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  • 1.
    Addle, Graeme R
    et al.
    GIW Industries Inc..
    Sellgren, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Design, selection, sizing and control considerations for cyclone feed slurry pumps1999Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 104, nr 3, s. 233-239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cyclone feed centrifugal slurry pumps in semi-autogenous grinding (SAG) mill and other cyclone feed circuits see coarse size slurries at high concentrations that can result in high wear if the pump is not designed, selected, sized and operated correctly. The high proportion of static head of the normal cyclone feed circuits usually results in a relatively flat system curve which in conjunction with the typically flat slurry pump curve results in large changes in operating flow with small changes in system head. When this is combined with the normal (or abnormal) fluctuations in the output from the mill upstream of the pumps, any shortcomings in the pump control system and/or matching of the pump means large fluctuations in flow and increased wear. This difficulty could be corrected by continuous variations in speed. A means of control by which the speed is changed in an appropriate way is suggested here. In this case then the pump-input power, the known water performance of the pump and the system flow, can be used to calculate an effective pump discharge pressure. By comparison with a calculated system head, the pump speed can be regulated such that the pressures are equal and the system stable for any practical variation of incoming flow or specific gravity.

  • 2.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Rehman, Yaser
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    A study of the sintering of diatomaceous earth to produce porous ceramic monoliths with bimodal porosity and high strength2010Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 201, nr 3, s. 253-257Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diatomite powder, a naturally occurring porous raw material, was used to fabricate ceramic materials with bimodal porosity and high strength. The effect of the sintering temperature on the density and porosity of dry pressed diatomite green bodies was evaluated using mercury porosimetry and water immersion measurements. It was found that the intrinsic porosity of the diatomite particles with a pore size around 0.2 µm was lost at sintering temperatures above 1200 °C. Maintaining the sintering temperature at around 1000 °C resulted in highly porous materials that also displayed a high compressive strength. Microstructural studies by scanning electron microscopy and energy-dispersive X-ray analysis suggested that the pore collapse was facilitated by the presence of low melting impurities like Na2O and K2O.

  • 3. Andersson, Tobias
    et al.
    Thurley, Matthew
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Minimizing profile error when estimating the sieve-size distribution of iron ore pellets using ordinal logistic regression2011Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, nr 3, s. 218-226Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Size measurement of pellets in industry is usually performed by manual sampling and sieving techniques. Automatic on-line analysis of pellet size based on image analysis techniques would allow non-invasive, frequent and consistent measurement. We evaluate the statistical significance of the ability of commonly used size and shape measurement methods to discriminate among different sieve-size classes using multivariate techniques. Literature review indicates that earlier works did not perform this analysis and selected a sizing method without evaluating its statistical significance. Backward elimination and forward selection of features are used to select two feature sets that are statistically significant for discriminating among different sieve-size classes of pellets. The diameter of a circle of equivalent area is shown to be the most effective feature based on the forward selection strategy, but an unexpected five-feature classifier is the result using the backward elimination strategy. The discrepancy between the two selected feature sets can be explained by how the selection procedures calculate a feature's significance and that the property of the 3D data provides an orientational bias that favours combination of Feret-box measurements. Size estimates of the surface of a pellet pile using the two feature sets show that the estimated sieve-size distribution follows the known sieve-size distribution.

  • 4.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    High-pressure compaction modelling of calcite (CaCO3) powder compact2011Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, nr 3, s. 259-268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical simulation of manufacturing processes with working conditions at high pressure (above 1 GPa) requires constitutive data of the powder for the whole range of pressure and density. Most of the test apparatuses commonly used to obtain such data is only working in the lower pressure regions. Because of the absence of high-pressure data, many parameters have to be guessed or extrapolated. A material used in high-pressure applications is Calcite (CaCO3). The material can be used as an insulator in high-pressure capsules it is also a common material in the earth core. An apparatus often used to generate high pressure during compaction is the Bridgman anvil apparatus. In this work experimental tests with a Bridgman anvil set-up using Calcite powder discs with different thicknesses were done. A nonlinear elastic-plastic cap model was developed to model the behaviour of powder material from low pressure and loose state to high pressure and solid state. The constitutive model was implemented in a finite element code. The constitutive data were identified by optimization of experimental data. Validation was done by numerically reproduce the mechanical behaviour of uni-axially pressing Calcite to different pressure (up to 5 GPa) including unloading. The load-displacement curves, density distribution and the surface displacement were measured and compared to the finite element results. The results of the compaction simulations agree reasonably well with the experimental results.

  • 5. Berg, Sven
    et al.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterisation of CaCO3 powder mix for high-pressure compaction modelling2010Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, nr 2, s. 198-205Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical properties of powders at high pressures are difficult to measure and therefore such data are rarely reported in open literature. Available test equipment mainly operates in the low-pressure region, 0-200 MPa. Calcite (CaCO3) is a mineral suitable for high-pressure processes, e.g. sintering of diamond compacts. It is also a very common material in the earth core and therefore of interest for geoscientists. In order to model the processes in the high-pressure region (above 1 GPa), knowledge of the mechanical properties of the powder in the entire pressure range is needed. Experimental studies have been conducted to investigate the pressure-density relationship of a CaCO3 powder and also to correlate the relative density to elastic and strength properties using experimental results. Further, a methodology has been introduced to provide a foundation for an elastic-plastic constitutive model. The mechanical behaviour of a CaCO3 powder mix has been investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The experiments showed increasing elastic modulus and strength with increasing density. An empirical expression of the dependence of the bulk modulus on density has also been introduced.

  • 6.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterization of CaCO3powder for use in compressible gaskets up to ultra-high pressure2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 215-216, s. 124-131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this study was to investigate the compaction properties for a CaCO3 powder mix up to ultra-high pressure (10GPa) and how these properties affect the gasket behaviour. Different parameters of the powder are investigated, i.e. initial density and internal moisture. A set-up, supporting the outer diameter of the compact, commonly used for gaskets in the belt apparatus was also investigated. The experimental results are in terms of pressure instrumentation in the Bridgman anvil apparatus together with load–displacement curves of the powder compacts. The instrumentation is done so that it can be used to calibrate constitutive models.

  • 7.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Frictional behaviour of CaCO3 powder compacts2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, s. 429-434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During powder compaction processes friction has an influence on the final shape and properties of components. It is therefore important to understand how the friction influences the compaction process. Since detailed friction measurements of the powder compact-tool interface are rare, simulation models of the powder compaction process often involve a more accurate description of the frictional behaviour. This limits the accuracy of the simulated results. More accurate numerical models can give improved results, especially in regards to the evolution of density and its distribution within the powder compacts.This study is as a step towards more advanced friction models for powder compaction simulations. A universal tribometer has been used to investigate the frictional behaviour of contact interfaces between a carbide counter surface and CaCO3 powder compacts with different densities. Both static and dynamic frictional properties were measured in a variety of conditions to build a fundamental foundation for friction modelling in powder compaction simulations.The results show that increasing the powder compact density decreases the dynamic friction coefficient but that the static friction coefficient remains fairly constant. The measured friction coefficient can be used to improve the simulation of a powder compact process. Also investigated is the change in friction coefficient that occurs in the compaction process when the surfaces are worn such that loose powder appears in the interface between the tool and the powder compact. This behaviour is important to take into account to accurately describe the compaction process.

