Can lid and method for manufacturing a can lid

Abstract

An apparatus for manufacturing can ends having a can end part made of sheet metal and at least one plastic part connected to the can end part, the apparatus comprising: two press tools that come together to form a press for pressing the can end part and the plastic part together; and an inductor that applies an alternating electromagnetic field to the area of ​​the press to inductively heat the can end part and the pressed plastic part, thereby joining the can end part and the pressed plastic part; wherein fluid passages are formed in at least one of the press tools, and a temperature regulating device is provided that is configured to convey a temperature regulating fluid through the fluid passages to stabilize the temperature of the press.

Description

Technical Field

[0001] The present invention relates to an apparatus for manufacturing a can end having a can end part made of sheet metal and at least one plastic part connected to the can end part, the apparatus comprising two press tools that cooperate with each other to form a press for press-forming the can end part and the plastic part together, and an inductor that inductively heats the can end part by providing an alternating electromagnetic field in the press-forming region, thereby joining the can end part and the pressed plastic part.

[0002] Can ends for beverage cans, food cans, etc. usually have an opening section that can be moved by a tear-open member fixed to the can end outside the can plane for opening the can. There are also known re-closable can ends in which a sealing frame made of plastic material, connected to the metal can end surface and surrounding the opening region, cooperates with a closure unit made of plastic material and connected to the metal opening section. Furthermore, the can end can be laminated, for example, by a plastic film that covers a microgap or a minute gap in a sealing manner. A very stable connection between the sealing frame, the closure unit, the film and other plastic parts and the metal can end part can be achieved by press-forming and heating.

[0003] The plastic part is partly melted by induction heating and thereby connected to the sheet metal part in an adhesive manner. Induction heating has the advantage that only the sheet metal part is directly heated because eddy currents can be generated only in the sheet metal part by induction. In contrast, the plastic part is indirectly heated by the metal part, and in particular the surface of the plastic part in contact with the metal part is melted, but it is not necessary to melt the entire surface of the plastic part.

[0004] High processing speed and high volume are typically required in the manufacture of can lids. Furthermore, can lid manufacturing is subject to strong price pressure. However, fast pressurization sequences are often accompanied by reduced reliability of the bonding process. In particular, insufficient bonding strength can lead to unwanted large amounts of waste. The subsequent disposal of defective can lids is undesirable due to the associated costs.

[0005] The objective of this invention is to enable the more reliable manufacture of can lids by simple means.

[0006] This objective is satisfied by an apparatus having the features described in claim 1 of this application.

[0007] According to the present invention, a temperature control device is provided, which is configured to transport a temperature-controlling fluid through the fluid path in order to stabilize the temperature of the press, with a fluid path formed in at least one of the press tools.

[0008] The temperature control device maintains the press temperature at a nearly constant level, thereby preventing gradual heating of the press tool by the heated can lid parts. In the apparatus of the present invention, press temperature drift due to heat conduction is prevented, and consistent conditions are guaranteed along with a long service life and high-speed press sequences. Process safety is significantly improved in this embodiment. Waste generated in the manufacture of can lids from composite materials can be significantly reduced or almost completely eliminated by the means of the present invention.

[0009] Fluid pathways may be formed in each of the press tools as needed, and a temperature control device is configured to transport temperature-regulating fluid through each of the fluid pathways to stabilize the press temperature.

[0010] The can lid part is preferably formed from aluminum or tin sheet. The plastic part may be a plastic film, preferably a polypropylene or polyethylene terephthalate film. According to the apparatus of the present invention, multiple different plastic parts can be coupled with one or the same metal part.

[0011] The press tool is preferably made of a high-temperature resistant plastic, particularly polyetherketone (PEK).

[0012] The temperature-regulating fluid is preferably a liquid, such as water. However, in principle, a gas can also be provided as the temperature-regulating fluid.

[0013] One press tool may have a shape complementary to one side of the can lid, and the other press tool may have a shape complementary to the other side of the can lid.

