MXPA97008345A - Process to produce iron for mold - Google Patents

Abstract

A submerged arc furnace (10) produces iron for milling and sources of old iron and steel scrap where little or no slag is produced. Old iron or steel scrap is supplied to the submerged arc furnace (10) with a silica source and a carbonaceous reducing agent. The old iron and the steel scrap melt while at the same time the silica melts in the presence of the carbonaceous reducing agent. The quantity of the silica source and the carbonaceous reducing agent are added in an amount suitable to selectively control the silicon and carbon content of the iron for molder resulting

Description

PROCESS TO PRODUCE IRON FOR MOLDING Field of the Invention The present invention relates to a process for producing iron for old iron and / or scrap steel mills. More particularly, the invention is directed to a process for producing iron for milling in a submerged arc furnace using old iron or steel scrap as the main sources of iron. Background of the Invention Mold iron, used for foundry and steel manufacture, is produced in the iron industry in different processes. The process used normally depends on the supply material and the proposed use of iron for the mill. A process to produce iron for milling uses a standard cupola furnace. A variety of iron sources such as old iron, scrap steel and iron ingots are supplied to the vertical shaft of the furnace fueled by coke combustion by an air stream. The charge added to the furnace usually contains various additives such as ferrosilicon to increase the silicon content of iron and slag-forming materials such as limestone to remove impurities such as sulfur. The iron produced by this process normally contains about 1 percent to 3 percent silicon and about 2 percent to 4 percent carbon. The furnace-type furnace unfavorably is a net oxidant of silicon with the result that as much as 30 percent of the available silicon is lost by oxidation and discharged into the slag. Normally, only about 70 percent of the available silicon is combined with iron. Silicon is an essential element of iron for molding and is usually added in the form of ferrosilicon since silicon can be easily combined with iron. Ferrosilicon is an expensive source of silicon in such a way that the losses of silicon by oxidation can considerably increase production costs. The cupola type furnace is convenient in many processes since it can have good energy efficiency and requires a relatively low capital investment. A cupola-type furnace can also be easily extended from a single unit for increased production and can be operated as a continuous loading and pouring process. Carbon is easily combined with iron and collected naturally in the cupola when the melted iron and steel drops pass through the hot coke and dissolve the carbon. The possibility of producing iron for milling depends in part on the efficiency of the process used and the cost of the loading materials. The cost of old iron and steel scrap depends on various factors including the iron content, the amounts of desirable and undesirable alloying constituents present and the particle size. The cost of old iron and scrap of very fine or light steel, such as drilling or lathe shavings, is usually much smaller than heavier scrap in such a way that it is convenient to use light scrap whenever possible. The use of light scrap in a cupola requires agglomeration or briquetting since the high volume of gases leaving the cupola carries an unacceptably high percentage of the furnace charge. The very fine or light scrap will be collected in the bag chamber or scrubber resulting in a low iron recovery and therefore an increase in the cost of operation. Iron for milling is also produced conventionally and commercially with the electric induction furnace. In the electric induction furnace the load, which may be old iron, scrap steel and iron ingots, is introduced into the furnace, melts; and then the additives are introduced, including silicon, carbon and a slag-forming material to cover the iron. The iron charge is heated by parasitic currents resulting from the electromagnetic induction of the alternating electric current flowing in the coil surrounding the charge. Silicon is normally added as ferrosilicon and carbon is added in the form of a graphite material with low sulfur content. The resulting iron generally has a silicon content of 1-3 percent and a carbon content of 2-4 percent. Unfavorably, the electric induction furnace is limited to a batch process where individual units are usually able to produce less than 20 tons of iron per hour. In addition, electric power is quite expensive due to the inefficiency of being a batch process. Other disadvantages include moderate to high costs of refractory products, high capital investment, costly labor, high cost of ferrosilicon and carburizing additives, and limited expansion capacity. Another process for producing iron for mills is by melting iron ore in a submerged electric arc furnace. Submerged arc furnaces have the advantage of directly melting minerals and producing convenient levels of carbon and silicon in the iron using the heat of the electric arc together with the simultaneous carbothermal chemical reduction of metal oxides by the carbonaceous reducing agents, such as coke and charcoal. The electrodes are immersed in the charge and slag layer that forms above the melted iron. This arrangement allows efficient heat transfer between the arc and the loading materials. However, the nature of the heat in the submerged arc furnace requires that the electrical conductivity of the load be controlled to allow simultaneous deep immersion of the electrodes to the load while avoiding excessive currents in the electrodes, which could cause that the electrodes will overheat. Iron ore has little electrical conductivity making it susceptible to melting in a submerged arc furnace. The previous production of iron for milling in submerged arc furnaces has been limited to the use of iron ore in the form of fines, coarse or granules as the main source of iron. An example of the use of a submerged arc furnace to melt the iron ore is disclosed in U.S. Patent No. 4,613,363 to einert. A disadvantage of conventional processes that produce iron using a submerged arc furnace is that the carbothermal reduction of minerals to produce iron requires large amounts of electrical energy, thereby increasing production costs. Alternatively, the most widely used processes for producing iron for mills (cupola and induction furnaces) require relatively expensive raw materials, such as old iron or steel scrap that are heavy; and previously reduced silicon sources such as silicon carbide or ferrosilicon, which are relatively expensive sources of silicon. All these characteristics have limited these previous processes to produce iron for molding. As a result, the iron industry has a continuous need for an economical and efficient process to produce iron for molding. