Can lid and method for manufacturing the same

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 can ends having a can end part made of sheet metal and at least one plastic part connected to said can end part, said apparatus comprising: two press tools which come together to form a press for pressing said can end part and said plastic part together; and an inductor for inductively heating the can end part by providing an alternating electromagnetic field in the pressure forming region, thereby bonding the can end part and the pressed plastic part.

[0002] Can lids for beverage cans, food cans, etc. usually have an opening section that can be moved by a tear-open member fixed to the can lid outside the can plane to open the can. Reclosable can lids are also known in which a sealing frame made of plastic material, connected to the metal can lid surface and surrounding the opening area cooperates with a closure unit made of plastic material and connected to the metal opening section. Furthermore, the can lid can be laminated with a plastic film, which covers in a sealing manner, for example, the microgaps. A very stable connection of the sealing frame, the closure unit, the film and other plastic parts with the metal can lid part can be achieved by pressure forming and heating.

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

[0004] Usually, high throughput rates and high volumes are required in the production of can ends. Furthermore, the production of can ends is subject to strong price pressure. However, fast pressing sequences are often accompanied by a decrease in the reliability of the bonding process. In particular, insufficient bond strength can lead to the generation of large amounts of unwanted waste. Subsequent disposal of defective can ends is undesirable due to the associated costs.

[0005] The object of the invention is to enable a more reliable production of can ends by simple means.

[0006] This object is met by a device having the features of claim 1.

[0007] According to the invention, a fluid pathway is formed in at least one of the press tools and a temperature conditioning device is provided configured to convey a temperature regulating fluid through the fluid pathway to stabilize the temperature of the press.

[0008] The temperature regulation device keeps the temperature of the press approximately constant, thereby preventing gradual heating of the press tool by the heated end parts. In the device of the invention, temperature drifts of the press due to heat conduction are prevented and constant conditions are guaranteed with long periods of use and fast pressing sequences. The safety of the process is significantly increased in this manner. Waste in the manufacture of composite can ends can be significantly reduced or almost completely eliminated by the means of the invention.

[0009] Fluid paths may be formed in each of the press tools as desired, with a temperature conditioning device configured to deliver a temperature conditioning fluid through each of the fluid paths to stabilize the temperature of the press.

[0010] The can lid part is preferably made of aluminum or tin plate. The plastic part can in particular be a plastic film, preferably a polypropylene or polyethylene terephthalate film. With the device of the invention it is possible to combine several different plastic parts with one or the same metal part.

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

[0012] The temperature regulating fluid is preferably a liquid, for example water, but in principle a gas can also be provided as the temperature regulating fluid.

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

[0014] The inductor may be configured for an electromagnetic field frequency of 1 kHz to 100 kHz, particularly around 20 kHz.

[0015] The inventive device can be configured for the production of can ends having a can end part made of sheet metal and a number of plastic parts joined to the can end part. Thus, two press tools, which can be attached to each other, can form a press for pressing the can end part and the number of plastic parts together. Then, during induction heating, the can end part can be joined with all of the pressed number of plastic parts, in particular simultaneously. In principle, the inventive device can be used to join a number of can end parts made of sheet metal with one or more plastic parts.

[0016] The temperature conditioning device may also comprise a cooling device for cooling the temperature conditioning fluid, a heating device for heating the temperature conditioning fluid and / or a fluid pump with an adjustable delivery rate. The temperature conditioning device may thus both heat and cool the press, if required. The temperature of the press can be changed relatively quickly and easily by the amount of temperature conditioning fluid delivered through the fluid passages per unit of time.

[0017] The temperature regulation apparatus preferably comprises an electronic control device configured to regulate or control the temperature of the temperature regulation fluid and / or the press according to predefined values, which allows particularly precise and continuous temperature regulation. This electronic control device may in particular be configured to continuously maintain the temperature of the temperature regulation fluid and / or the press at room temperature during operation of the apparatus.

