GB2262183A

GB2262183A - Providing passage through wall of container used as battery box

Info

Publication number: GB2262183A
Application number: GB9125939A
Authority: GB
Inventors: Philip Gordon Brocklehurst; Ralph Green
Original assignee: Silent Power F R Energies GmbH; Chloride Silent Power Ltd
Current assignee: Silent Power F R Energies GmbH; Chloride Silent Power Ltd
Priority date: 1991-12-05
Filing date: 1991-12-05
Publication date: 1993-06-09
Also published as: WO1993011570A1; AU3089192A; GB9125939D0

Abstract

A container includes at least one wall with inner and outer skins of metal defining a sealed region therebetween. A sealing cuff extends between apertures in the two skins to define a passage through the wall. The sealing cuff is made of a tube of corrugated metal, a first washer at one end of the tube welded around the aperture in one of the skins and a second washer at the other end of the tube welded around the aperture in the other of the skins. The first washer extends transversely inwards of the tube to assist in construction of the container. The region between the inner and outer skins may be evacuated of gases and contain thermally insulating material. Containers having external walls of this type can be used as battery boxes for batteries comprising one or more high temperature cells.

Description

A CONTAINER The present invention relates to a container having a wall with inner and outer skins of metal defining a sealed region therebetween, apertures in the two skins and a sealing cuff extending between the apertures to define a passage through the wall. The present invention is particularly applicable to a container having external walls of the kind described above. The region between the inner and outer skins may be evacuated of gases and contain thermally insulating material.

Containers of the kind described can be used as battery boxes for batteries comprising one or more high temperature cells. High temperature cells may be defined as cells which operate at an elevated temperature, typically above 10 OOC, more typically above 3000C.

One example of a high temperature cell is a sodium sulphur cell which operates at a temperature of about 350 0C such that the sodium and sulphur electrodes are in liquid form.

The cells forming the battery are enclosed in a container, of the kind described, which is effective as a thermally insulating box to reduce loss of heat from the cells when no power is being drawn therefrom. It is then necessary to provide lead-throughs for electrical connection between the cells in the interior of the container and terminals, or further electrical connections, on the exterior of the container. One or more passages through the wall of the container, for passage of a respective lead-through, are defined by a respective sealing cuff. As the region between the inner and outer skins of the container is evacuated, to provide some thermal insulation, the seal provided by the sealing cuff must be sufficiently hermetic to prevent an ingress of ambient atmosphere which would cause the vacuum to deteriorate to an unacceptable level.

It is an object of the present invention to provide an improved container and an improved method and apparatus for making a container.

According to the present invention, there is provided a container having a wall with inner and outer skins of metal defining a sealed region therebetween, aligned apertures in the two skins and a sealing cuff extending between the apertures to define a passage through the wall, the sealing cuff comprising: a tube of corrugated metal; a first washer at one end of the tube welded around the aperture in one of the skins; and a second washer at the other end of the tube welded around the aperture in the other of the skins; wherein the first washer extends transversely inwards of the tube.

Construction of the sealing cuff as a tube of corrugated metal, so that it has a bellows-like structure, provides a degree of flexibility between the inner and outer skins of the container. This flexiblity allows for differential movement between the inner and outer skins which may be caused by thermal mismatches or if the container should be subject to vibration. The flexiblity of the bellows-like structure itself also provides for increased tolerance to misalignment of the apertures in the inner and outer skins during manufacture. The region of the first washer extending transversely inward of the tube provides a region of the sealing cuff which is accessible from the exterior of the wall when both the inner and outer skins are in position.At this accessible region of the sealing cuff, a counter pressure can be applied to the first washer from the exterior of the wall so that the sealing cuff and said one of the skins can be held together while a joint is formed there between.

Advantageously the second washer also extends transversely inwards of the tube. In this way, the corrugated structure of the tube is distanced from any lead passing through the passage, and so mutual wear and tear of the corrugated structure and the lead, which might occur if the corrugated structure and the lead are adjacent one another, is avoided or at least alleviated.

Preferably, the minimum internal dimension of the second washer transverse of the tube is greater than an internal dimension of the first washer transverse of the tube. With this construction, any means used to apply pressure to that part of the first washer extending transversely inwards of the tube can easily pass through the second washer.

