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  • 1. Filipovic, Mirjana
    et al.
    Ericsson, Conny
    Överstam, Henrik
    Örebro University, Department of Technology.
    Behaviour of surface defects in wire rod rolling2006In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 77, no 6, p. 439-444Article in journal (Refereed)
    Abstract [en]

    Defects are often present in rolled products, such as wire rod. The market demand for wire rod without any defects has increased. In the final wire rod products, defects originating from steel making, casting, pre-rolling of billets and during wire rod rolling can appear. In this work, artificial V-shaped longitudinal surface cracks have been analysed experimentally and by means of FEM. The results indicate that the experiments and FEM calculations show the same tendency except in two cases, where instability due to fairly "round" false round bars disturbed the experiment. FE studies in combination with practical experiments are necessary in order to understand the behaviour of the material flows in the groove and to explain whether the crack will open up as a V-shape or if it will be closed as an I-shape.

  • 2.
    Jarl, Magnus
    et al.
    Örebro University, Department of Technology.
    Överstam, Henrik
    Örebro University, Department of Technology.
    FEM vid tråddragning: resultat av dragförsök med SKF8032007Report (Other academic)
  • 3.
    Jarl, Magnus
    et al.
    Örebro University, Department of Technology.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Finit Elementmodellering (FEM) vid tråddragning2002In: 1428 dagar med U2000: en presentation av forsknings- och utvecklingsprojekt inom Universitetsfonden 2000 1 januari 1999 –28 november 2002, 2002, p. 51-54Chapter in book (Other academic)
  • 4.
    Jarl, Magnus
    et al.
    Örebro University, Department of Technology.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Simulation of temperatures in the wiredrawing process2008In: Wire Journal International, ISSN 0277-4275, Vol. 41, no 2, p. 150-155Article in journal (Refereed)
  • 5.
    Jarl, Magnus
    et al.
    Örebro University, Department of Technology.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Simulation of temperatures in the wiredrawing process2007Conference paper (Refereed)
    Abstract [en]

    Hydrodynamic theory predicts higher pressure at higher drawing speed, but the opposite is true. The temperature in the area of wire and die interface influences lubricant properties, including viscosity. In this paper, the wiredrawing process was studied by means of coupled thermo-mechanical simulations using the Finite Element Method. The temperatures in the die, the wire, and the interface were evaluated, for different parameters such as wire steel grade, drawing speed, and die cooling conditions. This paper discusses their influence on lubrication.

  • 6.
    Larsson, Tord
    et al.
    Örebro University, School of Science and Technology.
    Kjellander, Johan
    Örebro University, School of Science and Technology.
    Överstam, Henrik
    Örebro University, School of Science and Technology.
    “Aerosoltrap” a new device for inertial dust separation: CFD simulations with experimental validation2013In: Particulate Science and Technology, ISSN 0272-6351, E-ISSN 1548-0046, Vol. 31, no 3, p. 221-225Article in journal (Refereed)
    Abstract [en]

    Inertial separation of dust from air/gas streams using settling- or baffle chambers is simple and cost effective. In order to increase the effectiveness of a single chamber AerosolTrap has been developed. This new device uses 4 chambers in series, stacked on top of each other. The aim of the present study is to examine the performance of AerosolTrap and investigate if CFD simulations can be used as a tool to optimize its geometry. Simulations and validating laboratory experiments have been performed using different flows and different mix of particles. The paper describes the methodology used and presents results that show that CFD simulations predict the general characteristics of the AerosolTrap well but underestimates the separation coefficient slightly.

