RU2734179C1 - Method of polishing inner surface of part - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electropolishing of internal surfaces of parts made of metals and alloys and can be used for treatment of hollow blades of turbomachines. Method comprises placing electrode and electroconductive medium in part inner cavity, providing contact of electroconductive medium with electrode and part surface, supply of the sign opposite to the electric potential to the part and the conducting medium through the electrode. Electroconductive medium used is cord shell made of fibers of anion exchangers, impregnated with electrolyte solution, providing conductivity of shell and ion removal of metal from inner surface of part with removal of microprotrusions therefrom, using a flexible electrode located inside the cord shell, placing the cord with the electrode, passing the cord through the cavity of the part, providing movement of the cord inside the part, electric potentials opposite to the sign are supplied to the part and to the electrode, which provide polishing.

EFFECT: technical result is improved quality and reliability of polishing inner surface of parts, especially cavities of complex shape.

6 cl, 2 dwg

Description

The invention relates to a technology for electropolishing the inner surfaces of parts made of metals and alloys and can be used for processing hollow blades of turbomachines to improve their performance.

With an increase in the surface roughness of critical metal parts operating under the influence of significant alternating loads, for example, shafts, gas turbine blades, etc., their performance characteristics sharply decrease. In addition, to provide the possibility of effective cooling of the hollow blades of turbines of gas turbine engines, perforations formed on the blade are used. The piercing of perforations in parts made of difficult-to-machine materials is performed by electrochemical blasting (US Patent No. 4,578,164. IPC C25F 3/16; C25F 3/00; В23Н 09/02. Method of electrolytically finishing spray-hole of fuel injection nozzle./ Publ. 1986 d), electrical discharge machining (RF Patent No. 2625378. IPC V23N 9/14, V23N 7/00 / Method of group hole piercing and a device for its implementation. / Publ. Bull. No. 20, 2017) or laser stitching (RF patent No. 2192341, IPC B23K 26/38, Method of piercing precision holes with laser radiation, publ. Bull. No. 31, 2002). The most widespread methods in this field are the methods of piercing perforations based on electrical discharge and laser processing. However, processing by these methods leads to the formation of holes in the piercing zone, including on their internal surfaces, defects that reduce the performance of the processed parts, and therefore require their removal.

In addition, there is the problem of polishing the internal surfaces of complex shapes, parts for various purposes.

There is a known method of electrochemical mechanical polishing of internal surfaces of parts (AS USSR No. 1085734. IPC В23Р 1/04, Method of electrochemical mechanical processing. Publ .: 04/15/1984.), Where the removal of the allowance along the length of the inner channel is carried out due to the shock reciprocating action tool.

The disadvantage of this method is the low quality of the processing of the inner surface of the part, since mechanical force is used on the surface layer of the material of the part.

There is a known method of electrochemical treatment of the internal surfaces of parts (patent RU No. 2166416, IPC В23Н 5/06, publ .: Bull. No. 13, 2001), which uses a bipolar cathode-tool made of alternating abrasive and conductive bars on its forming part , while the cathode-tool is simultaneously imparted with rotation and vibration to ensure contact of the anode-part and cathode-tool.

There is also known a method of polishing the inner surfaces of channels (RF patent No. 2251472. IPC B23H 5/06, publ .: Bull. No. 13, 2005). The method includes moving along the processing axis of a rod with a tool electrode.

There is also known a method of anodic-abrasive polishing of the inner surfaces of parts (RF patent No. 2588953, IPC V23N 5/06, publ. Bull. No. 19, 2016), which includes moving the electrode-tool along the inner surface of the part along its axis when connecting the part to the anode, and the tool electrode to the cathode.

There is also known a method of polishing internal surfaces of complex shapes by hydroabrasive treatment (AS USSR No. 1315258 IPC В24В 31/116, publ. 1987), including surface treatment due to the movement of a liquid with an abrasive mass.

