Rolling bearings contain seals to keep lubricant inside and contaminants outside the bearing system. These systems are often lubricated with grease; the grease acts as a lubricant for the bearing and seal and improves the sealing efficiency. In this thesis, the influence of lubricating grease on bearing seal performance is studied. Rheological properties of the grease, i.e. shear stress and normal stress difference, are evaluated and related to the lubricating and sealing performance of the sealing system. This includes the seal, grease and counterface. The grease velocity profile in the seal pocket in-between two sealing lips is dependent on the rheological properties of the grease. The velocity profile in a wide pocket is evaluated using a 1-dimensional model based on the Herschel-Bulkley model. The velocity profile in a narrow pocket, where the influence of the side walls on the velocity profile is significant, is measured using micro particle image velocimetry. Subsequently, the radial migration of contaminants into the seal pocket is modelled and related to the sealing function of the grease. Additionally, also migration in the axial direction is found in the vicinity of the sealing contact. Experimental results show that contaminant particles in different greases consistently migrate either away from the sealing contact or towards the sealing contact, also when the pumping rate of the seal can be neglected. Lubrication of the seal lip contact is dependent on several grease properties. A lubricant film in the sealing contact may be built up as in oil lubricated seals but normal stress differences in the grease within the vicinity of the contact may result in an additional lift force. The grease, which is being sheared in the vicinity of the contact, will also contribute to the frictional torque. It is important to maintain a lubricant film in the sealing contact to minimize friction and wear. Here the replenishment of oil separated from the grease, also referred to as oil bleed, is of crucial importance. A model is presented to predict this oil bleed based on oil flow through the porous grease thickener microstructure. The model is applied to an axial sealing contact and a prediction of the film thickness as a function of time is made. The work presented in the thesis gives a significant contribution to a better understanding of the influence of lubricating grease on the sealing system performance and seal lubrication conditions. / Godkänd; 2011; 20110824 (andbra); DISPUTATION Ämnesområde: Maskinelement/Machine Elements Opponent: Georgia Power Distinguished Professor Richard F Salant, Georgia Institute of Technology, Atlanta, USA Ordförande: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå Tid: Torsdag den 22 september 2011, kl 09.30 Plats: E231, Luleå tekniska universitet

