EP2644739A1 - Method for passivating a metal surface and domestic appliance, in particular domestic dishwasher with a wall portion - Google Patents

Abstract

Passivating a metal surface (A), preferably a metal surface of a wall part of a household appliance, preferably a metal surface of a wall part of a domestic dishwasher (100), comprises: generating an atmospheric plasma beam (26) in a working gas by an electric discharge; passing an acid-containing passivating agent (120) into the plasma beam; and applying the passivating agent-containing plasma beam to the metal surface, where a passivating salt is deposited on the metal surface by reacting the acidic passivating agent with the metal surface. An independent claim is also included for household appliance, preferably domestic dishwasher, household washing machine, or household dryer comprising at least one wall part, which at least partially comprises a corrosion-resistant metal, preferably a stainless steel, where at least one metal surface of a wall part is at least partially, preferably completely provided with a passivating salt.

Description

The present invention relates to a method for passivating a metal surface, preferably a metal surface of a wall part of a domestic appliance, in particular a metal surface of a wall part of a domestic dishwasher, wherein a Passivierungsmittel on the metal surface, preferably on the metal surface of a wall part of a household appliance, in particular on the metal surface of a Wandungsteils a household dishwasher, is applied.

Under a passivation of a metal surface, preferably a metal surface of a wall part of a household appliance, in particular a metal surface of a wall part of a domestic dishwasher, is understood in the context of this description, for example, the application of a corrosion inhibitor. Passivation may also include applying a means to reduce friction in processing a metal workpiece. Likewise, the passivation of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher, also means reducing the electrical resistance, ie an electrical insulation of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a Wall part of a household dishwasher.

An example of a passivation of a metal surface is the phosphating, in which a so-called conversion layer of firmly adhering metal phosphates is formed by chemical reactions of metallic surfaces with aqueous phosphate solutions. The phosphating is mostly applied to steel, but can also be used for galvanized or cadmium steels and aluminum. Main areas of application are corrosion protection, adhesion, friction and wear reduction as well as electrical insulation.

In the case of the phosphating known from the prior art, the layer formation takes place by precipitation of sparingly soluble phosphoric acid salts, so-called phosphates from an aqueous solution. Depending on the type of solution, these may be iron, zinc, or manganese phosphate layers.

In the case of non-layer-forming phosphating, the metal cations involved in layer formation originate from the base material; the metal cations from the phosphate solution are not involved in the layer structure.

In the case of layer-forming phosphating, the layer build-up is effected by metal cations from the phosphate solution; in addition, metal cations from the base material may be involved. The layer thicknesses range from a few hundred nanometers in the iron phosphating up to two micrometers and more in zinc and manganese phosphatings.

The phosphate layer produced in this way adheres very well to the substrate and, due to the microporous or microcapillary layer structure, allows good anchoring for subsequently applied coatings. In addition, the phosphate layer impedes the rusting at damaged points of the coating. Phosphate layers alone provide useful temporary corrosion protection that is often sufficient for storage prior to a subsequent processing step. Likewise, applications are known in which a phosphating is used for a permanent corrosion protection.

The phosphate coatings also have good sliding properties. This has an advantageous effect, for example, in the cold forming of steel. Here zinc phosphate layers are preferably used because of the easy shearing off. Manganese phosphate coatings, on the other hand, are used to reduce the wear on heavily loaded sliding partners.

The high electrical resistance of phosphate layers is used for at least partial electrical insulation. For example, in the case of magnetic sheets for magnetic cores, the phosphate layer can be used in order to isolate them from one another with a thin separating layer.

Furthermore, a method for passivating a metal surface is known in which complex chromic acid salts (chromates) are formed on metallic surfaces by the action of chromic acid. Such a process is called chromating.

Also in the chromating the base material of the metal surface is dissolved. The dissolved metal ions of the base material are then incorporated into the chromate layer. The chromate layers obtained in this way are - similar to the phosphate layers - part of the passivation layers, ie they are inorganic non-metallic protective layers. The most common function of chromate coatings is corrosion protection. However, chromate layers can also be used to create a primer for subsequent layers, as tarnish (for silver), to reduce the visibility of fingerprints or to change the appearance (gloss, color). Chromating processes can be applied to aluminum, magnesium, silver, cadmium and zinc.

All the methods described above have in common that they can be carried out by wet bath only in a wet-chemical manner in a plurality of working steps. Therefore, the expenditure on equipment in carrying out the process is considerable. Likewise, the cost of materials is coarse because a large proportion of the passivating agent used is not used.

In addition, definable surface areas of a workpiece can not be treated separately, but the entire workpiece must always be treated wet-chemically.

This problem arises in particular in the production of components which consist of non-corroding metal sheets, for example made of stainless steel sheets, and whose individual parts are joined together by means of welding. The resulting welds are not corrosion resistant in the same way as the metal sheet itself. Therefore, a separate corrosion protection is required as Passivierungsmaßnahme only for the area of the weld. at Wet chemical passivation, so for example phosphating it is then necessary to treat the entire component wet-chemically.

