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  • 1.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Braviken Paper Mill, Holmen Paper, SE-60188 Norrkoping, Sweden.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Low-consistency refining of mechanical pulp in the light of forces on fibres2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 225-229Article in journal (Refereed)
    Abstract [en]

    The aim of this investigation was to find new approaches to evaluate the performance of low-consistency refiners. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the zones in a TwinFlo refiner. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to increase approximately linearly with decreasing disc gap over the range, 0.1-0.2 mm. The power split was essential to know for calculating refining intensities expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap or at 0.03 N forces on fibres or at 0.7 J/m specific edge load. Disc gap, forces on fibres and specific edge load was found to predict fibre shortening approximately equally upon changes in power and flow rate through the refiner.

  • 2.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Braviken Paper Mill, Sweden.
    Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    LC Refining Intensity In The Light Of Forces On Fibres2014In: International Mechanical Pulping Conference, IMPC 2014, Espoo: Paper Engineers' Association (PI) , 2014Conference paper (Refereed)
    Abstract [en]

    The aim of this investigation was to find new approaches to evaluate the performance of a full sized two-zoned low-consistency refiner i.e. a refiner with two stators and one rotor in between. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the two zones. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to correlate approximately linearly with the disc gap. The power split was essential to know for calculating refining intensity expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap corresponding to 0.03 N force on fibres and 0.7 J/m specific edge load. Disc gap, force on fibres and specific edge load was found to predict the fibre shortening with approximately equal sufficiency upon changes in power and flow rate through the refiner.

  • 3.
    Björkqvist, T.
    et al.
    Department of Automation Science and Engineering, Tampere University of Technology, P.O.B 692, FIN-33100 Tampere, Finland.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Salminen, L. I.
    VTT Technical Research Center Finland, P.O.B. 1000, FIN-02044 VTT, Finland.
    Salmi, A.
    VTT Technical Research Center Finland, P.O.B. 1000, FIN-02044 VTT, Finland.
    Towards optimal defibration: Energy reduction by fatiguing pre-treatment2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 168-172Article in journal (Refereed)
    Abstract [en]

    A motive for fatiguing wood prior to defibration would be to reduce the energy consumption needed in mechanical pulping processes. Therefore, the effects of fatiguing pre-treatment were here studied on wood samples, on defibration and also on produced paper. The results indicate that pre-fatiguing changes the mechanic response of wood to be more favorable for harsh defibration which in turn is positive for the process efficiency.

  • 4.
    Engberg, Birgitta Anna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Salminen, Lauri I
    KCL, Helsinki, Finland.
    Salmi, Ari
    Helsinki University, Finland.
    Björkqvist, Tomas
    Tampere University of Technology.
    On the importance of fatigue for the rheological properties of wood2009In: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009, 2009, p. 239-244Conference paper (Refereed)
    Abstract [en]

    In this study the rheological properties of both native and fatigued wood was quantified under conditions relevant to mechanical pulping. This work was part of a Nordic cooperation project on "Basic phenomena in mechanical pulping. The new knowledge is intended to give us guidance on process development in mechanical pulping. The recent EES-concept [1] is assumed to offer low specific energy consumption mostly because of wood fatigue. A modulated loading device (MLD) developed at KCL was here used to fatigue wood samples. The samples were then evaluated by impulsive loading experiments carried out in an encapsulated Split-Hopkinson device (ESHD) developed at Mid Sweden University. Impulsive loadings, which extended to the non-elastic deformation region, were performed at four temperatures: 20, 65, 100 and 135°C. A higher testing temperature softened the wood samples to a high extent as could be expected. The results show that the reference samples (that was not subjected to fatigue treatment) had the highest stiffness in the investigation. The stress-strain curves of the fatigued samples were less steep, which indicate a softer more loosened material. It was evident that the fatigue treatment had loosened or weakened the wood material considerably and the differences were most pronounced at the two lowest testing temperatures.

     

     

  • 5.
    Engberg, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    A comparative study of models describing high consistency refining2011In: Proceedings of International Mechanical Pulping Conference, Pulp and Paper Technical Association of Canada, 2011, p. 96-100Conference paper (Refereed)
    Abstract [en]

    By using the same selected input data in three different refining models the model predictions could be compared both in relation to each other and related to experimental data. Predictions delivered by the Miles and May model deviated most from the estimates based on measured values. The fluid dynamical model and especially the entropy model showed good agreement both when it came to describing the specific energy distribution and the local refining intensity distribution over the refining radius. However, the entropy model had problems with predicting the mean fibre velocity close to the refiner inlet while the fluid dynamical model had a tendency to overestimate the fibre velocity when approaching the periphery. In conclusion, the models

    could deliver realistic estimates. Still, the models need to be developed to be able to depict refining actions even better. To validate new or improved models, more research involving measurements from refiner gaps are needed.