The second washer may extend transversely outwards of the tube. This outward extension of the second washer provides an interface between the second washer and said other of the skins at which a weld may be made. The outward extension further provides a region at which pressure can be applied to the second washer to hold the sealing cuff and said other of the skins together while a weld is formed therebetween.

The present invention is advantageously applied to containers in which said first washer is welded around the aperture in the outer of said skins. In particular, if the second washer extends transversely outwards of the tube, welding of the second washer to the inner of said skins can take place at an interface between the second washer and the outer skin which is accessible from the exterior of a container providing said inner skin. This allows access by an automated welding tool.

The container may include a sealing plate having an aperture aligned with the aperture in the outer skin, the sealing plate being located outside the outer skin and sealed to said first washer. Provision of such a sealing plate assists in making a seal between the outer skin and a lead-out structure, alleviating the problem of warping of an area of the outer skin around the aperture which may be caused by welding of the sealing cuff to the outer skin.

Advantageously, said first washer includes an axially extending step extending beyond the outer skin and providing an axially outwardly facing surface for locating the sealing plate. This construction can avoid the need to make any direct seal between the lead-out structure and the outer skin after welding has taken place.

The container preferably includes means for providing electrical insulation within the passage, said insulation means comprising at least a first part abutting the outer skin and a second part abutting the inner skin.

Said first and second parts may be separated by a tube of electrical insulation. Advantageously, said insulation means is formed of moulded ceramic components.

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a sealing cuff for use with the present invention; Figures 2 and 3 show parts of a first and a second embodiment of a container provided in accordance with the present invention; Figure 4 shows a part of a third embodiment of a container; Figure 5 shows a part of a fourth embodiment of a container provided in accordance with the present invention during a step of manufacture of the container; Figures 6 and 7 are, respectively, a side view and a plan view of an apparatus, in situ, for welding a sealing cuff to the inner skin of a container; and Figures 8 and 9 are, respectively, a side view and a plan view of an apparatus, in situ, for welding a sealing cuff to the outer skin of a container.

As shown in Figure 1, a sealing cuff 2 of stainless steel includes a tube 4 of corrugated metal. At one end of the tube 4 is provided a first washer 6 for attaching the cuff 2 to one skin of a wall having inner and outer skins in a container. The first washer 6 is configured to extend inwardly of the tube 4. Axially extending stepped portions are provided in the first washer 6 as indicated by the references 6a, 6b, 6c. At the other end of the tube 4 is provided a second washer 8 for attaching the cuff 2 to the other skin of the wall having inner and outer skins. The second washer 8 extends transversely inward of the tube 4 and includes axially extending stepped portions 8a, 8b.

The internal diameter of the corrugated tube 4 is typically 40mm which is greater than the internal diameter of the first and second washers 6, 8, typically 30mm.

Conveniently, the external diameter of the corrugated tube 4 is the same as the external diameter of the first and second washers 6, 8, typically 50mm.

Figure 2 shows a part of a container 10 including a lead-through 12. A wall of the container 10 includes an inner skin 14 and an outer skin 16 each made of a plate of stainless steel of thickness 0.7mm. The inner and outer skins 14, 16 are spaced apart, defining a sealed region 18 which is evacuated of gases and contains a thermally insulating material (not shown). Typically, the container 10 may be constructed by the provision of a larger box providing the outer skin 16 around a smaller box providing the inner skin 14. A passage extending between substantially aligned apertures in the inner and outer skins 14, 16 and through the insulating material 18, for passage of the lead-through 12, is defined by the sealing cuff 2 of Figure 1. A stepped portion 8b of the second washer 8 abuts the internal edge of the inner skin 14 and a seal is made therebetween by welding.At the outer skin 16, a seal is formed between a stepped portion 6b of the first washer 6 and the abutting edge of the outer skin by a weld. To accommodate the material of the weld, the stepped portion 6b has a thickness of lmm which is greater than the thickness of the circumferential edge of the outer skin 16 (0.7mm).

A copper cable 20 is electrically connected to the lead-through 12 via a metal cable connector 22. The connector 22 is held onto the lead-through 12 by means of a nut and washer 24a, 24b. The connector 22 is crimped onto the ends of the copper cable 20. A lead-out structure 26 is provided to cover the passage in the container 10 and to protect any uninsulated portions of the electrical connection between the lead-through 12 and the copper cable 20.

