US3884288A

US3884288A - Method and apparatus for tundish level control

Info

Publication number: US3884288A
Application number: US334578A
Authority: US
Inventors: Milton E Berry
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1973-02-22
Filing date: 1973-02-22
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20

Abstract

This disclosure relates to a Tundish Level Control System for controlling the level of molten metal in a tundish used on a continuous casting machine. The level of molten metal in the tundish is monitored by a device consisting of a radioactive source and detector unit. Molten metal is supplied to the tundish from a holding furnace disposed above the tundish and which may be tilted to pour metal into the tundish automatically as a function of the level of the metal in the tundish. The holding furnace is preferably rotated or tilted by a screwjack powered by an air motor which is controlled by an operational amplifier and associated control circuitry activated by pulses received from the radioactive detector.

Description

Berry States Pte [191 1 May 20, 1975 METHOD AND APPARATUS FOR TUNDISH LEVEL CONTROL [75] lnventor: Milton E. Berry, Carrollton, Ga.

[73} Assignee: Southwire Company, Carrollton,

[22] Filed: Feb. 22, 1973 [21] Appl. No.: 334,578

[52] U.S. Cl. 164/4; 164/155', 164/278; 222/56 [51] Int. Cl B22d 11/06; B22d 11/10 [58] Field of Search 164/4, 155, 278; 222/56 [56] References Cited UNITED STATES PATENTS 2,433,560 12/1947 Hurley 222/56 3,521,696 4/1967 Lowman et a1. 164/155 UX 3,730,254 5/1973 Namy 164/155 X OTHER PUBLICATIONS Cole et 211., Level Control System for Molten Metal in the Tundish ofa Continuous Casting Apparatus, Western Electric Technical Digest No. 9, January 1968.

Primary Examiner-Robert D. Baldwin Attorney, Agent, or Firm-Van C. Wilks; Herbert M. Hanegan; Stanley L. Tate ABSTRACT This disclosure relates to a Tundish Level Control System for controlling the level of molten metal in a tundish used on a continuous casting machine. The level of molten metal in the tundish is monitored by a device consisting of a radioactive source and detector unit. Molten metal is supplied to the tundish from a holding furnace disposed above the tundish and which may be tilted to pour metal into the tundish automatically as a function of the level of the metal in the tundish. The holding furnace is preferably rotated or tilted by a screwjack powered by an air motor which is controlled by an operational amplifier and associated control circuitry activated by pulses received from the radioactive detector.

13 Claims, 6 Drawing Figures CONTROL CIRCUIT 28 PATENTED MAY 2 0 M5 A Z 6 i F n r 1 2 M P m U U y HI 5 N N mm NW m E am 2% ME C mm m 5 R 8 RM Wm TN CE E6 E S M P FIG. 28

AIR MOTOR UP 64 AIR MOTOR DOWN RUN R5551 TIMER HOV ' METHOD AND APPARATUS FOR TUNDISH LEVEL CONTROL BACKGROUND OF THE INVENTION v This disclosure relates generally to the metal-forming arts, and more particularly to a system for controlling the flow of molten metal into a continuous casting machine adapted for the continuous casting of metal rod.

Wheel-band type continuous casting machines adapted for the continuous casting rod from molten aluminum and copper are well known in the art. These machines include large steel casting wheels having a casting groove formed in the periphery thereof and partially closed by an endless metal band defining a mold into which one end thereof the molten metal is introduced by means of a pouring spout from the bottom of a pour pot or tundish. The molten metal is cooled in the mold and emits therefrom as a cast metal bar. For normal production operation, it is desirable to maintain a. constant level of metal in the casting tundish. Generally, a constant metal level in the tundish will produce a constant metal flow into the mold, thus minimizing the necessity of providing flow control devices in the pouring spout itself.

Although the melting furnace and the casting machine are continuous devices producing at essentially constant rates, there is always a small difference between the output of the melting furnace and the output or production rate of the casting machine. Consequently, a holding furnace is provided between the melting furnace and the tundish to smooth out these differences and maintain an essentially constant metal flow to the casting machine. The holding furnace may be either manually or automatically controlled to pour metal into the tundish and maintain the volume therein at a constant level.