  • 7.
    Lundberg, Sven-Erik
    et al.
    Örebro University, Department of Technology.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Modelling of stress state, centre consolidation and roll force in billet rolling2007In: Steel Research International, ISSN 1611-3683, Vol. 78, no 6, p. 492-501Article in journal (Refereed)
    Abstract [en]

    Roll pressure models have been derived from theoretical studies, FEM simulations and experimental investigations. A model developed from slip line field theory has been shown to fit well to the experimental results. The finite element simulations overestimated the pressure function. This is a common problem in hot rolling experiments, since the problem of measuring the correct rolling temperature makes the estimation of the yield strength very difficult. The difference between the FE calculations and the experimental measurements is a measure for the error in the experimental temperature measurements rather than for the accuracy of the finite element method. Traditional modelling has not been an appropriate tool to evaluate the material flow in the centre of the billet. In spite of the fact that the entire stress state can be modelled by slip line field theory, the slip lines which determine the stress state in the centre coincide for actual geometries only in one single point. Thus the strain increments are known only in that single point. Since a material element passes that point instantaneously, it is not possible to find any finite strains in the centre by integrating any incremental function. By FEM, strain modelling is simple and the possibility to consolidate a porous bloom or ingot core can be determined. FE modelling requires an entirely new approach to the modelling problem. It is not reasonable to use FEM to evaluate only the temperature distribution for the use in roll force models from the previous century. Instead, a fully thermomechanically coupled FE model is suggested. However, the calculation time is still far too long to be used for on-line control purposes. For this application hybrid modelling can be a solution, where off-line FE models are combined with empirical modelling, and simplified models can be used for the process control.

  • 8.
    Myrén, Linda
    et al.
    Örebro University, Department of Social and Political Sciences.
    Wilhelmsson, Cecilia
    Örebro University, Department of Social and Political Sciences.
    Özdemir, Nermin
    Örebro University, Department of Social and Political Sciences.
    Edvardsson, Bo
    Örebro University, Department of Social and Political Sciences.
    Utredningsprocesser: tankar och upplevelser under barnavårdsutredningar2000Report (Other academic)
    Abstract [en]

    Two child protection cases are critically examined by studying papers and intervews with the mothers. These have negative experiences from the investigative work.The investigators distort the child protection investigations by biased selection of information. 

  • 9.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Evaluation of the improvement of rolling analysis by means of modern technology2006Conference paper (Other academic)
    Abstract [en]

    Modern wire rod rolling is characterised by high rolling speed and requirements on well-defined mechanical properties as well as close tolerances. Traditional methods for analyses of this kind of processes, such as the slip line field theory and the upper bound analysis, have proven not to be sufficient. Different methods for rolling analysis have been evaluated. Several FE approaches were compared to classical methods such as the upper bound and the slip line theory and the results was validated by practical experiments. The finite element method has proven to be a powerful tool in order understand the metal working process, it also gives the possibility to study phenomena not yet clarified.

  • 10.
    Överstam, Henrik
    Örebro University, Department of Technology.
    FEM vid tråddragning2003Report (Other academic)
  • 11.
    Överstam, Henrik
    Örebro University, Department of Technology.
    FEM vid tråddragning2004In: Stål 2004, 2004, p. 61-62Conference paper (Other academic)
  • 12.
    Överstam, Henrik
    Örebro University, Department of Technology.
    FEM vid tråddragning2002Conference paper (Other academic)
  • 13.
    Överstam, Henrik
    Örebro University, Department of Technology.
    FEM vid tråddragning: resultat av dragförsök med 18-8 och GF752003Report (Other academic)
  • 14.
    Överstam, Henrik
    Örebro University, Department of Technology.
    Finita Element Modellering (FEM) vid tråddragning2002In: Stål 2002, 2002, p. 54-55Conference paper (Other academic)
  • 15.
    Överstam, Henrik
    Örebro University, Department of Technology.
    The influence of bearing geometry on the residual stress state in cold drawn wire, analysed by the FEM2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 171, no 3, p. 446-450Article in journal (Refereed)
    Abstract [en]

    Finite element simulations have been performed in order to study the influence of bearing geometry on the residual stress-state in cold drawn wires. Experiments in full industrial scale have been performed in order to verify the FEM results. The residual stresses were measured with X-ray diffraction in both the axial and tangential direction. The material used was a high carbon steel for roller bearings, 100Cr6. It was found that the geometry of the bearing has a large influence of the residual stress-state. When the bearing is somewhat tapered, a gap in the beginning of the bearing is formed. This "double contact" reduces the axial and tangential residual stress to minimum or even to a compressive state. A cylindrical bearing gave no contact in the bearing at all due to elastic deformation. This resulted in a large axial and tangential residual stress. It was shown that even a small divergence from the desired bearing geometry due to the grinding of the die could affect the residual stress immensely.