As components, washing machine components, dishwasher components, pipe connections and other components which come into contact with water during use can be mentioned here by way of example.

Furthermore, a wet-chemical treatment with an acid-containing passivation agent is complex, especially for smaller components, if it is to be used as primer for a paint or varnish coating.

In addition, the problem arises in wet-chemical treatment, especially in the case of smaller component structures, that, due to surface tension effects, depressions or undercuts are not applied to the passivation agent over the entire surface. Therefore, gaps arise on the surface, which can adversely affect the subsequent use of the component.

The present invention is therefore based on the technical problem of simplifying and more effectively designing the method known from the prior art for passivating a metal surface, preferably a metal surface of a wall part of a domestic appliance, in particular a metal surface of a wall part of a domestic dishwasher.

Furthermore, a household appliance comprising at least one wall part, which consists at least partially of largely corrosion-resistant metal, in particular largely stainless steel, to be specified.

The above-mentioned technical problem is solved according to the invention by a method in which an atmospheric plasma jet is generated by electrical discharge in a working gas, in which an acidic passivating agent is introduced into the plasma jet, in which the passivation agent-containing plasma jet to the metal surface, preferably the metal surface of the wall part of the household appliance, in particular on the metal surface of the wall part of the household dishwasher, is applied and in by the reaction of the acidic passivating agent with the metal surface, preferably with the metal surface of the wall part of the household appliance, in particular with the metal surface of the wall part of the domestic dishwasher, a passivating salt on the metal surface, preferably on the metal surface of the wall part of the household appliance, in particular on the metal surface of the wall part of Household dishwasher, is deposited.

According to the invention, it has thus been recognized that the application of the passivating agent by means of an atmospheric plasma jet exploits many synergy effects. Before explaining these, first plasma sources and the properties of atmospheric plasma jets generated therewith will be explained.

A plasma source is understood to mean a source for a plasma jet directed into a spatial area, it being possible for the shape of the plasma jet to be round or flat. The plasma source may also generate a rotating plasma jet by a housing part, preferably the outlet opening is rotatably formed and rotates during the plasma generation about an axis. During the process of this plasma source along a surface, a wide strip of wider stripes is then treated.

The plasma source may have a plasma nozzle or a plurality of juxtaposed plasma nozzles in the form of a plasma shower. The plasma source may include a mount for positioning on the mover and supplies of working gas and electrical power.

The electrical excitation of the working gas can be done with different frequencies, for example in the microwave range in the range of or above 1 MHz or in the frequency range from 1 to 100 kHz. The voltage forms may vary between alternating voltages and pulsed DC voltages or be overlappings of the same. The discharges are microwave discharges or high-frequency spark discharges, which may take the form of discharge arcs (arc discharges) or tuft discharges. The voltage amplitudes are, like the frequency, adapted to the respective geometry of the plasma nozzle and are for example in the range 100 V to 10 kV. As the working gas is preferably used air, besides nitrogen and noble gases such as argon, even with the addition of other gases such as hydrogen are possible.

Such plasma sources can produce relatively cold plasma jets of relatively high chemical excitation energy. The jet temperature drops as a function of the distance to the outlet opening and is in the range below 300 ° C., preferably below 150 ° C. and preferably below 100 ° C. The high excitation energy of the working gas results from the high-frequency excitation in the excitation zone within the plasma source, in which only a small thermal excitation occurs. Therefore, one speaks of a non-thermal plasma. By choosing a suitable working gas and the parameters of the electrical voltage, the temperature and activity of the plasma jet can be influenced.

The present method is not limited to the use of previously described plasma sources. Other plasma sources, for example with other excitation mechanisms, may be used, even if their plasma jets have different temperatures and lower plasma powers. Even with such known plasma sources, the inventive method can be carried out.

A method for producing an atmospheric plasma jet, that is a plasma jet having an ambient pressure which is of the order of magnitude of the atmospheric pressure is, for example, from the document EP 1 335 641 A1 known. Here is a working gas, especially air, nitrogen, forming gas (mixture of nitrogen and hydrogen) or a noble gas, in particular argon or helium, passed through a channel in which by a high-frequency high voltage, a plasma jet via an electrical discharge, that is a corona discharge and / or an arc discharge is generated.

A method for plasma polymerization by means of an atmospheric plasma jet is described in the document EP 1 230 414 B1 disclosed. In this method, a precursor material is introduced into the plasma jet, there chemically and / or electronically excited, so that before, during or after the deposition of the excited precursor on a surface polymerization of the precursor begins.

According to the invention, the acidic passivating agent is then applied by means of an atmospheric plasma jet to the metal surface to be passivated, preferably the metal surface to be passivated of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher to be passivated, wherein the reaction of the acidic passivating agent with the metal surface preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher, a passivating salt is deposited on the metal surface. This achieves several advantages.

