Method for passivating a surface of a workpiece and device for passivating workpieces

Abstract

To provide a method for passivating a surface of a workpiece, which allows complete and sufficient passivation of the surface of the workpiece in narrow spaces of the workpiece, including in the case of workpieces with complex geometry, the method according to the invention comprises the following steps: - introducing at least one workpiece into a treatment chamber; - providing passivation means in the treatment chamber; - cyclically changing the pressure in the treatment chamber while the passivation means are located in the treatment chamber.

Description

[0001] Method for passivating a surface of a workpiece and device for passivating workpieces

[0002] The present invention relates to a method for passivating a surface of a workpiece, which comprises:

[0003] Placing at least one workpiece into a treatment chamber; and

[0004] Introducing a passivating agent into the treatment chamber.

[0005] Such a process is known from DE 10 2007 022 033 A1.

[0006] In this known process, the interior of a treatment chamber is flooded several times with a passivating agent, whereby the passivating agent is completely drained from the treatment chamber after each flooding.

[0007] If the workpiece to be passivated has narrow spaces such as small diameter holes, capillaries and small lumens, the penetration of the passivating agent into such narrow spaces is hindered by the surface tension of the passivating agent.

[0008] An exchange between the air present in the workpiece and the passivating agent occurs only insufficiently. Therefore, workpieces with complex geometries are not completely and sufficiently passivated, at least in such narrow spaces. Preliminary processes such as electropolishing cannot be fully carried out for these reasons either. The present invention is based on the object of creating a method for passivating a surface of a workpiece of the type mentioned above, which enables complete and sufficient passivation of the surface of the workpiece in narrow cavities, even with workpieces with complex geometries.

[0009] This object is achieved according to the invention in a method for passivating a surface of a workpiece having the features of the preamble of claim 1 in that the method further comprises the following: cyclically changing the pressure in the treatment chamber while the passivating agent is in the treatment chamber.

[0010] The present invention is based on the concept of generating cyclic pressure changes in the closed treatment chamber, wherein the treatment chamber is preferably evacuated to a lower pressure value and then ventilated to an upper pressure value.

[0011] Through these repeated pressure changes, the passivating agent is reliably introduced even into narrow cavities of a workpiece to be passivated.

[0012] If another fluid is present in the workpiece's cavities due to previous processes, this fluid is reliably exchanged for the passivating agent through the pressure changes. This ensures that the passivating agent can reliably wet all surfaces of the workpiece during the passivation process and that a seamless passivation layer can be reliably formed.

[0013] The passivating agent can be introduced into the treatment chamber after the workpiece has been placed there. This is preferably the case with chamber systems for the treatment of workpieces.

[0014] Alternatively, the passivating agent can be present in the treatment chamber before the workpiece is introduced into the treatment chamber. In this case, the passivating agent can also remain in the treatment chamber after the passivation treatment. This is preferably the case with serial immersion systems for treating workpieces.

[0015] Passivation of a workpiece refers to the removal of free iron molecules and the targeted creation of a protective layer on a metallic workpiece, which prevents or significantly slows down oxygen corrosion of the base material of the workpiece.

[0016] For the passivation of workpiece surfaces, the standards ASTM A380-06 and ASTM A967-05 are relevant. Furthermore, the specifications ISO 16048, AMS 2700, and QQ-P-35 are applicable.

[0017] The workpiece to be passivated can, for example, be made entirely or partially of a stainless steel material which has a chromium content of at least 11% by weight.

[0018] The workpiece to be passivated can in particular be manufactured using an additive manufacturing process.

[0019] The workpiece to be passivated can be a workpiece from the field of medical technology, for example, an implant or an instrument. The workpiece to be passivated can, for example, have a structured, particularly biocompatible, surface.

[0020] Such a surface can be intended in particular for adhesion to bone structures.

[0021] The workpiece to be passivated preferably has narrow cavities, such as holes or capillaries, into which liquids cannot easily penetrate from the outside.

[0022] In a preferred embodiment of the invention, it is provided that during the cyclical change of the pressure in the treatment chamber, the maximum pressure p0 is lower than the ambient pressure (approximately 1.0 bar).

[0023] Furthermore, it is advantageous if during the cyclical change of the pressure in the treatment chamber the minimum pressure p u is less than half of the maximum pressure Po.

[0024] Furthermore, it is advantageous if during the cyclical change of the pressure in the treatment chamber the minimum pressure p u is lower than the vapor pressure of the passivating agent.

[0025] The cyclic pressure changes in the treatment chamber create cavitation bubbles directly on the surfaces of the workpiece. Some of these cavitation bubbles are stable and change their volume during the pressure changes; the volume of the cavitation bubbles decreases with increasing pressure and increases with decreasing pressure.

[0026] These volume changes generate microcurrents in the passivating bath, particularly in the cavities of the workpiece to be passivated. During a low-pressure phase, the stable cavitation bubbles in the workpiece's capillaries expand, causing fluid to be expelled from the capillaries.

[0027] In a subsequent phase with higher pressure, the stable cavitation bubbles contract, sucking fluid into the capillaries.

[0028] Another portion of the cavitation bubbles is not stable, but rather forms transient cavitation bubbles. These transient cavitation bubbles implode when the pressure in the treatment chamber increases, resulting in very high flow velocities at the surface of the workpiece.

[0029] The microcurrents in the passivating agent bath cause a very effective exchange of fluid on the surfaces of the workpiece, especially on the surfaces of holes and / or capillaries of the workpiece.

[0030] A high concentration of oxygen on the surface of the workpiece to be passivated promotes the formation of oxides and the development of a passivation layer.

[0031] In a special embodiment of the passivation process, the oxygen concentration in the passivating agent within the treatment chamber is therefore detected by at least one measuring sensor.

[0032] If the oxygen concentration in the passivating agent falls below a lower limit, the oxygen concentration is increased by supplying air into the treatment chamber.

[0033] To enable such air supply to the passivating agent within the treatment chamber, the treatment chamber may be provided with at least one aeration nozzle. The oxygen concentration limit below which oxygen is supplied to the passivating agent is preferably at least 5 mg / l and / or preferably at most 8 mg / l.

[0034] The average cycle duration ti of changing the pressure in the treatment chamber is preferably at least 1 second, in particular at least 3 seconds, particularly preferably at least 5 seconds.

[0035] Furthermore, the average cycle time ti of changing the pressure in the treatment chamber is preferably at most 30 seconds, particularly preferably at most 10 seconds.

[0036] The passivation process, which comprises numerous pressure change cycles, is carried out during a treatment time of preferably at least one minute, in particular at least 5 minutes, particularly preferably at least 10 minutes.

[0037] Furthermore, the passivation process is preferably carried out during a treatment time of at most 60 minutes, in particular of at most thirty minutes, particularly preferably of at most 20 minutes.

[0038] In a preferred embodiment of the method according to the invention, it is provided that the treatment chamber is at least temporarily connected to a negative pressure source during the pressure change.

[0039] Such a vacuum source may, for example, comprise a vacuum pump, preferably a positive displacement vacuum pump.

[0040] Furthermore, the vacuum source may comprise a vacuum reservoir. Such a vacuum reservoir can preferably be separated from the interior of the treatment chamber by a valve or valve arrangement.

[0041] Furthermore, the vacuum reservoir is preferably connectable to a vacuum generator, for example a vacuum pump, in order to reduce the pressure in the vacuum reservoir.