  • 16.
    Överstam, Henrik
    Örebro University, Department of Technology.
    The influence of bearing geometry on the residual stress state in cold drawn wire, analyzed by the FEMManuscript (preprint) (Other academic)
  • 17.
    Överstam, Henrik
    Örebro University, Department of Technology.
    The interdependence of plastic behaviour and final properties of steel wire, analysed by the finite element method2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The finite element method (FEM) has been used in order to study the interdependence of plastic behaviour and final properties in steel wire. Three processes metal forming have been studied: billet forging, wire rod rolling, and cold drawing.

    The forging study focuses on the possibilities to eliminate voids, pores and pipes by altering the bite ratio in open die forging. Forging is used in wire manufacturing when dealing with materials that are difficult or impossible to roll, e.g. tool steels like high-speed steels, and powder metallurgically manufactured materials like tungsten-molybdenum filament wire. The elimination of inner defects by forging were successfully simulated by the FEM.

    The rolling study focuses on the problems due of the extreme finish rolling velocities in modern wire rod mills and modern technologies such as thermo-mechanical rolling and sizing. A design for a high-speed laboratory mill for studies of material behaviour at extreme strain rates was made. With a combination of two-high stands and three-roll units is it possible to obtain a smoother temperature distribution in the bar cross section.

    Two studies of the cold drawing process were made. The first describes the distribution of the plastic deformation due to the die geometry. It was found that the influence of the die angle on the amount of inhomogeneous deformation decreases with increasing area reduction. The frictional behaviour was also studied.

    The second study describes how the bearing geometry affects the residual stress-state in the wire. It was found that a small taper could change the residual stress state in the surface immensely. This was shown with FE simulations and verified by X-ray diffraction measurements. The results in this paper gives a tool for control of the residual stress-state in the wire. This gives a possibility to increase e.g. the fatigue strength in the final product.

    List of papers
    1. FEM-simulation of drawing out in open die forging
    Open this publication in new window or tab >>FEM-simulation of drawing out in open die forging
    2004 (English)In: Steel Research International, ISSN 1611-3683, Vol. 75, no 12, p. 812-817Article in journal (Refereed) Published
    Abstract [en]

    Experiments and finite element simulations were performed in order to study how the bite ratio influences the closing of inner flaws such as voids and pipes in the open die forging process. Square rolled blooms of carbon steel with a transversal hole in the centre were forged with a constant height reduction but with different bites in order to study the closing of voids during the process. Corresponding finite element simulations were performed in full 3D with full thermo-mechanical coupling. Also the influence of the friction and of the temperature gradient in the workpiece were studied. The elimination of an artificial defect by forging was successfully simulated by the finite element method. It is established that the closure of voids is highly dependent on the bite ratio. The closure of voids under the edge of the tool is however not improved by a higher bite ratio. There is a slight tendency that the situation under the tool edge is worse when the bite ratio is increased.

