DE3300650C2 - Process for electropolishing, in particular for the electrolytic brightening of metallic workpieces - Google Patents

Abstract

The invention relates to a method and a device for electropolishing, in particular for the electrolytic brightening of workpieces made of aluminum, aluminum alloys or other metals in an electrolyte solution, the base electrolyte of which consists of phosphoric acid or mixtures of phosphoric acid with other mineral acids such as sulfuric acid, nitric acid or the like and polyphosphates . When automating such a polishing system, there is the problem that the relatively long crane lifting times lead to signs of corrosion on the workpieces. The invention solves this problem by increasing the dynamic viscosity of the electrolyte solution (3) in the polishing baths (1) for aluminum to at least 20 · 10 -3 Ns / m2, which is achieved by increasing the polyphosphate content in the electrolyte solution. The electrolyte thus forms an enveloping, adhesive protective film on the workpieces when it is lifted over. To keep the process conditions constant over the long term, the invention provides that, while avoiding the addition of polyphosphates or other additives, the polyphosphates are formed in the process by controlling the total acid concentration, the operating temperature and the current load. To keep the process conditions constant, when a viscosity limit is exceeded, part of the electrolyte solution is pumped into a regeneration tank (5), where it is desludged, refreshed with fresh acid and returned to the polishing bath (1).

Description

20-30% by volume, preferably 23-26% sulfuric acid

50-60% by volume, preferably 55-59%

phosphoric acid

80-85% by volume total acid content, the remainder water without additives

is used and that is continuously maintained in the electrolyte solution a concentration of dissolved aluminum of 40-55 g / l, preferably 45-50 g / l and the electrolyte solution at a temperature of 70 to 8O ⁰ C, preferably 75 ⁰ C, with a current load of 120 to 150 Ah / 1.

6. The method according to claim 1 and 5, characterized in that for the regeneration of the electrolysis bath the electrolyte solution during the process from the electrolysis bath in a regeneration tank supplied, there desludged by adding water and / or sulfuric acid and by adding the removed volume of sludge corresponding amount of fresh acid is regenerated and fed to the electrolysis bath.

7. The method according to claim 1 or 6, characterized in that the regeneration of the electrolytic bath is regulated depending on the viscosity.

The invention relates to a method for electropolishing, especially for the electrolytic polishing of metallic workpieces in an electrolyte solution, where the base electrolyte consists of phosphoric acid or mixtures of phosphoric acid with other mineral acids, such as sulfuric acid, nitric acid or the like. As well as polyphosphates

From DE-AS 29 49 807 it is known metallic workpieces for electropolishing or electrolytic

jo shine in an electrolysis bath with the composition mentioned in the generic term. To At the end of the polishing process, the workpieces are removed from the electrolysis bath and placed in a water bath brought to rinse off the electrolyte residues

Lifting the workpieces from one bath to another was previously done by hand

When trying to rationalize such a polishing system and to accomplish the overhauling mechanically, but the problem arose that the electro-poisoned Workpieces had tarnished and etched areas after the water bath. The cause was that a crane needs about 15 to 30 seconds to lift the workpieces from the electrolytic bath into the water bath while a person can perform this activity in a much shorter time. During this relatively The electrolyte residue remaining on the surface of the warmer during lifting was etched by its long lifting time Aggressiveness on the surface. With the existing systems and the existing process technology the planned automation of the polishing system failed due to the mechanization of the workpiece transport.

In GB-PS 6 45 453 various compositions of polishing baths are described. After this Writing is the etching of the workpieces in the bathroom and when lifting by adding chromic acid prevented. However, the use of chromic acid is associated with considerable disadvantages.

The present invention is therefore based on the object of a plant and process technology to show, with the economical automation of the electropolishing process and in particular a machine lifting of the workpieces is made possible. The invention solves this problem with the features of the characterizing part of the main claim.

The method according to the invention has the advantage that it eliminates the problem of tarnishing and etching can fix simple measures. The viscosity of the electrolyte solution is set at least as high that the gel-like electrolyte residue film completely envelops the workpiece surface for the duration of the lifting whereby the electrochemical conditions on the workpiece surface are kept constant. The highly viscous protective film is also less aggressive towards the workpiece surface.

