US3652427A

US3652427A - Method for monitoring the oxygen and carbon contents in a molten metal

Info

Publication number: US3652427A
Application number: US886819A
Authority: US
Inventors: Harold W Flood; George H Hall; Herman P Miessner
Original assignee: Arthur D Little Inc
Current assignee: Arthur D Little Inc
Priority date: 1969-12-22
Filing date: 1969-12-22
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28

Abstract

Method and apparatus for continuously measuring the oxygen and carbon contents of a molten metal, particularly of iron in a BOF furnace. A wire containing as a component a metal which is a getter for oxygen continuously fed into the melt. A concentration cell is established and the EMF developed is used as a measure of oxygen content. Carbon content is a function of the reciprocal of the oxygen and is calculated therefrom. Automatic control over the oxygen feed results in automatic control over the carbon content. When the EMF of the cell is temperature dependent, means are incorporated for simultaneously measuring the melt temperature.

Description

United States Patent Flood et al. [451 ii 2, 1972 [54] METHOD FOR MONITORING THE 3,442,773 5/1969 Wlson ..204/| r OXYGEN AND CARBON CONTENTS IN 3,297,551 1/1967 Alcock ....204/l T A TEN E A 3,378,478 4/1968 Kolodney et al ..204/l T X 3,420,765 1/1969 Uhrenholdt ..204/225 X [72] inventors: Harold W. Flood, Acton; George H. Hall, 3,578,578 5/1971 Krusenstiema ..204/l95 Westford; Herman P. Miessner, Winchester, all Of Mass. Primary Examiner-G. L. Kaplan [73] Assignee: Arthur D. Little, llnc., Cambridge, Mass. AtwmeyT'BeSSIe Lepper [22] Filed: Dec. 22, 1969 [57] ABSTRACT [211 App]. No.: 886,819 Method and apparatus for continuously measuring the oxygen and carbon contents of a molten metal, particularly of iron in a BOF fumace. A wire containing as a component a metal [52] Cl 533 5 which is a getter for oxygen continuously fed into the melt. A [51] Int Cl 601' 27/28 concentration cell is established and the EMF developed is [58] Fie'ld 324/29 used as a measure of oxygen content. Carbon content is a 324/65R 266/35 function of the reciprocal of the oxygen and is calculated therefrom. Automatic control over the oxygen feed results in 5 6] References Cited automatic control over the carbon content. When the EMF of the cell is temperature dependent, means are incorporated for UNITED STATES PATENTS simultaneously measuring the melt temperature.

3,323,050 5/1967 Mausteller et al. ..324/29 X MANUAL MOTOR MANUAL MOTOR SPEED CONTROL SPEED CONTROL 4 Claims, 7 Drawing Figures POTENTIOMETER PATENTEDmzame 3,652,427

. Harold W. Flood George H. Hall Hermon P. Meissner INVENTORS Attorney PATEHTi-Inmzs 1912 3, 652.427

SHEET 2 UF 5 MANUAL MOTOR MANUAL MOTOR SPEED CONTROL 49 SPEED CONTROL POTENTIOMETER Harold W. Flood George H. Hall Hermon F? Meissner INVENTORS w At'rorggy PATENTED MAR 2 8 I972 SHEET 3 UF 5 CONTROLLER FOR MOTOR DIRECTION CONTROLLER FOR MOTOR DIRECTION l EMF SIGNAL PROCESS POTENTIOMETER O2 CONCENTRATION MEASUREMENT Fig. 3

E MF SIGNAL PROCESS POTENTIOMETER TEMPERATURE MEASUREMENT INVENTORS Harold W. Flood, George H. Hall Hermon P. Meissn e r v-At fo'r'ney 'INVENTORS Attorney SHEETS 0F 5 P'ATENTED MR 2 8 I972 Hordld w. Flood George H. Hall Hermon R-Meissner BY flw; 4

METHOD FOR MONITORING THE OXYGEN AND CARBON CONTENTS IN A MOL'IEN METAL This invention relates to the monitoring and controlling of the oxygen content in a molten metal, and more particularly to the continuous monitoring and controlling of oxygen in molten iron which is being lanced with oxygen to remove carbon to a predetermined level.

