EP0974682A1 - Method and apparatus for the chemical treatment of metalsurfaces - Google Patents

Abstract

The solution of the treatment bath (1) is circulated through a first pipe line (2) by a circulation pump (3). The solution and/or the gas to be added are introduced either into the first pipe line or into the process bath at a point where thorough mixing takes place due to the end of the pipe line. The end of this pipe line is either in the treatment bath or above the surface of the treatment bath. The pipe line (2) includes a suction pump (4) operating on the venturi principle. The inlet of the pump is provided with a second pipe line (6) for solutions or gases which are to be added.

Description

The invention relates to a method for the chemical treatment of metal surfaces, especially for phosphating or pickling, in which the Metal surfaces in contact with a solution of a process bath which contains several components in aqueous solution, the Composition of the process bath by adding solutions or gases, especially air, in a predetermined range.

When phosphating metal sheets, they are so-called phosphating solutions by immersion in a process bath or by spraying brought into contact with the solution. It can be very hard on the metal surface thin phosphate layer are created, which on the one hand protect against corrosion and on the other hand to improve the liability of what is subsequently applied Varnish is used. Thicker layers of phosphate are produced when these are Forming aid to facilitate forming processes. Next Phosphoric acid contains the solution mainly zinc, so that the metal surface is covered with a zinc phosphate layer. Next to it are in the Phosphating solution still other components, e.g. B. other metal ions such Manganese ions, and so-called accelerators, are used for uniform Ensure formation of the phosphate layer on the metal surface. In contrast, phosphate layers that act as sliding layers are based on the Usually on manganese phosphate.

Changed while using the same phosphating solution their composition, so that from time to time or continuously must be replenished. The usual phosphating solutions are in the Usually acidic, with a pH of around 1.5 to 4.5. If the phosphating solution acid sensitive components such as accelerators contains, which must decompose quickly in the acid phosphating solution these components are replenished particularly frequently. The For reasons of stability, acid-sensitive components are in one alkaline solution before and with this solution in the acidic Phosphating solution metered. The disadvantage at the dripping point is resulting local increase in pH to more than 4, which leads to a Precipitation of zinc ions as zinc phosphate leads, so that subsequently also zinc or zinc phosphate must be added.

This applies to an even greater extent if the phosphating solution becomes dull the free acid alkaline solutions or dispersions (e.g. Sodium hydroxide solution or sodium carbonate solution, hydroxylamine, zinc carbonate) can be added. Since these alkaline solutions greatly increase the pH at the point of addition, zinc phosphate precipitates more and more as sludge. At this Zinc phosphate sludge formation increases the free acid again, so again must be blunted. As a result, the valuable zinc phosphate If phosphating solution is lost, this valuable substance must be replenished become. This increases the operating costs of the process. On the other hand, the Sludge hinder the phosphating process, so that it from the phosphating bath must be separated and disposed of. This also affects the Costs of the phosphating process. The sludge formation is special pronounced when alkaline solutions the phosphating bath at one point are added, at which this is only slow with the phosphating solution be mixed. The effect of increasing the pH value could be achieved by mixing more quickly reduced and thereby the sludge formation can be reduced.

However, the composition of the phosphating solution does not only change by reducing the content of your components. It continues to be so undesirable if the iron ion content increases too much. It is known to ventilate the bath to reduce the iron content. This is done with compressed air introduced over fine-pored membranes arranged in the process bath, so that the Oxygen in the air oxidizes the iron ions, which then precipitate and form Lower the bottom of the bath container. The fine-pored membranes with a pore size of about 20 µm produce very fine air bubbles that work well in the process bath to solve. The consumption of the compressed air used for ventilation, which one represents a clear cost factor, can be achieved by using this fine-pored Keep membranes low. When the compressed air is switched off, however, considerable Problems because the fine membrane pores settle with phosphating sludge to. The crusted and clogged pores can not or only clean with considerable difficulty, so that the membranes usually need to be replaced frequently. Furthermore, the usually high Temperature of the phosphating solution, which can be up to 80 ° C, too rapid wear of the membrane units.

