The hygroscopic warping of laminated panels

Various combinations of particleboard substrates and overlay materials were investigated with respect to their warping tendencies when changes in moisture content occur. Warp, defined as the center deflection of the edge or the diagonal of a plate, was determined theoretically and experimentally. The results indicate that theoretical predictions, which are based on assumption of elasticity, are reasonably accurate. The effect of the glueline is minimal and linear expansion (LE) characteristics of the substrate are factors of significance. High LE-range particleboards have expansion values greatly exceeding those of most overlays. A 3-ply (balanced) construction is indicated to avoid objectionable warping. Low LE-range particleboards have expansion values comparable to those of most overlays. Two-ply construction is sufficient in these cases. Vinyl overlays cause only temporary warping due to one-sided moisture absorption of the substrate. Plastic deformation of the vinyl eliminates swelling stresses and permanent warp. Investigation of the possible adjustment of overlay material properties to better match those of the substrates is suggested.

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