• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 843
  • 610
  • Tagged with
  • 1454
  • 1441
  • 1186
  • 1170
  • 1169
  • 1168
  • 1168
  • 1168
  • 1165
  • 342
  • 155
  • 129
  • 109
  • 107
  • 104
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Interfacial (o/w) Properties of Naphthenic Acids and Metal Naphthenates, Naphthenic Acid Characterization and Metal Naphthenate Inhibition

Brandal, Øystein January 2005 (has links)
<p>Deposition of metal naphthenates in process facilities is becoming a huge problem for petroleum companies producing highly acidic crudes. In this thesis, the main focus has been towards the oil-water (o/w) interfacial properties of naphthenic acids and their ability to react with different divalent cations across the interface to form metal naphthenates.</p><p>The pendant drop technique was utilized to determine dynamic interfacial tensions (IFT) between model oil containing naphthenic acid, synthetic as well as indigenous acid mixtures, and pH adjusted water upon addition of different divalent cations. Changes in IFT caused by the divalent cations were correlated to reaction mechanisms by considering two reaction steps with subsequent binding of acid monomers to the divalent cation. The results were discussed in light of degree of cation hydration and naphthenic acid conformation, which affect the interfacial conditions and thus the rate of formation of 2:1 complexes of acid and cations. Moreover, addition of non-ionic oil-soluble surfactants used as basis compounds in naphthenate inhibitors was found to hinder a completion of the reaction through interfacial dilution of the acid monomers.</p><p>Formation and stability of metal naphthenate films at o/w interfaces were studied by means of Langmuir technique with a trough designed for liquid-liquid systems. The effects of different naphthenic acids, divalent cations, and pH of the subphase were investigated. The results were correlated to acid structure, cation hydration, and degree of dissociation, which all affect the film stability against compression.</p><p>Naphthenic acids acquired from a metal naphthenate deposit were characterized by different spectroscopic techniques. The sample was found to consist of a narrow family of 4-protic naphthenic acids with molecular weights around 1230 g/mol. These acids were found to be very o/w interfacially active compared to normal crude acids, and to form Langmuir monolayers with stability depending on the aqueous pH. At high pH, addition of Ca<sup>2+</sup> increased the film stability due to formation of calcium naphthenate at the surface.</p><p>A new experimental setup based on near infrared spectroscopy was used to monitor the formation, growth, and inhibition of calcium naphthenate particles in o/w systems. This method was found to be suitable for studies of particle formation rate and growth qualitatively under different experimental conditions.</p>
42

Flödessimulering av färdigvarulager

Möller, David January 2002 (has links)
No description available.
43

Masterplan för svetsavdelning : Förstudie

Tigér, Rickard January 2007 (has links)
<p>Det här examensprojektet har utförts på Volvo CE, Hauler & Loader Division, Arvika. Projektet ingick som ett avslutande moment i maskiningenjörsprogrammet vid</p><p>Karlstads universitet. Volvo i Arvika tillverkar hjullastare vilket man har gjort sedan mitten av 60-talet. Fabriken har idag ca 1150 anställda som tillsammans levererar över 6000 hjullastare per år.</p><p>Produktionsvolymen i Arvikafabriken ökar allt mer vilket medför att ett behov av många investeringar för att klara denna volymtillväxt har uppstått. Den huvudsakliga tillverkningen på svetsavdelningen består av fram- och bakramstillverkning. Problemet är att tillverkningen är trångbodd och att vissa ramflöden är i behov av förbättring.</p><p>Projektets uppgift bestod av att undersöka möjligheter och konsekvenser av att installera två nya svetsrobotar i befintlig byggnad och på sikt skapa en separat framram resp. bakramsverkstad. Arbetets huvudmål är att få höjd kapacitet i svetstillverkningen av ramar.</p><p>Resultatet av projektet visar att möjlighet finns att installera två nya svetsrobotar i de befintliga lokalerna, en robot för framramsvetsning samt en för bakramsvetsning. Ramtillverkningen är separerad med en verkstad för framramar i byggnad 1 samt en verkstad för bakramar i byggnad 2. (se bilaga 8, 50 och 51).</p><p>Flera flöden har förbättrats genom att arbetsstationer har flyttats vilket i sin tur har inneburit mindre transportbehov i verkstaden. Uppdelningen av tillverkningen av fram- och bakramar har lett till ett tydligare flöde. De nya flödena syns i produktionsscheman och layoutflödesscheman (bilaga 52-69).</p><p>Kostnaden för att genomföra projektet uppskattas till omkring 26 milj. kr.</p><p>Ett ytterligare koncept, ”koncept 2”, har utretts som innehåller en större utbyggnad av bakramsverkstaden för att klara en större expansion av tillverkningen. Det kommer att kosta ca 38 milj. kr.</p> / <p>This master’s thesis was performed at Volvo CE, Hauler & Loader Division, Arvika. The project was a part of the Mechanical engineering program at the University of Karlstad. Volvo in Arvika is manufacturing wheelloaders and has done that since back in the sixties. Today they are about 1150 employees who together deliver over 6000 loaders a year.</p><p>The production volume at the Arvika-plant is increasing and therefore there is a need for new investments in the plant. At the plant’s welding department the main manufacturing is the welding of front- and rear frames. The problem is that the manufacturing is cabined and some of the frame flows is in need of improvement.</p><p>The task of the project was to examine the possibilities and identify the consequences of installing two new welding robots in the existing building and create separate front and rear frame workshops. The main reason for that is to reach a higher capacity in the manufacturing of frames.</p><p>The result of the project shows that there are possibilities to install two new welding robots in the existing building, one for front frame welding and one for rear frame welding. The frame manufacturing has been separated with a workshop for front frames in building 1 and a workshop for rear frames in building 2 (see appendices 8, 50 and 51).</p><p>Several flows has been improved due to workstations have been moved resulting in less need of transports in the workshop. The separation of front and rear frame manufacturing causes the flow of frames to be more clear and visible. The new flows are shown in production diagrams and layout-flow diagrams (see appendices 52-69).</p><p>The cost for going through with the project is estimated to around 26 million sek.</p><p>An additional concept, “concept 2”, has been investigated which contains an extended workshop for rear frames to manage a larger expansion of the production. It will cost around 38 million sek.</p>
44

