US20120138253A1 - Advanced technology for iron-chrome alloys production and related plant - Google Patents

Advanced technology for iron-chrome alloys production and related plant Download PDF

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US20120138253A1
US20120138253A1 US13/387,628 US200913387628A US2012138253A1 US 20120138253 A1 US20120138253 A1 US 20120138253A1 US 200913387628 A US200913387628 A US 200913387628A US 2012138253 A1 US2012138253 A1 US 2012138253A1
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slag
metal
casting
crucible
furnace
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Paolo Appolonia
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/005—Manufacture of stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B3/00—General features in the manufacture of pig-iron
    • C21B3/04—Recovery of by-products, e.g. slag
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D25/00—Special casting characterised by the nature of the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D29/00—Removing castings from moulds, not restricted to casting processes covered by a single main group; Removing cores; Handling ingots
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D7/00—Casting ingots, e.g. from ferrous metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B3/00—General features in the manufacture of pig-iron
    • C21B3/04—Recovery of by-products, e.g. slag
    • C21B3/06—Treatment of liquid slag
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5211—Manufacture of steel in electric furnaces in an alternating current [AC] electric arc furnace
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5264—Manufacture of alloyed steels including ferro-alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5294—General arrangement or layout of the electric melt shop
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/54—Processes yielding slags of special composition
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0087—Treatment of slags covering the steel bath, e.g. for separating slag from the molten metal
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
    • F27B3/19—Arrangements of devices for discharging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/15—Tapping equipment; Equipment for removing or retaining slag
    • F27D3/1545—Equipment for removing or retaining slag
    • F27D3/159—Equipment for removing or retaining slag for retaining slag during the pouring of the metal or retaining metal during the pouring of the slag
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/527—Charging of the electric furnace
    • C21C2005/5276—Charging of the electric furnace with liquid or solid rest, e.g. pool, "sumpf"
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

  • This patent patent application relates generally to a method and relative plant for the production of ferro-chrome alloys and more particularly to a method and relative plant for the production of ferro-chrome alloys that allows metal-slag separation directly inside the furnace.
  • the present invention has as its object an innovative method and the relative plant for producing ferro-chrome alloys that allows metal-slag separation directly inside the furnace.
  • the production of ferro-chrome does indeed present multiple difficulties such as the difficult metal-slag separation, the lack of an optimal mineral/metal conversion yield, the loss of metal in slag, the pollution with slag of the metal, the instability in electrical conduction of the furnace, as well as the excessive use of manpower and a very critical environmental microclimate.
  • various technologies for solving these problems are known, but they do not offer a total solution. These technologies have been adopted in particular by the Norwegian company Elkem, producer of various types of ferro-alloys.
  • the first technology concerns the sintering of the mineral chromite.
  • the technology known in the state of the art is useful because it allows all available mineral resources to be exploited, but this means substantial investments in additional plants that increase the production costs of ferro-chrome.
  • the sintering of the mineral used by various companies such as Xstrata Merafe in which it is known as Premus Technology does not solve the technical problem of metal-slag separation in the casting step and of the porosity and low compactness of the metal produced. The fact that it is not possible to separate the slag from the metal in the casting step ensures that they have to be separated after solidification.
  • the heterogeneity of the chromites themselves determines a phenomenon of surface tensions of the liquid phase with it being impossible, after solidification, to have the two phases separate from one another, i.e. a commixture layer is formed between metal and slag that can no longer be separated, which determines a substantial loss of metal because it is too polluted.
  • a commixture layer is formed between metal and slag that can no longer be separated, which determines a substantial loss of metal because it is too polluted.
  • chrome oxide loaded into furnace-metal conversion yields do not exceed 80 ⁇ 82% determining a great loss of metal that affects the production costs.
  • the technical problem solved by the present finding consists in obtaining ferro-chrome alloys by carrying out the metal/slag separation directly inside the furnace.
