MANUFACTURE OF FOUR-SIDED SHEET METAL CONTAINERS

Abstract: Apparatus for making tapered four-sided sheet metal containers comprises a tapered four-sided mould 42 and folding means 26.1 for folding a sheet metal blank onto the mould. The folding means comprises a carrier 28 and four folding elements 30, 32 pivotally mounted on the carrier. When the mould and the folding means are displaced towards one another with the sheet metal blank 10 disposed between them, the folding elements pivot about their pivotal mountings and fold peripheral portions of the blank onto the sides of the mould.

Description: THIS INVENTION relates to apparatus for making tapered four-sided sheet metal containers, such as, for example, baking tins, bread pans or the like, and to a method of making such containers. French Patent No 407.201 discloses an apparatus for making four-sided sheet metal containers. The apparatus includes a four-sided mould in the form of an expandable collet, and a punch having four complemental rectangular walls defining a rigid cavity designed to accommodate the mould. A sheet metal blank is positioned between the punch and the mould, and the punch is then drawn downwards over the mould. The sheet metal is cut into a cruciform blank having four peripheral portions. The peripheral portions are folded onto corresponding sides of the mould as the punch is drawn over the mould. French Patent No 1228.575 discloses an arrangement of pivotable flaps designed to fold a metal blank over a corresponding mould. Folding of the peripheral portions of the blank does not take place simultaneously as the mould and the folding means are displaced towards one another. Rather, both the mould and the carrier are held together with the blank clamped between them during the entire folding process. According to the invention there is provided apparatus for making tapered four-sided sheet metal containers, which apparatus comprises a tapered four-sided mould, and folding means for folding a sheet metal blank onto the mould, the folding means comprising a carrier and four folding elements, the folding elements being arranged each to engage a peripheral portion of the blank to fold said peripheral portion onto the corresponding side of the mould wherein the mould has four corner edges which together define a first rectangle, each of the four sides of the mould extending from a corresponding one of said corner edges, the mould and the folding means being displaceable towards one another and folding of said peripheral portions of the blank taking place simultaneously as the mould and the folding means are displaced towards one another with the blank being disposed between them, characterised in that the four folding elements are mounted pivotally on the carrier, the folding elements being arranged to fold said peripheral portion by pivotal displacement of the folding elements with respect to the carrier; and in that the pivot axis of each folding element is parallel to the corresponding corner edge of the mould so that the pivot axes together define a second rectangle, the width of the second rectangle being greater than the width of the first rectangle and the length of the second rectangle being greater than the length of the first rectangle. Each folding element may have an outer portion extending outwardly from the corresponding pivot axis and an inner portion connected rigidly to the outer portion, the inner portion being arranged to be driven by movement of one of the corner edges of the mould relative to the folding element. The mould, in the region thereof corresponding to the rim of the container, may have a channel-like formation facing the folding means, the arrangement of each folding element being such that an outer edge of the folding element enters into the channel-like formation as the mould and the folding means are being displaced towards one another, thereby to form the corresponding peripheral portion of the blank with a return-folded edge strip at the rim of the container. Further according to the invention there is provided a method of making a tapered four-sided sheet metal container comprising the steps of providing a tapered four-sided mould having four corner edges which together define a first rectangle, each of the four sides of the mould extending from a corresponding one of said corner edges, providing folding means comprising a carrier and four folding elements, positioning a sheet metal blank between the mould and folding means, displacing the mould and the folding means towards one another, and simultaneously folding, using the folding elements, peripheral portions of the blank onto the corresponding side of the mould, characterised in that it includes the steps of pivotally displacing the folding elements with respect to the carrier to fold said peripheral portion onto the corresponding side of the mould, wherein the pivot axis of each folding element is parallel to the corresponding corner edge of the mould so that the pivot axes together define a second rectangle, the width of the second rectangle being greater than the width of the first rectangle and the length of the second rectangle being