The problems mentioned therefore lead to increased costs of the phosphating process.

Similar problems exist when replenishing process solutions for pickling stainless steel and / or titanium and its alloys. These are both strongly acidic and oxidizing to surface coverings break open and peel off and a uniform metallic surface produce. Such process solutions are for example in EP-B-505 606 described. It is to maintain the reduction-oxidation potential required, continuously or discontinuously, an oxidizing agent such as for example, supply hydrogen peroxide or air.

The invention is therefore based on the object, the economy of significantly improve the methods mentioned at the beginning. Another job of The invention is to increase the process reliability, since when replenishing individual components the proportion of the other components did not change shall be.

These objects are achieved according to the invention by a process for the chemical treatment of metal surfaces, in which the metal surfaces are brought into contact with a solution of a process bath (1) which contains several components in aqueous solution, the composition of the process bath (1) being added of solutions or gases, especially air, in a predetermined range,
characterized by
that one circulates the solution of the process bath (1) via a first line (2) and a circulation pump (3) and feeds the solution and / or the gas to be added into the first line (2) or into the process bath at a point where due to the end of the line (2) a strong mixing occurs, the end of the line (2) can be in the process bath or above the surface (10) of the process bath.

According to Figure 3, the end of the line (2) can be above the surface (10) of the process bath. You choose the distance of the end of the Line (2) from the process bath surface (10) so that no process bath solution in the line (2) can be drawn back. For example, this distance range from about 10 to about 50 cm. In this embodiment thus the process bath solution circulated through line (2) onto the surface (10) of the process bath (1) sprayed on, producing a strong turbulence mixed with the remaining process bath solution. The The solution to be added is then fed in at that point in the process bath, where this strong turbulence prevails. In Figure 3, this point is with the Reference numerals (11) indicated. The solution to be added can be fed in done, for example, by having a line for the solution to be added ends above the surface (10) of the process bath, so that at the point (11) the solution to be added freely on the surface of the Process bath can leak. Because of the great turbulence at this point the solution to be added quickly mixes with a large amount of the Process bath solution. Accordingly, one embodiment of the method is thereby characterized in that the solution to be added to the process bath at a Point feeds where a strong due to the end of the line (2) Mixing occurs and the end of the line (2) above the Surface (10) of the process bath is.

It can be in one embodiment of the invention Process bath solution (1) around a phosphating solution for layer-forming or act non-layer-forming phosphating of metal surfaces. The solution to be added is preferably a basic solution (for example an aqueous solution of sodium hydroxide, sodium carbonate or an alkaline amine solution, for example a solution of hydroxylamine) which mixed with the phosphating bath solution to blunt the free acid shall be. By adding this alkaline solution at a point where it due to strong turbulence quickly with a large volume of acidic Phosphating bath solution mixes, the formation of phosphating sludge (mainly zinc phosphate) largely avoided.

The function of the first line (2) can be from the line of the heating circuit and the function of the circulation pump (3) from the pump of the heating circuit be taken over. Usually the pump is the heating circuit the process bath is constantly active during plant operation and rolls the Process bath solution constantly via a heat exchanger (12) (Fig. 3), pumps for the spraying system in spraying systems or circulation pumps in diving tanks can be switched off during breaks or long interruptions. Accordingly, in one embodiment of the invention, the heat cycle can Design so that the process bath solution heated in the heat exchanger (12) not, as was previously the case, below the surface (10) of the process bath in the Process bath is fed, but that the line used for this (2) like described above the surface (10) of the process bath ends. The solution to be added is then placed at that point (11) on the Process bath surface where the exiting from the end of the line (2) Liquid jet on the process bath surface causes strong turbulence. In In this embodiment, the method according to the invention is thereby characterized in that the first line (2) is a heating line for the process bath represents, via which the solution of the process bath via a heat exchanger (12) in the process bath is returned.