On the one hand, the excitation energy contained in the plasma jet is transferred to the passivating agent by the introduction of the passivating agent into the plasma jet, without causing a large increase in the temperature of the passivating agent.

On the other hand, the passivation agent is uniformly swirled by the often already rotating flow in the plasma jet and thus evenly distributed when hitting the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher. The resulting turbulence leads to an almost complete wetting of the surface even in depressions and undercuts, even if they have small dimensions. The turbulence of the plasma jet and the passivating agent transported therein also leads to the fact that not remaining on the surface passivant is immediately removed and no rework or cleaning is necessary.

In addition, the application of the plasma jet on the surface causes a cleaning effect, so that in not too heavily soiled surfaces no pre-cleaning must be done before the passivation agent is applied. Only on heavily soiled surfaces that are not adequately covered by the plasma jet can be cleaned, a separate pre-cleaning is required. The number of working steps is thus significantly reduced in comparison with the wet-chemical method, and in a large number of applications, a method step is sufficient for the passivation of the metal surface, preferably the metal surface of a wall part of a domestic appliance, in particular the metal surface of a wall part of a domestic dishwasher.

A further advantage is that the surface of the metal of a domestic appliance, in particular the metal surface of a wall part of a domestic dishwasher, does not contaminate the metal surface, preferably the metal surface of a wall part of a domestic appliance, in particular the metal surface of a wall part, with the plasma jet a domestic dishwasher, such as in prior art wet-chemical processes by prior immersion baths or the like.

In the context of the invention, it has thus surprisingly been found that the application of a passivating agent by means of an atmospheric plasma jet to a metal surface, preferably to a metal surface of a wall part of a domestic appliance, in particular to a metal surface of a wall part of a domestic dishwasher, is an effective alternative to the known wet-chemical method represents.

On the one hand, an aqueous phosphoric acid may be used as the passivating agent, and metal phosphate may be deposited on the metal surface, preferably on the metal surface of a wall part of a household appliance, in particular on the metal surface of a wall part of a domestic dishwasher. On the other hand, a chromic acid can be used as the passivating agent and metal chromate can be deposited on the metal surface, preferably on the metal surface of a wall part of a domestic appliance, in particular on the metal surface of a wall part of a domestic dishwasher. Furthermore, citric acid or nitric acid can also be used as a passivation agent. In all cases it comes to the above described connection between acid anions and metal cations and for the formation of the respective metal salt, ie phosphate, chromate, citrate or salt of salt. There are mainly two positive effects in this process.

On the one hand, the acid anion of phosphoric acid, chromic acid, citric acid or nitric acid is excited by the plasma jet itself and is put into a reactive state, without inducing too high an elevated temperature of the acid portion of the plasma jet. On the other hand, the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher, itself activated by the plasma jet, whereby the reactivity of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a household dishwasher, is increased and the required metal cations are more easily generated during the chemical reaction with the acid anions. Thus, in the impact area of the plasma jet on the metal surface, preferably on the metal surface of a wall part of a household appliance, in particular on the metal surface of a wall part of a domestic dishwasher, the desired reaction and deposition of the metal salt occurs.

The reactivity of the acid anions can be adjusted in particular by a corresponding change in the parameters of the plasma generation. By a suitable choice of parameters, the treatment time can be reduced by the plasma jet. The treatment times thus achieved are well below the treatment times required in wet-chemical processes.

The acidic passivating agent supplied to the plasma jet, that is to say the aqueous acid solution, may or may not contain metal ions. A chromating can be carried out, for example, with sulfuric acid and sodium chromate. The resulting chromic acid then reacts with the surface. When using phosphoric acid as a passivating agent, however, this contains no metal ions. The reaction of the acid with the surface then leads to, for example, a metal chromate a metal phosphate.

The precise chemical and physical processes involved in the exposure of the plasma jet to a passivating agent have not yet been determined in detail. In any case, it has surprisingly been found that the acted upon by the method described above metal surfaces, preferably metal surfaces of a wall part of a household appliance, in particular metal surfaces of a wall part of a domestic dishwasher, have undergone a sufficient passivation for industrial production.

The approach described below is therefore preliminary. In the method according to the invention, the acid is excited before being applied in the plasma and thereby reacts much faster with the surface. The already described simultaneous cleaning and activation of the surface also has a positive effect on the reaction rate.

The classical wet-chemical chromating usually consists of two essential steps. First, the oxide layer (aluminum hydroxide) is completely removed with sodium hydroxide solution. After spooling with water, it is then immediately chromated. With the method according to the invention using the plasma, the removal of the oxide layer can be omitted. The further passivation of the material therefore takes place directly on the oxide layer.

As has already been stated above, the phosphating can be carried out in particular on steel and stainless steel as well as on galvanized or cadmium steels and aluminum. In contrast, the chromating can be applied in particular to aluminum, magnesium, silver, cadmium and zinc.

