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INVENTION
Patent of the Russian Federation RU2117718
METHOD OF ELECTROCHEMICAL POLISHING OF SILVER PRODUCTS AND ITS ALLOYS
Applicant's name: Joint-stock company of open type "Russian gems"
The name of the inventor: Mirzoev RA; Styrov M.I .; Stepanova N.I .; Alexeev Yu.B .; Alikberova N.S.
The name of the patent holder: Joint-stock company of the open type "Russian gems"
Address for correspondence:
Date of commencement of the patent: 1996.09.25
The invention is intended for use in the jewelry industry and can be used in restoration work or in precise instrument engineering and mechanical engineering, etc. SUMMARY OF THE INVENTION. A method is proposed for electrochemical polishing of articles made of silver and its alloys by means of an anode impulse current treatment, including their anodic dissolution in aqueous solutions containing salts of cyanic acid. In this case, the pulsed current of a relatively high repetition rate in the range 0.1-10.0 Hz is modulated by pulses of a relatively low frequency in the range 0.01-0.10 Hz, while the pulses applied to the bath have a rectangular shape, and their duty cycle Is determined by the impedance of the bath and is in the range 1.0 - 10.0. As a result, the passivation film is completely removed and the cleanliness of the polished surface R a = 0.16 is achieved at uniform gloss and arbitrary configuration of the products.
DESCRIPTION OF THE INVENTION
The invention relates to electrochemical methods for polishing articles made of silver and its alloys and is intended for use in the jewelry industry, but can also be used in restoration work, and in precision instrumentation and mechanical engineering and in local industry.
A method is known for electrochemical polishing of silver by means of an anode treatment at 18-20 ° C with a pulse current in an electrolyte of 10% chromic anhydride in concentrated ortho-phosphoric acid at a current density of 200-600 A / dm 2/1. The phosphate electrolyte used in this process has a low scattering power, which prevents efficient processing of complex silver products. The composition of the electrolyte and the current density used do not allow the polishing of silver alloys.
A method of electrochemical polishing of silver is also known, which includes treatment with a pulse current in a cyanide electrolyte using a device providing a pulse duration of 3.0 seconds, a pause time of 0.8-1.2 seconds, and a voltage of 1.1-1.8 V / 2 /.
This method is applicable only for polishing products of simple configurations of pure silver due to the long duration of the current pulses acting on the article (anode).
The method of electrochemical pulse polishing of silver articles by an anode impulse current treatment, which includes anodic dissolution in aqueous solutions of hydrocyanic acid salts with an initial current density of 20-200 A / dm 2 , duration of a current pulse of 0.3, is closest to the invention in terms of essential features and industrial applicability - 3,0 s with intervals between impulses 5,0 - 10,0 s, the electrolyte contains AgCN o C 20 - 60 g / l, KCN o C 30 - 50 g / l, K 2 CO 3 - up to 40 g / L / 3 /.
In comparison with other known analogues [1, 2], the method in question (3) has a number of advantages, providing, when polishing pure silver, the surface purity R a = 0.16 (grade 10 of purity) and uniform surface gloss; In addition, the processing time is shortened. This method has, however, a number of significant disadvantages that limit its use in the jewelry industry, especially in the mass production of jewelry.
The main disadvantage of the closest analogue (3) is that the method does not allow polishing of products from silver alloys and does not allow the processing process to be carried out with parameters providing high-performance and high-quality electrochemical polishing of products of arbitrary configuration made of silver. The reasons for these drawbacks are:
1. Formation on the anode-product of passivating films, different in composition, including - a black dense film, which can be completely removed only when the product is strongly swung in the electrolyte, which impedes the polishing process;
2. In the passivation film, in addition to AgCN, Ag 2 O and AgO, mixed oxide (AgCu) O is included, which allows the process of polishing silver alloy products to be realized only at a film thickness not exceeding the surface roughness height;
3. The dissolution of the protrusions on the surface of the processed articles is not sufficiently ensured, especially the complex products made of silver and its alloys, since the magnitude of the current decay after the first and subsequent pulses is small.
The aim of the invention was the development of a method for electrochemical pulse polishing of articles made of silver and its alloys that provides process parameters that are optimal for high-performance processing of products of arbitrary configuration to produce surfaces with high reflectivity and purity R a = 0.16 (10 cells).
The goal is achieved due to the fact that during the implementation of the method of electrochemical polishing of silverware and its alloys by means of an anode impulse current treatment, including their anodic dissolution in aqueous solutions containing cyanic acid salts, a pulsed current of relatively high repetition rate in the range 0, 1 - 10.0 Hz, is modulated by pulses of relatively low frequency in the range 0.01 - 1.00 Hz, and the pulses applied to the bath are rectangular, and their duty cycle is determined by the impedance of the bath and is in the range 1.0 - 10, 0.
As a result of secondary modulation, instant pulses and periods of current decay are formed, interrupted by a pause, during which the surfaces of the products are completely cleaned from the products of anodic dissolution of all constituents of the alloy, that is, from the passivation film.
From the data presented in Table 1, obtained as a result of the experimental work, the advantages of the claimed method become more clear.
Examples of a specific embodiment of the claimed method of electrochemical pulse polishing of articles of silver and its alloys.
For electropolishing were taken: products of pure silver, products made by electroplating from the alloy of silver 960 o and jewelry from the silver alloy 925 o .
Bath with electrolyte containing KAg (CN) 2-20 g / l, KCN 45 g / l, K 2 CO 3 80 g / l, equipped with a mechanical agitator.
Electrical contact of products with a current source was carried out by means of titanium clamps. Suspension products were loaded into the bath for 7 minutes with reciprocating movement of products with an amplitude of 6 cm, and at a frequency of 10 oscillations per minute, rectangular voltage pulses with a certain repetition frequency and modulation were applied to the bath.
The best quality of polished surface R a = 0.16 (grade 10 grade) with uniform gloss of the surface was achieved under the conditions shown in Table 2.
Compliance with the criterion of "Inventive level" is achieved through the use of secondary modulation; The use of this method does not require the creation of a new technology or the use of non-standard and expensive equipment. Therefore, the method is reproduced on an industrial scale and industrially applicable.
CLAIM
A method for electrochemical polishing of articles made of silver and its alloys by means of an anode impulse current treatment, including anodic dissolution in aqueous solutions containing cyanic acid salts, characterized in that the pulsed current of a relatively high repetition rate in the range 0.1-10.0 Hz is modulated Pulses of a relatively low frequency in the range 0.01-0.10 Hz, the pulses applied to the bath are rectangular, and their duty cycle is determined by the impedance of the bath and is in the range 1.0-10.0.
print version
Date of publication 03.01.2007gg
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