  • 8.
    Bergquist, Bjarne
    et al.
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Vanhatalo, Erik
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    In-situ measurement in the iron ore pellet distribution chain using active RFID technology2019Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    The active radio frequency identification (RFID) technique is used for in-situ measurement of acceleration and temperature in the distribution chain of iron ore pellets. The results of this paper are based on two experiments, in which active RFID transponders were released into train wagons or product bins. RFID exciters and readers were installed downstream in a harbour storage silo to retrieve data from the active transponders. Acceleration peaks and temperatures were recorded. The results imply that in-situ data can aid the understanding of induced stresses along the distribution chain to, for example, reduce pellet breakage and dusting. In-situ data can also increase understanding of product mixing behaviour and product residence times in silos. Better knowledge of stresses, product mixing and residence times are beneficial to process and product quality improvement, to better understand the transportation process, and to reduce environmental impacts due to dusting.

  • 9.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsmo, S.P.E.
    LKAB, Research & Development, 983 81 Malmberget.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Consideration of X-ray microtomography to quantitatively determine the size distribution of bubble cavities in iron ore pellets2013Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, s. 312-318Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray microtomography data of iron ore green pellets of approx. 12 mm in diameter were recorded using a commercial instrument. The reconstructed volume after thresholding represented a unique dataset consisting of a three-dimensional distribution of equiaxed objects corresponding to bubble cavities. This dataset was used to successfully validate a stereological method to determine the size distribution of spherical objects dispersed in a volume. This was achieved by investigating only a few cross-sectional images of this volume and measuring the profiles left by these objects in the cross-sectional images. Excellent agreement was observed between the size distribution of the bubble cavities obtained by directly classifying their size in the reconstructed volume and that estimated by applying the aforementioned stereological method to eight cross-sectional images of the reconstructed volume. Subsequently, we discuss the possibility of calibrating X-ray tomography data quantitatively using the size distribution of the bubble cavities as a figure of merit and the results obtained by applying the stereological method to SEM images as reference data. This was justified by considering the validity of the stereological method demonstrated by tomography, the accurate thresholding made possible by back-scattered electron imaging and the solid reproducibility of the results obtained by SEM. Using different threshold values for binarization of the X-ray microtomography data and comparing the results to those obtained by SEM, we found that X-ray microtomography can be used after proper calibration against SEM data to measure the total porosity of the bubble cavities but can only provide a rough estimate of the median diameter because of the limited resolution achieved in this study.

  • 10.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Forsmo, S.P.E.
    LKAB.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Quantitative image analysis of bubble cavities in iron ore green pellets2011Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 214, nr 3, s. 306-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scanning electron microscopy and image analysis was used for quantitative analysis of bubble cavities in iron ore green pellets. Two types of pellets prepared with and without addition of flotation reagent prior to balling were studied. The bubble cavity porosity amounted to 2.8% in the pellets prepared without addition of flotation reagent prior to balling. When flotation reagent was added prior to balling, the bubble cavity porosity increased by a factor of 2.4 and the median bubble diameter was decreased slightly. It was also shown that mercury intrusion porosimetry is not suitable for determination of the distribution of bubble cavities. Finally, our data suggested that the difference in total porosity determined by mercury intrusion porosimetry and pycnometry between the two types of pellets was due to the bubble cavities.

  • 11.
    Dobryden, Illia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yang, Xiaofang
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Weber, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    An atomic force microscopy study of the interaction between magnetite particles: the effect of Ca2 + ions and pH2013Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, s. 116-122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Force interactions between a microsize (m-s) magnetite probe and thin layers of synthesized magnetite particles as well as microsize (m-s) magnetite particles from magnetite concentrate were investigated using atomic force microscopy (AFM). Of special interest was the influence of Ca2 + ions and pH on the interaction between the probe and the two different magnetite particle surfaces. The probe and the magnetite surfaces were immersed in aqueous Ca2 + solutions (100, 10, and 1 mM) at various pH values (4, 6, and 10). The colloidal probe technique and a self-made computer program for automatic evaluation of adhesion forces were used. The analysis revealed an increase in adhesion force with increased calcium concentration at pH 6 for both the systems investigated. However, the adhesion behavior between the probe and the m-s and n-s magnetite particle surfaces is different at pH 10. The possible appearance of calcium carbonate precipitated onto the magnetite surfaces as well as the possible influence of already adsorbed silicate on magnetite particles from the concentrate is discussed. In addition to Ca, Cl and Na atoms, added to the working solutions, and the Fe and O detected signals, the SEM-EDS analysis also detected Si atoms on the surface of the m-s particles.

  • 12.
    Escalera, Edwin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ballem, Mohammed A.
    Nanostructured Materials, Department of Physics, Chemistry and Biology, Linköping University.
    Cordoba, José M.
    Nanostructured Materials, Department of Physics, Chemistry and Biology, Linköping University.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Odén, Magnus
    Synthesis of homogeneously dispersed cobalt nanoparticles in the pores of functionalized SBA-15 silica2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 221, s. 359-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cobalt nanoparticles were prepared at room temperature by reducing cobalt sulfate heptahydrate with sodium borohydride using functionalized SBA-15 mesoporous silica as a hard template. It was found that both external and internal fuctionalization of silica walls play a crucial role on the infiltration and reaction of the reagents in the silica framework. Subsequent heat treatment of the impregnated silica at 500 °C in air or nitrogen atmospheres leads to growth of crystals of the deposited cobalt and formation of cobalt oxide and cobalt nanoparticles, respectively. Dissolution of the silica template by NaOH resulted in well dispersed Co and Co3O4 nanoparticles ranging in size between 2 and 4 nm. The functionalization of the silica was studied by FTIR, N2-physisorption, and thermogravimetric techniques and the obtained nanoparticles were characterized by XRD, TEM and EDX analysis.

  • 13.
    Forsmo, Seija
    et al.
    Luleå tekniska universitet.
    Vuori, J.P.
    Helsinki University of Technology, Mechanical Process Technology and Recycling.
    The determination of porosity in iron ore green pellets by packing in silica sand2005Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 159, nr 2, s. 71-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porosity is a very important property of iron ore green pellets. At LKAB, the mercury porosimeter was replaced some years ago by the GeoPyc instrument, in which the sample volume is measured by packing in silica sand. Some critical features of the GeoPyc measurement are pointed out in this study. The green pellets need to be strengthened by spraying with a fast-drying lacquer before measurement. A system for continuous instrument control is needed to detect any wear on the measuring tools that might lead to erroneous measurement results. The reproducibility measured on steel spheres was +/- 1% (2 sigma), which is equal to the reproducibility given by the instrument manufacturer. The reproducibility measured on lacquer-strengthened green pellets used as in-house reference samples was, however, much better, 0.3% (2 sigma). The calibration error against mercury porosimetry was improved from +/- 0.6% to +/- 0.2% (2 sigma) after introducing the changes specified in the text. The GeoPyc instrument is easy to use and the problematic handling of mercury is avoided.

