Наукові праці Лісівничої академії наук України (Oct 2018)
Shape stability as a quality criterion for PCW-made blockboards
Abstract
The existing global planetary problems have given humanity impetus to rational use of wood, processing of wood residues and, in particular, investigation of the unutilised resource - used wood, the annual potential of which is about 2 million tons in Ukraine. PCW (Post-Consumer Wood) is the resource base of wood raw materials which is not used to the full extent, its reserves increase with the development of households and the woodworking industry. For more than 20 years, the UNFU has been actively searching for alternative sources of raw materials, which is a relevant problem, and new design and technological solutions are being developed for the manufacture of products based on PCW: blockboards, wood particleboards, fuel pellets, furniture panels and various workpieces. The research problem is the lack of resource-saving and environmentally sound technologies with practical recommendations for the use of PCW. A partial solution to this problem will provide the woodworking industry with additional alternative resources through recycling PCW into useful products. It is shown that the research aimed at improving shape stability of blockboards made by way of conventional and combined laying of PCW-made strips, and which, as evidenced by long-term use in dry premises, have a steady stress-strain state regardless of the anisotropy of wood, is of great practical interest and belongs to the promising area of scientific and technological activity at the UNFU. The purpose of the study is to investigate and analyze the shape stability of the PCW-made blockboards both of normal design and combined. The object of the study is the PCW-made blockboard. The subject of the studies – patterns of influence of the blockboard designs and combined laying of strips of different width on the shape stability of PCW-made blockboards. It is substantiated that PCW is a suitable secondary resource for manufacturing blockboards, since this wood has a low moisture content (W = 8 ± 3%) and steady internal stresses, which positively affects the shape stability - the stress-strain state of the blockboard structure. Identified are the patterns of influence of the width of strips (core) made of PCW and wood particleboard (WPB) on the strength of the combined PCW-made blockboards. It was found that all the values for the shape stability of the obtained PCW-made blockboards were lower than the normative (0.3 mm) in accordance with GOST 6449.3 "Fits and clearances. Form tolerance and arrangement of surfaces". It was established that the shape stability of PCW-made blockboards is influenced by the ratio of the thickness of the strip to its width. It is proved that in order to achieve shape stability within the normal range according to the standard, it is recommended that the width of the strips for gluing a blockboard should be taken no more than 2-4 its thickness. It was determined that the best quality as to the shape stability will be found with combined PCW-made blockboards in design: ВPCW = 30 mm; BWPB = 70 mm, the deviation from the plane being 0.081 mm. In order to ensure the shape stability of the PCW-made blockboard exposed to variable humidity, it is desirable to apply the ratio of sides in the cross section of strips as 1:3, and the grain angle on the end of the strips must be at least 45o. It is recommended that in the manufacturing of blockboards made of PCW and WPB, wooden strips of the radial section should be used in order to provide high shape stability. It is expedient to use faced PCW-made blockboards for manufacturing cabinet-type furniture products.
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