Although the method and apparatus of this invention are applicable to the monitoring and controlling of oxygen in many different molten metals, including among others copper, lead, nickel, silver, platinum, gold, tin and cobalt, the invention will be described in terms of its application to molten iron, and particularly to its use in connection with the basic oxygen furnace (BOF). However, it is to be understood that the invention in its broadest aspects is not limited to its use with the BOF system; and it will be apparent that it is also applicable to open hearth and electric furnace steelmaking.

The reduction of iron ore with coke in a blast furnace leaves residual carbon in the iron which must be removed. This is now generally done in a basic oxygen furnace BOF in which the oxygen is lanced under pressure at supersonic velocities onto the surface of the melt. The reactions involved in the melt are exothermic and the temperature and carbon content at any one time are functions of the amount of oxygen consumed in the reaction with carbon. Since the purpose of the BOF operation is to reduce the carbon content of the iron to a predetermined level, it is necessary to be able to determine the amount of carbon in order to determine the amount of oxygen required. Thus it is necessary to have some way to monitor and control the amount of oxygen in the melt which in turn serves as a control over the amount of carbon within the melt. It would also be highly desirable to have apparatus which made it possible to monitor the rate of change of oxygen (or carbon) content and the rate of change of steel temperature to cause the heat of steel to arrive at a predetermined oxygen (or carbon) endpoint at a desired temperature.

The most commonly used method of determining carbon content is to stop the oxygen lancing, withdraw a sample of the melt and analyze it spectroscopically. This of course gives a measure of the carbon content at the time that the oxygen lancing was stopped. This type of evaluation (stopping, withdrawing a sample and analyzing) must be repeated periodically until the desired carbon content is reached. If the oxygen lancing is carried out too long and as a result the carbon content is reduced below the desired concentration level, then some recarbonizing must be done. It is desirable to avoid the need for recarbonizing.

Once the carbon has been reduced to the desired level it may be necessary to kill the heat to prevent any residual dissolved oxygen from reacting with the carbon and thus altering the carbon level. This is typically done by adding aluminum to react with the oxygen. If at the end of the heat the precise amount of residual oxygen is known then it becomes a simple matter to calculate the stoichiometric quantity of aluminum required and add it immediately without having to allow for changes in oxygen concentration while time-consuming analyses are being made.

In the commonly used method of determining carbon content by spectrographic analysis of a sample during the BOF operation, it is necessary to spend from about to percent of the entire processing time in the BOF in making carbon content determinations. If this downtime could be eliminated or markedly reduced, it would mean that a BOF furnace could produce two or three additional batches in an 8-hour shift, assuming that the present cycle time (charge-to-charge) is now to minutes. This in turn would mean that a typical BOF furnace handling 200 tons in a single batch could handle an additional 200 to 600 tons per shift for each furnace. It can be seen that the provision of a method and apparatus capable of continuously and accurately monitoring and controlling the amount of oxygen being lanced into a BOF furnace would be highly desirable, both from an economic and quality-control basis.

Several probes for insertion into molten steel to measure oxygen content have recently been disclosed. (See for example US. Pat. No. 3,468,780 and Journal of Metals, 20: 74-76, June 1968.) These probes are of relatively complicated construction, they must be made of a refractory material and constructed to be gastight, and they require a continuous supply of gas for circulation therethrough. It would therefore be desirable to provide a means for measuring oxygen content which was simple in construction, easy to operate and amenable to integration with a computer system.

It is therefore a primary object of this invention to provide an improved method for continuously monitoring and controlling the oxygen content of a molten metal bath being treated with oxygen, the monitoring and controlling of the oxygen content being used to indirectly monitor and control the amount of carbon content in the molten metal. It is another object of this invention to provide a method of the character described which is particularly suited to monitor and control the temperature and the oxygen lanced into a BOF system in which the carbon content in molten iron is reduced to a predetermined level. It is yet another object to provide a method for automatically controlling and monitoring the oxygen content in combination with a method of automatically cutting off the flow of oxygen through the lance when the carbon is reduced to a predetermined minimum. An additional object of this invention is to provide a method of lancing oxygen into a molten iron bath to provide molten iron or steel at a predetermined temperature with a predetermined amount of carbon free of unreacted oxygen and containing desired alloying constituents.