Depending on the circulation rate of the process bath solution via the heating circuit (2) of Fig. 3, if the volume flow is too strong at the point where the solution emerging from the end of the line (2) meets the process bath surface, an undesirably strong spraying could occur. This can be prevented by not allowing the entire volume flow of the heating circuit to strike the bath surface through the end of the circulation line (2) above the bath surface (10). Rather, a branch line (9) (Fig. 3) is provided, through which a partial flow of the bath solution circulated in the heating circuit is fed in below the surface of the process bath and only a further partial flow through the end of the line (2) above the process bath surface (10) ) to be led. The volume fraction of the process bath solution circulated per unit of time, which is introduced directly into the process bath through the branch line (9), can be most easily determined by the cross-sectional ratios of the branch line (9) and the part of the circulation line (2) that continues after branching off this branch line (9) ) to adjust. For example, the cross-sectional ratios can be selected such that a bath volume of approximately 1 to approximately 10 m ³ / h is applied to the process bath surface from the end of the line (2) above the process bath surface (10).

The nozzle can be narrowed at the end of the pipe (2) Flow rate of the pumped process bath solution at the entry point in the bathroom can also be increased. This increases the desired Mixing effect when adding the solution to be added. Accordingly an embodiment of the method according to the invention characterized in that the end lying above the process bath surface the first line (2) constricted in a nozzle shape and the solution to be added to the Process bath gives up at a point where due to the end of the line (2) strong mixing occurs.

Furthermore, in an embodiment of the invention in which the end of the first line (2) is above the process bath surface, above the end the first line (2) into this line a second line (6) (Fig. 3) open, through which gas, in particular air, is sucked into the first line (2) It is particularly favorable for this that the end of the first line (2) narrowed in a nozzle shape so that due to the increased flow velocity An increased suction effect is created by the gas, especially air, in the Line (6) is sucked in. The place where the line (6) into the circulation line (2) opens out, for example about 10 to about 50 cm above the end the line (2). The gas sucked in is dispersed in the Line (2) circulated process bath solution and is with this in the process bath mixed in. To control the amount of gas sucked in, one can select the cross section of the second line (6) accordingly. On the other hand a controllable valve, preferably in connection with a flow meter, be provided as shown in Fig. 1 and 2.

The embodiments described above, the subject of Represent claims 2 to 6 are particularly suitable for process baths (1) Solutions for the layer-forming or non-layer-forming phosphating of Represent metals. The solution to be added is in particular an alkaline one Solution to dull the free acid, the possibly to be mixed gas oxygen-containing gas, especially air. Below are those Phosphating bath solutions described in more detail.

In a further embodiment of the method according to the invention, one can see before that the first line (2) is provided with a suction pump (4). About these Suction pump can in the solution to be added and / or the gas to be added the line (2) are fed, the solution to be added or the Gas to be added already inside the suction pump and in the subsequent one Section of the line (2) mixed with the process solution.

According to the invention, two essential advantages are achieved. Even when topping up no strong local component occurs in alkaline solution Increase the pH to the alkaline solution to be added before entry into the process bath with the process solution, for example the acidic one Phosphating solution is mixed. In addition to the often already existing Circulation pumps are only known for minor retrofitting investments Phosphating plants necessary, namely an inexpensive suction pump and the corresponding supply lines.

If the process bath is to be aerated, the costly use of Compressed air and membranes, as the ambient air is drawn in via the suction pump can be, which then mixes in the line with the circulated solution. The end of the line immersed in the process bath does not require a gas distributor and can therefore be an open pipe end. Even if the bubble diameter considerably larger than that emerging from the membranes Is compressed air bubbles, this can be done by adding a larger one at no additional cost Compensate for air flow and / or a longer ventilation period.

