Method and device for production of can with fold lines

Abstract

A can, and device and method for producing same, includes two circular end elements forming a base and lid. The can further includes a sleeve which has fold lines forming edges, the can sleeve having a circular cross-sectional area at both ends and a polygonal-sectional area in its central region. The polygonal cross-sectional area in the central region is at most decagonal.

Claims

1. A method for producing a can with fold lines, comprising steps of: providing a can sleeve having edges parallel to a longitudinal can axis; closing the can sleeve all round into a polygonally prefolded form having a first and second opening; bringing said first opening into a circular shape with a circular first end element; and after the can is filled, bringing said second opening into a circular shape with a circular second end element; wherein the polygonally prefolded form defines a polygon in a cross-section perpendicular to the longitudinal can axis, the polygon having ten or fewer sides; wherein the circular shape of said first and second openings is achieved by at least one of drawing the can sleeve onto a cylindrical intermediate shaping mandrel or by applying at least two intermediate shaping jaws from outside.

2. The method according to claim 1, further comprising a step of preforming with a preforming means at least one of the first and second openings so that the can is preshaped.

3. The method of claim 2, wherein the preforming means is an intermediate shaping mandrel.

4. The method of claim 2, wherein the step of preforming with a preforming means at least one of the first and second openings, is such that the can is preflanged.

5. The method according to claim 1, wherein at least one of the first or second end element is joined to the first or second opening with a tight seal, by at least one of a first or second sealing means.

6. The method according to claim 5, wherein at least one of the first or the second sealing means is pressed in a radial direction against an inside and outside of the first or of the second end element.

7. The method of claim 5, wherein the at least one of the first or second end element is rolled, flanged or sealed.

8. The method according to claim 1, further comprising a step of, tightly joining a sheet-like sealing element to an inside of one of two end regions of the can sleeve.

9. The method of claim 8 wherein step of tightly joining is accomplished by heat-sealing or adhesively bonding.

10. The method of claim 1, wherein said sealing element is sealed or adhesively bonded to an inside of said can sleeve.

11. The method of claim 1, said polygon is a hexagon or an octagon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in more detail below with reference to the figures of the drawing, using a hexagonal can sleeve as an example. Identical parts in different embodiments which perform the same functions are provided below with identical designations and reference numerals. In the drawing:

(2) FIG. 1 shows a plan view of the lid placed on the opening of a hexagonal sleeve which has been folded out;

(3) FIGS. 2a and b each show a longitudinal section along the line 1′-1″ and F′-F″, respectively, from FIG. 1;

(4) FIG. 3 shows a cylindrical intermediate shaping mandrel perpendicularly above an aligned can sleeve having a hexagonal base shape, in oblique view;

(5) FIG. 4 shows the can sleeve drawn onto the intermediate shaping mandrel, above a sealing means, in oblique view;

(6) FIG. 5 shows a sheet-like sealing element above the can sleeve positioned between two intermediate shaping jaws, in oblique view;

(7) FIG. 6 shows a second end element and

(8) FIG. 7 shows a can sleeve kept circular by a flange shaping device, in side view;

(9) FIGS. 8 to 11 show force-displacement curves for the pressure on can sleeves having a polygonal cross-section.

DETAILED DESCRIPTION OF THE INVENTION

(10) According to FIG. 1, a commercial, circular end element 4, e.g. a lid, having the radius R, rests concentrically on an unfolded, hexagonal can sleeve 2. The edge length K of the sleeve is 2Rπ/6. If the sleeve 2 is made circular at its opening, for example by applying an external circular shape (intermediate shaping jaws 6 in FIG. 5), so that the lid 4 can be inserted and/or, for example, rolled over the sleeve edge (FIG. 4, lower part), the edges 1 in the region of the lid 4 are drawn inwards when the can is closed.

(11) This inevitably causes the edges 1 to project slightly outwards in the middle of the can height between the two lids 4, 5, i.e. to be dished slightly outwards in their contour, axially relative to the can (FIG. 2a). In contrast, the six prism surfaces F of the sleeve 2 in the region of the two lids 4, 5 are each pressed outwards, which inevitably results in the surfaces F in the middle of the can height between the two lids 4, 5 projecting slightly inwards, i.e. arching slightly inwards in their contour, axially relative to the can, and hence being prestressed (FIG. 2b). Both result in an unexpectedly great increase in the rigidity and stability of grip of the can.

(12) FIG. 3 shows an intermediate shaping mandrel 3, which is positioned perpendicularly above a can sleeve 2. The prefabricated can sleeve 2 which is closed all round and provided with fold lines is removed from a stack of flattened can sleeves and set up as a hexagonal prism by pushing together two opposite fold edges. In this embodiment, the can sleeve 2 has six fold lines 14 oriented parallel to the longitudinal axis of the can sleeve 2. When the can sleeve 2 has been set up, the fold lines 14 form edges 1 over their entire length. Two edges of the piece of the paper and/or cardboard composite of which the can sleeve 2 consists are adjoined so as to overlap one another in the overlap region 16. The overlap region 16 is compressed to give the single layer thickness of the paper and/or cardboard composite. A prefabricated can sleeve could, however, equally well have two abutting edges which are joined to one another in a manner known per se by means of a joining strip.

