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  • 151.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    A new test method for measuring the galling resistance between metal powders and die tool materials in powder compaction2010In: 14th Nordtrib Conference, Storforsen, Sweden, 2010Conference paper (Refereed)
    Abstract [en]

    The friction characteristics and galling resistance between metal powder and die tool material in metal powder compaction is of outmost importance since they will influence the porosity and surface quality of the green body and consequently the porosity, tolerances and surface quality of the final sintered product. In the present study, a new test method for evaluating the tribological performance of die tool materials aimed for powder compaction is presented. The test method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. The capability of the test method was evaluated for different types of tool materials including two PVD coatings in contact with different types of metal powders to determine the friction characteristics and the adhesion and material transfer tendency at the sliding interface. Post-test examination of the tool surfaces using FEG-SEM, EDS and 3D surface profilometry were performed in order to evaluate the mechanisms controlling the friction behavior and the material transfer tendency.

  • 152.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    A new test method for measuring the galling resistance between metal powders and die tool materials in powder compaction2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 49-54Article in journal (Refereed)
    Abstract [en]

    The friction characteristics and galling resistance between metal powder and die tool material in metal powder compaction is of outmost importance since they will influence the porosity and surface quality of the green body and consequently the porosity, tolerances and surface quality of the final sintered product. In the present study, a new test method for evaluating the tribological performance of die tool materials aimed for powder compaction is presented. The test method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. The capability of the test method was evaluated for different types of tool materials including two PVD coatings in contact with different types of metal powders to determine the friction characteristics and the adhesion and material transfer tendency at the sliding interface. Post-test examination of the tool surfaces using FEG-SEM and EDS were performed in order to evaluate the mechanisms controlling the friction behavior and the material transfer tendency. The results show that the proposed test is a simple and fast method to obtain relevant data regarding the friction and galling characteristics of die tool materials in metal powder compaction. The mechanisms prevailing at the green body/die tool material interface, e.g. cold welding, can easily be monitored by the friction and acoustic emission signals. Of the die tool materials investigated the low friction PVD a-C:Cr coating displayed the lowest friction and highest galling resistance.

  • 153.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Influence of tool steel microstructure on the prevailing wear mechanisms in metal powder compaction2011In: Proceednings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 154.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Tribologi i samband med pulverkompaktering2011In: Stålforskningsdagar 2011 : materialteknik vid Högskolan Dalarna / [ed] Storck, Joakim, Borlänge, 2011Conference paper (Other academic)
  • 155.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Tribological evaluation of some potential tribo materials used in column lift rolling contacts: a case study2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 270, no 9-10, p. 720-724Article in journal (Refereed)
    Abstract [en]

    The friction and wear characteristics of some potential tribological pairs aimed for the wheel/rail rolling contact in column lifts were studied. Tribo tests were performed using a pin-on-disc equipment and the tribological pairs included; stainless steel against ball bearing steel, stainless steel against WC/C-coated ball bearing steel and stainless steel against cast nylon (polyamide 6). The influence of coating surface topography as well as stainless steel surface topography on the friction and wear behaviour of the tribological pairs was investigated. The results show that the WC/C-coating significantly improves the tribological performance of the stainless steel/ball bearing steel sliding couples but that the WC/C-coating show a limited life-time in sliding contact with stainless steel under the prevailing contact conditions. In contrast, the stainless steel/ball bearing steel sliding couples suffer from high friction and wear due to strong adhesion between the mating surfaces followed by metal transfer and severe adhesive wear. The stainless steel/cast nylon sliding couples show a somewhat intermediate behaviour regarding friction and wear where the friction is controlled by the generation of a polymer transfer film and wear of the cast nylon is controlled by the surface topography of the mating stainless steel surface. The results obtained are discussed in relation to the identified friction and wear mechanisms as characterized by SEM and EDX.

  • 156.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Friction characteristics and material transfer tendency in metal powder compaction2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 1903-1908Article in journal (Refereed)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and die tool material in metal powder compaction play an important role in the production of near-net-shape components of high density. A natural step to further increase the green density and simplify the sintering process is to reduce the amount of internal lubricant in the powder since the volume fraction of an organic lubricant will result in a significant contribution to the resulting porosity. However, this will significantly increase the adhesive contact and thus the friction between the die and the powder/green body during the powder compaction process. As a result, the compaction and ejection forces as well as the wear rate of the die and punch surfaces will increase. Consequently, improved knowledge concerning the friction mechanisms prevailing at the metal powder/die tool material interface is needed. The present paper will present data regarding the influence of type of tool and coating material on the friction characteristics and material transfer tendency during simulated powder compaction of a water atomized plain iron powder under no or starved lubrication conditions using two different laboratory tribo tests. Tool materials investigated include ingot cast tool steel, powder metallurgy (PM) tool steel and TiAlN and DLC-type PVD coatings. Post-test characterization using scanning electron microscopy and energy dispersive X-ray spectroscopy was used to analyse the tribo surfaces and especially the tendency to material transfer and tribo film formation. The results show that the material transfer tendency is mainly controlled by strong adhesive metal–metal contacts and that a PVD coating showing intrinsic low-friction properties and a smooth surface topography may significantly reduce the interaction between the mating surfaces promoting a stable friction and a low material transfer tendency.