Schichtgewichte") im Bereich von etwa 1 bis etwa 3 g/m² aufweisen. Solche Phosphatierlösungen werden vorzugsweise eingesetzt, um Phosphatschichten zu erzeugen, die als korrosionsschützender Haftgrund für eine nachfolgende Lackierung wie beispielsweise eine kathodische Tauchlackierung im Fahrzeugbau dienen. Andererseits kann es sich bei der Phosphatierlösung um eine sogenannte Eisenphosphatierlösung handeln. Im Gegensatz zu einer Niedrigzink-Phopshatierlösung enthält diese keine Schwermetallionen, die in die Phosphatschicht eingebaut werden. Auf Eisenoberflächen werden durch Behandlung mit einer solchen Phosphatierlösung nichtkristalline Phosphat- und Oxidschichten mit einem Schichtgewicht in der Größenordnung 0,3 bis 1,2 g/m² abgeschieden. Weiterhin sind Phosphatierlösungen bekannt, die im Vergleich zu den Niedrigzink-Phosphatierlösungen wesentlich höhere Gehalte an Zink (mehr als 3 g/l) und ggf. weiteren zweiwertigen Metallen aufweisen. Sie erzeugen kristalline Phosphatschichten mit einem Schichtgewicht deutlich oberhalb von 3 g/m². Diese dienen als solche oder nach einem Belegen mit Ölen oder Seifen als Umformhilfen für Umformprozesse durch Kaltfließen wie beispielsweise Rohr- oder Drahtzug. Zur Erzeugung von Gleitschichten für bewegte Maschinenteile wie beispielsweise Zylinder verwendet man saure Manganphosphatlösungen.The method according to the invention can be applied to process baths with phosphating solutions. The phosphating solutions can serve different technical purposes. For example, they can represent so-called low-zinc phosphating solutions, as are described, for example, in EP-A-228 151. These have a zinc content of between about 0.3 and about 2 g / l and produce zinc phosphate or zinc iron phosphate layers on the substrate, which can be doped with other metals such as manganese and which have area-related masses (

Layer weights ") in the range from about 1 to about 3 g / m ^2. Such phosphating solutions are preferably used to produce phosphate layers which serve as a corrosion-protecting adhesive base for a subsequent coating, such as, for example, a cathodic dip coating in vehicle construction In contrast to a low-zinc phosphating solution, the phosphating solution does not contain any heavy metal ions that are built into the phosphate layer up to 1.2 g / m ^2. Furthermore, phosphating solutions are known which, compared to the low zinc phosphating solutions, have much higher contents of zinc (more than 3 g / l) and possibly other divalent metals, which produce crystalline phospha Layering with a layer weight significantly above 3 g / m ² . These serve as such or, after covering with oils or soaps, as forming aids for forming processes by cold flow such as, for example, pipe or wire drawing. Acid manganese phosphate solutions are used to produce sliding layers for moving machine parts such as cylinders.

Phosphating solutions usually contain so-called accelerators contribute to the rapid and uniform formation of the phosphating layer. These are usually substances with an oxidizing effect, for example Nitrate, nitrite, chlorate and / or hydrogen peroxide. Sometimes these are what For example, for nitrite and hydrogen peroxide, acidic Phosphating solution is not stable, so it is not concentrated in a phosphating bath can be incorporated. Rather, they have to make it ready for use Phosphating bath are added continuously or discontinuously. For this The process according to the invention is particularly suitable for addition.

When phosphating iron-containing surfaces, Phosphating bath divalent iron, which in higher concentrations Phosphating process can interfere. Usually you remove one Excess iron by oxidizing the iron to the trivalent stage, so that it precipitates as poorly soluble phosphate and as phosphating sludge from the phosphating solution can be separated. Strongly oxidizing Accelerators also fulfill these in addition to the acceleration effect Task. However, if you set weakly oxidizing accelerators like For example, hydroxylamine, the divalent iron is only by contact oxidized to the trivalent stage with atmospheric oxygen and precipitated as phosphate. Intensive contact with air is particularly important for this. A special one A method for such air oxidation is described, for example, in EP-B-320 798 described. The method according to the invention enables the oxidation of especially divalent iron in a phosphating solution to the trivalent stage to perform effectively. Here you introduce the suction pump oxygen-containing gas such as, in particular, ambient air that flows in and after the Pump and especially in the preferably downstream static Mixer is brought into intensive contact with the phosphating solution.

The process according to the invention can be used not only in phosphating baths, but also in other process baths. Cooling lubricant tanks are an example and called lacquer coagulation baths. There is an inexpensive one Aeration is beneficial to limit the growth of anaerobic bacteria or kill these bacteria. The invention can be used for the same purpose Use ventilation also for neutral cleaning baths.

