Surface finishing using electrically conducive particles and abrasive particles

Abstract

A method for surface finishing an object, comprising: surface finishing at least one surface of the object by moving a combination of a plurality of electrically conductive particles and at least one abrasive particle relative to the object, the combination and the at least one surface being in a medium, the object being electrically connected with a first pole of at least one electric source and the medium being electrically connected with a second pole of the at least one electric source, and one or more particles of the plurality of electrically conductive particles comprising an electrolyte. Also, an object, a composition, a machine, an apparatus, and an assembly.

Description

[0001] SURFACE FINISHING OF SURFACES OF OBJECTS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of object surface finishing. More particularly, the disclosure relates to compositions, apparatuses, machines, assemblies and methods for surface finishing of objects leading to a change in surface condition (such as, e.g., roughness, waviness, gloss, etc.), and objects with surfaces finished with such compositions, apparatuses, machines, assemblies and methods.

[0004] BACKGROUND

[0005] Different systems for surface finishing, smoothing, polishing and other finishing of surfaces of objects are known.

[0006] For example, electropolishing methods (also known as electrochemical polishing, anodic polishing, or electrolytic polishing) have been long used for removing material from a workpiece, typically a metallic workpiece, by applying a certain voltage to the workpiece which can be made particularly high at the edges or tips thereof, so that at those edges or tips the unwanted projections are burned off by small arcs. Other electropolishing methods may comprise immersing a metal part in an electrolyte bath and polishing upon application of an electric potential difference.

[0007] Also, mechanical abrasion is also known for polishing surface, via the use of particles having specific geometries and sizes and having greater hardness than the material of the workpiece that needs to be polished or the surface of which is to be treated. In this case, these abrasive particles and the workpiece are moved relative to each other, so that friction actually exists between the particles and the workpiece.

[0008] Sandblasting is another known process of surface finishing and cleaning a hard surface by forcing solid particles -usually aluminum oxide particles- across the surface to be treated at high speed using compressed air.

[0009] Further, tribofinishing is also known as a frictional surface treatment. This material- to-material finishing process uses vibrations to polish custom-made machined mechanical parts. Tribofinishing (also known as chemical-mechanical polishing or CMP, vibroabrasion, tumbling or vibratory finishing) is used to modify the surface finish and edges of metal parts, by immersing the metal parts in an abrasive mixture (also known as “media”) set in vibratory, oscillatory or rotary motion in a tank. Ceramic media is typically used to polish and / or deburr metal, aluminum and plastic.

[0010] Some attempts to combine different technologies have been made. An example thereof can be found in patent document FR3093016B1 which relates to a method and an installation for polishing a metal part comprising immersing the metal part in an electrolyte bath upon application of an electric potential difference, with abrasive particles being dispersed in said electrolyte bath. And also in patent document DE2031833A1 , which relates to rounding metal articles using an electrolytic bath which contains abrasive and metal particles, said metal particles are described to produce particularly conductive current bridges, so that concentrated electric fields arise in their surroundings, with the help of which the adjacent edges or corners of the workpieces to be treated are rounded off.

[0011] A problem with these methods is that too much material is removed; and further, there is a lack of control of the surface finishing process. For instance, not being able to control the specific areas on which the material is removed, prevents selective polishing / grinding to be achieved; as a result, material is typically removed from all areas of the treated object surface, which may lead to loss of some characteristic aspects of the geometry of the object which may be desirable to keep (e.g., sharp edges).

[0012] DESCRIPTION

[0013] It has now been found that a combination of a first plurality of electrically conductive particles and at least one abrasive particle, such as, e.g., a second plurality of abrasive particles, may be suitably used for surface finishing an object, one or more of the electrically conductive particles of the first plurality of electrically conductive particles comprising an electrolyte. Such methods for surface finishing objects have been found to offer a great control of the surface finishing process, whilst timely achieving desired surface finishing results. The amount of material removed may be reduced whilst improving the selectivity of the material removal, in particular by offering a major control on the specific areas on which the material is removed on the surface of the object. These and other aspects and advantages of the surface finishing process and combinations of first and second pluralities of particles used therefor, will be elucidated in more detail below.

[0014] A first aspect of the disclosure relates to a method for surface finishing an object. The method includes surface finishing at least one surface of the object by producing of the one or more surfaces relative movement between the object and a combination of a first plurality of electrically conductive particles and at least one abrasive particle. In some embodiments, the at least one abrasive particle is a second plurality of abrasive particles. The first plurality of electrically conductive particles, and the at least one abrasive particle, (including the second plurality of abrasive particles when multiple abrasive particles are considered), may also be respectively referred to in the present disclosure as electrically conductive particles and abrasive particles. Also, unless stated otherwise, features and characteristics described in relation to electrically conductive particles and / or abrasive particles refer to both part of the respective plurality (i.e. , some particles thereof) and the entirety of the respective plurality (i.e., all particles thereof), and refer to the at least one abrasive particle when only one such particle is provided.

[0015] The combination and the at least one surface are in a medium. The object is electrically connected with a first pole of at least one electric source; and the electrically conductive particles and / or the medium containing the electrically conductive particles and / or a container containing the medium is electrically connected with a second pole of the at least one electric source. One or more (e.g., one, some, all) particles of the first plurality of electrically conductive particles comprise an electrolyte. The electrically conductive particles are, in some embodiments, free solid bodies.

[0016] The method surface finishes the at least one surface, or typically multiple surfaces of the object, by way of generating contact between the particles and the surface(s) so that material from the surface(s) can be effectively removed, thereby reducing roughness thereon by evening out peaks and valleys of material present on the surface(s) of the object, especially with major material removal from peaks than from valleys; in fact, with reduced material removal from valleys. In this sense, the surface finishing makes the at least one surface of the object to come into contact with the combination of the first plurality of electrically conductive particles and the at least one abrasive particle (including, e.g., the second plurality of abrasive particles), by way of movement of the object, by way of movement of the combination, or by way of movement of both.

[0017] The object may be a shaped part or an object with one or multiple electrically conductive surfaces, or an object according to the second aspect or the third aspect.

[0018] The relative movement may be achieved by moving one or both of the combination and the at least one surface. The relative movement between the combination and the at least one surface may be attained by way of any motion, such as displacing, rotating, mixing, stirring, vibrating, shaking, spraying, propelling, sucking, etc.; a plurality of motion types may be combined simultaneously or sequentially to provide linear motion and / or rotational motion.

[0019] The surface finishing includes contacting the electrically charged particles and the at least one abrasive particle with the at least one surface. The finishing achieved by the two types of particles provides a better result in terms of quality of the finishing compared to the quality of finishing by using just one type of such particles and / or other surface finishing techniques known in the art. The quality of the finishing can be assessed in terms of a roughness value that characterizes the roughness of the at least one surface (which will be lower than the original roughness value, i.e., the roughness value of the at least one surface prior to the finishing process). The quality of the finishing can also be assessed by the amount of material removed and the precision of material removal (to reduce dimensional tolerances in the finished object), both of which being preferably as low as possible to reduce removing material on the surface more than it is necessary, and also to prevent wasting material. It is noted that the attained roughness and material removal with the present method are lower than those resulting from conducting the finishing sequentially with the two types of particles.

[0020] The better result of the surface finishing by the two types of particles can also be expressed in terms of time required to conduct the finishing, which is lower than the time it would take to conduct the finishing with the two types of particles sequentially.

[0021] Further, the abrasive particle(s) can have a greater durability, i.e., their abrasive behavior lasts longer. In particular, since the electrolyte is typically comprised inside the electrically conductive particles, the electrolyte may be regarded as being encapsulated, and the abrasive particle or particles are not in constant contact with the electrolyte, avoiding degradation of the abrasive particle(s) by the electrolyte. Similarly, by having the electrolyte encapsulated the degradation of apparatuses used for surface finishing and the toxicity of using non-encapsulated electrolytes may be advantageously reduced.

[0022] This, in turn, may reduce the number of abrasive particles that needs to be supplied in the at least one abrasive particle, or new abrasive particles need to be supplied to the at least one abrasive particle less frequently owing to their longer useful lives, thereby also reducing the cost of the surface finishing process.

[0023] Oxide layers that tend to get formed on the at least one surface as part of the finishing by the electrically charged particles can sometimes also be partially or completely removed by the action of the abrasive particle(s) during the finishing. When there are such layers on the at least one surface, the electrically charged particles are less effective as there is a reduced electrical exchange between the particles and the surface. Hence, by removal of such oxide layers, the at least one abrasive particle assists in the finishing of the electrically conductive particles.

[0024] Also, the combination of electrically conductive particles and abrasive particles may advantageously reduce or avoid defects caused by the electrically conductive particles being accidentally temporarily adhered to the surface of the object during the surface finishing process, as the abrasive particle(s) may contact the adhered electrically conductive particles and release them. In the context of the present disclosure, surface finishing may encompass leading to a change in surface condition such as, e.g., roughness, waviness, gloss, etc., on one or more surfaces of an object to be surface finished. Consequently, surface finishing may encompass one or more of: smoothing of the one or more surfaces, polishing of the one or more surfaces, precision finishing of the one or more surfaces, rounding of the one or more surfaces, deburring of the one or more surfaces, providing corrosion resistance to the one or more surfaces, etc.

[0025] Abrasion, in the context of the present disclosure, is to be understood in a broad sense, including removing material from a surface to be surface finished, such as by scratching or scraping a surface to be surface finished, and / or plastically deforming a surface to be surface finished, which may flatten the surface to be surface finished.

[0026] In some embodiments, the surface finishing includes, while there is relative movement between the object and the combination of the first plurality of electrically conductive particles and the at least one abrasive particle, making the combination of the first plurality of electrically conductive particles and the at least one abrasive particle to contact at least one surface of the object so that the at least one abrasive particle surface finishes the at least one surface by abrasion and the first plurality of electrically conductive particles surface finishes the at least one surface by ion transport.

[0027] The surface finishing includes: abrasion surface finishing whereby abrasive particles remove material mainly from peaks of material, i.e., protrusions on the at least one surface, and flat surfaces; and ion transport surface finishing on the at least one surface, which is a form of electrical erosion, whereby electrically conductive particles remove material from peaks and flat surfaces but also from valleys of material, i.e., recesses on the at least one surface, and flat surfaces on the at least one surface as the particles electrically react with those on the surface(s) of the object. The ion transport removes metal ions from the surface(s) of the object. Moreover, at microscopic level, more material tends to be removed from peaks (namely, micro-peaks) than from valleys (namely, micro-valleys).

[0028] Abrasive particles generally remove material more coarsely than the electrically conductive particles. Hence, the abrasion is convenient for reducing the waviness on the at least one surface, i.e., major reduction of a total roughness value Rt or an average roughness value thereof Ra or a peak to valley height difference (absolute or averaged) value Rz thereof, and the ion transport-based material removal is convenient for reducing the roughness on the at least one surface.

[0029] By using the combination of electrically conductive particles and one or more abrasive particles, a surface finishing process is achieved of great precision and selectivity. As indicated previously, the amount of material removed may be reduced whilst improving the selectivity of the material removal, in particular by offering a major control on the specific areas on which the material is removed on the surface of the object. This typically increases the dimensional tolerance of the surface finishing process and improves the preservation of the geometry of the object being surface finished.

[0030] The improved selectivity allows reducing the amount of material to be removed to achieve a desired surface finishing effect, thereby not removing more material than necessary.

[0031] Moreover, this surface finishing may also increase the resistance of objects, especially those that tend to have traction loads applied thereon, because the finishing may introduce compressive residual stresses, thereby also increasing a stress cracking resistance of the at least one surface.

[0032] In some embodiments, making the combination of the first plurality of electrically conductive particles and the at least one abrasive particle to contact the at least one surface includes: making at least some electrically conductive particles of the first plurality of electrically conductive particles to contact a first portion of the at least one surface and releasing part of the electrolyte of said some electrically conductive particles on the first portion; and making at least some abrasive particles of the at least one abrasive particle (including, e.g., the second plurality of abrasive particles) to contact electrolyte released on the first portion, thereby altering a motion direction of said some abrasive particles to further contact a second portion of the at least one surface to surface finish the at least one surface.