  • 6.
    Engberg, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Logenius, Louise
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Mechanical properties of sulphonated wood in relation to wing refiner properties2014In: International Mechanical Pulping Conference, IMPC 2014, Espoo: Paper Engineers' Association (PI) , 2014Conference paper (Other academic)
    Abstract [en]

    To reach maximum effect of different pretreatments we need to know how wood properties can be changed and how this can be related to both refining conditions and pulp characteristics. To understand how the material properties were affected, sulphonated wood samples were tested using several new testing techniques. The data was correlated to pulp properties of batch refined chips to learn more how the initial defibration mechanisms and pulp properties were affected by the pretreatments.

  • 7.
    Engstrand, Per O.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Filling the Gap - Final Report2014Report (Other academic)
    Abstract [en]

    Executive Summary

    As energy prices continue to rise long-term it is very important to come up with suggestions toefficiency-improving solutions based on modifications of the existing refining technology withoutlarge investments. There are several suggestions to relatively large modifications of processsolutions, in design of refiner plate patterns, chip pre-treatment and chip feed strategies to existingrefiners, but these suggestions are often expensive and difficult to implement as the knowledge ofthe mechanisms prevalent in the refiner gap is still insufficient.

    To help solving this problem FSCN and CIT initiated the research project “Filling the Gap” togetherwith the companies Dametric, Holmen, Metso Paper, Norske Skog, Pöyry, SCA and Stora Enso cofinancedby the Swedish authorities Vinnova and the Swedish Energy Agency. The research projectwas designed with the intension to show how to improve the electric energy efficiency of chiprefining by means of utilizing fundamental knowledge of wood material properties relevant for chiprefining in relation to refining hypotheses and in combination with output variables from new andimproved refining zone measurement methods as; exact gap distance, temperature-, force- and fibrematerial radial distributions combined with the traditional out/in-put variables normally used. Thepotential of the above mentioned ideas as well as the specific goal of this project was to show how toreach 25% efficiency improvement in existing refiners and at the same time reduce refiner causedstops by >50% and plate wear also by >50%.

    The data produced within the project was utilized in two ways:

    1. To optimize refining conditions in a static way, i.e. optimization of conditions to maximizeenergy efficiency to reach the functional fibre properties aimed for.

    2. To maximize process stability and minimize quality variations at the functional fibreproperties aimed for.

    The general conclusion from the project is that we can show that there are great opportunities toimprove electric energy efficiency in refining according to the goal by means of using the abovementioned measurement techniques. More specifically the full-scale trials performed during theperiod 2010 – beginning of 2013 showed the possibility to improve the electric energy efficiency by25% at similar functional properties of the pulp, i.e. a reduction in electricity consumption by 20%. Inorder to implement similar strategies in other TMP or CTMP lines it will just as in this case benecessary to use the same measurement system and evaluation techniques together with verythorough and statistically well controlled pulp/fibre evaluation techniques. It would of course beinteresting to implement the same techniques on as many other production lines as possible withinthe participating companies, but it must be emphasized that the procedure is very demanding. Eachproduction line needs to perform a corresponding detailed process analysis as the one performed inthe mill case study of this research project. Furthermore it would also be necessary to utilize therefiner gap measurement techniques, especially the combination of temperature profile and gapdistance measurements, in a modern but still simple process control system making it easier for theoperator to continuously run the process in a more energy efficient mode. Implementation of thetechniques evaluated in pilot scale within this research project, i.e. fibre distribution and force3distribution measurements, would of course have potential to further improve the process efficiencyas well as improve the fibre property level.

  • 8.
    Ferritsius, Olof
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Ferritsius, Rita
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. StoraEnso Paper Kvarnsveden Mill.
    Rundlöf, Mats
    Capisco.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    The Independent State of Fibres in Relation to the Mechanical Pulping World2018In: IMPC 2018, Trondheim, Norway, 2018Conference paper (Refereed)
    Abstract [en]

    Paper and wood are highly inhomogeneous materials. When describing the mechanical pulp itself, we allcommonly ignore that it is an inhomogeneous material. We have realized that just a very small fraction of stifffibres are enough to impair the printability of the product. In this paper we share some of our reflections andattempts how to describe the inhomogeneous nature of mechanical pulps. A method denoted BIN is underdevelopment based on independent common factors and paying attention to the inhomogeneity of the material.The method may give the possibility to describe the nature of TMP/CTMP/SGW in a more relevant way comparedto todays practice. Hence the paper and board makers may be able to deliver more uniform products at “goodenough” level at lower costs. We have realized that because a method or opinion is well spread (sometimes usedby almost everybody) it does not necessarily mean that it is relevant. A couple of myths have been reflected uponand in our opinion they remain just myths. By putting more attention to reality and describing mechanical pulp asan inhomogeneous material we hope to be able to rid ourselves and the mechanical pulping community of someother myths circulating (some still to be discovered).