  • 157.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Hogmark, Sture
    Wear mechanisms of HSS cutting tools2008In: Gear Solutions, ISSN 1933 - 7507, Vol. June, p. 20-29Article in journal (Refereed)
  • 158.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Karlsson, P.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Gåård, A.
    Krakhmalev, P.
    Bergström, J.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 159.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Malmros, M.
    Bexell, Ulf
    Wiklund, U.
    Assessing the mechanical and electrical properties of aluminium oxid on aluminium using nanoindentation and nonoscratching2011In: Proccedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 160.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Sandberg, Odd
    Tribological evaluation of tool materials for powder compaction2010In: Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010, Florence, 2010, Vol. 5Conference paper (Refereed)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and tool material in metal powder compaction have been evaluated using a new tribo test method. The method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. In the present study a number of combinations of metal powder and tool materials have been evaluated with respect to the friction characteristics and the sticking and cladding tendency at the sliding interface. Post test scanning electron microscopy and energy dispersive X-ray spectroscopy in combination with 3D white light interferometry were used to analyse the tool material surfaces and material pick-up tendency. The tribological performance of potential powder compacting tool materials is discussed in relation to the identified friction and wear mechanisms.

  • 161.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Wadman, B.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schedin, E.
    Madsen, E.
    Bay, N.
    Influence of stainless steel surface texture on galling2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 162.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Optical properties of bistable nematic LCD structures2004Licentiate thesis, monograph (Other academic)
  • 163.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Adås, C.
    Madsen, L.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Tong, A.P.
    Xihua, L.
    Chigrinov, V.
    Properties of azo dye alignment layer on plastic substrates2005In: SID international symposium, Boston, 2005Conference paper (Refereed)
  • 164.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Birgerson, J.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Optical modes for single polarizer reflective BTN2002In: Eurodisplay 2002, Nice, France, 2002Conference paper (Refereed)
  • 165.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Birgerson, J.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Single polarizer reflective BTN with inner retardation compensation2002In: International display workshops, Hiroshima, Japan, 2002Conference paper (Refereed)
  • 166.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Madsen, L.
    Birgerson, J.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Optical properties of single-polarizer reflective bistable nematic displays2003In: SID international symposium, Baltimore, US, 2003Conference paper (Refereed)
  • 167.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Anchoring Energy Control and Bistable Surface Switching Based on Photo-Alignment Technology2004In: SID international symposium, Seattle, US, 2004Conference paper (Refereed)
  • 168.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Optical modes for direct-view single-polarizer reflective BTN-LCD2003In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 11, p. 1197-1202Article in journal (Refereed)
  • 169.
    Polavarapu, Prasad
    Dalarna University, School of Technology and Business Studies, Material Science.
    Studies of organic electrodes for LCDs2002Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 170. Prosek, T
    et al.
    Nazarov, A
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Thierry, D
    Serak, J
    Corrosion mechanism of model zinc–magnesium alloys in atmospheric conditions2008In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 50, no 8, p. 2216-2231Article in journal (Refereed)
    Abstract [en]

    Recently, superior corrosion properties of zinc coatings alloyed with magnesium have been reported. Corrosion behaviour of model zinc–magnesium alloys was studied to understand better the protective mechanism of magnesium in zinc. Alloys containing from 1 to 32 wt.% magnesium, pure zinc, and pure magnesium were contaminated with sodium chloride and exposed to humid air for 28 days. Composition of corrosion products was analyzed using infrared spectroscopy (FTIR), ion chromatography (IC), and Auger electron spectroscopy (AES). The exposure tests were completed with scanning Kelvin probe (SKP) and electrochemical measurements. Weight loss of ZnMg alloys with 1–16 wt.% magnesium was lower than that of pure zinc. Up to 10-fold drop in weight loss was found for materials with 4–8 wt.% Mg in the structure. The improved corrosion stability of ZnMg alloys was connected to the presence of an Mg-based film adjacent to the metal surface. It ensured stable passivity in chloride environment and limited the efficiency of oxygen reduction.