However, the above methods are either unsuitable (A.S. USSR No. 1085734, patent RU No. 2166416, patent RF No. 2588953) for removing defects in perforations on the blade, or they do not provide high quality and uniformity of their processing (A.S. . USSR No. 1315258).

However, the use in the known methods of polishing the internal surfaces of parts of mechanical action causes a deterioration in the quality parameters of the surface layer of materials, which leads to a decrease in its operational characteristics, especially in cases of processing such parts as turbine blades with a thin nib.

The most promising methods of processing parts of complex shape, in particular the blades of turbomachines are electrochemical methods of surface polishing [Grilikhes S.Ya. Electrochemical and Chemical Polishing: Theory and Practice. Influence on the properties of metals. L., Mashinostroenie, 1987], with the greatest interest for the area under consideration are methods of electrolytic-plasma polishing (EPP) parts [for example, Patent GDR (DD) No. 238074 (A1), IPC C25F 3/16, publ. 06.08.1986].

There is also known a method of polishing metal surfaces, including anodic treatment in an electrolyte [Patent RB No. 1132, IPC C25F 3/16, publ. 1996, BI No. 3], as well as a method of electrochemical polishing [US Patent No. 5028304, IPC B23H 3/08, C25F 3/16, C25F 5/00, publ. 07/02/1991].

However, the known methods of electropolishing do not allow high-quality polishing of the inner surfaces of parts, especially the inner surfaces of complex shapes.

The closest technical solution chosen as a prototype is the method ionic polishing the inner surface of the part, including placing the electrode and the electrically conductive medium in the inner cavity of the part, ensuring the contact of the electrically conductive medium with the electrode and the workpiece surface to be processed, supplying the opposite electric potential to the part and the conductive medium through the electrode introduced into the said medium [RF patent No. 2716330, IPCC25F 3/16.Method for machining perforations and the inner cavity of a turbomachine blade. Publ. Bul. No. 8, 2020]. The method involves the use of granules-anionites and an electrode-tool.

However, the known method [RF patent No. 2716330] does not allow for high-quality polishing of complex-shaped internal cavities.

However, the known prototype method [RF patent No. 2716330] has low reliability and cannot be used for polishing the inner surfaces of complex shapes with narrow sections, such as, for example, the inner cavities of the turbine blades of gas turbine engines (GTE), since the effects of shielding hard-to-reach areas the processed surface from the electrode inserted into the cavity, as well as the chaotic interaction of the surface with the granules, and the likelihood of adhesion of the granules to the treated surface, which leads to non-uniform surface treatment, and as a consequence to a decrease in the performance of the processed parts.

The problem to be solved by the claimed invention is to improve the quality and reliability of polishing the inner surface of parts, especially cavities of complex shapes, such as the inner cavities of turbine blades of gas turbine engines.

The technical result of the invention is to improve the quality and reliability of polishing the inner surface of parts, especially cavities of complex shapes, such as the inner cavities of GTE turbine blades by increasing the uniformity of its surface treatment, reducing the likelihood of defects and reducing its roughness.

The technical result is achieved due to the fact that in the method of ionic polishing of the inner surface of the part, including the placement of the electrode and the electrically conductive medium in the inner cavity of the part, ensuring the contact of the electrically conductive medium with the electrode and the treated surface of the part, supplying the opposite electric potential to the part and the conducting medium through the electrode introduced into the mentioned medium, in contrast to the prototype, uses a cord sheath made of anionite fibers impregnated with an electrolyte solution as an electrically conductive medium, which ensures the electrical conductivity of the said sheath and ion entrainment of metal from the inner surface of the part with the removal of microprotrusions from it; a flexible electrode located inside is used shell of the cord, place the said cord with the said electrode, threading the cord through the said cavity of the part, provide the movement of the said cord inside the cavity of the workpiece being processed, feed on the part l and on the mentioned electrode opposite in sign electrical potentials, providing ionic carryover of metal from the surface of the workpiece and its polishing to obtain a given roughness of the polished surface.