In recent years, electronically controlled automotive transmission systems, where wet clutches are used as intelligent differentials, have appeared in the market. These applications impose great demands on the transmission fluids and friction materials used as well as on controllability and vibration preventive (anti-shudder) properties of the clutch systems. This thesis focuses on transmission fluids used in wet clutches in all- wheel drive systems. The investigated all-wheel drive system, featuring a wet multi-plate clutch with a sintered brass based friction material, is described. A comprehensive literature review section outlines the state-of-art in this field and gives an insight into many of the problems commonly experienced in this type of application. Different methods used to investigate the function of wet clutch transmission fluids are also presented. Test equipment designed during this thesis work in order to determine the frictional characteristics of transmission fluids is described. This equipment measures friction torque, normal load, oil temperatures and the actual temperature experienced by the fluid in the contact zone. Base oil type and viscosity have been found not to significantly influence friction characteristics of a wet-plate clutch , indicating that the torque is primarily transmitted by asperity contacts rather than fluid films. Oil additives, on the other hand, have a considerable influence on friction, again leading to the conclusion that tribolayers on contacting asperities rather than fluid films govern friction. From these observations it can be concluded that the lubrication regime under the conditions studied are boundary lubrication, moving into mixed lubrication at high velocities and low temperatures. Results show the influence of several operating parameters on the frictional behavior of the clutch. Temperature is shown to have significant influence on the friction of transmission fluids which decrease with increasing temperature. It is therefore necessary to measure the true temperatures in the clutch contact in order to obtain realistic measurements of friction. A method which excludes the influence of temperature on measured friction data have been developed and verified. The influence of clutch disc pressure on friction is quite moderate compared to the influence of temperature and sliding velocity. The influence of velocity on friction is governed by the transmission fluid and friction material used in the clutch. 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 to compensate the relationship for temperature effects. A successful method to develop transmission fluids has been developed. Formulated fluids allow good anti-shudder properties to be combined with good lubrication performance for other machine elements present in the transmission. Interactions between different additives must be considered which can, in many cases, completely alter the friction characteristics since additives compete for the same adsorption surface. Extreme pressure additives have been found to be particularly troublesome when used in combination with other additives as far as their ability to maintain good anti-shudder properties is concerned. Based on the knowledge of clutch performance obtained from the research presented in this thesis, a model to predict transmitted clutch torque has been developed. This accurately determines the transferred torque from the current operating conditions and the thermal history of the clutch. It can be concluded that thermal effects have a significant influence on the torque transferred by the clutch, and it is therefore necessary to have a thermal model of the clutch combined with a temperature dependant boundary friction model based on empirical friction data for the friction material/transmission fluid combination of interest. / På senare tid har elektroniskt styrda drivlinor blivit allt vanligare i personbilar. I dessa transmissionssystem används ofta våta kopplingar för att överföra önskade vridmoment mellan olika axlar. För att uppnå lättkontrollerad och vibrationsfri momentöverföring ställs höga krav på de använda transmissionsoljorna och friktionsmaterialen. Denna avhandling behandlar främst transmissionsoljor för våta kopplingar i fyrhjulsdriftsystem. En beskrivning av det undersökta fyrhjulsdriftsystemet och den ingående flerlamellkopplingen ges. Dessutom beskrivs de friktionslameller av sintermässing som används i denna tillämpning. En omfattande litteraturstudie som syftar till att identifiera forskningsfronten inom området presenteras och ger en insikt i vilka problem som måste lösas i denna typ av applikationer. I anknytning till detta beskrivs även olika metoder som används för att undersöka funktionen hos våta kopplingar. För att undersöka friktionsegenskaperna hos olika transmissionsoljor har en testutrustning konstruerats. Denna utrustning mäter överfört vridmoment, pålagd kraft, oljetemperatur och kontakttemperatur i kopplingen. Både konstruktionen och typiska testcykler beskrivs detaljerat. Mätningar visar att basoljetyp och viskositet endast har en liten inverkan på friktionsegenskaperna (momentöverföringen), vilket tyder på att friktionen uppkommer i asperitetskontakter snarare än genom viskösa effekter i en oljefilm. Oljeadditiv har däremot kraftig inverkan på friktionen, även detta tyder på att friktionen genereras av additivskikt på yttoppar snarare än av en oljefilm. Sammantaget visar detta att den smörjregim som råder under undersökta förhållanden är gränsskiktssmörjning som går in i blandfilmssmörjning vid höga hastigheter och låga temperaturer. Resultat visar även hur en mängd olika parametrar påverkar friktionsegenskaperna i kopplingen. Studerade parametrar inkluderar temperatur, glidhastighet, tryck och oljesammansättning. Temperaturen har betydande inverkan på friktionsegenskaperna hos transmissionsoljor. Friktionen minskar med ökande temperatur. Därför är det nödvändigt att mäta den korrekta temperaturen i kopplingen för att få relevanta mätvärden på friktionen. En metod för att presentera mätdata på ett sätt där temperaturens inverkan elimineras har utvecklats och visat sig fungera väl. Friktionspåverkan från den pålagda normalkraften är liten jämfört med inverkan från temperatur och glidhastighet. Glidhastighetens påverkan på friktionen bestäms av den aktuella kombinationen av smörjolja och friktionsmaterial. Sambandet mellan friktion och glidhastighet ger en god bild av smörjmedlets vibrationsdämpande förmåga. Det är dock viktigt att detta samband mäts vid konstant temperatur eller att mätdata kompenseras på ett lämpligt sätt. En framgångsrik metod för att utveckla transmissionsoljor har utvecklats. Formulerade oljor har visat att det är möjligt att kombinera vibrationsdämpande egenskaper med goda smörjegenskaper med avseende på andra maskinelement i transmissionen. Växelverkan mellan olika additiv måste beaktas och kan i många fall leda till kraftiga förändringar i friktionsbeteendet eftersom alla additiv konkurrerar om att fästa på samma metallyta. Speciellt extremkontaktstrycksadditiv (EP) har visat sig vara svåra att kombinera med andra additivtyper. Baserat på den nyvunna kunskapen om kopplingars momentöverföring har en teoretisk modell utvecklats. Denna modell kan förutsäga vilket överfört moment kopplingen genererar under givna förhållanden. Eftersom temperatureffekter har stor inverkan på friktionen är det nödvändigt att ha en termisk modell av kopplingen som kan kopplas till en temperaturberoende friktionsmodell. Friktionsmodellen är baserad på empiriska friktionsdata för aktuell kombination av friktionsmaterial och smörjmedel. / Godkänd; 2005; 20061001 (ysko)