  • 171. Prosek, T.
    et al.
    Thierry, D.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Effects of chloride-to-chromate ratio on the protective action of zinc surface films under atmospheric weathering conditions2007In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 63, no 3, p. 258-267Article in journal (Refereed)
    Abstract [en]

    The formation and the corrosion protection of newly formed chromium-rich layers on bare zinc surfaces were studied to model the conditions in defected areas of both organic and conversion chromate coatings that are in contact with water environments contaminated with different amounts of chloride ions. Composition of the layers was idenified with Fourier transformed infrared spectroscopy (FTIR), x-ray absorption near-edge structure (XANES), and secondary ion mass spectroscopy (SIMS). The presence of chloride in the range from 0.06 mM to 1, 000 mM in the chromate treating solution had almost no effect on the amount of chromate adsorbed on zinc. Three independent techniques showed that a more than 4-order increase in chloride concentration results in the drop of the chromate content in the surface film only by 20% to 25%. Cr(VI)-to-total Cr surface ratio was close to 0.3 and constant under present experimental conditions. More chromium was detected in the outer region of the film, whereas chloride accumulated in the inner region. As a result of the linear increase of the surface chloride concentration with the chloride concentration in the chromate treating solution, the chloride-to-chromate surface molar ratio increased sharply. The rate of reduction of Cr(VI) to Cr(III) and the corrosion rate of zinc exposed to atmospheric weathering conditions increased significantly with the chloride-to-chromate ratio. The chromate coatings showed good stability and a high level of corrosion protection, up to the ratio of approximately 2. It represented a threshold value below which relatively low rates of the chromate reduction and zinc corrosion were observed, since the significant part of the chloride ions was inactivated in the first hours of exposure by the formation of insoluble corrosion products. A negative effect of the increasing chloride-to-chromate surface molar ratio on corrosion can be seen in the increasing ability to reduce oxygen on the zinc surface measured by the scanning Kelvin probe (SKP) technique. Inhibition of the cathodic reaction by chromate was less effective at higher ratios.

  • 172.
    Raju, Gorinta
    Dalarna University, School of Technology and Business Studies, Material Science.
    Photo Alignment of Thin Retardation Films for LCD Applications2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 173.
    Ramachandra, Kasarla
    Dalarna University, School of Technology and Business Studies, Material Science.
    PEDOT-PSS as Electrode for LCD's2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 174.
    Rehnström, Mattias
    Dalarna University, School of Technology and Business Studies, Material Science.
    Koldiffusionens inverkan på utmattnings-hållfastheten hos varmvalsade sexkantsstänger; The influence of carbon diffusion on the fatigue strength of hot rolled hexagonal rods2005Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    Helstångsborr och konstång kallas bergborrverktyg, som tillverkas av sexkantiga stänger med inre hål för ledning av spolvatten. Dessa spolhål är klädda med ferritiskt rostfritt stål. Innan valsning borras ett centrerat hål i stålämnet som ska valsas. I det borrade hålet appliceras ett rör av ferritiskt rostfritt stål och i det röret skjuts en manganstålskärna in. Efter valsning dras kärnan ut och ett spolhål med invändigt foder av rostfritt stål bildas. Under uppvärmningen och valsningen av stålämnet sker normalt en koldiffusion från manganstålskärnan till det rostfria fodret. Fodrets syfte är att skydda spolhålets yta mot erosion och korrosion. Syftet med arbetet var att hitta en metod som garanterar uppkolning av det invändiga fodret, samt att utreda vad uppkolningen betyder för den mekaniska hållfastheten i stängerna. Ett laboratorieförsök visade att det var bra, med avseende på uppkolning, att blanda stearat i kärnbestrykningsmedlet. Kärnbestrykningsmedlet penslas på manganstålskärnan innan den förs in i stålämnet som ska valsas, dess syfte är att minska friktionen vid kärnutdragningen efter valsning. Ett försök utfördes i valsverket med stearat i kärnbestrykningsmedlet. En grundlig undersökning utfördes på två hetor som valsats med stearat-bestrykningsmedel, samt på en traditionellt tillverkad heta för att ha som referens. Hetorna kapades till provstänger om 1,5 m, totalt undersöktes 55 st. Utvärderingen av verksförsöket visade att stängernas kvalitet blir tillräckligt bra om ingenting oförutsett händer i produktionen, oavsett om koltillskott är tillsatt i bestrykningsmedlet eller inte. Arbetet gav inte en garanterande metod, men visade att stängerna normalt håller hög kvalitet.

  • 175. Rendon, José
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 11, p. 2055-2061Article in journal (Refereed)
    Abstract [en]

    The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel. The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy. The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5-10 mu m in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.

