MXPA00007224A - Automatic command and control of cleansing baths by means of alkalinity regulation - Google Patents

Abstract

The invention relates to a method for automatic regulation of the alkalinity of cleansing baths by acid-base reaction, whereby the regulation is conducted in an automated and program-controlled manner, andthe results of the regulation can be transmitted to a remote location. The course of the regulations can be controlled from said location. Bath cleansing measures can be automatically initiated according to predetermined criteria or be requested from a remote location. The method reduces the number of personnel required for controlling the bath and bath cleansing and increases the certainty of the method.

Description

HANDLING AND AUTOMATIC CONTROL OF CLEANING BATHS BY MEANS OF THE REGULATION OF THE ALKALINITY The invention refers to a procedure for the automatic management and control of cleaning baths, where the free and / or overall alkalinity of the cleaning bath is determined as a parameter of measurement and control and, if necessary, it is adjusted to through addition measures. The procedure is specially designed for technical cleaning bathrooms in the metal processing industry, such as the automotive industry. It allows to automatically monitor the cleaning bath through the parameter of characteristic performance capacity "alkalinity" and if necessary automatically or through external requirements complement the cleaning bath or introduce additional measures of bath care. This method is especially conceivable in such a way that the results of the determinations are transmitted to a remote location of the cleaning bath. In addition, automatic measurements can be taken from a remote location of the cleaning bath, or the subsequent addition or other measures of bath care can be taken remotely. The "remote place of the cleaning bath" can be found, for example, in a higher process control system, in a control center of the plant in which the cleaning bath is located, or in a place outside the plant.

The cleaning of metal parts before further processing represents a common task in the metal processing industry. The metal parts may be soiled with pigments, powders, metal particles, corrosion protection oils, greases or processing aids. Before further processing, especially in the case of a corrosion protection treatment (eg phosphating, chrome-plating, anodization, reaction with complex fluorides, etc.), or before the application of a paint, these impurities must be removed through a suitable cleaning solution. Spraying, immersion, or combined procedures are contemplated for this purpose. Industrial cleaners in the metalworking industry are generally alkaline (pH value within a range greater than 7, for example 9 to 12). Its basic components are alkaline (alkali metal hydroxides, alkali metal carbonates, alkali metal silicates, alkali metal phosphates, alkali metal borates) as well as nonionic and / or ammonium surfactants. Frequently the cleaner contains additional complexing agents (gluconates, polyphosphates, salts of aminocarboxylic acids such as, for example, ethylene diamine tetraacetate or nitrile triacetate, salts of phosphonic acids such as, for example, Examples are salts of hydroxyethoxyphosphonic acid, phosphonobutantopcarboxylic acid, or other phosphonic or phosphonocarboxylic acids), corrosion protection agents such as, for example, salts of carboxylic acids with 6 to 12 carbon atoms, alkanolamine, as well as formation inhibitors. of foam such as, for example, alkoxylates of alcohols with 6 to 16 carbon atoms of closed end groups in the alkyl radical. Insofar as the cleaning baths do not contain ammonium surfactants, cationic surfactants can also be used. As nonionic surfactants, the cleaner contains, in general terms, ethoxylates, propoxylates and / or ethoxylates / propoxylates of alcohols or alkylamma with 6 to 16 carbon atoms in the alkyl radical, which can also be closed end groups. As ammonium surfactants, alkyl sulfates and alkyl sulfonates are very widespread. Alkyl benzene sulfonates are also contemplated, but from the perspective of environmental protection they have disadvantages. As cationic surfactants, especially cationic alkylammonium compounds with at least one alkyl radical having 8 or more carbon atoms are contemplated. The alkaline substances in the cleaning bath contribute to its cleaning capacity. For example, they saponify impurities that can be saponified such as, for example, fats and thus make them soluble in water. In addition they participate in the release of more soluble impurities from the upper surface of the metal, to the extent that the upper surfaces are negatively charged through the adsorption of OH ions, and thus cause an electrostatic repulsion. Through reactions of this type, possibly also through dragging, the alkalinity is consumed, in such a way that the cleaning effect decreases with the passage of time. Therefore, it is usual to check the alkalinity of the cleaning baths at certain times and, if necessary, add new active substances to the solution or replace them completely. This review is done either manually or locally through a titration robot. In this way, alkalinity is checked today, usually by titration with a strong acid. The service staff rates the alkalinity based on the consumption of acid and takes the required measures such as, for example, completing the bath or renewing it. This usual procedure currently requires that the service personnel at the control moments be near the cleaning bath. Among minors the desired control intervals, the greater the workload for service personnel for control measurement purposes.

