Vacuum Steam Technology for Rapid Plasticization and Bending of Maple

Abstract

Bending wood dates back to antiquity in the form of baskets from willow branches and when boats were no longer made of hollowed out logs. Fresh growth willow twigs are readily bent into practically any shape; however, when wood has been separated from the tree and dried it is more rigid, difficult to bend, and breakable. Steamed wood is less rigid since adding moisture and heat to wood results in plasticization. Steaming at atmospheric pressure is the common technique for wood bending where diffusion prevails as the predominant mechanism governing moisture movement. Applications using conventional atmospheric steaming are time consuming and can result in failed bends. While other wood plasticization methods exist, Vacuum Steam Technology offers a promising method that utilizes pressure differentials to accelerate the addition of steam to wood due to water vapor bulk flow and subsequently an accelerated temperature rise and moisture addition. The objectives of this work were: (1) determine whether cycles of vacuum and steaming could significantly improve the plastic-deformable state relative to the classic process of atmospheric steaming given equivalent treatment times when beginning with low moisture content (<10%) maple, and (2) compare the work required to bend to form between Vacuum Steam Technology treated maple and atmospheric-steamed maple when beginning with low moisture content (<10%) specimens. A procedure for Vacuum Steam Technology to enable rapid plasticization of maple specimens from a kiln-dried state was developed. Kiln dried maple specimens were either treated according to the Vacuum Steam Technology procedure or were atmospherically steamed for a time equivalent to the Vacuum Steam Technology treatment and then bent into a 180° semi-circular form. Vacuum Steam Technology treated specimens had 0 failed bends whereas the atmospheric steamed specimens resulted in 39% failed bends. Vacuum Steam Technology treated specimens resulted in 17% less work to bend. The results clearly indicate that Vacuum Steam Technology is a superior technique for attaining a plastic deformable state prior to bending when beginning with low moisture content maple. Additional results included time to temperature, rate of moisture content change, final moisture contents, specific gravity influence.