  • 14.
    Forsmo, S.P.E.
    et al.
    LKAB.
    Apelqvist, A.J.
    LKAB.
    Björkman, Bo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Samskog, Per-Olof
    Binding mechanisms in wet iron ore green pellets with a bentonite binder2006Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 169, nr 3, s. 147-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fundamental research during the past decade has been focussed on understanding the role of viscous forces on agglomerate deformability and strength. Much of this work has been done on glass spheres using Newtonian liquids as a binder. In this work, we show the variations in plasticity and strength of magnetite iron ore green pellets with varying liquid saturations and binder dosages (viscosities). For this purpose, a new measuring instrument was built to analyze the green pellet wet compression strength, plastic deformation and breakage pattern. Industrial iron ore green pellets are over-saturated and a supporting "network" of viscous liquid is formed on the green pellet surface. At least half, probably more, of the total binding force appeared to be due to the cohesive force of the network. The other half (or less) of the total compression strength can be explained by the capillary force. Due to irregularities on green pellet surfaces, both fully developed concave pore openings and saturated areas are expected to be found at the same time. Wet green pellets started showing plastic behaviour as they became over-saturated. In over-saturated green pellets, an explosive increase in plasticity with increasing moisture content was seen, due to the contemporary increase in porosity. Plasticity is an important green pellet property in balling and should gain the status of a standard method in green pellet characterization. It is suggested that the control strategy for the balling circuits be based on plastic deformation and compression strength of green pellets instead of the rather inaccurate drop number. The results also point out the importance of knowing whether the balling process should be controlled by adjusting the moisture content (plasticity) or by adjusting the bentonite dosage (viscosity). These two operations are not interchangeable-even if they would compensate in growth rate, the green pellet properties would differ. A new green pellet growth mechanism is suggested, based on the measured over-saturation. Firstly, green pellet plasticity needs to exceed a minimum level to enable growth. This limiting plasticity defines the material-specific moisture content needed in balling. Secondly, it is suggested that the growth rate be controlled by the viscosity of the superficial water layer rather than by the mobility of the pore water.

  • 15.
    Forsmo, S.P.E.
    et al.
    LKAB.
    Björkman, Bo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Samskog, Per-Olof
    A study on plasticity and compression strength in wet iron ore green pellets related to real process variations in raw material fineness2008Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 181, nr 3, s. 321-330Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The main binding force in wet iron ore green pellets has been found to be the cohesive force of the viscous binder. The wet compression strength (wet-CS) in green pellets is, however, also influenced by the green pellet plasticity. A certain degree of plasticity is needed to sustain the green pellet growth rate. Too much plasticity results in decreased bed permeability and production problems. As the plasticity increases, wet-CS decreases. The amount of moisture needed to create a given degree of plasticity depends on particle properties and on the particle size distribution. Therefore, it was of interest to study how wet-CS would be influenced by variations in raw material fineness, if the green pellet plasticity was kept constant, i.e. the green pellet properties would be compared under relevant industrial balling conditions. For this purpose, magnetite concentrates of different particle size distributions were balled in a laboratory drum and the moisture content for constant plasticity was determined for each of the materials. No difference in green pellet wet-CS as a function of the raw material fineness was found when the bentonite binder was used and the plasticity was adjusted to a constant level. Green pellets prepared of raw materials with narrow size distributions were just as strong as those with broader ones. This is because the main binding force is the cohesive force of the viscous binder. In green pellets balled without the bentonite binder, wet-CS increased with increasing specific surface area in the raw material, in a similar manner as has been shown in earlier agglomeration literature. In this case, the capillary forces prevail. Comparison of wet-CS at constant moisture, instead of constant plasticity, would lead to erroneous conclusions. Fineness, or rather the slope of the particle size distribution curve, had a major impact on the moisture content needed for constant plasticity. If the slope increases, more water is needed to keep the plasticity on a constant level. Implications of these results in control of industrial iron ore balling circuits are discussed.

  • 16.
    Forsmo, S.P.E.
    et al.
    LKAB.
    Forsmo, S-E
    LKAB.
    Björkman, Bo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Samskog, Per-Olof
    Studies on the influence of a flotation collector reagent on iron ore green pellet properties2008Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 182, nr 3, s. 444-452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of iron ore green pellets with varying additions of a surface-active flotation collector reagent (Atrac) were studied by small-scale balling. The compression strength and plasticity were measured with a semi-automatic measuring device and the pressure curves were saved and subjected to further mathematical treatment. The green pellet breakage was also filmed with a high-speed camera. Adding Atrac to the pellet feed seriously damaged the quality of green pellets, even in small dosages. This is because an increasing amount of air bubbles became so strongly attached on the particle surfaces that they could not be removed during compaction by balling. The adsorption of air in green pellets was seen as an increase in porosity and a decrease in the filling degree (proportion of pores filled with water). Both the wet and dry compression strength decreased. The air bubbles behaved in wet green pellets like large, plastic particles and the plasticity increased beyond an acceptable level. Breakage started inside the green pellets, along the air bubbles, and generated multi-breakage patterns in wet as well as dry green pellets. Green pellet breakage to crumbs instead of a few distinct segments, promotes the generation of dust and fines and leads to lower bed permeability in the pelletizing machine. The results show that the decrease in iron ore green pellet wet strength in the presence of surface-active agents is not fully described by the so called Rumpf equation, where surface tension and contact angle are used as variables to describe the capillary forces. The green pellet breakage in the presence of air bubbles took place by crack propagation along pore structures rather than through the loss of the capillary forces.

  • 17.
    Forsmo, S.P.E.
    et al.
    LKAB, Research & Development, 983 81 Malmberget.
    Forsmo, S-E
    LKAB, Research & Development, 983 81 Malmberget.
    Samskog, Per-Olof
    Björkman, Bo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Mechanisms in oxidation and sintering of magnetite iron ore green pellets2008Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 183, nr 2, s. 247-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermal volume changes and oxidation mechanisms in magnetite iron ore green pellets balled with 0.5% bentonite binder, as a function of raw material fineness and pellet porosity, are shown. When a pellet starts to oxidize, a shell of hematite is formed around the pellet while the core still is magnetite. Dilatation curves were measured under non-oxidizing and oxidizing atmospheres to separately describe thermal volume changes in these two phases. Dilatation measurements showed contraction during oxidation between 330 and 900 °C by 0.5%. The extent of contraction was not influenced by the raw material fineness or the original porosity in pellets. Sintering started earlier in the magnetite phase (950 °C) compared to the hematite phase (1100 °C). The sintering rate increased with increasing fineness in the magnetite concentrate. A finer grind in the raw material would, therefore, promote the formation of duplex structures with a more heavily sintered core pulling away from the less sintered outer shell. At constant porosity in green pellets, the oxidation time became longer as the magnetite concentrate became finer, because of the enhanced sintering. In practical balling, however, the increase in fineness would necessitate the use of more water in balling, which results in an increase in green pellet porosity. These two opposite effects levelled out and the oxidation time became constant when green pellets were balled at constant plasticity. Combining the results from the oxidation and dilatation studies revealed new information on the rate limiting factors in oxidation of iron ore pellets. At 1100 °C, the diffusion rate of oxygen was limited by sintering in the magnetite core, taking place before oxidation rather than by the diffusion rate of oxygen through the oxidized hematite shell, as has been claimed in earlier literature. The oxidation rate was at maximum at around 1100 °C. At 1200 °C, the rate of oxidation substantially decreased because both the hematite shell and the magnetite core show heavy sintering at this temperature. Dilatometer measurements showed large thermal volume changes in the presence of olivine, at temperatures above 1200 °C. This is explained by the dissociation of hematite back to magnetite. Dissociation leads to an increase in the volume of the oxidized shell, while sintering of the magnetite core is further enhanced by the olivine additive.

