Cleaning system for partial external cleaning of can blanks, method for partial external cleaning of can blanks, use of a cleaning system for partial external cleaning of can blanks

Abstract

The invention relates to a cleaning system (2) for the partial external cleaning of can blanks (3), comprising a conveying device (21) designed for conveying can blanks (3) along a movement path (4) with a superimposed rotational movement (6) about a rotational axis (5) oriented transversely to the movement path, and a cleaning device (51) comprising a cleaning belt (71) whose outer surface (72) defines a cleaning section (52) which extends at least partially along the movement path (4) and which is designed for contact between the cleaning belt (71) and a surface area (8) of the can blanks (3).

Description

[0001] The invention relates to a cleaning system for the area-specific external cleaning of can blanks, a method for the area-specific external cleaning of can blanks, a use of a cleaning system for the area-specific external cleaning of can blanks and a digital printing system for can blanks.

[0002] The can blanks are, for example, metal beverage can blanks, plastic or metal beverage bottle blanks, or metal aerosol can blanks. It is preferably assumed that the can blanks are rotationally symmetrical and are produced, for example, in a forming process from a disc-shaped metal base, in particular an aluminum blank, or in a plastic injection molding process or a plastic blow molding process. During the production of the can blanks, it may be provided that the respective can blank is at least partially coated with a release agent or a lubricant in order to carry out a manufacturing step, for example, a drawing-in process on a metal can blank.This can lead to the problem that an area of ​​the outer surface of the can blank, which is to be printed in a subsequent processing step using an inkjet digital printing process, has unfavorable adhesion properties for the printing ink to be applied in the inkjet digital printing process due to wetting with the release agent or lubricant.

[0003] The object of the invention is to provide a cleaning system for the area-specific external cleaning of can blanks, a method for the area-specific external cleaning of can blanks, a use of a cleaning system for the area-specific external cleaning of can blanks and a digital printing system for can blanks, with which an efficient and environmentally friendly cleaning of the can blanks can be achieved.

[0004] According to a first aspect of the invention, this problem is solved by a cleaning system for the partial external cleaning of can blanks, comprising a conveying device for conveying can blanks along a movement path with a superimposed rotational movement about a rotational axis oriented transversely to the movement path, a cleaning device with a cleaning belt whose outer surface defines a cleaning section which extends at least partially along the movement path and which is designed for contact between the cleaning belt and a surface area of ​​the can blanks.

[0005] The cleaning system is designed to clean a specific area of ​​the outer surface of the can blank, which will then be printed using an inkjet digital printing process. This does not preclude the possibility of printing other areas of the can blank's outer surface using the same inkjet digital printing process. The targeted cleaning of the outer surface of the can blank takes place in that area which, in a previous manufacturing step, was coated with a lubricant or release agent and which, without the cleaning process, would compromise the reliable adhesion of the ink applied using the inkjet digital printing process.

[0006] For example, in the case of a metal beverage can that is to be printed using inkjet digital printing, a deformation step is required in the area of ​​the can opening prior to printing. This deformation step is carried out as a pulling process, resulting in a narrowing of the can opening. To enable this pulling process, the can blank is coated with lubricant around the can opening. The lubricant is preferably a food-grade lubricant that is approved for human consumption by the relevant food safety authorities and can therefore remain on the can blank.

[0007] To ensure the adhesion of the ink applied using inkjet digital printing not only in areas of the outer surface away from the lubricant wetting, but also in the lubricant-wetted area, this area of ​​the outer surface must be cleaned. This cleaning should at least reduce the amount of lubricant on the outer surface of the can blank. In principle, a thermal process for evaporating the lubricant could be used for this purpose; however, this is disadvantageous in terms of energy efficiency and environmental impact from lubricant vapors.Alternatively, a washing process could be used, but due to the subsequent drying of the can blank that is necessary, energy efficiency is also considered a disadvantage, and depending on the detergent used, detergent residues remaining on the outer surface of the can blank can also be problematic for the adhesion of the printing ink.