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an efficient and economical process for producing cast iron using readily available and inexpensive supply materials. A further objective of the present invention is to provide a process for using old iron or steel scrap as the main source for producing iron for molding. Another object of the present invention is to provide a process for producing iron for molding in a submerged arc furnace. Another object of the present invention is to provide a process for melting old iron or steel scrap in a submerged arc furnace. A further objective of the present invention is to provide a process for melting silica and melting old iron or steel scrap simultaneously to produce iron for mold. Another object of the present invention is to provide a process for producing iron for molding where substantially no slag is formed. A further object of the present invention is to provide a process for melting old iron or steel scrap in a submerged arc furnace and increasing the silicon and carbon content of the iron to produce iron for molding. These and other objects of the present invention are basically achieved by a process for producing iron for milling comprising the following steps: supplying a load to a submerged arc furnace around the electrodes thereof, the load comprising a mixture of an iron source , a source of silicon and a carbonaceous reducing agent, the iron source comprising old iron or steel scrap and supplying electric power to the electrodes to generate an electric arc between them and heating the old iron or steel scrap, the source of silicon and the carbonaceous reducing agent in the furnace by the electric arc between the electrodes to melt the old iron or steel scrap and produce the iron for molding. The process of the present invention is capable of using old iron or cheap steel scrap in the submerged arc furnace to produce cast iron, while controlling the carbon and silicon content and substantially in the absence of slag formation. The silicon source is reduced to silicon in the presence of a carbonaceous reducing agent to increase and modify the silicon content of the iron for molding. The carbonaceous reducing agent produces carbon which dissolves in iron or steel. Other objects, advantages and remarkable features of the present invention will be apparent from the following detailed description, which, taken in conjunction with the appended drawings, discloses preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWING With reference to the drawing which forms part of these original disclosures: Figure 1 is a side elevational view partially in cross section of a submerged arc furnace for use in the process according to one embodiment of the present invention .

Detailed Description of the Invention The process of the present invention basically comprises the supply of old iron or steel scrap as a main source of iron, a source of silicon and carbonaceous materials which serve both as a carbon source for iron, reducing agents, to a submerged arc furnace to produce iron for molding. In preferred embodiments of the present invention, silica or a silica source is the main source of silicon. The heat produced by the electric arc in the furnace causes the carbonaceous reducing agent to reduce the silica to silicon which is taken up by the iron along with the carbon of the reducing agents. In preferred embodiments, the process is performed as a continuous process to simultaneously melt the iron sources and melt the silica sources in the presence of the carbonaceous reducing agent. As used herein, cast iron is used to define the resulting iron product having at least about 0.05 weight percent silicon and at least about 0.01 weight percent carbon. The kind of iron for milling includes various iron compositions, including, for example, iron ingots, gray iron, ductile iron, malleable iron and cast iron. The iron for milling produced by the invention can be used directly without further processing to make the desired product depending on the proposed use of the iron. In other embodiments, the resulting milling iron can be further processed to modify the composition and nature of the iron, for example, to produce steel. In embodiments of the invention, the resulting molten iron contains about 0.05 percent to 9.5 percent silicon and about 0.01 percent to 4.5 percent carbon with the rest of the iron and minor amounts of impurities such as sulfur, phosphorus, Manganese, aluminum, chromium, titanium and other metals. As used herein, the percentages are by weight unless otherwise indicated. In preferred embodiments of the invention, the iron for milling preferably comprises about 0.05 percent to 9.5 percent silicon and more preferably about 0.5 percent to 4.0 percent silicon and about 2.0 percent to 4.0 percent silicon. carbon. Normally, iron for milling contains less than 3.0 percent silicon, around 2.0 percent to 4.0 percent carbon and less than 1.0 percent sulfur, phosphorus, aluminum, manganese, chromium and other impurities. Preferably, the molten iron contains 0.10 weight percent sulfur or less. In embodiments, the iron for molds contains about 0.25 to 3.0 weight percent silicon. In other modalities, the iron for molds contains about 2.0 percent by weight of silicon. Referring to Figure 1, a submerged arc furnace suitable for performing the process of the present invention is illustrated. The submerged arc furnace 10 includes a bottom liner or hearth wall 12, side walls 14 and a roof or top wall 16 for defining a melting and melting zone 18 and collecting and removing dust, vapors and gases to a collection system . The supply openings 20 are provided in the roof 16 to supply the load or supply material to the furnace 10 by means of conveyors or supply materials 26. In an alternative supply system, the loading materials are introduced by emptying the supply directly in the of the existing load using a mechanical hopper loading scheme, as is known in the art. The outlet taps 22 are included in the side wall 14 to extract the melted metal 28 from the melting zone 18. A slag chute 24 can also be included in the side wall 14 to extract the slag 30 from the melting zone 18. The coating 34 of the furnace 10 can be cooled with a thin sheet of water (not shown).

