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The Danieli metallurgical equipment.

Body for certification of machine-building products <<STC Standartelektro-C>> has been certifying beginning from 2003 metallurgical equipment produced by the Danieli company for electric steel melting and rolling production.

Here under metallurgical equipment are meant arc steel melting furnaces; ladle-furnaces; vacuum degassing installations; machines for continuous casting of billets; heating furnaces; rolling mills; hot galvanizing units.

The Danieli products meet most state-of-the-art requirements and are in demand on the world market, including Russia. This is confirmed by estimation of technical solutions performed in the process of certification. The following technical peculiarities of certified equipment should be noted.

In arc steel melting furnaces produced by the Danieli steels of wide range of grades are molten, including steels for cold upset and die forging, special spring steels, bearing, high-carbon, free-cutting steels for production of motor vehicles, air-space and agricultural equipment, construction, production of seamless pipes (including pipes designed for operation under high pressure), stainless steels, nickel alloys, and tool steel [1]. The Danieli produces furnaces with fully bearing structure, split casing, a system for loading ferroalloys, and oriel outlet [1, 2].

One of peculiarities of arc steel melting furnaces of the Danieli are regulators of electrodes and foamy slag of the Hired Plus type, application of which enables increasing efficiency of operation of the furnaces and reduction of electric power consumption [3]. In a number of cases continuous feeding of scrap [3] and automatic sampling and temperature control [1, 4] are ensured. The Danieli supplies furnaces with modular system Danarc [2, 3], which replaces conventional lances for injection of oxygen, carbon, and lime. Modular system Danarc fulfills functions of the pool carbon depletion, supply of heat energy, and formation of a foamy slag. For injection of oxygen and carbon the Danieli also uses the Jet BOx[TM] (here inafter Jet BOx) system, which represents combined oxygen-carbon injection. This system ensures supply of oxygen nearer to the melt surface in comparison with traditional lances, due to which increases efficiency of oxygen use. For example, application of the Jet BOx system at the Dongkuk Steel Plant in South Korea ensured reduction of electric power consumption by 10 % and increase of the furnace productivity by 2-3 melts a day. Due to advancing fuel-oxygen burner (injector) into the furnace permeability of oxygen increases, whereby regulation of the process of carbon injection and slag foaming improves, consumption of electrodes reduces, and quick decarburization is ensured. Oxygen nozzles are installed on watercooled copper casing located in the distance from side wall of the furnace. Injection of carbon by the Jet BOx system enables intensive foaming of slag, while neighborhood with burners protects injection nozzles against their clogging by slag. Each injector of the Jet BOx system ensures flow of oxygen injection 42 [m.sup.3]/min, and its lances allow injecting solid particles as well [5].

The Danieli furnaces may operate on solid charging (including up to 100 % of pellets) or using in a charging up to 40 % of liquid cast iron. In the Danieli furnaces up to 28--35 melts per day are produced [4].

At Moldavian Metallurgical Plant operate arc furnaces of the Danieli with four bottom lances for supply of oxygen, which ensure oxidizing of carbon and melting of scrap in difficult for access zones and good mixing of liquid steel. Application of bottom lances in melting of steel in arc furnaces enables reduction of electric power consumption by 28--36 (kW-h)/t [6].

Gas treatment installations include primary tract for exhaust gases, a hood, a chamber filter, a sequentially installed cyclone and system of noise killers on chimney stack [4]. System for reburning technological gases is envisaged [6].

A ladle-furnace makes it possible to bring liquid steel refining operations outside melting furnace, which significantly reduces duration of melting from tapping to tapping and electric power consumption. In addition, practice of operation of ladles-furnaces, manufactured by Danieli, showed that they represent <<buffer accumulation>> of metal before continuous casting and enable precise organization of continuous casting works.

In the Danieli ladles-furnaces bottom blowing of metal by inert gas, most frequently by argon and in some cases by nitrogen, is used. Blowing of metal by inert gas in the ladle-furnace ensures uniform distribution of temperature and homogenization of chemical composition all over mass of the melt, improvement of steel and slag mixing, diffusion and uniform distribution of additives (ferroalloys) in liquid melt, whereby required chemical composition of steel, accurate temperature of the metal necessary for continuous casting, and reduction of consumption of ferroalloys are ensured. In the Danieli ladles-furnaces various grades of steel are processed--low- and medium carbon, low- and medium-alloyed, steel for shipbuilding, pipe steel, steel for production of galvanized strips, for deep drawing, for motor vehicle components, pressure vessels, corrosion-resistant, bridge, and many other kinds.

