Description

The present invention relates to a process for assembling tubular nodes which can be used, generally, in the field of trusses .

In engineering, and in the construction field in particular, a truss is a structure consisting of two- force elements only, where the elements themselves are organi zed so that the set formed thereby behaves like one single ob j ect .

The truss derived its origin from the need for using lighter and lighter structures to bridge bigger and bigger spaces , and it is formed by the above-mentioned main structural elements , that is longerons or pillars , formed by a core dismountable in single linear, vertical (uprights ) and slanted ( diagonal ) elements , usually consisting of tubular beams , intended to absorb the tangential stresses arising with inflection of longerons and which determine the relative sliding thereof , by the traction or compression action only .

Then, the trusses are not deformable complex structures , consisting of a set of beams connected therebetween in points called nodes . In the schematic representations , the nodes are considered like hinges even i f , to say the truth, they are fittings , since the beams are connected therebetween generally through bolts , rivets , nails or welding .

In simpler terms , herein and hereinafter, under truss a set of elements , such as rods or beams , is meant , which creates a rigid structure , then with straight beams the ends thereof are connected to j oints generally called nodes .

In this way, the beams are constrained at the nodes , so as to constitute a resistant and not deformable element .

The loads stressing the structure are applied in the nodes , consequently, each beam is stressed according to the line j oining its two nodes . The beams are defined tie rods when they are subj ected to tensile stress ; or compressed beams , when they are subj ected to compressive stress . The trusses can be flat , i f they extend on one single plane , or spatial , i f they are three-dimensional .

A node is implemented at each connection between beams , both planar and three-dimensional . Several types of nodes are distinguished : thereamong there are K- , N- , T- and KT- like , X- and Y-like ones ; they are distinguished by number and relative position between the beams concurring in the single node ( figure 1 ) .

Each node , then, has a tubular branch which is arranged to couple with the end of a tubular beam, and then each chord of the node in turn is a tubular chord, and in this case the node is defined closed .

However, it may be provided that a chord of the node could have an open semicircular shape , devised to adhere on a tubular beam portion, and in this case the node is de fined opened .

The present process relates to the assembling of composite material nodes , obtainable by several lamination techniques , and in particular the lamination technique known as filament winding .

The lamination is a technique for the production of a composite laminate material made of multiple layers , so that the composite material obtains more resistance and stability .

The lamination technique called filament winding technique is a consolidated technique for the production of mainly hollow and light articles or components , with a rigid skin . Filaments , wires or wicks impregnated or coated with a thermosetting resin are strictly wound around a mould, so as to form a layer of fibre which can be hardened, by forming a rigid thickness . This technique has the capability of producing low-weight and high-rigidity components . In order to obtain the wished low mass and the low inertia in the finished product , the mould has to be removed to leave the final product with an internal cavity . The filament winding technique provides the overlapping of fibres, already impregnated with low-viscosity resin, on a spool or mould element, arranged in rotation by means of a rotating spindle thereon the mould is mounted. Subsequently, the mould is extracted and eliminated. It is a rapid and affordable process, which guarantees good structural properties to the so-produced composite material, however it is forcedly limited to objects with substantially tubular and convex shape, that is without concavity .

Therefore, the filament winding technique is a technique for assembling composite material manufactured products, which generally have a tubular shape, and then it is particularly suitable for assembling beams for trusses.

However, it turns out to be problematic to apply this assembling technique to the nodes, indeed because they have tubular shapes, but they have branches.

Another lamination technique, which has problems wholly analogous to the filament winding technique, is the infusion lamination technique substantially consisting in stretching fibre tissues, for example, glass, carbon or aramid fibre, on a dry mould, and it is provided to make a resin to flow in the tissues, by implementing a pressure difference, artificially created, which causes the fibre impregnation .

US patent No. 4, 650, 620 A describes a filament winding technique wherein the filaments are wound around a mould and the mould then remains in the structure and becomes a part of it, usually as a part, but this prevents the extraction and the removal thereof even once the production is completed.

The technical problem underlying the present invention is to provide a process for assembling tubular nodes, in particular, but not exclusively, for trusses, made of composite material, allowing to obviate the drawback mentioned with reference to the known art.

Such problem is solved by a process as above specified characterized in that it comprises the assembling steps as defined in the enclosed claim 1. The main advantage of the process according to the present invention lies in the fact of allowing the production of nodes for trusses and for other structural functions with a lamination technique .

