Method for electrochemical polishing of metal workpieces and electrolyte medium suitable therefor
The use of a superabsorbent polymer-based electrolyte medium addresses the inefficiencies of existing electrochemical polishing methods by providing uniform material removal and preventing mechanical damage, resulting in high-quality polished surfaces on complex workpieces.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- OTEC PRAZISIONSFINISH GMBH
- Filing Date
- 2025-12-03
- Publication Date
- 2026-06-11
Smart Images
Figure IMGF000027_0001
Abstract
Description
[0001] Method for the electrochemical polishing of metallic workpieces and suitable electrolyte medium for this purpose
[0002] The invention relates to an electrolyte medium for the electrochemical polishing of metallic workpieces, which contains a liquid electrolyte. The invention further relates to a method for the electrochemical polishing of metallic workpieces, wherein such an electrolyte medium is placed in a container and electrically connected to a first electrode, wherein the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium in the container, wherein the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the electrolyte medium in order to polish it electrochemically.
[0003] For surface finishing of workpieces, so-called drag finishing processes are known, in which the workpiece is immersed in a bed of solid abrasive or polishing granules contained in a container and moved relative to it within the bed of granules. Drag finishing machines are typically used for this purpose; these machines represent a special type of vibratory finishing machine. In these machines, the workpieces to be processed are detachably fixed, for example, individually or on one or more clamping devices of a workpiece holder, in order to polish or grind them as a result of the relative movement with respect to the bed of granules. Such drag finishing machines often include a typically rotating part, essentially in the form of, for example, a...A rotary-driven plate, driven by a suitable gearbox, to which the workpiece holders are attached directly or indirectly, for example via lifting devices. This attachment is particularly eccentric with respect to the axis of rotation of the rotating part of the drag finishing machine. When this part – the so-called plate – of the drag finishing machine rotates, the workpiece holders attached to it describe a path. The workpieces, supported by the clamping devices of the workpiece holders, are immersed in the container, which is filled with a load of granular particles, often with the addition of liquid processing media such as water, surfactants, etc. Due to the relative movement of the workpieces with respect to the granules, their surface is treated in the form of a vibratory finishing process. Such drag finishing machines are known, for example, from DE 102 04 267 Gl, DE 200 05 361 Ul, or DE 10 2010 052 222 Al.
[0004] Alternatively or additionally, the container holding the granule particles can be moved relative to the workpieces, which are also moving (e.g., rotated around their own axis) or stationary, for example, around its own axis and / or along a path, such as a circular track. If only the container is moved and the workpieces themselves do not undergo any translational movement, this is also referred to as "immersion grinding" or "immersion polishing," a special form of drag finishing. Machines in which the workpiece holder supporting the workpiece during surface treatment is essentially stationary are also called immersion finishing machines. The granule particles can be of a wide variety of origins, depending on the workpieces being treated, and can be of natural origin (e.g., organic material such as walnut or coconut shells, wood, cherry pits, etc.), mineral origin (e.g.,...The materials used can be of silicates, oxides, etc.) and / or synthetic origin (e.g., plastics). Furthermore, as already mentioned, vibratory finishing is known to be carried out dry or – with the addition of a liquid processing medium, such as water, which may contain additives such as surfactants – in the form of wet processing.
[0005] To provide a rotational movement of the workpieces, such as around their own axis, as an alternative or additional to a translational movement relative to the granule particles, resulting in even more effective surface treatment, the workpiece holders of known drag finishing machines are often rotary-driven, for example by means of suitable motors (see, e.g., DE 10 2010 052 222 Al). Furthermore, workpiece holders for drag finishing machines are known whose clamping devices for the detachable fastening of the workpieces are rotatably mounted and can be set in rotation via a shaft rotatably mounted in the workpiece holder. For this purpose, the workpiece holder has, e.g.,A planetary gear with a central sun gear, which meshes with planet gears that are in turn rotationally fixed to a support shaft of a respective clamping device, which are arranged around the circumference of the sun gear of the workpiece holder. Due to such movement of the clamping devices rotatably mounted on the workpiece holder with the workpieces, which consists of a translational movement (in the direction of rotation of the support element or the "plate" of the drag finishing machine) and a rotational movement (about the axis of the respective clamping device or about the workpiece axis), by the processing medium, a uniform processing quality is achieved with shorter processing times compared to a purely translational movement. Furthermore, alternatively or additionally, the workpiece holder itself can be rotatably fixed to the support element of the drag finishing machine in a corresponding manner (cf. e.g.B of DE 20 2009 008 070 Ul ) .