  • 9.
    Holmgren, Sven-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Svensson, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Gradin, Per A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Lundberg, B
    An Encapsulated Split Hopkinson Pressure Bar for Testing of Wood at Elevated Strain Rate, Temperature and Pressure2008In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 32, no 5, p. 44-50Article in journal (Refereed)
    Abstract [en]

    This paper presents a device, based on a split Hopkinson pressure bar (SHPB) setup, by which it is possible to obtain stress vs. strain for a wood specimen at high deformation rate, high temperature and high steam pressure. The need for determining the mechanical properties of wood not only at high deformation rate but also at high temperature and pressure is motivated by the need to model the wood chip refining process in mechanical pulp-ing. At mechanical chip refining, e.g. in thermomechanical pulping processes, preheated wood chips together with added water are fed into the centre of a refiner which in essence consists of two circular discs. Most often one disc is stationary and the other is rotating. The wood chips are transported radially between the discs due to inertia. On their way, due to impacts from radial bars on the discs, they are eventually broken down to individual fibres and fibre fragments. The device presented here is an SHPB set-up, modified so that the bars and the specimen are encapsulated in a pressure vessel within which the temperature is constant. In this way effects of temperature gradients in the bars are avoided. Pilot tests have been carried out which verify the intended per-formance of the device.

  • 10.
    Logenius, Louise
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Fjellström, Helena
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Mechanical Properties of Sulphonated Spruce Wood2013Conference paper (Other academic)
    Abstract [en]

    The chip-refining stage in the production of high yield pulps as TMP and CTMP determines a large part of the optical and mechanical characteristics of the pulp. Softening of the raw material influences where the fiber walls fracture sites will be located.

    In the thermomechanical pulping (TMP) processes, refining is performed at temperatures close to the lignin softening temperature, which normally leads to fractures located in the in the primary wall and outer parts of the secondary wall. When wood material is chemically treated before chip-refining the position of the fracture is altered due to that the softening and swelling properties of the fiber walls are changed. In the chemi-thermomechanical (CTMP) process most of the fractures are, therefore, located in the middle lamella or in the primary wall due to introduction of charged groups in the lignin which facilitates the fiber separation. At alkaline pH phenolic lignin structures are sulphonated, at lower pH non-phenolic structures in the lignin are also sulphonated. In the mechanical pulping processes the wood material is subjected to both low strain rates (e.g. plug screw treatment) and high strain rates (refining). Since wood is a viscoelastic material it behaves differently at different strain rates.

    In this study, sulphonation has been carried out using different sulphite concentrations and pH-levels and we have thereby influenced the sulphonation degree as well as where in the lignin the sulphonation takes place.

    We used a hydraulic testing machine for low strain-rate testing and a Split-Hopkinson pressure bar device for high strain-rate testing to categorize pretreatments according to their material softening effect and the energy needed for fiber separation. This gives us increased fundamental knowledge of how the mechanical properties of wood are affected by the sulphonation in order to develop new/improved pretreatments.

  • 11.
    Logenius, Louise
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Nelsson, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Mechanical testing methods for evaluation of the mechanical properties of sulphonated wood2013Conference paper (Other academic)
  • 12.
    Moilanen, C.
    et al.
    Tampere University of Technology, Finland.
    Biörkgvist, T.
    Tampere University of Technology, Finland.
    Ovaska, M.
    Aalto University, Finland.
    Koivisto, J.
    Aalto University, Finland.
    Miksic, A.
    Aalto University, Finland.
    Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Salminen, L.
    A Fredrikson Research and Consulting Ltd., Jyväskylä, Finland.
    Saarenrinne, P.
    Tampere University of Technology, Finland.
    Alava, M.
    Aalto University, Finland.
    Modelling and simulation of radial spruce compression to optimize energy efficiency in mechanical pulping2016In: International Mechanical Pulping Conference 2016, IMPC 2016, TAPPI Press, 2016, p. 18-35Conference paper (Refereed)
    Abstract [en]

    Energy efficiency of mechanical pulping is rather low. One possibility to facilitate design of more energy efficient defibration is to model and simulate wood compression. This paper presents an effort to model the behavior of Norwegian spruce in radial compression at defibration circumstances. To identify strain rate dependent properties, compression tests were conducted at both quasi-static conditions and at high strain rate. All tests were done at relevant moisture content and up to defibration zone temperatures and strain rates. Additionally the tests were performed both on native wood and on pre-fatigued wood to include behavior dependency of fatigue. The compression tests were monitored on fiber level to separately model behavior of early- and latewood. The chosen continuum model structure for earlywood and latewood was Voight-Kelvin to enable explicit viscous behavior conditioned by strain rate in parallel to the elastic behavior. The presented model is the first wood compression behavior model individually for earlywood and latewood that is based on wood experiments at industrial defibration circumstances. The influences of temperature and pre-fatigue rise are both softening as expected, The utilization of the compression model was demonstrated in an initial multilayered wood compression simulation.

  • 13.
    Moilanen, C.
    et al.
    Tampere University of Technology, Finland .
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Björkqvist, T.
    Tampere University of Technology, Finland .
    Salminen, L.
    VTT Technical Research Centre of Finland, Finland .
    Saarenrinne, P.
    Tampere University of Technology, Finland .
    Local compression behaviour of pre-fatigured and chemically pre-treated wood at high strain rate and high temperature2014Conference paper (Refereed)
    Abstract [en]

    Radial compression behaviour of spruce wood was here studied in a steam environment at high strain rate and elevated temperatures. The difference in compression characteristics between earlywood and latewood was the main focus of the study. Effects of mechanical and chemical pre-treatments were also investigated. Mechanical pre-treatment affected the E- modulus of the samples more than the chemical pre- treatments. Also elevated temperature softened the wood. No significant compression of latewood could be registered with the methods tested.