It is another primary object of this invention to provide improved apparatus for monitoring and controlling the amount of oxygen introduced into a molten metal to indirectly control the amount of carbon contained within the melt. It is another object of this invention to provide an apparatus of the character described which is particularly suitable for use with a BOF system to provide a melt with a predetermined carbon content at a predetermined temperature and time, while at the same time making it possible to calculate precisely how much additive must be added to kill the excess oxygen in the melt. Another object of this invention is to provide apparatus of the character described which is particularly well suited to automatic computer control. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.

The invention accordingly comprises the several steps and the relation of one or more such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates partly in cross section and partly in diagram, a basic oxygen furnace having the monitoring and controlling means of this invention associated therewith;

FIG. 2 is a detailed circuit diagram illustrating exemplary means for manually adjusting the rate at which the wires are introduced into the melt, one wire of which passes down through the oxygen lance;

FIG. 3 is a detailed circuit diagram illustrating exemplary means for automatically adjusting the rate at which the wires are introduced into the melt, both wires of which pass down through the oxygen lance;

FIG. 4 is a plot (not to any scale) illustrating the general relationship between EMFs generated by the concentration cell set up and oxygen content for a series of temperatures;

FIG. 5 is a cross section of the wire of FIG. 1 illustrating the manner in which a concentration cell is established for measuring oxygen concentration;

FIG. 6 is a cross section of one embodiment of a shield for protection of the wires to be inserted into the melt; and

FIG. 7 is a diagram of one embodiment of this invention showing the means by which automatic monitoring and control of oxygen, and hence of carbon, content in the melt in a BOF furnace may be achieved.

In the method of this invention, oxygen content is determined by measuring the EMF of a concentration cell which is formed by continuously supplying a wire into the molten metal, the wire containing as one of its principal constituents a metal which is a getter for oxygen in the melt into which the wire is inserted. The reversible (null-balance) oxidation voltage developed between the wire electrode and the melt is dependent upon the dissolved oxygen content of the melt and, in many cases, it is a function of the melt temperature. In such cases where the oxygen content is temperature dependent such as in steel making it is necessary, also, continuously to determine the melt temperature. This is conveniently done by continuously supplying a second wire to the melt to form a thermocouple junction with the melt.

The dissolved oxygen concentration is directly related to the dissolved carbon concentration by virtue of their equilibrium with CO at 1 atmosphere during the blow. If the reversible oxidation voltages are known for the melt at the beginning of lancing and at the desired carbon content at the end of lancing, the system is readily calibrated to provide a useful measure of the instantaneous carbon content of the melt at any one time. By calibrating the system at several temperatures of interest, the relationship between dissolved carbon and output voltage can be noted and supplied to a computer which in turn develops appropriate signals for transmission to an oxygen feed-control system as well as to other components of the apparatus if desired. Such components may include, but are not limited to, the mechanisms which control the position of the oxygen lance, the amount of aluminum fed in to kill" the heat, and the amount of alloying constituents added.

The EMF's obtained from the concentration cell, along with that from the thermocouple if used, are amenable to any desirable data processing technique. The voltages can, of course, be read directly by an operator, but they are preferably introduced into a suitably-designed computer system as will be explained in detail in the discussion of the embodiment shown in FIG. 7.

FIG. 1 illustrates in simplified form a cross section of a typical BOF system, and adds in diagrammatic form the general circuitry involved in the method and apparatus of this invention in continuously monitoring and controlling oxygen content directly or carbon content indirectly. The apparatus shown in FIG. 1 provides for simultaneous measurement of the temperature of the molten steel since the EMF generated in the concentration cell is temperature-dependent in the system used in FIG. 1 to illustrate this apparatus embodiment.