In addition, the following additional methods of performing the method are possible: threading the said cord through the said cavity of the part is carried out by fixing an element of magnetic material on the inserted end of the cord, inserting the said element into the cavity of the part being processed, applying a magnet (or electromagnet) to the outer surface of the part to the said element, and moving the magnet according to the configuration of the inner cavity of the part, inserting said cord into said cavity of the part and withdrawing from said element together with said end of said cord leaving said cord inside the cavity; as the material of the mentioned fibers of anion exchangers, ion-exchange resins are used, obtained on the basis of copolymerization of either polystyrene, or polyacrylate and divinylbenzene, and the cross-sectional dimensions of the fibers are selected from the range from 0.05 to 0.6 mm with their length exceeding 4 mm, and the processing by the mentioned the cord is carried out by supplying a positive electric potential to the part, and a negative electric potential from 12 to 35 V to the said cord, and the said cord and the part are additionally carried out in vibration movement with a frequency of 50-400 Hz, which ensures uniform interaction between the said cord and the workpiece surface to be processed; as the material of the said fibers of anion exchangers, ion-exchange resins are used, obtained on the basis of copolymerization of either polystyrene or polyacrylate and divinylbenzene, and the cross-sectional dimensions of the fibers are selected from the range from 0.05 to 0.6 mm with their length from 4 mm or more, and the processing the mentioned cord is carried out in a pulsed mode with a change in polarity, with a pulse frequency range from 20 to 250 Hz, a pulse period from 4.3 to 72 μs, with a positive polarity current amplitude during a pulse from + 20 to 120 A and its duration 0.2 up to 1.4 μs, with a current amplitude of negative polarity during a pulse from 25 to 40% of the used current amplitude of positive polarity, and its duration 0.1 to 0.6 μs, with a rectangular or trapezoidal shape of output current pulses and the duration of pauses between pulses from 4 to 70 μs; a hollow blade of a turbomachine made of titanium alloy is used as a part, and one of the following aqueous solutions is used as electrolytes for impregnating said cord: or an aqueous solution of a mixture of NH ₄ F and KF with NH ₄ F content - from 8 to 14 g / l and KF - from 36 to 48 g / l, or an aqueous solution containing 30 - 50 g / l KF 2H ₂ O and 2 - 5 g / l CrO ₃ ; a hollow turbomachine blade made of nickel alloy is used as a part, and one of the following aqueous solutions is used as electrolytes for impregnating said cord: an aqueous solution of ammonium fluoride salt with a concentration of 6.0-9.0 g / l, or an aqueous solution of ammonium sulfate with a concentration of 0.8-3.4 g / l or an aqueous solution containing sulfuric and orthophosphoric acids, a block copolymer of ethylene and propylene oxides and the sodium salt of sulfonated butyl oleate in the following ratio, wt. %:

Sulphuric acid 10-30 Orthophosphoric acid 40-80 Block copolymer of ethylene and propylene oxides 0.05-1.1 Sulfonated butyl oleate sodium salt 0.01-0.05 Water rest

The inventive method for ionic polishing of the inner surface of a part, in particular the inner surface of a turbine blade of a gas turbine engine, during its manufacture is carried out as follows.

The essence of the invention is illustrated by drawings. FIG. 1 shows the process of threading a part of an anionite cord through the inner cavities to be processed. Figure 2 shows the options for threading through the processed internal cavities of the part of the cord made of anionites. Figures 1 and 2 contain: 1 - workpiece; 2 - cavities; 3 - element made of magnetic material; 4 - a cord of impregnated anion-resin fibers (arrows indicate the direction of the cord movement).