  • the new method for producing ferro-chrome alloys has been designed, which radically changes the casting and chemical system of the furnace, allowing a constant amount of the two liquids (metal and slag) to be kept inside the crucible.
  • This method is based on the principle of obtaining the “clean” ferro-chrome free from slag already in the casting step, thus eliminating all of the operations and interventions that are currently necessary, after casting, to obtain clean metal.
  • This new method also allows a good emulsion to be obtained that is essential to allow the metal just formed to degas, obtaining a metal free from blistering. In order to allow the application of the method object of the present finding it is necessary to make some plant modifications.
  • FIGS. 1 to 7 a preferred example embodiment of the present finding is represented, absolutely not for limiting purposes.
  • FIGS. 1 to 7 a preferred example embodiment of the present finding is represented, absolutely not for limiting purposes.
  • FIG. 1 shows a type of crucible of a 10 MW furnace in 1:50 scale with the three suitably sized electrodes at the centre and the offsetting of the two metal and slag casting holes;
  • FIG. 2 shows a type of refractory material with which the crucible of the 10 MW furnace must be coated in 1:50 scale;
  • FIG. 3 shows the complete plant including the crucible with the electrodes and the tanks for emptying and collecting the slag and metal.
  • FIGS. 4 to 7 show the SiO 2 —MgO—Al 2 O 3 ternary diagram and SiO 2 —MgOCaO quaternary diagram with 15% Al 2 O 3 fixed base and the viscosity diagrams of the three main elements constituting the slag: SiO 2 —Al 2 O 3 —MgO.
  • the plant in object comprises a crucible furnace ( 1 ) inside which there are three Söderberg electrodes ( 2 ), a hole for casting the metal ( 3 ) and a hole for casting the slag ( 4 ), as well as a plurality of tanks for emptying and collecting the metal ( 5 ′) and the slag ( 5 ).
  • the plant is equipped with the characteristics described hereafter.
  • the crucible must meet specific requirements of power density (watt/cm 2 ) over the useful surface and of volumetric capacity.
  • the power density that expresses the best yield of the chemical reduction process is 23 ⁇ 26 watt/cm 2 of useful surface.
  • the holes for casting metal and slag will be positioned at different heights on different axes.
  • the hole for casting the metal will be positioned in the direction of the axis of one of the electrodes, preferably the electrode facing towards the casting pit. This will allow the metal to flow out easily.
  • the hole will be raised by mm50 with respect to the sole-plate and will have a diameter of mm70.
  • the hole for casting the slag will be shifted by 60° with respect to the hole for the metal, and exactly in the middle of the two electrodes.
  • the slag hole will also have a diameter of mm70.
  • the hole for casting metal is positioned in the direction of an electrode so that it is located in the influence area of the radiation of the electrode, and consequently the temperature is optimal and this ensures a correct outflow of the metal in the casting step.
  • the casting hole is offset by 60° and will have a level shift of mm600 (MW10), of mm700 (MW13), of mm800 (MW20), with respect to the height of the metal hole, because it is necessary to take out the excess slag formed in the casting intervals in a position that is not influenced by the radiation of the electrodes.
  • mm600 MW10
  • mm700 MW13
  • mm800 MW20
  • the liquids in their ideal temperature phase are subjected to a circular convective motion that allows the liquid itself to be homogenised, and this can cause partial remixing of the two liquids (metal and slag), for which reason if we took out the slag in the direction of one electrode there could be seeping of metal in the slag casting step, due to possible internal turbulence.
  • the slag casting hole offset by 60° ensures that it is possible to operate in an area not directly influenced by the electrodes and therefore not directly involved in the convective motion. From the operative point of view the castings are thus separated, and from the lower casting hole the ferro-chrome free from slag is drawn, from the upper casting hole the slag free from metal is drawn.