[0033] Abrasive particles may change the way they come into contact with the at least one surface for surface finishing thereof because of the presence of the electrically conductive particles. For instance, as the electrically conductive particles function with ion transport such that they release electrolyte for electrical reactions between ions, the electrolyte might get in the way of one or more abrasive particles when colliding with the surface. The electrolyte influences how the particles flow on the surface of the object, and so the at least one abrasive particle tends to deviate when contacting the electrolyte and then reach a different position of the at least one surface where the abrasion takes place, thereby removing material. This phenomenon, in turn, increases the effectivity of the abrasion by the abrasive particle(s) because the relative movement between them and the surface can be less direct, which produces greater friction between the two.

[0034] In some embodiments, the electrolyte of one or more (e.g., one, some, all) electrically conductive particles of the first plurality of electrically conductive particles is inside the electrically conductive particles.

[0035] Liquid retention in the electrically conductive particles can occur due to porosity of the material or due to molecular structure such as a gel-like structure. Possible retention mechanisms within the scope of the present disclosure include: permeation, absorption, adsorption, retention in the interlaminar space.

[0036] The electrically conductive particles may be of any material capable of retaining liquid, such as, for example, polymeric materials, mineral, ceramic, organic compounds, inorganic compounds, of plant origin, and are preferably of polymeric material. Electrically conductive particles of a polymeric material may simply be referred to herein as polymeric particles.

[0037] Suitable polymeric materials may be, e.g., ion exchange resins.

[0038] In some embodiments, the electrically conductive particles are of a material selected from: strong and weakly acidic cationic resins, strong and weakly basic anion exchange resins and chelating resins, and more preferably are cationic exchange resins, as such resins contribute to capturing metal ions extracted in the electropolishing processes.

[0039] In ion exchange technology, resins are categorized as strong or weak based on the ionization characteristics of their functional groups, influenced by their pKa values, which determines their ion-exchange behavior in varying pH environments. Strong ion-exchange resins possess functional groups that remain fully ionized across a wide pH range, making them effective in diverse conditions. In contrast, weak ion-exchange resins have functional groups with higher pKa values, meaning their ionization, and thus their ion-exchange capacity, is more pH-sensitive. Generally, resins having groups with a pKa of up to 3 may be regarded strong acidic cationic resins also referred to as strong acid cation (SAC) resins. Resins having groups with a pKa of above 3 and up to about 6 may be regarded as a week acid cation (WAC) resins. Resins having groups with a pKa from 7 to about 10 may be regarded as weak base anion (WBA) resins, and resins having groups with a pKa higher than 10, e.g., about 12 or 13 may be regarded as strong base anionic (SBA) resins. Chelating resins may have groups with a range of different pKas depending on the nature of the chelating group of the resin, e.g., with a pKa ranging from 1 to 10.

[0040] In some embodiments, electrically conductive particles are of or comprise a SAC resin, in particular a SAC such as styrene-divinylbenzene with a macroporous or gel structure, having sulfonic acid (-SO3H) groups as functional components. These sulfonic acid groups have a pKa of approximately -2, ensuring they remain fully ionized across a broad pH range, including in highly acidic environments. This enables consistent cation exchange performance. Particular examples include Poly(perfluorosulfonic acid) resins, Perfluoro vinyl ether polymers with sulfonic acid groups, and Polytetrafluoroethylene (PTFE) with sulfonic acid side chains, which are highly resistant to pH fluctuations. Other strong acid cation resins include Phenol-formaldehyde sulfonic acid resin, sulfonated phenolic polymers, and crosslinked polyacrylic resins with sulfonic acid functional groups, all of which maintain high efficiency in both acidic and neutral conditions due to their low pKa values.

[0041] In some embodiments, electrically conductive particles are of or comprise a WAC resin, in particular a WAC such as Poly(acrylic acid) or Crosslinked poly(acrylic acid) resins. These resins feature carboxylic acid (-COOH) groups with a pKa typically in the range of 4.5 to 6.0, making them pH-sensitive and more suitable for environments that are moderately acidic to neutral. They are less effective in strongly acidic solutions due to partial ionization at low pH. Other WAC resins include Poly(acrylic acid-co-divinylbenzene), Poly(methacrylic acid), and crosslinked iminodiacetic acid-functionalized resins, all of which exhibit ion-exchange properties optimized for pH levels where carboxyl groups are ionized, ensuring effective cation capture and release in more controlled pH conditions.

[0042] In some embodiments, electrically conductive particles are of or comprise chelating resins, which enhance the selectivity for metal ions through functional groups such as iminodiacetic acid and aminophosphonic acid. These groups form stable chelates with specific metal ions. Iminodiacetic acid has a pKa of approximately 2.5 and 9.5, allowing for selective metal ion capture at different pH levels, while aminophosphonic acid has a pKa around 1.5 and 6.5, making it ideal for selectively recovering metals like calcium and other multivalent ions from complex solutions. Examples of such resins include Poly(styrene- divinylbenzene) resin functionalized with these chelating groups, crosslinked iminodiacetic acid or aminophosphonic acid resins, and thiourea-functionalized styrene-divinylbenzene resins. These resins are particularly useful for selective metal recovery in mixed or harsh chemical environments, providing high specificity even in the presence of competing ions.

[0043] In some embodiments, electrically conductive particles are of or comprise a SBA resin, in particular an SBA which utilizes functional groups like quaternary ammonium (- NR4+) that remain fully ionized across a wide pH range. These resins have a pKa greater than 12, ensuring consistent performance in both neutral and highly alkaline environments, where they can effectively exchange anions such as sulfate, nitrate, and chloride. SBA resins are highly stable and do not lose their ion-exchange capacity even in extreme pH conditions, making them ideal for processes requiring strong anion capture. Particular examples of SBA resins include crosslinked poly(styrene-divinylbenzene) resins functionalized with quaternary ammonium groups, and other resins with similar high-pKa ammonium-based functional groups. These resins are particularly suitable for applications involving the removal or recovery of strong acid anions from highly alkaline or near-neutral solutions.

[0044] In some embodiments, electrically conductive particles are of or comprise a WBA resin, in particular a WBA which includes functional groups such as primary, secondary, or tertiary amines (-NH2, -NHR, -NR2) that exhibit a pKa in the range of 7 to 10, meaning they are only partially ionized in moderately acidic to neutral pH environments. WBA resins are effective in absorbing weak acid anions, such as organic acids or carbonates, in environments where strong base anions are not as prevalent. Unlike SBA resins, WBA resins become less effective in strongly alkaline conditions, where their functional groups are not ionized, and they tend to lose their capacity in highly basic environments. Typical examples of WBA resins include crosslinked poly(styrene-divinylbenzene) resins functionalized with amine groups and copolymers of acrylic or methacrylic acids. These resins are commonly used in applications where selective removal of weak acid anions is required, especially in solutions with pH levels that can be easily controlled for optimal ion exchange.

[0045] In some embodiments, the particles of polymeric material are of a sulfonated divinylbenzene S-DVB and styrene copolymer, since it is a material resistant to acid and the oxidative action of the process. The material has the ability to act as an ion exchanger, which favors the extraction of metal from the surface to be surface finished (e.g., polished) by storing the ions.

[0046] Alternatively, the polymeric material particles are of a copolymer containing units derived from acrylic acid or methacrylic acid. This includes derivatives with different functional groups such as acrylic acid, acrylamide, cyanoacrylate, alkyl acrylates, among others, and the corresponding methacrylate analogs.

[0047] In some embodiments, electrically conductive particles are of polymeric materials including functional groups that are capable of capturing or retaining the metal ions generated during the process, such as acid, amino, or chelating groups, including the groups as described above. These functional groups can be of the acidic type, such as sulfonic or carboxylic groups. These acidic functional groups are especially useful in this application as they have good chemical resistance and are capable of retaining a wide variety of metal ions. In some embodiments, the polymeric materials include functional groups that are of the chelating type such as, for example, iminodiacetic, aminophosphonic, polyamine, 2-picolylamine, thiourea, amidoxime, isothiouronium, bispicolilamine, among others. These chelating groups have a high selectivity over the transition metals versus alkali or alkaline earth metals, which allows them to be more flexible in the formulation and does not require the use of distilled water.

[0048] Depending on the specific type of polymer and functional groups included, the exact composition of the electrically conductive, particles may vary and may be adjusted. As a mode of example, in some embodiments, electrically conductive particles are of a cationic resin of a gel copolymer styrene-divinylbenzene (DVB), which may preferably be sulfonated.

[0049] Ion exchange resins suitable as electrically conductive particles as described herein may typically be available commercially required characteristics to be used as polymeric material particles.

[0050] The electrically conductive particles may have at least a surface thereof that encapsulates the electrolyte, and such surface may be of a particular material such as, for example but without limitation, an ion-exchange resin, preferably cationic ion-exchange resin that are preferably acid, for example but without limitation, polystyrene divinylbenzene. The encapsulating surface may let the electrolyte escape, at least partially, upon the particle contacting a surface or another particle, and it may also let electrolyte on the surface of, e.g., the object to be surface finished, to be absorbed again into the particle.

[0051] In some embodiments, electrically conductive particles have a porous structure, which facilitates the exchange of fluids resulting in a faster process. Alternatively, in some embodiments, the particles have a gel-like structure. In this case the fluid exchange is more restricted, which results in a slower process, however, the particle-surface contact is more defined, resulting in a lower final roughness.

[0052] The electrically conductive particle may be of a porous material, whereby the electrolyte is be contained inside the porous of the material.

[0053] Preferably the particles are porous, this porosity is selected from: microporosity, mesoporosity, macroporosity and fractal porosity.

[0054] The shape of electrically conductive particles as described herein are preferably, in some embodiments, spheric and / or spheroid.

[0055] Typically, the porous material is not saturated with the electrolyte. Thereby, the electrolyte is typically released when in contact with the surface of the object to be surface finished.

[0056] The function of the electrolyte is twofold: on the one hand, it conducts electricity, and on the other, it dissolves the oxides that are formed on the surface to be treated.

[0057] In some embodiments, the electrolyte is an acidic aqueous solution, e.g., an aqueous solution of hydrofluoric acid (HF), sulfuric acid, sulfonic acids (e.g., methanesulfonic acid, MSA), phosphoric acid (such as orthophosphoric acid), carboxylic acids, citric acid, and hydrochloric acid. Preferably, the electrolyte may be an aqueous solution of sulfuric acid or MSA.

[0058] In some embodiments, electrically conductive particles comprise a combination of particles having different types of electrolyte (e.g., aqueous solutions of different acids), For instance, the electrically conductive particles may comprise particles comprising an aqueous solution of MSA and particles comprising an aqueous solution of sulfuric acid.

[0059] In some embodiments, the total concentration of the acids in the electrolyte may vary from 0.1 to 70 wt.% with respect to the total mass of the water plus the acid, in particular from 1 to 40 wt.%. In some embodiments, an acid concentration from 1 % and 10 wt.% relative to the mass of the water plus the acid is used.

[0060] In particular, a HF solution such as, e.g., a 90 to 99% water, H2O, and 10 to 1 % HF, by weight of acid to the total weight of water and acid may be used. As another example, an aqueous solution of sulfuric acid may be used having, e.g., a 90 to 99% water, H2O, and 10 to 1 % of sulfuric acid, in particular 5 to 1% of sulfuric acid, by weight of acid to the total weight of water and acid. Similarly, an aqueous solution of methanesulfonic acid (MSA) may be used having, e.g., a 90 to 99.5% water, H2O, and 10 to 0.5 % of MSA, in particular from 5 to 1 % of MSA, by weight of acid to the total weight of water and acid. Similarly, an aqueous solution of orthophosphoric acid may be used having 90 to 99.5% water, H2O, and 10 to 0.5 % of orthophosphoric acid, in particular from 5 to 1 % of orthophosphoric acid, by weight of acid to the total weight of water and acid.

[0061] In some embodiments, the electrolyte is an ionic liquid or a conductive liquid polymer.

[0062] In some embodiments, the surface finishing of the at least one surface of the object is carried out such that a ratio alpha a = - — - is greater than or equal to 0.010 s’1,

[0063] ^Tn-tp0[Sfing preferably greater than or equal to 0.015 s-1and / or 0.020 s-1and / or 0.050 s-1and / or 0.100 s'1and / or 0.150 s’1, where ARais a variation in average roughness Ra during the surface finishing (e.g., in percentage, in micrometers, etc.), Am is the variation in mass during the surface finishing (e.g., in percentage, or in micrometers or grams if represented as variation in thickness or mass of the object, etc.), and tpoiishingis the time that has elapsed during the surface finishing (e.g., in seconds).