A spray ring can be found immediately below the edge of the roof of the side wall by means of which the water is collected in a channel at the bottom of the side walls 14. In the embodiments of the invention, the roof or top wall can be divided in its longitudinal dimension to allow the loading material to be supplied at any point in the oven. Three alternating current electrodes 36 extend through the roof 16 to the melting zone 18. The electrodes are generally placed in a triangular configuration. In the embodiment of Figure 1, two electrodes are shown with the third electrode being placed behind one of the illustrated electrodes. The electrodes 36 are independently controllable to selectively adjust their vertical position within the oven and prevent overcurrents. The electrodes 36 can be raised or lowered to vary the length of the arch as is known in the art. The furnace is generally a three-phase alternating current-fed furnace with a variable voltage selection of 30-300 volts with a maximum current of approximately 100,000 amperes per phase. The electrodes may be, for example: graphite electrodes, precooked carbon electrodes; or Soderberg, or autocooking carbon electrodes, as is known in the art. The electrodes are preferably carbon electrodes of the various shapes known in the art. The exhaust duct 32 extends through the hood 16 positioned above the furnace to collect exhaust gases such as combustion gases, dust and vapors, emitted during the melting and melting phases of the process. The exhaust gases are taken to a baghouse to clean the gases before they are discharged into the atmosphere. The solids collected in the baghouse are recycled, processed, or disposed of in a conventional manner. In example, a suitable submerged arc furnace is produced by Elkem Technology of Oslo, Norway. In other embodiments, the submerged arc furnace may be a direct current (DC) arc furnace having a single electrode submerged in the charge with a suitable return electrode as known in the art, a plasma submerged arc furnace or an AC submerged arc furnace having at least two electrodes. The submerged arc furnace provides the continuous production of cast iron allowing the continuous supply of the furnace with the loading material and the melting of the melted metal from the lower regions of the furnace. The process can be easily extended for high production percentages, controlling at the same time the productivity and the output composition of the iron. A suitable supply conveyor, hopper loading system, or loading tubes as known in the art, can be used to continuously supply the loading materials to the furnace. The performance or production capacity of the furnace depends on the power fed to the furnace and the speed of supply of the kiln materials. The furnace can be designed for a power level in service of around 1 megawatt to 100 egawatts depending on the construction of the furnace, type of electrodes and charging materials. Generally, the alternating current furnace produces one ton of iron product for milling with an electric power input of around 600 kilowatt-hours. Depending on the loading materials, the characteristics of the product and the construction of the furnace, an AC submerged arc furnace can produce iron for milling at an input speed of between 500 to 1400 kilowatt-hours per ton of product . The process of the invention is preferably performed in the AC submerged arc furnace using a power and supply level so that the tips of the electrodes are embedded several feet in the base of the supply material in the furnace and inside the furnace. one foot of the molten metal pool puddle. In this way, the area of the arch is formed near the metal puddle or bathroom. The furnace is operated to maintain the temperature of the melted alloy in the furnace between 2100 ° F to 3200 ° F. In preferred embodiments, the temperature of the furnace hearth is kept high enough to allow adequate reheating of the melted metal for easy casting and handling or downstream processing. The tips of the electrodes that are immersed in the material and produce an arc near the melted metal provide a good heat transfer to the unprocessed material by radiation from the arc and the melted material and by convection of the hot carbon monoxide gas that is continuously being generated by the chemical reduction of metal oxides and silica by carbon in the lower regions of the load base. A standard submerged arc furnace includes a self-protection mechanism or control system to automatically raise the electrodes of the load to avoid excessive electrode currents which may result when the conductivity of the charge materials increases above a threshold level. When the electrodes are removed from the load base material in response to increases in the conductivity of the load, the temperature near the hearth of the furnace decreases and, if prolonged, may result in inadequate heating and melting of the furnace. scrap and incomplete melting of silica. It is important to have the base of charge supply at a height and electrical conductivity that allows the electrodes to be embedded deep into the base so that the arc forms around a foot above the metal bath. Achieving satisfactory immersion or penetration of the electrodes of the submerged arc furnace to the furnace load base depends on several factors including the specific electrical resistivity of the charged materials, their physical size, their distribution in the mixture and the selected operating voltage. for the oven. The operating voltage is selected to compensate the relationship between the voltage, the current of the electrodes and the resistance of the load