Patent Number: 047298707
Section: description

DETAILED DESCRIPTION OF THE INVENTION As is shown by FIG. 1, the plug 10 according to the invention is a solid metal cylindrical part having a small diameter cylindrical portion 12 fitting into the end of the tubular can 14 and a large diameter cylindrical portion 16, separated from portion 12 by a shoulder 18, which abuts against the end of can 14. As illustrated in FIG. 1, the external diameter of plug portion 16 is substantially equal to the external diameter of can 14. According to the invention, cylindrical portion 12 is designed in such a way that it can be fitted into can 14 by using a minimum force of approximately 15 daN, tightening being obtained by the elastic deformation of the can, which makes it possible to ensure the securing of the plug under optimum conditions prior to the carrying out of a good quality weld without filling metal. To this end, fig shows that the external diameter D of the cylindrical portion 12 is slightly smaller than the internal diameter d of the can. Three serrations 20 at 120.degree. from one another are formed on said cylindrical portion 12 according to the generatrixes thereof. As is more particularly illustrated by FIG. 2, each of the serrations 20 forms two beads 22, whereof the thickness e overhanging with respect to the norminal diameter D of the cylindrical portion 12 slightly exceeds (by approximately 1/100 mm) ##EQU1## so that the fitting of portion 12 into can 14 leads to a local elastic deformation of the interior of the can and the beads 22 adequate for ensuring the desired tightening. In known manner, the fitting of plug 16 into can 14 is facilitated by the bevelled shape of end 24 of cylindrical portion 12. When fitting has been completed, plug 16 and can 14 are welded at 26, without filler metal, along their respective junction plane. As can 14 is produced in successive batches, its internal diameter d can vary by a few hundreths of a mm between a maximum diameter d.sub.max and a minimum diameter d.sub.min. The diameter D of the cylindrical plug portion 12 is preferably chosen equal to the minimum diameter d.sub.min and the thickness e of the beads 22 formed by the serrations 20 is equal to ##EQU2## In the case of mass production from cans having an internal diameter varying between certain known limits, it is possible to ensure an automated fitting of the plugs into the cans with substantially no wastage and under tightening conditions very close to the ideal tightening of approximately 1/100 mmm for which all the defects observed with the prior art are eliminated. It should be noted that the number of serrations 20 formed on the cylindrical portion 12 of the plug can exceed 3. However, the fitting force of the plug rapidly increases with the number of serrations. Thus, whereas this force is 15 daN when three serrations are formed on the cylindrical portion 12 of a given plug, it increases to 30 daN if the cylindrical portion 12 of said plug had four serrations. FIG. 3 shows in exemplified manner a tool making it possible to form the serrations on the surface of the cylindrical plug portion 10. This tool comprises a body 30 having a bore 32 in which is located the cylindrical plug portion. Three holes 34 are made radially at the same level in body 30 of the tool and issue into bore 32. These holes 34 are distributed at 120.degree. from one another about the axis of body 30 and each of which receives a machining point 36, which is immobilized in the corresponding hole by means of a screw 38. The position of the points 36 is regulated by a member 40 shown in mixed line form in FIG. 3. Member 40 is centered in bore 32 and is provided at its end placed facing points 36 with a portion 40a, whose diameter determines the depth of the serrations to be made in the plug. When regulation or setting is at an end, the points 36 are immobilized by tightening screws 38. The machining of serrations 20 on plug portion 12 is then carried out by driving the latter into the bore 32 of the tool parallel to the axis of said bore. This operation is followed by finishing on the lathe making it possible to level the ends of the beads 22, so as to eliminate rough edges and calibrate said beads to the desired thickness e.