Two-position ladles with arches with inert atmosphere, a system for turning electrodes, operation of immersed into slag arc, and automatic control system may be supplied. Ladle-furnace installations of the Danieli company ensure high rate of heating, efficient removal of sulfur and nitrogen from liquid steel, and low consumption of electrodes. Two-position installation may simultaneously process steel in two ladles (in one of them steel is heated, in the other alloying elements are introduced and mixing is performed), whereby high productivity of the installation is achieved [1--3]. Specific power of arc is 1.8--2.2 MW per 1 [m.sup.2] of metal surface area depending upon ratio of diameter to height of the ladle [7].

The Danieli installations for vacuum-oxygen decarburization are designed for wide range of steel grades (carbon, stainless, austenite, ferrite corrosion-resistant, silicomanganese, chromium, chromium-silicon, chromium-vanadium, chromium-molybdenum, siliceous, free-cutting, chromium-nickel, bearing steels and steels with low content of carbon).

Synchronization of operation of installations for vacuum-oxygen decarburization with arc steel melting furnaces is envisaged. After vacuum-oxygen decarburization content of hydrogen in steel reduces 2--6 times depending upon its initial content and duration of blowing by oxygen.

The Danieli company produces installations for double vacuum-oxygen decarburization with two vacuum chambers. In the course of blowing by oxygen content of carbon and rate of decarburization are controlled by special instruments, due to which an additional economic effect is achieved. After vacuum-oxygen decarburization steel has good mechanical properties, in particular high ductility and low content of hydrogen. Rate of pressure reduction exerts great influence on final content of carbon in metal [2]. In addition to installation for vacuum decarburization gas analyzer of spectrometer type and auxiliary equipment are supplied [3, 2].

On MCCB produced by the Danieli, slabs of 70-270 mm thickness and 900--3250 [micro]m width, thin slabs for a strip of 90 [micro]m thickness, various blooms (for example, a square 650) of 250x300, 390x510 size, ect.,

billets: square 100--200 [micro]m, section billets 160-200 mm, beam billets 280x400 [micro]m etc,; strips of 0.7-0.8 mm thickness, super-thin, rolled and other strips are cast. According to chemical composition, on the Danieli machines low-, medium- and high-carbon steels, steels with super-low content of carbon; low-, medium- and high-alloy; high-strength low-alloy; stainless, including austenite with low content of carbon, austenite with titanium, martensite and ferrite, boron containing, siliceous, and other steels are cast. Among mentioned steels there are those designed for automotive industry, production of air-space and agricultural equipment, shipbuilding and construction industries, production of pipes, atmosphere-resistant structures, springs, shafts, solid wire, special structure, valve, bearing, free-cutting steel and steel designed for electric household appliances.

From the viewpoint of further technological process, on the Danieli MCCB steels designed for cold upset, cold die forging, manufacturing of steel structures, cold and hot rolled stock, drawing, and malleating are cast. Machines for continuous casting of the Danieli company have radius of curvature from 4 to 16 m and system of multipoint bending within wide range. Productivity of these machines is 0.35-2.90 mln t per year, casting speed is 1.0--7.5 m/min, number of strands is up to 7 [1--5].

The Danieli MCC of steel are equipped with a device for electromagnetic mixing of metal in the mould. In the process of mixing, movement of steel causes origination of two circulation loops in liquid metal (upper and lower ones) when steel hits opposite narrow facet of a slab and divides into two flows. Such phenomenon is called <<butterfly-like>> mixing. As a result of movement of the steel, number of crystallization centers increases that enables solidification with formation of equiaxial crystals and favorably affects quality of the metal. In addition, axial liquation and porosity reduce, and during rolling waviness of the surface reduces [3].

Multimode electromagnetic mixer consists of four electromagnetic agitators, installed along wide facets of the mould. Depending upon parameters of casting and the product itself these agitators may automatically either decelerate or accelerate movement of the flow, or mix steel at the level of meniscus by rotational movement. Application of this technology allows increasing MCCB productivity, increasing output of suitable product and reducing need in finishing cast items. Application of electromagnetic mixer eliminates fluctuation of meniscus, reduces by 40 % quantity of defects near surface of the billet, and reduces by 40--75 % number of surface defects at the beginning of the process (slag inclusions and spot defects) [1].

An important technical peculiarity of the Danieli MCCB is design of a zone for secondary cooling of the metal. Four-zone system of secondary cooling is used with application of the technology of cooling by water vapor, control of which is performed through three independent circuits with automatic regulation [4], whereby system of dynamic cooling control is available, which ensures correct solidification of the metal within the whole process.

In secondary cooling zone releasable rollers of small diameter are used. Such design limits bulging of the metal over axis, reduces deformation of crust, and increases stability of liquid metal level in the mould. Cooling chamber is equipped with exhaust blower. In the Danieli systems of delayed cooling, water-air drip cooling with adaptive regulation, and secondary sputtering cooling are used.