[0008] In contrast, the cleaning device's cleaning belt performs a mechanical cleaning of the outer surface of the can blank. This is achieved through a relative movement between the can blank and the absorbent, particularly sponge-like, cleaning belt, reducing the amount of lubricant on the outer surface of the can blank by 50 to 90 percent. Furthermore, the friction between the cleaning belt and the outer surface of the can blank, which occurs during this relative movement, ensures an even distribution of the lubricant remaining on the outer surface of the can blank.Since the lubricant tends to form droplets due to the surface energy of the typically painted outer surface and its own surface tension, reducing the amount of lubricant, in conjunction with the resulting friction, ensures that a large number of lubricant droplets remain on the outer surface after the cleaning process. However, these droplets are so small that they are covered by the ink droplets dispensed during the inkjet digital printing process in such a way that the adhesion of the ink droplets to the outer surface is not compromised. Furthermore, the lubricant droplets are preferably so small that the ink droplets are stable enough to prevent the lubricant droplet from penetrating the protective layer formed by the covering ink droplet, even in the event of subsequent frictional contact between the printed outer surface of the can blank and other objects.

[0009] For efficient cleaning, the cleaning system includes a conveying device designed to transport the can blanks along a path of movement, imparting a rotational motion to them. The axis of rotation of this motion is oriented perpendicular to the path of movement. For example, the path of movement may be straight and horizontal, and the cleaning of rotationally symmetrical can blanks, particularly those with a predominantly circular cylindrical shape, may be required. These can blanks can be fed to the cleaning system, for example, by a conveying system upstream of the cleaning system, such as a conveyor belt, and then pass through the cleaning system along the path of movement.Since the conveying device is designed to additionally impart a rotational movement to the can blanks, which is oriented perpendicular to the path of movement, it can be provided, for example, that the can blanks rotate around their rotational symmetry axes which are oriented in a vertical direction and thus perpendicular to the horizontal path of movement.

[0010] The cleaning belt is positioned on the conveyor system to ensure partial contact with the outer surface of the can blanks. The area of ​​the cleaning belt's outer surface that comes into contact with the can blanks' outer surface during conveying is also referred to as the cleaning section. This cleaning section extends along the conveyor's path, which may be longer than the cleaning section.

[0011] The cleaning belt can be made from a single material, for example, a natural material or plastic suitable for absorbing the lubricant. Preferably, the cleaning belt has a multi-layered structure and comprises a flexible, dimensionally stable carrier layer and an elastic absorbent layer made of a natural or plastic material, designed to absorb the lubricant. The carrier layer's function is to transmit forces between the cleaning device and the can blanks, while the elastic absorbent layer's function is to conform elastically to the outer surface of the can blanks under the influence of the forces acting between the cleaning device and the can blanks.This elastic adaptation is intended to ensure that during the relative movement between the cleaning belt and the can blank, as much of the lubricant as possible can be absorbed by the absorbent layer and that the lubricant remaining on the outer surface of the can blank is distributed as finely as possible.

[0012] Advantageous further developments of the invention are the subject of the dependent claims.

[0013] It is advantageous for the cleaning device to have a belt guide for the cleaning belt, wherein the belt guide includes a drive unit designed for linear movement of the cleaning belt along the cleaning path. The belt guide serves to guide the cleaning belt in such a way as to enable the desired force transmission from the cleaning belt to the can blanks. Furthermore, the belt guide serves to initiate a linear movement of the cleaning belt along the cleaning path in order to produce the desired relative movement between the outer surface of the can blank and the cleaning belt. This movement can optionally be synchronous, counter-rotating, or alternating between synchronous and counter-rotating motions between the cleaning belt and the can blank.In co-rotating motion, the local direction of movement of the cleaning belt at a point of contact with the can blank is aligned with the local direction of movement of the can blank at that point of contact. To achieve the desired relative motion between the can blank and the cleaning belt, the local speeds of the can blank and the cleaning belt differ at the point of contact. In counter-rotating motion, the local direction of movement of the cleaning belt at the point of contact with the can blank is aligned in the opposite direction to the local direction of movement of the can blank at that point of contact. A change between co-rotating and counter-rotating motion can be achieved, for example, by a linear oscillation motion of the cleaning belt.

[0014] The synchronous and / or counter-rotating motion of the cleaning belt is generated by a drive unit, which may be electric, hydraulic, or pneumatic, designed to move the cleaning belt linearly within the cleaning path. A purely linear drive, such as an electric linear actuator or a hydraulically or pneumatically operated telescopic cylinder, can be used for this purpose. Alternatively, the drive unit may be designed to provide a rotary motion, allowing the cleaning belt to be unwound from or wound onto a spool. In this case, a second spool is preferably provided, onto which the cleaning belt is wound or from which it is unwound.For example, the cleaning belt can be housed in a cassette in which two spools are rotatably mounted. The drive mechanism powers one of the spools to wind the cleaning belt onto it and simultaneously unwind it from the other spool. The cleaning path extends between the two spools, and guides can be provided for the cleaning belt to ensure it always runs parallel to the surrounding area.