[0064] By way of example, ARacan be computed as the ratio of the difference in average roughness Ra after surface finishing (i.e. , difference between Ra after surface finishing and Ra before surface finishing) divided by the average roughness Ra before surface finishing (and optionally multiplied by 100 to provide a percentage); and / or Am can be computed as the ratio of the difference in mass m after surface finishing (i.e., difference between m after surface finishing and m before surface finishing) divided by the mass m before surface finishing (and optionally multiplied by 100 to provide a percentage), and the mass being representable in a mass unit, e.g., grams, or in a length unit, e.g., micrometers, in the case of the latter, representing the thickness of the at least one surface or the object.

[0065] The aforesaid a ratio characterizes the reduction of roughness (Ra) with regards to the amount of material removed, especially with respect to the initial roughness and amount of material, and the time taken for that. The greater this ratio is, the more effective the smoothing process becomes as lower mass reduction and / or lower time is needed for reducing the roughness.

[0066] Methods as described herein provide mass reductions determined from the mass of the object before being subjected to the surface finishing process and after. In some embodiments, the mass reduction is of 1.0 % or less, in particular of 0.5 % or less, and more in particular of 0.25 % or less.

[0067] Although the alpha (a) ratio has been described as being - — - , it will be noted that an analogous ratio can be defined in the opposite way, i.e., , departing from the scope of the present disclosure. In such case, the ratio is smaller than or equal to 100 s, and preferably smaller than or equal to 66.66 s.

[0068] A method described herein may be used to obtain any desired Ra and / or Rt and / or Rz value, which may depend on the type of material, roughness of the initial object and final application. For instance, a method as described herein may be suitably used for reducing the roughness to very low values, suitable for very demanding applications. As a mode of example, methods as described herein may provide surface treated objects with Ra values from 0.05 to 5.0 pm, in particular from 0.10 to 2.5 pm, and more in particular from 0.3 to 1.0 pm. As a mode of example, methods as described herein may provide surface treated objects with Rz values from 0.50 to 20.0 pm, in particular from 1.0 to 15.0 pm and more in particular from 2.0 to 10.0 pm.

[0069] A method described herein can optimize the time required to achieve a Rz final roughness value over a certain initial Rz value, minimizing the material extraction, and as a consequence, the radius increase over an initial dimensional tolerance of a sharp edge. In some embodiments, the surface finishing of the at least one surface of the object is carried out such that a ratio beta B =100is greater than or equal to 2.5 s’1. In particular, the ratio P is greater than 2.5 s’1, more in particular between 3 and 15, such as, e.g., 3.785 s’1, and more in particular between 5 and 10 such as 5.729 s’1. Being A / ?z=Rz~Rz, where Rzlis the

[0070] Rz initial roughness, Rzis the final roughness value after a certain polishing time t, and Ar being Ar = where r‘ and r are the initial and final radius value of a sharp edge included on an object to be surface treated, respectively. Conventional abrasive methods known in the art comprise ratios of values <1 s’1. Conventional methods known in the art using only electrically conductive solid bodies comprise ratios p below 2.5 s-1in particular values betweenl and 2.25 s’1.

[0071] In some embodiments, a method described herein and / or the surface finishing step is carried out at a temperature from room temperature (e.g., from 10°C to 25°C) to 80°C, in particular from 30°C to 60°C and more in particular from 40°C to 50°C. These temperatures may advantageously contribute to reducing the time of the surface treatment to obtain a desired final roughness.

[0072] In the context of the present disclosure, unless otherwise indicated, all disclosed ranges include the endpoints as well.

[0073] A higher temperature can be advantageous to enhance the surface finishing as the resistance of the surface to be surface finished typically becomes lower, thereby easing the effect of the abrasive particle(s), but also of the electrically conductive particles as the kinetics of the electrochemical reactions are altered by the higher temperature.

[0074] A temperature above 60°C may be used for short periods of time or less frequently because it damages the electrolyte within electrically conductive particles of the first plurality of electrically conductive particles.

[0075] In some embodiments, a temperature during the surface finishing step is controlled (e.g., to work at a higher or lower temperature) to increase and / or reduce a speed of the surface finishing and / or to adjust the surface finishing for a given surface treatment time. In some embodiments, the relative movement between the object and the combination has a speed between 0.01 m / s and 5 m / s, in particular between 0.1 m / s and 1 m / s, and more in particular less than or equal to 0.5 m / s. In some embodiments, the relative movement between the object and the combination has a speed between 0.6 rpm (i.e., revolutions per minute) and 600 rpm (namely, between 3.768 rad / min and 3,768 rad / min, that is to say, between 0.0628 rad / s and 62.8 rad / s), in particular between 6 rpm and 300 rpm (namely, between 37.68 rad / min and 1 ,884 rad / min, that is to say, between 0.628 rad / s and 31.4 rad / s), and more in particular less than or equal to 60 rpm (namely, 376.8 rad / s, that is to say, 2 times pi or 6.28 rad / s).

[0076] The time of the surface finishing step may depend on the initial roughness properties of the object, and / or the desired final roughness, and / or the speed of the relative movement between the combination and the at least one surface.

[0077] As a mode of example, the time of the surface finishing step may vary from, e.g., 0.25 h to 5.0 h, in particular from 0.5 h to 3.0 h, and more in particular from 0.75 h to 2.0 h.

[0078] In some embodiments a method as described herein comprises a recirculation step, said recirculation step preferably comprising:

[0079] - removing at least part of the medium from the container,

[0080] - cleaning the at least part of the medium removed from the container, and

[0081] - returning the cleaned medium to the container.

[0082] What is described below relative to a machine comprising a recirculation system also applies to the recirculation step.

[0083] In some embodiments, a maximum size of one or more abrasive particles of the at least one abrasive particle is greater than an average width of cavities delimiting valleys in the at least one surface of the object, thereby precluding the second particles from coming into contact with walls of the cavities.

[0084] The selection of the maximum size of abrasive particle(s) of the at least one abrasive particle, be it a single abrasive particle or a second plurality of abrasive particles, can ensure that surface finishing by abrasion is mostly limited to protrusions and flat surfaces, which require the major material removal, especially the first ones. Limiting the influence of abrasive particles to such parts of the geometry of the at least one surface of the device avoids removal of material in parts of the surface where material is preferably not to be removed, which is in the valleys. As abrasion is generally coarser than electrical erosion, the abrasive particle(s) can focus on removing material on the portions where abrasion can be more effective.

[0085] In some embodiments, a maximum size of one or more abrasive particles of the at least one abrasive particle is between 0.1 mm and 25.0 mm, preferably between 0.5 mm and 15.0 mm, more preferably between 0.75 mm and 10 mm, and yet more preferably between 1 mm and 5 mm.

[0086] In some embodiments, a maximum size of one or more electrically conductive particles of the first plurality of electrically conductive particles is equal to or less than an average width of cavities delimiting valleys in the at least one surface of the object, thereby enabling the first particles to come into contact with walls of the cavities.

[0087] The selection of the maximum size of the electrically conductive particles can ensure that surface finishing by electrical erosion is made possible in recesses and flat surfaces, which require the minor and finer material removal. Particularly, these parts of the at least one surface tend to feature a small waviness, i.e., the roughness, in a minor scale but which still reduce the quality of the object.

[0088] Electrically conductive particles of the first plurality of electrically conductive particles may selectively remove material from the surface(s) of the object, thereby enabling targeted roughness reduction.

[0089] In some embodiments, a maximum size of one or more electrically conductive particles of the first plurality of electrically conductive particles is between 50 pm and 20 mm, in particular between 50 pm and 2000 pm, preferably between 200 pm and 1300 pm.

[0090] The particle size may be determined by methods known in the art. The maximum particle size may be determined by establishing the size of the smallest sieve through which a 100 percent of the particles in a plurality of particles pass.

[0091] In some embodiments, one or more abrasive particles (e.g., one, some or all) of the at least one abrasive particle have a density ratio DR fulfilling the following: 7 > DR > 0.7, and / or a mass ratio MR fulfilling the following: 2 > MR > 0.2; where DR = where pap is a density of the abrasive particles, and presis a density of the electrically conductive particles or a resin thereof; and where MR = the particles (or resin thereof) including the electrolyte; and where MR = where mapis a mass of the abrasive particles, and mresis a mass of the resin of the electrically conductive particles.

[0092] As a mode of example, the density of abrasive particles (pap) may be from 2.5 to 5.5 g / cm3, in particular from 3.0 to 5.0 g / cm3, yet more in particular from 3.5 to 4.5 g / cm3.

[0093] A combination of a first plurality of electrically conductive particles and at least one abrasive particle may be homogeneous or heterogeneous. In some embodiments, the combination is a mixture of a first plurality of electrically conductive particles and a second plurality of abrasive particles, which mixture may be homogeneous or heterogeneous.

[0094] In some embodiments, the combination is a mixture of a first plurality of electrically conductive particles and a single abrasive particle, which mixture is heterogeneous. In such a combination the single abrasive particle may be a fixed element or a loose element present in, e.g., a container containing the first plurality of electrically conductive particles. In some embodiments, a combination of the first plurality of electrically conductive particles and the at least one abrasive particle is a homogeneous mixture.

[0095] In some other embodiments, a combination the first plurality of electrically conductive particles and the at least one abrasive particle is a heterogenous mixture. For instance, the heterogenous mixture may have a ratio of the first plurality of electrically conductive particles to the at least one abrasive particle which is distributed differently, e.g., as a gradient, depending on the position in a container containing the combination. Such gradient may contribute to giving a different abrasive / galvanic effect on the object to be surface finished, depending on the desired application, by placing the object in different positions within the container during the surface finishing process. In a particular example, the combination contains higher amount of abrasive particles on the bottom of a container, thereby providing a higher material extraction rate by placing the object to be surface finished at the bottom of the container (e.g., at the beginning of a surface finishing process) and with the possibility of placing the placing the object to be surface finished immersed in the mixture higher in the container (e.g., towards the end of the surface finishing process), thereby giving a different finish to the surface of the object, e.g., a higher shiny surface finish, without the need for changing the polishing medium, thus optionally conducting the entire surface finishing in one step. A heterogenous mixture may be achieved by, e.g., having a combination wherein the density of the first plurality of electrically conductive particles is different from the density of the at least one abrasive particle, e.g., with the at least one abrasive particle having a higher density than the first plurality of electrically conductive particles. In some embodiments the at least one abrasive particle may be a second plurality of abrasive particles which second plurality is heterogeneous in size and / or density, thereby having particles of the second plurality of abrasive particles distributing themselves heterogeneously within the combination.

[0096] The density and the mass of the electrically conductive particles, in particular a resin of the electrically conductive particles, respectively referred to as pres, and mresrefers to the particles, or resin thereof, including the electrolyte contained therein.

[0097] The hardness of abrasive particles may be from 3 to 10 in the mohs scale, in particular from 5 to 9.75 mohs, more in particular from 6 to 9.5 mohs, and yet more in particular from 7.5 to 9.25 mohs.

[0098] The geometry of abrasive particles may typically include edges, owing to their surface and / or their shape. For instance, abrasive particles may be prismatic, e.g., of triangular base or other geometrical base; cylindric; cubic; rhombic; pyramidal; conic; and / or spheric.

[0099] The material of abrasive particles may be synthetic (i.e., manufactured) and / or natural (i.e., naturally sourced, e.g., mined minerals). In some embodiments, the abrasive particles are preferably synthetic abrasive particles. Some natural abrasive particles (e.g., zirconia alumina, diamond dust, etc.) may also be manufactured, and synthetic versions of naturally sourced abrasive particles may be preferred due to difficult availability and higher costs of the naturally sourced abrasive particles. Additionally, or alternatively, synthetic particles may be preferred as they may be more effective as abrasives, since they may be free of impurities that natural abrasive particles may comprise.

