Solid electrolyte for dry electrolytic polishing of metals with active moderator

Abstract

A solid electrolyte for metal dry electrolytic polishing, comprising: active particles of at least one type of ion exchange resin, said active particles being filled with an acid solution to generate chemical activity and electrical activity; at least one type of moderating particles of chemical action and / or of electrical conductivity of said active particles, such that said moderating particles reduce the erosion on the surface of the polished part caused by the exudates of said active particles.

Description

[0001] This application is a divisional application of application number 202180011666.5, filed on January 28, 2021, entitled "Solid electrolyte with active modifier for dry electropolishing of metal". Technical Field

[0002] This invention describes a solid electrolyte in a system for dry electrolytic polishing of metals. Therefore, this invention belongs to the field of metal polishing, particularly in industries requiring high-quality metal surface treatment, such as automotive, aerospace, medical, dental, decorative, jewelry, and watchmaking. Background Technology

[0003] Dry electropolishing using solid electrolytes is an emerging technology first described in patent ES2604830 in 2016. In this process, a metal component connected to the anode moves within a container containing solid electrolyte particles and a cathode. This results in metal removal at the points of contact between the metal surface and the particles, meaning that at roughness peaks, because current flows only at the contact points, a polishing process with good results is produced without affecting the apex or edges.

[0004] The particles used in this process are described in detail in document ES2721170 (A1). These particles are formed from ion-exchange resin particles that retain an acidic electrolyte liquid within them. These particles are highly reactive on metal surfaces. In metals that generate their own protection (meaning self-passivation of the metal), these particles produce excellent results, resulting in a good surface finish. The passivation layer counteracts the high reactivity of the particles. Polishing by dry electropolishing of self-passivating metals such as stainless steel, cobalt-chromium alloys, or titanium produces excellent results. In some self-passivating metals, when polished by dry electropolishing, a surface with an undesirable undulating pattern, similar to an "orange peel" surface, is obtained. This result is not optimal; therefore, a new dry electrolyte configuration that does not produce undesirable undulating patterns is needed.

[0005] This problem is exacerbated when dry electropolishing is used to polish non-self-passivating metals. Solid electrolyte particles are too corrosive for metals that do not naturally produce the protective layer. When solid electrolyte particles are used for dry electropolishing of materials such as carbon steel or low-alloy steel, the metal surface can be eroded and exhibit "craters" corresponding to the contact with the solid electrolyte particles.

[0006] Due to the industrial importance of some of these non-self-passivating metals (such as carbon steel found in tools, gears, motors, gearboxes, etc.), there is an industrial need for solid electrolytes that can polish non-self-passivating metals by means of a dry electropolishing process.

[0007] To date, there is no solid electrolyte capable of polishing non-self-passivating metals without creating craters on the surface using a dry electropolishing process, nor is there any solid electrolyte suitable for polishing self-passivating metals without producing undesirable undulating patterns. This invention provides a solid electrolyte for electropolishing metals that overcomes the aforementioned technical problems. Summary of the Invention

[0008] This invention describes the composition of a solid electrolyte for dry electropolishing of metals. The aforementioned solid electrolyte is configured as active particles of ion exchange resins containing different acids. As a novel assumption, it is proposed that during electropolishing, the solid electrolyte exudes acidic liquids through pressure, electrophoresis, or other means. These acidic exudates on the metal surface converge with electrochemical interactions, resulting in localized erosion. This localized erosion causes marks and pits that are detrimental to high-quality surface treatment. Based on this assumption, avoiding or controlling the acidic exudates will prevent localized erosion on the polished surface.

[0009] The proposed solid electrolyte system for polishing metals includes a solid electrolyte configuration containing active particles of ion exchange resin filled with acid solution and a subset of particles (referred to as moderating particles) that reduce, moderate, or regulate the activity of the active particles.

[0010] The active particles are particles of an ion exchange resin capable of retaining an electrolyte liquid within them. Preferably, the ion exchange resin is a sulfonated copolymer of styrene and divinylbenzene. In another preferred configuration, the resin is an acrylic gel polymer with functional groups. These polymers allow for the efficient exchange of metal ions generated during electropolishing. Preferably, the electrolyte liquid is an acid solution. Preferably, the acid solution comprises sulfuric acid and / or methanesulfonic acid. These compounds are strong acids that facilitate the flow of current and promote the dissolution of oxides formed on the surface to be polished.

