Іnfluence of technological parameters of pressing on properties of alder wood

Abstract

A using of small size wood (for example solid wood wastes from processing of solid wood and rotary peeling) from alder wood is expedient, as humanity has a lack of wood. Properties of softwood are worse than hardwood, therefore using of softwood is limitedly. Softwood is given necessary prop-erties by modification. A purpose of this research is to set the rational regime of pressing that wood stocks had necessary thickness, static hardness and roughness. Static hardness was been determined by a standard method. Wood was pressed across fibres in radial, tangential and radial-tangential directions. Static hardness of end surface and side surface which contacted with the plates of the press was been determined. Wood stocks were made thus: at start pressed on 3-5 %, warmed up in a press for the temperatures 145±5 ^оС, duration of warming up was 1 minute on 1 mm of thickness, then pressed to the certain thickness and maintained 1 hour. Stocks which thickness was h₀ were pressed to the thickness h_k and the degree of pressing was calculated thus ε_h0=(h₀-h_k)/h·100 %. Stocks were made as from boards and as from core after rotary peeling. Before pressing wood moisture was 12±1 % and density of wood was: from boards – 525 kg/m³ and from core after rotary peeling – 460 kg/m³. 12 duplicated supervisions were made for determining of static hardness. Results are given in a table 1, fig. 1 and equations of regression 1 and 2. Determining deformation, thickness was measured through 1 and 10 minutes and 24 hours after unloading out of a press. Also thickness of stocks was measured through 3, 10, 20, 30, 45, 60, 75 and 90 days after pressing, during this time wood was in such conditions t=18-20 ^оС, φ=70-75 %. The research results of roughness are pointed in a table 2. Pressing of alder wood enables to use it equally with hardwood. Alder wood is pressed across fibres to ε_h0=30-35 % if a side surface is exploited and to ε_h0=20-25 % for end surface. It is necessary wood is pressed to =40 % and more if alder wood from core after rotary peeling is used. Mathematical models are got on the basis of experimental information with satisfactory exactness describe dependence of static hardness of side and end surfaces. These mathematical models can be used for the calculation of optimum value of pressing degree in depending on initial and necessary hardness of stocks. Softwood, in that case of alder, is grinded badly, and as a result of pressing, at first, hardness grows and, accordingly, a grinding process gets better, secondly, the size of R_mmax and, accordingly, grinding expenses are diminishes. If wood is pressed to ε_h0=40% and more and in subsequent will be varnished, it is not necessary to make grinding. Heat treatment of wood in a press must be 60 minutes and more, it will be instrumental in achieving the set thickness h_к in every point of sample with assumptive rejections. The sizes of pressing and varnishing wood are not variable. In this work the influence of heat-mechanical modification on static hardness, roughness, deformation of wood after pressing and after some time was been explored.