[0015] It is advantageous if the conveyor belt, located away from the cleaning section, includes a belt washing device for the cleaning belt, designed for continuous washing. The belt washing device serves to subject the cleaning belt, which is contaminated with lubricant after contact with the outer surface of the can blanks, to a washing process in which at least the majority of the lubricant is removed from the cleaning belt. Accordingly, the belt washing device is arranged downstream of the cleaning section, so that the cleaning belt only passes through the belt washing device after it has traversed the cleaning section and picked up the lubricant from the can blanks.For the washing process to be carried out, the cleaning belt passes through the belt washing device along a straight or at least partially curved cleaning path, thus performing a relative movement, also known as a continuous motion. The belt washing device can have one or more spray nozzles with which a washing liquid, for example, water mixed with a grease-dissolving substance, is sprayed onto the outer surface of the cleaning belt. Additionally or alternatively, the belt washing device can have a washing drum that is at least partially enclosed by the cleaning belt and has a perforated surface from which the washing liquid can be forced into the cleaning belt.The belt washing system can be designed as a closed system, in which the washing liquid dispensed onto the cleaning belt remains within the system and is, for example, circulated in a closed loop. Alternatively, the belt washing system can be designed as an open system, in which excess washing liquid can leave the system and, for example, drip into a collection tray located below the system.

[0016] In a further development of the invention, the belt guide is provided with a belt drying device for the cleaning belt, located away from the cleaning section. This drying device is designed for continuous drying of the cleaning belt. Since drying of the cleaning belt is only to take place after it has already passed through the belt washing device, the belt drying device is arranged downstream of the belt washing device and thus also downstream of the cleaning section. Like the belt washing device, the belt drying device is designed for continuous treatment of the cleaning belt and comprises at least one drying component from the group consisting of: squeeze roller, perforated drum, and suction device.A squeeze roller is rotatably mounted on a machine frame of the cleaning system and locally compresses the cleaning belt. The elastic deformation of the belt forces the cleaning fluid and lubricant absorbed by the belt out. For example, the cleaning belt may be guided through a squeeze gap defined by two opposing squeeze rollers or by one squeeze roller and an opposing sliding surface. Additionally or alternatively, a perforated drum can be used to dry the cleaning belt. A perforated drum is, for example, designed as a circular cylindrical sleeve rotatably mounted on a machine frame of the cleaning system, with a multitude of holes machined into the sleeve wall.Furthermore, it is provided that the perforated roller is at least partially enclosed by the cleaning belt, whereby a pre-tension exerted on the cleaning belt creates a compression effect on the cleaning belt in the area of ​​the perforated drum, allowing washing fluid and lubricant to flow through the holes into the interior of the perforated roller and from there out through an opening at the end face of the perforated roller. In a suction device, a suction nozzle located directly opposite the cleaning belt is pressurized with negative pressure to extract the washing fluid and lubricant from the cleaning belt.

[0017] In a further embodiment of the invention, a first end section of the cleaning path is defined by a first deflection roller associated with the belt guide, which is at least partially enclosed by the cleaning belt, and a second end section of the cleaning path is defined by a second deflection roller associated with the belt guide, which is at least partially enclosed by the cleaning belt. This achieves an advantageous positioning of the cleaning belt along the cleaning path. Depending on the pretension of the cleaning belt, the cleaning path runs either in a straight line or in an arc between the first and second deflection rollers and is always tangential to both deflection rollers.

[0018] Preferably, the cleaning belt is designed as an endless circular ring. This allows the cleaning belt to be guided in a continuous, infinite circular motion along the cleaning path and, away from the cleaning path, for example with the aid of a belt washing device and a belt drying device, to be processed in such a way that an advantageous cleaning effect can always be ensured by the cleaning belt along the cleaning path.

[0019] It is advantageous for the conveying device to have an endlessly circulating conveyor belt that partially wraps around a first pulley, which defines the beginning of the path of travel, and a second pulley, which defines the end of the path of travel. The conveyor belt also partially wraps around a further pulley, which is connected to a drive motor. This allows the conveying device to provide continuous conveying motion for the can blanks along the path of travel, which is particularly important in the mass production of can blanks. The drive motor is designed to provide rotational motion to the further pulley, thereby causing the endless circulation of the conveyor belt around both the first and second pulleys.

