RU2451773C2 - Method for metal and alloy electrochemical polishing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electrochemical metal and alloy process and can be used in mechanical and instrument engineering, for instance, for finishing internal and external surfaces. According to the method electrochemical polishing is applied to metal and alloys in neutral aqueous saline solution at current density 0.2-10 A/cm², electrolyte temperature equal to ambient temperature, with operating detail vibrating, wherein electrochemical polishing is applied in cycles. One polishing cycle time is set to be no more than 2 sec, time between cycles is to be calculated, after each subsequent cycle surface roughness is calculated according to the following formula:

where

- roughness of the following cycle, mcm,

- roughness of the preceding cycle, mcm, n - cycle sequence number, k_v - volume electrochemical equivalent of the processed metal, cm³/A·min, χ - electrolyte specific conductivity, cm·^-1Ohm^-1 , η - current efficiency of the processed metal, U - electrode voltage, V, ΔU - voltage drop in electrolytic layers equal to algebraic sum of voltage drops in a cathode layer and an anode layer, V, δ_IEG - interelectrode gap, cm, τ - time of electrochemical polishing cycle, min.

EFFECT: invention may improve quality of electrochemical polishing by detecting surface roughness after each polishing cycle and enable obtaining machined surface without defects such as haze, pitting, etc.

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Description

The invention relates to the field of electrochemical processing of metals, in particular to the electrochemical polishing of metals and alloys, can be used in machine and instrument engineering, for example, for finishing internal and external surfaces.

Known methods of electrochemical polishing, which are anodic dissolution, leading to improved microgeometry of the treated surface [Application No. 49-38418, Japan MKI S23B 3/00, NKI-12A63]. Electrochemical polishing is carried out both in stationary and in a moving electrolyte [Lipkin Y.N., Bershadskaya T.L. Chemical polishing of metals. - M.: Mechanical Engineering, 1982. - 112 p.].

The disadvantage of existing methods is the toxicity of the electrolyte, low productivity.

The prototype adopted the method of electrochemical polishing [RU 2146580, B23 / H 3/00], carried out 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 reported to vibrate , 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:

where l is the shortest distance from the bottom of the bath to the workpiece surface; ν is the rate of rise of hydrogen bubbles, determined by the Stokes formula.

In the first two seconds of electrochemical polishing, the current distribution over the treated surface is determined by its microgeometry. The real surface is a combination of protrusions and depressions. According to calculations, the current density on the protrusions is 5-7 times higher than the current density in the depressions, which contributes to the intensive dissolution of the protrusions (surface smoothing).

The disadvantages of the method include the fact that after the first two seconds of treatment, due to the density difference of the anode layer of the electrolyte, convective diffusion begins, as a result of which the macroscopic distribution of the current density is disturbed and defects appear on the surface in the form of haze, pitting, etc.

The objective of the invention is improving the quality of processing and expanding technological capabilities.

The problem is achieved in that in the known method of electrochemical polishing carried out in a neutral aqueous solution of salts at a current density of 0.2 ... 10 A / cm ² , the electrolyte temperature equal to the ambient temperature, the workpiece is informed of vibration, the amplitude and frequency of which is set based of the electrochemical properties of the material of the workpiece, according to the invention, electrochemical polishing is carried out in cycles, while the cycle time is set to no more than 2 s, and the time between cycles is calculated according to rmule:

where z is the ion charge;

F is the Faraday number, C · mol ^-1 ;

i is the current density of the anodic dissolution, A / cm ² ;

D is the diffusion coefficient of the ions of the treated metal, cm ² / s;

C _S is the concentration of ions on the surface of the polished part, mol / cm ³ ,

moreover, the surface roughness after each subsequent cycle is determined from the ratio:

- шероховатость поверхности последующего цикла, мкм;Where

- surface roughness of the subsequent cycle, microns;

- шероховатость поверхности предыдущего цикла, мкм;

- surface roughness of the previous cycle, microns;

n is the sequence number of the cycle;

k _ν - volumetric electrochemical equivalent of the treated metal, cm ³ / A · min;

χ is the specific conductivity of the electrolyte, cm ^-1 · Ohm ^-1 ;

η is the metal current output;

U is the voltage at the electrodes, V;

ΔU is the voltage drop in the near-electrode layers, equal to the algebraic sum of the voltage drops in the near-cathode and anode layers, V;

δ _MEZ - the value of the interelectrode gap, cm;

τ is the cycle time of electrochemical polishing, min.