The lead-out structure 26 is joined to the outer skin 16 via a sealing plate 28. An aperture in the sealing plate 28 is aligned with the apertures in the two skins 14, 16. The sealing plate 28 is located by the outermost stepped portion 6c of the first washer 6 and supported by an axially outwardly facing surface of the stepped portion 6b. As the stepped portion 6b extends outwardly beyond the outer skin 16, the sealing plate 28 does not make direct connection with the outer skin 16.

In this way, the sealing plate 28 allows for any deformation of the outer skin 16 caused by heat generated due to welding and provides a planar surface to which the lead-out structure 26 can be joined.

A modification of the container of Figure 2 is shown in Figure 3. Like parts are designated by like reference numerals. In the embodiment of Figure 3, the sealing cuff 2 defines a passage for passage of a lug 30.

The lug 30 is mounted onto a stud 32 electrically connected to a bank plate 34 which makes parallel connection between a plurality of strings of cells. An annular ceramic insulator 36 provides electrical insulation between the lug 30 and the sealing cuff 2. A connector 38 extends from the lug 30 and is crimped onto a copper cable 40. The passage and the electrical connections are protected from the environment by a steel cover 42. A sealing gasket 44 between the outer skin 16 of the container and the cover 42 ensures that a suitable seal is made.

Figure 4 shows a further modification of a container including a sealing cuff 2. Like parts to the parts shown in Figures 2 and 3 are designated by like reference numerals. For ease of illustration, the detail of the first and second washers 6, 8 and their seal with the inner and outer skins 14, 16 has not been shown.

A plurality of lead-throughs in the passageway defined by the sealing cuff 2 provide connection between the interior and exterior of the container. For a battery comprising a plurality of high temperature cells, the lead-throughs provided include a plurality of fibre glass insulated leads 46 and a plurality of uninsulated current/voltage pins 48 for making electrical connection to eg. banks of high temperature cells. The leads 46 and pins 48 are held in position relative to one another and to the circumferential edges of the inner and outer skins 14, 16 by an inner disc 50 abutting the inner skin 14 and an outer disc 52 abutting the outer skin 16. The discs 50, 52 are made of moulded ceramics.Each end of a pipe 54, also of moulded ceramic, is received in a recess of the inner and outer discs 50, 52 to define a large central bore for passage of the bundle of fibre glass insulated leads. The pipe 54 provides a degree of support for the leads 46. Individual bores through the inner and outer discs 50, 52 are provided for passage of each of the uninsulated current/voltage pins 48. In this way, any risk of the lead-throughs 46, 48 moving relative to each other or to the inner and outer skins 14, 16, if the battery is subject to vibration, which may cause weakening of the contacts or an accidental electrical contact, is alleviated.

As the ceramic insulation in the aperture is made from separate components of moulded ceramic, as described, and not from a solid block of machined ceramic, the ceramic insulation is both less expensive and lighter. If necessary, additional pipes of moulded ceramic may be provided for the uninsulated pins, to reduce the risk of electrical contact between neighbouring uninsulated pins.

A second embodiment of a sealing cuff is shown in Figure 5. The sealing cuff 62 includes a tube 64 of corrugated metal. A first washer 66 is welded at a region 66a to one end of the corrugated tube 64 for attachment of the sealing cuff 62 to the outer skin 67 of a wall comprising two skins in a container. The first washer 66 further includes a stepped portion 66b which is accessible from outside the wall of the container and so can be welded to the outer skin 67 at the position indicated by the arrow A. A second washer 68 is- welded, at a region 68a, to the other end of the corrugated tube 64 for attachment of the sealing cuff 62 to the inner skin 69 of the wall.The second washer 68 includes a region 68b which extends transversely outward of the tube 64 providing an accessible portion of the second washer 68 which can be welded to the inner skin 69 at a point indicated by the arrow B. It will be noted that, in the arrangements shown, the point indicated by the arrow B is accessible to a welding tool from outside of a box which provides the inner skin 69.

Figure 5 shows the sealing cuff 62 in position between the inner and outer skins 69, 67 of a wall in a container with apparatus for holding the sealing cuff 62 in position while the first washer 66 is welded to the outer skin 67. A method and apparatus for joining the sealing cuff 62 to the inner and outer skins 69, 67 of a container will now be described with respect to Figures 6 to 9 of the drawings.