  • 176. Rybalochka, A.
    et al.
    Sorokin, V.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Palmer, S.
    Selection of cholesteric liquid crystals for liquid crystal display with high multiplexing level1999In: Advanced display technologies, 1999Conference paper (Refereed)
  • 177.
    SAHLIN, CARL
    Dalarna University, School of Technology and Business Studies, Material Science.
    Karakterisering av karbidtyp, storlek och storleksfördelning i Sandvik 13C26 Inverkan av olika processparametrar: Characterisation of type, size and size distribution of carbides in Sandvik 13C26 The influence of process parameters2006Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [sv]

    Sandvik 13C26 är ett rostfritt högkolhaltigt kromstål vilket i sitt härdade och anlöpta tillstånd används för tillverkning av eggar till rakklingor. Den höga kolhalten gör att materialet måste kallvalsas i ett mjukglödgat tillstånd med ferritisk grundmassa och utskiljda karbider/nitrider. Vid härdning av materialet som kunden själv utför, är medelpartikelstorleken en viktig egenskap för att härdningsprocessen skall vara kostnadseffektiv. Valsning och hasplingstemperaturer påverkar hur mikrostrukturen ser ut efter svalning till rumstemperatur, vilket i sin tur påverkar storleken, storleksfördelningen samt typen av karbider som skiljs ut i den efterföljande sfäroidiseringsglödgningen, vilken också har stor inverkan på karbiderna. Det mjukglödgade materialet genomgår en rad kallvalsningsoperationer och rekristallisationsglödgningar. I detta arbete har effekten av varierande tider och temperaturer vid tidigare nämnda processteg studerats genom att etsa prover, ta bilder i ett svepelektronmikroskop och sedan analysera dessa i ett bildanalysprogram. För att avgöra vilken processväg som gav det material med bäst så kallad härdrespons testades denna. Det visade sig att material med minst medelpartikelvolym gav bäst respons. En generell slutsats är att den sammanlagda tiden vid den temperatur då M23C6 tillväxer som mest, med andra ord i perlitnosen, är avgörande för medelpartikelstorleken.

  • 178.
    Sandberg, Jonas
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Åhman, Andreas
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skadefallsutredning av havererade lager för högtemperaturstillämpningar2011Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [sv]

    GIA industri AB är ett industriföretag som designar och monterar maskiner och hjälpmedel till gruv- och stålindustrin. GIA har blivit kontaktade av en kund där glidlagren till en lyftkrok på en skänklastare har skurit. Syftet med projektet var att utreda varför dessa glidlager har skurit och, om det var möjligt, föreslå lämpliga åtgärder för att undvika att liknande haverier sker i framtiden. Inledningsvis gjordes en omfattande litteraturstudie över olika vanliga lagerhaverier och vilka primära krav ett glidlagermaterial och tillhörande smörjmedel bör uppfylla. Utvalda provbitar från de skadade lagren undersöktes med hjälp av ljusoptisk mikroskopi, svepelektronmikroskopi, energidispersiv röntgenanalys och optisk ytprofilometri. Mikroskopistudierna visade att ytan var väldigt ojämn och att det skyddande fosfatskiktet var bortnött på flera ställen vilket gav kontakt metall mot metall där smörjningen inte fungerat optimalt, vilket skapat en kraftig adhesiv nötning. I tvärsnittsproverna kan man konstatera att de kraftigt nötta områdena är ytutmattade med en omfattande sprickbildning. Sprickorna har växt till och flagor har lossnat och blivit kvar i systemet och orsakat abrasiv nötning på ytan. Det hittades även stora mängder slagginneslutningar (Al2O3) i materialet och dessa var av modell större vilket är negativt då dessa är betydligt hårdare än det övriga materialet vilket ger upphov till höga spänningskoncentrationer och sprickbildning. Tänkbara orsaker till varför de aktuella lagren skurit är att konstruktionen av skänken saknat en värmeskyddande sköld och att lagren då utsatts för en för stor värmepåverkan då skänken använts för att frakta varm slagg i. Detta kan ha gjort att smörjmedlets viskositet har minskat och därmed inte uppfyllt sin bärande funktion och då gett materialet möjlighet att få en kontakt mellan metall och metall. Ett felaktigt valt smörjmedel och felaktigt bearbetade lagerytor är också mycket tänkbara orsaker till att lagren skurit. Materialets innehåll av defekter i form av hårda inneslutningar som kan skapa ytutmattning och sprickbildning är en annan tänkbar orsak. Troligast är att det är en kombination av dessa möjliga orsaker som gjort att lagren skurit. Hur man ska undvika liknande haverier i framtiden är svårt att säga då den direkta orsaken till varför lagren skurit inte kunnat fastställas.

  • 179. Sandell, A.
    et al.
    Karlsson, P. G.
    Richter, J. H.
    Blomquist, J.
    Uvdal, P.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Growth of ultrathin ZrO2 films on Si(100): film-thickness-dependent band alignment2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 13, article id 132905Article in journal (Refereed)
    Abstract [en]

    The band alignment of ultrathin ZrO2 films of different thickness formed on Si(100) have been monitored with synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy. The films were deposited sequentially by way of metal-organic chemical-vapor deposition in ultrahigh vacuum. A significant decrease in the conduction band offset is found for increasing film thickness. It is accompanied by a corresponding increase of the valence band offset. The variations originate in the formation of an interfacial layer characterized by a lower degree of Zr-O interaction than in bulk ZrO2 but with no clear evidence for partially occupied Zr 4d dangling bonds.