greater than the length of the first rectangle. The pivot axes may be displaced beyond the level of the first rectangle during completion of the folding process. While displacing the folding means towards the mould, the corner edges of the mould may be driven against a corresponding inner portion of each folding element, wherein the inner portion extends inwardly from it's pivot axis, thereby to cause pivoting of an outer portion of the folding element against the corresponding peripheral portions of the blank. The invention will now be described in more detail, by way of example, with reference to the accompanying drawings. In the drawings : Figure 1 is a plan view of a sheet metal blank for a bread pan in accordance with the invention; Figure 2 is an underneath view of the upper working parts of apparatus for making the bread pan; Figure 3 is a plan view of the lower working parts of the apparatus; Figure 4 is a diagrammatic, vertical section through the upper and lower working parts of the apparatus during an initial stage of the procedure to make a bread pan from the sheet metal blank of Figure 1; Figures 5 to 7 show the right hand side of the working parts of Figure 4 during subsequent stages as the upper and lower working parts are progressively brought together; Figure 8 illustrates the operation of a ram (as seen from above) to fold overlying corner strips of the blank; Figure 9 is a side view of one end of the bread pan when in its finished condition; Figure 10 is a three dimensional view of part of an edge frame for the pan, during an initial stage in its production; and Figure 11 illustrates diagrammatically the formation of the edge frame from a circular into a suitable rectangular shape. Referring first to Figure 1, reference numeral 10 designates a sheet metal blank for a bread pan. After folding of the blank as will be described hereinafter, a rectangular central portion 12 thereof becomes the bottom panel of the bread pan, peripheral portions 14.1 and 14.2 become major sides of the pan, and peripheral portions 16.1 and 16.2 become minor sides of the pan. Adjacent peripheral portions are separated by V-shaped cut-outs 18, the apex 20 of each cut-out being spaced from the corresponding corner of the bottom panel 12. Each of the peripheral portions 14.1, 14.2, 16.1, and 16.2 has a corner strip 22 along each opposite side edge thereof. Furthermore, each of the peripheral portions has an edge strip 24 along the free edge thereof. Referring now to Figures 2 to 4, reference numeral 26 in Figure 4 generally indicates apparatus for forming a bread pan from the blank of Figure 1. The apparatus comprises upper working parts 26.1 and lower working parts 26.2 which are mounted in a hydraulic press for forcibly bringing the upper and lower working parts together. The upper working parts 26.1 include a carrier 28 and four folding elements, namely a pair of major folding elements 30 and a pair of minor folding elements 32. The folding elements 30, 32 are pivotally mounted on the carrier 28 by means of hinges 34, each of the folding elements 30 being pivotal with respect to the carrier about a corresponding pivot axis 36, and each of the folding elements 32 being pivotal with respect to the flap carrier about a corresponding pivot axis 38. Biasing means (not shown) are provided to bias the folding elements 30, 32 to their horizontally extending positions as illustrated in Figure 4. The upper working parts 26.1 further include a pneumatic trapper 40 which is displaceable vertically with respect to the carrier 28 by means of pneumatic cylinders (not shown). The lower working parts 26.2 comprise a mould 42 which generally corresponds to the inside shape of an inverted bread pan. The mould has a rectangular upper face 44 which corresponds to the shape of the bottom panel 12. The upper face is defined by corner edges 45.1 and 45.2. The mould further has a pair of downwardly diverging faces 46 corresponding to the major sides of the bread pan, and a pair of downwardly diverging minor faces 48 corresponding to the minor sides of the bread pan. The spacing between the pivot axes 36 is greater than the spacing between the corner edges 45.1. Likewise, the spacing between the pivot axes 34 is greater than the spacing between the corner edges 45.2. At the bottom of each of the faces 46, 48 there is an upwardly facing channel-like formation 50 formed inwardly of outer ridges 51. Associated with the mould 42 there are a pair of ejectors 52 which, in Figure 4, are shown in their retracted positions. The ejectors 52 are upwardly displaceable to eject a folded blank from the mould 42. The operation of the apparatus will now be described with reference to Figures 4 to 7. First, the blank 10 is fed in a horizontal direction into the space between the upper and lower working parts 26.1, 26.2 and located horizontally by means of positioning devices (not shown). The trapper 40 is now lowered and holds the blank 10 against the upper face 44 of the mould 42, as illustrated in Figures 5 to 7. Thereafter, the carrier 28 is lowered onto the blank 10, the position of the blank with respect to the folding elements 30, 32 being