[0100] In some embodiments, abrasive particles (synthetic and / or natural) of the at least one abrasive particle are selected from alumina (aluminum (III) oxide: AI2O3), e.g., in the form of corundum, emery (impure corundum), and ceramic aluminum oxide, including white AI2O3, brown AI2O3 and gray AI2O3; zirconia (zirconium dioxide); zirconia alumina (a combination of aluminum (III) oxide and zirconium dioxide); iron(lll) oxide (e.g., ceramic iron oxide); borazon (cubic boron nitride or CBN); boron carbide; glass powder; steel abrasive; silicon carbide (carborundum); calcite (calcium carbonate); diamond dust; novaculite; pumice; sand; garnet; sandstone; rotten stone (Tripoli); powdered feldspar; staurolite; and slag (a by-product of processes for smelting ores and recycling metals, comprising a mixture of metal oxides and silicon dioxide).

[0101] In some embodiments, the at least one abrasive particle comprises the second plurality of abrasive particles comprising more than one type of abrasive particles, e.g., two, three or more different types of abrasive particles.

[0102] Embodiments of the disclosure include at least one abrasive particle or a second plurality of abrasive particles wherein the abrasive particles comprise or are of charged polymers combined with abrasive powders, also referred to herein as abrasive composites or abrasive composite particles. Abrasive powders may include powders particularly suited for specific applications such as in polishing, and chemical-mechanical planarization (CMP). For instance, the abrasive composites may include powders such as silica, alumina, cerium oxide, zirconium dioxide, silicon carbide, titanium dioxide, and nanodiamonds, dispersed in a charged polymer matrix. The charged polymer enhances the dispersion, electrostatic stability, and adhesion to substrates of abrasive particles comprising the same. Examples of charged polymers include polyacrylic acid (PAA), polyethyleneimine (PEI), polydiallyldimethylammonium chloride (PDDA), and poly(sodium acrylate).

[0103] In some embodiments, the abrasive composites typically comprise between 30% and 80% by weight of the abrasive powder and between 5% to 20% by weight of the charged polymer, any remaining percentage up to 100 % by weight, if necessary, consists of a solvent, such as water or alcohol, to form a stable colloidal suspension. The at least one abrasive composite particle varies in size from 2 nm to 500 nm, depending on the hardness and polishing requirements of the application. Densities of the abrasive composite particle(s) range from 2 to 7 g / cm3, and may be of, e.g., 2.6 g / cm3for abrasive composites comprising silica powder, 3.97 g / cm3for abrasive composites comprising alumina powder, and 5.6 g / cm3abrasive composites comprising for zirconium dioxide powder. The choice of a specific abrasive powder and / or charged polymer allows for tailored material properties and ultimately different removal rates. Some embodiments relate to abrasive composite particles with 60-70 wt.% silica combined with 10-20 wt.% PAA for semiconductor polishing, 50-65 wt.% alumina with 5-10 wt.% PDDA for hard substrates, and 40-60% cerium oxide with 5-15 wt.% PEI for optical glass polishing.

[0104] These abrasive composites provide improved abrasive performance by optimizing particle size, charge, and suspension stability. The use of charged polymers ensures enhanced control over the dispersion and adherence of the abrasive particles, leading to uniform material removal and smoother surface finishes across a variety of substrates.

[0105] In some embodiments, the combination of a first plurality of electrically conductive particles and at least one abrasive particle comprises at least one particle that is both electrically conductive and abrasive, in particular comprises a plurality of particles that are both electrically conductive and abrasive, also referred to herein as electrically conductive abrasive particle(s). In some embodiments, the combination of a first plurality of electrically conductive particles and at least one abrasive particle consists of a plurality of electrically conductive abrasive particles, in other words all the particles in the combination are electrically conductive abrasive particles.

[0106] In some embodiments, the at least one particle having both electrically conductive and abrasive properties comprises a composite material exhibiting both abrasive and electrical conductivity properties simultaneously, also referred to herein as electrically conductive abrasive composite material. In some embodiments, the electrically conductive composite material comprises an ion-exchange resin, and an abrasive powder. The ionexchange resin includes a resin such as those described above, e.g., sulfonated polystyrene divinylbenzene, or other ion-exchange resins including sulfonated polyacrylate, aminomethylated polystyrene, or quaternary ammonium-based resins. These resins provide a solid structure with controlled ion conductivity and tunable surface charge.

[0107] The abrasive powder includes an abrasive powder such as those described above, in particular a powder having charged abrasive particles such as silica, alumina (AI2O3), cerium oxide, zirconium dioxide, silicon carbide, titanium dioxide, or nanodiamonds.

[0108] In some embodiments, the abrasive powder is incorporated onto or into the ionexchange resin during a step in the manufacturing process of the first plurality electrically conductive particles, thereby providing electrically conductive abrasive particles. For instance, the charged abrasive particle or particles of the abrasive powder are embedded or attached to the ion-exchange resin matrix, enhancing the overall abrasive properties of the resin while retaining its ion-exchange capabilities, including the affinity to retain a liquid electrolyte thereby obtaining particles which are both abrasive and electrically conductive.

[0109] In some embodiments, the abrasive powder, e.g., comprising charged abrasive particles is incorporated onto the solid structure after the manufacturing process of the first plurality of electrically conductive particles in an additional processing step. This may involve embedding or incrusting the abrasive powder onto the surface of the first plurality of electrically conductive particles using methods such as compression, physical adhesion, or chemical reactions like grafting or surface functionalization. These methods ensure robust attachment of the particle(s) of the abrasive powder while maintaining the electrical conductivity and surface charge characteristics of the ion-exchange resin structure, thereby obtaining particles which are both abrasive and electrically conductive.

[0110] In some embodiments, the electrically conductive abrasive composite material has a ratio of abrasive powder may range from 0.1% to 80% by weight of abrasive powder based on the total weight of electrically conductive abrasive composite material, in particular from 1 % to 50%, more in particular 2% to 10%, by weight, depending on the specific application and desired properties of the final material.

[0111] In some embodiments of methods and compositions described herein, abrasive particles of the at least one abrasive particle are or comprise, e.g., AI2O3. In some embodiments, abrasive particles of the at least one abrasive particle comprise white AI2O3, brown AI2O3 and / or gray AI2O3, more in particular the abrasive particles may comprise a combination of white AI2O3 and brown AI2O3, and optionally also gray AI2O3 abrasive particles.

[0112] In some embodiments, the combination is a composition according to the fourth aspect.

[0113] In some embodiments, the surface finishing is carried out with a machine according to the fifth aspect, or with an apparatus according to the sixth aspect, or with an assembly according to the seventh aspect.

[0114] In some embodiments, the method further includes arranging the object such that at least the at least one surface is within the medium.

[0115] In some embodiments, the method further includes providing a container with the medium and / or the combination.

[0116] In some embodiments, the container is electrically connected with the second pole. In these cases, the medium gets electrically connected with the second pole through the container.

[0117] In some embodiments, an apparatus according to the sixth aspect or the apparatus of an assembly according to the seventh aspect is electrically connected with the second pole. In these cases, the medium gets electrically connected with the second pole through the apparatus. For example, a nozzle of the apparatus may be electrically connected with the second pole.

[0118] A second aspect of the disclosure relates to an object including one or more surfaces that are surface finished. The one or more surfaces are surface finished with a method according to the first aspect.

[0119] A third aspect of the disclosure relates to an object including one or more surfaces that are surface finished. At least one surface of the one or more surfaces has any one of the features described above in relation to the first aspect of the disclosure, such as, e.g., material thereof, roughness thereof, etc.

[0120] By way of example, at least one surface of the one or more surfaces fulfills, in the entire at least one surface, the following relationship — =[5.0, 6.5] and / or a reduced peak height value Rpk=[8.5, 16.5],

[0121] By way of another example, at least one surface of the one or more surfaces has, in the entire at least one surface, an average roughness value Ra less than or equal to 0.30, preferably less than or equal to 0.20 pm and / or 0.15 pm and / or 0.10 pm; and / or at least one surface of the one or more surfaces has, in the entire at least one surface, a peak to valley difference height (absolute or average) value Rz less than or equal to 2.50 pm, preferably less than or equal to 2.00 pm and / or 1 .50 pm and / or 1 .00 pm.

[0122] The roughness of the surface of the objects to be treated or after being treated may be measured by parameters, methods, and devices known in the art.

[0123] For instance, the Ra value, the Rt value, the Rz value and the Rpk value may be defined and measured according to ISO4287: 1997 standard. The objects of the second aspect and the third aspect may thus benefit from an efficient surface finishing process that removes roughness of at least one surface of the object in a controlled manner.

[0124] The one or more surfaces are, in some embodiments, electrically conductive surfaces. Such surface or surfaces may comprise, for example but without limitation, a metal, an alloy, a polymer (e.g., intrinsically conductive polymers or conductive polymer composites obtained by mixing insulating polymers with metals or other conductive materials such as graphene). For example, but without limitation, steel, stainless-steel (e.g., an austenitic stainless-steel such as AISI 316L stainless-steel, or maraging Stainless steel, such as 17-4 PH stainless steel), titanium, nichrome, aluminum, tungsten carbide, cast iron, brass, Inconel (a nickel-chromium-based superalloy), alloys with silicon, and cobaltchromium.

[0125] In some embodiments of the second aspect or the third aspect, the object is one of the following: a blade of a jet engine, a blade of a wind turbine, a clock or a watch part (e.g., a watch movement), a dental prosthesis, a casted part or object, a machined part or object, and an additively manufactured part or object.

[0126] A fourth aspect of the disclosure relates to a composition including a first plurality of electrically conductive particles and at least one abrasive particle. One or more (e.g., one, some or all) particles of the first plurality of electrically conductive particles comprises an electrolyte. In some embodiments, the at least one abrasive particle is or comprises a second plurality of abrasive particles. In some embodiments, the at least one abrasive particle is a single abrasive particle.

[0127] The composition can be used for surface finishing of surfaces of objects in an effective and controller manner. The composition combines the electrically conductive particles with abrasive particle(s) to achieve a surface finishing superior to the surface finishing resulting from the use the two types of particles sequentially, i.e. , not at the same time with a mixture of the two types of particles.

[0128] The composition can be used, for example, in a method according to the first aspect, a machine according to the fifth aspect, an apparatus according to the sixth aspect, and / or an assembly according to the seventh aspect.

[0129] The provision of acids within the electrically conductive particles can reduce the volume of acid of a medium to be used by the particles, or even remove the acid altogether. This, in turn, also reduces the volume of water needed and the toxicity of the apparatus, machine, assembly or method using the composition, thereby simplifying the industrialization thereof, making them more ecological and cost-effective.

[0130] In some embodiments, the composition further includes a medium with the first plurality of electrically conductive particles and the at least one abrasive particle (including, in some embodiments, the second plurality of abrasive particles) included therein. The medium may be non-conductive, mildly conductive or conductive. The medium may preferably be non-conductive with respect to the conductivity exhibited by the first plurality of electrically conductive particles, non-conductive being understood as less than 50 % of the conductivity exhibited by the first plurality of electrically conductive particles. A mildly conductive medium being understood as having a 50 - 75 % of the conductivity exhibited by the first plurality of electrically conductive particles, and a conductive medium being understood as having more than 75 % of the conductivity exhibited by the first plurality of electrically conductive particles, or having a conductivity which is even higher than the conductivity of by the first plurality of electrically conductive particles, e.g. up to 500 %, in particular up to 250 %.

[0131] As an example, a first plurality of electrically conductive particles may be considered as being electrically conductive if it sustains a current density on a electrochemical process equal to or greater than 0.01 A / cm2through a period of time beyond 10 s. As another example, the medium is regarded as being conductive when sustaining a current density equal to or greater than 0.025 A / cm2through a period of time beyond 10 s. The medium may be considered as being non-conductive when sustaining a current value over 10 s or a current density on an electrochemical process lower than 0.005 A / cm2through a period of time beyond 10 s. As another example, the medium is regarded as being non-conductive when sustaining a current value over 10 s or a current density on an electrochemical process that is equal to or lower than 0.0125 A / cm2through a period of time beyond 10 s. The conductivity term is to be understood as a mechanism under which at least part of the material is extracted from the surface to be finished, in some cases as a consequence of a roughness reduction. As an example, a non-conductive medium typically features a conductivity value equal to or below 200 pS / cm, in particular equal to or below 100 pS / cm, more in particular equal to or below 10 pS / cm.

[0132] The conductivity of the electrically conductive particles and / or the medium may be determined by means known in the art, by measuring the amount of current which passes through two electrodes, such as platinated titanium, separated a certain distance, such as 5 cm, said distance occupied by the particles or the medium, applying, e.g., an anodic pulse at 1 - 60 V DC (30 - 50V) to the electrodes and measuring the current being passed.

