Wooden components are, for example, constructed as plywood boards. In plywood boards, a number of thin wooden layers are glued and pressed together. The plywood boards have a relatively high strength to low weight ratio and can be easily processed, like cut or drilled. Another well-known board-like component is constructed as a so-called coreboard. Such coreboards have solid wood profiles which are glued together inside and which are covered by plywood boards on the outside. Such coreboards are generally used to construct solid furniture components or panelling for buildings.
However, the well-known components made of wood and having generally flat shape and grains extending in one direction cannot meet all application requirements of high stability, low weight and high flexibility as well as requirements in savings of wood-like material and labor, when using them for instance in construction work.
Proposals has been made to improve the properties of the components made of wood, like plywood. For instance, a method of making a corrugated vegetable-fiber board from material which have sufficient plasticity when wet and becoming rigid upon being dried out is disclosed in U.S. Pat. No. 2,058,334 (Mason). In this prior art method the sheet having a thickness of about 3.2 mm is treated by several wetting, oiling, heating, drying and pressing stages. The method, however, includes the disadvantages in that the corrugation process of one single sheet is time consuming, requiring at least one day to produce and in most cases the producing time is even longer. Several heating stages at relatively high temperatures are required, which increases the need of energy and thus further the costs. Furthermore, since the corrugated panel is made from one flat panel by the above mentioned treatments, the corrugations are slightly retaining in use and especially under severe conditions of alternative wetting and drying out. A further disadvantage is that the resulting corrugated sheet is not thick enough to meet the requirements of wide variety of applications. Furthermore, the stiffness of the panels in direction perpendicular to the corrugations has also been found insufficient.
GB Patent Application 2 087 793 discloses a corrugated building panel and method of manufacturing the same, said panel being formed of two plies of flexible paperboard or chipboard by steaming the two plies, applying an adhesive to facing side of one of the plies, corrugating the plies and thereafter immediately bonding the plies together. However, the method disclosed is capable to handle only sheets in the range of 0.9 to 1.3 mm in thickness and is merely related to paperboard sheets and not to sheets of wood-like fibrous material, like veneer. Furthermore, this proposal does not relate to the problem of stiffness of the produced panel or to the problem caused by the humid conditions, in which the panel might be used.
In GB Patent 1 360 105 a plywood construction is disclosed, in which plywood comprises a plurality of superposed interfitting corrugated veneers having their surfaces bonded together such that the grains of each veneer are crossing the ridges of the corrugations at an substantial angle to the ridges, the angle being always between 30 to 60.degree. and preferably 45.degree.. The method includes heat treatments of veneers with good bending properties in a steam filled atmosphere. Even though this solution has been able to give more rigid construction, there is a great loss of material when making corrugated plywoods, since the corners of the veneer sheets, which are substantially greater than the resulting corrugated panel, have to be cut off to achieve a corrugated panel having a square shape and corrugations extending from one edge to another. It is strongly pointed out in said GB Patent that if the angle of the grains is too great, i.e. over 60.degree., the veneers will splinter. An further disadvantage of that is that the appearance of the panel has nor fulfilled the aesthetic requirements due to the grains extending diagonally relative to the corrugations.
The object of the present invention is to overcome the disadvantages of the prior art proposals and to provide a new solution for a corrugated construction element and manufacture thereof, said element being sufficiently rigid for various applications and having good surface properties, but still being easy, quick and economical to manufacture and to process.
An another object of the invention is to provide a corrugated element comprising several and at least three layers of wood like sheets bonded to each other, said arrangements being such that at least one of the layers is arranged to be substantially perpendicularly placed relative to the corrugations.
A still another object is that the layers are arranged such that grains of one wood sheet are essentially perpendicularly placed relative to adjacent sheets.
A further object of the invention is to provide a corrugated panel of wooden sheets having an undulation of essentially small size.
A further object of the present invention is to provide a corrugated construction element of wooden material, which keeps its shape as formed i.e. retains the shape of corrugations unchanged in use.
A still further object of the present invention is to provide a corrugated component and a method for producing such a component such that the shape, size and spacing of the corrugations and the thickness of the layers of the element can be adjusted such that any desired form of undulations or corrugations can be provided.
An additional object of the present invention is to provide a method for continuous producing of the elements according to the invention.
A further objective of this invention is to arrange the method in such a way that the component can be given an aesthetically attractive exterior design.
A still further object is to provide a method by which the use of the prior art wetting or steaming of the boards is avoided.