Manufacture of thin-walled containers

Abstract

Metal containers, particularly for beer, have been made from stainless steel which is compatable with beer or aluminum which is specially coated to make a compatable inner surface. The stainless steel container is expensive when the wall thickness is such as to withstand rough handling and the cheaper aluminum container has a limited life depending on the internal coating. The present invention provides a double wall container of which the inner wall is of thin stainless steel. The invention solves the hitherto insurmountable problems of forming a thin walled inner vessel and expanding it inside an outer vessel so that the resulting inner vessel is without crevices which would otherwise be extremely difficult to clean to meet strict hygiene regulations.

What is claimed is: 
     
       1. A method of making a double wall container comprising an inner vessel of thin walled stainless steel surrounded by a rigid outer vessel .[.in which the inner vessel is a thin-walled vessel of stainless steel.]., comprising the steps of forming two or more co-operating pieces of the inner vessel from sheet stainless steel and forming the mating edges to enable the pieces to be welded together in a manner which permits subsequent flattening, straightening or smoothing of the welded seams, welding an entry boss to one of the pieces, holding the pieces together in correct relationship and welding the pieces to form a liquid tight container, inserting the inner vessel in .[.said.]. .Iadd.a larger .Iaddend.surrounding rigid outer vessel, and admitting fluid under pressure to the interior of the inner vessel to expand it .[.and cause it.]. to conform substantially to the internal shape of the outer vessel.[.,.]. .Iadd.and to flatten, straighten, or smooth .Iaddend..[.thereby flattening, straightening or smoothing.]. to a substantial degree the welded seam or seams of the inner vessel, .Iadd.the mating edge of at least one of the pieces being flanged outwards so that, in the area of the weld, the adjacent pieces are substantially parallel to each other, or make a small included angle, and the inner vessel being formed of two dome shaped pieces which are outwardly flanged at the rims and, after the rims are brought together, the two flanges are seam welded to give a liquid-tight joint .Iaddend.. .[.2. A method as claimed in claim 1, wherein the mating edge of at least one of the pieces is flanged outwards so that, in the area of the weld the adjacent pieces are substantially parallel to each other, or make a small included angle..]. .[.3. A method as claimed in claim 2, wherein the inner vessel is formed of two dome shaped pieces which are outwardly flanged at the rims and after being brought together the two flanges are seam welded to give a 
     
     
        liquid-tight joint..]. 4. A method as claimed in claim 1, wherein the inner vessel is enclosed in two dome shaped portions of an outer vessel and the assembly is mounted in an expansion rig without the two outer 
     
     
        vessel portions having been welded to each other. 5. A method as claimed in claim 4, wherein the interior of the inner vessel is coupled to a source of hydraulic fluid and by means of the pressure of the fluid the inner vessel is expanded to conform substantially to the inner surface of the outer vessel, the forces on the outer vessel being taken by the rig. 
     
     
           A method as claimed in claim 5, wherein the volume of hydraulic fluid admitted to the inner vessel is metered so that the volumetric capacity of 
     
     
        the container is established. 7. A method as claimed in claim 6, wherein the volume of hydraulic fluid admitted to the inner vessel is controlled so that the inner vessel is expanded to a predetermined volumetric 
     
     
        capacity. 8. A method as claimed in claim 1, wherein the entry boss is centrally located in an end face of an approximately cylindrical container and adhesive is applied between the inner and outer vessel at least in the 
     
     
        central area of the other end face. 9. A method as claimed in claim 4, wherein the two dome shaped portions are welded together after removal 
     
     
        from the expansion rig. 10. A method as claimed in claim 1, wherein a skirt is welded to the outer vessel to protect the entry boss from contact 
     
     
        with the ground. 11. A method as claimed in claim 10, wherein a second skirt is welded to the outer vessel in opposite location to the first 
     
     
        skirt. 12. A method as claimed in claim 10, wherein the skirt is provided with hand holes to facilitate handling. .[.and/or drain holes to allow 
     
     
        drainage of spillage.]. 13. A method as claimed in claim 1, wherein the entry boss is formed of a stainless steel liner having an outwardly turned flange at the top and an inwardly turned flange at the bottom and being internally threaded, said liner being surrounded by an aluminium sleeve which is sealingly secured thereto to provide a substantially cylindrical assembly which passes through an aperture in the outer vessel when the 
     
     
        inner vessel is assembled to the outer vessel. 14. A method as claimed in claim 13, comprising providing the underside of the inwardly turned flange with an annular upstand which lies concentric and approximately parallel with a flange formed around an aperture in the inner vessel to which the liner is to be welded, and welding the two together so that the upstand is 
     
     
        burned substantially away. 15. A method as claimed in claim 1, wherein the inner surface of the outer vessel is scored to facilitate exit of air from 
     
