RU2229543C2 - Process of electrochemical polishing - Google Patents

Abstract

FIELD: electrochemical machining of metal articles, mechanical engineering, instrumentation engineering. SUBSTANCE: proposed process can find use in finishing of internal and external surfaces. Process involves treatment of part in neutral aqueous solution of salts at density of current between 0.2-10 A/sq cm. Machined part is set in symmetry with reference to two flat electrodes which are connected to positive and negative poles of source of electric energy and imparted with vibration. Width L of flat electrode and outer diameter D of part are in ratio L/D≥3, resistance of cross-section of single electrode should be equal to or more than polarization resistance. EFFECT: expanded technological capability of process of electrochemical polishing, enhanced quality of machined internal and external surfaces of parts. 2 dwg

Description

The invention relates to methods for the electrochemical processing of metals and can be used in mechanical engineering and instrumentation, for example, when fine-tuning internal and external surfaces.

Known methods of electrochemical polishing, which is anodic dissolution, leading to a significant improvement in the microgeometry of the treated surface (roughness parameter from Ra = 0.04 μm to Rz = 0.025 μm), a high degree of specular reflection (gloss) [1].

A known method of bipolar electrochemical polishing of pipes on the outer and inner surfaces, which consists in the fact that current-carrying electrodes induce corresponding currents on sections of the moving pipe, and the pipe section charged positively undergoes electrochemical polishing [2].

The disadvantage of the existing method is the complexity of the technological equipment (for processing the inner and outer surfaces of the pipe, there is a separate electrolyzer circuit divided into two chambers: cathode and anode).

The bipolar method of electrochemical processing is used when polishing pipes, deburring, flashing holes, in technological processes of etching, degreasing, etc., for which various technological schemes for using a bipolar electrode have been developed [3, 4].

A known method of electrochemical polishing of metals and alloys, taken as a prototype, involving the process in a neutral aqueous solution of salts at a current density of 0.2-10 A / cm ² at an electrolyte temperature equal to the ambient temperature. The workpiece is informed of vibration, the amplitude and frequency of which is set based on the physicochemical properties of the material of the workpiece. The time of one polishing cycle is determined by the formula [5]. The bath and the workpiece are connected to a negative and positive current source, respectively.

The disadvantage of the existing method is the uneven processing of the inner surface of the part due to problems when removing the processed products and gas bubbles from the treated surface.

The objective of the invention is the expansion of technological capabilities of the process of electrochemical polishing and improving the quality of processing of the inner and outer surfaces.

The solution is achieved by the fact that in the known method of electrochemical polishing, carried out by vibration of the workpiece in a neutral aqueous solution of salts at a current density of 0.2-10 A / cm ² , according to the invention, the workpiece is installed symmetrically with respect to two flat electrodes connected to the positive and the negative poles of the current source, while the width of the flat electrode L and the outer diameter of the part D are in the ratio L / D≥3, and the resistance of a single electrolyte cross section p Avo or more polarization resistance.

A feature of the proposed bipolar circuit is that the workpiece is placed between two electrodes in an electrolyte medium and plays the role of a bipolar electrode, i.e. on its surface simultaneously occur anodic and cathodic reactions. The current to the workpiece is supplied through the electrolyte immediately over its entire surface. This solution of the current supply eliminates structural changes in the metal and burns, the processing error disappears.

The phenomena occurring on the workpiece associated with the appearance of surface charges of different signs are considered in [4].

With a ratio L / D≥3, the electric field lines are distributed evenly over the entire surface of the workpiece facing the cathode, which leads to a uniform surface treatment, with a ratio L / D <3, processing uniformity is not achieved due to the occurrence of edge effects.

The proposed method is illustrated in figures 1 and 2.

Figure 1 presents the scheme of electrochemical polishing: bath 1 for electrochemical polishing with a neutral aqueous solution of salt; the workpiece 2 installed in the fixture 3 with technological holes 4 and with a thread under the rod 5, which is connected to a vibration source 6; nozzle 7 with a cone-shaped hole for pumping electrolyte (device 3 and nozzle 7 are made of dielectric); two metal plates-electrodes 8 connected to the positive and negative poles of the current source 9, between which the workpiece is located.

Figure 2 presents the layout of the part and electrodes.

During vibration, the electrolyte is pumped through the nozzle hole 7, moving along the cavity of the workpiece 2, “pushes” the processed products and bubbles of the released oxygen and hydrogen gas through the technological holes 4 in the tool 3. The electrolyte is circulated inside the workpiece 2 always in one direction (up) due to the conical shape of the opening of the nozzle 7 for pumping electrolyte.

Processing is subjected simultaneously to the portion of the outer and inner surfaces of the workpiece 2, positively charged. To process the other half of the workpiece 2, it is enough to change the polarity of the electrodes 8 or rotate the workpiece itself relative to them.

During vibration, intensive removal of the processed products and gas bubbles from the treated surface is ensured (delayed separation of gas bubbles leads to uneven dissolution of the metal, the appearance of vertical grooves, and pinholes [4]).

The advantages of this method are the absence of burns, uniform processing and simplified current supply.

Example 1

Electrolyte 15% NaCl, f = 50 Hz, i = 0.2-10 A / cm ² , L _electrode = 150 mm, z = 140 mm; _Nar. = 3.4 μm, Ra _internal. = 4.1 μm.