[0011] Preferably, the active particles are spherical to facilitate movement on the surface of the part to be polished.

[0012] The active particles can all be of the same type, or they can be formed from two or more types. For example, in a preferred configuration, the active particles are formed from two portions of particles containing methanesulfonic acid, each with a diameter of about 0.7 mm, and one portion of particles containing sulfuric acid, each with a diameter of about 0.2 mm. This type of combination has the advantages of the speed of large particles and the penetration of small particles, as well as the advantages of combining the electrochemical and solubility effects of acids.

[0013] During electropolishing, the active particles have two functions: a chemical action that promotes the dissolution of oxides and salts on the surface to be polished; and a conductive function.

[0014] The purpose of moderating particles is to limit the chemical erosion effect of active particles and / or to limit the electrical conductivity of active particles. Distinguish between two types of moderating particles: those that modulate the chemical action of active particles and those that modulate the conductivity of active particles.

[0015] The chemically moderating particles of the active particles have the ability to absorb and / or neutralize the acidic exudates from the active particles.

[0016] A preferred embodiment of the chemically moderating particles for the active particles is particles of an acrylic gel polymer with amino functional groups that initially contain water or distilled water. Upon contact with the surface of a metal part, these particles absorb any possible acidic residues left by the active particles, which are neutralized within the particles by the amino groups. In this way, the uncontrolled acidic effect of the acidic residues is limited. Due to the gel properties, it is recommended to refresh or add moderating particles. For example, one can start with 0.5% by volume of moderating particles and add more particles after a given time, e.g., adding 0.5% of the initial volume of moderating particles every 2 hours of operation to maintain activity. These moderating particles are preferably used for polishing carbon steel.

[0017] A second preferred embodiment of the chemically moderating particles of the active particles is a polymer below its saturation point with the ability to absorb liquids, meaning partially dried particles. Preferably, they are ion exchange resins based on sulfonated styrene copolymers and divinylbenzene, similar to or equivalent to the resins of the active particles.

[0018] During dry electropolishing, these particles absorb acidic exudates remaining on the surface of the metal being polished. When the chemical action of the active particles becomes saturated with the milder particles, meaning they can no longer absorb more acid, a given additional percentage of milder particles can be added to maintain the milder activity. Saturated milder particles are not a problem because they function as if they were active particles.

[0019] A major advantage of these partially dried active granules, which exhibit mild chemical action, is that there are no limitations on the amount that can be used, as they actually become active granules after use.

[0020] A third preferred embodiment of the chemically moderating particles of the active particles is particles containing an internal basic solution. During dry electropolishing, these particles directly neutralize acid exudates on the metal surface and generate basic exudates that protect the surface from further acid erosion; therefore, they are particularly useful for sensitive metals. Preferably, the basic solution contains a base that does not react with air, is water-soluble, and has low volatility, such as monoethanolamine, diethanolamine, triethanolamine, triethylamine, a buffer solution with a phosphate or acetate base, etc. The greatest advantage of this system is its effectiveness in removing acidic waste from the metal surface. It is particularly recommended for very sensitive metal surfaces, such as low-alloy steels.

[0021] Active particles have moderate conductivity, while non-conductive particles are used.

[0022] The moderate conductivity of the active particles limits the number of electrically preferential paths from the cathode to the metal surface (anode). On the other hand, this increases the uniformity of more exposed and more blocked portions, as the possible number of electrical paths is balanced. However, the presence of these moderately conductive particles also locally and transiently disrupts the electrical contact of the surface, thereby disrupting the resonance established in the system (which causes fluctuations in the final orange-peel type surface finish). The greatest advantage of these moderately conductive particles is the resulting final surface finish, which exhibits higher quality and is virtually free of fluctuations.

[0023] These conductive, moderately conductive particles can be polymers, ceramics, etc., and their density and shape prevent mass separation of active particles.

[0024] The conductive moderating particles can be any non-conductive material that is acid-resistant or can resist contact with acid-active particles during processing for a given time. Preferred materials are polymers in which the main polymer chain contains only C-C bonds, such as polymers derived from styrene, divinylbenzene, ethylene, propylene, acrylates, acrylamide, vinyl, vinyl chloride, tetrafluoroethylene, Nafion, etc. The conductive moderating particles can be derived from silicon, such as silica gel and functionalized silica.

