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Publications (10 of 106) Show all publications
Heldin, M. & Wiklund, U. (2019). Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools. Nordic Pulp & Paper Research Journal
Open this publication in new window or tab >>Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
2019 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Refereed) Epub ahead of print
Abstract [en]

Groundwood pulping is a process that employs large machines, making them difficult to use in research. Lab scale grinders exist, but even though they are smaller, the sizes of the grinding stones or segments make them cumbersome to exchange and tailor. This study presents a method and an apparatus for investigating the detailed mechanisms and the energy requirements behind the fibre separation process. A well-defined grinding tool was used at three different temperatures to demonstrate that the equipment can differentiate levels of energy consumption and defibration rates, confirming the well-known fact that a higher temperature facilitates defibration. It is also shown how the equipment can be used to study the influence of grinding parameters, exemplified by the effect of temperature on the way fibres are separated and the character of the produced fibres. A key feature of the equipment is the use and evaluation of small grinding surfaces, more readily designed, produced, evaluated and studied. This reduces both the cost and time necessary for testing and evaluating. At the same time, a technique to produce well defined grinding surfaces was employed, which is necessary for repeatability and robust testing, not achievable with traditional grinding stones.

Keywords
Computed tomography, Energy efficiency, Groundwood pulping, Lab scale equipment, Test method
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382698 (URN)10.1515/npprj-2019-0063 (DOI)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-11-12
Heldin, M. & Wiklund, U. (2019). Evaluation of well-defined tool surface designs for groundwood pulping. BioResources, 14(4), 9575-9587
Open this publication in new window or tab >>Evaluation of well-defined tool surface designs for groundwood pulping
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 4, p. 9575-9587Article in journal (Refereed) Published
Abstract [en]

Groundwood pulping is a process in which logs are pressed against a rotating grinding stone. A conventional grinding stone is generally made of grinding particles in a vitrified matrix. As the particles are practically round, their contact with the wood is limited to occasional point contacts. The interaction between the particles and the wood occurs at random positions and at random times, only intermittently contributing to the defibration process. In this work, well-defined grinding tools with asperities giving line contacts rather than point contacts were tested. The tool surface asperities were elongated in shape and positioned with different density over the surface. The tools were tested in a lab-scale equipment at elevated temperatures, and their performance was compared to that of a conventional grinding stone. The grinding mechanisms varied between the different tools, and the specific grinding energy was reduced compared to the conventional tool.

Keywords
Groundwood pulping, Diamond tools, Energy consumption, Tomography, Grinding mechanisms
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382701 (URN)10.15376/biores.14.4.9575-9587 (DOI)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-10-21
Heldin, M. & Wiklund, U. (2019). Influences of load and temperature on groundwood pulping with well-defined tools. Wear, 438-439, Article ID 203051.
Open this publication in new window or tab >>Influences of load and temperature on groundwood pulping with well-defined tools
2019 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 438-439, article id 203051Article in journal (Refereed) Published
Abstract [en]

Groundwood pulping is an industrial process with a high energy demand, although only a minor part of the energy is used for actually separating the fibres and the rest for working them. Traditionally, the separation process employs a grinding stone having particles embedded in a softer matrix. The position and distribution of the particles have been random, causing their interaction with the wood to also be random. This makes studies of the mechanisms during the separation process difficult. Knowledge of the mechanisms in the separation process helps when designing future tools aimed at energy efficiency or tailored fibre properties. Recently, grinding surfaces having diamond particles brazed to a steel backing at fixed positions have been developed and commercialised. In this work, individual particles are not positioned at the tool surfaces. Instead, well-defined structured diamond films, soldered to a backing, are used as grinding tools. The grinding asperities of such films can be tailored to shapes that are not possible to achieve by using particles. Using this kind of tool in a lab scale grinding equipment, confirms the well-known fact that increased load or increased temperature both lead to lower energy consumption for fibre separation and longer, less damaged fibres.

