METHOD FOR THE JOINING TOGETHER OF BOARD-SHAPED PIECES

Abstract: A method for joining together of pieces (1, 2), advantageously of board-shaped structural elements, so that plastic to be cast, extruded or injected is used as the joint material, which said plastic becomes later gelled. According to the invention, moulds (3, 4) are fitted around the pieces (1, 2) to be joined together, which moulds, together with the gap allowed to remain between the pieces (1, 2), form a unified cavity structure. When this cavity structure is filled with the plastic, e.g. with a polymer mix, a through bead structure (8) that has a rivet effect is produced at the joint between the pieces (1, 2), which said bead structure, upon hardening, interconnects the pieces (1, 2) firmly.

Description: Method for the joining together of board-shaped pieces The present invention concerns a method in accordance with the preamble of claim 1 for the joining together of board-shaped pieces. The method for the joining together of structural elements to be described herein is, in the first place, intended as a mode of joining for the joining together of structural components of so-called sandwich structure. When structural elements are joined together which are provided with a hard surface layer and with a middle layer that is, e.g., foamy or otherwise of lower density, practical difficulties have been expe- rienced in respect of the modes of joining. If the joining takes place in the conventional way by using, e.g., corner beads, screws, rivets, etc., a problem is the local compression strength of the structure at the nearest surrounding of the rivet or screw. A corresponding construction is, of course, obtained by using a glue for the fastening of the beads at the corner or seam joints, either glue alone or together with screws, rivets, etc. Further, it is possible to imagine that an appropriate adhesive is applied between the element panels and that they are joined by means of the adhesive alone. In the former method, an abundance of expensive human labour is used, and in the glueing method a rigid seam that is readily torn is obtained,and often an ugly appearance as the glue is extruded unevenly from between the outer walls of the element. Glueing also requires a certain com¬ pressing force and a certain holding time before the seam reaches a sufficient so-called demoulding strength. The objective of the present invention is to eliminate the drawback occurring in the prior-art technology described above and to provide a method of an entirely new type for the joining together of structural elements. This objective is achieved by means of the method in accordance with the present invention, which method is characterized in what is stated in the characterizing part of claim 1. By means of the present invention, con¬ siderable advantages are achieved. Thus, - the strength of the structures becomes higher, - the overall weight of the structures becomes lower, - any other fastening components for the structures become unnecessary, - the appearance of the structures is improved, because finishing work becomes largely unnecessary (only removal of the casting naves by cutting) , - the assembly time is reduced essentially (in one casting position, several bodies can be assembled during one working shift (the formwork can be dis¬ assembled in less than 30 minutes from casting) , - the body components can be ready-painted before assembly, - sealing is unnecessary, as a result of which the service life of the structures is increased, because water and moisture cannot penetrate into the struc¬ tures at the joints, and - boards can be joined together at any angle whatsoever, both in a rigid way and in a flexible way. The method can be applied both to corner joints and to the joints of plane panels. By means of the same method, it is also possible to prepare hinges and flexible joints for constructions in which they are of advantage. In the following, the invention will be examined with the aid of the exemplifying embodiments in accordance with the attached drawings. Figure 1 is a perspective view of a vehicle body manufactured by means of the method in accordance with the invention. Figures 2, 3 and 6 illustrate application of the method in accordance with the present invention to corner joints. Figures 4, 5 and 11 illustrate the application of the method in accordance with the invention to a hinged joint. Figures 7 to 10 illustrate the application of the method in accordance with the invention to a butt joint between two board elements. in the method in accordance with the inven¬ tion, the joint material is preferably some elastomer that is cast or extruded, in particular polyurethane elastomer or silicon elastomer. In the example case in accordance with Figures 2 and 3, the objective is, by casting out of a polyurethane elastomer, to form a corner lining 8, which, at the same time, glues the components 1 and 2 to be cast together into contact with each other without any other mechanical fastening. Before the casting, the portions remaining under the cast must be sand-blasted or ground and treated with a suitable primer (lacquer, paint or glue) which permits adhesion of the material to be cast to the face con¬ cerned. The