The effect of sanding on the roughness of stained and lacquered wood surfaces

The roughness of wood surfaces after each stage of surface treatment (sanding, staining and applying lacquer) has been investigated. Previous research work was in most cases fo­cused on the direct study of the roughness as a result of sanding with various grit sizes of sandpaper and sanding directions. Those investigations were based on the earlier studies of metal surfaces. The problems of distinguishing structural surface irregularities of wood from roughness caused by processing have not been sufficiently investigated. In this paper the effect of grit size i. e. of the combination of grit sizes and directions in sanding treatment, on the roughness of wood surfaces has been investigated. The work was carried out on oak, beech and pine substrates after sanding, after staining (with water stain nitro-based stain and oil-based stain), and after applying up to three coats of nitro cellulose lacquer. The roughness measurement according to system M was performed using the profilograph - profilometer Rank Taylor Hobson (model Talysurf 6) over the sampling length of 0.8 mm. The values of roughness parameters Ra, Ry and R, were recorded. The combination of grif sizes and sanding directions 120 _|_ + + 150 _|_ + 180 || proved more effective than the combination 100 _|_ + 150 ||, the best effect being achieved on pine, and the least on beech surfaces. The structural characteristics of oak make it difficult to reach definite conclusions about this substrate. The roughness is increased after treating the wood with water stain, nitro-based stain and oil-based stain. The greatest roughness was found on beech samples treated with water stain, while nitro-based and oil-based stains caused equal roughness, through somewhat less expressed than water stain. The application of subsequent lacquer coats reduces the roughness. The relationship between the roughness values of the sanded and stained surfaces remains similar after applying lacquer.