Keywords
Grinding, Pulping, Wood tomography, Energy savings, Tool design
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382700 (URN)10.1016/j.wear.2019.203051 (DOI)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-11-12
Hiroko, M., Heinrichs, J., Wiklund, U., Kawamura, S. & Jacobson, S. (2019). Initiation wear of cemented carbide tools used in copper processing - evaluated in sliding contact. In: Proceedings of International Conference on the Science of Hard Materials, Khao Lak, Thailand: . Paper presented at International Conference on the Science of Hard Materials, March 25-29, 2019, Khao Lak, Thailand.
Open this publication in new window or tab >>Initiation wear of cemented carbide tools used in copper processing - evaluated in sliding contact
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2019 (English)In: Proceedings of International Conference on the Science of Hard Materials, Khao Lak, Thailand, 2019Conference paper, Oral presentation with published abstract (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-392919 (URN)
Conference
International Conference on the Science of Hard Materials, March 25-29, 2019, Khao Lak, Thailand
Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-09-11
Carlsson, J., Heldin, M., Isaksson, P. & Wiklund, U. (2019). Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale. Holzforschung
Open this publication in new window or tab >>Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale
2019 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434XArticle in journal (Refereed) Epub ahead of print
Abstract [en]

With industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.

Keywords
CT; Defibration; DVC; FE; Grinding; Wood
National Category
Paper, Pulp and Fiber Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-382716 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-11-20
Heldin, M., Carlsson, J., Isaksson, P. & Wiklund, U. (2019). On tool engagement in groundwood pulping - in-situ observations and numerical modelling at the microscale. In: The 11th Fundamental Mechanical Pulp Research Seminar, Norrköping, Sweden, April 2-4: . Paper presented at The 11th Fundamental Mechanical Pulp Research Seminar, Norrköping, Sweden, April 2-4, 2019..
Open this publication in new window or tab >>On tool engagement in groundwood pulping - in-situ observations and numerical modelling at the microscale
2019 (English)In: The 11th Fundamental Mechanical Pulp Research Seminar, Norrköping, Sweden, April 2-4, 2019Conference paper, Oral presentation only (Other academic)
National Category
Paper, Pulp and Fiber Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-389856 (URN)
Conference
The 11th Fundamental Mechanical Pulp Research Seminar, Norrköping, Sweden, April 2-4, 2019.
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-07-30 Created: 2019-07-30 Last updated: 2019-07-30
Hassila, C. J., Harlin, P. & Wiklund, U. (2019). Rolling contact fatigue crack propagation relative to anisotropies in additive manufactured Inconel 625. Paper presented at 22nd International Conference on Wear of Materials (WOM), APR 14-18, 2019, Miami, FL. Wear, 426-427(Part B), 1837-1845
Open this publication in new window or tab >>Rolling contact fatigue crack propagation relative to anisotropies in additive manufactured Inconel 625
2019 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part B, p. 1837-1845Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing is steadily gaining acceptance in certain industry segments as a process for the manufacturing of dense metallic components. The Ni-based superalloys belonging to the Inconel family have for many years been in focus for AM research and AM produced components are now becoming commercially available. However, it is still unclear how the microstructural anisotropy, inherent to most AM materials, affects the material performance in a given application. The anisotropy may e.g. influence the mechanical properties and the performance in certain tribological situations, such as when subjected to rolling contact fatigue. Like most AM methods, the powder bed fusion - laser beam process gives the produced components a relatively rough surface. To perform well in demanding tribological situations, the components are commonly machined to a smooth finish. In this work, Inconel 625 produced using PBF-LB is evaluated in a rolling contact fatigue test. Test cylinders (empty set 10 mm) have been produced using different build directions and scan strategies, resulting in varying microstructures and textures. In the rolling contact fatigue test, a cylindrical sample is mounted between two empty set 140 mm metal rollers, pulled together via a spring. After testing, the contact tracks are studied using SEM and EBSD to reveal cracks. Cracks were analysed with respect to the microstructure and anisotropies. It was found that the anisotropy influences both the nucleation and growth of cracks. The AM produced specimens were also found to be more prone to transgranular cracking than conventional Inconel 625, which predominantly displayed intergranular cracks.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Additive manufacturing, Inconel 625, Rolling contact fatigue, Anisotropies, Scan strategies
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:uu:diva-382825 (URN)10.1016/j.wear.2019.01.085 (DOI)000464585200096 ()
Conference
22nd International Conference on Wear of Materials (WOM), APR 14-18, 2019, Miami, FL
Funder
Swedish Foundation for Strategic Research , GMT14-048
Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-05-06Bibliographically approved
Wiklund, U., Emy, G., Grandin, M. & Toller, L. (2019). Wear mechanisms of tools for exploration drilling. In: Euromat 2019, Stockholm, Sweden: . Paper presented at Euromat 2019, European congress and exhibition on materials and processes, Stockholm, Sweden, September 1-5, 2019 (pp. 787).
Open this publication in new window or tab >>Wear mechanisms of tools for exploration drilling
2019 (English)In: Euromat 2019, Stockholm, Sweden, 2019, p. 787-Conference paper, Oral presentation with published abstract (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-393039 (URN)
Conference
Euromat 2019, European congress and exhibition on materials and processes, Stockholm, Sweden, September 1-5, 2019
Available from: 2019-09-13 Created: 2019-09-13 Last updated: 2019-09-13
Heinrichs, J., Mikado, H., Kawakami, A., Wiklund, U., Kawamura, S. & Jacobson, S. (2019). Wear mechanisms of WC-Co cemented carbide tools and PVD coated tools used for shearing Cu-alloy wire in zipper production. Wear, 420, 96-107
Open this publication in new window or tab >>Wear mechanisms of WC-Co cemented carbide tools and PVD coated tools used for shearing Cu-alloy wire in zipper production
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2019 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 420, p. 96-107Article in journal (Refereed) Published
Abstract [en]