     
        between the inner and outer vessels during expansion. 16. A method as claimed in claim .[.3.]. .Iadd.1.Iaddend., wherein the outer vessel is formed from two dome shaped portions of which one has a joggled rim to form a socket for the rim of the other portion, the socket so formed also providing an internal recess to accommodate the welded flanges of the 
     
     
        inner vessel. 17. A method as claimed in claim 16, wherein the dome shaped portions are provided with circumferential raised portions to act as 
     
     
        rolling ways. 18. A method as claimed in claim 17, wherein the extent of the raised portions is chosen to provide the required degree of expansion to the inner vessel during expansion to flatten, straighten or smooth the 
     
     
        welded seam or seams. 19. A method as claimed in claim 1, wherein the 
     
     
        outer vessel is of aluminium. .[.or reinforced plastics material.]. 20. A method as claimed in claim 1, wherein the stainless steel inner vessel is made from sheet stainless steel of 0.009 - 0.020 inches (0.2 - 0.5 mm) thickness. .Iadd. 21. A method as claimed in claim 10, wherein the skirt is provided with drain holes to allow drainage of spillage. .Iaddend..Iadd. 22. A method as claimed in claim 1, wherein the outer vessel is of reinforced plastics material. .Iaddend..Iadd. 23. A method of making a double wall container comprising an inner vessel of thin walled stainless steel surrounded by a rigid outer vessel, said method comprising the steps of: (a) forming an open-ended, thin-walled tube of stainless steel the end portions of which are bent outwardly to form circumferential flanges projecting substantially at right angles to the wall of the tube, the junction of each flange and the wall of the tube being smoothly curved;   (b) forming two thin end plates made of stainless steel and of size and shape to span the open ends of the tube;   (c) welding one of the thin end plates to each of the flanges on the tube along the overlapping portion, close to the radially-outer edges of the flanges and of the end plates, thereby forming a liquid tight inner vessel;   (d) inserting the inner vessel in a surrounding rigid outer vessel formed in two or more portions;   (e) mounting the assembly comprising the inner and outer vessels in an expansion rig;   (f) admitting fluid under pressure to the interior of the inner vessel to expand it to conform substantially to the internal shape of the outer vessel and to flatten, straighten, or smooth to a substantial degree the welded seams of the inner vessel, the forces on the outer vessel being taken by the expansion rig; and   
     
     
       (g) removing the assembly from the rig. .Iaddend..Iadd. 24.  A method of making a double wall container comprising an inner vessel of thin walled stainless steel surrounded by a rigid outer vessel, said method comprising the steps of: (a) forming an open-faced, thin-walled upper dome of stainless steel the rim of which is bent outwardly to form a circumferential flange projecting substantially at a right angle to the wall of the upper dome, the junction of the flange and the wall of the upper dome being smoothly curved;   (b) forming an open-faced, thin-walled lower dome of stainless steel the rim of which is bent outwardly to form a circumferential flange projecting substantially at a right angle to the wall of the lower dome, the junction of the flange and the wall of the lower dome being smoothly curved, the lower dome being of size and shape to span the open face of the upper dome;   (c) welding the upper and lower domes to each other along the over-lapping portions of their respective flanges, thereby forming a liquid tight inner vessel;   (d) inserting the inner vessel in a surrounding rigid outer vessel formed in two or more portions;   (e) mounting the assembly comprising the inner and outer vessels in an expansion rig;   (f) admitting fluid under pressure to the interior of the inner vessel to expand it to conform substantially to the internal shape of the outer vessel and to flatten, straighten, or smooth to a substantial degree the welded seam of the inner vessel, the forces on the outer vessel being taken by the expansion rig; and   (g) removing the assembly from the rig. .Iaddend..Iadd. 25. A method of making a double wall container comprising an inner vessel of thin walled stainless steel surrounded by a rigid outer vessel, said method comprising the steps of:   (a) forming at least two thin-walled components of stainless steel at least one of which has at least one edge portion bent outwardly to form a flange projecting substantially at a right angle to the wall of the component, the junction of the flange and the component of which it is a part being smoothly curved, the components being of size and shape to engage each other in facing relationship with the flange over-lapping a mating surface on the other component;   (b) welding the components to each other along the overlapping portion of the flange and the mating surface on the other component, thereby forming a liquid tight inner vessel;   (c) inserting the inner vessel in a surrounding rigid outer vessel formed in two or more portions;   (d) mounting the assembly comprising the inner and outer vessels in an expansion rig;   (e) admitting fluid under pressure to the interior of the inner vessel to expand it to conform substantially to the internal shape of the outer vessel and to flatten, straighten, or smooth to a substantial degree the welded seam or seams of the inner vessel, the forces on the outer vessel being taken by the expansion rig; and   (f) removing the assembly from the rig. .Iaddend.