Evaluating of wetting-induced effects on the surface stability of sanded wood
A sanding is a common woodworking operation to smooth the surface prior to apply surface finish or coating materials. All cutting processes damage the upper layer of wood surface and sanding also creates a deformation zone. This deformation zone is sensitive to artificial or environmental actions, especially to wetting. In order to determine the effect of wetting on the surface properties, to get insight into the dynamics of surface movement as a function of time during the wetting, special 3D surface roughness measurements were carried out and evaluated. For sanding of samples the most common grit sizes were selected and P100 and P180 sand papers were used. Measuring the weight of the samples the dynamics of evaporation of the applied water was also determined. The surface modification after wetting is caused by moisture gradients in the upper layer associated with swelling and shrinkage resulting in permanent deformations. For this layer the most characteristic roughness parameters are the average roughness Sa and the Abbott parameters Spk, Sk and Svk. The extent of roughness variation due to wetting is characterised by the ratio of roughness after wetting to the initial roughness value. The measurement results have shown that the simultaneous infiltration and evaporation rate has a definite influence on the surface roughness modification. The most stable wood species with the least modification were the ring-porous species, following by the diffuse-porous and conifers species. The evaporation rate measured followed the same sequence for wood species investigated.