  • 14.
    Moilanen, C. S.
    et al.
    Department of Mechanical Engineering and Industrial Systems, Tampere University of Technology, PO Box 589, Tampere, Finland.
    Saarenrinne, P.
    Department of Mechanical Engineering and Industrial Systems, Tampere University of Technology, PO Box 589, Tampere, Finland.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Björkqvist, T.
    Department of Automation Science and Engineering, Tampere University of Technology, PO Box 692, Tampere, Finland .
    Image-based stress and strain measurement of wood in the split-Hopkinson pressure bar2015In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 26, no 8, article id 085206Article in journal (Refereed)
    Abstract [en]

    The properties of wood must be considered when designing mechanical pulping machinery. The composition of wood within the annual ring is important. This paper proposes a novel image-based method to measure stress and planar strain distribution in soft, heterogeneous materials. The main advantage of this method in comparison to traditional methods that are based on strain gauges is that it captures local strain gradients and not only average strains. Wood samples were subjected to compression at strain rates of 1000-2500 s-1 in an encapsulated split-Hopkinson device. High-speed photography captured images at 50 000-100 000 Hz and different magnifications to achieve spatial resolutions of 2.9 to 9.7 μm pixels-1. The image-based analysis utilized an image correlation technique with a method that was developed for particle image velocimetry. The image analysis gave local strain distribution and average stress as a function of time. Two stress approximations, using the material properties of the split-Hopkinson bars and the displacement of the transmitter bar/sample interface, are presented. Strain gauges on the bars of the split-Hopkinson device give the reference average stress and strain. The most accurate image-based stress approximation differed from the strain gauge result by 5%. © 2015 IOP Publishing Ltd.

  • 15.
    Moilanen, C. S.
    et al.
    Department of Engineering Design, Tampere University of Technology, P.O. Box 589, FI-33101 Tampere, Finland .
    Saarenrinne, P.
    Department of Engineering Design, Tampere University of Technology, P.O. Box 589, FI-33101 Tampere, Finland .
    Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Björkqvist, T.
    Department of Automation Science and Engineering, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland .
    Image Based local strain measurement of wood2013In: Conference Proceedings of the Society for Experimental Mechanics Series, 2013Conference paper (Refereed)
    Abstract [en]

    A new method for local strain measurement of soft materials like wood is proposed. Norway spruce samples were subjected to radial compression in an encapsulated split-Hopkinson device (ESHD). High speed photography was used at two magnifications for image based analysis. The strain estimation was made from high magnification images showing compression on local, fiber level for 1-2 growth rings and from low magnification images showing compression on sample level, for 5-8 growth rings. Strain gauges on the ESHD bars give stress and average strain for comparison. Image analysis based on PIV technique gives local and average strain propagation as a function of time. Wood is an inhomogeneous material and thus, local strain is a more proper measure of the response of the material. The high magnification captures differences between earlywood and latewood while the low magnification gives the strain distribution over the whole sample. Both magnifications are important in order to understand the response of the wood material to the sudden compression. A way to estimate the stress field was developed. The results showed similarity to the strain gauge measurement results. © The Society for Experimental Mechanics, Inc. 2014.

  • 16.
    Moilanen, Carolina
    et al.
    Tampere Univ Technol, Finland.
    Björkqvist, Tomas
    Tampere Univ Technol, Finland.
    Ovaska, Markus
    Aalto Univ, Finland.
    Koivisto, Juha
    Aalto Univ, Finland.
    Miksic, Amandine
    Aalto Univ, Finland.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Salminen, Lauri I.
    VTT, Finland.
    Saarenrinne, Pentti
    Tampere Univ Technol, Finland.
    Alava, Mikko
    Aalto Univ, Finland.
    Influence of strain rate, temperature and fatigue on the radial compression behaviour of Norway spruce2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 6, p. 505-514Article in journal (Refereed)
    Abstract [en]

    A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80-100 degrees C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.

  • 17.
    Moilanen, Carolina S.
    et al.
    Department of Mechanical Engineering and Industrial Systems, Tampere University of Technology.
    Björkqvist, Tomas
    Department of Automation Science and Engineering, Tampere University of Technology.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Salminen, Lauri I.
    A Fredrikson Research & Consulting Ltd., Vähäkuja 2 A 2, Jyväskylä, Finland.
    Saarenrinne, Pentti
    Department of Mechanical Engineering and Industrial Systems, Tampere University of Technology, Finland.
    High strain rate radial compression of Norway spruce earlywood and latewood2016In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 23, no 1, p. 873-889Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of Norway spruce were studied and a compression model for mechanical pulping was developed. The split-Hopkinson pressure bar technique was combined with high-speed photography to analyse local radial compression. Data analysis focussed on the differences between mechanical properties of earlywood and latewood. Measurements were conducted at both room temperature and 135 C. The effect of prefatigue treatment was also studied. A simple material model was defined linearly in parts and fitted to the measurement data to quantify the differences. New results were found on the differences in inelastic behaviour of earlywood and latewood at large deformations. In addition, other results were in line with previously published results.