[0042] The internal volume of the vacuum reservoir can be evacuated by means of the vacuum generator to a pressure which is significantly lower than the pressure in the treatment chamber during phases of the passivation process during which the vacuum reservoir is separated from the treatment chamber by the valve or valve arrangement.

[0043] By subsequently equalizing the pressure between the vacuum reservoir and the interior of the treatment chamber, the pressure inside the treatment chamber can then be easily and significantly reduced, preferably below the vapor pressure of the passivating agent located inside the treatment chamber. This makes it possible to increase the effective depth of evaporation of the treatment agent inside the treatment chamber.

[0044] The effective depth is the distance (taken parallel to the direction of gravity) from the surface of the passivating agent bath up to which an evaporation process takes place in the passivating agent.

[0045] Furthermore, it is possible to provide a mechanism in the vacuum reservoir for separating liquid droplets entrained by the gas flow from the interior of the treatment chamber. Such a mechanism can comprise, for example, a wire mesh separator, an impact separator, and / or a condenser, which preferably has a cooled surface. Furthermore, a mechanism can be provided in the vacuum reservoir that actively or passively condenses the vapor of the treatment agent entrained by the gas flow from the interior of the treatment chamber.

[0046] Such a mechanism may, for example, comprise a condenser, which preferably has a cooled surface.

[0047] It is particularly advantageous if the vacuum storage tank is equipped with a heat exchanger.

[0048] In such a heat exchanger, which can act in particular as a condenser, heat from the gas flow passing from the treatment chamber into the vacuum reservoir can be transferred to a heat dissipation medium. When a vapor of the passivating agent condenses on the heat exchanger, the condensation heat released in this process can be transferred to the heat dissipation medium.

[0049] The heat dissipation medium may be a treatment agent to be supplied to the treatment chamber, for example a passivating agent or a rinsing liquid.

[0050] However, the heat dissipation medium can also be used to indirectly heat a treatment agent to be supplied to the treatment chamber, for example a passivating agent or a rinsing liquid.

[0051] For this purpose, it is particularly advantageous if the heat removal medium is used as a coolant in a heat pump. Furthermore, the heated heat removal medium can be used to heat a treatment agent in another treatment process or to heat a building.

[0052] The passivating agent is preferably an aqueous solution to which at least one acid is added.

[0053] For example, the passivating agent may comprise citric acid.

[0054] The proportion of citric acid may preferably be at least four% by weight and / or preferably at most ten% by weight.

[0055] Alternatively or additionally, the passivating agent may comprise phosphoric acid and / or nitric acid.

[0056] For example, an aqueous solution of nitric acid can be used as a passivating agent, which contains nitric acid in a proportion of at least 20% by volume and at most 55% by volume, in particular of at most 45% by volume, particularly preferably of at most 25% by volume.

[0057] Alternatively, the passivating agent may contain phosphoric acid in a concentration of at least 1.5% by volume and / or at most 3% by volume.

[0058] In a preferred embodiment of the invention, the passivating agent is an aqueous solution of phosphoric acid and nitric acid, wherein the passivating agent contains phosphoric acid in a concentration of 1.5% to 3% by volume and nitric acid in a concentration of 0.1% to 0.5% by volume. Furthermore, the passivating agent may contain nonionic surfactants in a concentration of preferably 0.05% to 0.5% by volume.

[0059] The basis of the aqueous solution is preferably deionized water with an electrical conductivity of maximum 10 |jS / cm.

[0060] In order to promote the generation of microcurrents directly on the surface of a workpiece to be passivated in combination with the cyclic pressure changes and thus to obtain an even stronger exchange of fluids in cavities of the workpiece, it can be provided that the passivating agent and / or the at least one workpiece is subjected to ultrasound during the change of pressure.

[0061] The ultrasonic frequency is preferably at least 20 kHz, particularly preferably at least 25 kHz.

[0062] Furthermore, the ultrasonic frequency is preferably at most 120 kHz, particularly preferably at most 80 kHz.

[0063] The ultrasonic power coupled into the interior of the treatment chamber is preferably at least 5 watts per liter of passivating agent in the treatment chamber, particularly preferably at least 8 watts per liter of passivating agent in the treatment chamber.

[0064] Furthermore, the ultrasonic power coupled into the treatment chamber is preferably at most 20 watts per liter of passivating agent in the treatment chamber, particularly preferably at most 15 watts per liter of passivating agent in the treatment chamber.

[0065] By amplitude modulation of the ultrasonic vibrations and / or by modulating the ultrasonic frequency (so-called "sweep" function), the effect of the exposure to the bath of passivating agent and / or the workpiece to be passivated can be further enhanced and the effect of the ultrasonic exposure can be evenly distributed over all surfaces of the workpiece to be passivated.

[0066] In a particular embodiment of the method according to the invention, it is provided that a workpiece to be passivated is introduced successively into several passivation stations which contain different passivating agents.

[0067] By providing several passivation stations in which different workpieces to be passivated are passivated simultaneously, the throughput of a passivation system used for the passivation process can be increased.

[0068] The bath of the passivation station into which the workpiece to be passivated is placed first is most contaminated, and the bath of the passivation station into which the workpiece is placed last is least contaminated. This further improves the surface quality and cleanliness of the passivated workpiece.

[0069] To process the passivating agent, the passivating agent can be partially conveyed in a cascade from the passivating station located further down the treatment sequence to the passivating station located further up the treatment sequence.

[0070] The passivating agent from the first passivation station in the treatment sequence can be partially discarded.

[0071] In the multi-stage passivation process, the treatment temperature and / or the acid concentration in the respective passivating agent can vary between the various passivation stations. It is particularly advantageous if the acid concentration in the passivating agent is lowest in the last passivation station in the treatment sequence, so that less acid is carried over from this passivation station, for example, to a subsequent rinsing station.

[0072] The treatment temperature in a passivation station further upstream in the treatment sequence may be at least 10% higher and / or at most 20% higher than the treatment temperature in a passivation station further downstream in the treatment sequence (whereby the percentages refer to the absolute temperature of the respective passivation agent).

[0073] Furthermore, it is advantageous if the concentration of the acid in the passivating agent in the passivating station further up in the treatment sequence is at least 50% higher than the concentration of the acid in the passivating agent in the passivating station further down in the treatment sequence.

[0074] Furthermore, it can be provided that the concentration of the acid in the passivating agent in the passivating station further upstream in the treatment sequence is at most 80% higher than the concentration of the acid in the passivating agent in the passivating station further downstream in the treatment sequence.

[0075] If a workpiece to be passivated is treated consecutively in two separate treatment chambers, it can be provided, for example, that the workpiece is immersed in the passivating agent in the first passivation station and that the workpiece is sprayed with the passivating agent and / or poured with the passivating agent in the subsequent passivation station. The present invention is further based on the object of creating a device for passivating workpieces that enables complete and sufficient passivation of the surface of a workpiece to be passivated, even if the workpiece has a complex geometry and / or narrow cavities.

[0076] This object is achieved according to the invention in a device for passivating workpieces having the features of the preamble of claim 14 in that the device comprises a pressure changing device for cyclically changing the pressure in the treatment chamber while passivating agent is present in the treatment chamber.

[0077] Particular embodiments of such a device according to the invention for passivating workpieces have already been explained above in connection with particular embodiments of the method according to the invention for passivating a surface of a workpiece.

[0078] In a particular embodiment of the device according to the invention, it is provided that the device comprises at least two treatment chambers, wherein a workpiece can be treated with a passivating agent in the first treatment chamber and a workpiece can be rinsed with a rinsing liquid in the second treatment chamber.

