Ferroalloy refractory for electric furnace

Ferroalloys are alloys consisting of one or more metallic or non-metallic elements and iron elements, and are used as deoxidizers, deoxidizers and alloy additives in the iron and steel and casting industries. Ferroalloy is one of the essential raw materials in iron and steel industry and mechanical casting industry. Its main uses: one is as a deoxidizer to eliminate excess oxygen in liquid steel; The other is to improve the quality and performance of steel as an alloy element additive. The furnace body is composed of furnace lining, steel structure (skeleton, furnace shell or coaming) and foundation pier.

The working conditions of refractory in ferroalloy electric furnace are very bad, the melting temperature of many varieties is far higher than the temperature of molten steel, lining erosion is very serious, refractory consumption accounts for the total cost of the product relatively large; In the smelting process of ferroalloy, the lining of different parts is in different working state.

The top refractory mainly bears the erosive impact of high temperature furnace gas and blast furnace slag, the temperature change during the feeding interval and the radiant heat of high temperature arc. Air flow impact and pressure change during material collapse.

The refractory wall is mainly subjected to the effect of arc radiation at high temperature and the temperature change during the feeding interval, the erosion and impact action of blast furnace gas and blast furnace slag at high temperature, the impact and wear action of solid material and semi-molten material, and the serious slag erosion and impact action near the slag line. In addition, when the furnace body tilts, there is additional pressure.

The furnace slope and bottom refractory mainly bear the upper burden or molten iron pressure, the temperature change during the feeding interval, the impact of charge and arc melting, the erosion impact of high temperature molten iron and molten slag.

Requirements for refractories:

(1) High refractoriness and softening temperature under load; Good heat and cold resistance and slag resistance, with a greater heat capacity and certain thermal conductivity.

(2) The lining of the ferroalloy furnace and the refractory used depend on the type of alloy and the structure of the furnace.

At present, domestic and foreign ferroalloy furnace lining materials generally have the following types:

(1) Carbon lining. Metal silicon and ferrosilicon, high carbon ferromanganese, manganese silicon alloy, silicon-chromium alloy, silicon-calcium alloy and other electric furnace using carbon lining. Western Europe, Japan, South Africa and other countries also use high carbon ferrochrome furnace lining. The place where the furnace is in direct contact with molten iron is made of charcoal brick or knotted charcoal paste, and the exterior is made of high aluminum brick or clay brick.

(2) Magnesium lining. Magnesia lining is used in refining electric furnace, and magnesia brick is used in high carbon ferrochrome electric furnace of China and former Soviet Union.

(3) High aluminum furnace lining. Vacuum furnace, Swedish high carbon ferrochrome furnace using high aluminum brick or high aluminum binder masonry lining.

Ferroalloy production also uses a variety of amorphous refractory materials, such as magnesium ramming materials, high aluminum castable, cold ramming charcoal paste. These materials are used to tie or repair lining, furnace cover, iron outlet and other vulnerable parts.

The inner lining of the electric furnace for smelting copper and nickel concentrate is generally magnesian refractory below the slag line (including the reverse arch of the furnace body) and clayey refractory above the slag line of the furnace top.

The top of the furnace is usually wet with high alumina bricks or clay bricks. If there is a large hole on the top of the furnace, it is appropriate to use refractory castable around the whole. There are also the use of ramming or buried with a water-cooled copper tube of the precast refractory castable top, it has better integrity and sealing than the brick top.

The inner lining of an electric furnace for the treatment of lead-zinc and tin concentrates. The molten pool is generally made of large blocks of carbon brick, but magnesite refractory materials are also available. Above the slag line, the outer wall and the top of the furnace shall be made of clayey refractory.

The anatomy of the furnace body of ferroalloy furnace shows that the brick joint is the channel for slag, metal, alkali metal and gas to infiltrate into the furnace lining, and the infiltration into the brick joint is the important reason for the destruction of furnace lining. Therefore, the basic requirement of lining masonry is to reduce lining gaps and improve its integrity and structural strength.

In addition, the following should be noted when laying an electric furnace:

(1) Refractories and thermal insulation materials used in furnaces, especially magnesium materials, shall be protected from moisture;

(2) The fireclay used for firebrick construction should have the same or similar fireclay and composition as the brick used;

(3) The fire-resistant masonry shall be constructed with staggered joints, and the brick joints shall be filled with mud; When laying bricks dry, brick joints should be filled with dry refractory powder.

For example, for the electric furnace for smelting copper and nickel concentrate, the reverse arch at the bottom of the furnace and the magnesium bricks on the side wall of the melting pool are generally used for dry laying, the brick joints shall not be more than 1mm, and the rest are all wet laying. The connection between the side wall and the reverse arch of the furnace bottom is a weak link, so it is necessary to process the bricks and lay them without triangular joints. When laying the reverse arch of the magnesium brick at the furnace bottom, the wet clay bricks at the bottom must be dried first.

In order to extend the service life of electric furnace and reduce production cost, correct use and maintenance are needed. The measures adopted in the production of refined ferrochrome are as follows: the operation of retaining iron is adopted to reduce the impact of charge on the bottom of the furnace and the effect of acid primary slag on alkaline refractories.

Using hot slag to repair furnace lining is the repair method of using heat transfer principle to maintain furnace lining. Its principle is the same as that of using ladle lining to refine iron chromium. Ladle lining is to put liquid slag into ladle during the process of furnace, and let part of slag condense on ladle wall to release the remaining liquid slag. Ladle with slag lining is used for the next furnace to connect molten iron.

It is helpful to prolong the lining life of refining electric furnace by heat injection. The basic requirements for the spraying materials are good fluidity, easy adsorption on the surface of refractory materials at high temperature, and rapid solidification and hardening; Easy to be sintered and felt to have sufficient strength; High temperature and slag resistance.