DE2854605A1 - METHOD AND CIRCUIT ARRANGEMENT FOR OPTIMIZING ELECTROLYTIC POLISHING - Google Patents

Description

LATSZERESZETI ESZKÖZÖK GYARA
2500 Esztergom,
Hungary

Method and circuit arrangement for optimization
of electrolytic polishing

The invention relates to a method for optimizing the electrolytic polishing ₃ a circuit arrangement for carrying out this method, so ^ a method
for the preparation of electrolytically polished workpieces for re-electroplating.

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Electrolytic polishing is widely used to increase the surface brightness of metal workpieces applied. The optimal conditions for electrolytic polishing are according to the previously known methods set very complicated.

Numerous suggestions have already been made for increasing the brightness that can be achieved with polishing and available to reduce energy consumption. The optimum was generally with the corresponding composition of the bath, the change the polishing voltage and the bath temperature. This optimum was significant. from the Material of the metal piece to be polished and the local conditions dependent.

The bath compositions or polishing ratios judged to be favorable are used by most Hidden from users as a manufacturing secret.

For electrolytic polishing, adjustable voltage values between the Anode and cathode electrode for the polishing current, i.e. the so-called Jaquett diagram periodically or continuously is controlled. From this graph over the polishing bath it can be seen that the metal becomes passive during polishing

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has enough. The polishing ability of the bath can, however cannot be decided with the help of the polarization curve of the anode, i.e. the Jaquett diagram.

The problem with conventional electrolytic polishing methods is that due to the aging of the bath or the increase in the current strength above a certain limit value electrolytic etching occurs during polishing. To avoid this phenomenon you can work can only be carried out by a specialist, whereby the polishing process must be continuously monitored.,

iElectrolytic polishing is often followed by Application of a newer galvanic layer. For spot-free application of the galvanic layer the passive surface layer created during polishing must be removed. During the Removal of this passive layer will corrode the metal surface using the usual methods Exposed to influences, whereby the surface brightness achieved by the polishing is deposited.

The invention provides such for optimal adjustment of the electrolytic polishing process Method, showing the progress of the polishing process in an objective way, and based on it

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of these displayed values, the various characteristic values that influence polishing (current density, Temperature, bath composition) can be changed in the direction of the optimal state.

A further aim of the invention was to create a circuit arrangement that enables the measurement and stabilization of the optimal conditions.

The invention was also set to the task of finding a method according to which the electrolytically polished workpieces can be prepared for re-electroplating without the achieved Reduce surface brightness.

The invention is based on the knowledge that during the electrolytic polishing the between the workpiece connected as anode and The voltage values measured in the bath exhibit periodic fluctuations., The correct polishing process is therefore followed by periodic fluctuations.

According to a further finding, the conditions required for polishing are optimal set in a simpler way when the current source e in a current generator with constant output— electricity is applied. By supplying energy with the help of a power generator, it is achieved

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that the polishing in terms of current is within the constant range of the Jaquett diagram he follows.·

In connection with the foregoing, it is characteristic of the method according to the invention that the potential difference between the anode and the bath enveloping the anode is measured during the polishing, the electrolysis takes place at a constant current density and the polishing parameters, d _# h. the current density, the bath temperature and the bath composition are set in such a way that the detected potential difference exhibits periodic fluctuations a reference electrode that measures the potential of the polishing bath is accommodated near the anode electrode, and that the anode and reference electrodes are connected to the input of a voltmeter «

'For post-electroplating, the electrolytic polished workpieces are prepared in such a way that the polishing bath residues from the surface of the workpiece can be removed by rinsing, then in one

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nichtaggreesivetf, slightly alkaline bath an o.nodi ~ cal treatment is carried out and after the following Rinsing process the workpiece is cathodically degreased.

The invention is hereinafter related with exemplary embodiments and detailed information on the basis of the drawings »In the drawings demonstrate:

Pig, 1 the circuit diagram of the implementation electroplating equipment suitable for the method according to the invention, Fig, 2 the on in Pig, I. Shown. Circuit arrangement characteristic current-voltage curve, Fig. 3 shows the circuit diagram of a possible

Embodiment of the current generator having the electroplating electrode
and

4 to 9 the voltage-time diagrams

in different examples of electroplating, whereby the during the Polishing between the anode electrode and the bath periodic changes in potential being represented,

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Fig. 1 shows the electroplating vessel 1, where in the electrolytic bath 2, the anode electrode 3 and the cathode electrode 4- were immersed. The for Energy required for electrolysis is provided by the power generator 5 fed to the electrodes. In the vicinity of the anode electrode 3 there is a reference electrode 6 with the bath 2, advantageously a saturated calomel electrode Contact. The voltmeter is used to measure the voltages arising between the bath 1 and the anode electrode 3 7 with the anode electrode 3 and the reference electrode 6 connected. The voltmeter 7 is advantageously a millivoltmeter, which can be used for this purpose but most commercially available pH meters can be used. The output of the voltmeter 7 is at one Recording device 8, e.g. a writing device or an oscilloscope connected, which the acquisition and enable the time-varying values of the measured voltages to be recorded.