  • 180.
    Satish, Palika
    Dalarna University, School of Technology and Business Studies, Material Science.
    Cell Gap Control in Flexible Displays2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 181.
    Selo Mustafa, Muhammed
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Tunell, Helena
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Kozlovsky, M.
    Synthesis, spectroscopic characterisation and alignment of novel azobenzene containing monomers2005In: Liquid crystals (Print), ISSN 0267-8292, E-ISSN 1366-5855, Vol. 32, no 7, p. 901-908Article in journal (Refereed)
    Abstract [en]

    A series of novel bifunctionalized photochromic monomers were synthesized, focusing on those with polymerizable acrylic/methacrylic groups attached to both ends of an azobenzene core via flexible spacers. The phase behaviour of the monomers was investigated using DSC, polarizing optical microscopy and X‐ray diffraction. The change in UV‐vis absorbance of the monomers under illumination with non‐polarized/polarized UV light was studied for both solutions and thin films; also studied was its relaxation in the dark. On illumination with LPUV light, in‐plane reorientation of the molecules normal to the polarization of the exciting UV light, and aggregation of the molecules in the films, were found.

  • 182.
    Skarp, Kent
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Adås, C.
    Franklin, G.
    Drejholt, E.
    Westling, T.
    Development of flexible LCDs2002In: Asian symposium on information display, 2002Conference paper (Refereed)
  • 183.
    Sohail, Ahmed
    Dalarna University, School of Technology and Business Studies, Material Science.
    Designing a multipanel LCD sign2002Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 184.
    Sreenath, Kurupati
    Dalarna University, School of Technology and Business Studies, Material Science.
    High Accuracy Alignment Assembly Fixture with Parallel Movement2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 185.
    Srinivas, Velaga
    Dalarna University, School of Technology and Business Studies, Material Science.
    Electronic Setup for One-Pixel and Low Multiplex Seven Segment Liquid Crystal Displays2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 186. Stanciu, V.
    et al.
    Wilhelmsson, O.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Adell, M.
    Sadowski, J.
    Kanski, J.
    Warnicke, P.
    Svedlindh, P.
    Influence of annealing parameters on the ferromagnetic properties of optimally passivated (Ga,Mn)As epilayers2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 12, article id 125324Article in journal (Refereed)
    Abstract [en]

    The influence of annealing parameters—temperature (Ta) and time (ta)—on the magnetic properties of As-capped (Ga,Mn)As epitaxial thin films has been investigated. The dependence of the transition temperature (TC) on ta marks out two regions. The TC peak behavior, characteristic of the first region, is more pronounced for thick samples, while for the second ("saturated") region the effect of ta is more pronounced for thin samples. A right choice of the passivation medium, growth conditions along with optimal annealing parameters routinely yield TC-values of ~150 K and above, regardless of the thickness of the epilayers

  • 187.
    Stenström, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Deposited copper as lubrication when drawing of titanium wire; a study of method.2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This work performed at Sandvik Materials Technology has studied the possibility of using copper as lubrication during Ti-wire drawing. A PVD-method was used to deposit Cu on Ti-wires. The PVD coated copper samples were compared to a reference material of solid Cu which first had to be recrystallized. Different reduction combinations were investigated in the wire drawing and the Cu-coated wires were drawn both without and with MoS2 lubrication. Values, including drawing forces, HV and tensile testing, from already drawn Ti-wires without Cu were included in the matrix and the drawing forces were then compared. Significant contributions of friction were present in the first draw of all unlubricated Cu-coated Ti-wires. The forces decreased considerably after the first draw. After four drawings, done on one of these wires, the forces then were in the same region as the lubricated wires at the same reductions. No clear tendencies of uneven hardening were observed regardless of friction or used reduction. Tensile testing after wire drawing could not be performed as the wires broke at the wrong places. Measurements of residual stress on worked and unworked Cu-layers showed no residual stress, surprisingly. This study shows that Cu can be used as lubrication if the process is optimized with respect to Cu layer thickness, drawing tool-angles and reduced tungsten carbide grain size in drawing tools. A smoothening draw is needed before reduction of the Ti-wire to help lower the friction.

  • 188.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science.
    Exploring improvement trajectories with dynamic process cost modelling: a case from the steel industry2010In: International Journal of Production Research, ISSN 0020-7543, E-ISSN 1366-588X, Vol. 48, no 12, p. 3493-3511Article in journal (Refereed)
    Abstract [en]

    Improvement trajectories are sequential managed chains of improvement initiatives required to handle changes in competition and market. This paper presents a five-step framework, based on dynamic process cost modelling, which was developed during a four-year research project at a major stainless steel producer, to support the selection of an improvement trajectory based on strategic requirements to combine high product diversity with cost reduction. The framework aims to develop insight into what manufacturing capabilities are required to reach the strategic goals by combining system dynamics simulation with process cost modelling and visual exploratory data analysis in an iterative modelling procedure. The applicability of the five-step framework is demonstrated through a case study from the steel industry, in which a goal driven analysis is used to assess process requirements based on performance and market considerations.