Interfacial (o/w) Properties of Naphthenic Acids and Metal Naphthenates, Naphthenic Acid Characterization and Metal Naphthenate Inhibition

Brandal, Øystein January 2005 (has links)
Deposition of metal naphthenates in process facilities is becoming a huge problem for petroleum companies producing highly acidic crudes. In this thesis, the main focus has been towards the oil-water (o/w) interfacial properties of naphthenic acids and their ability to react with different divalent cations across the interface to form metal naphthenates. The pendant drop technique was utilized to determine dynamic interfacial tensions (IFT) between model oil containing naphthenic acid, synthetic as well as indigenous acid mixtures, and pH adjusted water upon addition of different divalent cations. Changes in IFT caused by the divalent cations were correlated to reaction mechanisms by considering two reaction steps with subsequent binding of acid monomers to the divalent cation. The results were discussed in light of degree of cation hydration and naphthenic acid conformation, which affect the interfacial conditions and thus the rate of formation of 2:1 complexes of acid and cations. Moreover, addition of non-ionic oil-soluble surfactants used as basis compounds in naphthenate inhibitors was found to hinder a completion of the reaction through interfacial dilution of the acid monomers. Formation and stability of metal naphthenate films at o/w interfaces were studied by means of Langmuir technique with a trough designed for liquid-liquid systems. The effects of different naphthenic acids, divalent cations, and pH of the subphase were investigated. The results were correlated to acid structure, cation hydration, and degree of dissociation, which all affect the film stability against compression. Naphthenic acids acquired from a metal naphthenate deposit were characterized by different spectroscopic techniques. The sample was found to consist of a narrow family of 4-protic naphthenic acids with molecular weights around 1230 g/mol. These acids were found to be very o/w interfacially active compared to normal crude acids, and to form Langmuir monolayers with stability depending on the aqueous pH. At high pH, addition of Ca2+ increased the film stability due to formation of calcium naphthenate at the surface. A new experimental setup based on near infrared spectroscopy was used to monitor the formation, growth, and inhibition of calcium naphthenate particles in o/w systems. This method was found to be suitable for studies of particle formation rate and growth qualitatively under different experimental conditions.
45

