US3224868A - Method and apparatus for adding heat and charge material to molten metal under vacuum - Google Patents

Description

I I I I I l I 3,224,868 SIHARGE MATERIAL CK, JR

HEAT AND UNDER VACUU 14, 1962 H. S. PHILBRI FOR ADDING TEN METAL Filed June Elli/V6150 JFK/75f Fall/[i 44 707 METHOD AND APPARATUS T0 MOL Dec. 21, 1965 RM? WWW 25w w/Cm W i/ z n? United States Patent 3,224,868 METHOD AND APPARATUS FOR ADDING HEAT AND CHARGE MATERIAL TO MOLTEN METAL UNDER VACUUM Herbert S. Philbrick, In, Chicago, Ill., assignor to John Mohr and Sons, Chicago, Ill., a corporation of Illinois Filed June 14, 1962, Ser. No. 202,631 13 Claims. (Cl. 75-12) This invention relates to apparatus and method for adding heat to a ferrous alloy melt under vacuum. Further, the heat addition may be made concurrently with or in the absence of charge material addition.

Accordingly, a primary object of this invention is to provide apparatus for adding heat to a ferrous alloy melt from an arc struck between the melt and either a consumable or non-consumable electrode.

Another object is to provide a system for measuring the voltage drop between the electrodes and the bath during the addition of heat. This feature is of particular advantage, when consumable, as contrasted to stationary, electrodes are utilized because the rate of advance of the electrodes may be regulated from the voltage drop.

Yet another object is to provide apparatus for adding charge material to a ferrous alloy melt under vacuum at a continuous rate.

Yet another object is to provide a method of treating molten metal in which charge additions to the melt are made at a gradual rate to thereby avoid excessive loss of heat from cold additions, the danger of explosion, and to promote good mixing with the melt.

Yet a further object is to provide a method of accurately measuring the quantity of charge additions made to a melt under vacuum subsequent to the time when ladle additions may be made.

A further object is to provide apparatus for adding charge material to a ferrous alloy melt under vacuum conditions on a batch basis.

Another object is to provide a method of treating molten metal in which charge additions may be made to a melt either on a batch basis or at a gradual rate, at the option of the operator.

Other objects and advantages will be apparent from a reading of the following description of the invention.

The invention is illustrated more or less diagrammatically in the accompanying figures, wherein:

FIGURE 1 is a view, partly schematic and partly in section, of the novel system of this inventon;

FIGURE 2 is a detailed view to an enlarged scale of a portion of the system of FIGURE 1; and

FIGURE 3 is a 'detailed'view to an enlarged scale of structure for adding charge material to a melt on a batch basis which may be optionally included in the system of FIGURE -1.

Like reference numerals will be used to refer to like parts throughout the following description of the invention.

A vacuum tank assembly is indicated generally at 10. The tank assembly may be set within a depression in the floor or at floor level, the particular location depending to a considerable extent upon the available head-room.

The tank assembly consists essentially of a lower section or tank 11 and an upper section or cover 12. The tank section terminates at its upper edge in a flange 13. A corresponding flange 14, on the cover overlies the tank flange. Suitable sealing means, indicated generally at 15, provides an airtight seal between the cover and tank. A vacuum conduit 16 is connected to any suitable vacuum means, such as steam jet ejectors.

A receptacle of molten metal within the tank is indicated generally at 20. The receptacle in this instance is a conventional ladle such as might be found in any steel melt shop. Any suitable receptacle might be used however within the scope of the invention. The ladle is supported on a bearing ring 21 by a flange 22 which is Welded about the outer lower periphery of the ladle so as to overlie the upper bearing flange 23 of the bearing ring 21. The bottom of the tank is provided with a refractory lining 24 to protect the metal tank shell from excessive heat and prevent damage from overflow.

A heat shield is indicated generally at 28. The shield is arcuately shaped and consists essentially of an upper metal backing plate 29 and a layer of refractory 30 which is exposed to the heat of the melt 31 in the ladle. The heat shield is suspended from and movable with cover 12 by supporting arms 32.

