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Att välja trä
- 2020. - 10
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Samlingsverk (redaktörskap) (populärvet., debatt m.m.)
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| 3. |
- Bengtsson, Charlotte, et al.
(författare)
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Högtemperaturtorkat virke - varför minskar hållfastheten?
- 2001
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Rapport (refereegranskat)abstract
- The strengths of conventionally and high temperature dried spruce timber have been compared. Material from both southern and northern Sweden was included in the study. A total number of 1050 specimens (50mm x 150mm x 5m) were dried by using five different drying methods and then strength tested. The drying temperatures varied between 70°C and 125°C. The material was also strength graded by using a Cook Bolinder grading machine and the yield in class C30 was evaluated. Fracture energy (perpendicular to the grain direction) was measured for 25% of the tested material. The results show a decreased bending strength by, on the average, 5% for timber dried at 125°C compared to conventionally dried timber (at 70°C). For the 5th percentile value (characteristic value) corresponding decrease was 13%. The tensile strength was reduced more than the bending strength. The stiffness was not affected by high temperature drying, neither in bending nor in tension. The results also indicate that material from northern Sweden is more affected by high temperature drying than material from southern Sweden. No difference in fracture energy was found for the material dried by using the different drying methods. However, the maximum force measured during the fracture energy testing was significantly lower for the high temperature dried material. This indicated that the tensile strength perpendicular to the grain decreased during high temperature drying. The bending strength was lower after machine strength grading (class C30) for the high temperature dried timber compared to the conventionally dried timber. This was expected as the grading machine measures stiffness and the stiffness is, as shown, not affected by high temperature drying.
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- Källander, Björn
(författare)
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Climate control in vacuum dryers for convective heat transfer : Part 1: Demands on climate control
- 2002
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 36:6, s. 477-486
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Tidskriftsartikel (refereegranskat)abstract
- The European Drying Group (EDG) proposal on a wood drying quality standard defines demands on final moisture content variation of the dried wood. The final moisture content variation will depend on material parameters as well as the production process and the wood will always show a “natural” moisture content variation after drying. Thus the drying process has to be defined well enough to allow for the natural moisture content variation in order to fulfil the demands of the drying standards. As the average equilibrium moisture content of the wood in a vacuum drying kiln with pure steam atmosphere is determined by the pressure and the temperature, the demands on the climate control system to fulfil the demands of the drying standard can be calculated with regard to the natural moisture content variation of the wood. In the first part of this contribution the demands on climate control in vacuum dryers are calculated based on the EDG-standard and the natural moisture content variation. In the second part of the contribution the demands on climate control are compared with climate and moisture content measurements from industrial production in vacuum kilns. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.
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| 5. |
- Källander, Björn
(författare)
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Climate control in vacuum dryers for convective heat transfer : Part 2: Actual climates in industrial kilns and suggestions to improve kiln design
- 2003
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 37:1, s. 3-9
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Tidskriftsartikel (refereegranskat)abstract
- The first part of this contribution determined the demands on climate control in vacuum drying kilns that are necessary to achieve the final moisture content variation stipulated in the European Drying Group (EDG) proposal on wood drying quality standards. In this second part of the contribution, these demands are compared with measurements of actual climates and the resulting final moisture content in vacuum kilns during industrial production. The measurements show that none of the studied industrial vacuum kilns are capable of controlling climate with acceptable accuracy. The variations in drying climate lead to large variations in final moisture content and reduced production capacities. Drying quality and drying capacity would be greatly increased with improved kiln design and improved climate control systems. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.
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| 9. |
- Källander, Björn
(författare)
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Drying and thermal modification of wood - studies on influence of sample size, batch size, and climate on wood response
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research on wood drying and wood modification is primarily done in laboratories, using clear wood specimens treated under well-defined conditions in laboratory cabinets. Laboratory tests differ from industrial treatment both regarding the size and homogeneity of the material treated, and the size of the batch and kiln used.Knowledge about how the size of the material treated and the size of the batch or kiln influence the results is limited, which makes it difficult to utilize results from laboratory research in development of industrial processes. A better understanding of the influence of size can also improve the possibilities to design laboratory studies so that the results are easier to implement industrially.The studies presented in this thesis focus on how the size of the batches treated and the size of the individual wood samples treated influence the process and resulting properties of the wood. The aim of the studies, the so called researchquestion in the context of a PhD-thesis, is to help transfer knowledge gained from testing small wooden samples in laboratories to industrial treatment of full size timber.This thesis describes studies on vacuum drying, high temperature (HT) drying, and thermal modification of wood according to the Thermowood© process. Drying and thermal modification of wood have been studied under industrial andlaboratory conditions. Kiln climates and wood response have been determined during vacuum drying, conventional drying, high temperature drying, and thermal modification.The results show that both the size of the material treated and the size of the kiln or batch strongly influence the processes and the resulting wood properties.The results show that the sample size influences different material properties in different ways. Equilibrium moisture content is reduced less during thermal treatment of small clear wood specimens than during treatment of dimensionaltimber. Mass loss on the other hand is higher in small samples. Reduction in impact bending strength, mass loss, and reduction in EMC after thermal treatment of dimensional timber do not seem to be correlated.Laboratory treatment of small clear wood specimens show considerably stronger influence on the wood properties than treatment of similar samples together with industrial production.
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