Advanced technology for iron-chrome alloys production and related plant

Abstract

A method for producing ferro-chrome alloys comprising a stechiometric charge and stechiometric slag calculation step, a step of making the plant and the crucible furnace operate at normal regime, steps of casting the metal and the slag, a step of collecting the molten metal in suitable modular moulds made from spheroidal graphite cast iron, a step of removing the ingots contained in the moulds with suitable pincer means, a step of collecting the slag in suitable non-refractory bells or ladles, characterised in that the metal-slag separation takes place directly inside the furnace and in that said castings of metal and slag take place in successive steps so as to allow the drawing off of the liquids in the amounts formed between one casting and the next.

1 ) Method for producing ferro-chrome alloys comprising a stechiometric charge and stechiometric slag calculation step, a step of making the plant and the crucible furnace operate at normal regime, steps of casting the metal and the slag, a step of collecting the molten metal in suitable modular moulds made from spheroidal graphite cast iron, a step of removing the ingots contained in the moulds with suitable pincer means, a step of collecting the slag in suitable non-refractory bells or ladles, characterised in that the metal-slag separation takes place directly inside the furnace and in that said castings of metal and slag take place in successive steps so as to allow the drawing off of the liquids in the amounts formed between one casting and the next. 
     
     
         2 ) Method according to  claim 1 , wherein, when the amount of drawn off ferro-alloy has reached the set level in the crucible and there is a visible trickle of slag that begins to be transported by the flowing metal, the metal casting hole is plugged with a suitable machine that has already been set up. 
     
     
         3 ) Method according to  claim 1 , wherein said stechiometric slag calculation step requires that the following chemical-physical parameters be respected: melting point around 1650° C.; basicity index slightly below the condition of neutrality, i.e. between 0.83-0.87; viscosity within the range 1.1-1.2 poise. 
     
     
         4 ) Method according to  claim 1 , wherein, said slag is made up of Cr 2 O 3  in a concentration of between 2.5÷2.8%, SiO 2  in a concentration of between 42.0÷44.0%, Al 2 O 3 —in a concentration of between 12.0÷13.0%, MgO in a concentration of between −34.0÷36.0%, CaO in a concentration of between 1.0÷2.0% and FeO in a concentration of between 0.6÷0.8%. 
     
     
         5 ) Method according to  claim 2 , wherein the volume of liquid contained in the crucible is ⅓ of the volume of the charge. 
     
     
         6 ) Plant for producing ferro-chrome alloys comprising a suitably sized-crucible ( 1 ), three Soderberg electrodes ( 2 ) surrounded by six copper plates, a series of moulds ( 5 ) in cascade for the outflow and collection of the slag and metal ( 5 ′) and characterised in that it has a bottom hole for casting the metal ( 3 ) and an upper hole for casting the slag ( 4 ). 
     
     
         7 ) Plant—according to  claim 6 , said hole for casting the slag ( 4 ) is offset by 60° with respect to the upper hole for casting the metal ( 3 ). 
     
     
         8 ) Plant according to  claim 6 , wherein the bottom hole for casting the metal ( 3 ) is positioned in the direction of the axis of one of the electrodes ( 2 ). 
     
     
         9 ) Plant according to  claim 6 , wherein said casting holes ( 3 ,  4 ) have a diameter of 70 mm. 
     
     
         10 ) Plant according to  claim 6 , wherein said Söderberg electrodes ( 2 ) have the centres arranged at the vertices of an equilateral triangle. 
     
     
         11 ) Plant according to  claim 6 , wherein said Söderberg electrodes ( 2 ) laterally overlap for 1/12 of the diameter of action leaving a small area uncovered at the centre of the convergence of the 3 areas. 
     
     
         12 ) Plant according to  claim 6 , wherein said Söderberg electrodes ( 2 ) have a current density of between 7 and 4.5÷5 A/cm 2 . 
     
     
         13 ) Plant according to  claim 6 , wherein said crucible ( 1 ) comprises a refractory sole-plate and walls divided into three areas from the bottom towards the top: “double level” area ( 6 ), chemical reduction area ( 7 ), charge preheating area ( 8 ). 
     
     
         14 ) Plant according to  claim 13  wherein said sole-plate of the crucible consists of an Alocast CH95 cast based on 90% tabular alumina, of ceramic-bonded silico-aluminous bricks, of 92% perex magnesite bricks and of a last layer of 96% perex 21 magnesite bricks. 
     
     
         15 ) Plant according to  claim 13  wherein said “double level” area ( 6 ) and said chemical reduction area ( 7 ) consist of pitch-bonded magnesite bricks, which have as its components high-purity magnesite and 50% electro-cast magnesite. 
     
     
         16 ) Plant according to  claim 13 , wherein said charge preheating area ( 8 ) consists of pitch-bonded magnesite bricks. 
     
     
         17 ) Plant according to  claim 6  wherein said crucible ( 1 ) is characterised by a rim of magnesian ramming with added 30% graphite. 
     
     
         18 ) Plant according to  claim 6  wherein said crucible ( 1 ) is surrounded by a looped cooling plant located in the top part that distributes the water onto the outer metallic wall of the furnace.