Installation for the manufacture and inspection of metal containers

Abstract

An installation for the manufacture and inspection of metal containers, comprising a feeding device (101) for feeding metal discs (1), an extrusion press (102) for extruding the metal discs (1) and forming metal containers (10), each metal container (10) comprising a cylindrical body (11) with a side wall (12), a bottom (13) and an open end (14) opposite the bottom (13), and an inspection unit (200) for inspecting the metal containers (10) and for determining the thickness of the bottom (13) of the metal containers (10), characterized in that the inspection unit (200) comprises an X-ray emitter (20) and an X-ray receiver (21) for emitting X-rays from the X-ray emitter (20) to the X-ray receiver (21) through the bottom (13) of the metal containers (10), wherein a portion of the intensity of the X-rays is reflected by the bottom (13) of the metal containers (10) is absorbed, and a control unit (23),which is configured to determine the thickness of the bottom (13) of the metal container (10) based on the intensity of the X-rays absorbed by the bottom (13), wherein the X-ray emitter (20) is oriented towards the open end (14) of the metal container (10) and the X-ray receiver (21) is oriented towards the bottom (13) of the metal container (10).

Description

TECHNICAL AREA

[0001] The present invention relates to an installation for the manufacture and inspection of metal containers. STATE OF THE ART

[0002] Metal containers for holding beverages, food, or cosmetic and pharmaceutical products, such as beverage cans, deodorant spray cans, etc., are well-known. These types of metal containers are manufactured in continuous production lines from a metal disc, generally an aluminum or steel disc, which undergoes hot extrusion in an extrusion press in a process known as DWI (Draw and Wall Iron).

[0003] In this process, the metal disc is first extruded in an extrusion press to form a metal container comprising a cylindrical body with a side wall, a base, and an open end opposite the base. In a subsequent stage, the cylindrical body of the container is deformed in a neck forming machine (drawing machine) to create a neck at its open end. Finally, the container is completed—for example, in the case of aerosol cans—by placing an atomizer into the neck. The manufacturing process also includes other activities such as washing, applying coatings, painting, and screen printing on the container.

[0004] Technological advances in metal forming processes have led to containers with increasingly thinner profiles, making it essential to control the container thickness to detect the occurrence of defects that could compromise the structural integrity of the container.

[0005] Generally, container inspection is performed in a machine outside the container production line after the container is finished. Various dimensional parameters of the container are checked, including the side walls, or, in the case of aerosol cans, the connection between the neck of the container and the atomizer, using measuring sensors such as lasers. However, checking the thickness of the container base is particularly relevant because this parameter is directly related to the metal disc extrusion process, which takes place at the beginning of the metal forming process. That is, the thickness of the container base is essentially defined in the extrusion press, and any error in the base thickness affects the entire line, resulting in wasted resources in the production of a container that is later rejected.

[0006] EP3404357A1 discloses a method that allows the thickness of the bottom of a metal container to be determined on the container manufacturing line itself, thus making it possible to find out if the container thickness is defective before the container manufacturing is completed. The method comprises sending a first beam of electromagnetic radiation from a first measuring sensor, which strikes the inner surface of the bottom of the container along a horizontal line, and sending a second beam of electromagnetic radiation opposite the first beam from a second measuring sensor, which strikes the outer surface of the bottom of the container along another horizontal line, the horizontal lines of the beams having to coincide with each other.The distance between the measuring sensors and the bottom of the container is then calculated, and the thickness of the bottom of the container is determined by comparing the distances measured by the two measuring sensors.

[0007] WO9119164A1 discloses a system for quality control of geometrically regular shaped products using X-rays, for example, for measuring the wall thickness of metal tubes. CN111906151A discloses a method for checking the thickness stability of an aluminum strip using X-rays. US2004234027A1 discloses a system for measuring the layer thickness of a multilayer tube using X-rays. US2014183365A1 discloses a device for measuring the wall thickness of extruded products. REVELATION OF THE INVENTION

[0008] The invention relates to providing an installation for the manufacture and inspection of metal containers, as defined in the claims.