The samples were subjected to processing from steel St35, the outer diameter of the sample was cylindrical in shape 47 mm, and the inner diameter was 5.8 mm. The time of one treatment cycle was calculated by the formula [5] and averaged 2 seconds. The treatment was subjected simultaneously to the portion of the outer and inner surfaces of the workpiece, positively charged. To process the other half of the workpiece, the polarity of the electrodes was changed.

The unit electrolyte cross section is 1 / R = χ · z, where χ is the electrical conductivity (tabulated values) [7]; polarization resistance - r = dφ / di (according to the anodic and cathodic polarization curves) [6]

χ = 24.73 Ohm ^-1 · m ^-1 for 5M NaCl [7]

1 / R = χ · z = 24.73 · 0.014 = 0.346 (R≈3 Ohm)

r _{a, k} = dφ _{a, k} / di _{a, k} ; r _to ≈ 0.014; r _a ≈ 0.4 [6]

r = 2 r _to +2 r _a = 0.828 Ohms.

Initial surface roughness Ra of the outer surface of the _drug. = 3.4 μm, after the treatment cycle Ra _con. = 2.8 μm; during subsequent processing cycles roughness is changed as follows: Ra _beginning. = 2.8 μm - Ra _con. = 2.4 microns; Ra _beginning. = 2.4 μm - Ra _con. = 2.1 μm.

The initial roughness of the inner surface Ra internal _. = 4.1 μm. Roughness of the inner surface of the hole after the treatment cycle Ra _con. = 3.6 μm. On subsequent cycles, the processing is changed so roughness: Ra _beginning. = 3.6 μm - Ra _con. = 2.4 microns; Ra _beginning. = 2.4 μm - Ra _con. = 2.2 μm. The duration of one processing cycle is 2 seconds.

Compared with the prototype, the uniformity and quality of processing are improved.

Example 2

Electrolyte 15% NaCl, f = 50 Hz, i = 0.2-10 A / cm ² , L _electrode = 150 mm; z = 140 mm.

Samples of stainless steel 12X13 of cylindrical shape, an outer diameter of 45 mm, and a hole diameter of 11 mm were subjected to processing. The time of one processing cycle was calculated by the formula [5] and averaged 3 seconds. The treatment was subjected simultaneously to the portion of the outer and inner surfaces of the workpiece, positively charged. To process the other half of the workpiece, the polarity of the electrodes was changed.

The unit electrolyte cross section is 1 / R = χ · z, where χ is the electrical conductivity (tabulated values) [7]; polarization resistance - r = dφ / di (according to the anodic and cathodic polarization curves) [6]

χ = 24.73 Ohm ^-1 · m ^-1 for 5M NaCl [7]

1 / R = χ · z = 24.73 · 0.014 = 0.346 (R≈3 Ohm)

r _{a, k} = dφ _{a, k} / di _{a, k} ; r _to ≈ 0.014; r _a ≈ 0.4 [6]

r = 2 r _to +2 r _a = 0.828 Ohms.

For the outer surface: Ra _beginning. = 2.4 μm, after the treatment cycle Ra _con. = 1.7 μm; in subsequent processing cycles: Ra _beginning. = 1.7 μm, Ra _con. = 1.55 μm; Ra _beginning. = 1.55 μm, Ra _con. = 1.1 μm; Ra _beginning. = 1.1 μm, Ra _con. = 0.85 μm. The time of one processing cycle is 3 seconds.

Starting inner surface roughness Ra _beginning. = 3.2 μm. Roughness of the inner surface of the hole after the treatment cycle Ra _con. = 2.4 μm. On subsequent cycles, the processing is changed so roughness: Ra _beginning. = 2.1 μm - Ra _con. = 1.6 μm; Ra _beginning. = 1.6 μm - Ra _con. = 0.95 μm; Ra _beginning. = 0.95 - Ra _con. = 0.7 μm.

Compared with the prototype, the uniformity and quality of processing are improved.

Sources of information

1. Lipkin, Y.N., Bershadskaya, T.L. Chemical polishing of metals. - M.: Mechanical Engineering, 1982, 112 p.

2. Atanasyants A.G. Electrochemical manufacturing of parts for nuclear reactors. - M.: Energoizdat, 1987, 176 p.

3. Griliches S.Ya. Electrochemical polishing. - L .: Engineering, 1976, 208 p.

4. Frost II, Orlov V.F., Chugunov B.I. The bipolar method of electrochemical processing and some of its technological capabilities // Electronic material processing. - 1982. - No. 6. - S. 19-23.

5. Patent No. 2146580 (Russia) 7 В 23 Н 3/00. The method of electrochemical polishing of metals and alloys / Shestakov I.Ya., Babkina L.A. Claim 06/22/1998, No. 98111913/02. Publ. 03/20/2000. Bull. No. 8. Priority from 06.22.98.

6. Dikusar A.I., Engelhardt G.R., Petrenko V.I., Petrov Yu.N. Electrode and transfer processes during electrochemical dimensional processing of metals. - Chisinau: “STIINZA”, 1983.

7. Handbook of electrochemistry. / Ed. A.M. Sukhotina. - L .: Chemistry, 1981, 488 p.

Claims (1)

The method of electrochemical polishing of metal parts, including processing the part in a neutral aqueous solution of salts at a current density of 0.2-10 A / cm ² and when vibrating the part, characterized in that the part is installed symmetrically with respect to two flat electrodes connected to the positive and negative poles current source, while the width of the flat electrode L and the outer diameter of the part D are in the ratio L / D≥3, and the resistance of a single electrolyte cross section is equal to or greater than the polarization resistance.

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