Abstract: The invention relates to a method for increasing strength and/or reducing strength variations in multi-layer wood, plywood, and the like sandwich material. The method comprises measuring wood veneers (10) for dry substance density (?) with high-frequency electromagnetic resonance (TEM) and additionally analyzing the homogeneity and/or grain structure of wood veneers from a wood veneer surface in the way of its darkness (R). If the wood veneer comprises a number of local first regions, which are darker than a predominant darkness of the veneer surface, the wood veneer in question has its calculated dry substance density (?C) established to be lower than its initially measured value (?M).

Abstract: The invention relates to a method for increasing strength and/or reducing strength variations in multi-layer wood, plywood, and the like sandwich material. The method comprises measuring wood veneers (10) for dry substance density (&rgr;) with high-frequency electromagnetic resonance (TEM) and additionally analyzing the homogeneity and/or grain structure of wood veneers from a wood veneer surface in the way of its darkness (R). If the wood veneer comprises a number of local first regions, which are darker than a predominant darkness of the veneer surface, the wood veneer in question has its calculated dry substance density (&rgr;C) established to be lower than its initially measured value (&rgr;M).

Abstract: The invention relates to a prefabricated joint structure for joining an essentially wooden elongated beam (2) or similar to at least one other beam (2) over a predetermined length (A) of a relatively short joint portion (4) in the beam, the joint (1) being accomplished by pins, bolts or the like (5) penetrating the beam or beams. In each joint there are at least two jointing in a direction transverse to the main gain of the beam. The joint structure further comprises a metal nail plate (6), having a plate plane transverse to the length (T) of the jointing and whose nails (7) protrude from the plate plane and are embedded in the beam wood.

Abstract: The invention relates to a method for the hardening of wood material by impregnating it with a polymerizable substance and by polymerizing the polymerizable substance by means of heat. Heat transfer and cleaning in the polymerization have been improved through the impregnated wood material being in contact with water during the polymerization. The water is preferably hot and pressurized and serves at the beginning of the polymerization as a heating medium and during the polymerization as a cooling and cleaning medium.

Abstract: A method of enhancing the strength and of reducing strength variations of multi-layer wood, plywood or similar by measuring the density of the veneer sheets used in the production and by grading the veneer sheets accordingly. The density of the veneer sheets is measured in a manner known per se by using a high-frequency electromagnetic resonator (2). To build up layers of multi-layer wood, plywood or similar (12), veneer sheets confirmed to have a higher density are graded as surface sheets (13) and/or local density variations of central sheets (14) are reduced by mixing veneer sheets with various densities.