SU1744145A1 - Method of coating by dipping into metal melts - Google Patents

Abstract

Use: in the manufacture of machine parts in instrument making, rolled metal and household products to protect them from corrosion, to provide certain electrophysical properties, decorative finishing. SUMMARY OF THE INVENTION: 20 to 35 wt.% Of the coating material dissolved at a temperature not higher than 550CC are introduced into the melt of low-melting metals. The melt is heated to 550-800CC, and the exposure of the product in the melt is carried out for the time necessary for the product to reach a temperature 30 lower than the melt temperature, after which the product is removed and leached in water or water vapor. When coating products made from iron alloys, the melt is heated to 650 - 800fC, and from copper alloys - up to 550 - 650 ° C. 2 hp f-ly, 1 tab.

Description

The invention relates to the application of thin coatings by hot metallization during the immersion of products in the molten metal and can be used in the manufacture of parts for machine-building and instrumentation, rolled metal and household products to protect them from corrosion, to provide certain electrophysical properties, and decorative finishes.

Methods are known for producing metal coatings from low-melting metals and alloys, including cleaning the surface of products by chemical etching, fluxing and immersion, or by continuously passing a fusible metal or alloy through the melt, which they want to coat the surface and thereby obtain a coating. Thus, coatings are obtained by tin plating in low-melting metals and their alloys, for example,

aluminizing a sheet of steel and iron; “Coated with zinc, tin, lead tin.

A known method of hot metallization by immersion in a melt with a metal having a higher melting point, copper, by adding 25 wt.% Tin to it, in order to lower the melting point of the bath, which makes it possible to obtain a tinned layer of steel on the steel (75% Cu and 25% Zn) at 850 ° C.

The main disadvantage of these methods is the low resolution of the method, i.e. the impossibility of obtaining coatings by hot metallization with elements that have a high melting point, but coatings with which in the form of films are extremely relevant for practice.

The closest in technical essence to the invention is the method of nan2.

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diffusion coatings from low-melting transport melts (Na, LI), into which alimony coatings (Ni, Cr, Pd, etc.) are added as additives (from 1 to 5 wt.%). The process of formation of the coating occurs in the following sequence: dissolution of the elements of the coating in the low-melting transport melt, transfer them to the surface (product, diffuse them into the surface layers of the metal of the product, which ensures the formation of a diffusion coating in the form of solid solutions or compounds. The amount of additive is small (1-5 wt.%), since the process proceeds and is controlled in an automatic quasi-equal mode (in terms of the composition of the components) in the form: how much is dissolved (even a fraction of a percent), how much did s and diffused in the metal article.

The implementation of the prototype allows obtaining diffusion coatings, the main purpose of which is to increase the corrosion and wear resistance of structural materials.

However, it does not allow to realize the advantage of the hot metallization method: to obtain coatings in the form of a film of pure metal or a film containing a large amount (more than 70 wt.%) Of the coating metal; to conduct the process highly productively, for a very short time (seconds, minutes), as well as at relatively high temperatures (not 900 - 1000 ° C. and at 550 - 800 ° C).

The purpose of the invention is to increase the productivity of the process due to its intensification, expanding the range of material products by obtaining at 550 - 800 ° C in 10 - 180 seconds with hot metallization of uniform thickness coatings in the form of a film that is pure or containing a large amount (more than 70 May. %) of refractory metals, namely on steel products of Ni coatings. Ni-AI, Cu, Ti, Cr, Pd; on products from copper and its alloys of coatings Ag, Pd, Pd-Ag, Ag-Ni.

The goal is achieved by the fact that in the proposed method hot metallization is used in a bath of multicomponent solutions composed of several low-melting metals, at least 20 wt.% Of the coating metal should be dissolved in it. In this case, it is expedient to strive to select the composition of the melt-solution such that melt particles that may be present on the metal surface of the product dissolve quickly with water (water vapor), which is provided by introducing one of the alkaline baths into the melt.

metals. When providing a liquid state of the bath at temperatures not higher than 550 ° C, the working temperature of the bath during the metallization process should be 550 800 ° C (for steel products 650–800 ° C, and for copper products - 500–650 ° C), in addition, when the product is removed from the bath, the preferred temperature should be 30–50 ° C lower than the working bath temperature. Wherein

preferred is continuous movement of the product in the melt during the process (for example, continuous immersion and subsequent extraction from the melt), which ensures precipitation in fresh ones

the amount of the melt-solution not depleted by the coating element

This method allows high-performance and at low temperatures to obtain a uniform coating film.