By changing the viscosity, the process can be applied to different materials with different surface properties and be adapted to lifting times of different lengths.

^{A minimum viscosity of 20 · 10 -3} Ns / m ^{2 of} the electrolyte solution has proven to be favorable for the polishing of workpieces made of aluminum or aluminum alloys.

Another advantage of the process is that inhibitors such as chromic acid or the like are no longer required will. The highly viscous protective film is applied to the goods by controlling an already existing one

33 OO 650

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Electrolyte component, namely the content of poly- especially on the electrodes, to changes in the phosphates, created. The content of polyphosphates abandoned electrolyte components. This is how place is transcended the polyphosphoric bath to stabilize the electrolysis ho-phosphoric acid over several stages necessary amount of phosphate, as it is formed in DE acid

AS 29 49 807 is taught. The control of the poly 5 as a result of the electrochemical removal process

phosphate content in the electrolyte solution can occur on the surfaces of the anodically connected

Addition of polyphosphate compounds or aluminum parts to split the polyphosphoric acid

preparation of the polyphosphates in the process. re into polyphosphates and water, the water being of

In the case of mechanized electropolishing or glossing, the workpiece surfaces are diffused away. Through the

It is particularly important to have a precise adjustable content of polyphosphates in the vicinity of the plant

speed of the polyphosphate content of the electrolyte solution and shiny workpieces the dynamic viscosity

thus the viscosity. the electrolyte solution increased, with a minimum viscosity

Due to the formation of the polyphosphates in the electrolysis of the entire electrolyte solution of 20 · 10 ^-3 Ns / m ²

process you can aim for the desired viscosity very precisely. This minimum viscosity arises at

and thus consistently good polishing results with a total current load of the electrolyte solution of

achieve nits. Any additives such as wetting agents or 12ü Ah / 1 a.

Inhibitors can be dispensed with. After the polishing process is finished, the

For the mechanization of the process, a continuous work piece is lifted from the polishing bath. Through the

Detailed management of the process process according to the invention process conditions remains on the

Worth seeing According to the invention, there is a regeneration of workpiece surfaces, a viscous residual electrical film

tion from time to time or continuously. This has to be liable for the duration of the arrogance of the individual

The advantage that on the one hand the viscosity of the Elektrolytlö- workpiece completely envelops and because of his

solution, which only dissociates to a small extent due to the formation of polyphosphates and low water content

Metal removal would increase constantly, on the other hand it is also erated and therefore not very aggressive,

the electrochemical process conditions are constant 25 With a total acid concentration of approx.

being held. The removal is 80-85% by volume, the aluminum content can be up to 55 g / l

of the sludge, which is when the electrolyte solution is oversaturated. If this aluminum content is exceeded,

sung precipitates, important because an excess of sludge leads to the formation of precipitation products, which are called

Gloss conditions changed unfavorably In addition, sludge can be designated.

It is possible to switch the electrolysis bath off at the limit of 30 from a current load of approx. 150 Ah / 1

maximum absorption capacity for dissolved Metail to electrolyte solution so far consumed that no optimal

operate. len polishing results can be achieved. By par-

For each electrolyte there is a certain current-dependent regeneration of the electrolyte solution 3 then

load range, within which the optimum polisher results in the total current load below the aforementioned

nits can be achieved. Pressed for the electrical limit value according to the invention. By regenerating the

trolytes to shine aluminum this electricity electrolyte solution is also the aluminum content in the

load range between 120 and 150 Ah / 1. This preferred framework kept.

The state of the electrolyte solution 3 is determined by viscous

Regeneration within the optimization limits health and / or conductivity measuring devices 12 monitored,

keep. The regeneration takes place via a container, 40 Deviating from the drawing, these measuring devices can

in which a te can also be arranged within the polishing bath 1 by adding H ₂ O and / or H ₂ SO _4.