The method can also advantageously be used to add oxidizing substances use in a pickling solution, for example for pickling stainless steel and / or of titanium or its alloys. This will make it for the Pickling and / or passivation step required reduction-oxidation potential discontinued or maintained. For example, the method is suitable Reduction-oxidation potential of a pickling solution, as described in EP-B-505 606 is described to increase or maintain. For this one gives the Process solution via the suction pump, for example, a solution Oxidizing agent such as hydrogen peroxide in particular. The oxidizer has the task of the iron (II) and / or formed during the pickling step Oxidize titanium (III) to the next higher oxidation state. Because of the strong Turbulence in the suction pump and especially in one, preferably the Subsequent to the submersible static mixer, this oxidation reaction takes place very quickly.

From German patent application DE 197 55 350.8 it is known that divalent iron in a pickling solution thereby to the trivalent stage oxidize that in the presence of copper ions as a catalyst, the pickling solution mixed with an oxygen-containing gas such as preferably air. The The method according to the invention is suitable for carrying out this process, an oxygen-containing gas, preferably via the suction pump Ambient air, sucked in and mixed with the pickling solution.

A suction pump is preferably used, which works according to the Venturi principle works and is driven by the recirculated solution. A separate drive the pump is therefore not required.

For better mixing of the solution to be added or the one to be added Gases with the circulated solution are used in an advantageous embodiment the invention behind the suction pump a static mixer. How the suction pump working according to the Venturi principle requires the static one Mixer no separate drive. Also the investment costs for one Mixers are very small, and this mixer can as well at no additional cost the suction pump must be resistant to chemicals.

In a further advantageous embodiment of the invention, the one to be added is carried out Solution or the gas to be added to the suction pump via a second one Line to, in which a valve and a flow meter are arranged, so that a controlled and metered addition of gas and solution is possible. In particular the valve can also be timed to maintain running to facilitate the desired composition of the process bath. It is also possible and advantageous to integrate the valve in a control loop, which sensors for detecting the component concentrations in the process bath contains. This is a fully automatic monitoring and replenishment possible.

In this embodiment, the solution of the process bath is preferably left at a throughput of 0.1 to 5 m ³ / h, in particular from 0.5 to 1 m ³ / h, through the first line (2) and, if present, through the Flow suction pump.

Provided a continuous circulation of the process bath liquid with a significantly higher throughput is provided in the circulation line, it is proposed that one of the first line in which the suction pump is arranged the circulation line, which in this case branches off to the third line. The one you want Throughput through the first line can be selected by an appropriate choice Reach line diameter and / or through a throttle valve.

Alternatively, the solution and / or gas can also be metered in independently of a bath circulation. To this end, it is suggested that one admit the Solution and / or the gas to be added to a suction pump, the works on the Venturi principle and driven by a fresh water supply is, the solution to be added or the gas to be added with the Fresh water mixes.

The invention also relates to a plant for carrying out the invention Process, with a container for the process bath and a first line with a circulation pump with which the process bath can be circulated.

The above tasks are performed in one embodiment solved according to the invention in that one after the Venturi principle working suction pump is provided, at whose suction inlet a second line for a solution to be added and / or a gas to be added connected. In the first line it is preferably downstream behind the Suction pump arranged a static mixer.

It is further proposed that in the second line, one, in particular controllable, valve and a flow meter are provided. The valve can be controlled by a timer or part of a control loop be if additional measuring devices for detecting the concentrations in the Process bath and control electronics are provided.

A circulation of the process bath is already provided in some known systems, however, the flow through the circulation line is often considerably higher than the flow rate desired for the operation of the suction pump. In this case it is favorable if one branches off a third line from the circulation pump, the is designed so that the largest part of the circulated solution through this third line flows. The smaller part of the circulated solution then flows through the suction pump.

