US2664607A - Method of continuous casting - Google Patents

Description

Jan. 5, 1954 J L HUNTER 2,664,607

y METHOD OF CONTINUOUS CASTING Original Filed May 17, 1950 4 2 Sheets-Sheet l Jan. 5, 1954 J. HUNTER METHOD OF CONTINUOUS yCASTING Original Filed May 17, 1950 2 Sheets-Sheet 2 Both the launder i and box 35 are made of a suitable refractory material to withstand the high temperature of the molten metal. rihe box 35 is supported on a horizontal shelf fill which is formed integrally with the supporting structure of the machine, and the launder 34 is secured to the wall or other structure of the furnace well 32 adjacent to the tap hole 33. The box 35 is divided by a partition il into two chambers i2 and is which feed the two spouts 35 (Figure 4), and these chambers are connected by openings lll with the channel of the launder 3d near the bottom thereof, so that the metal flowing down the launder is admitted to the chambers.

The casting machine 22 is seen to comprise a pair of endless chains of articulated, water cooled mold blocks til, each of said chains being trained around horizontally spaced pairs of drive sprockets 5| and driven sprockets 62, and one of said chains being disposed directly above the other and Each of the mold blocks 6B is a massive block of hard, dense cast iron or steel, ground on all sides and in the machine as shown, having two shallow channels 55 and 65 formed in the outer face thereof. Each of the channels 65, 65 constitutes one half of the mold cavity for one of the bars of metal cast by the machine, and when the mating blocks of the adjacent courses of the top and bottom chains are brought together in proper registration with one another, they form a pair of laterally spaced, open end mold cavities of uniform cross section that extend longitudinally through the center of the machine. Transverse alignment of the mating mold blocks within extremely close tolerances is obtained by means of small rectangular end plates 5l which are securedby screws to opposite ends of each block in the top chain 63 and project outwardly for a short distance beyond the outer face of the block to form flanges that lit snugly down over the ends of the companionate block in the bottom chain 55.. The bottom block is thus confined between the end plates 5l', and is prevented thereby from shifting transversely with respect to the top block; hence the two blocks are always maintained in accurate transverse alignment with one another during the period of their conjunction.

Each of the mold blocks is connected to the adjoining blocks by hinge pins which project laterally beyond the ends of the blocks, and journaled on the ends of the said pins are rollers 'i4 which run on the peripheral edges of rigidly supported side plates 15. Each of the side plates 'I5 is elongated horizontally, with straight top and bottom edges and semicircular ends having their centers of curvature at the axes of the sprockets 6| and 52. rlChe side plates 'I5 of each chain S3, 54 are mounted on a supporting structure Si) located at one side of the chain mold assembly, and are attached thereto by a pair of laterally spaced, thick-walled steel pipes '16 of large diameter which project horizontally outward from a side wall plate l5 of the supporting structure 8i! between the sprockets 5| and 52. The structure Sil is made up of heavy steel plates welded together at their edges to form a closed, box-like 4 member of great strength and rigidity. The pipes 'I5 are closed at their outer ends, and are secured by bolts 8| to the supporting structure 8S, the said bolts passing all the way through the supporting structure as shown in Figure 4.

The driving and driven sprockets 6|, 62 are welded or otherwise suitably xed to drive shafts 85, between and immediately adjacent plates 15, the said shafts extending through circular openings in the plates. The outer end of the shaft 85 terminates in a threaded stud on which a nut 'IS is screwed, and the latter is drawn up tight against a collar TI that bears against the outside of the outer sprocket 6|. Each of the sprockets 5I, 62 is rotatably supported on the structure BU.

A spur gear is mounted on the end of the upper shaft 85 where it projects from the back of the supporting structure Bil, and is secured against rotation relative thereto by means of a key or the like. A corresponding spur gear is secured to the lower sprocket drive shaft. The top gear Q5 is meshed with an idler gear 55, which is meshed, in turn, with another idler gear that is also meshed with the bottom spur gear, and the last-named idler gear meshes with a pinion G8. Pinion 9B is driven by a sprocket IES through a friction clutch IilI, which is adapted to slip when overloaded, and thus protects the mold chains and driving mechanism from damage in the event that something becomes jammed.

Trained around the sprocket |80 is a roller chain ||Il which extends downwardly to and is trained around a sprocket mounted on the drive shaft of an electric motor |I2. A second sprocket I I 5 (Figure 4) on the motor shaft drives another chain l which is trained around a large sprocket I4 on shaft I I5, to drive the pinch rolls 2S. The electric motor |2 also drives the rotatable heads of the coolant distributor 24, and to this end, a sprocket |20 is mounted on the bottom drive shaft 85, which drives a chain |2| that is trained around another sprocket (not shown) on a shaft |23.