  • 189.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science.
    Product variety and upstream versus downstream flexibility2009In: Proceedings of the International 3'rd Swedish Production Symposium / [ed] Rosén, B.G., Göteborg, 2009, p. 304-309Conference paper (Refereed)
    Abstract [en]

    Niche market steel producers tend to manufacture a wide range of products that are sold in low quantities. Current steelmaking—continuous casting (SCC) technology forces producers to operate according to combined make–to–stock/make–to–order order policies and keep in–process inventory. This leads to intermediate cooling of workpieces, high energy consumption, and high inventory and reheating costs. This paper evaluates links between product range and process flexibility upstream and downstream form the customer order decoupling point. The operational capabilities that result from improved process flexibility make diversified low cost steel production possible. At the same time the environmental sustainability of production can be improved. The strategic importance of process flexibility improvements are discussed with reference to the concept of competitive frontiers.

  • 190.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science.
    Product variety, flexibility and energy use in hot rolling mills2012In: Enabling Manufacturing Competitiveness and Economic Sustainability: Proceedings of the 4th International Conference on Changeable,Agile, Reconfigurable and Virtual production (CARV2011),Montreal, Canada, 2-5 October 2011 / [ed] ElMaraghy, Hoda, Montreal: Springer, 2012, Vol. 2, p. 80-85Conference paper (Refereed)
    Abstract [en]

    Hot rolling consumes one third of the energy in a steel plant. Increasing product variety slows down production flow, causing heat losses and increased reheating energy consumption. A system dynamics model was developed to evaluate how flexibility influences energy use. Results indicate that world best practice requires high flexibility and low to intermediate product variety. Up to 28% less reheating was needed for low product variety, but no improvement was obtained for high product variety; a flexible steelmaking process for efficient production of small batches of steel would be required. The strategic nature of process flexibility investments is discussed.

  • 191.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science. Dalarna University, School of Technology and Business Studies, Materials Technology. Kungliga tekniska högskolan.
    Strategic and operational capabilities in steel production: Product variety and performance2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Steel producers that employ niche market strategies are continuously seeking to reduce production cost while maintaining a diverse product mix. The business model is typically based on marketing of high–strength special or stainless steels. However, the desire to avoid direct cost competition is over time gradually leading towards increased product variety and smaller order volumes (tonnes per order) for each product. This thesis analyses how production cost is linked to product variety in steel strip production. Results are based on new models for assessment of opportunities for performance improvement in high product–variety steel production. The need for flexible production processes increases with increasing product variety. Operational capabilities linked to process flexibility determine the extent to which steel producers can eliminate in–process inventory and accomplish close coupling between process steps. Niche market producers that invest in process flexibility improvements can lower production costs both due to reduced work–in–process and lower energy consumption. An additional benefit is reduced environmental impact. The following problems are addressed: • Development of a method to assess the influence of product variety on performance in steel production. • Development of models of continuous casting and hot rolling that account for product variety and cost effects with consideration of varying degrees of process flexibility. • Development of a strategy process model that focus on the strategic value of operational capabilities related to process flexibility. Investments in operational capabilities regarding process flexibility have a strategic impact. An appreciation for the effects of process flexibility should permeate the organisation’s daily work since the accumulated contribution of many, seemingly unimportant, incremental changes significantly influences the strategic opportunities of the company.

  • 192.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science.
    Stålforskningsdagar 2011: Materialteknik vid Högskolan Dalarna2011Book (Other academic)
  • 193.
    Storck, Joakim
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Lindberg, Bengt
    A lean production strategy for hot charge operation of a steel mill2007In: IET Conference publications, Issue 528, 2007, 2007, Vol. 528, p. 158-167Conference paper (Refereed)
    Abstract [en]

    This paper aims to show how a strategy based on lean production can aid the implementation of hot-charge operation in steel strip production. Key parameters in a lean strategy for steel manufacturing are identified, and it is shown that lean production targets the difficulties that are traditionally associated with hot charging. Hot charging amounts to a closer level of integration of the continuous casting and hot rolling processes. The conclusions are that implementation of hot charging can be seen as a waste-reduction process within a lean production strategy, and that there are substantial cost savings to be made once the full benefits of a lean production strategy are considered.