[0006] Furthermore, conventional drag finishing processes for polishing or grinding metallic workpieces of the aforementioned type have been further developed into electrochemical polishing processes in such a way that, on the one hand, the metallic workpiece is connected to a positive electrode (anode), and on the other hand, the granule particles flooded with a liquid electrolyte are connected to a negative electrode (cathode), whereby the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the majority of solid granule particles, e.g., in the manner described above.The surface quality of processed workpieces can often be improved using electrochemical polishing processes with an electrolyte medium containing both liquid electrolyte and granule particles. Such electrochemical polishing is also a process of abrasive surface treatment. When the electrodes are subjected to an electrical voltage via a voltage source, the electrical conductivity of the liquid electrolyte and / or the granule particles results in an electrical current flow, in addition to the purely mechanical surface treatment of the metallic workpieces. This current causes the surface anodic removal of material from the metallic workpieces. The electrodes can be supplied with, for example, either direct current or pulsed voltage.The workpieces are typically moved in the electrolyte medium to ensure the desired relative movement of the workpieces with respect to the solid granular particles of the electrolyte and to minimize the concentration gradient that forms on the surface of the workpieces. The selection of a suitable electrolyte medium is a crucial parameter, as it has been shown that some electrolytes that produce a flawless electropolishing result on one metal have virtually no effect on another, or result in a rough, uneven, or matte surface. For example, strong inorganic acids, particularly phosphoric acid and sulfuric acid, which may contain alcohols, are traditionally used for electropolishing aluminum and steel. A mixture of phosphoric acid and alcohols is suitable for copper and brass.
[0007] WO 2007 / 121999 A2 describes a liquid electrolyte in the form of an electrolyte solution intended for electropolishing metallic workpieces, as well as a method for electrochemically polishing workpieces using such a liquid electrolyte solution, wherein the electrolyte solution contains alkylbenzenesulfonic acid or alkylbenzenesulfonates, i.e., their salts or derivatives, a petroleum fraction with 17 to 35 carbon atoms, and optionally small amounts of ethanolamine. EP 2 646 603 Bl describes an improved electrolyte medium for the electrochemical polishing of metallic workpieces, in particular those made of copper, zinc, silver, tin, gold, etc.whose alloys, as well as a method for electrochemical polishing using such an electrolyte medium are known, which on the one hand contains a liquid electrolyte with ethoxylated alcohols, sulfonic acids and / or sulfonates, inorganic acids and liquid hydrocarbons as well as water, and on the other hand a proportion of plastic particles. In addition, electrolyte media have recently been proposed for the electrochemical polishing of metallic workpieces, which on the one hand comprise a plurality of solid porous granular particles on a polymer basis, and on the other hand a liquid electrolyte consisting of an electrically conductive, hydrophilic liquid, in particular from the group of strong inorganic acids and sulfonic acids, wherein the liquid electrolyte is absorbed exclusively in the pores of the granular particles and a gas or liquid is present in the remaining cavity volume of the granular particles.The granules are located in the atmospheric atmosphere, so that they are essentially dry on the outside (see, e.g., WO 2017 / 186992 Al, WO 2019 / 145588 Al, WO 2020 / 099699 Al, WO 2020 / 174112 Al, WO 2020 / 099700 Al or WO 2021 / 156530 Al). However, because the current flow is only induced at specific points as a result of contact between a single granule particle and the workpiece being processed, surface treatment of the workpieces in this way is very time-consuming.
[0008] The same applies to a "dry" electrolyte medium known from EP 4 074 868 Al for the electrochemical polishing of metallic workpieces, which on the one hand comprises a proportion of porous particles made of ion exchange resins with liquid acid-based electrolyte absorbed therein, and on the other hand comprises a proportion of particles which can absorb and chemically neutralize acid precipitates of the active particles or modulate their electrical conductivity.
[0009] ES 2 904 576 A1 describes another electrolyte medium for the electrochemical polishing of metallic workpieces, which also comprises, on the one hand, a plurality of solid porous polymer-based granules and, on the other hand, a liquid water-based electrolyte absorbed in the pores of the granules. Instead of a gas atmosphere present in the cavity volume of the granules, in this case a non-electrically conductive liquid, immiscible with the aqueous electrolyte, e.g., based on silicones or hydrocarbons, is used. Regarding the disadvantages, those stated above concerning the gas atmosphere in the cavity volume of the granules also apply, with the preparation of the electrolyte medium proving to be complex.A similar electrolyte medium for the electrochemical polishing of metallic workpieces can be found in WO 2022 / 123096 Al, which again comprises, on the one hand, a plurality of solid porous polymer-based granules and, on the other hand, a liquid electrolyte based on water or dilute acids, which is absorbed in the pores of the granules. The immiscible, non-electrically conductive liquid, e.g., based on silicones or hydrocarbons, within the cavity volume of the granules can, in this case, be either homogeneous or form a continuous phase of a water-in-oil emulsion, in which droplets of the aqueous electrolyte are emulsified as a dispersed phase.