Formation of Inclusions and their Development during Secondary Steelmaking

Thunman, Mikael January 2009 (has links)
Al–O relations in iron were investigated. Pure iron with varying Al content was equilibrated at 1873 K. The oxygen content of iron with higher Al content than 1.0 mass % was found to be much lower than previous works, while the oxygen content for Al content less than 1 mass% was found to be slightly higher. Further, a classification procedure of inclusions was developed using the commercial software INCA Feature. Three classes were made, spinel, TP-(CaO-Al2O3), and (CaO-Al2O3) class, corresponding to the inclusions found during degassing at Uddeholm Tooling. The results showed that the spinel phase disappeared after degassing along with a reduction in numbers for the two phase inclusion (TP-(CaO-Al2O3)). Pure calcium aluminates however showed an increasing trend in a majority of the heats. The chemical development of inclusions at OVAKO Steel in Hofors, Sweden was also established. According to the morphologies and compositions, the inclusions were classified into 5 different types, namely, (1) alumina inclusions, (2) calcium aluminate, (3) spinel+calcium aluminate, (4) calcium aluminate surrounded by a CaS shell, and (5) spinel+calcium aluminate surrounded by a CaS shell. Thereafter refractory lining samples with attached slag layer were taken from used ladles at the two steel plants. The morphologies of the slag layers and the phases present were examined. The precipitated phases found in the refractory were 3CaO.Al2O3, MgO.Al2O3 and CaO in the case of Ovako Steel and 3CaO.Al2O3 and 2CaO.SiO2 in the case of Uddeholm Tooling. To help the understanding, model calculations using THERMOCALC were carried out. The model predictions differed somewhat from the experimental observation, the predicted major phases were in line with the EDS analysis on the refractory samples. Finally experiments were carried out to study the slag entrainment related to the open-eye during ladle treatment. Ga-In-Sn alloy was used to simulate the liquid steel, while MgCl2-Glycerol(87%) solution was used to simulate the ladle slag. No noticeable amount of top liquid was observed in any of the samples taken from the metal bulk during gas stirring. To confirm this aspect, slag-metal interface samples were taken from an industrial gas stirred steel ladle. No entrapment was found in the steel. The accordance of the laboratory and industrial results suggests that the entrainment of slag into the steel bulk around the open-eye cannot be considered as the major contribution to inclusion formation. / QC 20100812
46

Finn fem fel : Ett verktyg för återmatning och hantering av fel i SDE's montering

Karlsson, Maija January 2008 (has links)
Examensarbetets syfte är att utforma rutiner och verktyg för att säkerställa att relevant information om allvarliga och frekventa problem når föregående processer. Den information som föregående processer tar emot ska vara av sådan karaktär att de vet vad de ska fokusera på i sitt förbättringsarbete. Strävan har varit att ta fram ett felrapporteringsverktyg där alla fel som påträffas i produktionen ska kunna gå att rapporteras in. Utifrån den datainsamling som har gjorts via sekundär- och primärdata har den information som ska rapporters in tagits fram. Felrapporteringen ska ske i en Lotus Notes databas, detta för att programmet redan finns inom SDE`s väggar. De fel som hittas och rapporters in i felrapporteringsverktyget riktas var och en mot ett ansvarigt område. Tillexempel om det fattas ett hål på en artikel och det hålet finns med på ritningen riktas felet mot inköp. Varje ansvarigt område ska månadsvis skriva ut och åtgärda sina tre ”fem i botten” scorecard i kategorierna konsekvens, kostnad och frekvens. Fem i botten scorecarden bygger på paretoprincipen, det betyder att scorecarden visar de fem största felen varje månad i de tre olika kategorierna. Den information som loggas in i felrapporteringsverktyget kommer även att vara ett reklamationsunderlag då inköp står som ansvarigt område. Dataanalysen kommer att göras i ett Business Intelligence verktyg som heter QlikView. Detta för att QlikView på ett smidigt sätt tar data från en eller flera databaser och gör det möjligt för användaren att snabbt och enkelt analysera informationen.
47

Flödessimulering av färdigvarulager

Möller, David January 2002 (has links)
No description available.
48

Ytrengöring av alfa-diamond : En studie och urval av ytrengöringsmetoder för hårda beläggningar / Surface cleaning of alfa-diamond : A study and selection of surface cleaning methods for hard coatings

Morling, Jonas January 2010 (has links)
Examensarbetets mål är att rengöra en diamantkomposit med en ytrengöringsmetod. Metoden skulle vara mera effektiv än den manuella sandblästring som används idag för att ytrengöra detaljen. Detaljen är liten och har ett vitalt spår som ska rengöras. Detta ställer höga krav på effektiva metoder. De metoder som tas upp teoretiskt i examensarbetet är bland annat blästring, trumling och laserrengöring. Ett urval av metoderna testades. Den metod som utmärkte sig främst I testerna var automatisksandblästring. Det gav lika bra resultat som manuell sandblästring men på en bråkdel av tiden som det tog för manuellsandblästring. Det gjordes även en investeringsberäkning i examensarbetet och den gav att trumling var den billigaste metoden. Slutsatsen är att automatisk sandblästring bör användas som metod. Metoden gav ett bättre resultat än övriga metoder och var mindre arbetskrävande än manuell sandblästring. / This goal of the thesis´ is to surface finish a diamond with an appropriate method. The method should be more effective than manual sandblasting, the current method in use. The part is small and it has a vital track that must be surface cleaned. This puts great demands on effective methods. The methods that are mentioned theoretically in the thesis are automatic sandblasting, tumbling and laser cleaning. A couple of methods were tested and evaluated. Automatic sandblasting was found to be most effective. That method gave an equal result compared to the manual sandblasting but with a fraction of the time compared to manual sandblasting. Within the thesis a capital budgeting have been done. The conclusion of the thesis was that the automatic sandblasting machine should be used.
49

