The measurement of compression wood and other wood features and the prediction of their impact on wood products

University dissertation from Luleå : Luleå tekniska universitet

Abstract: Wood is a complex and highly variable biological material formed to give the tree best possible conditions for sustaining life. Thus every piece of wood is possessed of unique qualities. The great challenge in the process of manufacturing wood products has always been to select pieces of wood with properties that fulfil requirements for the product. The importance of selecting the right piece of wood will increase along with demands from customers for products with specific properties, such as moisture content, warp, strength, biological and aesthetic features. In order to supply customers with the products they request, a considerably improved selection of the raw material is needed. The earlier an accurate selection can be done, the better. To improve this selection or pregrading process, knowledge of the relationships between different features and different aspects of quality, as well as methods for measuring external and internal features, must be developed. The main objective of this work was to contribute to improved predictability of the quality of dried sawn products using the features both of logs and of sawn green products as input. This work was divided into two parts: Part one focused on the possibility of learning how to predict the quality grades of centre planks by manually inspecting longitudinal radiograph images (LRI) that depict the density variation within a log. In a survey respondents were interviewed regarding their interpretations of the density related features visible in the LRIs of Scots pine logs (Pinus silvestris L). The purpose was to be able to use these interpretations in predicting the final quality of planks sawn from the logs. The LRIs were reconstructed with the aid of an X-ray CT scanner. Part two focused on the relationship between compression wood (CW) in foremost butt logs of Norway spruce (Picea abies (L.) Karst) and the warp of the sawn products, on how to detect CW and on how to predict warp. The logs used in the study were chosen among logs delivered to and sawn at commercial sawmills located in the northern part of Sweden in order to assure that conditions in the study match those extant in commercial sawmills. The most important findings in this thesis are: Longitudinal radiograph images of the density variation within a log can be a powerful aid in manual grading of logs with respect to the quality of the resulting sawn products. The shape of the sawn, but not dried, centre planks is an indicator of both the amount and distribution of compression wood. Basing the cutting of planks on their shapes while still green can considerably increase the total length of acceptably straight dried products. This improvement is achieved through the elimination of compression wood.

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