CZ144795A3 - Process of surface layer electrolytic coating - Google Patents

Abstract

The invention relates to a galvanic coating process to provide a structured surface coating on a workpiece with an electrically conductive surface and a device for implementing the process. Here, the object to be coated is the cathode in a galvanic bath. The process current is raised in steps during a nucleation phase (10, 11) in which the stepwise increase in the current results in the formation of a deposit of individual or adjacent bodies on the surface of the object. The process current is then kept constant during a ramp working period (12), resulting in the growth of the previously produced nuclei or bodies. The process may be cyclically repeated.

Description

(57) In electroplating articles with an electrically conductive surface, at the embryo formation stage (10,11), the current density is gradually increased gradually until a surface layer is formed on the surface, whereupon the current density is kept constant during the continuous plating time.

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surface layers

Method of galvanic deposition

BACKGROUND OF THE INVENTION The present invention relates to a process for the electrochemical (galvanic) deposition of a surface layer according to German patent application DS 42 11 881.6-24.

BACKGROUND OF THE INVENTION

Such surface structures are more or less well accomplished by a chemical etching process; following the formation of the layer or by mechanical treatment such as grinding or sanding. A hardwave layer is then applied to the structure thus formed. These various manufacturing operations are expensive and require complicated manufacturing techniques. The costs are essentially determined by mechanical or chemical machining operations for the production of structures.

In the field of forming metal layers, expensive and very difficult to disperse separation processes are also used, in which a specific surface structure is achieved by organic or inorganic foreign substances which are incorporated, for example, in a chromium layer and / or block the layer growth of chromium during the separation process, so that rough surfaces are formed. The foreign substances are spread in the glass-fiber.

German patent specification LS 33 07 748 relates to a method of electrochemical layer formation in which pulse current is used for embryo formation. If a suitable current density is used, the resulting embryos form a denitrical, i.e., tree-like, surface structure. The term current structure means the mean current density at the cathode surface.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved method for the electrochemical deposition of structural metal layers which do not need to be mechanically or chemically further treated and which can produce many structural metal layers as well as apparatus for carrying out this process. the formation of the embryo is fed in several stages.

This is done by the fact that during the voltage and / or current the current is limited

The development of the invention according to a predetermined. 0 in mA / cm for the degree of the current current density, in the case of the current density seams, the stages are fed to the bath reaches the structural effects, insisting that the degrees increase the current density by 1 starting value to each or each other, and from about 0.1 to 30 sec. and in such a number as to consist of a deposit of approximately spherical or object deposited. Thereafter, the dendritic bodies on the surface are fed a predetermined continuous working time with a current density in the range of 2-0% to 120% of the structural current density during the embryonic growth phase.

Other features of the invention are included; in the other sub-claims.

The structural layer is directly electroplated on the object. To this end, the article must have an electrically conductive surface, which is generally abraded, and would provide a smooth base for the structural layer. Prior to the coating process, the article is cleaned and degreased according to conventional electroplating rules. It is immersed as a cathode into a galvanic bath containing an anode. The distance between the anode and cathode is most often selected in the range between 1 and 40 cm. As electrolyte, chromium electrolites are preferably used, in particular chromosulfur mixture electrolites, chromoacid mixture electrolites or alloy electrolites.

A process current is applied between the anode and the cathode and the flowing current causes the material to be deposited on the object to be coated and used as the cathode. The invention proposes to attach positive impulses to the formation of nuclei. The process of forming a structure consists of the stage of formation of the seed and of the stage of growth of the seed. Initially, in the seed formation phase, the process current is increased to five and the process current in multiple stages is always a predetermined change in current density from 1 to 6 m.A / cm for one stage from the initial value to the structural current density. The initial value is 0 mA / cm, but may also be higher if the nucleation phase follows directly after the previous galvanic process phase. The time between two current bust increases. V * \ z η θ - · »2_ £ í 2. Z Π Θ

0.1 to 3D seconds. N use the step distances v · T -1 · v r-t 1 \ Z · c lick 1 second te, even with each current jump new germs are formed. In contrast to the pulse current of the layer, the process current is not returned to zero again after each positive jump, but is further increased by each current jump. In this way, in particular, rounder and more uniform plugs can be separated, respectively. bodies per object than is possible with the known pulse current method. The jet stages are fed in such a number of baths that a United States concussion is achieved on the surface of the article, consisting of individual or stacked spherical or ritual, i.e., tree-like bodies.

