Improved enamel rating process for metal objects

Abstract

An enamel rating process that aids determination of the location of a defect in a lacquer coating of a metal can by connecting the can to at least one contact of an external circuit; inserting an electrode into the can; filling the can with an electrolyte while applying a voltage to the electrode; and sensing any current flowing through the external circuit during filling of the can; wherein the level of the electrolyte upon sensing of a predetermined level of current flow is determined to identify the location of the defect.

Description

[0001] Improved Enamel Rating Process for Metal Objects

[0002] Field of the Invention.

[0003] The present invention relates generally to an enamel rating process and apparatus to enamel rate metal objects, such as metal containers including food and beverage containers and their lids.

[0004] Background

[0005] Metal containers may be used for all kinds of storage and product preservation purposes. These containers are frequently referred to as cans and are normally made of thin aluminium or steel plate. The plate is often coated with a layer of tin, known as ‘tinplate’ . The plate without the tin is referred to as the ‘black plate’ . It is important to make sure that the content of the can does not react with the metal of the container and therefore most cans are provided with a layer of lacquer (or enamel) that covers the entire inside of the can. This layer ensures that the content of the can does not corrode the metal and that the metal does not have any adverse effect on the content of the can. As such, it is critical to ensure that the lacquer layer forms a totally closed layer without any openings which would allow the metal and can content to contact one another.

[0006] Figure 1 illustrates one example of a can-making process according to the prior art, in particular in relation to a welded three-piece can making process. In this example, the process includes the steps of lacquering metal sheets that are cut from a coil, cutting the sheets into blanks using a slitter and then rolling and welding the blanks to form the cylindrical can. A base plate is seamed onto the base of the can, followed by a necking and flanging stage to create a foot that has a seal between the cylindrical sheet and base plate. These multiple stages of production may lead to defects in lacquer covering the can and therefore a sample of cans must be tested to ensure that the lacquer is not defective. Therefore, an enamel rating test is carried out on some of the cans prior to the palletizing stage to check the integrity of the lacquer coating applied to the interior surface of the can. Other types of can-making processes exist in the marketplace, and all require checking of the integrity of the lacquer coating to ensure there are no defects caused during production.

[0007] The method of checking the integrity of the lacquer layer is carried out by measuring the conductivity of the can. This destructive test was developed many years ago and involves filling the can with a conductive liquid or electrolyte, most commonly salt water. An enamel rater apparatus is used for carrying out the test which measures the conductivity of the can, the apparatus comprising an electronic gauge and a device for holding the can and connecting it to the gauge. The gauge includes a probe forming an electrode that is immersed in the electrolyte and the metal substrate (can) is connected via exterior contacts. A constant voltage of 6.3 V is applied to the electrode for around 4 seconds. The electrolyte has the potential to create an electrical circuit when the voltage is applied to the electrode, with negatively charged salt ions migrating to the positive electrode (anode) formed by the contacts attached to the metal substrate. However, this can only occur if there is a discontinuity in the lacquer coating. The lacquer coating is non-conductive so will be prevent any current flowing if it forms a continuous layer. If there is a hole in the coating, the conductive metal of the can will be exposed, completing the circuit and enabling current flow. The gauge detects and measures this flow to identify cans with a defective coating. Each particular product / content and can combination has a defect current level that should not be exceeded. The process is also carried out for a predefined period of time, normally 4 seconds. Thus, if the recorded level is too high, the can will be considered to be unsuitable for use and scrapped.

[0008] If current does flow indicating a faulty coating, it is useful to know where the damage has occurred. This may be done by reversing the electrical polarity of the circuit. This causes bubbles of gas to form on any exposed metal for easy visual identification. The electrical current passing through the electrolyte causes electrolysis, splitting the electrolyte into gases causing the formation of bubbles. Reversing the voltage changes the charge on the electrodes which results in bubbles forming at the region of the coating defect on the can. However, these bubbles can be very tiny and difficult to see. If they are very small, they may dissolve in the electrolyte as they are formed. Increasing the time for the test can assist in resolving this issue; the destructive nature of the test will increase the size of the defect, increasing the current recorded and increasing the size of the bubbles which will become easier to see. Once the bubbles can be seen, the defect location can be determined. This is a manual process and the operator of the enamel rater must identify the bubbles and their location.

[0009] For a particular product / content and can combination, there will be a maximum enamel rating value that is acceptable. For example, if the content of the can has an aggressive composition, the value of the enamel rating should be kept very low but if the content is not aggressive, a high enamel rating may be considered acceptable.

