RU2263728C2 - Method for providing of protective coatings on metal or alloy surface - Google Patents

Abstract

FIELD: mechanical engineering, radoelectronics, chemical industry, medicine, aviation, in particular, electrochemical processing of metal and alloy surface for forming thereon of corrosion, heat- and wear-resistant coatings for imparting dielectric and decorative properties thereto.

SUBSTANCE: method involves providing microarc oxidation by means of apparatus comprising electrode and porous shield, through which liquid electrolyte is fed and voltage is supplied to zone between surface portion to be processed and porous shield having variable section thickness, said electrolyte being fed with predetermined flow rate at increasing voltage of up to 190 V; performing oxidation process by moving said device over surface to be processed. Apparatus is furnished with system for sucking electrolyte with air from surface to be processed. Oxidation current density to electrolyte flow rate ratio is in accordance with dependence: 12>I/Q_electr.>8, where I is oxidation current density, cA/m²; Q is electrolyte flow rate, kg/s. Method allows volume of electrolyte consumed to be reduced by 1.5 times due to preventing electrolyte from spreading over surface under process and from pouring of electrolyte onto floor.

EFFECT: wider capabilities of method, reduced consumption of electrolyte, provision for localization of active microarc discharge zone and stabilizing of kinetic layer of chemical conversion facilitating in producing of homogeneous coating having improved quality, and also increased protective and decorative effect of resultant coating.

Description

The use relates to the electrochemical surface treatment of metals and alloys to form corrosion, heat and wear-resistant coatings on their surface and to give them protective dielectric and decorative properties and can be used, for example, in mechanical engineering, radio electronics, chemical industry, medicine, aviation, etc. .d.

There is a method of anodizing metals and their alloys, which consists in the fact that anodizing is carried out in a solution of sodium aluminate at a voltage of 100-1000 V, and the solution of sodium aluminate is fed by stream through a slot nozzle located at a distance of 5-10 mm from the surface of the seat with the possibility of movement a flat jet of mortar around the cylindrical surface of the seat at a speed of 0.5-1.0 m / min

RF patent №2163272, IPC C 25 D 11/02, filing date of the application on 12/14/1999, date of publication. 02/20/2001

The well-known "Method for the production of solid protective coatings on products from aluminum alloys", related to the field of electrolytic and plasma oxidation of the surface of aluminum alloys, in a narrower sense, to the method of oxidation in an alkaline electrolyte at a temperature of 15-50 ° C using alternating current with a frequency of 50 -60 Hz. At the initial stage and for the next 5-90 s, oxidation is carried out at a current density of 160-180 A / dm ² , after which it is reduced to a value of 3-30 A / dm ² . The process is carried out in the mode of spontaneous drop in the used power without regulation by the operator until the required thickness is obtained. An aqueous alkaline solution containing (g / l) is used as an electrolyte: 1-5 alkali metal hydroxide, 2-15 alkali metal silicate and 2-7 peroxide compounds (in terms of 30% hydrogen peroxide). The method is used to improve the protective properties of ceramic oxide coatings without additional energy consumption and increase the processing time due to higher microhardness, density and adhesion of the coating to the substrate.

Application WO 9931303 of June 24, 1999; IPC C 25 D 11/06; PCT / RU 97/00408 filing date 12/17/1997, IMS issue 50 No. 6/2000

The known "Method for producing nanocrystalline or nanocrystal-containing layers of metal oxide and mixtures of oxides on metals forming the locking layers", the coating being applied by anodizing using a spark discharge in an electrolyte with complexing agents, for example, with the formation of chelate complexes, with metal alkoxides with alcohol, mainly secondary and tertiary alcohol. With the correct selection of the concentration ranges of these components of the electrolytic baths and under the influence of the anodizing parameters, depending on the application, the resulting coating is given the desired properties, for example: adhesive strength, semiconductor effect, catalytic activity and surface properties.

German application No. 198841650 dated March 16, 00, IPC C 25 D 11/02; application filing date 09/11/98, ISM issue 50 No. 3-2001

The disadvantages of the above methods of surface treatment of metals include the complexity of processing in baths with electrolyte large parts and structures in the production environment.

Closest to the proposed invention is the "Method for the production of protective coatings on the surface of metals and alloys" by microarc oxidation using a device equipped with an electrode and a porous screen through which liquid electrolyte is supplied, and applying voltage between the treated surface area and the porous screen, and through a porous screen having a variable thickness of the section, carry out with a flow rate of 4-8 l / min with increasing voltage and current density up to 190, respectively B and 5 A / dm ² for 3-10 minutes, and the oxidation process is carried out by moving the device along the surface to be treated, while the vector of the velocity of movement and the vector of the maximum gradient of the thickness of the cross section of the porous screen are mutually perpendicular and depend on a certain ratio.

Patent for the invention of the Russian Federation No. 2194804 from 23.10.00, IPC C 25 D 11/02; C 25 D 11/06, date publ. 10.23.00 g.

