US2746105A - Control system for continuous casting - Google Patents

Description

May 22, 1956 T. w. RATCLEFFE CONTROL SYSTEM FOR CONTINUOUS CASTING Filed Nov. 10 1951 4 Sheets-Sheet 1 F l G. 1

INVENTOR 72;;{50/6 W/eazc/zfie mid/M,

ATTORNEY y 1956 T. w. RATCLEFFE 2,746,105

CONTROL SYSTEM FOR CONTINUOUS CASTING Filed Nov. 10, 1951 4 Sheets-Sheet 2 H 5/ w V y 55 f f2 z5- dogg FIG. 2

INVENTOR.

01W ATTORNEY y 22, 1956 "r. w. RATCLiFFE 2,746,105

CONTROL SYSTEM FOR CONTINUOUS CASTING Filed Nov. 10, 1951 4 Sheets-Sheet 3 //3 9 y LL k g i a \a a LO A m I m L:

g i a \k q 0' II INVENTOR jlzv/t? fate/3% fl/n ATTORNEY May 22, 1956 w. RATCLEFFE 2,746,105

CONTROL SYSTEM FOR CONTINUOUS CASTING Filed Nov. 10, 1951 4 Sheets-Sheet 4 SHAFT R H505 7/4 T 54 M 70/? 49 D/FE CONT/L I INVENTOR 7'0 T 0 (0 ,0 E F I 7 l DLW ATTORNEY United States Patent CONTROL SYSTEM FUR CGNTHNUOUS (JASTING Temple W. Ratciifie, Beaver, Pa., assignor, by rne'sne assrg'n'rnents, to The Babcock & Wilcox Company, Ears-2y City; N. J., a corporation of New Jersey Application November 1a, 1951, Serial No. 255,852 5 Claims. 01. z2 -s"1.2

The present invention relates to electrical control sysend thereof and the casting is withdrawn from the opposite end. With the pouring means and the withdrawal mechanism properly coordinated, the molten metal level within the mold will remain in substantially the same position. Under these conditions the apparatus can be operated for maximum casting production within the cooling capacity of the mold. Ordinarily it is of advantage to maintain the withdrawal rate of casting from the mold at a substantially uniform value while the pouring means is manually or automatically controlled to maintain the molten metal level at a uniform position in the mold.

The casting withdrawal mechanism is usually motor driven and is subject to close speed control so that the casting withdrawal rate can be maintained at any desired uniform value. The pouring means may include a bottom pour or tilting type of pour vessel discharging molten metal to either a hp pour intermediate vessel, a trough or a tun dish, from which the molten metal is bottom poured into the casting mold. It is diflicult to maintain a uniform pour rate from the pouring apparatus presently in use. Such difiiculties may be caused by erosion or slag additions in the pouring vessels and when a tilting type pouring vessel is used, the geometry of molten metal container ordinarily prohibits the use of a uniform angular motion in the tilting mechanismof the vessel;

In accordance with my presentinve'ntion, I provide a control apparatus actuated by movement of the molten metal level within the moldfrom a selected level. The

control responds to the rise orfall of molten metal level Within-the mold to regulate the rate of molten metal delivered to the mold. When the controller is utilized to regulate-the'pour rate from a tiltingtypevesseL-thecontrolchanges the tilting-rate ofthe vessel in response to-the deviation" of the molten metal level-fron'rits desired 'c'on trol locations. When-a controiler is used'with'a bottom pourtype 'of vessel, having a valve" or theliketherein; the controller opens or closes the valve in response to the change of molten nietal'lev'el'within the mold; This is "accomplished by temperature measurements at'the p're ferredrnolten metal level withiii'thembld with the con troller interpreting these readings to change the pouring ra'te correspondingly.

The various f'eaturesof novelty which characterize my invention are pointed out with -'particularity" in the claims annexed to'ar'rdfo'rming a part of this" specification! For abetter understanding of theinvention', its operating 'ad-' vantages and specific objects attained'b'y its use, reference should be'had to the accompanyingdrawings and descriptive rnatter whi'ch I have illustrated and described an embodiment of my invention.

