METHOD FOR MANUFACTURING WOOD POLES

Abstract: In the manufacturing of wood poles a number of sections are glued together along abutting side surfaces (7, 8) so that a tubular pole (19) with a central cavity is formed. The side surfaces (7, 8) which have been provided with glue are brought into intimate contact with each other so as to give a tube (19). Sealing covers (20, 21) or the like are placed at both ends of the tube so that these are sealed, whereafter air is pumped out from the central cavity (23) through one or both of the said covers so as to give a vacuum in the cavity in comparison with the external pressure, whereby the contact pressure between the abutting side surfaces increases. The vacuum is maintained until the glued joints (31) have been fixed.

Description: METHOD FOR MANUFACTURING WOOD POLES TECHNICAL SCOPE The invention relates to a method for manufacturing wood poles 5 consisting of a number of sections which are glued together along abutting side surfaces so that a tubular pole with central cavity is formed. Poles of this type can be used primarily as power line poles but also as masts of various types, columns for buildings, bridges etc. 10 STATE OF THE ART For many years power lines have been constructed using natural poles made from pressure-impregnated pine. Because of developπents in modern forestry however there has been a drastic reduction in the ' $ availability of full-grown timber and hence also of natural poles having the requisite dimensions. Because of this poles of glued timber have been developed which are designed to replace natural poles. Examples of such designs are shown in DE 665 210, GB 745 540, FR 2 348 345 and WO 80/02709. 0 In spite of the urgent demand for glued poles and in spite of the fact that a plurality of glued pole designs have been produced in past years, the tubular glued timber pole has not as yet however been widely employed for power lines and similar demanding appli- 5 cations. One reason for this is that from the production viewpoint these poles give rise to a number of problems which have not been satisfactorily solved using available techniques. These problems concern both the jointing and the gluing of the individual__sections, also the requisite impregnation of the glued construction. 0 DESCRIPTION OF THE INVENTION The aim of the invention is to solve the above-mentioned problem in providing initially a method for facilitating the jointing and gluing of the sections. Hence in accordance with the present invention it 5 is proposed that glue be applied to the side faces which are to be joined together, that the side faces provided with glue be brought . into intimate contact with each other so that a tube is obtained, that sealing covers or the like are applied at both ends of the tube so that this is sealed (instead of covers it is naturally possible to envisage plugs of various types) , that air is pumped out of the central cavity through one or both of the said covers or the like, thus giving a vacuum in the cavity in relation to the external pressure, whereby the contact pressure between the abutting side faces increases, and that the vacuum is maintained until these glued joints have become fixed. Possibly the outside of the tube is also subjected to an overpressure in comparison with the sur- rounding pressure, whereby the contact pressure between the abutting side edges is further increased. Because in accordance with the invention the air is pumped out so that the pressure drops in the pole, the boiling point of the glue also drops if the glued joint is in communication with the cavity. To prevent this a barrier is applied appropriately between the cavity and the glued joint. This barrier can for example consist of a thin extended sealing strip or a metal wire between the two abutting side faces near the inside of the tube. Preferably however, in accordance with one embodiment of the invention, the barrier is obtained by providing at least one of the two side faces with a slig ~ ht projection - a mini-tongue - which extends along one side face immediately inside the inner face of the tube. During assembly the mini-tongue is partially pressed into the abutting side surface so tha a complete seal is obtained. By this means the risk of boiling because of pressure reduction can be eliminated even if the pole is heated, which as such is favourable in order to accele-r rate the curing of the glue. T e individual sections are preferably given a trapezoidal shape, which as such is known. To facilitate jointing in accordance with the invention the side faces are preferably provided with round tongues and grooves which both from the viewpoint of production technique and for jointing the sections together is considerably more favourable than previously proposed tongue and groove shapes. To facilitate effective impregnation and to adapt the construction to suit the crack formation tendency of the timber, the individual sections are appropriately made up of 2 - 4 pieces of timber layers glued together with the sapwood facing the base in the trapezoidal sections. Further characteristics and advantages of the invention are outlined in the patent claims and are illustrated by the following descrip¬ tion of a preferred embodiment. BRIEF DESCRIPTION OF DIAGRAMS In the following description of a preferred embodiment reference will be made to the appended diagrams in which