One of significant technical peculiarities of MCCB produced by the Danieli is mechanism for swinging the mould and control system of this mechanism, which is dynamically readjusted depending upon grade of steel and speed of casting, whereby dynamic check of the billet width and parameters of the mould swinging is performed.

The Danieli MCCB are supplied with a system of dynamic soft reduction of an ingot with liquid core. This system together with a hardening chamber ensures hot fit of the billets.

The whole process in MCCB is completely automated; mathematical models of solidification and control of the position of liquid metal meniscus are used for the purpose of optimizing soft reduction and cooling of the ingot.

In MCCB a measuring device, which combines radioisotope and electromagnetic sensors for precise control and regulation of actual level of the metal in the mould and thickness of the mould lubrication, is used. System for preventing break of the crust and sticking of the ingot to the mould walls, which operates using chart of temperatures in the mould, is also used. The mould has variable conicity.

Application of the Danieli technology allows drastic reducing number of the mould components, which have to be replaced when passing over from one thickness of a slab to another. This enables significant reduction of capital investments and subsequent operation expenditures. This peculiarity is typical for all slab MCCD supplied by the Danieli, into composition of which enter systems for metal level control in the mould (of electromagnetic type), automatic regulation of the mould width, and braking of metal in the mould.

A number of technical peculiarities of the Danieli MCCB are connected with ladles (quick replacement of a ladle and change of a nozzle, double bogie for transportation and hoisting of an intermediate ladle, system for weighing intermediate ladle on the bogie, system of stopper control for regulation of steel flow from intermediate ladle). Both, open jet and closed methods of casting through immersed nozzles with a system of stoppers are used.

Other peculiarities are connected with a system of multipoint dressing, tilt stand of <<butterfly>> type, straightening-stretching machines, improved systems of power supply, distribution boards, control units, and lay-out systems of wiring of the boards.

For heating furnaces with walking beam systems for reducing formation of scale, reduction of specific electric power consumption, software for calculation of mathematical models, heating curve control, and organization of the furnace operation are developed. A water conditioning installation, a pusher mechanism, loading-unloading roller conveyers, a kickoff on the side of unloading, an engine control center, and an automatic control system are supplied together with the furnace.

On small-section-wire mills of the Danieli company steels of wide assortment of grades are rolled, including low- and high-carbon, structural steel for drawing and cold upset, spring, bearing and many other grades of steel. Productivity of these mills achieves 150 t/h, speed of rolled wire rolling is 110-120 m/s; mass of bundles most frequently constitutes 1.8--3.4 t. Some technological peculiarities of wire mills are rolling with welding, rolling without braiding of strings, feeding of hot-rolled breakdown from intermediate group of stands into finishing group over two separate lines (in this case rolling is performed in two independent finishing groups) [1, 2, 4].

The Danieli company developed for the first time in the world for wire mills a bearing-less coil-forming device, in which rotor of the working head is installed not in the bearings, as it used to be, but is held in rear position by the magnetic field. A new bearing-less coil-forming device ensures absence of vibrations even at the highest speeds of rolled wire reeling into bundles, low wear of the guiding tube, and increase of its service life. It does not require for maintenance due to absence of subject to wear mechanical parts, which enables significant reduction of operation expenditures [4].

The Danieli supplies small-section-wire mills with multi-blade scissors, fast-acting data analyzer, ergonomic control panel, chambers for hardening and tempering (located on the output side of finishing blocks), a line for controlled cooling of rolled wire, equipment for cold finishing of the products, fast-acting scissors for automatic cutting of front and rear ends of rolled wire before the coil stacking tripper, an electric equipment, automatics, and metal structure control system [1,2,4].

Reeling and unreeling of rolled wire is worth special mentioning. Developed by the Danieli technology ensures reeling without braiding hot-rolled metal into high-quality super-dense and super-heavy bundles and envisages unreeling of bundles without distortion of the products. That's why hot-rolled stock may be fed to the cold finishing line directly from bundles that makes unnecessary traditional operations of unreeling of cold bundles, dressing and stretching of rolled stock, its repeated reeling into bundles and significantly reduces expenditures for rolling processes [1].

On small-section-wire mills of the Danieli absence of skew during winding and residual axial stress, high density of bundles and ductility of the metal, and high yield of suitable metal are ensured.

Here are several examples of some technical decisions of the Danieli company, which concern mediumand heavy-section rolling mills. So, in 2003 the company supplied a unit for dressing high-speed rails with a manipulator for operative dressing of hardened rails. This system ensures the strictest allowances necessary for application of rails on high-speed railways. A barrolling mill with a cooler, devices for feeding and withdrawal of products, a unit for current multi-line dressing and cold cutting into measured length, a magnetic piler, and an automatic device for batching and binding is supplied [3].