[0010] It is desirable to be able to locate the exact position of the defect on the can so that this may be correlated to the equipment used in its manufacturing process to enable this to be addressed to correct the problem, thereby reducing the amount of scrap and customer complaints.

[0011] The performance of the enamel rating process also requires repeated manual activation of buttons to start different parts of the process. For example, in conventional processes, it is necessary to press a button to reverse the electrical polarity when a damaged can is detected. If significant numbers of cans are being processed, this results in substantially greater manual input being required and increases the overall time of the enamel rating process. It would be beneficial to reduce the number of times a switch has to be manually activated to provide increased automation of the process.

[0012] Additionally, the electronic unit used in the enamel rating process must be calibrated at least once a year under ISO requirements. This requires the unit to be sent off site or for an external person to visit the premises. During this time, the enamel rating process cannot be continued unless a spare unit is purchased or hired. If a fault develops in between two calibrations, this may go unnoticed and lead to faulty measurement results for a prolonged time. Non ISO standard calibration of the equipment can be carried out between these checks by the provision of built in calibration resistors into every test fixture. Standard operating procedures recommend that before every measurement cycle, the operator verifies the system calibration and linearity and subsequently measures the batch. After the operator has measured the batch, the calibration is verified again. However, this test verification to assist in eliminating errors that may occur in between ISO calibrations are not always carried out correctly, if at all.

[0013] It is an object of the present invention to provide an improved enamel rater process and apparatus that overcomes, or at least alleviates, the abovementioned problems.

[0014] Summary of the Invention.

[0015] Aspects of the present invention relate to improvements in both manual or automatic enamel rating processes and apparatuses. In one aspect, manual processing is enhanced by making it easier to see a defect in a coating of a metal container, such as a can, using a higher reverse polarity step. In other aspects, automatic processing is enhanced by enabling automatic detection of the location of a defect in a coating of a metal container without any human intervention. Other aspects to the invention are also disclosed herein.

[0016] According to a first aspect of the present invention there is provided enamel rating process for testing the integrity of a lacquer coating on a metal container, the process comprising; filling the metal container with an electrolyte and connecting the container to at least one contact of an external circuit; inserting an electrode into the electrolyte; applying an initial voltage to the electrode; and measuring any current flowing through the external circuit; wherein, upon detection of current flow, after a predetermined period of time the polarity of the circuit is reversed and the voltage is increased above the initial voltage.

[0017] Preferably, the initial voltage is 6-7V, preferably 6.3 V. The process according to the first aspect of the present invention preferably provides a much higher voltage for the reverse polarity step, preferably being at least 1.2 times higher, more preferably 1.5 times higher, especially at least double the initial voltage. Preferably, the voltage during the reverse polarity step to at least 10V, preferably at least 12.5V, especially at least 25 V or even 30V.

[0018] Reversal of the polarity of the circuit is preferably carried out after at least 2 seconds, more preferably 4 seconds.

[0019] This embodiment makes it easier to see the defect but may still require manual inspection of the product to identify the location of the bubbles and thereby determine region of the defect. Optionally, an image capturing device, such as a video or camera may be linked to a processor to automatically determine the location of the defect upon application of the higher voltage.

[0020] A second aspect of the present invention provides for automatic determination of the location of the defect on the can or other metal container. In this aspect there is provided an enamel rating process for determination of a location of a defect in a lacquer coating on a metal container, the process comprising; connecting the container to at least one contact of an external circuit; inserting an electrode into the container; filling the metal container with an electrolyte while applying a voltage to the electrode; and sensing any current flowing through the external circuit; wherein the level of the electrolyte is determined upon sensing of current flow to identify the location of the defect.

[0021] Preferably, the level of the electrolyte is determined upon reaching a predetermined threshold level of current flow.

[0022] Preferably a lower voltage is applied during filling of the container, that is a voltage lower than the standard voltage of 6-7V.

[0023] A third aspect of the present invention also provides an enamel rating apparatus for carrying out the process according to the second aspect of the present invention, the apparatus comprising: at least one electrode for insertion into a metal container; at least one contact of an external circuit for contacting the container; an electrolyte source; a power supply; and at least one detector to determine fill level.

[0024] Different types of detectors to determine fill level may be utilized in the method and apparatus of the second and third aspects of the invention, such as a camera, weighing apparatus, a capacitance feeler, an ultrasonic level detector and an optical time of flight sensor.