A stopper rod seated in the discharge port of the ladle is indicated generally at 34. Since the stopper rod per se does not form an essential part of the invention, except when utilized in combination with a voltage probe to be later described in detail, it is not further described in detail.

The upper surface of the tank cover 12 includes a pair of stove pipe projections 36, 37, which are welded airtight at their junction with the tank cover. Each projection includes a sliding vacuum seal 38, 39, respectively, within which reciprocates water-cooled polished electrode conducting and suspending rods 40 and 41, respectively. The lower ends of the rods are connected to electrodes 42, 43, respectively. The lower end of each electrode terminates a short distance above the surface of the melt 31 as shown in FIGURE 1.

Means for positioning the electrodes with respect to the surface of the melt are indicated generally at 44, 45. The system for controlling elevation of electrode 42 includes a motor 46 connected to a drum 47 upon which is reeled a line 48. Line 48 passes over pulleys 49, 50 and is attached to the upper end of rod 40. Motor 46 is a variable speed, variable load motor, and rod 42 will be raised or lowered depending upon the direction of rotation of the motor output shaft.

The means for regulating the height of electrode 43 is essentially the same and includes a motor 51 connected to drum 52 which controls line 53 passing over pulleys 54, 55.

A power system for adding heat to the melt includes a source of balanced three-phased power indicated generally at 58. In this instance the source comprises three commercial welding machines 59, 60, and 61, which convert three-phase A.C. power to DC. power. Although only three machines have been illustrated, it should be understood that a greater or lesser number can be employed depending upon the amount of heat necessary for any particular installation. The welding machines are connected across lines 62, 63.

A pair of motor controllers 64, 65, are connected in parallel across lines 62 and 63. Controller 64 is con nected to motor 46 by line 66, and controller 65 is connected to motor 51 by line 67. A tap 68 from the line between motor controllers 64, 65, leads to a voltage probe 69 immersed in the melt 31. In this instance the voltage probe is shown as incorporated in a conventional stopper rod seated in the discharge nozzle of a conventional bottom pour ladle.

The voltage probe consists essentially of a rod 70 of steel, or other conducting material, surrounded by a layer of refractory 71. The upper end of rod 70 is connected to the terminal end of line 68, and the lower end of rod 70 is electrically connected to conducting material 72 at its lower end. The conducting material 72 may for example be graphite which may be connected by a steel bolt or pin to the steel rod 70.

One possible construction of the sliding joint arrangement between the polished rod 40 and seal 38 is illustrated in FIGURE 2. The seal comprises a sleeve 75 welded to an aperture in projection 36. The sleeve in turn has a bore within which slides the polished steel rod 40. A pair of close- fitting seals 76, 77 preserve the vacuum within the tank. v 7

Rod 40 consists essentially of an outer housing 78 having a hollow bore 79. Cooling fluid is admitted to conduit 80 and exhausted through port 81 which opens into the bore 79. The lower end of housing 78 is closed by a plug 82 and its exterior is threaded to engage a fitting 83. Fitting 83 includes a shank 84 which terminates in a flange 85, the flange being embedded in the electrode 42. An eye-bolt 86 is Welded or otherwise suitably secured to the upper end of housing and is electrically connected to power line 63. I

In FIGURE 3 alternate structure is shown for adding charge material on a batch basis to the melt. A charge material container assembly is indicated generally at 88. The container assembly opens into the cover 89 and heat shield 90 of the vacuum tank through a delivery conduit 91 which passes through aligned apertures in the shell and heat shield. A pair of vacuum valves are indicated at 92, 93. Vacuum valve 92 may either form the upper end of the charge material container assembly or, alternately, it may be secured to a funnel or like member 94 for filling the container 95. Container 95 is connected to a source of vacuum through line 96 which has valve 97 therein. A tripping mechanism, such as the handle 98 which might be attached to a trap door or releasable bottom, enables the material in the container to pass into the melt at any predetermined time.

The charge material container assembly is located at any convenient position with respect to the ladle 20, and will of course be located in a position in which it does not interfere with the consumable electrodes or voltage probe assembly. Referring to FIGURE 1, for example, it might be located to the left of housing 36 or at any other position radially offset from the housings 36, 37 and circurnferentially spaced from the housings and voltage probe.