(2-15 µm) on the entire surface of the product, regardless of the complexity of the configuration with high adhesion with the base metal, depending on the composition of the film (metal coating) to provide the surface of the product

certain properties (increased corrosion resistance, electrical contact resistance, decorative properties).

The proposed method allows to obtain coatings with various metals, but

To do this, depending on the desired composition of the coating and the metal of the product, it is necessary to select the optimum composition of the bath and the mode of deposition, which are considered in specific examples. Composition

the low-melting bath should contain at least 20 wt.% of the more refractory metal of the coating. With a lower concentration of metal coating, the process of hot metallization of the product surface will not

ensure a uniform layer. The composition of the bath must ensure such dissolution of the coating metal at a temperature not higher than 550 ° C, since a higher temperature will require more significant

increasing the operating temperature of the process, and the latter leads to a dissolution of the metal of the product. The operating temperature for copper products should be 500 to 650 ° C. At temperatures below 500 ° C, the melt will not be fluidity and wetting, and at temperatures above 700 ° C, there is an intensive dissolution of copper products (despite a short time of tinning).

The bath temperature for steel products should be between 650 and 800 ° C, and this range is also governed by fluidity. Alkali metal must be introduced into the bath, which ensures quick removal of melt residues from the product surface with water or water vapor. It is necessary to immerse the product in the melt in a cold state. Immersion in the cold state provides near the surface of the product of the zone of supersaturated, supercooled melt, which causes the release of coating metal, which is more refractory than the main composition of the bath. After the product is heated in the bath to a temperature below the operating temperature of the bath by 30-50 ° C, it is advisable to remove the product from the bath, since the coating film can dissolve.

The method of hot plating in a low-melting melt is carried out as follows.

The products are pre-cleaned from the surface, degreased and immersed in the molten bath in a cold state. When the product is immersed in a bath, the liquid metal melt finally cleans the surface of oxide films and serves it. In the melt film adjacent to the cut surface, the condition of supersaturation of the melt with the metal of the coating is created due to the decrease in temperature and it is released on the surface of the products in the form of a film. Fusible elements of the melt have a lower adsorption capacity compared with the metal of the coating and therefore the selective element of the coating element occurs. After the product is in the bath for a short time, it is removed and the surface is cleaned with water from melt residues. The parameters of some coatings obtained by the method of hot metallization are listed in the table.

Example 1. Applying a plating coating on copper products (guitar and petal contacts). The coating was applied from sodium. 30 wt.% Pd were introduced into the sodium melt and a working melt was obtained, the melting point of which was 500 ° C. An iron crucible with a working melt (bath volume 150 cm) was heated in an electric furnace in an argon atmosphere to 650 ° C. Products (10 guitar and 10 lobe contacts) were placed in a woven wire basket in bulk. The basket was immersed in the melt to the bottom of the bath and removed from the melt at a rate of 0.5 cm / s. The total residence time of the products in the melt is 90 s. After the basket was removed from the bath and cooled, the copper contacts were washed in water. As a result, a glossy white coating in the form of a uniform film with a thickness of 6–8 μm was obtained at the contacts, a continuous, porous, surface is smooth without

traces of sticking, having a fine-grained structure. The composition of the coating is 90 wt.% Pc1 and 10 wt.% Cu.

Example 2. A silver melt coating was applied to brass contacts, analogously to example 1: 35 wt.% Ag, and the rest is lithium, so pl. which is 390 ° C. The coating was applied at 550 ° C. The immersion and withdrawal speed of the product basket was 1 cm / s, and the total time the products were in the melt was 30 s. After the coating process was completed, the contacts were rinsed in water. As a result, a silver-white coating was obtained, in the form of a uniform film with a thickness of 5–6 µm, continuous, non-porous, and the surface is smooth without traces of sticking. The composition of the coating is 94 wt.% Hell and 6 wt.% C.

