RU2620536C1 - Method of obtaining consumable electrodes for manufacturing castings from zirconium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: starting particulate materials milled, sieved, is compacted, compressed and fired to ensure the strength of the consumable electrode. As starting material use a dry particulate mixture of non-metallic materials in the form of zirconium oxide 79-84 wt % of coal tar pitch and 16-21 wt %.

EFFECT: invention provides a consumable electrodes without using expensive metal charge materials.

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Description

The invention relates to the field of metal smelting, devices for electroslag or electric arc smelting of metals, and in particular to methods for manufacturing castings from corrosion-resistant alloys used as structural materials.

In particular, these include zirconium alloys, which combine extremely high corrosion resistance with respect to mineral and organic acids, as well as strongly alkaline solutions, which in combination with high mechanical strength allows the use of zirconium for the manufacture of chemical equipment: pumps, valves, heat exchangers, filters, pipes and other equipment with reduced costs and improved production methods.

It can be used for the manufacture of castings from zirconium alloys in vacuum skull ovens with a consumable electrode by the method of arc melting.

A known method for the production of castings from highly reactive metals and alloys, including zirconium, in vacuum skull-type furnaces with a consumable electrode by the method of arc melting [1]. A water-cooled copper crucible, a consumable electrode, and molds are placed in a vacuum chamber. The consumable electrode is a charge ingot of an alloy of a given composition. After evacuation of the furnace, an electric arc is ignited between the electrode and the bottom of the crucible, and the crucible and electrode are heated at low power. When the power increases to its working values, the consumable electrode melts, the molten metal gradually fills the crucible. As the consumable electrode melts, it automatically lowers down. Due to the high thermal conductivity of the copper water-cooled crucible, a layer of hardened melt with a thickness of 10 ... 15 mm is formed on its walls, which is a skull lining.

The disadvantage [1] is the need for pre-fabrication of consumable electrodes from sponge metal charge materials by methods of foundry and metal forming. Therefore, the widespread use of this group of alloys is limited by the high cost of metal charge materials, due to the multi-stage and expensive operation of beneficiation, chemical processing and refining of initial ore materials.

The closest to the essence of the claimed invention, the prototype is a method for producing consumable electrodes from metal chips [2], which consists in the use of consumable electrodes made of metal chips of a given alloy composition. The method includes crushing and cleaning chips, thermal vacuum degassing at 550-650 ° C, exposure from 1 to 2 hours. Chip briquettes are pressed and loaded with a gap into the mold, which is heated to 400-450 ° C before pouring with the same alloy.

The disadvantage of the prototype [2] is the use as a charge of a metal material in the form of chips, as well as costly casting, which serves as a binder of a chip briquette.

The aim of the invention is to obtain a consumable electrode without the use of expensive metal charge materials.

The goals are achieved in that non-metallic materials in the form of zirconium oxide and coal tar pitch are used as starting components.

The invention can be carried out, for example, in the following way. As the charge material used ore material - zirconium oxide. As a reducing agent, carbon-containing raw materials, such as coal tar pitch, are used. It is preliminarily ground in a ball mill, ground in runners, dried in drying drums, sieved through a 0.5 mm sieve. Then the pitch is mixed with zirconium oxide. The mixture is processed on rollers, then ground in ball mills, sieved through a sieve. Electrodes in the form of cylinders are pressed from the obtained powder on hydraulic presses and burned in electric resistance furnaces at a temperature of 1480 ° C. Then the electrodes are installed in the melting and casting unit and an electric arc is ignited.

The reduction of zirconia with carbon occurs by the reaction:

where ZrO ₂ - zirconium dioxide;

C is carbon;

Zr is zirconium;

CO - carbon monoxide (II).

At arc burning temperatures (at least 3000 ° C), the only possible reaction products are zirconium and carbon monoxide; therefore, the equation represents a reaction proceeding in a solid phase. In the reaction zone, a deep degree of evacuation must be maintained to remove gaseous carbon monoxide in order to shift the reaction equilibrium towards the final products, as well as to protect the liquid metal from contamination with soluble impurities.

The drawing shows a table where the experimental data are presented, namely the research results, where the composition of the mixture was determined, which ensures the production of metal zirconium.

It is obvious from the table that if the content of coal tar pitch in the composition is less than 16% and more than 21%, the yield of metal zirconium during smelting decreases sharply, therefore, the optimal content of coal tar pitch in the composition is in the range from 16% to 21% and zirconium oxide from 79% to 84% (mass).

Thus, the proposed composition of the consumable electrode allows to obtain metallic zirconium without the use of expensive sponge metallic zirconium. If necessary, the obtained metal can be shipped and used without additional metallurgical operations as a casting alloy for producing shaped castings.

The examples of application of the present invention show its usefulness in the field of metal smelting, devices for electroslag or electric arc smelting of metals, and in particular to methods for manufacturing castings from corrosion-resistant alloys used as structural materials.

The present invention satisfies the criteria of novelty, since when determining the level of technology, no means have been found that have characteristics that are identical (that is, matching the functions performed by them and the form in which these signs are performed) to all the signs listed in the claims, including the purpose of the application.

The present invention has an inventive step, because it has not been identified technical solutions having features that match the distinguishing features of this invention, and not known the influence of distinctive features on the specified technical result.

The claimed technical solution can be implemented without the use of expensive metal charge materials by mixing non-metallic materials in the form of zirconium oxide and coal tar pitch and the manufacture of consumable electrodes from them.

Information sources

1. Foundry alloys and smelting: textbook. / A.P. Trukhov, A.I. Malyarov. - M: IC Academy, 2004 .-- 336 p.

2. RF patent No. 2197548, published: 01/27/2003.

Claims (2)

A method of producing consumable electrodes for the manufacture of castings from zirconium alloys, including grinding, sieving, compaction, pressing of the initial dispersed materials and firing to ensure the strength of the consumable electrode, characterized in that non-metallic materials in the form of zirconium oxide and coal tar pitch are used as the initial dispersed materials the following ratio of components of dry weight, wt.%: Zirconium oxide 79-84 Coal tar pitch 16-21

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