[0009] One aspect of the invention relates to an installation for the manufacture and inspection of metal containers, comprising a feeding device for feeding metal discs, an extrusion press for extruding the metal discs and forming metal containers, each metal container comprising a cylindrical body with a side wall, a bottom, and an open end opposite the bottom, and an inspection unit for inspecting the metal containers and determining the thickness of the bottom of the metal containers, wherein the inspection unit comprises an X-ray emitter and an X-ray receiver for emitting X-rays from the X-ray emitter to the X-ray receiver through the bottom of the metal containers, wherein a portion of the intensity of the X-rays is absorbed by the bottom of the metal containers, and a control unit configured toto determine the thickness of the bottom of the metal container based on the intensity of the X-rays absorbed by the bottom, wherein the X-ray emitter is oriented towards the open end of the metal container and the X-ray receiver is oriented towards the bottom of the metal container.

[0010] The thickness of the bottom of a metal container can vary in any area for various reasons, including defects in the raw material of the metal disc, misalignment of the extruder shaft in the extrusion press that extrudes the metal disc, and expansion or contraction of the extruder shaft due to press temperature. X-ray inspection allows the thickness to be determined at any point on the bottom of the container, as the X-rays allow the entire bottom of the container to be irradiated. In contrast, the EP3404357A1 measuring sensors, due to the nature of the laser beam, only allow thickness measurement along a horizontal line projected onto the bottom.Furthermore, the measuring sensors of EP3404357A1 must be perfectly aligned so that the lines projected onto the two surfaces of the container's base coincide, and any misalignment of the measuring sensors or any vibration of the containers during conveying can negatively affect the measurement; however, X-ray inspection obtains suitable measurements regardless of slight misalignments between the X-ray emission source and the X-ray receiver, and regardless of container vibration during conveying when measured. Unlike EP3404357A1, the thickness is determined on the container manufacturing line itself, and thickness control in a machine outside the production line is not required.

[0011] In addition, an inspection with X-rays also allows the determination of the circumference of the bottom of the metal container as well as the inspection of the molecular structure of the metal of the bottom in order to detect defects such as impurities, cracks or encrustations that would later lead to cracks.

[0012] These and other advantages and features of the invention become apparent with regard to the figures and the detailed description of the invention. DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a block diagram of an example installation for manufacturing metal containers. Fig. Figure 2 shows a schematic example of the forming of a metal disc into a metal container using an extruder of an extrusion press. Fig. Figure 3 shows the location of the X-ray inspection unit, which is located at the outlet of the extrusion press. Fig. Figure 4 shows a preferred arrangement of the X-ray emitter and the X-ray receiver for emitting X-rays onto the bottom of the container and for receiving X-rays in the receiver. Fig. Figure 5 shows a standard curve that links thickness values ​​of the metal containers with intensity values ​​of the X-rays absorbed by the material of the containers. Fig. Figure 6 shows X-ray images of the bottom of the metal containers, measured on a transfer unit. DETAILED REVELATION OF THE INVENTION

[0013] The production of metal containers, particularly aluminum or steel containers, for holding beverages, food, or cosmetic and pharmaceutical products (beverage cans, aerosol cans, etc.) requires a process that utilizes various machines arranged in a metal container manufacturing installation. Different types of machines can be used, depending on the tasks required to manufacture the container, and the machines can be arranged in various ways within the installation. Within these installations, containers are processed continuously on a container manufacturing line.

[0014] The 100 machines are automatically connected by means of transfer units 112, such as linear conveyor belts, rotary carousels, or similar elements, which transfer the containers 10 from one machine 100 to another. The production line is a high-speed line capable of processing approximately 200 containers per minute.

[0015] Fig. Figure 1 shows a block diagram of a non-restrictive example of an installation for manufacturing metal containers.This installation includes a feeding device 101 for feeding metal discs 1, an extrusion press 102 for extruding the metal discs 1 and forming metal containers 10, a cutter 103 for cutting the length of the container 10, a washing and drying assembly 104 for cleaning the container 10 after extrusion, an interior painting machine 105 for applying a coating to the interior of the containers 10, a painting machine 106 for coating the outside of the container 10 before printing a design, a decorating machine 107 for printing the design onto the container 10, a glazing machine 108 for coating the outside of the container 10 to protect the print, a neck forming machine 109 for forming the neck of the container 10, a crack detector 110 for detecting microcracks in any area of ​​the finished container 10, and a packaging machine. 111.The installation includes transfer units 112 for transferring the containers 10 from one machine 100 to another, ovens and coolers 113 to protect the various coatings applied to the containers 10, and accumulators 114 that allow the accumulation of containers 10 to synchronize the speed of all machines 100 in the installation. One oven 113 is located after the interior painting machine 105, followed by an accumulator 114, and another oven 113 is located after the glazing machine 108, followed by another accumulator 114. Another accumulator 114 is located after the washing and drying unit 104.

