BOTTLE CLEANING

Description

[0001] The present invention relates to a method for cleaning bottles in a bottle cleaning machine according to the preamble of claim 1. State of the art

[0002] Bottle washing machines are well known in the state of the art, particularly in the beverage processing industry. These are typically used to clean recyclable bottles or materials, such as glass bottles, before subsequent reuse.

[0003] For this purpose, bottle washing machines typically include an infeed area, which can, for example, be designed with multiple lanes, allowing bottles to be fed into the bottle washing machine in several adjacent lanes. From the infeed area, they are then transported by one or more conveyors, usually through a series of cleaning baths, such as cold water, warm water, and caustic baths, before being discharged from the bottle washing machine.

[0004] For example, JP 5 484 966 B2 discloses a bottle cleaning machine with a series of cleaning baths in which acid baths and neutralization or alkali baths alternate.

[0005] While existing bottle washing machines achieve quite good cleaning results, over time, lye can be carried over from a lye bath into one or more water baths connected to the lye bath. This can lead to lye contamination of the cleaned containers and impede subsequent use. Furthermore, calcification (solid deposits of lye residue that are no longer soluble in water) can occur, which can also negatively impact the cleaning results. Task

[0006] Based on the known state of the art, the technical problem to be solved is to prevent the carryover of lye and petrification of the bottles and equipment of the bottle cleaning machine as far as possible, but still to achieve acceptable cleaning results and to avoid negatively affecting the throughput of bottles as far as possible. Solution

[0007] This object is achieved according to the invention by the method for cleaning bottles in a bottle cleaning machine according to claim 1. Advantageous developments of the invention are covered in the subclaims.

[0008] According to the method according to the invention for cleaning bottles in a bottle cleaning machine in the beverage processing industry, it is provided that the bottles are transported by means of a transport device from an inlet area to an outlet area of the bottle cleaning machine and are first exposed to lye in a lye bath in the transport direction and then to water in a water bath area downstream of the lye bath, the method being characterized in that the water bath is exposed to an acid by an exposure agent when the transport device is at a standstill and then the bottles are exposed to the water from the water bath exposed to the acid after leaving the lye bath and before leaving the water bath.The application means comprise any devices suitable and designed for discharging an acidic liquid onto or toward at least one area of the water bath. They are therefore also arranged accordingly to discharging the acidic liquid at the desired locations. For this purpose, the application means can be connected to a suitable reservoir in which a volume of acid intended for applying the water bath is stored. In addition, however, the application means can also be arranged and connected to the water bath in such a way that they can draw water from the water bath and use it to apply the acid to the bottles.

[0009] According to the invention, the fact that the bottles are exposed to water in the area of the water bath is understood to mean that the water applied to the bottles can drain into the water bath. Therefore, the bottles are not necessarily immersed in the water bath, but can be transported, in particular suspended, over the water bath while being exposed to the water or the acid-treated water from the water bath.

[0010] The term "acid" is understood below to mean any aqueous solution with a pH value below 7. In particular, this refers to liquids in which the proportion of H +< ions is greater than the proportion of OH -< ions.

[0011] A standstill of the conveyor system means that the transport of the bottles along the conveyor system is interrupted, at least temporarily. This interruption can be planned or unplanned (generally due to operational disruptions). Advantageously, the standstill can also be set for a minimum duration. For example, a standstill of the conveyor system can last at least 10 minutes or longer, for example, 20 or 30 minutes. Likewise, the addition of the acid can be delayed until the start of the standstill. For example, the acid can be added 5 or 10 minutes after the start of the standstill.Furthermore, the restart of the machine can be delayed so that, regardless of the possibility of restarting the machine, the restart is carried out at the earliest 10 minutes after the end of the addition of the acid in order to provide sufficient time for the neutralization reaction.

[0012] The bottles can be loaded, but need not be, while the transport device is at a standstill; in particular, it can also be loaded only after the machine has been restarted.

[0013] By applying acid to the water bath, the inventive method allows for the dissolution of calcified residues of the lye in the water bath, as well as from the bottles, thus positively influencing the bottle cleaning results. Furthermore, carryover of the lye from the lye bath into the subsequent water baths is at least partially prevented or even compensated for.