Surface and Inner Deformation during Shape Rolling of High Speed Steels

Nordén, Kristina January 2007 (has links)
<p>Shape rolling is a common manufacturing process used to produce long products i.e. bars and wire. One of the problems that might occur during rolling is defect formation leading to rejection of the finished product. This work is a step towards a better understanding of the evolution of some of these defects. </p><p>The evolution and reduction of cracks during shape rolling is studied in this thesis. To accomplish this, artificial longitudinal cracks are machined along bars of high speed steel. The cracks are positioned at different sites evenly distributed along the periphery in intervals of 45°. Some of the cracks are left open and some are filled with carbon or stainless steel welds. FE simulations are performed using the commercial code MSC.Marc and the results from the simulations are compared with experimental ones. Generally, simulations predict less reduction than observed experimentally. For most positions, the cracks tend to reduce most effectively followed by carbon steel welds and stainless steel welds. </p><p>To evaluate the inner deformation of a cross section during shape rolling in an oval-round-oval-round series, sample bars of M2 high speed steel are prepared with grids made up by stainless steel wires. After collecting samples after each pass, they are X-rayed to create an image of the grid. The deformation of the wires can favorably be described by FE simulations of a bar originally rotated 10° when entering the first pass. The results suggest that the simulations describe the deformation during shape rolling well. </p>
50

Koning av båtmaster : Undersökning av möjligheter till effektivisering

Adolfsson, Fredrik January 2008 (has links)
<p>Taper making of boat masts is currently made with high work- and cassation costs. The main reasons are complex settings and varied demand, another is the craft like production method which makes the fixture use low.</p><p>Due to a higher demand when new masts are being produced the work cost will sink relative to the turnover given that the workforce is unchanged. This assumes a higher productivity in the fixtures.</p><p>To adapt the production to a higher demand and lower cassation costs measures will have to be made. A measure related to lower cassation costs is standardisation of the rail steering. To reduce the time for taper making the measure preloading is the single most affecting measure.</p><p>The production of boat masts varies highly over the year with a top rate in spring and bottom rate in the winter. Taper making is also very craft like which makes the volume flexibility low due to the skill of the operators. Currently there are three operators who fully possess the ability. The others, mainly at another function of the mast division, can only relieve the taper operator.</p><p>Among the suggested measures open fixture is mentioned in order to reduce the handling of masts. Currently, when handling longer masts, an AGV will have to be stopped by the operator in due to avoid collision. This problem occurs because of the fact that the fixture is being loaded in the length direction of the mast. With a new fixture, capable of cross loading, the time for handling will be reduced but the amount of time is difficult to estimate.</p> / <p>Koning av båtmaster görs i dagsläget med höga kassations- och arbetskostnader. De huvudsakliga orsakerna är svåra inställningar och varierad efterfrågan, en annan orsak är att tillverkningen är hantverksmässig vilket ger lågt fixturutnyttjande.</p><p>I takt med att nya masttyper börjat konas kommer arbetskostnaderna minska relativt intäkterna givet att de nya volymerna kan hanteras med nuvarande bemanning. Detta förutsätter högre produktivitet i fixturerna.</p><p>För att anpassa koningen mot en högre produktionsvolym och lägre kassationskostnader krävs åtgärder. Ett viktigt åtgärdsförslag för minskade kassationskostnader är standardisering av skenornas krökning. För tidsbesparing är åtgärden förspänning av master den enskilda åtgärden med störst påverkan.</p><p>Tillverkning av master varierar kraftigt med säsong, där vår utgör topp medan vintern utgör dal. Då all koning sker mot kundorder råder därmed en viss överkapacitet. Tillverkningen är hantverksmässig vilket medför låg volymflexibilitet då koning kräver utbildad personal. I dag finns endast 3 operatörer vid mastavdelningen som behärskar koning, övriga kan visserligen avlasta men för att koning skall kunna utföras krävs närvaro av någon av dessa tre.</p><p>Bland åtgärdsförslagen nämns öppen fixtur vilket kom till för att förenkla hanteringen av master. I dagsläget måste en AGV-vagn, som används vid pressens verktygshantering, stoppas av operatör vid koning av längre master. Detta för att masten måste laddas i längdled vilket kräver extra utrymme. En öppen fixtur förenklar förflyttningen av mast avsevärt men vilken tidsbesparing som nås är svår att uppskatta.</p>

Page generated in 0.1001 seconds