[0079] The device according to the invention for passivating workpieces is particularly suitable for carrying out the method according to the invention for passivating a surface of a workpiece.

[0080] The method according to the invention for passivating a surface of a workpiece is preferably carried out using the device according to the invention for passivating workpieces. For many applications of a workpiece to be passivated, in particular for applications as a medical technology product, the workpieces passivated using the method according to the invention or the workpieces passivated using the device according to the invention must not have any residues of the passivating agent on their surfaces after the passivation process. Particularly when a passivated workpiece has a cavity, a suitable process must be used to ensure that the passivating agent is sufficiently flushed out of such a cavity.

[0081] The passivation process can therefore be followed by a rinsing process.

[0082] The rinsing process can be carried out in the same treatment chamber as the passivation process.

[0083] Alternatively, the rinsing process may be carried out in another treatment chamber or in an open treatment tank.

[0084] For example, deionized water is used as a rinsing liquid.

[0085] The workpiece to be rinsed is preferably completely or partially immersed in the rinsing liquid.

[0086] If the rinsing process is carried out in a closed treatment chamber, the pressure in the treatment chamber can also be changed cyclically, as described in connection with the passivation process.

[0087] The cyclical pressure changes then force the rinsing fluid into the narrow passages and capillaries of the passivated workpiece, simultaneously flushing out the passivating agent. The rinsing effect can be enhanced by applying ultrasound to the rinsing fluid bath and / or the workpiece in the treatment chamber or open treatment tank, for example, using an ultrasonic transducer.

[0088] Further features and advantages of the invention are the subject of the following description and the drawings of exemplary embodiments.

[0089] The drawings show:

[0090] Fig. 1 is a schematic representation of a first embodiment of an apparatus for passivating workpieces, which apparatus comprises a treatment chamber for receiving at least one workpiece and a bath of a passivating agent, as well as a pressure changing device for cyclically changing the pressure in the treatment chamber while passivating agent is in the treatment chamber, wherein the pressure changing device comprises a separator and a vacuum pump as a vacuum generator;

[0091] Fig. 2 is a graph showing the pressure variation in the treatment chamber as a function of treatment time during a passivation process;

[0092] Fig. 3 is a schematic representation of a second embodiment of a device for passivating workpieces, in which the pressure-changing device comprises two vacuum reservoirs that are alternately brought into fluid communication with the treatment chamber; Fig. 4 is a schematic representation of a third embodiment of a device for passivating workpieces, in which the pressure-changing device comprises a cylinder with a displaceable piston and optional cooling, a separator, and optionally a vacuum pump as a vacuum generator;

[0093] Fig. 5 is a schematic section through a fourth embodiment of a device for passivating workpieces, comprising a plurality of treatment stations containing different passivating agents, wherein a workpiece to be passivated is introduced successively into a plurality of these treatment stations;

[0094] Fig. 6 is a schematic representation of a fifth embodiment of a device for passivating workpieces, in which the device comprises two treatment chambers, wherein a workpiece can be treated with a passivating agent in a first treatment chamber and a workpiece can be rinsed with a rinsing liquid in a second treatment chamber, and wherein the pressure changing device comprises a separator and a vacuum pump as a vacuum generator;

[0095] Fig. 7 is a schematic section through a treatment chamber for a device for passivating workpieces, wherein the treatment chamber comprises a tank that can be closed by means of a lid and the tank is provided with a suction channel at its upper edge;

[0096] Fig. 8 is an enlarged view of area I from Fig. 7; and

[0097] Fig. 9 shows a schematic longitudinal section through a test specimen for validating a method for passivating a surface of a workpiece, which is carried out, for example, with one of the devices for passivating workpieces shown in Figs. 1 to 8.

[0098] Identical or functionally equivalent elements are designated by the same reference numerals in all figures.

[0099] A device for passivating workpieces 102, shown schematically in Fig. 1 and designated as a whole by 100, comprises a treatment chamber 104 for receiving at least one workpiece 102 in an interior space 106 of the treatment chamber 104, which is surrounded by a wall 108 of the treatment chamber.

[0100] In order to be able to introduce a workpiece 102 into the interior 106 of the treatment chamber 104, it is preferably provided that the treatment chamber 104 comprises a tank 110 (see Fig. 8) which can be filled with a liquid 112, for example a passivating agent 114, up to a maximum level 118 and can be closed by means of a lid 116.

[0101] In order to be able to fill the treatment chamber 104 with treatment agent, in particular passivating agent, the interior 106 of the treatment chamber 104 is connected to a storage container 122 via a supply line 120.

[0102] The supply line 120 can be opened or closed by means of a valve 124 arranged therein.

[0103] The supply line 120 opens into a clean area 126 of the storage tank 122, which is filled with a treatment agent, in particular a passivating agent, prepared for a treatment process in the treatment chamber 104. The clean area 126 is separated from a contaminated area 130 of the storage tank 122 by a partition wall 128.

[0104] At the upper edge of the partition wall 128 there is an overflow 132 through which treatment agent can flow from the clean area 126 into the dirty area 130.

[0105] The treatment agent located in the dirty area 130 is prepared for use in the treatment chamber 104 by being transferred from the dirty area 130 of the storage tank 122 to the clean area 126 of the storage tank 122 via a filtration line 134.

[0106] A filtration pump 136, a filter 138 and a flow restrictor 140 are arranged in the filtration line 134.

[0107] Emptying of the treatment agent, in particular the passivating agent, from the interior 106 of the treatment chamber 104 is possible by means of an emptying line 148, which is preferably connected to a lowest point of the interior 106 of the treatment chamber 104 and opens into the dirt area 130 of the storage container 122.

[0108] The drain line 148 can be opened and closed by means of a valve 150 arranged therein.

[0109] To monitor the treatment process in the treatment chamber 104, the treatment chamber 104 is provided with various sensors, in particular with a pressure sensor 152, a temperature sensor 154, a lower level sensor 156 and / or an upper level sensor 158.

[0110] The lower level sensor 156 determines whether the interior 106 of the treatment chamber 104 is completely empty of treatment agent. The upper level sensor 158 determines whether the interior 106 of the treatment chamber 104 is completely filled with liquid treatment agent, in particular passivating agent.

[0111] In order to be able to cyclically change the pressure in the treatment chamber 104, the device 100 for passivating workpieces 102 further comprises a pressure changing device 160, which in the illustrated embodiment comprises an evacuation valve 296, a separator 166 and a vacuum generator 168.

[0112] The evacuation valve 296 is connected to a pressure change outlet 174 of the treatment chamber 104 via a pressure change line 172.

[0113] Furthermore, the evacuation valve 296 is connected to an inlet 180 of the separator 166 via an evacuation line 178.

[0114] Through the inlet 180, gas originating from the interior 106 of the treatment chamber 104, which is loaded with a vapor of the treatment agent and / or with droplets of the treatment agent, in particular the passivating agent, passes into the interior 182 of the separator 166, which can be designed, for example, as a cyclone in order to separate droplets contained in the incoming gas stream from the gas stream by centrifugal action.

[0115] Furthermore, the separator 166 can contain a condensation device 184, which comprises, for example, impact plates and / or a support fabric and / or a cooled heat exchanger, on which vapor of the treatment agent, in particular the passivating agent, can condense and thus be separated from the gas stream flowing through the separator 166. The gas stream, freed of droplets and / or vapor of the treatment agent by the separator 166, passes through a suction line 186 to a suction-side inlet 188 of the vacuum generator 168.