  • 18.
    Gao, Ming-Wei
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Effect of powder filling on selection and breakage functions in batch grinding1989Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 59, nr 4, s. 275-283Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of powder filling on selection and breakage functions is investigated. At three levels of powder filling, the selection functions are determined by one-size-fraction tests. The selection function decreases rapidly with increasing powder filling. When the powder filling is very low, the breakage function appears to be higher. Because of the non-normalization of the breakage function in this work a back-calculation method for determination of the breakage function is applied. For the non-normalized breakage function, if the selection function is known, it is possible to back-calculate a normalizable breakage function which gives the best simulation results. The effect of powder filling on product size distribution can be compensated by adjusting the grinding time. The material used was iron ore.

  • 19.
    Gao, Mingwei
    et al.
    Luleå tekniska universitet.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Prediction of product size distributions for a stirred ball mill1995Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 84, nr 2, s. 101-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simulation of the ultra-fine grinding process is a formidable task, attended to by many researchers using models from conventional ball mill grinding. It has been realised that the first-order breakage hypothesis is not valid in fine grinding and that the process mechanism differs substantially from that for ball mills. In this paper, the difference between ball mill grinding and stirred ball milling is discussed. A size-energy model is proposed for simulation of stirred ball milling. The product size distributions below 10 μm from a stirred ball mill were simulated by the model satisfactorily. The model is simple and has only two parameters. The model was tested under different milling conditions for a stirred ball mill.

  • 20.
    Grantham, Stephen G.
    et al.
    University of Cambridge.
    Forsberg, Fredrik
    Measurement of granular flow in a silo using digital speckle radiography2004Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 146, nr 1-2, s. 56-65Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the flow of a powder through a silo is investigated using Digital Speckle Radiography (DSR). This technique allows displacement measurements to be made on the sub-mm scale to an accuracy of 0.06 μm and a spatial resolution of 26 μm. The method performs an image cross-correlation on a random seeding of X-ray opaque material as it flows out of the silo with the powder. The flow is captured digitally using a continuous X-ray source and an image intensifier and Charge Coupled Device (CCD) camera to give real time measurements. The powder used is Al2O3 with an average particle size of 50 μm and the seeding material is tungsten powder, also with an average particle size of 50 μm. Clear flow behaviour is observed for two different sizes of outlet and the flow rate and strains occurring during the flow are also investigated.

  • 21.
    Gustafsson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Characterization modelling and validation of a two-point loaded iron ore pellet2013Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 235, s. 126-135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different stresses, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental and numerical work to investigate the mechanical properties of blast furnace iron ore pellets. To study the load deformation behaviour and the fracture of iron ore pellets, a number of point load tests are carried out and analysed. Material parameters for an elastic–plastic constitutive model with linear hardening for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. Two finite element models are developed for different purposes. For the material parameter determination, a perfectly spherical model is used. The constitutive model is validated with a finite element model based on a representative optically scanned iron ore pellet. The proposed constitutive model is capturing the force displacement relation for iron ore pellets in a two-point load test. A stress based fracture criterion which takes the triaxiality into account is suggested and calculated as the maximum equivalent effective stress dependent on the three principal stresses at fracture. The results of this study show that the equivalent effective stress in the vicinity of the centre of an irregular model of an iron ore pellet is very close to the results of a model of a perfectly spherical iron ore pellet. The proposed fracture criterion indicates fracture in the representative iron ore pellet model coincident with the location of the crack developed during the test of the optically scanned iron ore pellet.

  • 22.
    Gustafsson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Multi-particle finite element modelling of the compression of iron ore pellets with statistically distributed geometric and material data2013Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 239, s. 231-238Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The multi-particle finite element method (MPFEM) is used to simulate confined compression of iron ore pellets. The confined compression test consists of a cylindrical steel tube and two compressive platens. The iron ore pellets are confined by the tools and compressed. In the MPFEM model of the test, the iron ore pellets are represented by 1680 finite element (FE) discretised particles (7-16 mm). The size, shape and material properties of the pellets are statistically distributed. The contacts are modelled using the penalty stiffness method and Coulomb friction. The compression is simulated in two steps. In the first step, the iron ore pellet models are sparsely placed in the computational model of the steel tube and a gravity-driven simulation is conducted to make the pellets arrange themselves randomly. In a second step, the compression is simulated by a prescribed motion of the upper compressive platen. From the MPFEM simulation, the stresses inside the individual pellet models are evaluated, and the fracture probability of the iron ore pellets is derived and compared with experimental data. In addition, data on the global axial and radial stresses and axial displacement are presented and compared with experimental confined compression test data. The MPFEM model can reproduce the fracture ratio of iron ore pellets in uniaxial confined compression and is a feasible method for virtual fracture experiments of iron ore pellets.

  • 23.
    Gustafsson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments2013Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 241, s. 19-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, an experimental method for measuring the bulk properties and fracture loading relations for iron ore pellets is presented. Knowledge on the bulk behaviour and fracture data for iron ore pellets is of great importance for improving the material transportation systems and to increase the product quality. Trustworthy numerical simulations of iron ore pellets also demand reliable materials data for the models. Here, instrumented confined compression tests are carried out at different load levels. Measurement data of the axial and radial stresses and the axial displacement are recorded for each test. Measurements of fractured iron ore pellets are carried out at different loads giving rise to crushing up to 20% of the total material. From the measured data, the Poisson´s ratio, the bulk modulus and a plastic strain hardening function are determined. In addition, friction measurements of iron ore pellets are carried out at different loads and configurations. In conclusion, the test method developed here is usable for the determination of the bulk properties and fracture characteristics of iron ore pellets.

  • 24.
    Gustafsson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Experimental characterization of constitutive data of iron ore pellets2009Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 194, nr 1-2, s. 67-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For trustworthy numerical simulations of iron ore pellets flow, knowledge about the mechanical properties of pellets is needed. In this work, an elastic-plastic continuum material model for blast furnace iron ore pellets is worked out from an experimental data. The equipment used is a Norwegian simple shear apparatus, designed for compression and shear test of granular material with a grain size less than 100 mm. It consists of a cylindrical cell filled with pellets surrounded by a rubber membrane and a rigid top and bottom. Two types of tests are performed. One test is pure compression and unloading and the second is shearing at different stress levels. Evaluation of these tests is performed and the elastic-plastic behaviour of iron ore pellets is characterized. Determined constitutive data are two elastic parameters and a yield function. The presented material model captures the major characteristics of the pellets even though it is too simple to completely capture the complex behaviour shown in the experiments.

  • 25.
    Gustafsson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kato, Hidinori
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ogura, Takashi
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Experimental studies and modelling of high-velocity loaded iron-powder compacts2014Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 268, s. 293-305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A production technique with the capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts is high-velocity compaction (HVC). To extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate the development of production processes, numerical simulations can be utilised. In the development of high-precision simulation models, constitutive data of HVC specimens at high strain rates are required. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a split Hopkinson pressure bar (Kolsky bar) assembly. For this technique, a specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of the input bar and generates elastic-wave propagation.The powder material used for the experiments is a press-ready iron-based premix. Among specimens made by HVC and conventional compaction (CC), the effects of the specimen density and the strain rate on the compressive properties, such as failure stress, Young´s modulus and failure behaviour, are investigated. During dynamic compression, the failure behaviour of the specimens was also recorded using a high-speed video camera. The difference in the mechanical behaviour between HVC-pressed specimens and conventionally pressed specimens are also investigated. The stress–strain curves of HVC-pressed specimens are identical to those of conventionally pressed specimens, but the failure behaviour differs are concluded.A well-established numerical method for forming simulations also conducted for powder compaction is the finite element method (FEM). The impact loading of the powder is modelled and simulated using nonlinear three-dimensional FEM. To model the impact process, a constitutive relation for the powder behaviour is proposed, taking into account the strain rate and density variations. To capture the global response caused by cracking during impact, a damage model is implemented. The numerical results in terms of the stress and strain history in the specimen during impact are compared with the experimental measurements. In conclusion, the proposed material model captures the increase in the yield stress due to the higher strain rates and the decrease in stress due to cracking.

