RU2294987C1 - Process for applying electrolytic coatings onto surfaces of metals and alloys - Google Patents

Abstract

FIELD: electrolytic processes for applying anode coatings with use of moving electrolyte, possibly in machine engineering, radio electronics, instrument making, air craft and ship making industry branches.

SUBSTANCE: process comprises steps of micro-arc oxidizing with use of apparatus having electrode and porous screen through which liquid electrolyte is fed; applying voltage between treated surface portion and electrode; supplying electrolyte through porous screen with flow rate 4 - 8 l/min at rising voltage; moving apparatus on treated surface during coating applying procedure and realizing micro-arc oxidizing at voltage 200 - 250 V and electric current density 1.0 - 3.0 A/dm². At motion apparatus is subjected (in zone of tool and treated surface contact) to reciprocation and(or) to rotation motion at linear speed 10 -50 m/min and pressure 5 -30g/cm².

EFFECT: improved operational parameters of protection coating such as electric resistance and breakdown voltage.

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Description

The invention relates to electrolytic methods of applying anode coatings using a movable electrolyte and chemical reactions that take place on the surface of the processed products, to give them protective, dielectric, decorative and other properties and can be used in mechanical engineering, radio electronics, instrumentation, aviation, shipbuilding industries, etc. .d.

The well-known "Method of microarc obtaining protective films on the surface of metals and their alloys" RF patent No. 2061107, MKI C 25 D 11/06, publ. 05/25/96, "The method of applying an electrolytic coating to the surface of metals and alloys" patent No. 21202086, MKI C 25 D 11/00, publ. 05/27/98, "Method for applying a corrosion-resistant and wear-resistant oxide layer with a locally reduced thickness on the surface of a metal part", German patent No. 4442792, MKI C 25 D 11/02, publ. 05/04/98, "Method for producing a thin-walled ceramic coating", application PCT 9703231, MKI C 25 D 11/02, publ. 05/05/98

The disadvantages of these methods of surface treatment of metals include the difficulty of processing in bathtubs with electrolyte of large-sized parts, as well as the inability to surface treatment of parts directly in operating conditions.

Known application EPO 0340733, MKI C 25 D 11/04, publ. 11/08/89, the "Method of surface treatment in place." The disadvantage of this method is the inability to process large surfaces.

The closest in technical essence and taken as a prototype 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 a liquid electrolyte is supplied and applying voltage between the treated surface area and the porous screen characterized in that the supply of electrolyte through a porous screen having a variable section thickness is carried out with a flow rate of 4-8 l / min with increasing voltage and current strength up to 190 V and 5 A / dm ^2, respectively, for 3-10 min, and the oxidation process is carried out by moving the device along the surface to be treated, while the velocity vector and the maximum gradient of the thickness of the cross section of the porous screen are mutually perpendicular and depend on the following ratio:

where V is the velocity of the porous screen, mm;

Hmax - maximum thickness of the screen section, m;

Hmin is the minimum thickness of the screen section, mm;

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

RF patent No. 2194804, MKI C 25 D 11/02, publ. December 20, 2002

The disadvantages of this method are the reduced service properties of the protective coating, for example, electrical resistivity and breakdown voltage due to the uneven distribution of the coating material on the treated surface.

The technical result of the invention is to increase the service properties of the protective coating, for example, electrical resistivity and breakdown voltage, due to a more uniform distribution of the coating material on the treated surface.

The technical result of the invention is achieved due to the fact that in the electrolytic method of applying protective coatings to the surface of metals and alloys, including microarc oxidation using a device equipped with an electrode and a porous screen through which liquid electrolyte is supplied, voltage is applied between the treated surface area and the electrode, supply electrolyte through a porous screen with a flow rate of 4-8 l / min with increasing voltage, moving the device along the treated surface during the application Nia coating according to the invention microarc oxidation is conducted at a voltage of 200-250 V and a current density of 1.0-3.0 A / dm ^2, and by moving the device it attached to the tool in the contact area with the treated surface a reciprocating and / or rotary movement with a linear speed of 10-50 m / min at a pressure of 5-30 g / cm ² .

The relief of the surface of the applied coating in a cross section formed at low pressures (less than 0.1 g / cm ² ) represents a chaotic alternation of the peaks of the peaks and troughs of the applied material on the profilogram. In this case, the limiting value of the service properties of the coating is determined by the minimum thickness of the deposited protective material in the cavity, where the loss of coating properties occurs, for example, voltage breakdown. Subsequent polishing or electro polishing smooths the peaks of the peaks, but does not increase the working thickness of the deposited material in the cavity.

The application of pressure to the electrode during reciprocating and / or rotational motion during the coating process, when the coating material on the surface to be treated is in a plastic state, leads to its movement from the vertices to the depressions, increasing the effective working thickness of the coating at this point. This circumstance provides an increase in the characteristics of the service properties of the coating with the same parameters of the process of its application in comparison with the prototype.

