METHOD AND DEVICE FOR PRODUCING AN EDGE

Abstract

The present invention relates to a method and a device for folding a foil material half-shell edge which protrudes from a surface of the packaging of a packaged food product, said half-shells receiving the food product. The half-shells have flanges, at least some regions of which lie one on top of the other and which form the protruding edge. The aim of the invention is to improve a quick and reliable method which can be carried out with little effort for improving the appearance of food products packaged in foil half-shells. This is achieved in that during a relative movement between a packaged food product and a die, an edge region of the die presses against the protruding edge of the foils, whereby the edge of the foils is at least partly folded to lie substantially flush on one of the half-shells. The invention further relates to a device which corresponds to the method.

Claims

1. Method for folding an edge (4) of half-shells (2) of a foil-like material protruding from a surface of the packaging of a packaged food product (1) in which the food product (1) is received to lie substantially flush, wherein the half-shells (2) comprise flanges (3) lying one on top of the other at least in some sections and forming the protruding edge (4), characterized in that during a relative movement between a die (5) and the package, at least one edge region (8) of the opening (7) of the die (5) presses onto the edge (4) of the foils, whereby the edge (4) of the foils is at least partially folded to lie substantially flush at at least one half-shell (2).

2. Method according to claim 1, characterized in that at the edge region (8) of the die (5), at least one elastic element presses onto the edge (4) of the foils, whereby the edge (4) of the foils is at least partially folded to lie substantially flush at at least one half-shell (2).

3. Method according to one of the preceding claims, characterized in that at the edge region (8) of the die, bristles press onto the edge (4) of the foils, whereby the edge (4) of the foils is at least partially folded to lie substantially flush at at least one half-shell (2).

4. Method according to one of the preceding claims, characterized in that the die (5) is at rest and the packaged food product (1) is moved relative to the die (5) through the opening (7), or that the packaged food product (1) is at rest and the die (5) is moved relative to the packaged food product (1).

5. Method according to one of claims 1 to 3, characterized in that both the packaged food product (1) and the die (5) are moved.

6. Method according to one of the preceding claims, characterized in that the edge (4) of the foils is, during the passage through the opening (7) of the die (5), in a first step initially approached to the surface of the half-shells (2), and subsequently, in a further step, folded to lie substantially flush at at least one half-shell (2).

7. Method according to one of the preceding claims, characterized in that the relative movement between the die (5) and the packaged food product (1) extends one-dimensionally.

8. Method according to one of claims 1 to 6, characterized in that the relative movement of the packaged food product (1) first extends in a first moving direction through the opening (7) of the die (5), and subsequently transverse to the first moving direction to adapt the folding of the edge (4) to the outer shape of the food product (1).

9. Method according to one of the preceding claims, characterized in that the packaged food product (1) is moved relative to the die (5) with the aid of guide means (6).

10. Method according to claim 9, characterized in that the packaged food product (1) is held at the guide means (6) during the relative movement.

11. Method according to claim 10, characterized in that the packaged food product (1) is held at the guide means (6) by a vacuum.

12. Method according to one of claim 10 or 11, characterized in that the packaged food product (1) is held between the guide means (6) and a backing part (10).

13. Method according to claim 12, characterized in that the backing part (10) exerts a guide force onto the packaged food product (1), in particular by means of a resilient element (17).

14. Method according to one of claim 12 or 13, characterized in that at least part of the guide force between the guide means (6) and the backing part (10) is transmitted via the packaged food product (1).

15. Method according to one of claims 12 to 14, characterized in that the guide means (6) and the backing part (10) are spaced apart so that a folding of the edge (4) non-obstructed by these parts is ensured.

16. Method according to one of the preceding claims, characterized in that the protruding edge (4) has a proximal section (14) which is directly connected to the half-shells (2) and connects a distal section (15) of the edge with the half-shells (2), wherein the distal section (15) is folded onto the proximal section (14) before the folding of the edge to lie substantially flush.

17. Method according to claim 16, characterized in that, before the folding to lie substantially flat, the distal section (15) is directed with its front end towards the surface of at least one half-shell (2) and in particular touches it or is spaced apart from it.

18. Method according to one of claim 16 or 17, characterized in that the packaged food product (1) moves, with the proximal section (14) leading, through the opening (7) of the die (5) so that the proximal section (14) comes into contact with the edge region (8) of the opening (7), and the distal section (15) is at least partially folded to lie substantially flush at at least one half-shell (2).

