GB2031768A

GB2031768A - Making container bodies

Info

Publication number: GB2031768A
Application number: GB7840207A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1978-10-11
Filing date: 1978-10-11
Publication date: 1980-04-30
Also published as: DE2941155A1; DE2941155C2; GB2031768B; ZA795045B

Abstract

In this method and apparatus for making a container body having a side wall 11 and a seated-in bottom 10 a side wall portion of the body is held on a mandrel 19 while the bottom is seamed to one end of the side wall. Whilst still held on the mandrel 19 the other end of the side wall is then curled inwardly. <IMAGE>

Description

SPECIFICATION Containers This invention relates to a method and apparatus for making containers and more particu larly but not exclusively to a method and apparatus for making a bow sided rectangular body for a biscuit tin.

Biscuit tins are known which have a bow sided rectangular shape. In British Patent Number 1 509896 such a tin comprises a body and a removable lid. The body consists of a side wall and a seated in bottom. The side wall of the body has a free edge terminating in an inwardly directed curl which defines the mouth of the body. The body is closed a slip lid, a plug lid or a lid adapted to permit fitting in either mode. The lids are pressed from a single sheet of metal such as tinplate and therefore the shape of each lid is controlled precisely by the press tools which shape it. However, the body side wall is made from a rectangular flat blank of sheet metal.

The blank is folded to the body shape and the free ends are joined by an interlocking side seam. The operations of folding and side seaming may be unable to prevent variations in shape of the side wall arising from springback in the metal. The subsequent separate operations of curling and seating-in the bottom, done each in a separate press, may not be able to correct these variations and may, in themselves add a further variation in the height of the tin body. Therefore whilst the lids will be correctly shaped the bodies may not be as precisely shaped; consequently the lids may not be a good fit on the bodies and one objective of this invention is to provide a method and apparatus for making container bodies to improved dimensional tolerances.

A A further objective is to provide a method and apparatus for seating-in a bottom wall into the side wall of a container body curl the free edge of the side wall. Difficulty arises when these operations are carried out in a single tool because the force required to inwardly curl the body sidewall and the flange of the bottom wall to seat the bottom in the side wall is greater than the force required to curl the free edge. Therefore mere application curling forces in an axial direction to the seating edge of a side wall portion on a mandrel tends to push the side wall along the mandrel to produce an excessive degree of curling at the free edge and a seated-in seam deficient in folded material.

Accordingly, this invention provides a method for making a container body having a side wall and a bottom wall seated therein, said method comprising the steps of locating a tubular side wall portion of the body on a mandrel; laterally expanding the mandrel to frictionally hold the side wall portion so that first and second free edge portions thereof extend axially beyond the mandrel; locating a flanged bottom wall of the body within the first free edge portion with the flange thereof adjacent the first free edge portion; inwardly folding the first free edge portion and flange together into a seated-in engagement; curling the second free edge portion to form a curl; and contracting the mandrel to permit remov al of the container body from the mandrel.

In a preferred method the first free edge of the side wall portion and the flange of the bottom wall are folded into seated-in engage ment by relative axial motion as between a folding die and the mandrel. The second free edge of the side wall is inwardly curled by relative motion of a curling die and mandrel in an axial direction.

The tubular side wall portion is preferably preshaped to have a first free edge with a marginal free edge portion extending axially and inwardly from the rest of the side wall.

The lateral extension of the mandrel may be used to reform the preshaped tubular side wall portion to a bow sided rectangular shape.

In an alternative method a limit ring surrounds the mandrel to limit the lateral extension of the mandrel so that the side wall portion is clamped between the mandrel and the limit ring.

This invention further provides apparatus for making a container body, said apparatus comprising a folding die, a curling die and a mandrel; said mandrel having means to hold a preshaped tubular side wall portion with first and second free edges of the portion extending in an axial direction beyond the mandrel so that a flanged bottom wall may be placed on the mandrel within the first free edge portion; wherein relative motion as between the folding die and mandrel in an axial direction folds the first free edge into a seated-in engagement with the flange of the bottom wall; and relative motion as between the folding die and mandrel in an axial direction against a fixed curling die forms the second free edge to an internal curl.

