WO2003052401A1

WO2003052401A1 - Sensor unit and measuring unit for determining the concentration of minor constituents of a melt and method for the operation thereof

Info

Publication number: WO2003052401A1
Application number: PCT/EP2002/014363
Authority: WO
Inventors: Günter TÖPFER; Rüdiger Hartung; Roger Pross
Original assignee: Andion Gmbh
Priority date: 2001-12-14
Filing date: 2002-12-16
Publication date: 2003-06-26
Also published as: DE10161494A1; AU2002356665A1

Abstract

The invention relates to a sensor unit (1) for determining the concentration of minor constituents (26) of a melt (2), comprising a sensor support (4) that can be connected to a housing (3) and has an interior space (5), a measuring opening (6), and a connecting area (7). At least one sensor (8) and at least one reference electrode (9) are arranged inside the interior space (5) and are electrically insulated from the sensor support (4). In addition, means (9, 27, 32, 33, 35) are provided for determining an electrical potential between the housing (3) and the at least one sensor (8), whereby the at least one sensor (8) and the at least one reference electrode (9) are each separate components that can be mounted in a manner that enables them to be detached from one another and preferably joined to one another with positive engagement. The invention also relates to a corresponding measuring unit, a method for operating the sensor unit, and to a method for producing a refined metal by using a melt.

Description

sensor unit and measuring unit for determining the concentration of minor fractions in a melt and method for their operation

The invention relates to measuring devices and methods which are used for the qualitative and preferably quantitative determination of different constituents of hot gases and metal melts. The precise determination of the components of hot gases is particularly important in the context of

10 on control in combustion processes of great importance. In the field of molten metal, it is very important to know exactly the components of the molten metal and their concentration, since these have a direct effect on the material properties and quality of the metal and the cast material obtained from the molten metal.

15

For example, aluminum, as an important lightweight material in automotive engineering and in aerospace technology, is subject to ever higher requirements with regard to pressure tightness and mechanical-technological properties. Because of the tendency to absorb hydrogen from molten aluminum

20 zen is a common defect in aluminum and aluminum alloys, the "gas porosity", which significantly affects the properties of the casting. Their cause is particularly to be found in an excessive hydrogen content in the melt. A number of methods are therefore known for the quantitative determination of the hydrogen content in aluminum melts. In this

25 context, the hot extraction analysis, the Telegas method and the Hycon tester and aluminum melt tester method based on the "principle of the first bubble" may be mentioned as common methods. Of these, only the Telegas process offers the possibility of determining the hydrogen content directly in the melt. Because of the sensitivity and the susceptibility to failure of the equipment

30 for the foundry, but the Telegas process is for everyday use Foundry operation unsuitable. Another component of aluminum melts that is relevant for the quality of aluminum melts and the castings obtained from them is sodium.

One possibility of determining sodium by means of an electrochemically operating sensor is disclosed in Metallurgical and Materials Transactions 27b, October 1996, pp. 794-799. A disadvantage of these electrochemically working sensors is the complex structure and the associated vulnerability in everyday use in the foundry. This also applies to the sensors described in the W.F. Chu in Technischen Messen 56, 1989 are disclosed.

In particular, tasks result from the following technical contradictions to be resolved:

The measuring unit with the sensor dips into the melt together with the lance carrying it, in the case of online measurements over several hours or even over several days, the bath level being located above the connection point of the sensor unit to the lance. For cost reasons, at least the lance must be reusable after use or equipped with different sensors. The sensors from can have an ion conductor phase which are exposed to several temperature changes of up to 1000 ° C. in one sensor unit. In the event of thermomechanical destruction of the sensor, the functional reliability of the entire sensor unit should not be endangered, in particular parts of the sensor unit must not be contaminated by the melt surrounding the sensor unit.

Furthermore, with regard to the production of ion conductor phases, in particular those of the β or β "aluminum oxide type, preferably for the measurement of sodium in aluminum melts, it has to be taken into account that these according to the previous known methods are very complex and therefore disadvantageous. The high cost of the known methods results in particular from the fact that several grinding, mixing and calcining steps are necessary to produce an ion conductor phase. These process steps are each subjected to a quality control in order to keep quality fluctuations as low as possible. This leads to considerable expenditure in terms of time and equipment, which involves considerable manufacturing costs, although there are considerable fluctuations in the quality of the ion conductor phases despite the many manufacturing steps. The quality fluctuations of the ion conductor phases obtained from the conventional methods in turn lead to sensors with unsatisfactory measurement accuracies. For metal processing, this has the consequence that the accuracy of the concentration measurements is not sufficiently high. As a result, there are corresponding negative consequences for the quality and material properties of the metals and castings obtained from the molten metals. So far, these disadvantages can only be countered in an inadequate manner in that multiple measurements, parallel measurements and, if necessary, calibration measurements are necessary.