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 concerns a study of the performance of an industrial low-speed high-torque hydrostatic drive system. This type of hydrostatic transmission is commonly used in continuous operation in a wide range of heavy-duty drive applications. In many applications the transmissions have to compete with e.g. electromechanical drives, such as DC or AC electric motors combined with gearboxes. In such situations, energy efficiency is a key selection criterion in that even a small increase in the efficiency of high power industrial drives would give substantial savings. Apart from efficiency, lifetime and reliability requirements are important parameters for industrial drive systems, as unplanned stops in industrial working processes can be very costly. The work presented in this thesis is primarily focused on analysing the efficiency behaviour in the transmission, both on the system level and on the component level. Attention has also been paid to lifetime issues, with special emphasis on wear occurring in a sliding contact in a radial piston hydraulic motor. In Paper A the distribution of power losses in a variable axial piston swash plate pump is investigated. The pump under study is commonly used in stationary industrial hydrostatic transmission systems. The churning losses in the pump have been estimated experimentally by measurements in a test rig. The leakage flow and the power losses in the contacts between the piston and the cylinder and between the slipper and the swash plate respectively were simulated with the help of the simulation tool CASPAR. For the pump studied, the churning losses are significant under the operating conditions typically occurring in industrial drive applications. The simulation results indicate that the leakage to the pump casing mainly originates from the gaps between the pistons and their respective cylinders and between the slippers and swash plate. The aim of Paper B is to study two sliding contacts inside a radial piston hydraulic motor and investigate their influence on the torque and power losses. Moreover, it is investigated whether and when a change in the lubrication regime can be expected in these contacts. This is accomplished by a combination of experimental and theoretical studies, with a special focus on two lubricated sliding contacts: the distributor valve contact and the piston/cam roller contact. The theoretical analysis of the contacts indicates, among other things, that the piston/cam roller contact can enter the mixed lubrication regime at low motor speeds. At low running speeds, an increased wear rate has been noted in the contact between the cylinder bore and the piston skirt in a radial piston hydraulic motor. Paper C describes a comparative investigation into different hydraulic fluids' friction properties and wear protection abilities. To simulate the contact between the cylinder bore and the piston skirt in the hydraulic motor, tests were performed in a reciprocating test rig where the contact geometry was of the cylinder-plate type. In the model test a synthetic ester aimed at meeting the conditions in water turbine applications received a top ranking regarding both friction and wear protection properties. / Godkänd; 2003; 20070217 (ysko)

Increasing interest in productivity, safety and environmental issues have highlighted the area of maintenance and reliability. The increasing cost of maintenance covers both preservation and sustainable exploitation of resources and awareness in maintaining equipment in a way to ensure return on investment both in the short and long run. The information obtained from condition monitoring of existing turbine, plant, rails and pumps can provide an important basis for dimensioning of future systems and components. The main objective of this research work is to develop and apply methods for efficient condition monitoring, and hence reduce maintenance costs and provide a framework for development and implementation of computer based decision tools. Furthermore, methods enabling existing process data and cost effective transducers to be used together with modern data analysis and diagnostic tools for condition monitoring of complex mechanical systems have been examined and prototypes developed. The areas of investigation covered in this work are hydropower turbines, rails and the main cooling pumps in a nuclear power-plant. The interest in diagnostics for hydropower turbines was driven by the obvious risk of contamination of water by oil leaks and expensive refurbishments caused by wear of the Kaplan turbine vane bearings. The intrest in risk analysis was motivated by Vattenfall's intrest in gaining knowledge about the state of all turbines in the company. The aim of this project was to develop a generic model of hydropower turbine behavior using physics-based models based on material properties, load tolerances, etc.. An important question was whether it was possible to predict the wear rate and plan predictive replacement or maintenance. A systematic approach to find failure modes, their effects, their causes and consequences in combination with Fault Tree Analysis was needed. The objective of this project was to examine a systematic approach to map failure modes and their causes in an hydropower turbine. We have restricted the study to turbine units of the Kaplan, Francis and tube types. The objective of the study concerning rail track was to develop methods and equipment for detection of surface damage in rail track rail in addition to the present system of practice of visual examination. The equipment developed has to be used to obtain objective statistical data for evaluating maintenance methods and efforts. We have restricted the study to spalling and headchecks on the rail head surface and running edge. The method developed enables measurements of different types of surface damage such as spalling and shelling to be made with inductive transducers sensitive to the distance to the measured object. The assumption here is that the damage being detected is characterized by the absence of material from rail surface. The main object of condition monitoring of the cooling pumps was to be able to detect bearing wear in order to be able to plan and carry out restoration well ahead of breakdown or bearing seizure. The study was restricted to the main cooling pump motor and its main bearings. Condition monitoring of the pumps was done using a method based on current measurements. Analysis of the currents on the main cooling pump of the power plant proved that it is possible to monitor the condition of the pump in spite of the presence of electronic frequency converters which distorts the signal. / <p>Godkänd; 2002; 20070222 (ysko)</p>

