Method for crimping a tube end plate of a heat exchanger on a header box and heat exchanger obtained through this method
FIELD OF THE INVENTION 
     The present invention relates to a new method for crimping a header box in a tube end plate of a heat exchanger in such a manner that the header box compresses a deformable gasket providing a perfect tightness between the tube end plate and the header box. 
     BACKGROUND OF THE INVENTION 
     In the known technique, the crimping of the header box is most often realized by means of lugs protruding from the peripheral upright edge of the tube end plate, these lugs being folded back onto a protruding flange formed on the header box. 
     INFORMATION DISCLOSURE STATEMENT 
     The hereabove technique is practiced in particular in French Pat. No. 79-09343, in French Pat. No. 83-05785 as well as in French Pat. No. 1,039,911. In some cases, the folded lugs are reinforced by ribs. This is the object of the European patent application No. EP-A-0,054,815. 
     This arrangement which is largely used has the disadvantage that the lugs work in flexion and that at the moment the lugs are folded they can, sometimes, cause deformations of the upright edge of the tube end plate from which they protrude, with the result that these deformations can impair the tightness between the tube end plate and the header box. 
     In order to remedy the above disadvantage, Applicant has proposed in French Pat. No. 69-24782 to provide a header box-tube end plate connection made by means of fastening members protruding in the peripheral edge of the header box and by engaging these fastening members in openings of the upright edge of the tube end plate. Similar arrangements are also disclosed in French Pat. No. 79-29548. 
     Such an arrangement is satisfactory since the metal works in traction, but setting in place the header box sometimes causes relatively difficult problems, according to the nature of the metal of the tube end plate. It is actually possible, if the metal of the tube end plate is resilient, to provide a snap-in fitting but, if the metal is not resilient, the upright edge of the tube end plate has first to be flared out and then shrunk against the header box while maintaining this header box under pressure. 
     OBJECT OF THE INVENTION 
     The present invention relates to a realization for obtaining the same advantageous results as those produced by an introduction of fastening members protruding from the header box and extending through openings formed in the upright edge of the tube end plate, while permiting an easy mounting of the header box, whatever the nature, and particularly the resiliency of the metal constituent of the tube end plate. 
     SUMMARY OF THE INVENTION 
     According to the invention, the method for crimping a tube end plate of a heat exchanger on a header box in which there is provided a peripheral upright edge for enclosing an extra thickness defined by the header box, comprising the step of creating in the peripheral upright edge of the tube end plate, substantially at a level of the header box, a line of lesser resistance, stiffening a portion of the peripheral upright edge of the tube end plate which extends above the line of lesser resistance so stiffened, and folding the portion of the upright edge of the tube end plate such that the upright edge is at least partly folded back on the flange of the header box. 
     The invention applies also to a heat exchanger obtained according to the hereabove method. According to this second arrangement of the invention, the heat exchanger is of the tube and heat dissipator type with the tubes opening into at least one tube end plate which is covered by a header box crimped by a peripheral upright edge of the tube end plate; The upright edge of the tube end plate has; on a major portion at least of its periphery, a line of lesser resistance, stiffening means are provided on the upright edge above the line of lesser resistance, and the stiffening means are at least partly folded back on a peripheral edge of the header box in a position for which a heel portion of the header box compresses a deformable gasket. 
     Various other features of the invention will become more apparent from the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are shown by way of non limiting examples in the accompanying drawings, wherein: 
     FIG. 1 is a partly exploded partial perspective view of a heat exchanger embodying the invention; 
     FIG. 2 is a sectional view of the part of FIG. 1 taken substantially along line II--II of FIG. 1; 
     FIG. 3 is a sectional view of a part of FIG. 1 taken substantially along line III--III of FIG. 1; 
     FIG. 4 is a partly exploded partial perspective view, similar to FIG. 1, showing a variant; 
     FIG. 5 is a diagrammatic cross sectional view of a particular position of a tube end plate and of a header box prior to the working operation shown in FIG. 6; 
     FIG. 6 is a diagrammatic sectional view showing the working operation during which the tube end plate is crimped onto the header box; 
     FIG. 7 is a cross sectional view, similar to FIG. 5, showing, after crimping, the relation between the tube end plate and the header box; 
     FIG. 8 is a perspective view of an alternative embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the drawings, reference numeral 1 designates a header box of a heat exchanger. The header box 1 is made of a molded material, for example a synthetic material or a metal, and defines at its lower portion an extra thickness 2. The extra thickness 2 is formed on the whole periphery of the header box and delimits a lower portion 3 and an upper flange 4. 