The invention is generally based on the object of overcoming the disadvantages arising from the prior art and also contributing to the solution of the following objects. It is an object of the invention to provide a sensor unit and measuring unit with very small dimensions, which can be used quickly, accurately and simply, for determining components in molten metals. It is therefore also an object of the present invention to provide a sensor unit which on the one hand ensures an exact determination of minor constituents of a melt, the ease of maintenance and the operation of such a sensor unit being intended to be simplified. The sensor unit should be able to be repaired inexpensively and quickly if components due to the high thermal loads or due to increasing Wear must be replaced. Furthermore, a corresponding measuring unit is to be specified, which in particular ensures that a sensor unit according to the invention is immersed in a weld pool. In addition, methods for producing a refined metal and methods for operating a sensor unit for determining the concentration of minor constituents of a melt are to be specified, which result in significant cost advantages in particular with regard to the production of the metal or in the maintenance of the sensor unit.

These objectives are achieved by a sensor unit for determining the concentration of minor constituents of a melt according to the features of patent claim 1, a measuring unit according to the features of patent claim 10, a method for producing a refined metal by a melt according to the method steps according to patent claim 12 and a Ver - Drive to operate a sensor unit according to the features of claim 13. Further advantageous and particularly preferred configurations are described in the respective dependent claims. It should be noted that the features disclosed therein can occur individually or in any meaningful combination with one another.

The sensor unit according to the invention for determining the concentration of minor constituents of a melt comprises a sensor holder which can be connected to a housing (as an electrically conductive working electrode which is in contact with the melt in use) and which has an interior space, a measurement opening and a connection area. At least one sensor and at least one reference electrode, which are electrically insulated from the sensor holder, are arranged in the interior. Furthermore, the sensor unit comprises means for determining an electrical potential between the housing and the at least one sensor. According to the invention, the sensor unit is characterized in that the at least one sensor and the at least one reference electrode each because they are separate components that can be arranged releasably to one another, and in particular to one another in a form-fitting manner.

While in one-piece sensor reference electrode devices known to date, a one-piece, combined configuration was chosen, for example to ensure permanent contact between the reference electrode and the sensor or ion conductor phase despite different thermal expansion behavior, the invention proposes to form these components separately or physically separately from one another. The consequence of this is that the at least one sensor and the at least one reference electrode have a common contact surface, the at least one sensor or the at least one ion conductor phase preferably being in positive contact with the reference electrode. This contact is designed so that it can be solved without any technical effort. This type of contact makes particular use of pressing, pressing and / or pressing against one another. The use of Haftbzw. Adhesives are preferably avoided, but is also possible under certain conditions. The contact surface is designed in such a way that an electrical contact for determining a potential is ensured even under high thermal ambient conditions. The contact area has a dimension which is preferably between 0.05 mm and 5 mm ² . The size of the contact area means the sum of all partial areas that are used to determine only a minor component. If several minor components are measured, whereby a combination of sensor and reference electrode is provided, this value relates to the contact area before each such paired arrangement. The separate design of the sensor allows maintenance independent of the reference electrode. The sensor, which preferably only comprises an ion conductor phase in some areas, is significantly cheaper to produce than the reference electrode. In this respect, the operation of such a sensor unit can already be made more cost-effective that the sensor (in relation to the protected reference electrode), which can usually be replaced early and is inexpensive to produce, is independently replaced by the reference electrode.

According to a further embodiment, the at least one reference electrode and the measurement opening are connected to one another in a gas-permeable manner. It should first be noted that in the case of measuring probes known hitherto, which were used to measure concentrations of the components of an aluminum melt, the reference electrode was shielded in such a way that contact with, for example, gaseous components of the melt is prevented, since this often leads to failure of the reference electrode leads. This is particularly true for reference electrodes which are at least partially made up of sodium. With these reference electrodes, there is an increasing deterioration of the reference signal with continuous wear, which does not ensure an exact determination of the concentration of minor components of the melt. It is preferred that the reference electrode is a combination of:

(a) titanium dioxide and an alkali metal or alkaline earth metal titanate or

(b) tin dioxide and an alkali metal or alkaline earth metal stannate in, preferably intimate, mixture, the reference electrode preferably not being insulated from the medium to be measured. In addition, the reference electrode preferably comprises a metal powder, in particular a precious metal powder. This metal powder contributes to the electrical conductivity of the reference electrode and is preferably in a range from 1 to 70% by weight, in particular in a range from 30 to 50% by weight. Further details about sensors can be found in EP 0767 906 B1, the disclosure of which forms part of this application. The components mentioned in this section can also be obtained via a fluidized-bed drying process, which is described in more detail below in connection with the production of an ion conductor phase. Due to the arrangement of the reference electrode on the side of the sensor facing away from the measurement opening, the sensor on the one hand protects the reference electrode from the melt, but on the other hand also permits gas exchange with the interior of the sensor holder and the reference electrode located therein, i.e. even in the event of a sensor break the reference electrode keeps it in shape by pressing and prevents disintegration. Since the above arrangement has a high thermal load on the sensor, the functionality must be checked at regular intervals or after repeated use of the sensor. It has been found that certain components of the sensor, in particular, for example, an ion conductor phase (or an ion-conducting solid electrolyte) have a wear rate that differs from that of the reference electrode. This means that the functionality of the reference electrode and the sensor often have to be checked at different times and, if necessary, serviced or, under certain circumstances, also replaced.

