EP0543322A1 - Method for cleaning of metal parts - Google Patents

Abstract

A method and an apparatus for treating workpieces with a fluid, in particular for cleaning metallic workpieces prior to a subsequent heat treatment are disclosed. The workpieces are positioned in an air-tight washing vessel. The vessel is filled with an immersion bath substantially covering the workpieces and having a temperature of between 50 DEG C. and 90 DEG C. After closing the washing vessel it is evacuated down to a vacuum having a pressure being below the saturation vapor pressure of the fluid at the prevailing temperature. Thus, the fluid starts to boil although its temperature is substantially below the boiling temperature of the fluid at atmospheric pressure. After a certain period of time of maintaining the vacuum and the boiling, the vacuum is relieved and the bath is discharged.

Description

The invention relates to a method for treating workpieces with a liquid, in particular for cleaning metallic workpieces for a heat treatment following cleaning, and a device for carrying out the method.

A method and a device of the type mentioned above are known from DE-Z "HTM", 45 (1990), No. 5, page 273.

Methods and devices for treating workpieces with a liquid, hereinafter referred to as "washing", in particular for cleaning and / or rinsing metallic workpieces, are typically used in linked heat treatment systems. This includes, for example, vacuum heat treatment, piercing, roller hearth, Vertical retort or multi-purpose chamber furnace systems in which bright heat treatments, various annealing processes and hardening processes as well as diffusion processes such as nitriding, nitro carburizing, carbonitriding and carburizing can be carried out.

In the case of conventional devices and methods of the type mentioned at the outset, baths were used which were essentially selected solely from the point of view of their effectiveness, whereas in earlier times there were fewer questions about the use of raw materials and, in particular, of environmental compatibility. For this reason, chlorinated hydrocarbons (CHC), e.g. tetrachlorethylene (Per) or trichlorethylene (Tri), were used in the past to clean metallic workpieces.These were ideal cleaning agents, especially for removing greases and pigment dirt, the environmental impact of which but were only known and taken into account at a later date.

Regarding environmental protection, regulations have come into force in numerous countries with the aim of drastically reducing or completely reducing the use of chlorinated hydrocarbons (CHC), especially tetrachlorethylene and trichlorethylene, and the use of halogenated hydrocarbons (CHC) to disallow.

Trichloroethene (tri) is now suspected of causing cancer, so that this cleaning agent has practically been withdrawn from circulation in Europe.

In various countries around the world, there is now very strict environmental protection legislation. In the The Federal Republic of Germany, for example, was stipulated by the 2nd Federal Emission Protection Ordinance that chlorofluorocarbons (CFCs), which were previously used as coolants and 1.1.1-trichloroethane, which had previously been used as cleaning agents, may no longer be used after a short grace period.

The "Clean Air Act" was supplemented in the United States on October 27, 1990, and the amendments came into force when President Bush signed it on November 15, 1990. These legislative changes represent an enormous tightening of federal legislation in the United States from 1977. Section III of the amendments, for example, specifies certain branches of industry that are to be covered with different priorities. Degreasing and metal cleaning is given priority number 1. In this context, chlorinated hydrocarbons (CHC) are expressly mentioned, especially trichlorethylene. The amendments to the law provide for a drastic reduction in the production and sale of such substances, for example from the basic production quantity (100%) in 1989 to 15% in 1997. For violations, the amendments provide for severe penalties.

On the other hand, in the heat treatment of metallic workpieces, it is necessary to clean the workpieces properly before the heat treatment or other surface treatment, in particular if they had previously been subjected to another type of processing, for example forming or machining.

The types of contamination that occur on metallic workpieces are varied. So these impurities consist, for example, of cooling lubricants, greases, lapping pastes and pigments or of hardening oils, dusts and metal chips. If such workpieces are to be subjected to a subsequent surface treatment, it is essential to remove dirt from the workpiece surface. Soiled surfaces have a significant influence on the treatment result, for example when nitriding, nitro-carburizing or carburizing. In the aforementioned hardening processes (diffusion processes), substances such as nitrogen and / or carbon penetrate from the outside of the workpiece into the outer layers of the metallic workpiece via diffusion processes. If the surface is now contaminated at certain points, the diffusion processes directed from the outside, for example during gas nitrocarburizing, cannot take place or can take place only in a slowed or delayed manner. As a result, workpiece surfaces are obtained which are not or only partially hardened in the area of the contaminants.

However, a clean surface is also essential for vacuum heat treatments, bright annealing processes, coatings or the like.

Against the background of the problems mentioned above, considerable efforts have already been made for some time to create cleaning solutions on an environmentally compatible basis, for example water-based, which are harmless for people who come into contact with these solutions, but which on the other hand have good cleaning results provide.

Such water-soluble cleaning agents, for example highly wash-active, mostly surfactant-containing substances, however, have a reduced solubility for fats compared to chlorinated hydrocarbons (CHC), so that the cleaning process supported by a relative movement and very highly concentrated solutions of these agents must be used and the cleaning process must be supported by a relative movement between the workpiece to be cleaned and the cleaning liquid.

In known devices for cleaning metallic workpieces, the relative movement between the workpiece and the cleaning liquid is achieved in that the workpieces are sprayed by means of pivotable arms, specifically with a high exit velocity of the treatment liquid. In this way, the workpieces are sprayed with the treatment liquid and the cleaning effect is a combination of a mechanical detachment of the dirt particles and a chemical effect. The emulsification of the fats and oils, caused by high discharge speeds, has a disadvantageous effect on the bath condition .

It has been found that in the case of workpieces of complex shape, for example crankshafts or pressure housings with bearing points, it is necessary to provide complex mechanical devices, such as articulated pivotable spray arms, in order to be able to clean the entire surface. Furthermore, with the known methods it is difficult to clean bulk goods or stacked batches, since even with spray arms which can be pivoted several times, it is very difficult to reach the workpieces located in the interior or core of a stacked batch on all sides. This is due to the fact that the other workpieces, which are arranged spatially around a workpiece, shield this central workpiece, so that even a cleaning liquid sprayed or sprayed onto the batch with high pressure cannot penetrate to all surfaces.

Devices have also become known in which the entire batch or the entire bulk material is immersed in a bath and the relative movement between workpieces and liquid is caused by pumps, propellers, circulation systems, by nozzle devices or by raising or lowering the entire batch.

Despite these considerable technical expenditures, it was found that there is no through-flow in the batch, but that there is possibly only a small amount of liquid or column moving back and forth in the batch, and that the moving fluid essentially flows around the outer contour of the batch.

It was also found that when using aqueous cleaning solutions with highly wash-active substances that have a large number of ionic components, even after numerous rinsing processes, a kind of lubricating film remains on the surface of the workpieces, which is due to strong ionic interactions between the wash-active substances and the metallic surface is. This lubricating film considerably impairs diffusion in later gas nitriding processes, for example. Ultimately, this can lead to substances in the cleaning agent which have previously removed the existing impurities now themselves affecting the surface.