Figure 6 shows a cross-sectional side view of an arrangement for TIG welding the second washer 68 of a sealing cuff 62 to the inner skin 69 of a container.

Figure 7 is a view along the line VII-VII of Figure 6, partly in cross-section and with the welding tool (98) in a slightly different position for ease of illustration.

As shown in Figures 6 and 7, the portion 68b of the second washer 68 is held against the inner skin 69 by a bell-shaped clamping sleeve 80. The bell-shaped sleeve 80 is preferably made of a heat-conductive material, such as copper, and so is also effective as a heat sink during the TIG (tungsten inert gas) welding process. The bell-shaped sleeve 80 is itself held in position by a nut 82 threaded over one end of a clamping bolt 84 which has an external thread 84a. At the other end of the clamping bolt 84 is a bore having an internal thread 84b. A screw 86 extends through a threaded aperture 88 in a support plate 90, bearing against a washer 92, to engage with the internal thread 84b of the clamping bolt 84 and so support the clamping bolt 84 in position.The clamping bolt 84 is also effective to hold a copper heat sink 94 against the inner skin 69 of the container. A sleeve 96 around the clamping bolt 84 assists in defining the position of the clamping bolt 84 relative to the aperture in the inner skin 69.

To locate the sealing cuff 62 in position, the clamping bolt 84 is first secured on the support plate 90 by means of the screw 86. The sleeve 96 and annular heat sink 94 are then located onto the free end of the clamping bolt 84. The support plate 90, which may support more than one clamping bolt 84 for use with an inner skin 69 having a plurality of apertures, is then positioned inside the container so that the clamping bolt 84 extends through an aperture in the inner skin 69. The sealing cuff 62 is slid onto the sleeve 96 on the clamping bolt 84 so that the second washer 68 abuts against the inner skin 69. The bell-shaped clamping sleeve 80 is slid over the free end of the clamping bolt 84 and the nut 82 is screwed onto the external thread 84a of the clamping bolt 84 to lock the bell-shaped clamping sleeve with its open end against the portion 68b of the second washer 68.

Mounting of a TIG welding torch 98 onto the clamping bolt 84 is shown, in greater detail, in Figure 7. A bush support 100 is threaded onto the free end of the clamping bolt 84. A phosphor bronze bush 102 in an aluminium housing 104 is slid onto the bush support 100.

The bush 102 carries a pivot bracket 106 to which the welding torch 98 can be releasably mounted by means of a screw 108 and clamp sleeve 110. The orientation of the welding torch 98 with respect to the clamping bolt 84 and hence the portion 68b of the inner washer 68 is determined by the bracket 106 and the bush 102. During the welding process, the bush 102 is rotated relative to the bush support 100 so that the welding torch 98 effects an annular weld between the portion 68b and the inner skin 69.

As described previously, the walls of a container may be relatively thin, having a thickness of the order of 0.7mm. Heat generated during the welding process may therefore cause warping of the inner skin 69 in the region around the weld despite the provision of heat sinks.

Figure 6 illustrates an apparatus for locating the free edge of the inner skin 69 so that its position is predetermined irrespective of any deformation of the inner skin 69 caused by the welding process. This reduces the risk of the free edge 69a of the inner skin becoming so deformed that the lid of the container cannot be fitted thereon.

As shown in Figure 6, the support plate 90 is carried on a base 112 and stands on a base 114 of the container. Separation of the support plate 90 and the inner skin 69 of the container at a position distant from the welding region is determined by a packing strip 116 which is secured to the support plate 90 by a screw 118.

A box clamp 120 is mounted to fit over the free edge 69a of the inner skin 69. The box clamp 120 includes a threaded bore 120a. When the support plate 90 is located in position relative to the inner skin 69, a screw 122 engages the threaded bore 120a through an aperture in the support plate 90. In this way, the position of the free edge 69a of the inner wall 67 is determined with respect to the support plate 90 and hence with respect to the remainder of the container at a position distant from the welding region.

After the second washer 68 has been welded to the inner skin 69 of the wall in the container, the inner skin 69 is placed in position next to the outer skin 67 of the container e.g. by placing a box providing the inner skin 69 within a larger box providing the outer skin 67 so that the first washer 66 of the sealing cuff 62 can be welded to the outer skin 67. Welding of the first washer 66 to the outer skin 67 is shown in Figures 8 and 9.

