Finnforest Oy

Teknillinen Korkeakoulu

Matti Kairi

Pertti Helminen

Pekka Ahtila

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 () for dry substance density (&#x3c1;) 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 (&#x3c1;) established to be lower than its initially measured value (&#x3c1;). On the other hand, if the wood veneer has a substantially uniform darkness, the wood veneer in question has the longitudinal and lateral distribution of its dry substance density evaluated and, if those are substantially uniform, the calculated dry substance density (&#x3c1;) of the wood veneer in question is established for a sorting process to be higher than its initially measured value (&#x3c1;). Wood veneers are sorted on the basis of said calculated dry densities for at least two different density categories. In a first density category (A), the dry substance density is higher than in a second density category (B). Wood veneers are laid on top of each other for multi-layer wood, plywood, or some other sandwich material (), the veneers included in the first density category serving as surface veneers () and the veneers included in the second density category serving as middle veneers ().

Analyzing and sorting of wood veneers

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. On the prefabricated joint portion (4) in each beam (2), at least one single-sided nail plate (6) has been fitted against the outer surface of the beam, the width (W1) of the plate plane of the nail plates in a direction perpendicular to the main beam grain (D) being greater than the distance (W2) between the holes (15) for the two jointing (5) in this direction, and the nails (7) of the nail plates (6) being embedded in the wood nearly parallel to the jointing holes. The holes (15) in the jointing perforate the beams (2) in the area of the plate planes of the nail plates, and they have been formed both in the nail plate (6) and in the beam (2) after the nail plates have been fixed to the beam by pressing, in order to provide joint portions (4) retaining dimensional accuracy irrespective of external influences and apt for later assembly into joints (1).

Prefabricated joint structure for a wooden beam

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.

Growing community of inventors

Lohja, Finland

Matti Kairi