The BOF furnace 10 of FIG. 1 is shown in very simplified form to comprise an outer metal vessel 11 lined with a suitable refractory 12. Within the vessel is contained the melt 13 generally having a slag layer 14, which is to be lanced by introduction of high-pressure, supersonic velocity oxygen 15 delivered from lance 16. The construction of this lance is wellknown and is not part of this invention. It will of course be appreciated by anyone skilled in the art that the furnace 10 may be tilted or rotated for discharging the melt; but this mechanism for rotating is not shown inasmuch as it is wellknown. A first wire 17, containing as one principal constituent a getter for the oxygen dissolved in melt 13, is fed from a supply roll 18 to contact an electrical junction-forming member 19 and pass over a guide roll 20 before entering a protective sheath 21. Wire 17 may contain any suitable metal as the oxygen getter which is above the melt metal in the electromotive series. By suitable is meant a metal which will not contaminate the melt and which has a sufficiently high melting point in the form it is present in the wire to permit it to be inserted through the slag layer 14 and into the melt 13 to be monitored. In the case of molten iron or steel suitable oxygengetter metals include aluminum, magnesium, chrominum, manganese and zinc. The getter metal may be alloyed with one or more other metals. Examples ofsuch alloys include, but are not limited to Alumel (94.5% Ni, 2.5% Mn, 2% Aland 1% Si); Thermenol (80.5% Fe, 16.0% Al and 3.5% Mo); Nimonic (50.0% Ni, 20% Cr, 18.0% percent Co, 5% Fe, 2.5% Ti and 1.5% A1); and Inconel 700 (52.0% Ni, 19.0% C0, 15.0% Cr, 5.0% Mo, 4.5% A1, 3.5% Ti and 1.6% Fe).

Since the wire 17 fed into the melt 13 is continuously being melted, suitable means are provided to continuously advance wire 17 at a rate equivalent to that at which it is consumed in the melt. The driving means are preferably automatically controlled to ensure continuous and sufficient penetration of the wire tip through the slag layer 14 into the melt 13. The movement of wire 17 in the embodiment of FIG. 1 is accomplished through the use of a driving pinch roll 22 which is driven by a motor 23 mechanically linked, such as through shaft 24, to roll 22. Adjustments in the operation of motor 23, and hence adjustments in the speed of the movement of wire 17, may be made either manually or automatically. Apparatus for effecting manual control is illustrated in FIG. 2 and for effecting automatic control in FIG. 3. These means for adjusting the rate at which wire 17 is inserted into melt 13 are better described in detail following the general description of the overall apparatus of FIG. 1.

Since the oxygen concentration in the melt of a BOF system such as shown in FIG. 1 is temperature-dependent it is necessary also continuously to measure the melt temperature. Although this may be done by several ways, the most simple and direct way is to feed a second wire into the melt, this second wire containing as a constituent a metal capable of forming a thermocouple junction with the melt. Therefore, in the apparatus embodiment of FIG. 1, in a manner similar to that used to insert wire 17 a second wire 25 is drawn from supply roll 26, contacted with an electrical junction forming member 27, passed over a guide roll 28 and driven down through a protective sheath 29 by means of a pinch roll 30, which in turn is driven by motor 31 mechanically linked through shaft 32 to pinch roll 30. The speed at which pinch roll 30 turns may be controlled either manually or automatically as described in conjunction with the discussion of FIGS. 2 and 3.

Wire 25 is formed of one or more metals capable of forming a thermocouple junction with the metal of the melt. These second wire metals will be those which are below the melt metal in the electromotive series and which do not contaminate the melt. In the case of molten iron or steel, the preferred thermocouple wires are those which contain nickel, tin, cobalt, or copper. The so-called precious metals are also satisfactory, but their cost will normally be prohibitive for this purpose.

