A METHOD OF MANUFACTURING A TRUSS BEAM

Abstract: A carcase (1) is firstly manufactured by arranging a plurality of elongate members (4) of a composite material around a plurality of spacer members (2). A plurality of taut wires (5, 5') is subsequently wound around the carcase (1) such that each elongate member (4) is contacted by one of the wires (5, 5') in the plane of each spacer member (2). The wires (5, 5') may be subsequently adhered to the carcase (1), preferably by means of melting a thermoplastics coating of the wires (5, 5') and allowing the coating to set. The beam produced by this method is lightweight and strong.

Description: A Method of Manufacturing a Truss Beam The invention relates to a method of manufacturing a truss beam. Truss beams are commonly made either of steel or of composite material, steel beams are strong but are very heavy and thus awkward to handle. Comparatively strong beams of composite material are produced in sections using a tool which inevitably increases the cost of manufacture. Furthermore, such beams of composite material have large solid sections which cause the beams to be undesirably heavy. The invention seeks to provide a strong, lightweight truss beam which is easy and cheap to manufacture. The invention provides a method of manufacturing a truss beam characterised by the steps of: (a) manufacturing a carcase (1) comprising a plurality of elongate members (4) spaced apart by a plurality of planar spacer members (2); and (b) subsequently winding a plurality of taut flexible elements (5,5') around the carcase (1) such that each elongate member (4) is contacted by one of the flexible elements (5,5') in the plane of each spacer member (2) and is held in place thereby. Preferably some of the flexible elements are wound around the carcase such that the edges of the spacer members are contacted by the same some flexible elements between adjacent elongate members. Preferably each flexible element is fixed to the carcase at each point of contact therebetween. Preferably the elongate members are tubular. Preferably the elongate members are of a composite material comprising thermosetting or thermoplastics resin and fibres. Preferably the materials used are selected such that their modulii of elasticity, Poisson's ratios and densities have values of the same order. Preferably the materials used are selected such that they have modulii of elasticity, Poisson's ratios and densities of substantially the same values. Preferably each flexible element is electrically conductive material and preferably has a coating of a thermoplastics material. Preferably the flexible elements are made to adhere to the carcase by passing an electrical current therethrough. The spacing of the elongate members of a beam produced according to the method described above allows a beam of low mass per unit length to be produced. The flexible elements contact the elongate members in the plane of each spacer member in order to press the elongate members towards the spacer members and retain a close fit therebetween. The beam thus produced then behaves as a single member for mechanical purposes: the flexible elements carry the majority of any stresses which are applied to the beam. The beam is therefore strong and lightweight. It may also be manufactured in substantial lengths, rather than in sections An embodiment of the invention is shown in the accompanying drawing, wherein; Fig. 1 is a perspective view of three spacer members arranged along a tube or shaft; Fig. 2 is a perspective view of a carcase comprising the spacer members and shaft of Fig. 1 and further tubes arranged in a predetermined manner; Fig. 3 is a perspective view of the carcase of Fig. 2 with a first wire wound around the tubes; and Fig. 4 is a perspective view of the carcase of Fig. 3 with a second wire wound around the tubes. As can be seen from the drawings, the method according to the invention begins with the manufacture of the carcase 1. Spacer members 2 of a composite material of glaεsfibres and a thermoplastics resin are spaced at equal intervals along a shaft or tube 3. The shaft or tube 3 is arranged on a vertically rotatable turntable to increase the accessibility of the beam during manufacture. Elongate members in the form of tubes 4 also of a similar composite material are then arranged in predetermined positions in relation to the spacer members 2. A plurality of wires 5 is then wound in a predetermined pattern around the carcase 1. This pattern may be a spiral pattern. Each tube 4 is contacted by a wire 5 in the plane of each spacer member 2. The edges of each spacer member 2 are crossed by a wire 5 between adjacent tubes 4. Further wires 5' are then added to increase the stability and strength of the beam. The further wires 5' are also wound in a spiral pattern, preferably rotating in the opposite direction to the first wires 5. The further wires 5' also contact the tubes 4 in the plane of each spacer member 2 and the edges of the spacer members 2 are each crossed by a wire 5* between adjacent tubes 4. Each of the wires 5,5' has a core of electrically conducting material and a coating of a thermoplastics material. The wires 5, 5' are made to adhere to the carcase 1 by passing a current through the core such that the thermoplastics coating is melted. The thermoplastics resin of the composite material of the tubes 4 and spacer members 2 is also melted in the region adjacent each point of contact with the wires 5,5'. When the current is cut off and the wires 5,5' cool, the thermoplastics resin sets joining the wire 5,5' to the tubes 4 and the spacer members 2. Although the elongate members described above are . tubular, it would be equally acceptable to utilise solid bars of relatively lightweight construction or tubular members filled with foam or synthetic material. Different arrangements of elongate members around the spacer members are possible: the arrangement shown in the representations is by way of example only. The invention is not limited to elongate members of composite material - it is envisaged that elongate members comprising thin-walled steel or aluminium tubes would also be suitable. The flexible elements may be wires, lines or bands of steel or other metal, or could comprise non-metallic materials of high tensile strength such as carbon- or glass-reinforced resin. The flexible elements may have a coating of a plastics material and may be adhered to the carcase by means other than those described above, e.g. by direct application of heat to to thermoplastics coating. Alternatively, the fexible elements may be fixed to the carcase at either end of the beam or at periodical intervals. The fixing may take any suitable form, e.g. by tying, welding or repeated winding. Patterns other than spirals may be used, provided that the elongate members are contacted by the flexible elements in the plane of each spacer member. A suitable thermoplastics resin which may be used for the elongate members and the coating of the wires is that known in Sweden as "Aramid". Nylon could also be used. This is by way of example only. It should be understood that a single flexible element refers to a wire of the like running from one end of the beam to the other. It would, of course, be possible to arrange for successively wound flexible elements to be connected end to end and wound back and forth along the beam.