    Place, publisher, year, edition, pages
    Düsseldorf: Verlag Stahleisen, 2004
    Research subject
    maskinteknik
    Identifiers
    urn:nbn:se:oru:diva-3208 (URN)
    Available from: 2004-11-18 Created: 2004-11-18 Last updated: 2017-10-18Bibliographically approved
    2. Finite element modelling and laboratory simulation of high speed wire rod rolling in 3-roll stands
    Open this publication in new window or tab >>Finite element modelling and laboratory simulation of high speed wire rod rolling in 3-roll stands
    2003 (English)In: Steel Research International, ISSN 1611-3683, Vol. 74, no 7, p. 431-443Article in journal (Refereed) Published
    Abstract [en]

    Modern wire rod rolling is characterized by high finish rolling speed and requirements on close tolerances and well defined mechanical properties of the rolled product. In some senses the technological development has run in advance of the scientific knowledge of the phenomena involved in the process. Thus at present no laboratory mill is in operation for rolling speeds above 40 m/s. The modern technologies on thermomechanical rolling and sizing give certain phenomena difficult to handle for the mills, and especially finish rolling at low reductions and temperatures performed in three-roll units sometimes give surprises on grain size distribution and allied properties of the wire rod. Traditional plastic analysis has proven not to be sufficient to analyse the processes involved in high speed rolling of close tolerance wire rod with well-defined properties. Simulations by means of the Finite Element Method on the other hand have proven to be a powerful tool for this kind of analysis, even if the initial difficulties in creating a suitable model require certain care. Also the calculation capacity must be sufficient for making relevant three-dimensional thermomechanically coupled studies. The high speed rolling of wire rod can be simulated under full-scale conditions, and with correct boundary condition in the high-speed laboratory wire rod mill at Orebro University. By utilizing both conventional two-high stands and three-roll units it has been possible to design a laboratory rolling mill for any rolling condition that can occur in wire rod mills. Rolling speeds up to 80 m/s can be combined with thermo-mechanical rolling in any interesting temperature range, and with total flexibility of reductions. Further, fundamental studies of high-speed deformations can be performed in full-scale and with correct frictional conditions and geometries. Thanks to the flexibility in layout and combinations with other equipment in the laboratory also other processes can be simulated.

    Place, publisher, year, edition, pages
    Düsseldorf: Verlag Stahleisen, 2003
    Research subject
    Mechanical Engineering
    Identifiers
    urn:nbn:se:oru:diva-4062 (URN)
    Available from: 2007-06-21 Created: 2007-06-21 Last updated: 2017-10-18Bibliographically approved
    3. Development and validation of FEM models for wiredrawing
    Open this publication in new window or tab >>Development and validation of FEM models for wiredrawing
    2004 (English)In: Wire Journal International, ISSN 0277-4275, Vol. 37, no 5, p. 73-76Article in journal (Refereed) Published
    National Category
    Engineering and Technology
    Research subject
    Mechanical Engineering
    Identifiers
    urn:nbn:se:oru:diva-3210 (URN)
    Available from: 2004-11-18 Created: 2004-11-18 Last updated: 2017-10-18Bibliographically approved
    4. The influence of bearing geometry on the residual stress state in cold drawn wire, analyzed by the FEM
    Open this publication in new window or tab >>The influence of bearing geometry on the residual stress state in cold drawn wire, analyzed by the FEM
    (English)Manuscript (preprint) (Other academic)
    Research subject
    Mechanical Engineering
    Identifiers
    urn:nbn:se:oru:diva-3211 (URN)
    Available from: 2004-11-18 Created: 2004-11-18 Last updated: 2017-10-18Bibliographically approved
  • 18.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Eriksson, Conny
    Fagersta Stainless.
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    The importance of proper roll pass design and entry guiding on the improvement of the surface quality in wire rod rolling2006In: Der Kalibreur, ISSN 0022-796X, Vol. 67, p. 51-65Article in journal (Refereed)
  • 19.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Eriksson, Conny
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    The importance of proper roll pass design and entry guiding on the improvement of the surface quality in wire rod rolling2005Conference paper (Other academic)
  • 20.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    Development and validation of FEM models for wire drawing2003In: Interwire 2003, 2003, p. 138-147Conference paper (Refereed)
  • 21.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    Development and validation of FEM models for wiredrawing2004In: Wire Journal International, ISSN 0277-4275, Vol. 37, no 5, p. 73-76Article in journal (Refereed)
  • 22.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    FEM vid tråddragning: simulering i 2D av SKF 8032002Report (Other academic)
  • 23.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    FEM vid tråddragning: slutrapport2003Report (Other academic)
  • 24.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    FEM-simulation of drawing out in open die forging2004In: Steel Research International, ISSN 1611-3683, Vol. 75, no 12, p. 812-817Article in journal (Refereed)
    Abstract [en]