The present invention wil l be described hereinafter according to some preferred embodiment examples thereof , provided by way of example and not with limitative purposes with reference to the enclosed drawings , wherein :

* figure 1 illustrates various types of nodes for trusses obtainable with the process according to the invention;

* figure 2 shows a perspective view of a Y-like node of open type ;

* figure 3 shows a perspective view of a K-like node of open type ;

* figures 4A, 4B, 4C, 4D and 4E illustrate the steps for producing a K-like node of open type with the process for assembling composite material tubular nodes for trus ses according to the present invention;

* figures 5A and 5B illustrate additional steps for producing and implementing the K-like node of the preceding figures ;

* figure 6 shows a perspective view of a first mould for producing a double T-like node of closed type , usable in the process for assembling composite material tubular nodes for trusses according to the present invention;

* figure 7 illustrates an additional step for producing and implementing the double-T node of figure 6 ;

* figure 8 shows a perspective view of a first mould for producing a double-T node of closed type , usable in the process for assembling composite material tubular nodes for trusses according to the present invention;

* figure 9 shows a perspective view of the mould of figure 8 ;

* figures 10A, 10B, I OC, and 10D illustrate the steps for producing a double-T node of closed type with the proces s for assembling composite material tubular nodes for trusses according to the present invention;

* figure 11 illustrates and additional step for producing and implementing the double T-like node of the preceding figures ;

* figures 12A, 12B, 12C, 12D and 12E illustrate the steps for producing a Y-like node of closed type with the proces s for assembling composite material tubular nodes for trusses according to the present invention; and

* figure 13 illustrates an additional step for producing and implementing the Y-like node of the preceding figures .

With reference to figures 1 to 3 , various types of the nodes for trusses of tubular type are represented, which can be produced by applying the filament winding technique or another lamination technique ; figures 2 and 3 in particular relate to a Y-like node and a K-like node , both ones of open type .

It is meant that the filament winding technique is a preferred production mode , but other lamination techniques can be used even within the present invention .

Generally, the nodes of figure 1 comprise an open main chord 1 , with semicylindrical shape which is apt to couple with the cylindrical surface of a beam 2 ; and two derived bars 3 branching from the main chord with a predetermined angulation; they have a closed tubular form, and they are arranged to be put on a beam end .

With reference to figure 2 , the Y-type node is devised to perform a node function among three elements of a truss , by connecting tubes made of composite material with the same nominal diameter with a female coupling for the continuous element and male coupl ing for the diagonal beams .

This process might turn out to be laborious and not easy especially for beams having sustained length thereon the closed nodes should be made to slide . In order to simpli fy and make easier the mounting, the possibility of using an open Y-like node was considered .

Even the K-type node ( figure 3 ) has a double coupling configuration : the coupling will be of female type on the hori zontal beam and it will be of male type for the ti lted beams , by guaranteeing the sealing thereof .

The process for assembling compos ite material tubular nodes for trusses according to the present invention provides the use of a mould, in particular a mould of male type , wherein a lamination procedure is arranged to add thickness towards outside the surface of the mould ( figure 5A) .

With this procedure , it is necessary to si ze accurately the external thickness by keeping into consideration, apart from the internal diameter, the variation of the external diameter based upon the thickness of the laminate .

Advantageously, the laminate can be applied with a procedure of filament winding lamination .

This procedure results to be optimum for coupling with diagonal beams , since the most finished surfaces of the node and of the tube result to be in contact .

The most finished surfaces of the node are those which are obtained in contact with the mould, and it will be required only to take into account the layer of the structural adhesive .

In the process for assembling composite material tubular nodes for trusses according to the present invention, it was determined that the optimum configuration appears to be the one obtained with moulds of male type . In fact , the mould of male type reduces sensibly the risk of dimensional errors due to the manual processing . Moreover, the lamination from female mould results to be uneasy due to small-si zed diameters .

The lamination, then, takes place outside the mould ( figure 5A) which will be characteri zed by three portions characteri zed by geometries with precise draft angles to allow their separation and the laminate detachment . With reference to figure 4A, the mould then comprises a mould base 4 which is formed by a flanged hal f-cylinder .

Generally, the mould base 4 comprises a cylindrical portion and connecting areas with respective appendix elements o f the mould, intended to the production of the derived bars of the node .

Said connecting areas are flanges 5 : along the semicircumference of the mould base 4 the flange 5 is tilted by an angle of 45 ° , whereas along the generatrix the angle will be 90 ° ; this to facilitate cutting and tapering the node during the finishing phase .

The two appendix elements 6 are fastened to the mould base by bolts : this is allowed thanks to a metal thread inserted into the mould fibreglass . The appendix elements 6 have a tapering of at least 0 . 6 ° to allow an easy draft of the node .

Once the lamination has ended ( figure 4B ) , one proceeds with the sequence of dismounting the mould to allow the draft :

1 . One proceeds with removing the bolts , this allows to be able to remove downwards the cylindrical mould base 4 which, thanks to its geometrical shape , does not resist particularly to the draft .

2 . One proceeds with removing a first appendix element 4 .

3 . Once removed the first appendix element 4 , it i s possible to remove the second appendix element 4 .

With reference to figures 6 and 7 , the production of a double T-like mould of closed type is illustrated, with a mould which was arranged based upon the same solution idea described previously .

The mould with appendixes consists of three portions , that is with two portions in case of simple T-like node , which are easily dismountable to allow the draft of the laminated node .

The main mould consists of a mould base 4 consisting of a calendered plate with diameter equal to the external diameter of the tube .

Then, it comprises a cylindrical or semicylindrical , in this case cylindrical , portion for the lamination of the main chord of the node , which in this case constitutes a hollow metal cylinder, cut along a genetrix thereof .