This licentiate thesis deals with a hybrid experimental and numerical method, the so-called Hybrid Technique, to study film thickness and pressure distribution and to investigate the behaviour and properties of lubricants in highly loaded EHL conjunctions. The Hybrid Technique combines experimental studies and advanced numerical calculations. In the experimental part of the hybrid approach Optical interferometry and a Ball &amp; Disc system are applied to obtain the colour intensity images of the EHL contact. The images that captured by a colour video system are then subjected for image analysis to evaluate the film thickness maps from the colour interferograms. The pressure distribution is obtained numerically by solving the equation of elastic deformation. Using the Hybrid Technique the pressure and lubricant film thickness in the contact are obtained without having made any assumptions regarding rheological behaviour of the lubricant. This makes the described approach to a very useful tool in investigations of EHL conjunctions under extreme conditions or in the study of multi-phase lubricants. A detailed description of the Hybrid Technique is given. Method is tested out on oil lubricated and grease lubricated contacts. Results are presented and discussed. / <p>Godkänd; 1999; 20070403 (ysko)</p>

The objective of this licentiate thesis was to study the effect of tool wear for sheet metal forming tools and how the wear process can be simulated in an efficient manner. Three Papers are appended to this licentiate thesis. Paper A covers the influence of tool geometry in deep drawing. In paper B is the way of calculating with finite element analysis described. The wear of a steel cylinder oscillating against a steel plate was studied experimentally. The worn shape of the cylinder was then compared with a numerical simulation of the shape. Paper C shows how numerical simulations can be used to simulate wear of deep drawing tools. The wear of two different deep drawing tools has been investigated. The shape of the tools before and after wear have been compared as well as the stresses and strains in the formed cups. / Godkänd; 2000; 20070317 (ysko)

För att erhålla mjukare växlingsförlopp och samtidigt få lång livslängd på våta kopplingar i automatväxellådor krävs förbättrad konstruktion. För att förbättra konstruktionen behövs mer kunskap om inkopplingsförloppet av våta kopplingar. En testrigg för att undersöka inkopplingsförloppet har byggts. Driftsparametrar och inkopplingskarakteristik efterliknar förhållanden i en verklig automatväxellåda. I apparaten kan hastighet, drivmoment, tröghet, pålastningshastighet och oljetillförsel varieras. Normalkraft, bromsmoment, glidhastighet och temperatur mäts som funktion av tiden. Experimentella studier av inkopplingsförloppet har utförts. Både friktionskarakteristik och effekt och temperatur har undersökts. Resultaten visar hur en lamellkoppling beter sig under ett inkopplingsförlopp. Inverkan av olika driftsparametrar på inkopplingstid, utvecklad energi, temperaturhöjning med mera har också undersökts. En enkel beräkningsmodell har utvecklats för att simulera inkopplingsförloppet. Modellen överensstämmer väl med mätningarna. Friktionskoefficienten vid inkopplingen av en våt lamell varierar över tiden men beror ej av driftsparametrarna. Förutom friktionen vid medelhastighet som minskar med glidhastighet, drivmoment och tröghet. Temperaturökningen är direkt proportionell mot den utvecklade energin och båda dessa ökas mest av glidhastighet. Drivmoment och pålastningshastighet har störst inverkan på inkopplingstiden. / Godkänd; 1997; 20070418 (ysko)

<p>Godkänd; 1997; 20070418 (ysko)</p>

Godkänd; 1995; 20080330 (ysko)