Abstract:

Objective: From the perspective of wood-cutting friction, this study analyzes the influence of wood moisture content, micro-pit texture area ratio, and different wood sections on surface adhesion, aiming to provide a theoretical basis for further research on the mechanism of how texture surfaces affect wood-cutting friction. Method: A contact angle measuring instrument was used to determine the surface wettability under different texture area ratios. With Larix gmelinii (larch) as the research subject, a high-precision uniaxial mechanical testing system was employed to investigate the effects of wood moisture content, micro-pit texture area ratio, and different wood sections on adhesion, and to explore the correlation between contact angle and adhesion. Result: The contact between a flat cemented carbide sample and the tangential section of wood was taken as an example. When the wood moisture content increased from an oven-dried wood to an air-dried wood (about 12%), and further to the fiber saturation point (FSP) (about 24%), the surface adhesion gradually rose from 0.41 mN to 0.45 mN and then 0.48 mN, respectively, showing a slow increase. Beyond the fiber saturation point, when the moisture content further increased to green wood (about 72%), the surface adhesion significantly increased from 0.48 mN to 0.89 mN (85.4% increase). When further increasing moisture content from green wood moisture content to water-saturated wood, the increase in surface adhesion tended to a slower down and stabilized. When the wood moisture content was 12%, the texture area ratio increased from 0% to 30%, and its surface adhesion decreased from 0.45 mN to 0.31 mN. When the wood moisture content was 72%, as the texture area ratio increased, the surface adhesion initially decreased from 0.89 mN to 0.74 mN. When the texture area rate further increased to 30%, its surface adhesion rebounded to 0.78 mN. Moreover, the transverse section exhibited stronger adhesion than the tangential section. Conclusion: The adhesion force increases with the rise in wood moisture content. When wood’s moisture content rises from oven-dried wood to the FSP, its surface adhesion force shows a slow increase. At this stage, the adhesion primarily originates from van der Waals forces and the weak capillary action of multilayer water molecule films adsorbed on the wood surface, resulting in relatively low adhesion. When the moisture content increases to green wood moisture levels, the adhesion rises significantly. In this case, the two surfaces adhere through liquid capillary action, forming a liquid bridge, and the dominant factor contributing to wood surface adhesion shifts to capillary forces. However, as the wood moisture content continues to increase, the water molecule layer on the wood surface thickens, causing capillary forces to stabilize and leading to a relatively stable adhesion force. Micro-pit textures can reduce the adhesion force between cemented carbide and the wood surface. Surface texturing treatment decreases the contact area and disrupts the continuity of the water film at the interface between the wood and the micro-textures, reducing the liquid bridge area and resulting in lower adhesion between the two. An increase in contact angle leads to higher surface adhesion, which can be indirectly influenced by texture-regulated wettability. The adhesion force between the cross-sectional surface of wood and cemented carbide is greater than that between the tangential section and cemented carbide.

Key words: wood cutting, micro-texture, wood moisture content, surface adhesion, friction