It is meant that a main mould for each coupling diameter can be arranged .

On the main mould holes with established angles are provided, acting as connecting areas 5 , whereon appendix elements 6 , or appendixes , are fastened .

The appendixes 6 are fastened to the cylinder through a system of bolts easily accessible from the inside of the cylinder itsel f . After the installation of the appendixes a series of circular templates 7 will be placed, in order to avoid that the cylinder deforms during lamination, by j eopardi zing the node shape .

On the so-mounted mould the lamination is performed, which involves the whole external surface ( figure 7 ) . At the end of such phase , it is necessary to remove the templates and to unscrew the bolts fastening the appendixes to the main mould . Then one will proceed with contracting the cylinder of the mould base 4 by a lever or screw closing mechanism which will allow the surfaces to slide over each other by reducing the diameter thereof and by allowing the draft . The appendixes 6 will be removed from the already demoulded piece .

Analogously, an open T-type node can be produced, wherein the same configurations of the closed version are provided : both for the trunk-appendix coupling range and for the angulation of the appendixes .

In order to ease installation and gluing, depending upon the use destination of the node , speci fic processing for the application of an adhesive coupling layer is provided .

On this regard, it is possible to provide in the mould a series of holes on the surface of the mould base 4 for inj ecting glue . The mould base 4 can even include a series of grooves inside the node during lamination .

The open T-type node is produced, as in case of closed node , by lamination from male mould . The mould will be formed by three mountable portions ; the mould base formed by a calendered plate with the nominal diameter of the tube/pillar thereto the appendixes will be applied .

With reference to figures 8 and 9 , a second mould vers ion is shown, which can be used in the process for assembling composite material tubular nodes for trusses according to the present invention .

In this version, the mould base , which forms the cylindrical portion of the main chord of the node , is formed by dismountable elements 8 which couple along respective longitudinal edges .

Even the appendix elements , designated with 9 , 8 couple to each other and to the dismountable elements 8 of the mould base in the same way .

In this way, a male mould for a double or single T-like node of closed type is implemented, which can be used for the connection to the pillars of the lattice structure and, as said previously, it allows to have the finished internal surface , whereas towards outside the raw thickness of the manufactured product will be obtained .

The lamination then takes place outside the mould formed by four dismountable portions to allow the draft the laminated piece .

A hollow cylinder will be then obtained, divided into four portions , two thereof provided with a cyl indrical proj ection for implementing the portion j oining with the beams .

In order to allow opening the mould, the contact surfaces between the portions will be implemented with a tapering of at least 0 . 6 ° . The draft takes place by extracting the dismountable elements 8 and the appendix elements 9 according to a pre-established order ( figures 10A to 10D) which substantially depends upon their tapering . The numbering coupled with each piece illustrates the extraction order .

Figure 11 illustrates the completion of node processing, with the deposition of adhesive layers and with coupling of the truss to the beams .

It is noted that such system then guarantees to maintain the measure of the internal diameter, whereas the external diameter increases due to the thickness of performed lamination . This node could be suitable to an application outside the tubes , but to say the truth the external diameter of the tubes made of filament winding increases too based upon the lamination thickness and then it would not be possible to obtain a suf ficiently precise coupling on the beams . On the pillars , instead, the coupling would take place in a suf ficiently precise manner since between the internal diameter of the node and the external diameter of the pillar only the gluing thickness would have to be considered . Although the external diameter of the pillar varies due to the application of the lamination thickness , this involves a much smaller variation in curvature of the resting surface i f compared to the percentage variation on the diameter of the beams .

With reference to figures 12A, 12B , 12C, 12D, 12E and 13 a mould for the application of the process for assembling composite material tubular nodes for trusses according to the present invention is illustrated, in particular for the production of a Y-like node of closed type .

The male mould, for the Y-type node used for connecting the diagonal connecting beams in the lattice structure , allows to have the finished internal surface , whereas towards outside the raw thickness of the manufactured product will be obtained .

The male mould consists of five portions which are distinguished by geometries with precise draft angles allowing their separation and then their longitudinal extraction from the piece laminated towards outside .

The hori zontal diameter of the node is implemented with four portions which constitute , together, the mould base , also here consisting of dismountable elements coupled therebetween longitudinally .

One of these dismountable elements include an appendix element 9 which implements the diagonal bar . The numbering coupled to each piece illustrates the extraction order .

The above-described system, with its pos sible configurations , is a system that is highly configurable with ease .

Apart from the described cases and the hypotheses of si zing diameters and thicknesses , the preliminary study relates to , the final product can be customi zed and studied to be adapted to any configuration by geometry and si ze based upon the use type and installation environment .

It is meant and all measures and quotes reported in figures have purely exempli fying value and do not constitute in any way a limitation of the requested protection .

To the above-described process for assembling composite material tubular nodes for trus ses and to the related moulds , a person skilled in the art , with the purpose o f satis fying additional and contingent needs , could bring several additional modi fications and variants , however all within the protective scope of the present invention, as defined by the enclosed claims .