2,746,105 Patented May 22, 195s Qt thedr'awings: H A Fig. 1 is an elevation of a continuous casting apparatus incorporating thecont'rolof the present invention; A v Fig. 2 isan enlarged elevation, in section, of a portion of the apparatus shown in Fig. 1; I v p 7 Figs; 3, 4, 5 and 5 are fragmental elevation views, in section, showing different temperature sensitive devices installed in the wall of the mold shown in Fig. 2; v Fig. 7 is a schematic diagram of the control system; and Fig. 8 is simplified diagram of a portion of the control system shown in Fig. 7. I 7 p The present invention is illustrated in the drawings as applied to a continuous casting unit for steel and other high melting temperature alloys wherein the pouring means is of the lip-pour tilting type. However, it will be understood the control method and apparatus hereinafter described can be successfully used in casting metals having lower melting temperatures, or with pouring me ans of the bottom pour type wherein a valve is utilized to regulate the rate of metal flow from the pouring vessel;

As shown in Fig. l, the metal pouring means includes a vessel 10 arranged for lip pouring, and a tun dish. 11 arranged to receive molten metalfrom the vessel 10 and to deliver a substantially slag-free stream of metal to a selected position in the open upper end of a continuous casting mold assembly 12. v v v The vessel 10 is arranged ffor tilting movement about a transverse horizontal axis' d'efinedby trunniou's .13 extending outwardly on' oppositeisides of an L-shaped frame 14 supporting the vessel. The trunnions are supported in trunnion' bear'ing s 15 each of which is mounted on a pedestal 16. The tilting movement of the vessel isobtained in a' suitable manner, such as by means of a drum hoist 1'7 driven by ava'ri ablespeed motor 18. The speed of the motor 18 is' regulated by a control system hereinafter described, and indicated generally at 19, in Eig'. 1-. The'hoist 17 is com ted to" the vesse l 19 by a cable 20 and a yoke 21 which is' attached to the platform of the frame 14supportin'g'the vessel. s I

Beneath therriold 12, the cas'ting 22 formed therein isengaged'by a'set'of pinch'rolls 23 driven by sa tgariable speedmotor 241 The casting leaving the mold 12 is subjected'to the'dire'ctcooling'eifects of a water spraly from aplurality of jets formed the encircling manifoldZSQ, and is'restrained against transverse movement byguide shoes 26"or the like positioned in the space between the mold 12 and the pinch muses; I, a The upper end portioiijo'f the casting mold assembly 12 is'shown in Fig; 2; While in the mold assembly, the molten metaldeliv'ered thereto by the pouring ves sel aiiil tun dish, and the embyro casting" formed' therein are iii contact with or adjacent to'the inner surface of a'iwat'e'i' cooled vertically elongated'metallic molding'tube or'liiilr 30 which is open at its upper andlower ends and'isof the desired casting cross-section. The upper op'eri e'n'd' of the tube is supported in a top plate 31, whereby'the tube is pendantly supported from the fixed level of the plate and is free to expand axially therefrom. The plate forms the top wall'ofan annular chamber 32 defined by a cylin drical'm'eniber 33 mounted on a load carryingbottom plate 34; I 7 A metallictu'bular skirt 35 of corresponding crosssectional shape 'sui'roundsthe mold liner and is arranged to'confine a flow'of cooling liquid against the surface lOf the mold liner substantiallythroughoutits length. The' skirt is also pendantly supported at its upp'er'en'd by attach? ment to the plate 34." Above the plate 34,"afbafHe projectsupwardly into the'chamber 32 coop'erate with the liner'lafland'platedl to define a discharge wei from the chamber 3 2 into the water passage 40prov1ded between the linrmfand skirt 351 p w p p Cooling water inlets l open'td thechamber32"at"uni form circumferentially spaced positions in the lower portion of the cylindrical member 33. The upper end or the weir 38 section is shaped to form an anti-cavitational entrance nozzle to the water passageway-40. This construction insures the flow of a uniform solid stream of cooling water into the entire circumference of the flow passageway 40. In addition, the converging entrance to the passageway provides for an acceleration of the water velocity to a rate, in the annular passageway 40, which will be within the range of turbulent flow, thus insuring a high rate of heat. transfer from the outer face of the liner 30 to the cooling water.

