RU1820921C - Method for electrolytic iron plating in chlorine electrolytes - Google Patents

Abstract

SUMMARY OF THE INVENTION: electrolysis is carried out in two stages: at the first stage, at an alternating current of industrial frequency with a subsequent decrease in the reverse current, at the second stage, after a decrease in the reverse current, at the first stage, the process is conducted with a continuous increase in the reverse current density from (5.5--6, 5) up to „(9 - 20.5) A / dm2 with speed

Description

The invention relates to the field of deposition of metal coatings by electrolytic method, in particular to the field of electrolytic deposition of iron coatings, and can be used in galvanic shops of repair enterprises .-.,:. . .

An object of the invention is to increase the uniformity of the coating, improve its working life and reduce dendriticity during application. ..; . .. v -. ; .

This goal is achieved in that electrolytic ironing in chloride electrolytes is carried out on an asymmetric alternating current of industrial frequency, followed by a decrease in the reverse current in the initial stage and hereinafter

(after the initial period) a continuous uniform increase in the density of the reverse current from the value (5.5 - 6.5) to (d - 20.5) A / dm2 with a speed of (0.4-28) A / dm, h, while the value cathode current is different (54 -64) A / dm2.

In the future, it is possible to increase the uniformity of the distribution of the iron coating due to the fact that due to the increase in the return tick to (9-20.5) A / dm2, the polarizability of the electrode during the reverse period decreases (1.5-1.8) times.

The method allows (1.5 - 2) times to improve the running-in of the coating, to reduce the running-in wear, since the surface layers of the coating have lower values of microhardness on the surface

(N / VB 4500 - 4700 MPa) and a dislo density of N 0 O hO

Oj

cations than in the rest of the coating (N, mv | # 6100 - 6200 MPa). As a result, under conditions of boundary friction, a plasticized less hard metal layer is formed in which localization of shear strain occurs and which facilitates running-in. The indicated necessary properties of the surface layer are achieved by gradually increasing the reverse current to (9 - 20.5} A / dm2 towards the end of electrolysis. With an increase in the reverse current, sludge forms with softer dislocations.

A decrease in (2–3) times the dendrito mass on the coating occurs as a result of an increase in the reverse current. Dendrites occur due to the development of crystalline roughness and in the places of cracking of the coating. In turn, cracks arise with an increase in internal stresses, and dendritic formation increases with increasing roughness and internal stresses. Dendritic formation increases with increasing coating thickness during electrolysis. The reverse current, in order to suppress the buildup of roughness and internal stresses, should increase during the coating process in the process of increasing its thickness. The proposed method allows this to be done up to 0 br. 20.5 A / dm2.

The lower limit of the rate of increase in density (reverse current sample 0.4 A / dm2 h is due to the fact that at a rate less than 0.4 A / dm2 h, the value of 0br increases for a long time and does not reach values at which the coatings are very uniform, microhardness and density of surface dislocations the coating layer is larger and the performance is poor.

The upper limit of the rate of increase in the reverse current density is 28 A / dm2 h, based on the fact that, at a higher speed, the uniformity of precipitation will deteriorate sharply. Initial wear also increases during running-in of the coating. Intermediate (between 0.4 and 28 A / dm2 h) values of the rate of increase in the reverse current density ensure a smooth achievement of the necessary (optimal from the point of view of increasing the uniformity of the coating, improving its run-in ™ and reducing dendrite formation) 10br. when applying iron coatings of various thicknesses (practically from 0.1 to 1.5 mm), i.e. at various durations of the electrolysis process.

The cathodic component of the deposition current during the coating process remains unchanged in the range of (54 - 64) A / dm2. At 1 Ex. 54 A / dm2 reduction occurs

the productivity of the ironing process and cathodic polarization, as a result of which the structure of the precipitate will be coarser crystalline, which will affect the hardness and wear resistance of the coating. At 1 Ex. 64

A / dm, noticeable dendriticity is observed, burning of parts, coating quality deteriorates.

The permissible range of reverse current density values at the initial moment of the main mode is (5.5-6.5) A / dm2. The lower boundary of the interval is due to the fact that with 1 arr. less than 5.5 A / dm2, the uniformity of sediment distribution is impaired. In case 10br. at the initial moment

the main mode will be more than 6.5 A / dm2, taking into account the stated rate of increase of 1 sample. (0.4 - 28) A / dm2 h towards the end of the process polarizability Pobr. will go beyond the value (Pobr. 20.5 A / dm2) and thereby the condition will be violated: Pobr. Ppr

The uniformity of the distribution of the coating was evaluated under production conditions by the method of a rod cathode, which had seven rods of different lengths: depth

the first recess was 10%, the last 100%. The metal distribution was judged by the thickness D of the sediment at the ends of the rods. The dependence of the dot number of the rod No. is more flat, indicating a better distribution of the coating. Figure 1 shows graphs of the distribution of sediment at the ends of the rods during deposition in a known manner and according to the invention. For a quantitative criterion of the actual uniformity of the distribution of the iron coating, the uniformity coefficient Cp is taken.

