The cupping of lumber depending onchangeoftheir moistureand geometric characteristics

Abstract

Laminated panels are common among structural elements for the production of a variety of wood products. Most studies of laminated structures are limited to the analysis of their physical and mechanical characteristics. In the case of using laminated panelsas the facade surfaces of joinery and furniture, the importance of their aesthetics is also important. The quality of the laminated structures is conditioned by the properties of its individual sections, so it is important to take into account the properties of these sections for the rational choice of the scheme for the formation of the laminated structure and to predict its quality. The main reasons for the possible change in the shape of the surfaces of the laminated structures are described. Drying and swelling lead to a change in the size and shape of both parts and products of wood and lumber used for their manufacturing. The warpingof lumber is a pronounced defect. The main causes of the lumber warpingare the anisotropy of the properties of the wood and the unevenness of its structure, as well as the uneven change in moisture in different structural directions. The lumber, depending on their location in the log, has unequal resistance to the transverse cup warping. When calculating moisturedeformations, the concept of relative deformation of drying is used. Quantitative characteristics of wood drying are the corresponding coefficients of drying characterizing the change in geometric dimensions. If the drying of the layers of the board is not equal, then such boards will have a transverse cup warping. In order to solve the problem of rational choice of the formation scheme of laminated panel structures and predicting their quality even before gluing, the mathematical model for the theoretical study of the shape change of lumber was developed. Obtained engineering formulas for calculating the coefficients of wood drying show that the form change of lumber depends mainly on its size, moisture and location in the log. To determine the magnitude of the shrinkage coefficients of the lumber layers, it is advisable to use the shrinkagecoefficients in the radial and tangential directions.