In an alternative embodiment, the invention relates to a system for Performing the method according to one or more of claims 2 to 6, with a container for the process bath (1) and a first line (2) with a Circulation pump (3) and a heat exchanger (12) with which the solution of the Process bath can be circulated, characterized in that the end of the line (2) is above the process bath. This embodiment differs of known systems, such as those used for layer-forming or non-layer-forming phosphating of metal surfaces are used, characterized in that the line (2) leading over the heat exchanger is not below the surface (10) of the process bath ends, but above. It can additionally be provided that in the flow direction behind the Heat exchanger (12) branches off from the first line (2) a third line (9), through which a partial flow of the circulated solution of the process bath in the Process bath below whose bath surface is returned. By choice different cross-sections for the first line (2) and the third line (9) can be specified which proportion of the heat exchanger circulated process bath solution through the branch line (9) or through the Branch of the branch line (9) continuing part of the line (2) on the Surface of the process bath is applied.

Figur 1

ein Fließbild eines ersten erfindungsgemäßen Ausführungsbeispiels,

Figur 2

ein Fließbild eines zweiten erfindungsgemäßen Beispiels und

Figur 3

ein Fließbild eines dritten erfindungsgemäßen Beispiels.

Two exemplary embodiments are explained in more detail below with reference to drawings. Show it

Figure 1

2 shows a flow diagram of a first exemplary embodiment according to the invention,

Figure 2

a flow diagram of a second example according to the invention and

Figure 3

a flow diagram of a third example according to the invention.

In all drawings, the same reference numerals have the same meaning and may therefore only be explained once.

In the example according to FIG. 1, process bath 1 is aerated. The process bath with a volume of about 50 to 200 m ³ is circulated without interruption via a first line 2 and a circulating pump 3, the circulated liquid flow being 0.6 m ³ / h. In the first line 2 is a suction pump 4 working according to the Venturi principle, z. B. a water jet pump, and a static mixer 5 is arranged.

At the suction inlet of the suction pump 4, a second line 6 is connected through which air is supplied via a valve 7 and a flow meter 8 can.

In the example according to FIG. 2, the solution of the process bath 1 is circulated by means of the circulation pump 3 via a third line 9 with a throughput of 10 m ³ / h and more. A part of the circulated solution, namely 0.6 m ³ / h, reaches a first branch 2 via a branch point, in which the suction pump 4 and the static mixer 5 are arranged. Otherwise, this example corresponds to the example according to FIG. 1. In the present example according to FIG. 2, however, not only air can be supplied to the process bath, but also the mixing in of liquids, e.g. B. concentrates for replenishing individual components is provided here. It should also be pointed out that in the example according to FIG. 1, instead of air or in addition to air, liquids can also be fed to the process bath 1 by means of the second line 6.

In the example in Fig. 3, the first line (2) represents the circulation line of the Heating circuit. By a pump (3), which is shown in Fig. 3 for example in Flow direction is in front of the heat exchanger (12), but also behind it Heat exchanger could be, part of the process bath solution (1) on the Pumped heat exchanger (12) and heated in the process. At least part of the pumped process bath solution flows through the end of the circulation line (2), that ends above the surface (10) of the process bath solution (1). Optionally can a branch line (9) can be provided through which a partial flow through the Line (2) circulated process bath solution below the bath surface in the Process bath is returned. The reference number (6) is an optional Line indicated through which a gas in the line (2) above its end can be sucked into the circulated process bath solution, if desired via a control valve and / or a flow meter. If you do this Provides suction line (6), they are preferably arranged so that their open Comes to lie above the process bath surface. If by a Malfunction process bath solution rises back into the gas line (6) this arrangement ensured that this process bath solution in the process bath runs back without causing any damage. With the reference number (11) is that Marked location where by the impact of the circulated process bath solution the surface (10) of the process bath is particularly turbulent and where in one of the embodiments of the invention solution to be added.