It is necessary to provide some electrical connection with the melt 13 which serves as one electrode of the concentration cell established at the tip of wire 17 and as the second metal of the thermocouple junction formed with wire 17. This electrical connection may be made in any of several ways. In the embodiment of FIG. 1 this is done through a single wire 33 which is welded or otherwise connected to the external wall of outer metal vessel 11 of the furnace, the electrical circuit being completed through any metal which may flow through tiny cracks in the refractory lining 12. Alternatively, the connection may be made through any metal which has solidified along the internal wall of the furnace.

The electrical circuits are completed within what is generally designated in FIG. 1 to be the signal conditioner converter 34 which may have visual display means 35 which may be one or more voltmeters to read the voltages developed by the concentration cell and the thermocouple, or indicators calibrated to read oxygen and/or carbon content and temperature directly. The signal conditioner/converter 34 is connected to wire 17 through the junction member 19 through a suitable connecting line 36 and to wire 25 through junction member 27 through connecting line 37. Signals from the signal conditioner/converter 34 are transmitted to a signal transformation means 38 (e.g., a computer) to be used in any desired manner. In the apparatus embodiment of FIG. 1, the

signal transformation means 38 is shown to be connected to the oxygen valve 39 which controls the amount of oxygen from source 40 which flows, by way of line 41, into lance 16. The signal transfonnation means is also shown in FIG. 1 to be connected to a control means 42 which controls the amount of any other additives (e.g., aluminum to kil1"'the heat and/or alloying constituents) being delivered from a weighing system 43 onto an inclined chute 44 for delivery into the melt within furnace 10.

It will, of course, be appreciated by those skilled in the art of electronic circuitry design, data processing and computercontrolled operations that the equipment illustrated in FIG. 1 is diagrammatic and merely illustrative of a wide range of specific equipment components which may be used and which are capable of processing electrical signals and employing them to control or effect predetermined operations.

Wires l7 and 25 are continuously being melted so long as their tips are extended into melt 13. It is therefore necessary to advance these wires continuously during their operation and at the same time to determine whether or not their tips do in fact extend into the melt. This in turn also requires that means be provided to enable adjustments to be made in the rates of wire feeds.

In the apparatus of FIG. 2, in which like numerals refer to like components of FIG. 1, the rates of advance of the wires are controlled through visual observation and manual operation. Wire 17 (through junction member 19 and line 36) and melt 13 (through wire 33) are connected to the terminals of a potentiometer 45 which may be calibrated to read in millivolts, oxygen concentration, carbon concentration, or a combination of two or more of these parameters. Affixed to motor 23 which rotates pinch roll 22, through a suitable lead 46, is a manual motor speed controller 47. The operator observes the potentiometer reading and then adjusts the motor speed controller 47 to just maintain a steady reading on the potentiometer. If the voltage should fall off rapidly or be erratic he will know that the wire tip is not extendingthrough the slag into the melt. A minimum rate of wire feed is desirable to minimize wire consumption. In like manner potentiometer 43 can be read to adjust the speed of motor 31 to control the rate of advance of wire 25 by motor speed control connected through lead 49 to motor 31.

FIG. 2 illustrates a modification of the apparatus in which the electrically and thermally insulating sheath 21 and its associated wire 17 extend down through lance 16. This arrangement is suitable where the oxygen is discharged at a small angle from near the periphery of the lance 16 leaving a passage-way through which the wire extends. Normally in such an arrangement the oxygen gas should supply adequate insulation from the intense heat of the melt where the oxygen is introduced.

It will normally be advantageous to provide some automatic means for controlling the rate of wire feed into the melt. It

may also be desirable to insert the wires only after a predetermined time of lancing has been carried out and/or to periodically withdraw the wires. A mechanism for such automatic control and for periodically inserting and withdrawing of the wires is illustrated in FIG. 3 in which like numerals refer to like elements in FIGS. 1 and 2. Wire 17 and melt 13 are connected to the terminals of a potentiometer through a timerrelay circuit generally indicated at 61. This timer-relay circuit comprises a timer 62 which operates a switch 63 which alternately connects the terminals of the concentration cell for oxygen concentration determination to potentiometer 60 or to a continuity control relay circuit 64. The continuity control relay circuit in turn comprises a power supply 65, a switch 66 and a relay 67; and it is connected through leads 68 and 69 to a controller 70 adapted to control the direction of rotation of motor 23 which is connected to controller 70 through leads 71.