Another problem that arises when cleaning metallic workpieces is the drying of the workpieces after cleaning and possibly rinsing.

In conventional systems, the metal workpieces were removed from the bath or the spraying device and then by means of heated circulating air by evaporation with the help the natural heat of the parts or dried by blowing off or by means of a convection heater.

However, this procedure had the disadvantage that the workpieces were exposed to the atmosphere for a certain time. Complete drying, especially for tightly packed batches, for scooping workpieces, e.g. workpieces provided with blind holes, concave spots and the like are not guaranteed.

This can lead to surface changes even after a very short period of time, because freshly washed and rinsed metallic workpieces are highly active on their surface, so that corrosion stains can be determined within a very short time. If cleaning or rinsing liquids are also used which still contain dissolved salts, the salts can form as salt stains on the workpiece surface during drying. This also leads to considerable problems in the subsequent diffusion heat treatments.

After all, conventional heating systems in the form of circulating air heating systems are very energy-intensive because their efficiency is very poor.

Finally, another problem with the conventional cleaning of metallic workpieces is that the cleaning agents used can only be used in a certain temperature range. If, for example, a cleaning bath has an excessively high temperature (close to 100 ° C), the cleaning agents are chemically changed and their cleaning effect deteriorates considerably. On the other hand, if the cleaning bath is not warm enough (below the cloud point or just above it), the cleaning effect also diminishes because the washing activities are no longer adequately thermally supported. The higher viscosity of the greasing complicates the chemical washing process.

From the aforementioned DE-Z "HTM", 45 (1990), No. 5, page 273, a method and a device for cleaning metallic workpieces have become known, with which the disadvantages described above are already partially avoided. In the known device, a washing tank is used, in which the workpieces remain during cleaning, optionally rinsing and drying. When cleaning and rinsing the workpieces, they are kept in an immersion bath, which is agitated by injecting air into the tank bottom and by pumping around. Vacuum drying is used to dry the workpieces.

Although this procedure has the advantage that sufficient agitation of the treatment bath is achieved by injecting air, because the rising air bubbles take dirt particles with them through adhesive forces, even if they are heavier than the treatment liquid. In addition, the fact that the workpieces remain in one and the same tank means that the workpieces come into contact with the ambient atmosphere only to a very small extent. Finally, vacuum drying means that drying is possible in an energy-saving manner.

But this known device with the known method used has the disadvantage that in the important first phase of the cleaning process, namely when the tank is flooded, there is no sufficient cleaning effect, in particular with regard to coarse dirt, that contact of the wet workpieces occurs during the subsequent process steps with the Outside atmosphere still lasts for a certain time and that finally the workpieces in certain areas (blind holes, cavities, scooping surfaces) are not sufficiently washed around by agitated bath.

A method for cleaning office machines and similar mechanical devices is known from DD-PS 91 177. Afterwards, the office machines mentioned are to be cleaned in a bath in which bubble columns rise, which are formed by a pulsating gas flow.

From FR-PS 1 410 251 a cleaning device for hospital equipment is known in which cleaning fluid is moved by spraying and the like by means of compressed air.

From US-PS 2 567 820 a cleaning device for small machine parts is known, in which the machine parts are introduced into a basket-like vessel, the bottom of which is formed by a grid. Below the grille is a tube ring, the top of which is provided with outlet openings for air bubbles.

From DE-GM 84 37 870 a device for washing metallic workpieces is known, in which the washing liquid is sprayed onto the workpieces by means of nozzles, at a speed between 18 and 55 m / s.

From DE-OS 37 15 332 a method and a device for cleaning workpieces are known, in which the workpieces are also placed in an immersion bath into which air or another gas is blown. The dirt particles carried along by the gas bubbles are separated by means of an overflow at the upper edge of the bath.

The invention is therefore based on the object of developing a method and a device of the type mentioned in such a way that the above disadvantages are avoided and that the cleaning effect of metallic workpieces is improved overall.

• a) Einfahren der Werkstücke in einen Waschtank mit einem Fassungsvermögen zwischen 1 m³ und 10 m³;
• b) Einlassen eines die Werkstücke im wesentlichen umgebenden Tauchbades einer Behandlungs-Flüssigkeit mit einer Temperatur zwischen 50°C und 90°C;
• c) druckdichtes Verschließen des Waschtanks derart, daß oberhalb des Tauchbades ein Luftraum verbleibt;
• d) Evakuieren eines im Luftraum vorhandenen Luft/Dampfgemisches bis zu einem Unterdruck, der unterhalb des Sättigungsdampfdrucks der Behandlungs-Flüssigkeit des Tauchbades bei der Temperatur liegt;
• e) Aufrechterhalten des Unterdrucks bei siedendem Tauchbad für eine vorbestimmte Zeit;
• f) Entspannen des Luftraumes auf Umgebungsdruck; und
• g) Ablassen des Tauchbades.

According to the method mentioned at the outset, the object on which the invention is based is achieved by the following method steps:

• a) moving the workpieces into a wash tank with a capacity between 1 m³ and 10 m³;
• b) admission of an immersion bath of a treatment liquid with a temperature between 50 ° C. and 90 ° C. which essentially surrounds the workpieces;
• c) pressure-tight closing of the wash tank in such a way that an air space remains above the immersion bath;
• d) evacuating an air / steam mixture present in the air space to a vacuum which is below the saturation vapor pressure of the treatment liquid of the immersion bath at the temperature;
• e) maintaining the vacuum at the boiling immersion bath for a predetermined time;
• f) relaxing the air space to ambient pressure; and
• g) lowering the immersion bath.

The object underlying the invention is completely achieved in this way.

The procedure according to the invention namely causes "underpressure boiling", ie boiling of the immersion bath already at a temperature which is significantly below the temperature at which the immersion bath would boil under ambient pressure.

It is therefore possible in this way to generate steam bubbles in the immersion bath at a temperature which is clearly below, for example, 100 ° C., which rise in the immersion bath and bead up the workpieces. However, the vapor bubbles are not only generated at the bottom of the wash tank, as in known methods, they are also generated at every location of the immersion bath, i.e. also inside blind holes, scooping surfaces and the like, which remain unreached in conventional immersion baths with injected air bubbles.

In this way, these normally inaccessible areas of workpieces can also be agitated by the formation of bubbles. In these areas there is also the known advantage that the rising bubbles take dirt particles with them through the adhesive effect and therefore remove them from the normally inaccessible areas.

A further significant advantage of the method according to the invention is that it is possible to work with temperatures of the immersion bath which are clearly below the boiling temperature at ambient pressure, for example 100 ° C. It is therefore also possible to use treatment liquids whose chemical treatment additives only develop their optimum effect at temperatures significantly below 100 ° C and therefore could not be used in boiling treatment baths in the conventional procedure, because the additives mentioned adversely change their chemical properties at 100 ° C. .

The method according to the invention thus opens up a completely new spectrum of treatment options because treatment media can now also be used which could not previously be used for the reasons mentioned.