[0016] Although the machines 100 can be arranged in different ways and different types of machines 100 can be used, each installation for producing metal containers 10 includes at the beginning of the installation a feeding device 101 for feeding metal discs 1 and then an extrusion press 102 for extruding the metal discs 1 and forming metal containers 10, which comprise a cylindrical body 11 with a side wall 12, a bottom 13 and an open end 14 opposite the bottom 13.

[0017] Fig. Figure 2 shows a schematic example of the forming of a metal disc 1 into a container 10 by means of an extruder 1020 of the extrusion press 102, which forces the deformation of the disc 1 material and its forming into the container 10. The extrusion process is widely known and is not described in detail.

[0018] The invention proposes an installation for manufacturing and inspecting metal containers, configured for the following: feeding a metal disk 1, extruding the metal disk 1 to form a metal container 10 comprising a cylindrical body 11 with a side wall 12, a bottom 13, and an open end 14 opposite the bottom 13, and inspecting the metal container 10 to determine the thickness of the bottom 13. The inspection includes positioning the metal container 10 between an X-ray emitter 20 and an X-ray receiver 21, emitting X-rays from the X-ray emitter 20 to the X-ray receiver 21 through the bottom 13 of the container 10, with a portion of the intensity of the X-rays being absorbed by the bottom 13 of the container 10, and determining the thickness of the bottom 13 of the container 10 based on the intensity of the X-rays absorbed by the bottom 13.

[0019] The bottom 13 of the container 10 to be measured has a nominal thickness value of between 0.3 and 2 mm.

[0020] X-rays are high-energy (ionizing) electromagnetic radiation with a wavelength between 10 -9 and 10 -12 The distance is measured in meters. Based on its energetic nature, this radiation is able to pass through materials of different types and thicknesses.

[0021] Before the emitted X-rays strike the container, they exhibit a substantially uniform intensity distribution. Photon absorption and scattering after interacting with the container material leads to a change in the X-rays, which carries information about the structures through which the X-rays pass. The intensity of the X-rays passing through the material is attenuated depending on the material's thickness; therefore, the material's thickness can be determined by recording the unabsorbed intensity.

[0022] The absorption of X-rays in a material is governed by Lambert-Beer's law, which allows us to determine the intensity transmitted by the material. As shown in the following equation, this law states that transmitted radiation undergoes exponential decay as it passes through a material. I=I0e−μt where: I0 is the intensity of the X-rays emitted by the X-ray emitter, I the intensity of the X-rays received in the X-ray receiver is, µ is the absorption coefficient of the material at the bottom of the container, and t is the thickness of the material of the bottom of the container.

[0023] The invention therefore proposes inspecting the bottom 13 of the metal containers 10 using an X-ray inspection unit 200, which determines the thickness of the bottom 13 of the containers 10. The inspection unit 200 comprises an X-ray emitter 20 and an X-ray receiver 21 and can be placed at any point in the production line, for example, arranging the emitter 20 and the receiver 21 inserted between one of the transfer units 112 that transfer the containers 10 between the machines 100. The inspection unit 200 can also be arranged so that it is inserted between two transfer units 112, in which case the inspection unit 200 can be another of the machines 100 in the installation, or the emitter 20 and the receiver 21 can even be arranged in one of the machines 100 already present in the installation, such as the neck forming machine 109.

[0024] However, and preferably, the inspection is carried out after the extrusion of the metal disc 1, when the metal container 10 is hot, at a temperature ranging between 100 and 300 °C. In other words, the inspection is carried out at the outlet of the extrusion press 102, or even more preferably in the transfer unit 112, which transfers the hot and freshly extruded containers 10 from the extrusion press 102 to the next machine 100 of the installation, for example, the cutter 113. In this way, any container 10 that does not meet the thickness specifications can be discarded before it is processed in the next machine 100 of the installation.Given their nature, X-rays can be used to inspect the container 10 in a hot state, something that is not possible with measuring systems of a different type, such as the laser beam measuring sensors from document EP3404357A1, which cannot perform a measurement in a hot state because the heat emitted by the container prevents measurement with a laser beam.