  • 194.
    Storck, Joakim
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Lindberg, Bengt
    Assessment of best scheduling practice in continuous casting and hot rolling of stainless steel strip by system dynamics simulation2007In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 344, p. 897-904Article in journal (Refereed)
    Abstract [en]

    A rapid flow of materials with little intermediate buffering between steel mill and hot strip mill has many benefits. One is energy savings due to raised charging temperature in the reheat furnaces of the hot strip mill. Another is that tied capital is freed up, thereby improving mill economy. Still, it is not unusual that average lead-time is in the order of days, or even weeks. The aim of the present work was to show how lead-times from casting to rolling could be improved by changes in the scheduling function. A System Dynamics model of a stainless steel strip production facility with continuous caster and hot rolling mill was created. The model was used to study the dynamics of the system in response to changes in parameters that defined the scheduling configuration. More frequent schedule updating generally resulted in less work in process (WIP) and shorter lead times from casting to rolling, with resulting higher charging temperatures. The amount of oscillation in the system was also reduced. More frequent work roll changes were required when scheduling frequency increased, resulting in an increased fraction of setup time in relation to total processing time. Therefore, a development towards increased scheduling frequency may have to be complemented by efforts to reduce changeover times. The conclusion was that dynamic scheduling routines with frequent schedule updating result in better overall performance of the system due to lower WIP and better heat utilization. Dynamic scheduling routines with frequent updates make the system respond better to changes in the system and give better overall performance. The result is lower WIP, increased energy efficiency and less oscillation in the system.

  • 195.
    Sunil, Yallapragada
    Dalarna University, School of Technology and Business Studies, Material Science.
    Investigations of Various LC Effects2004Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 196.
    Tahir, Mohammed
    Dalarna University, School of Technology and Business Studies, Material Science.
    LOWWEAR varmvalsning WP12012In: Strategiskt stålforskningsprogram för Sverige 2007–2012: En sammanfattning av forskningsprogrammet och de ingående projekten, presenterade vid Jernkontorets programkonferens, 4–5 september 2012, Stockholm: Jernkontoret , 2012, p. 18-18Conference paper (Other (popular science, discussion, etc.))
    Abstract [sv]

    En konstruktion av slitage och temperaturprofiler in-line¬mätare designades och ett modifierat valslitage beräkningsmodell presenteras där inflytandet från arbetsvalsmaterial och det valsade materialets egen-skaper utvärderades. HSS, HiCr och IC arbetsvalsar utvärderades. Olika par i färdigverk med olika valsar-rangemang, skillnader i slitage mellan övre och undre valsar och påverkan av smörjning undersöktes.  Genom att anpassa modellen till olika valsningsförhållanden; varmvalsverk, plåtverk och steckelverk, erhölls möjligheten att undersöka modellen i drift.

    En studie av valsmaterial (Vancron 40, Sverker 3 and Vanadis 23) med avseende på valsslitage, ytkvalitet och påkladdning genomfördes. Valsmaterialen utvärderades experimentellt i laboratorium och i pilotvals-verk. Fyra olika industriella smörjmedel utvärderades. Vancron 40 gav lovande materialkvalitet tack vare sina goda egenskaper gällande ytfinhet i kombination med motstånd mot påkladdning och motstånd mot adhesiv nötning.

  • 197.
    Tahir, Mohammed
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Absalyamova, V.
    The use of solar energy in steel industries2011Conference paper (Refereed)
    Abstract [en]

    The purpose of this study is to make a design and simulation of the solar photovoltaic system which would attempt to cover the energy demand of the initial part of the pickling line hydraulic system at the SSAB steel plant. Proposed photovoltaic pumping systems in this work are to run the system into the hydraulic pump directly, developing of PV systems which produce energy in DC form. The second proposed photovoltaic technology is a type of PV system which delivers power to an AC load. © 2011 IEEE.

  • 198.
    Tahir, Mohammed
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Holmberg, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    The impact of tapered work rolls in the finishing mill during hot rolling2012In: Iron & Steel Technology Conference Proceedings, Warrendale, PA: Association for Iron & Steel Technology , 2012, p. 1601-1609Conference paper (Refereed)
    Abstract [en]