[0020] In an advantageous embodiment of the invention, a rolling surface oriented parallel to the path of travel is arranged opposite a conveyor belt section extending between the first and second pulleys. This rolling surface, together with the conveyor belt section, defines a conveying gap for the can blanks, which is matched to the outer diameter of the can blanks. The rolling surface is designed to support the typically circular cylindrical side walls of the can blanks. The distance between the conveyor belt section and the rolling surface is dimensioned such that force transmission between the conveyor belt and the rolling surface occurs in a spatial direction perpendicular to the rolling surface. This force transmission results in a normal force acting from the rolling surface onto the side walls of the can blanks.This normal force, together with a coefficient of static friction that depends on the material properties of the outer surfaces of the can blanks and the material properties of the rolling surface, determines a static friction force directed in the direction of the path of travel. This static friction force results in a torque on the can blank and induces the desired rotational movement of the can blank, which is superimposed on the linear movement of the can blank as it is conveyed along the path of travel. This superimposed rotational movement ensures that the can blank comes into contact with the cleaning belt over its entire circumference during conveying along the path of travel, thus ensuring complete cleaning of the lubricated outer surface area of ​​the can blank.

[0021] Preferably, the unwinding surface and the conveyor belt section are aligned parallel to each other, and the outer surface of the cleaning belt is oriented at an angle between 0 and 45 degrees to the unwinding surface or the conveyor belt section. Preferably, the angle between the outer surface of the cleaning belt and the unwinding surface or the conveyor belt section is adjustable to ensure the largest possible contact area between the cleaning belt and the can blank. The angle setting for the cleaning belt depends in particular on the geometry of the can blank, which is typically tapered conically in the area of ​​its opening.

[0022] It is advantageous if a transport device extending at least along the path of travel is arranged between a conveying plane defined by the conveyor belt section and a rolling plane defined by the unwinding surface. This transport device comprises a circulating conveyor belt designed to support a base area of ​​the can blank. The purpose of the transport device is to provide additional support for the can blanks so that they can be guided along the path of travel in a statically determinate manner. Preferably, the path of travel is oriented horizontally, and the conveyor belt, which may be designed, for example, as an endless belt or an endless link chain, is arranged vertically below the conveyor belt section and the rolling surface, forming a horizontally oriented support surface for the can blanks.It is particularly preferred that the can blanks rest on the conveyor belt with the can bottom facing down, so that the openings of the can blanks are located vertically above the unwinding surface.

[0023] According to a second aspect of the invention, the object of the invention is achieved by a method for the partial external cleaning of can blanks, comprising the following steps: moving a conveyor belt along a path of movement, feeding a can blank into a conveying gap which is bounded by a conveyor belt section and a rolling surface arranged opposite the conveyor belt section, in order to convey the can blank along a path of movement with a superimposed rotational movement about an axis of rotation oriented transversely to the path of movement, in order to bring the can blank into contact with a cleaning belt, the outer surface of which defines a cleaning section which extends at least partially along the path of movement, wherein the external cleaning of the can blank is caused by contact between the cleaning belt and a surface area of ​​the can blanks.

[0024] According to a third aspect of the invention, the object of the invention is achieved by using a cleaning system according to the invention for selective external cleaning of can blanks.

[0025] The object of the invention is achieved according to a fourth aspect of the invention with a digital printing system for printing can blanks using the inkjet digital printing process, which comprises a cleaning system according to the invention and a digital printing machine, wherein the digital printing machine is arranged downstream of the cleaning system along a conveyor path for can blanks.

[0026] With a digital printing machine, each can blank can be individually decorated, or several can blanks can be decorated with the same design. The digital printing process involves the contactless application of ink droplets, dispensed by one or more digital printheads, to the outer surface of the can blank. The ink used is typically cured with ultraviolet light after application to the can blank's surface. To ensure optimal printing of the can blanks with the digital printing machine, minimizing the impact of lubricant residue on the ink's adhesion to the outer surface, the digital printing machine is integrated into the can production line in such a way that the can blanks to be printed have already been cleaned by the cleaning system before being fed into the machine.

[0027] In a further development of the digital printing system, it is provided that the digital printing machine has a machine frame with a rotatably mounted workpiece rotary table with can holders for securing individual can blanks, a drive device for initiating a rotary step movement onto the workpiece rotary table and at least one inkjet digital print head for printing on an outer surface of a can blank held in a can holder of the workpiece rotary table.