  • the data relative to some example embodiments of the crucible absolutely not for limiting purposes:
  • Another essential characteristic of the method object of the present finding is the sizing of the electrodes. This is calculated taking into consideration the characteristics of the transformer that is the true heart of the furnace, since the entire plant is designed and structured according to the power (KW) and the currents (KA) of the secondary. Knowing that the coking of the electrode paste in the Söderberg electrode is very delicate and takes a long time, it is suitable for the current density per cm 2 of the electrode not to exceed certain values. It is known that an increase in the diameter of an electrode must correspond to a maximum desirable current density value.
  • the established values are the following: from ⁇ 800 mm to ⁇ 1000 mm it will have to be a maximum of 7 A/cm 2 ; from ⁇ 1100 mm to ⁇ 1300 mm it will have to be a maximum of 5.5 ⁇ 6 A/cm 2 over ⁇ 1300 mm it will have to be a maximum of 4.5 ⁇ 5 A/cm 2 .
  • the decreased current density as the diameter of the electrode increases substantially reduces the risk of cracking and consequent breaking.
  • centre distance centre-centre
  • FeCr which is produced with minerals with ratio 2.8 ⁇ 3.2
  • there is a very resistive charge for which reason we shall ensure that the areas covered by the action of the electrodes overlap at the sides for 1/12 of the action diameter (3D/12), leaving a small area uncovered at the centre of the convergence of the 3 areas.
  • the cardboard positioning and the gaps suitable for promoting expansion must be managed by a refractory expert, who knows the expansion coefficients of the individual types of bricks and their permanent linear variation, and only thus can the lifetime of the sole-plate be ensured, which can easily exceed four years of work.
  • the sole-plate is thus made refractory: the bottom of the sole-plate is insulated by a layer of 100 mm with casting of the alocast CH95 type based on 90% tabular alumina that allows excellent insulation, chemical and mechanical resistance. It is essential that the levelling be carried out horizontal. This layer can be overloaded after 7 ⁇ 8 days of maturing of the cast.
  • the ceramic-bonded silico-aluminous bricks are placed adhering to the insulating cast.
  • the remaining thickness of 800 mm to complete the sole-plate, will be divided into two equal parts: 400 mm of layer adhering to the silico-aluminous will be of the 92% perex magnesite type bricks baked at high temperature.
  • the last layer of 400 mm will be of the 96% perex 21 magnesite type baked at a high temperature, with high resistance to high temperatures and to slag. In these last layers of the sole-plate high quality bricks are used because they will be directly in contact with the permanent liquid layer in the furnace.
  • the walls of the crucible are also refractory with two different qualities of bricks and with 4 different length measurements.
  • the inner part of the crucible is divided into three well-defined areas, and each one has a well-defined role in the chemical reduction process. From the bottom to the top we have the “double level” area ( 6 ), the chemical reduction area ( 7 ) and the preheating area of the charge ( 8 ).
  • the “double level” area ( 6 ) starts from the sole-plate and has a variable height according to the power of the furnace, for example in a 10 MW furnace the height will be mm 600. For this height the best pitch-bonded magnesite bricks will be used, which have high-purity magnesite and 50% electro-cast magnesite as components.
  • Said bricks have a high mechanical resistance to heat and to chemical attack. These bricks have a length of mm 900 and ensure an excellent seal against the permanent liquid in the “double level” area. In the coating of the walls, the bricks will not adhere to the iron of the structure, but rather a gap of mm100 will be created over the entire circumference from the sole-plate up to the end part of the crucible. A magnesian ramming containing 30% graphite will be placed in this gap so as to be able to discharge the excess heat accumulated by the refractory bricks as quickly as possible towards the outside. The graphite gives greater thermal conductivity, and this is to the benefit of the lifetime of the bricks.
  • the chemical reduction area ( 7 ) is the part of the crucible most subjected to the irradiation of the electric arcs of the three electrodes, for which reason bricks of the highest quality are used, the same type as the “double level” area.