Another advantage of the method described above is that the application of the passivation, for example by means of phosphating, can be selectively applied to certain surface areas. One example is welding seams between joined stainless steel sheets, which are commonly used for drums and interior linings of washing machines or dishwashers. Since the stainless steel sheets are already sufficient against corrosion are protected, but the welds are no longer sufficiently resistant to corrosion due to the structural changes within the metal, there is only a need for a subsequent passivation in the area of the welds. Thus, in a preferred manner, the method described above is carried out such that at least the weld between two metal surfaces, preferably between two metal surfaces of a wall part of a domestic appliance, in particular between two metal surfaces of a wall part of a domestic dishwasher, is acted upon by the plasma jet.

Preferably, the metal surface, preferably the metal surface of a wall part of a domestic appliance, in particular the metal surface of a wall part of a domestic dishwasher, during the welding or immediately after welding with the plasma jet can be acted upon. In this case, the thermal energy still stored in the weld seam and the adjoining metal can be utilized for increased reactivity of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher, and thus for an increased effectiveness of the passivation. Furthermore, an application of the method described in a weld in the cooled state is possible.

In addition to the spatially limited application of the plasma jet, for example, on a weld, the method described can also be carried out so that the application of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a domestic dishwasher, with the passivation agent for producing a primer for a subsequent paint application or painting is performed. In this case, a surface, in particular full surface treatment of the metal surface, preferably the metal surface of a wall part of a household appliance, in particular the metal surface of a wall part of a household dishwasher, performed. The subsequent coating with a paint or a paint then leads to a good adhesion and durable coating. For such an application, in particular the rotating plasma nozzles described above are suitable.

The passivating agent can be supplied to the plasma jet in various ways. Since the generation of the plasma jet from a flow of working gas passes through different regions of space starting from the discharge region, through the nozzle region and the free jet outside the plasma source, the passivation agent in each of these spatial regions can be supplied to the plasma jet.

Thus, in a preferred manner, the passivation agent in the discharge region can be supplied to the resulting plasma jet. In this case, the working gas is excited together with the passivating agent by means of the electric discharge. The effect of the discharge on the passivation agent is thus very strong and it depends on the type of passivating agent, whether it is suitable for the direct action of the discharge.

Furthermore, the passivation agent can be fed downstream of the discharge area to the resulting plasma jet. On the one hand, the passivating agent can still be introduced from within the plasma source into the flow of the plasma jet before the plasma jet leaves the plasma jet. On the other hand, the passivation agent can also be supplied to the plasma jet outside the plasma source. In the latter case, the passivating agent does not or only barely comes into contact with the plasma source itself, so that the influence of the acid portion on the parts of the plasma source can be minimized.

For a better distribution of the passivating agent, this can be introduced in an advantageous manner by means of an atomizer, in particular a spray nozzle. Thus, even when adding the passivating agent to the working gas or to the plasma jet, a fine and uniform distribution is achieved, which has a positive effect up to the impact of the plasma jet on the metal surface, preferably the metal surface of a wall part of a domestic appliance, in particular the metal surface of a wall part of a domestic dishwasher. The passivating agent can also be added to the plasma jet in a different way.

The aforementioned technical problem is inventively solved in a household appliance, in particular in a domestic dishwasher, in a household washing machine, a household dryer or the like, at least comprising a wall part, which consists at least partially of largely corrosion-resistant metal, in particular largely stainless steel, in that at least a metal surface of a Wandungssteils at least partially, preferably predominantly, in particular completely, is provided with a passivating salt, wherein the passivating salt is a product of a reaction of a plasma jet applied to the metal surface of the Wandungsteils and acidic passivating agent with the metal surface of the Wandungsteils.

This also results in the aforementioned advantages of the invention. In particular, it has thus been recognized that the application of the passivating agent by means of an atmospheric plasma jet exploits many synergy effects.

With regard to favorable manufacturing and / or structural properties, it may be advantageous if at least two of the wall parts at least partially, preferably predominantly, in particular completely, by means of a welded joint, in particular a weld are connected to each other and if the welded joint, in particular the weld, the at least two of the wall parts at least partially, preferably predominantly, in particular completely, connects to each other, at least partially, preferably predominantly, in particular completely, is provided with a passivating salt. The surface of the welded joint, in particular the weld, is thus simplified and effectively passivated. The already described turbulence of the plasma jet leads to an almost complete wetting of the surface even in depressions and undercuts, even if they have small dimensions. The turbulence of the plasma jet and the passivating agent transported therein also leads to the fact that not remaining on the surface of the weld, in particular the weld passivating agent is immediately removed and no rework or cleaning of the weld, in particular the weld is necessary.

Thus, the passivation of the weld, in particular the weld can be made effective and effective, it is at least partially, preferably predominantly, in particular completely, at least partially, at least partially, preferably predominantly, in particular completely, preferably also in a mutual Area with a respective area width of at least 3 mm, preferably of at least 5 mm, in particular of at least 10 mm, provided with a passivating salt.

