Abstract
The upper cell layers of machined solid wood surfaces will usually be damaged and compacted due to cutting forces. The deformation zone may be instable due to temperature and moisture variations as a consequence of artificial surface treatment or environmental interaction. Therefore, an evaluation method of surface stability in this respect would be desirable. In the frame of the new developed surface roughness evaluation method an individual wetting procedure has been developed, whilst surfaces have been characterized by 3D roughness measurement. The stability of surfaces is characterized by appropriate roughness ratios measured before and after wetting. The core depth Sk of the Abbott parameters is the most sensitive indicator to any changes in the deformation zone. Different machining processes may produce surfaces with different stability but wood species have also definite influence on the surface stability, probably due to their density and moisture conduction properties. Latter is supported by the fact that the half-time of moisture evaporation from surfaces may differ considerably. In these experiments, planed and precision-planed surfaces were compared. According to the working principle of the precision planers the planing tool is held stationary whilst the work piece does the feeding motion, thus the blade produces a very thin slice. Using this machine, the machining roughness can be reduced to minimum as it is possible to avoid formation of cycloid arcs (like in case of traditional planing) and also possible to avoid dust formation (like in case of sanding). Investigations were conducted on Norway spruce (Picea abies), larch (Larix decidua), scots pine (Pinus sylvestris), sessile oak (Quercus petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula) and beech (Fagus sylvatica). Black locust and the sessile oak have had most stable surfaces by both machining methods. The deformation zone of precision planed surfaces has been proven to be more stable than the one of planed surfaces for all wood species. Keywords: Cutting parameters, deformation zone, planed surface, roughness, surface stability
Highlights
Surface roughness can have a huge impact on finishing costs and the perceived quality of wood products, there is a lack of consensus on how to measure and evaluate wood surface roughness
The optical surface roughness measuring methods have limitations regarding the usability on wood surfaces due to errors induced by light reflections
The aim of this paper are: to compare the stability of surfaces due to wetting produced with the two machining types and to rank the wood species according to their stability for the two machining types, to experience the suitability of the different standardized 3D roughness parameters to describe the status of the wood surface during wetting and to determine the character and measure of surface deviation by monitoring the displacements of the surface and by analysing the differences between the initial and stabilized surfaces
Summary
Surface roughness can have a huge impact on finishing costs and the perceived quality of wood products, there is a lack of consensus on how to measure and evaluate wood surface roughness. Machining processes and species are the factors that significantly affect surface roughness, as opposed to the plane of section factor or the direction of the stylus tracing (Laina et al 2017). Contact stylus surface roughness measuring method is the most common for wood surfaces. Specific recommendations are given (Gurau and Irle 2017) regarding the selection of the stylus-measuring instrument, and the Maderas. Universidad del B í o - B í o measuring conditions. The optical surface roughness measuring methods have limitations regarding the usability on wood surfaces due to errors induced by light reflections. To measure the surface roughness during the surface movement due to the wetting process, only the optical methods are suitable thanks to their measuring speed and contactless measuring principle
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