Acta Univ. Agric. Silvic. Mendelianae Brun. 2011, 59, 59-72
Published online 2014-06-14

Analysis of causes of warping the plywood sheets

Jaroslav Hrázský1, P. Král

1Ústav základního zpracování dřeva, Mendelova univerzita v Brně, Zemědělská 1, 613 00 Brno, Česká republika

The aim of the paper was to analyse the shape stability of plywoods. Following operations were monitored: storing the construction veneers, spreading the gluing mixtures, prepressing, pressing and the storage of plywoods. The shape stability of plywoods is affected by various factors and technological parameters of particular operations. It is one of the important parameters to assess the quality and use of plywood sheets in practice. On the basis of the analysis of the present condition of the problems a methodical procedure was prepared to determine causes of warping the plywood sheets. According to this procedure an experiment was created. Within this experiment parameters were determined, which affect warping the plywoods. The moisture and temperature of veneers and pressed plywood sheets rank among the most important parameters affecting shape stability. The size of the camber of pressed plywood sheets was also determined. Results showed that the warping of plywood sheets resulted particularly from the area distribution and variation of the moisture of veneers and plywoods, which was also related to temperature. These values of moisture and temperature result, e.g., from the relative air humidity and temperature, pressing parameters but also storing in stacks and appropriate storage. On the basis of the effect of determined parameters mentioned in this paper, the larger or smaller warping of plywood sheets originates, which is expressed by the shape change and size of their camber.


7 live references