materials to achieve a deeper immersion of the electrodes to the load. The resistance of the load base can be varied by changing the materials of supply and the size of the materials to optimize the operation in order to obtain the deeper penetration of the electrodes in the load base for a certain operating voltage. The amount of electrical energy required per ton of iron alloy produced depends to a large extent on the degree of oxidation or reduction of the charged metallic materials, the amount of silica and other oxides required to reach the desired composition or target, the optimization of the operation of submerged electrodes and the skill of the oven operator. Alloys that contain about 0.5 percent to 4 percent carbon and about 0.25 percent to 2.5 percent silicon typically require around 500 to 650 kilowatt-hours per ton of alloy produced. The higher silicon percentages and consequently the lower carbon percentages require an increase of about 10 kilowatt-hours for highly non-oxidized iron sources for each additional increase of 0.1 percent in silicon above 2.5 percent silicon in the alloy. The raw materials that constitute the load that will be supplied to the submerged arc furnace are preferably mixed before being supplied to the furnace. Alternatively, the different components of the load can be supplied simultaneously with materials separated in the furnace at a controlled rate and in the desired proportions. The composition of the resulting molten iron depends on the composition of the load and the degree of chemical reduction that occurs in the furnace. The loading materials comprise an iron source which includes old iron or steel scrap, a source of silicon and a carbonaceous reducing agent as discussed below in more detail. Generally, silica is the main source of silicon. The melting of the iron and the melting of the silica in preferred embodiments is substantially in the absence of an oxygen supply or oxidizing agent and the absence of slag-forming materials. Old iron and steel scrap are available as goods as is known in the metal industry. Market prices and the class of various types of old iron and steel scrap are regularly reported in various industry publications such as American Metal Market. Old iron and steel scrap as known in the art is classified according to the particle size and composition of the metal. For example, a type of steel scrap is defined as: "Steel for milling, 21 max." Suitable sources of iron for use in the present invention include mill scale, direct reduced iron (DRI), hot briquette iron (HBI), iron carbide, iron filings, iron lathe shavings, crushed steel for automobiles and cans of steel and mixtures thereof. The composition of old iron or steel scrap will influence the composition of the resulting molten iron. Various sources or classes of old iron can be mixed before being supplied to the kiln to provide the desired inlet and outlet compositions. The iron source generally comprises at least about 50 percent scrap, preferably about 75 percent scrap and more preferably about 90 weight percent old iron or steel scrap. The source of iron can be based entirely on old iron or steel scrap. Old iron or steel scrap can be mixed with other iron or steel materials to increase or decrease the percentage of various alloying metals in the resulting foundry iron composition. For example, direct reduced iron (DRI) and hot briquetted iron (HBI) which normally contain about 90 percent iron and have few undesirable residual elements, such as copper, can be added to increase the iron content of iron for milling, thereby diluting the alloying materials and reducing the percentage of undesirable metals, such as copper, chromium and manganese, which are present in the other fillers, such as the steel scrap used to produce the iron for the mill. The quantity and type of materials combined with old iron and steel scrap are determined in part by the efficiency of the furnace in the use of its components and the relative cost of the supply materials. For example, scrap heavy steel that has few undesirable residual elements, is expensive compared to cast iron filings or steel lathe shavings, so that large amounts of heavy scrap, while desirable from the point of view of residual elements, are usually undesirable from an economic point of view. By comparison, steel lathe shavings, which are small in particle size and cheap compared to heavy steel scrap, generally contain high levels of undesirable residual elements. The use of the submerged arc furnace allows the use of very finely calibrated scrap materials, which, being less expensive than heavy scrap is an economic advantage to produce iron for milling over other processing methods. The particle size of the filler material is important to obtain adequate heating and melting of the scrap although there is no absolute limit. Old iron or steel scrap generally has a size of 60 centimeters or less in any dimension. An adequate size of old iron or steel scrap is about 25 millimeters or less. In alternative modalities, the particle size of old iron or steel scrap is less than 0.5 centimeters. The particle size of the supply is selected to be easily handled and charged to the furnace and melted without bridging the electrodes or between the electrodes and the side walls of the furnace. The submerged arc furnace in accordance with the preferred embodiments is capable of handling scrap with small particle size of less than .25 of an inch in the largest dimension, such as cast iron filings and steel lathe shavings which are traditionally difficult to obtain. process without the steps of previous processing such as agglomeration