To form the individual elements, that together form a zipper, a pre-formed Cu-alloy wire is sheared using cemented carbide tools. The wear caused by the relatively soft copper alloy on the much harder tool is generally quite slow. However, millions of elements are to be sheared so eventually the wear becomes unacceptable and the tool needs to be exchanged. To improve product quality, as well as minimize down time and material consumption, the tool life needs to be prolonged. To achieve this the wear process needs to be better understood. Uncoated tools used for an increasing number of shearing events have been studied in detail using high resolution SEM and EDS, to map the propagating wear and get an insight into the wear mechanisms. Transfer of material from the Cu-alloy to the tool occurs and the wear is highly concentrated to specific areas. This wear occurs on a very fine scale, limited to within individual WC grains at each event. Tools coated with PVD CrC and PVD CrN have been studied for comparison with the uncoated cemented carbide. Both coatings successfully protect the cemented carbide tool from wear, however occasional flaking occurs and then the cemented carbide becomes exposed and subsequently worn. The differences in performance and wear mechanisms between the uncoated and coated tools are discussed, with focus on the capability of the coatings to prolong the tool life.

Keywords
Cemented carbide, Cutting, Shearing, Wear, Cu-alloy
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:uu:diva-375796 (URN)10.1016/j.wear.2018.12.075 (DOI)000456176100009 ()
Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-02-15Bibliographically approved
Tavares da Costa, M. V., Neagu, C., Fayet, P., Wiklund, U., Li, H., Leifer, K. & Gamstedt, E. K. (2018). Comparison of test methods estimating the stiffness of ultrathin coatings. Paper presented at 13th Coatings Science International Conference (COSI), JUN 26-30, 2017, Noordwijk, NETHERLANDS. Journal of Coatings Technology and Research, 15(4), 743-752
Open this publication in new window or tab >>Comparison of test methods estimating the stiffness of ultrathin coatings
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2018 (English)In: Journal of Coatings Technology and Research, ISSN 1935-3804, Vol. 15, no 4, p. 743-752Article in journal, Editorial material (Refereed) Published
Abstract [en]

A key engineering parameter of thin coatings is their stiffness. Stiffness characterization of ultrathin coatings with a nanometer scale thickness is experimentally challenging. In this work, three feasible methods have been used to estimate the Young’s modulus of metal coatings on polymer films. The methods are: (1) nanoindentation, (2) strain-induced elastic buckling and (3) peak-force measurements integrated in atomic force microscopy. The samples were prepared by atomic layer deposition of TiO2 (6 and 20 nm thick) and mixed oxides of TiO2 and Al2O3 (4 and 20 nm thick). The differences in estimated Young’s modulus are interpreted in terms of the underlying assumptions and test conditions. Their specific advantages and drawbacks are also compared and discussed. In particular, the nanoindentation necessitates a sufficiently sharp indenter tip to make localized measurements dominated by the coating. The strain-induced elastic buckling method is simple in practice, but showed a large scatter due to variation in local coating thickness and irregular deformation patterns. The stiffness characterization using atomic force microscopy gave the most consistent results, due to a sharp tip with a radius comparable to the thinnest coating thickness. All methods gave a higher Young’s modulus for the TiO2 coating than for the mixed oxide coating, with a variation within one order of magnitude between the methods.

National Category
Nano Technology Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:uu:diva-352043 (URN)10.1007/s11998-018-0085-0 (DOI)000439757000009 ()
Conference
13th Coatings Science International Conference (COSI), JUN 26-30, 2017, Noordwijk, NETHERLANDS
Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2018-10-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0969-848x

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