  • the bricks will have a length of 650 mm and a variable height depending upon the power of the furnace, for example in a 10 MW furnace height 1000 mm, 13 MW height 1100 mm, 20 MW height 1200 mm. In this area between the bricks and the structure there will also be a rim of 100 mm of magnesian ramming with added 30% graphite.
  • the last area is that for preheating the charge ( 8 ).
  • Said area of the crucible is the least stressed one, both because the temperatures are relatively low, and because they are not subjected to the electric arcs.
  • the type of bricks used from the analytical point of view differs little from the bricks used in the wall below, but it is not made with 50% electro-cast magnesite, and therefore it is less valuable than the previous one.
  • the laying of the bricks must be rigorously managed by a refractory expert. In order to then keep the removal of excess heat accumulated by the bricks constant, promoted by the rim of magnesian ramming with added graphite, it is necessary to provide water cooling of the crucible.
  • the cooling plant foresees a circular loop located in the upper part of the crucible, which distributes the water over the outer metallic wall simply as a thin film and it is collected on the bottom of the structure through channels connected to one another that will carry the water to the collection point of the whole system that concerns the circulation of cooling water of the furnace.
  • This is a simple provision that has the purpose of preventing possible areas of overheating of the crucible, as sometimes concentrations of heat can occur caused by management anomalies of the furnace both of the electrical and of the chemical type.
  • this provision also acts as an alarm signal, because in the case of anomalies that continue for any length of time, the area involved by overheating causes a clear formation of steam that any worker at the furnace can easily recognise, thus allowing attention to be drawn to the phenomenon and an attempt to be made to discover its causes.
  • the furnace suitable for the method in object fundamentally changes only in the sizing of the crucible, in how it is made refractory, and in the formulation of the charge and of the slag that must meet the chemical-physical requirements necessary to obtain the desired results.
  • SiO 2 —MgO—Al 2 O 3 ternary diagram FIGS. 4 and 5
  • these three compounds form about 90% of the components of the slag.
  • the other 10% consists of roughly 3% Cr 2 O 3 , 0.7% FeO, 1.5% CaO and other minor compounds like sulphides, phosphorus pentoxide, etc. It should be specified that the values used on the viscosity diagram are not percentages by weight, but rather concentrations in grams/mols of the substances under examination.
  • a slag of this type has two clear anomalies, i.e. high temperature and high viscosity. Indeed, a higher melting point clearly means greater electrical energy consumption and an increase in the melting speed of the charge. This subtracts a certain amount of mineral from the chemical reduction and jeopardises the gas-solid exchange which is essential to optimally exploit the oxide-metal transformation yield. Moreover, the excessive melting speed of the minerals means that a magma layer forms that wraps around the coke and hinders its reducing action. The high viscosity is another of the negative factors. As we have already seen, in the case in which there is excessive melting with respect to reduction, the high viscosity literally traps the coke preventing its gas-solid exchange action. Moreover, in the casting step this coke would all come out from the casting hole dragged by the slag that is too dense. Of course, this would lead to the stechiometric decrease of the coke being charged with easily foreseeable consequences:
  • MgO and CaO are notoriously fluidifying, but this is so in the case in which they act upon an acid substance like SiO 2 that structurally has a tetrahedral crystallisation that tends to extend in a laminar manner, is a complex bond that has difficulty flowing (low fluidity).
  • the basic substances like MgO and CaO break this compact frame making the liquid very flowable (fluid).
  • FIG. 6 shows us the progression of the viscosities of the three main elements making up the slag: SiO 2 —Al 2 O 3 —MgO.
  • SiO 2 —Al 2 O 3 —MgO the amounts of the substances under examination are not expressed in percentage weight but in grams/mols percentage because each substance corresponds to a different molecular weight. It should be noted how an increase in Al 2 O 3 leads to an increase in viscosity.