  • 26.
    Hazim, Ammar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Göktepe, Burak
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Active fuel particles dispersion by synthetic jet in an entrained flow gasifier of biomass: Cold flow2016Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 302, s. 275-282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulverized fuel (PF) burners play a key role for the performance of PF fired gasification and combustion plants, by minimizing pollutant emission, fuel consumption and hence fuel costs. However, fuel diversity in power generation plants imposes limitations on the performance of existing PF burners, especially when burning solid fuel particles with poor flowability like biomass sawdust. In the present study, a vertically downward laminar flow was laden with biomass particles at different particle mass loading ratios, ranging from 0.47 to 2.67. The particle laden flow was forced by a synthetic jet actuator over a range of forcing amplitudes, 0.35–1.1 kPa. Pulverized pine particles with a sieve size range of 63–112 μm were used as biomass feedstock. Two-phase particle image velocimetry was applied to measure the velocity of the particles and air flow at the same time. The results showed that the synthetic jet had a large influence on the flow fields of both air and powdered pine particles, via a convective effect induced by vortex rings that propagate in the flow direction. The particle velocity, particle dispersion and hence inter-particle distance increased with increasing forcing amplitude. Moreover, particles accumulated within a specific region of the flow, based on their size. The effect on particle dispersion was more pronounced in the forced flows with low mass loading ratios

  • 27. He, Mingzhao
    et al.
    Wang, Yanmin
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Parameter effects on wet ultrafine grinding of limestone through slurry rheology in a stirred media mill2006Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 161, nr 1, s. 10-21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wet ultra-fine grinding of a limestone powder ( less than or equal 100 μm) has been investigated in a stirred media mill with respect to the effect of slurry rheology. The grinding results obtained by various parameters (i.e., molecular weight of a dispersant, solids concentration, additive dosage, addition method and beads load) are evaluated in terms of energy efficiency and the fineness of a product. A polymeric dispersant called Dispersant S40 with a molecular weight of 5500 gives the best grinding results. For a certain level of beads load, an optimal solids concentration exists. In the case of the additive dosage of Dispersant S40 at 0.1 wt.% or more, a smaller additive amount of Dispersant S40 gives a higher energy efficiency and a smaller median size at a lower level of specific energy input. However, the excessive amount of the dispersant could cause a cushion layer formed on milling beads and thus lowers stress intensities from the collisions of milling beads, leading to an inefficient milling operation. This can be avoided by either the multi-point addition of the dispersant or a higher beads load ( greater than or equal 83 vol.%). In addition, it was found that the higher the beads load, the better the cumulative energy efficiency, and the smaller the product size at the same specific energy consumption. For a given solids concentration, the relationships between the specific surface area and the particle size of an FP product and the additive amount of Dispersant S40 are explored, respectively. Furthermore, an empirical particle size-energy model provides a good fit (R2 > 0.991) to the grinding results under the experimental conditions investigated.

  • 28. He, Mingzhao
    et al.
    Yanmin, Wang
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Slurry rheology in wet ultrafine grinding of industrial minerals2004Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 147, nr 1-3, s. 94-112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wet ultrafine grinding has been increasingly used for production of ultrafine powders in various industries. It has been known that slurry rheology significantly influences the grindability of industrial minerals in wet ultrafine grinding. This review represents some previous work with respect to slurry rheology in ultrafine grinding. In this review, some methods for the characterization of the slurry rheology and some empirical equations modelling rheological behaviours of slurries were presented. The semiempirical model incorporating slurry rheology, solids concentration, particle size and slurry temperature was described. In addition, on-line measurement for the slurry rheology control was also discussed. In the case of ultrafine grinding, various parameters (such as solid concentration, particle size and distribution, particle shape, temperature, rotation and pH, use of dispersants), which affect the slurry rheology, have been described. It was revealed that the optimization of the rheological behaviours of slurry in ultrafine grinding could increase throughput, energy efficiency and product fineness as well. It is suggested to further study the mechanisms of slurry rheology in the presence of chemical dispersants in wet ultrafine grinding. It is desired to develop a model, which can represent a relation among slurry rheology, comminution parameters, amount of dispersant, energy efficiency and particle size characterization.

  • 29.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Constitutive models for powder materials1991Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 67, nr 2, s. 127-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Constitutive models to describe the mechanical material behaviour of hardmetal powders are studied. Three classes of constitutive relationships are examined, described as cap plasticity, multisurface plasticity and endochronic plasticity. A representative model of each class is studied in detail, An optimization technique is used to fit the constitutive parameters to empirical test data on multiaxially loaded hardmetal powder specimens. Of all models tested, an endochronic model proposed by Bazant shows the best agreement with the empirical test data. Different phenomena can be simulated with the model by adding certain constitutive functions. It is, however, difficult to fit the model to test data because of the large number of model parameters, most of which have no physical meaning

  • 30.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Hockauf, Matthias
    Luleå tekniska universitet.
    Eriksson, Mikael
    Swedish Ceramic Institute.
    Berggren, Carina
    Nobel Biocare AB.
    Simulation of high velocity compaction of powder in a rubber mould with characterization of silicone rubber and titanium powder using a modified split Hopkinson set-up2005Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 154, nr 1, s. 33-42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper introduces a method for characterization of silicone rubber and titanium powder in high velocity compaction using the split Hopkinson set-up. The impact test data has been used to estimate parameters in constitutive models for rubber and powder. A finite element study has been performed with different geometrical design of the high velocity compaction of titanium powder against an aluminium mandrel using a rubber mould as pressing medium. One goal of this study is to investigate if and how the manufacturing method can be applied for making dental copings. A conclusion of the experimental work is that it is possible to characterize rubber material and powder material for high velocity compaction of metal powder by the use of a modified split Hopkinson pressure bar set-up. The numerical simulation shows qualitatively good agreement with the experience from practical tests. In conclusion, the work shows the possibility to numerically study the geometric design and to optimize the densification behaviour of a complex high velocity compaction process.

  • 31.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Modelling and numerical investigation of the residual stress state in a green metal powder body2005Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 155, nr 3, s. 196-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Die pressing of metal powder results in a green body. After release from the die, the green body must have enough strength to be handled, to endure transport to a sintering furnace and heating to the sintering temperature. Drilling, turning and milling, which are common operations in the green state, require a green body of high strength, with no defects and excellent mechanical properties. A plane strain finite element model is used to analyse pressing of metal powder into a rectangular bar. The powder behavior is described by a "cap" model, which is implemented as a user material subroutine in the non-linear finite element program LS-DYNA. To improve modelling of strength in the green state a new non-linear density dependent failure envelope has been used. The model is adjusted to the properties of a water atomised metal powder from Hoganas AB. To resolve the severe stress gradient at the side surface of the green body, the smallest element size was chosen to be 65 μm. The aim of this work is to numerically capture and understand the development of the residual axial stress in particular at the side surface. The influence of kinematics, friction, compacting pressure and die taper are studied. Results from the numerical study show that the thickness of the compressive stress region close to the side surface of the green body varies between 50 μm and 600 μm along the surface. Compacting pressure, "upper punch hold down" and die taper geometry all have a significant influence on the residual stress state while die wall friction has only a small influence. The numerical results are in agreement with results from X-ray and neutron diffraction measurements.

