US3542117A - Continuous casting machine - Google Patents

Description

United States Patent [72] Inventors Herbert Lemper; 2,709,842 6/1955 Findlay 164/260 Thomas E. Rodwiclr; Paul M. Lowy, 2,815,551 12/1957 llessenberg et a1... 164/260X Pittsburgh, Pennsylvania 3,088,181 5/1963 Littlewood et al. l64/26l [21] Appl. No. 620,779 3,154,815 11/1964 Bieri 164/261X [22] Filed March 6, 1967 3,258,815 7/1966 Reinfeld et a1. 164/83X [45] Patented Nov. 24, 1970 3,293,707 12/1966 Olsson 164/83 [73 1 Ass'gnee Mesh g g g l Primary ExaminerJ. Spencer Overholser a Como" 8 Assistant ExaminerR. Spencer Annear A tt0rney- Buell, Blenko 84 Ziesenheim [54] CONTINUOUS CASTING MACHINE 9 Claims, 5 Drawing Figs.

US. Cl. "I... "in. Counterbalancing means for a vertically oscilla. 164/83' 164,260. 164,282 tory mold structure used in a continuous casting machine. The [S l] ht. Cl. B22d 17/32, impractical mantel-weights or springs used in conventional 322d practices are eliminated by forming the mold structure as a [50] Field of Search 164/82, 89, recipmcambk phmger in a suitably shaped cylinder surround 260,261 4,4382 ing the mold structure. The plunger is supported within the cylinder by means of compressed fluid introduced therein [56] Rehnnm and under sufficient pressure to counterbalance the weight of the UNITED STATES PATENTS mold structure. A compressor or other source of compressed 3,047,915 8/1962 Barnard et a]. 164/154 fluid is coupled to the cylinder, together with an accumulator 3,344,841 10/1967 Rys; 164/154X to maintain the compressed fluid within the cylinder at a sub- 3,358,743 12/ 1967 Adams 164/273X stantially constant pressure irrespective of the position of the 1,385,595 7/1921 Van Ranst 164/83 mold structure along its reciprocatory path.

L 106 L 71 78 d2 8 a M 16 52 5'0 48 r 14 26 26 lg 20 24 my Patented Nov. 24, 1970 Sheet wzd Paul M Lou/g- P atented v Nov. 24, 1970 Sheet 3 of 2 I my. 2.

INVENTORY M z M W w 4% Z P V. B

THEIR H I FOAM FY15 speed control and matching.

The mold-oscillating mechanism also includes an irreversible gear unit so-t'hat the oscillatory'load of the rather heavy mold structure cannot be translated back as negative torque to the oscillator drive.

The present invention relates to'machines for the continuous casting of steel or'other metallic material and more'particularly to mold oscillating mechanisms and drive control means incorporated in such machines.

Although the'invention is described herein with reference to steel-fabricatingequipment, it-will be appreciated that the invention is of general utility in other continuous casting procedures. i

it has long been known that the'highest casting speeds and best surfacequality of a continuous casting can be attained by oscillating the mold of the continuous casting machine. Usually the mold is moved downwardly, or in'the direction of travel of the continuously cast slab or billet at a speed ranging from 100 percent to about 105 percent of the speed'of the casting. The mold structure is then returned'upwardly or in mechanism and connecting linkages. This inv turn causes highly undesirable fluctuations in motor speed, which impair the surface quality of the casting. The speed regulator usually coupled tothe drive means is unable to cope with these speed I fluctuations because of their high repetition rate and time delays inherent in the drive means.

More specifically, conventional mold oscillator drive means are deficient in at least three respects, which'aggravate the problem of speed fluctuations, and proper control of themold oscillations. One of the principle causes of motor speed fluctuations is the overhauling torque on the cam during the quick return or upstroke'of the mold structure. Although the weight of the mold structure is usually counterbalanced in some fashion, the totalrnass of the mold structure plus the counterweight is considerably increased, and the inertial forces thereof increase the overhauling or negative'torque at the drive means through the cam and gear' reduction unit usually associated therewith. It is one of the features of our invention, therefore, to isolate the drive means output from the overhauling torques applied to the cam through'the provision of a selflocking or irreversible speed reduction unit. Thus, the torques applied to the output shaft of the reduction unit cannot be transmitted therethrough to-the drive meanscoupled to the input shaft of the unit. As a result when overhauling or negative torque forces are transmitted back to the cam shaft, the latter can only speed up to an extent which matches the no load speed of the drive means.

