Method for adhesive connection and member therefor

Abstract: A method for the adhesive connection of elements of a structure the axes of which intersect one another comprises the operations of arranging the elements (1, 5) by interposing between them an intermediate connection member (7) of plastics material having opposite faces (7a, 7b) which have respective seats each of which has a complementary shape to that of a portion of one of the elements (1, 5) to be connected interposing an adhesive material between the intermediate member (7) and the elements (1, 5), and bringing the elements (1, 5) together with the intermediate member (7) interposed between them and holding them together in such a way that the elements (1, 5) engage in the seats of the intermediate member (7) and holding them together until polymerisation of the adhesive material is achieved.

Description: The present invention relates to a method for the adhesive connection of elements of a structure the axes of which intersect one another, according to the pre-characterising portion of appended claim 1. Such a method is known by EP-A-0 194 020. In particular, reference is made here to a structure composed of a plurality of elongate elements connected together at nodal points such as, for example, a vehicle framework. In the conventional technique, in order to connect together elements which are to be adhesively connected an adhesive is interposed between the elements and they are held together until polymerisation of the adhesive is achieved. However, the connection achieved in this conventional technique often does not provide a satisfactory strength, especially if the elements to be connected together are of different materials or of the same material of a particular type. This happens, for example, with light structures in which sections, especially box section elements of various materials, are normally used and it is often necessary to connect together materials such as aluminium/aluminium, aluminium/plastics material, plastics material/plastics material, plastics material/ ferrous material, or aluminium/ferrous material where the term "plastics material" also includes any composite material with a matrix of plastics resin. The principal object of the present invention is that of providing a method for connecting together elements of a structure by adhesive, which makes it possible to obtain an improved connection strength with respect to the connection strength which can be obtained using previously known systems. This object is achieved thanks to the features set forth in claim 1. Thanks to these characteristics the method according to the invention makes it possible to obtain a significantly improved adhesive connection strength, in particular thanks to the use of the intermediate connection member by which it is possible to obtain an improvement in the connection strength of up to 30-40% greater than that obtainable by utilising conventional techniques. The subject of the present invention are also a connection member for the adhesive connection of elements of a structure and a structure, having respectively the features indicated in claims 6 and 10. WO 89/11401 discloses a connection member having recesses in opposite surfaces. Further characteristics and advantages of the present invention will become clearly apparent from the following detailed description made with reference to the attached drawings, provided purely by way of non-limitative example, in which: Figure 1 is a schematic perspective view of a pair of elements to be connected together by the method forming the subject of the invention; and Figure 2 is a sectional side view of the elements of Figure 1 once connection has taken place. With reference to the drawings, the reference numerals 1 and 5 respectively indicate a pair of elongate elements to be connected together in such a way that their axes intersect with one another at a node 2 of a structure, for example a frame of a vehicle. In the case illustrated both the elements 1 and 5 are box-section elements and, for example, the element 1 may be made of composite plastics material such as glass fibre embedded in a matrix of thermosetting resin, whilst the element 5 may be an aluminium alloy section. In the region intended to be joined to the element 5 the element 1 has a projection 3 the shape of which substantially corresponds to a cavity defined by the end of the element 5 but of smaller dimensions. The projection 3 can have the shape of a parallelepiped as illustrated in the drawings, or else, if the element 1 is a section obtained following an extrusion process, the projection 3 will be formed in the shape of a rib which extends longitudinally along the element 1 and parallel to its axis; in this case the end of the element 5 to be disposed adjacent the element 1 will be provided with suitable seats for receiving this rib. Between the element 1 and the element 5 is interposed a connection