[0018] The inductor is arranged on an outer surface of one of the press tools, preferably forming a clearance or gap, and there is no need to receive the inductor in a complicated manner in one of the press tools. In a preferred embodiment, the inductor is arranged on an outer surface that is arranged opposite the receiving area of ​​the can lid.

[0019] The fluid passages are preferably formed in the outer surface of the press tool on which the inductor is arranged, which allows for particularly effective temperature control.

[0020] In one embodiment of the invention, at least one of the press tools is formed by two tool parts bonded together, with the fluid passages being formed between the bonded parts. Such a press tool is relatively simple and inexpensive to manufacture, since the fluid passages only need to be formed as a recess or an array of opposing recesses, and not as holes, for example. However, typically, the press tool with the fluid passages can be designed in one piece, for example as a 3D printed component.

[0021] The tool parts may be adhesively bonded together to ensure leak tightness of the fluid passages.

[0022] Alternatively or additionally, the tool parts can be joined to one another in a mating manner via projections and associated receivers to ensure high strength. A particular advantage of mating joints is that no or less adhesive is required. Furthermore, mating joints provide emergency tightness in the event of adhesive failure.

[0023] The projection and receiver may each have a dovetail-like cross-section, which provides an undercutting engagement with a correspondingly high bond strength.

[0024] According to an embodiment of the invention, the protrusion enters and engages in the receptacle forming a free space, which is at least partially filled with a seal and / or adhesive. A separating layer consisting of a seal and / or adhesive between the two tool parts is not essential.

[0025] In that the fluid passage at least partially has a helical path, a uniform and areal temperature control of each of the tool parts is achieved. The rounded contact surfaces of the tool parts with the helically extending fluid passage can in particular be completely and uniformly covered.

[0026] In another embodiment of the invention, the inductor comprises a strand, for example a strand of copper. In this respect, the cross section of the individual conductors is dimensioned such that only small eddy currents are generated by the transverse magnetic field. In the presence of the above-mentioned temperature regulation device, it is not essential to provide a water-cooled waveguide as the inductor, and the advantages of the strand can be used. However, in general, the inductor can be designed as a waveguide and can itself form a fluid path.

[0027] The inductor may have a central section, in particular a helical central section, extending in a ground plane and at least one peripheral section, in particular an annular peripheral section, offset from the ground plane. According to a particular embodiment of the invention, the peripheral section is arranged around the can end arranged in the press. This allows heating of the can end part from the planar side and from the periphery, which allows a particularly fast and uniform heating process.

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

[0029] The above objects are achieved by a method in which the temperature of at least one of the press tools is stabilized by conveying a temperature regulating fluid through a fluid passage formed within the press tool.

[0030] The method according to the invention may comprise method steps resulting from the features specified in the above description associated with the apparatus.

[0031] The can lid part and / or the plastic part are preferably coated with an adhesive before being bonded, thereby improving the stability of the bond. The adhesive preferably comprises the same plastic as the plastic part to be connected to the can lid part. A particularly good adhesion and a particularly firm bond are obtained.

[0032] Further developments of the invention can be seen from the dependent claims, the description and the accompanying drawings.

[0033] The invention will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0034] [Figure 1] 1 is a simplified cross-sectional perspective view of an apparatus according to the invention for producing can ends; [Diagram 2] FIG. 2 is a cross-sectional view of the press tool and inductor of the apparatus shown in FIG. [Diagram 3] FIG. 3 is a partial enlarged view of the press tool shown in FIG. 2. [Figure 4] FIG. 3 is a plan view of the configuration of FIG. 2. [Diagram 5] 2 is a partial cross-sectional view of a can lid manufactured by the apparatus shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The apparatus shown in Fig. 1, designed according to an embodiment of the invention for producing can ends, comprises a press device 11 having a lower rack 12 and an upper press part 13 movable relative to each other. The upper press part 13 is linearly and movably guided in the lower rack by a guide cylinder 14. Attached to the lower rack 12 and to the upper press part 13 are press tools 15, 16, each made of polyetherketone, forming an opening and closing press 20. The press tool 15 attached to the lower rack 12 has a cavity 17 for receiving a closure element 18 (Fig. 5) of a can end 19. Furthermore, the press tool 15 attached to the lower rack 12 is molded to the shape of the upper side of the can end 19. The press tool 16 attached to the upper press part 13 is molded to the underside of the can end 19.