  • 18.
    Nelsson, E.
    et al.
    Holmen AB, New Business Development.
    Sandberg, C.
    Holmen Paper AB, Paper Product Developmen.
    Svensson-Rundlöf, E.
    Holmen Paper AB, Paper Product Developmen.
    Paulsson, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Akzo Nobel Pulp and Perfomtance Chemicals AB.
    Granfeldt, Thomas
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Valmet AB.
    Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Mill scale production of TMP with double disk refining-The effects of a mild sulfonation, atmospheric preheating and refining temperatures2016In: International Mechanical Pulping Conference 2016, IMPC 2016, TAPPI Press, 2016, p. 249-259Conference paper (Refereed)
    Abstract [en]

    The aim of this work was to study the effects of a mild dosage of sodium sulfite in chip impregnation at diffen temperatures during atmospheric preheating and during refining for production of TMP for printing papers usi high intensity double disk refining. Two trials were performed in the 800 bdt/day double disc line at I Braviken paper mill (Holmen Paper AB, Sweden) using Norway spruce chips. During the trials, chips w( impregnated in an Impressafiner where chips were preheated at 1.8 bar(g) for a few seconds and th compressed before impregnation. During impregnation, sodium sulfite was added to chips at pH 9 in dosages 0.6 or 1.2%. Reference pulps without addition of sulfite were also produced. In the first trial, the effect different temperatures and retention times (80°C for 6 minutes vs. 96°C for 9 minutes) in the atmosphe preheating bin following impregnation was evaluated both with and without the addition of 1.2% sodium sulf In the second trial, the effect of different refining temperatures (refiner house pressures of 4.6 or 6.4 bar(g), 1 or 167°C) was evaluated with different additions of sodium sulfite (0.0, 0.6 or 1,2%) during impregnation. The results from the two trials showed that the increase in refiner house pressure increased the tensile index pulps both with and without addition of sodium sulfite, when compared at certain SEC. However, the increase preheater bin temperature and retention time did not increase the tensile index of pulps but rather led to a sm reduction in tensile index when combined with an addition of 1.2% sodium sulfite. The two different methc used to increase the temperature in the system led to different effects in the disc gap at certain SEC. The disc j temperature was increased by both methods but disc gap was only reduced at certain SEC when the refini temperature was increased by increasing the refiner housing pressure. The difference in the effect on the disc j may hold the answer to the different effects seen in tensile index.

  • 19.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Svensson-Rundlöf, E
    Muhic, D
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Substantially improved energy efficiency in mechanical pulping by new feeding segment design and low dosage sulfonation in mill scaleArticle in journal (Refereed)
  • 20.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Svensson-Rundlöf, Eva
    Muhic, Dino
    Valmet AB.
    Rohdén, Lennart
    A. Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Improved energy efficiency in thermomechanical pulping through co-optimixation of intensity by segment design and wood softening by sulfonation2014In: International mechanical pulping conference IMPC 2014, 2014Conference paper (Other academic)
    Abstract [en]

    A mill scale trial was performed where chips were mechanically pretreated and impregnated with sodium sulfite (<7.2 g/kg). Pretreated chips were refined in two parallel double disc refiners (RGP68DD) using two different conditions: Turbine™ segment at higher production rate (higher intensity) and Low Shive™ segment at normal production rate (lower intensity). By combining the Turbine segments with chip pretreatment using a sodium sulphite charge of 3.6 g/kg it was possible to reduce the specific energy consumption by 15%, while maintaining pulp properties, compared with the lower intensity refining without pretreatment.

  • 21.
    Persson, Johan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Granfeldt, Thomas
    Valmet AB.
    Feeding of double disc refiners - modeling of particle flow2018In: IMPC 2018, Trondheim, Norway, 2018Conference paper (Refereed)
    Abstract [en]

    Improvements to the energy efficiency of double disk refiners are hampered by the feeding rate in tothe machine. This study aims to evaluate parameters towards a complete model, which will help tobring clarity to the limiting factors in feeding rate. A combined computational fluid dynamic anddiscrete element model is used to evaluate the flowrate of a hopper discharge unaided, and aided by agas flow with varying density. The results of the study shows that it is essential to capture the exactgeometry of the double disk feeding in relation to the woodchips in the complete model. The resultsalso shows that while it is essential to include the gas phase in the full model, the model is not sensitiveto small variance in the density of the gas.

  • 22.
    Saari, Valtteri
    et al.
    Tampere University of Technology, Finland.
    Björkqvist, Tomas
    Tampere University of Technology, Finland.
    Engberg, Birgitta Anna
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Strain distribution in annual rings under compression by high speed photography2009In: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009, 2009, p. 245-251Conference paper (Refereed)
    Abstract [en]

