NO151732B - DEVICE FOR FITTING A LINING TO METAL CAPS - Google Patents

Description

The present invention relates to a device for fastening

of a lining for metal capsules, the lining consisting of an inner lining layer of thermoplastic resin which is attached to the inner wall of the bottom of the metal capsule, an induction heating device consisting of a high-frequency current generator and a high-frequency heating coil of electrical conductors lying next to it of each other with opposite current flows, a transport device which transports the metal capsule through the induction heating device, a supply device for the thermoplastic resin for the inner surface of the metal capsule and a device for fixing the inner lining layer in the metal capsule by thermal adhesion.

The metal capsules according to the present invention can be screw lids or crown caps as well as burglar-proof closures, as the metal capsules are produced by a deep-drawing process from a metal plate and possibly subjected to a thread forming process, and the inner lining layer is connected to the bottom of the metal capsule by means of heat to form a seal.

The material for the production of such metal capsules can be

be made of plates of non-magnetic metal such as aluminum or aluminum alloys (which for the sake of simplicity will be referred to below as aluminium), of copper or brass, or plates of ferromagnetic metals such as e.g. low carbon steel.

Until now, such metal capsules that serve to close containers such as e.g. bottles, provided with a sealing inner lining of cork or thermoplastic resin such as vinyl chloride, polyethylene or mixtures thereof,

as the use of the latter material is constantly increasing. For the thermal connection of the inner lining with the inner surface of the metal capsule bottom, the inside of the bottom is usually provided with an adhesive primer material, and the inner lining layer is attached, while the metal capsule bottom before or after the application of the inner lining layer is heated to approx. 10 0 to 200°C.

A device of the type indicated at the outset is e.g. known from Japanese OS No. 47-41 398, where the metal capsules transported on a conveyor are heated by

of a high-frequency heating coil having a hairpin shape

and is arranged under the conveyor. However, it has been found by experiments carried out by the applicant that such an induction heating device is indeed capable of

in an efficient way to heat metal capsules of ferromagnetic material, because a concentration of the magnetic flux is thereby possible, while this is not the case at least with metal capsules of non-magnetic material such as e.g. aluminum. Since the conveyor, which has a considerable thickness, is placed between the high-frequency heating coil and the metal capsule, the mutual induction coefficient is given such a low value that the temperature in the metal capsule can be raised little. In the case, in order to increase the mutual induction coefficient, the thickness of the conveyor is reduced to an impractical extent to thereby make the high-frequency heating coil and the metal capsule approach each other, these metal capsules will float and jump on the conveyor, so that the heating process is impossible. The jumping is caused by the repulsions generated by the interaction of the induced current, which is induced in and adjacent to the bottom of the aluminum capsule, and the magnetic field from the high-frequency heating coil. Metal sleeves of ferromagnetic material are generally magnetized by the magnetic field induced from the high-frequency current so that an attractive force is produced which acts in the direction of the high-frequency heating coil. In this case, the attractive force is stronger than the repulsive force originating from the induced current, so normally no jumping of the metal capsule occurs, although it is not guaranteed in all cases. Experience has shown that metal capsules of ferromagnetic material such as white tin also jump or float, depending on various conditions determined by the weight, size and shape of the metal capsules, the intensity and frequency of the flux at the high-frequency heating coil and the distance between the bottom of the metal capsule and the high-frequency heating coil.

In addition, from Japanese OS No. 41-5588 a device is known for attaching a seal in metal capsules, especially crown caps, which usually consist of a ferromagnetic material such as white tin or tin-free steel plates.

According to the device described there, the metal capsules are heated during transport using hot air to approx. 160°C, with their extensions being placed in the recessed protrusions formed over a number of grooves formed at a distance along the circumference of a turntable. On the one hand, the heating process lasts quite a long time due to the use of hot air so that the device cannot be compactly designed, because an elongated heating station is necessary for heating at a high working speed of approx. 1000 subjects per minute. On the other hand, there is a problem that the edges of the metal capsules are also heated, which is both unnecessary and energy-consuming.

According to the device of the type mentioned at the outset, the purpose of the present invention is to provide a device for fixing the lining in metal capsules, the lining consisting of an inner lining layer of thermoplastic resin which is attached to the inner wall of the bottom of the metal capsule, achieving an improved and uniform heating of the metal capsule without there being a risk of an edge forming and the transport will be inhibited so that no dead time occurs.

According to the invention, this task is solved in that the conductors' distance varies and that a guide wall opposite the conductors and the bearing of the high-frequency heating coil is arranged as a lower guide.

Further features of the device according to the invention are specified in the subclaims.

The device according to the invention is equally suitable for non-magnetic as for ferromagnetic material for the metal capsules. With the device according to the invention, a very good and uniform heating of the metal capsules can advantageously be achieved, as the jumping that occurs due to the interaction of the high-frequency current and the induction current due to the repulsive force is compensated in a suitable way so that no edge formation in the metal capsules, but is heated evenly and production at a high working speed is made possible.

In the following, the invention will be described in more detail with the help of non-implementation examples. Fig. 1 shows a top plan diagram which schematically shows an induction heating device for continuous heating of aluminum metal capsules in connection with the assigned pre- and post-treatment stations. Fig. 2 shows an enlarged vertical view along a line II-II in fig. 1. Fig.3 is a perspective view schematically showing the bottom of a metal capsule and the conductors for the high-frequency heating coils arranged near the bottom. Fig. 4 is a graphical representation of the relationship between the distance between the bottom of the metal capsule and the heating coil on the one hand and the temperature rise (in a relative value) in the bottom on the other hand. Fig. 5 is a top plan view schematically showing a second embodiment of the continuous induction heating device. Fig. 6 a partially enlarged front vertical view of the heating device according to fig. 5.