[0025] In one embodiment, the process comprises filling the metal container with electrolyte at a fixed flow rate. Preferably, the voltage is applied upon commencement of filling of the container. Preferably a voltage lower than 6-7V is applied during filling of the container prior to detection of a defect. It is to be appreciated that with a non-faulty coating, the current will be zero (representing a container with a complete insulating lacquer layer preventing the formation of an electrical circuit). If, during the fill process, a current exceeding a predetermined threshold level is detected, the level sensor determines the amount of liquid that has been dispensed which is indicative of a height level of the defect that is present on the container.

[0026] More preferably, the process according to the second aspect of the invention includes the step of immediately removing the applied voltage from the electrode upon detection of the threshold current and filling the container before applying the voltage again, thereby ensuring that the real enamelrate reading is not affected by the process. This time the voltage is applied for the prescribed time (normally 4 seconds) and after that time the reading is taken.

[0027] In another embodiment, the level sensor comprises a weighing apparatus. Preferably, the empty container is placed on a weighing scale and the electrode is lowered into the container. The container is then filled up with the electrolyte. When a predetermined threshold current level is detected, the weight of the electrolyte dispensed is used to determine the elevation of the electrolyte in the container which may be used to determine the location of the defect in the lacquer coating. Again, if a current is detected before the container has been fully filled, the voltage will be removed and the can fully filled before the voltage is re-applied to allow a standard, complete enamel rating test to be carried out.

[0028] It is to be appreciated that the method and apparatus of the second aspect of the present invention may provide an output to a processor which may be configured to monitor and record the position of any defect located on a container. In this manner, the method and apparatus allows for full automation of the enamel rate test using appropriate electronic means.

[0029] The voltage may be applied continuously during filling of the container. In yet another embodiment of the present invention, a pulsed voltage may be applied during filling of the container, preferably wherein the pulsed voltage is less than 6.3 V.

[0030] Preferably, each pulse is a few micro-to milliseconds. If, during the pulse, a current flows it will be evident that a lacquer defect has occurred between the last pulse and the present one. This information can be used to determine the elevation of the defect in the container, for example by providing an output to a processor. The time pulses used in this embodiment are so short that they do not have a noticeable effect on the final enamel rate reading.

[0031] In another embodiment of the process according to the present invention, the thickness of the lacquer coating on the metal container may be measured and monitored to assess any fault in the thickness of the coating. In this respect, the metal container with an insulating lacquer layer and conducting liquid inside the container forms a capacitor, with the metal container and conducting liquid forming two parts of the capacitor and the lacquer forming the dielectric separating the two electrodes. This is another significant advantage of the present invention in that it allows detection of both a fault in the lacquer (for example in the form of a hole) and detection of a fault in the thickness of the lacquer applied whereas previously these types of fault would have to be checked using different types of enamel raters.

[0032] Once the base of the container is covered in electrolyte and the capacitance caused by the base is seen as a parasitic capacitance, the liquid level in the container determines the capacitance of the capacitor. If the liquid is filled with a constant flow rate the capacitance should increase linearly. This linear pattern may be recorded and serve as a reference. Any deviation from the linear pattern is caused by a lacquer layer that is either too thin or too thick wherein a thinner layer will show an increase of capacitance compared to the reference and a smaller capacitance will indicate and increased lacquer thickness. Thus, an increase or decrease in capacitance level may be used to determine the location of the defect in the layer.

[0033] In order to automate the process further, it is preferable to reduce the number of manual interventions that have to take place during the enamel rating process. To this end, another aspect of the present invention provides a process wherein the step of reversing the polarity of the voltage occurs automatically, for example switching automatically between the polarities after predetermined periods of time.

[0034] Additionally, the present invention provides an improved enamel rating process and enamel rater apparatus for enhanced calibration prior to carrying out the checks for faults in the lacquer coating. Preferably, the process and apparatus includes a feedback loop for adjusting the applied voltage based on a measured or reference voltage to provide a required output voltage at a measurement site.

[0035] Preferably, the apparatus comprises a main processor which handles data processing from the selection of inputs, including at least one, preferably all, of a main electrode, a voltage sense, a current sense, contact probe and a level probe to provide an output to a display, such as an LCD display which may include a touchscreen. The apparatus may be controlled via the touchscreen and / or a jog wheel may be provided for control of the apparatus by the user. Additionally, further probes may be included to increase the accuracy of the readings, such as a conductivity and / or temperature probe.

[0036] The feedback loop is preferably a digital feedback loop that measures the voltage on the actual container fixture and if it is too low tells the processor to increase the voltage until the desired voltage has been achieved.