or briquetting. For example, lamination and lamination debris sheets are generally 6 inches or less and DRI / HBI are about 1-1 / 4 to 6 inches in the largest dimension. The particle size of old iron or steel scrap can vary from small fines or filings to large pieces. The upper limit of size is generally the face-to-face space between the electrodes in an AC submerged arc furnace or between the electrode and the refractory wall of the furnace in a DC submerged arc furnace to avoid bridging . Old iron and steel scrap are highly conductive compared to iron ore so that in the use of scrap materials as the iron sources in the present process, the electrical conductivity and resistivity of the supply must be selected and controlled for allow deep immersion of the electrodes. The electrical resistivity of the supply can be modified by the selection of the particle size of the supply and the type of materials. Reducing the particle size of the supply material increases the resistivity of the supply. The most efficient particle size will depend on its inherent resistivity and the dependence of the permeability of the furnace charge to the passage of the exhaust gases in the particle sizes of the charged materials. Processing costs to reduce particle size are also considered in the selection of the particle size of the charge. In preferred embodiments, the supply material does not substantially contain iron ore although minor amounts of iron minerals may be added to modify the resistivity of the supply. Highly oxidized laminate waste or resistive iron sources can also be used to modify the resistivity. The filler material also includes an amount of a silicon source such as, for example, silica, silica source or silicon dioxide in a reducible form. Silica is the preferred silicon source. The source of the silicon dioxide may be some commercially available material which can be melted and reduced to silicon in the submerged arc furnace in the presence of a carbonaceous reducing agent simultaneously with the melting of old iron and steel scrap. Silicon is produced in a form that can be combined directly with iron. In preferred embodiments, the source of silicon is a quartzite of high purity. In alternative embodiments, other sources, as known in the art, can be used as a mineral containing silica, waste and sand that has been washed to remove clays and other impurities. Normally, the charge is substantially absent from ferrosilicon or silicon carbide. In preferred embodiments, the silicon source contains at least about 98 weight percent silica. The impurities are preferably removed to prevent the formation of slag in the furnace as the slag increases the energy demand for the melting and melting of the supply. The quartzite used in preferred embodiments as the main source of silica is substantially free of clays and other foreign materials such as metal oxides which would contribute to the formation of undesirable slag., as well as the undesirable contamination of the iron for resulting milling with metals in trace condition. Quartzite is a quartzite crystal of high purity usually calibrated or ground quartzite that contains at least 95 percent silica. The particle size of the silica source is determined by the particular dimensions of the furnace, the electrodes and the residence time of the supply materials in the furnace to ensure complete reduction to silicon in the presence of a reducing agent. Generally, quartzite has a particle size of 4 inches or less although large kilns may use larger particles. The silica source preferably contains less than 0.5 weight percent aluminum, magnesium, zinc and titanium oxides. Some of these metals, such as zinc, can be oxidized and removed by a flow of air or oxygen through the furnace and removed in the baghouse. Other metal oxides are reduced in the furnace to metal that can be combined with iron. The amount of the silicon source added to the furnace with the supply is determined by theoretical calculations of the desired silicon content of the resulting molten iron. The amount of the added silicon source is also based on stoichiometric calculations taking into account the calculated silicon content of the old iron and other supply materials and the calculated losses due to the predicted volatilization in the reduction of silica to elemental silicon. The silicon source can be added in the amount of 0.01 percent to 20 percent by weight based on the weight of old iron or steel scrap. Typically, the silicon source is less than about 10 percent and preferably less than about 5 percent by weight of the old iron or steel scrap. Generally, about 90 percent or more of the available silicon is combined with iron while the remaining silicon is lost as silica vapor and, if formed, as slag. Silicon recoveries typically greater than 90 percent are experienced when alloys of 3 percent or less of silicon content are produced. The carbonaceous reducing agent can be a carbon source capable of reducing the silica in the furnace. Examples of suitable carbonaceous reducing agents include animal charcoal, charcoal, coal, coke such as petroleum or bituminous coke, wood chips and mixtures thereof. The preferred carbonaceous materials have a high fixed carbon content and also have a low ash content, low moisture content, low levels of calcium oxide and aluminum oxide and low levels of sulfur and phosphorus. The carbonaceous materials in preferred embodiments also have high reactivity and high electrical resistance. A preferred carbonaceous material is hardwood splinter free from the bark of a hardwood such as oak. The wood chips provide a carbon source to reduce the