[0025] Fig. Figure 3 shows a schematic view of the preferred location of the inspection unit 200. The inspection unit 200 is located at the outlet of the extrusion press 102 when the containers 10 are hot, at a temperature ranging from 100 to 300 °C. The installation includes a transfer unit 112, which transfers freshly extruded containers 10 from the extrusion press 102 to the next machine 100 of the installation, specifically to the cutter 103. The transfer unit is inserted between the X-ray emitter 20 and the X-ray receiver 21. The transfer unit 112 is a conveyor belt that conveys the containers 10, which are supported by its side wall 12. The X-ray emitter 20 and the X-ray receiver 21 of the inspection unit 200 are arranged perpendicular to the forward movement of the conveyor belt.

[0026] Even more preferred is the installation configured for determining the setting parameters of the extrusion press 102 for extruding the metal disc 1 and forming the metal container 10, determining, by inspection, the thickness of the base 13 of the container 10 being extruded in the extrusion press 102, and modifying the setting parameters of the extrusion press 102 if the thickness 13 does not meet a predetermined thickness value. This process of determining the thickness and modifying the setting parameters of the press is repeated until the thickness meets the predetermined thickness value.

[0027] The modification of the setting parameters of the extrusion press 102 includes at least the modification of the position of the extruder 1020, wherein the position of the extruder 1020 is set by moving the extruder forwards or backwards along its longitudinal axis in relation to the metal disc 1 to be extruded.

[0028] When initiating the process of manufacturing a metal container 10, the setting parameters of the extrusion press 102 are defined during the setup of the extrusion press 102 to produce the cylindrical body 11 of the container 10 from the metal discs 1. However, until the appropriate temperature is reached, many containers 10 will have to be rejected because the thickness does not meet the specified thickness value. If the thickness of the bottom 13 of the container 10 does not meet the defined specifications, for example, if the thickness in at least one area of ​​the bottom is less than the specified thickness, the container may be deformed or, even worse, crack during a subsequent manufacturing process or during the filling process.

[0029] Traditionally, an operator manually adjusts the extruder's position until the press begins producing containers of the required thickness. The extruder's length changes due to temperature, expanding as the temperature rises and contracting as it cools, for example, when the line shuts down. For instance, the extruder is a 500 mm long shaft that can expand or contract by 0.5 to 1 mm, affecting the thickness of the resulting containers. When the press starts and reaches the appropriate temperature, the extruder's length changes gradually, requiring the operator to manually adjust its position to achieve the required container thickness until the press reaches a stable temperature and, consequently, a consistent thickness of the produced containers is achieved.This manual adjustment can cause a significant number of rejections due to human error and a lot of wasted time; however, measuring with X-rays at the press output using a closed control loop allows the press to be adjusted automatically, thus reducing the number of rejected containers and the time required.

[0030] As in the Fig. 3 and Fig. As observed in Figure 4, the X-ray emitter 20 is preferably oriented towards the open end 14 of the container 10, and the X-ray receiver 21 is oriented towards the bottom 13 of the container 10. This ensures that the radiation passes completely through the bottom 13 of the container 10 and also ensures that the bottom 13 is close to the receiver 21, which performs the function of capturing the radiation emitted by the emitter 20. If the radiation were emitted in the opposite direction, that is, from the bottom 13 to the open end 14, a measurement of the bottom thickness that is as reliable as that obtained with the arrangement of Fig. 4 measurements received, not reached.

[0031] Even more preferred and as in Fig. As observed in section 4, the X-ray emitter 20 emits an X-ray beam 22 which has a focal point aligned with the center of the bottom 13 of the container 10. The center of the focal point is therefore approximately aligned with the center of the bottom 13 of the container 10, such that any geometric distortion resulting from conicity and other effects is symmetrical with respect to the center of the bottom of the container 10.