The method according to the invention can also be used particularly advantageously in the case of stacked goods or bulk goods which could not be adequately agitated with known methods and devices for injecting air bubbles into the treatment bath, because here too the air bubbles flow past the large number of workpieces. In most applications, there are no longer any tricks, for example rotating drums in an immersion bath, in which a bulk material is accommodated in order to expose it to air bubble agitation with regard to all bulk material workpieces (e.g. screws and the like).

In a preferred embodiment of the method according to the invention, the negative pressure is set so that it corresponds to the saturation vapor pressure of the treatment liquid of the immersion bath at the temperature minus at least the hydrostatic pressure at the bottom of the wash tank.

This measure has the advantage that the entire immersion bath is brought to a boil, even if the water column in the wash tank is relatively high.

In a further embodiment of the method according to the invention, a gas is blown into the immersion bath during steps d) and e).

This measure has two different advantages. On the one hand, the injected serves as a purge gas for a vacuum pump connected to the wash tank, which thus sucks an air / steam mixture out of the wash tank, the air component being passed through the vacuum pump and the steam fraction being able to be condensed out, as will be explained below. On the other hand, the gas injection has the advantage that an additional Agitation can be achieved, which leads to an increased treatment effect in a conventional manner.

In a preferred development of the exemplary embodiment mentioned, the gas is therefore blown in from the bottom of the wash tank in such a way that gas bubbles flow around the workpieces.

In this way, the known advantage arises that the entire tank, i.e. the entire batch of workpieces is surrounded by gas bubbles as evenly as possible.

In a further preferred exemplary embodiment of the invention, the air / steam mixture is passed through a condenser, the treatment liquid which condenses out in the condenser being further preferably returned to a liquid tank. This measure has the advantage that thickening or salting-out of the treatment liquid is avoided, which would occur if steam was always removed from the treatment bath while the dissolved treatment substances remained in the bath. By recycling the condensed treatment liquid, this effect is avoided, so that the method according to the invention can also be used independently in long-term operation, i.e. without refilling treatment liquids.

In preferred embodiments of the invention, a rinsing liquid or alternatively a cleaning liquid is used as the treatment liquid.

It is preferred if the cleaning agent is water, to which a gentle, fat-dissolving cleaning agent is added, the no chemical reactions with the surface of the workpieces occur and / or such chemical reactions are not supported.

This measure has the advantage that no residues of the cleaning agent remain on the surface of the workpieces after washing processes.

In a further preferred embodiment, the cleaning agent is neutral to slightly alkaline.

On the one hand, this measure has the advantage that metals or metal alloys in these pH ranges are not attacked by aqueous media and that such media are environmentally neutral and harmless to the people who handle the media.

In a further preferred embodiment of the invention, steps b) -g) are carried out several times in succession with the same or different treatment liquids.

This measure has the advantage of very great flexibility because only rinsing processes, only cleaning processes or combined cleaning or rinsing processes or other treatment processes can be carried out in succession.

In this case, it is particularly preferred if a fully demineralized water is used as the rinsing liquid and this is mixed with a detergent after step g) and used as a cleaning liquid for a further subsequent process implementation.

This measure has the advantage that even a "used" rinsing bath is subsequently used as a cleaning bath can, whereby fully demineralized water is particularly suitable as a starting substance for a cleaning liquid.

In further exemplary embodiments of the invention, the immersion bath is circulated during step e) and cleaned outside the wash tank.

This measure has the advantage that long-term operation can be guaranteed without the need to supply and remove treatment fluids.

It is further preferred if the immersion bath is mechanically agitated during step e). This measure also has the advantage known per se that the treatment effect is increased if, in addition to the existing chemical effects and the particle removal by means of steam bubbles, a mechanical action is also exerted on the surface of the workpieces.

In exemplary embodiments of the invention, it is expedient if step e) is carried out for a duration of between 1 min and 20 min.

This treatment period for the "negative pressure cooking" has proven to be expedient, but it can also be extended downwards and in particular upwards if this is necessary in individual cases.

It is also particularly preferred if steps d) - f) are carried out pulsatingly.

This measure has the advantage that the treatment bath can be "boiled up" one or more times, with the result that the workpieces are flushed through particularly vigorously.

In a further preferred variant of the method according to the invention, the workpieces are first flushed with a pressure-free surge of the treatment liquid throughout step b) for a period of between 1 min and 10 min, the surge having a flow rate between 100 m³ / h and 100 m³ / h per m² workpiece surface and the treatment liquid is continuously drained from the wash tank via an outlet, while the outlet is then closed until the wash tank is filled to an overflow by the surge.

This measure has the advantage that in the very critical first phase of the treatment, e.g. of the cleaning process, by rinsing the workpieces with an unpressurized surge of a very large flow rate, the workpieces are already treated or cleaned to a very large extent, with the result that e.g. the subsequent cleaning steps can start with a considerably clean workpiece than is the case with the conventional procedure.

The pressure-free gush pouring over the workpieces with a very high flow rate also penetrates into inaccessible areas of the workpieces, forms vortices there and also takes dirt particles from there. This cannot be achieved with conventional devices in which thin liquid jets are directed onto the workpiece under high pressure, because there, on the one hand, only punctiform areas of the workpiece surface can be applied and, on the other hand, as already mentioned, inside areas are inaccessible.

Compared to the also known methods of air injection, the above-mentioned procedure has the advantage that the workpieces are rinsed for a long time even before the cleaning bath is let in, that is to say during a time when the air is injected or steam bubbles are generated would have no effect.

In a further preferred embodiment of the method according to the invention, the workpieces are rinsed during step g), preferably covering the entire area by means of the pressure-free surge of the treatment liquid mentioned above and a flow rate which corresponds to 80% to 100% of the flow rate mentioned.

This measure has the advantage that the workpieces are never exposed to the outside air flowing in when the immersion bath is drained, which, given the high temperature at which the workpieces are located, would immediately lead to signs of corrosion and the like, since the workpieces start at this time their surface are highly active.

It is further preferred for this if, after step g), a negative pressure, preferably between 60 mbar and 350 mbar, is set for a duration of 3 minutes and 10 minutes in the wash tank.

This measure has the advantage that the workpieces can be dried in the same wash tank by means of negative pressure. The warm workpieces, which at this time are at the temperature of the immersion bath, that is to say at a temperature of, for example, 85 ° C., have generally stored enough inherent heat to evaporate the residues of treatment liquid still adhering. If a negative pressure is generated in the wash tank at this time, the evaporating liquid components removed and the workpieces are completely dry before the wash tank is opened again and the workpieces come into contact with the ambient air.

Finally, the object on which the invention is based is also achieved by a device with a pressure-tight lockable wash tank which has a capacity of between 1 m³ and 10 m³, with first means for moving workpieces into the wash tank, with second means for letting the workpieces into essentially surrounding immersion bath, with an air space remaining in the wash tank above the immersion bath, and with means for generating a negative pressure in the wash tank, provided the means for generating a negative pressure are connected to the air space and are designed such that they evacuate the air space to a negative pressure which is below the saturation vapor pressure of the treatment liquid of the immersion bath at the temperature for a predetermined time.