    Fatigue is essential in mechanical pulping when producing flexible paper fibers energy efficiently from stiff wood fibers. Fatigue propagation depends mainly on strain variation. The objective of the study is to determine how compressive strain is distributed between earlywood and latewood. Uneven distribution of local strain variation is likely to cause different amount of fatigue for earlywood and latewood and thus affects the usability of these fibers in the paper products. To characterize the material's response to mechanical defibration at high strain rates a unique testing equipment was utilized. The ESHD (Encapsulated Split-Hopkinson Device) at Mid Sweden University allows generation of such high strain rate pulses. Combining this with high speed photography at 50 000 fps offered the possibility of quantitative strain field mapping by image analysis. Since both wood temperature and moisture content affect strain behavior, moisture content was in this study kept constant at 45 %. Testing temperature was varied between 20°C and 135°C. Additionally, four levels of compressive fatigue treatment in the radial direction, prior to the high strain rate tests, were used to investigate how different parts of the annual rings were changed due to the fatigue treatment. In the measurements, it was noted that the strain was concentrated in the softer earlywood layers and there were unexpectedly little strain in the latewood layers. The temperature and the fatigue level clearly affected the magnitude of the strains. Higher temperature and fatigue level increased the strain difference between earlywood and latewood in the sample.

     

     

  • 23.
    Salmi, Ari
    et al.
    VTT Tech Res Ctr Finland, Espoo, Finland.
    Salminen, Lauri I.
    VTT Tech Res Ctr Finland, Espoo, Finland.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Bjorkqvist, Tomas
    Tampere Univ Tech, Dept Automat Sci & Eng, Tampere, Finland.
    Haeggstrom, Edward
    Univ Helsinki, Elect Res Lab, Dept Phys, Div Mat Phys, Helsinki, Finland.
    Repetitive impact loading causes local plastic deformation in wood2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 2, p. Art. no. 024901-Article in journal (Refereed)
    Abstract [en]

    The relationship between the impactor velocity and the amount of strain localization in a single impact compression of cellular solids is known. However, few studies report on the effects of repeated high frequency compression. We therefore studied the mechanical behavior of Norway spruce, a cellular viscoelastic material, before, during, and after cyclic high frequency, high strain rate, compression. A custom made device applied 5000-20 000 unipolar (constrained compression and free relaxation) fatigue cycles with a 0.75 mm peak-to-peak amplitude at 500 Hz frequency. The consequences of this treatment were quantified by pitch-catch ultrasonic measurements and by dynamic material testing using an encapsulated Split-Hopkinson device that incorporated a high-speed camera. The ultrasonic measurements quantified a stiffness modulus drop and revealed the presence of a fatigued low modulus layer near the impacting surface. Such a localized plastic deformation is not predicted by classical mechanics. We introduce a simple model that explains several changes in the mechanical properties caused by fatiguing. The high speed images indicated pronounced strain localization in the weakest (thinnest walls) parts of the earlywood layers, and revealed strain propagation as a function of time. We present a hypothesis explaining why there is a fatigued layer formed in a piece of wood that has sustained cyclic compression and free relaxation. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676206]

  • 24. Salmi, Ari
    et al.
    Salminen, Lauri I.
    Montonen, Risto
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Björkqvist, Tomas
    Haeggström, E.
    Lucander, Mikael
    Cyclic impacting of wood results in localized fatigue2011In: Proceedings of International Mechanical Pulping Conference 2011 (Xi'an, China 2011), 2011Conference paper (Other academic)
  • 25. Salminen, Lauri
    et al.
    Salmi, Ari
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Björkqvist, Tomas
    Haeggström, Edward
    Lucander, Mikael
    Cyclic loading and fatigue of wood2011In: Progress in Paper Physics Seminar2011: Conference Proceedings / [ed] U. Hirn, 2011, p. 243-245Conference paper (Other academic)
  • 26.
    Sandberg, Christer
    et al.
    Holmen Paper AB, Norrköping.
    Nelsson, Erik
    HEAD Engineering AB, Nacka strand.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Effects of chip pretreatment and feeding segments on specific energy and pulp quality in TMP production2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 448-459Article in journal (Refereed)
    Abstract [en]

    Increased wood softening and refining intensity have earlier been utilized to improve refining efficiency in mechanical pulping. We have evaluated a combination of increased softening by low dose sulphite chip pretreatment and increased intensity by feeding segment design in a TMP line for production of high quality printing papers. Norway spruce wood chips were preheated, compressed in an Impressafiner and impregnated with water or sodium sulphite solutions (Na2SO3 charges 3.6 and 7.2 kg/t). Chips were refined in two parallel 68" double disc refiners using two different refining conditions: standard bidirectional segments at normal production rate (9 t/h) and feeding segments at increased production rate (11.1-12.1 t/h). The feeding segments enabled a 30 % increase in production rate. Refining with feeding segments at 12.1 t/h production rate combined with chip pretreatment with 3.6 kg/t sodium sulphite reduced the specific energy 360 kWh/t (19 %) compared to refining with standard segments and no pretreatment. Pulp properties were similar for the two configurations. The combination of feeding segments and chip pretreatment with water reduced the specific energy 180 kWh/t (9 %). Implementation of most of the technology presented has reduced the electrical energy use for the mill by approximately 80 GWh/year.