shown in dotted outline in Figure 2. The width and length respectively of the rectangle defined by the pivot axes 36 and 38 are slightly greater than the width and length of the rectangular face 44. As the carrier 28 is lowered further, the mould 42 thus presses via the blank 10 against those portions of the folding elements 30, 32 which are on the inside of the pivot axes 36 and 38, causing the folding elements to pivot in the direction of arrows A, against their bias. As shown in Figure 5, this pivotal displacement of the folding elements 30, 32 bends all the peripheral portions 14.1, 14.2, 16.1, and 16.2 simultaneously around the corners at the periphery of the face 44. As the free edges of the folding elements 30, 32 move inwardly of the ridges 51, the edge strips 24 are bent, as illustrated in Figure 6. Further lowering of the carrier 28 causes the free edges of the folding elements 30, 32 to enter into the channel-like formations 50 to form a return bend where the edge strips 24 join the rest of the corresponding peripheral portions 14.1, 14.2, 16.1, and 16.2 and brings the peripheral portions hard up against the corresponding faces 46, 48 of the mould 42, as illustrated in Figure 7. Furthermore, the folding elements 30 and 32 will bend the corner strips 22 of the major portions 14.1, 14.2 through 90°, so that the blank will now be as shown in Figure 8 with the corner strips 22 of the minor portions 16.1, 16.2 overlying the corner strips 22 of the major portions 14.1, 14.2. Where the corner strips 22 meet, adjacent the apices 20, a pleat 53 (see Figure 9) is formed in the blank. Each pleat 53 extends from the corresponding corner of the bottom panel 12 to the corresponding apex 20. Because the spacing of the pivot axes 34 and 36 is wider than that of the corner edges 45.1 and 45.2, the carrier 28 is able to move down sufficiently far for the pivot axes 34 and 36 to move downwardly beyond the level of the corner edges 45.1 and 45.2. The carrier 28 is now retracted so that it returns to the position illustrated in Figure 4. The folded blank 10 remains behind on the mould 42. A pair of rams 54 (only one of which is shown in Figure 8) are now displaced inwardly from opposite ends of the folded blank and fold the overlying corner strips 22 over in the direction of arrows B in Figure 8 until the corner strips, and also the pleats 53, lie flat against the major portions 14.1, 14.2. Finally, an edge frame 56 is dropped into the channel formed by the return-folded edge strips 24, and the edge strips clinched (as shown at 58 in Figure 9) to retain the edge frame in position. The trapper 40 is now retracted and the ejectors 52 operated to eject the folded blank from the mould 42, whereupon the folded blank is removed from between the parts 26.1 and 26.2. It will be appreciated that the separation between the carrier 28 and the face 44 of the mould 42 should be sufficient to enable the folded blank to be removed from between these two parts. By virtue of the spacing between the apices 20 and the corners of the bottom panel 12, the pleat has a height 60 (see Figure 9). This will ensure that the bread pan is water-tight up to the level 61, which is sufficient for the purposes of a bread pan. In the example illustrated the height of the pan is about 11cm and the distance 60 about 2cm. If the height 60 is too small the level to which the pan is water-tight is too small. On the other hand, if the height 60 is too great, the weight of the pan will be unnecessarily high as a result of the unnecessarily wide corner strips 22. The edge frame 56 can be made of any suitable material. However, it has been found advantageous to construct the frame 56 from sheet metal, as will be described with reference to Figure 10 and 11. First, a strip of sheet metal 62 is folded double longitudinally as illustrated in Figure 10. The length of doubled up sheet metal is then formed by rollers into a ring 64 and the ends joined by a halved lap joint as indicated at 66 in Figure 10. Spot welding or some other suitable form of connection may be used for this purpose. The ring 64 is then placed in a tensioning device having opposed flat heads 68. The ring is flattened against each of the heads 68 by means of pneumatic cylinders (not shown) and the heads then moved apart in the direction of arrows C by means of a hydraulic cylinder (not shown). This forms the ring 64 into a rectangular frame for use with the bread pan. If a suitable ductile sheet metal is used, it is possible to stretch the ring somewhat to form frames of different sizes from the same length of strip 62. As the joint 66 is normally the weakest point of the ring 64, the ring is arranged in the tensioning device so that that part of the ring which is in the region of the joint is clamped to one of the heads 68. This will minimise the tension in the ring at the joint when the ring is stretched. The edge frame 56 could be fitted while the folded blank is still in position on the mould 42. However, it may be advantageous to fit the edge frame to the folded blank in a separate operation remote from the apparatus 26, i.e. after the folded blank has been ejected from the apparatus.