19. Method according to one of the preceding claims, characterized in that the flanges (3) are bordered and/or sealed to each other before the folding of the edge (4) to lie substantially flush.

20. Method according to one of the preceding claims, characterized in that the packaged food product (1) completely passes through the die (5).

21. Device for folding an edge (4) of a packaged food product (1) to lie substantially flush, which comprises a die (5) with an opening (7) formed by an edge region (8) of the die (5), a packaged food product (1) which is received between half-shells (2) of a foil-like material (5), wherein the half-shells (2) comprise flanges (3) at least partially lying one on top of the other and forming an edge (4) protruding from the surface of the packaging, and guide means (6) by which the packaged food product (1) and the opening (7) of the die (5) are movable relative with respect to each other, characterized in that, during a relative movement of the packaged food product through the opening of the die (5), the protruding edge (4) can be brought into contact with the edge region (8) of the opening so that the protruding edge (4) may be at least partially folded to lie substantially flush at at least one of the half-shells (2).

22. Device according to claim 21, characterized in that the edge region (8) has at least one elastic element pressing onto the protruding edge (4).

23. Device according to one of claims 21 and 22, characterized in that the edge region (8) has bristles which press onto the protruding edge (4).

24. Device according to one of claims 21 to 23, characterized in that the clearance (A) between the edge of the die (5) bordering the opening (7) and the half-shells (2) is, at least in some sections, smaller than the width (B) of the protruding edge (4).

25. Device according to one of claims 21 to 24, characterized in that the clearance (A) between the edge of the die (5) bordering the opening (7) and the half-shells (2) corresponds, at least in some sections, to the thickness (D) of the protruding edge (4).

26. Device according to one of claims 21 to 25, characterized in that the guide means (6) comprise retention means (11) for the packaged food product (1).

27. Device according to claim 26, characterized in that one or several suction elements are provided as retention means (11).

28. Device according to one of claims 21 to 25, characterized in that a backing part (10) opposite the guide means (6) is provided with which the packaged food product (1) may be held between the guide means (6) and the backing part (10).

29. Device according to claim 28, characterized in that the backing part (10) exerts a compressive force onto the packaged food product (1) which is directed opposite to the direction of the relative movement of the food product (1) through the opening (7) of the die (5).

30. Device according to claim 29, characterized in that the backing part (10) includes a resilient element (17) which may exert a compressive force onto the packaged food product (1).

31. Device according to one of claims 21 to 30, characterized in that it furthermore comprises a pre-bending element (12) for approaching the edge (4) to the surface, having an opening (7) whose edge region is further spaced apart from the half-shells (2) than the thickness (D) of the flanges (3) lying one on top of the other in some sections.

32. Device according to one of claims 21 to 31, characterized in that the die (5) is fixed and the guide means (6) are movable, or that the guide means (6) are fixed and the die (5) is movable.

33. Device according to one of claims 21 to 32, characterized in that the die (5) and the guide means (6) are movable.

34. Device according to one of claims 21 to 33, characterized in that the die (5) and the guide means (6) are movable relative with respect to each other in one single direction or in several directions.

35. Device according to one of claims 21 to 34, characterized in that the edge region of the opening of the pre-bending element (12) tapers towards the edge region (8) of the opening (7) of the die (5).

36. Device according to one of claims 21 to 35, characterized in that the pre-bending element (12) is embodied as a chamfer (13) of the edge region (8) of the opening (7).

37. Device according to one of claims 21 to 36, characterized in that the flanges (3) at least partially lying one on top of the other are bordered and/or sealed to each other.

38. Device according to one of claims 21 to 37, characterized in that the guide means (6) and the backing means (10) are spaced apart.