[0010] An improved electrolyte medium is known from WO 2024 / 056315 Al, which comprises a plurality of solid granular particles and a liquid electrolyte. The granular particles can, in particular, be from the group of ion exchange polymers, which may be formed, for example, from copolymers of styrene with sulfonated ethylstyrene and / or with sulfonated divinylbenzene, acrylic resins with acrylic acid and / or methacrylic acid units, or the like. Such ion exchange polymers, which have a porous structure and can absorb liquid within their pores, depending on the pore structure, up to approximately their own weight, are highly cross-linked and consequently relatively hard and brittle, so that they break under high pressure.The liquid electrolyte comprises an emulsion with a continuous phase of an electrically conductive, hydrophilic liquid and a dispersed phase emulsified therein, consisting of a hydrophobic liquid that is immiscible with the electrically conductive, hydrophilic liquid but has a lower electrical conductivity. In this way, due to the relatively high electrical conductivity of the electrolyte medium, effective and time-efficient surface treatment of metallic workpieces with high surface quality and relatively low energy consumption is possible, since the electrically conductive, hydrophilic liquid present in the void volume of the solid granule particles, as the (polar) continuous phase of the liquid electrolyte, always ensures an electrically conductive connection between the workpiece to be treated, which is usually anodically contacted, and the cathode.The (nonpolar) dispersed phase emulsified in the aforementioned continuous phase consists of a hydrophobic liquid that is immiscible with the electrically conductive, hydrophilic liquid and, in contrast, has lower electrical conductivity. This hydrophobic liquid may also be essentially non-conductive. On the one hand, it serves to effectively protect the metallic workpieces from even localized corrosion during electrochemical surface treatment. Due to its fine dispersion within the electrically conductive, hydrophilic liquid of the continuous phase, the lower or non-conductive hydrophobic liquid is able to readily deposit on the surface of the treated workpieces during surface treatment and exert an anti-corrosive protective effect. On the other hand, the lower or non-conductive hydrophobic liquid is also able to...non-electrically conductive hydrophobic liquid of the dispersed phase to adjust the electrical conductivity and pH value of the electrolyte medium according to the invention by varying its proportion.
[0011] From WO 2016 / 193736 Al and US 2013 / 0319878 Al, a method for the electrochemical polishing of metallic workpieces is also known, in which an electrolyte medium is used that contains, on the one hand, a liquid electrolyte and, on the other hand, colloidal silicon dioxide (SiO2), which acts as a gelling agent. However, silicon dioxide particles not only exhibit very high hardness, so that there is a risk of mechanical damage to the workpiece during electrochemical polishing, but they also form a very firm, viscous colloidal dispersion, which makes electrochemical polishing of mechanically sensitive workpieces impossible and leads to very high heat generation during processing.
[0012] A further disadvantage of all the aforementioned electrolyte media can be that the granular particles—whether porous and impregnated with a liquid electrolyte or essentially compact—may not come into contact with the entire surface of the workpiece, particularly in the case of relatively delicate pieces with complex surface structures, such as jewelry, medical prostheses including dental prostheses, etc. This can lead to local areas with poor surface quality. Furthermore, relatively hard granular particles, especially those made of silicon dioxide, can cause mechanical damage to the polished surface and / or excessive material removal, which must be avoided, particularly when the workpieces are made of expensive metals, such as precious metals, and / or must be manufactured with very tight tolerances, as is the case with prostheses.
[0013] CN 103 695 992 A describes a process for the surface treatment of stainless steel using an electrolyte medium comprising, on the one hand, a liquid electrolyte such as phosphoric acid, sulfuric acid, and water, and on the other hand, among other things, a superabsorbent material consisting of 20 to 25 g / L of gelatin. However, a disadvantage of polysaccharides in general, and gelatin in particular, is that they bind the surrounding liquid very strongly and, especially at room temperature, tend to form a solid mass, which precludes the polishing of mechanically sensitive, delicate workpieces. Furthermore, introducing gelatin into the electrolyte requires first boiling the electrolyte to dissolve the gelatin. It is also known to use polysaccharides in the form of gelatin or cellulose in small proportions of less than approximately 2 g / L.-% to be used as a viscosity regulator for liquid electrolyte media (see e.g. CN 105 603 501 A or CN 104 878 442 A).
[0014] The invention is based on the objective of further developing an electrolyte medium for the electrochemical polishing of metallic workpieces of the type mentioned above in a simple and cost-effective manner, while at least largely avoiding the aforementioned disadvantages, in such a way that a flawless surface quality is ensured even when electrochemically polishing relatively complex workpieces. The first part of this objective is achieved according to the invention in an electrolyte medium for the electrochemical polishing of metallic workpieces, which contains a liquid electrolyte, by further comprising a proportion of at least 2 masses of...-% , based on the total electrolyte medium, contains at least one superabsorbent from the group of cross-linked polymers , wherein the at least one superabsorbent has a liquid absorption capacity of at least twice its mass , so that the polymer material of the superabsorbent swells and is able to form a hydrogel , wherein the at least one superabsorbent is selected from the group of polyacrylates , polyacrylamides including copolymers of acrylic acid and / or its salts with acrylamide , polyvinylpyrrolidones , polyurethanes and polyalkene terpolymers .
[0015] In terms of process engineering, the invention further provides a method for the electrochemical polishing of metallic workpieces to solve this problem, wherein an electrolyte medium of the aforementioned type is placed in a container and electrically connected to a first electrode, wherein the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium located in the container, wherein the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the electrolyte medium in order to polish it electrochemically.
