Nondestructive measurement of spiral grain with X-rays in laboratory and in industry

Sammanfattning: Wood is a biological material with great variability. Every piece of wood is a unique individual. This is an advantage of wood when it is used in products where the wood structure is visible but a drawback in the manufacturing process. It has become more and more important to control the variability of wood as customers increasingly demand sawn products with special properties regarding dimension, moisture content, warp and last, but not least, biological or aesthetic features. To be able to fulfill these requirements, the right logs have to be selected for a certain product before the sawing process. Spiral grain is a fundamentally simple concept in which the wood grain, as seen on the outside of a log, runs around it in a spiral rather than parallel with the axis. Even the most casual observer will have seen indications of spirality in the cracks running around old dead trees or around well-weathered transmission poles. Spiral grain is a wood feature that is formed in the living tree. Timbers sawn from trees with severe spiral grain have a great tendency to twist when the moisture content changes. This is a big problem in the wood products manufacturing process. Some of these problems could be avoided if the magnitude of the spiral grain angle could be measured early in the manufacturing process and logs with severe spiral grain sorted out. However, a non-destructive method for measurement of spiral grain in logs is lacking both for industrial purposes and for research purposes. The main objective of this work was to develop and evaluate a non- destructive method for measurement of spiral grain in logs for research purposes and to analyse if there are any possibilities to develop a method that can be used in the industry.