  • 27.
    Svensson, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Frictional studies and high strain rate testing of wood under refining conditions2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When producing thermomechanical pulps (TMP), wood chips and fiber material are loaded mechanically in a disc-refiner to separate the fibers and to make them flexible. In the process, much of the energy supplied is transferred to the fiber material through cyclic compression, shear and friction processes. Therefore, compression and friction characteristics are needed in order to gain a better grasp of the forces acting during refining. To this end, in this thesis, the compressive and frictional behaviors of wood were investigated under simulated chip refining conditions (i.e., hot saturated steam, high strain rate compression, and high sliding speed). Two new, custom-designed, experimental setups were developed and used. The equipment used for compression testing was based on the split Hopkinson pressure bar (SHPB) technique and the friction tester was a pin-on-disc type of tribotester (wear rig). Both pieces of equipment allow a testing environment of hot saturated steam.

     

    In the wood–steel friction investigation, the influence of the steam temperature (100-170°C) was of primary interest. The wood species chosen for the friction tests were spruce (Picea abies), pine (Pinus sylvestris, Pinus radiata), and birch (Betula verrucosa). When performing measurements in the lower-temperature region (100-130°C), the friction coefficients registered for the softwoods were generally low and surface properties such as lubrica­tion were suggested to have a great influence on the results; however, in the higher-tempera­ture region (~130 -170°C), the friction coefficients of all investigated wood species were probably determined by bulk properties to a much greater extent. When most of the wood extractives had been removed from the specimens, testing results revealed distinct peaks in friction at similar temperatures, as the internal friction of the different wood species are known to have their maxima at ~110–130°C. One suggested explanation of these friction peaks is that reduced lubrication enabled energy to dissipate into the bulk material, causing particularly high friction at the temperature at which internal damping of the material was greatest. During the friction measurements in the higher-temperature region, the specimens of the different wood species also started to lose fibers (i.e., produce wear debris) at different characteristic temperatures, as indicated by peaks in the coefficient of friction. In refining, the generally lower shives content of pine TMP than of spruce TMP could partly be explained by a lower wear initiation temperature in the pine species.

     

    Wood stiffness is known to decrease with temperature, when measured at low strain rates. The results presented in this thesis can confirm a similar behavior for high strain rate compression. The compressive strain registered during impulsive loading (using a modified split Hopkinson equipment) increased with temperature; because strain rate also increased with temperature. Accordingly, the strain rates should determine the strain magnitudes also in a refiner, since the impulsive loads in a refiner are of similar type. Larger strains would thus be achieved when refining at high temperatures. The results achieved in the compression tests were also considered in relation to refining parameters such as plate clearance and refining intensity, parameters that could be discussed in light of the stress–strain relations derived from the high strain rate measurements. Trials recorded using high-speed photography demonstrated that the wood relaxation was very small in the investigated time frame ~6 ms. As well, in TMP refining the wood material has little time to relax, i.e., ~0.04–0.5 ms in a large single disc refiner. The results presented here are therefore more suitable for comparison with the impulsive loads arising in a refiner than are the results of any earlier study. It can therefore be concluded that the modified SHPB testing technique combined with high-speed photography is well suited for studying the dynamic behavior of wood under conditions like those prevalent in a TMP system.

  • 28.
    Svensson, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Friktionens inverkan på energiförbrukning vid mekanisk massaframställning2006In: Nordisk Papper & Massa, ISSN 1651-2995, Vol. 7, no 6, p. 20-22Article in journal (Other academic)
  • 29.
    Svensson, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Tribology under refining conditions2004In: Proceedings of the 4th Fundamental Mechanical Pulp Seminar: June 7-8, 2004, Stocholm, Sweden, 2004Conference paper (Other scientific)
  • 30.
    Svensson, Birgitta A.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Holmgren, Sven-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Gradin, Per A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    High Strain Rate Compression and Sliding Friction of Wood under Refining Conditions2007In: International Mechanical Pulping Conference 2007, TAPPI, 2007, Vol. 2, p. 983-994Conference paper (Other academic)
    Abstract [en]

    Compression and friction characteristics are needed in order to gain a better grasp of the forces acting during refining. To this end, both stress-strain relations and frictional behavior of wood were investigated under simulated chip refining conditions (hot saturated steam, high strain rate compression, and high sliding speed). Two new, custom-designed, experimental set-ups were used. Both pieces of equipment allow a testing environment of hot saturated steam. The wood-steel friction investigations indicate that when making measurements in the lower temperature region (100C-130C), surface properties such as lubrication have a great influence on the coefficients of friction. Traces of lubricating layers, comprising fatty acids, were found on friction-tested pine surfaces using a staining technique and light microscopy; in the higher-temperature region no traces of lubrication could be detected in this way.

  • 31.
    Svensson, Birgitta A.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Nyström, Staffan K.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Gradin, Per A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Frictional testing of wood: Initial studies with a new device2009In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 1, p. 190-196Article in journal (Refereed)
    Abstract [en]

    In the chip refining process used for mechanical pulp production, wood fibers are treated in a flat and narrow gap between rotating plates. The process is very energy consuming and much of the electrical energy supplied to the refiner is transferred to the fiber material through friction forces. Even though friction has been discussed frequently over the years among pulp and paper researchers worldwide and held to be of great importance, little has been proven due to the complexity of the refining equipment and the extreme conditions prevailing during operation. This paper presents a new apparatus for studying the frictional properties of wood, in lab-scale, under chip refining conditions. Friction tests can be carried out in a steam atmosphere under high temperature/pressure with maximum sliding velocity as high as 150 m/s. Initial studies at room temperature showed that the coefficient of friction between spruce wood and smooth steel increased linearly with the moisture content of the wood specimens. Impregnation by wood extractives lowered the friction coefficient for dry wood surfaces sliding at high speed. When tests were performed in a saturated steam environment, pressurized to various degrees, the frictional properties were strongly affected and varied by the temperature of the surroundings � which always has been considered as constants in analytical and numerical models of process operation.