[0028] Such digital printing machines are known, for example, from the patent applications EP 2 860 515 A1, EP 3 473 446 A1 and EP 4 155 082 A1.

[0029] An advantageous embodiment of the invention is shown in the drawing. Here, the drawing shows: Figure 1 is a strictly schematic representation of a digital printing system with a cleaning system and a digital printing machine; Figure 2 is a perspective view of the cleaning system according to the Figure 1 , wherein the cleaning system comprises a conveying device, a cleaning device and a transport device, Figure 3 a perspective view of the cleaning device and the transport device, and Figure 4 a perspective view of the cleaning device according to the Figures 2 and 3 in a view from below.

[0030] One in the Figure 1 The digital printing system 1 shown comprises a cleaning system 2 and a digital printing machine 81.

[0031] The digital printing machine 81 comprises a workpiece rotary table 83 rotatably mounted about a rotary axis 82 and several workpiece fixtures 84, arranged in pairs on the workpiece rotary table. The workpiece fixtures 84 are individually rotatable about rotational axes 85 by means of drive means (not shown) and are designed to hold tube-shaped can blanks 3. In an annular area 87, which extends radially around the workpiece rotary table 83 and is swept by the workpiece fixtures 84 during a rotational movement of the workpiece rotary table 83, several workstations 88 to 98 are arranged, which are designed for processing and / or inspecting the can blanks 3.

[0032] Workstation 88 is a loading station where, for example, the can blanks 3 are pushed onto the workpiece holders 84 in pairs by a transport device 99, which is coupled to a loading system 7 (not shown in detail). The task of the loading system 7 is to arrange the can blanks 3, which are transported in a line along the movement path 6 with a vertical orientation of their rotational symmetry axis (coaxial with the rotational symmetry axis 5), in pairs and to transfer them into a horizontal orientation of their rotational symmetry axes so that workstation 88 can pick up the can blanks 3 from the loading system 7 and feed them to the digital printing machine 81.

[0033] As an example, at workstation 89, a first optical scan of the can blanks 3 determines their rotational position, for instance, to ensure correct rotational alignment of the can blanks 3 for a printing process at workstation 90. This is particularly important if the surface of the objects to be printed has features that must align with the printed image in a predetermined way. These features can be, for example, local indentations and / or raised areas (embossing) in and / or on the surface of the can blanks 3 and / or pre-printed areas that serve as a primer for the subsequent printing.

[0034] The workstation 90 is designed as an inkjet printing station, at which the can blanks 3 are printed during a rotational movement around respective rotational axes 85 using at least one inkjet printhead (not shown) in a predetermined area, preferably over the respective circumference.

[0035] Workstation 94 is designed as an inspection unit. The other workstations, 91 to 93 and 95 to 97, are used for further processing of the can blanks 3, for example, for curing the printed image or applying a protective varnish to the print.

[0036] At workstation 98, an unloading process takes place in which the can blanks 3 are removed from the mandrel-shaped workpiece holders 84 by means of a transport device 100 and fed to a further transport system not shown in detail.

[0037] The workpiece rotary table 84 performs a rotary step movement for the stepwise processing of the can blanks 3 at the respective workstations 88 to 98, in which the workpiece holders 84, arranged in pairs, are transported from a position opposite one of the respective workstations 88 to 98 to a position opposite one of the subsequent workstations 88 to 98. The rotary step movement is performed as a sequence of acceleration from standstill, deceleration from the reached target speed, and a subsequent standstill period. Preferably, a drive for the workpiece rotary table 83 (not shown in detail) is designed such that the acceleration and deceleration of the workpiece rotary table 83 are freely adjustable over a wide range, and the standstill period is completely adjustable, and can be adapted to the requirements of processing the respective can blanks 3 at the workstations 88 to 98.

[0038] The cleaning system 2 is arranged on the power supply of the digital printing machine 81 and is designed for at least partial cleaning of a circumferential surface on the outer circumference of the can blanks 3, as shown in the Figures 2 to 4 is shown in more detail below.