The means to hold the preshaped tubular side wall portion on the mandrel is preferably a plurality of pusher blocks moveable outwardly to frictionally engage with the side wall portion surrounding the mandrel. The frictional engagement may be assisted by the provision of a limit ring against which the side wall portion is clamped by outward movement of the pusher blocks.

The pusher blocks may if desired be shaped to reform a cylindrical tubular side wall to a bow sided rectangular shape.

In a preferred apparatus the folding die is mounted on a top tool having a sprung pressure pad adapted to press the bottom wall onto the top of the mandrel while the first free edge of the side wall and the flange of the bottom wall are folded into seated-in engage ment.

Various embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a tin having a lid and a body; Figure 2 is a fragmentary view of the side wall and lid of the tin sectioned on that line A-A', with a like tin stacked thereon; Figure 3 is a series of sketches depicting a sequence of manufacturing operations; Figure 4 is a plan view of a bottom tool for seating in a bottom wall into a side wall of the tin of Figs. 1 and 2; Figure 5 is an elevation of the bottom tool of Fig. 4 sectioned on the line B-B' and a top tool also shown in section, the tools being open and the mandrel retracted; Figure 6 is a like view to Fig. 5 but with the mandrel extended to engage with the preshaped tubular side wall portion; Figure 7 shows the tools during seating-in;; Figure 8 shows the tools after curling; and Figure 9 shows a modified apparatus.

In Figs. 1 and 2 the tin 1 has a built up body 2 and a slip lid 3. The tin is depicted during the removal of a sealing tape 4 which sealed the joint between the lid and body.

Such a seal is suitable for keeping dry products such as biscuits.

The lid 3 has been stamped from tinplate to comprise a central panel 5, a peripheral stack control wall 6 dependent therefrom, a ledge 7 surrounding the stack control wall 6 and a skirt 8 dependent from the ledge. The free edge of the skirt is in the form of a flattened curl 9 which permits the application of known plastic sealing tapes to seal the joint between the lid and the body.

The body 2 is built up from two components to have, a bottom wall 10 and a side wall 11 joined by a seated-in seam 12. The bottom wall 10 is stamped from a sheet metal blank. The side wall portion is formed from a rectangular blank of sheet metal which is bent into a tubular side wall portion the adjacent free ends being joined by a seam. Although a locked side seam 13 is shown in Figs. 1 and 2, soldered lap seams or welded side seams may be used. The mouth of the body 2 is defined by an internal curl 14. In plan view the body has the shape of a bow sided rectangle.

In Fig. 2 part of a second body 2A is shown by dashed lines to be resting on the lid 3. The seated in seam 12A rests upon the ledge 7 of the lid 3 so that the stack control wall 6 prevents lateral movement of the seated-in seam 1 2A upon the lid 3.

It will be understood that in order to achieve a good fit of the lid 3 on the body 2 for sealing, and the fit of the body seated-in seam on a lid for stacking the body, must be built up to close tolerances.

For brevity the sketches of Fig. 3 depict only the stages of manufacture necessary for understanding of our method. Fig. 3a shows a rectangular blank from which the body side wall is made. The blank has a first free edge 21, a second free edge 22 and the customary cropped ends 42, 43 which facilitate the formation of an interlocked side seam.

In Fig. 3b the first and second free edges 21, 22 have been bent upwardly to enable them to act as start curls.

In Fig. 3c the side wall blank of Fig. 3b has been formed to a cylinder and the cropped ends 42, 43 have been interlocked to form a side seam 13. The free edge 22 is denoted. If a round tin is to be made then the cylinder of Fig. 3c is a suitable side wall portion to accept a bottom wall.

