RU2676380C1 - Method of obtaining coatings for items made of valve metal alloys - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to the field of electroplating and can be used in mechanical engineering and related industries. Method includes electrochemical oxidation with a duration of 30–100 minutes in reverse flows of acidic or alkaline electrolyte solutions, wherein oxidation is carried out without the use of special baths, installing parts inside the counter-electrodes of stainless steel, in cavities, the shapes of which correspond to the shapes of the parts, and the dimensions exceed the corresponding external dimensions of parts by 4–10 mm, while electrolyte solutions are passed through these cavities, ensuring their consumption from 0.2 to 5.0 liters per 1 dmthe area of the oxidized surfaces of the parts and changing the direction of their flow on the opposite, after half the time of oxidation.EFFECT: obtaining high-quality uniform coatings on surfaces of parts with low-tech surface areas.1 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of electrochemical surface treatment of parts from valve metal alloys in electrolyte solutions, in particular to electrochemical oxidation, the most common varieties of which are anodizing and microarc oxidation, and can be used in mechanical engineering and other industries.

The valve group consists of metals on the surfaces of which natural dense oxide films with unipolar conductivity are formed, i.e. metals such as aluminum, titanium, magnesium, etc.

Anodizing and microarc oxidation make it possible to increase the thickness of natural oxide films by orders of magnitude, obtaining coatings based on them, mainly formed as a result of the interaction of valve group metals with oxygen released from electrolyte solutions, and having high strength, electrical insulation and anticorrosion properties.

Traditional technologies of anodizing and microarc oxidation are implemented in special baths made of materials inert with respect to solutions; usually, corrosion-resistant (stainless) steels are used as such materials. Bathtubs should have significant dimensions so that the processed products are freely placed in them. In order to prevent solutions from overheating and dissolving formed coatings during processing, their volumes in bathtubs should be orders of magnitude larger than the volumes of processed products, and bathtubs should be equipped with cooling and mixing systems. Bathtubs, as a rule, are dimensional and expensive designs. Therefore, the development of methods for the electrochemical oxidation of parts from valve metal alloys without the use of bathtubs is of great interest for manufacturing practice.

One of the conditions for obtaining high-quality uniform coatings on parts is to provide good conditions for washing their surfaces with solutions. However, in the implementation of traditional technologies of anodizing and microarc oxidation, the mixing of solutions in the baths is carried out by mechanical or pneumatic mixers (mixers), the use of which cannot ensure good washing of non-technological surface areas, which include holes, grooves, troughs, grooves, etc. Therefore, it is not possible in practice to obtain high-quality uniform coatings on such surfaces using traditional anodizing and microarc oxidation technologies.

In connection with the foregoing, the main idea of the invention is to obtain high-quality uniform coatings on parts from valve metal alloys of parts with non-technological surface areas by electrochemical oxidation without the use of bathtubs.

From the sources of patent information, methods are known for producing coatings on parts of aluminum alloys by anodizing in baths with acidic solutions of electrolytes [Patent RU 2354759. Method for producing coatings / Chufistov O.E., Demin SB, Chufistov EA, Boriskov D. E., Kholudintsev P.A. - Bull. No. 13 of 05/10/2009] and microarc oxidation in baths with alkaline solutions of electrolytes [Patent RU No. 2136788. A method for producing coatings / Atroshchenko ES, Chufistov OE, Kazantsev IA, Durnev VA - Bull. No. 25 dated 09/10/1999]. However, these methods are implemented in bathtubs and do not allow to obtain high-quality uniform coatings on the surfaces of parts with non-technological areas. For example, when machining parts with through holes with a diameter of up to 10 mm and a length of more than 10 mm, the thicknesses of the coatings on the walls of the holes in their middle zones do not exceed 10% of the thicknesses of the coatings on the outer surfaces.