Furthermore, the at least one wall part, which consists at least partially of largely corrosion-resistant metal, in particular substantially stainless steel, preferably a part of a domestic dishwasher, comprising at least the following components and / or assemblies: a washing container for receiving items to be washed, means for acting on the items to be washed Rinsing fluid, an at least partially made of largely corrosion-resistant metal, in particular substantially stainless steel existing container hood as the upper part of the washing container with two side walls, a top wall and a rear wall, a rinse tub as the bottom wall of the washing, a closable with a door filling opening for items to be washed on the washing, and a frame member having a rinsing liquid sealing function at the front end of the container hood. Due to the passivation according to the invention, the previous manufacturing process of a domestic dishwasher, in particular the at least one welding process on a domestic dishwasher can be significantly improved, both in technological and in financial terms, for example due to a reduction in investment and / or operating costs and a reduction in production times.

On the one hand, the passivating agent may in turn contain an optionally diluted phosphoric acid, so that the salt deposited and passivating on a metal surface comprises metal phosphate. On the other hand, the passivating agent may include an optionally diluted chromic acid such that the metal salt deposited and passivating salt comprises metal chromate. In both cases, there is the above-described connection between acid anions and metal cations and the formation of the respective metal salt as phosphate or as chromate.

The invention will be explained in more detail below with reference to embodiments, reference being made to the accompanying drawings.

Fig. 1

ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Passivierung einer Oberfläche, bei der ein Passivierungsmittel in einem Bereich der Düsenöffnung in den Plasmastrahl eingebracht wird;

Fig. 2

ein zweites Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Passivierung einer Oberfläche, bei der ein Passivierungsmittel in einem Bereich des Entladungsvolumens in den Plasmastrahl eingebracht wird;

Fig. 3

ein drittes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Passivierung einer Oberfläche, bei der ein Passivierungsmittel in einem Bereich vor der Düsenöffnung in den Plasmastrahl eingebracht wird;

Fig. 4

eine schematische Perspektivdarstellung eines Spülbehälters einer frontseitig bestückbaren und erfindungsgemäßen Haushaltsgeschirrspülmaschine bei abgenommener Rückwand; und

Fig. 5

eine schematische Darstellung einer passivierten Schweißverbindung, deren Oberfläche mittels einer in Fig. 1 dargestellten und erfindungsgemäßen Vorrichtung zur Passivierung einer Oberfläche behandelt wurde.

In the drawing show

Fig. 1

a first embodiment of a device according to the invention for passivation of a surface, in which a Passivierungsmittel is introduced in a region of the nozzle opening in the plasma jet;

Fig. 2

A second embodiment of a device according to the invention for passivation of a surface, in which a Passivierungsmittel is introduced in a region of the discharge volume in the plasma jet;

Fig. 3

A third embodiment of a device according to the invention for passivation of a surface, in which a Passivierungsmittel is introduced in a region in front of the nozzle opening in the plasma jet;

Fig. 4

a schematic perspective view of a washing container of a front-mounted and inventive household dishwasher with removed rear wall; and

Fig. 5

a schematic representation of a passivated welded joint, the surface by means of a in Fig. 1 has been treated and device according to the invention for the passivation of a surface treated.

In the following, the implementation of the method according to the invention will be explained with reference to three exemplary embodiments, which differ in terms of the area in which the acidic passivation agent is supplied to the plasma nozzle. Therefore, like reference numerals designate like elements in the various embodiments.

The Fig. 1 shows a plasma source 2 and a supply device 3. The plasma source 2 has a nozzle tube 4 made of metal, which tapers conically to a nozzle opening 6. At the nozzle opening 6 opposite end, the nozzle tube 4, a swirl device 8 with an inlet 10 for a working gas, for example, for air or nitrogen gas. An intermediate wall 12 of the twisting device 8 has a ring of inclined in the circumferential direction employed holes 14, through which the working gas is twisted. The downstream conical tapered part of the nozzle tube 4 therefore becomes flows through the working gas in the form of a vortex 16, whose core extends on the longitudinal axis of the nozzle tube 4.

At the bottom of the intermediate wall 12, an electrode 18 is arranged centrally, which protrudes coaxially in the direction of the tapered portion in the nozzle tube 4. The electrode 18 is electrically connected to the intermediate wall 12 and the remaining parts of the twisting device 8. The swirl device 8 is electrically insulated by a ceramic tube 20. To the electrode 18, a high-frequency high voltage is generated, which is generated by a transformer 22. The inlet 10 is connected via a hose, not shown, with a variable flow rate pressurized working gas source. The nozzle tube 4 is grounded. The applied voltage generates a high frequency discharge in the form of an arc 24 between the electrode 18 and the nozzle tube 4. The term "arc" is used here as a phenomenological description of the discharge, since the discharge occurs in the form of an arc. The term "arc" is also used as a discharge form for DC discharges with substantially constant voltage values.