silica to elemental silicon, as well as a means to reduce the electrical conductivity of the supply in the furnace so that the electrodes can be immersed deep in the submerged arc furnace to maintain the temperature of the Desired melting of the scrap and the melting of the silica. The supply may contain about 5 percent to 40 weight percent of the carbonaceous reducing agents based on the weight of the iron. Preferably, the supply contains at least about 5 percent carbonaceous reducing agents based on the weight of the iron. The amount of the carbonaceous reducing agent added to the supply is determined by calculating the stoichiometric amount of fixed carbon required to reduce the silica to silicon and the amount of free carbon required to provide the desired carbon content in the resulting molten iron. The theoretical calculations are based on the fixed carbon content of coal, charcoal, coke, wood chips and other carbonaceous reducing agent according to standard calculations known in the metallurgical industry. The amount, type and particle sizes of the carbonaceous reducing agent affect the resistivity of the supply material. For example, charcoal can be used in large proportions to increase resistivity since preferred vegetable carbons have a higher resistivity than coke or coal. The process can be done in the complete absence of the coke. The particle size of the carbonaceous reducing agent is selected according to the composition of the delivery materials, the reactivity and the resistivity or electrical conductivity of the delivery composition. An adequate size of wood chips is usually about 6 inches or less in the longest dimension. A suitable size for coke for metallurgical use is about 1/2 inch or less. Coal is usually around 2 inches or less while animal coal and charcoal are generally 6 inches or less in the largest dimension. The composition of the charge preferably contains only minor amounts of sulfur, phosphorus, calcium, aluminum, chromium, zinc and other metals which are not desirable in the iron alloys for molding. The use of filler materials that have few impurities contributes to the formation of slag or very little formation. Operating the submerged arc furnace substantially in the absence of slag has the added benefit of the heat of the melted iron by preheating the supply material that is charged to the furnace as there is no slag or very little that protects the melted iron from the supply material. Whenever possible, slag formation is generally avoided as the presence of slag increases energy consumption and reduces the efficiency of scrap melting and the reduction of silica to silicon. Excessive slag formation also inhibits the flow of supply materials to the furnace heating zone and increases the likelihood of a supply bridge in the furnace. In embodiments where the supply material contains large amounts of sulfur or other impurities, a slag-forming component may be added as necessary. Suitable slag-forming components include limestone (calcium carbonate), lime (calcium oxide), or magnesia although other slag-forming components known in the art can be used. When necessary for efficient operation, lime having a particle size of less than 3 millimeters can be used. In preferred embodiments, the process for producing iron for milling is performed in a submerged arc furnace in the absence of iron ore and coke and generally produces an iron product for milling having a temperature of between 2100 ° F to 3200 ° F and less than 0.1 percent by weight of slag compared to 1 percent to 10 percent by weight slag from conventional iron processes for smelting using a submerged arc furnace. In general, iron for milling occurs substantially in the absence of slag. The embodiments of the process of the invention are disclosed in the following non-limiting examples. EXAMPLES 1-12 Steel scrap from clean steel pieces and pieces of cut plate with little surface oxide was mixed with coke, quartzite and wood chips to produce a supply mixture for each example. The metal analysis of the scrap is shown in Table 1. The quartzite was a washed Spanish quartzite of great purity with a particle size of less than 3 millimeters. The coke was fine from metallurgical coke having a particle size of less than 3 millimeters. The wood chips were Norwegian oak having an average particle size of 75 mm by 50 mm by 15 mm. The scrap had an average particle size of 25 millimeters by 5 millimeters by 4 millimeters. The wood chips had about 17 weight percent fixed carbon and the coke had about 93 weight percent fixed carbon for examples 1-8 and the coke had about 86.5 weight percent fixed carbon for examples 9-12.

TABLE 1 The supply material for Examples 1-12 were mixed in the proportions shown in Tables 2 and 3. The percentage values for the wood, coke and quartzite chips presented in Table 3 are by weight based on the weight of the Scrap.

TABLE 2 TABLE 3 The furnace used in examples 1-12 was a bench scale submerged arc furnace made by Elkem Technology, Norway. The submerged arc furnace was a single-phase, two-electrode alternating current furnace with 300kVA transformer capacity, maximum current 3000 A, with secondary voltage receptacles of 15-150V in 1.5 V steps. The furnace was made by loading 16 kilograms of steel scrap and 5 kilograms of coke in the oven and the electrodes lowered to touch the scrap. The energy was turned on to melt the scrap metal. The mixed supply material was charged to the oven to keep the oven half full with scrap. The melted metal was extracted and analyzed. The analysis of each Example is shown in Table 4. The furnace bath cast temperatures were around 1250-1550 ° C.