The use and operation of the invention are as follows:

Steel to be treated may be prepared in any conventional source, such as an-electric furnace. Partial or full alloying additions may be made in the furnace as desired.

The steel is then tapped into the degassing receptacle 2.0, in this instance a ladle, and transferred to vacuum tank assembly 10. Although a convenional foundry ladle 20 has been illustrated, any suitable receptacle such as a teapot kettle or a specially designed crucible may be employed.

Tank cover 12 is then swung in place over the tank 11. As soon as the seal is formed between the overlying flanges 13 and 14, the vacuum system is cut in and a vacuum drawn through pipe 16. Arcs are then struck between the electrodes 42 and 43 and the melt 31 and heat is thereby supplied to the bath.

If non-consumable electrodes are employed, such as graphite, the electrodes will be maintained relatively stationary and the gap betwen the electrodes and the melt will be relatively constant. In this event, the electrodes will function primarily to furnish heat to the melt. Various degassing procedures may be employed while the melt is exposed to the vacuum. For example, a purging agent, such as an inert gas, may be bubbled upwardly through the melt to set up a circulation which brings undegassed metal from remote areas in the ladle to the surface where it may be exposed to the vacuum. This necessarily takes a few minutes. The heat loss during the degassing process can be calculated and an equivalent amount of heat supplied from power source 58.

" If a purging agent is not employed, and the metal is merely degassed by exposure to vacuum, the time may be somewhat longer but this may be readily compensated by merely adding additional heat.

Under some circumstances it may be advantageous to make certain alloy additions late in the degassing process. For example, ferro-chrome, which is a deoxidizer, may advantageously be added late in the cycle since addition early in the cycle might tend to inhibit degassing. In this event, an additional amount of power may be supplied to compensate for the alloy addition which usually will be made in solid form, although it might be made in molten form within the scope of the invention.

One of the most unique features of the invention is the ability to add alloy materials under vacuum without the use of vacuum locks or addition hoppers. In this event, the electrodes 42, 43, would be composed of ferro-alloys of the alloys to be added to the melt, and the electrodes slowly fed downwardly into the melt. In this event the approximate time at which any particular alloy addition should be made may be determined by its position in the consumable electrode, or the ferro-alloys may be merely mixed together in a mass before being formed into the electrodes. In either event, measurement of the alloy addition can be made at any time by observing the displacement of the electrode.

When the alloy additions are made in the form of consumable electrodes, the voltage probe 69 will be elfective to indicate the voltage drop between electrodes and bath. The voltage drop will be relayed to the motor controller 64, 65, which in turn will speed up or retard the rate of advance of the electrodes towards the bath by appropriate control of motors 46, 51. The primary circuit will comprise line 63, rod 40, electrode 42, melt 31 to electrode 43, rod 41, and power line 62.

The voltage probe will comprise a circuit consisting of line 63, motor controller 64, line 68, probe 69, melt 31, electrode 42, rod 40, and back to line 63. Since the potential of the bath will be known, or readily determinable, the motor controller can be calibrated to read the voltage drop directly between the electrode 42 and melt 31. The motor 46 will then be governed by the voltage input motor controller 64.

Substantially the identical circuit will be provided for motor controller 65 and electrode 43.

If on the other hand it is desired that charge material additions be made in batch form, the structure of FIG- URE 3 may be employed. In this event the operator will merely watch a vacuum gauge or determine by some other appropriate method the best time for adding the charge materials to the melt. As soon as that time is determined, handle 98 is tripped, thereby releasing the charge material in the container into the melt. If vacuum valves 92, 93 are employed, valves 92 and 97 will be closed and valve 93 opened at the time of addition. Once the initial addition has been made valve 93 can be closed and valves 92, 97 manipulated to first charge the container 95 with a second batch, and then exhaust the container preparatory to a second batch addition. The process may of course be repeated as often as necessary.