  • 32.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gustafsson, Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling the non-linear elastic behaviour and fracture of metal powder compacts2015Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 284, s. 496-503Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the powder metallurgy (PM) pressing process the mechanical properties of the green body are highly dependent on the material density. During the ejection stage of the pressing process the elastic behaviour is important especially for the crack formation in the powder compact. Experiments show a non-linear and also stress dependent elastic behaviour of green bodies. In this study diametral compression tests have been used to study elastic deformation during crack formation in a tensile fracture process of metal powder discs compacts. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite (uf-4) and 0.6% Kenolube. Tensile strength is used as a failure condition and limits the stress in the fracture interface. To control the tensile fracture, a cohesive zone model is used. The softening rate of the fracture model is obtained from the corresponding rate of the dissipated energy. The deformation of the powder material is modelled with an elastic-plastic cap model where an easy-to-use model for non-linearity in the elastic state due to stress is presented. The model is implemented in a finite element code and tested in simulation of a diametral compression testing. Results from simulations correlates well with experimental results and demonstrates the importance of including the non-linear elastic effect of the powder compacts. Results also show the necessity to accurate model the elasticity in the tooling to correct capture force-displacement response and fracturing processes.

  • 33.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Sommer, Kristin
    Tensile strength and fracture energy of pressed metal powder by diametral compression test2007Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 176, nr 2-3, s. 148-155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A critical property in the metal powder pressing process is the strength of the green body. Diametral compression test or the Brazilian disc test is one method to characterise green tensile strength. Pre-alloyed water atomised iron powder has been pressed into discs with different densities. The characteristics of the fracture development and load response are studied in detail. Crack initiation and the tensile fracture process of pressed metal powder discs are studied. Methods to determine the tensile strength and fracture energy of pressed metal powder are presented. A cohesive material behaviour is found in the experiments. Both tensile strength and fracture energy are strongly dependent on density in the measured range.

  • 34.
    Kaialy, Waseem
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Alhalaweh, Amjad
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Velaga, Sitaram
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Nokhodchi, Ali
    Chemistry and Drug Delivery Group, Medway School of Pharmacy, University of Kent.
    Influence of lactose carrier particle size on the aerosol performance of budesonide from a dry powder inhaler2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 227, s. 74-85Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this study was to evaluate the effect of carrier particle size on properties of dry powder and its effect on dry powder inhaler (DPI) performance. Commercial α-lactose-monohydrate, a commonly used carrier in DPI formulations, was carefully sieved to obtain different lactose size fractions, namely Lac A (90–125 μm), Lac B (63–90 μm), Lac C (45–63 μm), Lac D (20–45 μm), and Lac E (< 20 μm). The lactose samples were analysed in terms of size, shape, solid state, density, and flowability. Lactose particles were blended with budesonide (< 5 μm) powder to generate five different formulations. These formulations were then evaluated in terms of budesonide-lactose adhesion properties, drug content homogeneity, and in vitro aerosolisation performance. The results demonstrated that lactose samples with smaller particle volume mean diameter have higher amorphous lactose content, higher true density (linear, r2 = 0.9932), higher surface smoothness (linear, r2 = 0.8752), smaller angularity (linear, r2 = 0.921), smaller bulk density, higher porosity (linear, r2 = 0.914), poorer flowability, and higher specific surface area. In general, the smaller the lactose particles the smaller are the budesonide-lactose adhesion properties. Budesonide formulated with smaller lactose particles exhibited smaller aerodynamic diameter and higher amounts of budesonide were delivered to lower stages of the impactor indicating improved DPI aerosolisation performance. However, the use of lactose particles with smaller volume mean diameter had a detrimental effect on budesonide content homogeneity and caused an increase in the amounts of budesonide deposited on oropharyngeal region. Therefore, particle size of the lactose within dry powder inhaler formulations should be selected carefully. Accordingly, higher drug aerosolisation efficiency of lactose particles with smaller size may have to be balanced due to considerations of other disadvantages including poorer flowability, reduced formulation stability, higher potential side effects, and higher dose variability.

  • 35.
    Karlsson, Tomas
    et al.
    Luleå tekniska universitet.
    Klisinski, Marek
    Luleå tekniska universitet.
    Runesson, K.
    Chalmers University of Technology.
    Finite element simulation of granular material flow in plane silos with complicated geometry1998Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 99, nr 1, s. 29-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model with few material parameters is proposed for finite element simulation of the transient flow of cohesionless granular materials in silos. The constitutive model used is essentially a fluid model and, consequently, it is best established in the Eulerian format. The model allows the simulation of initial stress transients at the beginning of the discharging process. After long time, when the solution approaches steady state, the flow pattern that is developed represents either a mass or funnel flow situation. Numerical examples of transient stress fields are given, and the flow patterns in advanced silo geometries are studied. The numerical results are in good agreement with analytical solutions and experiments known from the literature

  • 36.
    Malm, Lisa
    et al.
    Boliden Mineral, Department of Process Technology, Boliden, Sweden.
    Sand, Anders
    Boliden Mineral, Department of Process Technology, Boliden, Sweden.
    Bolin, Nils-Johan
    Boliden Mineral, Department of Process Technology, Boliden, Sweden.
    Rosenkranz, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Ymén, Ingvar
    RISE- Research Institutes of Sweden AB, Bioscience and Materials/Surface, Process and Formulation, Sweden.
    Dynamic vapor sorption measurement and identification of mineral species in industrial-scale flotation cell samples2019Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 356, s. 1016-1023Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to understand flotation performance in industrial-scale, it is of relevance to understand the surface properties and mineral species of materials contained in the various parts of the cell. In this work XRPD X-Ray Powder Diffraction) and DVS (Dynamic Vapor Sorption) were used to characterise the different minerals and the wettability of the sample collected at different depths in an industrial scale flotation cell.

    DVS is a novel technique for wettability measurement in mineral processing, of higher robustness and reproducibility compared to the Washburn technique.

    In the turbulent zone of the cell, the wettability properties are relatively similar, and decreases in the froth and concentrate. Differences in radial position were only found near the froth phase close to the shaft of the agitator.

    The main finding was that wettability information obtained by DVS could be correlated with mineral composition and particle size distribution.

  • 37.
    Mangalaraja, R.V.
    et al.
    University of Concepción.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Hedström, Peter
    Camurri, C.P.
    University of Concepción.
    Ananthakumar, S.
    Université Montpellier.
    Odén, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microwave assisted combustion synthesis of nanocrystalline yttria and its powder characteristics2009Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 191, nr 3, s. 309-314Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microwave assisted combustion synthesis is used for fast and controlled processing of advanced ceramics. Single phase and sinter active nanocrystalline cubic yttria powders were successfully synthesized by microwave assisted combustion using the organic fuels urea, citric acid and glycine as reducing agents. The precursor powders were investigated by thermogravimetry (TG) and differential scanning colorimetry (DSC) analyses. The as-prepared precursors and the resulting oxide powders calcined at 1100 °C in oxygen atmosphere were characterized for their structure, particle size and morphology. The thermal analyses (TG/DSC), X-ray diffraction (XRD) and Fourier transform infra red (FT-IR) results demonstrate the effectiveness of the microwave assisted combustion synthesis. The scanning electron microscopy (SEM) observations show the different morphologies of as-prepared powders and transmission electron microscopy (TEM) shows the particle sizes in the range of 30-100 nm for calcined powders for different fuels. The results confirm that the homogeneous, nano scale yttria powders derived by microwave assisted combustion have high crystalline quality and the morphology of the as-prepared precursor powders depends on the nature of organic fuel used.