However, in Fig. 3d the cylinder of Fig. 3c has been pulled to a side wall portion 11 A of rectangular shape, to permit fitting onto the mandrel of Figs. 4 to 8. During this preliminary pulling to shape the side seam is held between clamps to prevent it unfolding.

In Fig. 3e the bottom wall 10 has been fitted within the first free edge 21 shown in Fig. 3d and joined to the side wall portion 11 A by seated-in engagement. The second free edge 22 has been inwardly curled to form an internal curl 14.

In Figs. 4 to 8 an apparatus is shown which is adapted to control and hold the side wall portion 11A to receive a bottom wall portion 1 0A and thereafter join them by means of a seated-in seam and form an internal curl, to form the body of Figs. 1 and 2.

The method of joining the side wall to the bottom and curling the free edge of the side wall can be understood by brief reference to Fig. 6 in which the apparatus can be seen to include a folding die 15 in a top tool 16; a curling die 17 mounted on a base plate 18; and a mandrel 19.

The mandrel 19 has a means in the form of pusher blocks 20 to hold a preshaped tubular side wall portion 11 A so that a first free edge 21 extends above the mandrel and a second free edge 22 extends below the mandrel 19.

In Fig. 6 a side wall portion 11A surrounds the mandrel 19 and a bottom wall portion 1 0A lies on the mandrel within the first free edge 21.

The folding die 15 is about to be brought down to engage with the first free edge 21 and fold it into seated-in engagement with the flange 23 of the bottom wall portion 1 OA.

After the seating-in operation the top tool pushes the mandrel 19 downwards to carry the second free edge 22 of the side wall portion to be curled by the curling die 17.

The side wall portion 11A is held on the pusher blocks 20 so that no sliding takes place during seating-in. As seating-in is completed before curling there is no risk of the curling operation robbing the seated-in seam of metal.

Details of the apparatus will become apparent in the following description of the sequence of operations depicted with reference to Figs. 4 to 8.

In Fig. 4 the apparatus can be seen to have four contoured pusher blocks 20 arranged symmetrically around a guide block 24. The guide block has a central cavity extending perpendicular to the plane of Fig. 4, and in which is a wedge member 25 used to move the pusher blocks 20 outwards from the guide block 24.

At the outer periphery of each block there is a bridge piece 47 which bridge the gap between each block and the next block adjacent. Each bridge piece is pivotably attached to a pusher block and so that it can pivot upwards when the blocks are contracted.

When the blocks are expanded the bridge pieces pivot downwards to make with the top of the blocks a continuous peripheral surface against which the seating-in operation is performed.

A slot 45 is provided in one of the pusher blocks. The side seam is fitted into this slot 45 before the pusher blocks are expanded.

As each pusher block 20 works in a like manner to all the other pusher blocks 20 the sequence of motion will be described by reference to the upper right block 20A in Fig. 4, in which details of the block are shown by dashed lines.

The block 20A can be seen to have a pair of stepped bores 26, a narrower portion of the bore being near the guide block 24 and wider portion extending from the narrower portion of the bore to the contoured surface 27 of the block. A stud 28 is fitted in each bore with the stud head in the wider portion of the bore and the threaded end fitted in the guide block 24. A spring 29 extends between the head of the stud 28 and the narrower portion of the bore so that the block is resiliently urged towards the guide block 24.

Referring to Figs. 4 and 5, the movement of each pusher block 20 is guided in two ways; firstly by a guide peg 30 which extends down from the block 20A into a slot 31 in a support plate 32 upon which the pusher blocks slide; and secondly by pusher pins 33 extending from the pusher blocks 20 into the guide block 24.

In Fig. 5 the pusher blocks 20 are retracted and the push pins 33 can be seen in the guide block 24 where they engage with rollers 34 which are used to transmit the extension force from the wedge member 25.