It is advantageous to achieve, with the seed formation phase, a thickness of the structural layer from 4 µm to 10 µm. This usually requires 10 to 240 current stages. Particularly good results are obtained with 50 to 60 degrees. At the end of the last current stage the current density reached is the structural current density <

Upon reaching this structural current density, the seed formation phase, which constitutes the actual formation of the structure, is substantially closed. The arrangement of the resulting structure is dependent on many parameters, in particular the current density of the structure, the number, size and time spacing of the current stages, the bath temperature and the electrolytes used. Changing the current density to one degree, as well as the time between two increases in current density, can vary during the seed formation phase. Depending on the current density, different surface structures may be formed, which are mainly characterized by different roughness depths. The ideal parameters of the production process can simply be determined empirically. As a rule, it is possible to increase the bath temperature and higher by:

The acid density in the electrolyte also decreases the current density.

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This structural current density is two to three times the current density used in normal DC current formation. The DC current is applied at a current of 2 ‘densities in the range of 15 to 60 mA / cm. The current density is dependent on the electrolyte and the bath temperature. Ordens densities in the range of 30 to 180 mA / cm are possible in the formation of the structural layer.

This is followed by the growth phase of the seeds. The process current with a current density in the range from 80% to 120% of the structural current density is fed during a predetermined step working time. During a continuous working time, an approximately uniform current flows, resulting in an increase in the structure formed on the object. Depending on the duration of the continuous working time, this structural layer may appear more or less vigorous. The growth takes place at the highest points of the structural layer more rapidly than at the deep points between the bodies deposited in the seed formation phase. This first results in a further increase in roughness during the growth phase of the seeds. The step working time is in the range of from 1 to 600 seconds, preferably about 30 seconds.

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Z \ Z from working time the tebolo- gical current is reduced to its final value, often to zero. This drop in the process current to the final value can be made in a stepwise manner, but a continuous drop is also possible. Here, too, good results are achieved with a stepwise change in the process current. The current stages are preferably in the range from -1 to -β mA / cnr for the stage and the time between the two current stages preferably ranges from 0.1 to 1 sec of the cunt stage.

Three manufacturing steps have been described above: / continuously increasing the process current during the seed phase to reach the structural current density, maintaining the process current within the structural current density range during a continuous working time (seed growth phase) and subsequently reducing the process current to the final value. These production steps represent the production cycle of the structure. They may be cyclically repeated. This is particularly advantageous when stronger surface texturing is required. The final value of the previous cycle always corresponds to the starting value of the next cycle. The number of repetitions is dependent on the desired surface structure and layer thickness. Good results were achieved with two to twenty fold repetitions. The final values of the individual cycles may be differently high.

It is advantageous if the object on which the layer is to be formed has been immersed in a bath, preferably nut, for some time before the start of the manufacturing process. This waiting time mainly serves temperatures, that is, the material of the article tastes the temperature of the electrolyte.

Good results are obtained if a base layer is applied by direct current prior to application of the structural layer under the conditions usual in normal chromium plating. This is accomplished by the fact that at the beginning of the formation of the layer a base pulse is applied to one mic alignment, receiving a three-voltage or current current density (15 to 60 current values of conventional pulses). In this case, a mA / cm @ -1 is used which corresponds to normal chromium plating. This basic impulse lasts approximately 600 seconds. In order to creep the change in concentration due to the prior DC treatment in the boundary layer phase prior to the formation of the structure, it is advantageous to include a current-free intermediate time of approximately 60 seconds after the base pulse and before the start of the structure formation.

This method can be used in many areas of components for special structural properties. It is known to produce surface layers on structural parts by means of galvanic processes. Frequently, certain requirements are placed on the surface structure of the workpiece to be coated. For example, certain lubricant depots may have cylindrical sliding surfaces for storing lubricants, the medical and optical apparatuses must have a surface; with low reflection. Certain reflective grades are also required for functional and decorative applications in the furniture and medical armature industry. In the graphics industry, printing machines with wet friction rollers with a special rough surface are required. In the forming technique, chrome-plated tools can be used to give the workpiece a structured surface. For example, the sheet surface gets a structured surface when rolled with chromium-plated rolls of the structure.

The apparatus for carrying out the described method consists of a galvanic bath containing an electrolyte solution with a metal concentration. Suitable electrolytes are chromium electrolytes, in particular electrolytes of chromosulfur mixtures, electrolyte / chronically selected mixtures, or alloyed electrolytes. One preferred electrolyte has a concentration of from 180 to 300 grams of chromium trioxide (CrO) per liter. In addition, foreign additives such as sulfuric acid (HgSO4), hydrofluoric acid, fluorosilicic acid (HgSiPg) and mixtures thereof may be added. A preferred electrolyte contains 1 to 3.5 grams of sulfuric acid (H 2 SO 4) per liter. The galvanic bath is generally heated, the electrolyte temperature preferably being 30 to 35 ° C.