With a substantially uniform pinch roll speed, it is desirable to control the pouring rate of molten metal delivered to the mold to maintain the level of molten metal substantially uniform, for example at the position indicated at B. This can be accomplished, in the manner hereinafter described, by the use of means for detecting the presence of molten metal at the desired level, or a variation of the actual molten metal level from the desired level, with the detecting means transmitting the actual molten meta surface level information to the controlling means. A variety of molten metal level detecting means can be used, whether actuated by penetrating radiation,-radiant. electric contact or by temperature measurements of the embryo casting below or within the mold assembly. It will be understood that whatever detecting means are used, the apparatus should not deleteriously interfere in any marked degree with the cooling mechanism of the mold.

A change in the actual level of the molten level in the mold has been found to cause a measurable temperature change in the mold, i. e. a drop in the molten metal level below a predetermined position in the mold will cause a drop in the mold wall temperature suflicient to be detected by a temperature sensitive element such as a thermocouple imbedded in the mold at this initial predetermined positron. Likewise an increase in the molten metal level will cause a detectable temperature rise on the thermocouple as the metal level passes the thermocouple position. Thus it has been found that thermocouples or other tempera ture sensitive means imbedded in the mold wall can be used to detect the presence or absence of molten metal at selected positions within the mold, and such indications can be correlated to actuate a control mechanism to regulate the pour rate of metal to the continuous casting unit.

Temperature sensitive means for this purpose are inse rted in the wall of the mold liner 30, as illustrated in Figs. 3, 4, 5 and 6. In Fig. 3 the temperature sensitive means consists of a series of thermocouples 44 imbedded at spaced longitudinal positions in the wall of the liner, with the cold junction ends 45 of each thermocouple positioned external of the mold in a zone of substantially uniform temperature and connected in series so that a variation in molten metal level between and intermediate the positions A, B and C, for example, will create corresponding detectable changes in the voltage generated by this series thermocouple, which changes can be utilized to regulate the pouring rate of molten metal delivered to the mold assembly 12. V

The thermocouples illustrated in Fig. 4 are likewise connected in series, with, however, the cold junctions 46 thereof positioned adjacent the cold face of the mold liner wall. The thermocouple arrangements shown in Figs. 3 and 4 have proven to be practical for the detection of a change in the molten metal level within the casting mold, particularly when the mold wall thickness is relatively great, for example, approximating one half inch or more. I prefer however to use a resistance thermometer in the mold wall, such as illustrated in'Figs. 5 and 6, since such temperature sensitive means employ fewer connections, and are simpler to install and maintain in an operative condition. a

As shown in Fig. 5, a platinum resistance element 47 is imbedded in the mold liner wall with the lead wires therefrom extended upwardly through the wall, and connected with the controller, as hereinafter described. In Fig. 6, the temperature sensitive element consists of a segment 48 of the mold liner wall having lead wires extending from opposite ends of the segment upwardly through the wall and likewise connected with the controller.

The installation of the temperature sensitive elements in the mold liner wall can be conveniently accomplished by cutting a suitable keyway-like groove longitudinally in the cold face of the mold, inserting the elements with their connecting leads, and placing a flat key in the cold surface side of the mold which is soldered in position with the outer wall surface and thereafter refinished to provide a smooth surface for the How of cooling water thereover. 7

It will be noted the mold wall 'hot face temperature does not exceed 450 F., even though the molten metal in contact with the hot face of the mold will initially be at a temperature as high as 3000 F. This is due to the high efiiciency of the mold cooling system utilized in the described casting unit.

The electric energy transmitted through the lead lines from the temperature sensitive element is impressed on a measuring circuit which includes a slidewire drive motor. The slidewire drive motor is positioned by the circuit which is operated on the well known null balance principle wherein an unknown resistance is measured by comparing it with an adjustable resistance. As shown in Fig. 5 an adjustable resistance R is adjusted to a value closely equal to the resistance of the platinum resistance element 47 when the molten metal level in the mold is in a desired position, for example, at the position repre sented by the symbol B. r

