tool steels with higher matrix hardness due to better resistance to tool steel damage. Initial friction and critical contact pressure to galling was influenced by the strength of the sheet material. Material transfer happened at low pressures and the friction value was high in a case of sheet materials with lower proof strength, possibly due to the sheet contact against the tool steel matrix resulting in high adhesion and quicker tool damage. It was demonstrated that, in addition to hardness of the tool steel matrix and sheet material proof strength, tool steel microstructural features like size, shape, distribution and height of hard phases are important parameters influencing galling. Tool steels comprising homogeneously distributed, small and high hard phases better prevented the contact between sheet material and the tool steel matrix. Thus, a metal to metal contact with high friction was more efficiently avoided, which resulted in better tool performance.

This thesis aims at increased knowledge in two fields of tribological research; both related to making currently used combustion engines greener. The first field regards the possibilities of using a boric acid fuel additive to increase fuel efficiency. The second field is about the severe wear phenomenon scuffing, which can become problematic when cargo ships are operated on low-sulphur fuel to reduce sulphuric emissions. Tribological tests were developed and performed to simulate the applications. Advanced surface analysis was performed to understand changes occurring on the outermost surface of sliding components, which affect friction and wear. Samples from engines were studied to verify the relation between the lab tests and the applications. In the case of boric acid, the coefficient of friction was below 0.02 for large parts of the tests, but varied with test parameters. The corresponding reduction in friction was up to 78% compared with tests without the additive. As an attempt to assess if the substantial fuel savings found in field tests with passenger cars (6%) can be explained by friction reduction in boundary and mixed lubricated parts of the piston assembly, assumptions were presented that would lead to fuel savings close to these 6%. Boric acid was detected on surfaces after the tests, and the tribofilm appearance depended on test parameters. The tribofilms were shown to be affected by storage time and test temperature; a finding that is vital for future studies. In the case of scuffing, mechanisms were studied and accumulation of wear debris had a significant role on scuffing initiation in the lab scale scuffing tests. Regarding the possibility to test materials scuffing resistance, there was a large scatter in the results, and thereby difficult to draw conclusions. Two new piston ring materials were identified to perform somewhat better than the currently used. In conclusion, findings that could facilitate immediate improvement of fuel efficiency of today’s combustion engine vehicles as well as findings that strengthen available hypotheses on scuffing mechanisms are presented. The latter offers improved understanding of scuffing and thereby give possibilities to counteract the higher risk associated with operation on cleaner fuel.

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

The grinding rollers of raw mill 7 operate in very harsh conditions and, because of this, suffer from excessive failure mode due to lip seal deterioration. Foreign material penetrates the deteriorated lip seal and enters the bearings resulting in bearing failure. Failure mode brings about high maintenance costs for the cement-producing company Cementa AB. This thesis aims to accomplish two things. 1- Hypothesize a set of root causes for failure mode and link them to existing literature studies to determine what actions should be taken to prevent or at least postpone failure mode. 2- Generate several new conceptual designs for the sealing mechanism by either creating a revolutionary sealing design or taking inspiration from standard seals currently on the market. The generated concepts aim to provide Cementa AB with a new perspective as well as mitigate some or all the root causes for failure mode if implemented. The hypothesized root causes for failure mode are categorized through the creation of a problem tree and are defined as lip seal failure, lubricative pressure and contamination, tribologically improper friction, vibration, and finally very harsh conditions that are indigenous to raw mills in general and that are seemingly incompatible with the current sealing mechanism. Revolutionary concepts are brainstormed entirely from an experimental perspective, while standard concepts are inspired by established sealing technology on the market. Both alternatives are then conceptually adapted to the grinding roller of raw mill 7 and, with inaccurate scaling, 3D modelled with the aid of Autodesk Inventor. 7 concepts, revolutionary and standard combined, are generated as a result. The revolutionary concepts have been deemed non-viable due to the limited timeframe and scope of the thesis. Instead, the selected seal for the upgrade is a labyrinth seal, which is a non-contact standard seal that has the potential to mitigate many of the root causes for failure mode. The literature studies on the hypothesized root causes also indicate that there are actions that could postpone failure mode should Cementa AB chose to retain the original sealing mechanism for a longer period. / Valsarna i råkvarn 7 arbetar under mycket tuffa förhållanden och på grund av detta lider maskinen av en överdriven mängd haverier till följd av läpptätnings försämring. Främmande material tränger igenom den försämrade tätningen och kommer in i lagren vilket resulterar i lagerhaveri. Detta medför höga underhållskostnader för det cementproducerande företaget Cementa AB. Denna avhandling syftar till att åstadkomma två saker. 1-Hypotesera en uppsättning av grundorsaker till lagerhaveri och länka dem till befintliga litteraturstudier för att avgöra vilka åtgärder som kan vidtas för att förhindra eller åtminstone skjuta upp lagerhaveri. 2-Generera flera nya konceptuella konstruktioner för tätningsmekanismen genom att antingen skapa en revolutionerande tätningsdesign eller hämta inspiration från standardtätningar. De genererade koncepten syftar till att ge Cementa AB ett nytt perspektiv såväl som att mildra några eller alla grundorsaker till lagerhaveri om de implementeras. De hypotiserade orsakerna till lagerhaveri kategoriseras genom skapandet av ett problemträd och definieras som trasig läpptätning, smörjningstryck och förorening, tribologiskt felaktig friktion, vibrationer och slutligen tuffa förhållanden som är inhemska för råkvarn generellt. Revolutionära koncept är brainstormade helt ur ett experimentellt perspektiv medan standardkoncept är inspirerade av etablerad tätningsteknik på marknaden. Båda alternativen är sedan konceptuellt anpassade till valsen i råkvarn 7 och, med oegentlig skalning, 3Dmodellerad med hjälp av Autodesk Inventor. 7 koncept, revolutionerande och standard kombinerat, genereras som resultat. De revolutionära koncepten har bedömts vara icke-livskraftiga på grund av avhandlingens begränsade tidsram och omfattning. Istället är den valda tätningen för uppgraderingen en labyrinttätning som är en icke-kontakt standardtätning som har potential att mildra många av orsakerna till lagerhaveri. Litteraturstudierna om de hypotiserade grundorsakerna tyder också på att det finns åtgärder som kan skjuta upp lagerhaveri om Cementa AB väljer att behålla den ursprungliga tätningsmekanismen under en längre period.

