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Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.ORCID iD: 0000-0003-3950-8840
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial, Ångström Tribomaterials Group)ORCID iD: 0000-0002-7432-592X
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.ORCID iD: 0000-0002-0969-848x
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.

Place, publisher, year, edition, pages
2019.
Keywords [en]
CT; Defibration; DVC; FE; Grinding; Wood
National Category
Paper, Pulp and Fiber Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
URN: urn:nbn:se:uu:diva-382716OAI: oai:DiVA.org:uu-382716DiVA, id: diva2:1307927
Funder
Swedish Energy Agency, 37206-2Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-11-20
In thesis
1. Designing grinding tools to control and understand fibre release in groundwood pulping
Open this publication in new window or tab >>Designing grinding tools to control and understand fibre release in groundwood pulping
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mechanical pulping is a very energy demanding process in which only a fraction of the energy is used for the actual separation of wood fibres. The rest of the energy is lost, partly in damaging already separated fibres and partly as heat during viscoelastic deformation of the wood. Groundwood pulping is one of the major mechanical pulping processes. In this process, a piece of wood is pressed against a rotating grinding stone. The stone surface has traditionally been made of grinding particles fused to a vitrified matrix. Though the process is close to 200 years old, the detailed mechanisms of the interactions between the grinding particles and the wood surface are still not fully understood. The random nature of the grinding stones combined with the heterogeneous nature of wood creates a stochastic process that is difficult to study in detail. This work utilizes well-defined tools, that facilitate testing and analysis, to increase the understanding of the tool-wood-interaction. In-situ tomography experiments were performed with such well-defined tools, to study the deformations and strains induced in the wood as the tool asperities engage the wood surface. Numerical simulations were used to study the influence of asperity shape, and to show how the induced strains promote intercellular cracks and fibre separation. Several well-defined tool surfaces were designed and tested in a newly developed lab-scale grinding equipment, to study their performance in terms of energy consumption and the quality of the produced fibres. It was shown that the well-defined grinding surfaces, with asperities the same size as a fibre diameter, can be designed both to achieve drastically lower energy consumption compared with that of traditional stones and to produce long and undamaged fibres. This thesis shows that it is possible to design future tools that can help reducing the energy consumption in industrial pulping.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1817
Keywords
Groundwood pulping, Grinding mechanisms, Diamond grinding tool, Energy efficiency
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-382719 (URN)978-91-513-0672-8 (ISBN)
Public defence
2019-08-23, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-05-29 Created: 2019-05-02 Last updated: 2019-08-15

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Carlsson, JennyHeldin, MagnusIsaksson, PerWiklund, Urban

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