Description

[0056] In the drawings:

[0057] FIG. 1a shows a vertical section through a food product packaged in foil half-shells and a die and guide means before an edge is folded to lie substantially flush according to a first embodiment of the invention,

[0058] FIG. 1b shows a vertical section through the packaged food product of FIG. 1a after the edge has been folded to lie substantially flush,

[0059] FIG. 2 shows a vertical section through a packaged food product with flanges sealed to each other before and after the edge is/has been folded to lie substantially flush according to a second embodiment of the invention,

[0060] FIG. 3 shows a vertical section through a packaged food product with flanges bordered to each other before and after the edge is/has been folded to lie substantially flush according to a third embodiment of the invention,

[0061] FIG. 4 shows a vertical section through a packaged food product with flanges bordered and sealed to each other before and after the edge is/has been folded to lie substantially flush according to a fourth embodiment of the invention,

[0062] FIG. 5 shows a vertical section through a fifth embodiment of a device according to the invention for folding an edge to lie substantially flush having guide means, retention means, a die, a pre-bending element, a backing part, and a resilient element with a packaged food product,

[0063] FIG. 6a shows a vertical section through a detail of a food product directly before the contact with a die according to a sixth embodiment of the invention,

[0064] FIG. 6b shows a vertical section through the detail of the food product of FIG. 6a during folding in contact with the die,

[0065] FIG. 6c shows a vertical section through the detail of the food product of FIGS. 6a and 6b with a folded edge directly after the contact with the die,

[0066] FIG. 7a shows a vertical section through the detail of a packaged food product according to a seventh embodiment of the invention directly before the contact with a die having bristles,

[0067] FIG. 7b shows a vertical section through the detail of FIG. 7a during the contact of the edge with the bristles of the die while the edge is being folded to lie substantially flush,

[0068] FIG. 8a shows a vertical section through a detail of a packaged food product according to an eighth embodiment of the invention directly before the contact with a die having an elastic element,

[0069] FIG. 8b shows a vertical section through the detail of FIG. 8a during the contact of the protruding edge with the elastic element while the edge is being folded to lie substantially flush.

[0070] The method according to the invention and the device according to the invention relate to the packaging of food products. These food products may in particular be hollow chocolate figurines with any external shape, for example the external shape of eggs, stylized animals or human figurines.

[0071] Proportions in size and dimensions represented in the Figures are not drawn to scale but are selected to represent the features of the invention clearly. In general, the thickness of the foil is clearly smaller than the thickness of the outer hull of a hollow food product. The combination of optional features of the invention is given by way of example and is not to be considered in a restricting manner.

[0072] FIG. 1a shows a first embodiment of a device according to the invention for folding an edge of a packaged food product to lie substantially flush in a schematic sectional view before the contact with the die. The food product has the outer shape of an egg. The joint face of the foil half-shells in which the flanges lie one on top of the other is perpendicular to the image plane. The direction of the relative movement of the packaged food product with respect to the die is designated by the arrow R and lies in the image plane.

[0073] The packaged food product 1 is received in two foil-like half-shells 2, which comprise flanges 3 flatly lying one on top of the other. The flanges together form a protruding edge 4, which may be brought into contact with an edge region 8 of the die 5 during a relative movement whose direction is represented by means of an arrow R. In the shown embodiment, the device moreover includes guide means 6 by means of which the relative movement may be performed. In this Figure, the guide means are designed as movable male mould while the die is mounted at rest.

[0074] The external shape of the food product has the shape of an egg and is rotationally symmetric. The two foil half-shells have identical shapes, their contact plane lying in the plane of the largest cross-section of the packaged food product when they receive the food product between them. Since the cross-section of the food product preferably tapers from this plane on, it may be better inserted in the foil half-shells during the packaging process. The foil-like half-shells are therefore configured as half-shells in the shown embodiments. Instead of identical half-shells, a packaging according to the invention may be also formed by mirrored half-shells or half-shells of different shapes.

[0075] The foil half-shells with the protruding flanges are preformed from foil sections cut to size, for example by means of deep-drawing. The curvature of the foil half-shell resulting from deep-drawing corresponds to the outer contour of the food product which is received and packaged in the half-shells.

[0076] As a packaging material, an aluminium foil may be employed which may be externally provided with a print to create, in connection with the shape of the food product, an attractive appearance of the packaged product. The foil may have a thickness of 5 to 100 m, in particular 10 to 50 m, and particularly advantageously 15 to 40 m. However, the foil material is not restricted to aluminium nor metallic materials.

[0077] The protruding edge 4 has a width B and a thickness D. Between the edge of the die bordering the opening and the half-shells, there is a clearance A perpendicular to the relative movement. The shown arrow R indicates the direction of the relative movement of the packaged food product in relation to the die 5. Here, in the represented embodiment, the packaged food product is not necessarily moving. The relative movement of the food product in the direction of the arrow may also be realized by a resting product and a moving die.