The pressure applied to the device during the coating process in the zone of contact of the tool with the working surface of less than 5.0 g / cm ² and a linear velocity of less than 10 m / min are insufficient for effective deformation of the vertices.

When the pressure applied to the device during the coating process in the contact zone of the tool with the working surface is more than 30 g / cm ² and the linear velocity is more than 50 m / min, wrinkles occur during deformation of the tips of the protrusions of the coating material, and at higher pressure peeling of the coating from the treated surface occurs.

An example of a specific implementation:

A part with a cleaned and degreased surface was mounted on a baking sheet to collect the draining electrolyte.

The workpiece of any size and configuration was connected as an anode to electric current, and as a cathode a device was connected consisting of an electrode made in the form of a mesh metal drum with a porous cylindrical screen mounted on the drum, for example, from rubber, forming a closed internal cavity. An electrolyte was forced into the closed cavity of the drum under pressure, which through the openings of the mesh part of the drum and porous rubber fell onto the surface to be treated, and the drum was given rotational and / or reciprocating motion relative to the contact zone of the tool with the surface to be treated.

To test the parameters of the method, experiments were carried out to determine the pressure applied to the device and the linear velocity in the zone of contact of the tool with the surface to be treated under production conditions.

For the experiment, a VT1-0 grade sheet of titanium connected as an anode was used.

An electrolyte was an aqueous solution of trisodium phosphate (Na ₃ HO ₄ · 12H ₂ O) with a concentration of 15 g / l at a temperature of 25 ° C. Forcing the electrolyte by force through a rotating electrode and a porous screen, it was fed into the contact zone of the electrode with the workpiece surface with a flow rate of 4.0; 6.0 and 8.0 l / min. Gradually increasing the voltage up to 200 V and the current density up to 3 A / dm ² , and then the voltage up to 250 V and the current density up to 1 A / dm ² , the process of microarc oxidation began, which continued at the indicated parameters in the future. In the process of microarc oxidation in the contact zone with the treated surface, a pressure of 1.0 was applied to the electrode with a porous screen; 5.0; 15.0; 30.0 and 40.0 g / cm ² and was given to it a rotational and / or reciprocating movement corresponding to a linear speed of 8.0; 10.0; 25.0; 50.0 and 60.0 m / min. Processing was carried out for 1.0; 3.0; 5.0; 10.0 and 12.0 minutes.

After the oxidation process was completed, the surface of the sheet was washed and dried, and then the applied coating was subjected to tests for electrical resistivity, breakdown voltage, and the roughness index was determined. The test results of the properties of the coating obtained by the proposed method and the prototype method are presented in the table.

Table
Comparative tests of properties obtained by the claimed and known methods. Way Method Parameters Coating properties Voltage Current density, A / dm ² Electrolyte consumption, l / min Processing time, min Speed of movement, m / min Pressure g / cm ² Breakdown voltage, V

Roughness indicator

Electrical resistivity, (Ohm · m) · 10 ² Proposed 250,0 1,0 4.0 1,0 8.0 1,0 800 12.0 2.6 250,0 1,0 4.0 3.0 10.0 5,0 1000 7.0 12.6 250,0 1,0 6.0 5,0 25.0 15.0 1200 1.00 18.1 200,0 3.0 8.0 10.0 50,0 30,0 1100 1,60 20.6 200,0 3.0 8.0 12.0 60.0 40,0 300 1.30 1,1 Famous 190.0 5,0 6.0 7.0 10.0 - 650 27.0 3.0 Notes:
1. The table shows the average results after testing three samples per point.
2. The surface roughness index represents the ratio of the five largest peaks H _max to the five largest depressions H _min profile within the same base length. The linear values of the protrusions Hmax and depressions H _{min were} determined by a profilograph with a resolution of 0.5 μm.
3. The breakdown voltage was determined using the UPU-10 installation (OH.0972.029-80) by stepwise changing the voltage through 50 V from 0 to 3.0 kV and the exposure time at each stage for 1.0-1.5 minutes.

Technical and economic efficiency from the application of the proposed method in comparison with the known will be expressed in increasing the reliability and service life of the equipment, the surface of the details of which will be processed by the proposed method.

Claims (1)

The electrolytic method of applying protective coatings to the surface of metals and alloys, including microarc oxidation using a device equipped with an electrode and a porous screen, through which liquid electrolyte is supplied, applying voltage between the treated surface area and the electrode, supplying electrolyte through a porous screen with a flow rate of 4-8 l / min with increasing voltage, the movement of the device on the treated surface in the coating process, characterized in that the microarc oxidation of the leads ut at a voltage of 200-250 V and a current density of 1.0-3.0 A / dm ² , and when moving the device it is given a reciprocating and / or rotational movement with a linear speed of 10-50 m in the zone of contact of the tool with the work surface / min at a pressure of 5-30 g / cm ² .