In continuous casting machines wherein the mold structure is oscillated vertically, various forms of counterbalancing means have been used in an attempt'to achieve substantial reduction in drive requirements. In accordance with known practices, counterweights and springs have been variously used. Counterweights have proven to be impractical because the corresponding increase in total mass increases the positive and negative acceleration forces requiredto overcome the inertia of the structure plus the counterweight. This problem is seriously aggravated at the high casting speeds of present day machines. Moreover, the use of counterweights considerably increase the overhauling torque mentioned previously.

Attempts have been made to overcome the disadvantages of counterweights through the use of counterbalancing springs. Owing to floor space limitations, however, a counterbalancing spring with a high spring rate must be used. This type of spring in turn produces large reactional forces at the extreme deflections of the spring, which forces likewise result in high cam loadings and large drive requirements.

To overcome these deficiencies of the prior art, we provide a compressed air or other compressed fluid counterbalancing means. The mold structure, in accordance with our invention, is arranged as a reciprocating plunger in a suitably shaped cylinder surrounding the mold structure. Desirably, accumulator means are associated with the compressed fluid system to maintain substantially constant the available balancing forces at maximum plunger or mold structure displacements. The fluid-operated cylinder offers a further advantage in that it cushions the abrupt changes in inertial forces caused by corresponding by abrupt changes in cam shape. A further advantage is the facile adjustment of counterbalancing force through a simple adjustment of fluid pressure in the accumulator means.

Another problem encountered in the operation of conventional continuous casting machines is the undesirable transfer of the aforementioned load and drive fluctuations from the mold oscillator mechanism to the straightener mechanism forming part of a continuous casting machine. This problem results from the mechanical coupling which hitherto has been used between the oscillator and straightener drives. Such mechanical coupling has been necessary in order to maintain the required speed relation between the oscillational speed of the mold structure and the speed of the straightener mechanism, during the forward or downward portions of the mold oscillation cycle. In order that the speed relationship be made adjustable to accommodate changing casting conditions a variable type of mechanical drive has been required. However, variable speed drives are undesirable because of their high maintenance costs and lack of repeatability.

. Therefore, in accordance with another feature of our invention we have overcome the last-mentioned problems by providing a speed-matching control system which permits the use of separately driven drive mechanisms for the oscillator and the straightener components of the continuous casting machine. As a result the disadvantages of conventional mechanical couplings are eliminated, and the desired speed relationship or matching is maintained between separate oscillator and straightener drives by a suitable and novel speed control and matching circuitry.

In one arrangement of our control circuit a highly accurate speed regulator of conventional design is coupled to each of the mold oscillator and straightener drive means. Each of the speed regulators is coupled in feedback relation to a tachometer in turn coupled to the associated drive means. The

reference drive speed for the straightener regulator is provided by a signal derivedfrom the line speed of the casting. On the other hand, the speed reference for the oscillator regulator is obtained from the tachometer feedback of the straightener drive, with the result that the mold oscillator drive follows precisely the straightener drive but isnot mechanically coupled thereto. Speed matching of the oscillator drive with the straightener drive is made possible and adjustable by providing a potentiometer or other adjustable resistance means between the feedback connection of the straightener regulator this purpose the potentiometer desirably is provided with dial means for recording settings corresponding respectively to differing casting conditions.

Other objects, features, and advantages of the invention will become apparent as the following description of certain presently preferred embodiments thereof and presently preferred methods of practicing the same proceeds.

In the accompanying drawings we have shown certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same in which:

FIG. 1 is a schematic elevational view, partially sectioned, of one form of continuous casting machine arranged in accordance with the invention;

FIG. 1A is an enlarged, partial view of a portion of the mold oscillator drive means shown in FIG. 1;

FIG. 1B is a cross-sectional view of the mold structure of the continuous casting machine illustrated in FIG. I and taken generally along reference line IB-IB thereof;

FIG. 2 is a sectional view of the drive means shown in FIG. 1A and taken along reference line II-II thereof; and

FIG. 3 is a schematic circuit diagram of one form of speed control means for a continuous casting machine arranged in accordance with our invention.

