FI77594C - Method of manufacturing tubular wooden structures. - Google Patents

Description

77594

The present invention relates to a method for the production of tubular wooden structures having a closed perimeter and consisting of a plurality of glued-together wooden parts.

A well-known way to eliminate the various strength properties and unevenness of natural wood and the tendency for cracks to form is to glue together smaller pieces of wood into larger structures, such as in the manufacture of plywood or glulam. Such wood-based composites have many good properties as structural materials, but have been used mainly in massive load-bearing structures and less often in tubular or other hollow structures, despite the fact that such often have optimal strength properties. This is due in part to the difficulty of forming curved surfaces from tightly bonded wood parts and the difficulty of subjecting the cavity structures to the required compressive pressure.

Swedish patent application 8104714-4 discloses a method for producing tubular wooden structures by wrapping glue-coated plywood in several layers on a joint and then curing the glue. Since thin plywood bends very well, it is possible in this way to directly produce a tubular shape with the necessary curved surfaces associated with it. However, the problems of using the required high compression pressures remain, as the core must be able to withstand high pressures and must have internal heating. The pipes must also be wrapped relatively tightly so that they do not detorate too much under the effect of the applied compression pressure. The problems increase when the adhesive system used also requires a high temperature and a long curing time.

It is an object of the present invention to provide an improved method of manufacturing tubular wood structures which avoids the above problems. The object of the invention is in particular to enable a simple manufacture using high pressures, alternatively high temperatures in connection with compression. These objects 2 77594 are achieved as set out in the claims.

According to the invention, since the entire circumference of the pipe is not manufactured at once, but instead radial sectors from the surface of the pipe, which are then glued together, normal manufacturing and pressing methods can be used in connection with the manufacture. In particular, it becomes possible to manufacture pipe sections in standard heated compression molds where high pressures can be used. Nevertheless, the pipe sections can be made of plywood or preformed wood sections in order to preserve the possibility that curved surfaces can be formed directly. In these steps, where the most glue is required, it is possible to use cheap glues. When the circumferential edge surfaces of the pipe sections are joined in the second stage, the total joint surface and the compressive strength requirements are much smaller and more expensive adhesives with lower compression temperature and curing time requirements can be used without economic disadvantages. This means that the cavity in the structure no longer constitutes a significant constraint on the compression conditions used and therefore also on the economics of manufacturing at this stage.

As mentioned above, the parts of the jacket surface of the pipe should in themselves be assembled from glued parts so that the pipe has structural strength. The choice of the gluing method at this stage is largely determined by the final shape of the pipe. Rectangular tubular cross-sections with predominantly flat jacket sections can be considered for several applications. Normal plywood or glued layers of wood strips or rods can then be used relatively simply as tubular parts in the product. However, as load-bearing and strength requirements increase, for example under structural conditions, a less rectangular cross-section is desired and instead a cross-section with at least rounded corners and preferably a nearly circular or oval cross-section.

il 3 77594 This means the manufacture of pipe sections with a curved jacket surface, which makes manufacture difficult. In these cases, it is most suitable that the pipe sections are made of plywood, which can be more easily formed into curved surfaces than thicker sections. The thickness of the plywood can be between 1 and 6 mm, preferably between 1.5 and 5 mm.

The pipe sections are then preferably manufactured by applying an adhesive to the plywood layers, joining them and pressing them in a mold having the desired shape of the pipe surface. Alternatively, plywood strips may be wrapped around the core to provide a prior art pipe which is then split into finished pipe sections for compression. The curved surfaces are preferably subjected to radial compressive forces to apply uniform pressure to all parts of the surface. However, from a manufacturing point of view, it is simpler to be able to use forces acting against a uniform pressure and perpendicular to the direction of compression, for example at joints between pipe sections, which can advantageously be achieved by pressing the material between tapered compression sections to produce a wedge effect. To avoid radial forces, it may be suitable to make the pipe from more than two pipe sections. Alternatively, the two-half tube can be made slightly oval, for example so that the short axis is 50-90% of the long axis or preferably 60-85% of the long axis, whereby the parts become smoother than in the case of a circular cross-section if the distribution takes place along a long axis.

In more cases of loading, it is most recommended that the direction of the wood fibers be kept mainly in line with the longitudinal direction of the pipe. If the direction of the fibers forms an angle with the longitudinal axis, the fiber directions of the different layers must be transverse so that the pipe has maximum strength against the tensile load. A fiber orientation between 0 and 45 ° with respect to the longitudinal axis reduces the risk of cracking and increases the resistance under many load situations.

4,77594

Of course, most of the total glue consumption of the finished pipe is spent on the interconnection of plywood. Although all wood adhesives, such as formaldehyde-based curable adhesives, can in principle be used, phenol resin-based, possibly modified with resorcinol resin, in particular, are preferred for economic and strength reasons at this stage of production. These adhesives require compression pressures of the order of 5-20 kg / cm 2, compression temperatures of the order of 100-150 ° C and compression times of the order of 5-60 minutes depending on the material thickness.