According to a further embodiment of the sensor unit, the at least one reference electrode is arranged on a side of the at least one sensor facing away from the measurement opening, the at least one sensor preferably being gas-permeable. The gas permeability causes the pressure in the melt and the interior to be set to the same pressure, which means that the gas components have no negative influence on the measurement results. The gas permeability relates in particular to partial sections of the sensor which is arranged between the melt or the gas stream and the ion conductor phase. It should also be stated here that it is preferably only a gas permeability, and consequently there is no penetration of the sensor with liquid or solid melt components. The measuring opening has the task of ensuring intimate contact of the medium (melt, gas) with the sensor. Afford. The arrangement of the sensor near the measurement opening is to be carried out in such a way that a seal is preferably formed so that liquid or solid melt components cannot flow past the sensor into the interior. This seal must also withstand the thermal requirements at temperatures up to 1000 ° C.

It is further proposed that the at least one sensor comprises at least one ion conductor phase. The ion conductor phase can preferably be described by at least one of the following parameters:

i) gas-tight in accordance with the helium standard leak rate less than 10 ^"5 mbar 1 / s, ii) electrically non-conductive in accordance with IN 60672 part I-III, iii) temperature change resistance at more than 8, preferably 8-20, temperature changes according to DIN 51068 part II.

The ion conductor phase preferably comprises an oxidic ceramic type, in particular of the β or β "aluminum oxide type, such as of the NASICON or LISICON type. The production comprises, for example, the following stages:

1. Mix to a starting component mixture of

1.1 if necessary a phase stabilizer,

1.2 a matrix component present in excess of the other starting component,

1.3 a line ion component, as the starting component, by means of

1.4 a dispersant to a dispersion.

2. Granulation of the dispersion, the granulation taking place in a fluidized bed dryer,

3. Form quakes, and 4. Sintering, the ion conductor phase preferably being formed during the sintering.

Stabilizers known to the person skilled in the art, preferably lithium or magnesium compounds which are soluble or finely dispersed in the dispersing medium, are used as phase stabilizers. No or only small amounts of the phase stabilizers are required for the phase formation of the β or β "aluminum oxide phase. Phase mixtures of β or β" aluminum oxide types are also possible by controlling the amount of phase stabilizers. The matrix component of the ion conductor phase is preferably aluminum oxide for the β or β "aluminum oxide type, with this aluminum oxide being able to be mixed with other oxides, for example titanium oxide, to achieve stoichiometric defects.

Suitable line ion components of the ion conductor phase are line ion components known to the person skilled in the art, preferably sodium, potassium, strontium or barium compounds which are soluble or finely dispersible in the dispersant. Their grain size is preferably less than or equal to the grain size of the matrix component. It is preferred that the matrix component is used in particulate form, at least 25% by weight and preferably at least 50% by weight of the matrix component being a particle size in the range from 0.5 μm to 20 μm. In addition, it is preferred that the phase stabilizer and the conduction ion component likewise have these particle sizes in the same proportions. It is particularly preferred for the phase stabilizer and the ion conductor component to be present colloidally, preferably in solution, in the dispersant. If necessary, this can be achieved by means of a solvent, preferably an alginate, EDTA salt or stearate. The quantitative ratios of the individual starting components in the finished ion conductor phase mostly depend in a first approximation independently of the precisely used quantitative ratios of the starting components according to the phase equilibria, which can be found in the phase diagrams for the individual finished ion conductor phases. It has therefore proven useful to use at least as much of a starting component in a corresponding manufacturing process as corresponds to the stoichiometry of the phase balance of the desired finished ion conductor phase.

The ion conductor phase is preferably shaped by pressing the granules contained in the granulation in a suitable molding tool. The pressing can be isostatic or uniaxial. The shaping is preferably carried out at a pressing pressure of below 200 MPa (megapascal), preferably below 100 MPa, in order to obtain a green body suitable for the sintering process that now follows. It is preferred that the granules are introduced into the mold together with a molding aid, preferably a plasticizer, such as a thermoplastic polymer or a wax, as such or in a water emulsion, by injection molding or hot molding.

In this context, a method for producing the ion conducting phase is briefly advantageous that at least one, preferably all, of the following parameters are observed during granulation in the fluidized bed dryer:

pl: supply air temperature in the range from 50 to 130, preferably from 60 to

100 and particularly preferably from 70 to 95 ° C. p2: spray pressure in the range from 1.5 to 3, preferably from 1.7 to 2.5 and particularly preferably from 1.8 to 2.1 bar, p3: spray rate in the range from 50 to 400, preferably from 70 to 300 and particularly preferably from 100 to 250 g / min, p4: air quantity in the range from 100 to 600, preferably 200 to 550 and particularly be250 to 400 m3 / h.

Deviations from the parameters can result from the design and size of the fluidized bed dryer as well as from other boundary parameters. Each of the following parameter combinations represents a special embodiment of the method: plp2, plp2p3, plp3 and p2p3.

Any commercially available heatable fluidized bed dryer can be used, an electrically heated fluidized bed dryer being particularly preferred. Such fluidized bed dryers are available, for example, from Glatt GmbH in Germany.

In one embodiment of the method, a binder is used in the granulation in the fluidized bed dryer, which also has a positive effect on the homogeneity of the granules. The amount of binder used is in the range from 0.01 to 25, preferably from 0.1 to 15 and particularly preferably from 1 to 6% by weight, in each case based on the matrix component. The binders used are trial alcohols, in particular triethanolamine, and polyalkylene glycols, in particular polyethylene glycol, preferably with a molecular weight in the range from 100 to 500, preferably from 150 to 300 g / mol, or Ci to C ₅ alkyl cellulose, preferably methyl cellulose, into consideration, the alkyl cellulose being particularly preferred.

