Effect of Loading Size and Reaction Wood Proportion on Longitudinal Warping During Pressure Steaming

This study evaluates the effect of loading size on the longitudinal warping of beech wood containing reaction wood. Reaction wood in hardwood species has properties that negatively affect not only the usability of wood products but also the processing of the wood in which it is found. To investigate these effects, steam pressure treatment and three levels of mechanical loading (700, 2000, 4000 kg·m−2) were used, along with the effect of the proportion of reaction wood. Steam pressure treatment generally caused greater warping, particularly in unloaded specimens, due to increased release of internal growth stresses. Mechanical loading effectively reduced deformation, with the most pronounced effects observed at 700 and 2000 kg·m−2; further increases in loading did not provide any significant additional benefits. Although the proportion of reaction wood ranged from 14% to 56%, there was no obvious statistical correlation with deformation, suggesting that the distribution and degree of development of reaction wood have a greater impact than its total content. Overall, hydrothermal treatment induces the release of internal stress, leading to warping, while moderate mechanical loading can successfully limit warping. Understanding these interactions is key to processing beech wood with reaction wood and to improving the quality of finished products.