Due to the swirling flow of the working gas of this arc 24 is channeled in a vortex core on the axis of the nozzle tube 4, so that it branches only in the region of the nozzle opening 6 to the wall of the nozzle tube 4. The working gas, which rotates in the region of the vortex core and thus in the immediate vicinity of the arc 24 with high flow velocity, comes into intimate contact with the arc 24 and is thereby partly transferred to the plasma state, so that an atmospheric plasma jet 26 through the nozzle opening 6 from the plasma source 2 exits.

The feeding device 3 has a mixing tube 28, the wall of which has an opening 30 at one point, into which an atomizer 32 is inserted with a precise fit. Connected to the atomizer 32 is a feed 34 for supplying the passivating agent 120, through which the passivating agent 120 passes into the atomizer 32 where it is atomized to a fine mist.

The passivating agent 120 leaving the atomizer 32 passes directly into the plasma jet 26 and is conveyed therewith in the direction of a metal surface A, preferably a metal surface A of a wall part of a domestic appliance 100, in particular a metal surface A of a wall part of a household dishwasher 100 (see also FIG 4 and FIG. 5 ), carried away. On the metal surface A, the passivation agent 120 then impinges in the manner described above, so that a passivation layer B is formed. If, for example, phosphoric acid is used as the passivation agent 120, then a metal phosphate layer is formed in the passivation layer B.

The thickness of the passivation layer B may vary and depends on the operating parameters. Among other things, the thickness of the passivation layer B depends on the amount of the passivation agent 120 introduced into the plasma jet 26. In the case of dilute phosphoric acid, a value of about 50 g / h as the application rate has been found to be favorable.

The Fig. 2 shows a second embodiment of a device for passivation of a surface. The device has a previously based on Fig. 1 In this case, therefore, the passivation agent 120 is introduced into the region of the plasma source 2, in which the arc discharge is ignited and operated. Again, the wall of the nozzle tube 4 at one point an opening 30.1, in the exact fit of the atomizer 32.1 is inserted. Connected to the atomizer 32.1 is a feed 34.1 for supplying the passivating agent 120, through which the passivating agent 120 passes into the atomizer 32.1 and is atomized there to form a fine mist.

The passivating agent 120 leaving the atomizer 32 passes directly into the plasma jet 26 and is conveyed therewith in the direction of a metal surface A, preferably a metal surface A of a wall part of a domestic appliance 100, in particular a metal surface A of a wall part of a household dishwasher 100 (see also FIG 4 and 5 ), carried away.

The Fig. 3 shows a third embodiment of an apparatus for plasma passivation of a metal surface A. The device has a previously with reference to Fig. 1 and 2 described plasma source 2 for generating a plasma jet 26 and a downstream of the nozzle opening 6 arranged atomizer 32.2 to the atomizer 32.2 a supply 34.2 is connected, passes through the passivation agent 120 in the atomizer 32.2 and is atomized there. The passivation agent 120 emerging from the atomizer 32.2 passes into the plasma jet 26 which is generated in the plasma source 2 and leaves the nozzle opening 6 and is connected to the plasma jet 26
in the direction of a metal surface A, preferably a metal surface A of a wall part of a household appliance 100, in particular a metal surface A of a wall part of a domestic dishwasher 100 (see also 4 and 5 ), further transported.

In the described Fig. 1 to 3 the plasma source 2 is respectively moved from right to left over the metal surface A, so that a Passivierungsspur on the metal surface A is formed in the width of the treatment width of the plasma jet 26. The passivation track can be used to passivate a welded connection 122, in particular a welded seam (see Fig. 5 ). The passivation track can also be used for a surface passivation of a metal surface A, if the plasma source 2 is optionally moved systematically over the entire metal surface A to be passivated.

The Fig. 4 1 shows a schematic perspective view of a washing container 102 of a domestic dishwasher 100 which can be equipped at the front and according to the invention. The household appliance shown is merely one example of a domestic appliance 100, which could also be a domestic washing machine, a household dryer, a household washer dryer, a microwave oven, a sterilizer or the like.

The domestic dishwasher 100 shown comprises the washing compartment 102 for receiving items to be washed and a person skilled in the art, however, not shown for clarity means for acting on the items to be washed with rinsing liquid, such as spray arms and spray nozzles. Furthermore, it comprises at least one Part of largely corrosion-resistant metal, in particular largely stainless steel existing container hood 104 as the upper part of the washing container 102 with two side walls 106.L, 106.R, a top wall 108 and a removed rear wall 110. Furthermore, includes a flushing trough 112 as the bottom wall 114 of Rinsing container 102, a well-known, but not shown for clarity with a door filling opening for items to be washed on the washing container 102 and a specialist known, but not shown for clarity frame part with sealing function for rinsing liquid at the front end of the container hood 104th

The two side walls 106.L, 106.R, the top wall 108 and the rear wall 110 form as respective wall portion 116, the upper part of the washing container 102 and consist, as already mentioned, at least partially made of largely corrosion-resistant metal, in particular largely stainless steel.