If head rom permits the charge material container may advantageously be so positioned as to gravitationally discharge into the melt. Similarly, although a vacuum lock type system has been illustrated, it is within the scope of the invention to so arrange the structure as to enable the container 95 to exhaust simultaneously with the creation of a vacuum in the main vacuum tank, preferably through conduit 91.

Preferably, the vacuum addition system of FIGURE 3 is built into the system of FIGURE 1. If alloy addition is to be made by a consumable electrode the FIGURE 3 system will merely be valved off.

Although a preferred embodiment of the invention has been illustrated and described and several alternatives discussed, it will at once be apparent to those skilled in the art upon reading the above description that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is the intention that the invention be limited not by the foregoing description but only by the scope of the appended claims when read in conjunction with the pertinent prior art.

I claim:

1. Apparatus for adding heat to molten metal under vacuum, said apparatus including, in combination,

a molten metal receptacle containing a melt,

said molten metal receptacle having a non-electrically conducting lining in contact with the molten metal contained therein to thereby preclude passage of current through the receptacle,

structure forming a vacuum environment in a space above the melt,

means for creating a vacuum in the space above the melt,

a pair of electrodes,

said electrodes being spaced from, but in electrical contact with, the melt and forming, with the arc, part of an electrical circuit which includes a source of DC. current,

a voltage probe in the circuit and immersed in the melt, said voltage probe being effective to measure the voltage drop between the electrodes and the melt, and

means, responsive to operation of the voltage probe, for

controlling the current flow in the DC. circuit.

2. The apparatus of claim 1 further characterized, firstly in that the electrodes are consumable, and, secondly, in that the means for controlling current flow includes means for advancing the electrodes towards the melt,

said means including a motor and a motor controller for each electrode,

each controller being responsive to changes in voltage from the voltage probe to increase and retard the rate of advance of the electrodes toward the melt.

3. The apparatus of claim 2 further characterized in that the voltage probe is integral with a stopper rod associated with the molten metal receptacle.

4. The apparatus of claim 2 further characterized in that the electrodes include alloying material whereby alloy additions may be added to the melt as the electrodes are advanced.

5. The apparatus of claim 2 further characterized in that the voltage probe is connected in the circuit in parallel with the arc of each electrode.

6. The apparatus of claim 5 further characterized in that the voltage probe includes an intermediate conductor element,

said intermediate conductor element being connected, at its upper end, in series with each controller, and at its lower end, to a terminal connector immersed in the molten metal,

said terminal connector having a higher melting point than the melt and having the ability to retain its electrical conductivity when exposed to the heat of the melt.

7. The apparatus of claim 6 further characterized by and including a layer of refractory about the intermediate conductor,

said refractory layer protecting the intermediate conductor from the heat of the melt.

8. A method of measuring the quantity of alloy additions to a melt under vacuum, said method including the steps of forming a consumable conductor containing a predetermined amount of alloys to be added to the melt under vacuum,

striking and maintaining an are between the consumable conductor and the melt,

measuring the voltage drop between the melt and the consumable conductor from a voltage probe immersed in the melt,

advancing the consumable conductor towards the melt at a predetermined rate, by motor means controlled by an indication of the voltage drop as measured by the voltage probe,

measuring the displacement of the consumable conductor, and

correlating the linear displacement of the consumable conductor from its initial position to the total quantity of alloys in the consumable conductor to thereby determine the quantity of alloy added to the melt.

9. A method of treating molten metal, said method including the steps of,

subjecting a ferrous alloy melt to a vacuum sulficiently low to effectively degas the melt,

adding heat to the melt by striking and maintaining an are between an advancing consumable electrode and the melt,

continually measuring the voltage drop between the bath and the consumable electrode from a voltage probe immersed in the melt,

generating a current proportional to the voltage drop,

and

controlling the rate of advance of the consumable electrode under the influence of motor means in response to the strength of the aforementioned generated current.

10. The method of claim 9 further characterized by and including the step of adding alloys to the melt at a rate associated with the rate of advance of the consumable electrode toward the melt, said alloys being incorporated in the consumable electrode.