No description available.

This thesis presents the design and development of a versatile test rig specifically tailored for measuring frictional properties of diverse materials across a wide range of velocities and pressures. The ability to accurately quantify frictional behaviour under varying conditions is essential for understanding material performance in numerous applications, such as automotive, aerospace, and manufacturing industries. The primary objective of this research is to design a test rig capable of simulating real-world operating conditions, facilitating the evaluation of frictional forces experienced by different materials. The experimental setup incorporates a carefully designed sliding mechanism, pressure control system, and instrumentation to measure frictional forces with high precision. The test rig's sliding mechanism is built to accommodate various material samples, allowing for controlled movement along different planes with adjustable velocities. By subjecting these samples to controlled loads, the influence of pressure on frictional behaviour can be systematically investigated. Moreover, the test rig features to replicate conditions encountered in practical scenarios. To ensure accurate measurements, the frictional forces are captured using high-resolution load cells and strain gauges integrated into the test rig. This thesis contributes to the field of material science and engineering by providing a comprehensive framework for evaluating frictional behaviour under controlled conditions. The developed test rig serves as a reliable and versatile platform for studying material performance, guiding the design and development of more efficient and reliable systems in numerous industrial applications. / Denna avhandling presenterar designen och utvecklingen av en mångsidig testrigg speciellt anpassad för att mäta friktionsegenskaperna hos olika material vid olika hastigheter och tryck. Förmågan att exakt kvantifiera friktionsbeteendet under varierande förhållanden är avgörande för att förstå prestandan hos material inom många applikationsområden, såsom fordons-, flyg- och tillverkningsindustrin. Det primära målet med denna forskning är att designa en testrigg som kan simulera verkliga driftsförhållanden och underlätta utvärderingen av friktionskrafter som upplevs av olika material. Den experimentella uppställningen inkluderar en noggrant utformad glidmekanism, ett tryckkontrollsystem och mätutrustning för att mäta friktionskrafter med hög precision. Testriggens glidmekanism är utformad för att kunna hantera olika materialprover och möjliggör kontrollerad rörelse längs olika plan med justerbara hastigheter. Genom att utsätta dessa prover för kontrollerade belastningar kan tryckets inverkan på friktionsbeteendet systematiskt undersökas. Testriggen har dessutom funktioner för att återskapa förhållanden som uppstår i praktiska scenarier. För att säkerställa korrekta mätningar fångas friktionskrafterna med hjälp av högupplösta lastceller och töjningsgivare som är integrerade i testriggen. Denna avhandling bidrar till materialvetenskap och ingenjörskonst genom att tillhandahålla ett omfattande ramverk för att utvärdera friktionsbeteende under kontrollerade förhållanden. Den utvecklade testriggen fungerar som en pålitlig och mångsidig plattform för studier av materialprestanda och vägleder design och utveckling av effektivare och pålitligare system i många industriella applikationer.