After compression of the pipe sections, the longitudinal radial edge surfaces must generally be matched in terms of flatness and shape so that they can be glued together into a final pipe shape with a closed cross-section. In order to achieve maximum strength and the best control of the relative position of the parts during compression, the finger joint is considered to be the best for this step. When the edge surfaces are made flat, simpler machining is achieved, so that the groove or tongue can preferably be placed in place. The pipe can in principle be formed from an arbitrary number of parts, but it is generally sufficient and, especially from the point of view of compression, it is most suitable that the pipe is made of two halves.

When joining the pipe sections, the joint surface is relatively small and the consumption of glue is low. In this case, a fast-curing wood glue is preferably used, which does not require high temperatures or a long pressing time, since the sealing can then take place in a very simple press without shaped surfaces and with a simple heating medium. Resorcinol or resorcinol / phenol-based resins are considered to be the most suitable wood adhesives.

Because the pipes are made of glued wooden parts, they can be made to an arbitrary length and can also be extended longitudinally by gluing. The cross-section of the pipes does not have to be constant, but they can be a sign

II

5 77594 to make a cone shape.

The pipes made according to the invention can be used as transport lines, but they have special advantages as load-bearing components in beams. They can also be used as columns, for example for lighting or wiring purposes, in which case they are preferably made conical. Oval cross-sections as described above may also be advantageous in columns because higher bending strength may be required in some direction, for example across the lead direction relative to it.

Tubes for outdoor use can preferably be impregnated against rot. Adhesive joints in the structure can make it difficult for the liquid impregnating agent to penetrate and it is therefore recommended that the wooden parts be impregnated before they are glued together into pipe parts. This impregnation can possibly be supplemented by impregnation of the finished pipe. Other impregnation, for example with flame retardant chemicals, can take place in a similar manner.

Impregnation of wood parts before gluing together can take place both when the wood parts, for example plywood, are dried and when they are not dried. Suitable methods of use for raw plywood include dipping, spraying and brushing, in which case the materials must be allowed time to diffuse before the impregnated material is dried. In addition to the operating methods described above, pressure impregnation (e.g., Bet-hell, Lowry, etc.) can be used when handling dry plywood.

All known wood preservatives are suitable for impregnation against decay, but it is particularly important to use materials for the columns which provide long-term protection due to good adhesion. Examples of such are acidic copper waves such as CC (copper / chromium), CCA (copper / chromium / arsenic), CCB (copper / carbon / boron), and CCP (copper / chromium / phosphorus). In order to achieve particularly good diffusion and adhesion properties, ammoniacal systems containing an ammoniacal copper solution, possibly also arsenic or organic components, such as straight or branched fatty acids, fatty amines or quaternary ammonium compounds, are preferred. Spruce is a suitable wood material for columns but difficult to impregnate, which, however, can be diffusion impregnated in thin pieces or plywood using especially ammoniacal systems. The invention thus makes it possible to use spruce, since impregnation can take place before the wooden parts are glued together.

The protection of the columns can be further improved if insecticides are also added during impregnation and if the open lower end of the column and its outer surface a few meters above the ground are covered with an impermeable plastic sock, preferably with a water-repellent collar at the top to prevent water penetration between the column and the sock.

Example;

A circular column with a length of 10 m, a diameter of 400 mm and a jacket thickness of 30 mm was made of two semi-circular halves. Each half was formed from 15 layers of 2 mm thick plywood applied with about 200 g / m 2 of phenolic adhesive (Casconol 1550) and the halves were joined in a semicircular compression mold and pressed for about 20 minutes at a pressure of 10 kg / cm 2 and a compression temperature of about 140 ° C. The axial edge surfaces of the halves were joined together by finger joining with resorcinol / phenol adhesive (Cascosinol 1711) using a constant compression pressure of about 8 kg / cm 2, a temperature of about 100 ° C and a compression time of about 10 minutes.

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Claims (9)

77594 A method of manufacturing tubular timber structures with a closed circumference, wherein elongate pipe sections of glued wood plywood, the cross-section of which forms open sectors of the finished pipe circumference, are joined together by gluing to a closed pipe circumference, characterized in that the elongate pipe sections are two pipe halves together using a uniform compression pressure. Method according to Claim 1, characterized in that the cross-section of the tubular wooden structure is substantially circular. Method according to Claim 1, characterized in that the pipe sections are formed from plywood with a thickness of 1 to 6 mm. Method according to Claim 3, characterized in that the thickness is 1.5 to 5 mm. Method according to Claim 1, characterized in that the wooden parts of the pipe sections are glued together with a phenol-resin-based adhesive. Method according to Claim 1, characterized in that the pipe sections are connected to one another by means of a finger joint. Method according to Claim 1, characterized in that the wooden parts are joined together with a resorcinol-based resin. Method according to Claim 1, characterized in that the fibers of the wooden parts are substantially parallel to the longitudinal axis of the tube. A method according to claim 1, characterized in that the direction of the fibers of the wooden parts forms an angle of less than 90 ° with the longitudinal axis of the pipe.