It is further preferred that the granules have a residual moisture content below 5, preferably below 4 and particularly preferably in the range from 0.1 to 3% by weight, based on the granules. At least 20, preferably at least 50 and especially preferably at least 75% by weight of the granules have a pond size in the range from 1 to 200, preferably from 20 to 150 and particularly preferably from 50 to 120 μm.

The shaping is preferably carried out via a Veφressen of the granules obtained from ^"granulation in a suitable mold. The Veφressen can be carried isostatic or uniaxial. Preferably, the shaping at a pressure of less than 2, preferably less than 1 t / sq cm, to one for the now It is preferred that the granules are introduced into the mold together with a molding aid, preferably a plasticizer, such as a thermoplastic polymer or a wax, as such or in a water emulsion, by injection molding or hot molding.

Also suitable as plasticizers are trial alcohol amines, in particular triethanolamin, and polyalkylene glycols, in particular polyethylene glycol, preferably with a molecular weight in the range from 200 to 20,000, preferably from 1,000 to 10,000 g / mol. The molding aids are each used in an amount in the range from 0.1 to 30, preferably from 0.5 to 20 and particularly preferably from 1 to 10% by weight of dry matter, based on the granules.

According to a further embodiment of the sensor unit, at least one reference electrode is arranged to be movable by at least one spring element at least in the direction of an axis of the sensor unit, a stroke of 0.05 mm to 10 mm, in particular of 0.1 mm to 1, being preferred for the reference electrode mm, is realized. It is preferred that the at least one spring element exerts a force on one side of the reference electrode, so that the latter provides a freely accessible contact surface, in particular on the opposite side, which after assembly of the sensor unit with the ion conductor teφhase comes into contact. In this respect, it is particularly advantageous that the spring force effects such a position of the reference electrode that it is displaced during assembly due to the contact with the ion conductor phase against the force of the at least one spring element. This creates a kind of pre-tension that ensures intimate and permanent contact of the reference electrode with the ion conductor phase. The specified stroke is based on the one hand on the storage of the reference electrode in a type of receptacle, the stroke preferably being realized largely within this receptacle or within a foot part comprising this receptacle. It is also feasible that special detents are provided here that allow the maximum stroke, for example, only for the repair or maintenance of the reference electrode. In particular, it must be ensured that the contact surface of the reference electrode with a component surrounding the reference electrode (for example a foot part) lies in one plane or even protrudes slightly in the direction of the ion conductor phase.

It is particularly advantageous that the at least one spring element is part of the contacting of a sensor conductor with the at least one reference electrode. This contacting takes place, for example, via clamping means, which maintain their functionality even at high temperatures. In this case, electrical contact between the reference electrode and the sensor conductor is ensured even if there is a relative movement between a sensor conductor arranged in a base part and the at least one reference electrode. This relative movement is brought about or compensated for by a spring element which is arranged near the transition from the sensor conductor to the reference electrode. Different materials can be used for this, preferably an essentially uniform elastic behavior over a wide temperature range is ensured. The spring element is preferably mounted in the head of the lance, in particular above the melt to keep its thermal loads low. The spring force is transmitted via the contact.

According to a further embodiment, the housing has a connecting section which is in contact with the connecting region of the sensor holder in such a way that a stop surface is formed which has an angle to the direction of the axis of the sensor unit, which is preferably between 30 ° and 70 °. In this respect, it is ensured here that a sufficiently large stop surface is provided in the connection area, which prevents components of the melt which impair the measurement result from penetrating into the interior of the sensor unit. In this connection area or on the stop surface, additional materials or structural configurations are applied, if necessary, which prevent accumulation or penetration into this area, so that a smooth decoupling of the sensor holder from the housing is guaranteed even after repeated use if necessary. The connection between the housing and the sensor holder is designed to be detachable, with a non-detachable connection or even a one-piece design possibly also being possible.

According to yet another embodiment of the sensor unit, the at least one sensor is arranged in at least one support structure, the at least one sensor preferably protruding on the side of the support structure facing away from the measurement opening, in particular with a protrusion of 0.1 mm to 3 mm. The support structure has the function of ensuring an exact positioning of the ion conductor phase with respect to the reference electrode. The support structure may be gas-permeable, and under certain circumstances a type of breakthrough can also be provided which allows direct contact of the medium to be examined with the ion conductor phase. Furthermore, the support structure has the function, for example, of electrically isolating the ion conductor phase from the sensor holder or the housing. This is the case, for example made of an electrically non-conductive material (e.g. boron nitride). Additively or alternatively, however, it is also possible for only partial areas, in particular the contact area towards the housing or towards the sensor holder, to be electrically insulated. This insulation can accordingly be provided on the one hand on or in the supporting structure, but on the other hand also on the sensor holder. The protrusion ensures permanent contacting of the reference electrode with the ion conductor phase, even if they are designed with a flat or flat contact surface. It is particularly advantageous that both the reference electrode with respect to the foot part and the ion lead phase protrude with respect to the support structure, so that the contact between the reference electrode and the ion lead phase is not impaired by the surrounding components.

