The invention relates to a method and an apparatus for removal of an overprint from a cylindrical metal packaging, applicable in the management of production surplus of metal packaging in the form of cans, particularly beverage cans.

The production process of beverages sold in cylindrical metal packaging, usually a can, starts in a plant producing empty cans. Aluminium or steel sheet is formed into the shape of a can, and then, graphics is applied onto the so-formed sheet metal by the dry offset method. In the next step, a protective varnish layer is applied onto the printed can. The empty can with the decoration applied is brought to a filling plant, where it is filled with a beverage and capped. The product is then packed into a bulk container and transported to distribution centres, and then directly onto shop shelves.

In the process sequence mentioned above, an unintended production surplus may arise. Application of incorrect graphics onto an empty can in the plant which manufactures empty cans is an example of such surplus. The situation occurs e.g. as a result of discrepancies between different language versions of descriptions on the can. The most common scenario in such a case is that the whole manufactured batch is scrapped.

An alternative to this complete disposal is the application of substitute labels. After filling and seaming of the incorrectly overprinted can, a heat-shrinkable or self-adhesive label is applied in the filling plant. A drawback of this method is that the end-user may easily remove the substitute label and find the original overprint. This problem may be solved by the removal of the overprint before the application of the substitute label, however there are no commercially available devices which allow for removing graphics from a cylindrical metal packaging at an industrial scale in a way that is repeatable, safe, and does not cause damage to the can structure. A Polish application No. 409024 provides a method for tarnishing the surface of metal cans by brushing, characterised in that after a can is formed and cleaned, it is fixed on an arbour and its surface is tarnished using at least one flat or round brush made of metal wire or plastic, and after tarnishing, the can is subjected to further treatment. The invention also relates to an apparatus for tarnishing can surface.

A Japanese patent specification JP 2008037467 provides a method for carrying out brushing on cans using abrasives.

Methods for tarnishing an overprint by using various types of grinding wheels are also known. Thus a Japanese patent specification JP 2007168019 discloses a method for carrying out the tarnishing of a can as a hairline processing effect, which uses an elastic grindstone with an abrasive in conjunction with a flowing cleaning liquid.

Moreover, a German invention No. DE 4427315 refers to an apparatus which uses a knife to remove labels from bottles and cans.

Furthermore, an invention No. WO 20121471 10 is referred to as a label removal system used for reusable containers, where the beverage container is pressed against a support plate and a rotary brush abrades the label from the container. The system comprises of an electric motor, by which, via proper coupling mechanisms, the supporting plate for the can is rotated around an axis parallel to the brush axis.

Apart from the devices and methods known in prior art, there is also a possibility to remove overprint by manual, mechanical rubbing of the can until the overprint is removed. However, this process does not provide a reproducible quality and is not economically efficient in mass industrial production.

It should be added that in the prior art, removal of overprints using processing lines was attempted, but they were all unsuccessful. This was due to the resulting destruction of the cylindrical metal packaging or incomplete cleaning, which consequently meant the inability to apply a new overprint.

To summarise, currently there is no solution in the prior art which has a method and an apparatus allowing for thorough and complete removal of an overprint from a cylindrical metal packaging at an industrial scale. Moreover, the dust occurring during the abrasion of an overprint is detrimental for human health and it complicates further processing of the packaging.

The goal of the invention was to develop a method and an apparatus which provide permanent removal of an incorrect overprint without damaging the cylindrical metal packaging. The method and the apparatus should also enable application of a new overprint onto the cleaned packaging and should be safe for human health. Moreover, the goal of the invention was to enable industrial scale application of the method and apparatus.

The essence of the method for removal of an overprint from a cylindrical metal packaging using a rotary abrasive element consists of the following: one end of the overprinted metal packaging is placed in a holder and pressed against the holder from the other side, then it is put into a rotary motion with a rate from 100 to 1000 RPM, and thereon, the abrasive element, rotating with a rate from 100 to 8000 RPM is moved to the printed surface of the rotating packaging. The overprint layer is abraded from the packaging surface, while water is being sprayed towards the packaging surface.

In a preferred embodiment, the holder with the overprinted metal packaging is put into the rotary motion by a cog belt driven by the electric motor. A hold-down roller is placed onto the other end of the cylindrical packaging. The hold-down roller is equipped with a spring and presses the metal packaging down to the holder. Thereon the metal packaging placed between the holder and the hold-down roller moves towards a cylindrical brush, which rotates around an axis parallel to the rotation axis of the metal packaging and is driven by an electric motor.

The essence of the apparatus for removal of an overprint from a cylindrical metal packaging consists of a rotary holder and a hold-down roller, between which the overprinted cylindrical packaging is fixed, and an abrasive element in contact with the overprinted packaging surface, whilst a nozzle sprays water towards the packaging surface that has been cleaned of the overprint.