[0014] It can be provided that the bottles in the area of the water bath are sprayed with water containing the acid by means of a spray device, such as a nozzle or atomizer. The spray device can be identical to the application means, i.e., the latter is designed as a nozzle or atomizer and is connected to the water bath via a return line or similar line, so that water from the water bath can be applied to the bottles by means of the spray device / application means.

[0015] In one embodiment, the bottles in the area of the water bath are sprayed with water containing the acid by a spray device. This allows the backflow of the acidic water from the water bath to be used to loosen calcifications on the bottles and to reverse or compensate for the carryover of alkalis from the alkali bath.

[0016] It can also be provided that the amount of acid to be added is determined before the acid is added, depending on a pH value measured in the water bath. The longer it has been since the water bath was last exposed to acid, the more alkali will have been carried over into one or more water baths in the meantime. To compensate for this alkali, in addition to the calcification of the bottles, it is advantageous to add a suitable amount of acid to return the pH value to that of neutral water, if possible. This is ensured by measuring the pH value of the water bath, since the amount of acid to be added can be determined based on this pH value and the generally known amount of liquid in the water bath.

[0017] According to the invention, the bottle washing machine and / or the transport device are restarted after a neutralization phase has elapsed. Restarting involves at least ending the standstill of the transport device, so that the bottles are transported further along the transport device through the bottle washing machine. The "neutralization phase" comprises a period of time long enough to bring the neutralization reaction in the water bath (i.e., the reaction of the acid with the alkali) into a near equilibrium state throughout the entire water bath. This means that the pH value in the water bath at the end of the neutralization phase assumes the same value as far as possible throughout the water bath.

[0018] By waiting for this neutralization phase, it can be ensured that after the transport device and / or bottle cleaning machine has started up, normal operation can be resumed with the most complete possible removal of the calcification and entrained lye in the water bath.

[0019] In a further development of this embodiment, the duration of the neutralization phase depends on a measured pH value and / or a predefined downtime after the completion of the acid exposure to the water bath. Using a predefined downtime (e.g., 20 minutes, 25 minutes, or similar) allows for better planning of the bottle cleaning machine's operation. However, if significant amounts of alkali are carried over into the water bath over the operating period, this can be disadvantageous, as complete neutralization may not be achieved during the downtime. In such cases, continuous pH measurement can be useful in order to adjust the duration of the neutralization phase so that as much of the alkali as possible is neutralized by the acid.

[0020] In a further embodiment, it is provided that the bottles are transported upstream of the lye bath through a pre-soak and are exposed to water therein, wherein the method comprises a periodic exposure of the pre-soak with a second acid by a second exposure agent, wherein the periodic exposure of the pre-soak takes place when there are no bottles in the pre-soak.

[0021] This is particularly preferred during maintenance work on the bottle cleaning machine, when no bottles are being transported in the bottle cleaning machine.

[0022] This can be determined, for example, after several hundred hours of operation or depending on the total throughput of cleaned bottles or the total consumption of caustic solution, or similar operating parameters. However, the periodic cleaning of the pre-soak can also depend, in particular, on the pH value of the pre-soak. By subjecting the pre-soak to a second acid, components of the bottle washing machine, such as the conveyor system or similar devices, can also be freed from deposits that inevitably accumulate over the course of operation.

[0023] In a further development of this embodiment, it is provided that the pre-soak is supplied with the second acid independently of the supply of bottles downstream of the lye bath.

[0024] Furthermore, it can be stipulated that the pre-soak is treated with a second acid periodically after more than 200 operating hours of the bottle washer or after more than 300 operating hours of the bottle washer. Intervention in the normal operating process should then be as infrequent as possible to avoid disruption.

[0025] Furthermore, the first and second acids can be identical. This minimizes the number of required acid storage containers, thus keeping the complexity of the bottle washing machine to a minimum.

[0026] Furthermore, it can be provided that the acid and / or the second acid comprise acetic acid and / or citric acid and / or sulfuric acid.

[0027] As already mentioned, acids are ultimately acidic liquids with a pH value lower than 7. The fact that these acidic liquids include acetic acid, citric acid or sulfuric acid is therefore to be understood as meaning that acid residues of the corresponding acids (in the case of citric acid, for example, C 6 H 5 O 7 3-< ) are present in the solution.