According to a further aspect of the invention, a measuring unit is proposed which comprises at least one lance which is connected to at least one sensor unit according to the invention. If, for example, the concentrations of different constituents of the melt are determined, an appropriately designed lance can also be equipped with several, in particular 2, 3 or 4, sensor units. The connection is preferably made releasable, so that a quick and easy removal of the sensor unit from the lance is ensured. The lance is preferably hollow, the corresponding conductors being guided through in a protected manner inside the lance. It is particularly advantageous that a releasable connection between the lance and foot part and / or between the lance and housing is provided.

According to yet another aspect of the invention, a method for producing a refined metal by a melt is proposed, the following steps being included: Determining a proportion of at least one minor component present in the melt alongside a main metal with a sensor unit according to the invention or with a measuring unit according to the invention for determining an actual concentration of the minor component,

Adjusting the proportion of the minor component to a target concentration by increasing or decreasing the proportion of the minor component,

Pour the melt if the actual and target concentration match.

According to yet another aspect of the invention, a method for operating a sensor unit for determining the concentration of minor constituents of a melt is proposed, which comprises at least the following steps:

At least once, preferably several times, determining a proportion of at least one minor component present next to a main metal in the melt; - Detection of at least one parameter for determining the functional state of the sensor unit;

Comparing the at least one parameter with a predefinable limit value; Evaluation of the comparison with regard to a necessary repair of the sensor unit, with at least one sensor with at least one ion conducting phase being replaced separately by at least one reference electrode in the course of such a repair. This repair is preferably carried out only after at least three times, preferably at least six times, and particularly preferably twenty times, the concentration of minor components of a melt. Alternatively and / or cumulatively, such a repair can also be carried out depending on the immersion time in the melt. The detection of the at least one parameter is carried out by a sensor familiar to a person skilled in the art, the parameters which are particularly preferred for this are mentioned below.

If the sensor unit has a sensor holder which can be connected to a housing and which has an interior, a measurement opening and a connection area, with at least one sensor and at least one reference electrode being arranged in an electrically insulated manner in the interior and with respect to the sensor holder, it is particularly advantageous that when detaching the connection of the sensor holder to the housing, the at least one separate sensor is simultaneously removed from the at least one reference electrode. This means in particular that at the same time a relative movement of the ion conductor phase with respect to the reference electrode is realized, be it as a result of gravity or a design-related driving force, such as is generated, for example, by a spring element or a corresponding thread. This significantly simplifies the repair and therefore also results in significant cost advantages.

It is also proposed that the at least one parameter is the temperature. When the temperature is recorded, for example in the interior of the sensor unit, it can be determined how often the sensor unit has already been used, since temperature peaks can be counted in this way. Furthermore, the temperature can be used to determine whether thermal overloading of certain components of the sensor unit or overheating or cooling of the melt has possibly occurred. The recorded temperature For example, compared with a limit temperature, an alarm or a corresponding repair being triggered when such a limit temperature is exceeded. This triggering of the alarm or the repair measures can be initiated visually, manually or automatically.

It is further proposed that the at least one parameter is time. For example, it is advantageous to record both the temperature and the time. If, as already explained above, a relatively high temperature occurs, it may only be relevant if this temperature occurs over a predefinable period. If both limit values are exceeded at the same time, an alarm can be triggered or appropriate maintenance can be initiated.

It is further proposed that the at least one parameter is the specific concentration of the minor component itself. In this respect, it is proposed that a kind of plausibility check of the acquired measurement data be carried out, for example a tolerance field relating to the concentration to be determined being specified. If this tolerance field is significantly exceeded or if there is a particularly high variation in the measured concentration, this can also be used as an indication that an alarm is triggered and that the sensor may need to be changed.

It is particularly advantageous that several parameters are combined to form a characteristic value and compared with a limit value. This means that a large number of different parameters are evaluated or weighted and, when combined to form a characteristic value, allows significant significance with regard to the functionality of the sensor unit. In addition to the parameters mentioned above, other parameters from the production process are also available. The invention is explained in more detail below with reference to the drawings, the embodiments shown being particularly preferred. However, it should be noted that the invention is not limited to the examples shown.

Show it:

1 is a sectional view of an embodiment of a measuring unit,

2 shows a further embodiment of a measuring unit in section,

3 shows a further embodiment of the measuring unit in the disassembled state,

4 shows a detail of an embodiment of a sensor unit,

5 shows a flowchart for the sequence of the measuring method with a sensor according to the invention and the sensor monitoring with regard to its duration of use and temperature changes,

6 shows a further embodiment of the sensor unit, and

Fig. 7 shows an embodiment of an evaluation unit.

1 shows schematically and in section a modular measuring unit 23, a sensor unit 1 for immersion in a molten metal 2 being attached to a lance 24. The melt 2 comprises a main metal 25 and at least one minor component 26, the concentration of which is determined by means of the sensor unit 1 according to the invention. The sensor unit 1 or the The measuring unit 23 is immersed up to the indicated melting level 34, it being ensured that a housing 3 of the sensor unit 1 is in contact with the melt 2. To determine the concentration, an electrical potential is determined between the housing 3 and at least one sensor 8, the sensor 8 being arranged in an electrically insulated manner from the housing 3 or the sensor holder 4.

