US3040397A

US3040397A - Continuous casting machine

Info

Publication number: US3040397A
Application number: US781130A
Authority: US
Inventors: Theodor H W Haussner; Easton Rufus
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1958-12-17
Filing date: 1958-12-17
Publication date: 1962-06-26
Anticipated expiration: 1979-06-26

Description

June 26, 1962 T. H. w. HAUSSNER ETAL 3,040,397

CONTINUOUS CASTING MACHINE 2 Sheets-Sheet 1 Filed Dec. 1'7, 1958 II N 11 mam their June 1962 T. H. w. HAUSSNER ETAL 3,040,397

CONTINUOUS CASTING MACHINE 2 Sheets-Sheet 2 Filed Dec. 17, 1958 r 1,. 2 Mi w 1 5 r 5 7 MW MZ U 7. 9 w W 7. no w 5 l-lL Hm & I w

3,048,397. Patented June 26, 1%62 3,0405% CONTINUOUS CASTING MACHENE Theodor H. W. Haussner and Rufus Easton, Pittsburgh, Pa., assignors to Koppers Company, fine, a corporation of Delaware Filed Dec. 17, 1958,, Ser. No. 781,130 9 Claims. (Cl. 22--57.3)

This invention relates to continuous casting and more particularly to an improved process and apparatus for continuously casting metal into molded billets of indefinite length.

In carrying out the continuous casting of metal into billets, there is conventionally employed an open ended mold into one end of which the molten metal is poured and through the other end of which an at least partially solidified billet having the contour of the mold is withdrawn. customarily, the mold is cyclically reciprocated a predetermined and fixed amplitude in an advance movement and a retracting movement.

The mold advance movement is usually synchronized with the rate of withdrawal of the billet such that there is no relative movement between the mold and metal being cast. During the mold advance period, the molten metal partially solidifies forming an outer shell conforming to the contour of the mold. As the metal solidifies and forms the outer surface of the shell, the shell tends to adhere and cling to the mold. In the event the shell is not sufficiently thick prior to initiation of the retraction motion of the mold, the shell may rupture and the center core of the molten metal may escape through these ruptures to the bottom of the mold causing damage to the machine or, in anyevent, the rupturing causes an imperfect casting surface.

In one of the prior methods, the mold is advanced in.

synchronism with the rate of Withdrawal of the billet such that there is no relative movement therebetween and at the end of the advance movement the mold is rapidly retracted at a uniform rate greater than the advance rate. This method has been employed commercially with a mold reciprocating cycle having a mold advance move ment synchronized with the rate of withdrawal of the billet for three-fourths of the cycle and a rapid mold retracting movement at three times the rate of withdrawal for one-fourth of the cycle. In order that efficient use be made of this method, it is essential that the time between the successive movements of the cycle from advance to retract and vice versa be maintained at a minimum. To accomplish this, there are applied acceleration forces capable of substantially instantaneous changing the direction of movement and achieving the required velocities. These acceleration forces vary directly with the square of the rate of withdrawal of the billets i.e. casting speed.

'In the event that it is desired to operate in accordance with this method at casting speeds required by present day commercial practices ranging about 200inches per minute, acceleration forces approximating 128 feet per second per second are created. These acceleration forces result in excessive stresses on the machine oftentimes causing elastic deformation of the operating parts, particularly the elements of the reciprocating mechanism. The deformation of these machine elements tends to alter the reciprocating characteristics of the mold whereby imperfect casting results. Furthermore, at the above created accelerations, since they exceed gravity acceleration, it is necessary that the various items associated with the reciprocating mold be firmly fixed thereto so that they will not be shaken off or moved out of position. This oftentimes cannot be accomplished.