member 7 of plastics material which has faces 7a and 7b which are substantially opposite one another, each of which is shaped in a manner complementary to the respective portions of the elements 5 and 1 to be connected. In particular, the face 7a will have hollow seats for receiving the end of the box section element 5 and the face 7b will have flat surfaces adapted to be disposed on the outer surface of the element 1 and a cavity the shape of which corresponds to the projection 3. Conveniently, the member 7 has projections which make it possible to define contact surfaces with the elements 1 and 5 of greater area than the directly facing contact surfaces of the elements themselves and which would be usable as the adhered surfaces if the intermediate member 7 were not present. These projections can for example be constituted by external prolongations 7c and internal extensions 7d of the face 7b which faces towards the element 1 and/or side walls 7e directly perpendicular to the prolongations 7c and 7e and parallel to the outer surfaces of the element 5, which allow the end portion of the section 5 to be surrounded. Thanks to the presence of the member 7 the elements 1 and 5 are completely separated from one another by a thin wall which is interposed between these two elements in such a way that the adhesion takes place exclusively between the element 1 and the element 7, and between the element 7 and the element 5. The plastics material constituting the element 7 will be chosen in dependence on the materials of which the elements 1 and 5 are made, in such a way as to optimise the connection strength taking into account the adhesive material utilised. Experimental tests conducted by the Applicant have made it possible to verify that the most suitable materials for the production of the member 7 are nylon, PET, and PBT filled with glass in a percentage variable between about 50 and 60%. In the case of adhesive material constituted by polyurethane or epoxy resins it has been determined that nylon 6/6 is particularly suitable for the production of the member 7, this material also called polyhexamethylenedipamide having the following known chemical structure: -[-NH-(CH 2 ) 6 NH-CO-(CH 2 ) 4 -CO-] n - The nylon 6/6 utilised is preferably filled with glass to 50% utilising E glass fibres (aluminoborosilicate glass) with diameter between 9 and 13 µm with a length between 0.3 - 0.4 mm and 10 mm. In order to further increase the connection strength the member 7 may incorporate an auxiliary mechanical connection device for connection to one of the elements to be connected, for example the element 1. In the embodiment illustrated in the drawings this auxiliary device is formed by a rod 9 having a head 9a embedded in the member 7 and a threaded end portion 9b opposite the head 9a. The rod 9 is fitted through a pair of aligned through holes 10 formed in the element 1 transversely of its axis in correspondence with the projection 3, and the free end 9b projecting from the element 1 is locked by a nut 11. If the intermediate member 7 is obtained by moulding the rod 9 can be introduced into it when the material from which it is made is in the molten state. Alternatively the rod 9 can be coupled to the member 7 during connection of the member 7 to the element 1. To achieve adhesive connection between the elements 1 and 5 the adhesive material is interposed between the element 5 and the member 7 and between the member 7 and the element 1 and then the member 7 and the element 1 are engaged together and the element 5 and the member 7 are engaged together and the assembly is subjected to a polymerisation process, for example at a temperature between 60 and 100°C for about 15 to 30 minutes if an adhesive of polyurethane type is used, or between 120 and 170°C for about 30 minutes if an epoxy adhesive is used. As an example the composition of a structural two-part polyurethane adhesive composed of a resin A and a resin B is set out below, which can be used to connect the two elements 1 and 5 with the interposition of the intermediate member 7. This adhesive is particularly suitable for automatic dispensing. The resin A has a viscosity of 200,000/210,000mPas and a specific gravity of 1.5 ± 0.05 g/ml and comprises the following components in percentages by weight: glycols 52% calcium carbonate 38% amorphous silica 0.2% aliphatic amines 0.8% zeolite (silicates) 6% titanium oxide 3% The resin B has a viscosity of about 110,000/120,000 mPas and a specific gravity of 1.8±0.05 g/ml, the components of which expressed in percentages by weight are: aromatic isocynates of MDI 28% aluminium silicate 17% calcium carbonate 49% phthalic plastifier 6% The ratio of the mixture of the resins A and B is: by weight 100/130 by volume 100/100 The post-life of the adhesive is 7/10 minutes with a slip ≤ 2.5mm and a shear separation strength after a cycle of 10 minutes at 80°C and 7 days at T.A. SMC/SMC free of dust, of 55 daN/cm 2 .