Fig. 1 gives a perspective view of a section of the type from which the pole is to be manufactured in accordance with the inven¬ tion. Fig. 2 gives a perspective view which illustrates pole manufacture. Fig. 3 illustrates the same feature, in side view. Fig. 4 gives a section IV-IV in Fig. 3. Fig. 5 shows a section V-V in Fig. 3. Fig. 6 illustrates the conditions prevailing in the glued joint. DESCRIPTION OF PREFERRED EMBODIMENT With reference initially to Fig. 1, a section for manufacture of the pole in accordance with the invention is generally designated as 1. The section 1 has a profile shaped like an isosceles parallel trapezoid and is made up of three glued laminations 2, 3 and 4. The base surface of the section is designated as 5, its top surfaces as 6 and its two side surfaces as 7 and 8. The two side surfaces 7 and 8 are provided with tongues and grooves in the form of grooves 9 and tongues 10. During assembly the sections 1 are arranged so that the side faces 7 on adjacent sections are placed against each other, whereby the tongues 10 fit into the grooves 9. The base surfaces 5 form the outside and the top surfaces 6 form the inside of the finished pole. The tongue and groove 9, 10 are parallel with the edge lines 11, 12 between the side surfaces 7, 8 and the top surface 6. In accordance with the embodiment illustrated the section 1 is absolutely uniform, i.e. has the same cross sectional area along its entire length, so that the tongue and groove 9, 10 are also parallel with the lower edge lines 13, 14, but it is also possible to plane the base surface 5 so that the section 1 tapers. This has been indicated by the dashed line 13' which in this case is not parallel with the tongue and groove 9, 10. The three lamina¬ tions 2, 3, and 4 are further sawn and laid in such a way that the sapwood faces towards the base surfaces 5, i.e. towards the outside in the finished pole. The laminations 2, 3 and 4 are furthermore composed appropriately, in a manner which forms ' part of the state of the art, of finger-jointed sections, so that the desired length can always be obtained. Fig. 1 shows also that the tongue and groove 9, 10 is placed considerably closer to the edge lines 11, 12 than to the edge lines 13, 14 so that the base surface 5 can be planed down, if so required, without cutting the tongue and groove at the narrow¬ est end. About 2mm from the edge line 12 the side surface 8 is also provided with a small projection in the form of a "mini-tongue" 30 which extends along the entire length of section 1. The mini-tongue 30 is about 1mm wide and i to Imm in height. Its function is to provide a seal for the glue in the glued joints 31, Fig. 6, so that the glued joint cannot conmunicate with the cavity 23. In Fig. 6 the thickness of the glued joint 31 has been exaggerated for the sake of clarity. During jointing the side surfaces 7- and 8 are provided with glue and are then placed in a fixture 15, Fig. 2 and Fig. 3, with semi¬ circular-shaped support 16. First of all a number of sections 1 are placed in this support 16, the sections being orientated, with respect to each other in the desired manner by means of the round tongues and grooves 9, 10. Then a vertical ring 17 is placed at both ends, after which the layer is completed by adding further sections 1. Some straps 18 are then wound around the whole assembly and tightened so that the side faces 7, 8 are pressed firmly against each other. The two ends of the tube 19 thus formed are cut off so that the end faces are absolutely even, after which the ends are sealed by a pair of covers 20 and 21. The covers 20, 21 consist of plates 22, the outsides of which are domed so that they can withstand an external overpressure relative to the central cavity 23 of the tube 19. On the inside the covers 20, 21 are absolutely flush and provided with a ringshaped fairly wide rubber packing 24. One cover 20 is provided with an extraction pipe 25 which is connected with the cavity 23, whilst the other cover 21 is provided in a corresponding manner -with a manometer 26 for measuring the pressure in the cavity 23. Thus when the covers 20, 21 with packings 24 have been placed against both ends of the tube 19 and are pressed against the ends at a certain pressure, the air in the cavity 23 is pumped out through the pipeline 25. Until the vacuum produced in the cavity 23 is so great that the covers 20, 21 are sucked firmly in place, the covers 20, 21 can be held in position manually. The pumping out of the air then continues until the pressure in the cavity 23 has dropped to the desired level, appropriately to about 0.1 kp/cm.. Subsequently this same pressure difference is maintained between the pressure in the cavity 23 and the surrounding pressure until the glued joints 31 in the tube 19 have become fixed. During the assembly of the sections the mini-tongues 30 are pressed against the opposing side face 7 and to some extent are also pressed into this.. Hence the tongues 30 function as a seal which effectively cuts off the glue -in the glued joint* 31 from the cavity 23. When the air is pumped out of the cavity 23, the glue in the glued joints 31 is consequently not sucked into the cacity 23 and the glue does not -^yiϊ E start to boil because of the pressure reduction in the cavity 23. When the glue in the glued joints 31 has hardened so that the joints have become fixed, the straps 18 are removed