To overcome the acceleration difficulties encountered in the above method, a second method proposes to reverse the velocity ratios employed by the first method so that the mold advance movement is three times the velocity of the mold retract movement. At this ratio of velocities, when the mold advance velocity is synchronized at the same rate as the casting speed, acceleration forces are only oneninth as high as thosecreated by the first method at any given casting rate. While this second method eliminates the acceleration difficulties, the period of the mold advance movement is somewhat less than one-fourth of the total reciprocating cycle. This reduction of the period in which the solidifying molten metal remains in relatively motionless contact with the mold results in the formation of thinner outer shell which is subject to rupturing as described above.

The third method proposes to utilize a reciprocating mold cycle of indeterminate periods dependent upon the adhesion characteristics of the, metal as it solidifies within the mold. As described above, the molten metal tends to adhere to the mold as it cools therein creating a resistance therebetween. The third method uses this resistance or friction between the casting and mold to move the mold in its feed advance movement. Retraction of the mold is accomplished by compression springs. In operation, as the shell of the casting gradually solidifies, the adhesion forces cause the. mold to move in the direction of withdrawal against a gradually increasing opposite force exerted by the compression springs. When the forces exerted by the spring exceed the adhesion forces, the casting is released therefrom such that the mold is rapidly returned to its retracted position under the influence of the springs.

In practice, the third method has been satisfactory at low casting rates ranging from about 30 to 50 inches per minute, but has not been useable at high casting speeds, particularly at speeds ranging between 200 to 250 inches per minute as is required in the continuous casting of ferrous metals. At these relatively high velocities of casting, the acceleration forces required to move the mold table from its retracted position in synchronism with the rate of casting are of greater magnitude than the strength of the solidifying shell. The shell therefore ruptures and this method becomes unsuitable at high velocities.

It is an object of the present invention to provide a new and novel method for continuously casting metal in a manner such that the difiiculties and limitations of the prior processes are avoided.

This is accomplished by cyclically reciprocating the mold in timed relation with a selected rate of withdrawal of the billet. Each of the mold cycles includes a mold advance movement for displacing the mold from an upper starting position to a lower position, and a mold retracting movement for returning the mold to its starting position. The advance movement is controlled with respect to the rate of withdrawal such that there is substantially no relative movement between the billet and advancing mold The mold retracting movement is independently controlled to occur at a'speed which at least equals the speed of the advance movement. Maintaining this relationship of the mold advance and retracting movement results in the formation of sufficiently thick shell which is substantially non-rupturing.

In order to avoid the acceleration difliculties encountered heretofore, the mold is initiated into its mold ad vance movement at accelerationsnot exceeding 64 feet per second per second and preferably less than 32 feet per second per second. By maintaining the initial acceleration within these limits, the deformation of the mold reciprocating mechanism and the tendency of the auxiliary equipment to fly off the table is substantially eliminated.

Heretofore, the distance of mold travel has been fixed such that the total time of swichronous movement of the mold is always dependent solely upon casting rate. This is not always satisfactory since, it has been found that under some circumstances depending primarily upon the characteristics of the metal being cast, it may be desirable to shorten or increase the length of travel soas to yield optimum products.

It is accordingly proposed by the present invention to provide an arrangement for adjusting the length of travel of the mold.

In carrying out the invention, there is provided a reciprocally mounted open-end mold into which the molten metal is poured; means for withdrawing at a selected constant casting rate an at least partially solidified billet from the mold; means for reciprocating said mold, the means for reciprocating the mold including means for controlling the speed of advance of said mold in synchronism with the casting rate, means for controlling the speed of retraction independently of said casting rate, and means for initiating the mold advance movement at an acceleration less than 64 feet per second per second.

Further objects and features will hereinafter appear.

In the drawings:

FIG. 1 is a partial fragmentary schematic drawing of a continuous casting machine showing. a reciprocating mold and a portion of the mold reciprocating mechanism embodying the present invention.

FIG. 2 is a schematic drawing of the mold reciprocating mechanism embodying the present invention.