Claims: A method for the adhesive connection of elements in a structure the axes of which intersect with one another, comprising the following operations: arranging a first element (1) and a second element (5) to be connected together, in which at least one of these elements (5) is a box section element, arranging an intermediate connection member (7) of plastics material (1, 5) having respective seats each of which has a shape complementary to a connecting portion of one of the said elements (1, 5) to be connected, interposing an adhesive material between the intermediate member (7) and the elements (1, 5) to be connected, bringing said elements (1, 5) together with the intermediate member (7) interposed between them in such a way that the elements (1, 5) engage the seats defined by the intermediate member (7), and holding them together until polymerisation of the adhesive material is achieved, characterised in that the connecting portions of said elements (1, 5) are coupled with the intermediate member (7) by inserting them into hollow seats provided in corresponding substantially opposite faces (7a, 7b) of the intermediate member (7) until the connecting portions abut against base walls of the hollow seats, so that the connecting portions of said elements (1, 5) are surrounded by the intermediate member (7) and are separated from each other by a thin wall of the intermediate member. A method according to Claim 1, characterised in that one of the two elements (1, 5) is provided with a projection (3) and one of the seats in the intermediate member (7) is shaped in such a way as to receive at least a portion of the said projection (3). A method according to Claim 1 or Claim 2, characterised in that the intermediate connection member (7) includes an auxiliary mechanical connection device (9, 11) for connection to one of the said elements (1, 5). A method according to Claim 3, characterised in that the auxiliary mechanical connection device is a rod (9) incorporated in the intermediate member (7), which can engage a corresponding hole (10) formed in one of the two elements (1, 5), this rod (9) having a threaded end (9b) which can be engaged by a clamping nut (11). A method according to any of the preceding Claims 1 to 4, characterised in that the intermediate connection member (7) is shaped in such a way as to define contact surfaces with the said elements (1, 5) which are larger than the mutual facing contact surfaces of the elements (1, 5) themselves. A connection member of plastic material for use in the adhesive connection of elements of a structure, said member (7) having at least two hollow seats provided in its substantially opposite faces (7a, 7b) and outwardly delimited by side walls, the seats being adapted to receiving respective connecting portions of elements (1, 5) to be connected by means of the connection member with adhesive material, characterised in that it has an integral structure defining both the seats and a wall interposed between the seats for separating them from each other, and an auxiliary mechanical connection device (9, 11) adapted to be connected to one of said elements (1, 5), said device extending outwardly of one of the seats from an end portion embedded in the base of the seat. A connection member according to Claim 6, characterised in that it is made of glass-filled nylon 6/6. A connection member according to any of Claims 6 or 7, characterised in that it is shaped in such a way as to define contact surfaces with the said elements (1, 5) which are larger in area than the mutually facing contact surfaces of the element (1, 5) themselves. A connection member according to any of Claims 6 to 8, characterised in that the auxiliary mechanical connection device is a rod (9) which can engage a corresponding hole (10) formed in one of the two elements (1, 5), this rod (9) having a threaded end (9b) engageable by a locking nut (11). A structure comprising at least two elongated structural elements of which at least one element is a box-section element, the elements being connected to each other so that their axes intersect with one another, and an intermediate connection member (7) of plastics material interposed between said elements (1, 5), the intermediate member (7) having seats the shape of each of which is complementary to a corresponding connecting portion of a respective element (1, 5), said seats receiving said connecting portions and an adhesive material, characterised in that said seats are hollow seats provided in corresponding substantially opposite faces (7a, 7b) of the connection member (7), the seats receiving the connecting portions in abutment with the base walls of the hollow seats, the walls of the hollow seats surrounding a corresponding connecting portion of a respective element (1, 5) so that the connecting portions are separated from each other by a thin wall of the connection member (7).

Inventors: DA RE MARIO, DA RE', MARIO
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1995
Main classification: F16B11
IPC codes: F16B11