These measures have the advantage that conventional wash tanks can be used which only need to be slightly modified in order to be able to carry out the method according to the invention.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

Fig. 1

eine äußerst schematisierte Gesamtansicht eines Ausführungsbeispiels einer Vorrichtung zum Reinigen metallischer Werkstücke;

Fig. 2

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "druckloses Überspülen";

Fig. 3

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "druckloses Überspülen und Auffüllen";

Fig. 4

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "Umwälzen mit Gasblasenagitation";

Fig. 5

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "druckloses Überspülen und Ablassen";

Fig. 6

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "Vakuumtrocknen";

Fig. 7

eine Darstellung, ähnlich Figur 1, zur Erläuterung des Verfahrensschritts "Unterdruckkochen";

Fig. 8

eine Variante des in den Figuren 1 - 7 dargestellten Waschtanks, mit seitlicher Lufteindüsung;

Fig. 9 und 10

eine äußerst schematisierte Seiten- bzw. Vorderansicht einer weiteren Variante des erfindungsgemäßen Waschtanks, in horizontaler Bauweise.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

Fig. 1

an extremely schematic overall view of an embodiment of a device for cleaning metallic workpieces;

Fig. 2

a representation, similar to Figure 1, to explain the process step "pressure-free rinsing";

Fig. 3

a representation, similar to Figure 1, to explain the process step "pressure-free rinsing and filling";

Fig. 4

a representation, similar to Figure 1, to explain the process step "circulation with gas bubble agitation";

Fig. 5

a representation, similar to Figure 1, to explain the process step "pressure-free rinsing and draining";

Fig. 6

a representation, similar to Figure 1, to explain the process step "vacuum drying";

Fig. 7

a representation, similar to Figure 1, to explain the process step "vacuum cooking";

Fig. 8

a variant of the wash tank shown in Figures 1-7, with side air injection;

9 and 10

an extremely schematic side or front view of a further variant of the wash tank according to the invention, in a horizontal design.

A device 10 shown in FIG. 1 has a wash tank 12, a first tank 14 for a first treatment liquid, a second tank 16 for a second treatment liquid, a vacuum station 18, a filter device 20 and a device 22 for injecting a gas into the wash tank 12 on.

The wash tank 12 is circular in cross-section and closed at its top with a lid 26. In the interior of the wash tank 12 there is a holding device 28 which is provided for receiving a batch of workpieces 30. The holding device 28 can be inserted into and removed from the wash tank 12 from above in the vertical direction with the lid 26 open.

The workpieces 30 are preferably metallic workpieces, i.e. Conventional machine parts, which are preferably to be subjected to a heat treatment, for example nitro carburizing, at a later point in time. The workpieces 30 therefore have design-related cavities, bores and the like, which can be open upwards, downwards or to the side.

Furthermore, a drum 32 is held in the holding device 28, which is provided with a horizontal shaft 34. The shaft 34 extends laterally through the wall of the wash tank 12 and is driven by a drive 36 outside the wash tank 12.

The drum 32 is used for receiving bulk material, not shown here. The drum 32 is designed such that it is provided with openings on its circumference so that liquid and gas bubbles can pass through it while the bulk material contained in the drum 32 is retained.

The wash tank 12 is provided with an overflow 38 at its upper edge. In the drawing, the overflow 38 is shown on the wash tank 12 as an overflow running around the outside. A preferred embodiment of the invention, however, is characterized in that the overflow runs on the inside of the wash tank 12. In this way, process sequences are moved into the interior of the wash tank 12, which is advantageous with regard to vacuum applications.

The overflow 38 is connected on the one hand via a line 40 to the second tank 16, which in the exemplary embodiment shown contains a cleaning liquid 42. Furthermore, the overflow is connected via a line 48 to the first tank 14, which contains a rinsing liquid 47 in the exemplary embodiment shown. The lines 40 and 48 are provided with valves in order to be able to establish or block the connection between the overflow 38 and the tanks 14 and 16, as will be explained in detail below.

The second tank 16 containing the cleaning liquid 42 is connected via a line 41 to the suction side of a pump 43. The pump 43 is connected on the output side via a line 44 to a pipe socket 46 which is arranged in the bottom of the wash tank 12. Corresponding valves are also provided between tank 16 and pump 43 or pump 43 and pipe socket 46, as will be explained below.

The pump 43 is also connected on its suction side via a line 45 to the first tank 14 containing the rinsing liquid 47.

The tanks 14 and 16 are each provided with a heater 49 in the area of their bottom.

On the basis of the second tank 16 it is shown in FIG. 1 that the tank 16 is provided with a laterally arranged pre-separator 50 which is connected to the actual interior of the tank 16 via an overflow. The pre-separator 50 is also connected to the tank 16 via a line (not shown) and a pump, so that liquid can be pumped into the tank 16 by the pre-separator 50. The tanks 14 and 16 are provided with an overflow weir so that floating dirt of the liquids 42 and 47 get into the pre-separator 50. A skimmer again runs in the pre-separator 50 in order to collect the dirt and then to be able to remove it.

The pre-separator 50 is also connected to the filter device 20, which in turn has a filter 55 and an oil separator 54. The filter device 20 is not absolutely necessary, it can also be connected.

The filter 55 serves to separate solids from the liquid coming from the pre-separator 50. The purpose of the oil separator 54 is to separate oily phases from this liquid, the separated oil phase being able to be removed via an oil extraction 57 and brought to a disposal point. Liquid leaving filter 55 can be returned to tank 16.

The vacuum station 18 has a vacuum pump 70 which is connected to the interior of the wash tank 12 via a line 71. The line 71 preferably opens into the wash tank 12 just below the overflow 38.

On the pressure side of the vacuum pump 70, it is connected to a cold trap 72 and a collector 73. There is also a valve in line 71, as will be explained later.

The wash tank 12 can be closed in a vacuum-tight manner in the region of the cover 26 or the overflow 28.

The device 22 for injecting a gas into the wash tank 12 has a pressure container 60 in which a gas under pressure is stored. The pressure vessel 60 can in turn be connected to a compressor, not shown in FIG. 1. It is also possible to use a blower at this point. The gas processed in device 22 is preferably air, but a non-reactive protective gas can also be used. It is also possible to design the device 22 such that the gas is warmed up before it is fed to the wash tank 12.

The pressure vessel 60 is connected by means of a line 61, in which corresponding pressure control or pressure reducing valves are arranged, to a connecting piece 62 extending through the wall of the wash tank 12. From there, the line 61 leads to a plate-shaped hollow body 63, which is arranged in the region of the bottom of the interior of the wash tank 12. The plate-shaped hollow body 63, the plate plane of which extends approximately horizontally, preferably fills the inner cross section of the wash tank 12 as completely as possible in the region of the floor. In each In this case, the aim should be that the dimensions of the hollow body 63, in vertical view, are approximately the same size as the dimensions of the holding device 28.