[0016] According to the invention, the electrolyte medium therefore comprises, in addition to a liquid electrolyte, such as may be known from the prior art, at least one superabsorbent from the group of cross-linked polymers comprising at least approximately 2% by mass, based on the total electrolyte medium, wherein the at least one superabsorbent is capable of absorbing more than twice its mass of liquid electrolyte, so that the polymer material of the superabsorbent swells and is able to form a hydrogel. Such hydrogels are characterized in particular by the fact that they form elastic, easily deformable, gel-like particles with irregular shape and size, or even a more or less uniform gel-like mass.Surprisingly, it was found that such a superabsorbent, which absorbs at least part of the liquid electrolyte and is particularly capable of swelling to form a hydrogel, leads to an extremely homogeneous, uniform material removal behavior at a relatively low current density during electrochemical polishing. This applies especially to workpieces with a delicate or complex surface structure, such as those of the type mentioned above, which can also be electropolished in hard-to-reach surface areas that are inaccessible to the relatively hard granule particles, including those made of ion-exchange polymers, as provided for in the prior art.The superabsorbent, which is in a hydrogel-like state, also possesses a significantly lower hardness and thus reliably prevents even very minor wear marks on the electropolished workpiece. The polymeric superabsorbent is usually not electrically conductive itself, but becomes electrically conductive through the absorbed liquid electrolyte, allowing the superabsorbent, when mixed with the liquid electrolyte, to exhibit electrochemical activity during electrochemical polishing.
[0017] The superabsorbent of the electrolyte medium according to the invention, from the group of cross-linked polymers, is here from the group of polyacrylates, preferably from the sodium (Na) group. + ) , potassium (K+ ) and ammonium polyacrylate
[0018] (NH4 +) , including the copolymers of acrylic acid and / or its salts with acrylamide, the polyvinylpyrrolidones, the polyurethanes and the polyalkene terpolymers, such as acrylonitrile butadiene styrene copolymers (ABS), ethylene propylene diene monomer rubbers, etc. , were selected. Such polymer-based superabsorbents exhibit a low degree of cross-linking, which enables them to absorb at least their own weight in electrolyte liquid and thereby form a hydrogel without the formation of dimensionally stable, relatively hard and brittle particles, as is the case, for example, with prior art ion exchange polymers, which may have a similar polymer structure but possess a significantly higher degree of cross-linking, so that their liquid absorption capacity is essentially limited to their pore volume and no hydrogels can be formed.The superabsorbents used according to the invention, based on the aforementioned (slightly) cross-linked polymers, also ensure a simple and rapid production of the electrolyte medium by simply mixing them with the liquid electrolyte, thereby avoiding "hardening" of the electrolyte medium at moderate temperatures, as occurs, for example, with polysaccharide-based superabsorbents.
[0019] It is assumed that the excellent electrochemical polishing properties of the superabsorbent according to the invention, which has absorbed the liquid electrolyte, are primarily due to the fact that, during the movement of the workpiece to be electropolished relative to the electrolyte medium, the superabsorbent always conforms to the surface of the workpiece and the liquid electrolyte is mechanically forced out of the gelled superabsorbent, so that the surface of the workpiece, which is in contact with the gelled superabsorbent, is always practically completely wetted with liquid electrolyte. Conversely, the gelled superabsorbent is able to absorb the metal ions electrochemically dissolved from the surface of the workpiece and transport them away from the workpiece towards the cathode.Due to the viscosity of the gel-shaped superabsorbent, a higher concentration gradient is created on the surface of the workpiece than with purely liquid electrolytes. This means that the roughness peaks protruding from the microstructure of the workpiece surface are predominantly supplied with fresh liquid electrolyte, which is mechanically "squeezed out" of the hydrogel of the superabsorbent. This results in increased material removal at these roughness peaks compared to the roughness valleys, ensuring an overall material-saving process.The electrolyte medium according to the invention proves to be very gentle on the workpiece in mechanical terms, reliably preventing any risk of even local mechanical damage to the workpiece surface, as can occur in the case of conventional electrolyte media with more or less hard granule particles, if the latter have a relatively high hardness and / or are moved along the workpiece surface at a relatively high relative speed or pressure, or even become wedged in delicate cavities of the workpiece.
[0020] The electrolyte medium according to the invention is fundamentally suitable for the electrochemical polishing of all known metals or metal alloys, whereby the chemical composition of the liquid electrolyte component can be adapted to the respective workpiece material in a manner known as such. By way of example only, suitable metal materials for electropolishing, such as gold (alloys), silver (alloys), palladium (alloys), copper (alloys) including brass and bronze, titanium (alloys), steels including stainless steel, nickel (alloys), chromium (alloys), etc., are mentioned in this context.
[0021] As is known from the prior art, the electrolyte medium according to the invention otherwise serves for the electrically conductive contact of the workpiece, wherein the electrolyte medium ensures the establishment of an electric current flow between the anode (positive electrode), which is usually connected to the metallic workpiece, and the cathode (negative electrode), which is connected to the electrolyte medium and can, for example, be arranged on the container of a corresponding electrochemical polishing device. It should also be noted at this point that the term "electrochemical polishing" within the meaning of the present invention includes electrochemical smoothing as well as electrochemical brightening.