Heretofore, it has been difficult to maintain a uniform pour rate from the holding furnaces presently in use, and also difficult to maintain a constant level of molten metal in the tundish. Such difficulties have been caused by erosion or slag conditions in the pouring vessels, and, when a tilting-type pouring vessel is used, the geometry of the molten metal container ordinarily prohibited the use of a'uniform angular motion in the tilting mechanism of the vessel.

SUMMARY OF THE INVENTION It is, therefore, a primary object of this invention to more closely control the molten metal flow into the casting groove of a continuous casting machine.

More particularly, it is an object of this invention to reduce the differences between the melting furnace production rate and the casting machine production rate in a continuous casting system by monitoring and controlling the level of molten metal in the tundish.

Still more particularly, it is an object of this invention I to provide a system as above described wherein the level of molten metal in the tundish is maintained by a holding furnace controlled as a function of the level of the molten metal in the tundish.

Briefly, these and other objects of the invention that may hereinafter appear are accomplished in accordance with this invention by providing a monitoring system for determining the level of molten metal in the tundish. This monitoring system consists of a radioactive source mounted on one side of the tundish and a detector unit mounted on the diametrically opposite tions thereof cut away for clarity, of the tundish level beam being emitted from the radiation source side of the tundish. Preferably, the radioactive source may be cobalt 60 or other radioactive materials such as radium or cesium -l37. The radioactive material may be either in a rod or a point shape and contained within suitably shielded holders mounted on brackets on the outside of the tundish. The holders are preferably leadlined containers equipped with a lever-operated shutter to facilitate control of the radiation beam emitted from the source. With the shutter-operating lever in the on" position, a narrow radiation beam will emerge from the front of the container. With the shutteroperating lever in the off position, the radiation beam is blocked by several inches of lead within the shutter structure and the container then constitutes a safe storage receptacle for the radiation source.

The detector unit may consist of a scintillation crystal for use with a rod source, or multiple scintillation crystals to be used with a point source, or Geiger tubes or Geiger-Muller tubes to be used with a point source. The detector unit is suitably mounted on the outside of the tundish and is adapted to measure the radiation on the opposite side of the tundish.

The radioactive source emits an essentially constant gamma radiation and the amount of radiation reaching the detector is inversely proportional to the amount of molten metal contained within the tundish between the source and the detector. The sourceand the detector are positioned at a preselected elevation with respect to the tundish such that when the level of molten metal drops below that elevation, the radiation received by the detector will generate voltage pulses at its output which will activate the circuit of an operational amplifier. The amplifier compares the amplitude of the pulses with a standard reference voltage signal and generates a control signal to tilt the holding furnace so that it will pour additional metal into the tundish under predetermined conditions.

The holding furnace is mounted for rotation so that it may be tilted by means of a screwjack powered by a constant speed air motor. The control circuit is programmed such that the air motor will be energized only for a given interval of time, and will then automatically be deenergized for'another given interval of time prior to a subsequent interval of activation should the level of metal in the tundish still not be corrected to its proper level.

With the above and: other objects in view that may hereinafter appear, the nature of the invention may be more clearly understood by reference to-the several views illustrated in the attached drawings, the following detailed description thereof, and the appended claimed subject matter:

IN THE DRAWINGS FIG. 1 is a fragmentary elevation view, having porcontrol system of this invention, and illustrates a portion of an open casting wheel having molten metal delivered thereto through the pouring spout of a tundish, a rotatable holding furnace disposed above the tundish,

a gamma ray emitter and detection device positioned in monitoring relation to the tundish, a control circuit, and an air motor adapted to tilt the holding furnace as a function of the metal level in the tundish for feeding additional metal thereto.

FIGS. 2a and 2b are schematic diagrams of the control circuit of this invention, FIG. 2a showing the path of the control signal from the detector pulse generator through the operational amplifier to the control relays of the furnace-tilting motor, and FIG. 2b showing an associated circuit which permits intermittent timed control of the furnace-tilting operation.

FIGS. 3a, 3b and 3c are enlarged vertical sectional views of the tundish of this invention, and illustrate various types of radioactive source and detector units that may be usedwith the tundish in accordance with this invention.

DETAILED DESCRIPTION Referring now to the drawings in detail, there is illustrated in FIG. 1 the tundish level control system of this invention which is designated generally by the numeral 10. The system includes an open casting wheel 12 having a casting groove 14 formed in the periphery thereof. The casting groove 14, in cooperation with an endless metal band (not shown) defines a mold in the casting wheel 12 into which molten metal M is delivered through a pouring spout 16 of a tundish 18.