Also known are methods for producing coatings on aluminum alloy parts, including microarc oxidation in baths with alkaline solutions of electrolytes when chilled oxygen is fed onto oxidized surfaces [Patent RU 2339745. Method for producing coatings / Chufistov OE, Demin SB, Chufistov E .BUT. - Bul. 33 dated November 27, 2008; Patent RU 2354758. A method of producing coatings / Chufistov O.E., Boriskov D.E., Chufistov E.A. - Bull. 13 of 05/10/2009]. Oxygen supply due to improved mixing and cooling of the electrolyte solution, enriching it with oxygen provides an increase in oxidation performance, as well as an increase in thickness, physical and mechanical properties and uniformity of coatings on the outer surfaces of the parts and the surfaces of the through holes. These methods make it possible to obtain relatively uniform coatings on parts with non-technological areas. For example, when machining parts with through holes with a diameter of up to 30 mm and a length of more than 50 mm, the thickness of the coatings on the walls of the holes in their middle zones can reach 88% of the thickness of the coatings on the outer surfaces. However, these methods are implemented in bathtubs and are characterized by high technological complexity and cost, require the use of additional equipment and special tools for supplying chilled oxygen.

The closest in technical essence to the proposed method is a method for producing coatings on the surfaces of blind holes of parts made of aluminum alloys, including electrochemical oxidation in baths with acidic or alkaline solutions of electrolytes, which are pumped into the holes half the processing time and pumped out from the holes through the special half of the time which are counter electrodes with respect to parts [Patent RU 2471895. The method of producing coatings on the surfaces of blind holes Alley made of aluminum alloys. Chufistov O.E., Artemov II, Chufistov E.A., Agapova T.A., Gusenkov E.V. - Bull. No. 1 dated January 10, 2013]. Pumping and pumping contributes to the renewal of electrolyte solutions inside blind holes and provides an increase in electrochemical oxidation performance, as well as an increase in the thickness, physicomechanical properties and uniformity of coatings on the outer surfaces of parts and the surfaces of blind holes. For example, when machining parts with blind holes with a diameter of up to 10 mm and a depth of up to 50 mm, the thickness of coatings on the walls of the holes in their middle zones can reach 95% of the values of the thickness of coatings on the outer surfaces of the parts. However, this method is also implemented in bathtubs, and its use is effective only for processing parts with blind holes.

The objective of the proposed invention is to develop a simple, reliable way to obtain uniform coatings on the surfaces of parts with non-technological sections of surfaces from valve metal alloys by electrochemical oxidation without the use of special baths.

The technical result of solving the problem lies in obtaining on the surfaces of parts made of alloys of valve metals with non-technological sections of the surfaces of high-quality uniform coatings by electrochemical oxidation without the use of special baths.

The problem is solved in a method for producing coatings on parts made of valve metal alloys, including electrochemical oxidation lasting 30 ... 100 minutes in reverse flows of acidic or alkaline solutions of electrolytes, and oxidation is carried out without the use of special baths, installing parts inside stainless steel counter electrodes in cavities , the shapes of which correspond to the shapes of the parts, and the dimensions exceed the corresponding external dimensions of the parts by 4 ... 10 mm, while through these cavities let electrolyte solutions, providing their consumption from 0.2 to 5.0 liters per 1 dm ² of surface area of oxidizable parts and changing the direction of flow is reversed, after half the time of oxidation.

The method is intended for use in serial and mass production and is implemented as follows. First, a counter electrode consisting of two half-forms is made of stainless steel. The counter electrode assembly must have internal cavities for accommodating the workpieces, which should have approximately the same shapes as the workpieces, but the dimensions of these cavities should exceed the corresponding dimensions of the parts by 4 ... 10 mm. This is necessary so that between the surfaces of the cavities and parts during processing there are guaranteed clearances of 2 ... 5 mm, ensuring free flow of the solution and preventing contact of the parts and the counter electrode to avoid short circuits. In addition, the counter electrode must have openings for aluminum wires in an insulating braid to fix parts in internal cavities and connect them to a current source, as well as openings for supplying fresh solution to internal cavities and for draining the spent solution from them. At the same time, the holes for supplying the solution should be located so that the solution from them was supplied to non-technological surface areas to improve their washing conditions. Also, in order to avoid uncontrolled leakage of the solution, it is desirable that the counter electrode is sealed, therefore, between its half-forms it is possible to install seals made of a material inert with respect to the solution (plastic, silicone, rubber, etc.).