From EP-A-806 244 a method is known by which the pH value of a solution is automatically determined and acid or bleach is automatically added in case of deviations. The object of this document is to maintain the pH value of a fluid stream at a predetermined value. In this procedure, an acid-base titration is not carried out. Therefore it is necessary to control the operating capacity of this installation from the place. It is not possible to intervene remotely in the course of pH measurements m take measures of addition. The object of the present invention is to automate and document the controls of cleaning baths through the determination of the alkalinity in such a way that at least the results of the determination of alkalinity are stored and / or provided in a database. Preferably the measuring device used should review and calibrate and in the case of a malfunction should transmit an alarm report to a remote location. In addition, it should preferably be possible to review the operating capacity of the measuring device and the results of the remote measurement. In addition, it must be possible from a remote place to intervene in the development of the measurement and in the bath care measures. Through the desired remote controls, the requirement of personnel for the control and management of the cleaning bath. This object is achieved through a procedure for the automatic determination of the alkalinity of a cleaning bath having surfactants or of several cleaning baths having surfactants through an acid-base reaction with an acid where, in a programmed manner, with the use of a suitable measuring device a) a sample of a predetermined volume is taken from a cleaning bath, b) if desired, the fats are removed from the sample, c) selects whether the free alkalinity and / or the global alkalinity should be determined, d) the sample is titrated through the addition of an acid or an acid is placed and titrated with the sample, e) the result of the titration and / or is stored in a database and / or is taken as a basis for further evaluations. The test volumes obtained in step a) can be programmed in the handling part of the measuring device for the procedure to be used. Preferably the size of the sample volume can be altered from a remote location. In addition, the management program can be designed in such a way that the sample volume to be used depends on the result of a previous measurement. For example the volume of sample can be selected larger and larger as the alkalinity of the cleaning bath decreases. The accuracy of alkalinity determination can be optimized in this way. Within the framework of the method according to the present invention, "remote location" means a place that is not immediately in contact with the cleaning bath or at least not in optical contact with said cleaning bath. The remote location can be, for example, a central control system which, within the framework of a global process for the surface treatment of metal parts, has the partial purpose of controlling and operating the cleaning bath. The "remote place" can also be a central address from which the entire process is controlled and directed and which is, for example, in another room than the cleaning bath. As a "remote place" you can also see a place outside the floor where the cleaning bathroom is located. It is also possible for specialists to check and operate the cleaning bath, which is outside the floor where the cleaning bath is located. Therefore it is much less often necessary for specialized personnel to be in the place of the cleaning bath. Suitable data transfer lines through which you can transmit the results of the Alkalinity determinations as well as handling commands are available in the state of the art. Between the extraction of samples and the actual measurement it may be desirable to release the fat samples in the optional step b). In the case of a cleaning bath with little fat, this is not necessary. In the case of a high fat content in the cleaning bath, valves of the measuring device can be plugged and sensors such as, for example, electrodes, become soiled. Therefore it is advisable to remove the fat from the sample. This can be done automatically by filtration or by using a cyclone or a centrifuge. In step c) it is selected whether the free alkalinity and / or the overall alkalinity will be determined. This can be introduced in the course of the program. For example, a determination cycle of both free alkalinity and global alkalinity can be determined. However, the program may also choose to determine one of these two values more frequently. This may be the case, for example, when previous determinations have indicated that one of the two values is altered more quickly than the other. Obviously, the choice of the determination of free alkalinity or total alkalinity can also be determined through an external requirement. By "external requirement", we understand here and below that in the course of the Automatic determination can be intervened either through a superior process management system or manually through a data transfer line. The concepts "free alkalinity" and "total alkalinity" are not defined unequivocally and are handled differently according to the users. For example, certain pH values can be defined, in which determinations must be made, in order to determine either free alkalinity or global alkalinity, for example pH = 8 in the case of free alkalinity, pH = 4.5 in the case of global alkalinity. These pre-established pH values must be integrated into the management system for the automatic determination procedure. Alternatively to established pH values, free alkalinity and total alkalinity can be determined by the inflection points of certain indicators. Alternatively, inflection points can be chosen in the pH value curve and defined as equivalence points for free alkalinity or global alkalinity. For the actual determination of the alkalinity in step d) the acid-base reaction is used with an acid. Preferably a strong acid is selected for this purpose. The sample can be titrated by adding an acid to the pre-established criteria for free alkalinity or for global alkalinity. Alternatively the acid can be present and be certified through this sample. The result of the titration is then provided and / or stored in a database (part e). The database can be found at the location of the determination or in a remote computer unit. By "providing the results of the titration" we understand that these results are transmitted either through a data transfer system or they are presented on a screen or printed. In this way the place of presentation or delivery of the results may be the "remote place" defined above. It is preferred that the results of the individual determinations are stored for at least a pre-established time interval in a database in such a way that they can be evaluated later, for example, within the framework of quality assurance. However, the results of the alkalinity determinations must not necessarily be supplied directly as such or stored in a database. They can be integrated directly as a basis for additional calculations, where the results of these additional calculations are displayed and stored. For example, instead of alkalinity, the tendency of the value of alkalinity and / or its relative change can be shown. Or the current values of alkalinity can be transformed into "percentage of theoretical value".