Reference list

1

Process bath

2nd

first line

3rd

Circulation pump

4th

Suction pump

5

static mixer

6

second line

7

Valve

8th

Flow meter

9

third line

10th

Bathroom surface

11

Dosing point for the solution to be added

12th

Heat exchanger

Claims (21)

Process for the chemical treatment of metal surfaces, in which the metal surfaces are brought into contact with a solution of a process bath (1) which contains several components in aqueous solution, the composition of the process bath (1) being obtained by adding solutions or gases, in particular air , stops in a given area,
characterized by
that one circulates the solution of the process bath (1) via a first line (2) and a circulating pump (3) and feeds the solution to be added and / or the gas to be added into the first line (2) or into the process bath at a point where due to the end of the line (2) a strong mixing occurs, the end of the line (2) may be in the process bath or above the surface (10) of the process bath. A method according to claim 1, characterized in that the feed solution to be added to the process bath at a point where due at the end of the line (2) there is a strong mixing and where End of the line (2) above the surface (10) of the process bath. Method according to claim 2, characterized in that the first line (2) represents a heating line for the process bath, through which the solution of the Process bath returned via a heat exchanger (12) in the process bath becomes. A method according to claim 3, characterized in that from the first Line (2) branches off a third line (9) via which a partial flow of circulated solution of the process bath is returned to the process bath. Method according to one or both of claims 3 and 4, characterized characterized in that the end of the first line (2) is nozzle-shaped narrowed. Method according to one or more of claims 3 to 5, characterized characterized in that above the end of the first line (2) in this Line opens a second line (6) through which gas, in particular air, in the first line (2) is drawn in. A method according to claim 1, characterized in that the solution to be added and / or the gas to be added from a suction pump (4) feeds, with the solution to be added or the gas to be added of the circulated solution mixes. Method according to claim 7, characterized in that a suction pump (4) is used which works according to the Venturi principle and is driven by the circulated solution. Method according to one or both of claims 7 and 8, characterized in that a static mixer (5) is used behind the suction pump (4). Method according to one or more of claims 7 to 9, characterized in that the solution to be added or the gas to be added is fed to the suction pump (4) via a second line (6) in which a valve (7) and a flow meter (8 ) are arranged, Process according to one or more of claims 7 to 10, characterized in that the solution of the process bath (1) is passed through with a throughput of 0.1 to 5 m ³ / h, in particular of 0.5 to 1 m ³ / h lets the first line (2) flow. Method according to one or more of claims 7 to 11, characterized in that the solution of the process bath (1) is circulated by means of a third line (9) from which the first line (2) branches off. Process for the chemical treatment of metal surfaces, in which the metal surfaces are brought into contact with a solution of a process bath (1) which contains several components in aqueous solution, the composition of the process bath (1) being obtained by adding solutions or gases, in particular air , in a predetermined range, characterized in that the solution to be added and / or the gas to be added is fed to a suction pump which works according to the Venturi principle and is driven by a fresh water supply, the solution to be added or the gas to be added containing the fresh water mixes. Method according to one of the preceding claims, characterized characterized in that it is in the solution of a process bath (1) Phosphating solution is. Method according to one or more of claims 1 to 13, characterized characterized in that it is in the solution of a process bath (1) Pickling solution for stainless steel and / or for titanium or titanium alloys System for carrying out the method according to one or more of claims 7 to 15, with a container for the process bath (1) and a first line (2) with a circulation pump (3) with which the process bath (1) can be circulated, characterized that in the first line (2) a suction pump (4) working according to the Venturi principle is provided, to the suction inlet of which a second line (6) for a solution to be added and / or a gas to be added is connected. System according to claim 16, characterized in that a static mixer (5) is arranged in the first line (2) downstream behind the suction pump (4). Installation according to Claim 16 or 17, characterized in that a valve (7), in particular a controllable valve, and a flow meter (8) are provided in the second line (6). System according to one of Claims 16 to 18, characterized in that a third line (9) branches off from the circulating pump (3) and is designed in such a way that the majority of the circulated solution flows through this third line (9). Plant for carrying out the method according to one or more of the Claims 2 to 6, with a container for the process bath (1) and a first Line (2) with a circulation pump (3) and a heat exchanger (12), with which the solution of the process bath can be circulated, characterized in that that the end of the line (2) is above the process bath. Installation according to claim 20, characterized in that in Flow direction behind the heat exchanger (12) from the first line (2) a third line (9) branches off, through which a partial flow of the circulated Solution of the process bath is returned to the process bath.

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