[0028] In one embodiment, the pH value in the water bath and / or in the pre-soak is continuously measured. For this purpose, a suitable pH sensor can be provided that measures the concentration of H +< and / or OH -< ions. This can also trigger an unscheduled shutdown of the bottle washing machine if the carryover of the alkali into the water bath(s) exceeds a critical value. This also allows monitoring the effectiveness of the acid treatment of the bottles.

[0029] In a further embodiment, an error message is issued to an operator of the bottle washing system if a measured pH value in the water bath and / or the pre-soak does not fall below a predetermined pH value within a predetermined time interval during the acid treatment and / or if a predetermined amount of acid is not dosed into the water bath within a predetermined time interval. This embodiment can advantageously be combined with the continuous measurement of the pH value in the water bath and / or the pre-soak and enables monitoring of the functionality of the treatment agents, since if these are not functioning, the pH value does not fall from the alkaline range to neutral water within the usual time. Checking the flow rate allows a determination, independent of the pH value, as to whether the acid introduced is sufficient.This can be used in particular as a redundant system in case the pH measurement fails to determine whether the introduced acid achieves the desired effect.

[0030] The bottle cleaning machine for cleaning bottles in the beverage processing industry comprises an inlet area and an outlet area for bottles and a transport device for transporting the bottles from the inlet area to the outlet area, wherein at least one lye bath and one water bath are arranged one after the other in the transport direction of the bottles in the transport device and the containers can be subjected to a lye in the area of the lye bath and to water in the area of the water bath, wherein downstream of the lye bath, application means for applying an acid into the water bath are arranged and upstream of the lye bath, a pre-soak is arranged in which bottles can be subjected to water, wherein the bottle cleaning machine is designed to carry out a method according to one of the above embodiments.

[0031] In one embodiment, second loading means are provided which are arranged and designed to introduce acid into the pre-soak.

[0032] Furthermore, the application means may comprise one or more nozzles and / or one or more atomizers. These are then designed to apply the acid not only into the water bath but also onto the bottles. Short description of the Figures

[0033] Fig. 1 shows an embodiment of a bottle cleaning machine Fig. 2A + B show different arrangements and designs of the loading means Detailed Description

[0034] In Fig. 1 a bottle cleaning machine 100 is shown.

[0035] Similar to bottle washing machines commonly used in the beverage processing industry, the bottle washing machine 100 also includes an inlet area 150 through which bottles are fed into the bottle washing machine. This can occur either sequentially or in parallel paths, for example, or in a mass flow, so that containers or bottles can preferably be fed continuously to the bottle washing machine 100.

[0036] Furthermore, a transport device 140 is provided, which can transport the picked-up bottles through the bottle cleaning machine and discharge them at an outlet area 160 on the bottle cleaning machine. The transport device can be implemented, for example, in the form of a continuously rotating chain or with the aid of individual carriages that can be moved independently of one another through the bottle cleaning machine, for example, forming a linear drive with a rail or driven by a mechanical drive. There are no limits to the designs of the transport devices, and other variants not illustrated here as examples can also be implemented.

[0037] Furthermore, the bottle cleaning machine comprises at least one caustic bath 120 and one water bath 127 in the transport direction of the bottles along the arrows shown. The transport device 140 extends through the bottle cleaning machine such that the bottles transported by the transport device 140 are at least partially, preferably completely, immersed in the caustic bath. However, the transport device extends over the at least one water bath 127 such that the bottles are preferably not immersed in it.

[0038] If the bottles are transported suspended in the transport device, the transport device 140 or the area of the transport device 140 extends into the caustic bath 120 to such an extent that preferably at least 90% of the bottle, preferably the entire bottle, extends into the caustic bath so that the interior of the bottle is also filled with caustic. This ensures complete cleaning of the bottle in the caustic bath.

[0039] In an embodiment in which the bottles are also immersed in the water bath, the same applies to transport in the upper area of the bottle cleaning machine, where the bottles are transported upside down, for example. In this embodiment, the transport device 140 extends far enough into the water bath 127 that the distance of the transport device from the water surface is at least equal to the length of a bottle being transported by the transport device, so that the entire bottle is also rinsed with water and thus cleaned.

[0040] Additional baths can also be provided. For example, a pre-soak 110 can be arranged upstream of the lye bath 120 but downstream of the inlet area 150, which ultimately consists of one or more water baths (cold and / or warm). The pre-soak 110 can also comprise two or more water baths (cold and / or warm) arranged one behind the other (in the direction of transport). For the purposes of the invention, "cold" baths (regardless of whether they are alkaline solutions or pure water) are those whose temperature is at most equal to the ambient room temperature (i.e., usually 20°C). Warm baths are those whose temperature is at least above room temperature, for example, 30°C, 40°C, or 60°C.