As discussed above, it is generally desirable to maintain a constant metal level in the tundish 18 so that the rate of pouring into the mold of the casting wheel 12 I can be maintained at a uniform rate. To this end, a holding furnace 20 is disposed in juxtaposed relation to the tundish 18 so that molten metal M can be selectively delivered thereto through an outlet opening 22 of the holding furnace 20. As will be hereinafter more clearly described, the holding furnace 20 is mounted for rotation about a horizontal axis so that it may be tilted to bring the outlet opening 22 thereof into an open flow condition with respect to the tundish 18. The tilting of the holding furnace 20 is accomplished by a screwjack assembly 24 which is powered by a constant speed air motor 26. The air motor 26 is selectively operated by a control circuit 28 that is activated in response to electrical signals emitted from a radiation detector unit 30.

The radiation detector unit 30 is mounted on the outside of the tundish 18 at a predetermined point diametrically opposite a radiation source 32 which is mounted on the other side of the tundish 18. The source 32 may be any suitable radioactive material such as cobalt 60, radium, or cesium 137.

As seen most clearly in FIGS. 3a, 3b, 3c, the source 32 may be in the form of a rod 34, or a point shape 36. In each case, a suitable lead-lined housing 38 is provided to provide the necessary shielding. A shutter mechanism (not shown) may be provided to selectively control the amount of gamma rays emitted by the particular source material 32 from its respective housing 38. The shutter mechanism (not shown), or other suitable mechanism, is so positioned that the housing 38 will direct the gamma rays through the tundish 18 toward the respective detector unit 30.

With further reference to FIGS. 3a, 3b, 3c, the detector unit 30 is selected to be appropriate for the particular source 32 which is being utilized. For example, when the rod-type source 34 is being used (FIG. 3a), the detector unit 30 may be in the form of a scintillation crystal 40. When a point source 36 is used as in FIGS. 3b and 3c, the detector unit 30 may be in the form of either Geiger tubes or Geiger-Muller tubes 42 (FIG. 3b), or multiple scintillation crystals 44 (FIG.

3c). In each case, the amount of radiation reaching the respective detector unit 30 is inversely proportional to the amount of molten metal M in the tundish 18 disposed between the source 32 and the detector unit 30. Consequently, when the level of molten metal M drops below a preselected level, the amount of radiation reaching the detector unit 30 will be of a given intensity to activate the control circuit 28 so as to operate the motor 26 and screwjack assembly 24 to tilt the holding furnace 20 sufficiently to supply a given amount of molten metal M to the tundish 18.

The control circuit 28 is shown schematically in FIGS. 2a and 2b. Radiation passing into the detector unit 30 produces voltage pulses in a pulse generator 48 which are applied to an operational amplifier 50 that is adapted to compare the amplitude of the voltage pulses with a preselected adjustable reference signal, and in response thereto, transmit control signals to the motor 26 through

relays

52 or 54 for operating the screwjack assembly 24 either up or down to tilt the holding furnace 20 as appropriate.

The circuit illustrated in FIG. 2b permits the motor 26 to be energized only for predetermined periods of time at given intervals. Thus, when the control signal is transmitted by the operational amplifier 50 to either of the

relays

52, 54, switches 56 or 58, which are contacts on the respective relays 52, 54, will close thereby transmitting the control signal through normally closed timed-to-open contacts 60 or 62 and limit switches 64 or 66 to energize the motor 26 in the appropriate direction. Preferably, the motor 26 is timed to run for l to 10 seconds depending upon gear ratios and motor speeds. At the expiration of the predetermined period, the timed-to-open contacts 60 or 62 will open thus deenergizing the motor 26. The limit switches 64, 66 prevent overtravel and thus assure that the holding furnace 20 will operate only within certain limits of rotation.

Simultaneous with the closing of the contacts 56 or 58, the control signal will also cause a closing of either of contacts 68 or 70. Thus, at the expiration of the predetermined operating period, normally open timed-

toclose contacts

72, 74 will close thereby transmitting the control signal to a RUN relay 76 which will energize a RESET TIMER relay 78 that runs for preferably 20 to 90 seconds before resetting the circuit and thereby permitting a subsequent energizing of the motor 26 should the level of molten metal in the tundish 18 still not be corrected to its proper level.

