EP0569780A1 - Process for anodising metallic workpieces - Google Patents

Abstract

In a process for anodizing metallic workpieces (4), in particular aluminium and aluminium-alloy workpieces, the workpieces are exposed to an electrolyte flow in an electrolyte bath (2) freely or by means of a workpiece chamber. The electrolyte flow is removed from the electrolyte bath by a pipe circuit or the like and after being passed through a cooler (8), is fed back into the electrolyte bath. To create continuously uniform temperatures at the workpieces and in the electrolyte bath by providing reliable heat removal, the cooled electrolyte flow is fed back against the direction of movement of the Joule heat produced in the electrolytic process into and through the electrolyte bath. <IMAGE>

Description

The invention relates to a method for anodic oxidation of metallic workpieces, in particular made of aluminum and aluminum alloys, in which the workpieces are exposed to an electrolyte flow freely or by means of a workpiece space in an electrolyte bath, which are removed or removed from the electrolyte bath via a pipe circuit or the like Passed through a cooler in the electrolyte bath is returned cooled.

It is known that the anodic oxidation of workpieces generates Joule heat through the electrolytic process, which must be dissipated as a result of heat build-up to avoid uncontrollable and uneven layer formation on the workpieces. It is known to cause this heat to be dissipated by blowing air into the electrolyte bath. It is also known to draw off electrolyte from an upper corner of the electrolyte bath, to return it to the electrolyte bath from the lower end after being circulated via a cooler in the direction of the rising heat. However, these known cooling processes do not allow for reliable heat dissipation over the entire workpiece space, which leads to temperature differences in the electrolyte bath with uneven layer formation on the workpieces, to increased aluminum fogging solutions and thus to considerable sludge formation and unfavorable disposal.

It is an object of the invention to provide measures in a device of the above type which are continuously uniform due to reliable heat dissipation Allow temperatures on the workpieces and in the electrolyte bath.

According to the invention, this object is achieved in that the electrolyte flow is cooled and returned to the electrolyte bath counter to the direction of movement of the Joule heat generated during the electrolytic process. For this purpose, it is provided that the flow of the cooled electrolyte passes through the electrolyte bath from top to bottom. The cooled electrolyte flow is preferably carried out at a flow rate of essentially 0.6 to 3.0 m / sec, preferably 0.2 to 5.0 m / sec and with a circulation frequency of 4 to 12, optionally up to 300 throughputs per hour the electrolyte bath moves. The cooling of the electrolyte flow can be done in any way, e.g. by an external cooler or by an internal cooler housed in the electrolyte bath. By means of the process steps, the cooled electrolyte flow, when it is returned to the electrolyte bath, first meets the strongly heated part of the electrolyte located in the upper part of the electrolyte bath, in order to gradually encounter less warm electrolytes as the electrolyte bath continues to flow through. As a result of the mixing taking place, the temperature of the electrolyte bath is uniform over the entire volume of the same with constant temperatures on the workpieces, which is a prerequisite for building up oxide layers of uniform thickness on the workpieces. In addition, the redissolution of aluminum is reduced to a minimum, which results in low sludge formation with favorable disposal.

In a device for performing the method it is provided that the workpieces are free at a distance of Side walls and bottom of a receptacle for the electrolyte bath or a workpiece space attached in the receptacle are arranged so that between the workpieces or the workpiece space and the bottom of the receptacle tubes or flow plates for suction of the electrolyte and in the area near the upper end of the receptacle between the workpieces or the workpiece space and the side walls open pipes or flow plates for returning cooled electrolyte and that a pump device and a cooler for the electrolyte are formed between the suction and return of the electrolyte. The tubes and flow plates for the suction and return of the electrolyte expediently extend essentially over the entire length of the workpieces or the workpiece space, which leads to a uniform outflow and inflow of electrolyte. It goes without saying that the tubes or flow plates for the return of cooled electrolyte can optionally be formed above and / or to the side of the workpieces or the workpiece space. However, the tubes or flow plates for returning cooled electrolyte are preferably formed in the upper third of the height of the workpieces or the workpiece space in the electrolyte bath. It is also advantageous if the cooled electrolyte flow passes into the electrolyte bath with a predetermined orientation. For this purpose, the tubes or flow plates for returning cooled electrolyte can have outlet openings and / or outlet nozzles directed diametrically to the workpieces or the workpiece space. The outlet openings and / or outlet nozzles expediently extend with outlet axes directed obliquely upwards and towards one another. The cooled electrolyte can thus initially be over a partial height through the next to the workpieces be located areas of the electrolyte bath and then pass through deflection next to and between the workpieces.