CQ < in? n These examples show that quartzite is melted simultaneously with the melting of scrap metal. The carbon and silicon content of the resulting iron is proportional to the silica and fixed carbon in the supply. EXAMPLE 13 A computer simulated operation consisted of a supply mix containing 2000 pounds of old iron, 100 pounds of wood chips, 85 pounds of coal, 20 pounds of coke and 75 pounds of quartzite loaded into a submerged current arc furnace. alternates at an alloy production rate of 75,590 tons per hour. The projected power input to the furnace was 50,000 kilowatts. The supply of simulated old iron was composed of 40 percent crushed steel for automobiles, 15 percent melt waste again, 15 percent scrap steel # 1, 20 percent Cast Iron filings, 5 percent percent plate / tin cans and 15 percent lathe shavings mixed with low chromium content. The supply mix had a calculated alloy composition of 2.5 percent silicon, 3.85 percent carbon, 0.40 percent manganese, 0.10 percent chromium, 0.15 percent nickel, 0.15 percent copper, 0.01 percent of sulfur, 0.05 percent of phosphorus and 0.03 percent of tin with the rest of the iron where the percentages are by weight. The resulting projected iron product extracted from the furnace had an iron content of 92.5 percent, a carbon content of 3.85 percent and a silicon content of 2.50 percent by weight with the rest of the impurities. The calculated energy consumption was 650 kilowatt-hours per ton of iron alloy. EXAMPLE 14 A computer simulated production batch consisted of a supply mix containing 2000 pounds of old iron, 100 pounds of wood chips, 210 pounds of coal, 20 pounds of coke and 393 pounds of quartzite loaded into a submerged arc furnace. of alternating current at a projected alloy production speed of 34.68 tons per hour. The power input of the selected oven was 50,000 kilowatts. The projected old iron was a blend that comprised 40 percent crushed steel for automobiles, 15 percent melt wastes again, 10 percent mixed lathe shavings, 20 percent Cast Iron filings, 5 percent of plate / tin cans and 10 percent lathe shavings mixed with low chromium content. The supply mix had a calculated alloy composition of 9 percent silicon, 1.5 percent carbon, 0.4 percent manganese, 0.18 percent chromium, 0.09 percent nickel, 0.19 percent copper, 0.14 percent of sulfur, 0.03 percent of phosphorus and 0.02 percent of tin and the rest of the iron, where the percentages are by weight. The resulting projected iron alloy extracted from the furnace had an iron content of 87.87 percent, a carbon content of 1.50 percent and a silicon content of 9.01 percent by weight with the rest of the impurities. The calculated energy consumption was 1370 kilowatt-hours per ton of iron alloy. EXAMPLE 15 A computer simulated lot consisted of a supply mix containing 2000 pounds of old iron, 100 pounds of wood chips, 35 pounds of coal, and 55 pounds of quartzite loaded to an AC submerged arc furnace at a rate of Projected alloy production of 80,922 tons per hour. The selected furnace power was 50,000 kilowatts. The input of old iron was composed of 40 percent crushed steel for automobiles, 15 percent waste melted back melt, 10 percent mixed steel lathe shavings, 20 percent Cast Iron filings, 5 percent percent plate / tin cans and 10 percent lathe shavings mixed with low chromium content. The simulated supply mixture had an alloy composition of 2 percent silicon, 2 percent carbon, 0.40 percent manganese, 0.10 percent chromium, 0.15 percent nickel, 0.15 percent copper, 0.01 percent of sulfur, 0.05 percent of phosphorus and 0.03 percent of tin and the rest of the iron where the percentages are by weight. The resulting projected iron alloy extracted from the kiln had an iron content of 94.52 percent, 2.05 percent silicon and 2.00 percent carbon with the rest of the impurities. The calculated energy consumption was 600 kilowatt-hours per ton of iron alloy. While various embodiments have been shown to illustrate the invention, those skilled in the art will understand that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

Claims (33)

1. CLAIMS 1. A process for producing iron for milling by comprising the following steps: supplying a load to a submerged arc furnace around its electrodes, the charge comprising a mixture of an iron source, a source of silicon and a carbonaceous reducing agent, the iron source comprising old iron or steel scrap, supplying electrical power to the electrodes to generate an electric arc between them and heating the old iron or steel scrap, the silicon source and the carbonaceous reducing agent in the furnace by the electric arc between the electrodes to melt the old iron or steel scrap and produce the iron for molding.