There is now a metal surface 116.0 of a Wandungssteils 116 at least partially, preferably predominantly, in particular completely, provided with a passivating salt 118, wherein the passivating salt 118 is a product of a reaction by means of a plasma jet 26 (see Fig. 1 to 3 ) applied to the metal surface 116.0 and acidic passivant 120 (see Fig. 1 to 3 ) with the metal surface is 116.0. The passivating salt 118 then forms a passivation layer B (see Fig. 1 to 3 ) out.

Moreover, the two side walls 106.L, 106.R of the upper part of the washing compartment 102 are each provided with a welded connection 122, in particular a welded seam. The respective welded connection 122 extends horizontally along the corresponding side wall 106, L, 106, R, which may optionally connect them / at least partially, preferably predominantly, in particular completely, to each other, and which at least partially, preferably predominantly, in particular completely, with a passivating salt 118 may be provided. The indicated welds 122 are merely exemplary in nature; they can basically be provided at any point of the washing container 102, in particular the container hood 104.

And the Fig. 5 shows a schematic representation of a passivated welded joint 122, in particular a passivated weld whose surface is 122.0 by means of a in Fig. 1 was treated and device according to the invention for the passivation of a metal surface A was treated (see Fig. 1 to 3 ).

So there are two of the wall parts 116.1, 116.2, in particular the said wall parts of a domestic dishwasher 100 at least partially, preferably predominantly, in particular completely, connected to each other by means of a welded joint 122. The welded connection 122, which connects the two wall parts 116.1, 116.2 at least regionally, preferably predominantly, in particular completely, is then provided with a passivating salt 118 at least regionally, preferably predominantly, in particular completely. The passivating salt 118 then forms a passivation layer B.

The welded connection 122 which connects the two wall parts 116.1, 116.2 at least regionally, preferably predominantly, in particular completely, is at least partially, preferably predominantly, in particular completely, also in a mutual area 122.1, 122.2 with a respective area width 122.B1, 122.B2 of at least 3 mm, preferably of at least 5 mm, in particular of at least 10 mm, provided with a passivating salt 118. The mutual area 122.1, 122.2 preferably extends in mirror image to the welded connection 122, in particular to its center line 122.M.

The plasma source 2 is moved in the depth direction T (arrow) over the metal surface A, so that a Passivierungsspur on the metal surface A is formed in the depth of the plasma jet 26.

The passivation agent 120 used in the figures includes an optionally diluted phosphoric acid, and the metal-deposited and passivating salt includes metal phosphate. Alternatively, the passivating agent 120 may include an optionally diluted chromic acid, citric acid or nitric acid, and the metal surface deposited and passivating salt may include metal chromate, metal citrate or metal salt of salt.

The above-described and / or reproduced in dependent claims embodiments and refinements of the invention may, except in cases of clear dependencies or incompatibilities, individually or in any combination with each other are used.

In summary, it should be noted that by the invention, a known from the prior art method for passivating a metal surface, preferably a metal surface of a wall part of a household appliance, in particular a metal surface of a wall part of a domestic dishwasher, so further developed that it has a simplified and more effective design. <B><u> REFERENCE LIST </ u></b> 2 plasma source 3 feeder 3.1 feeder 4 nozzle tube 6 nozzle opening 8th swirl device 10 inlet 12 partition 14 drilling 16 whirl 18 electrode 20 ceramic tube 22 transformer 24 Electric arc 26 plasma jet 28 mixing tube 30 opening 30.1 opening 32 atomizer 32.1 atomizer 32.2 atomizer 34 supply 34.1 supply 34.2 supply 100 Household appliance; Domestic dishwasher 102 rinse tank 104 container hood 106.L Side wall 106.R Side wall 108 top wall 110 rear wall 112 wash tub 114 bottom wall 116 wall part 116.1 wall part 116.2 wall part 116.0 metal surface 118 Passivating salt 120 passivating 122 welded joint 122.1 Area 122.B1 area width 122.2 Area 122.B2 area width 122.M center line 122.0 surface A metal surface B passivation T Depth direction (arrow)

Claims (15)

