SU1730207A1 - Method of chrome-plating - Google Patents

Abstract

Use: chrome plating lengthy products. SUMMARY OF THE INVENTION: Includes cathode treatment in a standard DC chromium plating electrolyte with a density of 60-240 A / dm2. Every 10–30 min, the treatment is interrupted for 0.5–1.0 s and during this time, rectangular cathode current pulses are applied with an amplitude of 600–1000 A / dm2, a frequency of 2–25 Hz, and a duty cycle of 2–10. 1 tab.

Description

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The invention relates to electroplating, in particular to electrolytic chrome plating.

The known method of electrolytic chromium plating, when, in order to improve the physicomechanical properties of the coating, deposition is carried out using a direct current, on which a high frequency current (f 1 MHz) is applied.

The method does not provide sufficient tightness and uniformity in thickness. In addition, the use of a powerful high-frequency generator is associated with large additional costs.

The known method of chromium plating involves passing a direct current through a bath, on which

alternating current with a frequency not exceeding 20 Hz; the ratio between ac and dc is 4: 1. The large amplitude of the variable component causes a significant ripple ratio of the current feeding the bath, this leads to a decrease in the hardness of the chrome plating to 800 MPa, which is unacceptable.

The known method of electrolytic chromium plating at a constant current when a pulsed current with a density of 100-500 A / dm and a pulse frequency of 1-20 Hz is applied.

The method does not provide a sufficient reduction in porosity and increased tightness. Emerging large VHV | so about yu

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Heat stress leads to cracking of the coating and, as a result, to an increase in the fracture, to a decrease in the tightness.

The closest to the proposed method is the coating process, which includes treatment with a direct current of 60 A / dm in a universal chromium plating electrolyte of 250 g / l CgOz and 2.5 g / l H2SO4

The disadvantages of this method are low protective and physico-mechanical properties of coatings.

The purpose of the invention is to increase the corrosion resistance and wear resistance of coatings.

This goal is achieved in that the method involves the deposition on a direct current with a density of 60-240 A / dm2, which is interrupted every 10-30 minutes for a time of 0.5-1.0 s, during which rectangular cathode pulses are applied. a current with an amplitude of 600–1000 A / dm2, a frequency of 2–25 Hz, and a duty cycle of 2–10.

Electrodeposition on a standard chromic electrolyte is conducted on a direct current with a density of 60–240 A / dm2 for 10–30 min, as a result of which a primary layer of chromium precipitate is formed. Then the direct current is interrupted for a time of 0.5-1.0 seconds. During this period, powerful cathode current pulses with an amplitude of 600–1000 A / dm are applied at a frequency of 2–25 Hz and a duty cycle of 2–10. As a result, a microlayer structure of coatings is formed with a high corrosion resistance, lower porosity, high hardness.

DC Initial Density

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60 A / dm is selected. When the DC density is less than 60 A / dm and the transit time is up to 10 m, a sharp decrease in the deposition rate is observed. The final DC density is chosen to be 240 A / dm2 within 30 m. When chromium plating with a large current density value with increasing time there is a sharp decrease in the protective properties, the formation of dark brown stripes of gout on the projections of the cathode.

The initial amplitude of the pulse current is 600 A / dm2, because its reduction does not allow one to achieve a noticeable improvement in the physicomechanical properties of the coating. The final amplitude of the impulse current density was chosen 1000 A / dm2. At this amplitude of the impulse current density, coatings with a hardness of 1100 kg / mm are deposited, possessing high protective properties with low porosity (up to 2.5%). A further increase in the amplitude leads to burning of the coatings and to a non-attractive appearance. The duration of the pulsed current is chosen based on the fact that a decrease in their duration of less than 0.5 s leads to an increase in the length of the interlayer boundaries, i.e., the concentration of lattice defects increases, which contributes to the further development of micro-fracture. An increase in the pulse current duration of more than 1.0 s leads to a decrease in the strength characteristics and microhardness.

The initial height of the polarizing current pulses is chosen 2 Hz and a duty cycle equal to 2. At frequencies less than 2 Hz and a duty cycle less than 2, there is a strong increase in the internal stresses of the coating and a violation of its continuity. The final frequency of the pulses is 25 Hz with a duty cycle of 10, as a further increase in the frequency and duty cycle leads to the formation of poor-quality precipitation.

Example. Electrodeposition of chromic coatings was performed from a standard electrolyte composition, g / l: chromic anhydride 250, sulfuric acid 2.5; temperature 55 - 60 ° C. Electrodeposition was subjected to products of high strength steel grades. Coating thickness 90-100 microns. To obtain comparative data, parallel to the deposition of chromium was carried out on a direct current of 60 A / dm2 density and when superimposed on a direct current of powerful pulses. The deposition time is 120 min. The average pulse current density was 800 A / dm2.

The properties of the obtained coatings are presented in the table. Microhardness was measured on a PMT-3 instrument.

The porosity of the coatings was determined by applying reagents, which, penetrating through the pores of the coating, give a colored compound to the substrate metal.

Adhesive strength was determined qualitatively by scratching the mesh.

The technical and economic effect of the implementation of the method is mainly determined by the reduction of parts rejection due to the increased tightness of the coating.

Claims (1)

Invention Formula The method of electrolytic chromium plating, including cathode treatment in a standard electrolyte at a direct current with a density of 60 - 240 A / dm2, characterized in that, in order to increase the corrosion resistance and wear resistance of coatings, the treatment at a constant current interrupted every 10-30 minutes for a time of 0.5-1.0 s, during which rectangular pulses of the cathode current are supplied The time of occurrence of corrosion in days was determined in a salt fog chamber. Wear resistance with a specific pressure of P - 50 kg / mm for AO dimension g. an amplitude of 600-1000 A / dm, a repetition rate of 2-25 Hz, and a duty cycle of 2-10.