[0133] In some embodiments, the medium is a fluid that may comprise gas and / or liquid, e.g., air, water, aqueous solutions, non-conductive liquids etc.

[0134] A gas medium, such as air, may be advantageously used to facilitate processing, as no liquid needs to be added and then removed from the system and the surface treated objects.

[0135] A liquid medium may be advantageously used to modulate the properties of the system. A liquid medium may be referred to as a moderator liquid. If a liquid medium is used the composition of the liquid medium may vary greatly and may be adjusted to specific objects to be surface treated, and / or specific first plurality of electrically conductive particles and at least one abrasive particle.

[0136] A non-conductive liquid, as described herein, is a fluid that when being at rest at room temperature does not significantly conduct electrical current. A non-conductive fluid may typically be immiscible in the liquid electrolyte contained in the solid electrolyte particles. In this way, a non-conductive fluid may contribute to keeping the liquid electrolyte inside the electrically conductive particles, whereas the non-conductive fluid is kept outside the same. In some cases, the non-conductive liquid is miscible, such as water, DMSO, Propylene Carbonate, Ionic liquids, DES, or it is a partially miscible liquid. Without being bound to any theory with regards to a non-conductive liquid, by covering the surface of the object to be surface treated, may contribute to one or more of, e.g.,:

[0137] Surface protection against localized acid attacks;

[0138] Reduction of atmospheric oxidation;

[0139] Greater control over the electrochemical process;

[0140] Higher selectivity in the peaks; and / or Final finish with lower roughness.

[0141] A non-conductive liquid may be selected from hydrocarbons, organic solvents, water immiscible solvents, organic compounds, essential oils, silicone and silicone oils, and fluorinated solvents, and emulsions, among others. They can be used alone or in combination with each other.

[0142] Hydrocarbons may be particularly selected from C5-C30 hydrocarbons, more in particular from C6-C16 hydrocarbons.

[0143] Water immiscible solvents and organic compounds may be selected from, for example, aliphatic alcohols like 1 -octanol, organic carbonates like propylene carbonate, ethylene carbonate, among others.

[0144] Silicones and silicone oils as described herein, are understood to be those oligomers, polymers, cycles or other structures that include O- Si bonds in their main chain. Silicone oils may include dimethylsiloxane units -OSi(Me2)- as well as cyclic ones such as hexamethylcyclotrisiloxane, in particular polydimethylsiloxanes may be used.

[0145] Fluorinated solvents are understood as solvents that incorporate at least one fluorine atom in their chemical structure and may include fluorinated and perfluorinated fluids.

[0146] Emulsions may typically be a non-conductive non-polar continuous phase containing conductive polar solution micelle, typically water-in-oil type emulsions (w / o). The conductive polar solution of micelles may have the same composition as the electrolyte of the electrically conductive particles. As the non-polar continuous phase is non-conductive, the emulsion at rest without solid electrolyte particles is non-conductive. As a mode of example, an emulsion-based non-conductive liquid may comprise:

[0147] - A non-conductive liquid such as a non-conductive liquid mentioned above;

[0148] - A conductive solution as a dispersed polar phase;

[0149] Optionally, surfactants to stabilize the emulsion.

[0150] When a liquid medium is used, the proportion of liquid medium to electrically conductive particles may be from 2 to 10 L of liquid medium, in particular from 4 to 7 L, per 5 to 15 kg of electrically conductive particles, in particular from 6 to 11 kg. Such proportion has been found to work particularly well for combinations further comprising abrasive particles as described herein.

[0151] The first plurality of electrically conductive particles and the at least one abrasive particle may be, e.g., dispersed in the medium or sedimented in the medium. Generally, when the particles and the object are moved relatively to each other the first plurality of particles and the at least one abrasive particle will be dispersed in the medium. This may be achieved as described above by way of any motion, such as displacing, rotating, mixing, stirring, vibrating, shaking, spraying, etc. The medium can be selected to improve the effectiveness of the combination of the two types of particles.

[0152] In some embodiments, the medium makes the combination to be in dry suspension, e.g., when a liquid such as a, e.g., moderator liquid is used as the medium, or makes the combination to be dry, wherein a gas is used as the medium.

[0153] The materials and quantities of the medium and the combination can be selected to produce a combination of solid particles and liquid that forms a dry suspension. The dry suspension can ease the application of the surface finishing process to more complex surfaces in terms of the geometries and shapes thereof, while at the same time reducing oxidation of the at least one surface and / or providing a shinier finishing on the at least one surface.

[0154] In some embodiments, a yield strength of one or more (e.g., one, some or all) abrasive particles of the at least one abrasive particle is greater than a yield strength of the at least one surface of the object.

[0155] In some embodiments, a hardness of one or more (e.g., one, some or all) abrasive particles of the at least one abrasive particle is greater than a hardness of the at least one surface of the object.

[0156] A yield strength and / or hardness that is greater for abrasive particles than for the at least one surface enhances the surface finishing effected by the abrasive particles on the at least one surface. By way of example, the yield strength of the at least one surface may be between 90 MPa and 2000 MPa, in particular between 300 and 1000 MPa.

[0157] The selection of the characteristics and proportions of the electrically conductive particles and the abrasive particle(s) is preferably such that they produce little or no electricfield screening on the at least one surface, which would otherwise reduce the amount of surface finishing attained.

[0158] A fifth aspect of the disclosure relates to a machine for surface finishing of an object. The machine includes: a container adapted to receive a medium; a holding device adapted to attach the object such that at least a portion thereof can be in contact with the medium; moving means for moving the object relative to the medium within the container and / or vice versa, i.e., for moving the medium relative to the object; and at least one electric source having a first pole of the at least one electric source electrically connected with the object at least when attached to the holding device, and a second pole of the at least one electric source electrically connected or connectable with, e.g., electrically conductive particles of a composition and / or a medium containing the electrically conductive particles and / or the container containing the medium.

[0159] In some embodiments, the machine further comprises a recirculation system said recirculation system comprising: means for removing at least part of the medium from the container, means for cleaning the at least part of the medium removed from the container, to provide a cleaned medium, and means for returning the cleaned medium to the container.

[0160] In some embodiments, the at least part of the medium removed from the container comprises fragments of abrasive materials derived from the at least one abrasive particle during the surface finishing process, such as abrasive dust. In such embodiments cleaning comprises removing fragments of abrasive materials from the medium.

[0161] Means for removing the at least part of the medium from the container, in some embodiments comprises, e.g., a pump that absorbs the medium from the container, through a fluid outlet placed in the container and directs the medium towards the means for cleaning. In some embodiments a filter may be placed in the container before the outlet to retain, e.g., electrically conductive particles and / or abrasive particles in the container. The presence of such a filter in some embodiments advantageously prevents the obstruction of the outlet while absorbing only the medium avoiding the removal of the electrically conductive particles and abrasive particles from the container. In some embodiments. Such a filter may be a mesh and, in some embodiments, a concatenation of meshes of different sizes may be used.

[0162] Means for cleaning the at least part of the medium from the container, in some embodiments, comprises a filter unit, a precipitation unit and / or centrifugation unit, capable separating, e.g., the abrasive dust present in the medium removed from the container, by filtration, precipitation and / or centrifugation. A filter unit may include, e.g., a mesh, a concatenation of meshes of different sizes or a porous filter capable of retaining the abrasive dust present in the medium, and letting cleaned medium through.

[0163] Means for returning the cleaned medium to the container, in some embodiments, comprises a pump to reintroduce the cleaned medium trough an inlet into the container.

[0164] In some embodiments a temperature control unit can be included in the recirculation system to control the temperature of the medium during the recirculation process.

[0165] In some embodiments, the at least part of the medium removed from the container comprises fragments of abrasive materials derived from the at least one abrasive particle during the surface finishing process together with electrically conductive particles and / or at least one abrasive particle. In such embodiments cleaning comprises separating the electrically conductive particles and / or the at least one abrasive particle from the medium and any fragments of abrasive materials, and cleaning the electrically conductive particles and / or the at least one abrasive particle to remove any abrasive fragments adhered thereto and separately cleaning the medium by removing fragments of abrasive materials from the medium. The cleaned electrically conductive particles and / or the at least one abrasive particle and the cleaned medium may be returned to the container together or separately.

[0166] In addition to effectively surface finishing at least one surface of the object to be surface finished, the machine may have low hazard properties thanks to a reduced use of acid material and the presence of acid material being within the electrically conductive particles. Acids not only may be toxic, which is then complex to dispose of, but they also tend to influence the mechanical properties of the object to be surface finished and, moreover, get deposited on walls (one of the walls may also be the base or floor) of the container, thereby getting the container dirty and inoperable when much of the rests of the acid attaches to the walls. In such working conditions, material removed from the surfaces of the object could also get deposited on the walls of the container, thereby requiring the cleaning of the container and, sometimes, the medium more often.

[0167] The machine of the present disclosure may also have reduced emissions of gases, which is also preferred for safety and ecological reasons.

[0168] In some embodiments, the assembly further includes a composition according to the fourth aspect.

[0169] In some embodiments, the machine further includes a stainless-steel coating on the first and / or second pole. In some embodiments, the machine further includes a mesh on the first and / or the second pole.

[0170] The abrasive particles can damage the pole of the at least one electric source that is not the pole connected to the object. In preferred embodiments, at least the pole connected to the medium is made of platinum for larger electrical conductivity.

[0171] Stoppage times of the machine because a pole, either the cathode or the anode, needs to be replaced frequently, not to mention the lower cost-effectivity because of the materials for the replacement, negatively influence the productivity of the assembly. The stainless-steel coating or the mesh reduces the wear of such pole.

[0172] The mesh preferably has holes of a diameter greater than the diameter of the electrically conductive particles but lower than the diameter of the abrasive particle(s), thereby letting the electrically conductive particles come into contact with the pole but no so for the abrasive particle(s). The mesh may be of an electrically conductive material such as, e.g., a metal, an alloy, a conductive polymer, etc.

[0173] In some embodiments, the machine further includes the object to be surface finished.

[0174] In some embodiments, the machine further includes the medium.

[0175] In some embodiments, the machine further comprises a temperature control system for adapting a temperature during surface finishing.

[0176] A sixth aspect of the disclosure relates to an apparatus for surface finishing an object. The apparatus includes a propelling device for propelling a composition according to the fourth aspect.

[0177] The apparatus makes possible to surface finish one or more surfaces of an object by rushing the composition on the one or more surfaces, even if the portion of the composition coming into contact with the surface(s) then stops contacting the surface(s); namely, the portion of the composition surface finishes the object during the time it is contacting the latter as the portion of the composition is rushed. By rushing the object with different portions of the composition, either continuously or sequentially, the surface finishing is attained.

[0178] To avoid material waste, the used portions of the composition can be collected through an optional recycling system that, in some embodiments, delivers the recycled portions to the apparatus for further reuse, i.e., for further surface finishing with the recycled composition.

[0179] The composition is propelled such that there is electrical conductivity between the apparatus and the object to allow electrically conductive particles to conduct surface finishing on the surface(s) of the object. To this end, preferably a distance between the apparatus, particularly a nozzle thereof, and the object is as short as possible to ease the electrical conductivity between the apparatus, the composition and the object, as the electrically conductive particles may have to be arranged within the composition so as to form an electrical bridge; depending on the electrical conductivity of a medium through which the first plurality of electrically conductive particles and the at least one abrasive particle flow, the distance may be greater or lower.

[0180] As the composition is rushed, abrasive particle or particles come into contact with the surface(s) of the object and also conduct surface finishing.

[0181] In some embodiments, the apparatus includes two nozzles and, optionally, two propelling devices.

[0182] A portion of the composition with at least some electrically conductive particles of the first plurality of electrically conductive particles may be propelled from a first nozzle onto the surface(s) of the object for surface finishing thereof, and another portion of the composition with at least some abrasive particles (e.g., one, some, all) of the at least one abrasive particle may be propelled from a second nozzle onto the surface(s) for surface finishing thereof.

[0183] Such dual rushing of the surface(s) of the object may ease the control of the surface finishing as the electrical conductivity of the portion of the composition with the electrically conductive particles may be better controlled, especially in terms of how the particles are to flow within the composition while propelled to have electrical conductivity, which is also dependent upon a medium.

