The sawmill process itself is not complicated. What makes it complex is the diversity of the raw material, the logs that are processed in the sawmill, and the divergent production with many different end products. In the sawmill various number of measurement and scanning equipments are installed. These are used for controlling the various processes and for measuring how well they are carried through.
The main objective of this thesis is to build knowledge of how we can make the sawing process, one of the main steps within the sawmill process, more efficient with respect to both volume yield and value recovery by new equipment and new production strategies. The intention has been that the conclusions in this thesis can contribute to a knowledge base that can be of assistance in decisions regarding control process parameters and production strategies for a sawmill.
There is a possible economic saving by increased volume yield for the sawmills if the saw kerf width can be reduced, but there is a fear that the presence and magnitude of saw mismatch will be affected by this. Saw mismatch occurs on the sawn boards due to displacement in axial direction of the saw blades in double arbor saw machines as a consequence of wear, heat or mechanical disturbance. It is shown in this thesis that it was possible to measure saw mismatch automatically during sawmill operation by laser triangulation and that the measurements were comparable to manual measurements. It is also suggested how the presence and magnitude of saw mismatch can be evaluated when measurements are carried out in a sawmill.
Another study addressed in the thesis is the consideration of applying an
alternative log rotation for each log than the in Scandinavia industrial praxis of horns down (log crook faced upwards). This possibility for a greater profit return comes in question since the development of an industrial computed tomography scanner makes the internal knot structure of the log available.
Log breakdown simulations of about 600 Scots pine (Pinus sylvestris [L.]) logs and 800 Norway spruce (Picea abies [L.] Karst.) logs mainly from different geographic locations in Sweden showed that there is a potential value increase when rotating each log for greatest profit return. The potential value increase was dependent of the rotational error of the sawing machine and the price differences between quality grades. For the 600 Scots pine logs and the 800 Norway spruce logs in the study an increased average value increase of 13% was obtained if applying the rotation that maximizes the value of each log instead of the horns down position. An introduced rotational error of the sawing machine reduced the value potential to 6%. There was a weak correlation between the log rotation that maximizes the value of each log and the outer shape of the logs. This means that the outer shape can not be used as an indicator of how the log should be rotated for greatest profit return. One subject of discussion in the thesis is also the importance of representative input data in order to make as general conclusions as possible. The Swedish stem bank has been an important factor in many studies made in the field of wood technology. It is a well-documented data set and computed tomography scanning of logs has made it possible to represent internal wood features in log breakdown software. Since computed tomography scanning of logs is a time consuming process the number of scanned logs are relatively small. Now that an industrial computed tomography scanner operating at production speed is entering the market this opens up new possibilities. Hopefully simulation studies that are performed on larger industrial data sets coming from logs processed in the sawmills at a daily basis is not too far away.
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