TECHNICAL FIELD

[0001 ] The present invention relates to a pipe-shaped pole made in sections of laminated wood. The invention also relates to a method for manufacturing the pole. A pole of the described kind may preferably be used as a power line pole or as a pole for lighting.

[0002] Solid poles of wood have been used to a large extent for many decades as poles for power lines, telephone lines and as lamp posts. Laminated wood and composites of wood material have been designed and used as a substitute for solid wood.

[0003] In spite of the fact that hollow poles of laminated wood as well as poles of wood chips are known in the art, it has not been possible to successfully produce poles of wood laminate. Hollow pipe-shaped poles composed of wood veneers are shown in the patent document US 2,543,901 . These known poles of laminate are produced from wood veneers laid in a spiral in the longitudinal direction of the pole to provide support for the side walls in the pipe of laminate. This further strengthens the side walls but renders the pole complicated and expensive to produce. [0004] Patent document CA 1325096 shows a method of manufacturing a pole of laminated wood. This document illustrates pipe sections of laminated wood, where these pipe sections are cylindrical, hollow and planed at the ends. At least two such pipe sections are joined together with their plane ends against each other by means of gluing, whereby a pole is created consisting of these at least two pipe sections.

DESCRIPTION OF THE INVENTION

[0005] The present invention relates to a pole that is composed of two or more pipe sections built up as cylindrical pipes made of laminated wood. The pipe sections are glued to each other at their longitudinal ends, where these make contact with each other at joints between pipe sections. The pipe sections have inner cylindrical cavities with an inner diameter D. To create a stable pole, joint pipes are arranged which are inserted into the two longitudinal ends confronting each other. These joint pipes are also made in the form of cylindrical pipes of laminated wood but have an outer diameter D. The joint pipes have an inner cylindrical cavity. [0006] Those surfaces of the joint pipe which abut the inner walls of the respective pipe section, into which the joint pipe is inserted, are preferably glued to each other.

[0007] The invention also relates to a method for manufacturing the pole according to the invention. The method is described in detail in the description of embodiments below.

[0008] According to one aspect of the invention, a pole is presented having

characteristic features according to the device specified in the independent claim 1. [0009] According to a further aspect of the invention, a method for manufacturing the pole is presented, wherein the method is specified in the independent claim 7.

[0010] Further embodiments of the invention are presented in the dependent claims. [001 1] A pole designed according to the inventive aspect has many advantages. The pipe sections may be manufactured in standard lengths, for example 2-metre lengths. In this way, a user may keep a stock of such pipe sections and, according to requirement, assemble poles together for, for example, power lines of the desired length, where then 8-metre, 10- metre or 12-metre poles are fabricated according to the requirement that arises. Further, the finished poles are light since they do not contain such much material. Two persons may, for example, carry and erect a lighter variant of such a pole manually, without any mechanical help. Because the glue that is used impregnates the veneer layers, preserving properties are also imparted to the wood in the pole. A pole manufactured according to the invention is estimated to be in use for at least 30 years also when its lowermost part is buried in the ground. Further, poles of the described kind may replace the solid poles, currently usually creosote-impregnated, which are used as poles for electricity and telecommunication lines, hence causing reduced influence on the environment. Another advantage of the pole according to the invention is that it has very strong joints due to the joint pipes that are used in the joints between the pipe sections. This results in considerably higher stability and reduced risk of rupture at the joints compared with poles according to the prior art as described in patent document CA 1325096, in which pipe sections are glued to each other edge to edge. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic picture of a complete pole in four sections according to the invention.

Figure 2 illustrates a perspective view of a detail of a joint in a pipe section into which a joint pipe is inserted.

Figure 3 illustrates how an additional pipe section is fitted outside the projecting joint pipe in

Figure 2 for achieving a joint between two pipe sections.

Figure 4 shows how two halves of a pipe section are glued to each other.

Figure 5 shows in cross section how a pipe section is built up from inner and outer pipe parts glued to each other, where it is also clear that the longitudinal joint of the outer pipe part is displaced 90 degrees in relation to the longitudinal joint of the inner pipe part.

Figure 6 shows the corresponding joining as in Figure 4 but where longitudinal contact surfaces between pipe halves are provided with fingers.