[0032] One of the possible effects caused by the conicity of the beam 22 is the extended optical path at any point away from the center of the conical beam 22, and the centered arrangement of the beam with respect to the base minimizes this effect. Furthermore, it is important to consider that the base of the container is not perfectly flat but twisted / convex, which is why it is preferable for the beam to be centered approximately in the middle of the base, because otherwise, considering the angle of the optical path and the slight angle of the base of the container, a double effect on the perceived thickness would occur.

[0033] The X-ray receiver 21 receives the X-rays after they have passed through the bottom 13 of the container 10 and obtains an X-ray intensity signal that corresponds to the intensity emitted by the X-ray emitter 20 minus the intensity absorbed by the bottom 13 of the container 10, where the absorbed intensity is proportional to the thickness of the bottom of the container. The X-ray receiver 21 also allows an X-ray image of the bottom of the container to be obtained in grayscale, where the shades of gray are proportional to the absorbed intensity and therefore proportional to the thickness of the bottom of the container.

[0034] A control unit 23 is responsible for processing the signal received in the X-ray receiver 21 in order to determine the thickness of the bottom 13 of the containers 10 based on the intensity of the X-rays absorbed by the bottom 13.

[0035] The thickness of the bottom 13 of the container 10 is determined by comparing the intensity of the X-rays received in the receiver 21 after passing through the bottom 13 with a transfer function that links the intensity values ​​with the thicknesses of the material of the metal containers 10, the transfer function being as follows: −Ln[I / I0]=μt where: I0 is the intensity of the X-rays emitted by the X-ray emitter 20, I the intensity of the X-rays received in the X-ray receiver 21 is, µ is the absorption coefficient of the material of the bottom 13 of the metal container 10, and t is the thickness of the material of the bottom 13 of the metal container 10.

[0036] The transfer function corresponds to a standard curve, as in Fig. Figure 5 illustrates this. The standard curve is obtained from known thickness values ​​of the material of the metal container 10 and the X-ray transmittance, which was calculated previously. The standard curve links thickness values ​​to the mathematical expression given above: Ln [ I / I0]

[0037] To obtain the standard curve, parts were used that are completely flat and have a constant thickness, similar to the metal containers 10 themselves. First, the actual thickness of these parts was determined using precision instruments, and then the intensity of the radiation absorbed by the parts was determined using inspection equipment 200. Accordingly, actual thickness values ​​of the containers 10 are obtained, and the behavior of the containers relative to the X-rays is known from these values. Therefore, when a metal container 10 is inspected with the inspection unit 200 in the installation, its thickness can be determined using the previously calculated standard curve.

[0038] As in Fig.As shown in Figure 6, an X-ray image is obtained of each of the inspected metal containers 10, and the X-ray image consists of areas that were previously calibrated using the standard curve to assign a thickness to each area. Specifically, each pixel of the image is assigned a thickness value obtained using the standard curve. Likewise, each pixel has a grayscale value, with the grayscale value assigned to a thickness value also determined using the standard curve. In other words, an X-ray image of the bottom of the metal container is obtained in which each pixel of the image is encoded with a thickness value.

[0039] In addition, the X-ray images allow the determination of the circumference of the bottom of the metal container as well as the detection of problems in the molecular structure of the container's material, since any defect that appears in the X-ray image can be observed in a non-homogeneous shade of gray.

[0040] For container inspection, an inspection unit 200 with the following specifications was used. The X-ray emitter 20 is a Spellman XRBD100PN210HR. This device has an emission capacity of up to 100 kV and 210 W. The available parameters are 35-100 kV and 0.5-4 mA. The X-ray receiver 21 is a 14-bit linear X-ray detector. The receiver is a Hamamatsu C14300-12U, which has twelve 128-pixel modules with a total reading length of 614.4 mm. The pixel size of this model is 0.4 mm.

[0041] To enable the determination of the thickness of the bottom 13 of the metal containers 10, the energy and current parameters of the X-ray emitter 20 identified below were selected.

[0042] The energy used is related to the penetration force with respect to the container material and also to the response signal received in the receiver 21 when the X-rays are received. The lower the energy, the higher the contrast obtained in the material, but the lower the signal received in the receiver. Furthermore, for radiation protection purposes, it is recommended to use the lowest possible energy. Accordingly, and preferably, the X-ray emitter 20 is configured to emit X-rays with an energy between 35 kV and 55 kV.