11. The apparatus of claim 1 further including structure for adding charge material at a predetermined time to the melt while the melt is subjected to vacuum, said structure comprising a charge material container, said container having a delivery conduit opening into the melt in a charge delivering position with respect thereto,

means for drawing a vacuum in the container, and

structure for holding and then delivering a batch of charge material from the container to the melt upon the lapse of a predetermined time.

12. The apparatus of claim 11 further characterized in that the electrodes are non-consumable.

13. The apparatus of claim 11 further characterized in that the means for drawing a vacuum in the container functions independently of the means for creating a vacuum in the space above the melt, and

further including structure for isolating the charge material container from the vacuum above the melt whereby the charge material container may be operated as a vacuum lock.

References Cited by the Examiner UNITED STATES PATENTS 1,631,512 6/1927 Berlin 12 2,518,580 8/1950 Trofimov 1313 X 2,958,719 11/1960 Beecher.

FOREIGN PATENTS 628,104 8/ 1949 Great Britain.

831,315 3/1960 Great Britain.

848,192 9/ 1960 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

DELBERT E. GANTZ, MORRIS O. WOLK,

Examiners.

Claims (2)

1. APPARATUS FOR ADDING HEAT TO MOLTEN METAL UNDER VACUUM, SAID APPARATUS INCLUDING, IN COMBINATION, A MOLTEN METAL RECEPTACLE CONTAINING A MELT, SAID MOLTEN METAL RECEPTACLE HAVING A NON-ELECTRICALLY CONDUCTING LINING IN CONTACT WITH THE MOLTEN METAL CONTAINED THEREIN TO THEREBY PRECLUDE PASSAGE OF CURRENT THROUGH THE RECEPTACLE, STRUCTURE FORMING A VACUUM ENVIRONMENT IN A SPACE ABOVE THE MELT, MEANS FOR CREATING A VACUUM IN THE SPACE ABOVE THE MELT, A PAIR OF ELECTRODES, SAID ELEVTRODES BEING SPACED FROM, BUT IN ELECTRICAL CONTACT WITH, THE MELT AND FORMING, WITH THE ARC, PART OF AN ELECTRICAL CIRCUIT WHICH INCLUDES A SOURCE OF D.C. CURRENT, A VOLTAGE PROBE IN THE CIRCUIT AND IMMERSED IN THE MELT, SAID VOLTAGE PROBE BEING EFFECTIVE TO MEASURE THE VOLTAGE DROP BETWEEN THE ELECTRODES AND THE MELT, AND MEANS, RESPONSIVE TO OPERATION OF THE VOLTAGE PROBE, FOR CONTROLLING THE CURRENT IN THE D.C. CIRCUIT.

8. A METHOD OF MEASURING THE QUANTITY OF ALLOY ADDITIONS TO A MELT UNDER VACUUM, SAID METHOD INCLUDING THE STEPS OF FORMING A CONSUMABLE CONDUCTOR CONTAINING A PREDETERMININED AMOUNT OF ALLOYS TO BE ADDED T THE MELT UNDER VACUUM, STRIKING AND MAINTAINING AN ACR BETWEEN THE CONSUMABLE CONDUCTOR AND THE MELT, MEASURING THE VOLTAGE DROP BETWEEN THE MELT AND THE CONSUMABLE CONDUCTOR FROM A VOLTAGE PROBE IMIMERSED IN THE MELT, ADVANCING THE CONSUMABLE CONDUCTOR TOWARDS THE MELT AT A PREDTERMINED RATE, BY MOTOR MEANS CONTROLLED BY AN INDICATION OF THE VOLTAGE DROP AS MEASURED BY THE VOLTAGE PROBE; MEASURING THE DISPLACEMENT OF THE CONSUMABLE CONDUCTOR, AND CORRELATING THE LINEAR DISPLACEMENT OF THE CONSUMABLE CONDUCTOR FROM ITS INITAL POSITION TO THE TOTAL QUANTITY OF ALLOYS IN THE CONSUMABLE CONDUCTOR TO THEREBY DETERMINE THE QUANTITY OF ALLOY ADDED TO THE MELT.

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