Figure 7 illustrates the polar displacement of longitudinal glued joints when outer and inner pipe parts are made with quarter sections of laminated wood.

Figure 8 illustrates how the stratified layers of thin veneers are pressed together by means of a press tool to form pipe halves into said pipe parts.

Figure 9 shows two pipe halves for an outer pipe part and two pipe halves for an inner pipe part and how these are glued to each other with the aid of a press tool.

Figure 10 illustrates a complete pole that has been joined together from pipe sections by means of finger joints and where also the joint pipes that are located inside the pole are illustrated adjacent thereto. DESCRIPTION OF EMBODIMENTS

[0012] In the following, a number of embodiments of the invention will be described with reference to the accompanying drawings. The drawings show only schematically the principle of the invention and do not claim to show any proportions between different elements thereof according to scale.

[0013] Figure 1 shows a complete pole 1 according to the invention. The exemplified pole according to the invention is composed of four pipe sections l a. The pole may be made in the desired length by, for example, joining together 3 or 5 pipe sections la. [0014] The pipe sections la consist of cylindrical pipes of laminated wood. The lamination has been achieved by gluing together a plurality of layers of veneer in order to form the pipe section la in the manner described below. As mentioned, a longitudinal cylindrical cavity extends along the interior of the pipe sections la. The pipe sections la have an inner diameter D.

[0015] Joint pipes 2 are designed and built up in a manner corresponding to that of the pipe sections la, that is, they consist of hollow cylindrical pipes of laminated wood. The joint pipes 2 have an outer diameter D.

[0016] When manufacturing a pipe section la, the longitudinal ends thereof have been planed off perpendicular to the longitudinal direction. In one variant of the embodiment of the pole, the ends of the pipe sections are milled to be provided with finger cutters that fit into one another so that glued finger joints can be achieved, which is described below. Figures 2 and 3 illustrate how the pipe sections la are joined together. A joint pipe 2 is inserted, by approximately half its length, into one end of a first pipe section la in the cylindrical cavity thereof having the diameter D, which diameter is the same as the outer diameter D of the joint pipe 2. A second pipe section la is then fitted onto that part of the joint pipe which projects from the first pipe section la, until the ends of the first and second pipe sections make close contact with each other. The joint pipes 2 may be shorter than the pipe sections 1 a and yet impart sufficient stability to the pole being formed. The joint pipes 2 may preferably be glued to the inner surfaces of the pipe sections la where joint pipe and pipe section la make contact with each other. A joint is made, in a manner corresponding to that which has been described, for each additional pipe section la that is added to the pole. A joint pipe 2 may, of course, be of the same length as a pipe section la. Such a length of the joint pipe 2 may be preferable at, for example, the lowermost joint of the pole 1, whereby the pole 1 is given higher stability in the lateral direction when being raised. Preferably, joint pipes 2 are used which have the same length as a pipe section so that the joint pipes will approximately make contact with each other end to end. The glue being used is preferably an MUF (Melamine Urea Formaldehyde) glue.