     The header box 1 is provided for covering a metal tube end plate 5 in which ends of tubes 6 are tightly connected, with heat dissipators in the form of corrugated fins 7 being interposed between the tubes 6. The tube end plate 5 defines a peripheral groove or gutter 8. 
     The peripheral upright edge 9 of the tube end plate 5 is provided, substantially at the position that the flange 4 of the header box has finally to occupy, with a row of holes or openings 10 for creating a line of lesser resistance shown at 11 in the drawings. 
     A plurality of waves 12 are formed above the line 11 of lesser resistance, the waves 12 leaving therebetween a succession of substantially planar portions 13 which are in the same vertical plane as the inner face of the upright edge 9. 
     FIGS. 2 and 3 thus show that the waves 12 leaves completely clear the peripheral groove 8 of the tube end plate, thereby permitting an easy fitting of the extra thickness 2 of the header box 1 in the peripheral groove 8, after having placed therein a deformable flexible gasket 14. The waves 12 have for their effect to stiffen the upper portion of the upright edge 9 above the line 11 of lesser resistance. 
     In order to crimp a tube end plate 5 on the header box 1, a tool is used which is designated as a whole by reference 15 in FIG. 6. As shown, the tool 15 defines a passage 16 for the tubes 6 and heat dissipators 7 and forms, in its upper portion, a shoulder 17 above which extend the crimping walls 18. The height of the crimping walls 18 is greater than the height of the upright edge 9 of the tube end plate 5. 
     As shown in the drawings, the tube end plate 5 to which are fixed the tubes 6 and heat dissipators 7 is engaged into the tool 15 (FIG. 6) up to the waves 12 come in abutment against the top 19 of the tool 15. 
     Unless already done, the flexible gasket 14 is fitted into the peripheral groove 8 of the tube end plate. Then the header box 1 is engaged in the peripheral groove 8 in such a manner that the heel portion 3 of the extra-thickness 2 of the header box 1 comes to bear against the gasket 14. A pressure in direction of the arrow f 1  is then exerted on the header box 1. The pressure has first for effect to compress the gasket 14 in the bottom of the peripheral groove 8, then, the pressure being still exerted, a progressive deformation of the portion of the upright edge 9 appears at the line 11 of lesser resistance. This deformation is caused by the waves 12 which slide along the crimping walls 18 of the tool 15 and therefore cause the substantially planar portions 13 of the upright edge 9 to tilt towards top of the flange 4 of the extra thickness 2 of the header box 1. The deformation goes on until the outer walls of the waves 12 are brought in a substantially vertical plane. Therefore, the waves 12 have a cam effect. 
     In this arrangement, the holes or openings 10 defining the line 11 of lesser resistance cover the side edge of the flange 4 which is thus, partly at least, enclosed while the portions 13 are folded back on the top of the flange 4. 
     FIGS. 4 and 8 show slight variations according to which notches 20 are formed in the flange 4 in order to define teeth 21 therebetween, the teeth 21 being provided to be in register with the holes 10 of the tube end plate. As shown in FIG. 8, it is advantageous that the holes 10 have a diameter (if they are of a round shape) or a width (if they are of an oblong, rectangular or trapezoidal shape), which is superior to width of the teeth 21 in order to compensate for the manufacturing tolerances existing between the header box and the tube end plate. The line 11 of lesser resistance is then substantially at the base of the teeth 21. 
     Since the teeth 21 are registered with the holes 10 at the end of the crimping operation, the teeth 21 are inserted into the holes 10 and, therefore, the connection provided by the mutual engagement of the parts is reinforced to a greater degree. 
     Although not necessary, it is advantageous, in order to make the crimping operation easier, to provide slits or notches 22, for example at the four corners of the upright edge 9 of the tube end plate. 
     The invention is not limited to the embodiments shown and described in detail and various modifications can be made without departing from the scope of the invention as shown in the appendent claims. Particularly, the slits or notches 22 can be replaced by waves which are compressed at the moment of the crimping operation. Likewise, the line of lesser resistance can be defined in a different way than by opening; it is possible that they are formed by a thinned out portion, for example a continuous or discontinuous groove of the tube end plate. It is also possible that the openings be connected by a portion of lesser resistance, particularly when the header box forms teeth 21.