[0078] The clearance A is smaller than the width B of the protruding edge. During the passage of the die in the moving direction designated by the arrow R, the protruding edge comes into contact with the edge region of the die. In the process, the edge region exerts a compressive force onto the protruding edge which is transmitted to the guide means via the food product. By the compressive force, the protruding edge deforms plastically and is at least partially folded to lie substantially flush at one of the half-shells.

[0079] In the shown first embodiment, the opening of the die has a closed contour without interruptions. Across the entire circumference of the packaged food product, the protruding edge comes into contact with the edge region of the die and is deformed thereby. Equally, an open or interrupted contour of the die opening is possible by which parts of the protruding edge do not come into contact with the edge region.

[0080] During the folding of the foil edge to lie substantially flush, compressive forces may act on the food product due to the process. To avoid damages, the forces may be adapted to the stability of the food product, depending on the occurring forces and environmental influences, for example ambient temperature.

[0081] Below, the same reference numerals are assigned to the same elements in the Figures.

[0082] FIG. 1b shows the packaged food product of FIG. 1a, however after the originally protruding edge has been folded to lie substantially flush. After the relative movement between the packaged food product and the die and the contact between the edge region of the die and the protruding edge caused during the contact, the formerly protruding foil edge is approximately tangentially folded to lie substantially flush at the surface of the packaged food product.

[0083] FIGS. 2 to 4 show food products pre-packaged in half-shells of a foil-like material wherein the flanges of the half-shells lying one on top of the other are connected to each other in different ways. Left of the parting line M drawn in perpendicularly, the protruding edge is in each case shown before folding, and right of the parting line, the edge is partially folded to lie substantially flush at the surface of one of the half-shells.

[0084] FIG. 2 shows a packaged food product before and after the edge has been folded to lie substantially flush according to a second embodiment of the invention, wherein the protruding edge is formed by two flanges of the half-shells lying one on top of the other and which are sealed to each other at the sealing area 9. Sealing may be accomplished by means of material-bond joining processes, such as gluing, fusing, soldering or welding. To this end, the metal foils may be coated on the inner side facing the food product either completely or in sections with a thermoplastic polymer, for example polypropylene or polyethylene, so that the thermoplastic layers lying one on top of the other at the flanges will fuse due to heating and form the sealing as a result thereof.

[0085] FIG. 3 shows a packaged food product before and after the folding of the edge to lie substantially flush according to a third embodiment of the invention, wherein the flanges forming the edge are bordered to each other. The front face of the bordered edge points in the direction of the upper half-shell and is spaced apart from it. During the bordering of the edge, the two flange faces initially lie one on top of the other and form the protruding edge. Then, a distal section of the edge is bent over by about 180 so that it is placed onto the proximal section and pressed against it. The bordered edge is secured against a release of the connection. By the bordering of the edge, it has an increased thickness which is approximately four times the foil layer. The distal section of the edge points with its front face towards the upper foil half and is spaced apart from its surface.

[0086] FIG. 4 shows a packaged food product before and after the folding of the edge to lie substantially flush according to a fourth embodiment of the invention, wherein the flanges of foil half-shells forming the edge are both sealed and bordered to each other. As is also shown in FIG. 3, the distal section of the edge is directed towards the upper foil half-shell and spaced apart from it. The thickness of the protruding edge is approximately four times one foil layer.

[0087] FIG. 5 shows a fifth embodiment of the device for folding an edge of a packaged food product to lie substantially flush. Next to the packaged food product 1, which is packaged in two half-shells 2 having flanges 3 and forming a protruding edge 4, a die 5 with an edge region 8 defining an opening 7 is shown. Furthermore, the device has a pre-bending element 12, which is designed as a chamfer 13 of the edge region 8 of the opening 7. The packaged food product is held between guide means 6 and a backing part 10. By means of a resilient element 17, the backing part exerts a compressive force onto the packaged food product. The guide means comprise retention means 11 designed in the form of suction elements. The suction elements hold the packaged food product by means of a vacuum created by a vacuum generator 18.

[0088] In this embodiment, there is no contact between the guide means 6 and the backing part 10. The retention force exerted by the backing part 6 onto the packaged food product 1 is completely transmitted via the packaged food product 1 to the guide means 6. Thereby, neither the guide means nor the backing part come into contact with the protruding edge, whereby a non-obstructed folding of the edge to lie substantially flush at the surface of the half-shells may be ensured.