Fig. 7 is a section along the line VII-VII in fig. 6.

Fig. 8 is a schematic top plan view of a further embodiment of the device. Fig. 9 is a schematic top plan view of a heating device where a horizontal guide wall is itself moved to transport the metal capsules.

Fig. 10 is a section along the line X-X in fig. 9.

Fig. 11 is a top plan view schematically showing a conductor arrangement of the heating coil. Fig. 12 to 15 schematically show conductor arrangements of the heating coils modified in relation to fig. 11. Fig. 16 shows a further embodiment of the heating coil as shown in fig. 11. Fig. 17 is an enlarged cross-section along the line XVIII-XVIII in fig. 16. Fig. 18 is a vertical cross-section similar to fig. 17, showing the relationship between the heating coil and a ferrite core according to a further embodiment. Fig. 19 shows a vertical cross-section of the device and the construction of a heating coil and a metal capsule according to a further embodiment. Fig. 20 is an enlarged cross-sectional view showing a significant part of the device according to fig. 19. Fig. 21 is a circuit diagram showing the potential differences in the electrical conductors in fig. 19, and

fig. 22 is a further embodiment of fig. 20.

In fig. 1 shows a first embodiment of the present invention, where a turntable 2 which acts as a conveyor for a series of metal capsules 5 is provided at its circumference with a number of semi-circular grooves 3 so that the metal capsules which are emptied from a shaft 4 are loaded one by one into the semi-circular grooves 3 upside down, i.e. with the bottom 5b downwards. The metal capsules 5 are guided in the direction of rotation by the turntable 2 as shown in fig. 1, to an induction heating device 1. The metal capsules 5 are guided to slide on guides not shown before and after they enter and leave the induction heating device 1.

The induction heating device 1 contains a high-frequency heating coil which is fed with electric current from a high-frequency oscillator 6, a horizontal guide wall or corridor 8 and a vertical guide wall 15. According to fig. 2, the heating coil consists of tb arranged next to each other electrical conductors 7 in which the currents flow in opposite directions. When the current directions according to fig. 3 in the two electrical conductors 7 are opposite, the currents induced in the bottom and the lower side parts of the capsules 5 made of aluminum or a non-magnetic material can flow in a closed circuit 12 in such an amount that the temperature rise due to joule- heat is established. In case of equal current directions, the closed current circuit 12 according to fig. 3 not established so that the current induction performance is too low to be able to cause any significant temperature rise. For the same reason, there is also no significant rise in temperature when a single conductor is used as a heating coil. Although two conductors 7 are arranged in the embodiment shown, with regard to the speed of temperature rise and the evenness of the temperature distribution at the bottom of the metal capsules 5, more than two conductors 7 can be used when the metal capsules 5 have a larger outer diameter.

The center distance between the two conductors 7 is smaller than the bottom 5b diameter or less than the minimum length of the base 5b in the case of non-cylindrical metal capsules 5. When one of the conductors 7 is displaced relative to the base 5b, the resulting heating efficiency decreases so much that the metal capsule 5 cannot be heated. To improve the heating efficiency and to equalize the temperature distribution, the arrangement is made so that the said center distance for the two conductors 7 is practically equal to or slightly greater than the radius of the base 5b and that the center of the base 5b is located practically on the center line between the conductors 7.

The inside of the conductor 7 is cooled with water and the diameter increases corresponding to the diameter of the metal capsules 5 to be heated. In the event that the diameters of the metal capsules are 15

to 25 mm, 25 to 40 mm and 41 to 60 mm, the preferred diameters of the conductors 7 are respectively :about. 3 to 4 mm, 5 to 6 mm and 7 to 8 mm. This is partly because, as the diameter of the metal capsules becomes larger, it becomes necessary to supply the conductor with a higher current value and partly because if the diameter of the conductor is extremely small, the losses in it due to joule heat will consequently increase, whereas if the diameter of the conductor is far too large, the electromagnetic coupling between the conductor and the capsules will consequently be reduced correspondingly, so that the heating efficiency is destroyed.

It is preferred to prevent the mutual induction coefficient between the conductor and capsule base from being finely affected by the small change in the distance between them, which will often result in the change in the flow rate of the current to be induced in the capsule base and consequently in the temperature rise that is achievable. In order to prevent the capsule bottom and the conductor from being short-circuited, it is further preferred to stabilize the conductor in positions during the heating treatment by fixing the conductor with the aid of an adhesive 11, such as epoxy resin, as will be seen from fig. 2, to a bearing 10 which is made either of a synthetic resin such as a phenolic resin known under the trade name "BAKELITE", in the case that a vacuum tube oscillator is used, or of a highly permeable insulating material such as ferrite, in the case that a semiconductor oscillator is used.

Although any high frequency oscillator 6 can be used, a vacuum tube oscillator with a frequency range between 100 kHz - 10 MHz or a semiconductor oscillator, e.g. a transistor or thyristor, for a frequency range between 5 and 80 kHz.

When using a semiconductor oscillator, the bed 10 consists of a highly permeable insulating material to increase the electromagnetic coupling between the conductor 8 and the base 5b in the metal capsule 5 so that both the heating efficiency and the evenness of the temperature rise in the base 5b can be improved. When using a vacuum tube oscillator, on the other hand, the use of a highly permeable insulating material will increase the impedance for the part of the conductor 7 which corresponds to the distance between the individual metal capsules 5 due to the high operating frequency so that the flow of current would be impeded. By using a bed 10 of such an insulating material, a smaller effect would thus be achieved.

The semiconductor oscillator also has the advantage that it does not require an output current transformer for adjusting the output impedance so that it can have an increased efficiency at a reduced size. Such an oscillator can be operated with a low voltage in order to feed its high frequency energy as such to the conductor 7.

