RU2701909C1 - Pulse-cyclic electrochemical processing method - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to electrochemical methods of dimensional processing of metals and alloys and can be used for high-efficiency processing of hard-to-process metals and alloys with provision of modes of elimination of short circuits. Pulse-cyclic electrochemical treatment method involves treatment of part in electrolyte solution by voltage pulses, duration of which is longer than charging time of double electric layer, but shorter than short-circuit development time: t< t< t, where tis dual electric layer charging time; tis duration of voltage pulse; tis short circuit development time in electrolyte.EFFECT: invention provides higher reliability of pulse-cyclic electrochemical processing.1 cl, 1 tbl

Description

The invention relates to electrochemical methods of dimensional processing of materials, carried out in a pulsed mode, can be used for highly efficient processing of machine parts, devices, mechanisms from hard-to-machine engineering materials (metals and alloys) in general engineering, instrumentation, microprocessing with a radical increase in process reliability due to a decrease in probability short circuits.

Known methods of dimensional electrochemical processing of metals and alloys (Davydov A.D., Kozak E. High-speed electrochemical shaping. M: Nauka. 1990 - 272 p.). This book describes the theory, methods, physical foundations, modes of electrochemical processing, including in pulsed mode. Data on the processes of processing disturbance as a result of short circuits are given.

Electrochemical processing is carried out as a result of anodic dissolution of the workpiece material in neutral aqueous solutions of salts (electrolytes) with the application of an external polarizing voltage. The method is unique, as it is carried out without wear of the electrode-tool, and provides high surface quality of parts from difficult materials (stainless steels, viscous alloys, etc.).

The most significant disadvantage of this method is the high probability of short circuits between the electrode-tool (cathode) and the workpiece (anode). The phenomenon of short circuit causes radical destruction of the electrode-tool and the workpiece. As a result of enormous short-circuit currents (up to several thousand amperes), there is a thermal violation of the geometry of the electrode-tool, a “stick” on the surface of the workpiece, which makes it impossible to use them further. This problem is especially relevant when switching to electrochemical processing at small interelectrode gaps (MEZs) and increasing the current density to hundreds of amperes per cm ² . A further decrease in the MEZ during microelectrochemical treatment led to an increase in the current density to 1000-2000 A / cm ² .

Among the known methods for eliminating short circuits, the following can be distinguished:

1. The transition from the implementation of ECHO in continuous mode to cyclic mode (scheme II Baenko).

2. The use of pulsed currents (Altynbaev AK).

3. The use of pulse-cyclic processing schemes (Sedykin F.V.)

4. The use of short circuit protection systems (Gepshtein B.C., Nemilov EF, Strukov KV and others).

5. The use of vibration of the electrodes (Morozov B.I.)

6. The use of electrolyte purification systems.

All methods used are a posteriori, since they function upon the occurrence and development of a short circuit. The response time of systems based on the above methods is longer than the initiation time of a short circuit.

There is a method of electrochemical processing in which the reduction in the probability of short circuits is achieved by combining complex kinematic movements and controlling them to eliminate the instability of the AIDS system (Patent RU 2330746 Method for dimensional electrochemical processing of metals B23H 3/00 10/08/2008). The process is carried out in an electrolyte solution by voltage pulses when using the cyclic mode and oscillations of the electrode-tool.

The disadvantage of this method is:

1) lack of reliability of the method due to the complex structural-kinematic scheme of the method, including vibration of the electrode, periodic "feeling" of its anodically dissolving surface;

2) lack of information on the conditions for the development of short circuits. The objective of the proposed processing method is to increase the reliability of the process due to the radical elimination of short circuits during electrochemical processing when choosing the conditions for energy supply, preventing the occurrence of a short circuit (voltage pulse duration).

The proposed method of electrochemical processing is carried out using voltage pulse durations shorter than the short circuit development time.

The most effective way to increase the reliability of the process of electrochemical processing is to reduce the duration of voltage pulses (t _imp ). However, at t _imp >> t _rkz . it is impossible to completely eliminate short circuits, where t _rkz is the time for the development of a short circuit in the working medium (electrolyte) (breakdown delay time).

To exclude short circuits in the proposed method, the condition

where t _zar is the charging time of the double electric layer.

To implement the method produced:

1) calculation of the minimum allowable voltage pulse duration based on the calculation of the charging time of the double electric layer.

The charging time of a double electric layer can be estimated as

where C is the specific capacity of the double electric layer, f / m ² ; U is the overvoltage in the double electric layer, V; J is the current density, A / m ² .

From theoretical electrochemistry it is known that for traditional conditions of dimensional electrochemical processing

C = 0.2 F / m ² ; U = (0.2 - 0.8) V; J = 10-2000 A / cm ² .

For the indicated conditions for the implementation of the process of electrochemical processing, dependence (2) calculated the range of the minimum values of the duration of the voltage pulse (see table).

Thus, t _imp ^min should be in the range of 2-160 ns. Recently, the implementation of such voltage pulse durations has become feasible in connection with the creation of a new electronic technology that provides the formation of powerful voltage pulses of a given duration.

2) selection of the maximum voltage pulse duration.

To eliminate short circuits, the condition

_imp t <t _RHCs.

From the works of Ushakov V.Ya. and Nugolnykh K.A. (Ushakov V.Ya. Pulse electric breakdown of liquids. Tomsk, TSU publishing house, 1975. 258 s .; Nugolnykh K.A., Roy N.A. Electric discharges in water., M .: Nauka, 1971, 155 s. .). It is known that during the breakdown of liquids in the thermal mode, there is a breakdown delay, depending on the specific heat, electrical conductivity of the liquid, and electric field strength. Estimated breakdown delay time can be calculated by the formula:

where c is the heat capacity of the liquid; γ ₀ - conductivity of the solution; E-electric field strength; and - coefficient.

This time corresponds to the time of occurrence of the so-called “white noise” (precursor to a short circuit).

Experimental estimates in the above studies give t _rkz <30 μs.

Thus, t _imp ^max <30 μs.

3) the implementation of the processing process with the duration of the voltage pulses in the selected range.

The proposed method of pulse-cyclic electrochemical processing was experimentally tested under the following conditions:

The interelectrode gap is 5-20 microns.

Pulse duration: t _imp1 = 1.0 μs; t _imp2 = 100 μs.

Voltage - 12 V.

The type of electrolyte is an aqueous solution of 10% NaNO ₃ .

The workpiece material is 1X18H9T stainless steel.

Material of the electrode-tool: brass L61.

The diameter of the tool electrode is 5.0 mm.

The initial temperature of the electrolyte is 23 ° C.

The coefficient of voltage pulses is 20, 40, 60%.

The experiment was carried out in two stages:

1) for the duration t _imp1 <t _pkz ;

2) for the duration t _imp2 > t _pkz .

It was found that when using pulses with a duration of 1.0 μs, no short circuits were observed, and when using pulses of a duration of 100.0 μs, traces of thermal effects were detected on the surfaces of both electrodes in the form of holes with a diameter of about 2 millimeters and a depth of about 0.2 mm.

Claims (3)

A method of pulse-cyclic electrochemical treatment of a part, comprising treating the part in an electrolyte solution with voltage pulses, characterized in that the processing is carried out by voltage pulses, the duration of which is longer than the charging time of the double electric layer and less than the development time of a short circuit: t _zar <t _imp <t _rkz , where t _zar is the charging time of the double electric layer; t _imp - voltage pulse duration; t _rkz - time of development of a short circuit in the electrolyte.