A simplified wiring diagram of a typical measuring unit using the null balance principle is illustrated in Fig. 8. As shown, S represents the bridge electric supply: T the resistance of the platinum element 47; R the manually adjustable, and F and G fixed, resistors; and M the slidewire motor. The electric amplifier and motor control M. C. regulates the operation of the reversible slidewire motor M to continuously balance the circuit in accordance with the changes of temperature in the resistance 'of the element 47. As shown in Fig. 5, the adjustable resistance R is positioned adjacent the mold assembly 12. 7

It will be appreciated the slidewire drive motor of the measuring unit could be directly connected with, or through suitable power amplifying means to, an adjustable rheostat in the speed control circuit of thepouring means rate control. Such a control arrangement would be of the modulating type and would increase or decrease the pour rate substantially immediately in response to changes in the molten metal level within the casting mold. This type of control is, however, subject to fhunting and is difl'icult to maintain in an operative condition. I prefer to utilize a pair of measuring units which are alternately'connected in timed sequence with the temperature sensitive means, with each slidewire drive motor in turn transmitting rotational movement to a differential gear mechanism in response to the unbalance between the resistances T and R. Simultaneously the other slide- Wire motor is transmitting rotational movement to the differential gear in accordance with the unbalance between the resistance measured at the end of the previous period of connection with the temperature sensitive element. 7

The arrangement of equipment to accomplish this control sequence is illustrated in Fig. 7. Asshown in the drawing, the measuring units'X and Y, with their control circuits such as illustrated in Fig. 8, are each provided with a shaft 51 and 52 respectively driven by the slidewire motor and connected with a differential gear 53. The output shaft 54 from the differential gear is connected with a rheostat in the motor speed control circuit 49 of the hoist 17.

The lead wires 50 from the resistance element 47 in the mold liner wall 30 are connected with the measuring unit X, and a set of branch wires 56 join the wires 50 with the measuring unit Y, so that the units X and Y are electrically connected in parallel. A separate set of wires 57 and 58 connect the units X and Y in parallel with a source of electricity Z. Each set of wires connected with the units X and Y are provided with contact switches 1B, 1C, 1D, and 1E, all of which are gang operated by a magnetic coil 1. Switch contacts 1B and 1B are closed when 10 and ID are open, i. e. when the coil 1 is deenergized. When coil 1 is energized, contacts 1B and 1B are open and 1C and ID are closed.

The coil 1 is alternately energized and deenergized in a timed sequence by the operation of the timers CCA and CCB in the timing control circuit illustrated in Fig. 7. As shown, the circuit is in the dead board position. Energizing the circuit, energizes coil 1, closes contact 1A, and thereby reverses contacts 13, 1C, 1D and 1E from the position shown, so that the measuring unit X is connected with the element 47 and resistance R, while Y is connected with the source of energy Z. Closing the contact 1A starts the timer CCA. At the end of the desired time period the timer CCA causes the contact A to close, energizing coil 2 and reversing contacts 2A, 2B and 2C.

Opening contact 2A deenergizes coil 1 to reverse the contacts 1A, 1B, 1C, 1D and IE, to the position shown in Fig. 7. With 1A open, timer CCA is automatically reset and ready to operate for a timed period when the set period of operation has elapsed on timer CCB. Closing contact 2C starts timer CCB which will operate for a set period of time until at the end of the timed period of operation on CCB the contacts B momentarily open to deenergize coil 2 and to again reverse contacts 2A, 2B and 2C (i. e. to the position shown in the drawing). Thereafter, the cycle of timer operation is repeated.

In operation, the resistance R is adjusted to a value equal to the resistance T when the molten metal level within the mold is at the desired position. For example, when the molten metal is at the position B of Fig. 5 the resistance T of the resistance element 47 should equal the resistance R, which is common to both of the units X and Y. Thus, when the actual molten metal level is above or below the position B the resistance of the element 47 will change and the value of the resistance T in the modified Wheatstone bridge circuit will operate the motor M in one of the units X and Y, shifting the position of the slide wire to balance the circuit. The direction of rotation of the motor M will depend upon whether the resistance T is greater or lesser than that of the resistance R, i. e. whether the actual molten metal level is above or below the desired position B.