When the described metal capsule 5 of non-magnetic material is transported over the conductor 7, due to the retroactive force between the conductor 7 and the metal capsule 5, it comes into a liquid state where it jumps. The previously mentioned guide wall 8 prevents a non-heating of the metal capsule 5 due to this jumping; in addition, it is provided on its lower or inner side with a guide sliding surface 8a on which the edge 5a of the metal capsule 5 is transported to slide by means of the conveyor mechanism. At the same time, the guide wall 8 acts to adjust the distance between the bottom 5b of the metal capsule 5 and the conductor 7 to thereby ensure an even temperature distribution in the bottom 5b.

The guide wall 8 only needs to satisfy the following conditions: it must not be deformed or damaged by the impact coming from the bouncing metal capsule 5; its lower side must not be so rough that a smooth sliding movement of the edge 5a of the metal capsule 5 is prevented; it must be free of wear or damage that would counteract such a sliding movement. The guide wall 8 can therefore preferably consist of a ceramic plate, in particular a reinforced or reinforced refractory glass plate with a thickness of approx. 5 to 10 mm. A corresponding transparent glass plate of this type is preferred because it can provide an easy observation of the heating process.

As can be seen from curve a in fig. 4, in order to increase the mutual induction coefficient between the conductor 7 and the bottom 5b so that this bottom 5b can be heated to the predetermined temperature, the distance between the upper side 7a of the conductor 7 and the bottom b of the metal capsule 5 must be less than 1 mm, preferably

show 0.5 mm, when a not very permeable material is used. However, a reduction of the distance to less than 0.1 mm is not desirable with regard to a possible short circuit. On the other hand, when the bed 10 is made of highly permeable insulating material, the distance between the top side 10a of the bed 10 and the bottom 5b of the metal capsule 5, as can be seen from the curve b in fig. 4, be less than 2 mm and preferably 1 mm. Because the ferrite used as the highly permeable insulating material is very brittle, the upper side 10a of the bearing 10 must also be protected with an insulating layer, e.g. a bakelite plate with a thickness of approx. 0.5 mm. It is therefore difficult to reduce the intermediate distance to a size of less than 0.5 mm.

In the event that the heights of the metal caps 5 in each lot lie within a preselected range, the distance between the upper side of the conductor 7 and the bottom 5b can be regulated simply by adjusting the height of the guide wall 8.

In the event that, after processing a specific group of metal capsules 5, slightly higher metal capsules 5 of a later batch are to be loaded, the guide wall 8 can be shifted upwards by adjusting its height. In this case, if necessary, a pressure can be exerted on the guide wall 8 from above by means of a pneumatically controlled pressure piston, so that said distance remains in the preselected area.

In order to make the temperature distribution in the capsule bottom 5b as even as possible, the imaginary plane determined by the upper lines of the two conductors 7 can advantageously be extended parallel to the lower side of the guide wall 8.

In the embodiment described above, the distance between guide wall 8 and high-frequency heating coil is adjusted corresponding to the height of the metal capsule 5 to a predetermined size, the height of the metal capsules 5 in each part being kept within a predetermined tolerance range.

However, the relevant metal capsules 5 are generally subjected to an edge trimming process according to a drawing process so that they are given a predetermined height at their skirts, and also a beading and knurling process. Although, in the relevant processing processes, the metal capsules are of the same type and have an identical height at their skirts, the heights of the metal capsules in practice after the beading and knurling processes differ by +0.2 mm in the processing parts. Thus, when the height of the guide wall 8 is fixed, there is a maximum difference of approx. 0.4 mm in the distance between bottom 5b and the conductor's upper side 7a. As can also be seen from fig. 4, this difference in height of 0.4 mm will result in a change in the temperature rise in the bottom 5b in an order of magnitude of several times 10°C.

In fig. 5 - 7 shows a modified embodiment of the continuously working high-frequency induction heating device 1, where the bottoms 5b of the metal capsules 5 can be heated evenly even when there is a small spread in the heights of the metal capsules. This embodiment differs from the former mainly with regard to the construction of the guide wall 8. The parts corresponding to the parts according to fig. 1 is thus denoted by the same reference numerals.

The guide wall 8 is shaped into elongated plates whose width is somewhat greater than the outer diameter of the metal capsules 5, its lower end sides being tapered in such a way that a smooth movement of the edges of the metal capsules 5 is ensured.

The guide wall 8 is arranged opposite the conductor 7. According to fig.

7, it is true that the width of the guide wall 8 is somewhat greater than the outer diameter of the metal capsules 5, but no significant difficulties will arise when it is almost equal to or less than the outer diameter of the metal capsules 5. The 8 longitudinal sides of the guide wall can either have a curvature in the longitudinal direction or be straight. In any case, the guide wall 8 is essentially arranged along the same arc around the center point of the turntable, even when it is composed of several components. Regarding the length of the guide wall 8, there is no particular limitation, but in view of facilitating the height adjustment during the work operations, the length can preferably be of such a size that a plurality of metal capsules 5 are allowed to pass simultaneously under it. With such a length, it is possible to reduce the production of non-conforming objects during the heating process in the event that the metal capsules 5 which are heated are replaced by those in another lot which have different heights. The total length of the heating device should thus be approx. 80 cm. As will be explained in more detail, the guide wall 8 preferably consists of several individual components in the form of plates. If the distance between the individual plates of the guide wall 8 is too large, the part of the metal capsule 5 which is located in said space can be moved upwards until the overall metal capsule 5 is so inclined that the inlet under the subsequent plate of the guide wall 8 is obstructed and the overall work operation is interrupted. In the worst case, said special metal capsule 5 can bounce up from the heating device 1. It is therefore necessary that the adjacent plates of the guide wall 8 are arranged so close to each other that an unobstructed or pressure-free transfer of the metal capsules 5 from one plate of the guide wall 8 to the other is ensured.

