FI103674B - A method of electrochemically depositing a surface of a machine part - Google Patents

Description

103674

A method of electrochemically depositing a surface of a machine part

The present invention relates to the production of an electrochemical (galvanic) coating by a process according to German patent application DE-42 11 881.6-24.

Such coating structures are more or less well produced by chemical etching processes during coating or by mechanical machining methods 10 such as grinding or sandblasting. A hard chromium layer is then added to the surface thus made. These various production steps, which are essential for production, are costly and also require complex process technology. The costs are essentially determined by the mechanical or chemical machining steps required to produce the structure.

15

In the area of fabricating metal layers, time-consuming and, r. only very difficult to control dispersion separation processes, in which a given surface structure is obtained by organic or inorganic foreign substances which are incorporated, for example, into the chromium layer and / or which prevent the chromium layer from growing during the separation process to produce coarse surfaces. Foreign substances act as disintegrators in the electrolyte.

DE-33 07 748 relates to a process for electrochemical coating using pulsed current for nucleation. If a suitable electric current density is used, the resulting nuclei form a coniferous structure. In this way, rough, coniferous surfaces can be produced in a single operation. Electrical current. *. density means the average density of the electric current at the cathode surface.

It has been an object of the invention to provide an improved process for electrochemically fabricating structural metal layers and as a basis for mechanical or chemical post-treatment that can be produced by a variety of structural metal layers, as well as. apparatus for carrying out this method.

This object is solved according to the characterizing features 35 of the claims.

2 103674

The structural layer is applied directly to the object to be galvanically coated. For this purpose, its surface must be electrically conductive, generally providing a smooth surface for the structural layer. Prior to this coating process, the target is cleaned and degreased according to standard galvanizing techniques. It is immersed as a cathode in a galvanic bath which also has an anode. The distance between the anode and the cathode is usually selected between 1 and 40 cm. The electrolyte is preferably a chromium electrolyte, in particular a sulfuric acid chromium electrolyte, a sulfuric acid chromium electrolyte or an alloy tongue electrolyte.

10 Process voltage can be provided between the anode and the cathode, and the current applied to the material to be coated as the cathode can be affected by electrical current. According to the invention, it is proposed that positive current hops are used to form the cores. The process of producing the structure comprises a nucleation step and a nucleation growth step. Next, in the core formation step, the process voltage and process current are increased in several steps, each with a predetermined change from 1 to 6 mA / cm 2 per step, from the initial value to the structural current. The initial value is 0 mA / cm 2, but may also be higher if the nucleation step immediately follows the preceding galvanic process step and no current is allowed to fall to zero in the meantime. The time between the two current density increments is between about 0.1 and 30 seconds. With each jump, you can create. new kernels. In contrast to pulse current plating, the process current does not return; after a positive jump back to zero, but it increases with each current jump. In this way, it is possible to distinguish kernels or objects in particular that are more rounded and flatter than the \: 25 that would be possible with the known pulse flow method. or a structural layer consisting of conical pieces is provided on the surface of the object.

It is advantageous to aim for a structural layer thickness in the core formation step of between 4 and 10 µm. Usually this requires operation between 10 and 240 current phases and I get quite good results in 50-60 phases.

I i · r :. The current density achieved after the end of the last current phase is the structural current - 1 ·. ; 35 density. When this structural current density is reached, the core formation step, the actual structure formation, is largely completed. The composition of the resulting structure is dependent on a number of parameters, in particular the selected circuit current density, the number, magnitude and time interval of the current phases, the bath temperature and the electrolyte used. The change in current density per phase, as well as the time between two current density increases, can be varied during the nucleation phase. Depending on the nature of the current, different surface structures can be produced which are essentially characterized by different pattern depths. Simply experiment with the ideal process parameters. As a rule, at higher bath temperatures and higher acid content in the electrolyte, higher structural current densities can also be used.

10 This structural current density is, as a rule, two to three times the current density used in conventional DC plating. DC coating operates in the current density range of 15-60 mA / cm2. The value of the current density is then dependent on the electrolyte and the bath temperature. Current densities of 30 to 180 mA / cm2 are possible in structural coating.

15

This is followed by the growth of the nuclei. In this case, a process current with a current density of 80-120% of the structural current density is used during a predetermined ramp time. During ramp operation, a relatively steady current flows, leading to an increase in the structure of the object. Depending on the duration of the ramp time, this structural layer may receive a more or less intense stamp. Growth ends. then, at the highest points of the structural layer faster than at the deeper points ;; The ramp time is most often in the range of 1-600 seconds, preferably about 30 seconds.