The anode and cathode are immersed in the electrolysis bath solution, the object to be coated constituting the cathode or at least a portion of the cathode. When using a chrome electrolyte, platinum or a lead-tin alloy (PbSn2) is preferably used as the anode material. The anode and cathode are coupled to the power supply device. The process current can be increased in several stages, always up to the structural current density. The time intervals between two dem determinable changes in the current density from 1 A / cm or oro degree from the initial value to the current increases are adjustable between 0.1 and 30 seconds. Upon reaching the structural current density, a technological current having a current density ranging from 80% to 120% of the structural current density can be connected for a predetermined continuous working time. In order to achieve a uniform layer formation, the device can be equipped with a rotary drive for continuously rotating the object. The distance between the anode and the article to be coated is selected in the range of 1 to 40 cm, preferably 25 cm.

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Overview of the drawings

The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings.

Fig. 1 is a schematic representation of a device for galvanic deposition of structural layers.

Fig. 2 is a graphical representation of the current density over time of the structural layer.

FIG. 3 is a 200: 1 photographic representation of the surface structure of an article provided with a surface layer formed in the manufacturing process described in FIG. 2.

Figure 4 is a 500: 1 photographic representation of the surface structure shown in Figure 3.

FIG. 5 is a graphical representation of the current density over time in the manufacture of the structural layer.

FIG. 6 is a graphical representation of the current density over time of the structural layer

Fig. 7 is a graphical representation of the current density over time in the manufacture of the structural layer.

Examples of the invention

Giant. 1 shows a galvanic deposition filled with an electrolytic hematic representation of structural layers with liquid 1 forming an apparatus for a galvanic bath tank. The object is immersed in the galvanic bath. The object to be coated comprises a cathode 2. The anode 3 and cathode 2 are connected to a controlled electrical power source 4. The power source 4 may be a current source or a voltage source. Because, as far as electrical influences are concerned, current densities at the cathode, these effects are decisive for layer formation, the production process can be more accurately controlled by the current source. The use of a voltage source, on the other hand, has the advantage that the cost of the electrical circuit means is lower. If other parameters, such as bath temperature and electrolyte concentration, do not change significantly, the production process can also be well controlled by a voltage source.

Electric power source 4 is controlled by the program as regard the control unit 5. The control unit 5 can be pre-enter any příp.proudu voltage waveforms, which are then automatically fed by four sources of energy ^- electrode.

Giant. 2 shows a graphical representation of the time course of the technological current density in the manufacture of the structural layer. The horizontal axis in Fig. 2 is time 03a, the vertical y axis is the current density. This is an exemplary embodiment with a possible production sequence, which will be described in more detail below. Giant. 3 and 4 show a photographic representation. structural layers produced in this way.

As a galvanic bath, a chromium electrolyte mixture of 200 grams of chromium trioxide (Cr 2 O) and 2 grams of sulfuric acid (H 2 SO 4) was used. ie the workpiece to be coated is a rotationally symmetrical component, a wet friction roller for the printing industry. In order to create suitable structural chrome plating, first of all steel, it is abraded with a depth of yftm. For this, a 30 [mu] m thick nickel layer and / [mu] t chrome free layer without cracks are applied. 10, so prepared for structural chromium plating in order to achieve the most uniform layer possible. The workpiece forms a cathode, as an anode is used platinum ttane or Pb3n7. The anode-cathode electrode gap is set to 25 cm.

During the first production phase 7, the process current remains disconnected. This phase serves to acclimatize the workpiece to the galvanic bath. The workpiece takes over the temperature from the electrolyte. After approximately one minute, direct current is applied between the anode and cathode. This current remains connected during phase 8, which lasts about 600 seconds. In this process, a base layer of trembling is applied to the giant by direct current. The current density used is also common in normal chrome plating, namely 20 mA / 8m “. After application of the base layer by direct current, the second phase 9 is de-energized.

Then the actual production of the structure begins. During phases 10 and 11, the current density in degrees increases to the structural current density 14. The characteristic data of the degrees (the height of the current stages and the time distance between the two current steps) changes during the increments. During the first phase 10

0 - degrees increases to 40 mA / cm of density from 2.5 mA / cmý for degree. The time 28 between the current in To derives the change in the two current stages is 5 d density increases during the phase of seconds. It was then executed at 62 interest rates at a structural current density of 100 mA / cm, the time between two ore sons being 6 seconds (the current density, ie its deflection, shown in 2, is not to scale, the same is true for the graphs in FIG. 3 and 6.

After reaching the structural current density, this current density is maintained during the incoming working time 12, while the direct current flowing leads to the growth of the structural layer formed in phases 10 and 11. The duration of the continuous working time is 60 seconds. Then, the current density again decreases in steps to a final value of 0 mA / cm in 22 steps. The time between two current steps is 4 seconds.

For technical reasons and in the case of a wet friction roller of practical use, a further 4 to S / µm layer of chromium with microscopic cracks is applied to the chromium layer produced by the method according to the invention. This is done by a nice direct current and it will not be explained in more detail under conventional galvanic conditions.