In the control circuit shown (see Fig. 8), the slidewire contact H will be at its midpoint when the resistances T and R are equal, i. e. when the molten metal level is at its desired position within the mold. A change in the molten metal level will cause a proportional change in the resistance of the element 47 and an unbalance in the measuring unit with the slidewire motor moving the contact H to balance the circuit. Movement of the contact H simultaneously causes rotational movement of the shaft of the slidewire motor and of one side of the difierential gear 53. At the same time the shaft of the other measuring unit will be rotating due to the return of the slidewire contact H thereof to its midpoint by reason of an equal flow of energy through the resistors F and G of the measuring unit.

As an exmple of the operation of the control system described, it will be assumed the molten metal level had dropped to a position approximating C, as shown in Fig. 5. Under these circumstances, the control would act to increase the delivery rate of molten metal to the continuous casting mold. Let it further be assumed that the unbalance on the measuring unit X at the endof this timed period, during which unit X was connected with the element 47, can be represented by the number +16. The number 16 is an arbitrary unit selected for purposes of illustration and may represent the number of revolutions made by the shaft 51 while the sign or indicates the direction of movement, with indicating a direction tending to increase the rate of metal delivery to the mold. If it is further assumed the level had been maintained at the desired position during the preceding measuring period, the contact H of unit Y would be at its mid-- point and the shaft 52 would not move under the influence of Z during this period. Thus, the net effect 'on the shaft 54 would result in an increase in the speed of the hoist motor 18 equivalent to the +16 movement of the shaft 51.

During the next or second timed period, the unit X is connected with the element Z, with the slidewire contact H returned to its midpoint with shaft rotation from +16 to 0 by the influence of Z. At the same time the measuring unit Y will be responding to the position of the molten metal level in the mold. Although the control system will have greatly increased the delivery rate of molten metal to the mold the molten metal level will still be low and will not reach the position B. Thus at the end of the timed period the unit Y will retain a +8 value, for example. The net effect of the movement of the shafts 51 and 52 on the shaft 54 will be 8, since the return from +16 to 0 on the shaft 51 will be in a negative direction i. e. +16, and the movement of the shaft 52 will be in a position direction i. e. +8.

During the next or third timed period the shaft 52 will return from +8 to 0 under the influence of Z, with rotation in a negative direction equal to 8 units. At the same time, with the unit X connected with the temperature sensitive element 47, the shaft 51 rotates in pro portion to the deviation between the actual molten metal level and the position B. If the actual metal level is still low the shaft 51 will rotate in a positive direction, for example +4, with the net result of a 4 rotation on the diiferential output shaft 54 (-8+4=4). Alternately, if the actual metal level is actually higher than the desired position B, the shaft 51 will rotate in a negative direction. If this value is, for example, 4 the net result on the rotation of the output shaft will be the addition of the 8 units from the unit Y plus the --4 units from the unit X, or a net of -12 units. Such a condition would of course indicate that the rate of pour was excessive and the pouring rate would be reduced an amount proportional to the l2 units delivered to the rheostat hoist motor control.

While in accordance with the provisions of the statutes I have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may be made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. Continuous casting apparatus including a fluid cooled mold, power means for regulating the rate of delivery of molten metal to said mold, means adapted to withdraw the casting from said mold, a thermo-sensitive element associated with said mold and adapted to respond to changes in the position of the molten metal level within the mold by a change in electric flow from said thermosensitive element, and speed control means responsive to said changes in electric energy flow to regulate the rate of molten metal delivery to said mold comprising a slidewire motor adapted to compare the electric flow from said thermo-sensitive element with an electric flow standard and to cause mechanical movement proportional to the difference between said energy flows, and an operative connection between said slidewire motor and said power means to regulate the speed of the latter in response to the movement of the former.

2. Continuous casting apparatus including a mold, power means for regulating the rate of delivery of molten metal to said mold, means adapted to Withdraw the casting from said mold, a resistance thermometer positioned to respond-to changes in the position of the molten metal level within the mold from a selected level by a change in electric voltage flow, and speed control means re sponsive to said changes in electric voltage flow to regulate the rate of molten metal delivery to said mold comprising a pair of slidewire motors alternately connected with said thermo-sensitive element and with a standard source of electric voltage flow, the voltage fiow from said resistance thermometer causing a slidewire motor movement proportional to the difference between the act and selected molten metal levels within the mold while the voltage 'flow from said standard source causes the other slidewire motor to return to a position equivalent to the selected mold metal level, and a conjoint connection between said slidewire motors and said power means.