Part 1 is fixed on the holder (Fig. 1 and Fig. 2) and a cord 4 with an internal electrode is threaded through the inner cavity 2 of part 1. Threading the cord can be carried out in any of the known ways, for example, by threading a flexible cable attached to the cord, followed by pulling through the cavities 2 of the part 1 of the cord 4. The figures (Fig. 1) show a variant of threading the cord 4 through the cavities 2 by means of an element 3 made of magnetic material ... In this case, the element 3 is introduced into the opening of the cavity 2, then using a magnet (or electromagnet) moving relative to the outer surface of the part 1 in accordance with the configuration of the cavity 2, which, by acting on the element 3 with a magnetic field, passes the cord 4 into the inner cavity 2 of the part 1. Part 1 with a threaded cord 4 is placed in the working chamber of the polishing installation (not shown) and the cord 4 is continuously moved in cavity 2 (Fig. 1 and Fig. 2) (for example, by rewinding it from one reel to another). At the same time, in the cord 4, the braid of which is made of anion-resin fibers, the required level of electrolyte content is maintained. To intensify the process, the cord 4 can be additionally set in vibration. On the workpiece 1 and located inside the cord 4, along its entire length, the flexible electrode is supplied with an electric potential between the workpiece 1 and the flexible electrode, and the inner surface of the workpiece 1 is polished until a given roughness is obtained. After finishing the processing, the finished part 1 is taken out and put into a container for storage. In this case, depending on the configuration of the cavities of the part 1, you can use different options for threading the cord 4 (figure 2).

Electropolishing of part 1 (Fig. 1) is carried out by means of electrochemical processes (ionic entrainment of material of part 1) between part 1 and a flexible electrode through the braid of the cord 4, made of anionite fibers impregnated with an electrolyte solution, which ensures the electrical conductivity of the cord 4 and ionic entrainment of metal from the surface internal cavities of part 1 with the removal of microprotrusions from it.

An electric potential is supplied to the part 1 and the electrode of the cord 4, which ensures the ionic entrainment of metal from the surface of the cavities of the part 1 and its polishing until a given roughness of the polished surface is obtained.

Ion exchange resins obtained on the basis of copolymerization of either polystyrene or polyacrylate and divinylbenzene are used as anion resin fibers for cord 4. The cross-sectional dimensions of the fibers are selected from the range from 0.05 to 0.6 mm with a length of 4 mm or more.

Electropolishing with cord 4 is carried out either by applying a positive electric potential to part 1 and a negative electric potential to the flexible electrode of cord 4, ranging from 12 to 35 V, or in a pulse mode with a polarity change, with a pulse frequency range of 20 to 100 Hz, a pulse period of 50 μs to 10 μs, with a current amplitude of positive polarity during a pulse of +50 A and their duration of 0.4 to 0.8 μs, with a current amplitude of negative polarity during a pulse of 20 A, and their duration of 0.2 to 0.4 μs, with a rectangular shape of the output current pulses and the pause duration between pulses from 49.6 μs to 9.2 μs.

When polishing the cavities of a turbomachine blade made of a titanium alloy, one of the following aqueous solutions is used as electrolytes for impregnating the sheath of the anion exchange resin: or an aqueous solution of NH ₄ F and KF with NH ₄ F content - from 8 to 14 g / l and KF - from 36 to 48 g / l, or an aqueous solution containing 30 - 50 g / l KF 2H ₂ O and 2 - 5 g / l CrO ₃ .

When polishing the cavities of a turbomachine blade made of nickel alloy, one of the following aqueous solutions is used as an electrolyte for impregnating the sheath of the cord made of anionites: an aqueous solution of ammonium fluoride salt with a concentration of 6.0 - 9.0 g / l, or an aqueous solution of ammonium sulfate with a concentration 0.8-3.4 g / l or an aqueous solution containing sulfuric and orthophosphoric acids, a block copolymer of ethylene and propylene oxides and the sodium salt of sulfonated butyl oleate in the following ratio, wt. %:

Sulphuric acid 10-30 Orthophosphoric acid 40-80 Block copolymer of ethylene and propylene oxides 0.05-1.1 Sulfonated butyl oleate sodium salt 0.01-0.05 Water rest

The polishing process is carried out until a given value of the surface roughness of the cavities of part 1 is obtained.