The temperatures of the bath 2 are set with the aid of a temperature controller connected to the vessel 1 9 held constant. This device can take the form of any temperature controller known in the art to have.

Fig. 2 shows the current-voltage diagram typical of electrolysis, i.e. the Jaquett diagram.

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The measured voltage here is to be understood as the voltage between the anode and the cathode., The As is known, the current strength becomes electrolysis in the area between points D and E of the Jaquett diagram independent or almost independent of the voltage values. Electrolysis is usually used for electrolytic polishing in this voltage-current- Range set. In the case of the invention Arrangement, the electrolysis is carried out by means of the current generator 5 at a constant current strength.

When the bath 3 is composed of electrolytes commonly used in electrolytic polishing becomes, the voltage during proper polishing between the anode electrode 3 and the Yeast electrode 6 have fluctuations. This is how the voltage difference between the anode electrode 3 and the area of the close to it becomes Bath 2 fluctuate periodically over time. Frequency, symmetry and amplitude of the fluctuations are with the quality of the electrolytic polishing in connection with which care should be taken during the polishing got to.

The current generator 5 provides the amperage required during the electrolysis., Although there are already numerous electricity generators on the market

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However, our experience has shown that the electricity generator is very cheap 5 to be put together according to the circuit arrangement of FIG.

The direct current supply unit, not shown in the figure, is connected with its positive terminal directly, but with its negative terminal via the fuse B1, the control resistor R ^ and the pass transistor T * to the negative terminal that supplies the stabilized current. The base of the pass transistor T is driven by the drive transistor Tp, the emitter resistor R _{2 of} which is connected to the positive terminal, but the collector resistor Rc is connected to the negative terminal of the unregulated branch. The base of the drive transistor T ₂ is controlled by the collector of the control transistor T ₁ , the emitter of which is directly connected to the unregulated negative branch. The base of the control transistor T ₁ is connected to the wiper of the potentiometer P _{1 via the resistor R z} . The control resistor Rp is switched on between the one version of this potentiometer and the emitter of the Re gel trans istors T _1. the

Another version of the potentiometer P ₁ is on the E inst ellpötent iometer P ₂ at the partial point of the

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Z-diode Z _ß and the resistor H ₂ connected voltage divider,

The principle of operation of the current generator is based on the fact that the current flowing through the control resistor and the stabilized voltage derived from the voltage divider control the control transistor T in such a way that the emitter current of the pass transistor Tz remains constant regardless of the load. This current value can be set by adjusting the wiper of the potentiometer P ^ * ^m wide range. The drawn between the dashed lines load resistance R ^ on Fig., 5 represents the through the. electrolytic process resulting load.

The experience gained in connection with the periodic phenomena is illustrated with the help of the following examples. example 1

The construction on Pig. 1 was abraded smooth for electrolytic polishing Nickel silver plate inserted, with the anode electrode 3 was the * nickel silver plate. Each 100 ml of the bath 2 contained 80 ml of phosphoric acid and 20 ml of normal amyl alcohol. The bathroom contained over the in Traces of Pluoridione, whose maximum concentration

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tion did not exceed 0.5 g / ml. The polishing was carried out at a temperature of 28 ^° C. and a constant current density of 30 mA / cm ² . The surface reflection of the Neusilberplatte was, according to the Long-Lichttachoneter before the start of polishing 20% ₉ Thereafter, the plate surface was electrolytically polished, and in 5 to 15 minutes was obtained having a brightness of 75% or more mirror-like, pleasing surface.

During the polishing, the output waveforms of the voltmeter 7 were recorded: this diagram is shown in Fig. M- . It can be seen here that 10.5 periods elapsed in 10 minutes and a peak is deformed on the curves. Example 2

Instead of the nickel silver plate used in Example 1, a brass plate Sr 63 (63 % copper and 27 % Nikkei) was polished.

The surface brightness of this plate was 20 % before polishing, but it increased to 80 % after polishing.

Fig. 5 shows the output voltages of the voltmeter 7. Compared to the previous example, the number of periods was 13 and the waveform was pointed significant differences.