[0116] The vacuum generator 168 can be designed, for example, as a vacuum pump 190, preferably as a displacement vacuum pump.

[0117] The gas flow then enters a pressure line 194 via a pressure-side outlet 192 of the vacuum generator 168 and from there, for example, into the environment of the device 100.

[0118] The pressure change device 160 further includes a vent valve 298.

[0119] The vent valve 298 is connected to the pressure change outlet 174 of the treatment chamber 104 via the (branching) pressure change line 172.

[0120] Furthermore, the ventilation valve 298 is connected to a ventilation line 198 through which ambient air can be supplied to the ventilation valve 298.

[0121] The pressure change device 160 can be switched from an evacuation state, in which the evacuation valve 296 connected to the evacuation line 178 is open and the ventilation valve 298 connected to the ventilation line 198 is closed, to a ventilation state, in which the ventilation valve 298 connected to the ventilation line 198 is open and the evacuation valve 296 connected to the evacuation line 178 is closed. Furthermore, the pressure change device 160 can be switched to a holding state, in which both the evacuation valve 296 and the ventilation valve 298 are closed, so that the pressure in the treatment chamber 104 is kept substantially constant.

[0122] The switching of the evacuation valve 296 and / or the venting valve 298 between the open and the closed state can in principle be carried out in any manner, for example mechanically, electromechanically, pneumatically, hydraulically or electromagnetically.

[0123] All switchable valves of the device 100 and the sensors, for example the pressure sensor 152, the temperature sensor 154, the lower level sensor 156 and the upper level sensor 158, are connected by means of signal and control lines (not shown) to a control device (not shown) of the device 100 for passivating workpieces 102, so that the control device can receive and further process signals from the sensors and can switch the switchable valves from one state to the other state.

[0124] The control device of the device 100 is preferably programmable, so that a control program for controlling a method for passivating workpieces 102 can be carried out by means of the control device and the sensors and actuators controlled by it.

[0125] Condensate accumulated in the separator 166 during operation of the device 100 can be removed from the interior 182 of the separator 166 by means of a condensate lock 200.

[0126] The condensate lock 200 comprises a first lock valve 204 connected to a condensate outlet 202 of the separator 166, a second lock valve 206 arranged downstream of the first lock valve 204, and a lock chamber 208 arranged between the first lock valve 204 and the second lock valve 206.

[0127] The condensate separated in the separator 166 enters the lock chamber 208 of the condensate lock 200 by opening the first lock valve 204 while simultaneously closing the second lock valve 206.

[0128] After filling the lock chamber 208 with condensate, the first lock valve 204 is closed and the second lock valve 206 is opened.

[0129] The second lock valve 206 is connected to the dirt area 130 of the storage tank 122 via a condensate line 210, so that the condensate separated in the separator 166 reaches the storage tank 122 via the condensate lock 200.

[0130] By means of the device 100 for passivating workpieces described above, a method for passivating workpieces is carried out as follows:

[0131] Before passivating a workpiece 102, all surfaces of the workpiece 102 must be freed of all filmy, particulate, and other contaminants, as well as cleaning agent residues. Therefore, prior to the passivation process, the workpiece 102 is thoroughly cleaned, followed by rinsing of all surfaces of the workpiece 102.

[0132] The treatment chamber 104 of the device 100 is provided with a closure device, for example with a lid 116.

[0133] This closure device enables an airtight closure of the treatment chamber 104. When the closure device is open, in particular when the cover 116 is lifted, the workpiece 102 to be treated is introduced into the interior 106 of the treatment chamber 104.

[0134] The workpiece 102 can be held on a workpiece holder 212.

[0135] After the workpiece 102 has been introduced into the interior 106 of the treatment chamber 104, the treatment chamber 104 is hermetically sealed by means of the closure device.

[0136] If no bath of the treatment agent, in particular the passivating agent, is yet present in the interior 106 of the treatment chamber 104, a desired amount of treatment agent is drawn from the storage container 122 through the supply line 120. For this purpose, the valve 124 in the supply line 120 is open.

[0137] The pressure change device 160 is initially in the evacuation state, in which the evacuation valve 296 is open and the vent valve 298 is closed. The vacuum generator 168, in particular the vacuum pump 190, is in operation and draws gas, which may be loaded with vapor of the treatment agent and droplets of the treatment agent, through the pressure change line 172, the evacuation line 178, the separator 166, and the suction line 186 to the suction-side inlet 188 of the vacuum generator 168.

[0138] In this process, droplets of the treatment agent entrained with the extracted gas are separated in the separator 166. Furthermore, the vapor of the treatment agent entrained with the gas condenses in the condensing device 184. The treatment agent collected in the lower region of the separator 166 can be fed to the contaminated area 130 of the storage tank 122 via the condensate lock 200 and the condensate line 210 when a predetermined fill level is reached or after a predetermined operating time interval.

[0139] The separator 166 can also serve as a vacuum storage device.

[0140] In this way, the pressure in the interior 106 of the treatment chamber 104 is reduced from atmospheric pressure (approximately 1.0 bar) to a lower pressure value p u reduced. After reaching the lower pressure value p u the pressure in the treatment chamber 104 is changed cyclically during a passivation period, i.e. from the lower pressure value pu increased to an upper pressure value p0 and then back to the lower pressure value p u lowered (see Fig. 2).

[0141] This process can be repeated periodically.

[0142] Between the pressure increase phases and pressure reduction phases, the pressure in the treatment chamber 104 can be maintained at the lower pressure value p u or remain at the upper pressure value p0 by switching the pressure changing device 160 to the holding state in which the evacuation valve 296 and the vent valve 298 are closed.

[0143] To increase the pressure in the treatment chamber 104, the pressure change device 160 is switched by the control device to the ventilation state, in which the evacuation valve 296 is closed and the ventilation valve 298 is opened, so that ambient air passes through the ventilation line 198 and the pressure change line 172 into the interior 106 of the treatment chamber 104. The lower pressure value p u is preferably at least 20 mbar and / or preferably at most 500 mbar, in particular at most 300 mbar.

[0144] The upper pressure value p0 is preferably at least 700 mbar and / or preferably at most 1 bar.

[0145] The cycle duration ti of a complete printing cycle is preferably at least 1 second, in particular at least 3 seconds, particularly preferably at least 5 seconds.

[0146] Furthermore, the cycle duration ti of a complete printing cycle is preferably at most 30 seconds, particularly preferably at most 10 seconds.

[0147] The workpiece 102 is arranged in the interior 106 of the treatment chamber 104 such that it is at least partially or completely immersed in a bath of the treatment agent, in particular the passivating agent.

[0148] If the workpiece 102 comprises narrow tubes, so-called capillary tubes, it is advantageous if these capillary tubes are aligned substantially vertically, with one end of each tube extending into the passivating agent and the opposite end of the tube extending into the gas-filled region of the interior 106 of the treatment chamber 104. The hydrostatic pressure then draws the passivating agent into the capillary tubes.

[0149] This process reliably exchanges the fluid that is present on the surface of the workpiece 102 or in bores or capillaries of the workpiece 102 due to previous processes.

[0150] This ensures that the passivating agent can completely wet all surfaces of the workpiece 102 during the passivation process, so that a passivation layer forms on all surfaces of the component 102. The passivation process, which includes numerous pressure change cycles, is carried out during a passivation time of preferably at least 1 minute, in particular at least 5 minutes, and particularly preferably at least 10 minutes.