The sensor unit 1 shown has an axis 12, the arrangement of the components of the sensor unit 1 preferably being symmetrical about this axis 12. The sensor unit 1 comprises a sensor holder 4 connected to the housing 3, which has an interior 5, a measurement opening 6 and a connection area 7. The connection area 7 is shown here as a threaded section, the housing 3 and the sensor holder 4 together forming an oblique stop surface 19 with respect to the axis 12. This connection area 7 is essentially sealed so that at least no liquid or solid components of the melt 2 can penetrate into the interior 5. To receive the sensor 8 in the sensor holder 4, the latter has a collar 30 which on the one hand delimits the measuring opening 6, but on the other hand provides a contact surface for receiving the sensor 8.

The sensor 8 comprises two or four ion lead phases 10, which are arranged in a support structure 21, wherein the ion lead phases 10 can be made of the same or, if appropriate, also of a different material. The support structure 21 here consists of an electrically non-conductive material, so that the ion conductor phases 10 are arranged insulated from the sensor holder 4. Furthermore, the ion conductor phases 10 are positioned in the support structure 21 in such a way that they have a protrusion 22 which ensures reliable contact with the corresponding reference electrodes 9. On the side opposite the reference electrodes 9, the ion conductor phases 10 are before 31 allows direct contact with the melt 2. In order to prevent a melt bath movement or a relatively high pressure from being exerted on the ion conductor phases 10, the sensor unit 1 is equipped with an orifice 28 which provides a kind of calming volume. The diaphragm 28 is provided over its circumference with a plurality of outlets 29 which are arranged in a distributed manner in order to allow a gas in the calming volume to flow out, so that contact with the measurement medium is also established / ensured in this way.

Furthermore, the sensor unit 1 has a base part 15, which fixes two or four reference electrodes 9. The reference electrodes 9 arranged on the end face of the foot part 15 are each connected to the corresponding sensor conductor 27 via spring elements 11. The spring elements 11 are preferably parts of the contact between the sensor conductor 27 and the reference electrodes 9, so that a relative movement of the reference electrodes 9 with respect to the foot part in the direction of the axis 12 is ensured.

The housing 3 is also provided with at least one (sliding) contact 33, which in turn is connected to an evaluation unit 35 via a housing conductor 32. Such an evaluation unit comprises, for example, a potentiometer which determines the voltage between the housing 3 in contact with the melt 2 and the reference electrode 9. The evaluation unit 35 can include additional components, for example for data acquisition, data recording or a data comparison. Acoustic, visual or other displays can also be included.

FIG. 2 shows a further embodiment of a measuring unit 23. The evaluation unit 35 is again connected via the housing conductor 32 to the contacts 33, which via the housing 3 are connected to the melt 2 when determining the contact. center related. The housing 3 is connected to the sensor holder 4 via a stop surface 19, which is arranged at an angle 20 to the axis 12 of the sensor unit 1. The sensor holder 4 in turn serves to receive a sensor 8 which is arranged in an electrically insulated manner due to an insulation 36 which surrounds the sensor 8 on the circumference. In connection with the sensor 8 and the lance 24, the sensor holder 4 forms a closed interior 5 in which the foot part 15 with the reference electrode 9 is also arranged. The reference electrode 9 is in turn connected to the evaluation unit 35 via a sensor conductor 27.

The reference electrode 9 is supported here in the foot part 15 so that it can execute a stroke 13. This stroke 13 allows the sensor 8 to be pressed against it, an intimate electrical contact of the reference electrode 9 with the ion conductor phase 10 being ensured by the spring element 11, which in the embodiment shown is arranged in the lance head or in the region outside the melt 2.

In the embodiment shown, the sensor 8 is used, for example, to determine a gaseous component of the melt 2, in particular the hydrogen concentration. Since the hydrogen concentration cannot be determined directly, here the sensor 8 is designed with an auxiliary electrode 38 which produces ions as a result of a specific hydrogen concentration, which results in a corresponding activity or functionality of the ion conductor phase 10. In this respect, the auxiliary electrode 38 serves as an intermediary or converter. To form an intermediate space 37 in which there are gaseous components of the melt 2, the sensor unit 1 has a membrane 39 which closes the measuring opening 6 for solid and liquid components of the melt 2. A gas-permeable medium required for this is known to the person skilled in the art and must be selected depending on the minor constituent to be determined. 3 shows schematically and in section a disassembled embodiment of the sensor unit 1. The lance 24 is at least partially surrounded by the housing 3, which has a connecting section 18 (shown here as a thread), which is used for detachable connection to the sensor holder 4. In the interior of the lance 24, the base part 15 is arranged, which receives the contacts 33, the reference electrode 9 and the associated housing conductor 32 or the sensor conductor 27 (very simplified representation of the reception of the reference electrode). In addition, the foot part 15 is provided with a sensor 40 (for example for recording the temperature) and a corresponding line 41 for forwarding the measurement signal.

