No description available.

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

No description available.

During the production of metal zippers, cemented carbide (CC) tools are used to cut preformed brass wire into small elements. Even though the cemented carbide is much harder than the copper alloy, it gets worn and eventually the tool must be replaced. This wear mechanism, which allows soft copper alloys to gradually wear hard CC, must be better understood in order to extend tool life. The mechanism is believed to be tribochemical, as oxides have been found on the surface of the wear mark. Given that most metals oxidize in the presence of oxygen, it is relevant to examine if oxidation of tungsten carbide and cobalt contribute to the wear. The purpose of this work has been to study the influence of oxygen availability on the slow wear of cemented carbides during copper alloy processing. A simplified sliding test rig, developed in a previous study, was used. A small CC cylinder slid against a large rotating copper or brass cylinder in a “crossed cylinders” configuration. The point of contact was encapsulated by a 3D-printed cover. Some tests were done in an oxygen deficient atmosphere, where the cover was continuously filled with flowing nitrogen gas. One test was performed with compressed air flowing through the cover, and one was performed without flowing gas. The wear marks on the CC cylinders were analyzed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and optical profilometry. The wear volume of these marks was also calculated. SEM pictures showed that both brass and copper transferred to the cemented carbide. When the test was performed with brass, zinc oxide was found in the wear mark. When it was performed with copper, no oxide was found.

In recent times, there has been an increased interest in replacing conventional metals and synthetic fiber composites in various automobile parts with natural fiber polymer composites. These natural fiber composites offer benefits over conventional materials in terms of reduction in weight, lower cost, comparable high specific properties such as specific stiffness and strength, low abrasion property, and availability of these materials. Environmetal concerns and the need to make eco-friendly materials also encouraged the use of natural fiber polymer composites (NFPC) for various automotive applications, as their usage reduces the emission of harmful pollutants, thereby providing a safer and cleaner environment. The reduction in weight of these materials also helps to reduce fuel consumption in cars. Therefore, this study focused on the investigation and characterization (mechanical, thermal, and tribological) of hemp fibers reinforced polypropylene made with virgin (Biolite) and recycled (Revo) composites, consisting of different fiber loadings from 10% to 30% for possible automotive applications. The result showed an improvement in the compressive properties of the composite as hemp fiber loading increases, with the recycled composite exhibiting a better compression performance in comparison to virgin composites. Revo 41 had the best compressive strength  and a 35% higher value than Biolite 2 of the same hemp fiber loading. However, there was a decrease in the fracture toughness of the composites as hemp fiber loading increases. This was more significant at about 27% from Biolite 1 to Biloite 2, Revo 41 experienced a slight improvement of 15% in fracture toughness with 20% hemp fiber loading. Revo 35 composite which had more degradation steps showed the best thermal performance at low temperature region with a degradation temperature of 276°C, while Biolite 1 at 444°C exhibited the best thermal stability at high temperature degradation. In comparing the tribological behavior of pure polypropylene with the composites, the composites exhibited a better tribological performance as there was a slight decrease in the coefficient of friction and wear rates of composites as the hemp fiber loading increases. Revo 41 of 20% hemp fiber fiber loading had the best wear performance. Considering its strength and slightly better tribological performance, Revo 41 is considered the best performing composite for automotive applications in comparison to the other composites.

Cross-country skiing has turned into the most highly competitive winter sport, with skiers having the ability to win by merely milliseconds. Every year researchers, ski - technicians, and athletes come together to prepare the ski base surface that gives the best possible results. However, much current information is based on the ski technician’s experience. Therefore, this project has been carried out to help to bridge the gap between ski technician’s knowledge and experimental research. The ski bases are passed through several surface preparation steps before competitions. Stone grinding and hand texturing are two of them. Since grinding cannot be specifically applied as per the environmental conditions, it is followed by texturing. This application of grinding and texturing changes the surface topography of the ski base, which will affect the contact area between the ski base surface and snow/ice and the wettability of the ski base. For this project, work is focused on how the application of different grinds and hand textures affects the wettability of the ski base. This project illustrates the change in wettability of ultra-high molecular weight polyethylene (UHMWPE) and its composites under the application of ten different commercial grinds followed by three other hands texturing. Surface topography was observed under an Optical profilometer, and wettability was measured by measuring the contact angles of droplets on these ski base materials. It was found that the hydrophobicity of ski base materials can be increased to a certain level by increasing the Arithmetic mean roughness (Ra) of specimens. Different ski base materials showed different hydrophobic behaviour when roughness was increased. Applying hand textured to different ground specimens again improved the hydrophobic behaviour of the ski base.