[0017] A method for manufacturing a first variant of the inventive pole will be described in the following. Figure 8 describes a first press tool 3 with a longitudinal semi- cylindrical recess. In this recess there is placed a desired number of layers of veneer 4 with, for example, a layer thickness of 2 mm. The fibre direction of the layers of veneer may preferably be crossed between different layers in order to impart increased bearing capacity to the pipe wall. According to the example, a number of layers are used such that the wall thickness d of the pipe section is in the order of 25 mm (see Fig. 5). Glue is applied on each layer except on a centermost layer. When all the veneer layers have been placed, a second semi-cylindrical press tool 5 is moved towards the recess in the first press tool 3. The first 3 and second 5 press tools are moved towards each other with great forces F and thus press the veneer layers 4 against each other so that these adopt the shape, a semi-cylindrical shell, which is created in the space between the two press tools 3 and 5. During the pressing, the veneer layers 4 are heated in a known manner (e.g. with the aid of high-frequency technology and/or contact heat) to accelerate the setting of the glue between the layers of veneer. When the glue is sufficiently set, a blank for a semi-cylindrically shaped shell that forms a laminated wood may be taken out from the mould 7. Said shell may be divided into two longitudinal parts, since a centermost layer of veneer has not been coated with glue and thus an outer and an inner part of the shell may be detached from each other. This leads to the formation, after planing of the blank along a diametrical plane, of a first inner pipe half 8a and a first outer pipe half 9a (Fig. 4). In a corresponding manner, a second inner pipe half 8b and a second outer pipe half 9b are manufactured. [0018] To finally manufacture a complete pipe section la, a press mould 10 according to Figure 9 is used. This press mould 10 comprises a first extrusion die 10a and a second extrusion die 10b, both of these having confronting and corresponding semi-cylindrically shaped recesses. In this press mould 10 there is placed a complete pipe section 1 a with glue applied between the contact surfaces of the inner pipe part 8a, 8b and the contact surfaces of the outer pipe part 9a, 9b, respectively. The gluing is suitably performed in advance in a cradle, where glue is applied on the inner surface of the second outer pipe half 9b, whereupon the two inner pipe halves 8a, 8b are placed against each other as shown in Figure 4 inside the second outer pipe half 9b. Glue may also be applied on the longitudinal edges of the two inner pipe parts 8a, 8b. The inner pipe halves 8a, 8b are rotated about 90 degrees in relation to the outer pipe half 9b along the common longitudinal axis thereof. After this, glue is applied on the edges between the outer pipe halves 9a, 9b and the inside of the fist outer pipe half 9a, whereafter this first outer pipe half 9a is applied across the inner pipe halves 8a, 8b. After glue has been applied on all the surfaces and all pipe halves have been joined together, the pipe section la is placed in the press mould 10, as mentioned, for setting, heating and pressing thereof. The upper extrusion die 10a is applied across the pipe parts. A pressure P is applied across the extrusion dies 10a and 10b. An inner press tool 1 1 is inserted inside the cavity formed between the inner pipe halves 8a, 8b. This inner press tool is influenced by a pneumatic pressure source to expand towards the inside of the inner pipe part 8a, 8b in a manner which is clear from Figure 9. A pressure is thus applied to both the outside of the outer pipe part 9a, 9b and the inside of the inner pipe part 8a, 8b. This causes outer 9a, 9b and inner pipe parts 8a, 8b to be pressed under high pressure against each other for the time during which the glue is setting. At the same time, heat is supplied in a known manner to accelerate the setting process. After the setting, a finished pipe section la may be removed from the extrusion dies 10, 10b. Thus, the pipe section l a is built up of an inner pipe part 8a, 8b and an outer pipe part 9a, 9b, which are both pipes of laminated wood and glued to each other and rotated in relation to each other to distinguish the planes of longitudinal glued joints from each other. The wall thickness of a finished pole 1 , when this has been composed of pipe sections la and joint pipes 2, is here defined as w = d for the pipe section la plus d for the joint pipe 2.

[0019] The complete pipe section la may be made with stronger joints by milling the cylinder halves 8a, 8b, 9a, 9b and shaping them with finger cutters along the longitudinal edges and at their ends. When joining the cylinder halves together, these are then glued together with so-called finger joints along their entire length where the edges of the cylinder halves meet. Also the joint pipes 2 are provided with corresponding finger joints along the longitudinal edges that meet each other (Figs. 6 and 10).

[0020] When a complete pipe section la has been finished, finger cutters may be arranged also at the ends of the pipe sections l a, whereby the pipe sections l a, when being joined together into a pole 1 , may be glued to each other by means of finger jointing end to end into a stronger joint than if completely plane edges had been used on the ends. Figure 6 shows schematically, at the circles 6b, that the ends of pipe sections 1 are provided with finger cutters to prepare for end jointing between pipe sections la. Milling of the ends is preferably carried out when the pipe section l a has been glued and is complete.

[0021] The joint pipes 2 are manufactured in the same way as the pipe sections l a. That part of a pipe section l a which surrounds a joint pipe inserted into the pipe section la may be screwed to the joint pipe 2 to impart increased stability to the joint in question. The semi- cylindrical shells in the inner and outer parts of the joint pipes 2 may be glued to each other along the edges where these shells meet, or they may advantageously be finger-jointed along their length in the same way as has been described for the pipe sections 1 a.