[0037] A further aspect of the present invention provides for on-site calibration of the process and apparatus using a calibration box or housing that may be connected to the enamel rater apparatus. The housing includes a processor for comparing an applied current with a measured current, the processor making any necessary corrections to the applied current via a look-up table within the processor. For example, the calibration box loads the enamel rater with an initial current and then checks that the measured reading is the same, comparing the current measured by the apparatus with values stored on its look-up table. If the measured current is different, a correction process may be initiated through a digital feedback, with the calibration box instructing the enamel rater apparatus to increase or decrease its current reading until the reading of the apparatus is the same as the values stored on the look up table of the calibration box. After initial current tests, the calibration box may load different current values to the apparatus and verify that gauge readings are the same as the calibration box values stored on its look up table. The calibration box may also make sure the voltages measured by the calibration box and the enamel rater apparatus are always the same. Once measurements are the same, the calibration box updates the current and voltage reference settings of the gauge which will be the new voltage and current measurement reference of the enamel rater for the enamel rating test.

[0038] The box may use an advanced algorithm to provide precise, reliable and durable measuring using the enamel rater apparatus of the present invention. The calibration box preferably comprises a main processor that controls a combination of resistors for calibration of the system. It may also process internal temperature monitoring and real time clock and calendar RTCC for accurate calibration. It may also be provided with its own on-board power supply and an onboard ADC to measure voltage output of the enamel rater.

[0039] The present invention also provides additional optional features that may be incorporated into an enamel rating process and apparatus to further improve its efficiency.

[0040] Preferably, the apparatus includes a conductivity and / or a temperature probe to measure conductivity and temperature levels.

[0041] Another optional feature is an inspection light which is automatically switched on when a faulty can is detected by the apparatus. This will save time and enable manual viewing of the faulty can. Other aspects of the invention include a process or apparatus to include barcoding or QR coding of containers such as cans to allow their identification on a production line. In embodiments, the apparatus includes at least one barcode reader or QR code reader to read barcoded or QR coded cans to determine a production line of the cans. This enables faults to be correlated to a particular production line and thus allow correction of the fault. Additionally, or alternatively, the apparatus may include an interface with USB-Human Interface Devices (HID) enabling devices such as fingerprint readers, proximity card readers and the like to gather information that is linked to a can under test.

[0042] Other aspects of the invention include a process and apparatus for measuring any contamination of the electrode. Yet a further aspect relates to a process and apparatus for measuring the conductivity of the electrolyte.

[0043] A process for measuring contamination of the electrode may comprise measuring resistance between the electrode and a reference probe at spaced apart intervals of time, wherein a change in resistance indicates contamination of the electrode. Preferably, an alarm is activated upon reaching a predetermined level of contamination. An apparatus for measuring contamination of the electrode may also be provided, the apparatus comprising a reference probe for insertion in the metal container at a spaced apart distance from the electrode, the apparatus further comprising a resistance gauge to measure a change in resistance between the reference probe and the electrode.

[0044] Optionally a conductivity probe may be provided to monitor the conductivity of the electrolyte in the enamel rater.

[0045] Other improved features include monitoring and control of the temperature of the electrolyte and a built-in manual providing instructions for use of the enamel rater.

[0046] It is to be appreciated that any of the aspects of the present invention may be provided in combination with the other aspects of the invention. Brief Description of the Drawings

[0047] For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which:

[0048] Figure l is a schematic view of one example of a can-making process according to the prior art;

[0049] Figure 2A is a schematic diagram of an enamel rater set-up according to the prior art;

[0050] Figure 2B is a schematic diagram of circuity for a conventional enamel rating process according to the prior art;

[0051] Figure 3 is a block diagram of hardware for an enamel rater according to an embodiment of the present invention; and

[0052] Figure 4 is a block diagram of a calibration system for an enamel rater according to an embodiment of the present invention.

[0053] Detailed Description

[0054] The present invention provides an improved enamel rater and enamel rating process which allows easier and more accurate detection of the location of a defect within the lacquer coating of a metal substrate, in particular a can. Additionally, the equipment and process have been more fully automated with improved calibration checks.

[0055] As previously discussed in relation to Figure 1, the can-making process can result in defects in the lacquer coating and therefore a sample of cans are subjected to an enamel rating process as shown in Figures 2A and 2B of the accompanying drawings.