Example 3. The bronze contacts, analogously to example 1, were coated with an alloy (75 wt.% Pd + 25 wt.% Ni) from a melt of low-melting metals (85 wt.% Na + 10 wt.% LI + 5 wt.% Pb) . The coating was applied at 550 ° C. The immersion and withdrawal speed of the product basket is 1 cm / s, the total time the products are in the melt is 40 s. After the coating process was completed, the contacts were rinsed in water. As a result, a matte coating with a thickness of 5–7 µm was obtained; a continuous, non-porous, uniform surface is smooth without any sticking. The composition of the coating is 70 wt.% Pb + 20 wt.% NI + 10 wt.% Ci.

Example 4. For flat samples of size: 30 x 10 x 2 of art. 3 as in Example 1, an alloy coating (60 May% Cu and 40 wt.% Ni) was melted (50 wt.% Ca + 50 wt.% LI). The coating was applied at 680 ° C. Dip rate and sample extraction 0.5 cm / s. The residence time of the samples in the melt is 2 minutes. After the coating process was completed, the samples were washed in water. As a result, a white-blue tint coating in the form of a thin film with a thickness of 8–9 µm was obtained; the continuous non-porous surface is smooth without traces of sticking.

Example 5. For flat samples of size 30 x 10 x 2 mm from Art. 3 analogously to example 1, coating of alloys (76 wt.% Cu + 24 wt.% Zn) and melt of low-melting metals (50 wt.% Na + 40 wt.% Li + 5 May% Ca + 5 wt.% Pb. Was applied. The coating was applied at 650 ° C. The immersion and extraction rate of the samples in the melt was 0.5 cm / s, the total residence time of the samples in the melt was 1.5 minutes, and after the application was completed, the samples were washed in water. shade in

in the form of a thin uniform film with a thickness of 9–10 µm, solid, non-porous without traces of sticking to the surface.

According to the proposed method, not diffusion saturation occurs, but hot metalization of the product surface with a metal of a multicomponent melt based on low-melting metals containing a large amount of metal coating of at least 20 wt.%; the product is immersed in a bath in a cold state and is processed at time and temperature conditions different from the prototype; the application of this method ensures the production of a coating in the form of a metal film of the coating (or with its high content, more than 70 wt.%); reduces coating time and temperature.

The proposed method can be recommended for coating (Pb, Ni-Pd, Pd-Ag, Ag-NI) on electrocontacts made of copper, bronze and brass for decorative finishing of household and artistic products; to increase the corrosion resistance of steel products (parts and rolled products) in sea water and moist air (TI-Cu), for decorative finishing (Cu-Zn, Cu-Ni).

Technical and economic indicators are compared with diffusion

coatings obtained from melts in reducing the time by 9-12 times and lowering the process temperature.

Claims (3)

1. Method of coating of metal melts, including immersion of products in a heated melt of low-melting metals containing the coating material, and exposure, characterized in that, in order to increase the productivity of the method due to its intensification, expand the range of material materials, the input 20 to 35% by weight of the coating material dissolved at a temperature not higher than 550 ° C, the melt is heated to 550-800 ° C, and the exposure is carried out for the time required for the product to reach temperatures 30 to 50 ° C below the temperature of the liquid metal melt, after which the product is removed and leached in water or water vapor. 2. A method according to claim 1, characterized in that the heating during the coating of the parts made of iron alloys is carried out up to 650-800 ° C. 3. The method according to claim 1, characterized in that the heating during the coating of the parts made of copper alloys is carried out up to 550 - 650 ° C. PdNa500 76 Si 50 Na W 11 1.8 ,, 21, Zn 5 Sa + 5 Gb 60 C 40 Ml 50 Sa 50 I 90 11 10 Sa 95 U} Ca 2 b 500 500 490 30650650-30-62090 35650650-50-60090 30680660- i5-405 20 25800800-40-760180 20750750-30-720170 Continuous nonporous uniform topchina 6-8 microns, the composition of 90 and ac.% Pd 10 masi Cu Solid, uniform, without traces of 9-μm thick naps, golden brown Solid uniform, non-porous, kino and 8-9 microns, white and blue hue Solid uniform non-porous, 9-U microns in thickness, white-gray tint, composition of 90 wt. X N1 + 10 wt.% Fe Solid, non-porous, uniform toltsinoi 5-7 microns, composition - 9 mdsgsg + 9 Mac.t Fe