[0089] By the resilient element 17, a compressive force is exerted via the backing part 10 onto the packaged food product and is forwarded via the food product to the guide part 6 without permanently deforming or damaging the food product. The resilient element may be designed, for example, in the form of one or several coil springs, pneumatic or hydraulic springs or actuators or energy accumulators.

[0090] The retention means designed as suction elements of the guide means operated with a vacuum are also suited, apart from their function of holding the packaged food product during the folding of the edge to lie substantially flush, for gripping the packaged food product before folding, for example by a conveyor means or by a tool by which a procedure step preceding the edge folding step has been performed. Similarly, the food product may also be placed again, after the edge folding, onto a conveyor means or into a tool for subsequent procedure steps.

[0091] When the packaged food product is passed in the direction of the represented arrow R, the protruding edge initially comes into contact with the pre-bending element 12, subsequently with the chamfer 13, and finally with the edge region of the opening of the die. During the contact with the pre-bending element and the chamfer, the protruding edge is thus first deformed and continuously approached to the surface of the half-shells before it is folded to lie substantially flush at the surface of the half-shells not before it passes the opening and contacts the edge region.

[0092] The protruding edge has a proximal section 14 and a distal section 15. The proximal section 14 here connects the distal section 15 with the foil half-shells 2. During the relative movement of the packaged food product through the opening of the die 5, represented by the arrow R, the proximal section 14 comes into contact with the edge region 8 of the die 5 so that the distal section of the edge is at least partially folded to lie substantially flush at one of the half-shells.

[0093] FIGS. 6a to 6c each show a detail of the food product with the edge in a sectional representation at different points in time during the folding of the edge according to a sixth embodiment of the invention. The represented arrows R and E show the respective direction of the movements of the packaged food product relative to the position of the die.

[0094] In FIG. 6a, the protruding edge is shown directly before the contact with the pre-bending element 12. The die 5 has a pre-bending element 12, an edge region 8 and a chamfer 13 extending between the edge region 8 and the pre-bending element 12. The clearance A between the edge region of the die and the surface of the half-shell corresponds to the thickness D of the protruding edge. During the passage of the die, the protruding edge is folded to lie substantially flush at the surface of the half-shell without being appreciably compressed in the direction of its thickness. The direction of the relative movement of the packaged food product is shown by arrow R.

[0095] In FIG. 6b, the already pre-bent edge is shown in contact with the chamfer. During the represented procedure step, the edge is pre-formed before the final folding. In the exemplified embodiment, the edge slides, during the deformation, over the chamfer, whereby it is continuously bent in the direction of the surface of the half-shells.

[0096] In FIG. 6c, the folded edge is shown directly after the passage through the opening of the die. After the contact with the edge region 8 of the die, the edge is folded to lie substantially flush at the surface of one of the half-shells 2. In this position, the food product may be moved in the direction shown by arrow E relative to the die, or the die may be moved relative to the food product in the correspondingly opposite direction so that the edge may be even better adapted to the outer contour of the packaged food product. This second movement does not have to be perpendicular to the first one but may be in any direction transverse to it. To improve the folding of the edge to its entire circumference, this second movement may extend in several directions to press the edge against the surface of the packaged food product from various directions. Apart from the two represented moving directions, both one single direction and any number of different directions and components of movement are possible.

[0097] FIGS. 7a and 7b each show a detail of the packaged food product 1 with a protruding edge 4 and a die 5 having bristles 19 according to a seventh embodiment of the invention. The relative movement of the packaged food product 1 extends relative to the position of the die 5 and in the direction of the arrow R.

[0098] The shown active principle corresponds to that in FIGS. 6a to 6c. Equal or corresponding elements of the invention are designated with corresponding reference numerals.

[0099] FIG. 7a shows the die 5 and the food product 1 just before the contact of the bristles 19 with the surface of the packaged food product 1. The distance between the bristles 19 and the food product 1 is here optionally selected such that the bristles 19 graze over the surface of the packaged food product 1 already before the contact with the protruding edge 4. Upon contact with the edge 4, the bristles 19 exert a compressive force onto it leading to a folding of the edge 4 to lie substantially flush. While the edge 4 is being pressed against the surface of the packaged food product 1, the bristles 19 deform elastically and resume their original shape after the food product 1 has passed the die 5. During the elastic deformation and the subsequent relaxation or return to the original shape, the bristles cause a spring force which depends on the degree of deformation and acts on the edge and leads to a folding of the edge to lie substantially flush.