casting temperature of the polyurethane elastomer is +15 to +60 C, and the best result is given by parts at a temperature of +60 C onto whose face the casting takes place. The casting is also possible at lower temperatures. In such a case, the ultimate strength is reached in a few days. The piece 1,2 can be detached from the mould 3,4 in both cases in less than 30 minutes, and the ultimate strength is required only, e.g., when hinges are to be used. In the machinery of casting and extrusion of polyurethane elastomers, the raw-materials are preheated to a temperature of +60 to +80 C, at whic temperature their casting takes place. Metal parts should preferably always be preheated. The poly¬ urethane elastomers are, if necessary, coloured by means of pigments of different colours, which are mixed into the polyol. In the following. Figures 1 to 3 will be examined. The casting of the corner bead between the roof 2 and a wall 1 as well as between a side wall and an end wall (section A-A) takes place as follows: A wall board 1 and a roof board 2 are placed in position so that a gap of about 3 mm remains between them. The outer mould bead 3 and the inner mould bead 4 are placed in position, and a hole 6 of about 8 mm is drilled through the outer mould bead 3 and through the roof 2, whereby a duct as straight and short as possible is obtained into the lower part of the corner joint portion. After the mould beads 3 and 4 have been locked into their positions, the casting is performed, whereat the raw-materials mixed by the machine flow through the nozzle 5 into the filling hole 6 and further into the free space remaining between the mould beads 3 and 4 as well as between the wall board 1 and the roof board 2, and fill the said free space. The filling of the space is noticed by means of the raw-material flowing out through the air hole 7. Since the polymerization of the polyurethane elastomer starts within 5 to 15 seconds from the mixing of the raw-materials, the corner bead being cast must be inclined so that one end of the body is placed higher than the other end, and the filling holes 6 are placed sufficiently close to each other. In such a case, no separate air holes are needed, but material is extruded until the material starts flowing out of the next filling hole. At verti¬ cal corners, no inclination is required, but the filling takes place from the bottom upwards, and each used filling hole 6 is closed by means of a plug. Another mode, besides inclination, is to form casting cavities of a certain magnitude by means of partition walls, which may be made of pieces of polyurethane elastomer shaped equal to the profile to be cast (length, e.g., 5 mm), whereby the casting can really be performed in the horizontal plane and, when cast, the polyurethane elastomer is bound completely together with the pieces of partition walls. The casting space may be, at the maximum, so large that polymerization has not started at the mouth of the filling hole. In this method, air holes are necessary. The casting pressure is no higher than the liquid pressure equal to the height of the object to be cast, so that supporting of the mould beads does not cause diffi¬ culties. The section B-B (Fig. 3) shows the connecting of a wall 1 and a bottom 10 to each other and to an outer corner bead 9 of steel, which said corner bead, at the same time, also functions as a "by-passing bead". In this case, the casting takes place into the recess placed at the top edge of the outer corner bead 9 and into the casting cavity formed by the inner mould bead 4 and by the wall board 1 and the bottom board 10. The casting of the outside may be performed straight as open casting, and the casting of the inside in the way described in Fig. 2. Thereby, the outer corner bead 9 becomes attached to the wall board 1 by the cast recess and to the bottom board 10 underneath the casting cavity. The wall board and the bottom board adhere to each other both by means of the "baseboard" and by means of the end of the bottom board. In the same way, by means of the same tech¬ nique, it is possible to form the edges of openings, the hinge arrangements for doors and gates, as well as the preparation of seals. Section C-C (Figs. 4, 5 and 11) shows the edges of a door and of a door opening as well as the hinge arrangement. The mould beads 3 and 4 are installed outside and inside the hinge zone of the wall 1 and of the door 11. Into the inner mould bead 4, an auxiliary mould bead 13 is installed, whose function is to form the inside of the hinges, and by means of the length of the auxiliary mould bead 13, it is possible to determine the desired thickness of the hinge (maximum 2 to 3 mm) , and by means of the width of the auxiliary mould bead 13, on the other hand, the magnitude of the elongation of the hinge 12, 21 (width at least 3 mm). The hinge and the edge formation can be cast in the vertical position, as can also the corner joint. Fig. 6 shows a corner joint for the sections A-A as designed correctly in view of the strength of materials. The most important application of a corner joint is the joining together of two sandwich boards. A casting cavity 16 prepared in the way shown in Figs. 7 and 9 (zone D) is suitable for joining together