I / Dmin

 Cr 75ЈG where Dmin is the minimum coating thickness,

obtained at the most remote portion of the cathode: for our conditions - on the rod

Der - average thickness.

The microhardness of the coatings was measured on a PMT-3 device with a pyramid load of 0.1 kG. The same instrument was used to measure the thickness of the sediment on the end sections.

The value of the initial wear was determined on a SMC-2 friction machine. The axle box was made of cast iron SCH-21-40: the area of contact of the block with the roller 1 cm. The mass of worn metal was weighed on

analytical balance ADV-200 with an accuracy of 0.1 mg (according to the results of three measurements).

The degree of dendritic formation was evaluated by the percentage of dendrites relative to the total mass.

Example. The electrodeposition of iron coatings was carried out from electrolyte chloride, composition, g / l: iron chloride 400: hydrochloric acid 1.0; pH 0.8: at temperature (20 - 35 ° С). Substrate material steel

The pattern of changes in the parameters of the polarizing current during the coating process reflects the curve of the amplitude of the current density versus time (Fig. 2).

The coating process consists of two phases: initial and main mode. The initial mode is carried out on an asymmetric alternating current of industrial frequency. In this case, the direct component of the current remains unchanged, while the reverse component changes in amplitude in the direction of decreasing. Initial mode parameters: amplitude direct current density Ir.np. 95 A / dm (average direct current density Icp.np 60 A / dm2); amplitude reverse current density (i.e., 79 A / dm2 (average reverse current density (compare 50 A / dm2); cathode-anode ratio / Si. With these parameters, the process is carried out for 1.5 min. Then The reverse current is stepwise changed. The new stage is characterized by a different cathode-anode ratio and lasts several minutes. The last stage of the initial mode is the stage with the amplitude of direct current density (e.g. 95 A / dm2 (average direct current density) Icp.np.60 A / dm2), amplitude reverse current density (i.e. 9.5 A / dm2 (average density of the reverse current (compare 6 A / dm2) and the codode-anode ratio fU 10. This ends the initial mode. Its duration is 7 minutes. Values of the cathode-anode ratio: / 1,2; / 2 2 ; / Yz 4;.

The main mode is a continuation of the initial one. Initial parameters of the main mode: amplitude direct current density Ir.np. 95 A / dm2 (average direct current density Icp.np.60 A / dm2); amplitude density of the reverse current d 00r. 9.5 A / dm (average reverse current density (compare 6 A / dm2); cathode-anode ratio / 10. Then the process is carried out with a uniform increase in time the amplitude of the reverse current at a constant amplitude at a constant amplitude of the forward current The specific value of the slew rate

time of the average reverse current density in the range (0.4 - 28) A / dm2 h, the outcome is selected based on the required sludge thickness and the duration of the process. So, with a sediment thickness of 0.1 mm and a deposition time of 0.5 hours

rate of increase in average reverse current density vcp. 28 A / dm2 h and then at the end of the process the amplitude density of the direct current is equal to (e.g. 95 A / dm2 (average direct current density (compare 60 A / dm2);

amplitude density of reverse current 1t.obr. 31.7 A / dm2 (average reverse current density (compare 20 A / dm2); cathode-anode ratio / 3 3.

Parameter value (i.e. and / in any

the moment of the main mode can be easily determined from the current value of the deposition time in the main mode.

The invention is illustrated by the examples presented in the table.

Using the method according to the invention allows (20 - 25)% to increase the uniformity of the-distribution of the iron coating; (1.5 - 2) times improve the running-in of the coating; (2 - 3) times reduce the weight

dendrites on the coating.

Claims (1)

SUMMARY OF THE INVENTION A method of electric ironization in chloride electrolytes, including electrolysis on alternating current of industrial frequency, followed by a decrease in the reverse current at the initial stage, and hence, in order to increase the uniformity of the coating, to improve its running-in ™ and dendritic formation during its application, after reducing the reverse current in the initial stage, the process is conducted with a continuous uniform increase in the reverse current density from 5.5 - 6.5 to 9 - 20.5 A / dm2 s at a speed of 0.4-28 A / dm2 h. The direct current density value is 54 - 64 A / dm2. AND" MKM W OA 0.4 W 2345 6 7 A wryWTW 0g / g. / "V4 -