    Experiments and finite element simulations were performed in order to study how the bite ratio influences the closing of inner flaws such as voids and pipes in the open die forging process. Square rolled blooms of carbon steel with a transversal hole in the centre were forged with a constant height reduction but with different bites in order to study the closing of voids during the process. Corresponding finite element simulations were performed in full 3D with full thermo-mechanical coupling. Also the influence of the friction and of the temperature gradient in the workpiece were studied. The elimination of an artificial defect by forging was successfully simulated by the finite element method. It is established that the closure of voids is highly dependent on the bite ratio. The closure of voids under the edge of the tool is however not improved by a higher bite ratio. There is a slight tendency that the situation under the tool edge is worse when the bite ratio is increased.

  • 25.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    Finite element method at wire drawing2003Conference paper (Other academic)
  • 26.
    Överstam, Henrik
    et al.
    Örebro University, School of Science and Technology.
    Johansson, Helena
    Örebro University, School of Science and Technology.
    Jarl, Magnus
    Örebro University, School of Science and Technology.
    Temperatures at wire-drawing: simulations and verification efforts2011In: Hutnik: vol 78, 2011, p. 98-100Conference paper (Other academic)
    Abstract [en]

    Temperatures are very important in the wire drawing process. They are hard to measure direct, but a combination of simulations and measurements can give valuable information

  • 27.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    A new approach to roll force and torque modelling in wire rod and bar mills2008In: Der Kalibreur, ISSN 0022-796X, Vol. 69, p. 61-72Article in journal (Refereed)
  • 28.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    A new approach to roll force and torque modelling in wire rod and bar mills2007Conference paper (Other academic)
  • 29.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    Jarl, Magnus
    Örebro University, Department of Technology.
    Finite element modelling and laboratory simulation of high speed wire rod rolling in 3-roll stands2003In: Steel Research International, ISSN 1611-3683, Vol. 74, no 7, p. 431-443Article in journal (Refereed)
    Abstract [en]

    Modern wire rod rolling is characterized by high finish rolling speed and requirements on close tolerances and well defined mechanical properties of the rolled product. In some senses the technological development has run in advance of the scientific knowledge of the phenomena involved in the process. Thus at present no laboratory mill is in operation for rolling speeds above 40 m/s. The modern technologies on thermomechanical rolling and sizing give certain phenomena difficult to handle for the mills, and especially finish rolling at low reductions and temperatures performed in three-roll units sometimes give surprises on grain size distribution and allied properties of the wire rod. Traditional plastic analysis has proven not to be sufficient to analyse the processes involved in high speed rolling of close tolerance wire rod with well-defined properties. Simulations by means of the Finite Element Method on the other hand have proven to be a powerful tool for this kind of analysis, even if the initial difficulties in creating a suitable model require certain care. Also the calculation capacity must be sufficient for making relevant three-dimensional thermomechanically coupled studies. The high speed rolling of wire rod can be simulated under full-scale conditions, and with correct boundary condition in the high-speed laboratory wire rod mill at Orebro University. By utilizing both conventional two-high stands and three-roll units it has been possible to design a laboratory rolling mill for any rolling condition that can occur in wire rod mills. Rolling speeds up to 80 m/s can be combined with thermo-mechanical rolling in any interesting temperature range, and with total flexibility of reductions. Further, fundamental studies of high-speed deformations can be performed in full-scale and with correct frictional conditions and geometries. Thanks to the flexibility in layout and combinations with other equipment in the laboratory also other processes can be simulated.

1 - 29 of 29
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