Abstract
Abstract 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.
Highlights
In groundwood pulping, both the efficiency of the process and the quality of the product depend on the mechanisms occurring in the contact between the wood and the tool
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 labscale grinding experiments, this paper aims to study such mechanisms
We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding
Summary
Both the efficiency of the process and the quality of the product depend on the mechanisms occurring in the contact between the wood and the tool. Most previous research on the fibre separating mechanisms in groundwood pulping has focused on fatigue and peeling of fibres due to compressive and shearing forces (Atack and May 1962; Salmén and Fellers 1981), most often on a larger scale than the actual geometries of the grinding tool or the fibres themselves. This is a consequence of the assumption that fatigue pre-treatment followed by fibre peeling are necessary mechanisms when separating the fibres, whereas less energy is required if the fibres can be separated without prior fatigue. Lab-scale grinding experiments are combined with finite element (FE) modelling to gain knowledge of the interactions occurring in the groundwood pulping process
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