In Fig. 5 a side wall portion 11A of a body is shown in situ resting on the curling die 17 and surrounding the mandrel 19. It will be seen that the side wall portion 11 A has been preshaped to have its free edges turned inwards slightly by a previous operation. This slight turn aids the seating-in and curling about to be done.

In Fig. 6 the wedge member 25 has been moved downwards by external means to engage with the rollers 34 and so push upon the pusher pins 33 to move the block 30 outwards to grip the inside of the side wall portion 11A by frictional engagement. In so doing, the blocks 20 also pull the side wall portion 11 A to conform to envelop their contoured surfaces 27, with a first free edge 21 extending above the mandrel 19 and a second free edge extending below the mandrel into the curling die 17.

A bottom wall portion 1 0A has been fitted within the first free edge portion 21 to lie on the top of the mandrel 19.

In Fig. 7 the top tool 16 has been brought down so that while a sprung pressure pad 35 holds the bottom wall portion 1 0A flat on the mandrel 19, the folding die 15 turns the first free edge 21 of the side wall portion and the flange 23 of the bottom wall portion, into a seated in engagement with one another. The details of the seated-in engagement can be seen in Fig. 2.

When the seating-in operation is completed the top tool 16 continues its downward travel to push the mandrel 19 downwards and carry the second free edge of the body into the curling die to form the inward curl shown in Fig. 2. During this downward motion the support plate compresses a resilient buffer 46 preferably made of a polyurethane material.

The force required to compress the resilient buffer is much greater than the force required to form the seated engagement therefore seating in is completed before curling commences. The curling operation is stopped when the support plate engages the base plate 18, as shown in Fig. 8.

As the top tool is raised the resilient buffer 46 lifts the mandrel to the feed position shown in Fig. 5. The wedge member 25 is raised by the external means to allow the blocks 20 to retract under the influenced springs 29 so that the completed can body may be removed from the mandrel.

It will be understood that the outward movement of the pusher blocks imposes a hoop stress on the side wall portion. Whilst side wall portions having a soldered or welded side seam are well able to cope with such hoop stresses, folded or interlocked "dry" side seams may become unfolded, especially if the side wall material is thin or weak.

The modified apparatus of Fig. 9 is characterised by the provision of strikes blocks 36 and a bottom tool limit ring 37. When the pusher blocks 20 move outwards the side wall material is clamped against the internal surfaces of the limit rings 36 and 37 so that the risk of a side seam unfolding is reduced.

The lower limit ring 37 is supported on springs such as that denoted 40 and held upon the curling die 17 by studs 41 so that in Fig. 9 the lower limit ring 37 clamps the side wall portion 11 A against the pusher blocks 20. The striker blocks 36 mounted on the top tool move the lower limit ring 37 in conjunction with the relative movement of the mandrel 19.

In all other respects the apparatus of Fig. 9 works in the manner already described with reference to Figs. 4 to 8.

It will be understood that various alternative embodiments of the apparatus are within the scope of the invention because the tubular side wall portion of the body is held positively on the mandrel.

For example, instead of lowering the top tool 16 to engage with the first free edge 21 of the body, the mandrel 19 may be raised to bring the first free edge 21 to engage the folding die 15 mounted on the top tool 16.

Also instead of using the motion of the top tool 16 to push the mandrel downwards to bring the second free edge 22 into engagement with the curing die 17, the curling die may be raised to engage with the second free edge to form the curl.

The pusher blocks may be provided with suitable surface contours to permit the reshaping of the side wall to any of a variety of cross sectional shapes such as square, rectangular, or generally rounded shapes.

Various methods may be used to make the tubular side wall blank such as that denoted 11. The preliminary flat side wall blank is usually folded to a cylinder which has a longitudinal seam formed by interlocking or welding. The cylinder is then reshaped to be substantially rectangular so that the tubular side wall portion may easily be placed around the mandrel.

The preliminary inward turning starts curls of the first and second free edges may be formed in the flat blank before forming up or alternatively may be formed on the substantially rectangular body by dies.