[0022] The superabsorbent of the electrolyte medium according to the invention preferably has a liquid absorption capacity for the liquid electrolyte of at least approximately three times, in particular at least approximately four times, preferably at least approximately five times, most preferably at least approximately ten times, for example at least five ten or twenty times, its mass, wherein the superabsorbent—as already mentioned—swells upon absorbing the liquid electrolyte and forms a hydrogel. The liquid absorption capacity of the superabsorbent can be adjusted, for example, by the—low—degree of cross-linking of the polymers used according to the invention.
[0023] The ratio of liquid electrolyte to superabsorbent can be adjusted within wide limits depending on the shape and material of the workpieces to be processed. By increasing the proportion of liquid electrolyte relative to the superabsorbent, the consistency of the electrolyte medium can be adjusted from a relatively viscous gel with relatively high viscosity (the electrolyte medium contains, for example, less liquid electrolyte than can be absorbed by the superabsorbent) to a very low-viscosity, predominantly liquid gel (the electrolyte medium contains, for example, almost as much or even more liquid electrolyte than can be absorbed by the superabsorbent).The electrolyte medium can essentially be in the form of a viscous polymer mass of the superabsorbent gelled with the liquid electrolyte, or it can consist of a viscous mass of polymer particles of the superabsorbent gelled with the liquid electrolyte, whereby the proportion of liquid electrolyte relative to the superabsorbent can be adjusted within practically arbitrary limits, so that, for example, the gelled mass of the superabsorbent can be essentially saturated (i.e., the proportion of liquid electrolyte essentially corresponds to the liquid absorption capacity of the superabsorbent), unsaturated (i.e., the superabsorbent could absorb even more liquid electrolyte), or supersaturated (i.e., the superabsorbent has exceeded its liquid absorption capacity and there is free electrolyte in the gelled mass of the superabsorbent).
[0024] In many applications, it has proven advantageous if the electrolyte medium contains a proportion of at least one superabsorbent.
[0025] - of at least about 3% by mass, in particular of at least about 4% by mass, preferably of at least about
[0026] 5% by mass, such as from at least approximately
[0027] 6% by mass or at least approximately 7% by mass, and / or
[0028] - of at most approximately 65% by mass, in particular of at most approximately 50% by mass, preferably of at most approximately
[0029] 35% by mass, most preferably at most about 30% by mass or at most about 25% by mass, in each case based on the total electrolyte medium including the proportion of liquid electrolyte.
[0030] In many applications, it has proven advantageous in this context for the electrolyte medium to have a viscosity
[0031] - of at least about 1 mPas, in particular of at least about 10 mPas, preferably of at least about 100 mPas, most preferably of at least about 1 Pa, and / or
[0032] - of at most about 125 Pas, in particular of at most about 100 Pas, preferably of at most about 50 Pas, most preferably of at most 10 Pas.
[0033] Furthermore, depending on the metal material of the workpiece to be treated, it may be advantageous because the liquid electrolyte of the electrolyte medium has an electrical conductivity.
[0034] - of at least about 50 pS / cm, in particular of at least about 0.1 pS / cm, preferably of at least about
[0035] 10 pS / cm, most preferably at least about 50 pS / cm, such as at least about 100 pS / cm, and / or
[0036] - of at most about 50 mS / cm, in particular of at most about 10 mS / cm, preferably of at most about 5 mS / cm, such as of at most about 3 mS / cm.
[0037] Furthermore, the pH value of the liquid electrolyte of the electrolyte medium according to the invention can be adapted to the respective metal material of the workpiece to be electropolished in a manner known as such, wherein the pH value of the liquid electrolyte can usually be set, e.g., between about 0 and about 12, in particular between about 0 and about 10, preferably between about 0 and about 8, such as between about 1 and about 7.
[0038] Furthermore, it can be advantageous if the electrolyte medium contains inclusions of at least one gas, particularly air, in order to, for example, adjust the electrical conductivity of the electrolyte medium or to reduce it with an increasing proportion of non-electrically conductive gas. Such a gas component, essentially in the form of gas bubbles, can be actively introduced into the electrolyte medium, for example, by stirring or aerating it, or gas bubbles can also form, for example, during electrochemical polishing at the electrodes as a result of the electrochemical reaction. The gas can be present, for example, in the spaces between particles of the superabsorbent gelled with the liquid electrolyte, or it can be essentially distributed throughout the gelled mass of the superabsorbent.
[0039] Alternatively or additionally to a gas component of the aforementioned type, for corresponding reasons, the electrolyte medium may also contain at least one hydrophobic liquid that is immiscible or poorly miscible with the liquid electrolyte and, in contrast, has low or even essentially non-electrical conductivity, such as oils, e.g., silicone oil or the like, which may advantageously be largely chemically inert. "Immiscible or poorly miscible" here means that the hydrophobic liquid forms a phase boundary with the liquid electrolyte. In particular, the hydrophobic liquid may also form the continuous phase of an emulsion whose dispersed phase is formed by the same or another (hydrophilic) liquid electrolyte.
[0040] According to one embodiment of the electrolyte medium according to the invention, it can be provided that the liquid electrolyte is formed from an electrically conductive, substantially homogeneous mixture, wherein the mixture in particular
[0041] - at least one electrically conductive liquid from the group of polar organic solvents, in particular from the group of alcohols, and / or
[0042] - at least one acid and / or its salts, and / or
[0043] - Contains water. Other components include, for example, surfactants, liquid hydrocarbons such as alkanes, alkenes, aromatics, etc., or other components known as such of electrolytes known as such for electrochemical polishing.