2. 2. The process of claim 1, comprising the constant supply of the load and the continuous removal of the molten iron from the furnace.
3. 3. The process of claim 1, further comprising the melting of old iron or steel scrap and the production of iron for milling having a carbon content of 0.01 percent to 4.5 percent by weight.
4. The process of claim 1, comprising the melting of old iron or steel scrap and the production of cast iron with a silicon content of 0.05 percent to 9.5 percent by weight.
5. The process of claim 1, wherein the source of silicon is substantially quartzite or pure sand.
6. The process of claim 1, wherein the carbonaceous reducing agent is selected from the group consisting of wood chips, animal charcoal, charcoal, coal, petroleum coke, bituminous coke and mixtures thereof.
7. 7. The process of claim 1, comprising the melting of old iron or steel scrap and the production of iron for milling substantially in the absence of the slag.
8. The process of claim 1, wherein the iron source comprises at least 50 weight percent old iron or steel scrap.
9. The process of claim 1, wherein the iron source comprises at least about 90 weight percent old iron or steel scrap.
10. The process of claim 1, wherein the filler comprises about 0.01 percent to 20 weight percent silica as the source of silica based on the total weight of the old iron or steel scrap.
11. The process of claim 1, wherein the filler comprises at least about 5.0 weight percent of the carbonaceous reducing agents based on the weight of the iron in the filler.
12. The process of claim 1, wherein the process is performed in the absence of coke as a filler.
13. The process of claim 1, wherein the submerged arc furnace is an alternating current submerged arc furnace having at least two separate electrodes, each with a lower end, the process comprising immersing the ends of the electrodes in the load with the ends separated above a bath of molten metal in the furnace to produce an arc zone above the bath.
14. The process of claim 13, comprising immersing the ends of the electrodes in the load at least about 2 feet.
15. 15. The process of claim 13, comprising immersing the electrodes in the charge wherein the ends of the electrodes are separated from the molten metal bath by about 1 foot.
16. 16. The process of claim 1, wherein the furnace includes at least one electrode, the process comprising applying an electrical potential of 100 volts to at least one electrode.
17. The process of claim 1, wherein the silicon source is silica and the process further comprises melting the silica in the presence of the carbonaceous reducing agent to produce silicon and producing the iron for the mill having a silicon content of 0.05 percent to 9.5 percent by weight.
18. 18. The process of claim 1, where the submerged arc furnace is a plasma submerged arc furnace.
19. 19. The process of claim 1, further comprising melting the old iron or steel scrap to produce the iron for the mill having a carbon content of 2 percent to 4 percent by weight.
20. The process of claim 1, further comprising melting the old iron or steel scrap to produce the iron for the mill having a silicon content of 0.5 percent to 4.0 percent by weight.
21. The process of claim 1, further comprising melting the iron source in the furnace at a temperature between 2100 ° F and 3200 ° F.
22. 22. A continuous process for producing iron for milling comprising the following steps: continuously supplying a load comprising a mixture of old iron or steel scrap, a source of silica and a carbonaceous reducing agent to a submerged arc furnace around its electrodes , supply electrical power to the electrodes to generate an electric arc between them and melt the old iron or steel scrap and simultaneously melt the silica source in the presence of the carbonaceous reducing agent by the electric arc between the electrodes to produce silicon and produce cast iron having a silicon content of 0.05 percent to 9.5 percent by weight and a carbon content of 0.01 percent to 4.5 percent by weight substantially in the absence of the slag.
23. 23. The process of claim 22, wherein the old iron or steel scrap has a particle size of less than 60 centimeters.
24. 24. The process of claim 22, wherein the old iron or steel scrap has a particle size of less than 0.5 centimeters.
25. 25. The process of claim 22, wherein the charge is substantially in the absence of iron ore and ferrosilicon.
26. 26. The process of claim 22, wherein the filler contains at least about 5.0 percent by weight of wood chips based on the weight of the iron in the filler.
27. 27. The process of claim 22, wherein the source of silica is substantially pure quartzite.
28. The process of claim 22, wherein the mill iron has a silicon content of 0.25 percent to 3.0 percent by weight.
29. 29. The process of claim 22, wherein the mill iron has a silicon content of 2.0 percent by weight.
30. 30. The process of claim 22, comprising supplying the charge to the furnace substantially in the absence of the coke.
31. The process of claim 22, wherein the carbonaceous reducing agent is selected from the group consisting of charcoal, wood chips, coal, coke and mixtures thereof.
32. 32. The process of claim 22, wherein the old iron or steel scrap contains at least about 98 weight percent iron.
33. 33. The process of claim 22, comprising operating the furnace at a bath temperature between 2100 ° F and 3200 ° F.