Frangible elements in sheet material

Abstract

A frangible element or weakened line in sheet material, especially tinplate, which is useful in opening means for containers. A method and apparatus for making the line is described. The frangible element lies between two portions of the sheet of greater thickness than the frangible element, to which it is joined by rounded steps or other rounded formations, and a hollow indentation, e.g., a bead, lies in one of the portions. By using a series of indentations, these can be arranged so that the opening of a tear-open panel in the container wall can be controlled more easily.

What is claimed is: 
     
       1. Sheet material having a first portion, a rounded step in the top surface of the first portion of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, a rounded formation in a surface of the sheet leading from the frangible element to a second portion of the sheet material, the second portion having a thickness greater than that of the frangible element and having formed therein at least one hollow indentation. 
     
     
       2. Sheet material according to claim 1 wherein the said formation is a rounded step. 
     
     
       3. Sheet material according to claim 2 wherein the two steps are in the same direction and are in opposite surfaces of the material. 
     
     
       4. Sheet material according to claim 1 wherein at least the parts of the first and second portions adjacent the frangible element are in parallel planes. 
     
     
       5. Sheet material according to claim 1 wherein the said rounded formation is a rounded formation in the opposite surface of the sheet from the rounded step and in the same direction as the step. 
     
     
       6. Sheet material according to claim 1 wherein the material is tinplate. 
     
     
       7. Sheet material according to claim 1 wherein .[.there.]. .Iadd.at least one indentation .Iaddend.is a hollow bead in the second portion adjacent the rounded formation. 
     
     
       8. Sheet material according to claim 7 wherein there is a further indentation in the second portion more remote from the rounded formation. 
     
     
       9. Sheet material according to claim 1 wherein the material of the first and second portion is at least about three times thicker than the material of the frangible element. 
     
     
       10. Plated sheet material having a first portion, a rounded step in the top surface of the first portion of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, a rounded formation in a surface of the sheet leading from the frangible element to a second portion of the sheet material, the second portion having a thickness greater than that of the frangible element and having formed therein at least one hollow indentation, the plating on the surface of the sheet material being unbroken in the region of the frangible element, the step and the rounded formation. .[. 
     
     
       11.  A container wall formed of sheet metal having a thinned portion of a width greater than its thickness comprising a frangible element bounding a tear-open panel, an elongate deformation in the tear-open panel extending alongside and close to the thinned portion comprising substantially parallel curves in the two surfaces of the tear-open panel..]. .[.12. A container wall according to claim 11 wherein a handle is secured to the tear-open panel of the wall bounded by the thinned portion whereby said thinned portion may be ruptured and the tear-open panel lifted from the wall..]. .[.13. A container wall according to claim 12 formed of tinplate wherein the handle is hinged to allow initial downward puncture of the frangible element on lifting the handle..]. .[.14. Sheet material having a first portion, a downward formation in the top surface of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, the downward formation in the bottom surface of the sheet leading from the frangible element to a second portion of the sheet material, the second portion having a thickness greater than that of the frangible element and having formed therein a hollow bead close to the 
     
     
        frangible element..]. .[.15.  Sheet material according to claim 14 wherein the first and second portions of the sheet material are of substantially uniform thickness and the frangible element has a thickness less than half that of the uniform thickness..]. .[.16. Sheet material according to claim 14 comprising a container wall wherein each downward formation forms a closed figure in the wall, one downward formation lying inwardly of the other and substantially parallel thereto, the downward formations bounding a frangible element of substantially constant width..]. .[.17. A container wall according to claim 16 wherein the width of the frangible element 
     
     
        exceeds its thickness..]. 18. .[.Sheet material according to claim 14.]. .Iadd.Sheet material having a first portion, a downward formation in the top surface of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, a downward formation in the bottom surface of the sheet leading from the frangible element to a second portion of the sheet material, the second portion having a thickness greater than that of the frangible element and having formed therein a hollow bead close to the frangible element, .Iaddend.wherein the downward formation in the top and bottom surfaces are both in the form of rounded steps, a portion of the sheet material between the steps constituting the frangible element, the material having a shoulder adjacent one of the steps on the opposite side thereof from the frangible element.Iadd., .Iaddend.the hollow bead in the sheet material being adjacent the other step on the side opposite from the frangible element. 
     
     
          . .[.Sheet material according to claim 14.]. .Iadd.Sheet material having a first portion, a downward formation in the top surface of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, a downward formation in the bottom surface of the sheet leading from the frangible element to a second portion of the sheet material, the second portion having a thickness greater than that of the frangible element and having formed therein a hollow bead close to the frangible element, .Iaddend.wherein the downward formations in the top and 
     
     
        bottom surfaces are both in the form of rounded steps. .[.20.  Sheet 
     
     
        material according to claim 14 formed of tinplate..]. 21. Sheet metal having a first portion, a downward formation in the top surface of the sheet leading to a frangible element comprising metal of smaller thickness than the first portion, a downward formation in the bottom surface of the sheet leading from the frangible element to a second portion of the sheet metal of thickness substantially the same as that of the first portion, an area of the second portion adjoining the thinned portion being planar except for a deformation there.[.-.]. in formed between substantially parallel curved depressions in the metal surfaces close to the thinned portion. .[.22. Sheet material having a first portion, a downward formation in the top surface of the sheet leading to a frangible element comprising material of smaller thickness than the first portion, a second portion of thickness greater than that of the frangible element joining the frangible element on the other side from the first portion and a series of indentations in the second portion..]. .[.23. Sheet material according to claim 22 wherein a single elongate bead is provided in the second portion close to the frangible element and a series of indentations is provided in the second portion on the opposite side of the single bead 
     