¹ uxazuo microscope images SL Behavioral chromium layer, which was formed in the manner described for FIG. 2. The structural layer of approximately Kulice ovitých, individual Ké mutually superposed bodies tural layer has a surface roughness comprising predominantly a partially • viewing the strukRz = 8 at JHM · Carrier 25+. The term "carrier 4762 also defined as the mater fraction is by the fraction fraction".

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Giant. 5 shows the current density over time of another method for forming a structural layer. The production phases 7, 8 and 9 were already discussed in the embodiments of FIG. 2. In the following phase 15, the current density is increased in 110 equal steps to a structural current density of 100 mA / cm &quot;. The time between two current steps is 4 seconds. Consequently, after a short current-free torque, the production cycle starting from the 15 _x 16 and 17 phases is repeated again.

Giant. 6 shows the current density over time of another method. After a waiting phase of 7 to acclimatise to ob PRODUCT DELIVERY electroplating bath ^n?? Fin ^e IKP £ 18 of direct current, which in a way corresponding to eight pulse you nosměrného current in Fig. 2. Subsequently, the follow directly nuclei forming phase 19 in which the current density is then stepped up to the structural current density 24. The current density is then maintained during the continuous working time 20 at the structural density and t

-heoehem to the final value of the following phase again

21, continuously decline26. After a short embryonic waiting time of 28 23, the current current density becomes steadily current value 26 by increasing the current density to a new structure 25. In this case, the initial seed formation phase 23 is equal to - to which the current density drops at the end of the previous structure production cycle. The current density is then maintained at the structural current density 25 during the continuous working time 27 and, in connection thereto, drops to a new final value of 0 mA / cm &quot;.

Giant. 7 shows the current density over time of another variant of the manufacturing method. Production department;; 8 to 9 have already been explained in FIG. 2. The production stream is then increased stepwise to the structural current density 30 during phase 29. Then, during a continuous working time 32, a production current having a current density value 80C of the structural current value 30 is supplied.

In between, there is an idle standby time 31. After the continuous working time / 32, the production flow is reduced to a final value during phase 33. This final value serves as an initial value for the second structure cycle of the structure, starting with a stepwise increase in current in phase 35. To achieve a new structural current density 36, a production current of 120% of the structural current density 36 is fed during continuous working time 38. again, the idle time is again 37

Claims (12)

NTOYá Claims Method for the electrochemical (galvanic) deposition of a surface layer according to German patent application P 42 11 881.6-24, characterized in that during the seed formation phase the electrical voltage and / or the electric current is applied in several stages. Method according to claim 1, characterized in that the steps are each increased by a predetermined change in the current density OV by 1 to 6 mA / cm / 'for the step from the initial value to the structural current density (14, 24, 25). wherein the time (28) between the two increases in current density is about 0.1 to 30 seconds and the steps are fed to the bath until a structural layer consisting of individual or stacked approximately spherical or tree-like bodies is deposited on the and then fed in the seed growth phase during a predetermined continuous working time (12) with a current density within the range of the structural current density. 16) production S0% to Method according to claim 1 or 2, characterized in that the duration in bl π z.n and the individual 3 stages is seconds. 4. Method according to claims 1 to 3, vv: X, XX, X 2 £. * 2 2 LC ⁿ C oud density increases in 10 and: D ¹ 1 Ό2Τ.Χ0'l · The method of any one of 4, characterized in (14, 24, 25) is in 5 kii 1 to mA / cm. of the preceding claims having a structural current in the range of 30 mA / cm to 180 Method according to one of the preceding claims 1 to 5, characterized in that the continuous working time (12, 16) is between j and 600 seconds, preferably approximately 30 seconds. Method according to any of the preceding sheets, characterized in that the production flow is reduced to a final value (26) after the continuous working time. Method according to claim 7, characterized in that after the continuous working time, the production flow decreases steadily with a predetermined change from -1 to -8.2 to the final value. mA / cm * Method for applying a surface layer to an electrically conductive surface of an object, characterized in that the method according to one of claims 7 or S is repeated cyclically two to twenty times, wherein the final value of the preceding cycle always corresponds to the initial value of the subsequent sibling. Method according to claim 9, characterized in that the final values (26) are differently high. Method according to any one of the preceding claims 1 to 10, characterized in that a DC pulse (6, 18) with a current density of 15 to 60 mA / c is applied before the structures are formed. to form a base layer of direct current. Use of the method according to any one of the preceding claims 1 to 11, characterized in that it is used to form cylindrical surface structures for lubricant storage containers, to set defined degrees of reflection from surfaces in optical, medical devices and for functional and decorative applications in the furniture and medical opening, for the creation of surfaces with defined roughness in products of the graphic industry and for the creation of structured surfaces for tools.