[0056] As illustrated in Figures 2A and 2B of the accompanying drawings, a selection of cans 10 are tested prior to the palletizing stage 12 to check the integrity of their lacquer coating. The enamel rater includes can stand 14 and an electrolyte container 16 linked to an enamel rater gauge 18. In a conventional enamel rating process a test probe 20 is immersed in an electrolyte 22 within the can 10 or other container to be tested and electrical contacts are attached to the metal container. A voltage of 6.3VDC is applied to the test probe for 4 seconds. If no coating was applied to the metal can, an electrical circuit would be created as electricity would be able to flow through the electrolyte creating a current flow. However, if the can is completely coated with the insulative coating or lacquer, no current will be able to flow. Thus, if a current is measured, this indicates a flaw, such as a scratch, in the applied coating. The electrical polarity of the circuit may then be reversed which results in bubbles being created in the region of the flaw, enabling the location of the coating fault to be detected. The current measured may be displayed on a LCD screen (not shown) of the gauge and the defective cans are disposed of after testing.

[0057] In one embodiment of the process according to the present invention, the enamel rating process is carried out in accordance with the prior art, but a significantly increased voltage is used for the reverse polarity step. It is standard in the art to apply the same voltage, generally 6.3 V as that used for the initial step. The process of the present invention applies a much higher voltage for the reverse polarity step, preferably being 2-6 times higher than the standard voltage.

[0058] By not just reversing the polarity but at the same time increasing the voltage considerably, the amount of gas (i.e. bubbles) generated, also increases considerably. This makes finding the defect location faster and easier. Thus, the first aspect of the present invention increases the voltage during the reverse polarity step to at least 10V, preferably least 12.5V, especially at least 25V or even 30V.

[0059] This embodiment makes it easier to see the defect but may still require manual inspection of the product to identify the location of the bubbles and thereby determine region of the defect. Potentially an image capturing device, such as a video or camera may be linked to a processor to automatically determine the location of the defect upon application of the high voltage.

[0060] The enamel rater may have a maximum power supply and therefore it may be necessary to limit the wattage to a maximum for the particular power supply. A further aspect of the present invention allows for automatic determination of the location of the defect on the can or other metal container. In one embodiment, instead of filling the whole can with a conducting electrolyte before a central electrode is inserted in the liquid, the electrode is inserted into the can before any liquid is introduced into the can. Once the electrode is in place the can gets filled with electrolyte and a liquid level sensor is used to identify at what point a defect is detected. Different types of level sensor may be utilized in the method and apparatus, such as weighing apparatus, a capacitance feeler or ultrasonic level detector.

[0061] Optionally, a lower voltage is applied during filling of the container, that is a voltage lower than the standard voltage of 6-7V. The use of a lower voltage than the normal voltage may be preferably as it means that if a defect is encountered during this process, the current will be lower and therefore the damage caused by this process before a real, standardized test is commenced will be lower.

[0062] In one embodiment, the can is filled with electrolyte at a fixed flow rate. The rating voltage will be applied right from the moment the can is being filled up. The rating current will normally be zero (as most of the cans have a complete insulating lacquer layer preventing the formation of a circuit). If during the fill process a current exceeding a threshold is detected, the amount of liquid that already has been dispensed is indicative of the height level of the defect that is present.

[0063] The voltage will then be immediately removed from the electrode and the can will be fully filled before the voltage is applied again, thereby ensuring that the real enamelrate reading is not affected. This time the voltage is applied for the prescribed time (normally 4 seconds) and after that time the reading is taken.

[0064] In another embodiment, the can is placed on a weighing scale and the central electrode is lowered into the can. The can is then filled up with electrolyte. In this embodiment, it is not a requirement to have a known flow rate. Instead, the weight of the liquid dispensed will be used to determine the elevation of the liquid in the can at the time when a current starts to flow which can then be used to determine the location of the defect in the lacquer coating. Again as above, if a current is detected before the can has been fully filled, the voltage will be removed and the can fully filled before the voltage is applied again to allow a standard, complete enamel rating test to be carried out.

[0065] The above method allows detection of the level in the can where the defect is present and therefore this method allows for full automation of the enamel rate test using appropriate electronic means. This was not possible before as the defect location had to be determined by a human looking for bubbles during the reverse polarity testing. In this embodiment, reversing polarity of the voltage becomes superfluous as no manual inspection is required.

[0066] In yet another embodiment of the present invention, instead of filling the can according to any of the above methods and waiting to see if a current starts flowing before the can is fully filled, it is also possible to fill the can and to, during the filling process, apply a rating voltage (that could be lower than normal), for a very short pulse (a few micro-to milliseconds). If during the pulse a current flows it will be evident that a lacquer defect has occurred between the last pulse and the present one. This information can be used to determine the elevation of the defect in the can. The time pulses are so short that they do not have a noticeable effect on the final enamel rate reading.

