The effects of compression rolling on sawn timber
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The effects of a mechanical process termed "Compression rolling" on the structure of sawn timber have been investigated in the course of this work. 1. A wood rolling mill was designed on the basis of preliminary experiments and the experiences of previous workers. The multi-functional rolling device contains a series of innovations which were necessary to test the effects of different rolling parameters on the timber structure. 2. A multifactorial, randomized, fully-replicated block design was set up to determine the effects of the process on the diffusivity and on the permeability of Nothofagus fusca heartwood (New Zealand red beech). The results showed that the process had a pronounced effect on permeability, which was assessed after a pressure treatment with CCA preservatives, whereas the drying characteristics were only modified to a minor degree. 3. The importance of level of saturation at the time of rolling was determined. With a decrease in moisture content structural alterations were increasingly confined to microscopic damage, whereas application of the process to highly saturated boards resulted in substantial macroscopic damage. Thus any advantage in compression rolling with respect to drying is vitiated by having to pre-dry before hand! 4. Detailed scanning electron microscopical (SEM) examination was undertaken to observe anatomical alterations induced by compression rolling of red beech. Most noticeable was the effect on the vessels and on the intra- and intervascular structure (perforation plates, tyloses and vessel to vessel pits), which appeared deformed and occasionally collapsed and ruptured. 5. The SEM was used to investigate the effects of hot water soaking and compression rolling. The recorded improvements in drying rate were attributed to the dilution and partial extraction of phenolics from the ray parenchyma and its redistribution, whereas the subsequent rolling process was not able to increase further the radial or tangential drying rate. 6. The effects of rolling on the structure and permeability of the heartwood of two refractory softwoods (Pseudotsuga menziesii and Picea sitchensis) were determined. In both species permeability was only improved to a small extent and the improvement observed was confined to small bands mainly within the latewood. 7. Similar structural alterations in both species at macroscopical and microscopical level are indicative of an irregular strain distribution throughout the boards. This was attributed to a large variation in density and inherent permeability between earlywood and latewood.