  • Al 2 O 3 carries out its tetrahedral crystallisation action not only in the lamellar way like SiO 2 , but also in three dimensions and therefore it gives the liquid a compact weft that is practically impenetrable even by substances with a higher specific weight. This is the negative factor that prevents the metal FeCr from decanting from its own slag. This negative factor has always created great management, quality and environmental difficulties. Regarding this, it must be kept in mind that the stechiometric calculation of the slag formulation must be carried out specifically according to the origin of the base mineral and, in any case, respecting the following chemical-physical parameters:
  • the slag must have the concentration values of the various elements as expressed below:
  • the oxide-metal transformation yield is around 93 ⁇ 94%. Slag is obtained with 2.5 ⁇ 2.8% Cr 2 O 3 and considering that the amount of slag produced per ton of FeCr is 1:1.6 ⁇ 1.7 this means that in slag we lose (2.7 ⁇ 1.65) 4.5% Cr 2 O 3 .
  • the smoke produced by the furnace (dust) collected by the purifiers is on average 30 ⁇ 35 Kg for 1 ton of FeCr, and that this smoke contains about 30% Cr 2 O 3 , and therefore there are 11 Kg Cr 2 O 3 for 1 ton of FeCr equal to 1.1%. The sum of the losses is 5.6%, with a little unquantifiable loss, and assuming 93% as oxide-metal transformation yield is per se precautionary.
  • Kg 381: 0.95 (average content in a Quarzite) Kg 400 of anhydrous quartzite to be added to the charge.
  • the ferro-alloy will thus be made up as follows:
  • FeO 297 ⁇ 0.777 Fe 230
  • the slag will be made up as follows:
  • Kg 1492+5% of oxides not classified but contained in the raw materials such as Sodium oxide, Potassium, sulphides, Phosphates, the total of the slag will be Kg 1.570.
  • the basicity index was respected.
  • the setting up of a furnace requires special care because the entire brickwork must be allowed to get up to temperature with a certain graduality to allow the suitable dilations. From this derives the need to graduate the supply of energy and the feeding of the first charges into the furnace, so that the whole system does not undergo sudden and localised thermal shocks.
  • the metal and slag castings can be programmed in alternate steps so as to allow the liquids to be drawn off in the amounts formed between one casting and the other.
  • the perforation is carried out in the metal casting hole (the lower one) already having the tap-hole machine ready and the pure metal, free from slag, is left to flow into the suitable modular moulds ( 5 ) made of spheroidal graphite cast iron positioned in cascade ( FIG.
  • the castings of the metal are collected in suitable modular moulds made of spheroidal graphite cast iron that, after about 2 hours, will allow us to remove the ingot contained in the mould with a suitable pincer attached to the overhead crane.
  • the modular moulds offer great advantages because they allow the individual pieces (front, central, rear) that over time can decarburize and thus crack, to be replaced without having to replace the entire mould. It is a simple maintenance intervention that leads to savings in production costs. With the same intervals, but at staggered times with respect to the metal, the casting of the slag is carried out from its hole arranged at a higher level than that for the metal and offset by 60°.
  • the slag casting does not have special provisions during its drawing off, it is left to flow and is collected in the suitable bells (non-refractory ladles) made of spheroidal graphite cast iron arranged in cascade.
  • the suitable bells non-refractory ladles
  • the casting also automatically finishes and simple plugging is carried out. In doing so an amount of liquids (metal and slag) will always remain in the furnace, which will ensure stability in electrical conductivity and power, and the metal-slag separation can thus occur and, promoted by the circular convective movement of the liquids at high temperature, the degassing and emulsion of the metal will take place.
  • the casting area becomes more comfortable and safer because there are no longer movements of moulds containing Ferro-chrome that are transported and tipped, but rather a simple picking up of the ingot through a pincer that places it in the cooling area.

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WO2020099910A1 (fr) 2018-11-13 2020-05-22 Franchi Massimo Four pour la production d'alliages de ferrochrome
WO2023096525A1 (fr) * 2021-11-28 2023-06-01 Татьяна Михайловна ПАРПОЛИТО Four pour la production d'alliages de fer et de chrome

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