Particularly favorable mixing of amounts of electrolyte heated by the electrolytic process with cooled amounts of electrolyte can still be achieved if the return-side tubes and / or flow plates and / or nozzles to the workpieces or to the workpiece space are individually or jointly pivotable and / or movable in the electrolyte bath are. The movements of the pipes and / or flow plates and / or nozzles can equally be carried out continuously, intermittently or cyclically, the frequencies of the movements being controllable manually or automatically. An intimate mixing of the differently tempered amounts of electrolyte can also be advantageously achieved if workpieces and / or workpiece space itself are designed to be pivotable and / or movable in the electrolyte bath. The movements of the same can in turn be continuous, intermittent or cyclical with fixed or adjustable frequencies.

Finally, provision is also made to assign pressure compensation vessels, in particular pipe sections or flow plate sections, to the pipes and / or the flow plates for suction and return of electrolyte, which preferably form pressure compensation chambers together with the pipes and / or flow plates for the return and / or suction. For this purpose, the pipe sections or flow plate sections can be made in one piece with the pipes and / or flow plates for the return and the suction.

To improve the surface quality of a metallic material, e.g. Workpieces formed from aluminum or aluminum alloys are proposed for this, for which the workpieces are exposed to an acidic or alkaline pickling solution in a pickling bath. In a further development of the inventive concept, the pickling solution is to be removed from the pickling bath at the bottom, then moved past cooling bodies from bottom to top and subsequently cooled in a countercurrent to the exothermic heat generated during the pickling process and passed turbulently through the pickling bath from top to bottom over the workpieces. Here, in the valley areas of the workpiece surfaces, the removal of workpiece particles is slowed down by the hydrogen developed during the pickling process, while the mountain areas of the workpiece surfaces are removed by the pickling liquid flowing into the workpieces while continuously removing the exothermic heat and carrying along the hydrogen that forms on the mountain areas. In this way, with short pickling times, smoothing of workpiece surfaces and, as a result of low, essentially constant pickling temperatures, minimization of the removal, reduction in the use of chemicals and, in turn, relief for the disposal and the environment are achieved.

For the purpose of cooling, the pickling solution is preferably moved past the bottom of the heat sink in the pickling bath, namely on the sides facing away from the workpieces, and is subsequently turbulently directed back to the workpieces from top to bottom over the region of the side of the heat sink facing the workpieces. It goes without saying that the cooling of the pickling solution can also be brought about by moving it past or moving it through in external heat sinks.

In a device for carrying out the pickling processes, the heat sinks can be arranged at a distance from those in the receptacle for the pickling solution and the workpieces introduced and the side walls of the receptacle, and between the workpieces and the bottom of the receptacle, pipes or flow plates for suctioning off the pickling solution and the extracted pickling solution can be dispensed via nozzles into the areas between the heat sinks and the side walls, while the cooled pickling solution can be returned to the workpieces over the areas of the heat sinks facing away from the side walls of the receptacle. The pickling process can be advantageously intensified by sole or joint continuous, intermittent or cyclical swiveling or shifting movements of the pipes, flow plates and / or dispensing nozzles for the pickling solution. The same effects can also be achieved by corresponding movements of the workpieces and / or the workpiece space in the pickling bath.