[0039] As the depiction of the Figure 1 In the diagram, which is to be understood as a top view looking vertically downwards onto the digital printing system 1, the can blanks 3 are conveyed by a conveyor 21 along a purely exemplary horizontal path of movement 4 through the cleaning system 2. This involves a superposition of a linear movement of the can blanks 3 along the path of movement 4 and a rotational movement of the can blanks 3 about a point perpendicular to the path of movement 4. Figure 1A rotation axis 5 oriented normal to the plane of representation is generated. This superposition of movements causes the can blanks 3 to come into contact with a cleaning section 52 of a cleaning device 51, which extends section by section along the movement path 4, over their entire circumference, but not necessarily over their entire outer surface.

[0040] The cleaning section 52 runs parallel to the movement path 4 and is arranged such that a shoulder area 8 of the can blanks 3 comes into contact with a cleaning belt 53. The superposition of the linear and rotational movements of the can blank 3 creates a wiping motion between the cleaning belt 53 and the shoulder area 8. This wiping motion removes a significant portion of the lubricant applied to the shoulder area 8 as a result of a previous forming step on the can blank.

[0041] In the Figure 2 is cleaning system 2, which is in the Figure 1 The cleaning system 2 is shown schematically in a perspective view. It comprises the cleaning device 51 and the conveying device 21. The following description refers to the Figures 2 to 4For example, the cleaning device 51 has a rectangular support frame 53 to which the individual components of the cleaning device 51 are attached. Some of the components are attached directly to the support frame 53, while other components are connected to the support frame 53 via unlabeled, purely exemplary plate-shaped brackets.

[0042] The cleaning device 51 comprises a drive motor 54 mounted on the support frame 53, a belt washing device 55, and a belt drying device 56. Furthermore, the cleaning device 51 includes, by way of example, a total of nine deflection rollers 61 to 69, some of which perform specific functions described in more detail below. The deflection rollers 61 to 69, together with the components described in more detail below, which also interact with the endlessly circulating cleaning belt 71 designed as a closed ring, form the belt guide.

[0043] The first deflection roller is arranged at a first corner 57 of the support frame 53 and, together with the second deflection roller 62, which is arranged at a second corner 58 of the support frame 53, serves to tension the cleaning belt 71 along the cleaning path 52. To ensure an advantageous cleaning effect of the cleaning belt 71, a support strip 74 extending between the first deflection roller 61 and the second deflection roller 62 is assigned to the rear side of the cleaning belt 71. However, the cleaning effect for the can blanks 3 can also be achieved without the support strip 74. The support strip 74 is connected to the support frame 53 by means of adjustable holders 12, the holders 75 being designed for adjusting the position of the support strip 74 in at least one spatial direction, preferably in two mutually perpendicular spatial directions, and in particular in three mutually perpendicular spatial directions.

[0044] At the end of the cleaning section 52, the cleaning belt 71 partially wraps around the second deflection roller 62 and then runs towards the third deflection roller 63, which serves as a drive roller and converts a rotational movement of the drive motor 54 into a circular movement of the cleaning belt 71. Starting from the third deflection roller 63, the cleaning belt 71 runs towards the fourth deflection roller 64, which is part of the belt washing device 55. By way of example, it is provided that the belt washing device 55 includes a 180-degree wrap around the fourth deflection roller 64 and that a spray head 75 is arranged adjacent to the fourth deflection roller 64. The spray head 75, purely by way of example, carries two spray nozzles oriented in opposite directions, as shown in the illustration. Figure 4Only one spray nozzle 76 is visible, while the other spray nozzle is concealed by a splash guard 77, designed purely as an example of a bent sheet metal part, arranged around the belt washing device 55. The spray nozzle 76, as well as the spray nozzle of the spray head 75 (not visible), are designed to spray a washing liquid, for example, water mixed with a grease-dissolving substance, onto the front surface 72 of the cleaning belt 71, which serves as the outer surface along the cleaning section 52. For this purpose, the spray head 75 is connected (not shown) to a washing liquid pump, which pumps the washing liquid from a tank (not shown) and supplies it under pressure to the spray head 75.

[0045] After passing through the belt washing unit 55, the cleaning belt 71 is deflected several times by the deflection rollers 65 to 69 and passes a perforated drum 78, several squeeze rollers 79, and a suction unit 80. The perforated drum 78 is designed as a sleeve-shaped hollow body, with one cylindrical wall of the perforated drum 78 provided with a plurality of bores. Opposite the perforated drum 78, a support plate 14 is arranged, which supports the force transmission from the perforated drum 78 to the cleaning belt 71 and thus enables local compression of the cleaning belt 71. This forces washing fluid from the cleaning belt 71 into the bores in the cylindrical wall of the perforated drum 78, allowing it to flow out through bores in the end face of the perforated drum 78.