The disadvantage of the above method is the significant loss of consumed electrolyte due to spreading it on the treated surface, leaks on the floor when coating in the production conditions on large parts or structures, products with a variable profile.

The technical result achieved using the proposed system of suction of electrolyte with air from the zone of treatment of the oxidized surface includes a reduction in the volume of the used electrolyte by one and a half times, due to the prevention of spills of electrolyte on the treated surface and spills to the floor, while the localization of the active zone of the microarc discharge with stabilization of the kinetic layer of chemical transformations, contributing to the formation of a more homogeneous and better coating. The technical result is achieved by the fact that in the "Method for the production of protective coatings on the surface of metals and alloys" by microarc oxidation using a device equipped with an electrode and a porous screen, through which a liquid electrolyte is supplied and voltage is applied between the treated surface area and the porous screen with a variable section thickness through which the electrolyte is supplied at an increasing voltage of up to 190 V, and the oxidation process is carried out by moving the device along the surface, while the velocity vector and the maximum gradient vector of the thickness of the cross section of the porous screen are mutually perpendicular and depend on the following relationship:

где

Where

V is the velocity of the porous screen, m / s;

N _max - the maximum thickness of the cross section of the screen, m;

H _min - the minimum thickness of the cross section of the screen m;

U is the voltage of the electric current between the screen and the workpiece, V.

Therefore, the device for oxidation is equipped with a suction system of the electrolyte with air from the treated surface, and the ratio of the oxidation current density and electrolyte consumption are in the range according to the formula:

где

Where

I is the oxidation current density, kA / m ² ;

Q is the electrolyte consumption, kg / s.

The method is as follows. A part with a cleaned and degreased surface is mounted on a baking sheet. The workpiece is an anode; a special movable device with a stainless steel plate is used as a cathode. The device is equipped with an electrolyte pumping system through a porous screen and an electrode and an electrolyte suction system using air from the workpiece surface. The pumped electrolyte is fed through a porous screen and an electrode to an oxidizable surface. When voltage is applied to the electrode and the part, electric discharges occur on its surface and the microarc oxidation process takes place, while the electrolyte seeping through the fiber of the porous screen washes the treated surface, cools the part and is sucked with air from the treatment zone into the container. By moving the device along the surface of the part, a protective oxide coating can be obtained on the entire oxidized surface or in its individual places.

Experiments have been carried out that make it possible to implement this method in a production environment and obtain positive results.

For testing, a PT-ZV alloy sheet with a thickness of 4 mm and an area of 1 m ^{2 was used} . As a cathode, a stainless steel plate with an area of 0.3 dm ^{2 was used} .

The composition of the electrolyte: Na3PO4 · 12H2O, the rest is water. When pumping the electrolyte through a fibrous screen and an electrode with a flow rate of 0.06 kg / s and gradually increasing the voltage to 190 V and current density i = 5 kA / m ² , the process of microarc oxidation on the surface of the part under the electrode begins. At the same time, the electrolyte with air is sucked out of the treatment zone, which prevents the electrolyte from spreading over the surface of the part, while the anodization process in the spreading electrolyte is excluded, the oxidation process occurs at certain boundaries, within the vacuum zone, the active zone of the microarc discharge is localized with a stabilization of the kinetic layer of chemical transformations , contributing to the formation of a more homogeneous and better coating in the microarc oxidation zone. Moving the device on the treated surface at a speed of 1.0-0.7 m / min, we obtain a given oxide layer. After oxidation, the sheet was washed and dried. The resulting coating meets the requirements.

Application of the proposed technical solution in the production environment for the production of protective coatings on the surfaces of metals and alloys, the production of multi-colored protective coatings, the restoration of lost coatings of large-sized parts and structures will significantly reduce the electrolyte consumption, avoid non-technological losses, improve the quality of the coating and the operating safety of the installation as a result of localization electric field within the vacuum zone created by the ejected air stream wok y electrode, while the high-speed movement of the electrode with a porous screen with a final reduction processing time oxidizable surfaces.

Claims (1)

A method of obtaining a protective coating on the surface of metals and alloys, including microarc oxidation using a device containing an electrode and a porous screen through which a liquid electrolyte is supplied, with a voltage applied between the treated surface area and the porous screen with a variable thickness, and the electrolyte is supplied with a given flow rate with increasing voltage up to 190 V, and the oxidation process is carried out by moving the device along the treated surface, and the vector c to grow and move the maximum gradient vector sectional thickness of the porous screen are mutually perpendicular and are dependent on the following relationship:

where V is the velocity of the porous screen, m / s; N _max - the maximum thickness of the cross section of the screen, m; H _min - the minimum thickness of the cross section of the screen, m; U is the voltage of the electric current between the screen and the workpiece, V, characterized in that the oxidation device is equipped with an electrolyte suction system with air from the surface to be treated, and the ratio of the oxidation current density and electrolyte consumption is set in the following relationship:

where I is the oxidation current density, kA / m2; Q is the electrolyte consumption, kg / s.