Method for passivating a metal surface (A), preferably a metal surface (A) of a wall part of a household appliance, in particular a metal surface (A) of a wall part of a domestic dishwasher, in which an atmospheric plasma jet (26) is generated by electrical discharge in a working gas, in which an acidic passivating agent (120) is introduced into the plasma jet (26), in which the plasma jet (26) containing the passivating agent (120) touches the metal surface (A), preferably the metal surface (A) of the wall part (116; 116.1, 116.2 ) of the domestic appliance (100), in particular on the metal surface (A) of the wall part (116; 116.1, 116.2) of the household dishwasher (100), and in which the reaction of the acidic passivating agent (120) with the metal surface (A), preferably with the metal surface (A) of the wall part (116; 116.1, 116.2) of the household g device (100), in particular with the metal surface (A) of the wall part (116; 116.1, 116.2) of the household dishwasher (100), a passivating salt (118) on the metal surface (A), preferably on the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular on the metal surface ( A) of the wall portion (116; 116.1, 116.2) of the household dishwasher (100) is deposited. Process according to Claim 1, in which an optionally diluted phosphoric acid is used as passivating agent (120) and metal phosphate on the metal surface (A), preferably on the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular on the metal surface (A) of the wall part (116; 116.1, 116.2) of the household dishwasher (100). Process according to Claim 1, in which an optionally diluted chromic acid is used as passivating agent (120) and metal chromate on the metal surface (A), preferably on the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular on the metal surface (A) of the wall part (116; 116.1, 116.2) of the household dishwasher (100) is deposited. Method according to one of Claims 1 to 3, in which the metal surface (A), preferably the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular the metal surface (A) of the wall part (116; 116.1 , 116.2) of the household dishwasher (100), a welded connection (122), in particular a weld seam, and at least the weld joint (122), in particular the weld seam, is acted upon by the plasma jet (26). Method according to Claim 4, in which the metal surface (A), preferably the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular the metal surface (A) of the wall part (116; 116.1, 116.2) of Household dishwasher (100), during welding or immediately after welding with the plasma jet (26) is applied. Method according to one of claims 1 to 3, wherein the application of the metal surface (A), preferably the metal surface (A) of the wall part (116; 116.1, 116.2) of the domestic appliance (100), in particular the metal surface (A) of the wall part (116 116.1, 116.2) of the household dishwasher (100), with the passivation means (120) for producing a primer for a subsequent paint application or painting is performed. Method according to one of claims 1 to 6, wherein the Passivierungsmittel (120) is supplied in the discharge region of the resulting plasma jet (26). Method according to one of claims 1 to 6, wherein the passivation means (12) downstream of the discharge region to the resulting plasma jet (26) is supplied. A method according to claim 7 or 8, wherein the passivation means (120) is introduced by means of an atomizer (32; 32.1; 32.2), in particular a spray nozzle. Household appliance (100), in particular household dishwasher, household washing machine, household dryer or the like, comprising at least one wall part (116; 116.1, 116.2) which consists at least partly of largely corrosion-resistant metal, in particular largely stainless steel,
characterized,
in that at least one metal surface (A) of a wall part (116; 116.1, 116.2) is provided with a passivating salt (118) at least regionally, preferably predominantly, in particular completely, wherein the passivating salt (118) is a product of a reaction of a plasma jet (26) on the metal surface (A) of the Wandungssteils (116; 116.1, 116.2) applied and acidic Passivierungsmittels (120) with the metal surface (A) of the Wandungssteils (116; 116.1, 116.2). Household appliance (100) according to claim 10,
characterized,
in that at least two of the wall parts (116.1, 116.2) are connected to each other at least regionally, preferably predominantly, in particular completely, by means of a welded connection (122), in particular a welded seam, and that the welded connection (122), in particular the weld seam, the at least two of the wall parts (116). 116.1, 116.2) at least partially, preferably predominantly, in particular completely, connects to each other, at least in regions, preferably predominantly, in particular completely, with a passivating salt (118) is provided. Household appliance (100) according to claim 11,
characterized,
that the welded connection (122), in particular the weld seam, connects at least two of the wall parts (116.1, 116.2) at least regionally, preferably predominantly, in particular completely, at least regionally, preferably predominantly, in particular completely, also in a mutual region (122.1, 122.2) having a respective area width (122.B1, 122.B2) of at least 3 mm, preferably of at least 5 mm, in particular of at least 10 mm, with a passivating salt (118) is provided. Household appliance (100) according to claim 10, 11 or 12,
characterized,
in that the at least one wall part (116; 116.1, 116.2), which consists at least partially of largely corrosion-resistant metal, in particular largely stainless steel, is part of a household dishwasher (100) which comprises at least the following components and / or assemblies: a rinsing container (102 ) for receiving items to be washed; Means for loading the items to be washed with rinsing liquid; an at least partially made of largely corrosion-resistant metal, in particular largely stainless steel existing container hood (104) as the upper part of the washing container (102) with two side walls (106.L, 106.R), a top wall (108) and a rear wall (110);
a rinse pan (112) as a bottom wall (114) of the rinse tank (102); a closable with a door filling opening for items to be washed on the washing compartment (102); and a frame member having a rinsing liquid sealing function at the front end of the container hood (104). Household appliance (100) according to one of claims 10 to 13,
characterized,
in that the passivating agent (120) comprises an optionally diluted phosphoric acid and that the salt deposited and passivating on a metal surface (A) comprises metal phosphate. Household appliance (100) according to one of claims 10 to 13,
characterized,
in that the passivating agent (120) contains an optionally diluted chromic acid and that the metal salt (A) deposited and passivating salt comprises metal chromate.

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