[0044] According to another embodiment, the liquid electrolyte may be formed by an emulsion, wherein the emulsion in particular comprises a continuous phase of at least one electrically conductive, hydrophilic liquid and a dispersed phase emulsified therein of at least one hydrophobic liquid that is immiscible or poorly miscible with the electrically conductive, hydrophilic liquid and, in contrast, is of low or essentially non-electrically conductive nature. Such a liquid electrolyte suitable for electrochemical polishing processes is known as such from WO 2024 / 056315 A1 cited above, which is hereby incorporated into the present disclosure.
[0045] In the case of such a liquid electrolyte, which is in the form of an emulsion, it may be advantageously provided that
[0046] (a) the electrically conductive, hydrophilic liquid of the continuous phase of the emulsion
[0047] - at least one liquid from the group of polar organic solvents, in particular from the group of alcohols, and / or
[0048] - at least one acid and / or its salts, and / or
[0049] - Water contains , and / or
[0050] (b) the hydrophobic liquid of the dispersed phase of the
[0051] The emulsion contains at least one liquid from the group of, in particular aliphatic, hydrocarbons and / or silicone oils.
[0052] Further examples of advantageous components of such a liquid electrolyte are given in WO 2024 / 056315 Al.
[0053] According to a further development of the electrolyte medium according to the invention, it can also be provided that it contains solid particles, which are selected in particular from at least one material from the group consisting of minerals, metals and / or their oxides, glass, plastics, ion exchange resins, and natural materials, especially wood, wherein the particles are in particular porous. The electrolyte medium according to the invention can therefore be combined, as required, with granular particles known from conventional electrolyte media, whereby either essentially non-electrically conductive granular particles or electrically conductive granular particles can be used, which can be compact or porous so that the liquid electrolyte can penetrate them. In this context, porous granular particles made of ion exchange resins, such as those found in […], have proven to be particularly advantageous.such as those commercially available under the trade name "Amberlite" have a polymer matrix of sulfonated styrene-divinylbenzene copolymers and can be designed as cation exchangers (e.g., Na+, H+, etc.) or as anion exchangers (e.g., CI) (see, for example, US 2005 / 0155868 Al), whereby they acquire a relatively high electrical conductivity, in particular, when a liquid electrolyte or, for example, pure water penetrates their pore system.
[0054] In the inventive method for the electrochemical polishing of metallic workpieces, wherein an electrolyte medium of the type described above is supplied to a container and electrically connected to a first electrode, wherein the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium in the container, wherein the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the majority of solid granule particles in the electrolyte medium, the relative movement of the metallic workpiece with respect to the solid granule particles can be carried out in any known manner, as is known, for example, in conventional drag or immersion finishing processes. With regard to such relative movement of the workpiece with respect to the solid granule particles during surface treatment, it can therefore, for example, involve
[0055] - a rotational movement of the workpiece and / or the container, in particular essentially about a symmetry axis of the workpiece and / or the container; and / or
[0056] - a translational movement of the workpiece in relation to the container, in particular essentially in the form of a trajectory curve; and / or
[0057] - a vibration excitation of the workpiece and / or the container, e.g. by means of ultrasound, piezo actuators, unbalance drives or the like.
[0058] Furthermore, to avoid damage to the workpieces by bumping against each other and / or against the wall of the container, it can be advantageous if the metallic workpiece is clamped on a workpiece holder that is movable relative to the container and also allows for simple electrical contacting of the (respective) workpiece.
[0059] Regarding simple electrical contact with the electrolyte medium, the first electrode can, for example, be electrically connected to the container, while the second electrode is electrically connected to the workpiece holder, which is movable relative to the container and to which the workpiece is clamped. The first electrode can, for example, be integrated into the container or designed as an electrode assembly that can be inserted into it.
[0060] Furthermore, according to a first method variant, it can be provided that the electrodes are subjected to an electrical voltage in at least one process stage such that essentially a direct current voltage is applied to the electrodes, wherein the first electrode intended for electrical connection with the electrolyte medium is subjected to a negative voltage (cathode) and the second electrode intended for connection with the workpiece is subjected to a positive voltage (anode). The electrochemical processing is therefore carried out essentially with direct current.
[0061] According to a second method variant, it can alternatively or additionally be provided that the electrodes are subjected to an electrical voltage in at least one process stage such that a pulsed electrical voltage is applied to the electrodes, wherein the first electrode intended for electrical connection with the electrolyte medium is subjected to a pulsed negative voltage (cathode) and the second electrode intended for connection with the workpiece is subjected to a pulsed positive voltage (anode). Such a pulsed voltage, which can, for example, exhibit a periodic voltage profile between a voltage maximum and zero and / or between a voltage maximum and a correspondingly lower voltage minimum greater than zero, has proven advantageous in many cases for effective and uniform surface treatment.