    Few studies were done to assess the knowledge of the impact of tapered work rolls in the finishing mill during hot rolling. Hansson, L.et al. studied the use of advanced process models for plate and strip rolling in the Scandinavian Steel Industry [1]. Their work thatincludes simulations of work roll shift with tapered and CVC rolls have results a basis for new investments for profile and flatnesscontrol equipment in steel rolling mills. Rosenthal D. et al. studied a method of influencing the strip contour in the edge region of arolled strip [2]. Special CVC rolls were used as work rolls for influencing the strip contour in the edge areas and to study.Concerning this project, early analysis of work roll data suggested that the tapering of the work rolls was subordinated to the CVCprofileand that a greater than allowed tapering would not affect the result of the rolling process. A grinded profile which is out oftolerance on the other hand, would result in a change in CVC-profile.The purpose of this project was to study the impact of the tapering on the work rolls during hot rolling in the finishing mill. Customgrinded work rolls of CVC-type have been placed in finishing mill, stand 6 (F6) and the axial loads during the following rolling hasbeen studied and evaluated. The deviation of the centre of a strip, flatness of a strip as well as the equivalent camber of the work rollshave also been analyzed for further evaluations of the impact on the rolling results.Theoretically calculation model of the profile of the CVC work rolls and axial force directed toward roll edges was described. Customgrinded work rolls of CVC-type have been placed in mill stand number 6 and the axial loads during the following rolling has beenstudied and evaluated.The impact of tapered work rolls towards CVC profile, axial force, the deviation of the centre of a strip and flatness was presented.The work project finally resulted in new guidelines in grinding of the work rolls in the finishing mill.The work is done in the finishing mill of the strip rolling mill, Figure 1. The strip rolling mill comprising six-high rolling stands wherework rolls and backup rolls at stand 2 to 6 are containing CVC work rolls.Data of the specific strip rolling mill, the type and the characteristics of the used work rolls and strip properties were described [3].Due to different rolling conditions; high temperature in the early stands (thermal cracks) and low temperature and high incident rate inthe last stands (mechanical damage), HSS and HCr rolls were used in stands F1-F3 and IC rolls in stands F4-F6. The studied work rollwas of IC type.

  • 199.
    Tahir, Mohammed
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jonsson, N.G.
    Lagergren, J
    Wikström, L.
    Hedenlund, H
    Evaluation of tool material Vancron 40 with regard to wear, surface quality and galling2012In: Proceedings of  JSI 2012 - 30th International Steel Industry Conference, December 18-19, Paris, France, Paris: B&W , 2012, , p. 2Conference paper (Refereed)
    Abstract [en]

    Resistance to adhesive wear on tool material can be improved by increasing the tool hardness, high ductility and decreasing of friction coefficient between the tool and the work material. In a similar way, resistance to galling can be increased by increasing the tool hardness and decreasing of friction. The purpose of this project was to investigate the use of Vancron 40 as work rolls in cold rolling of stainless steel in cluster rolling mills. Considerable factors were among others, the influence of different industrial lubricants, minimizing of temperature rising during rolling, lowering of rolling forces, longer life of rolls, easier grinding of rolls, increase the oil film bearing at normal cold rolling conditions and improving surface roughness of the final products.

    For using of work rolls in cold rolling cluster mills, roll material Vancron 40 was evaluated with regard to roll wear, surface quality and galling. Currently used roll type ASP23 was used as reference roll in the evaluation. The experiments were performed, as much as possible, in accordance to steel industries recommendations. The experiments were conducted with a 4-high pilot rolling mill at Swerea MEFOS in Luleå which is equipped for rolling of both flat and long products. The experiment was done for different industrial mineral-based lubricants. Lubrication was applied in a controlled form to the upper and lower work rolls and in the contact zone. To achieve the proposed final thickness, five passes were rolled. The characteristic of the upper and the lower work rolls, during rolling, was also examined. The pilot experimental results gave promising result in surface roughness, galling and roll material hardness. Due to its chemical and physical properties, Vancron 40 is believed to be the best solution to resist adhesive wear and galling in cold rolling process that require higher accuracy. 

  • 200.
    Tahir, Mohammed
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jonsson, Nils-Göran
    Lagergren, Jonas
    Ceron, Ermanno
    Technical University of Denmark.
    Off-line testing of alternative of industrial lubricants and different tool materials for cold rolling of stainless steel2013Conference paper (Other academic)
    Abstract [en]

    The present study tests different roll materials and lubricants for cold rolling, using a strip reduction test equipment at The Technical University of Denmark. Aims was to study the roll/tool material wear resistance and the resistance towards galling, i.e. lubricant film breakdown causing pick-up of work piece material on the roll surface and subsequent scoring of work piece surfaces. The four industrial lubricants investigated all consisted of mineral oil with fatty acid additives. The work piece material was stainless steel, AISI 304. The materials tested were NARVA 12B from Åkers, using the cold work tool steel SVERKER 3 from Uddeholm (AISI D2), SUPRA 3 from Åkers using the PM tool steel VANADIS 23 from Uddeholm and Åkers special finely distributed carbides and nitrides tested roll material, using an anti-seizure PM tool steel VANCRON 40. Evaluation of resistance to wear was done; during 20 % strip reduction NARVA 12B/SVERKER 3 showed a low surface roughness when lubricant “A” was used and during both 10 % and 20 % strip reduction VANCRON 40 showed a low surface roughness when lubricant “C” was used. Together with the lubrication the surface topography of the roll material is expected to influence friction. Evaluation of resistance to galling was done. Results showed VANCRON 40 to be especially prone towards galling.

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