Wire 25, designed to measure melt temperature, has a similar system associated with it, this system comprising a potentiometer 80, a timer-relay circuit 81 having a timer 32,

switch 83 and continuity relay circuit 34 which in turn includes a power supply 35, switch 66 and relay 37. Leads 33 and 89 connect the timer-relay circuit to motor controller 90 which is connected to motor 31 through leads 91. The operation of both of these systems is identical and therefore it need be described only for the system associated with wire 17.

In the embodiment illustrated in FIG. 3 the wire 17 is advanced into or withdrawn from the melt through the control of the direction of rotation of pinch roll 22 mechanically linked to motor 23. The direction of rotation of pinch roll 22 is in turn controlled by the direction of rotation of motor 23 which is determined by the flow of current into controller 70 from the system described above.

In operation, it will generally be convenient to set timer 62 so that it actuates switch 63 periodicallyfor example closing the circuit to the potentiometer for a predetermined length of time (e.g., 50 seconds) and then closing the circuit to the continuity control relay for an equal length of time. Automatic control of the feeding of wire 17 into melt 13 is accomplished by sensing the position of the wire in relationship to melt 13 at timed intervals to measure the wire melting rate and effect the necessary corrective action on the direction of rotation of motor 23 through the controller 70. The speed of motor 23 is adjusted so that it feeds wire 17 into melt 13 at a rate which is in slight excess of the wire melting rate, e.g., at a rate of about 7 inches per minute if the melting rate is about 6 inches per minute.

During the first half of the cycle, the timer 62 is adjusted to actuate switch 63 so it is in the position shown in FIG. 3. Potentiometer 60 is therefore connected into the system and records EMF values which are a function of oxygen concentration. It may also, of course, be calibrated to read directly in oxygen or carbon concentrations. During this half of the cycle the motor 23 is rotating to turn pinch roll 22 to advance the tip of wire 17 into melt 13.

Then during the second half of the cycle, timer 62 reverses the position of the switch such that it connects in the continuity control relay circuit 64 as shown by the dotted line position of the switch terminals in FIG. 3. During this continuity checking part of the cycle, relay 67 will become energized and switch 66 will become closed to complete the circuit which includes wire 17 and melt 13 (by way of lead 33) as well as leads 63 and 69 which connect in controller 70. The overall effect is to reverse the polarity on the leads of motor 23 and to drive pinch roll backwards, thus causing the withdrawal of wire 17 from melt 13. As soon as the electrical contact between wire 17 and melt 13 is broken as the result of the wire withdrawal, relay 67 is deenergized and opens switch 66 to allow controller 70 to again operate in its normal, forward driving motion to advance wire 17 again into melt 13 until an electrical connection is again made at which time the withdrawal process will begin again. Then finally, the time 62 actuates switch 63 again into a measuring circuit to connect in potentiometer 60 to begin the cycle again and continue the advancement of wire 17 into the melt.

This mechanism of control means that the wire will always be advancing into melt 113 except during periods of sampling depth penetration. The net result is to automatically ensure wire-melt contact and a wire forward advance rate proportional to the rate at which it is being consumed. It will of course be apparent that such an operation can be performed by a high-speed sensing circuit so that a servo-controlled driving mechanism can vary the rate of wire insertion by paralleling the inputs of the temperature wire 25 and oxygen concentration wire 17 to a programmer function such that an associated computer can operate to control the servo-driven mechanism.

FIG. 4, is a series of plots of EMF developed by the cell created versus oxygen dissolved to molten steel (or the reciprocal of carbon) for different temperatures of the molten iron or steel, the temperatures increasing from T, to T These plots illustrate the necessity for determining the temperature of the melt for iron or steel if the oxygen and/or carbon contents are to be accurately determined. It should, however, be noted that in some systems the cell voltage may not be sufficiently temperature-dependent to require continuous temperature determination; or the temperature of the system may remain relatively constant in which case the operator may have sufficient confidence in the process not to require continuous determination of the temperature.