Counter-pressure is applied to the first washer 66 to locate the first washer in position against the outer skin 67 by an assembly which includes a support plate 132. The support plate 132 has an aperture 134 which can be aligned with the apertures in the outer and inner skins 67, 69 of the container. The support plate 132 may have more than one aperture 134 as shown in Figure 9. A collar 136 is welded to the support plate 132 with its bore in alignment with the aperture 134. A clamp screw 138 threadedly engages the collar 136 and support plate 132.

The clamp 138 has an internal bore into which a clamp bolt 140 is slid so that the head 140a of the bolt 140 abuts the head 138a of the screw 138. The other end 140b of the bolt 140 is threaded.

An annular heat sink 142 of copper is slid onto an unthreaded portion of the clamp bolt 140 so that one end 142a of the heat sink abuts against the end of the clamp screw 138. The other end 142b of the heat sink 142 is configured to fit against a part of the washer 66 (internal of the corrugated tube 64) to apply pressure on the first washer 66.

The support plate 132 and assembled clamping structure is placed in position so that the clamp bolt 140 extends through the inner and outer skins 69, 67 with the end 142b of the heat sink 142 abutting against the first washer 66.

A spacer sleeve 144 is slid onto the clamp bolt 140 (after the clamp 140 is passed through the inner and outer skins 69, 67). A phosphor bronze nut 146 is then screwed onto the threaded end 140b of the clamp bolt until the spacer sleeve 144 abuts against a recess in the heat sink 142. In this way, a counter pressure is applied to the first washer 66 to locate the first washer 66 against the outer skin 67 of the container for welding.

From the foregoing, it will be appreciated that the internal diameter of the first washer 66 is less than the internal diameter of the second washer 68 so that the end 142b of the heat sink 142 can pass through the second washer 68 but abut against the first washer 66.

Alternatively, the heat sink 142 may include retractable jaws which are retracted to allow the heat sink to pass through the second washer and extended to apply pressure to the first washer.

As shown in Figure 8, the support plate 132 is mounted on a base 148 which stands on the base 114 of the inner box. A set screw 150 engages the support plate 132, via a washer 152, and a packing strip 154, abutting the inner skin 69, to define the position of the support plate 132 relative to a portion of the inner skin 69 near its base.

A clamp plate 156 is used to support the outer skin 67 against the pressure of the heat sink 142 during the welding process. In the clamp 156 is provided an aperture 158 having a diameter which is greater than the diameter of the aperture in the outer skin 67, so that the interface between the portion 66b of the first washer and the edge of the outer skin 67 is accessible to a welding tool 160. One end of the clamp plate 156 is supported by a clamp bolt 162 which passes through apertures in the clamp plate 156 and the support plate 132 to threadedly engage with a wing nut 164. Washers 166 are located between the head of the bolt 162 and the clamp plate 156 and also between the support plate 132 and the wing nut 164.

The separation of the clamp plate 156 and the support plate 132 is defined by a spacer 168. The spacer 168 corporates with a ledge 170 in the support plate 132 and with an overhang 172 in the clamp plate 156. The spacer 168 may be supported by a plurality of clamp bolts 162 along the length of the clamp and support plates 156, 132 or may be provided as an annular member around each clamp bolt 162. In this way, the separation of the inner and outer skins 69, 67 with respect to the support plate 132, and hence with respect to each other, is determined.

The welding tool 160 is releasably mounted on a bracket 174 by means of a screw 176. The bracket 174 is itself supported on a phosphor bronze bush 178 in an aluminium housing 180. The bush 178, and hence the welding tool 160, is located with respect to the outer skin 67 and the first washer 66 by a bush support 182 which slides onto the phosphor bronze nut 136. Control of the orientation and movement of the welding tool 160 to make an annular weld between the portion 66b of the first washer 66 and the outer skin 67 is arranged in a known manner.

As described, a welded seal is made between each end of the sealing cuff 62 and, respectively, the outer and inner skins 67, 69 of a container. The seal so produced is sufficiently hermetic for the region between the outer and inner skins 67, 69 to be evacuated of gases to provide a degree of thermal insulation.

Modifications to the embodiments described within the scope of the present invention will be apparent to those skilled in the art.