[0025] The shape of the conductive moderating particles can be spherical, lens-shaped, prismatic, disc-shaped, cylindrical, irregular, etc.

[0026] The size of the conductivity-mitigating particles is related to the size of the active particles. Since their function is to generate an electrical "mask" on the surface of the metal to be polished, preferably, the average size of the conductivity-mitigating particles is equal to or greater than the average size of the active particles.

[0027] In a preferred embodiment, the active particles are spheres of a sulfonated copolymer of polystyrene and divinylbenzene containing an acid solution, with an average gel size of 0.7 mm, and the conductivity-modifying particles are vinyl chloride (PVC). The polymer has a density ranging from 1.1 g / mL to 1.4 g / mL, similar to the density range of divinylbenzene from styrene copolymers and resins, which is about 1.2 g / mL to 1.3 g / mL. Their similar density contributes to the uniform distribution of the different particle types.

[0028] In another preferred embodiment, one-third of the volume consists of irregularly shaped PVC non-conductive particles and two-thirds consists of active particles. This similar volume ratio, for example, 20% to 45% PVC non-conductive particles plus 80% to 55% active particles, represents a uniform distribution of non-conductive particles within the active particles. Optimal results are achieved when the particles are uniformly distributed, or when accumulation is resolved through the vibration and movement process itself. This is achieved through a near two-to-one volume ratio.

[0029] Particles with moderate electrical conductivity and / or chemical action can have additional functionalities.

[0030] Mild particles with conductive and / or abrasive chemical properties can be abrasive particles with additional functions during the process. These mild particles with conductive and / or abrasive chemical properties complement the electropolishing action that has an abrasive-polishing effect. In addition to the simple abrasive effect on the metal surface, these abrasive particles have a novel surface cleaning effect. In dry electropolishing, oxide accumulation occurs under given conditions, which can be counteracted by increasing the negative pulse or avoided by changing the type of solid electrolyte. An alternative to these variations is to use mild abrasive particles, which perform this cleaning process and remove surface oxides without requiring changes to the optimized process parameters. The vibration of this set of particles, together with the movement of the part to be polished in the system, provides sufficient kinetic energy without requiring adjustments to the dry electropolishing system. The greatest advantage of this type of mild abrasive particles is their dual function as an activity modifier and as an abrasive for cleaning and polishing surfaces.

[0031] The conductive and / or abrasive chemically modulating particles are very hard particles. By way of example and not limitation, these abrasive modulating particles are salts such as alumina, calcium carbonate, silicon carbide, cubic boron nitride, boron carbide, iron oxide, etc.; non-crystalline materials such as sand, coarse-grained, broken glass, or similar materials; ceramic materials; minerals such as dolomite, diamond, novaculite, pumice or pumice stone, sandstone, corundum, garnet, feldspar, staurolite, etc.

[0032] They can consist of polishing pastes containing mildly conductive and / or abrasive chemically active particles, kept in a given amount of moisture or liquid. This type of paste is typically used to polish metals by hand or by some tool-based abrasive method.

[0033] When a polishing paste and active particles are used to treat a metal surface to be polished, the paste protects the surface from uncontrolled erosion by the active particles, thus enabling the polishing process to occur simultaneously through a dry electrolyte and through the abrasive media. The motion and vibration of the dry electropolishing process complement the abrasive action, while the slurry used for the abrasive action protects the metal surface from excessive chemical or electrical erosion by the active particles. The polishing paste used for polishing acts as a protective layer on the surface. Polishing pastes include those with conductive properties and others that are non-conductive. In the case of conductive polishing pastes, they perform chemical protection; in the case of non-conductive polishing pastes, they perform both chemical and electrical mitigation. The greatest advantage of using polishing paste as a polishing modifier is that the polishing process can be used simultaneously or continuously. The synergistic effect of these two processes significantly reduces operation time while producing a high-quality surface finish.

[0034] Solid electrolytes used for dry electropolishing of metals may contain one or more types of active particles and one or more types of mild particles.

[0035] In the first preferred embodiment, the volume composition range of the electrolyte used for dry electropolishing of metals is as follows:

[0036] - 0% to 99.9% of active particles containing methanesulfonic acid with a diameter of approximately 0.7 mm.