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Example 3

The electrolysis was carried out with a solution of 80 ml of phosphoric acid, 14 ml of normal amyl alcohol and 6 ml of water per 100 ml, each liter of solution containing 1.6 g of sodium sulfate. With this one Bath can be dispensed with the fluoride ions.

The polishing was performed on a Neusilberplatte with a Ausgai ^ shelligkeit of 20% at 24 ⁰ C and with a current density of 30 mA / cm performed. After polishing, the nickel silver plate achieved a surface brightness of 90 %.

On Fig. 6, the output signals of the Voltmeter 7 shown. From this it can be seen that in this bath the higher surface brightness with frequent fluctuations in the voltage values and waveforms with minor distortions. There were 24 periods for 10 minutes.

The same bath can also be used for polishing austenitic chromium-nickel steel at 35 ⁰ O and aluminum at 50 to 60 ° 0. Example 4

For electrolytic polishing of a nickel silver 22 plate a bath was used, each of which contained 10Ö0 ml of 897 ml of phosphoric acid, 50 ml of normal amyl alcohol, Contained 50 ml isoamyl alcohol and 3 ml sulfuric acid. There was also copper

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sulphate is present in a concentration of 1 g / l and nickel sulphate in a concentration of 2 g / l. The polishing was carried out ^{at 22 ° C.}

The initial brightness of the nickel silver plate increased from 20 % to 95% at a constant current density of 20 mA / cm ^2.

In order to show the relationship between the periodic phenomena and the current density, the polishing was carried out at three different current densities. The diagram "A" in FIG. 7 relates to 30 mA / cm ² , the ¹¹ B "to 20 mA / cm ² and the" C ^H to 15 mA / cm ² .

It is clear from FIG. 7 that the number of periods also decreases as the current density decreases and the peaks of the curve become flat at low voltage levels. If the current density is increased, the number of periods and the curves also increase become symmetrical at the beginning, in that their lower part becomes more pointed and their upper part more blunt. In diagram A it can be seen that the amplitude of the periodic processes occurs when the current densities are too high very soon decreases and then these periodic processes subside and finally stop. Here is the bath unsuitable for polishing.

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Example 5

A nickel silver plate was ^{polished in a bath at 24 °} C. The bath contained 90 ml of phosphoric acid and 10 ml of isoamyl alcohol per 100 ml. In addition, sodium fluoride was present in the bath at a concentration of 2 g / l.

The polishing was carried out at a current density of

11 mA / cm, which resulted in a surface brightness of 99 % .

The timing of the output signals of the voltmeter 7 shows Pig. 8. For this It can be seen in the picture that the individual periods have a pointed shape on both sides.

In this bath, the excellent polishing properties with a much lower Energy expenditure achieved. The pointed waveform is very useful for adjusting the polishing. The current density can - without significantly affecting the polishing effect - between 5 and 15 mA / cm can be set.

In addition to nickel silver, the bath is also suitable for polishing brass and copper., Example 6

An austenitic, acid-resistant 18/8

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Chromnickelstah ^ plate was electrolytically polished at a temperature of 28 ⁰ G. For every 100 ml of the polishing bath, 60 ml of phosphoric acid, 30 ml of sulfuric acid and 10 ml of water were used. The bath also contained traces of fluoride ions.

At a constant current density of 21 mA

per cm the initial brightness of the steel plate increased from 20 % to 98% after polishing,

The diagram in FIG. 9 shows the timing of the output signals at the voltmeter 7 _#;

If 5 g / l tartaric acid is also added to the bath, so a current density of only 11 mA / approx enough to achieve an equally favorable polishing effect. The efficiency of the polishing becomes with it significantly increased.

Similar periodic processes take place in the known polishing bath, which is used in conventional austenitic steel. This bath is shown in FIG. If tartaric acid is added to this bath in a concentration of 5 to 10 g / l, the required current intensity is reduced by about 20 % ^{at a polishing temperature of 30 ° C.}

On the basis of the above examples can be an inference be found that the fluctuations

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the voltage values between the bath and the anode electrode is a favorable side effect of the well carried out polishing.

The lower deformation of the signals means a lower current density, the upper one, however high current density. The current density must therefore be set in such a way that the signal shape is symmetrical If the current density increases further, that surface layer on the anode electrode breaks down, which causes the periodic processes and etchings, the oscillation, occur on the surface, dies away and stops.

It can also be seen that with the As the bath temperature increases, the oscillation frequency also increases. This increase is due to the Aggressiveness of the solution is limited because instead of polishing, as a result of chemical dissolution, the Etching occurs.

It is easy to see that the correct bath is one that operates at low temperatures and low current density is effective at high frequencies.