By simply detaching the sensor holder 4 from the housing 3, a separation of the reference electrode 9 from the sensor 8 having an ion conductor phase 10 is effected at the same time. This remains, for example as a result of an enclosure or a lock on the collar delimiting the measuring opening 6, a clamping force preferably also supported by the insulator 36, which is located on the inner wall of the sensor holder 4, to simultaneously carry the sensor 8 when the sensor holder 4 is released ,

4 shows schematically and in section a partial view of a contacting of the reference electrode 9. The contacting of the sensor conductor 27 to the reference electrode 9 is realized with a spring element 11 and a receptacle 14. The spring element 11 or the receptacle 14 has the effect that the reference electrode 9 can execute a stroke 13, the reference electrode 9 being mounted in a guided manner in the foot part 15. The detail shown here shows the reference electrode 9 in a pressed-in state, the side of the reference electrode 9 serving as the contact surface even disappearing or immersing in the interior of the foot part 15. A position of the reference electrode 9 under pre-tension is imminent moves only when the ion conductor phase 10 or the sensor 8 (not shown) is arranged in its assembled, ready-to-use position. At least the stroke 13 is only partially executed.

5 shows a particularly preferred method for operating or monitoring the function of a sensor unit or measuring unit. It is first queried whether a new sensor is used which corresponds to the "new" state. If this is the case, the time counter for the measurement duration and the temperature change counter are set to zero. If the sensor is used or older, the sensor is The sensor is blocked or the time counter and the temperature change counter are set to the values that correspond to the state of the sensor. This can be done, for example, by a data processing unit in which the sensor identification is read in, for example, via a bar code. The status "hot ", which is set when the sensor is immersed in the melt. When "hot" is reached, the time counter is switched on or on. If the time counter has reached a value "TMAX" for the maximum permissible period of use of a particular sensor, this is indicated to the user, for example by an alarm, and the sensor is blocked for further measurements , If "TMAX" is not reached, it is checked whether the sensor is defective and is therefore in the "Defective" state. If this is the case, the sensor is blocked for further measurements - if necessary via an alarm. If the sensor is not defective, the measurement can take place. If the sensor is removed from the melt after the measurement has ended, the sensor cools down, so that the "cold" state is reached. After reaching the "cold" state, the time counter is stopped and the temperature change counter is increased by one unit that corresponds to the number corresponds to the measurements, counted further. It is now determined that either the intended maximum permissible number of measurements according to the temperature change counter and / or the intended maximum permissible measurement time according to the time counter and thus the maximum permissible service life If "TMAX" is reached, the sensor may be blocked via an alarm. Otherwise, further measurements can be carried out with this sensor by continuing to query the "hot" state for a further measurement. The data necessary for the states of the respective sensor are stored in the data processing unit.

6 and 7 show a system for measuring the sodium activity in aluminum melts at temperatures between 660 and 800 ° C. with a sensor unit according to the present invention. This system can also be used to monitor the temperature of the melt in this area. With the correct setting and application, its measurements largely agree with the values determined by thermal or spectral analysis.

The system shown in FIG. 6 comprises a lance 24 with a holding device 17 and an exchangeable sensor 8 as well as an evaluation unit 35. The holding device 17 serves to fix the lance 24, which can be fixed in a changeable manner by means of a clamping lever 16. The holding device 17 is preferably designed with a joint, so that the lance 24 with the sensor 8 can simply be immersed in the weld pool by rotation.

The lance 24 and the evaluation unit 35 are connected to one another by transmission cables (only indicated). The housing 3 with the sensor 8 dips into the molten bath and supplies data, the changes of which appear, for example, on a display 42 of the evaluation unit 35. In addition, a widely visible traffic light 48 on the evaluation unit 35 signals whether the sodium content is in the “green range” or whether its preset limits have been exceeded or fallen short. The life of the sensor 8 depends on its stress. On the display 42 of the evaluation unit 35 an error message appears if the installed sensor 8 is unusable and needs to be replaced. The evaluation unit 35 shown in FIG. 7 is dust-tight and protected against splash water. The embodiment of the evaluation unit 35 shown comprises an operating area with a display 42, a lock 43, a control lamp 44 and a release button 45. The lock 43 has the task of securing the evaluation unit 35 against undesired use. The control lamp 44 signals whether the evaluation unit 35 is ready for operation or whether energy is provided via the mains connection 46.

The data determined by the lance 24 reach the evaluation unit 35 via the sensor conductor 27 and the housing conductor 32. The evaluation of the data or the optical and / or EDP implementation of this data takes place inside the evaluation unit 35. For outputting or signaling the The evaluation unit 35 offers two options for data, which can be used individually or in combination with one another.