Referring again to FIG. 1, the holding furnace 20 includes a cylindrical refractory-lined crucible portion 80 that is mounted for rotation about a horizontal axis disposed parallel to the axis of rotation of casting wheel 12. The molten metal M from a melting furnace (not shown) is introduced to the interior of the crucible portion 80 through a radial opening 82 closed by a suitable cover or hatch 84 which may be opened by being pivoted about a pin 86. The crucible portion 80 is mounted on generally U-shaped brackets 88 which are rotatably mounted on support rollers 90 carried by a structural frame (not shown).

The crucible portion 80 of the holding furnace 20 includes an axially extending outlet nozzle 94 having an offset spout portion 96. When the holding furnace 20 is rotated such that the spout portion 96 of the outlet nozzle 94 is downwardly depending, the molten metal M will be permitted to flow from the interior of the crucible portion 80, through the opening 22 and nozzle 94, downwardly into the tundish 18.

The holding furnace may be rotated or tilted by means of the screwjack assembly 24 which includes a cooperating rotatable screw 100 and nut assembly 102. Consequently, when the motor 26, is energized through the controlcircuit 28, the screw 100 will be caused to rotate, thereby causing the nut assembly 102 to translate either up or down thus tilting the holding furnace 20 to control pouring of the molten metal M therefrom.

In the preferred embodiment of the invention, the motor 26 is a constant speed air motor that will be energized by the control circuit 28 for only a certain preset time and will then automatically stop and wait another preset time before again being energized to tilt the holding furnace 20. Consequently, the level of molten metal in the tundish 18 will be permitted to stabilize after each incremental pouring of molten metal from the holding furnace 20 before the motor 26 is again energized to further tilt the holding furnace 20 in the event that the level of molten metal M in the tundish 18 has not been corrected to its proper level.

In other embodiments of the invention, a direct current variable speed motor or a hydraulic cylinder having a widely adjustable hydraulic supply system may be utilized to tilt the holding furnace 20 in place of the constant speed air motor 26. In such embodiments, sufficient control of tilting of the holding furnace 20 may be obtained without the necessity of the control circuit 28. It should be understood that the control circuit 28 may be used for any tilting system which uses an essentially constant-speed tilting device such as A.C. electric motors, hydraulic cylinders, and hydraulic motors.

It should be apparent, therefore, that there is provided in accordance with this invention a novel tundish level control system which enables the casting rate of a continuous casting machine to be more closely controlled and made more uniform with the rate of production of the melting furnace. The invention makes it possible to maintain a constant level of molten level in the tundish 18, and to replenish the supply of molten metal in the tundish 18 from a tiltable holding furnace 20 as a function of the level of metal in the tundish 18 as measured by a monitoring system consisting of a radioactive source and complementary detector unit.

Although only a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that further minor modifications may be made therein without departing from the spirit of the invention.

I claim:

1. A method of maintaining a predetermined level of molten metal in the tundish of a continuous casting machine by controlling the continuous pouring of molten metal therein from a rotatably mounted holding furnace, comprising:

monitoring the level of molten metal in the tundish,

generating a signal in response to said monitoring indicative of said level,

comparing said signal with a reference signal and generating a control signal through a control cir cuit in response thereto if said comparison indicates that said level has deviated from said predetermined level,

rotating said holding furnace in response to said control signal for a predetermined selected interval of time to vary the rate of pouring of molten metal therefrom into said tundish, preventing the rotating of said holding furnace subsequent to said selected interval for a given interval of time independently of the casting rate, and

thereafter again rotating said holding furnace in response to said control signal if the level of molten metal in said tundish still deviates from said predetermined level,

said steps of rotating and preventing continuing successively until said level reaches said predetermined level.

2. A method as defined in claim 1, wherein said control signal is used to activate a timer which measures said given interval during which rotation of said holding furnace is prevented, and resetting the control circuit after elapse of said given interval.

3. A method as defined in claim 1, wherein the step of rotating said holding furnace to vary the rate of pouring includes increasing the hydraulic head of the molten metal in the holding furnace above the outlet thereof to increase the rate of pouring of the molten metal.

4. A method as defined in claim 1, wherein the step of rotating said holding furnace to vary the rate of pouring includes decreasing the hydraulic head of the molten metal in the holding furnace above the outlet 7 thereof to decrease the rate of pouring of the molten metal.