Many automotive components are made of Al-Si coated ultra-high strength boron steel (UHSS) and are produced by hot stamping process. In this process, the workpiece is heated to an austenitizing temperature and is then formed and quenched simultaneously between the tools to achieve the desired shape and high strength. During hot stamping process, friction and wear occur which affect formability and maintenance intervals for tool replacement and repair. To repair worn tools, metal is deposited by fusion welding technique. The tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS has not been studied in detail and there is a need to investigate if the modified tool surface will affect friction and wear. Hot stamping, similar to many manufacturing processes, is affected by the global mega trend of digitalization and Industry 4.0. To monitor the process and optimize the control and operation are the main aims. In view of this, tribological condition monitoring is a promising approach that can allow measurement of physical properties such as vibrations, temperatures, and acoustic emission to be coupled to the tribological response of the system. The aim is to monitor the hot stamping process and enable early detection of changes in friction and wear which can be used for e.g. optimized maintenance and minimized scrap. The aim of this M.Sc. thesis was to improve the robustness of hot forming processes by studying the tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS under conditions relevant for hot stamping. Another aim was to obtain more predictable tool maintenance by the implementation of acoustic emission measurement system on a hot-strip tribometer and correlating condition monitoring signals to friction and wear phenomena. The tribological tests were carried out using a hot-strip tribometer in conditions representative of a hot stamping process of automotive components. Acoustic emission during sliding between hot work tool steel and different automotive component material surfaces was measured at room temperature in the same strip drawing tribometer and correlated to friction and wear of the surfaces to get more predictable maintenance intervals. Tool steel specimens were welded with the same material as the base material QRO90. Before conducting the tribological test, the repair welded tool steel pin cross-section was polished, etched, and observed under optical microscope and SEM to analyze the effect of Tungsten Inert Gas (TIG) welding process on the microstructure. The analysis was completed with EDS to study the elements in the microstructure. Microhardness was measured to obtain the microhardness profile from the repair welded tool steel pin surface to the bulk in order to study the effect of different microstructures on the mechanical properties. The weight and surface roughness of the pins were measured before the tribological test. After the test was finished, the weight of the pins was measured to calculate the weight difference. The sliding surface of the pins and the strips were photographed. The sliding surface of the pins was also observed and analyzed using SEM and EDS after the test to study wear characteristic of the repair welded tool steel at high temperatures. Acoustic emission signal from the sliding was studied using Toolox44 pins with surface roughness 300-400 nm and with lay direction parallel and perpendicular to sliding direction. Toolox44 pins were sliding against uncoated UHSS, as-delivered Al-Si coated UHSS, and heat-treated Al-Si coated UHSS strips. Acoustic emission was measured during the sliding at the same time as COF measurement. Weight of the pins was measured before and after the test and the wear damage on both surfaces was photographed. COF, AE signals in the time and frequency domain, and wear damage were compared and analyzed. It is found that repair welded tool steel has similar COF compared to the original hot work tool steel with the largest weight gain from the test at 700 ⁰C due to compaction galling mechanism with slower lump formation and the presence of wear particles, transfer layer, and formation of lumps. The weight gain is smaller from the test at 750 ⁰C due to faster lump formation. The weight loss from the test at 600 ⁰C is due to abrasive wear mechanism. SEM micrographs revealed that the repair welded tool steel surface and transfer layers can be found beneath a transfer layer. Wear particles adhered on the repair welded tool steel surface come from broken transfer layer or directly from Al-Si coated UHSS. A change in wear mechanism is indicated by acoustic emission burst signals or gradual amplitude change in the time domain. Frequency analysis of AE signals revealed a change in wear mechanism due to the formation of transferred material in the form of a lump causes AE signals with peaks at higher frequencies above 0.3 MHz to shorten.