Referring more particularly to the drawings and initially to FIG. 1, an exemplary continuous casting machine is arranged in accordance with our invention and includes in this example a vertically reciprocable mold structure denoted generally by reference character and having a generally vertically casting cavity 12 therein. The cavity 12, together with the verticalto-horizontal guide roll structure 14 are arranged along a radius of curvature to which the casting 16 is conformed, as in conventional practices, in moving from the vertically casting mold structure 10 to the horizontal straightening mechanism identified generally by reference character 18.

For maintenance of equipment and for starting the casting 16 a portion of the guide roll structure 14 is pivotally mounted for movement to the chain outline position 20 thereof. When initiating the casting a flexible dummy bar (not shown) or the like can be secured to the initially formed end portion of the casting adjacent the lower mold aperture 22 in order to thread the casting through the roll guides 14, the straightener mechanism 18 and the remaining components of the casting machine (not shown). A suitable dummy bar for this purpose is described and claimed in a copending, coassigned application of Herbert Lemper entitled FLEXIBLE DUMMY BAR filed Sept. 9, I966, U.S. Pat. Ser. No. 578,313, now U.S. Pat. No. 3,442,322. I

In the straightener mechanism 18 the casting 16 engages guide rollers 24 and thereafter in succession a series of straightener roll stands 26.

In this arrangement of the invention, molten steel is supplied to the mold structure 10 from tundish 28, which may concurrently serve a plurality of similar mold structures associated with other strands (not shown) of the casting machine.

In order to maintain the highest practical casting speeds and the optimum surface quality of the casting, as aforesaid, it is necessary to oscillate vertically the mold structure 10. This is accomplished by an oscillator drive including reduction unit 30 and an electric motor drive 32. As better shown in FIGS. 1A and 2, the reduction unit 30 includes spur gear 34 and worm gear 36 mounted on shaft 38 for rotation therewith by worm 40 mounted on the output shaft of the drive motor 32 and enmeshed with the worm gear 36. In this example the worm 40 forms part of a gear assembly having a ratio such that an overhauling torque applied to the reduction unit 30 cannot reverse the worm 40 so as to couple the overhauling torque to the motor electric drive 42.

The spur gear 34 is enmeshed with a related spur gear 42 mounted on shaft 44 together with cam 46 for rotation therewith. Likewise mounted on the reduction unit 30 is a pivoted cam follower 48 having a follower wheel 50 disposed in engagement with the cam periphery. The follower 48 is pivoted to the casing of the reduction unit 30 as denoted by reference character 52 and an operating link 54 in turn is pivotally connected to the cam follower 48 and to an oscillating lever 56. The lever 56 is pivoted at its fulcrum 58 to the adjacent supporting framework of the continuous casting machine, and the other end of the lever 56 is pivotally coupled to the vertically movable portion 60 of the mold structure 10. Accordingly, oscillating movements of the connecting link 54 by the cam follower 48 are translated into correspondingly opposite oscillating movements of the mold plunger 60. In this arrangement the cam 48 is of dual surface configuration. When the cam is rotated in the direction denoted by arrow 62 the curved portions 64 of its periphery permit the mold plunger 60 to descend at a relatively slower speed consistent with the lineal speed of the casting while the relatively steep portions 66 of the cam 46 raise the mold plunger 60 at a faster rate. Accordingly, two oscillation cycles are imparted, in this example, to the mold plunger 60 for each rotation of the cam 46. The amplitude of the oscillation is dependent upon the particular pivot aperture 68 at which the connecting link 54 is pivoted.

As pointed out previously, it is highly desirable to provide a suitable counterbalancing means for the oscillating portion of the mold structure 10 without introducing additional mass or reactive forces. Referring again to FIG. 1 of the drawings one form of counterbalancing means is illustrated therein and arrangedin accordance with our invention. Thus, the aforementioned mold plunger 60 having the mold cavity 12 is coupled in this example to the other end of the lever 56 by a second connecting link 70. The link 70 is pivotally connected at its upper end, as denoted by reference character 72, to the plunger 60 and at its lower end to the lever 56.

The mold plunger 60 is mounted for reciprocation within cylinder 74. As better shown in FIG. 1B the plunger 60 is of stepped, generally cylindrical configuration and thus is provided with circumferentially extending shoulder 76. The inner wall surface of the cylinder 74 is of complementary configuration, and the inner periphery thereof is stepped to form an inwardly disposed circumferentially extending shoulder 78. The necked down portion of the mold plunger 60 is sealed to the constricted or shouldered portion 78 of the cylinder in this example by a pair of O-rings or the like 82. In a similar manner the thickened portion 84 of the mold plunger 60 is sealed to the upper end portion of the cylindrical wall by similar sealing means such as O-rings 86.