5. A method as defined in claim 1 wherein the step of monitoring the level of molten metal in the tundish includes emitting gamma rays from a radioactive source positioned at a selected elevation on one side of the tundish, and detecting the impingement of said rays on a detector unit positioned on the other side of the tundish as a function of the amount of molten metal in the tundish at the selected level.

6. A method as defined in claim 5 including generating pulses in response to the impingement of radiation on the detector, applying the pulses to an operational amplifier, and transmitting a control signal from the amplifier through a control circuit to selectively rotate said holding furnace to supply molten metal to the tundish.

7. In a continuous wheel-band type casting machine for the continuous casting of molten metal having an arcuate mold defined by a groove formed in the periphery of the wheel which is partially closed by an endless band, a tundish disposed in juxtaposed relation to the wheel for supplying molten metal to the mold, a rotatably mounted holding furnace for supplying molten metal to the tundish, means for monitoring the level of molten metal in the tundish, and means responsive to said monitoring means for rotating said holding furnace in either direction to control the pouring of molten metal from said holding furnace into said tundish during the casting operation; the improvement comprising control circuit means operatively connected with said monitoring means and said rotating means for activating said rotating means for at least one predetermined selected interval when the level of molten metal in said tundish varies from a predetermined level, said control circuit means further including means independent of the casting rate for preventing the activating of said rotating means for a given interval after each of said at least one predetermined selected interval of activation said preventing means including timer means for resetting said control circuit means after elapse of said given interval.

8. A casting machine as defined in claim 7 wherein said monitoring means include a radioactive source and detector.

9. A casting machine as defined in claim 8 wherein said radioactive source is a gamma ray emitting rod.

10. A casting machine as defined in claim 8 wherein said radioactive source is in a point shape and said detector includes multiple scintillation crystals.-

II. A casting machine as defined in claim 7 wherein said means for rotating includes a screwjack assembly powered by a constant speed air motor.

12. A casting machine as defined in claim 7 wherein said means for rotating said holding furnace includes a motor, said control circuit means includes an operational amplifier adapted to compare a signal generated by said monitoring means with a standard reference signal indicative of a desired level of molten metal in said tundish. said amplifier including means for generating a control signal in response to said comparison, and

normally closed timed-to-open contacts for transmitting said control signal to said motor, said contacts elapse of said given interval.

Claims

1. A method of maintaining a predetermined level of molten metal in the tundish of a continuous casting machine by controlling the continuous pouring of molten metal therein from a rotatably mounted holding furnace, comprising: monitoring the level of molten metal in the tundish, generating a signal in response to said monitoring indicative of said level, comparing said signal with a reference signal and generating a control signal through a control circuit in response thereto if said comparison indicates that said level has deviated from said predetermined level, rotating said holding furnace in response to said control signal for a predetermined selected interval of time to vary the rate of pouring of molten metal therefrom into said tundish, preventing the rotating of said holding furnace subsequent to said selected interval for a given interval of time independently of the casting rate, and thereafter again rotating said holding furnace in response to said control signal if the level of molten metal in said tundish still deviates from said predetermined level, said steps of rotating and preventing continuing successively until said level reaches said predetermined level.

4. A method as defined in claim 1, wherein the step of rotating said holding furnace to vary the rate of pouring includes decreasing the hydraulic head of the molten metal in the holding furnace above the outlet thereof to decrease the rate of pouring of the molten metal.

10. A casting machine as defined in claim 8 wherein said radioactive source is in a point shape and said detector includes multiple scintillation crystals.

11. A casting machine as defined in claim 7 wherein said means for rotating includes a screwjack assembly powered by a constant speed air motor.

12. A casting machine as defined in claim 7 wherein said means for rotating said holding furnace includes a motor, said control circuit means includes an operational amplifier adapted to compare a signal generated by said monitoring means with a standard reference signal indicative of a desired level of molten metal in said tundish, said amplifier including means for generating a control signal in response to said comparison, and normally closed timed-to-open contacts for transmitting said control signal to said motor, said contacts being adapted to open upon the expiration of said predetermined selected interval of activation.

13. A casting machine as defined in claim 12 wherein said preventing means includes timer means, and said control circuit means further includes normally open timed-to-close contacts for transmitting said control signal to said timer means which includes means to close said normally closed timed-to-open contacts after elapse of said given interval.