[0062] Finally, alternatively or additionally, according to a third method variant, it can be provided that the electrodes are subjected to an electrical voltage in at least one process stage such that the polarity of the electrical voltage applied to the electrodes is temporarily reversed at least once, in particular several times, preferably periodically, during the electrochemical polishing of the workpiece, so that the first electrode intended for electrical connection with the electrolyte medium temporarily has a negative and temporarily a positive voltage, and the second electrode intended for electrical connection with the workpiece temporarily has a positive and temporarily a negative voltage.In this case, therefore, in contrast to conventional electrochemical polishing processes in which the electrodes are supplied with a continuous (first process variant; see above) or pulsed (second process variant; see above) direct current (i.e., with short interruptions of the voltage source) such that the first electrode (cathode) in conductive contact with the electrolyte medium has a negative voltage and the second electrode (anode) in conductive contact with the workpiece has a positive voltage, the polarity of the electrical voltage applied to the electrodes is temporarily reversed at least once during the electrochemical polishing of the workpiece, so that the first electrode in conductive contact with the electrolyte medium temporarily has a positive voltage and the second electrode in conductive contact with the workpiece temporarily has a negative voltage.It was found that this method can achieve a perfectly smooth, glossy surface even on metallic workpieces that are otherwise difficult to electropolish (e.g., resulting in a matte surface with a kind of "needle texture"). This applies particularly—though not exclusively—to workpieces containing or consisting entirely of precious metals, such as gold-palladium and white gold-palladium alloys. Furthermore, this method ensures more reproducible and homogeneous material removal with some metal alloys and guarantees very high processing efficiency.While metallic workpieces, which are usually subjected to a positive voltage via the second electrode (anode), experience material removal, particularly at the roughness peaks of their surface, and local metal oxides are generated, which can reduce diffusion, it is assumed that the temporary reversal of the electrical voltage (i.e., the workpieces are briefly subjected to a negative electrical voltage) can, on the one hand, reduce such locally present metal oxides and thus increase the mobility of surface metal atoms, and on the other hand – supported by the granule particles moving relative to the workpiece – cause the deposition of metal ions in the roughness valleys on the surface of the workpiece, so that roughness valleys are "filled".An electrochemical polishing process with such a voltage profile of the electrodes is known as such from DE 10 2024 112 828.3, which was not yet published at the priority date of the present patent application and is hereby made the subject of the present disclosure.
[0063] Of course, the above process stages can also be combined and workpieces can be electrochemically polished one after the other as required using one or more of the aforementioned process variants.
[0064] The following are exemplary embodiments of electrolyte media according to the invention, which serve only for illustration and do not limit the invention:
[0065] Example 1:
[0066] (a) Superabsorbent: Sodium polyacrylate with a proportion of
[0067] 1 part by weight to 10 parts by weight of the liquid electrolyte;
[0068] (b) Electrolyte: - 5 wt% thiourea,
[0069] - 7 wt% thiocyanate, in particular from the group ammonium, sodium and potassium thiocyanate ,
[0070] - < 10 wt% surfactants, e.g. isotridekanol, ethoxylated, remainder: water.
[0071] (a) Superabsorbent: Sodium polyacrylate with a proportion of
[0072] 1 part by weight to 10 parts by weight of the liquid electrolyte;
[0073] (b) Electrolyte: - 12.5 wt% sulfamic acid,
[0074] - 5% by mass of thiourea,
[0075] - 2.5 wt% tartaric acid (2,3-dihydroxybutanedioic acid) ,
[0076] - 0.5 wt% sulfuric acid (96%) ,
[0077] The rest: water.
[0078] Example 3:
[0079] (a) Superabsorbent: Sodium polyacrylate with a proportion of
[0080] 1 part by weight to 10 parts by weight of the liquid electrolyte;
[0081] (b) Electrolyte: - 14 wt% isotridecanol ethoxylated
[0082] (2-5 EO) ,
[0083] - 14 wt% benzenesulfonic acid (C10-C13,
[0084] sodium salt) ,
[0085] - 32 wt% aliphatic hydrocarbon mixture,
[0086] - 16% by mass ethylene glycol ,
[0087] - Remainder: Water.
Claims
Patent claims 1. Electrolyte medium for the electrochemical polishing of metallic workpieces, which contains a liquid electrolyte, characterized in that it further contains a proportion of at least 2 wt.%, based on the total electrolyte medium, of at least one superabsorbent from the group of cross-linked polymers, wherein the at least one superabsorbent has a liquid absorption capacity of at least twice its mass, so that the polymer material of the superabsorbent swells and is able to form a hydrogel, wherein the at least one superabsorbent is selected from the group of polyacrylates, polyacrylamides including copolymers of acrylic acid and / or its salts with acrylamide, polyvinylpyrrolidones, polyurethanes and polyalkene terpolymers.
2. Electrolyte medium according to claim 1, characterized in that the at least one superabsorbent is selected from the group of polyacrylates, in particular from the group of sodium, potassium and ammonium polyacrylates.
3. Electrolyte medium according to claim 1 or 2, characterized in that the superabsorbent has a liquid absorption capacity of at least three times, in particular at least five times, preferably at least ten times, its mass.