In embodiments of the invention, the plate-shaped hollow body 63 can be constructed from stainless steel sheets, the stainless steel sheet forming the upper plate surface being provided with openings 65. The openings 65 consist of bores which have a diameter of approximately 1 mm and are arranged at a distance of preferably 25 mm from one another.

As an alternative to a hollow body 63 made of stainless steel sheets, a porous ceramic can also be used, which encloses an air distributor pipe and through whose pores the air flows.

Finally, the device 10 shown in FIG. 1 also has an electronic control unit 75, via the inputs 76 of which process parameters can be entered, while the outputs 77 control the units of the device 10, in particular the numerous valves and pumps.

The methods which can be carried out with the device 10 according to FIG. 1 are to be explained in more detail below with the aid of the state diagrams according to FIGS. 2-7.

To prepare one of the methods according to the invention, the cover 26 of the wash tank 12 is opened (not shown) in order to move the holder 28 with the workpieces 30 into the wash tank 12 from above by means of a crane or the like.

When this has happened, the wash tank 12 is closed again by closing the lid 26. In this phase of the invention In terms of the process, the closure does not yet have to be vacuum-tight, but it should at least protect against splashing water.

The first actual method step is now shown in FIG. 2.

By means of the control unit 75, to which the desired process parameters have previously been entered, the heater 49 in the second tank 16 is initially set with the cleaning liquid 42 in preparation for carrying out the method, and in parallel the heater 49 in the first tank 14 is also set with the rinsing liquid 47, provided that a rinsing process is desired. In this way, the cleaning liquid 42 and optionally the rinsing liquid 47 are heated to a temperature between 50 ° C. and 90 ° C., preferably in the range between 80 ° C. and 90 ° C. This is a temperature at which cleaning agents and detergents (if added) have their optimal working range, since the agents mentioned change chemically at even higher temperatures and the cleaning and rinsing effects decrease at lower temperatures.

As soon as the liquids 42 and possibly 47 are at the desired working temperature, the control unit 75 opens the necessary valves. On the one hand, a valve 41a is opened in line 41, which connects second tank 16 to the suction side of pump 43. Furthermore, a valve 51a in the line 51 is opened, which connects the pressure side of the pump 43 to the surge shower 52. Finally, a valve 67a in line 67 is opened, which connects line pipe 65, which acts as a drain, of wash tank 12 to second tank 16 via line 66.

As a result of these switching measures, a circuit of cleaning liquid 42 is established, which leads from the second tank 16 via the valve 41a, the line 41, the pump 43, the line 51, the valve 51a to the surge shower 52. The delivery rate of the pump 43 and the flow cross-sections of the valves 41a and 51a are so dimensioned via the electronic control unit 75 that an unpressurized surge 80 of cleaning liquid 42 emerges from the surge shower 52, the flow rate of which is in the range between 100 m³ / h and 300 m³ / h per m² surface of the workpieces 30 is set.

The surge 80 thus flushes the workpieces 30 without pressure and reaches the second tank 16 again via the pipe socket 65 which acts as a drain, the lines 66 and 67 and the opened valve 67a.

The workpieces 30 are pre-cleaned by the non-pressurized surge 80 because the surge 80 entrains and removes adhering dirt, in particular pigment dirt, but also greases.

The cleaning liquid 42 preferably consists of an aqueous solution of a non-foaming neutral cleaner with temporary corrosion protection. Such a neutral cleaner has a relatively weak oil emulsifying effect, but is absolutely environmentally friendly and does not attack the goods to be cleaned, nor do people who handle this liquid are affected in any way. The weakly alkaline temporary corrosion protection remains as a thin protective layer on the workpieces and can be completely evaporated at temperatures above 300 ° C without leaving any residue.

The method step explained above with reference to FIG. 2 is carried out for a period of preferably between one minute and 10 minutes.

When the said period of time has expired, the control unit 75 switches to a next method step, which is illustrated in FIG. 3.

During this further process step, the connection to the second tank 16 via the pump 43 to the surge shower 52 remains unchanged. In contrast to the previous method step, however, the valve 67a in the line 67 is now closed, so that the wash tank 12 has no drain.

As a result, an immersion bath 83 is formed in the wash tank 12, the level 85 of which rises continuously, as indicated by an arrow 86.

The wash tank 12 thus fills continuously with a warm cleaning immersion bath 83 and this process step continues until a fill level indicator (not shown) detects that the liquid level 85 has reached the overflow 38. As soon as this is the case, the present method step is ended.

FIG. 4 shows the next process step in which the bath 83 is circulated and agitated.

For the purpose of circulation, the connection between the second tank 16 and the surge shower 52 is initially maintained but, for example by reducing the delivery capacity of the pump 43, for example by 30% to 80% reduced, so that only a much smaller surge 80 'emerges from the surge shower 52.

The control unit 75 now opens a valve 40a in the line 40 between the overflow 38 and the second tank 16, so that the cleaning liquid 42 flowing over the overflow 38 can flow into the second tank 16.

As soon as the liquid level 85 has reached the overflow 38, the valve 51a in the line 51 to the surge shower 52 can alternatively be closed and a connecting valve 51b can be opened, which connects the pressure side of the pump 53 to the bottom of the wash tank 12. By supplying liquid from the bottom of the wash tank 12, it is achieved that only liquid which is provided with rising dirt by rising gas bubbles leaves the wash tank 12 and not liquid which was supplied via the surge shower 52 immediately flows into the overflow 38.

At the same time, the control unit 75 actuates the device 22 for injecting gas by opening a valve 61a in the line 61 between the pressure vessel 60 and the plate-shaped hollow body 63.

As a result, gas bubbles emerge from the plate-shaped hollow body 63 to a large extent and wash around the workpieces 30 with simultaneous agitation of the cleaning bath 83.

The gas or the air which emerge from the plate-shaped hollow body 63 are there under a pressure which is slightly above the ambient pressure prevailing there in the area of the openings 65. The compressed air exits through the numerous openings 65 as small gas beads from the plate-shaped Hollow bodies 63, which then flow rapidly upwards to the overflow 38 due to the pressing pressure and their buoyancy.

Those air bubbles that strike the underside of the workpieces 30 are deflected laterally by them, so that a dense stream of pearls flows through the vertical walls or bores of the workpieces 30, provided that they run vertically or inclined to the vertical. The bubbles are also guided along the top of the workpieces 30 by adhesive forces and by the turbulence existing in the liquid, so that there is also a strong movement of the cleaning liquid 42 there.

The air bubbles flowing out of the openings 65 do not run through the numerous impingement points of the holding device 28 or the workpieces 30 contained therein in a straight line direction, but in a serpentine, partially swirled path.

The air bubbles also pass through the drum 32, so that the bulk material received there is also flowed around in a pearly manner when the drum 32 rotates.