  • 38.
    Misiulia, Dzmitry
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effects of the inlet angle on the collection efficiency of a cyclone with helical-roof inlet2017Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 305, s. 48-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of inlet angle on the collection efficiency of a cyclone with helical-roof inlet have been computationally investigated using Large Eddy Simulations with the dynamic Smagorinsky-Lilly subgrid-scale model for five different inlet angles (7°, 11°, 15°, 20° and 25°). Forty thousand individual particles were tracked through the unsteady flow field using the Lagrangian approach. In order to reveal the collection efficiency of a cyclone with helical-roof inlet properly, simulation time should not be < 3.5 times the average flow residence time. Particles which diameter is close to the cyclone cut size have the longest residence times while particles of 10–25 μm in diameter have the shortest. Based on the simulations, expressions for the cut size and Euler number normalized with the mean axial velocity in a cyclone with helical-roof inlet of different inlet angles are derived. The results show that, increasing the inlet angle increases the cyclone cut size and as a result reduces cyclone collection efficiency. At the same time, it decreases the cyclone pressure drop coefficient (Euler number) leading to lower pressure losses. For most cases where high separation efficiency at moderate pressure drop is required the optimum inlet angle is in the range 10–15°.

  • 39.
    Misiulia, Dzmitry
    et al.
    Department of Machines and Apparatus for Chemical and Silicate Production, Belarusian State Technological University, Minsk, Belarus.
    Antonyuk, Sergiy
    Institute of Particle Process Engineering, University of Kaiserslautern, Kaiserslautern, Germany.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    High-efficiency industrial cyclone separator: A CFD study2019Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flow within an industrial scroll-inlet high-efficiency cyclone separator has been studied using RSM and LES simulations. Of particular interest is the effect of the gas outlet configuration, i.e. outlet scroll and radial bend, on the flow pattern, pressure drop and cyclone efficiency. A surprising phenomenon is that the inner vortex splits into two vortices for the cyclone with a conventional outlet pipe while if the cyclone is equipped with an outlet scroll or radial bend there is no split. The outlet scroll and radial bend increase the pressure losses by 5.1% and 6.4%, respectively. These installations, moreover, significantly destabilize the pressure losses and the amplitude of instantaneous pressure drop oscillations increases from 0.65% to 16.2% and 33.96%, respectively. The investigated outlet scroll and radial bend have practically no effects on the cyclone efficiency since the flow in the main separation zone is not affected by the gas outlet configuration.

  • 40.
    Misiulia, Dzmitry
    et al.
    Department of Machines and Apparatus for Chemical and Silicate Production, Belarusian State Technological University.
    Antonyuk, Sergiy
    Institute of Particle Process Engineering, University of Kaiserslautern.
    Andersson, Anders Gustav
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Tord Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effects of deswirler position and its centre body shape as well as vortex finder extension downstream on cyclone performance2018Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 336, s. 45-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The performance of a cyclone is studied when changing the position of the deswirler in the vortex finder, its centre body shape and a downstream vortex finder extension. This is done with simulations applying a Reynolds stress model for the turbulence. An extension of the vortex finder (from 2.64 dvf to 6.8 dvf) has almost no effect on cyclone pressure drop or collection efficiency. Moreover, the extension does not affect the pressure losses in the vortex finder. The closer the deswirler is installed to the vortex finder inlet the more significant is its effects on cyclone performance. A streamlined ellipsoidal shape of the deswirler centre body is preferable to a cylindrical one since it leads to lower pressure losses. Installation of the deswirler with a streamlined ellipsoidal centre body 2.64 diameters downstream the vortex finder inlet reduces pressure losses in the vortex finder by 74% as compared to a standard set-up. This leads to a 32% reduction in total pressure drop without deteriorating the separation capability of the cyclone.

  • 41. Mouzon, Johanne
    et al.
    Odén, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Alternative method to precipitation techniques for synthesizing yttrium oxide nanopowder2007Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 177, nr 2, s. 77-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Yttrium oxide nano-powder has been successfully synthesized by a novel approach. In the first step, a foamy structure was produced by combustion synthesis using yttrium nitrate and glycine. This was followed by the addition of sulfate ions and calcination at 1100 °C for 4 h. The sulfated and unsulfated powders were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller method (BET). The sinterability of the resulting powders was also studied by dilatometry. The studies indicated that this method not only allows for producing weakly-agglomerated nano-particles, but is also a very time-efficient process in comparison to precipitation techniques. Moreover, the possibility of performing all processing steps in a fully automated batch reactor was also considered.

  • 42.
    Orumwense, Osawaru A
    Luleå tekniska universitet.
    Kinetics of fine grinding in an annular ball mill1992Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 73, nr 2, s. 101-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The grinding principles of the annular ball mill were studied using the mass balance approach. Heterogeneous breakage rate was the characteristic behaviour observed. The non-linearity arises partly from the operating parameters, the slurry rheology and the spatial distribution of particles. The degree of non-linearity could be minimised in some cases by careful choice of the operating conditions. The breakage functions were usually observed as non-normalisable. The comminution products were simulated using the kinetic parameters obtained by a simple linear approximation technique. Fairly good correlation was obtained between the experimental and the calculated product size distributions

  • 43.
    Orumwense, Osawaru A
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Surface and structural changes in wet ground minerals1991Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 68, nr 1, s. 23-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of mill type, specific surface area and dispersants on the crystal lattice and surface properties as deduced from X-ray analysis of wet-milled dolomite, calcite and quartz are discussed. The structural characteristics of powders produced by grinding in both the CoBall and low amplitude Vibro-energy mills are similar, and differ only where the particle size difference is appreciable. Peak intensity reduction and a slight line broadening appear to be the common X-ray diffraction characteristics of the three wet-milled minerals. The lubrication action and enhanced heat conduction of a wet grinding environment are possibly responsible for the differences observed in the crystal habits of wet- as compared to dry-ground minerals.

  • 44.
    Parian, Mehdi
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Mwanga, Abdul
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Lamberg, Pertti
    Keliber Oy, Kaustinen.
    Rosenkranz, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Ore texture breakage characterization and fragmentation into multiphase particles2018Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 327, s. 57-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ore texture and the progeny particles after a breakage in the comminution have been a subject of interest in mineral liberation studies and are the missing link between geology and mineral processing in the concept of geometallurgy. A new method called Association Indicator Matrix (AIM) established based on co-occurrence matrix was introduced to quantify the mineral association of ore texture and its progeny particles. The Association Indicator Matrix can be used as a criterion for classifying ore texture as well as analyzing breakage behavior of ore texture. Within the study, the outcome of breakage analysis with Association Indicator Matrix was used to forecast particle population of iron ore texture after crushing. The particle size of forecasted particles was taken from experimental and frequency of breakage in phases was defined based on Association Indicator and liberation of minerals. Comparison of liberation distribution of iron oxide minerals from experimental and forecasted population shows a satisfactory agreement.