The guide wall 8 with the described construction is supported

by means of a carrying mechanism 9 which is constructed as follows: A stationary horizontal weight arm 9b is attached in its central part to the upper horizontal part of a bracket 9a which is generally Z-shaped, the lower horizontal part of which is attached to a vertical guide wall 15 .Two vertical bolts 9c are inserted vertically movable in the vertical bores formed near the two ends of the horizontal weight arm 9b.

A pair of generally C-shaped support frames 9d with their horizontal middle portions are attached to the lower ends of the respective vertical bolts 9c so that their vertical positions can be adjusted by turning two nuts 9e screwed to the upper threaded portions of the vertical bolts 9c and which is placed on the stationary horizontal weight arm 9b. Between the upper sides of the support frames 9d and the lower sides of the stationary horizontal weight arms 9b, a pair of pressure springs 9f are introduced, through which the vertical bolts 9c extend so that the resistances produced by the spring pressures 9f are applied when the support frames 9d are to be raised.

The aforementioned guide wall 8 is fixed in a horizontal position to the inner side of the support frames 9d near their two longitudinal end portions by means of a pair of pointed stop screws 9g.

The parts which form the carrier mechanism 9, with the exception of the pressure springs 9f, preferably consist of a non-magnetic material such as brass.

By means of the above-described support mechanism 9 for the guide walls 8, the difference in height between the different metal capsule groups can be compensated so that the temperature in the metal capsule bottoms 5b can be maintained practically constant.

Before the machining operations, the distance between the

the lower sides of the respective horizontal plates of the guide wall 8 and the upper side of the bearing 10 adjusted by means of the nuts 9e to a size corresponding to the minimum height of the metal capsules 5. During the processing operations, the metal capsules 5 are transported, while they are exposed to the floating forces originating from the electromagnetic couplings with the conductor 7. When these floating forces are overcome by the sum of the weight of the horizontal guide wall 8 and the pre-tensioning forces of the compression springs 9f, the metal capsules 5 can are transported without floating over the bearing 10, although their skirts 5a have different heights. During this transport, the skirt 5a and bottom 5b of the metal capsules 5 slide along the lower side of the guide wall 8, respectively. the rent's 10 upper side. As a result of this, the aforementioned gap can be kept at a predetermined level so that the temperature rise in the metal capsules 5 also remains constant. If the metal capsules 5 e.g. of another part which is higher than the minimum level is loaded into the device, the guide wall 8 and consequently the vertical bolts 9c will be raised by their differences from the minimum height, as can be seen from fig. 6.

On the other hand, if the buoyant forces are stronger than the sum of the weight of the horizontal guide wall 8 and the originally preset pressures of the pressure springs 9f, the metal capsules 5 can float on the overlay 10. Since, however, the buoyant forces are independent of the height of the individual metal capsules 5, and since if the pressure springs have sufficient length, the pressures of the springs 9f essentially remain unchanged even with the significant variation of approx. + 0.2 mm in the guide walls 8, the buoyancy forces of the metal capsules 5 remain independent regardless of the height of the capsule skirts. As a result of this, the said gap is also kept at a predetermined size so that the temperature rise in the capsule bottoms 5b is unchanged for batches. In this "floating" state, the metal capsules 5 slide with their upper sides 5a along the lower side of the guide wall 8, while their lower ends resp. bottom 5b is kept out of contact with the upper side of the bearing 10.

In the following, a case will be described in which the induction heating device 1 is used to attach a lining of polyethylene to the inside of the bottom 5b of a metal capsule 5.

An adhesive primer such as e.g. is produced

by dispersing oxidized polyethylene or maleic anhydride-modified polyethylene in an epoxy phenolic varnish, the inside of the bottom of a metal capsule 5 of aluminum is applied with

an outer diameter of 28 mm and a height of 16 mm.

The metal capsules 5, which have a thickness of 0.2 mm, are then subjected to a firing process and fed from the shaft 4 into

in the semi-circular grooves 3 in the turntable 2. The metal capsules 5 are then transported to the induction heating device 1, which has a length of 80 cm, so that they can be exposed mainly at their bottoms to the induction heating device 1. Provided that the transistor oscillator 6 has a frequency of 25 kHz and an output power of 10 kW, that the distance between the bottom of the metal capsule 5 and the upper side of the bed 10 is 0.7 mm, that the number of the metal capsule 5 to be simultaneously loaded into the induction heating device 1 is 2 0 and that the time period for each metal capsule

5 to pass through the induction heating device 1 is 1 second, the capsule bottoms 5b are heated to a temperature ranging from 140 - 160°C (measured by means of a thermo-paint) and discharged from the induction heating device 1. The indicated temperature range is sufficient to ensure

a complete adhesion between the adhesive primer and the polyethylene at a molding station. The thus heated metal capsules 5 are further transported through the guide to a mechanism or extruder 14 which supplies a molten polyethylene pellet, where at their bottom centers in each metal capsule 5 a molten polyethylene pellet is supplied. The metal capsules 5 are then further transported to the not shown molding station where the molten polyethylene pellets are pressed into a plate by means of a cooled piston and harden into liners on the inside of the bottoms 5b so that the

desired metal capsules. As the skirts 5a are only slightly heated, there is no danger of the hardening of the polyethylene material being delayed by the heat supplied from the skirt 5a.