[0151] Furthermore, the passivation process is preferably carried out during a passivation time of at most 60 minutes, in particular of at most 30 minutes, particularly preferably of at most 20 minutes.

[0152] The temperature of the passivating agent during the passivation process is preferably at least 20 °C, in particular at least 30 °C, particularly preferably at least 50 °C.

[0153] Furthermore, the temperature of the passivating agent during the passivation process is preferably at most 90 °C, in particular at most 70 °C, particularly preferably at most 65 °C.

[0154] To carry out the passivation process, a passivating agent is used as a treatment agent.

[0155] The passivating agent preferably has the following chemical composition:

[0156] The passivating agent is based on deionized water with an electrical conductivity of maximum 10 pS / cm.

[0157] The passivating agent further contains phosphoric acid in a concentration of 1.5% to 3% by volume, nitric acid in a concentration of 0.1% to 0.5% by volume, and nonionic surfactants in a concentration of 0.05% to 0.5% by volume. Alternatively, an aqueous solution of nitric acid can be used as the passivating agent, for example, which contains nitric acid in a proportion of at least 20% by volume and at most 55% by volume, in particular at most 45% by volume, and particularly preferably at most 25% by volume.

[0158] Furthermore, an aqueous solution of citric acid can be used as an alternative passivating agent, wherein the proportion of citric acid is preferably at least 4% by weight and / or preferably at most 10% by weight.

[0159] The pH value of the passivating agent is preferably at least 1.8 and / or preferably at most 2.2.

[0160] Due to the cyclic pressure changes in the treatment chamber 104, cavitation bubbles are generated directly on the surfaces of the workpiece 102 or of the multiple workpieces 102. Some of these cavitation bubbles are stable and change their volume during the pressure changes; the volume of the cavitation bubbles decreases with increasing pressure and increases with decreasing pressure.

[0161] These volume changes generate microcurrents in the bath of the passivating agent and in particular in cavities of the workpiece 102 to be passivated.

[0162] In a low pressure phase, the stable cavitation bubbles in the capillaries of the workpiece 102 expand, causing fluid to be expelled from the capillaries.

[0163] In a subsequent phase with higher pressure, the stable cavitation bubbles contract, sucking fluid into the capillaries. Another portion of the cavitation bubbles is not stable, but rather forms transient cavitation bubbles. These transient cavitation bubbles implode when the pressure in the treatment chamber 104 increases, resulting in very high flow velocities at the surface of the workpiece 102.

[0164] The microcurrents in the bath of passivating agent cause a very effective exchange of fluid on the surfaces of the workpiece 102, especially on the surfaces of bores and / or capillaries of the workpiece 102.

[0165] A high concentration of oxygen on the surface of the workpiece 102 to be passivated promotes the formation of oxides and thus the formation of a passivation layer.

[0166] In a preferred embodiment of the passivation process, the oxygen concentration in the passivating agent within the treatment chamber 104 is therefore detected by at least one measuring sensor.

[0167] If the oxygen concentration in the passivating agent falls below a lower limit, the oxygen concentration is increased by supplying air into the lower region of the treatment chamber 104. To enable such a supply of air into the passivating agent, the treatment chamber 104 can be provided with at least one bead nozzle.

[0168] The limit value of the oxygen concentration below which oxygen is supplied to the passivating agent is preferably at least 5 mg / l and / or preferably at most 8 mg / l.

[0169] In order to promote the generation of microcurrents directly on the surface of a workpiece 102 to be passivated in combination with the cyclic pressure changes and thus to achieve an even stronger exchange of fluids, it can be provided that the device 100 is equipped with at least one ultrasonic oscillator 214, by means of which the bath of the treatment agent in the interior 106 of the treatment chamber 104 and / or the workpiece 102 can be subjected to ultrasound.

[0170] The ultrasonic frequency is preferably at least 20 kHz, particularly preferably at least 25 kHz.

[0171] Furthermore, the ultrasonic frequency is preferably at most 120 kHz, particularly preferably at most 80 kHz.

[0172] The ultrasonic power coupled into the interior 106 of the treatment chamber 104 by means of the ultrasonic oscillator 214 or by means of several ultrasonic oscillators 214 is preferably at least 5 watts per liter of passivating agent in the treatment chamber 104, particularly preferably at least 8 watts per liter of passivating agent in the treatment chamber 104.

[0173] Furthermore, the ultrasonic power coupled into the treatment chamber 104 is preferably at most 20 watts per liter of passivating agent in the treatment chamber 104, particularly preferably at most 15 watts per liter of passivating agent in the treatment chamber 104.

[0174] By amplitude modulation of the ultrasonic vibrations and / or by modulating the ultrasonic frequency (so-called "sweep" function), the effect of the exposure to the bath of passivating agent and / or the workpiece 102 can be further enhanced and the effect of the ultrasonic exposure can be evenly distributed over all surfaces of the workpiece 102 to be passivated.

[0175] In order to uniformly and completely passivate all areas of a workpiece 102 held on the workpiece holder 212, or all workpieces 102 of a group of workpieces 102 held simultaneously on the workpiece holder 212, it is advantageous if the device 100 comprises a rotating device by means of which the workpiece holder 212 and thus the workpiece 102 or the workpieces 102 can be rotated about a rotation axis during the passivation treatment.

[0176] The axis of rotation is preferably aligned essentially horizontally.

[0177] This rotational movement prevents air bubbles from accumulating in the workpiece 102 or in the workpieces 102 and preventing wetting with the passivating agent.

[0178] Furthermore, with the aid of the rotating device, it is possible to empty cavities of the workpiece 102 or the workpieces 102 if the mouth openings of the cavities are located above the surface of the passivating agent bath in the treatment chamber 104.

[0179] Alternatively or in addition to such a rotating device, the device 100 can also comprise a vertical movement device for the workpiece 102 or for a plurality of workpieces 102. By means of such a vertical movement device, the workpiece 102 or the workpieces 102 can be moved along the direction of gravity relative to the bath of passivating agent. The flow of the passivating agent generated by this relative movement promotes the exchange of the passivating agent on the surfaces of the workpiece 102 to be passivated.

[0180] The filter 138 arranged in the filtration line 134, through which impurities are removed from the passivating agent that has entered the dirty area 130, may comprise a solids filter.

[0181] Furthermore, the filter 138 may also comprise a magnetic retaining device by means of which iron molecules can be removed from the passivating agent. Such a magnetic retaining device preferably comprises at least one permanent magnet.

[0182] Such a magnetic retaining device is advantageously integrated into a housing of the filter 138.

[0183] During the recycling of the passivating agent in the filtration line 134, the concentration of the acid content in the passivating agent can also be monitored and, if necessary, brought into the desired range by adding acid or by adding water.

[0184] Such concentration monitoring can be carried out, for example, by measuring the conductivity of the passivating agent or by using a refractometer.

[0185] For many applications, the workpieces 102 passivated by the device 100 must not have any residue of the passivating agent on their surfaces for further processing. Particularly when a passivated workpiece 102 has a cavity, a suitable process must be used to ensure that the passivating agent is sufficiently rinsed out of such a cavity.

[0186] The passivation process described above can therefore be followed by a rinsing process.

[0187] For example, deionized water is used as a rinsing liquid.

[0188] To perform the rinsing process, the passivating agent is emptied into the storage container 122 via the open valve 150 and the drain line 148. Subsequently, the interior 106 of the treatment chamber 104 is at least partially filled with the rinsing liquid by means of a rinsing liquid supply (not shown in the drawing).