(13) Here, the intermediate shaping mandrel 3 has a cylindrical base shape. That end face of the intermediate shaping mandrel 3 which points towards the can sleeve 2 has a feed bevel 13 for the can sleeve 2. Here, a shaping means 7, by means of which a can sleeve 2 can optionally be preshaped for further steps of the method, is arranged at the bottom of the intermediate mandrel 3.

(14) The can sleeve 2 is drawn onto the intermediate shaping mandrel 3 by pressing the latter against the can sleeve 3. Intermediate shaping jaws 6 shown in FIG. 5 support the can sleeve 2 laterally in the end region at the other end.

(15) FIG. 4 shows the can sleeve from FIG. 3 drawn onto the intermediate shaping mandrel 3, above a sealing means 9 equipped with a first end element, e.g. lid, 4. The can sleeve 2 drawn onto the intermediate shaping mandrel 3 then likewise has a cylindrical shape. The fold lines 14, too, rest against the intermediate shaping mandrel 3 and no longer form edges.

(16) Here, the sealing means 9 is in the form of a conventional rolling means. In addition to a holder not visible in FIG. 4 and intended for the first end element 4, the rolling means has two pairs 10 of rollers, of which only the pair of rollers which presses from outside against the end piece 4 is visible. The now cylindrical can sleeve 2 is inserted into the circular gap of the first end element 4. By turning the intermediate shaping mandrel 3 and the holder relative to the pairs 10 of rollers, the end element 4 is joined to the can sleeve 2 with a tight seal. The can sleeve 2 now joined at one end to the first end element 4 can now be pulled off again from the sealing means 9.

(17) FIG. 5 shows the can sleeve 2 which is joined at one end to the first end element 4 and is positioned at the other end between two intermediate shaping jaws 6, under an expanding punch 17 known per se. Here, the expanding punch 17 is equipped with a sealing element 11—for example in the form of an aluminium membrane.

(18) After the can has been filled, the can sleeve 2 is converted into an intermediate cylindrical shape at the other end in a region adjacent to the internal opening by moving together the two intermediate shaping jaws 6. Thereafter, the sealing element 11 is inserted into the region by means of the expanding punch 17 and is heat-sealed tightly to the inner surface 12 of the can sleeve 2.

(19) FIG. 6 shows a second end element 5 in the form of an inserted lid. The inserted lid can be mounted at the other end, for example after the heat-sealing of the sealing element 11 on the can sleeve 2. The intermediate shaping jaws 6 can optionally have been removed again from the can sleeve 2 since the sealed sealing element 11 is sufficient to produce a circular cross-sectional area of the can sleeve 2. The imposing of the circular cross-sectional area can be supported by an inserted lid.

(20) The can which has now been filled and provided with both end elements 4 and 5 has, with the exception of the two end regions of the can sleeve 2, one edge each along the six fold lines 14, the contour of which edge becomes steadily more pronounced towards the central region. Here, the can sleeve has a hexagonal cross-sectional area of the central region. In the central region of the can sleeve 2—i.e. in the region in which as a rule it is also gripped—the can according to the invention therefore also has the maximum stability of grip.

(21) FIG. 7 shows an alternative processing step which is carried out at the other end on the can sleeve 2. The can sleeve 2 is provided with a circular flange by a flange shaping means 8 which has a shaping punch 18 and two counterparts 19. The flange shaping means 8 can be heated in a manner known per se.

(22) FIGS. 8 to 11 show force-displacement diagrams under external compressive load, perpendicular to the can axis, on cardboard cans of 73 mm diameter and 120 mm height, with a wall thickness of the cardboard sleeve of 0.4 mm and a fold radius of 2 mm. In each case, the force F in Newton is plotted along the ordinate and the indentation depth s in mm is plotted along the abscissa. The curves are denoted in each case by numbers from 2 to 10, indicating the number of fold lines (edges).

(23) In FIGS. 8 and 9, the curves of the mean values of in each case 8 measurements of the pressure on the can at the height in the middle of the can are plotted, in particular in each case on the edge in FIG. 8 and in the middle of the respective prism surfaces in FIG. 9. Pressure was applied using a punch of 20 mm diameter, starting from an initial pressure of 1 N. It is found that hexagonal and octagonal can sleeves show by far the greatest resistance to deformation; in contrast, decagonal can sleeves on the one hand and biangular or tetragonal can sleeves on the other hand, which in each case already have a greater resemblance to a cylindrical can sleeve, retract to a considerable extent.

(24) A similar result is obtained if—as shown in FIG. 10—the values of the pressure on the edge are measured at ¼ or at ¾ of the can height or if—as shown in FIG. 11—the values of the pressure on the middle of the edges are measured using a punch of 10 mm diameter and have an initial pressure of only 0.1 N.

(25) The values are further improved if the can sleeve has an internal circumference which is 0.5 to 1 mm smaller than the lid circumference coming into contact with it, since the can sleeve then has to be expanded slightly at its opening and is prestressed thereby.