together with the * covers 20, 21 and the supporting rings 17. For this purpose the latter can be provided with a pair of clamps 27. The pole 19 can then be transferred to store for subsequest curing. Finally the pole 19 is impregnated with creosote oil both from the outside and from the inside in a known manner. As the sapwood faces the outside of the pole and the grain is orientated in the manner indicated in the diagrams, this greatly facilitates the penetration of the impreg- nation agent. To increase the gluing pressure it is feasible and possible in accordance with the invention to subject the outside of the pole 19 to an overpressure, whilst at the same time a vacuum is produced in .the cavity 23. The .entire structure illustrated in Fig. 2 and Fig. 3 is then placed in a pressure vessel in which a positive pressure is brought about by means of compressors, whilst the air is simultaneously pumped out through the pipe 25. To shorten the gluing time it is also possible to heat up the residual air in the cavity 23. For this purpose a further connecting pipe 28 can be pro¬ vided so that hot air is made to circulate through the cavity 23 so that the pole is heated up from the inside before the air is pumped out. Even whilst the vacuum is maintained in the cavity 23, it is possible to allow certain quantities of hot air to circulate within the cavity. If a positive pressure is also applied to the outside, it is possible in the same way to heat the air in the pressure vessel so as to obtain a temperature rise also from the outside with a view to shortening the gluing time. Whilst the glue is curing, the pressure in the cavity is checked continuously so that it is maintained at the desired level. The gluing pressure for vacuum gluing in accordance with the inven- tion, possibly combined -with positive pressure treatment, is cal¬ culated as follows: D = T, where m 2 t = vacuum + possible overpressure, kp/cm D = external diameter of tubular pole, cm m = gluing pressure, kp/cm 2, in glued joint 31 The dimensions of the pole can be varied within wide lie-its. For practical reasons the upper limit can be taken as 40 m, whilst a lower economic limit is about 0.5 m. The external diameter can also be varied within wide limits. For efficient handling only a restricted number of dimensions for the sections 1 should be employed. But even with a very restricted number of section sizes the external diameter can be varied between circa 350 and 1 300mm, which gives a wall thickness range between circa 50 and circa 225mm. For manufacturing it is best to use a glue which is made and marketed by the Norwegian- company Dyno A/S under the tradeπame Dynosol S 204, together with the hardener recommended for this 2 Dynosol H 627 which requires a gluing pressure of cirka 2.0 kp/cm . With the method in accordance with the invention this gluing pres¬ sure can be achieved for all the demensions encountered in practice without it being necessary to apply a positive pressure. 2 If the vacuum amounts to 0.9 kp/cm (0.1 atmospheres gauge) in an assumed example where D •= 48αιι and * =• * 9cm the following gluing pressure is obtained: D -. 0.9 . 48 = 2..4. -kp/.cm2 2 . 9

Claims: PATENT CLAIMS 1. Method for manufacturing wood poles consisting of a number of sections (1) which are glued together along abutting side faces (7, 8) so as to form a tubular pole (19) with central cavity (23), c h a r a c t e r s e d in. that the said side faces (7, 8) which have been provided with glue are brought into intimate contact with each other so as to give a tube (19), that sealing covers (20, 21) or the like are placed at both ends of the tube so that these are sealed,.that air is pumped out from the central cavity (23) through one or both of said covers so as to give a vacuum in the cavity in comparison with the external pressure, whereby the contact pressure between the abutting side faces increases, and that the vacuum is maintained until the glued joints (31) have become fixed. 2. Method as in claim 1, c h a r a c t e r i s e d in that sealing devices (30) are arranged between the cavity (23) and the -glued joints (31) so as to prevent the cavity communicating with the glued joints whilst the glue is curing. 3. Method as in claims 1 or 2, c h a r a c t e r i s e d in that the sections (1) have trapezoidal shape, whereby the abutting side faces (7, 8) are provided with circular tongues and grooves (9, 10) and that the number of sections (1) is more than (10). 4. Method as in claim 3, c h a r a c t e r i s e d in that the sections are made up of 2 - 4 pieces of timber layers (2, 3, 4) which are glued together with the sapwood facing the base (5) of the trapezoid. 5. Method in accordance with any of claims 1 - 4, c h a r a c ¬ t e r i s e d in that combined with the said vacuum on the inside, the outside of the tubular pole is subjected to a positive pressure as compared with the surrounding pressure, whereby the contact pressure between the abutting side faces is further increased. 6. Method in accordance with any of claims 1 - 5, c h a r a c ¬ t e r i s e d in that the tube (19) is heated during the gluing «f hot air in the cavity (23) and/.or by hot air process by means of hot a i r m t n on the outside of the tube. OMPI

Inventors: EKLUND TORE
Applicants: EKLUND TORE, NYA VARMLANDS AB
Application year: 1981
Main classification: E04H12
IPC codes: B27M3, E04C3, E04H12