Referring now to the drawings, molten metal M is poured from a tiltable ladle it} into a tundish ill from which a stream flows through an outlet 13 into the upper open end of a tubular mold 15. The mold 15 is formed with an outer jacket 17 through which water is circulated by way of conduits 1? and 21. Supporting the mold 15 on one end for vertical reciprocation are piston shafts 23 which are slidably mounted in a stationary table 25. Mounted on the lower end of each of the shafts 23 extending below the table 25 is piston head 27 forming part of the mold reciprocating mechanism generally designated as A which serves to lower and advance the mold in the direction of the withdrawal of the billet B. Urging the mold upwardly or retracting the mold to its starting position, are compression springs 24 disposed between the stationary table 25 and mold 15.

Frictionally engaging the periphery of the solidified or partially solidified billet B as it emerges from the lower end of the mold 115 are pinch rollers 29 which grasp and Withdraw the billet B from the mold 15. The rate at which the billet B is withdrawn is controlled by a variable speed motor 31 which drives the pinch rollers 29 by way of

counter shafts

33 and 35.

The speed of the withdrawal of the billet or casting rate is set within a range of to 300 inches per minute to achieve maximum production in accordance with the solidification characteristics of the particular metal being cast. Thus, for example, for maximum production of nonferrous metals the casting rate is normally set within a range of 20 to 60 feet per minute, and for casting ferrous metals the casting rate is set within a range of 50 to 300 feet per minute.

In order to provide sufl'icient time for the metal to solidify within the mold, the latter is normally advanced with the billet as it is being withdrawn by the pinch rollers 29. This advance movement is carried out at substantially the same speed as the casting rate in order that there be no relative movement between the constantly downwardly moving billet and the mold 15. In this manner the molten metal solidifies into an at least partially solidified billet capable of withstanding handling.

To adjust the speed of the mold advance movement to synchronize with the casting rate, there is employed the mold reciprocating control mechanism A. As shown, the mold reciprocating mechanism comprises hydraulically operated linear movers 37 including cylinders 38 and the pistons 27 supporting the mold 15. The linear movers 37 are operated by an electro-hydraulic arrangement including a hydraulic speed control means generally designated as S, a fluid direction control means generally designated as D for selectively controlling the flow of liquid through the hydraulic speed control means S, and a mold positioning mechanism generally designated as P for automatically actuating the directional flow means D.

The hydraulic speed control means 5 includes a twoway hydraulic control valve 41 for controlling the flow of hydraulic fluid to and from the linear movers 3'7 and the hydraulic fluid supply. A control valve suitable for this purpose may be of the type described in the December 9, 1957, issue of Product Engineering on pages 94 to 98. When the valve is in the position of the arrow a, the pump 43 forces fluid from the reservoir 42 through the line 45, the valve 41, port 47 upwardly through check valve line 49, line 5'7 and into the upper portions of the cylinders 38 by way of lines 53a and 53b respectively.

The pump 43 is of the constant volume type which delivers and maintains a fixed volume of fluid into the system for each revolution. The volume of fluid delivered to the linear movers varys directly with the rotary speed of the pump. While the pump may be driven by a separate motor in the preferred form as shown, it is driven by the pinch drive motor 31 by way of secondary shafting and a variable speed reducing unit 55. By adjusting the speed at the reducing unit 55, the desired volume of fluid is delivered to the linear movers so as to move the mold downwardly against the resistance of the springs 24 at the same speed as the casting rate.

In this manner during the mold advance movement, there is substantially no relative movement between the constantly moving billet and the mold so that the molten metal solidifies within the mold. Upon initial adjustment of the mold advance speed to substantially equal any given casting rate, synchronized movement of the moldand the casting will continue at all casting rates, since the pump will rotate in proportion to the rotary speed of the pinch roller drive motor 31.

Upon completion of the mold advance movement, the control valve 41 is reversed to the position shown by the arrow b, such that the fluid is drained from the cylinders and the compression springs 24 are effective to retract the mold 15 to its initial starting position. The fluid drains from the linear movers 37 by way of the lines 53a and 53b, line 57, needle valve 59, check valve line 61, line 63, line 49, through the port 47, out of port 65, and returned to the reservoir 42. The fluid being constantly pumped from the reservoir 42 passes through the control valve 41 by way of port 67 and port 69 and recirculates through the filter system B back into the reservoir 42 as shown.