Finally, while maintaining the process steps used for anodic oxidation, measures for the electrolytic or chemical sheen of metallic materials, in particular aluminum or aluminum alloys, are achieved through the use of a chromic acid, chromic acid-free or alkaline electrolyte, which comes from the area between the workpieces and sucked off the bottom of the receptacle via pipes or flow plates in the receptacle and given off to internal or external heat sinks and subsequently returned to the workpieces and / or the workpiece space as a cooled electrolyte flow against the direction of movement of the Joule heat generated during the electrolytic process. This will reduce Process times achieved while minimizing metal redissolution.

Ultimately, measures for activating the rinsing of the workpieces treated by pickling, glossing and anodic oxidation can advantageously be achieved in that the rinsing liquid, e.g. Water or water mixed with rinsed off portions of an electrolyte or a pickling concentrate below the workpieces and / or the workpiece space are sucked out of the receptacle via pipes or flow plates and subsequently heated by means of radiators or not heated by the rinsing bath turbulently from the top to the bottom of the workpieces and / or the workpiece space is continuously returned. It goes without saying that the rinsing processes can be repeated as often as desired and can also be carried out after or before each process.

Fig. 1

eine Vorrichtung im Querschnitt,

Fig. 2

den Längsschnitt zu Fig. 1 nach der Linie II-II der Fig. 1,

Fig. 3

einen Schnitt nach der Linie III-III der Fig. 2,

Fig. 4

eine Vorrichtung im Querschnitt in abgewandelter Ausführung,

Fig. 5

eine Vorrichtung gemäß Fig. 4 in abgewandelter Ausführung, im Querschnitt mit Bewegungsangaben,

Fig. 6

ein Fließbild einer Vorrichtung, schematisch,

Fig. 7

Absaugrohre für eine Vorrichtung gemäß Fig. 6, im Schnitt, nach der Linie VII-VII der Fig. 6,

Fig. 8

ein Fließbild einer Vorrichtung, in abgewandelter Ausführung,

Fig. 9

Absaugrohre im Schnitt nach der Linie IX-IX der Fig. 8,

Fig. 10

eine Vorrichtung zum Beizen von Werkstücken im Querschnitt mit Bewegungsangaben,

Fig. 11

ein Fließbild einer Vorrichtung gemäß Fig. 10,

Fig. 12

eine Vorrichtung zum Beizen in abgewandelter Ausführung im Querschnitt,

Fig. 13

ein Fließbild einer Vorrichtung gemäß Fig. 12 und

Fig. 14

eine Darstellung des Prozeßablaufes beim Beizvorgang.

The exemplary embodiments shown in the drawing show how the invention can be carried out. Here mean:

Fig. 1

a device in cross section,

Fig. 2

1 along the line II-II of FIG. 1,

Fig. 3

2 shows a section along the line III-III of FIG. 2,

Fig. 4

a device in cross section in a modified version,

Fig. 5

4 in a modified version, in cross section with movement information,

Fig. 6

a flow diagram of a device, schematically,

Fig. 7

Suction pipes for a device according to FIG. 6, in section, along the line VII-VII of FIG. 6,

Fig. 8

a flow diagram of a device, in a modified Execution,

Fig. 9

Suction pipes in section along the line IX-IX of Fig. 8,

Fig. 10

a device for pickling workpieces in cross section with movement information,

Fig. 11

10 shows a flow diagram of a device according to FIG. 10,

Fig. 12

a device for pickling in a modified version in cross section,

Fig. 13

a flow diagram of a device according to FIG. 12 and

Fig. 14

a representation of the process flow in the pickling process.

1 to 5, 1 designates a receptacle for the electrolyte bath 2, which receives workpieces 4 connected to an anode 3 or a workpiece space and cathodes 5. The Joule heat generated during the electrolytic process moves automatically from bottom to top in the electrolyte bath 2. Between the workpieces 4 and the bottom 1 'of the receptacle 1, in the exemplary embodiment, pipes 6 extending over the entire length of the workpieces 4 are arranged, which are connected to a pump device 7 and a cooler 8 (FIG. 6). The tubes 6 have holes 9 for the suction of electrolyte. In the upper region of the receptacle 1, tubes 10 are formed which are connected to the cooler 8 and which open into the electrolyte bath 2 via nozzles 11 or perforations (not shown). The tubes 10 are connected to tube sections 12 (FIG. 2) serving as compensation chambers. The pipe sections 12 are expediently made in one piece with the pipes 10.