[0184] A same propelling device or two propelling devices may be used to propel the respective portions of the composition, which may be propelled simultaneously or sequentially. In some embodiments, the propelling device is adapted for propelling the composition together with a medium.

[0185] In some embodiments, the apparatus further includes at least one pole of at least one electric source. In some embodiments, the apparatus further includes the at least one electric source.

[0186] In some embodiments, the apparatus further includes a stainless-steel coating on the at least one pole. In some embodiments, the apparatus further includes a mesh on the at least one pole for protection thereof.

[0187] In some embodiments, the apparatus further includes a composition container or a connection port for fluid coupling.

[0188] In some embodiments, the apparatus further includes a composition according to the fourth aspect.

[0189] In some embodiments, the apparatus further includes the object to be surface finished.

[0190] A seventh aspect of the disclosure relates to an assembly. The assembly includes an apparatus according to the sixth aspect; a holding device adapted to attach the object; and at least one electric source having a first pole of the at least one electric source electrically connected with the object at least when attached to the holding device, and a second pole of the at least one electric source electrically connected (or connectable) with, e.g., electrically conductive particles of a composition and / or a medium containing the electrically conductive particles and / or a container containing the medium .

[0191] The medium is, in some cases, conductive whereas, in some others, it is non- conductive. In some cases, the medium is immiscible with respect to a conductive solution retained by a first plurality of electrically conductive particles whereas, in some other cases, it is miscible. In some cases, the medium is a Newtonian fluid whereas, in some other cases, it is a non-Newtonian fluid.

[0192] The medium includes, in some embodiments, agents to change the thixotropic properties, such as fumed silica to aliphatic carbon-based liquid achieving a higher shear thickening behavior enhancing the abrasive action over the electrolytic action. The contrary effect is obtained when using a shear thinning medium, which also falls within the scope of the present disclosure.

[0193] In some embodiments, the assembly further includes a composition according to the fourth aspect.

[0194] In some embodiments, the assembly further includes a stainless-steel coating on the first and / or second pole.

[0195] In some embodiments, the assembly further includes the object to be surface finished. In some embodiments, the wear stresses produced by the at least one abrasive particle may generate contaminants, such as dust or oxide powders, which can be detrimental to the electrolytic performance of the apparatus and / or assembly. The contaminants can interfere with or even halt the galvanic activity of the first plurality of electrically conductive particles, particularly by obstructing ion-exchange pathways or compromising the electrical conductivity of the material. Over time, such wear-induced contaminants tend to reduce the efficiency and lifespan of the assembly if not properly managed.

[0196] In some embodiments of the fifth aspect or the sixth aspect or the seventh aspect, the assembly or the apparatus or the machine includes a recirculation and cleaning system designed to purge and eliminate contaminants generated during operation of the assembly or the apparatus or the machine, e.g., during service conditions. This purging and elimination can be achieved through various techniques, such as precipitation, decantation, centrifugation, and filtration.

[0197] In some embodiments, the recirculation or cleaning process is carried out, by the recirculation and cleaning system, in a discrete manner, while in some other embodiments, the process is carried out continuously under working conditions to ensure ongoing contaminant removal. In certain cases, a fluid or liquid is introduced into the system to facilitate the removal of contaminants and improve the efficiency of the purging process.

[0198] The use of this recirculation and cleaning system enhances, in some embodiments, the longevity of the electrolyte, with some implementations achieving up to a 100% increase in the lifespan of the electrolyte. By maintaining a cleaner operating environment, the machine and / or the apparatus and / or the assembly preserves the electrolytic and galvanic performance of the first plurality of electrically conductive particles, ensuring sustained functionality and reducing downtime associated with contaminant buildup.

[0199] The different aspects and embodiments of the present disclosure defined in the foregoing and the below can be combined with one another, as long as they are compatible with each other. Additional advantages and features will become apparent from the detailed description that follows and will be particularly pointed out in the appended claims.

[0200] BRIEF DESCRIPTION OF THE DRAWINGS

[0201] T o complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0202] Figure 1 shows an object with part of a surface thereof zoomed-in to show an exemplary roughness.

[0203] Figures 2 and 3 show compositions and arrangements for surface finishing an object in accordance with some embodiments.

[0204] Figures 4 and 5 show how compositions according to the present disclosure may contact surfaces of objects in accordance with some embodiments.

[0205] Figure 6 shows a machine in accordance with some embodiments.

[0206] Figure 7 shows an assembly in accordance with some embodiments.

[0207] Figure 8 shows a picture of an object treated with a method as described herein according to Example 1 before (A) and after (B) the surface treatment.

[0208] Figure 9 shows a micrometric picture of the surface of an object with a method as described herein according to according to Example 1 before (A) and after (B) the surface treatment.

[0209] Figure 10 shows the roughness measurements of the surface of an object treated with a method as described herein according to according to Example 1 before (A) and after (B) the surface treatment.

[0210] Figure 11 shows a picture of objects treated with a method as described herein according to according to Example 2, before the surface treatment (time 0) (A); after 30 minutes of the treatment (B); after 60 minutes of the treatment (C) and after 90 minutes of treatment (D).

[0211] Figure 12 shows the roughness profiles of objects treated with a method as described herein according to according to Example 2, before being treated (time 0) (A); after 30 minutes of the treatment (B); after 60 minutes of the treatment (C); and after 90 minutes of treatment (D).

[0212] Figure 13 shows a picture of objects treated according to comparative examples 2a(A), 2b (B) and 2c (D) alongside an object treated with a method as described herein according to Example 2 at 90 minutes (C).

[0213] Figure 14 shows a picture of objects treated with a method as described herein according to Example 3, before the surface treatment (raw sample) (A); after a treatment with electrically conductive particles without abrasive particles (B); after a treatment with a combination of electrically conductive particles and abrasive particles (C); and after a treatment with abrasive particles first and then separately with electrically conductive particles (D).

[0214] Figure 15 shows a topographic profile of a corner of objects treated with a method as described herein according to Example 3, before the surface treatment (raw sample) (A); after a treatment with electrically conductive particles without abrasive particles (B); after a treatment with a combination of electrically conductive particles and abrasive particles (C); and after a treatment with abrasive particles first and then separately with electrically conductive particles (D).

[0215] Figure 16 shows the radius measurements of a corner of objects treated with a method as described herein according to Example 3, before the surface treatment (raw sample) (A); after a treatment with electrically conductive particles without abrasive particles (B); after a treatment with a combination of electrically conductive particles and abrasive particles (C); and after a treatment with abrasive particles first and then separately with electrically conductive particles (D).

[0216] Figure 17 shows the roughness profiles of objects treated with a method as described herein according to according to Example 3, before being treated (raw sample) (A); after a treatment with electrically conductive particles without abrasive particles (B); after a treatment with a combination of electrically conductive particles and abrasive particles (C); and after a treatment with abrasive particles first and then separately with electrically conductive particles (D).

[0217] Figure 18 shows the variation of Ra (A) and Rz (B) with time of three faces of an object treated with a method as described herein according to according to Example 4 with a combination comprising ceramic abrasive particles.

[0218] Figure 19 shows the variation of Ra (A) and Rz (B) with time of one faces of an object treated with a method as described herein according to according to Example 4 with a combination comprising composite abrasive particles.

[0219] Figure 20 shows the radius measurements of a corner of an object treated with a method as described herein according to Example 4 with a combination comprising ceramic abrasive particles at the top of the object (A) and the bottom of the object (B).

[0220] Figure 21 shows the radius measurements of a corner of an object treated with a method as described herein according to Example 4 with a combination comprising composite abrasive particles at the top of the object (A) and the bottom of the object (B).

[0221] DETAILED ESCRIPTION OF THE DRAWINGS

[0222] Figure 1 shows an object 10 with part of a surface 11 thereof zoomed-in to show an exemplary roughness for illustrative purposes only.

[0223] The surface 11 of the object 10 has a waviness due to peaks or protrusions 13 and valleys or recesses 12. The valleys or recesses 12 are formed within cavities that may have a width W between delimiting walls thereof. On many occasions, the surface 11 of the object 10 would ideally be completely flat, and smoothly rounded where there are changes in the geometry or shape of the surface.

[0224] For the sake of the illustration only, electrically conductive particles 2 according to the present disclosure, which one, some or all are free solid bodies that contain an electrolyte, are represented surface finishing a portion of the surface 11 , particularly the portion that is illustrated zoomed-in to show that such particles 2 surface finish the surface generally at microscopic level (e.g., 10 pm or smaller). Likewise, abrasive particles 3 according to the present disclosure are represented surface finishing another portion of the surface 11 , particularly a portion containing peaks or protrusions 13, and more specifically, the peaks or protrusions 13 themselves. That is to say, the abrasive particles 3 surface finish the surface generally at macroscopic level (e.g., 50 pm or greater).

[0225] Generally, the electrically conductive particles 2 are to surface finish portions of the surface 11 corresponding to valleys or recesses 12, whereas the abrasive particles 3 are to surface finish portions of the surface corresponding to peaks or protrusions 13, even though both types of particles 2, 3 may also surface finish surfaces that are flat or substantially flat. To this end, in some embodiments, the maximum size (e.g., a diameter) of the electrically conductive particles 2 does not exceed the average width W of the cavities. Additionally, or alternatively, in some embodiments, the maximum size (e.g., a diameter) of the abrasive particles 3 exceeds the average width W of the cavities.

[0226] Figure 2 shows a composition 1 for surface finishing an object 10 in accordance with some embodiments.

[0227] The composition 1 includes a first plurality of particles 2 in the form of electrically conductive particles 2, and at least one particle 3 in the form of abrasive particles 3, that in some embodiments is a second plurality of particles 3 in the form of abrasive particles 3. Hereinafter, the examples described will refer to a second plurality of particles 3 for the sake of clarity only, but it will be understood that the scope of the present disclosure also includes examples in which there is one abrasive particle 3. The composition includes, in some embodiments, a medium 5 that is to at least partially fill up a container 20 yet, in some other embodiments, the medium 5 is part of the container 20. For the sake of clarity only, the electrically conductive particles 2 have been represented as white-filled circles and the abrasive particles 3 have been represented as black-filled rhomboids, it will be noted that these shapes are in no way limiting and, thus, either type of particles 2, 3 may feature other shapes.

[0228] An object 10 to be surface finished is arranged in the container 20 such that one or more surfaces 11 of the object 10 to be surface finished are in contact with the medium 5. To that end, the object 10 is preferably attached to a holding device or support (not illustrated) that keeps the surface or surfaces 11 in this manner. The object 10 is electrically coupled with a first pole, e.g., anode 31 , or cathode, of at least one electric source 30, either directly (i.e. , there is direct electrical contact between the object 10 and the first pole) or indirectly (i.e., one or more objects or electronic components are electrically connected between the object 10 and the first pole), whereas the container 20 is electrically coupled with a second pole, e.g., cathode 32, or anode, of the at least one electric source 30, either directly or indirectly.

[0229] The composition 1 is arranged within the container 20, particularly the medium 5 within the container 20 has the first and second pluralities of particles 2, 3.

[0230] A relative movement between the composition 1 and the object 10 makes at least some of the electrically conductive particles 2 and some of the abrasive particles 3 to come into contact with the surface / s 11 . The contact between the two types of particles 2, 3 and the surface / s 11 results in the surface finishing of the particles. The surface finishing may involve the ion transport of the electrically conductive particles 2, and the abrasion of the abrasive particles 3.

[0231] In other embodiments in which, for example, one or more internal surfaces of the object 10 are to be surface finished, and / or one or more external surfaces of the object 10 that are difficult to access are to be surface finished, an apparatus or an assembly as those described with reference to Figure 7 may be used. Alternatively, the object 10 may be arranged in a fashion similar to that illustrated in Figures 2 and 3, and one or more conduits be arranged adjacent to the surface or surfaces to be surface finished so that, for example, the medium 5 may be sucked through the conduit(s) to force the composition 1 to come into contact with the surface(s) to be finished.

[0232] Figure 3 shows another composition 1 for surface finishing an object 10 in accordance with some embodiments.

[0233] Unlike the composition 1 of Figure 2, it can be appreciated that the composition 1 of Figure 3 is such that a majority of the abrasive particles 3 stays at a lower height of the medium 5 whilst the surfaces 11 of the object 10 to be finished are at a higher height. By contrast, the electrically conductive particles 2 are substantially distributed across the entirety of the medium 5.