[0189] During the rinsing process, the pressure in the treatment chamber 104 can also be changed cyclically, as described above in connection with the passivation process.

[0190] Due to the cyclic pressure changes, the rinsing liquid is flushed into the constrictions and capillaries of the passivated workpiece 102, whereby the passivating agent is simultaneously flushed out.

[0191] The rinsing effect and thus the removal of the passivating agent from the surfaces of the workpiece 102 can be promoted by subjecting the bath of the rinsing liquid and / or the workpiece 102 in the treatment chamber 104 to ultrasound, for example by the ultrasonic oscillator 214, for example by generating microcurrents close to the surface.

[0192] A second embodiment of a device 100 for passivating workpieces 102, shown schematically in Fig. 3, differs from the first embodiment shown in Fig. 1 in that the pressure changing device 160 of the device 100 comprises a plurality of, in the illustrated embodiment two, vacuum accumulators 224, which are arranged fluidically between the treatment chamber 104 and the vacuum generator 168, in this case in the form of a vacuum pump 190.

[0193] A first vacuum reservoir 224a is connected via a first supply line 226a, in which a first supply valve 228a is arranged, to a pressure change line 172 connected to the treatment chamber 104. Furthermore, the first vacuum reservoir 224a is connected via a first discharge line 230a, in which a first discharge valve 232a is arranged, to an evacuation line 178 leading to the inlet 180 of the separator 166. A suction line 186 leads from the outlet of the separator 166 to the suction-side inlet 188 of the vacuum generator 168.

[0194] A second vacuum reservoir 224b is connected to the pressure change line 172 via a second supply line 226b, in which a second supply valve 228b is arranged.

[0195] Furthermore, the second vacuum reservoir 224b is connected to the evacuation line 178 via a second discharge line 230b, in which a second discharge valve 232b is arranged.

[0196] Each of the vacuum reservoirs 224 can be cooled by means of a heat exchanger 234, through which a coolant or a heat dissipation medium flows during operation of the device 100, in order to condense a vapor of a treatment agent, in particular a passivating agent, from the gas stream entering the respective vacuum reservoir 224.

[0197] Furthermore, in this embodiment, the pressure change device 160 comprises a vent line 198 in which a vent valve 236 is arranged and which opens into the pressure change line 172.

[0198] An adjustable flow restrictor 238 may also be arranged in the vent line 198, preferably downstream of the vent valve 236.

[0199] Furthermore, the device 100 comprises a bypass line 240, which directly connects the evacuation line 178 to the treatment chamber 104. A bypass valve 242 is arranged in the bypass line 240, through which the bypass line 240 can be opened or closed.

[0200] Through the bypass line 240, the interior 106 of the treatment chamber 104 can be directly pressurized by means of the vacuum generator 168, in the illustrated case by means of the vacuum pump 190, down to the lower pressure value p u be evacuated, for example at the beginning of the passivation process or at the beginning of a rinsing process, bypassing the vacuum reservoir 224.

[0201] In this embodiment, the vacuum reservoirs 224 are used to reduce the pressure in the treatment chamber 104 during the pressure reduction phases of the pressure swing cycles of the passivation process and / or the rinsing process.

[0202] For this purpose, during the passivation process or rinsing process, one of the vacuum reservoirs 224, for example the second vacuum reservoir 224b, is evacuated by means of the vacuum generator 168, while the other vacuum reservoir 224, for example the first vacuum reservoir 224a, is in fluid communication with the interior 106 of the treatment chamber 104 during one or more pressure reduction phases, so that a gas stream (possibly loaded with droplets of the treatment agent and / or with a vapor of the treatment agent) flows from the interior 106 of the treatment chamber 104 into the interior of the vacuum reservoir 224a.

[0203] During this phase, the first supply valve 228a is open and the first discharge valve 232a is closed.

[0204] At the same time, the second supply valve 228b is closed and the second discharge valve 232b is opened, so that the gas is sucked out of the second vacuum reservoir 224b through the evacuation line 178 and the interior of the second vacuum reservoir 224b is evacuated to a pressure which is preferably below the lower pressure value p u lies.

[0205] Due to the cooling by means of the heat exchanger 234, a vapor of the treatment agent, in particular the passivating agent, carried therein condenses out of the gas stream entering the first vacuum reservoir 224a in a pressure reduction phase.

[0206] If the pressure in the interior 106 of the treatment chamber 104 due to the fluid connection with the first vacuum reservoir 224a drops to the lower pressure value p uhas been reduced, the first supply valve 228a is closed and the vent valve 236 in the vent line 198 is opened so that ambient air passes through the vent line 198 and the pressure change line 172 into the interior 106 of the treatment chamber 104.

[0207] When the pressure in the interior 106 of the treatment chamber 104 has risen to the upper pressure value p0, the pressure changing device 160 is switched back to the evacuation state in which the vent valve 236 is closed and the first supply valve 228a is open.

[0208] In this way, several pressure reduction phases can be carried out by means of the first vacuum accumulator 224a until the pressure in the vacuum accumulator 224a drops to the lower pressure value p uor has risen to a higher pressure value, so that the interior 106 of the treatment chamber 104 can no longer be evacuated through fluid communication with the first vacuum reservoir 224a. Starting with the next pressure reduction phase, the roles of the two vacuum reservoirs 224a and 224b are then reversed. For this purpose, the second discharge valve 232b is closed and the second supply valve 228b is opened, allowing a gas flow from the interior 106 of the treatment chamber 104 into the second vacuum reservoir 224b.

[0209] At the same time, the first supply valve 228a is closed and the first discharge valve 232a is opened, so that the gas accumulated in the first vacuum reservoir 224b and the condensate accumulated therein can be discharged through the first discharge line 230a and the evacuation line 178 to the separator 166 and to the vacuum generator 168.

[0210] Otherwise, the second embodiment of a device 100 for workpieces 102 shown in Fig. 3 corresponds in terms of structure, function and method of manufacture to the first embodiment shown in Fig. 1, to the above description of which reference is made in this respect.

[0211] A third embodiment of a device 100 for passivating workpieces 102 shown in Fig. 4 differs from the first embodiment shown in Fig. 1 in that the pressure changing device 160 in this embodiment additionally comprises a pressure reducing device 242, by means of which the pressure in the interior 106 of the treatment chamber 104 can be reduced instead of the vacuum generator 168 or in addition to the vacuum generator 168.

[0212] In the embodiment shown in Fig. 4, the pressure reduction device 242 comprises a working cylinder 244 in which a piston 246 is arranged displaceably along a displacement direction 248.

[0213] A gas connection 250 of the working cylinder 244 opens into a receiving chamber 252 of the working cylinder 244, the volume of which can be changed by displacing the piston 246. The gas connection 250 is connected to the pressure change line 172 via a supply line 254, in which a supply valve 256 is arranged.

[0214] A first check valve 258 is arranged in the supply line 254, which prevents fluid from flowing back from the working cylinder 244 into the interior 106 of the treatment chamber 104.

[0215] Furthermore, the gas connection 250 of the working cylinder 244 is connected via a discharge line 260 to the storage container 122, preferably to the dirt area 130 of the storage container 122.

[0216] A second check valve 262 is arranged in the discharge line 260, which prevents fluid from flowing back from the storage tank 122 into the working cylinder 244.

[0217] The piston 246 in the working cylinder 244 can be retracted up to a partition 264 in order to increase the volume of the receiving space 252 in the working cylinder 244.