In the flow diagrams of FIGS. 6 and 8, tubes 6 with tube sections 6 ′ serving for pressure equalization are provided for the suction of electrolyte, the tubes 6, as can be seen in FIG. 7, each having holes 9 and the tubes 6 of FIG. 8 likewise Have perforations 9 for the transfer of electrolyte in the direction of the pump device 7, while the tubes 10 of FIGS. 6 and 8 can be provided with nozzles 11.

Over the duration of the electrolytic process, Joule heat rises from bottom to top, with increasing temperature increase in the electrolyte bath 2. Via the perforations 9 of the tubes 6 or flow plates, electrolyte is introduced into the cooler 8 by the pump device 7 and from there via tubes 10 or flow plates is returned to the electrolyte bath 2 by means of nozzles 11. Here, the cooled electrolyte flow first encounters a more heated electrolyte and then a less strongly heated electrolyte. The interaction of the cooled electrolyte flow with strongly heated electrolyte quantities or in the later course between the cooled electrolyte flow with less strongly heated electrolyte quantities ensures uniform mixing on all levels and for the exclusion of unfavorable temperature differences in the electrolyte bath 2.

Finally, FIG. 5 shows a device with tubes 6 and / or 10 and / or workpieces 4 or tubes 6 and / or 10 which can be pivoted and / or moved in the electrolyte bath in connection with pressure compensation tubes 12, 6 '. The different possible directions of movement of the pipes or workpieces are indicated by directional arrows 15.

With 16,17 connections on the cooler 8 for the supply and discharge of cooling medium, with 19 and 20 the supply and discharge of the cooler 8 for electrolyte and 18 a power source.

In Fig. 10, 21 denotes a receptacle for an acidic or alkaline pickling solution 22, in which workpieces or a workpiece space 23 is accommodated. Suction tubes 24 for the pickling solution 22 are provided between the workpieces or workpiece space 23 and the bottom 21 ′ of the receiving container 21, which are in contact with a pump device 25, which in turn arranges the pickling liquid 22 via pipes 27 provided with nozzles 26 in the areas 28 between in the receiving container 21 Promote heat sinks 29 and side walls 21 ″ of the receptacle 21. As can be seen in particular from the associated flow diagram according to FIG. 11, the heat sinks 29 rest with their lower ends 29 'via pipes 30 and a valve 31 on a cooling tower 32 which is connected to a cold water basin 34 via a further pipe 33. From the cold water basin 34, the water serving as cooling liquid can be introduced into the upper ends 29 ″ of the cooling bodies 29 by means of a cold water pump 35 via pipes 36.

In the case of pickling processes on workpieces, exothermic heat is generated under the action of the pickling solutions 22 during the removal of workpiece particles and moves upward in the pickling solution 22 in the direction of arrow 37. Depending on the pickling temperature, more or less large sludge formation is caused by the removed workpiece particles. The temperature of the pickling solution 22, which is reduced in temperature at the cooling bodies 29, increases by moving against the exothermic heat, Direction of arrow 37, exothermic heat and is subsequently cooled in the cooling areas between the heat sinks 29 and the side walls 21 ″. By cooling the pickling solution and moving in countercurrent, arrow direction 38, to the exothermic heat 37, set pickling temperatures can be maintained within narrow limits. This leads to a reduction in the pickling time of around 30 to 50 percent. When it is returned, the cooled pickling liquid 22, as shown in FIG. 14, strikes and removes tip areas 39 of the workpiece surface 40, while removal in the valley areas 41 of the workpiece surface 40 is limited by the hydrogen 42 enclosed therein. By removing the tip areas 39, the workpiece surface 40 is smoothed in a short time and with reduced sludge formation.