of, e.g., panels 14, 15 with plywood faces. The same is shown in Figs. 8 and 10 (zone E) , which illustrate the joining together of metal-faced sandwich panels 14,17,18. By means of this joint technique, a suffi¬ cient shear strength is obtained for the joint seam when standard-width (120 cm) vertical panels are used for the construction of a vehicle body. As far as is known, such joining has not been even possible in prior art, but glue-jointed plywood board delivered by the factory has been used, whose cost per square metre is almost double as compared with the standard boards. Also, the term of delivery is about 5 to 6 weeks from order. In the method in accordance with the inven¬ tion, it is advantageous and necessary that the pieces to be joined together are kept apart from each other at the moment when the joint material is filled into the space between them, whereby the elastomer to be cast, extruded or injected has access into all parts of the joint gap and can flow into the pores in the material in the interior of the panel, thereby creating a contact area sufficient in view of the strength properties. Moreover, by means of the method described in the present invention,' it is advantageously possible to prepare joints similar to riveting, which increase the strength of the joint. In the way shown in Figures 8 and 10, by way of example, metallic members 19, 20 have been bent, which increase the strength of the joint and which may be, e.g., perforated, whereby the fluid joint elastomer also penetrates into these holes and, by means of its shear strength, increases the strength of the whole joint. As is shown in Figures 7 and 9, into pieces to be joined together by means of butt joints, a groove 16 of the shape of two letters V placed opposite each other has been machined, and the.resin can be cast along the said groove. When the casting is performed over a certain length of the mould, the mould is shifted forwards, and the new cast joins the preceding cast without a seam, which said preceding cast has not yet polymerized completely but has a sufficient gel strength. The opposite part of the mould, through which the elastomer resin is fed in, must, of course, have suitable air holes in order that a continuous joint could be pro¬ duced. When the method is used, the casting pressure does not have to be essentially higher than the hydro¬ static pressure of the fluid being cast, so that robust fastenings of the mould pieces are not required. As can be understood, by means of the method, it is also possible to cast sealing strips, e.g., around door openings by one operation so that they become ready-attached to the parent piece. The method described in the present appli¬ cation is most advantageously suitable for use in the manufacture of box elements manufactured in series. Examples of such box elements are typically vehicle bodies, railway wagons and cars, ship cabins, workmen's cabins, summer cottages, small houses, etc.

Claims: WHAT IS CLAIMED IS: 1. Method for the joining together of pieces (1 , 2) , in particular of board-shaped structural elements, according to which method - mould structures (3, 4) are fitted around the desired joint (8), which said mould structures, together with the pieces (1 , 2) to be joined, form cavities (16) at both sides of the joint, - such a plastic to be cast, extruded or injected is fed into the cavities (16) as becomes gelled after the feeding and forms a bead-.like joint (8) of the shape of the cavities (16), and the mould structures (3, 4) are removed upon hardening of the joint (8), c h a r a c t e r i z e d in that at the joint, a gap interconnecting the cavities (16) is allowed to remain between the pieces (1, 2) so as to produce such a unified cavity structure in which the plastic fed into the cavity forms a rivet-like joint (8) firmly connecting the pieces (1 , 2) to each other. 2. Method as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the joint plastic consists of polyurethane or polyurethane elastomer. 3. Method as claimed in claim 1 or 2, c h a r a c t e r i z e d in that mould components (3, 4) shaped out of polyolefins are used as the mould material. 4. Method as claimed in claim 1 or 2, c h a r a c t e i z e d in that moulds made of teflon or provided with teflon coating are used as the moulds (3, 4) . 5. Method as claimed in claim 1 or 2, c h a r a c t e r i z ed in that the pieces (1 , 2) to be joined together are heated in advance to a temperature substantially close to the same temperature at which the elastomer to be used is cast into the desired joint space (16) limited by the moulds (3, 4). 6. Method as claimed in claim 1 , c h a r ¬ a c t e r i z e d in that the plastic seam (8) that is formed is later coated with polyvinylidene fluoride (PVDF) . 7. Method as claimed in claim 1, wherein boards (1 ) covered with metal sheet material (17, 18) are joined together, c h a r a c t e r i z e d in that the metal sheet material (17, 18) is, before the plastic is fed in, folded into the cavities (16) so as to intensify the rivet effect.

Inventors: SALAKARI ANTERO, SALAKARI, ANTERO
Applicants: SALAKARI MAIJA LEENA, SALAKARI, MAIJA-LEENA
Application year: 1984
Main classification: F16S1
IPC codes: B29C45, B29C65, B29C70, E04B1