To agitate the cleaning bath 83, the valve 61a can either be kept open continuously by the control device 75, the intensity of the agitation being able to be influenced by the air flow. Alternatively, however, it is also possible to alternately open and close the valve 61a in a predetermined manner, so that pulsating pressure surges are used. In this way, for example, the compressed air can be briefly pressed into the wash tank 10 at 5-10 bar at intervals of approximately 10-15 seconds.

Particularly in the case of workpieces 30 which are heavily contaminated with solids, such as pigment dirt, sand, drilling chips or drilling mud, in the initial phase of a cleaning process, very high pulsating pressure and high frequencies are used. The intensive turbulence means that these solid parts are torn off the workpieces 30 solely by the mechanical action. Furthermore, it has been found that the solid parts, although they have a higher density than the cleaning liquid 42 received in the wash tank 12, quickly surface to the surface due to adhesive forces, i. be brought into the area of the overflow 38. There these impurities are fed to the tank 16 via the line 40. If the material to be cleaned is extremely dirty, a coarse filter can also be provided in the area of the overflow 38.

The use of the aforementioned, non-foaming neutral cleaner ensures that no excessive foam is formed even when it is blown intensively into the wash tank 12.

Since the cleaning liquid 42 is at the working temperature, the workpieces 30 are degreased by means of the detergent substances in the detergent, for example anionic surfactants, i.e. cleaned of adhering lubricating oils and the like.

It goes without saying that the amount of the circulated liquid which is supplied by the pump 43 in this process step can also be adjusted depending on the degree of contamination of the workpieces 30. The delivery capacity of the pump 43 can also be changed over the course of this method step, for example by working first with a higher throughput and then with a lower throughput.

The method step explained above with reference to FIG. 4 is preferably carried out for a period between 3 minutes and 15 minutes.

After the aforementioned period has elapsed, the control unit 75 switches to the next method step, which is explained with reference to FIG. 5.

For this purpose, the control unit 75 switches the pump 43 back to a delivery rate that corresponds wholly or almost to the delivery rate of the method step explained with reference to FIG. 3. A surge 80 now emerges from the surge shower 52, the flow rate of which is between 100 m³ / h and 300 m³ / h. At the same time, however, the valve 67a in the line 67 is opened again, so that the bath 83 runs out of the wash tank 12, as indicated by the arrow 86 'pointing downward on the liquid level 85 in FIG. 5.

The continuous pressure-free rinsing of the workpieces 30 in the process step illustrated in FIG. 5 has the following meaning:
If, by draining the bath 83, the liquid level 85 drops, it can happen that dirt particles that float during emptying settle on the workpieces 30 when the liquid level 85 passes through these workpieces. However, this is prevented by the fact that abundant fresh, ie cleaned, cleaning liquid 42 is constantly supplied from above, namely from the surge shower 52, because the workpieces 30 are then continuously rinsed even when the bath 83 is drained.

On the other hand, switching on the unpressurized surge 80 has the sense that the workpieces 30 do not come into contact with ambient air, or almost not. When the bath 83 is drained, an air supply (not shown) must be made possible in the interior of the wash tank 12 so that the bath 83 can run off. However, this supplied fresh air could cause chemical reactions on the surfaces of the workpieces 30 that are highly active at this time, which is undesirable. For this reason, too, it is expedient to cover the workpieces 30 with a film of liquid at all times by continuously flushing them without pressure.

When the bath 83 has expired, which can be recognized by suitable fill level sensors (not shown), the control unit 75 switches over to the next method step, which is shown in FIG. 6.

For this process step, the cover 26 of the wash tank 12 must be closed in a pressure-tight manner.

The control unit 75 now opens a valve 71a in the line 71 between the interior of the wash tank 12 and the vacuum pump 70. At the same time, the vacuum pump 70 is switched on.

It must be borne in mind at this point that the workpieces 30 at this time have the temperature of the bath 83, i.e. are at a temperature of, for example, 80 ° C and 90 ° C.

The vacuum pump 70 now generates a vacuum in the interior of the wash tank 12. At about 800 mbar, the evaporation of the residual liquid starts on the workpieces 30 and the water vapor is, as indicated in FIG. 6 with arrows 90, via the line 71 sucked off. The vacuum pump 70 now reduces the pressure in the wash tank 12 to 200-300 mbar, which corresponds to the steam pressure at a water temperature of 60 ° C - 80 ° C. The liquid still on the workpieces 30 consequently evaporates, the evaporation process taking place more quickly on flat surfaces than in the area of bores, cavities or so-called scooping surfaces, ie depressions of the workpieces 30 opening upwards.

The drying process is maintained for a period of between 3 minutes and 10 minutes. As soon as the last liquid has evaporated from the workpieces 30, the pressure in the interior of the wash tank 12 drops suddenly, for example to 70-80 mbar, because there is no longer any liquid to evaporate. The drying process is ended by the control unit 75 by means of a suitable time control or, if appropriate, by a pressure sensor (not shown) which registers and reports this pressure drop.

Depending on which method is desired, a treatment step with a further treatment liquid can now follow or even before the drying process, for example rinsing the workpieces 30 with the rinsing liquid 47 contained in the first tank 14 same, so that in this respect reference can be made to the description of FIGS. 2-5.

The following is important in this context:
During the entire duration of the process, in particular during the process steps in which the bath 83 is circulated, the liquid in question, for example the cleaning liquid 42, is continuously cleaned, as initially described 1 was explained in connection with the filter device 20.

This means that the device 10 operates completely independently, i.e. no need to add or remove treatment fluids during operation.

Only when one of the liquids is no longer usable due to aging must it be reprocessed or disposed of using suitable devices and replaced with a new treatment liquid. During normal operation of the device 10, on the other hand, it is only necessary to dispose of the filtered dirt components.

It is also preferred if demineralized water is used as the basis for the treatment liquids. The fully demineralized water can initially be used as a rinsing liquid 47, because this prevents salt stains from forming on the workpieces after the rinsing during the drying process (FIG. 6), which interfere with the subsequent heat treatment, in particular with nitro carburizing.

In addition, the rinsing liquid 47 can be prepared by adding suitable cleaning agents even when it can no longer be used as a rinsing liquid and can be used as a cleaning liquid 42 for subsequent washing processes. In this way too, extreme use can be made of the liquids used without having to refill new liquids.

7 shows a possibility according to the invention for agitating the bath 83.

In the arrangement according to FIG. 7, the line 71 'between the vacuum pump 70 and the wash tank 12 is expediently connected to the cover 26.

The method step to be illustrated below with reference to FIG. 7 is to be understood as an alternative or supplement to the method step of agitation explained above with reference to FIG. 4.

According to the method step shown in FIG. 7, to agitate the bath 83, the vacuum pump 70 is switched on via the control device 75 and at the same time the valve 71a 'in the line 71' is opened.

Since the bath 83 is filled up to the overflow 38 in this process state, the vacuum pump 70 generates a strong negative pressure in the remaining small air space 91 in the area of the surge shower 52.