[0046] Three squeeze rollers 79 are assigned to the seventh deflection roller 67, each designed to press the cleaning belt 71 against the seventh deflection roller 67 and thereby squeeze cleaning fluid out of the cleaning belt 71. The three squeeze rollers are kinematically coupled to one another via a common adjusting device 15, which allows the distance between the squeeze rollers 79 and the seventh deflection roller 67 to be set. Alternatively, each of the squeeze rollers 79 can be individually configured to adjust its distance from the seventh deflection roller 67.

[0047] After being deflected around the eighth deflection roller 69 and the ninth deflection roller 69, the cleaning belt 71 passes the suction device 80, which includes a suction shoe 16 that is adjustable on a U-shaped suction frame 17. The suction shoe 16 has a Figures 2 to 4a non-visible cavity open in the direction of the cleaning belt 71, which can be pressurized to allow the extraction of washing fluid from the cleaning belt 71.

[0048] The perforated drum 78 with the associated support plate 14, together with the squeeze rollers 79 and the suction device 80, forms the belt drying device 56. Depending on the application, it may be provided to use only the perforated drum 78 with the associated support plate 14, or only the squeeze rollers 79, or only the suction device 80, or a combination of two of these components in an embodiment of the belt drying device not shown.

[0049] The one in Figure 2The conveying device shown has a purely exemplary rectangular support frame 22 composed of profile parts, on which three pulleys 31, 32, 33 are rotatably mounted, which are designed to guide an endlessly circulating conveyor belt 23 forming a closed ring, as shown strictly schematically in the Figure 1 is shown. Furthermore, a drive motor 24 is attached to the support frame 22, which is designed to provide a rotational movement and can transmit this rotational movement to a pulley 34. The pulley 34 associated with the drive motor 24 sets the conveyor belt 23 into a circular motion, whereby a direction of movement is imprinted on the conveyor belt 23, which is in the Figure 2The direction 25 of the path of movement 4 shown in Figure 1 is determined by the conveyor belt. The conveyor belt 23 is designed such that it runs at least largely straight between the first pulley 31 and the second pulley 32 and defines a conveyor belt section 26 in this area, in which the conveyor belt 23 can come into force-transmitting contact with the side walls of can blanks 3. A force-fit transmission of force takes place from the conveyor belt 23 to the side walls of the can blanks 3, with the necessary support of the can blanks 3 being provided by a rolling surface 27 arranged opposite the conveyor belt section 26. The rolling surface can, for example, be fixed to the support frame 54 of the cleaning device 51 or to a transport device 41 described in more detail below and extends along the path of movement 4.Thus, the conveyor belt 23 and the rolling surface 27 define a conveying gap 27 through which the can blanks 3 are moved along the movement path 4 with a superposition of a linear movement along the movement path 4 and a rotational movement about the rotation axis 5 oriented transversely to the movement path 4.

[0050] In order to enable a beneficial cleaning effect for the shoulder area 8 of the can blank 3, which is usually most heavily coated with lubricant, the following is necessary according to the illustration of the Figures 2 and 3 It is provided that the flat front surface 72 in the area of ​​the cleaning section 52 is aligned at an angle of 20 degrees to the rolling surface 27 (preferably adjustable by means not shown), so that the most complete possible contact between the cleaning belt 71 and the shoulder area 8 of the can blank 3 is ensured.

[0051] Particularly preferred is the arrangement in which the conveying device 21 and the cleaning device 51 are jointly mounted on a transport device 41 and thus have a defined spatial orientation relative to each other. The transport device 41, by way of example, has an endlessly circulating conveyor belt 42, with transport rollers (not shown) arranged at the ends of the transport device 41 to deflect the conveyor belt 42. The conveyor belt 42 is designed to support the can blanks 3 at their base.Preferably, the conveyor belt 42 is made of a material that has a low coefficient of static friction and a low coefficient of sliding friction compared to the can blanks 3, so that the can blanks 3 lie on the conveyor belt 42 with low friction and the movement of the can blanks 3 is caused at least almost exclusively by the force being introduced by means of the conveyor belt 23 and the rolling surface 27.

Claims

1. Cleaning system (2) for area-wise external cleaning of can blanks (3), comprising a conveying device (21) designed for conveying can blanks (3) along a movement path (4) with a superimposed rotational movement (6) about a rotational axis (5) oriented transversely to the movement path, and a cleaning device (51) comprising a cleaning belt (71) whose outer surface (72) defines a cleaning section (52) which extends at least sectionally along the movement path (4) and which is designed for contact between the cleaning belt (71) and a surface area (8) of the can blanks (3).