25 *:, · · After the ramp time, the process current is reduced to its end value, often to zero. This process stream computation can be done in a single jump, but it is also possible with stepwise computation. Here, too, good results were achieved by the stepwise change of the process stream. The current phases are then preferably in the range of -1 · -8 mA / cm 2 and the time between the current phases is preferably selected in the range of 0.1 to 1 second.

• · · • «« • · • *: „. 'Three procedural steps have been explained above: the gradual increase of the process stream:. during the nucleation step until reaching the structural current density, keeping the process current in the structural current density region during the ramp operating time (nucleation step) and finally dropping the process current to the terminal value. These procedural steps form a series of steps for producing the structure. They are reproducible in step 4 103674 series. This is advantageous especially when a strong surface structure is desired. In this case, the main value of the previous phase sequence corresponds to the starting value of the next phase sequence. The number of repetitions depends on the surface texture desired. Good results were obtained with repetitions ranging from two to 20 times.

5 The end values of individual phase series may be of different magnitudes.

It is advantageous to immerse the object to be coated in the bath for a short time, preferably one minute after the process has started. This waiting time serves above all temperature equilibrium, i.e., the base raw material reaches approximately electrolyte temperature.

Good results can be obtained if, before the structural layer is applied, first a dc base layer under normal conditions is first applied. This is achieved by applying a basic pulse (voltage or current pulse) at the start of the coating.

A current density of 15-60 mA / cm2 is then used, which corresponds to the current values commonly used in conventional chromium plating. This basic pulse lasts approximately 600 seconds. In order to eliminate the pretreatment dc concentration changes in the phase boundary before the structure is made, it is advantageous to add a fully uninterrupted Interval after the base pulse and before the structure is produced.

This method is used in many fields of technology to provide special surface properties of components. Coating of components using a galvanic process is known. The surface structure of a coated workpiece '(' 'is often subject to certain requirements. For example, the sliding surfaces of cylinders become' .25 have designated lubricant storage locations for receiving lubricants *: and medical or optical devices shall have a surface with low reflectance I · · · v '. * · *: Printing machines require dehumidification cylinders with a special "rough" surface. In design technology, structural chromed tools can be used to give the workpiece a structural surface. the surface can be modified with structural chromed rolls by passing it through them.

· »• · • f; The apparatus for carrying out the procedure described consists of a galvanic bath containing: a metal electrolytic bath solution. The preferred electrolyte is considered to be chromium electrolyte, especially sulfuric acid chromium electrolyte, succinic chromium electrolyte or alloy electrolyte. The preferred electro-103674 5 lits has a concentration of 180-300 grams of Cr3O3 per liter of chromic acid. In addition, foreign additives such as sulfuric acid H2SO4, hydrofluoric acid H2F2, hydrofluoric acid H2SiF6 and mixtures thereof may be added thereto. The preferred electrolyte contains 1-3.5 grams of sulfuric acid per liter of H2SO4. The galvanic bath is heated normally and the electrolyte temperature is preferably 30-55 ° C.

One anode and one cathode are immersed in the electrolytic bath solution, whereby the object to be coated forms a cathode or is at least part of the cathode. When using chromium electrolyte, platinum-plated platinum or PbSn7 is preferred as the anode material. 10 The anode and cathode are connected to the device for supplying a process current. The process current can be increased in several steps, always with a predetermined current density change of 1-6 mA / cm2 per phase, from the initial value to the structural current density. The time interval between power ups is adjustable between 0.1 and 30 seconds. Once the structure has been reached, a process stream with a current density within the range of 80-120 of the structure current is available for a pre-adjustable 15 ramp time. To achieve a uniform coating, the device may be provided with a rotary drive to continuously rotate the object. The distance between the anode and the object to be coated is selected from 1 to 40 cm, preferably 25 cm.

The invention will be explained in detail by the following embodiments, which refer to. Fig. 1 schematically illustrates a device for galvanically coating structural layers; Figure 2 graphically illustrates the time course of current density density when fabricating a structural layer; Fig. 3 is a photograph of a 200: 1 scale surface structure of a subject, · · v ·, made according to the sequence of procedures described in Fig. 2; Fig. 4 is a photograph of a 500: 1 scale of the surface structure of Fig. 3 and Fig. 5 is a graphical representation of the temporal current density period of the structural layer; 9 9 9 · · * FIG. 6 graphically illustrates a temporal current density cycle period of producing a structural layer and; Fig. 7 graphically illustrates the time course of the current layer density generation of the structural layer: 35.