The negative pressure is now set so that the bath 83 begins to boil despite the temperature of 100 ° C. being below the boiling point of water at atmospheric pressure. For this purpose, the vacuum must be set so that it corresponds to the saturation vapor pressure of water at the respective lower temperature and the hydrostatic pressure in the wash tank 12 is also taken into account, i.e. the height of the liquid column inside the tank.

For example, if the temperature of bath 83 is 85 ° C, this corresponds to a saturation vapor pressure of 600 mbar. If the liquid column in the wash tank 12 is 2 m high, another 200 mbar of hydrostatic pressure must be subtracted from this, which leads to a required pressure of 400 mbar. At 80 ° C Temperature of bath 83 and a saturation vapor pressure of 500 mbar, after subtracting 200 mbar, a pressure of 300 mbar results as compensation for the hydrostatic pressure at a water column of 2 m.

If the required pressure of 400 (85 ° C.) or 300 (80 ° C.) mbar is thus set, the bath 83 begins to boil, even though its temperature is below 100 ° C.

The boiling of the bath 83 has the result that steam bubbles form at every point in the bath 83, that is to say not only on the surfaces of the workpieces 30, but rather also in cavities, bores, blind bores, scoops and the like. The vapor bubbles thus also arise at those locations on the workpieces that cannot be reached by air bubbles that were generated by the device 22 for injecting gas. In addition, the rising steam bubbles take along dirt particles via adhesive forces, with the result that blind bores, scooping surfaces and the like can also be cleaned by taking dirt particles with them. It goes without saying that the intensity of the boiling can be varied by adjusting the negative pressure accordingly via the vacuum pump 70. The dirt carried up by the steam bubbles during the vacuum cooking collects on the surface of the bath and can be removed from the wash tank 12 in the manner already described via the overflow 38 after the cooking phase has ended.

The cooking of the bath 83 can be provided both during cleaning and during rinsing, because the chemical cleaning process is supported during cleaning, while the difficult to access spaces can be rinsed out in the manner mentioned during rinsing. It goes without saying that the Vacuum cooking a circulation and / or agitation of the bath 83 is possible.

For this purpose, the suction side of the pump 43 is connected to the pipe socket 65 via a line 95, a valve 95a being arranged in the line 95.

By means of a corresponding suction power of the pump 43, the corresponding treatment liquid can now be sucked off the pipe socket 65 despite the negative pressure prevailing in the wash tank 12 and added again via the surge shower 52. It is understood that in this case as well, suitable measures can be used to continuously clean the respective treatment liquid (not shown).

It is also expedient if a condenser 92 is arranged in the line 71 'because the vacuum pump 70 sucks off the vapor of the respective treatment liquid in the manner described and this vapor should not get into the vacuum pump 70. For this reason, an appropriate supply of air will ensure that the vacuum pump 70 always draws in a mixture of air and steam, the steam in the condenser 92 then precipitating out and being supplied to the respective tanks for the treatment liquids. This has the advantage that the treatment liquids do not thicken, i.e. Salt up by keeping the water loss as low as possible.

The amount of steam for the vacuum pump 70 is reduced by the amount of condensed steam, so that the vacuum pump 70 can be economically small.

Since the vacuum pump 70, as already mentioned, can only pump out saturated air, the air required by the vacuum pump 70 becomes preferably supplied via the hollow body 63. You can measure the air required by the vacuum pump 70 so that it just corresponds to the amount of flotation air.

The method of vacuum cooking explained above with reference to FIG. 7 can now be integrated in a variety of ways into the method steps explained further above with reference to FIGS. 2-6:
In a first alternative, vacuum cooking can be used permanently in the immersion process, with the result that cooking is carried out under vacuum during the entire cleaning or rinsing time.

In a second alternative, vacuum cooking in the immersion process can also be used for floating, i.e. each for part of the cleaning or rinsing time.

In a third alternative, the vacuum cooking method can also be used in a pulsating manner by appropriate setting by means of the control device 75, be it during the entire cleaning or rinsing time or during individual time segments. A pulsating vacuum boiling can be achieved in this case by strongly evacuating the wash tank 12 until the boiling effect sets in or almost sets in, in order to then bring to a boil by the sudden addition of fresh air, i.e. to cause a pressure release.

The fresh air can be supplied via the hollow body 63 or also via the surge shower 52.

Finally, a fourth alternative is also possible, in which the vacuum cooking in the immersion process in addition to the circulation and is also used for agitation by means of air injection.

The step of vacuum cooking can last from 1 min to 20 min.

FIG. 8 shows a variant of a device 100, only one wash tank 104 being shown here, which largely corresponds to the wash tank 12 of the device 10 according to FIGS. 1-7. Therefore, essentially only the deviating elements will be described below and in Fig. 8 the same reference numerals have been used for corresponding components.

The wash tank 104 is also designed as a container which is approximately circular in cross section and is provided on its bottom with a pipe socket 105, which is intended here to represent the pipe socket 46 and 65 of the wash tank 12 according to FIGS. 1-7.

The wash tank 100 also has a drum 106 which can be rotated about a horizontal axis 108 via a drive 107. Hexagonal workpieces 110, 110 '...... are contained in the drum 106. In the area of a cover 112, the wash tank 104 is provided with an overflow 111, which is connected both to the second tank 16, which contains the cleaning liquid 42, and to the first tank 14, which contains the rinsing liquid 47. Furthermore, the wash tank 104 is connected to the vacuum station 18 via a side connection. To carry out the “negative pressure cooking” method, a connection piece 114 can also be present in the cover 112. The surge shower 113 is arranged on the inside of the cover 112 and, in the manner already explained several times, serves to flush the workpieces 110 accommodated in the interior of the wash tank 104 with a surge without pressure.

In a cleaning process, as was explained in detail above in relation to FIG. 4, the wash tank 104 is filled with the cleaning liquid 42 up to the overflow 111. In the wash tank 104 there is a holder 118 which carries various other workpieces 120.

A device 122 for injecting gas (in the exemplary embodiment shown in FIG. 8, the gas is nitrogen) consists of a hollow body 126 which has a bottom part 130 and a side part 131.

The side part 131 extends on one side of the holder 118 and surrounds it at least over a large part of its circumference.

The hollow body 126 is again provided on the side facing the holder 118, as previously described, with numerous openings, which are designed as nozzles 128 in the embodiment shown in FIG. 8.

The nitrogen coming from the pressure vessel 60 emerges from the nozzles 128 in the form of fine beads or bubbles 127. As already described, the bubbles 127 flow completely around the workpieces 120, as is indicated, for example, by an arrow 136.

Providing the side part 131 also produces a laterally directed bubble flow, as is indicated, for example, by the arrow 139. This creates an upwardly curved line because the bubbles emerging from the side nozzles 128 soon tend to rise due to the buoyancy.

The pressure of the gas bubbles 127 emerging from the side nozzles 128 is adjusted during a cleaning process so that they reach at least approximately the longitudinal central axis of the wash tank 104, i.e. seen in the section of Fig. 8, as indicated by the arrow 138, extend at least over half the width in the lateral direction.