The parts are attached to the wires in an insulating braid, the wires are connected to one of the poles of the electric current source (if the oxidation is carried out at constant current, the parts are connected to the positive pole) and the parts are fixed in the half-shape of the counter electrode. In this case, approximately the same gaps of 2 ... 5 mm should be provided between the surfaces of parts and cavities of the counter electrode from all sides, and the aluminum wire must be reliably insulated from the contact with the counter electrode by an electrical insulating braid, in addition to which electrical insulating materials (bushings) can be used, which are inert with respect to to the solution.

Then, the counter-electrode half-forms are interconnected, fixed and, using an aluminum wire in an electrical insulating sheath, they are connected to the free pole of the electric current source, opposite in sign to the pole to which the parts were previously connected (if oxidation is carried out at a constant current, then the half-forms are connected to the negative pole).

Next, pipelines are connected to the holes for supplying and discharging the solution, one of which is connected to a pump with an adjustable flow rate. The suction part of the pump and the free end of another pipe (not connected to the pump) are placed in a container with an electrolyte solution. It is important to note that the pipelines, pump, tank and connecting elements must be made of materials that are chemically inert with respect to the solution, i.e. stainless steel, plastic, glass, silicone, etc. It is also desirable that the suction part of the pump be at the bottom of the tank, where the temperature of the solution is lower.

The counter electrode with parts is positioned so that the solution inside it moves from bottom to top, i.e. so that the hole for supplying a fresh solution is below, and the hole for draining the spent solution is on top. This is necessary to remove from the gaps between the surfaces of the cavities of the counter electrode and parts of gas bubbles that are formed during the decomposition of the solution during oxidation and reduce the intensity of coating formation on the surfaces of the parts.

Then they begin to pass electric current through the circuit and use a pump to pump a solution from the tank into the counter electrode, which, passing through the gaps between the surfaces of the parts of the counter electrode cavities, is drained through the pipeline back into the container. At the same time, it is possible to rotate with a certain frequency around the axis of the wire, on which the parts are fixed, for a more uniform washing of non-technological parts sections with a fresh solution.

After 15 ... 50 minutes, which make up the first half of the oxidation time, they stop passing an electric current through the circuit and pump the solution into the counter electrode. The pump is disconnected from the pipeline, the liberated end of which is placed in a container with an electrolyte solution, and for pumping the solution into the counter electrode on the opposite side, the pump is connected to the free end of another pipeline and the suction part of the pump is placed in a container with an electrolyte solution. In this case, the counter electrode is rotated so that the hole for supplying fresh solution is at the bottom, and the hole for draining the spent solution is at the top.

After that, they begin to pass electric current through the circuit and use a pump to pump a solution from the container into the counter electrode, which, passing through the gaps between the surfaces of the parts of the counter electrode cavities, is drained through the pipeline back into the container. At the same time, it is possible to rotate with a certain frequency around the axis of the wire, on which the parts are fixed, for a more uniform washing of non-technological parts sections with a fresh solution.

After 15 ... 50 minutes, which constitute the second half of the oxidation time, they stop passing electric current through the circuit and pump the solution into the counter electrode, disconnect the pipelines from it, disconnect its half-forms, remove parts from them, which are washed with water and dried.

The passage of the electrolyte solution through the cavities of the counter electrode in which the workpieces are fixed, when creating a potential difference between the surfaces of the counter electrode and the parts, creates conditions for the intense interaction of oxygen released from the solution and valve metals contained in the surface layers of the parts with the formation of oxide coatings on them. In this case, the solution in the gaps between the surfaces of the cavities of the counter electrode and parts quickly heats up with Joule heat and changes its chemical composition, losing the ability to release oxygen, which is necessary for the formation of the coating. However, by supplying a fresh solution from the container into the cavity of the counter electrode, the spent solution is washed out of the gaps between the surfaces of the counter electrode cavities and parts and flows back into the container. In the tank, the solution cools and restores its chemical composition. Due to this, the intensity of coating formation on the surfaces of parts is maintained at the required level.