[0041] Analogously, an additional bath 126 for post-leaching can be arranged downstream of the caustic soda bath 120 but upstream of the water bath 127. A caustic soda with a pH lower than the pH of the caustic soda in the caustic soda bath 120 can be provided. Additionally, additional water baths 128 for cleaning or rinsing the bottles can optionally be provided downstream or upstream of the water bath 127. In principle, the baths 126 to 128 (and additional baths) can be arranged in an area 125 generally referred to as the "post-treatment area," downstream of the caustic soda bath 120 and upstream of the outlet area 160. The bottles are preferably transported across this area and only exposed to water or a corresponding solution in the area of the individual baths, so that the water or solution can drip / run off the bottle into the water bath.

[0042] The bottle cleaning machine 100 additionally comprises at least one application means 111, which is arranged such that it can apply an acid to at least the water bath 127. Furthermore, the invention provides that the water treated with acid is subsequently applied to the bottle in the area of the water bath. This can be done either by a separate spray device. Alternatively, the application means can be connected to the water bath via a return flow or another line, so that the water treated with acid can also be applied to the bottle by the application means itself. The acid can preferably be applied to the entire surface of the bottle by the application means or the separately provided spray device.

[0043] In a further embodiment, which is not mandatory, a second loading means 112 can be arranged in the region of the pre-soak 110 such that the loading means 112 can introduce acid into the pre-soak.

[0044] The method according to the invention preferably comprises, in addition to the usual transport of the bottles through the bottle cleaning machine and at least the lye bath 120 and the water bath 127, the addition of the acidifying agent to / from the water bath 127, particularly in the event of a standstill of at least the transport device, at least for a time interval of a few seconds to a few minutes. For example, the application can last 5 to 10 seconds or even 1 to 5 minutes. The longer the application lasts, the "milder" the acid can be selected. This means that the pH of the acidic solution is less than 7, but higher the longer the application duration.

[0045] The minimum duration during which the water bath 127 is subjected to acid can be selected so that the deposits to be removed are dissolved from the water bath and / or the pH value of the water bath reaches a desired value. The then more acidic water of the water bath 127 can also be advantageously used to remove deposits from the bottles using the spray device described above or the agent itself. The bottles need not be subjected to acid treatment while the machine is at a standstill, but can also be scheduled after restarting.

[0046] The use of acids with a buffering effect is particularly advantageous here. The buffering effect of the acid can prevent re-lyeification of the water bath after the machine has been started up, at least temporarily. The use of citric acid is particularly advantageous here, as it develops a buffering effect even in alkaline environments and is also food-safe.

[0047] In the event that the acid is not introduced into the water bath during operation of the transport device, but rather during a standstill of the transport device, it is particularly preferred if the transport device is restarted after the standstill only after a certain period of time, the so-called neutralization phase. The neutralization phase has a duration that is preferably long enough to achieve a constant pH value throughout the water bath 127. If the transport device is restarted only after this constant pH value has been reached, the cleaning result and, in particular, the pH value of any liquid residues remaining on the surfaces of the bottles is as constant as possible.

[0048] Several approaches are conceivable for determining the length of the neutralization phase (time duration). For example, using a suitable sensor (e.g., optical or a pH sensor in the water bath itself), the initial pH of the water bath can be determined when the machine is at a standstill. The amount of acid to be added can then be dosed accordingly to achieve complete equilibrium and thus neutral water. Since the chemical reactions in the water bath proceed according to an exponential function after the addition of the acid, the time after which at least 99% of the neutralization reactions in the water bath have taken place and the pH thus approximately corresponds to the target pH can be set as the neutralization phase.

[0049] Alternatively, the pH value of the water bath can be continuously monitored by the sensor and the transport device can only be started again when a predetermined pH value, for example 7.1 or 7.01, is reached.

[0050] In this embodiment, the downtime of the transport device means a typically unplanned or at least non-periodic event, or a completely unforeseen event, such as a machine malfunction in the inlet or outlet area of the bottle washing machine or other malfunctions. Preferably, the water bath 127 is exposed to acid during each of these events.