[0037] - 0% to 99.9% of sulfuric acid-containing active particles with a diameter of approximately 0.2 mm. The total volume of active particles is greater than or equal to 50%.

[0038] - 0% to 50% conductive non-conductive mild particles.

[0039] - 0% to 10% of the initial milding particles of the chemical action of hydrogel polymers.

[0040] Particles containing methanesulfonic acid are highly chemically active in dissolving basic oxides. Particles containing sulfuric acid (a diprotic strong acid) are highly conductive. Furthermore, the combination of particles of different sizes increases the contact points between particles and between particles and surfaces. To counteract the high activity of this group of active particles, this configuration incorporates conductive, moderate particles that locally and transiently block electroactivity, performing chemical action and cleaning within a given time. The chemically moderated particles of the aqueous gel polymer clean the surface of exudates from the active particles. This configuration is suitable for sensitive metal parts, such as steel or carbon steel for tools, and has shapes including hollow and recessed designs.

[0041] In the second preferred embodiment, the volume composition range of the electrolyte used for dry electrolyte electropolishing of metals is as follows:

[0042] - 90% to 99.9% of the active particles contain at least acid.

[0043] - 0.1% to 10% of hydrogel polymer soothing particles.

[0044] This configuration is used to control acid exudates generated by active particles. It maintains high electroactivity, almost equivalent to a configuration with only active particles, but with the advantage of preventing exudate accumulation on metal surfaces. This configuration is desirable for sensitive material components, such as steel or carbon steel used in tools. Its high activity makes it suitable for large-scale applications.

[0045] In the third preferred embodiment, the volume composition range of the electrolyte used for metal dry electrolyte electropolishing is as follows:

[0046] - 10% to 80% of active particles containing methanesulfonic acid and / or sulfuric acid with a diameter of about 0.7 mm.

[0047] - 10% to 40% of active particles containing methanesulfonic acid and / or sulfuric acid with a diameter of approximately 0.2 mm. The total volume of active particles is greater than or equal to 50%.

[0048] - 5% to 50% non-conductive mild particles.

[0049] This configuration is particularly suitable for dry electropolishing to achieve high-quality surface finishes more quickly in metals with self-passivating capabilities. For metals such as stainless steel and titanium, excellent results can be obtained where undulations are not visible even at ten times magnification.

[0050] In the fourth preferred embodiment, the initial volume composition range of the electrolyte used for dry electropolishing of metals is as follows:

[0051] - 90% to 99.9% of the active particles contain at least one acid.

[0052] - 0.1% to 10% partially dried granules.

[0053] This configuration allows for the elimination of exudates from the active particles. A significant advantage is that once the partially dried particles are saturated, a certain amount (e.g., 0.5% of the initial volume) of new partially dried particles can be added, which can maintain absorption activity over time. Detailed Implementation

[0054] A solid electrolyte containing aqueous acrylic acid mild particles.

[0055] This configuration is designed for polished carbon steel without creating craters or marks on the surface.

[0056] ● 9.950 kg of active particles, formed by a highly cross-linked ion exchange resin of styrene and divinylbenzene copolymer (to limit exudation), namely Purolite Supergel SGC 650 H and an aqueous solution containing 5% methanesulfonic acid.

[0057] ● 0.050 kg of mild granules, which are ion exchange resins of acrylic polymers and have amino functional groups containing distilled water.

[0058] This electrolyte is used to polish carbon steel, during which a 12V positive DC current is applied to the part during 0.5-second and 0.5-second pauses, and an additional 0.050 kg of acrylic soothing particles and water are used per hour.

[0059] Electrolytes with non-conductive mild particulate solids

[0060] The configuration was designed to be made of polished stainless steel and to achieve the final result without the orange peel-like undulations.

[0061] ● 6.650 kg of active particles, formed from ion exchange resin spheres of a copolymer of styrene and divinylbenzene with an average size of approximately 0.7 mm, which is Mitsubishi Relite CFS and is an aqueous solution containing 10% sulfuric acid.

[0062] ● 3.350 kg of nonconducting mild granules, formed from irregularly plasticized PVC.

[0063] The electrolyte is used to polish stainless steel, where electrical pulses of +17V for 20ms, 0V for 10ms, -17V for 30ms, and 0V for 10ms are applied to the part to obtain a surface that is visually imperceptible even at 10x magnification.