  • 45. Pourghahramani, Parviz
    et al.
    Altin, Erguen
    Institute of Particle Technology, Friedrich-Alexander University, Cauerstr. 4, D-91058 Erlangen.
    Mallembakam, Madhusudhan Rao
    Institute of Particle Technology, Friedrich-Alexander University, Cauerstr. 4, D-91058 Erlangen.
    Peukert, Wolfgang
    Institute of Particle Technology, Friedrich-Alexander University, Cauerstr. 4, D-91058 Erlangen.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Microstructural characterization of hematite during wet and dry millings using Rietveld and XRD line profile analyses2008Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 186, nr 1, s. 9-21Artikel i tidskrift (Refereegranskat)
  • 46. Pourghahramani, Parviz
    et al.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Changes in the structure of hematite by extended dry grinding in relation to imposed stress energy2007Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 178, nr 1, s. 30-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of extended dry milling in different mills on the structural changes of hematite concentrate has been investigated using a combination analysis of XRD line broadening, BET and particle size measurements. Structural changes were followed by XRD line broadening analysis using integral breadth method and Warren–Averbach approach. For analysis, the stress energy was estimated by considering different grinding variables in different mills and changes in the structure discussed in terms of stress energy. Within comparable range of stress energy, lower BET surface area was produced by grinding in the vibratory mill. The maximum surface area increased to 18,400 m2/kg in the vibratory mill after releasing 51,300 kJ/kg energy. The conversion of the 80% of initial hematite to amorphous phase during extended dry grinding by tumbling, planetary and vibratory mills, needs 4000, 8500 and 50,000 kJ/kg energy respectively. It was understood that vibratory mill introduces the minimum lattice strain and gives the largest crystallites when applying the same level of stress energy. The smallest crystallites with grinding in tumbling, vibratory and planetary mills were obtained about 17.3, 13.5 and 5.6 nm after releasing 5230, 51,300 and 15,600 kJ/kg respectively. For these levels of stress energy, in turn, the microstrain <εL=10 nm2>1/2 exceeds 4.4 × 10− 3, 3.9 × 10− 3 and 5.3 × 10− 3. It was further revealed that higher concentrations of defects (Amorphization and excess energy) per unit surface area were induced by grinding in the planetary and tumbling mills. A theoretical calculation of the energy contribution to the long-lived defects indicated that products from tumbling and planetary mills have higher excess energy compared to the products from vibratory mill for the same stress energy. The maximum theoretical excess energy was estimated about 75.4, 80.0 and 81.3 kJ per mole of the ground hematite with tumbling, vibratory and planetary mills after releasing 5230, 51,300 and 15,600 kJ/kg of stress energy respectively. Grinding in vibratory mill needs much more energy to reach the same effect as the other used mills. A comparison of specific energy input and stress energy among the used mills points out that for generation of the same levels of stress energy, the planetary mill consumes more energy than the other used mills.

  • 47.
    Raudoniene, Jolanta
    et al.
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Skaudzius, Ramunas
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Zarkov, Aleksej
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Selskis, Algirdas
    Center for Physical Sciences and Technology, Vilnius, Lithuania.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Kareiva, Aivaras
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius, Lithuania.
    Garskaite, Edita
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Wet-chemistry synthesis of shape-controlled Ag3PO4 crystals and their 3D surface reconstruction from SEM imagery2019Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 345, s. 26-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple chemical solution-based synthesis route has been developed to prepare uniform and shape-controllable Ag3PO4 crystals. Tetrapod- and cube-shaped crystals having a size of about 9–10 μm were prepared from AgNO3 and NH4H2PO4 precursors, and pseudo-octahedral (equiaxial) crystals were prepared from AgNO3 and (NH4)2HPO4. TEM analysis revealed Ag3PO4 crystals to be electron beam sensitive materials, which under a voltage of 200 kV decompose to the metallic Ag, thereby demonstrating the difficulty in determining crystal facets and structural defects using conventional electron diffraction studies. UV–Vis diffuse reflectance spectroscopy was used to study the correlation between structural and optical properties of surfaces of Ag3PO4 crystals. Furthermore, a spatial 3-dimentional (3D) reconstruction of Ag3PO4 surface structures was performed from SEM images. The reconstruction produced realistic 3D mesh models, insomuch that the 3D reconstructed structures provided extra information about the examined crystals. Results suggested that the proposed synthesis route and performed spatial reconstruction of Ag3PO4 had the potential for simulating processing conditions to produce various microcrystals and explore material surface structures and reconstruction of microstructures.

  • 48.
    Sellgren, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Addie, Graeme
    GIW Industries Inc..
    Cost-effective pumping of coarse mineral products using fine sands1997Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 94, nr 3, s. 191-194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coarse mineral particles with sizes of up to 200 mm can be pumped energy-effectively together with sands (< 1 mm) under nearly pseudohomogeneous conditions at volumetric solids concentrations of up to 40%. Recent experimental results indicate that particles with sizes of 0.1-0.5 mm play an important role in reducing pipe wall friction. Experimental results in pipelines with diameters of up to 0.44 m have here been used in a brief demonstration of industrial applications: integrated systems for waste rock transportation together with fine-grained tailings, coarse mineral particle pumping from open-pit mines or to disposal with dry deposition and recirculation of water and fine particles. Experiments with a crushed rock product (20-38 mm) pumped at a volumetric concentration of 13% showed that the friction losses were reduced considerably by particle degradation during the circulation in the pipeline loop. Circulatory effects must therefore be carefully considered when using coarse-particle loop results in the design of industrial once-through systems

  • 49.
    Sepman, Alexey
    et al.
    RISE ETC AB.
    Ögren, Yngve
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wiinikka, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Optical techniques for characterizing the biomass particle flow fluctuations in lab- and pilot-scale thermochemical systems2017Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 313, s. 129-134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The work demonstrates the performance of the optical extinction technique for real-time diagnostics of the fluctuations in biomass particle flows. The online measurements of fluctuations of density were used to determine the biomass particle mass flow fluctuations. Biomass flows were produced using laboratory biomass particle feeder (mass flux up to 10 g/min) and the hopper-screw feeding system of the pilot-scale entrained flow rector, mass flux up to 500 g/min, located at SP ETC in Piteå. The experiments showed that the time-averaged extinction appeared to be linearly related to the real particle mass flow. The relatively fast variations in biomass feeding rates measured using the extinction technique were confirmed by fast balance measurements (in laboratory feeder experiments) and by real-time tunable diode laser CO and H2O concentrations measured in the reactor core of the entrained flow gasifier.

  • 50.
    Sivamohan, R.
    et al.
    Luleå tekniska universitet.
    Vachot, P.
    Comparative study of stirred and vibratory mills for the fine grinding of muscovite, wollastonite and kaolinite1990Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 61, nr 2, s. 119-129Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Muscovite, wollastonite and kaolinite were wet attrition ground in a pilot stirred ball mill (continuous type) as well as a vibratory mill (batch type). The objectives were to compare the two mills' ability to meet a given specification, study process variables' effects in the case of muscovite and wollastonite, and achieve delamination in the case of muscovite. It is shown that the vibratory mill (SWECO) is less efficient than the stirred mill (DRAIS), at least when 12-mm media are used in SWECO. The highest performance of DRAIS is reached when using a low amount of polymer-type dispersant (0.35 g/100 g solids) and a low pulp density (12 wt.% solids) for muscovite. Bead size had no influence under the experimental conditions, but the bead charge had a strong positive influence. With wollastonite, the smaller grinding media (0.3 - 0.4 mm) and a low pulp density (25 wt.% solids) led to the best efficiency. A low amount of polymer-type dispersant and higher amounts of beads in the mill had a strong positive influence

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