Claims

1. A container having a wall with inner and outer skins of metal defining a sealed region therebetween, apertures in the two skins and a sealing cuff extending between the apertures to define a passage through the wall, the sealing cuff comprising: a tube of corrugated metal; a first washer at one end of the tube welded around the aperture in one of the skins; and a second washer at the other end of the tube welded around the aperture in the other of the skins; wherein the first washer extends transversely inwards of the tube.

2. A container according to Claim 1 wherein the second washer extends transversely inwards of the tube.

3. A container according to Claims 1 or 2 wherein the minimum internal dimension of the second washer transverse of the tube is greater than an internal dimension of the first washer transverse of the tube.

4. A container according to any one of the preceding claims wherein the second washer extends transversely outwards of the tube.

5. A container according to any one of the preceding claims wherein said first washer is welded around the aperture in the outer of said skins.

6. A container according to Claim 5 further including a sealing plate having an aperture aligned with the aperture in the outer skin, the sealing plate being located outside the outer skin and sealed to said first washer.

7. A container according to Claim 6 wherein said first washer includes an axially extending step extending beyond the outer skin and providing an axially outwardly facing surface for locating the sealing plate.

8. A container according to any one of the preceding claims wherein the apertures and washers are circular.

9. A container according to any one of the preceding claims further including means for providing electrical insulation within the passage, said insulation means comprising at least a first part abutting the outer skin and a second part abutting the inner skin.

10. A container according to Claim 9 wherein said first and second parts are separated by a tube of electrical insulation.

11. A container according ~ to Claims 9 or 10 wherein said insulation means is formed of moulded ceramic components.

12. A method of manufacturing a container according to any one of Claims 1 to 11, the method including the steps of: providing a sealing cuff with said second washer welded around the aperture in said other of the skins; offering said first washer of the sealing cuff to the aperture in said one of the skins; applying pressure to said first washer at a position transversely inwards of the corrugated tube to hold said first washer against said one of the skins; and welding said first washer around the aperture in said one of the skins.

13. A method according to Claim 12 wherein the step of providing a sealing cuff with said second washer welded around an aperture in said other of the skins comprises the steps of: positioning the sealing cuff with said second washer around said aperture in said other of the skins; applying pressure to said second washer to hold said second washer against said other of the skins; and welding said second washer around said aperture in said other of the skins.

14. A method according to Claim 13 wherein said second washer extends transversely outward of the tube, the step of welding said second washer comprising the step of welding said second washer to said other of the skins at a surface external of the tube.

15. A method according to any one of Claims 12 to 14 wherein said step of offering said first washer to the aperture in said one of the skins comprises the step of offering said first washer to said outer skin.

16. A method according to Claim 15 further comprising the steps of locating a sealing plate with an aperture outside the outer skin so that the aperture of the sealing plate is aligned with the apertures in the outer skin and sealing the sealing plate to said first washer.

17. A method according to Claim 16 wherein said step of sealing the sealing plate to said outer washer comprises the step of joining the sealing plate to a surface of said first washer which extends outwardly of said outer skin.

18. Apparatus for manufacturing a container defined by any one of Claims 1 to 12, the apparatus including pressure means for applying pressure to hold said first washer to said one of the skins, said pressure means comprising a clamping plate for abutting a surface of said one of the skins exterior of said region and counter-pressure means for extending through the tube of the sealing cuff to apply pressure to said first washer at a position transversely inward of the tube.

19. Apparatus according to Claim 18 wherein the clamping plate includes an access aperture aligned with the aperture in said one of the skins, said access aperture being larger than the aperture in said one of the skins to provide access to an interface of said first washer and said one of the skins from the exterior of said region.

20. Apparatus for manufacturing a container defined by Claim 4 or any one of Claims 5 to 12 dependent on Claim 4, the apparatus including pressure means for applying pressure to hold said second washer to said other of the skins, said pressure means comprising a bell-shaped sleeve having an open end for applying pressure to a portion of said second washer transversely outwards of the tube and counter-pressure means for applying pressure to a surface of said other of the skins exterior of said region.

21. A method of making a weld to a container comprising at least one wall and an end for engaging at least one wall, the method including the step of clamping the free edge of a wall relative to the remainder of the container during the step of welding at a welding region in said wall.

22. Apparatus for carrying out the method of Claim 21 comprising welding means and means for clamping a free edge of the wall.