[0064] Non-conducting mild particulate solid electrolyte

[0065] The configuration was designed to be made of polished stainless steel and the final result was achieved without the orange peel-like undulations.

[0066] ● 5,000 kg of active particles, formed by ion-exchange spherical resin of a copolymer of styrene and divinylbenzene with an average size of approximately 0.7 mm, namely Mitsubishi Relite CFS and an aqueous solution containing 5% methanesulfonic acid.

[0067] ● 1.150 kg of active particles, formed from ion exchange resin spheres of a copolymer of styrene and divinylbenzene with an average size of approximately 0.2 mm, which is Purolite PCR 45K and is an aqueous solution containing 10% sulfuric acid.

[0068] ● 3.350 kg of nonconducting mild granules, formed from irregularly plasticized PVC.

[0069] The electrolyte is used to polish stainless steel, in which electrical pulses of +17V, 20ms; 0V, 10ms; -17V, 30ms; 0V, 10ms are applied to the part to obtain a surface that is visually imperceptible even at ten times magnification.

Claims

1. A solid electrolyte for dry electrolytic polishing of metal surfaces, comprising: • Multiple active particles, each containing a sulfonated ion exchange resin based on polystyrene-divinylbenzene (PST-DVB), the active particles being filled with an acid solution to provide chemical and electroactive activity; • One or more types of mildening particles, comprising chemically active mildening particles capable of absorbing and chemically neutralizing acidic exudates released by said active particles; and / or The moderating particles are used to reduce undesirable electrochemical erosion of the polished surface caused by the acidic exudates from the active particles.

2. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 1, characterized in that, The moderating particles are also selected from non-conductive moderating particles configured to reduce the overall conductivity of the electrolyte by interrupting the conductive paths formed between the active particles.

3. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 1, characterized in that, The soothing particles comprise particles of an acrylic gel polymer that initially contains amino functional groups of water or distilled water, the soothing particles utilizing the amino functional groups to neutralize the acidic exudates absorbed into the particles.

4. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 1, characterized in that, The soothing particles are particles that retain an alkaline solution, and the soothing particles utilize the alkaline solution of the soothing particles to neutralize acidic exudates that come into contact with the outside of the particles.

5. The solid electrolyte for dry electrolytic polishing of metal surfaces according to any one of the preceding claims, characterized in that, At least one type of the soothing particles is a non-conductive particle.

6. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 5, characterized in that, The average size of the moderating particles is equal to or greater than the average size of the active particles.

7. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 2, characterized in that, The chemically active and / or conductive mildening particles are abrasive particles capable of performing surface cleaning processes.

8. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 7, characterized in that, The grinding particles are particles of minerals, salts, ceramic materials, or amorphous materials.

9. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 7, characterized in that, The abrasive particles are polishing paste that comes into contact with the metal surface.

10. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 5, characterized in that, The soothing particles are polymers whose main chain contains only C-C bonds.

11. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 2, characterized in that, Its volume composition range is as follows: - 0% to 99.9% of active particles containing methanesulfonic acid with a diameter of approximately 0.7 mm. - 0% to 99.9% of active particles containing sulfuric acid with a diameter of approximately 0.2 mm. - 0% to 50% non-conductive mildening particles, - 0% to 10% of mildening particles containing hydrogel polymers, The percentage of at least one type of mildening particles is at least 0.5%.

12. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 3, characterized in that, Its volume composition range is as follows: - 90% to 99.9% of the active particles contain at least acid. - 0.1% to 10% of hydrogel polymer soothing particles.

13. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 2, characterized in that, Its volume composition range is as follows: - 10% to 80% of active particles containing methanesulfonic acid and / or sulfuric acid with a diameter of approximately 0.7 mm. - 10% to 40% of active particles containing methanesulfonic acid and / or sulfuric acid with a diameter of about 0.2 mm, wherein the total volume of said active particles is greater than or equal to 50%. - 5% to 50% non-conductive mild particles.

14. The solid electrolyte for dry electrolytic polishing of metal surfaces according to claim 12, characterized in that, Its volume composition range is as follows: - 90% to 99.9% of the active particles contain at least acid. - 0.1% to 10% partially dried granules.