On the other hand, in the event that the distance between the extruder 14 for the molten polyethylene pellets and the above-mentioned casting station 16 is relatively large, as is the case with the modified device according to fig. 8, the molten polyethylene pellets are at the time they reach the molding station 16. so much cooled that the adhesion strength is reduced or that stress cracking is generated in the lining layer during use. In this case, the high-frequency heating coil according to fig. 8 extend over the extruder 14 all the way to the molding station 16. The supply mechanism 14 which delivers the molten polyethylene pellets is usually in the form of an extruder by which the molten polyethylene which has been extruded in jet form is cut by means of a steel cutter into pellets or pills. Thus, when the steel cutter is heated by means of the induction heating device 1, the molten polyethylene can stick to the cutter so that it cannot perform its cutting function. In order to prevent this difficulty, the conductors 7 used in pairs can be arranged preferably in the vicinity of the extruder 14 so that they (1) lie close to each other at a position displaced from the bottoms 5b (fig. 8), (2) that they are buried relatively away from the upper side of the bed 10, (3) that they are arranged near the upper side of the bed 10, but outside the metal-capsule passage relatively far away from each other, (4) that two independent conductors 7 are arranged on both sides of the extruder 14, separated from each other in its vicinity.

Although the preceding description is directed mainly

on metal capsules 5 of non-magnetic material such as aluminum, also metal capsules 5 of a ferromagnetic material such as tin can sometimes bounce or float, depending on the conditions determined by the weight, size and shape of the capsule, intensity and frequency of the flux through the conductor 7 and the distance between the bases 5b

and the conductor 7. For the above reasons, the device can also be used with such metal capsules 5.

By means of the compactly constructed induction heating device 1, the bottoms 5b of metal capsules 5, especially of a non-magnetic material, can be heated in a number of more than 1000 pieces per minute. Even with a small variation in the heights of the metal capsules, the floating stroke of the metal capsules 5 is limited by means of the pressure springs 9f so that the bottoms 5b can be heated evenly. Moreover, the skirts 5a, which do not require any heating, will only be exposed to a small temperature rise so that the quality of the products can be prevented from being destroyed and the power losses can be reduced.

In fig. 9 and 10 shows an embodiment of an induction heating device 21 in which the horizontal guide wall 22 is itself moved to transport the metal capsules 5. The guide wall 22 in this case consists of an endless belt which is driven in the direction of the arrow by means of drive discs 23. In this embodiment, the metal capsules 26 that are loaded onto the high-frequency heating coil 25

in the induction heating device 21 from a shaft 24, transported on the guide wall 22, while they are caused to float as a result of the high-frequency current and are held firmly by the guide wall 22's lower side. When the metal capsules 26 arrive at the exit of the heating device 21, they are pushed out across their direction of movement by means of a shock piston 27 or the like. and then loaded into a subsequent station 28.

A similar function can be achieved, when the endless belt

which acts as guide wall 22 is replaced by a turntable.

In the embodiments described above, the conductors for the high-frequency heating coil 25 are arranged parallel and at an equal distance from each other in the passage for the metal capsules 26 so that the metal capsules 26 during transport are always heated in the same parts so that the temperature rise in the bottom of the metal capsules 26 can be irregular.

This can be avoided by the embodiment according to fig. 10 to 15 where the reciprocating conductors forming the heating coils are arranged in a tapered shape along the conveyor passage.

As can be seen from fig. 11 which shows a heating coil 30 in a straight line along a passage 100, the heating coil 30 consists of two pairs of forward and backward directed conductors, i.e. the heating coil 30 consists of two conductors 34 or 36 whose distance is reduced from a high-frequency power source 32 in transport direction A for the metal capsules 5, while the heating coil 30 consists of corresponding conductors 34a and 36a whose mutual distance decreases from the common power source 32 in the opposite direction to the transport direction. The high-frequency current from the power source 32 is branched in the conductors 34 and 34a, the branched currents being returned to the power source 32 through the other conductors 36

and 36a. It is of course that the current passages are reversed in the event that the phases of the high frequency power source 32 are reversed.

Although in the embodiment shown two pairs of conductors 34, 36 respectively. 34a, 36a are provided for carrying out an impedance matching with the high-frequency power source 32, these conductors 34, 36 can also be replaced by one or more pairs of the conductors 34, 36.

Since the conductors 34, 36 and 34a, 36a according to this embodiment are arranged in the tapering form, the metal capsules 5 are continuously heated while being transported along the passage 100 at such adjacent parts to the respective conductors 34, 35 which are hatched, so that their relatively large areas in relation to the diameter of the conductors can be heated evenly during the transport operation, as will be easily understood. As can be seen from fig. 11, a metal capsule 5 is first heated at its central portion and its heated zone is then progressively shifted to its peripheral portion. Then the metal capsule 5 gets its outermost circumference heated essentially at the center of a heating station, i.e. in the area of the connection of the high-frequency power source 32 to the heating coil 30, and then gets its heated zone shifted! gradually towards the middle part of the base 5b during its transport until the total area of the base 5b is uniformly heated. After this, the metal capsule 5 is transferred to a subsequent attachment step. In an embodiment that corresponds to the device shown in fig. 11, in which the total length L of the heating coil 30

along the passage 10 0 is 1 meter, where the coil distance at the power source 32 area, i.e. the maximum coil width is 30 mm and the coil width W 2 at both ends of the heating coil 30 is 10 mm, while the metal capsules 5, which have a diameter of 38 mm, are transported with at a speed of 0.8m/s, each metal capsule 5 needs 1.25 seconds to pass through the heating section, the temperature difference after passing the metal capsule 5 (ie the ratio in percent of the difference between the maximum and minimum temperature in relation to the maximum temperature) lies within 10%. Compared to the usual device which has as much as 40% temperature discrepancy measured immediately after passing through the heating station in terms of the maximum temperature, the evenness of the temperature distribution can be significantly improved according to the present invention.