6 103674

Figure 1 is a schematic representation of a device for making a structural layer of galvanic layer. The container filled with electrolytic fluid 1 forms a galvanic bath. The plated object 2 and the anode 3 are immersed in the galvanic bath. The plated object forms the cathode 2. The anode and the cathode are connected to a controllable electrical energy source 5 4. The energy source may be a current or voltage source. Because, with respect to electrical effects, the current or current density at the cathode affects the coating, the process can be precisely controlled by a power source. In addition, the advantage of using a voltage source is the reduced need for electric switching. As long as other parameters, such as bath temperature and electrolyte concentration, do not substantially change, the process can also be well controlled with 10 voltage sources.

The electrical power source 4 is controlled by a programmed control unit 5. The control unit can supply the desired time voltage or current cycles, which are then automatically transmitted through the energy source 4 to the electrodes.

15

Figure 2 graphically illustrates the time course of process current density when producing a structural layer. The horizontal axis of Figure 2 is a time axis, the vertical axis y shows the current density. This is an exemplary embodiment for a possible method flow, which will be explained in detail below. Figures 3 and 4 show photographs of the structural layer produced by this method.

1 '' '': -. The galvanic bath uses a sulfuric acid chromium electrolyte containing 200 grams of earth per liter of Cr03 and 2 grams of sulfuric acid per liter of H2SO4. The workpiece to be coated is a symmetrical component in the direction of rotation, which /. 25 is the dehumidification cylinder in the printing industry. To create a suitable starting surface for structural chromium plating, the steel St52 cylinder is first finely ground to a roughness depth R 2 <3 mm. Thereafter, a 30 mm thick nickel layer is applied in accordance with the general conditions of electroplating and a 10 mm thick non-cracked chromium-t.i. The workpiece thus prepared is rotated in a galvanic bath For a more even deposit of $ 30. The workpiece forms a cathode, platinum-titanium or PbSn7 is used as the anode. The distance between the anode and the cathode • · is adjusted to 25 mm.

i i: ': During the first process step 7, the process power is off. The purpose of this step 35 is to adapt the workpiece to the galvanic bath. During this time, the temperature of the workpiece becomes the same as that of the galvanic bath. After about one minute, direct current is applied between the anode and the cathode. It is kept on 103674 7 for a duration of step 8 which lasts approximately 600 seconds. In this case, the workpiece is coated with a chrome dc base coating. The current density used is the same as usual for normal chromes, here 20 mA / cm2. After applying the DC floor coating, a second step 9 without power follows.

5

After that, the actual production of the structure begins. During steps 10 and 11, the current density is gradually increased to the structural current density 14. The characteristic information of the stages (the height of the current phases and the time between the two current phases) are then varied during the rise. During the first step 10, the current is increased in step 16 to 40 mA / cm 2. This corresponds to a change in current density of 2.5 mA / cm2 per phase. The time 28 between the power phases is 5 seconds. Thereafter, the current density is increased during step 11 to a structural current density of 100 mA / cm 2 in step 62, with a time interval of 6 seconds between the two current phases (the current flow shown in FIG. 2 is not scaled, the same applies to FIG. 5).

Once the structural current density has been reached, this current density is maintained during ramp time 12. The flowing direct current then results in an increase in the structural layer produced in steps 10 and 11. The ramp time is 60 seconds. Thereafter, the current density is again reduced in steps, in 22 steps, to a terminal value of 0 mA / cm 2. The time between two current phases is then 4 seconds.

For operational reasons, in the case of a dehumidifying cylinder, it is further subjected to a chromium layer after the process according to the invention,. 25 4-8 mm thick micro-cracked chromium plating. This is done by galvanizing technology under normal DC conditions and is not explained further in this connection.

t 4 m · Figures 3 and 4 show microscopic images of a chromium structural layer produced. : T: 30 according to the method described in connection with Figure 2. The structural layer consists mainly of ball-shaped, individual and partly overlapping parts. In the shown structural layer, the surface roughness Rz is 8 mm 25% '; · Bearing part. The "bearing part" is also defined in DIN 4762 as "ma ·: .j: material part".

35

Figure 5 shows the time course of the current density in connection with the steps of another structural coating method. The process steps 7, 8 and 9 were already explained in connection with Fig. 2 8 103674. Subsequently, in the next step 15, the current density is increased by 110 similar steps to a structural current density of 100 mA / cm 2. The time between power phases is 10 seconds. The current density of the ramp operating time, which is 16-60 seconds, is calculated this time in 22 similar steps to 0 mA / cm2. Time two-phase color 5 has 4 seconds. In this connection, after a short, uninterrupted moment, the entire process step sequence consisting of steps 15, 16 and 17 is repeated.