[0067] In another embodiment of the process according to the present invention, the thickness of the lacquer coating on the metal container may be measured and monitored to assess any fault in the coating thickness or the coating distribution on the container. The metal container with an insulating lacquer layer and conducting liquid inside the container forms a capacitor, with the metal can and conducting liquid forming two parts of the capacitor and the lacquer forming the dielectric separating the two electrodes.

[0068] Once the base of the can has been covered in electrolyte and the capacitance caused by the base is seen as a parasitic capacitance, the liquid level in the can determines the capacitance of the capacitor. If the liquid is filled with a constant flow rate the capacitance should increase linearly. This linear pattern will be recorded and serve as the reference. Any deviation from the linear pattern will be caused by a lacquer layer that is either too thin or too thick where thinner layer will show an increase of capacitance compared to the reference can and a smaller capacitance will indicate and increased lacquer thickness. Thus, this increase or decrease in capacitance level may be used to determine the location of the defect in the layer.

[0069] It is to be appreciated that the level may be determined by other methods, such as weighing, ultrasonics, a camera or a capacitance sensor.

[0070] Prior hereto separate enamel rating machines were used to detect a fault in the lacquer coating (eg in the form of a hole or scratch) and to detect a fault in the thickness of the lacquer coating. In this respect, it is critical that a container not only has a continuous coating without any holes or scratches but additionally the coating must be of a set thickness. The process of the present invention allows detection of both a fault in the lacquer and a fault in the thickness of the lacquer whereas previously these types of fault would have to be checked using different types of enamel raters.

[0071] The automatic determination of the location of the defect in the coating of the can or other metal container greatly assists the speed of processing of the coated metal products. In order to automate the process further, it is preferable to reduce the number of manual interventions that have to take place during the enamel rating process. To this end, another aspect of the present invention provides a process wherein the step of reversing the polarity of the voltage occurs automatically.

[0072] According to the prior art, the enamel rating process is semi-automatic. Manual intervention is only necessary once a defect is detected, wherein a button is pressed to reverse the polarity. The application of reverse polarity then stops when the can is removed. However, if a vast number of cans are being rated in sequence, this switching on to reverse the polarity significantly reduces the overall speed of the process. Furthermore, the constant use of the reverse polarity button often leads to it being damaged. The present invention provides automatic reversal of the polarity for a predetermined amount of time before automatically reverting to normal polarity. If a coating on a can is flawed, this will be visible during the reverse polarity step and the can may be removed but if the can is good, the reverse polarity will have no effect on the can. This will be determined by appropriate sensors and software and the process can continue, automatically switching back after the predetermined period of time to normal polarity. In this manner, the process increases the speed of the testing.

[0073] Existing automatic enamel raters require defective cans to be rejected and placed on to a manual retest conveyor wherein the defective can is subjected to a manual repeat test in the laboratory to find the position of the defect. Embodiments of the invention overcome this problem by enabling the location of the defect to be detected automatically, simplifying both the enamel rating process and apparatus.

[0074] Additionally, the present invention provides an improved enamel rating process and enamel rater apparatus for enhanced calibration prior to carrying out the checks for faults in the lacquer coating. Conventionally, the enamel rater apparatus has to be recalibrated at least annually to ensure the readings obtained via the apparatus are correct. This requires an onsite visit from a specialist operator or, more often, requires the apparatus to be sent away for a period of time. This is clearly undesirable because it is both costly and time consuming. In an embodiment of the present invention, the process and apparatus includes a calibration step or box to enable re-calibration of the apparatus on site.

[0075] Figure 3 of the accompanying drawings illustrates one embodiment of hardware architecture for an enamel rating apparatus and process according to the present invention. This may be connected to a calibration box according to another aspect of the invention, as shown in Figure 4. Referring to Figure 3, the hardware comprises a main board 50 housing the main processor (MCU1) 52 which handles data processing from a measurement board 70 and presents the output to a display 54, such as an LCD display which may include a touchscreen. The control of the gauge may be via the touchscreen or a jog wheel 56 and the main board 50 includes data storage 58 which may be accessed via communication ports 60. The measurement board 70 processes the voltages and current measured by the gauge and includes microprocessor 72 (MCU2) for communicating with the main board 50. The test fixtures 80 include the probes and sensors for conductance of the enamel rating test, including main probe 82, voltage sense 84, current sense 86, contact probe 88 and level probe 90. Additionally, further probes may be included to increase the accuracy of the readings, such as a conductivity and / or temperature probe (not shown).