By the one in fig. 12 shown modification, the heating coil<* >30 consists of a conductor 34 or 36 which run together so that their mutual distance in the transport direction A of the metal capsule 5 increases. This device according to fig. 12 is advantageously suitable for heating workpieces whose outer peripheral parts cool faster than the inner parts, due to the fact that the middle parts of the bottom of the metal capsule 5 are heated earlier.

A further modification according to fig. 13 is essentially similar to the device according to fig. 12, as the divergence between the heating conductors changes, however, in the passage 100 area. In a transitional part indicated by the reference number 200 in fig. 13, the conductors 34, 36 have a greater tapering slope than the other parts. As a result of this, the metal capsules 5 which are transported at a predetermined speed in the direction of arrow A along the passage 100 are supplied with less heating energy at the transition portion 200 than at the remaining portions. According to experiments carried out by the applicant, it has been found that the configuration according to fig. 13 was particularly suitable for ensuring the desired even heating operations of workpieces such as aluminum capsules 5 of the type in which the temperature rise in the intermediate part of the metal capsules 5 bottoms is steeper than in the middle part and the outer peripheral parts.

A further modification corresponding to that in fig. 13 is shown in fig. 14, where a portion B having a steeper taper slope is formed at the front end of the passage 100. In the configuration according to fig. 14, the outer peripheral parts of a workpiece are heated more strongly than the central part.

In a further modification according to fig. 15, the steeper tapering part B is formed near the rear edge of the passage 100. This arrangement is particularly suitable in the event that the middle parts of the metal capsules 5 are to be heated more strongly.

In addition to the above-mentioned modifications, where the conductors taper over their total length, these conductors can, if desired, also have a parallel running portion on the transport passage.

For the high-frequency power source 32 used, as mentioned, a vacuum tube oscillator or a semiconductor oscillator can be used.

It is thus possible to adapt the heating temperature appropriately to the characteristics of the metal capsules to be processed, to heat the metal capsules 5 evenly and to heat a desired part of the metal capsules to a temperature different from that of the other parts, in accordance with the types of the workpieces.

The bottoms of the metal capsules 5 can be heated to obtain any desired temperature distribution by arranging a ferrite core under the conductors at a portion of the passage in the preceding embodiments. In the event that the ferrite core is buried under the conductors, the electromagnetic coupling between the conductor and the metal capsules 5 is increased so that the heating efficiency in the particular part is improved.

By arranging a ferrite core at any position of the transport passage, even and local heating can be achieved.

This construction will be described in more detail with the help of fig. 16 to 18. In this embodiment, the heating coils 30 consist of two conductors 34 or 36 as similar in fig.

11, is arranged in a tapering form along the transport passage. According to fig. 16, the heating coil 30 consists in particular of two conductors 34 respectively. 36 and 34a respectively. 36a which first tapers off from the high-frequency power source 32 to the transport direction A of the metal capsules 5 and secondly converges or tapers off from the common power source 32 in the opposite direction to the transport direction. As before, the high-frequency current is distributed by the power source 32 on the conductors 34 and 34a and via the conductors 36 and 36a is led back to the power source 32. In the case of reversed phase of the high-frequency power source 32, of course, the conductors 34, 36 also have the opposite phase.

Also in this case, the two pairs of conductors 34, 36 for impedance matching to the power source 32 can be replaced by one or more pairs of conductors 34, 36.

The embodiments shown are characterized in that, according to fig. 16 and 17, ferrite cores 37a, 37b and 37c are arranged in any positions below the heating coils 30.

A bearing 38 consisting of bakelite for the heating coil 39

is provided with grooves in which the ferrite cores 37a 37a to 37c are fixedly mounted. As a result of this, at the heating station equipped with the ferrite cores 37a to 37c, the electromagnetic coupling between the heating coil 30 and the metal capsules 30 is increased so that the resulting heating efficiency is increased accordingly.

In the shown arrangement of the conductors 34 and 36 respectively. 34a and 36a, the same heating of the metal capsules 5 as described above in connection with fig. 12.

When the metal capsules 5 to be heated have disc-shaped bottoms, in the case of heating coils 30 with straight-line expanding or tapered configuration according to fig. 11, the intermediate part of the bottoms 5b will be heated more than the middle and the outer peripheral parts of the metal capsules 5, so that an uneven temperature distribution is established. In the embodiment according to fig. 16 to 18, however, the heating effect is improved at both ends of the heating station, i.e., the zones for heating the middle portions of the metal capsules 5 and at the middle portion of the heating station, i.e., the zone for heating the outer peripheral portion of the metal capsules 5, by means of the ferrite cores 37a to 37c. The metal capsules 5 can thus be heated to a remarkably uniform temperature distribution.

Although the ferrite cores 37a, 37b, 37c according to fig. 16 may

be arranged on both end parts and the middle part of the heating station, their position can be desirably chosen in accordance with the temperature characteristics of the metal capsules 5 and with the tapered shape of the heating coils 30. Moreover, the metal capsules 5 can be heated to achieve either — a uniform temperature distribution or a local different temperature distribution.

Moreover, the distances between the ferrite cores 3 can be 7a - 37c

and the heating coils 30 according to this embodiment are selected as desired, and the electromagnetic coupling change between the heating coils 30 and the metal caps 5 due to the provision of the ferrite cores 37a - 37c can also be adjusted. It should be noted that the present embodiment can be applied to metal capsules made of a ferromagnetic material such as iron.