As better shown in FIG. 1 of the drawings, the mold plunger 60 is illustrated in its uppermost position, as indicated by the solid outlines thereof. The lowermost position of the plunger 60 is denoted by its dashed outline 88. Therefore, during the entire reciprocatory cycle of the mold structure 60 an annular space of varying length remains between the plunger shoulder 76 and the cylinder shoulder 78 of the mold structure. A suitable pressurized fluid such as compressed air is introduced into the space 90 to serve as a fluid cushion, which in this example, is maintained under sufficient pressure to counterbalance the entire weight of the plunger 60. The weight of the plunger 60 is thus counterbalanced without increasing the mass which must be moved by the oscillator drive 32. The inertia of the counterbalanced mold plunger 60 remains the same in contradistinction to the conventional practice of using counterweights. Likewise the use of pressurized fluid counterbalancing means does not involve the application of reactive forces to the oscillator drive 32 as occasioned by the use of conventional spring-counterbalancing means.

Pressurized fluid is supplied to the space 90 by means of an inlet conduit 92 coupled to the cylinder 74 through which compressed fluid is supplied by a suitable pump denoted by reference character 94. Desirably an accumulator tank 96 is coupled in the inlet conduit 92 between the pump 94 and the cylinder 74. The tank 96 preferably is of sufficient volume that the contraction and expansion of the space 90 during reciprocation of the mold plunger 60 will not significantly increase or decrease the pressure of the fluid within the compressed fluid system including, .of course, the space 90. Duringreciprocation of the mold plunger, pressurized fluid will be caused to flow to and from the accumulator tank 96 as indicated by doubleheaded arrow 98.

Desirably a suitablepressure control means 100 is mounted in the accumulator tank 96, in order to control an on/off switch 102 in the power leads 104 of the pump 94 in the conventional manner. Thus when the pump 94 is energized pressurized fluid is transmitted to the accumulator tank 96 through the inlet conduit 92' as denoted by arrow 106. The pressure control 100 can of course be adjusted .to a fairly small cyclic pressure variation in accordance with known practices, in order to maintain the fluid pressure in the counterbalancing space 90 substantially constant.

As denoted previously, from the mold structure the continuous casting 16 is conducted along an 'arcuate path whereby the casting is' turned from its vertical casting direction to a horizontal disposition for further fabrication. Therefore, the casti'ng16 must be straightened as noted previ ously in the straightener 18. Also, it is essential that the speed of the plunger 60 during the downward component of its oscillation cycle be exactly matched in accordance with a predetermined speed ratio, with the speed of the straightener rolls 108. It is also essential that the aforementioned speed ratio can be reproducibly adjusted in order to adapt the continuous casting machine to different casting conditions. As noted above it has not-beenpossible with conventional apparatus to maintain a predetermined speed matching with a high degree of accuracy. Moreover, it was not possible to vary the speed ratio between the straightener rolls 108 and the down component of the mold oscillation cycle in a reliably reproducible manner.

Accordingly, as better shown in FIG. 3 we have provided the straightener roll drive 26 witha conventional high accuracy-speed regulator 28 having tachometer feedback 112. A reference signal is supplied to the straightener speed regulator 110 through conductor 114. The conductor 114 is connected to suitable and conventional mechanism 115 for indicating the speed of the casting 16 in the form of a relatedelectrical signal. The tachometer 112 output is one of the straightener drive motors 26 is fed back in the usual fashion to the associated speed regulator 110 through conductor 116 but is also conducted to a conventional, high accuracy speed regulator 118 for the mold oscillator drive motor 32. The signal from the tachometer 112 thus forms the speed reference signal on input conductor 120 for the last-mentioned of oscillator speed regulator 118. A conventional tachometer 122 is also coupled to the oscillator drive motor 32 and its output is fed back through conductor 124 to the oscillator speed regulator 118.