In the device of FIG. 12 and the associated flow diagrams of FIG. 13, the pickling solution 22, which heats up during the downward movement, is sucked off via separate suction pipes 24, which are connected to a pump device 25. The pump device 25, as described above, conveys pickling solution into the cooling areas between the cooling bodies 29 and side walls 21 ″ and further after diversion on the workpieces or workpiece space 23.

With 43 a fresh water supply to the cold water basin 34 is designated with a valve 44. 45 shows possible directions of movement for workpieces or the workpiece space 23 and directions of movement for the drain pipes 24 or nozzles 26 (FIG. 10).

Claims (27)

Method for anodic oxidation of metallic workpieces, in particular made of aluminum and aluminum alloys, in which the workpieces are exposed to an electrolyte flow freely or by means of a workpiece space in an electrolyte bath, or the like via a pipe circle. removed from the electrolytic bath and, after being passed through a cooler, returned to the electrolytic bath in a cooled manner, characterized in that the cooled electrolyte flow is fed back into and through the electrolytic bath against the direction of movement of the Joule heat generated during the electrolytic process. A method according to claim 1, characterized in that the electrolyte bath is flowed through from top to bottom by the cooled electrolyte flow. Method according to claims 1 and 2, characterized in that the cooled electrolyte flow is moved through the electrolyte bath at a flow rate of essentially 0.6 to 3.0 m / sec. Process according to claims 1, 2 and 3, characterized in that the cooled electrolyte flow is moved through the electrolyte bath essentially at a circulation frequency of 4 to 12 / hour. Method according to claims 1 and 2, characterized in that the electrolyte flow is passed through a cooler external to the electrolyte bath. Method according to claims 1 and 2, characterized in that the electrolyte flow is passed through a cooler arranged internally in the electrolyte bath. Device for carrying out the method according to claim 1, characterized in that the workpieces (4) freely at a distance from the side walls (1 '') and bottom (1 ') of a receptacle (1) for the electrolyte bath (2) or one in the receptacle ( 1) attached workpiece space are arranged so that between the workpieces (4) or the workpiece space and the bottom (1 ') of the receptacle (1) pipes (6) or flow plates for suction of the electrolyte and in the upper end of the receptacle (1 ) the area between the workpieces or the workpiece space and the side walls (1 '') of the receptacle opens out towards pipes (10) or flow plates for the return of cooled electrolyte, and that a pump device (7) and a cooler (8 ) are designed for the electrolyte. Apparatus according to claim 7, characterized in that the tubes (6, 10) or flow plates for the suction and return of electrolyte extend essentially over the entire length of the workpieces (4) or the workpiece space. Apparatus according to claim 7, characterized in that the tubes (10) or flow plates for the return of cooled electrolyte are formed in the upper third of the height of the workpieces (4) or the workpiece space in the receptacle (1). Apparatus according to claim 7, characterized in that the tubes (10) or flow plates for the return of cooled electrolyte are arranged above and / or next to the workpieces (4) or the workpiece space in the receiving container (1). Apparatus according to claim 7, 9 and 10, characterized in that the tubes (10) and / or flow plates for the return of cooled electrolyte are assigned diametrically to the workpieces (4) or the workpiece space and outlet openings and / or outlet nozzles (11) directed towards one another for the electrolyte. Apparatus according to claim 11, characterized in that the outlet openings or outlet nozzles (11) for the electrolyte are formed with outlet axes directed obliquely upwards to one another. Apparatus according to claim 12, characterized in that the return-side tubes (10) and / or flow plates and / or nozzles for the electrolyte to the workpieces (4) or the workpiece space are individually or jointly designed to be pivotable and / or movable. Apparatus according to claim 13, characterized in that the tubes (10) and / or flow plates and / or nozzles are designed to be continuously, intermittently or cyclically pivotable or displaceable. Device according to claim 7, characterized in that the workpieces (4) and / or the workpiece space are designed to be pivotable and / or movable in the electrolyte bath (2). Apparatus according to claim 15, characterized in that the workpieces (4) and / or the workpiece space are designed to be continuously, intermittently or cyclically pivotable and / or movable in the electrolyte bath (2). Apparatus according to claim 7, characterized in that the tubes (6, 10) and / or flow plates for suction and / or