     
        from the frangible element..]. .[.24.  Sheet material according to claim 23 wherein the frangible element is in the form of a continuous figure in the sheet, and the elongate bead is formed inwardly of and parallel to the frangible element..]. .[.25. Sheet material according to claim 23 wherein the said series is a series of beads parallel to the single elongate bead..]. .[.26. Sheet material according to claim 22 wherein a series of beads is formed close to the frangible element..]. .[.27. Sheet material according to claim 26 wherein the frangible element is in the form of a continuous figure in the sheet and the series of beads is formed inwardly of and parallel to the frangible element..]. .[.28. Sheet material according to claim 22 wherein the indentations are so arranged in the second portion that the sheet material has a plurality of substantially parallel lines of low resistance to flexing separated by areas of relatively high resistance to flexing..]. .[.29. A container wall formed of sheet material according to claim 22 wherein the sheet material may be bent along successive lines across the sheet between the indentations when 
     
     
        the frangible element is broken through..]. .[.30.  A container wall according to claim 29 having a pair of downward formations each in the form of a closed figure in the wall, one downward formation lying inwardly of the other and substantially parallel to it, the downward formations bounding a frangible element of substantially constant width defining a tear-open panel..]..Iadd. 31. In an easy-opening container wall of metal sheet having top and bottom surfaces, the improvement comprising: a tear-open panel portion;   a portion framing said tear-open panel portion;   an elongate frangible element formed in said container wall joining said framing and panel portions, said element revealed in cross section as having a region of reduced thickness relative to said framing and panel portions adapted to rupture when said panel is torn open and first and second concave surfaces respectively formed in said top and bottom sheet material surfaces and respectively joining said region to said framing and panel portions; and   at least one hollow protuberance in said container wall formed adjacent the frangible element so as to accommodate excess metal displaced as a result of the formation of the region of reduced thickness. .Iaddend..Iadd. 32. The improvement in a container wall according to claim 31 wherein said first and second concave surfaces in said top and bottom sheet material surfaces are laterally offset with respect to each other. .Iaddend. .Iadd. 33. The improvement in a container wall according to claim 31 wherein the top and bottom surfaces of the said metal sheet are planar in the region of reduced thickness and, at their respective lateral edges remote from the respective concave surfaces adjoin respective coplanar surfaces of the panel and framing portions. .Iaddend..Iadd. 34. The improvement in a container wall according to claim 31 wherein at least one hollow protuberance is located in the panel portion. .Iaddend..Iadd. 35. The improvement in a container wall according to claim 31 wherein at least one hollow protuberance is an elongate hollow bead which extends beside the frangible element. .Iaddend..Iadd. 36. The improvement in a container wall according to claim 31 wherein the said region of reduced thickness has a thickness about one-third that of the general thickness of the said framing and panel portions. .Iaddend..Iadd. 37. The improvement in a container wall according to claim 31 wherein the framing and panel portions lie generally in different, parallel planes. .Iaddend..Iadd. 38. The improvement in a container wall according to claim 34 wherein the framing portion has a shoulder formed by a reverse fold in the sheet adjacent the frangible element. .Iaddend. .Iadd. 39. The improvement in a container wall according to claim 31 wherein the metal sheet is tinplate. .Iaddend..Iadd. 40. The improvement in a container wall according to claim 31 further having a handle secured to the panel portion for use in tearing it open, the handle having a nose portion and being arranged to pivot so that the nose portion moves in a direction which is inwardly of the container, when the wall is part of a container, to cause initial rupture of the frangible element. .Iaddend..Iadd. 41. The improvement in a container wall according to claim 31 wherein the frangible element is continuous in the metal sheet. .Iaddend..Iadd. 42. The improvement in a container wall according to claim 31 further having a handle mounted on the panel portion for use in tearing the panel out, and wherein there are a plurality of said hollow protuberances in the panel portion in the form of elongate hollow beads each extending in its direction of elongation beside the frangible element with adjacent beads separated between their respective ends by gaps at which the sheet is substantially planar, the gaps being generally arranged in pairs, the two gaps of each pair being respectively to either side of a central line of the panel portion passing through the point of mounting of the handle so that there are provided in the panel portion, corresponding to the pairs of gaps, spaced lines of low resistance to flexing transverse to the said central line, separated by areas of relatively high resistance to flexing. .Iaddend. .Iadd. 43. In an easy-opening container wall of metal sheet having a tear-open panel bounded by a frangible element, the improvement wherein a handle is mounted on the panel portion for use in tearing the panel out, and wherein there is a plurality of hollow protuberances in the panel portion in the form of elongate hollow beads each extending in its direction of elongation beside the frangible element with adjacent beads separated between their respective ends by gaps at which the sheet is substantially planar, the gaps being generally arranged in pairs, the two gaps of each pair being respectively to either side of a central line of the panel portion passing through the point of mounting of the handle so that there are provided in the panel portion, corresponding to the pairs of gaps, spaced lines of low resistance to flexing transverse to the said central line, separated by areas of relatively high resistance to flexing. .Iaddend..Iadd. 44. The improvement in a container wall according to claim 43 wherein the said beads lie on a line parallel to the frangible element. .Iaddend..Iadd. 45. The improvement in a container wall according to claim 43 wherein the said beads are spaced from the frangible element. .Iaddend..Iadd. 46. The improvement in a container wall according to claim 45 wherein an elongate hollow bead extends beside the frangible element between it and the said beads spaced from it. .Iaddend.