Spiral grain occurs naturally more or less in all trees. Instead of running parallel to the pith, the grain runs spiralled around the trunk like a helix. Since wood is an orthotropic material with higher shrinkage perpendicular to than parallel with the grain, the tree will twist when dried, and so will a plank or board cut from it. The tracheid effect utilizes the light-conducting properties of the softwood tracheids to measure the direction of spiral grain. A small laser point was projected on the wood surface. The light transmitted in the wood and scattered back forms an elliptic shape extended in the direction of the fibres. The ellipse of light was registered with a CMOS camera and the orientation of the ellipse's major axis was computed by image processing in real time. A camera system for measuring spiral grain on the debarked surface of a log was installed at a sawmill. In normal production, centre planks of Norway spruce were marked with colour in six different groups according to the size and direction of spiral grain measured by the camera system. All marked planks were manually measured for twist after drying. Measurements on 843 pieces show a coefficient of determination of 0.76 between spiral grain under bark and twist after drying.

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic-ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists

For a long time, process improvements in sawmills have focused on high productivity measured in volume per hour and volume recovery. As sawmills become increasingly efficient, the importance of focusing on value recovery becomes obvious. In order to maximize value recovery, sawmills need the ability to sort logs according to properties such as strength. The aim of this study was to compare the results of predicting the strength of center boards based on x-ray scanning of logs with the results obtained by machine strength grading using a bending machine. The study was based on 131 Norway spruce (Picea abies (L.) Karst.) sawlogs that were scanned with an x-ray LogScanner and then sawn into boards. The bending stiffness of the center boards was tested using a strength-grading machine, and the bending strength was tested according to EN 408. Models for prediction of bending strength based on machine strength grading and x-ray LogScanner measurements were calibrated using partial least squares regression. The study showed that the x-ray LogScanner (r2 = 0.44) and machine strength grading (r2 = 0.43) had similar accuracy in predicting bending strength. The combination of both methods resulted in significantly higher accuracy (r2 = 0.56). The root mean square error (RMSE) was 8.5 MPa for the bending machine, 8.4 MPa for the x-ray LogScanner, and 7.4 MPa for the combination of both methods. Consequently, the combination is an interesting alternative. Future studies should include a larger number of boards and focus on the effect of log carriers and on finding the reasons behind outliers.

The market makes lot of different demands on sawn wood products. There are requirements regarding strength, straightness, durability, aesthetic appearance, etc. Most of these demands can be fulfilled by the inherent properties of the trees in the forest. The challenge is to utilize the wood properties to fulfil the market demands in an efficient way. The raw material has to be selected so every customer gets the right piece of wood with the required properties. In order to achieve this, the raw material has to be characterized with different scanning techniques in several steps before and during the breakdown process. In this presentation some examples and experiences from industrially implemented scanning techniques will be described. We can today, after some years of R&D efforts, see how X-ray LogScanners are implemented in the industry. So far they are used for measurement of diameter under bark, internal knot structure, annual ring width, heartwood content and commodity grades. The full potential of this technique is, however, not being fully utilized yet. Equipment for measurement of spiral grain on logs and sawn wood has also been implemented industrially. It has been proven that with the aid of this equipment boards that will twist during drying can be sorted out and treated separately, thus enabling production of straighter timber. The third type of equipment that will be presented is a heartwood scanner. With this scanner, sawmills select Scots pine planks with high heartwood content that are suitable for applications where improved durability is required. These examples show that scanning technology is a key factor for a successful integration between market and forest.

As sawmills become increasingly efficient, the importance of focusing on value recovery becomes obvious. To maximize value recovery, sawmills require the ability to sort logs according to quality. This study compares four different combinations of three-dimensional (3D) and X-ray scanning that can be used to grade logs automatically. The study was based on 135 Scots pine (Pinus sylvestris L.) logs that had been scanned with both a 3D scanner and an X-ray scanner with two X-ray sources. The percentage of boards with correct grade sawn from automatically graded logs varied from 57% when using only 3D scanning to 66% when using a combination of 3D scanning and X-ray scanning in two directions. The highest possible result, with ideal log grading, was 81%. The result also shows that the combination of a 3D scanner and one X-ray direction results in higher accuracy than a scanner based on two X-ray directions