The forced movement of the cord 4 through the cavities and its vibration make it possible to ensure uniform treatment of the entire cavity surface of the part 1 and thereby increase the quality and uniformity of its properties.

The use of granules, as is done in the prototype [RF patent No. 2716330], either leads to the formation of point defects caused by adhesion of granules to the treated surface of the part, or, when processing cavities of complex shape, does not allow its polishing.

When implementing the method, the following processes occur. When the cord 4 moves in the cavity 2, its simultaneous contact with the processed surface of the part 1 and the flexible electrode located in the cord core occurs, thereby creating uniform conditions for the course of electrochemical processes. In this case, electrochemical processes (ionic entrainment of material from the treated surface) between the part (anode) and the cord with an internal flexible electrode (cathode) occur due to the contact of the anionite fibers of the cord 4. When cord 4 comes into contact with microprotrusions on the treated surface of part 1, ionic entrainment occurs masses from microprotrusions, as a result of which the surface is leveled, its roughness decreases and the surface is polished.

The following studies were also carried out on polishing the internal cavities of parts (blades of turbomachines) made of nickel and titanium alloys. An unsatisfactory result (NR) was considered a result in which no polishing effect was observed on the polished surface. In the absence of defects on the surface of the part, the result was recognized as satisfactory (U.R.)

In all cases, the following modes of processing parts turned out to be universal.

Cord made of anionite fibers with dimensions

- the cross-section of fibers (0.03 mm (N.R.), 0.05 mm (U.R.), 0.1 mm (U.R.), 0.2 mm (U.R.), 0 , 4 mm (U.R.), 0.6 mm (U.R.), 0.8 mm (N.R.));

- fiber length more than 4 mm, (3 mm (N.R.), 5 mm (U.R.), 50 mm (U.R.), 150 mm (U.R.), 500 mm (U.R.) .), 1000 mm (U.R.), 5000 mm (U.R.); more than 5000 mm (U.R.).

The used anion exchangers are ion exchange resins obtained on the basis of copolymerization of either polystyrene or polyacrylate and divinylbenzene. Grades used in the proposed invention of anion exchangers based on synthetic resins: Anionite 17-8ChS, Anionite Purolite A520E, Lewatit S 6328 A (based on styrene-divinylbenzene copolymer), Lewatit M500, Lewatit MonoPlus MK 51, Lewatit MP 68 ”, Purolite C150E, Purolite A-860 (macroporous strong base anion exchange resin based on acrylates), sulfonated styrene-divinylbenzene copolymer anionite. The listed anion exchangers impregnated with the above electrolyte compositions showed a positive result when polishing the inner cavities of the blades made of nickel and titanium alloys.

In pulse mode with polarity reversal:

- pulse frequency range from 20 to 100 Hz: 15Hz (N.R.), 20Hz (U.R.), 40Hz (U.R.), 60Hz (U.R.), 80Hz (U.R.), 100Hz (N.O.), 120Hz (N.O.)

- pulse period from 50 μs to 10 μs: 60 μs (N.R.), 50 μs (U.R.), 40 μs (U.R.), 30 μs (U.R.), 20 μs ( U.R.), 10 μs (W.R.), 5 μs (N.R.);

- current amplitude of positive polarity during a pulse of +50 A and their duration 0.4 μs to 0.8 μs: 0.2 μs (N.R.), 0.4 μs (U.R.), 0.6 μs (U.R.), 0.8 μs (W.R.), 10.0 μs (N.R.);

- with a current amplitude of negative polarity during the pulse - 20 A, and their duration is 0.2 μs to 0.4 μs, 0.1 μs (N.R.), 0.2 μs (U.R.), 0, 3 μs (W.R.), 0.4 μs (W.R.), 0.5 μs (N.R.);

- with a rectangular shape of the output current pulses (U.R.),

- and the duration of pauses between pulses from 49.6 μs to 9.2 μs - (U.R.) out of range - (N.R.).