Due to the fact that, as it moves in the cavity of the counter electrode, the solution heats up and changes its chemical composition, losing the ability to release oxygen, on the parts located closer to the pipeline through which the fresh solution is supplied, coatings are formed much faster than on parts located closer to the pipeline through which the spent solution is drained. However, due to the fact that after half the time of oxidation, the direction of flow of the solution through the cavities of the counter electrode is reversed, disconnecting the pump from one pipeline and connecting it to another, the thicknesses of the coatings on all parts are aligned.

Correspondence of the shapes of the cavities of the counter electrode to the shapes of the workpieces, provided that the dimensions of the cavities are 4 ... 10 mm higher than the corresponding dimensions of the parts, allows you to get approximately the same gaps between the surfaces of the cavities and parts 2 ... 5 mm This is necessary to ensure approximately equal values of the field strength between the surfaces of the cavities and surfaces of the parts, as well as similar conditions for the interaction of the surfaces of the parts with the solution.

The dimensions of the cavities of the counter electrode and the flow rate of the solution in each case should be selected individually. However, the gap between the surfaces of the hole and the rod should not be less than 2 mm, because otherwise it is impossible to completely exclude the possibility of contact of parts and the counter electrode, which can cause a short circuit and local destruction of the coating. However, it is undesirable for the gap to exceed 5 mm, since the increase in the gap is associated with an increase in the overall dimensions of the counter electrode and an increase in the flow rate of the solution without significant quantitative and qualitative changes in the oxidation process and kinetics of coating formation.

The flow rate of the solution is largely determined by the type of oxidation used. With less energy-intensive anodizing, a lower solution consumption is required than with more energy-intensive microarc oxidation. In this case, the flow rate of the solution should not go beyond the interval 0.2 ... 5.0 l / min per 1 dm ^{2 of the} machined surface of the hole. At a lower flow rate, the solution between the surfaces of the cavities of the counter electrode and parts slowly updates, heats up and changes its chemical composition, which causes a slowdown in coating formation. At higher costs, the cost of processing increases without significant quantitative and qualitative changes in the oxidation process and the kinetics of coating formation.

The proposed method is illustrated by the processing circuits of parts in FIG. 1 and 2.

In FIG. 1 shows a diagram of the processing of spherical parts with holes, which are plugs of ball valves. Through the pipeline 1 and the connecting pipe 2, the solution is pumped into the cavity of the counter electrode, consisting of half-molds 3 and 4, and washing the surfaces of the parts 5 connected to the pole of the current source by wires 6, is discharged through the connecting pipe 7 and pipe 8. The direction of the flow of the solution is shown by arrows.

In FIG. 2 shows a diagram of the processing of cylindrical parts with radial openings, which are sensor housings. Through pipelines 1 and connecting nozzles 2, the solution is pumped into the cavity of the counter electrode, consisting of half-molds 3 and 4, and, washing the surfaces of parts 5 connected to the pole of the current source by wires 6, is discharged through connecting nozzles 7 and pipelines 8. The direction of flow of the solution is shown by arrows.

Example 1. Two groups of spherical parts, which are plugs of ball valves made of AMg6 alloy, having an outer radius of 15 mm, with central through holes of 15 mm diameter, were anodized in accordance with the circuit shown in FIG. 1. Each group had 4 parts. Anodizing with a total duration of 32 minutes was carried out in a solution of oxalic acid (30 g / l) at a constant current density at the anode (parts) of 2 A / dm ² . The first group of parts was processed according to traditional technology in a bath using a mechanical mixer. The second group of parts was processed according to the proposed method in a specially made counter electrode, into which 0.5 liters of fresh solution per minute were uniformly pumped per 1 dm ^{2 of} the surface area of all processed parts, including the surface area of the holes. Between the surfaces of the cavities of the counter electrode and the spherical surfaces of the workpieces, gaps of 2.5 ... 3.0 mm were provided. 16 minutes after the start of the anodization, the direction of the solution flow in the cavities of the counter electrode was reversed until the end of the anodization. The wires on which the parts were fixed, for the uniformity of the formed coatings every 8 minutes together with the parts were rotated around the axis by 180 ^about .