[0022] A pole according to the invention is composed of, for example, 3, 4 or 5 pipe sections la which are assembled lengthwise. Into a first pipe section la, a joint pipe 2 is inserted, preferably up to half the length of the pipe section 1 a, and glued together as described. A first end of a second pipe section la is fitted outside the approximately half length of the joint pipe 2 which projects from the first pipe section la (Fig. 3). A further joint pipe 2 is inserted into the second end of the second pipe section, whereafter a third pipe section la is fitted onto this further joint pipe and joined together in the described manner. The desired number of pipe sections la are joined into a final pole 1 in the described manner (Fig. 1 , Fig. 10). If desired, each end of the final pole 1 is advantageously filled with half a joint pipe 2 to give also the ends of the pole 1 the same structure as the central parts of the pole. [0023] A further variant of a pole according to the inventive aspect will be described in the following. This relates to a pole that is designed to withstand larger stresses in the form of breaking forces from snow, ice, wind, etc. Such stronger embodiments may be required if the pole 1 is used, for example, as a mast for mobile telephony. [0024] According to this alternative embodiment, there are instead used quarter- cylindrical shells which are joined together into outer and inner pipe parts. Thus, an extrusion die 3 is used to form shells which only need to comprise one-fourth of the periphery of a circle. In this way, much thicker shells of laminated wood can be achieved. In this example, outer pipe parts with, for example, a thickness of 20 mm and inner pipe parts with, for example, a thickness of 20 mm are manufactured, thus resulting in a pipe section la with the wall thickness d=40mm. The joint pipe 2 is made in a corresponding way and is given the wall thickness d=40 mm. For the complete pole 1 , when being composed from a plurality of modules of pipe sections la and inside these modules of joint pipes 2, this results in a wall thickness w of the pole which amounts to 80 mm in this alternative, stronger embodiment. Further, pipe sections la may be made longer than 2 m if this is considered advantageous. The diameters of inner pipe parts and outer pipe parts in a pipe section are adapted such that the outer diameter of the pipe section la becomes 440 mm according to the example. [0025] When manufacturing a pipe section 1 a according to the alternative embodiment, the process for gluing together quarter sections of outer pipe parts with inner pipe parts will thus be somewhat different from that in the example above (shown in Fig. 6). In this example, all of the quarter-cylindrical shells for inner and outer pipe parts are brought together in the press according to Figure 6 and joined together into a cylindrical shell that constitutes a pipe section la or a joint pipe 2. It is shown in Figure 7 that longitudinal joints in outer and inner pipe parts, when these are rotated 90 degrees in relation to each other, do not align with each other but are rotated about 45 degrees in relation to each other. Finger joints are made at longitudinal contact surfaces between the quarter sections that are jointed together into cylindrical pipe sections l a and joint pipes, respectively. Also in this embodiment the joint pipes 2 are thus jointed together in a manner corresponding to that of the respective pipe section l a when completing such a joint pipe 2. However, it may be suitable for the ends between joint pipes 2, where these meet each other, not to be joined by means of finger joints. [0026] Figure 10 shows a complete pole 1 , where the pipe sections la of the pole are jointed together by means of finger joints 12 at those ends of the pipe sections la where these meet each other. To illustrate the composition of a pole 1 more clearly, the joint pipes 2, which according to the description are glued to the inner surface of the pipe sections la, are shown as a longitudinal pole part made with dashed lines at the side of the jointed pipe sections l a. It is also shown by means of arrows that these joint pipes are located inside the pipe sections l a.

[0027] In the two examples above, the alternative poles have an outer diameter of 25-30 cm and 44 cm, respectively. These two outer diameters are only examples. The wall thickness w of a completed pole is 25 mm and 80 mm, respectively. Also these values are examples. It is doubtful whether sufficient strength is attained in a pole, where the wall thickness w is below 20 mm. For shorter poles, however, w - 15 mm could be used. Thicker walls than, for example, w = 1 10 mm can probably be excluded since a pole 1 with such thick walls will be both heavy and expensive. Thus, a suitable wall thickness w may be between 15 and 1 10 mm. Preferably, the wall thickness w should be 20 mm < w < 90 mm.

[0028] Definition: the concept cylindrical shall mean any type of cylinder, that is, a cylindrical body may have a cross section with an arbitrarily closed curve. The curve may, example, be elliptical.