[0218] On the side of the partition wall 264 facing away from the receiving space 252, the piston 246 is provided with a collar 266 which can be acted upon by a gaseous or liquid actuating fluid from its two different sides, so that the piston 246 can be displaced pneumatically or hydraulically.

[0219] The part of the working cylinder 244 containing the receiving space 252 can preferably be cooled by means of a heat exchanger 268, which can be supplied with a coolant through a coolant line 270. Cooling by means of the heat exchanger 268 allows a vapor of the treatment agent, in particular the passivating agent, which is carried along by the gas passing from the interior 106 of the treatment chamber 104 into the receiving space 252 to condense.

[0220] During a pressure reduction phase of the pressure swing cycles in the treatment chamber 104, the receiving space 252 in the working cylinder 244 is enlarged by moving the piston 246 (upward in Fig. 5), thereby creating a negative pressure. The supply valve 256 is opened, so that the negative pressure in the working cylinder 244 sucks gas out of the interior 106 of the treatment chamber 104. During this pressure reduction phase, the evacuation valve 296 and the venting valve 298 are closed.

[0221] In a subsequent pressure increase phase, the ventilation valve 298 connected to the ventilation line 198 is open, while the evacuation valve 296 and the supply valve 256 are closed.

[0222] Thus, in this pressure increase phase, the interior 106 of the treatment chamber 104 is ventilated through the ventilation line 198 and the pressure change line 172.

[0223] The piston 246 is displaced along the displacement direction 248 (downward in Fig. 5) in order to reduce the volume of the receiving space 252.

[0224] The gas and condensate accumulated in the receiving space 252 are transferred through the discharge line 260 into the storage tank 122, preferably into its dirt area 130.

[0225] The vacuum generator 168, which in this case is designed, for example, as a vacuum pump 190, and the separator 166 are optional in this embodiment of a device 100 for passivating workpieces 102 and can serve, in particular, to reduce the interior 106 of the treatment chamber 104 from atmospheric pressure down to the lower pressure value p u to evacuate.

[0226] Otherwise, the third embodiment of a device 100 for passivating workpieces 102 shown in Fig. 4 corresponds in terms of structure, function and method of manufacture to the first embodiment shown in Fig. 1, to the above description of which reference is made in this respect.

[0227] In a fourth embodiment of a device 100 for passivating workpieces 102, shown schematically in Fig. 5, the device 100 is designed as a series immersion system.

[0228] This system has a plurality of treatment stations, for example a cleaning station 272, an intermediate rinsing station 274, a first passivation station 276, a second passivation station 278, a first rinsing station 280, a second rinsing station 282, a third rinsing station 284 and a drying station 286.

[0229] The stations 272 to 286 are preferably arranged substantially linearly one behind the other along a transport direction 288.

[0230] Each of the treatment stations is filled with a bath 290 of a treatment agent, such as a cleaning fluid, a rinsing fluid, or a passivating agent, corresponding to its respective function. The workpieces 102 can be transported from treatment station to treatment station by means of a transport device 292, immersed in the respective bath 290 of a treatment agent, and removed from the bath 290 after completion of the treatment in the respective bath 290.

[0231] The transport device 292 may be provided with a rotating device 294 for rotating a workpiece 102 arranged thereon.

[0232] Likewise, one or more of the treatment stations can each be provided with a workpiece holder 212 which can be rotated by means of a rotating device (not shown) - preferably about a horizontal axis of rotation.

[0233] At least the passivation stations 276 and 278 are provided with a cover (not shown in Fig. 6) for closing the interior 106 of the passivation station 276 or 278, which is each designed as a treatment chamber 104, in order to be able to carry out in these passivation stations 276, 278 the passivation process described above in connection with the first embodiment of a device 100 for passivating workpieces 102 shown in Fig. 1, in which the pressure in the interior 106 of the respective treatment chamber 104 is changed cyclically.

[0234] By providing several passivation stations 276, 278 in the passivation system, the throughput for passivating workpieces 102 can be increased.

[0235] It can be provided that the entire passivation process is carried out in only one of the passivation stations 276 and 278, and the workpieces 102 to be passivated are alternately introduced into one of these passivation stations 276, 278. Alternatively, it can also be provided that each workpiece 102 to be passivated is introduced successively into several passivation stations 276, 278, so that several passivation processes are carried out on each workpiece 102 in different passivation stations 276, 278.

[0236] In this process, the bath 290 of the passivation station 276, into which the workpiece 102 is introduced first, is most heavily contaminated, and the bath 290 of the passivation station 278, into which the workpiece 102 is introduced last, is least contaminated. This further improves the surface quality and purity of the passivated workpiece 102.

[0237] To process the passivating agent, the passivating agent can be partially conveyed in a cascade from the passivating station 278 located further back in the treatment sequence to the passivating station 276 located further up in the treatment sequence.

[0238] The passivating agent from the passivation station 276, which is first in the treatment sequence, is partially discarded.

[0239] In the multi-stage passivation process described above, the treatment temperature and / or the concentration of the acid in the respective passivating agent may be different in the various passivation stations 276, 278.

[0240] It is particularly advantageous if the concentration of acid in the passivation agent is lowest in the passivation station 278 located last in the treatment sequence, so that less acid is carried over into the subsequent rinsing station 280. For example, it can be provided that the treatment temperature in the passivation station 276 located further upstream in the treatment sequence is at least 10% higher and / or at most 20% higher than the treatment temperature in the passivation station 278 located further downstream in the treatment sequence (the percentages refer to the absolute temperature of the respective passivation agent).

[0241] Furthermore, it is advantageous if the concentration of the acid in the passivating agent in the passivation station 276 located further upstream in the treatment sequence is at least 50% higher than the concentration of the acid in the passivating agent in the passivation station 278 located further downstream in the treatment sequence and / or if the concentration of the acid in the passivating agent in the passivation station 276 located further upstream in the treatment sequence is at most 80% higher than the concentration of the acid in the passivating agent in the passivation station 278 located further downstream in the treatment sequence.

[0242] As an alternative to being designed as a series immersion system, a system for passivating workpieces 102 can also be designed as a single-chamber system with several storage containers for the various treatment agents, such as rinsing agents and passivating agents with different concentrations of acids.

[0243] Evaporation losses from the baths 290 in the passivation stations 276 and 278 can be compensated for by supplying rinsing liquid from one of the subsequent rinsing stations 280, 282, or 284. These rinsing liquids are already enriched with a low concentration of passivating agent due to the carryover of passivating agent from one of the passivation stations 276 and / or 278 and are already tempered to the desired treatment temperature. By supplying rinsing liquid from one of the rinsing stations 280, 282, or 284 to the bath 290 of passivating agent in one of the passivation stations 276 or 278, energy savings and resources such as water and acid for the passivating agent are achieved.

[0244] The process stations of the device 100 according to the embodiment shown in Fig. 5 are each provided with a closed fluid circuit, which in particular comprises a pump for flow through the respective treatment chamber in order to avoid deposits.

[0245] Otherwise, the fourth embodiment of a device 100 for passivating workpieces 102 shown in Fig. 5 corresponds in terms of structure, function and method of manufacture to one of the embodiments shown in Figs. 1, 3 or 4, to the above description of which reference is made in this respect.

[0246] A fifth embodiment of a device 100 for passivating workpieces 102, shown schematically in Fig. 6, differs from the embodiments shown in Figs. 1, 3 and 4 in that the device 100 comprises two treatment chambers 104, wherein the pressure changing device 160 for both treatment chambers 104 comprises only a single vacuum generator 168, for example in the form of a vacuum pump 190, and a separator 166.