Claims: Apparatus for making tapered four-sided sheet metal containers, which apparatus comprises a tapered four-sided mould (42), and folding means for folding a sheet metal blank (10) onto the mould, the folding means comprising a carrier (28) and four folding elements (30,32), the folding elements being arranged each to engage a peripheral portion (14.1,14.2,16.1,16.2) of the blank (10) to fold said peripheral portion onto the corresponding side (46,48) of the mould wherein the mould has four corner edges (45.1,45.2) which together define a first rectangle, each of the four sides (46,48) of the mould extending from a corresponding one of said corner edges, the mould and the folding means being displaceable towards one another and folding of said peripheral portions (14.1,14.2,16.1,16.2) of the blank taking place simultaneously as the mould and the folding means are displaced towards one another with the blank being disposed between them, characterised in that the four folding elements (30,32) are mounted pivotally on the carrier (28), the folding elements (30,32) being arranged to fold said peripheral portion (14.1,14.2,16.1,16.2) by pivotal displacement of the folding elements (30,32) with respect to the carrier (28); and in that the pivot axis (36,38) of each folding element (30,32) is parallel to the corresponding corner edge of the mould (42) so that the pivot axes together define a second rectangle, the width of the second rectangle being greater than the width of the first rectangle and the length of the second rectangle being greater than the length of the first rectangle. Apparatus as claimed in claim 1, characterised in that each folding element (30,32) has an outer portion extending outwardly from the corresponding pivot axis (36,38) and an inner portion connected rigidly to the outer portion, the inner portion being arranged to be driven by movement of one of the corner edges (45.1,45.2) of the mould (42) relative to the folding element. Apparatus as claimed in either one of the preceding claims, wherein the mould (42), in the region thereof corresponding to the rim of the container, has a channel-like formation (50) facing the folding means, characterised in that the arrangement of each folding element (30,32) is such that an outer edge of the folding element enters into the channel-like formation (50) as the mould (42) and the folding means are being displaced towards one another, thereby to form the corresponding peripheral portion (14.1,14.2,16.1,16.2) of the blank (10) with a return-folded edge strip (24) at the rim of the container. A method of making a tapered four-sided sheet metal container comprising the steps of providing a tapered four-sided mould (42) having four corner edges (45.1,45.2) which together define a first rectangle, each of the four sides (46,48) of the mould extending from a corresponding one of said corner edges, providing folding means comprising a carrier (28) and four folding elements (30,32), positioning a sheet metal blank (10) between the mould (42) and folding means, displacing the mould and the folding means towards one another, and simultaneously folding, using the folding elements (30,32), peripheral portions (14.1,14.2,16.1,16.2) of the blank (10) onto the corresponding side (46,48) of the mould (42), characterised in that it includes the steps of pivotally displacing the folding elements (30,32) with respect to the carrier (28) to fold said peripheral portion (14.1,14.2,16.1,16.2) onto the corresponding side (46,48) of the mould, wherein the pivot axis (36,38) of each folding element is parallel to the corresponding corner edge (45.1,45.2) of the mould so that the pivot axes (36,38) together define a second rectangle, the width of the second rectangle being greater than the width of the first rectangle and the length of the second rectangle being greater than the length of the first rectangle. A method as claimed in claim 4 characterised in that it includes the step of displacing the pivot axes (36,38) beyond the level of the first rectangle during completion of the folding process. A method as claimed in either claim 4 or claim 5 characterised in that it includes the further step, while displacing the folding means towards the mould (42), of driving the corner edges (45.1,45.2) of the mould (42) against a corresponding inner portion of each folding element (30,32), wherein the inner portion extends inwardly from its pivot axis (30,38), thereby to cause pivoting of an outer portion of the folding element (30,32) against the corresponding peripheral portion (14.1,14.2,16.1,16.2) of the blank (10).

Inventors: BAIN, KENNETH JOHN DUNCAN, BAIN, STEVEN, ISAACS, PETER, WORSHIP, LESLIE ARTHUR
Applicants: BAIN, KENNETH JOHN DUNCAN, BAIN, STEVEN, ISAACS, PETER, WORSHIP, LESLIE ARTHUR
Application year: 1989
Main classification: B21D51
IPC codes: B21D51