[0234] The composition 1 and the medium 5 can be configured to determine how the particles 2, 3 will behave within the medium 5 since different configurations may lead to different surface finishing behaviors. Differential surface finishing whereby more dense particles stay at a lower height and less dense particles stay at a higher height is made possible, thereby having different proportions of particles at different height; this, in turn, may cause a greater surface finishing speed (i.e., greater roughness reduction) at lower heights than at higher heights.

[0235] In these embodiments, the abrasive surface finishing can be reduced by only making a minority of the abrasive particles 3 (which will be the ones that come into contact with the surfaces 11) stay at a high height in the medium 5, yet surface finishing based on ion transport can be conducted according to the number of electrically conductive particles 2 that may come into contact with the surfaces 11 . Such surface finishing can be preferred when the precision surface finishing is to be performed. It is, in any case, noted that precipitation of the abrasive particles is not convenient since it reduces the effect of the surface finishing process, thus a proportion of abrasive particles 3 to electrically conductive particles 2 (or vice versa) to is preferably selected to avoid precipitation of the abrasive particles and enable surface finishing effects by the abrasive particles 3 as well. However, in some embodiments precipitation of the abrasive particles 3 it is preferred as it results in a heterogeneous mixture of abrasive particles 3 and electrically conductive particles 2, which may offer different properties in different areas of the combination and thus being able to perform several surface finishing steps using a unique (heterogeneous) combination by placing the object to be surface finished at different heights within the combination.

[0236] Figure 4 shows how electrically conductive particles 2 of a composition according to a particular case of the present disclosure may contact surfaces of objects in accordance with some embodiments, whereas Figure 5 shows how abrasive particles 3 of a composition according to the present disclosure may contact surfaces of objects in accordance with some embodiments.

[0237] The electrically conductive particles 2 are shown moving towards a first portion 11a on the surface of an object 10 in a somewhat direct manner. For a more effective surface finishing by ion exchange, a velocity vector of the particles 2 is preferably as close as possible to a normal to the surface; namely, the angle formed by the velocity of the electrically conductive particles 2 and the surface is as close to 90° as possible.

[0238] In a particular case, when the electrically conductive particles 2 collide with the surface, they release some electrolyte and have ions of the surface of the object 10 removed therefrom, thereby effectively removing material from the surface. With such behavior, the first portion 11a is the portion where there is a largest material removal because of the electrically conductive particles 2. Then, the electrically conductive particles 2 tend to deviate on the surface of the object 10, for instance towards a second portion 11b thereof or a third portion thereof 11c, yet in some cases the release of electrolyte in those portions 11 b, 11c is lower than that released in the first portion 11a because the relative movement is less direct and, so, the removal of ion metals from the surface also becomes lower.

[0239] Turning to the abrasive particles 3, which are also shown moving towards the first portion 11a on the surface of the object 10, in some embodiments they can reach such portion of the surface when there is electrolyte thereon due to the effect of electrically conductive particles 2 having contacted that part of the surface. The abrasion in that portion in such situation is reduced as the abrasive particles 3 also tend to deviate on the surface of the object 10. Like the electrically conductive particles 2, the abrasive particles 3 can travel towards other portions such as the second portion 11b and / or the third portion 11c where there is less electrolyte. With less electrolyte and / or with a motion of the abrasive particles 3 relative to the surface being such that more friction may exist between the two, the abrasive effect of the abrasive particles 3 becomes greater, and so does the material removal. In several configurations of the disclosure, a more effective surface finishing by abrasion is obtained when a velocity vector of the abrasive particles 3 is preferably as close as possible to a tangent to the surface; namely, the angle formed by the velocity of the abrasive particles 3 and the surface is as close to 0° (or 180°) as possible.

[0240] Therefore, in said particular embodiments, part of the finishing conducted by electrically conductive particles 2 is not largely affected by the potential abrasion of the abrasive particles 3, and vice versa, namely, part of the finishing conducted by abrasive particles 3 is not largely affected by the potential material removal due to ion transport of the electrically conductive particles 2. Accordingly, the finishing can be conducted by both types of particles 2, 3 at the same time.

[0241] Figure 6 shows a machine 300 in accordance with some embodiments.

[0242] The machine 300 includes: a container 321 (for example, the container 20 illustrated with reference to any one of Figures 2-3) adapted to receive an object to be surface finished (for example, the object 10 illustrated with reference to any one of Figures 1-5); a holding device 322 that has means for having the object to be surface finished attached to the holding device 322 (either the means of the holding device 322 attach to the object, or the object attaches to the means of the holding device 322); moving means 323 that produce relative movement between the object and a medium (or a container having the medium arranged therein); and at least one electric source 324 (for example, the electric source 30 illustrated with reference to any one of Figures 2-3).

[0243] The holding device 322 is or comprises, for example, but without limitation, at least one moving arm, and / or at least one claw, and / or at least one clamp, and / or at least one screw, etc.

[0244] The moving means 323 produce relative movement such as, e.g., displacing, rotating, mixing, stirring, vibrating, shaking, spraying, propelling, sucking, or a combination thereof. The moving means 323 are or comprise, for example, but without limitation, at least one vibrating apparatus, and / or at least one propeller, and / or at least one wave formation apparatus and / or at least one fluid turbulence generation apparatus, etc.

[0245] The machine 300 may further include (as illustrated with a dashed border for the sake of clarity only) a composition 325 that at least includes a plurality of electrically conductive particles and a plurality of abrasive particles.

[0246] Additionally, or alternatively, the machine 300 may further include a stainless-steel coating 326 on one or both poles of the at least one electric source 324.

[0247] Figure 7 shows an assembly 310 in accordance with some embodiments.

[0248] The assembly 310 at least includes: an apparatus 327 for surface finishing an object (for example, the object 10 illustrated with reference to any one of Figures 1-5), the apparatus includes a propelling device for propelling a composition; the holding device 322 adapted to attach the object to be surface finished; and the at least one electric source 324.

[0249] The assembly 310 may further include (as illustrated with a dashed border for the sake of clarity only) the composition 325 and / or the stainless-steel coating 326.

[0250] In this text, the term “includes”, “comprises” and derivations thereof (such as “including”, “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0251] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

[0252] The present disclosure is illustrated with the following examples without being limited thereto or thereby.

[0253] EXAMPLES

[0254] Several objects were subjected to a surface treatment by the following general method: holding the object with a moving arm and connecting the object to a pole of an electric source, connecting a container comprising particles in a medium (i.e., either one of or a combination of electrically conductive particles and a second plurality of abrasive particles) to the opposite pole of the electric source; immerging the object into a container contained in a medium, whereby the object was completely covered by the particles; and moving the object inside of the particles thereby moving the particles relative to the object and allowing the contact of the particles with the surface of the object, for a specific amount of time; the object was removed from the particles, to provide a surface treated object.

[0255] The electrically conductive particles used were styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter: 8.5 kg of particles of type A comprising an aqueous solution of sulfuric acid (3.74 %) and 2.2 kg of particles of type B comprising an aqueous solution of methanesulfonic acid (MSA) (1.89 wt.%). When only particles of type A or B are used the total amount of particles is 10.7 kg.

[0256] The abrasive particles used comprise a combination of gray AI2O3 (6.5 kg), white AI2O3 (3 kg) and brown AI2O3 (2 kg) abrasive particles.

[0257] The particles were in a medium comprising a C5 - C30 hydrocarbon (4.27 L), water (620 mL), ethoxylated alcohol (85 mL), sulfonic acids petroleum sodium salts (42.5 mL) and MSA (46 mL).

[0258] The objects used were blocks of stainless-steel having a prismatic (or cylindrical) shape with a length of about 6 cm and a width and thickness (or diameter) of about 2 cm.

[0259] The objects were moved inside the particles achieving a relative movement between the particles and the object. The movement used was an orbital and vertical movement. The orbital movement was of a radius of 10 cm, a frequency of 0.4 Hz and alternating the sense of the rotation every 30 seconds. The vertical movement had a path of 5 cm and a frequency of 0.28 Hz.

[0260] The object was moved inside the particles for a time as detailed for each example below.

[0261] The roughness measurements of the surface of the objects (Ra and Rz) were performed according to ISO4287: 1997 standard, using a cut off of Lc = 0.8 mm, N=5 and Ls = 2.5 pm.

[0262] Example 1

[0263] In Example 1 a block of stainless steel was used in the shape of a chess piece: a bishop, to illustrate the effect of the surface polishing on a piece wherein the profile of the surface of the object is of importance.

[0264] In Example 1 , the surface treatment was performed with electrically conductive (of type A and B) and abrasive particles as indicated above, at a voltage of 45 V obtaining a current of 4.5 A, and a current density of 0.1 A / cm2.

[0265] The characteristics of the object treated were measured before initiating the treatment (time = 0 min) and at 120 minutes of the treatment

[0266] Figure 8 shows a picture of the treated stainless steel chess piece of Example 1 before (A) and after (B) the surface treatment. As it can be appreciated the object has been polished to a great degree with a great preservation of the geometry of the object.

[0267] Figure 9 shows a micrometric picture of the treated stainless steel chess piece surface of Example 1 before (A) and after (B) the surface treatment. As it can be appreciated the surface of the object displays great smoothness after the surface treatment applied.

[0268] Figure 10 shows the roughness measurements of the treated stainless steel chess piece surface of example 1 before (A) and after (B) the surface treatment. As it can be appreciated the reduction of roughness of the surface is greatly reduced going from valleys at around - 20 microns and peaks at around 40 microns to a plateau around 0 microns.

[0269] Example 2 and Comparative Examples 2a, 2b and 2c

[0270] For each of Example 2 and Comparative Examples 2a, 2b and 2c, four blocks of stainless steel were used in prismatic shape. Each block was surface treated for a specific amount of time as detailed in the below table noting the starting roughness (Ra and Rz) and mass and the final roughness and mass after the treatment time. From the recorded values the percentage of roughness and mass reduction were calculated and the alpha ratio was determined as described above using formula: a = - — - wherein ARa is the % of Ra reduction, Am is the percentage of mass reduction and tpoiishing is the time of the treatment n seconds.

[0271] The surface treatment was performed at a voltage of 45 V obtaining a current of 1 A, and a current density of 0.1 A / cm2.

[0272] Example 2 was performed with electrically conductive particles of type A and B, Comparative Example 2a was performed with electrically conductive particles of type A, Comparative Example 2b was performed with electrically conductive particles of type B.

[0273] Comparative Example 2c and 2d were performed in two steps: Step 1 only with abrasive particles (3 h for example 2c and 1 h for example 2d) and Step 2 only with electrically conductive particles of type A and B as described above (1h in both cases).

[0274] These conditions are summarized in the following table:

[0275] Figure 11 shows a picture of the objects treated according to Example 2, before being treated (time 0) (A); after 30 minutes of the treatment (B); after 60 minutes of the treatment (C) and after 90 minutes of treatment (D). As it can be seen the surface of the object becomes smoother with time without significantly losing the sharpness of the edges.

[0276] Figure 12 shows the roughness profiles of the objects treated according to Example 2, before being treated (time 0) (A); after 30 minutes of the treatment (B); after 60 minutes of the treatment (C); and after 90 minutes of treatment (D). As it can be seen the profile goes from a roughness of about -20.0 to 20.0 pm to a roughness of almost zero at 60 minutes, and practically a plateau around 0 pm at 90 min.

[0277] Figure 13 shows a picture of the objects treated according to the comparative Examples 2a (A), 2b (B) and 2c (D) alongside Example 2 at 90 minutes (C), as it can be seen from the picture the object treated according to Example 2 offers the best overall characteristics in terms of surface smoothness and sharpness of the edges.

[0278] Example 3: Effect on the profile of the object surface treated using different surface treatments

[0279] The effect of the surface treatment on the profile of the stainless-steel prisms was also studied, comparing A) the stainless-steel prism before being subjected to the treatment (Raw) and after being subjected to different treatments as described above: B) with electrically conductive particles without abrasive particles; C) with a combination of electrically conductive particles and abrasive particles; and D) with abrasive particles first and then separately with electrically conductive particles, as described above for Example 2.