[0036] An inductor 21 arranged in the area of ​​the press 11 is constructed in a known manner to provide an alternating magnetic field, which preferably has a frequency in the range of 1 kHz to 100 kHz in the area of ​​the press 20.

[0037] Furthermore, a temperature regulation device 25, shown only diagrammatically, is arranged in the region of the pressing device 11 and is arranged to convey water or a similar temperature regulation fluid via a line arrangement 27 through a fluid path 29 formed in the upper pressing tool 16 and visible in Figures 2 and 3. The fluid path 29 preferably has a spiral path. The temperature regulation device 25 comprises a cooling device and a controllable pump, which are not shown in detail in Figure 1. Furthermore, the temperature regulation device 25 has an electronic control device 30, which is suitable for temperature regulation 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 which are joined together. A fluid passage 29 is formed between the joined tool parts 31, 32. The two parts 31, 32 are bonded together and are additionally connected in a form-fitting manner as will be explained in more detail below.

[0039] A projection 35 having a dovetail-like cross-sectional shape is provided on the underside of the upper tool part 32 and, as shown, engages in a reciprocally shaped receiver 37 provided on the upper side of the lower tool part 31. As shown, the projection 35 has a narrower width than the receiver 37, so that free spaces 39 are formed on either side of the projection 35. An adhesive 41 for bonding the tool parts 31, 32 is introduced into the free spaces 39. The mating engagement of the projection 35 in the receiver 37 aids in the adhesive connection.

[0040] 3, the receivers 37 are formed by recesses which are separated from one another by dovetail-like intermediate regions 40 in 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 FIG. 2. The transmission of the alternating electromagnetic field does not take place via a waveguide, but preferably via a copper strand 43 with a number of individual conductors. The inductor 21 is arranged above the upper press tool 16, forming a gap 45, and is preferably glued or molded thereto. Furthermore, the surface shape of the inductor 21 is adapted to the contour of the upper press tool 16. The inductor 21 has in particular a central section 47 which extends in a spiral manner in a ground plane 49. An annular peripheral section 51 of the inductor 21 is arranged offset from the ground plane 49 and is arranged around a contact surface 53 intended for the can lid 19 (FIG. 5). The annular peripheral section 51 is composed of a number of individual windings 55, as shown. The spiral path of the central section 47 can be seen in the plan view of FIG. 4.

[0042] The can lid 19, partially shown in Fig. 5, comprises a base body 64 made of sheet metal, in particular aluminium or tin sheet. The base body 64 comprises a fixed metal end region 65 and an upwardly pivotable opening section 8. The underside 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 arranged 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 pivotable opening section 66.

[0043] The method according to the invention can be used to manufacture the can lids 9 shown in Figure 4 with the apparatus shown in Figure 1. For this purpose, a closure element 18 made of plastic is placed in the lower press tool 15 with the face facing the can lid 19 facing upwards. A substrate 64, with a plastic film 67 pre-applied on its underside, is placed on the closure element 18. The press 20 is then closed and the inductor 21 is activated.

[0044] Due to eddy currents in the material, the substrate 64 is heated, for example to about 200° C. The heated substrate 64 heats the plastic film 67 and the closure element 18, which then partially melts. This results in a plastic weld connection between the substrate 64 and the plastic film 67 on the one hand, and between the substrate 64 and the closure element 18 on the other hand. To improve the plastic weld connection, an adhesive can be used, which preferably comprises the same plastic as the plastic film 67 or the closure element 18. After the melt connection of the plastic film 67 and the closure element 18 to the metal substrate 64 has occurred, the press 20 is opened and the finished can end 19 is removed.