In the simplest cases, the method according to the present invention operates in such a way that steps a) to e) are repeated after a pre-established time interval. This pre-established time interval is governed by the requirements of those who handle the cleaning bath and can be any desired time interval within a range of approximately 5 minutes to several days. For quality assurance it is preferred that the preset time interval is, for example, within a range of 5 minutes to 2 hours. For example, measurements can be made every 15 minutes. The method according to the present invention can, however, also be carried out in such a way that steps a) to e) are repeated at increasingly shorter time intervals to the extent that the results of two successive determinations are more different The control system for the method according to the present invention can also decide on its own whether the time interval between the individual determinations should be shortened or extended. Obviously the control system must be provided with instructions so that it can choose a time interval based on given differences between results of successive determinations. In addition, the method according to the present invention can be carried out in such a way that steps a) a e) can be carried out at any desired time point based on an external requirement. For example, the case of an immediate control of the alkalinity content of the cleaning bath can be presented when quality problems arise in subsequent steps of the process. The alkalinity measurement can also be controlled based on time (according to defined time intervals) or on the basis of events (in the case of certain changes or in the case of external requirements). Preferably, the method according to the present invention is carried out in such a way that the measuring device employed has the corresponding self-monitoring and calibration capability if necessary. One can contemplate the case in which after a given time interval or after an established number of determinations or based on an external requirement through control measurements of one or several standard solutions, the capacity of operation of the measuring device used. To revise it is titled a standard solution with a known content of free and global alkalinity. This revision is the closest to reality when a standard cleaning solution is used as a standard solution whose conformation is as close as possible to the cleaning solution to be checked. Preferably, the standard solutions are they keep out of contact with air or in a protective gas (for example, nitrogen). An essential point in the case of reviewing the operating capacity of the measuring device is the control of the sensor used. For example, it may be a pH-sensitive electrode, especially a glass electrode. With the help of a regulatory solution as a standard solution, it can be checked whether the electrode provides the expected voltage, if it corresponds to the expected time or if its slope (change in voltage depending on the pH change) is within the expected range. If this is not the case, the measuring device activates a local alarm or, preferably, at a remote location. The alarm warning can contain an intervention proposal through a control program of the measuring device or through the management system. For example, it can be proposed that the electrodes be replaced or cleaned. In the method according to the present invention, it can also be contemplated that the control capacity of one or several standard solutions is used to check the operating capacity of the measuring device used when the results of two successive measurements show a difference corresponding to a level predetermined. In this way, it can be differentiated if variations in the alkalinity of the cleaning bath are real and require Take care of the bathroom or if it is a measurement system error. Depending on the result of the review of the measuring device used, alkalinity determinations that are made between the current control measurement and the previous control measurement can be given a state characteristic that characterizes the reliability of these alkalinity determinations. For example, if successive control measurements to check the measuring device employed indicate that this measuring device is functioning correctly, the alkalinity determinations may receive a "correct" status characteristic. If the results differ from the control measurements by a pre-established minimum value, for example, the condition characteristic of the alkalinity determinations can be established as "doubtful". Furthermore, it can also be contemplated that, according to the result of the revision of the measuring device used, an automatic determination of the alkalinity and / or one or more of the following actions be carried out: analysis of established deviations, correction of the measuring device, end of the determination of the alkalinity, sending a status report or an alarm signal to a higher process management system or to a monitoring device, also in a remote place. The measuring device can also, if desired, according to pre-established criteria, determine for itself if it still has operational capacity in such a way that it can continue with the determination of the alkalinity or if deviations are observed that require manual intervention. To monitor the acid-base reaction of the cleaning solution with the acid used for the titration, different sensors are suitable. In accordance with the state of the art, a pH-sensitive electrode, such as a glass electrode, is preferably used. This provides a pH dependent voltage signal that can be further evaluated. The use of such an electrode is particularly simple and therefore preferred. To monitor the acid-base reaction of step d), however, it is also possible to use an indicator from which its pH-dependent interaction with electromagnetic radiation is measured. For example, said indicator can be a classic color indicator whose color change can be measured photomatically. An alternative is the use of an optical sensor. In this case, for example, it is a layer of an inorganic or organic polymer with a fixed dye, which changes color at a certain pH value. The color change is based, as in the case of a classic color indicator, on the fact that hydrogen ions or ions hydroxide that can diffuse into the layer react with the dye molecules. The change in the optical properties of the layer can be determined photometrically. Alternatively, a film such as, for example, organic