[0280] The effect on the profile was assessed visually. As can be appreciated from the picture of Figure 14, the raw sample (A) appears to have a higher roughness, for not being shiny, and a sharp corners. In contrast the shine increases for the samples B-D, indicating a decrease of the roughness on the surface. However, differences can be appreciated on the smoothness of the surfaces and the sharpness of the corners of the objects, the object surface treated with a combination of electrically conductive particles and abrasive particles (sample C) the surface appears to be both shiny and smooth, whilst the sharpness of the corners appears to be highly maintained.

[0281] To visualize more closely the surface of the objects, for each object the topography of two surfaces forming one of its corners was measured by combining confocal microscopy and profilometry to analyze the transversal section of the object. A circular fit is applied to the corner region to determine the curvature radius. The use of high-resolution imaging and topographical measurement ensures precise surface analysis.

[0282] The corresponding images are shown in Figure 15 A (for the raw sample A), B (for sample B), C (for sample C), D (for sample D).

[0283] The effect on the profile was also quantified by measuring the radius of the corners of the prisms before surface treatment (A) and after each of the surface treatments indicated above (B-D). The radius of the corner of each object was measured using a profilometer analysis of a transversal section obtained by confocal microscopy. The radius measurements are shown in Figures 16 A-D for each object (A-D).

[0284] The roughness of the surface of the raw object (A) and the objects subjected to the surface treatments (B-D) was measured. The roughness measurements of each object are shown in Figure 17 A-D, respectively.

[0285] The different treatment conditions and the measurements obtained are detailed in the following table. From the images and the radius and roughness measurements, it can be seen that the use of electrically conductive particles without abrasive particles (B) the geometry is preserved very well (the radius is very low) but there is no decrease in roughness and in the remanent waviness of the 3D printed layers after applying the surface treatment for a long time (t = 450 min) . With the treatment with abrasive particles first and then separately with electrically conductive particles (D) is a high drop in roughness with high polishing times and leaving the radii very rounded (highest radius measured). With the treatment using a combination of electrically conductive particles and abrasive particles (C), on the other hand, there is a low polishing time and a good compromise between the final roughness obtained and the final deformation (relatively low radius values).

[0286] Example 4: Composite abrasive particle(s) compared with Ceramic abrasive particle(s)

[0287] The performance of combinations of electrically conductive particles with plastic abrasive particles was compared to combinations of electrically conductive particles with ceramic abrasive particles.

[0288] The electrically conductive particles used were styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter: 6.6 kg of particles comprising an aqueous solution of methanesulfonic acid (MSA) (1.89 wt.%).

[0289] The composite abrasive particles used comprised 5 kg of a polymer charged with alumina powder dust with a truncated quadratic pyramid of 5 mm diagonal with a density of about 2.2 g / cm3.

[0290] The alumina powder dust described above was also used as such as the ceramic abrasive particles, for direct comparison with the composite abrasive particles.

[0291] Two particle combinations (A and B) were prepared by mixing into a liquid medium.

[0292] The liquid medium comprised a C5 - C30 hydrocarbon (3.5 L), water (1100 mL), ethoxylated alcohol (65 mL), sulfonic acids petroleum sodium salts (38.5 mL) and MSA (39 mL).

[0293] The composition of each combination is detailed in the following table:

[0294] The medium comprising the particles was placed in a container and connected to a current by applying a voltage of 18V with a t+ of 10 ps; a t- of 100 ps; and a tp of 10 ps.

[0295] The objects used to be surface finished were blocks of stainless steel having a prismatic - shape with a length of about 6 cm and a width and thickness of about 2 cm. The stainless-steel objects were moved inside the medium with the particles achieving a relative movement between the particles and the object. The movement used was an orbital and vertical movement. The orbital movement was of a radius of 10 cm, a frequency of 0.4 Hz and alternating the sense of the rotation every 30 seconds. The vertical movement had a path of 5 cm and a frequency of 0.28 Hz.

[0296] Initial roughness measurements were taken for three faces of the stainless-steel objects, and subsequently at 60, 90, and 120 minutes of polishing. Figures 18 A and 18 B respectively show the variation of Ra and Rz with time of the stainless-steel object treated with the combination comprising ceramic abrasive particles (Combination A) for three faces. Figures 19 A and 19 B respectively show the variation of Ra and Rz with time of the stainless-steel object treated with the combination comprising composite abrasive particles (Combination B) for one face.

[0297] The radius of a corner of the objects treated was also measured, for the top of the object (placed towards the bottom of the container during the surface treatment) and for the bottom of the object (placed towards the top of the container during the surface treatment). Figure 20 shows the graph obtained for the radius measurements for the treatment using ceramic abrasive particles of a corner at the top of the object (Figure 20 A) and at the bottom of the object (Figure 20 B). Figure 21 shows the graph obtained for the radius measurements for the treatment using composite abrasive particles at the top of the object (Figure 21 A) and at the bottom of the object (Figure 21 B). The results of the radii measured are also shown in the following table.

[0298] As it can be seen whereas the use of ceramic abrasive particles provides a higher reduction of roughness (Ra and Rz) in a shorter period of time (Figures 18 and 19) the composite abrasive particles provide a better conservation of the profile, as evidenced by a lower increase of the radius when the composite particles were used. Further, when comparing the effect of the process performed at the top and at bottom of the object it can also be observed that the radius increase is more homogeneous for the composite particles (Figure 21) when compared to the ceramic particles (Figure 20). This may be explained because by changing the abrasive particles from ceramic to composite, as their density changes, the abrasive particles ratio over the conductive particles also changes. When the ratio of abrasive particles with respect to electrically conductive particles increases at the bottom of the container (where the top of the object is placed) and decreases at the top of the container (where the bottom of the object is placed). Increasing the ratio increases the abrasiveness while increasing the final radius obtained, as a result of the deformation during the abrasion process.

[0299] As it can be observed in Figures 20 and 21 , the increase of the radius is more pronounced at the top of the object (placed more towards the bottom of the container) than at the bottom of the object (placed more towards the top of the container). However, for the combination comprising composite abrasive particles the radius increase is more homogeneous (at the top and at the bottom of the object). This may be explained because composite abrasive particles present a more homogeneous mixture when compared to ceramic abrasive particles.

Claims

CLAIMS1. A method for surface finishing an object, comprising: surface finishing at least one surface of the object by producing relative movement between the object and a combination of a first plurality of electrically conductive particles and at least one abrasive particle, the combination and the at least one surface being in a medium, the object being electrically connected with a first pole of at least one electric source; and the electrically conductive particles and / or the medium containing the electrically conductive particles and / or a container containing the medium being electrically connected with a second pole of the at least one electric source, and one or more particles of the first plurality of electrically conductive particles comprising an electrolyte.

2. The method of claim 1 , wherein the at least one abrasive particle comprises a second plurality of abrasive particles.

3. The method of claim 1 or claim 2, wherein the combination of the first plurality of electrically conductive particles and the at least one abrasive particle, comprises at least one particle that is both electrically conductive and abrasive.

4. The method of any one of the preceding claims, wherein the surface finishing comprises, while there is relative movement between the object and the combination of the plurality of electrically conductive particles and the at least one abrasive particle, making the combination of the first plurality of electrically conductive particles and the at least one abrasive particle to contact at least one surface of the object so that one or more abrasive particles of the at least one abrasive particles surface finishes the at least one surface by abrasion and the first plurality of electrically conductive particles surface finishes the at least one surface by ion transport.

5. The method of any one of the preceding claims, wherein the electrolyte of the one or more electrically conductive particles is inside the electrically conductive particles.

6. The method of any one of the preceding claims, wherein the surface finishing of the atA / ? least one surface of the object is carried out such that a ratio a = - - - is greater than^ftp0USilng or equal to 0.015 s’1, where A / ?ais a variation in average roughness Ra during the surface finishing, Am is the variation in mass during the surface finishing, and tpoiishingis the time that has elapsed during the surface finishing.

7. The method of any one of the preceding claims, wherein the surface finishing of the at least one surface of the object, wherein the object includes a sharp edge and the surface finishing is carried out such that a ratio beta B =100is greater than or equal to 2.5 s’1,wherein ARZisRz~*z, Rzlbeing the initial roughness, Rzbeing the final roughness valueRz after a polishing time t, and wherein Ar is, rland r being the initial and final radius value of the sharp edge included on the object.

8. The method of any one of the preceding claims, wherein a maximum size of one or more abrasive particles of the at least one abrasive particle is greater than an average width of cavities delimiting valleys in the at least one surface of the object, thereby precluding the abrasive particles of the at least one abrasive particle from coming into contact with walls of the cavities.

9. The method of any one of the preceding claims, wherein a maximum size of one or more electrically conductive particles of the first plurality of electrically conductive particles is equal to or less than an average width of cavities delimiting valleys in the at least one surface of the object, thereby enabling the electrically conductive particles to come into contact with walls of the cavities.

10. The method of any one of the preceding claims, wherein one or more abrasive particles of the at least one abrasive particle have: a density ratio DR fulfilling the following: 7 > DR > 0.7, and / or a mass ratio MR fulfilling the following: 2 > MR > 0.2; where DR = — ,Pres where papis a density of the one or more abrasive particles, and presis a density of a resin of the electrically conductive particles of the first plurality of electrically conductive particles; and where MR =where mapis a mass of the one or more abrasive particles, and mresis a mass of the resin of the electrically conductive particles of the first plurality of electrically conductive particles.

11. The method of any one of the preceding claims, comprising a recirculation step said recirculation step comprising- removing at least part of the medium from the container,- cleaning the at least part of the medium removed from the container, and- returning the cleaned medium to the container.

12. An object comprising one or more surfaces that are surface finished, the one or more surfaces being surface finished with a method according to any one of the preceding claims.

13. An object comprising one or more surfaces that are surface finished, wherein at least one surface of the one or more surfaces has, in the entire at least one surface, an average roughness value Ra less than or equal to 0.30, preferably less than or equal to 0.20 pm; and / or at least one surface of the one or more surfaces has, in the entire at least one surface, an absolute peak to valley average value Rz less than or equal to 2.50 pm, preferably less than or equal to 2.00 pm.

14. The object of any one of claims 12-13, wherein the object is one of the following: a blade of a jet engine, a blade of a wind turbine, a clock or a watch part, a dental prosthesis, a casted part or object, a machined part or object, a shaped part or object, and an additively manufactured part or object.

15. The method of any one of claims 1-11 , wherein the object is an object according to any one of claims 12-14.

16. A composition comprising: a first plurality of electrically conductive particles, and one or more particles of the first plurality of electrically conductive particles comprising an electrolyte; and at least one abrasive particle.

17. The composition of claim 16, further comprising a medium with the first plurality of electrically conductive particles and the at least one abrasive particle comprised therein.

18. The composition of any one of claims 16-17, wherein the at least one abrasive particle comprises a second plurality of abrasive particles.

19. The composition of any one of claims 16-18, wherein the combination of the first plurality of electrically conductive particles and the at least one abrasive particle, comprises at least one particle that is both electrically conductive and abrasive.

20. A machine for surface finishing an object, comprising: a container adapted to receive a medium; a holding device adapted to attach the object such that at least a portion thereof can be in contact with the medium;moving means for moving the object relative to the medium within the container and / or for moving the medium relative to the object; at least one electric source having a first pole thereof electrically connected with the object at least when attached to the holding device, and a second pole of the at least one electric source electrically connectable with electrically conductive particles of a composition and / or the medium containing the electrically conductive particles and / or the container containing the medium; and a composition according to any one of claims 16-19 and / or a stainless-steel coating on the first and / or second pole.

21. The machine of claim 20 further comprising a recirculation system said recirculation system comprising- means for removing at least part of the medium from the container,- means for cleaning the at least part of the medium removed from the container, and- means for returning the cleaned medium to the container.

22. An apparatus for surface finishing an object, comprising: a propelling device for propelling a composition; at least one pole of at least one electric source; and the composition according to any one of claims 16-19 and / or a stainless-steel coating on the at least one pole.

23. An assembly comprising: an apparatus for surface finishing an object, the apparatus comprising a propelling device for propelling a composition; a holding device adapted to attach the object; at least one electric source having a first pole thereof electrically connected with the object at least when attached to the holding device, and a second pole of the at least one electric source electrically connectable with electrically conductive particles of a composition and / or a medium containing the electrically conductive particles and / or a container containing the medium; and a composition according to any one of claims 16-19 and / or a stainless-steel coating on the first and / or second pole.

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