The bath temperature is increased by the heat generated during the electrolysis. With help according to a corresponding regulation, the bath temperature

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door are appropriately kept at the value experienced as optimal. With regard to the fact that the current generator 5 ensures the constant current density,
the polishing quality is only influenced to a small extent by the smaller fluctuations in the bath temperature. The regulation of the temperature mentioned is therefore only necessary for larger facilities.

The temperature required for polishing
is essentially the function of the bath composition, and it can be determined empirically after appropriate training on the basis of the recorded curve together with the optimal bath temperature and bath composition. Shape and other characteristics of this
Curves can serve as a base for the type of changes required.

In practice there is often a requirement to produce a pleasing Glavanian coating on the electrically polished surfaces. the
The surface layer created during the electrolytic polishing makes the post-electroplating
difficult, and therefore the post-plating coatings are stained.

If the application of a further gal-

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vanic layer is required, the polished workpiece must be rinsed with Pliesswasser that with it removes the bath residue from the surface of the workpiece will.

The polished workpiece is then appropriately placed in a slightly alkaline, non-aggressive bath, z, B. in a sodium hydroxide solution at a concentration of 200 g / l briefly to be treated anodically for about 0.5 to 1 minute · This treatment is typical a current density of 40 mA / cm is required.

The anodic treatment must be followed by a short cathodic degreasing of 2 minutes, normal Degreasing baths can be used. The purpose of this treatment is to neutralize the Polishing acids, as well as the removal of any electrolytic contamination. That kind of thing treated polished workpiece can already be galvanized with the required layer after rinsing will. The electroplating can do so without the danger the staining can be carried out. Finally, an aesthetic high-gloss surface is to be obtained.

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Claims (15)

Claims Il method for optimizing electrolytic polishing, in which a workpiece to be polished in a
Polishing bath is anodically treated, characterized , that during the polishing the potential difference between the anode and the bath enveloping the anode is measured, the electrolysis is carried out with a constant current density and the polishing characteristics in this way
be set so that the detected potential difference has periodic fluctuations. 2. The method according to claim 1, characterized in that the periodic potential fluctuations by a Change in the constant current density can be set. 3. The method according to claim 1, characterized in that that the periodic potential fluctuations are adjusted by changing the bath temperature. 4. The method according to claim 3, characterized in that the bath temperature is kept constant by a control will. 5. The method according to claim 1, characterized in that 49- (24.028-3443) -Df-Bk 9098 39/0648 2354605 that the periodic potential fluctuations are adjusted by changing the bath composition. 6. The method according to claim 1 using a bath of a mixture of phosphoric acid and normal amyl alcoholj characterized in that fluoride ions entered into the bath in a maximum concentration of 0.5 g / l will. 7. The method according to claim 1 using a bath of a mixture of phosphoric acid, normal amyl alcohol and water, characterized in that sodium sulfate in a concentration of 1.4 to 1.8 g / l is entered. 8. The method according to claim 1, characterized in that a bath consisting of a mixture of 900 ml of phosphoric acid, 50 ml normal amyl alcohol, 50 ml isoamyl alcohol and 3 ml Sulfuric acid is used, which also contains copper sulfate in a concentration of 1 g / l and nickel sulfate in a concentration of 2 g / l. 9. The method according to claim 1, characterized in that a bath is used which contains 90 ml of phosphoric acid, Contains 10 ml isoamyl alcohol and 2 g / l sodium fluoride per 100 ml. 10. The method according to claim 1, characterized in that a bath is used which contains 60 ml of phosphoric acid, 30 ml Contains sulfuric acid and 10 ml of water per 100 ml and fluoride ions in a maximum concentration of 0.5 g / l. 11. The method according to claim 10, characterized in that the bath tartaric acid in a concentration of 909839/0648 2354605 5 g / l is added. 12. Circuit arrangement for performing the method according to claim 1, with anodes immersed in a polishing bath and cathodes and a power source connected to them, characterized in that in the polishing bath (2) in the A reference electrode (6) which detects the potential of the polishing bath (2) is arranged near the anode (3), and the anode (3) and the reference electrode (6) are connected to the input of a voltmeter (7). 13. Circuit arrangement according to claim 12, characterized in that the current source is a current generator (5), in particular a direct current generator. m . Process for the preparation of electrolytically polished workpieces for re-plating, in which the polishing bath residues are removed from the surface of the workpiece after electrolytic polishing by rinsing, characterized in that the workpiece is subjected to an anodic treatment in a non-aggressive, slightly alkaline bath and after subsequent rinsing process is cathodically degreased. 15. The method according to claim 14, characterized in that the anodic treatment in a sodium hydroxide solution is carried out at a concentration of 200 g / l for 0.5 to 1 minute. 909839/0648