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Sliding Friction Between Wood and Steel in a Saturated Steam Environment
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (FSCN – Fibre Science and Communication Network)ORCID iD: 0000-0003-3381-5516
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Responsible organisation
2006 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 32, no 1, 38-43 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2006. Vol. 32, no 1, 38-43 p.
Keyword [en]
FRICTION FACTOR, PICEA ABIES, PINUS RADIATA, SATURATED STEAM, STEEL, TEMPERATURE, WOOD
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-4044ISI: 000237632600008Scopus ID: 2-s2.0-33646820341Local ID: 4531OAI: oai:DiVA.org:miun-4044DiVA: diva2:29076
Available from: 2008-09-30 Created: 2009-06-08 Last updated: 2016-09-28Bibliographically approved
In thesis
1. Frictional studies and high strain rate testing of wood under refining conditions
Open this publication in new window or tab >>Frictional studies and high strain rate testing of wood under refining conditions
2007 (English)Doctoral 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.

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet, 2007. 88 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 31
Keyword
Friction, High strain rate testing, Wood, Mechanical pulping, Tribology, Refining, Energy consumption
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-8895 (URN)978-91-85317-64-6 (ISBN)
Public defence
(English)
Supervisors
Available from: 2013-04-16 Created: 2009-05-06 Last updated: 2013-04-16Bibliographically approved

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