GB1019677A - Improvements in or relating to containers - Google Patents

Abstract

1,019,677. Making tubular rivets; riveted joints; stamping. CONTINENTAL CAN CO. Inc. Feb. 19, 1964 [June 11, 1963], No. 6971/64. Headings B3A, B3Q and B3U. A method of forming a tubular rivet from a sheet comprises the steps of forming a largediameter relatively shallow protrusion and then acting on the protrusion in a series of compressive reforming steps to re-form the protrusion by decreasing the diameter thereof and forcing material of the protrusion laterally inwardly to form a closed tubular rivet having a wall thickness substantially the same as the thickness of the original sheet. The rivet is formed in a can end 15 which includes an end panel 19, having a score line 18 defining a tearstrip 19 and is used to attach a pull tab 24. An apparatus for forming the rivet comprises a first die set, Fig. 7 (not shown), consisting of parts 29 and 30 which form a part spherical protrusion 28. This protrusion is then re-formed in three stages by die sets of the type shown in Fig. 5 (not shown), which progressively reduce the diameter and increase the height of the protrusion. Each die set comprises a base 36, a pad 37 and a stepped die insert 40. There is a spring 43 under the insert which normally maintains the insert with its shoulder 44 abutting a shoulder 39 of the pad 37. A spring-loaded pressure ring 45 accommodates a punch 48 which has a bore 49 having a rounded lower corner 50. The metal of the protrusion is reformed into a tubular member with the metal in compression so that there is a slight increase in the thickness of the metal. Fig. 11 (not shown) shows the final shape of the rivet 23, and illustrates an upper die member 87 which has a projecting rib 88 to form the score line 18. A pull tab 24 is then placed over the rivet and the assembly is acted on by a punch and die unit in which a pressure ring 92, Fig. 12 (not shown), has a shape for engaging the pull tab 24 around the rivet 23 and a punch 94 having a convex end 95 which effects a slight outward folding of tubular body portion 82 at its intersection with the end wall 83 to form a bead 96. A final die set generally similar to that shown in Fig. 12 but having a flat-ended punch effects a further outward folding to define a definite annular bead which clamps the pull tab to the tear strip 19. In a modification, Fig. 14 (not shown), the die insert of the third reforming stage has a recessed tap and in the bore of the punch there is a further punch, complementary in shape to the die insert so that a tubular rivet is formed which has an upstanding annular bead. In a further modification, Fig. 15 (not shown), the pull tab has an upstanding flange around the rivet receiving hole which reinforces the tab.