After oxidation, the parts were washed with water, dried, and coating thickness was measured by standard methods [6]. The measurement results are shown in table 1.

Table 1

Coating Thickness Measurement Results

Group number
the details Thickness, microns outer spherical surface inner cylindrical surface one 45.89 6.83 2 46.01 39.97

The data shown in table 1 show that the proposed method using a compact counter electrode allows more uniform coatings to be obtained by anodizing on the surfaces of parts with non-technological areas than traditional treatment using a bath.

Example 2. Two groups of cylindrical parts, which are sensor housings made of alloy D16, with a length of 65 mm and an outer diameter of 15 mm, having two radial through holes with a diameter of 6.5 mm, were subjected to anodic-cathodic microarc oxidation in accordance with the scheme, shown in FIG. 2. Each group had 4 parts. Microarc oxidation with a total duration of 40 minutes was carried out in a solution of caustic potassium (5 g / l) and liquid glass (5 g / l) at a current density on the parts in the anode half-cycle of 12 ... 13 A / dm ² . The first group of parts was processed according to traditional technology in a bath using a mechanical mixer. The second group of parts was processed according to the proposed method in a specially made counter electrode, into which 4.0 liters of fresh solution per minute were uniformly pumped per 1 dm ^{2 of} the surface area of all processed parts. Between the surfaces of the cavities of the counter electrode and the surfaces of the workpieces, gaps of 4.0 ... 4.5 mm were provided. 20 minutes after the start of oxidation, the direction of the flow of the solution in the cavities of the counter electrode was reversed until the end of the oxidation. The wire on which the parts were fixed, for uniformity of the formed coatings, every 5 minutes together with the parts were turned around the axis by 180.

After oxidation, the parts were washed with water, dried, and coating thickness was measured by standard methods [6]. The measurement results are shown in table 2.

table 2

Coating Thickness Measurement Results

Group number
the details Thickness, microns outer end surface outer cylindrical surface inner cylindrical surface one 102.04 106.27 9.82 2 103.68 106.39 91.57

The data shown in table 2 show that the proposed method using a compact counter electrode allows micro-arc oxidation on the surfaces of parts with non-technological areas more uniform coatings than traditional treatment using a bath.

Thus, the proposed method solves the tasks.

Information sources

1. Patent RU 2354759. A method for producing coatings / Chufistov O.E., Demin S.B., Chufistov E.A., Boriskov D.E., Kholudintsev P.A. - Bull. No 13 on 05/10/2009.

2. Patent RU No. 2136788. A method for producing coatings / Atroshchenko E.S., Chufistov O.E., Kazantsev I.A., Durnev V.A. - Bull. No. 25 dated 09/10/1999.

3. Patent RU 2339745. A method of producing coatings / Chufistov O.E., Demin SB, Chufistov EA - Bull. 33 dated 11/27/2008.

4. Patent RU 2354758. A method for producing coatings / Chufistov O.E., Boriskov D.E., Chufistov E.A. - Bul. 13 dated 05/10/2009.

5. Patent RU 2471895. A method for producing coatings on the surfaces of blind holes of parts made of aluminum alloys. Chufistov O.E., Artemov II, Chufistov E.A., Agapova T.A., Gusenkov E.V. - Bull. No. 1 dated 01/10/2013.

6. Testing equipment: Ref. in 2 t. / Ed. Klyueva V.V. - M.: Mechanical Engineering, 1982. - T. 1. - 528 s.

Claims (1)

A method of producing coatings on parts from valve metal alloys, including electrochemical oxidation lasting 30-100 minutes in reverse flows of acidic or alkaline solutions of electrolytes, characterized in that the oxidation is carried out using stainless steel counter electrodes with internal cavities in which the parts are installed, wherein the cavity shapes correspond to the shapes of the parts, and the dimensions exceed the corresponding external dimensions of the parts by 4-10 mm, and the electrolyte solutions let through Data of the cavity at a rate of from 0.2 to 5.0 liters per 1 dm ² of surface area of oxidizable parts and changing the direction of flow is reversed after half the time of oxidation.

Images