Preferably, the rotary holder is terminated with a profiled cone, which is in contact with the base of the packaging and has a diameter that is at least equal to that of the metal packaging, and is coupled with the electric motor by a cog belt. The hold-down roller is bearing-supported and comprises of a spring and has a conical cross-section shape. The abrasive element is constituted by a cylindrical brush consisting of abrasive disks and is driven by an electric motor.

The invention will find its application in industrial-scale management of production surpluses of metal packaging in the form of cans, particularly beverage cans.

The method according to the invention is presented in the following embodiment illustrated with a drawing of Fig. 1.

Example.

An overprinted metal packaging 1 is fixed between a driving roller 2 and a hold-down roller 5. The so-fixed packaging is put into a rotary motion with a rate of 350 RPM. Simultaneously, a rotary brush 7, rotating with a rate of 1500 RPM, is placed in parallel to the packaging. When the brush contacts with the packaging surface, the overprint is brushed off the surface. The surface subjected to abrasion is sprayed with water.

The apparatus according to the invention is illustrated as an embodiment in the drawing, where Fig. 1 is a diagram of the apparatus, Fig. 2 shows a cross-section of a fragment of the metal packaging and a fragment of a driving roller, Fig. 3 displays a fragment of the metal packaging and a bearing-supported hold-down roller with a spring, Fig. 4 reveals a top view of an abrasive disk as a part of a cylindrical brush, and Fig. 5 shows a side view of the cylindrical brush with an arbour.

The apparatus comprises of a driving roller 2, which has a diameter that is preferably at least equal to that of the packaging. The roller is terminated with a profiled cone 10 made of stainless steel. The cone facilitates the centring of the packaging on the roller and prevents its ejection during the process. The driving roller is coupled with an electric motor 4 using a cog belt 3.

Another element consists of a hold-down roller 5. The hold-down roller is pressed by a spring 6. The hold-down roller is bearing-supported and rotates freely together with the metal packaging 1 driven by the driving roller. The hold-down roller is terminated with a ring 11 matching the circular hollow on the edge of the lid of the metal packaging. The ring has a conical cross-section, facilitating its placement in the cap hollow. The hold-down roller provides vertical stabilisation, and the ring, analogously as the cone, centres the metal packaging on the upper roller and prevents the packaging' s ejection from between the rollers. During the cleaning process, the hold-down roller, the driving roller and the metal packaging are rotating around the same axis. Another element of the cleaning system is constituted by an arbour 13, fixed along an axis parallel to the rotation axis of the metal packaging and terminated with a thread. A cylindrical brush 7 having abrasive disks 12 is installed on the arbour. The arbour is put into rotary motion by an electric motor 8. An externally threaded thick-walled pipe is installed on the arbour. The upper position of the pipe is fixed by a shoulder on the arbour. The bottom position is supported by two nuts screwed on the threaded end of the arbour. Synthetic abrasive disks are placed onto the pipe. The abrasive disks are of the same size. The discs are stacked on top of one another. The stack of discs forms a cleaning column. The diameter of the internal opening of the abrasive disks should enable smooth sliding of the disks onto the pipe. The cleaning column is positioned on the pipe using nuts placed on both sides of the pipe. The nuts have flanges enlarging the contact area of the nut with the disk. Due to the threading of the whole length of the pipe, precise raising and lowering of the position of the cleaning column is possible using the mentioned nut pair. The arbour is bearing-supported on a hub inside a profile made of acid-proof steel. The profile fixing the arbour is equipped with four steel bars with longitudinal passages. Using the bars and screws, the profile is placed between two lateral profiles with screw holes. By using bars with longitudinal passages, a precise adjustment of the distance between the driving arbour and the packaging is possible. The distance adjustment allows for regulation of the pressure of the cleaning column onto the packaging during the cleaning process. The apparatus has a spray nozzle 9, intended for cooling of the metal packaging and the cleaning column, as well as preventing the dissemination of dust formed during the cleaning process. The spray nozzle directs water onto the packaging during its cleaning. After the cleaning, the water is collected in tanks placed under the nozzles. Using flocculating agents, preferably aluminium sulphate(VI), the dust present in the water forms larger particles, which are further separated using filter bags. The water after filtration may be reused in the same spray system.

The first operation consists of placing an oveiprinted metal packaging 1 on the driving roller 2, which moves due to the presence of the cog belt 3. The cog belt 3 sets the driving roller 2 into rotary motion and is driven by the electric motor 4. The hold-down roller 5 equipped with a spring 6, is placed above the metal packaging 1 and provides pressure on the metal packaging 1. The hold-down roller 5 rotates freely in the same axis as the metal packaging 1 driven by the driving roller 2. Then the metal packaging 1 situated between the driving roller 2 and the hold-down roller 5, moves towards the cylindrical brush 7, which rotates around an axis parallel to the rotation axis of the metal packaging 1. The cylindrical brush 7 is driven by the electric motor 8. The rotating cylindrical brush 7 brushes off the overprint layer from the metal packaging 1. While the spray nozzle 9 sprays water towards the metal packaging 1 cleaned of the overprint layer.