The side part 131, which at least partially surrounds the holder 118, ensures that rapid cleaning is possible even with workpieces 120 of complex shape.

The hollow body 126 can be subdivided into a top section 134, a middle section 135 and a bottom section via separating slides 132 and 133, so that, depending on the type of goods received in the wash tank 104, gas 141 only in the area of the bottom or also one or more one above the other arranged side areas is pressed.

The rising gas beads 127 also generate a secondary flow, as indicated by an arrow 137. The liquid received in the wash tank 104 then flows in a circulating circuit.

Finally, FIGS. 9 and 10 show yet another exemplary embodiment of devices according to the invention, as can be used to carry out the method according to the invention.

9 and 10, in turn, denotes a device for cleaning, in particular, metallic workpieces, which comprises a wash tank 151. A holder 152 for workpieces is in turn provided in the wash tank 151. In contrast to the arrangements of FIGS. 1-8, however, the arrangement is so that the holder 152 can be removed from the wash tank 151 in the horizontal direction via a loading door 153. The loading door 153 is preferably displaceable in the vertical direction, as indicated by an arrow.

The liquids and gases can be supplied and discharged via lines 154, 155 and 156 in the manner already explained in detail, with no differences arising in the course of the method.

This also applies in particular to the surge shower 157, which also delivers a pressure-free water surge in the device 150, even if the area of action is greater in the horizontal construction shown in FIGS. 9 and 10 than in the vertical arrangement in FIGS. 1-8.

Another special feature of the device 150 is that the wash tank 151 is arranged on a frame 160 which at the same time holds the tanks 161, 162 for the treatment liquids. In the illustrated embodiment, two tanks 161, 162 are again provided for the cleaning liquid and the rinsing liquid.

It goes without saying that various developments of the invention are possible without leaving the scope of the invention. For example, an additional heater can be provided in the wash tank 12 in order to be able to work with cooler parts or to be able to dry even with large amounts of water remaining by the additional heater applying the required additional heat of vaporization.

Ultrasonic generators can also be provided in the wash tank 12 in a manner known per se, in order to cope with extreme physical Forces to cause cavitation in the treatment liquid. In this way it is possible to be able to remove inorganic substances which are difficult to adhere to the workpieces, as well as impurities which have worked into the surface of the workpieces.

Claims (20)

Method for treating workpieces (30; 110, 120) with a liquid, in particular for cleaning metallic workpieces for a heat treatment following cleaning, with the method steps: a) moving the workpieces (30; 110, 120) into a wash tank (12; 104; 151) with a capacity of between 1 m³ and 10 m³; b) admission of an immersion bath (83) essentially surrounding the workpieces (30; 110, 120) of a treatment liquid (42, 47) with a temperature between 50 ° C and 90 ° C; c) pressure-tight closing of the wash tank (12; 104; 151) in such a way that an air space (91) remains above the immersion bath (83); d) evacuating an air / steam mixture present in the air space (91) to a vacuum which is below the saturation vapor pressure of the treatment liquid (42, 47) of the immersion bath (83) at the temperature; e) maintaining the vacuum at the boiling immersion bath (83) for a predetermined time; f) relaxing the air space (91) to ambient pressure; and g) lowering the immersion bath (83). A method according to claim 1, characterized in that the negative pressure is set so that it corresponds to the saturation vapor pressure of the treatment liquid (42, 47) of the immersion bath (83) at the temperature minus at least the hydrostatic pressure at the bottom of the wash tank (12; 104; 151). Method according to Claim 1 or 2, characterized in that a gas is blown into the immersion bath (83) during steps d) and e). Method according to claim 3, characterized in that the gas is blown in from the bottom of the washing tank (12; 104; 151) in such a way that gas bubbles (127) flow around the workpieces (30; 110, 120). Method according to one or more of claims 1 to 4, characterized in that the air / steam mixture is passed through a condenser (92). Method according to claim 6, characterized in that the treatment liquid (42, 47) condensed out in the condenser (92) is returned to a liquid tank (14, 16). Method according to one or more of claims 1 to 6, characterized in that a rinsing liquid (42) is used as the treatment liquid. Method according to one or more of claims 1 to 6, characterized in that a cleaning liquid (47) is used as the treatment liquid. A method according to claim 8, characterized in that the cleaning agent (42) is water, to which a gentle, fat-dissolving cleaning agent is added, which does not undergo chemical reactions with the surface of the workpieces (30; 110, 120) and / or such chemical reactions supported. A method according to claim 9, characterized in that the cleaning agent is neutral to slightly alkaline. Method according to one or more of claims 1 to 10, characterized in that steps b) to g) are carried out several times in succession with the same or different treatment liquids (42, 47). A method according to claims 7 and 8 and 11, characterized in that a fully demineralized water is used as the rinsing liquid (47) and a detergent is added to this after step g) and is used as a cleaning liquid for a further subsequent process implementation. Method according to one or more of claims 1 to 12, characterized in that during step e) the immersion bath (83) is circulated and cleaned outside the wash tank (12; 104; 151). Method according to one or more of claims 1 to 13, characterized in that the immersion bath (83) is mechanically agitated during step e). Method according to one or more of claims 1 to 14, characterized in that step e) is carried out for a period between 1 min and 20 min. Method according to one or more of claims 1 to 14, characterized in that steps d) to f) are carried out pulsating. Method according to one or more of claims 1 to 16, characterized in that the workpieces (30; 110, 120) during step b) initially for a period of between 1 min and 10 min with a non-pressurized surge (80) of the treatment liquid ( 42, 47) are flushed over the entire surface, the surge (80) being set at a flow rate between 100 m³ / h and 300 m³ / h per m² workpiece surface and the treatment liquid (42, 47) being continuously removed from the wash tank (12; 104; 151) is drained off via a drain (65; 105), while then the drain (65; 105) is closed until the wash tank (12; 104; 151) through the surge (80) to an overflow (38; 111) is filled. Method according to one or more of claims 1 to 17, characterized in that the workpieces (30; 110, 120) are rinsed during step g). Method according to one or more of claims 1 to 18, characterized in that after step g) in the wash tank (12; 104, 151) a negative pressure, preferably between 60 mbar and 350 mbar, is set for a duration between 3 min and 10 min . Device for carrying out the method according to one of claims 1 to 19, with a pressure-tight lockable wash tank (12; 104, 151), which has a capacity between 1 m³ and 10 m³, with first means for moving in workpieces (30; 110, 120 ) in the wash tank (12; 104; 151), with second means for admitting an immersion bath (83) essentially surrounding the workpieces (30; 110, 120), an air space (91) in the wash tank (83) above the immersion bath (83) 12; 104; 151) remains, and with means for Generating a vacuum in the wash tank (12; 104; 151), characterized in that the means for generating a vacuum are connected to the air space (91) and are designed such that they are able to evacuate the air space (91) to a vacuum, which is below the saturation vapor pressure of the treatment liquid (42, 47) of the immersion bath (83) at the temperature for a predetermined time.

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