The retraction movement of the mold 15 is accom-' plished as rapidly as possible under the influence of the springs 24. Located in the line 61 is an adjustable needle valve 59 which serves to control the return flow of the hydraulic fluid from the cylinders 38 and lines 53a and 53b and thereby the return speed of the mold 15. The return flow is set so as to achieve to the shortest retraction time consistent with smooth cyclical movement of the mold 15 and, in accordance with the present invention, is always set at a rate which results in a mold retraction speed preferably below but never greater than the mold advance speed.

The

check valves

71 and 73 located in the

lines

49 and 61 respectively are arranged so that the needle valve is effective to, perform its function only during the mold retraction movement and not during the mold advance movement.

Upon returning to its starting position, the mold 15 is again initiated into its advance movement at a speed substantially equalling the casting rate within a minimum time such that the total time of synchronous movement of the mold 15 and the gradually solidifying billet B may be maintained at a maximum during the length of travel of the mold. To accomplish the reversal of the mold to its mold advance movement within the minimum time, there is applied an independently controlled acceleration force which is obtained by adjusting the pressure and volume of the hydraulic fluid to the cylinders 38. This is accomplished by an accumulator 75 and valve 77 which are connected to line 49 by way of line 63 so that upon adjustment of the accumulator and valve, the initial volume and pressure of the hydraulic fluid into the cylinders 38 to lower the mold may be determined. To avoid theextreme accelerations encountered heretofore, while at the same time achieving minimum time to obtain synchronous speed of the mold 15 and the billet B, the accumulator 75 and valve 77 are set to result in initial accelerations of no greater than 64 feet per second per second and preferably at 32 feet per second per second.

The mold advance and retracting movements are automatically accomplished by way of the valve directional control unit D and mold position control P. The position of thetwo-way control valve 41 in the positions a and b, as shown by the arrows, is controlled by a two- Way hydraulic and double solenoid operated pilot valve 79. Connected to the pilot valve 79 by way of lines 81 and 83 is a hydraulic piston 85 connected to the control valve 41 by a shaft 87. In the position a of the pilot valve 9, fluid is supplied from the tank 89 by way of a motor driven pump 91 through

ports

93 and 95, and line 83 into the hydraulic ram piston 85 so as to move the control valve to the position a and cause the flow of hydraulic fluid into the valves 37 and actuate the mold 15 in its mold advance movement as described above. When the pilot valve 79 is in the position indicated by the arrow b, fluid is pumped from the reservoir 89 by way of line 81, and ports 93 and. 97, such that the ram piston 85 reverses, whereupon the control valve 41 moves to the position shown by the arrow b and the fluid drains from the cylinders 38 and the mold 15 retracts under the influence of the springs 24.

way of

lines

107 and 109, respectively, to a photo switch relay 111 which is connected to a suitable source of current. A second similar positioning unit is disposed above the first unit for determining the lower position of the mold and includes a photo cell 113 and light source 115 and

light sources

105 and 115 is a plate 133 which is attached to the mold 15 for reciprocation therewith. Formed in the plate 15 are

openings

135 and 137 which are spaced to determine the length of travel of the mold table. When the mold is at its initial position, the light from the source 105 passes through the opening 135 and strikes the photo cell 103 thereby to actuate the relay 111 and energize the solenoid 131 whereupon downward movement of the mold is initiated at the desired acceleration and speed as described above. The mold 15 moves downwardly until the opening 137 aligns with the light source 115, whereupon the latter energizes the photo cell 113 and, accordingly, the photo cell switch relay 123, solenoid 131, and the pilot valve 79 so that the mold retracts as previously described.