[0014] Inductors can be configured for electromagnetic field frequencies from 1 kHz to 100 kHz, particularly around 20 kHz.

[0015] The apparatus of the present invention may be configured for manufacturing a can lid having a can lid part made of sheet metal and a plurality of plastic parts joined to the can lid part. Thus, two press tools that can be joined together can form a press that presses the can lid part and the plurality of plastic parts together. Then, during induction heating, and especially simultaneously, the can lid part can be joined to all of the pressurized plurality of plastic parts. In principle, according to the apparatus of the present invention, a plurality of can lid parts made of sheet metal and one or more plastic parts can be joined.

[0016] The temperature control device may also include a cooling device for cooling the temperature-controlled fluid, a heating device for heating the temperature-controlled fluid, and / or a fluid pump with adjustable flow rate. Thus, the temperature control device can perform both heating and cooling functions of the press, if necessary. The press temperature can be changed relatively quickly and easily by the amount of temperature-controlled fluid conveyed through the fluid passage per unit of time.

[0017] The temperature control device preferably includes an electronic control device configured to adjust or control the temperature of the temperature-regulating fluid and / or press according to a predetermined value. This allows for particularly precise and continuous temperature control. The electronic control device may, in particular, be configured to continuously maintain the temperature of the temperature-regulating fluid and / or press at room temperature during the operation of the device.

[0018] The inductor is positioned on the outer surface of one of the press tools, preferably forming a gap or void. The press tool does not need to support the inductor in a complex manner. In a preferred embodiment, the inductor is positioned on the outer surface opposite to the receiving area of ​​the can lid.

[0019] The fluid passage is preferably formed on the outer surface where the inductor is located within the press tool. This allows for particularly effective temperature control.

[0020] In one embodiment of the present invention, at least one press tool is formed from two tool parts joined together, with a fluid passage formed between the joined parts. Such a press tool is relatively simple and inexpensive to manufacture because the fluid passage only needs to be formed as a single recess or as an array of opposing recesses, and does not need to be formed as a hole, for example. However, press tools with fluid passages can usually be designed as a single part, for example, as a 3D printed component.

[0021] These tool parts can be bonded together with adhesive to ensure leak-free airtightness of the fluid passage.

[0022] Alternatively or additionally, tool parts are joined in a manner that they interlock with each other via projections and associated receiving parts, ensuring high strength. A special advantage of interlocking joints is that adhesive is unnecessary or minimal. Furthermore, interlocking joints provide emergency airtightness in the event of adhesive failure.

[0023] The projection and the receiving part may each have a dovetail-like cross-section. This results in an undercutting engagement with a correspondingly high joint strength.

[0024] According to embodiments of the present invention, a projection enters and engages with a receiver while forming a free space, and the free space is at least partially filled with a sealant and / or adhesive. A separation layer consisting of a sealant and / or adhesive between the two tool parts is not essential.

[0025] By having a fluid passage that at least partially forms a helical path, uniform and area-specific temperature control can be achieved for each tool part. The rounded contact surface of the tool part with the helically extending fluid passage can, in particular, be completely and uniformly covered.

[0026] In another embodiment of the present invention, the inductor includes stranded wire, such as stranded copper wire. In this respect, the cross-section of the individual conductors is sized such that only small eddy currents are generated by a transverse magnetic field. When the above-mentioned temperature control device is present, it is not essential to have a water-cooled waveguide as an inductor, and the advantages of stranded wire can be utilized. However, typically, the inductor can be designed as a waveguide and can itself form a fluid path.

[0027] The inductor may have a central section extending within the base plane, particularly a helical central section, and at least one peripheral section offset from the base plane, particularly an annular peripheral section. According to a particular embodiment of the present invention, the peripheral section is positioned around a can lid placed in a press. This allows heating to the can lid part from both the planar side and the periphery, which enables a particularly rapid and uniform heating process.