The method of electrochemical polishing is illustrated in the drawing.

In FIG. depicts a diagram of an installation that implements the inventive method of polishing metals and alloys.

The installation is a bath 1 electropolishing, which is filled with an aqueous solution of 2 sodium chloride. Part 3 is installed at a distance δ of the _MEZ from the side surfaces of the bath, connected by the rod 4 to the vibration source 5. The rod 4 is connected to the positive pole of the power source 6, and the bath 1 to the negative pole.

During electrochemical polishing, parts 3 report vibration from source 5 with frequency f, amplitude A and supply voltage from power source 6. The polishing process is carried out cyclically, the duration of one polishing cycle does not exceed 2 s. The time between cycles is calculated by the formula (1), to calculate C _S use the known dependence [Scorcheletti V.V. Theoretical electrochemistry. - M .: Chemistry, 1969. - 608 p.]:

Concrete example

Processing samples were made of steel 12X13. Initial surface roughness R _z 4.3 μm; volume electrochemical equivalent of steel 12X13 k _ν = 2.1 · 10 ^-3 cm ³ / A · min; specific electrolyte conductivity (15% NaCl in water) χ = 0.17 cm ^-1 · Ohm ^-1 ; current output of the treated metal η = 0.8; voltage at the electrodes U = 8B; voltage drop in the electrode layers ΔU = 2.3V; current density in the workpiece i = 1 A / cm ² ; vibration frequency of the anode (workpiece) f = 50 Hz; vibration amplitude A = 0.5 mm; the time of one cycle is set equal to 1 s. The concentration of iron ions at the surface of the workpiece defined by the formula (3), C _S = 0,48 mol / cm ³ and a calculated time between cycles by the formula (1), was obtained _mfi ≥1,45 τ seconds.

At an interelectrode distance of δ _MEZ = 4 cm, using dependence (2), which takes into account the electrochemical properties of the processed material and polishing parameters, after the first polishing cycle, the calculated surface roughness parameter was determined

The measured value of the surface roughness parameter

The second cycle of electrochemical polishing lasting 1 s was carried out after a pause of 1.45 s. After the second cycle of electrochemical polishing, the calculated value of the surface roughness parameter

The measured value is

.After the third cycle, the results are as follows:

.

After the fourth cycle -

After the fifth cycle -

After the sixth cycle -

Final surface roughness R _z = 2.3 μm.

Deviations of the calculated values of the surface roughness from the measured are not more than 15%.

The surface roughness in the proposed method does not depend on the shortest distance to the bottom of the bath, but is determined by the interelectrode distance δ of the _MEZ , i.e. the distance between the polished surface (anode) and the cathode (side surface of the bath). The distance between the bottom of the bath and the workpiece in the proposed method can be any that extends the technological capabilities of the method.

Using the dependence of the surface roughness after each polishing cycle on the electrochemical properties of the processed material and processing parameters allows us to analytically evaluate the surface roughness without conducting experiments, thereby simplifying the use of the method in electrochemical polishing technologies.

Claims (1)

The method of electrochemical polishing of metals and alloys in a neutral aqueous solution of salts at a current density of 0.2-10 A / cm ² , an electrolyte temperature equal to the ambient temperature, vibration of the workpiece with an amplitude and frequency specified based on the electrochemical properties of the material, characterized in that electrochemical polishing is carried out in cycles, while the time of one polishing cycle is set to no more than 2 s, and the time between cycles is calculated by the formula:

,
where z is the charge of the potential-determining ion,
F is the Faraday number, C · mol ^-1 ,
i is the current density of the anodic dissolution, A / cm ² ,
D is the diffusion coefficient of the ions of the treated metal, cm ² / s,
C _S is the concentration of ions on the surface of the polished part, mol / cm ³ ,
moreover, the surface roughness after each subsequent cycle is determined from the dependence:

Where

- roughness of the subsequent cycle, microns,

- roughness of the previous cycle, microns,
n is the sequence number of the cycle,
k _ν - volumetric electrochemical equivalent of the treated metal, cm ³ / A · min,
χ is the specific conductivity of the electrolyte, cm ^-1 · Ohm ^-1 ,
η - current output of the treated metal,
U is the voltage at the electrodes, V,
ΔU is the voltage drop in the near-electrode layers, equal to the algebraic sum of the voltage drops in the near-cathode and anode layers, V,
δ _MEZ - the value of the interelectrode gap, cm,
τ is the cycle time of electrochemical polishing, min.

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