General

The Duplex Shop has two primary tasks, i.e. cast iron processing and steelmaking. 

The Duplex Shop consists of two divisions: the converter division, which includes the following sections: mixer, converter, and auxiliary - bottom plate plant, and the open-hearth division, which includes the following sections: furnace, charge stock, casting, and mix preparation.

I. Converter Division.

After weighing on the scales, the vanadium cast iron received from the blast-furnace workshop is discharged into a 450 t mixer.  The mixer is continuously heated by oil fuel and is designed to store cast iron, maintain the cast iron temperature within stable limits of 1,320-1,370°C, and homogenize its chemical composition.  The cast iron is drained from the mixer into a hot-metal transfer ladle (22 t) and delivered to the converter for tapping and blowing through.  The mixer is not subject to routine repairs.

The vanadium cast iron is processed in 22 t converters to obtain vanadium slag (raw material for ferrovanadium production) and a semi-finished product (refined cast iron) used to make steel and as a commercial product, by blowing through with compressed air at a pressure of 6 atm. through special blow-through tuyeres mounted in the converter bottom.

The blowing-through time is 2 to 6 minutes depending on the cast iron temperature and chemical composition, as well as on the semi-finished product purpose (open-hearth furnace, casting machine, synthetic semi-finished product).  The duration of one blow-through cycle is 18-24 minutes.  The Bessemer division has a total of 3 converters – two operational and one under repairs or standby. 

The maximum one shift output of the semi-finished product was achieved in 1998, totaling 958 t (48 melts).

II. Open-Hearth Division.

This division is designed to make and pour steel into moulds to obtain steel ingots which are forwarded to the 800 blanking mill for rolling to produce blanks for the factory's section mills.

Basic Division Equipment

The basic equipment includes two open-hearth furnaces with 270 t liquid metal loads, operating on the basis of the scrap-ore process (30-40% of metal stock and 60-70% of liquid semi-finished product).

All the charging materials are delivered to the workshop’s stockyard via two railway tracks.  Metal scrap for open-hearth furnace charging is prepared in the factory’s drop-hammer plant and delivered to the stockyard in 1 m3 charging boxes by specially fitted wagons.  Ferroalloys and other free-flowing materials are delivered to the stockyard in the Ministry of Railways cars or in the local wagons and unloaded into specially fitted hoppers.  Three electric overhead cranes are used to unload the wagons and deliver the materials to the open-hearth furnaces on the racks.  The scrap and other materials are charged into the furnace by two charging cranes (with an overarm capacity of 5 t).

The furnaces are heated by grade 100 oil fuel and natural gas (insertion heat ratio 30/60).  The grades of steel made include over 60 positions.  Steel is discharged into two 130 t steel-teeming ladles and poured from the bottom into flared mold boxes with hot tops.  The weight of one ingot varies from 1,920 to 1,930 kg depending on the steel grade.  One steel-pouring train (with a total of 4 trains) includes 11 casting cars, with each car having two 8-slot (8 –mold) stands mounted.  The steel-pouring trains are prepared by two stations of the train preparation section.

Once the steel has been poured and the hot tops removed, the train with ingots proceeds to the 800 mill’s ingot storage. 

IV. Design of Open-Hearth Furnaces No. 5 and No. 6.

The open-hearth furnaces are positioned in the duplex workshop's furnace bay.  A mix of natural gas and oil fuel is used to heat the furnaces.  The natural gas excess pressure is 4.5-6.0 kgf/cm2.  the oil fuel’s share by heat is 35-45%. 

Basic open-hearth furnace.  The furnace roof arch is optimally stressed, 460 mm thick.

The furnace end is two-channel.  The ramp roof inclination is 250.

The regenerative checkers are laid on the basis of the Siemens system, with the checker volume being 211 m3 and 221 m3.

The furnace slag chambers are pull-out type.  The volume of two slag chambers (4 boxes) is 52 m2.  The roofs of the slag chambers and regenerators of OHF No. 5 are curved, magnesite-chrome, and those of OHF No. 6 - suspend arch.

Compared to standard furnaces, the furnaces have an insufficient area of the hearth bottom (the area of standard furnaces being 85 m2).

Also, compared to standard furnaces, the furnaces have an insufficient regenerator capacity (211 m3 and 221 m3 instead of 290 m3 as in the case of standard furnaces). 

The effective heat surface is not sufficient, either, in comparison with standard furnaces.

The main flue’s cross-sectional area is 4.33 m2, while the standard furnace flue’s cross-sectional area is 4.7 m2.

The front and rear hearth walls have skewback channels of evaporation cooling.

Slag removal from the slag chambers is mechanized.

The reversing mechanisms include sloping flue dampers with air boxes.

There is a smoke damper mounted in the main flue.

The smoke stack is brick made, Н = 80 м.

To service the furnaces, there are two charging machines with an overarm capacity of 5 t.

Oxidants, fluxes, metal stock, deoxidants, and alloying elements are delivered to the furnace bay balcony in charging boxes from the charge leant-to by two charging box magnet cranes.

The charging box capacity is 0.75 m3 and 1.0 m3.

Free-flowing materials are loaded in the charge leant-to by a grabbing crane. 

The slag thimble has a capacity of 11 m3 and is installed on the undercarriages under the furnace’s operating platform.

Metal is discharged into 130 t ladles over a bifurcated spout.

Exhaust heat is used in the KU-80 heat recovery boiler mounted behind the open-hearth division’s main building.

CB-55 blower fan No. 12 is used to boost air into the furnace, with the fan driven by the A-91-655 electric motor (980 rpm and 70 kW maximum power).

The D 20x2 induced-draft fan creates the necessary furnace draft to extract flue gases in an orderly manner.