return of electrolyte pressure compensation vessels, in particular pipe sections (12, 6 ') or flow plate sections, which are assigned together with the pipes ( 6, 10) and / or the flow plates form pressure compensation chambers. Apparatus according to claim 17, characterized in that the pipe sections (12, 6 ') or flow plate sections serving as pressure compensation vessels are formed in one piece with the pipes (6, 10) and / or flow plates for the suction and return of electrolyte. Process for the pretreatment of the anodic oxidation of metallic workpieces, for example made of aluminum or aluminum alloys, in particular pickling, in which the workpieces can be exposed in an etching bath freely or by means of a workpiece space to an acidic or alkaline pickling solution, characterized in that the pickling solution is removed from the pickling bath below, then moved past the heat sinks from bottom to top and subsequently cooled in a countercurrent to the exothermic heat generated during the pickling process by the pickling bath in a turbulent manner is passed down over the workpieces or the workpiece space. A method according to claim 19, characterized in that the heat sinks are arranged in the pickling bath and that the pickling solution for cooling on the side facing away from the workpieces or the workpiece space moves past the heat sinks from bottom to top and subsequently over the area of the workpieces or the Side of the heat sink facing the workpiece space is passed turbulently back and forth over the workpieces or the workpiece space. A method according to claim 19, characterized in that the pickling solution for cooling moves past cooling bodies external to the pickling bath and is returned to the pickling bath from top to bottom over the workpieces or the workpiece space. A method according to claim 19, characterized in that the pickling solution for cooling is moved through cooling bodies external to the pickling bath and is fed back into the pickling bath from top to bottom over the workpieces or the workpiece space. Apparatus for carrying out the pickling process according to claims 19 and 20, characterized in that the workpieces can be introduced freely or by means of a workpiece space (23) into a receiving container (21) receiving a pickling solution 22, that at a distance apart from the workpieces or the workpiece space (23 ) between these and the side walls (21 '') of the receptacle (21) heat sink (29) and between the workpieces or the workpiece space (23) and the bottom (21 ') of the receptacle (21) tubes (24) or flow plates for Suction of pickling solution (22) are arranged and that the extracted pickling solution (22) can be dispensed via nozzles (26) opening into the areas (28) between the heat sink (29) and side walls (21 '') and the cooled pickling solution (22) can be dispensed via the the area of the heat sink (29) facing away from the side walls (21 '') of the receptacle (21) can be returned to the workpieces or the workpiece space. Apparatus according to claim 23, characterized in that the tubes (24), flow plates and / or nozzles (26) for the pickling solution (22) to the workpieces or to the workpiece space (23) individually or jointly continuously, intermittently or cyclically pivoting or are movable in the receiving container (21). Apparatus according to claim 23, characterized in that the workpieces and / or the workpiece space (23) are arranged continuously, intermittently or cyclically in the pickling bath so that they can be pivoted and / or moved. Process for the electrolytic or chemical shining of metallic workpieces, in particular made of aluminum or aluminum alloys, in which the workpieces are exposed to an electrolytic solution for anodic treatment either freely or by means of a workpiece space in a receiving container, characterized by the use of a chromic acid or chromic acid-free or alkaline electrolyte, which sucked from the area between the workpieces or workpiece space and the bottom of the receptacle via pipes or flow plates to the receptacle and discharged or guided past heat sinks and subsequently as cooled Electrolyte flow against the direction of movement of the Joule heat generated during the electrolytic process is returned to the workpieces. Process for rinsing metallic workpieces, in particular made of aluminum or aluminum alloys, treated in anodic oxidation or by pickling, in which the workpieces contain a rinsing liquid either freely or by means of a workpiece space in the receptacle. Are exposed to water, characterized in that the rinsing liquid alone or mixed with rinsed portions of an electrolyte or pickling concentrate from the area between the workpieces and the bottom of the receptacle is sucked off via pipes or flow plates, subsequently heated by means of radiators or only turbulently from above by the rinsing bath is returned down to the workpieces.

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