3. Continuous casting apparatus including a fluid cooled mold, a pouring vessel for delivering molten metal to one end of said mold, power driven means for regulating the pouring rate of molten metal from said pouring vessel, means for withdrawing the continuous casting from the opposite end of said mold, means sensitive to changes in the actual molten metal level Within said mold from a selected position, and speed control means operatively connected with the power driven means of said pouring vessel and said molten metal level sensitive means for regulating the rate of molten metal delivery to said mold comprising a pair of measuring elements operable in proportional response to said changes in molten metal level from a selected position in the mold, a timer control system alternately connecting each of said measuring elements with said metal level sensitive means While the other of said measuring elements is connected to modify the proportional response of said first measuring element, and means for combining the proportional responses of both of said measuring elements to regulate said power driven means.

4. In combination with a continuous casting mold, a pouring vessel for delivering molten metal to one end of said casting mold, a variable speed motor drive to regulate the pouring rate from said vessel, means for withdrawing an embryo casting from the opposite end of said mold, detecting means associated with said fluid cooled mold whereby a change in the molten level within said mold causes a change in voltage output from said detecting means, a pair'of slidewire motors associated with Wheatstone bridge circuits connected with said detecting means to compare the voltage output therefrom with an adjustable standard voltage, a shaft connected with each of said slidewire motors and with a differential gear, the output shaft of said differential gear connected with a speed control rheostat in the variable speed motor drive circuit of said pouring vessel, and a timing circuit for alternately connecting each of said slidewire motors with said detecting means while the companion slidewire motor is connected with a standard adjustable voltage source of electricity.

5v in combination with a continuous casting mold, a.

pouring vessel for delivering molten metal to one end of said casting mold, a variable speed motor drive to regulate the pouring rate from said vessel, means for withdrawin an embryo casting from the opposite end of said mold, temperature sensitive means positioned in the wall or" said fiuid cooled mold whereby changes in the molten metal level within said mold causes a change in the voltage output from said temperature sensitive means, a pair of slidewire motors associated with Wheatstone bridge circuits connected with said temperature sensitive means to compare the voltage output therefrom with an adjustable standard voltage, a shaft connected with each of said slidewire motors and with a difierential gear, the output shaft of said differential gear connected with a speed control rheostat in the variable speed motor drive circuit of said pouring vessel, and a timing circuit for alternately connecting each of said slidewire motors with said temperature sensitive means while the companion slidewire motor is connected with a standard adjustable voltage source of electricity.

References Cited in the file of this patent UNITED STATES PATENTS France Aug. 4, 1947

Claims (1)

1. CONTINUOUS CASING APPARATUS INCLUDING A FLUID COOLED MOLD, POWER MEANS FOR REGULATING THE RATE OF DELIVERY OF MOLTEN METAL TO SAID MOLD, MEANS ADAPTED TO WITHDRAW THE CASTING FROM SAID MOLD, A THERMO-SENSITIVE ELEMENT ASSOCIATED WITH SAID MOLD AND ADAPTED TO RESPOND TO CHANGES IN THE POSITION OF THE MOLTEN METAL LEVEL WITHIN THE MOLD BY A CHANGE IN ELECTRIC FLOW FROM SAID THERMOSENSITIVE ELEMENT, AND SPEED CONTROL MEANS RESPONSIVE TO SAID CHANGES IN ELECTRIC ENERGY FLOW TO REGULATE THE RATE OF MOLTEN METAL DELIVERY TO SAID MOLD COMPRISING A SLIDEWIRE MOTOR ADAPTED TO COMPARE THE ELECTRIC FLOW FROM SAID THERMO-SENSITIVE ELEMENT WITH AN ELECTRIC FLOW STAND ARD AND TO CAUSE MECHANICAL MOVEMENT PROPORTIONAL TO THE DIFFERENCE BETWEEN SAID ENERGY FLOWS, AND AN OPERATIVE CONNECTION BETWEEN SAID SLIDEWIRE MOTOR AND SAID POWER MEANS TO REGULATE THE SPEED OF THE LATTER IN RESPONSE TO THE MOVEMENT OF THE FORMER.

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