[0028] The present invention relates to a method for manufacturing a can lid having a can lid part formed of sheet metal and at least one plastic part coupled to the can lid part, wherein the can lid part and the plastic part are pressed together between two press tools, and an alternating electromagnetic field is supplied to the pressing area by an inductor while being pressed together, heating the can lid part, thereby coupling the can lid part to the pressed plastic part.

[0029] The above object is achieved by a method in which at least one temperature of the press tool is stabilized by the conveyance of a temperature-regulating fluid passing through a fluid passage formed in the press tool.

[0030] The method according to the present invention may have method steps resulting from the features specified in the above description in association with the device.

[0031] Preferably, the can lid part and / or the plastic part is coated with an adhesive before being joined. Thereby, the stability of the joint is improved. This adhesive preferably contains the same plastic as the plastic part connected to the can lid part. Particularly good adhesion and a particularly firm bond are brought about.

[0032] Furthermore, the development of the present invention can be understood from the dependent claims, the specification and the attached drawings.

[0033] The present invention will be described below for illustrative purposes with reference to the drawings.

Brief Description of the Drawings

[0034] [Figure 1] It is a simplified cross-sectional perspective view of an apparatus according to the present invention for manufacturing a can lid. [Figure 2] It is a cross-sectional view of the press tool and the inductor of the apparatus shown in FIG. 1 [Figure 3] It is a partially enlarged view of the press tool shown in FIG. 2. [Figure 4] It is a plan view of the configuration of FIG. 2. [Figure 5] This is a partial cross-sectional view of a can lid manufactured by the apparatus shown in Figure 1. [Modes for carrying out the invention]

[0035] The apparatus shown in Figure 1, designed according to an embodiment of the present invention for manufacturing can lids, includes a press apparatus 11 having a lower rack 12 and an upper press part 13 that are movable relative to each other. The upper press part 13 is guided linearly in the lower rack by a guide cylinder 14. Each of the press tools 15, 16, formed of polyetherketone to form an opening and closing press 20, is mounted on the lower rack 12 and the upper press part 13. The press tool 15 mounted on the lower rack 12 has a cavity 17 that receives the closure element 18 (Figure 5) of the can lid 19. Furthermore, the press tool 15 mounted on the lower rack 12 is molded to the shape of the upper side of the can lid 19. The press tool 16 mounted on the upper press part 13 is molded to the lower side of the can lid 19.

[0036] The inductor 21 located in the area of ​​the press device 11 is configured in a well-known manner to supply an alternating magnetic field. This alternating magnetic field preferably has a frequency in the range of 1 kHz to 100 kHz in the area of ​​the press 20.

[0037] Furthermore, the temperature control device 25, shown only schematically, is located within the area of ​​the press device 11 and is configured to transport water or a similar temperature control fluid via a line configuration 27 that passes through a fluid path 29, which can be seen in Figures 2 and 3. The fluid path 29 preferably has a helical path. The temperature control device 25 includes a cooling device and a controllable pump, which are not shown in detail in Figure 1. In addition, the temperature control device 25 has an electronic control device 30 suitable for temperature adjustment or temperature control.

[0038] As can be seen particularly in Figure 3, the upper press tool 16 is formed by a lower tool part 31 and an upper tool part 32 that are joined together. The fluid path 29 is formed between the joined tool parts 31 and 32. The two parts 31 and 32 are bonded to each other and additionally connected in a form-fitting manner, as will be described in detail below.

[0039] The projection 35, having a dovetail-like cross-sectional shape, is located on the underside of the upper tool part 32 and engages with a reciprocally shaped receiver 37 located on the upper side of the lower tool part 31, as shown in the figure. As shown, because the projection 35 is narrower than the receiver 37, free space 39 is formed on both sides of the projection 35. The adhesive 41 for bonding the tool parts 31 and 32 is introduced into the free space 39. The reciprocal engagement of the projection 35 into the receiver 37 assists in the adhesive connection.