[0076] The voltage used for enamel rating is chosen by the software in microprocessor 72 (MCU2). MCU2 will send a signal to the DAC in a rater voltage supply board 95 to make a certain voltage. This voltage is transported through cables to the actual fixture where the metal container or can is held for measurement. However, the current through the wires will cause the voltage to drop in the connecting wires which means that the actual voltage for enamel rating is no longer what the microprocessor (MCU2) said it should be. To compensate for this, the analog-to-digital convertor ADC1 measures the voltage on the actual can fixture and if it is too low tells the microprocessor (MCU2) to increase the voltage. This is effectively a digital feedback loop that will keep increasing the voltage until the desired voltage has been achieved as indicated by ADC 1.

[0077] In this process the microprocessor (MCU2) learns. If, for example, the voltage required is 6.3 volts, the MCU will start generating the DAC what it believes should generate the 6.3 volts at the point of measurement. If, through the feedback loop of the ADC, it learns that for a particular current it needs to send 6.4 volts to achieve the 6.3 at the point of measurement, then the MCU can store that information so in the future it will know what it needs to send to achieve the desired voltage at the measurement point.

[0078] A further aspect of the present invention provides for on-site calibration of the process using a calibration box 200 that can be connected to the enamel rater gauge 300, see Figure 4. The calibration works in a similar way to the learning of the microprocessor 72 of Figure 3. First the calibration box loads the enamel rater with a current of say 1 mA at 6.3 volts. It will then make sure that the voltage output of the enamel rater is 6.3 volts at the point of the main probe and verify if the current reading of the gauge is precisely 1mA. If the measured current is different, a correction process will be initiated through digital feedback wherein the calibration box will provide an output instructing the enamel rater to increase or decrease its current reading until the reading is 1mA. The calibration box will load different current values to the gauge and verify the readings are the same as the values stored on the look-up table of the calibration box. The calibration box will also make sure the voltage on the main probe is always at 6.3 volts in a similar manner using a correction process and digital feedback.

[0079] Figure 4 illustrates one embodiment of a calibration box that may be attached to the enamel rater IS810 for automatic calibration of the system. The box uses an advanced algorithm to provide precise, reliable and durable measuring using the enamel rater gauge of the present invention. The calibration box comprises a main processor MCU that controls a combination of resistors for calibration of the system. It also processes internal temperature monitoring and real time clock and calendar RTCC for accurate calibration. It also has its own on-board power supply PSU and an onboard ADC to measure voltage output from the enamel rater.

[0080] The present invention also provides additional optional features that may be incorporated into an enamel rating process and apparatus to further improve its efficiency. For example, as mentioned in relation to Figure 3, a conductivity and / or a temperature probe may be incorporated into the circuit to measure conductivity and temperature levels. In this respect, both the conductivity and temperature affect the enamel rater readings and therefore it is beneficial to be able to correlate the two. Another optional feature is an inspection light which is automatically switched on when a faulty can is detected by the apparatus. This will save time and enable manual viewing of the faulty can. Other features include using the barcode or QR code of the cans to determine production line, for example providing barcode or QR code readers to read cans and identify the production line of any faulty cans. This enables faults to be correlated to a particular production line and thus allow correction of the fault. Other improved features include monitoring and control of the temperature of the electrolyte and a built-in manual providing instructions for use of the enamel rater.

[0081] Other aspects of the invention include a process and apparatus for measuring any contamination of the electrode. A process for measuring contamination of the electrode may comprise measuring resistance between the electrode and a reference probe at spaced apart intervals of time, wherein a change in resistance indicates contamination of the electrode. Preferably, an alarm is activated upon reaching a predetermined level of contamination. An apparatus for measuring contamination of the electrode may also be provided, the apparatus comprising a reference probe for insertion in the metal container at a spaced apart distance from the electrode, the apparatus further comprising a resistance gauge to measure a change in resistance between the reference probe and the electrode.

[0082] Other features that may included with any combination of features of the invention already discussed are control and monitoring of external devices to enable the enamel rater to be interconnected with various systems. In this manner, speed of testing is increased. Additional features also include connectivity through the Ethernet, RS485 and USB to enable remote gathering of test data, firmware updates as well as remote control and monitoring of the system.

[0083] Further modifications to the enamel rater may be made without departing from the principles embodied in the examples described and illustrated herein.

Claims

CLAIMS:

1. An enamel rating process for testing the integrity of a lacquer coating on a metal container, the process comprising; filling the metal container with an electrolyte and connecting the container to at least one contact of an external circuit; inserting an electrode into the electrolyte; applying an initial voltage to the electrode; and measuring any current flowing through the external circuit; wherein, upon detection of current flow, after a predetermined period of time, the polarity of the circuit is reversed and the voltage is increased above the initial voltage.