On the one hand, the data interface 47 allows the data generated by the lance 24 to be forwarded immediately, for example in order to carry out a more detailed analysis in an external computer. Furthermore, the evaluation unit 35 has a traffic light 48 for optical signaling. The traffic light has colored lights that can be seen from far away, so that it can be recognized at any time whether the sodium content is correct or whether there is a fault. To initiate such a measurement, the trigger button 45 is actuated, a corresponding light from the traffic light 48 lighting up in each case as a function of the acquired measurement data. LIST OF REFERENCE NUMBERS

sensor unit

melt

casing

sensor mount

inner space

Messöffhung

connecting area

sensor

reference electrode

Ionenleiteφhase

spring element

axis

stroke

admission

footboard

clamping lever

holder

connecting portion

stop surface

angle

supporting structure

Got over

measuring unit

lance

main metal

Less component

sensor Head cover

outlet

collar

breakthrough

housing ladder

Contact

melting mirror

evaluation

isolation

gap

auxiliary electrode

membrane

pickup

management

display

lock

indicator light

release button

mains connection

Data Interface

traffic light

Claims

claims

1. Sensor unit (1) for determining the concentration of minor components (26) of a melt (2) comprising a sensor holder (4) which can be connected to a housing (3) and which has an interior (5), a measurement opening (6) and one

Connection area (7), at least one sensor (8) and at least one reference electrode (9) being arranged in the interior (5) and electrically insulated from the sensor holder (4), and means (9, 27, 32, 33, 35 ) for determining an electrical potential between the housing (3) and the at least one sensor (8), characterized in that the at least one sensor (8) and the at least one reference electrode (9) are each separate components which are detachable from one another , and preferably can be arranged positively with one another.

2. Sensor unit (1) according to claim 1, characterized in that the at least one reference electrode (9) and the measuring opening (6) are connected to one another in a gas-permeable manner.

3. Sensor unit (1) according to claim 1 or 2, characterized in that the at least one reference electrode (9) is arranged on a side of the at least one sensor (8) facing away from the measuring opening (6), the at least one sensor (8) is preferably gas permeable.

4. Sensor unit (1) according to one of the preceding claims, characterized in that at least one sensor (8) comprises at least one ion conductor phase (10).

5. Sensor unit (1) according to one of the preceding claims, characterized in that at least one reference electrode (9) by means of at least one spring element (11) is arranged to be movable at least in the direction of an axis (12) of the sensor unit (1), for the reference electrode (9) preferably a stroke (13) of 0.05 mm to 10 mm, in particular of 0.1 mm to 1.0 mm, can be realized.

6. Sensor unit (1) according to claim 5, characterized in that the at least one spring element (11) is part of the contacting of a sensor conductor (27) with the at least one reference electrode (9).

7. Sensor unit (1) according to claim 5, characterized in that the at least one spring element (11) is arranged in the upper part of the lance (24), which is colder in use.

8. Sensor unit (1) according to one of the preceding claims, characterized in that the housing (3) has a connecting section (18) which is in contact with the connecting region (7) of the sensor holder (4) in such a way that a stop surface (19th ) is formed, which has an angle (20) to the direction of the axis (12) of the sensor unit (1), which is preferably between

30 ° and 70 °.

9. Sensor unit (1) according to one of the preceding claims, characterized in that the at least one sensor (8) is arranged in at least one support structure (21), the at least one sensor (8) on the

Measuring opening (6) facing away from the support structure (21) preferably protrudes, in particular with a protrusion (22) of 0.1 mm to 3 mm.

10. Measuring unit (23), characterized in that it comprises at least one lance (24) which, preferably detachably, can be connected to at least one sensor unit (1) according to one of the preceding claims.

11. Measuring unit (23) according to claim 10, characterized in that a releasable connection between the lance (24) and foot part (15) and / or lance (24) and housing (3) is provided.

12. A method for producing a refined metal by a melt (2), comprising the following steps:

Determination of a proportion of at least one minor component (26) present next to a main metal (25) in the melt (2), with a sensor unit (1) according to one of Claims 1 to 9 or with a measuring unit (23) according to Claim 10 or 11 for determination an actual concentration of the minor component (26),

Adjusting the proportion of the minor component (26) to a target concentration by increasing or decreasing the proportion of the minor component (26), pouring the melt (2) if the actual and target concentrations match.

13. A method of operating a sensor unit (1) for determining the concentration of minor components (26) of a melt (2), in particular according to one of claims 1 to 8, comprising at least the following steps: - Determining one at least once, preferably several times

Proportion of at least one minor component (26) present next to a main metal (25) in the melt (2);

Detecting at least one parameter for determining the functional state of the sensor unit (1); Comparing the at least one parameter with a predefinable limit value;

Evaluation of the comparison with regard to a necessary repair of the sensor unit (1), wherein at least one sensor (8) with at least one ion conducting phase (10) is exchanged separately by at least one reference electrode (9) as part of such a repair.

14. A method of operating a sensor unit (1) according to claim 12, wherein the sensor unit (1) has a sensor holder (4) which can be connected to a housing (3) and which has an interior (5), a measurement opening (6) and a connection area ( 7), the at least one sensor (8) and the at least one reference electrode (9) being arranged in the interior (5) and electrically insulated from the sensor holder (4), in which the sensor holder (4) is released when the connection is released the housing (3) the at least one separate sensor (8) simultaneously from the at least one reference electrode

(9) is removed.

15. A method for operating a sensor unit (1) according to claim 12 or 13, wherein the at least one parameter is the temperature.

16. The method for operating a sensor unit (1) according to any one of claims 12 to 14, wherein the at least one parameter is time.

17. A method for operating a sensor unit (1) according to one of claims 12 to 15, wherein the at least one parameter is the specific concentration or activity of the minor component (26) itself.

8. The method for operating a sensor unit (1) according to one of claims 12 to 16, in which several parameters are combined to form a characteristic value and compared with a limit value.