[0247] Each of the treatment chambers 104 is connected via an evacuation valve 296 to an evacuation line 178 leading to the separator 166 and via a ventilation valve 298 to a ventilation line 198. In the treatment chambers 104, a passivation process or a rinsing process can be carried out on a workpiece 102, or a passivation process is carried out in one treatment chamber 104 and a rinsing process in the other treatment chamber 104.

[0248] In all these cases, a cyclic pressure change process is carried out in each of the two treatment chambers 104, wherein the pressure reduction phases and the pressure increase phases of these cyclic pressure change processes are phase-shifted relative to one another such that the pressure in one of the treatment chambers 104 is reduced by evacuation by means of the vacuum generator 168, while the pressure in the other treatment chamber 104 is increased by ventilation via the respective ventilation valve 298.

[0249] The treatment chambers 104 are thus alternately brought into fluid communication with the separator 166 and the vacuum generator 168 by staggered opening and closing of their respective evacuation valves 296. The vacuum generator 168 therefore only needs to evacuate one of the treatment chambers 104 at a time, allowing a cyclic pressure change in both treatment chambers 104 using only a single vacuum generator 168.

[0250] Otherwise, the fifth embodiment of a device 100 for passivating workpieces 102 shown in Fig. 6 corresponds in terms of structure, function and method of manufacture to the first embodiment shown in Fig. 1, to the above description of which reference is made in this respect.

[0251] Figs. 7 and 8 schematically illustrate a particular embodiment of a treatment chamber 104, which can be used in any of the above-described embodiments of a device 100 for passivating workpieces 102. The treatment chamber 104 comprises a tank 110 that can be filled with a bath 290 of a treatment agent, in particular a passivating agent.

[0252] At its upper edge, the tank 110 is provided with a suction channel 300, which is connected to the respective pressure change line 172 of the respective device 100.

[0253] The suction channel 300 can, for example, have a rectangular, preferably a substantially square, cross-section.

[0254] The interior of the suction channel 300 is connected to the interior 106 of the treatment chamber 104 via a passage opening 302.

[0255] The passage opening 302 can, for example, be formed as a gap extending in a longitudinal direction.

[0256] The passage opening 302 can be closed by means of a cover 304.

[0257] The cover 304 can be pivotally mounted on a wall 306 of the suction channel 300 by means of a hinge.

[0258] The treatment chamber 104 may further comprise a guide 308 on which the lid 116 of the treatment chamber 104 is guided displaceably - preferably in the horizontal direction.

[0259] In this case, it can be provided that a lower edge region 310 of a substantially vertically oriented side wall 312 of the cover 116 is received in an interior space 314 of the guide 308. The guide 308 can, for example, have a substantially U-shaped cross-section.

[0260] In order to perform a validation of the passivation process carried out with any of the above-described embodiments of an apparatus 100 for passivating workpieces 102, a test specimen 316 shown in Fig. 9 in a schematic longitudinal section can be used.

[0261] For this purpose, the test specimen 316 is attached to a location on a workpiece carrier 102 to be passivated, which is representative for the effectiveness test.

[0262] The geometry of the test specimen 316 is selected such that it corresponds to the workpiece 102 that is most difficult to passivate of the workpiece variants of a production line to be passivated by means of the respective device 100 for passivating workpieces 102.

[0263] For this purpose, the test specimen 316 is preferably provided with at least one rest space 318 and with at least one, preferably several, capillaries 320.

[0264] A measuring strip 322 is arranged in at least one of the cavities 318 and / or in at least one of the capillaries 320.

[0265] The measuring strip 322 is provided with a sensitive surface 324 (so-called "smart surface") that reacts to the passivating agent.

[0266] The sensitive surface 324 of the measuring strip 322 changes upon contact with the passivating agent. For example, the measuring strip 322 can be a pH measuring strip, which changes color upon contact with the passivating agent.

[0267] Alternatively or additionally, the measuring strip may also comprise a stainless steel material, for example, the stainless steel material with the workpiece number 1.4401. The passivation effect exerted by the passivating agent on the stainless steel material can be measured using one of the methods described in ASTM A 967 or, alternatively, by XPS (X-ray photoelectron spectroscopy) measurement of the chromium and iron content on the surface of the stainless steel material.

[0268] The effectiveness of the passivation process is tested after completion of the passivation treatment. For this purpose, the measuring strip 322 is removed from the test specimen 316, and the change in the sensitive surface 324 of the measuring strip 322 is examined using a suitable test method.

[0269] In order to be able to insert the measuring strip 322 in a simple manner into a cavity 318 or into a capillary 320 of the test body 316, the test body 316 is preferably formed in several parts, wherein at least two parts of the test body 316 abut one another along a contact surface 326 when the test body 316 is composed of the several parts.

Claims

Claims: Method for passivating a surface of a workpiece (102), comprising the following: Inserting at least one workpiece (102) into a treatment chamber (104); Providing a passivating agent (114) in the treatment chamber (104); cyclically changing the pressure in the treatment chamber (104) while the passivating agent (114) is located in the treatment chamber (104). A method according to claim 1, characterized in that during the cyclical changing of the pressure in the treatment chamber (104), the maximum pressure (p0) is lower than the ambient pressure. A method according to claim 1 or 2, characterized in that during the cyclical changing of the pressure in the treatment chamber (104), the minimum pressure (p0) is lower than the ambient pressure. u) is less than half the maximum pressure (po). Method according to one of claims 1 to 3, characterized in that during the cyclical changing of the pressure in the treatment chamber (104) the minimum pressure (p u ) is lower than the vapor pressure of the passivating agent (114). A method according to any one of claims 1 to 4, characterized in that the mean cycle time (ti) of changing the pressure in the treatment chamber (104) is at least 1 s and / or at most 30 s. A method according to any one of claims 1 to 5, characterized in that the treatment chamber (104) is connected to a vacuum source at least temporarily during the pressure change. A method according to claim 6, characterized in that the vacuum source comprises a vacuum pump (190). A method according to claim 6 or 7, characterized in that the vacuum source comprises a vacuum reservoir (224). A method according to claim 8, characterized in that the vacuum reservoir (224) is provided with a heat exchanger (234). A method according to any one of claims 1 to 9, characterized in that the passivation agent (114) comprises phosphoric acid and / or nitric acid.A method according to claim 10, characterized in that the passivating agent (114) contains phosphoric acid in a concentration of at least 1.5% by volume and / or at most 3% by volume. A method according to any one of claims 1 to 11, characterized in that during the pressure change, the passivating agent (114) and / or the at least one workpiece (102) is subjected to ultrasound. A method according to any one of claims 1 to 12, characterized in that a workpiece (102) to be passivated is successively placed in several passivation stations (276, 278) which contain different passivation agents (114). A device for passivating workpieces (102) comprises a treatment chamber (104) for receiving at least one workpiece (102) and a bath (290) of a passivation agent (114); and a pressure changing device (160) for cyclically changing the pressure in the treatment chamber (104) while the passivation agent (114) is located in the treatment chamber (104). Device according to claim 14, characterized in that the device (100) comprises at least two treatment chambers (104), wherein a workpiece (102) can be treated with a passivating agent (114) simultaneously in the first treatment chamber (104a) and a workpiece (102) can be rinsed with a rinsing liquid in the second treatment chamber (104b).

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