Rail rolling mills are supplied with electric equipment, automatics, a technological process control system, a robotized system for accelerated automatic replacement of rolls and guides, engineering networks, and auxiliary structures.

Medium-section mills for rolling beams and channel sections are completed with a device for accelerated readjustment of programs, a cooler, a machine for dressing in the mill flow, edging saws, automatic pilers and banders, a laser caliber HIPROFILE (which ensures continuous measurement and control in the flow of the rolled item parameters), and equipment for heat treatment in the mill flow [4].

Mills for rolling flange beams are supplied with fast-acting mechanisms for change of rolls, a cooler, dressing equipment built into the mill line, automated equipment for finishing and batching of products, electric equipment, and automation system.

Rolling mills for round rolled sections are completed with the HIGAUGE devices for measuring diameter of billets, an automatic system for technological process of low-temperature rolling control, coolers, equipment for cold finishing of products, and equipment for heat treatment [1].

Technical peculiarities of hot galvanizing lines are a system for leveling coating thickness by compressed air, the basis of which are nozzles, angular position of which as well as their position relative the strip may be regulated over vertical and horizontal, a direct-fired furnace, a high-pressure air blower for feeding compressed air into the system, vertical section of electrolytic degreasing, a unit for finishing surface, a straightening-stretching machine, and a chromate treatment section. Application of zinc coating is performed using three-roll blocks [4, 2].

Heating furnaces for dip galvanizing lines are developed in the following versions: a section with open flame followed by a radiation tube complete with close circuit jet cooler; only with radiation tubes and jet coolers; a section with open flame followed by the chamber for soaking equipped with electric heaters and jet coolers.

All of them have vertical or horizontal arrangement and operate at speed from 17 to 200 m/min. Heating flame systems are designed and tested for operation with all kinds of fuel (from natural to coke and mixed gas, when burners are equipped with auxiliary burners for ignition of the main one, or only with ignition and detection system both for free flame burners and burners with a radiation tube). Furnaces in the Danieli hot galvanizing lines may operate with a strip from 0.25 to 4 [micro]m thickness and width from 650 to 1650 [micro]m [3].

The Danieli company developed scissors of drum type for strip mills, which are characterized by high quality of cutting and strict allowances as to the length of cutting. The scissors are equipped with two straight knifes attached to their drum at a special angle of inclination [3]. The Danieli company has also developed super-scissors with PNC for longitudinal cutting. Using these scissors, to which the cutting tool (to be automatically replaced) is reliably attached, it is possible to cut superplastic strip into high number of bands. For example, cutting of steel for injection needles, ultimate strength of which is about 500 N/m[m.sup.2] at relative elongation 50 %, is tested: a strip of 0.12 [micro]m thickness was cut into bands of 9 [micro]m width (later 6 [micro]m) in continuous mode. In these scissors brakes with vacuum booster of the drive are used, which reduce friction and external action on the strip [1].

At present certification of sheet mills, vacuum pans, and mini-plants of the Danieli company manufacture is carried out.

CONCLUSIONS

1. The Danieli metallurgical equipment is certified: arc steel melting furnaces, gas treatment installations, ladles-furnaces, installations for vacuum-oxygen decarburization of steel, MCCB, heating furnaces, small-section-wire mills, medium- and heavy-section mills, water hardening lines, hot galvanizing units, tribo-apparatuses, and scissors. All this equipment received Russian certificates of correspondence.

2. Metallurgical equipment of the Danieli company manufacture corresponds to high technical level and state-of-the-art requirements, contains many original technical solutions, and is in high demand on the world market.

[1.] DaNews. Selection of Danieli Group publications for 2004.

[2.] (2005) DaNews. Danieli Droup, 141.

[3.] (2003) DaNews. Danieli Droup, 135.

[4.] (2003) DaNews. Danieli Droup, 136.

[5.] (2003) Steel Times International, 11.

[6.] Lopukhov, G.A. (2005) Application of oxygen in arc steelmaking furnaces. Elektrometallurgiya, 3, 2 -27.

[7.] Dyudkin, D.A., Grinberg, S.E. (2005) Some aspects of technology and structure of ladle-furnace unit. Ibid., 8, 25 -28.

* The article is published in abridged version.

V.M. SOJFER

Company <<STC Standartelektro-C>>, Moscow, RF
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Title Annotation:ELECTROMETALLURGY OF STEEL AND FERROALLOYS
Author:Sojfer, V.M.
Publication:Advances in Electrometallurgy
Article Type:Report
Date:Apr 1, 2006
Words:3309
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