polymers, whose refractive index changes as a function of the pH value can be used. If, for example, a light conductor with such a polymer is covered, it can be achieved that on the one side of a threshold value for the refractive index a total reflection occurs in the light conductor in such a way that the lightning of light continue driven. On the other side of the threshold value of the refractive index, however, a total reflection is not obtained in such a way that the light beam leaves the light conductor. At the end of the light conductor it is possible to detect whether or not the light propagates through the light conductor. A device of this type is known as an "ophthalm". They can also be used as inorganic or organic solid sensors whose electrical properties are altered with the pH value of the solution that surrounds them. For example, an ion conductor whose conductivity depends on the concentration of H + ions or OH "can be used." Measuring the constant or variable conduction capacity of the sensor current can determine the value of pH of the medium in which it is found, preferably the measurement system used in the process according to the present invention so that the state of filling and / or consumption of the reagents employed (acids, standard solutions and test solutions, possibly auxiliary solutions) is automatically monitored and in such a way that when exceeding a state of Minimum pre-set filling will produce an alarm signal. This way you can prevent the measuring device from being functional due to the lack of necessary chemical substances. The monitoring of the filling state can be carried out with known methods. For example, containers containing chemicals can be found on a scale that records the weight of the corresponding chemical substances. Or a float can be installed. Alternatively, the minimum filling state can be checked through a conductive electrode that is immersed in the container containing the chemicals. The warning signal provided by the measuring device is preferably transferred to a remote location in such a way that corresponding measurements can be taken from said remote location. In general terms, it is preferably contemplated within the framework of the present invention that the results of the determinations and / or of the control measurements and / or of the calibrations and / or of the status signals are transferred continuously or well at pre-established intervals and / or with base in requirements to a remote place. In this way the control staff does not have to be in the cleaning room and constant information is received regarding the actual alkalinity content. Depending on the result of the determinations and the control measurements, correction measures can be taken, either through the system or manually. The simplest correction measure consists of adding one or more complementary components (solution or powder) to the cleaning bath when the alkalinity is below a pre-established minimum value (free alkalinity and / or global alkalinity) or when a device is activated through an external command. This can be done, for example, in an automated way insofar as, according to the reported alkalinity content, a certain amount of complementary solution or complementary powder is added to the cleaning bath. The magnitude of the addition portion or the time interval between the individual additions in the case of predetermined pre-established addition portions may vary. This can be achieved, for example, through pumping or weight management. In a method according to the present invention it is also contemplated that in the case of deviations determined from the predicted value (especially when the capacity of the control is established by means of control measurements). operation of the measuring device), a certain amount of complementary components is added to the cleaning bath. On the other hand, this addition can also be made based on an external command, for example coming from a remote place, independently of the current alkalinity content. In a further embodiment of the present invention, the cleaning bath is completed based on consumption with a pre-established amount of complementary components per consumed unit (basic addition). For example, in the case of a car body cleaning bath, it is possible to determine the quantity of additional components to be added per cleaned body. The control according to the present invention of the alkalinity serves to control and document the performance of this prescribed addition as well as by an additional fine dosage depending on the result (addition in the case of being below the predicted value, interruption of the addition in the case in which the predicted value is exceeded) reaching a more constant operation of the cleaning bath. In this way, variations in quality can be reduced. Obviously the method according to the present invention requires to have the corresponding installation. This installation consists of a control, preferably a computerized control, which controls the Development of measurement based on time and / or events. It must also have the necessary containers for reagents, ducts, valves, addition and measurement devices, etc., to control and measure the sample current. The materials must be suitable for the purpose for which they are used, for example stainless steel and / or plastic. The electronic control devices of the measuring device must have a corresponding input-output interface in order to communicate with a remote location. The process according to the present invention allows to check the alkalinity of cleaning baths from the place and to take the required correction measures without manual intervention. For this reason the safety of the process is increased and it is possible to obtain a constant reliable cleaning result. Deviations from the expected values can be recognized early and corrected either automatically or manually before the cleaning result gets worse. On the other hand, preferably, the measurement data is transferred to a remote location in such a way that the service or supervisory personnel is always informed of the state of the cleaning bath, even if it is not close to said bath. Therefore, the personnel requirement to control and manage the toilet can be considerably reduced. cleaning. By documenting the data obtained in the method according to the present invention, the requirements of modern quality control can be supported. The consumption of chemical products can be documented and optimized.