2. The process according to claim 1, wherein the initial voltage is 6-7V, preferably 6.3V.

3. The process according to claim 1 or claim 2, wherein the voltage for the reverse polarity step is at least 1.2 times higher than the initial voltage, preferably 1.5 times higher, especially at least double the initial voltage.

4. The process according to claim 2, wherein the applied voltage during the reverse polarity step is at least 10V, preferably at least 12.5V, more preferably at least 25 V, especially at least 30V.

5. The process according to any one of claims 1 to 4, wherein reversal of the polarity of the circuit is carried after at least 2 seconds, preferably 4 seconds.

6. The process according to any one of the preceding claims, further comprising an image capturing step to automatically determine the location of the defect upon application of the higher voltage.

7. An enamel rating process for determination of a location of a defect in a lacquer coating applied to a metal container, the process comprising; connecting the container to at least one contact of an external circuit; inserting an electrode into the container; filling the metal container with an electrolyte while applying a voltage to the electrode; and sensing any current flowing through the external circuit;wherein the level of the electrolyte is determined upon sensing of current flow to identify the location of the defect.

8. The process according to claim 7, wherein the voltage applied during filling of the container is less than 6.3 V.

9. The process according to claim 7 or claim 8, wherein the level of the electrolyte is determined upon reaching a predetermined threshold level of current.

10. The process of claim 9, wherein the predetermined threshold level is 1mA or less, preferably 0.1mA.

11. The process according to any one of claims 7 to 10, wherein the level of the electrolyte is detected by reference to at least one of the following parameters selected from flow rate, height, capacitance and weight of the container upon detection of the threshold current or any other means.

12. The process according to claim 11, comprising filling the metal container with the electrolyte at a fixed flow rate and applying the voltage upon commencement of filling of the container, wherein upon detection of a current exceeding the predetermined threshold level, the level sensor determines the amount of electrolyte dispensed by reference to the flow rate to provide a height level of the defect that is present on the container.

13. The process according to claim 11, comprising placing an empty metal container on a weighing scale and inserting the electrode into the container, filling the container with the electrolyte and upon detection of the predetermined threshold current level, weighing the amount of electrolyte dispensed to determine an elevation of the electrolyte in the container to determine the location of the defect in the lacquer coating.

14. The process according to claim 11, 12 or 13, wherein the electrolyte is provided at a constant flow rate and a change in thickness of the lacquer coating on the metal container determines the location of the defect in the thickness of the coating, the process comprising sensing a change in capacitance during filling of the container, wherein a non-linear change in capacitance determines the location of the defect.

15. The process according to any one of claims 7 to 14, further comprising the step of immediately removing the applied voltage from the electrode upon detection ofthe threshold current, completely filling the container and re-applying the voltage to the filled container.

16. The process according to claim 15, wherein the voltage is re-applied for a prescribed time, preferably 2- 4 seconds and after that time a further reading is taken.

17. The process according to 15 or claim 156 further comprising applying a series of pulsed voltages during filling of the container wherein detection of the predetermined threshold current level during a pulse of voltage determines the location of the defect.

18. The process according to claim 17, wherein each applied pulse of voltage is less than 6.3 V.

19. The process according to claim 17 or claim 18, wherein each pulse of voltage is a few micro-to milliseconds.

20. An enamel rating apparatus for carrying out the process according to any one of claims 7 to 19, the apparatus comprising: at least one electrode for insertion into a metal container; at least one contact of an external circuit for contacting the container; an electrolyte source; a power supply; and at least one detector to determine fill level.

21. The apparatus as claimed in claim 20, wherein the detector to determine fill level is selected from at least one of a camera, weighing apparatus, a capacitance feeler, an ultrasonic level detector and an optical time of flight detector.

22. The apparatus as claimed in claim 20 or claim 21, further comprising an output to a processor configured to monitor and record the position of any defect located on a container.

23. The apparatus as claimed in claim 22, further comprising a feedback loop for adjusting the applied voltage based on a measured or reference voltage to provide a required output voltage at a measurement site.

24. The apparatus as claimed in claim 23, further comprising a main processor which handles data processing from a selection of inputs, including at least one of a mainelectrode, a voltage sense, a current sense, contact probe and a level probe to provide an output to a display.

25. The apparatus as claimed in any one of claims 20 to 24 further comprising at least one of a conductivity probe and a temperature probe to measure conductivity and temperature levels.

26. A calibration box configured for connection to an enamel rater apparatus, the box comprising a housing including a processor for comparing an applied current with a measured current, the processor making any necessary corrections to the applied current via a look-up table within the processor.

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