  • 32.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Holmgren, Sven-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Gradin, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lundberg, B
    High Strain Rate Compression of Spruce Wood in a Saturated Steam EnvironmentManuscript (preprint) (Other academic)
  • 33.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Nyström, Staffan K
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Gradin, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Bergfors, E
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Tribology under refining conditions: initial studies sevo motor2003In: 2003 International Mechanical Pulping Conference, 2003, p. 233-237Conference paper (Refereed)
    Abstract [en]

    The refining process is not yet fully understood and more fundamental knowledge is a key to improvements in the future. A tribological view on refining could give new understanding and ideas for improvement of the process efficiency. This paper presents a new apparatus for studying the frictional properties of wood � under refining conditions. A laboratory scale friction tester has been constructed where friction tests can be carried out in a steam atmosphere under high temperature/pressure and with maximum sliding velocity as high as 200 m/s. Initial studies in room temperature show that the coefficient of friction is proportional to the moisture content of wood at a sliding velocity of 24 m/s and with a normal load of 8 N. Wood extractives lowered the friction on dry surfaces and especially at high sliding velocity. The lubricating capacity of a variety of different resin model components among the extractives was also examined, but no significant effects has been found on wood specimens of 30 and 70 % in moisture contents.

  • 34.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, M.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Sliding Friction Between Wood and Steel in a Saturated Steam Environment2006In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 32, no 1, p. 38-43Article in journal (Refereed)
    Abstract [en]

    To understand friction under refining conditions, measurements of sliding friction between wood and steel were made in a steam environment. To achieve various testing temperatures (100-170°C), the steam pressure was set to various levels. Two wood species, Norway spruce and Radiata pine, were examined in this study. The friction coefficients of native wood increased with temperature up to a critical point where fibres started to wear from the surface. This point was observed at a lower temperature for Radiata pine than for Norway spruce. After extracting the samples with acetone and dichloromethane, friction-augmenting effects were observed and local friction maxima appeared for both spruce and pine at ∼125°C. It is suggested that these local maxima are due to energy-dissipative processes and related to the softening temperature of lignin. Experiments with sulphonated samples of Norway spruce supported this suggestion.

  • 35.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, Mats
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Sliding friction between wood and steel in a saturated steam environment2005In: International Mechanical Pulping Conference: IMPC 2005: Oslo, Norway, 7-9 June 2005, 2005, p. 31-37Conference paper (Other academic)
    Abstract [en]

    To understand friction under refining conditions, measurements of sliding friction between wood and steel were made in a steam environment. To achieve different testing temperatures (100-170ºC) the steam pressure was set to various levels. Two wood species, Norway spruce and Radiata pine, were examined in this study. The friction coefficients of native wood increased with temperature up to a critical point where fibers started to wear off from the surface. This point was observed at a lower temperature for Radiata pine than for Norway spruce. After extracting the samples with acetone and dichloromethane, friction-augmenting effects were observed and local friction maxima appeared for both spruce and pine around 125ºC. It is suggested that this local maxima is due to energy dissipative processes and related to the softening temperature of lignin. Experiments with sulfonated samples of Norway spruce supported this suggestion.

  • 36.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Vesterlind, Eva-Lotta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Frictional properties of native and chemically modified birch wood2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 325-330Article in journal (Refereed)
    Abstract [en]

    The chemithermomechanical pulping of hardwoods has attracted increasing interest in the past decade. This study investigates the frictional behavior of both native and chemically treated birch under simulated chip-refining conditions (hot saturated steam, high sliding speed). Chip pretreatment, i.e. chemical impregnation and pre-heating done when birch chemithermomechanical pulp is produced, affects energy consumption during refining; the study found that frictional forces may be an important parameter in this respect. The coefficient of friction peaks at approximately 115°C for both native and extracted birch. It was shown that sulfonating native birch decreased its coefficient of friction over the temperature range investigated (100�170°C). The coefficient of friction had a broad and flat peak in the 130�150°C temperature interval for the specimens treated with 3% sodium sulfite at pH 13.5. Furthermore, it was clear that pH had a profound influence on the coefficient of friction. A high pH lowered the coefficient of friction, likely due to well lubricated contacts. The friction arising between birch (Betula verrucosa) and steel was shown to be higher than that between spruce (Picea abies) and steel. The higher stiffness and density of the birch wood, together with a more porous bulk structure leading to rough test surfaces, are some factors possibly accounting for these high friction coefficients. Also, the differences in the amount and composition of the extractive substances in birch and spruce may contribute to the differing frictional behaviors of these species.

1 - 36 of 36
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