In the mode without polarity change: electropolishing was carried out by applying a positive electric potential to the part, and a negative electric potential from 12 to 35 V to the cord (inner electrode of the cord): 8 V (N.R.), 12 V (U.R.), 20 V (U.R.), 30 V (U.R.), 35 V (U.R.), 45 V (N.R.),

The first group: parts (samples and blades) made of titanium alloys of grades VT9, VT-1, VT3-1, VT8. The blades were treated with a cord with a sheath of anionite fibers impregnated with an electrolyte of the composition: an aqueous solution of a mixture of NH ₄ F and KF with NH ₄ F content from 8 to 14 g / l and KF from 36 to 48 g / l and polishing was carried out at a current density of 1.2 to 1.8 A / cm ² until the minimum possible surface roughness was achieved.

Processing conditions for the proposed method.

Electrolyte composition: aqueous solution of NH ₄ F mixture and KF with NH ₄ F content (6 g / L - N.R., 8 g / L - U.R., 10 g / L - U.R., 12 g / L - U.R., 14 g / l - U.R., more than 14 g / l - N.R.) and KF (32 g / l - N.R., 36 g / l - U.R., 42 g / l - U.R. , 45 g / l - U.R., 48 g / l - U.R., 52 g / l - N.R.)

The second group: parts (samples and blades) from nickel alloys of grades ZhS6U, ZhS32. The blades were treated with a cord with a sheath of anionic resin fibers impregnated with an electrolyte and polished at a current density of 1.5 to 2.1 A / cm ² until the minimum possible surface roughness was achieved.

Processing conditions for the proposed method.

Anionite fiber cord impregnated with an electrolyte composition: an aqueous solution of ammonium fluoride salt with a concentration of 6.0 - 9.0 g / liter (5.0 g / liter (N.R.), 6.0 g / liter (U.R .), 7.0 g / liter (U.R.), 8.0 g / liter (U.R.), 10.0 g / liter (U.R.), 12.0 g / liter (H .R.)) And at a current density of 1.5 to 2.1 A / cm ² (1.3 A / cm ² (N.R.), 1.5 A / cm ² (U.R.), 1 , 6 A / cm ² (U.R.), 1.9 A / cm ² (U.R.), 2.1 A / cm ² (U.R.), 2.3 A / cm ² (H .R.)).

Compared with the known polishing method [RF patent No. 2716330], when processing parts with complex internal cavities from nickel and titanium alloys according to the proposed method, the formation of defects in the form of unpolished surface areas was practically not observed, while during processing according to the known polishing method [RF patent No. 2716330] the formation of defects in the form of local untreated areas and point defects (as a result of adhesion and soldering of granules) occurred. On average, when processing according to the prototype method [RF patent No. 2716330], about 66% of cases of defects were observed, from the number of all processed parts (nickel alloys - 59%, titanium alloys - 74%). At the same time, a number of internal cavities of the blades made of nickel alloys could not be processed using the prototype method [RF patent No. 2716330].

Thus, the proposed method of ionic polishing of the inner surface of a part made it possible to achieve the technical result set in the invention - an increase in the quality and reliability of polishing the inner surface of parts, especially cavities of complex shapes, such as the internal cavities of GTE turbine blades by increasing the uniformity of its surface treatment, reducing the likelihood of occurrence defects and a decrease in its roughness.