The mechanism by which wire 17 containing the oxygen getter generates an oxidation voltage resulting from the establishment of a concentration cell is illustrated in FIG. 5. It will be assumed for the sake of this illustration that the oxygen getter constituent of wire 17 is aluminum. As shown in FIG. 5, the tip 100 of the wire 17 is aluminum oxide, formed by the reaction of the aluminum in wire 17 with oxygen dissolved in the melt. The wire 17 and the melt 13 serve as the electrodes and the aluminum oxide 100 serves as the electrolyte through which the oxygen ions travel.

The cell reactions may be written as follows:

26 Q reduction at. Al 0 A; Al 0 25 oxidation In a similar manner, other refractory oxides with ion-carrying capacities at steel bath temperatures and with the ability to form adherent skin on a wire may be used. In this system the EMF developed is directly proportional to the oxygen concentration and the actual voltage varies with temperature-the higher the temperature, the greater the voltage.

FIG. 6 illustrates an embodiment of one suitable sheath means for shielding the

wires

17 and 25 which are to be continuously fed into the molten metal. In order to maintain the wires structurally intact and electrically isolated until they are inserted into the metal, it will normally be preferable to provide some type of thermal and electrical shielding around the wires. One embodiment ofa suitable thermal shielding is illustrated in FIG. 6 in cross section. Such a shielding is applicable to the protection of either

wire

17 or 25 of FIGS. 1-3. In the embodiment of FIG. 6 there is provided means for circulating a fluid coolant, these means comprising an inner and outer

concentric cylinders

101 and 102, respectively, which are closed at each end to define an annular fluid channel 103 through which a coolant is circulated by introducing in through inlet 104 and withdrawing it through outlet 105. Wire 17 (or 25) is held in spaced relation with the internal walls of inner cylinder 101 by means of one or more ceramic guide rings 106 as the wire is advanced down through passage 107. The sheath may be terminated by a refractory ring 108 affixed to the bottom end of the fluid channel housing. Thus the wire 17 (or wire 25) is thermally and electrically shielded along essentially its entire length which extends within the furnace until it enters the melt 13.

The signal or signals, in the form of voltages, which are transmitted to the signal conditioner/converter lend themselves to any one of a number of data processing techniques. These signals are particularly suitable for processing by automatic computer techniques. FIG. 7 illustrates one embodiment of a complete monitoring and control system constructed in accordance with this invention and designed to utilize a computer to automatically control steel making in a BOF system.

The two measured variables, EMF of temperature and EMF of the oxygen content, are the subject of this invention which provides these two outputs. The unique relationships between the temperature EMF and oxygen content EMF makes it possible to derive a measure of melt temperature and oxygen content by use of analytic expressions or empirical relationships. Thus it is possible to enter the two quantities into a computer for computation of these two parameters. The computer is able to monitor the melt temperature obtaining in the process and derive a measure of the difference between the melt temperature and a prescribed temperature-time relationship which is desired for the process. In this way it may serve as part of a feedback control system. When the melt temperature is less than the desired temperature, the computer can direct the oxygen control to increase the oxygen supply, thereby raising the melt temperature. If the melt temperature rises above the desired temperature, then the computer can direct a decrease in oxygen supply rate. In this way, a precise control of the melt temperature to a desired temperature or time/temperature profile is maintained by use of the computer. When the desired carbon content is reached, the oxygen supply is cut off and if desired the stoichiometric amount of aluminum (or other metal) required to kill the heat is calculated and delivered to the melt in the ladle.

