The influence of certain factors on thickness loss after the hot gluing of cut lamellas into solid wood layered boards

Abstract

An experimental laboratory investigation has been carried out into the hot gluing of solid wood layered boards made out of 5.3 mm thick solid-wood lamellas, the latter being produced by the lengthwise veneer cutting technique, the object of the research being to determine some of the reasons (humidity of wood before heating, temperature of wood before cutting into lamellas, and temperature and pressure during the gluing of boards) for the permanent thickness loss which occurs during gluing. Spruce wood (Picea abies (L.) Karst.) was used in the experimental tests. Before cutting into lamellas, this wood was classified into two humidity groups, and heated to three different temperatures. The dried lamellas were used, after suitable preparation, for the two outer layers, which were glued, together with a middle layer of sawn lamellas, by the hot gluing process. A total of 162 laboratory boards, of length 500 mm, width 475 mm and thickness from 24 to 25 mm, were hot glued, using melamin-urea-formaldehyde glue, at three different gluing temperatures and three different gluing pressures. Regression analysis of the measured results of thickness loss showed that the influence of the studied factors on thickness loss was linear, and that thickness loss depends the most on gluing pressure, followed by gluing temperature. It was also found that a higher wood humidity results in a slightly greater thickness loss than the wood’s temperature before cutting into lamellas.