4. Electrolyte medium according to one of claims 1 to 3, characterized in that it contains a proportion of at least one superabsorbent. - of at least 3 wt%, in particular of at least 4 wt%, preferably of at least 5 wt%, and / or - of at most 65% by mass, in particular of at most 50% by mass, preferably at most 35% by mass, most preferably at most 25% by mass, in each case based on the total electrolyte medium.
5. Electrolyte medium according to one of claims 1 to 4, characterized in that (a) the electrolyte medium has a viscosity - of at least 1 mPas, in particular of at least 10 mPas, preferably of at least 100 mPas, most preferably of at least 1 Pas, and / or - of at most 125 Pas, in particular of at most 100 Pas, preferably of at most 50 Pas, most preferably of at most 10 Pas; and / or (b) the liquid electrolyte has an electrical conductivity - of at least 50 pS / cm, in particular of at least 0.1 pS / cm, preferably of at least 10 pS / cm, most preferably at least 50 pS / cm, and / or - of at most 50 mS / cm, in particular of at most 10 mS / cm, preferably of at most 5 mS / cm; and / or (c) the liquid electrolyte has a pH value between 0 and 12, in particular between 0 and 10, preferably between 0 and 8, most preferably between 1 and 7, exhibits .
6. Electrolyte medium according to one of claims 1 to 5, characterized in that it has inclusions of at least one gas, in particular air.
7. Electrolyte medium according to one of claims 1 to 6, characterized in that it further contains at least one hydrophobic liquid which is immiscible or poorly miscible with the liquid electrolyte and which, on the other hand, is less electrically conductive, wherein the hydrophobic liquid in particular forms the continuous phase of an emulsion, the dispersed phase of which is formed by the same or a further liquid electrolyte.
8. Electrolyte medium according to one of claims 1 to 7, characterized in that the liquid electrolyte is formed from an electrically conductive, substantially homogeneous mixture, wherein the mixture is in particular - at least one electrically conductive liquid from the group of polar organic solvents, in particular from the group of alcohols, and / or - at least one acid and / or its salts, and / or - Water contains .
9. Electrolyte medium according to one of claims 1 to 8, characterized in that the liquid electrolyte is formed by an emulsion, wherein the emulsion in particular comprises a continuous phase of at least one electrically conductive, hydrophilic liquid and a dispersed phase emulsified therein of at least one component of the electrically conductive, hydrophilic liquid. exhibits a liquid that is immiscible or poorly miscible, but has a lower electrical conductivity and hydrophobic properties.
10. Electrolyte medium according to claim 9, characterized in that (a) the electrically conductive, hydrophilic liquid of the continuous phase of the emulsion - at least one liquid from the group of polar organic solvents, in particular from the group of alcohols, and / or - at least one acid and / or its salts, and / or - contains water, and / or (b) the hydrophobic liquid of the dispersed phase of the emulsion contains at least one liquid from the group of, in particular, aliphatic, hydrocarbons and / or silicone oils.
11. Electrolyte medium according to one of claims 1 to 10, characterized in that it further contains solid particles, which are selected in particular from at least one material from the group consisting of minerals, metals and / or their oxides, glass, plastics, ion exchange resins and natural materials, in particular wood, wherein the particles are in particular porous.
12. Method for electrochemical polishing of metallic workpieces, wherein an electrolyte medium according to one of claims 1 to 11 is added to a container and made electrically conductive with a first electrode. is connected, whereby the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium located in the container, whereby the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the electrolyte medium in order to polish it electrochemically.
13. Method according to claim 12, characterized in that the relative movement of the metallic workpiece with respect to the electrolyte medium contained in the container is controlled by at least one relative movement from the group - rotational movement of the workpiece and / or the container, in particular essentially around an axis of symmetry of the workpiece and / or the container; - translational movement of the workpiece in relation to the container; and - Vibration excitation of the workpiece and / or the container occurs.
14. Method according to claim 12 or 13, characterized in that the metallic workpiece is clamped on a workpiece holder movable relative to the container.
15. Method according to one of claims 12 to 14, characterized in that the first electrode is electrically conductively connected to the container, and that the second electrode is connected to a workpiece holder movable relative to the container, on which the workpiece is mounted. is tensioned, is electrically conductively connected.
16. Method according to one of claims 12 to 15, characterized in that the electrodes are subjected to an electrical voltage in at least one stage of the process such that - an electrical direct voltage is essentially applied to the electrodes, whereby the first electrode intended for electrical connection with the electrolyte medium is subjected to a negative voltage (cathode) and the second electrode intended for connection with the workpiece is subjected to a positive voltage (anode); and / or - a pulsed electrical voltage is applied to the electrodes, whereby the first electrode intended for electrical connection with the electrolyte medium is supplied with a pulsed negative voltage (cathode) and the second electrode intended for connection with the workpiece is supplied with a pulsed positive voltage (anode); and / or - the polarity of the electrical voltage applied to the electrodes is temporarily reversed at least once, in particular several times, preferably periodically, during the electrochemical polishing of the workpiece, so that the first electrode intended for electrical connection with the electrolyte medium temporarily has a negative and temporarily a positive voltage, and the second electrode intended for electrical connection with the workpiece temporarily has a positive and temporarily a negative voltage.