[0100] During the passage through the opening 7 of the die 5 in the direction of the arrow R, the bristles graze over the face of the edge facing outwards after the folding as represented in FIG. 7b. This permits to achieve an over-pressing of the edge, i. e. to realize a change of the angle of the edge by more than 90 relative to the area in which the flanges of the foil half-shells lie one on top of the other, and to fold the edge to lie substantially flush in particular at surface areas of the packaged food product which are not oriented in parallel to the moving direction of the packaged food product through the opening of the die. Such areas may be convex or concave. Relative to the area in which the flanges of the foil half-shells lie one on top of the other, these surface areas may be inclined so that they recede from the edge region of the die while the foil edge is in contact with the edge region and is folded.

[0101] The outer extension of the outer contour of the protruding edge may comprise concave sections and indentations directed inwards in the circumferential direction. Thanks to the bristles, the method and device may be well adapted to those and other complex circumferential contours of the edge. The bristles make it easier to deform and fold the edge even at indentations or discontinuous extensions at the circumference of the edge.

[0102] In the represented embodiment, only the bristles of the die come into contact with the protruding edge. As an alternative, first a rigid part of the die may press onto the edge and the bristles may only be used for the last step of pressing on the already pre-bent edge. In the sense of the invention, a combination of the bristles with a pre-bending element, a multiaxis movement or other already described features is also possible.

[0103] The material and the geometry of the bristles should be selected such that during the edge folding, the bristles will be elastically deformed. The bristles should be sufficiently elastic to exclude a damage of the food product when the bristles are deformed by the contact and the compressive forces occurring in the process. Simultaneously, the bristles should be rigid enough to be able to plastically deform the protruding edge.

[0104] To improve the distribution of compressive forces on the surface of the packaged food product and the edge during folding, or to optimise the folding quality, the bristles may have different lengths and/or different distances to the surface of the packaged food product.

[0105] FIGS. 8a and 8b each show a detail of the packaged food product 1 with a protruding edge 4 and a die 5 having an elastic element 20 according to an eighth embodiment of the invention. The relative movement of the packaged food product 1 relative to the die 5 extends in the direction of the arrow R.

[0106] The embodiment of the invention represented in FIGS. 8a and 8b differs from the variation in FIGS. 7a and 7b in that the edge region of the die has a rubber lip 21 as elastic element 20. Corresponding reference numerals are assigned to corresponding features.

[0107] The elastic element 20 is designed in the form of a rubber lip 21 in the represented embodiment of the invention, however, it is not restricted to this design. The functioning of the elastic element 20 is analogue to that of the bristles 19. Thus, the elastic element 20 is also suited to realize an over-pressing of the edge 4 by more than 90 and to adapt the edge to surface sections of the packaged food product which are not in parallel to the moving direction of the packaged food product through the opening of the die. To this end, the elastic element 20 grazes over the surface of the packaged food product 1, presses onto the edge 4 to fold it to lie substantially flush, and subsequently grazes over the side of the then folded edge facing outwards.

[0108] The elastic element may be made of rubber, silicone, or an elastic polymer. During the edge folding process, it may be bent over as shown in FIG. 8b. It is also possible that the elastic element is compressed in one or several directions, for example transverse to the moving direction of the packaged food product. After the contact with the packaged food product, the elastic element resumes its outer original shape. The elastic element should have an elasticity which is on the one hand suited to plastically deform the edge, but on the other hand cannot damage the packaged food product. Similar to the bristles, the elastic element exerts a spring force onto the foil edge during its deformation which acts on the edge.

[0109] The elastic element and the bristles may be provided across the entire circumference of the acting edge region of the die opening, or only in partial sections of the edge region. Different sections where there may be elastic elements and/or bristles may alternate with sections of the edge region which are rigid, i. e. act on the edge without any elastic element or bristles. It is also possible to combine elastic elements, bristles and stiff sections of the edge region so that they act on the edge one after another and thus realize a step-wise folding and pressing on of the edge.