The container bodies made according to this method and by means of the apparatus described may be made from sheet metals such as tinplate, aluminium and the like. The sheet metal may be plain or decorated.

Claims

1. A method for making a container body having a side wall and a bottom wall seated therein, said method comprising the steps of locating a tubular side wall portion of the body on a mandrel; laterally expanding the mandrel to frictionally hold the side wall portion so that first and second free edge portions thereof extend axially beyond the mandrel; locating a flanged bottom wall of the body within the first free edge portion with the flange thereof adjacent the first free edge portion; inwardly folding the first free edge portion and flange together into seated-in engagement; curling the second free edge portion to form a curl; and contracting the mandrel to permit removal of the container body from the mandrel.

2. A method according to claim 1 wherein the first free edge of the side wall portion and the flange of the bottom are folded into seated-in engagement by relative axial motion as between a folding die and the mandrel.

3. A method according to claim 1 or claim 2 wherein the second free edge of the side wall portion is inwardly curled by relative axial motion as between the curling die and the mandrel.

4. A method according to any preceding claim wherein the first free edge portion of the tubular side wall portion is preshaped to have a marginal edge portion extending inwardly from the rest of the sidewall portion between the location of the side wall portion around the mandrel.

5. A method according to any preceding claim wherein the lateral extension of the mandrel reforms the side wall portion to a bow sided rectangular shape.

6. A method according to any preceding claim wherein a limit ring surrounds the mandrel to limit the outward expansion of the mandrel by clamping the sidewall against the mandrel.

7. A method according to any preceding claim wherein the mandrel is held stationary and the folding die is moved towards the mandrel to fold the first free edge into a seated-in engagement with the bottom; and thereafter continued movement of the folding dies moves the mandrel to bring the second free edge into engagement with the curling die.

8. Apparatus for making a container body, said apparatus comprising a folding die, a curling die and a mandrel; wherein said mandrel has means to hold a preshaped tubular sidewall portion with first and second free edges of the portions extending in a axial direction beyond the mandrel so that a flanged bottom wall may be placed on the mandrel within the first free edge portion; relative motion as between the folding die and mandrel in an axial direction folds the first free edges into a seated-in engagement with the flange of the bottom wall; and a relative motion as between the curling die and mandrel in an axial direction forms the second free edge to an internal curl.

9. Apparatus according to claim 8 wherein the means to hold the preshaped tubular side wall portion include a plurality of pusher blocks movable outwardly to frictionally engage with the inside of the side wall portion surrounding the mandrel to hold the side wall portion on the mandrel.

10. Apparatus according to claim 8 or claim 9 wherein the mandrel remains stationary and the folding die is moved towards the mandrel to fold the first free edge into engagement with the bottom; and thereafter continued movement of the folding die moves the mandrel to bring the second free-edge into engagement with the curling die.

11. Apparatus according to any of claims 8 to 10 wherein a limit ring surrounds the pusher blocks so that when the blocks are moved outwards the side wall portion is clamped between the limit ring and blocks to prevent axial movement of the side wall in relation to the mandrel.

12. Apparatus according to any of claims 9 to 11 wherein each pusher block has a bridge piece adapted to make with the top of a next adjacent block a continuous peripheral surface on the mandrel.

13. Apparatus according to any of claims 8 to 12 wherein the blocks are shaped so that outward movement of the blocks holds a preshaped tubular side wall to a bow sided rectangular shape.

14. Apparatus according to claims 8 to 13 wherein the folding die is mounted on a top tool having a spring pressure pad adapted to press the bottom wall against the top of the mandrel while the first free edge of the side wall and flange of the bottom are folded into a seated-in engagement.

15. A container body made substantially according to any of claims 1 to 7 or by means of apparatus according to any of claims 8 to 14.

16. A method substantially as herein be fore described with reference to the accompany drawings.

17. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.