Figure 6 illustrates the time course of another current of the method series. After the waiting step 7 10 for the workpiece adaptation to the bath follows a DC pulse 18 which in its own way corresponds to the DC pulse 8 of Figure 2. when step 21 drops it stepwise to endpoint 26. After a short wait 22, step 15 is followed by a rebuild step 23 with a gradual increase in current density to a new structural current density 25. In this case, the start current density of the nucleation step 23 is the same as the end value 26, to which the current density was calculated at the end of the last structuring phase. The current density is then maintained again during the ramp working time 27 at the structural current density 25 and then calculated as a hyp-20 at the new end value of 0 mA / cm 2.

Figure 7 shows the time course of the current density of another alternative to the method flow, j Method steps 7-9 were already explained in connection with Figure 2. The process stream is increased then, in step 29, stepwise to the structural current density 30. Thereafter j; . 25 is used during ramp duty 32 process currents with a reference density value of 80% of build / current density 30. Between these is left an unstoppable rest time 31. Ramp duty time 32! After the completion of the process, the process current is reduced to its end value during step 33. This endpoint serves as the starting value for the second set of structural yield steps that begin with • · · v: step 35 incremental current boost. After the new structural current stream 30 has been reached, the process flow to be applied is current during ramp working time 38. with a density of 120% of the structural current density 36. Again, a powerless rest time 37 is omitted.

I I

Claims (12)

1. Method for electrochemical (galvanic) coating of a machine part with DC current coating, at least during the initial pulse of the electrical voltage! V and / or electric current cores of falling material are formed pk the surface to be coated and furthermore, at least with a subsequent pulse, growth of:. . the nuclei of falling material by precipitating more precipitating material, characteristic; This is due to the fact that, during the nucleation phase, the electrical voltage and / or electric current is increased in several stages at intervals between 0.1 and 30 seconds and that the changes in current density in the phases are between 1 and 6 mA / cm2. 103674 A method according to claim 1, characterized in that the stages each include a pre-definable change in current density between 1 and 6 mA / cm 2 per stage from the initial value to the structural current density (14, 24, 25), wherein the period ( 28) between two increases in current density is about 0.1-30 seconds, and the bath is subjected to such a large number of stages that a structural coating is produced consisting of a layer of individual or bonded, roughly spherical or convex particles on the surface of the surface, and thereafter, during a pre-defined frame work period (12, 16) in the growth stage of the core, a process stream whose current density is in the intervals of 80-120% of the structural current density is used. 10 Method according to claim 1 or 2, characterized in that the individual stages last for about 7 seconds. Method according to at least some of claims 1-3, characterized in that the current density is increased in the 10-240 stages. Method according to at least some of claims 1-4, characterized in that the structural current density (14, 24, 25) is in the ranges 30-180 mA / cm 2. Method according to at least some of claims 1-5, characterized in that the frame work period (12, 16) is 1-600 seconds, preferably about 30 seconds. Process according to at least some of claims 1-6, characterized in that the process stream is lowered to a final value (26) after the frame work period. . . 25 · · · Process according to claim 7, characterized in that the process stream after the frame work period is gradually reduced to a final value with a respective pre-defined change, which is -1 - -8 mA / cm2 per stage. • · · • · «•« «• ·« v; 9. A method for coating the surface of an electrically conductive article, characterized in: v. characterized in that the process is repeated according to the method according to claim 7 or 8 in spoon sequences from two to twenty times, the final value of the respective stage I sequences corresponding to the initial value of the following spoon sequence. '' ·! Method according to claim 9, characterized in that the final values (26) are different Large. 103674 Method according to at least some of claims 1-10, characterized in that, before the production of the structure, a direct current pulse (8, 18) is used whose current density is 15-60 mA / cm 2 to produce a direct current bottom coating. Use of at least one method according to any one of claims 1-11, characterized in that it is applied - to produce the surface structure of a lubricant site receiving lubricant cylinder - to regulate the degree of reflection of the surface of defined optical medical devices. rates and for functional and decorative purposes in the furniture and hospital material industry, - to produce a surface of a certain degree of roughness in the graphic industry, - to produce structural surfaces on tools. 15 • · • t · · · · * # · · IM • · I • · I • _ · · · • *? • · «• Ml I I I • · 9 m • • · • ·« • · I I 4. I II I I I - · I III 4 «I * i» I * · M · · <IL. i n T '· a