[0051] However, in order to avoid a reduction of the pH value in the water bath 127 into the acidic range (pH < 7), it may be expedient for the bottles to be exposed to acid by the exposure means 111 not during every standstill, but only when the pH value measured in the water bath exceeds a certain limit (e.g., 7.8 or 8.5). For example, if two immediately consecutive malfunctions lead to standstills of the transport device, the water bath can be exposed to acid during the first standstill after a pH value greater than 8 is detected in the water bath 127. However, if a pH value of 7.3 is detected after the second standstill, such exposure to acid does not occur because the measured pH value is below the specified limit.During a third standstill following the second standstill, for which a pH value of 8.4 is measured, the acid can be applied again.

[0052] If the acid is introduced into the water bath regardless of a possible downtime of the transport system, this introduction is preferably controlled based on the pH value. Regardless of the elapsed operating time or other parameters, the introduction / discharge of the acid can be controlled based on the pH value measured in the water bath (for example, using a pH sensor). This can be done according to the limit values described above. For example, the acid can be introduced when a pH limit of 8.5 is exceeded. Other values are also conceivable.

[0053] In one embodiment, it is provided that the pre-soak 110 is further subjected to acid by the (second) application means 112. This embodiment (which can also be combined with the embodiment described above) provides that the pre-soak is subjected to acid at periodic intervals (for example, after 200 operating hours or after 300 operating hours). Alternatively or additionally, the pre-soak can also be subjected to acid depending on the pH value in the pre-soak. Preferably, the second application means 112 are arranged in the region of the pre-soak such that not only the pre-soak itself, but also components of the transport device (for example, a chain) can be subjected to acid. Deposits that also form during regular operation (calcifications due to lye residues and the like) can be removed in this way.Pressurizing the pre-soak and the equipment in the pre-soak area allows the acid to be "carried over" to other areas, so that calcifications and other contaminants can also be dissolved there and, if necessary, the pH value can be adjusted. In any case, no bottles are in the pre-soak area when acid is applied to the pre-soak. In particular, the pre-soak can be applied when the bottle washer is running empty, for example, during maintenance work.

[0054] To ensure the functionality of the acidifying agents, the pH sensor described above can still be used. This can be installed not only in the water bath 127, but also, or alternatively, in the pre-soaking area. During the scheduled acid application (either while the transport system is at a standstill or periodically), it can be checked whether the measured pH value is decreasing as expected. This means that the pH value should decrease by a certain value within a specified period of time (seconds or minutes), provided all devices are functioning correctly.

[0055] If it is determined that the pH value is decreasing too slowly or not decreasing at all, a control unit of the bottle washing machine can interpret this to mean that the agitators 111 and / or 112 are not functioning correctly and a fault message can be issued to the bottle washing machine operator. This fault message can, for example, include information about the faulty agitator (for example in the form of an indication on a display) and / or a warning (acoustic or visual) to warn the operator accordingly. In addition to the warning, an interaction option can be created for the operator that enables the fault to be rectified. For example, precise instructions for rectifying the fault can be displayed and the operator can be prompted to follow the displayed instructions and, for example, the necessary steps.

[0056] Although not explicitly stated above, the same acid (e.g., citric acid, sulfuric acid, or the like) can be applied to the water bath and the pre-soak by the first and second agents. However, different acids can also be used. Since the application of the acid in the area of the water bath 127 by the agents 111 preferably exerts a buffering effect to at least temporarily prevent the pH from rising during the further cleaning of bottles, buffer solutions can be used here. In particular, citric acid can be used.

[0057] The abrasive agent 112 preferably dissolves deposits that may extend throughout the entire transport system. A buffering effect of the acid used is not necessary here, but the acid should be suitable for removing calcifications as effectively as possible. A strong acid, particularly sulfuric acid, can be used for this purpose.

[0058] Of course, the use of other acids, especially acetic acid, is also conceivable.

[0059] Fig. 2 shows special embodiments for the loading means 111 and 112. All described embodiments can be used for both the loading means 111 and the loading means 112.

[0060] In the Fig. 2aIn the embodiment shown, the application means 200 are arranged such that the acid is applied from the side of the bottle 130 facing away from the water bath toward the water bath. The application means are thus arranged "above" the transport device 140. If the application means are used simultaneously to apply the water bath containing the acid to the bottles, this embodiment can ensure that the acid is introduced into the interior of the bottles, provided the openings of the bottles 130 in the transport device are accessible from above. The application means 200 can comprise a plurality of nozzles or atomizers 201-204. This allows the most economical use of the acid possible.