[0040] According to Figure 3, the receiver 37 is formed by recesses separated from each other by dovetail-like intermediate regions 40 of the lower tool part 31. Thus, the dovetail-like projections 35 alternate with the dovetail-like intermediate regions 40.

[0041] The shape of the inductor 21 in the end region on the press side is shown in Figure 2. The transmission of the AC electromagnetic field does not occur via the waveguide, but preferably via stranded copper wire 43 having multiple individual conductors. The inductor 21 is positioned above the upper press tool 16, forming a gap 45, and is preferably bonded to or molded to the upper press tool 16. Furthermore, the surface shape of the inductor 21 is adapted to the outer shape of the upper press tool 16. The inductor 21 has, in particular, a central section 47 that extends helically within the base plane 49. The annular peripheral section 51 of the inductor 21 is positioned offset from the base plane 49 and around the contact surface 53 provided for the can lid 19 (Figure 5). The annular peripheral section 51 consists of multiple individual windings 55, as shown. The helical path of the central section 47 can be seen in the plan view of Figure 4.

[0042] The can lid 19, partially shown in Figure 5, includes a base 64 made of sheet metal, particularly aluminum or tin sheet. The base 64 includes a fixed metal end region 65 and an upwardly rotatable opening section 8. The lower side of the can lid 19 is laminated with a plastic film 67. In contrast, a closure element 18, consisting of a sealing frame 69 and a closure unit 70, is located on the upper side of the can lid 19. The sealing frame 69 is connected to the fixed end region 65, and the closure unit 70 is connected to the upwardly rotatable opening section 66.

[0043] The method according to the present invention can be used to manufacture a can lid 9 shown in Figure 4 using the apparatus shown in Figure 1. For this purpose, a closure element 18 made of plastic is placed in a lower press tool 15 with the side facing the can lid 19 facing upward. A base 64 with a plastic film 67 attached to its underside is placed on the closure element 18. Then, the press 20 is closed to activate the inductor 21.

[0044] Due to eddy currents within the material, the substrate 64 is heated to, for example, about 200 degrees Celsius. The heated substrate 64 heats the plastic film 67 and the closure element 18, causing them to partially melt. This results in a plastic weld connection, on the one hand between the substrate 64 and the plastic film 67, and on the other hand between the substrate 64 and the closure element 18. To improve the plastic weld connection, an adhesive may be used, preferably containing the same plastic as the plastic film 67 or the closure element 18. After the molten bonding of the plastic film 67 and the closure element 18 to the metal substrate 64 has occurred, the press 20 opens and the completed can lid 19 is removed.

[0045] During the operation of the press 20, a temperature control device 25 (Figure 1) ensures that the temperature of the press tools 15 and 16 remains stable. For this purpose, the temperature control device 25 pumps water through a fluid passage 29 in the upper press tool 16, which is connected to the line configuration 27. In this way, the temperature control device 25 maintains the temperature of the press 20 at approximately room temperature, thereby preventing the press tools 15 and 16 from gradually overheating due to the heated substrate. This improves process safety as much as possible. If extended temperature control performance is required, an additional fluid passage may be formed in the lower press tool 15 through which water is similarly pumped. Furthermore, the inductor 21 may be designed as a waveguide and may be water-cooled. [Explanation of symbols]

[0046] 11 Pressing device 12 Lower rack 13 Upper press parts 14 Guide Cylinder 15 Lower Press Tool 16 Upper press tool 17 Cavity 18 Closure Elements 19 Can lid 20 Press 21 Inductors 25 Temperature adjustment device 27-line configuration 29 Fluid passage 30 Electronic control devices 31 Lower tool parts 32 Upper Tool Parts 35 Protrusion 37 Receiving 39 Free space 40 Intermediate area 41 Adhesive 43. Stranded copper wire 45 gap 47 Central Section 57 Base plane 51 Peripheral Section 53 Contact surfaces 55 Single winding 64 Base 65 Fixed end region 66 Opening section 67 Plastic film 69. Sealing Frame 70 Closure Units