Sedimentation of the enriched metal salts from the electrolyte solution 3 in the polishing bath 1

Electrolyte takes place. is temporarily or continuously via lines 4 and pump

By measuring the viscosity, it is possible to remove the poopes 10 and place them in a regeneration container 5

Lyphosphate formation and thus the level of the Strombela- 45 promoted from which the regenerated electrolyte solution

stung in the process to be monitored and fed back to the polishing bath 1 on cumbersome via return lines 9

dispense with chemical analyzes. will.

In the subclaims, the electrolyte assemblies are located in the upper part of the regeneration tank 5

composition and the operating conditions in a single mixing zone 6, to which on the one hand the withdrawn

guide example for aluminum and aluminum alloy 50 electrolyte solution 3 and on the other hand from storage container

ments taught. tern 8 for sulfuric and phosphoric acid fresh solution

The drawing shows the system for carrying out the feed. By means of a mixer 11, the age according to the invention Method based on a switching solution and the fresh solution mixed together, according to the scheme for example shown. while at the same time due to the relative calm in the regenerative

1 with the gloss bath is referred to, in which the 55 tion container 5 brought from the old solution Electrolyte solution 3, which can sediment from 20-30% by volume, preferably sludge, in the settling zone 7. in the 23-26% by volume, of sulfuric acid, 50-60% by volume, pre-regeneration tank 5 can additionally, depending on the dimensions 55-59% by volume, £ .n phosphoric acid, with a desired reduction in the total aluminum acid content of 80-85% by volume and the remainder, a sludge formation through hydrolytic there is a lot of water. The electrolyte solution 3 contains 60 cleavage of the aluminum in the electrolyte no further surcharges, complexes are enforced. By increasing the

The total current load is between 120 and the water content or the sulfuric acid content in the

150 Ah / I. The Al content is 40-55, preferably electrolyte solution, sludge is formed. Of the

45 to 50 g / l. The operating temperature is set to 70 until sludge that has settled out can be

8ifC, preferably 75 ° C kept. 65 tion container 5 via its own drain line 13 to

With the aforementioned chemical composition, further processing can be taken. The recorded

the electrolyte solution 3 and the operating conditions is fresh and thus regenerated electrolyte solution 3

as a result of electrochemical reactions, the polishing bath 1 is drawn back via return lines 9.

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leads, thereby ensuring that in the polishing bath 1 the same electrolyte composition is always present. In the case of repatriation, the refreshed Electrolyte can be passed through an evaporation / evaporation system, not shown, where excess Water is removed.

In the return line 9 to the polishing bath 1, a turbidity measuring device 14 is installed, which measures the sludge content controlled and when a maximum sludge concentration is exceeded triggers an alarm

Aeration pipes 2 are arranged above the bottom of the polishing bath 1, for constant circulation the electrolyte solution 3.

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Claims (5)

33 OO 650 claims: 1. Process for electropolishing, in particular for electrolytic brightening of metallic ones Workpieces in an electrolyte solution, the base electrolyte being phosphoric acid or mixtures consists of phosphoric acid with other mineral acids and polyphosphates, characterized in that that the dynamic viscosity of the electrolyte solution by increasing the contained in it Amount of polyphosphates is increased so much that the electrolyte residue on the workpiece surfaces when lifting from the electrolysis bath to a downstream processing stage forms a tightly adhering film and that the electrolytic bath is regenerated. Z method according to claim 1, characterized in that that while avoiding the addition of tensile impact materials, the polyphosphates in the process Control of total acid concentration, operating temperature and current load made will. 3. The method according to claim 1 or 2, characterized in that for monitoring the electrolysis bath the viscosity of the electrolyte solution is measured. 4. The method according to claim 1 or 2, characterized in that for the electrolytic brightening of workpieces made of aluminum or aluminum alloys, the dynamic viscosity of the electrolyte solution is set to at least 20 · 10 ^-3 NS / m ² . 5. The method according to claims 2 and 4, characterized in that the electrolytic Shine of workpieces made of aluminum or aluminum alloys an electrolyte solution of the chemical composition