[0045] During operation of the press 20, a temperature regulating device 25 (FIG. 1) ensures that the temperature of the press tools 15, 16 is stable. For this purpose, water is pumped by the temperature regulating device 25 through a fluid passage 29 of the upper press tool 16 connected to a line arrangement 27. In this way, the temperature regulating device 25 maintains the temperature of the press 20 approximately at room temperature, thereby preventing a gradual heating of the press tools 15, 16 by the heated substrate. This increases the safety of the process as much as possible. If extended temperature regulating capabilities are required, additional fluid passages may be formed in the lower press tool 15, through which water is likewise pumped. Furthermore, the inductor 21 may be designed as a waveguide and may be water-cooled. [Explanation of symbols]

[0046] 11 Press equipment 12 Lower Rack 13 Upper press part 14 Guide cylinder 15 Lower Press Tool 16 Upper Press Tool 17 Cavity 18 Closure Elements 19 Can Lids 20 Press 21 Inductor 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 Reception 39 Free space 40 Intermediate area 41 Adhesive 43 Copper stranded 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 Unit

Claims

1. 1. An apparatus for manufacturing can lids (19) having a can lid part (64) made of sheet metal and at least one plastic part (18, 67) connected to said can lid part (64), said apparatus comprising: two press tools (15, 16) that come together to form a press (20) for pressing together said can lid part (64) and said plastic part (18, 67); an inductor (21) for inductively heating the can lid part (64) by applying an alternating electromagnetic field in the area of ​​the press (20) and thereby joining the can lid part (64) and the pressed plastic part (18, 67); a fluid passage (29) is formed in at least one of the press tools (15, 16), and a temperature regulating device (25) is provided configured to convey a temperature regulating fluid through the fluid passage (29) to stabilize the temperature of the press (20).

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

3. 3. The apparatus according to claim 1 or 2, characterized in that the temperature regulating device (25) comprises an electronic control device (30) configured to regulate or control the temperature of the temperature regulating fluid and / or the press (20) according to predefined values.

4. 4. The device according to claim 1, wherein the inductor (21) is arranged on an outer surface of one of the press tools (15, 16), preferably forming a gap (45).

5. 5. The device according to claim 4, characterized in that the fluid path (29) is formed in a press tool (15, 16) on whose outer surface the inductor (21) is arranged.

6. 6. An apparatus according to claim 1, wherein at least one of the press tools (15, 16) is formed by two tool parts (31, 32) joined to one another, and the fluid path (29) is formed between the two tool parts (31, 32) joined to one another.

7. 7. Apparatus according to claim 6, characterized in that the tool parts (31, 32) are glued together.

8. 8. Device according to claim 6 or 7, characterized in that the tool parts (31, 32) are connected to one another in a mating manner via projections (35) and associated receivers (37).

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

10. 10. The device according to claim 8 or 9, characterized in that the projection (35) engages in the receiver (37) while forming a free space (39), the free space (39) being at least partially filled with a sealant and / or adhesive material (41).

11. 11. Apparatus according to any one of the preceding claims, characterized in that the fluid passage (29) has at least locally a helical path.

12. 12. The device according to any one of the preceding claims, characterized in that the inductor (21) comprises a stranded wire (43).

13. 13. The device according to claim 1, wherein the inductor (21) has a central section (47) extending in a ground plane (49), in particular a helical central section (47), and at least one peripheral section (51), in particular an annular peripheral section (51), offset from the ground plane (49).

14. 14. Apparatus according to claim 13, characterized in that the peripheral section (51) is arranged around a can lid (19) arranged in the press (20).

15. 1. A method for manufacturing a can lid (19) having a can lid part (64) formed of sheet metal and at least one plastic part (18, 67) joined to the can lid part (64), comprising the steps of: The can lid part (64) and the plastic part (18, 67) are pressed together between two press tools (15, 16), While pressed together, an inductor applies an alternating electromagnetic field to the area of ​​the press (20) to heat the can lid part (64), thereby bonding the can lid part (64) to the pressed plastic parts (18, 67); 10. An apparatus according to claim 9, wherein the temperature of at least one of said press tools (15, 16) is stabilized by conveying a temperature regulating fluid through a fluid path (29) formed in said press tools (15, 16).

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