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Claims (7)

1. A method of ionic polishing of the inner surface of a part, including placing an electrode and an electrically conductive medium in the inner cavity of a part, ensuring contact of an electrically conductive medium with an electrode and a workpiece surface to be treated, supplying an opposite electric potential to the part and a conductive medium through an electrode introduced into said medium, which is different the fact that the conductive medium is a cord sheath made of anionite fibers impregnated with an electrolyte solution, which ensures the electrical conductivity of the said sheath and ionic entrainment of metal from the inner surface of the part with the removal of microprotrusions from it, a flexible electrode located inside the cord sheath is used, the said cord is placed with the said electrode, threading the cord through the said cavity of the part, provide the movement of the said cord inside the cavity of the workpiece being processed, serve on the part and on the said electrode opposite in sign e electrical potentials that provide ionic removal of metal from the surface of the workpiece and its polishing to obtain a given roughness of the polished surface. 2. The method according to claim 1, characterized in that the threading of said cord through said cavity of the part is carried out by fixing an element of magnetic material at the inserted end of the cord, inserting said element into the cavity of the part to be processed, applying a magnet to the outer surface of the part to said element (or electromagnet) and, moving the magnet according to the configuration of the internal cavity of the part, the said cord is inserted into the said cavity of the part and the said element is withdrawn together with the said end of the said cord, leaving the said cord inside the cavity. 3. The method according to claim 1, characterized in that as the material of said fibers of anion exchangers, ion-exchange resins obtained on the basis of copolymerization of either polystyrene or polyacrylate and divinylbenzene are used, and the cross-sectional dimensions of the fibers are selected from the range from 0.05 to 0, 6 mm with a length of more than 4 mm, and the processing with the mentioned cord is carried out by supplying a positive electric potential to the part, and a negative electric potential from 12 to 35 V to the said cord, and the mentioned cord and the part are additionally set in vibration motion with a frequency of 50-400 Hz, providing uniform interaction between the said cord and the workpiece surface to be processed. 4. The method according to claim 1, characterized in that as the material of said fibers of anion exchangers, ion-exchange resins obtained on the basis of copolymerization of either polystyrene or polyacrylate and divinylbenzene are used, and the cross-sectional dimensions of the fibers are selected from the range from 0.05 to 0.6 mm with their length from 4 mm to 45 mm, and processing with the mentioned cord is carried out in a pulsed mode with a change in polarity, with a pulse frequency range from 20 to 250 Hz, a pulse period from 4.3 to 72 μs, with a current amplitude of positive polarity during a pulse from + 20 to 120 A and its duration 0.2 to 1.4 μs, with a current amplitude of negative polarity during a pulse from 25 to 40% of the used current amplitude of positive polarity and its duration 0.1 to 0.6 μs, with a rectangular or trapezoidal shape of output current pulses and a pause duration between pulses from 4 to 70 μs. 5. The method according to any one of claims. 1-4, characterized in that a hollow blade of a turbomachine made of titanium alloy is used as a part, and one of the following aqueous solutions is used as an electrolyte for impregnating said cord sheath: an aqueous solution of a mixture of NH ₄ F and KF with NH ₄ F content from 8 to 14 g / l and KF from 36 to 48 g / l or an aqueous solution containing 30-50 g / l KF · 2H ₂ O and 2-5 g / l CrO ₃ . 6. The method according to any one of claims. 1-4, characterized in that a hollow blade of a turbomachine made of a nickel alloy is used as a part, and one of the following aqueous solutions is used as an electrolyte for impregnating said cord sheath: an aqueous solution of ammonium fluoride salt with a concentration of 6.0-9, 0 g / l, or an aqueous solution of ammonium sulfate with a concentration of 0.8-3.4 g / l, or an aqueous solution containing sulfuric and orthophosphoric acids, a block copolymer of ethylene and propylene oxides and sodium salt of sulfonated butyl oleate in the following ratio of components, wt. %: sulphuric acid 10-30 orthophosphoric acid 40-80 block copolymer of ethylene and propylene oxides 0.05-1.1 sodium salt of sulfonated butyl oleate 0.01-0.05 water rest

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