[0043] Even more preferably, the X-ray emitter 20 is configured to emit X-rays with an energy of 42 kV. Although it is true that the lower the energy used, the higher the contrast obtained in the measured signals, in the thinner areas of the bottom of the container 10, the signal received by the X-ray receiver 21 generates a lot of noise; therefore, the energy value of 42 kV is preferred in order to reduce the noise of the received signal.

[0044] Current is a parameter proportional to the emitted X-ray photon intensity. To obtain a better image, it is recommended to use the highest possible current, although for radiation protection reasons, the lowest possible current is recommended. Accordingly, and preferably, the X-ray emitter 20 is configured to emit X-rays with an intensity between 3 and 4 mA. Even more preferably, the X-ray emitter 20 is configured to emit X-rays with an intensity of 3500 µA. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3404357A1 [0006, 0010, 0024] WO 9119164A1

[0007] CN 111906151A

[0007] US 2004234027A1

[0007] US 2014183365A1

[0007]

Claims

[1] Installation for the manufacture and inspection of metal containers, comprising a feeding device (101) for feeding metal discs (1), an extrusion press (102) for extruding the metal discs (1) and forming metal containers (10), each metal container (10) comprising a cylindrical body (11) with a side wall (12), a bottom (13) and an open end (14) opposite the bottom (13), and an inspection unit (200) for inspecting the metal containers (10) and for determining the thickness of the bottom (13) of the metal containers (10), characterized in that the inspection unit (200) comprises an X-ray emitter (20) and an X-ray receiver (21) for emitting X-rays from the X-ray emitter (20) to the X-ray receiver (21) through the bottom (13) of the metal containers (10), wherein a portion of the intensity of the X-rays from the bottom (13) of the metal container (10) is absorbed,and a control unit (23) configured to determine the thickness of the bottom (13) of the metal containers (10) based on the intensity of the X-rays absorbed by the bottom (13), wherein the X-ray emitter (20) is oriented towards the open end (14) of the metal container (10) and the X-ray receiver (21) is oriented towards the bottom (13) of the metal container (10). [2] Installation according to claim 1, wherein the inspection unit (200) is arranged at the outlet of the extrusion press (102), wherein the metal containers (10) are hot, at a temperature ranging from 100 to 300 °C. [3] Installation according to claim 2, wherein the control unit (23) is further configured to: determine setting parameters of the extrusion press (102) which extrudes the metal disc (1) to form the metal container (10), determine, by inspection, the thickness of the bottom (13) of the metal container (10) being extruded in the extrusion press (102), and modify the setting parameters of the extrusion press (102) if the thickness (13) does not meet a predetermined thickness value. [4] Installation according to claim 3, comprising a transfer unit (112) that transfers freshly extruded metal containers (10) from the extrusion press (102) to the next machine (100) of the installation, wherein the transfer unit (112) is inserted between the X-ray emitter (20) and the X-ray receiver (21). [5] Installation according to one of the preceding claims, wherein the X-ray emitter (20) emits an X-ray beam (22) having a focus center aligned with the center of the bottom (13) of the metal container (10). [6] Installation according to one of the preceding claims, wherein the control unit (23) is further configured to determine the thickness of the bottom (13) of the metal container (10) by comparing the intensity of the X-rays received in the X-ray receiver (21) after they have passed through the bottom (13) with a transfer function that links the intensity values ​​with thicknesses of the material of the metal containers (10), and wherein the transfer function is as follows: −Ln[I / I0]=μt where: I0 is the intensity of the X-rays emitted by the X-ray emitter (20), I the intensity of the X-rays received in the X-ray receiver (21) is, µ is the absorption coefficient of the material of the bottom (13) of the metal container (10), and t is the thickness of the material of the bottom (13) of the metal container (10). [7] Installation according to one of the preceding claims, wherein the X-ray emitter (20) is configured to emit X-rays with an energy between 35 kV and 55 kV. [8] Installation according to claim 7, wherein the X-ray emitter (20) is configured to emit X-rays with an energy of 42 kV. [9] Installation according to one of the preceding claims, wherein the X-ray emitter (20) is configured to emit X-rays with an intensity between 3 and 4 mA.

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