2. Cleaning system (2) according to claim 1, characterized by the fact that the cleaning device (51) has a belt guide for the cleaning belt (71), wherein the belt guide includes a drive device (54) designed for linear movement of the cleaning belt (71) along the cleaning path (52).

3. Cleaning system (2) according to claim 2, characterized by the fact that the belt guide away from the cleaning section (52) has a belt washing device (55) for the cleaning belt (71), which is designed for continuous washing of the cleaning belt (71).

4. Cleaning system (2) according to claim 3, characterized by the fact that the belt guide away from the cleaning section (52) has a belt drying device (78, 79, 80) for the cleaning belt (71) which is designed for continuous drying of the cleaning belt (71).

5. Cleaning system (2) according to one of claims 2 to 4, characterized by the fact thata first end area of ​​the cleaning section (52) is determined by a first deflection roller (61) associated with the belt guide, which is at least partially enclosed by the cleaning belt (71), and that a second end area of ​​the cleaning section (52) is determined by a second deflection roller (62) associated with the belt guide, which is at least partially enclosed by the cleaning belt (71).

6. Cleaning system (2) according to any one of claims 1 to 5, characterized by the fact that the cleaning belt (71) is designed as an endless circumferential ring.

7. Cleaning system (2) according to any one of claims 1 to 6, characterized by the fact thatthe conveying device (21) has an endlessly circulating conveyor belt (22) which partially encircles a first pulley (31) which defines a beginning of the movement path (4) and which partially encircles a second pulley (32) which defines an end of the movement path (4), wherein the conveyor belt (23) partially encircles a further pulley (34) which is associated with a drive motor (24).

8. Cleaning system (2) according to claim 7, characterized by the fact that Opposite a conveyor belt section (26) extending between the first pulley (31) and the second pulley (32) a rolling surface (27) is arranged which is aligned parallel to the path of movement and which together with the conveyor belt section (26) defines a conveying gap (28) for the can blanks (3) which is matched to an outer diameter of the can blanks (3).

9. Cleaning system (2) according to claim 8, characterized by the fact thatthe rolling surface (27) and the conveyor belt section (26) are aligned parallel to each other and that the outer surface (72) of the cleaning belt (71) is aligned at an angle between 0 degrees and 45 degrees to the rolling surface (27) or to the conveyor belt section (26).

10. Cleaning system (2) according to claim 8 or 9, characterized by the fact that A transport device (41) extending at least along the path of travel is arranged between a conveying level determined by the conveyor belt section (26) and a rolling level determined by the unrolling surface (27), which has a circulating conveyor belt (42) designed for supporting a bottom area of ​​the can blanks (3).

11. Method for the partial external cleaning of can blanks, comprising the steps of: moving a conveyor belt (23) along a movement path (4), feeding a can blank (3) into a conveying gap (28) which is bounded by a conveyor belt section (26) of the conveyor belt (23) and a rolling surface (27) arranged opposite the conveyor belt section (26) in order to convey the can blank (3) along a movement path (4) with a superimposed rotational movement about a rotational axis (5) oriented transversely to the movement path (4) in order to bring the can blank (3) into contact with a cleaning belt (71) whose outer surface (72) defines a cleaning section (52) which extends at least section by section along the movement path (4), wherein the external cleaning of the can blank (3) is caused by contact between the cleaning belt (71) and a surface area (8) of the can blanks (3). becomes.

12. Use of a cleaning system (2) according to one of claims 1 to 10 for area-specific external cleaning of can blanks.

13. Digital printing system (1) for printing can blanks (3) using inkjet digital printing, comprising a cleaning system (2) according to one of claims 1 to 10 and a digital printing machine (81), wherein the digital printing machine (81) is arranged downstream of the cleaning system (2) along a conveyor path for can blanks (3).

14. Digital printing system (1) according to claim 13, characterized by the fact thatthe digital printing machine (81) comprises a machine frame with a rotatably mounted workpiece rotary table (83) with can holders (84) for securing individual can blanks (3), a drive device for initiating a rotary step movement onto the workpiece rotary table (83) and at least one inkjet digital print head for printing an outer surface of a can blank (3) held on a can holder (84) of the workpiece rotary table (83).

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