the length of travel of the mold 15 thereby to prolong the time of mold advance movement. As previously pointed out, it is during this movement that there is substantially no movement between the mold and billet such that solidification takes place. To achieve such an ex tension of travel of the mold 15, there is used in the present invention as shown a photo switch relay having incorporated therein a conventional electronic delay circuit (not shown) which is manually adjustable by way of adjustment screws 139. Adjustment of the screws 139 serves to set the period of response between the

timethe photo cells

103 and 113 are energized by their respective light sources 105 and and the energization of the respective relays 111 and 123. That is to say, the impulse of the

photo cells

103 and 113 and the energization of the relays 111 and 123 may be delayed a selective period so that the pilot valve 79 for changing the direction is actuated only after the openings and 137 override a selected distance the positions determined by the

openings

135 and 137 in the plate 133. A relay including such a delay element and suitable for this purpose is manufactured by the Photoswitch Division, Electronics Corporation of America, Cambridge, Massachusetts, under Model Nos. 20DA2 and 20DJ2.

In this manner, the length of travel of the mold 15 may be varied to obtain the required time for solidifying the molten metal during the advance stroke. It is to be observed that this adjustment of the length of travel may be made during operation of the machine. The adjustment of length of travel during operation is of significance since oftentimes it is difficult to determine with any degree of accuracy the precise time required to form a shell. However, as a general rule, the length of travel will be short for high hot strength metals and long for low hot strength materials.

From the foregoing description, it should be readily apparent that the present invention has many advantages.

First, the mold is reciprocated in a manner such that the mold retraction speed is determined independently of the casting rate and within a period not greater than the mold advance movement atall casting rates ranging from 20 to 300 inches per minute.

to compensate for diiferent characteristics of the particu lar metal being cast.

What is claimed is:

1. In an apparatus for continuously casting metal comprising am open ended mold, means for pouring molten metal into one end of said mold, means for withdrawing at a constant rate an at least partially solidified billet from the other end of said mold, means mounting said mold for reciprocating in an advance movement and a retracting movement and including piston means for advancing said mold and spring means for retracting said mold, hydraulic fluid means for actuating said piston means including (a) means for selectively advancing said mold at the same speed as said withdrawal rate, including means for controlling the flow of said hydraulic fluid to and from said piston means, (b) means operative at the limits of movement of said mold for automatically reversing said means for controlling the flow of said hymeans for controlling the flow of said hydraulic fluid to and from said piston means.

3. The apparatus of claim 2 wherein said pilot valve actuates an hydraulic means which in turn actuates said means for controlling the How of said hydraulic fluid.

4. The apparatus of claim 2 and further including electromechanical means for sensing the limits of movement of said mold, the last said means being connected to said reversing means whereby said means for sensing the limits of movement of said mold actuates said pilot valve.

5. The apparatus of claim 3 and further including electromechanical means for sensing the limits of movement of said mold, the last said means being connected to said reversing means whereby said means for sensing the limits of movement of said mold actuates said pilot valve.

6. The apparatus of claim 3 and further including adjustment means for varying the length of travel of said mold.

7. The apparatus of claim 1 further including adjustment means for varying the length of travel of said mold.

3 8. The apparatusof claim 1 wherein the acceleration of said mold advance movement is never greater than 64 feet per second per second.

9. The apparatus of claim 1 wherein the acceleration of said mold advanvce movement is never greater than 32 feet per second per second.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,183 Junghans Nov. 1, 1938 2,135,184 Junghans Nov. 1, 1938 2,682,691 Harter July 6, 1954 2,743,492 Easton May 1, 1956 2,815,551 Hessenberg et a1 Dec. 10, 1957 2,818,616 Rossi Jan. 7, 1958 2,835,940 Wieland May 27, 1958 FOREIGN PATENTS 1,031,134 France Mar. 8, 1953 776,285 Great Britain June 5, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,040,397 June 26, 1962 Theodor H. W. Heussner et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 24, after "pinch" insert roller same column, line 50, for "B" read F column 5, line 54, for "121" read 131 Signed and sealed this 26th day of February 1963.

SEA L) fittest:

ISTON G. JOHNSON DAVID L. LADD testing Officer Commissioner of Patents