Fig. 18 shows another modification of the present device which is characterized by the fact that the ferrite core 37 surrounds the conductors 34 and 36 of the heating coil 30 in order to increase the electromagnetic coupling between the conductors 34, 36 and the metal capsules 5. The ferrite cores 37, which are E-shaped, have two tracks 3 7x and 37y in which the conductors 34 and 36 are arranged.

As a result, the magnetic concentration is increased

of the conductors 34 and 36 so that said electromagnetic coupling is increased accordingly.

With the corresponding arrangement of the ferrite cores, the temperature distribution in the bottoms of the metal capsules 5 can thus be varied as desired.

The following description relates to a further embodiment of multiple turns of heating coils which are connected to a high voltage and high frequency power source of the vacuum tube oscillator type so that it can effectively heat a metal shell made of a non-magnetic material such as aluminium.

The differences between this embodiment and the one described in fig. 1 consists in that in the heating station there are arranged three turns of heating coils which form the tank coil in the vacuum tube oscillator circuit so that the electrical power from its source 6 can be transformed into high-frequency oscillations. The construction of the heating station is shown in detail in its cross-section in fig. 19.

In fig. 19, the conductors 40 to 46 forming the high frequency induction heating coil are firmly buried in a bearing 47 which is arranged in a stationary position under the outer circumference of a turntable 46 which is made of a silicone resin, polytetrafluoroethylene or bakelite. The metal capsules 5 which are transported by the rotary table 46 are subjected to induction heating at the heating station. During this transport, the metal capsules 5 are guided through a vertical wall or a guide wall 48 which is fixedly mounted near the outer circumference of the turntable 56, and through a guide roof or a horizontal guide wall 49 which is arranged above and near it outer circumference of the turntable 46. As mentioned earlier, when transported on the high-frequency heating coil, metal capsules 5 of non-magnetic material are prone to float and jump due to the reaction forces established between the conductor and the metal capsules 5. Since the horizontal guide wall 4 9 is arranged above the metal capsules 5, as shown in fig. 19, these capsules 5 are transported by the turntable 46, while their side edges slide on the opposite lower side 49a of the guide wall 49. As a result, the bottoms 5b of the metal capsules 5 always remain at a predetermined distance from the respective conductors 40 to 45 so that the lower side or the bottoms 5b of the metal capsules

5 is comparatively evenly heated inductively. As a result, an adhesive primer may 5 0

which has been applied to the inside of each bottom 5b is heated to a temperature sufficient to effect its adhesion.

As mentioned earlier, better results are achieved with regard to effective heating of the metal capsules 5 of non-magnetic material, when the distance between the conductors 40 - 46 and the metal capsules 5 is smaller. As will be apparent from the characteristic curve as shown in fig. 4, it is necessary that the above-mentioned distance is less than 2 mm and preferably 0.5 to 1.5 mm. If this distance is reduced too much, the problem arises that the risk of a dielectric breakdown between the conductors 4 0 - 4 5 and the metal capsules 5 is increased inversely proportionally. This problem is solved by the arrangements of the conductors as shown in fig. 19.

Fig. 20 shows in detail the arrangement of the conductors 40 - 45 and the metal capsules 5 in the embodiment according to fig. 19.

According to fig. 20 are the three conductors 40, 42 and 44 which form

the forward current passages arranged in the left half B of the induction heating station. The remaining three conductors 41, 43 and 45 which form the reversed current

passenger, on the other hand, is arranged in the right half C.

In the embodiment shown, three turns of the high-frequency heating coil can therefore be formed. Since the two groups of managers 40, 42, 44 respectively. 41, 43, 4 5 as mentioned above are arranged in the respective halves of the heating station, the generated induction currents flow while forming closed circuits in the metal capsules 5 so that an effective temperature increase can be achieved due to the joule heat. The conductors in each half thus lead a current flux in an identical direction in a manner known per se, so that an effective electromagnetic induction can be achieved.

The high frequency oscillator 6 with the vacuum tube oscillator operates at a frequency of 100 kHz to 10 MHz. The effective voltage generated in the tank coil, which acts as a heating coil for the oscillator 6, is at approx. 10 kV. The high-frequency oscillator 6 is connected in its one terminal in series with the respective conductors, i.e. in the order of 40, 41,

42, 43, 44 and 45, while its other terminal is grounded.

In the described embodiment, it is very important that

the conductors that are close to the ground, i.e. conductors 44 and 45

is arranged near the metal capsules 5, while the conductors 4 0.42 or 41,43, which are away from the grounding, i.e. on the high-voltage side, are arranged continuously away from the metal capsules 5. Compared to the conductors 44 and 45, the conductors 42 and 43 are thus separated from the metal capsules 5, while the conductors 40 and 41, which are connected to the high-voltage side, is placed further away from the metal capsules 5. The metal capsules 5 are thus normally at ground potential, and the potentials for the respective conductors relative to the Riull potential have, according to fig. 21 the values Vg for conductor 45, V5

for conductor 44, V4 for conductor 43, V3 for conductor 42, V 2 for conductor 41 and V^ corresponding to the potential of the high-voltage side of conductor 40. Between the individual conductors 4 5 to 4 0 and each metal capsule 5, these potentials Vg to V are thus established ^. In the embodiment shown, the conductors are on the high-voltage side and with higher potential differences, e.g. the conductors 4 0 and 41, arranged further away from the metal capsules 5, so that

the potential gradients can be limited to a level substantially equal to those between the remaining conductors and the capsules. It is quite natural that the managers 40, 4 2 respectively. 41,43 which are arranged further away from the metal capsules 5 contribute less to the generation of induced currents in the metal capsules 5. According to the embodiment shown, however, a plurality of turns of the high-frequency heating coil is used so that the conductors 40-45 can be arranged significantly closer to the metal capsules 5 than in the above-mentioned device, and the conductors on the high-voltage side are used in part to generate the induced currents so that the overall efficiency can be significantly improved compared to the known technique. In contrast to the known technique, the potential gradients between the conductor on the grounded side and the metal capsules can be limited to a significantly low value so that the high-frequency voltage to be generated can be increased. As a result of the increases in the voltage and in the number of turns of coils and the reduction in the distances between the conductors 40-45 and the metal capsules 5, the overall heating efficiency by means of the induced currents can be improved to a considerable extent.