[0061] Fig. 2bshows a further embodiment in which the application means 210 can also comprise a plurality of nozzles or nozzle openings or atomizers (205-208). In the embodiment shown here, these are arranged such that the acid is not introduced into the water bath in a targeted manner, but is first applied to the bottles, from which it then flows into the water bath. Thus, in this embodiment, the acid is applied laterally to the bottles 130. With a suitable arrangement of the application means 210, it can be additionally ensured that parts of the transport device or other components of the bottle cleaning machine can also be applied.

[0062] It should be noted that the Fig. 2a and also the Fig. 2bInstead of the loading means, the arrangement of separately provided spraying devices for spraying the bottles with water treated with acid taken from the water bath can also be illustrated. As already described, separate spraying devices can be provided in addition to the loading means. In this case, the loading means can be designed in such a way that they can only introduce the acid directly into the water bath, but cannot treat the bottles with the acid. The water (treated with acid) taken from the water bath via a suitable reflux / return line or line can be fed to the spraying device (200 in the case of Fig. 2a and 210 in the case of Fig. 2b ). This can then comprise one or more nozzles or atomizers, analogous to the application means (201-204 in the case of the Fig. 2a and 205 to 208 in Fig. 2b), which then dispense the acid-treated water from the water bath onto the bottles. From these, the water then drains back into the water bath.

[0063] While not explicitly shown here, a control unit, for example in the form of a computer, such as a personal computer or similar, is assigned to the bottle cleaning machine, which is preferably connected to any pH value sensors and the application means provided in order to control them, for example, depending on the measured pH value or after detection of a standstill or, for example, after reaching a certain operating time, so that acid is applied to bottles.

Claims

1. Method for cleaning bottles in a bottle cleaning machine (100) in the beverage processing industry, wherein the bottles are transported by means of a transport device (140) from an inlet area (150) to an outlet area (160) of the bottle cleaning machine and, in the direction of transport, are first exposed to a lye bath (120) containing lye and, downstream of the lye bath, to a water bath (127) containing water, wherein the water bath (127) is exposed to an acid by means of an exposure device when the transport device (140) is at a standstill, and the bottles are then exposed to the water of the water bath (127) containing the acid after leaving the lye bath (120) and before leaving the area of the water bath (127), characterized in that the bottle cleaning machine and / or the transport device is restarted after a neutralization phase has elapsed, and wherein the neutralization phase comprises a period of time which is long enough to bring a neutralization reaction in the water bath to an approximate state of equilibrium throughout the entire water bath.

2. Method according to claim 1, wherein the bottles are sprayed with the acid-containing water in the area of the water bath (127) by a spraying device.

3. Method according to claim 1 or 2, wherein the amount of acid to be applied is determined prior to the application of the acid depending on a pH value measured in the water bath (127).

4. Method according to one of claims 1 to 3, wherein the bottles are transported upstream of the lye bath (120) through a pre-soaking device (110) and are supplied with water therein, and wherein the method comprises periodically supplying the pre-soaking device (110) with a second acid by means of a second supply means (112), wherein the periodic supplying of the pre-soaking device (110) takes place when there are no bottles in the pre-soaking device (110).

5. Method according to claim 4, wherein the pre-soaking device (110) is periodically supplied with a second acid after more than 200 operating hours of the bottle cleaning machine (100) or after more than 300 operating hours of the bottle cleaning machine (100).

6. Method according to one of claims 1 to 5, wherein the acid and the second acid are identical.

7. Method according to one of claims 1 to 6, wherein the acid and / or the second acid comprise acetic acid and / or citric acid and / or sulfuric acid.

8. Method according to one of claims 1 to 7, wherein a pH value in the water bath (127) and / or in the pre-soaking device (110) is measured continuously.

9. Method according to one of claims 1 to 8, wherein a fault message is output to an operator of the bottle cleaning machine (100) if a measured pH value in the water bath (127) and / or the pre-soaking device (110) does not fall below a predetermined pH value within a predetermined time interval during the application of acid and / or a predetermined amount of acid is not dosed into the water bath within a predetermined time interval.