With this arrangement, the speed of the oscillator drive motor 32 can be matched exactly, according-to the desired speed ratio, withthespeed of the work roll drive 26 since the oscillator speed regulator 118 is controlled by the speed of the straightener drive motor 26'. As the straightener speed regulator 110 is controlled bythe line speed, the circuit arrangement of FIG. 3 thus preserves the predetermined desired speed relationship between the straightener drive, motors 26 andthe.

oscillator drive motor 32. For example, theoscillator drive can be closely controlled to maintain the speed of the down component of the mold plunger 60 exactly at a'given percentage of the lineal casting speed, which relationship in turn is related to line speed.

-In order to provide means for varying the speed matching or speed ratio between the straightener drive motors 26 on the one hand and the oscillator drive on the other, reproducible speed ratio-adjusting means are providedby the invention, and can be calibratedto differing speed ratios if desired. One form of such ratio-adjusting means includes potentiometer 126 coupled in speed reference conductor 120 of the oscillator speed regulator 118. The potentiometer 126 is capable of adjusting the ratio. of tachometer 112 output to the oscillator speed regulator 118 in relation to the tachometer 112 feedback to the straightener speed regulator 110. Thus'a given potentiometer setting always produces a given speed ratio between the straightener drive motors 26 and the oscillator drive motor 32.

In view of the foregoing it will be evident that novel and efficient forms of continuous casting machines have been disclosed herein. The various features of the invention cooperate to produce a controllable and uniform speed of casting, which is reproducibly variable to meet different casting conditions.

While we have shown and described certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same,-it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scopeof the following claims.

We claim:

1. A continuous casting machine comprising a mold structure open at opposite ends, means for mounting said mold structure for reciprocation and for reciprocating the mold structure in the direction of said casting, and separate counterbalancing means coupled to said mold structure for applying a fluid pressure thereto for supporting at least part of the weight of said mold structure, said counterbalancing means being disposed for least partially removing the load of said mold structure from said reciprocating means.

2. In a continuous casting machine having an oscillatable mold structure and a straightener mechanism for straightening a casting issuing from said mold structure, said mold structure and said straightener mechanism being positioned in tandem along a path of said casting, the combination comprising oscillator drive means for said mold structure, straightener drive means for said straightener mechanism, a speed regulator and tachometer coupled to each of said drive means, circuit means for coupling each of said tachometers in feedback relation to the speed regulator of the associated drive means and for coupling an output of the tachometer of one of said drive means to the reference input of the speed regulator of the a other drive means, and additional circuit means .for coupling the reference input of the other of said speed regulators to casting speed-sensing means.

3.'The combination according to claim 2 wherein variable resistance means are coupled between said reference input of said other drive means speed regulator and said tachometer output of said one drive means for varying the matched speed ratio between said drive means.

4. The combination according to claim 1 wherein said mold structure includes a mold plunger mounted for reciprocation in an outer shell closely surrounding the plunger, said shell and said plunger having spaced juxtaposed projections formed thereon respectively and defining a fluid cushion spaced therebetween and within said shell.

- Y 5. The combination according to claim 1 wherein said continuous casting machine includes a straightening mechanism for straightening a casting issuing from said mold structure,

drive means for said straightening mechanism, said mold structure and said straightening mechanism being positioned in tandem along a path'of said casting, and circuit means are coupled between said oscillating means and said straightening drive means for maintaining a predetermined speed ratio therebetween.

6. The combination according to claim 4 wherein a fluid inlet conduit is coupled to said shell in communication with said cushioning space, and compressor and accumulator means are coupled to said inlet conduit.

7. The combination according to claim 4 wherein said mold plunger and said shellare of complementary stopped outer and inner configurationsrespectively, the stepped portions of said plunger being sealed respectively to the stepped portions of said shell to enclosed said fluid cushion space.

8. The combination according to claim 1 wherein said reciprocating means include a drive motor and gear reduction unit, said unit comprising an irreversible worm coupled to the output shaft of said drive motor.

tachometers in feedback relation to the associated speed regulator, said circuit means in addition coupling an output of one of said tachometers to a reference input of the speed regulator associated with the other of said tachometers, and additional circuit means for coupling the reference input of the other of said speed regulators to casting speed sensing means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 542 ,117 Dated November 24 1970 Inventor) Herbert Lemper et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 51 "rollers" should read rolls Column 5, line 42, "is" should Signed and sealed this 4th day of May 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, J' Attesting Officer Commissioner of Patent ran I-IA Ann [in read of line 48 "of should read or line 68 after "drive" insert moto' 32 Column 7 line 6 after "positioned" cancel the peri'

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