Claims

1. An apparatus for manufacturing a can lid (19) having a can lid part (64) made of sheet metal and at least one plastic part (18, 67) connected to the can lid part (64), wherein the apparatus is Two press tools (15, 16) that join together to form a press (20) for pressurizing and forming the can lid part (64) and the plastic parts (18, 67), The system includes an inductor (21) that induces heating of the can lid part (64) by introducing an alternating electromagnetic field into the space between the two press tools (15, 16), thereby joining the can lid part (64) and the pressurized plastic parts (18, 67), The inductor (21) is disposed on the outer surface of one of the two press tools (15, 16), and the one press tool is made of an insulator. The apparatus is characterized in that a fluid passage (29) is formed in at least one of the press tools (15, 16), and a temperature control device (25) is provided which is configured to transport a temperature control fluid through the fluid passage (29) to stabilize the temperature of the press (20).

2. The apparatus according to claim 1, characterized in that the temperature control device (25) has a cooling device for cooling the temperature control fluid, a heating device for heating the temperature control fluid, and / or a fluid pump capable of adjusting the amount of fluid being transported.

3. The apparatus according to claim 1 or 2, characterized in that the temperature control device (25) has an electronic control device (30) configured to adjust or control the temperature of the temperature control fluid and / or press (20) according to a predetermined value.

4. The apparatus according to claim 1, characterized in that the inductor (21) is arranged on the outer surface of the one press tool to form a gap (45).

5. The apparatus according to claim 1, characterized in that the fluid passage (29) is formed within one press tool on which the inductor (21) is arranged on the outer surface.

6. The apparatus according to claim 1, characterized in that at least one of the press tools (15, 16) is formed by two tool parts (31, 32) joined together, and the fluid passage (29) is formed between the two tool parts (31, 32) joined together.

7. The apparatus according to claim 6, characterized in that the tool parts (31, 32) are bonded to each other.

8. The apparatus according to claim 6 or 7, characterized in that the tool parts (31, 32) are connected to each other in an interlocking manner via a projection (35) and associated receiver (37).

9. The apparatus according to claim 8, characterized in that the projection (35) and the receiver (37) each have a dovetail-like cross-sectional shape.

10. The apparatus according to claim 8, characterized in that the projection (35) engages with the receiver (37) while forming a free space (39), and the free space (39) is at least partially filled with a sealing material and / or adhesive material (41).

11. The apparatus according to claim 1, characterized in that the fluid passage (29) has a helical path at least locally.

12. The apparatus according to claim 1, characterized in that the inductor (21) includes stranded wire (43).

13. The apparatus according to claim 1, characterized in that the inductor (21) has a central section (47), particularly a helical central section (47), that extends within a base plane (49), and has at least one peripheral section (51), particularly an annular peripheral section (51), that is offset from the base plane (49).

14. The apparatus according to claim 13, characterized in that the surrounding section (51) is arranged around a can lid (19) disposed within the press (20).

15. A method for manufacturing a can lid (19), The steps include preparing a can lid part (64) made of sheet metal and at least one plastic part (18, 67), The step includes joining the plastic parts (18, 67) to the can lid part (64), In the joining step, the can lid part (64) and the plastic parts (18, 67) are pressed together between two press tools (15, 16) that form a press (20). While they are being pressed together, an alternating current electromagnetic field is supplied by an inductor to the space between the two press tools (15, 16), heating the can lid part (64), thereby bonding the can lid part (64) to the pressurized plastic parts (18, 67). The inductor (21) is disposed on the outer surface of one of the two press tools (15, 16), and the one press tool is made of an insulator. A manufacturing method characterized in that the temperature of at least one of the press tools (15, 16) is stabilized by conveying a temperature-regulating fluid through a fluid passage (29) formed within the press tool (15, 16).

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