Claims: Cla ims : 1. A method of manufacturing a truss beam characterised by the steps of: (a) manufacturing a carcase (1) comprising a plurality of elongate members (4) spaced apart by a plurality of planar spacer members (2); and (b) subsequently winding a plurality of taut flexible elements (5,5') around the carcase (1) such that each elongate member (4) is contacted by one of the flexible elements (5,5') in the plane of each spacer member (2) and is held in place thereby. 2. A method as claimed in claim 1, wherein some of the flexible elements (5,5') contact free edges of the spacer members (2) between adjacent elongate members (4). 3. A method as claimed in claim 1 or 2, wherein the flexible elements (5,5') are fixed to the carcase (1) at each point of contact therebetween. 4. A method as claimed in any one of the preceding claims, wherein the elongate members (4) are tubular. 5. A method as claimed in any one of the preceding claims, wherein the materials of the beam are selected such that they have modulii of elasticity (E..), Poisson's ratios (V..) and densities (p) with values 1J of the same order of magnitude. 6. A method as claimed in claim 5, wherein the materials of the beam are selected such that they have substantially the same modulus of elasticity (E..), Poisson's ratio (V..) and density (p). 7. A method as claimed in claim 6, wherein the elongate members (4), the spacer members (2) and the flexible members (5,5') all comprise the same material. 8. A method as claimed in any one of the preceding claims, wherein the elongate members (4) are of composite material comprising thermoεetting or thermoplastic resin and fibres. 9. A method as claimed in any one of the preceding claims, wherein the spacer members (2) are arranged substantially equidistantly along the carcase (1). 10. A method as claimed in any one of the preceding claims, wherein each flexible element (5,5') is electrically conductive. 11. A method as claimed in any one of the preceding claims, wherein the flexible elements (5,5') and the carcase (1) are locally heated at their mutual intersections in order to melt the thermoplastics coating and thus adhere the flexible elements (5,5') to the carcase (1). 12. A method as claimed in any one of claims 1 to 10, wherein the flexible elements (5,5') are made to adhere to the carcase (1) by passing an electrical current therethrough. 13. A method as claimed in any one of the preceding claims, wherein each flexible element (5,5') has a coating of thermoplasics material. 14. A method as claimed in any one of the preceeding claims, wherein the beam is manufactured with the spacer members (2) arranged on a rotatable shaft (3). 15. A method of manufacturing a truss beam of composite material substantially as hereinbefore described with reference to the accompanying drawings. 16. A truss beam manufactured by a method according to any one of the preceding claims.

Inventors: GRANDINETTI JOHN, GRANDINETTI, JOHN
Applicants: DEVONS DAVID JON, INTEGRATED TECH LTD, DEVONS, DAVID, JON, INTEGRATED TECHNOLOGIES LIMITED
Application year: 1988
Main classification: E04C3
IPC codes: E04C3