In the present embodiment, the distances between any of the conductors can also be suitably chosen in accordance with the potential difference between them, the potential gradient between them being limited to lower than a predetermined value, so that the dielectric breakdown between the conductors 40-45 can be prevented. Although the distances between conductors 4 0 and 4 2 and between conductors 4 2 and 4 4 in the left half are preset equal, the distance between conductors 4 0 and 44 is greater so that the potential gradient between two of these conductors can be kept smaller. In the left half C, the distance between the conductors 41 and 45 is set greater than between two of the remaining conductors, so that the potential gradient between any two of these conductors can be limited lower than the preset value.

In the embodiment according to fig. 20, the conductors 40 and 41 on the power source side are not aligned with the remaining conductors 42, 44, respectively. 43, 45, but is arranged in another step so that the advantage is obtained that the respective conductors 4 2,'. 44, can be buried in bed 47 in a relatively compact manner. As shown in a modification according to fig. 22, however, all conductors 40 - 45 can be arranged in a row or in any shape in accordance with the shape of the metal capsules 5. The components according to fig. 22 are indicated with the same reference numbers as those in fig. 20, and their repeated explanations are omitted here.

According to the two-stage arrangement of the heating coil according to fig. 20, however, the contribution from the conductors 40 and 41 on the high voltage side to the induction heating process is greater than with the device according to fig. 22 with the single row,

so that the total efficiency can consequently be increased to a higher level, namely, as it has been shown, to twice the efficiency resp. the effect of the embodiment according to fig. 22.

In the described embodiments, the conductors consist of copper pipes through which cooling water flows to prevent heat release due to the resistance losses in the conductors themselves.

As mentioned earlier, according to the present embodiment, the conductors 40-45 and the metal capsules 5 can be arranged closely next to each other without causing their dielectric breakdown so that the induction heating efficiency can be improved considerably.

Also, the relative arrangements of the conductors are 40 - 45

chosen in accordance with the potential differences between them so that the dielectric breakdowns between them can be prevented without accident.

Moreover, it is possible to provide a high-frequency induction heating device of small size but with high efficiency, with which the heating of the metal capsules of non-magnetic material such as aluminum can be significantly improved.

With the existing high-frequency induction heating device, however, there is a problem that the heating energy portions to be transferred to the individual metal capsules 5 vary with the number of metal capsules to be loaded on the heating station. Specifically, the impedance and frequency of the heating coil from the conductors varies significantly, depending on the mutual inductances of the metal capsules. E.g. the load impedance and the frequency of the heating coil deviate significantly, when first 18 metal capsules 5 are to be loaded simultaneously on the heating station and then when a single metal capsule is to be loaded. Because the portions of energy to be transferred to the metal capsules 5 in these cases vary greatly, the problem arises that correspondingly high fluctuations occur in the heating temperature. Particularly in the step of manufacturing the metal capsules 5, if the number of the metal capsules 5 to be continuously loaded onto the heating device varies to such an extreme degree that the supply of the metal capsules to the heating device becomes equal to zero, this results in the previously mentioned problem in that the heating temperature is spread to a considerable extent due to the variations in the load impedance and the frequency of the heating coil.

Claims (8)

1. Device for attaching a liner to metal capsules, the liner consisting of an inner liner layer of thermoplastic resin which is attached to the inner wall of the bottom of the metal capsule, an induction heating device consisting of a high-frequency current generator and a high-frequency heating coil of electrical conductors located at side of each other with opposite current flows, a transport device which transports the metal capsule through the induction heating device, a supply device for the thermoplastic resin for the inner surface of the metal capsule and a device for fixing the inner lining layer in the metal capsule by thermal adhesion, characterized in that the conductors (7; 34 , 36; 34a, 36a; 40-45) distance varies and that a guide wall (8, 8a) lying opposite the conductors (7; 34, 36; 34a, 36a, 40-45) and the high-frequency heating coil bearing (10) is arranged as lower guide. 2. Device as stated in claim 1, characterized in that the guide wall (8) is designed as a plate. 3. Device as stated in claim 1 or 2, characterized in that the guide wall (8) on the lower end of a support frame (9d) is adjustable (9g) fixed on a vertical movable bolt (9c) which is guided through a stationary support mechanism (9 , 9a, 9b) for a limited vertical movement, and that a spring (9f) is fixed between the stationary support mechanism (9, 9a, 9b) and the support frame (9d). 4. Device as set forth in one of claims 1 to 3, characterized in that the guide wall (8) consists of a plurality of oblong plates which lie closely behind each other. 5. Device as specified in one of claims 1 to 4, characterized in that the guide wall (8) consists of a similarly reinforced and/or heat-resistant glass plate. 6. Device as set forth in one of claims 1 to 5, characterized in that the distance between the conductors (34, 36) of the high-frequency heating coil (30) in a first part of the transport passage (A) is varied in a tapering manner in relation to the tapering device in another party. 7. Device as stated in one of claims 1 to 6, characterized in that an insulating material (37, 37a, 37b, 37c) with high permeability is arranged under part of the conductors (34, 36; 34a, 36a) of the high-frequency heating coil (30). 8. Device as specified in one of claims 1 to 7, characterized in that the distances between the individual conductors (40 - 45) are adjusted corresponding to the potential difference between them.