Claims (1)

1. CLAIMS A procedure to automatically determine the alkalinity of one or several cleaning baths containing surface-active substances through an acid-base reaction with an acid, where it is programmed with the use of a suitable measuring device a) extraction of a sample of a prescribed volume of a cleaning bath, b) if desired, remove the fats from the test, c) select if you want to determine the free alkalinity and / or the global alkalinity, d) the sample is titled by adding an acid or an acid is found in advance and the acid is titrated with the sample, e) the result of the titration is provided and / or stored in a database and / or serves as the basis for evaluations additional A method according to claim 1, characterized in that steps a) to e) are repeated after a pre-established time interval. A method according to claim 1, characterized in that steps a) to e) are repeated after shorter time intervals to the extent that the results of two successive determinations are more different. A method according to claim 1, characterized in that steps a) to e) are carried out based on an external requirement. A method according to one or more of claims 1 to 4, characterized in that, after a preset time interval either after a pre-set number of determinations or based on an external requirement, through a control measurement One or more standard solutions reviews the operating capacity of the measuring device used. A method in accordance with one or more of claims 1 to 4, characterized in that through the control measurement of one or more standard solutions, the operating capacity of the measuring device used when the results of two successive determinations present a difference that corresponds to a pre-established value. A device in accordance with one or both of claims 5 and 6, characterized in that according to the result of the review of the measuring device used the alkalinity determinations made between the current control measurement and the previous control measurement receive a mark of state that qualifies the reliability of these determinations of the alkalinity. A method according to one or both of claims 5 and 6, characterized in that according to the result of the revision of the measuring device employed, the automatic determination of the alkalinity is followed and / or one or more of the following actions: analysis of established deviations, correction of the measuring device, end of alkalinity determinations, sending a status report or an alarm signal to a process control system or to a monitoring device. A method according to one or more of claims 1 to 8, characterized in that a pH-sensitive electrode is used in the embodiment of step d). . A method according to one or more of claims 1 to 8, characterized in that in the embodiment of step d) an indicator is used whose interaction with a pH-dependent electromagnetic irradiation is measured. . A method according to one or more of claims 1 to 8, characterized in that in the embodiment of step d) a substance whose color and / or refractive index and / or conductivity is used is used. Electrical changes with the pH value of the solution in which it is located. . A method in accordance with one or more of claims 1 to 11, characterized in that the filling state of the reagents used is monitored automatically and, when it is below a pre-established minimum filling state, a warning occurs. . A method according to one or more of claims 1 to 12, characterized in that the results of the determinations and / or of the control measurements and / or of the calibrations and / or of the status signals are transferred continuously either at pre-established time intervals and / or according to requirements to a different place of the place of determination. . A method according to one or more of claims 1 to 13, characterized in that when the alkalinity is below a pre-established minimum level or in the case of a requirement, a device is activated that adds one or more in the cleaning bath. complementary components.