One embodiment of an apparatus suitable for this automatic control is diagrammatically shown in FIG. 7 in which like numbers refer to like elements in FIGS. l-3. Voltage signals, which are a function of temperature only, from the thermocouple junction of wire 25 with the melt are sensed by an appropriate device such as a potentiometer, and then transmitted to an analog-to-digital computer 116. In a similar manner voltage signals, which are a function of oxygen content and developed by the concentration cell at the tip of wire 17 are sensed by an appropriate device 117 such as a potentiometer, and then transmitted to an analog-to-digital converter 118. The information in digital form is then fed to a digital computer 119 which is programmed to determine the rate of temperature change with time (dT/dt as well as the actual melt temperature, the latter value then being used to determine oxygen content based upon previously-determined relationships which exist among temperature, EMF and oxygen content. The oxygen content or its reciprocal which represents carbon content along with the dT/dt information is employed to generate an appropriate signal which is convened back to analog form by a digital-to-analog converter 120. The analog signal is then transmitted to oxygen valve 39 which controls the flow of oxygen from oxygen supply 40 to lance 16. In like manner, signals may be processed and used to control the amount of aluminum (or other metals) used to kill the heat, the control the position of the oxygen lance itself, to add alloying constituents, and to control oxygen consumption to finish the heat at a predetermined time, at a predetermined temperature and with a predetermined amount of carbon. Being able to control the final temperature of the heat is important for it is necessary to have a melt at one temperature for introduction into continous-casting molds and at a higher temperature for introduction into ingot molds.

It will be apparent to those skilled in the art that the voltage signals may be handled in any of a number of ways using various well-known forms of information processing apparatus and that the system lends itself to almost any type of data processing installation whether it is at a remote location or is located nearby. The embodiment of FIG. 7 is exemplary of only one of these and it is to be understood that analog, digital or any suitable combination of analog and digital computer systems may be used.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A method of monitoring the concentration of oxygen in a molten metal, comprising the steps of a. continuously feeding into a molten metal the tip of a wire which melts in said molten metal and contains as one constituent a metal which is a getter for oxygen dissolved in said molten metal and which is capable of forming a refractory oxide on its surface when immersed in said molten metal, thereby to establish a concentration cell wherein said wire and said molten metal serve as electrodes and said refractory oxide as electrolyte; and

b. detecting and measuring the electromotive force developed by said cell as a function of oxygen concentration.

2. A method in accordance with claim 1 including the steps refractory oxide as electrolyte: of determining the temperature of said molten metal simulb. detecting and measuring the electromotive force taneously with said measuring said electromotive force and developed by said cell; determining said oxygen concentration as a function of said c. simultaneously determining the temperature of Said molelectromotive force and said temperature 5 ten iron; and

3. A method of monitoring the concentration of oxygen in d. determining oxygen concentration as a function of said molten iron, comprising the steps of cell electromotive force and said temperature.

a. continuously feeding into said molten iron the tip of a 4. A method in accordance withclaim 3 wherein the step of wire which melts in said molten metal and contains as one determlmflg 531d f 'f p comprlses Inserting the p of a constituent a metal which is a getter for oxygen dissolved secolfd comammg oneconstfmenf a metal 'f p of in molten iron and which is capable of forming a refractofomlll'fg a -{P .l Wnh F "when and ry oxide on its Surface when immersed in said molten detecting and measurmg the electromotrve force developed by iron, thereby to establish a concentration cell wherein thermmouple-luncuon' said wire and said molten iron serve as electrodes and said

Claims

2. A method in accordance with claim 1 including the steps of determining the temperature of said molten metal simultaneously with said measuring said electromotive foRce and determining said oxygen concentration as a function of said electromotive force and said temperature.
3. A method of monitoring the concentration of oxygen in molten iron, comprising the steps of a. continuously feeding into said molten iron the tip of a wire which melts in said molten metal and contains as one constituent a metal which is a getter for oxygen dissolved in molten iron and which is capable of forming a refractory oxide on its surface when immersed in said molten iron, thereby to establish a concentration cell wherein said wire and said molten iron serve as electrodes and said refractory oxide as electrolyte: b. detecting and measuring the electromotive force developed by said cell; c. simultaneously determining the temperature of said molten iron; and d. determining oxygen concentration as a function of said cell electromotive force and said temperature.
4. A method in accordance with claim 3 wherein the step of determining said temperature comprises inserting the tip of a second wire containing as one constituent a metal capable of forming a thermocouple junction with said molten iron, and detecting and measuring the electromotive force developed by said thermocouple junction.