Shaft |23 extends forwardly through the supporting structure Bil (as shown in Figure 3) and is operatively connected to the coolant distributor mechanism 24 to drive the same. As described in detail in Patent No. 2,631,343, the coolant distributor 24 comprises a housing |25 which supports two vertically spaced, rotatable heads |34 and |35, that are driven from shaft |23 in the same direction and at the same rate of speed as their respective mold block chains S3 and 64. The heads |313, |35 are connected by flexible hoses I'I5 and I9! to inlet and outlet ttings on the ends of the mold blocks. A pump |64 driven by a motor |55 circulates coolant from a reservoir tank |10, through swiveled fluid couplings |59, heads |313, 135, inlet hoses N5, mold block coolant passageways, return hoses lill, back into the tank |13, and out through overflow pipe |12.

On leaving the machine at the exit end thereof, the solidified bars of metal are guided laterally into the pinch rolls 25 between outer rolls 223 and tandem inner rollers 22| (Figure li) which are rotatably supported on a horizontal shelf 2.22 projecting laterally from the supporting structure 85. The pinch rolls 25 comprise an upper roll 223 and a lower roll 221i which extend transverse to the direction of travel of the cast bars, and which are rotatably supported at their ends in bearing blocks 225. The bearing blocks 225 are slidable vertically between laterally spaced pairs of guide posts 226, which are mounted on a horizontal a bridge rmember .23 l.

#accesar y shelf plate i'tt f projecting i laterally vfrom the v`side Aof the supporting structure its, .the `top Aends 4of each pair of posts .being,connected-together by Long bolts .232 extend upwardly through the shelf23, guideposts-ZZS, bridgemember Ito securefthe side frames into a solid structure. An adjusting .screw 233 is threaded` downwardly through the bridge member 22! and engages the top bearing block 225 to adjust the spacing between the rolls 223,224.

The bottom rollV 224 is connected atitsback end to the sprocket shaft l I5 and is driven thereby in theclockvfise direction, as viewed in Figure 2; the top roll 223 being driven by the bottom roll inthe oppositeidirecticn and at thesamerate of speed through a pair of intermeshed gears (not shown) which are enclosed within a housing 23,4 (Figuresg and 4).

bestshown FiguresJ `3 `and 2, the .tworolls `223, 2f-2li are water cooled, l,and to this end 4rare provided withcylindrical bores 2,35 (Figuref), through which va pipe :236 of somewhat smaller outside diameter is passed. vFitted on extensions of the roll necks andpipes/Zbeyond the gear housing 23d are swivel couplings 248 which deliver Y' water to theinner pipe236 and exhaust the water rfrom the space between ythe'pipe Aand the-walls of the bore The inlet sides of the couplings 22E ere connected to pipes 24| which are joined together and connected to the main Water pipe Il! while the outlet side of the couplings is connected to a pipe 2h32 (Figures 1 and 3) that returns the used water to the tank i ll).

The rolls 223 and 224 have two important functions: iirst, they are driven at a speed carefully computed to regulate the speed of the bars to the linear speed of the chains E3, 64, less the linear rate of thermal contraction of the cast bars that has taken place between the point in the machine where the metal becomes solid and the point of contact of the rolls 223, 224; and second, they perform the work of pushing the bars into the holding oven 36, thereby relieving the chains 63, 54, of this relatively heavy load. The ilrstnamed function is important because of the low tensile strength of most metals at temperatures near the melting point. Aluminum, for example, is characteristically hot-short at temperatures just below its melting point, and in the hot-short temperature range the tensile strength of the metal is substantially zero. The rapid cooling of the metal in the casting machine causes a very considerable amount of shrinkage in the bar, and if the bar is allowed to leave the mold blocks at the same speed as the linear travel of the chains 53, 612, the lengthwise shrinkage of the bar within the mold cavities of the machine will cause the bar to pull apart or at least crack, in its weak, hot-short zone. The pinch rolls 223, 224 hold back on the bar so that the amount of shrinkage is taken up, and the exit speed of the bar from the machine is somewhat less than the linear speed of the chains 53, 64. For example, when casting aluminum alloy with a coeiiicient of thermal expansion of .0000254 per degree centigrade, with a distance of 40 inches between the solidication zone and the point of engagement of the bar by the pinch rolls, and temperature drop of 120 C., the cooling shrinkage theoretically amounts to ,122 inch. Assuming that the casting machine is operating at 60.00() inches per minute (5 ft. per min), the peripheral speed of the pinch rolls would be not more than 59.878 in. per min. In practice, it would be desirable to operate the pinch rolls at a slightly slower peripheral speed .tot accommodate any additional shrinkage Athat 4nfii-ght'result from a slightly .greatertemperature `drop due to. colder coolantwater, slower operating ,speed ofthe machine, or=the like, The proper peripheralspeedof the vpinch rolls is obtained byzproportioning the sprockets Hs and llt so that a rotational: speed isl obtained which iscor- `rect iforthe .diameters of the rolls 223 and '224.

Thezsecond-@named function is important where long lengths of bar have to be'pushedinto the oven. .In such instances, the work #required to overcomefriction of the bar sliding over its supports'within the `oven may exceed the pushing 'capacity of the casting machine, since the "machineihas only the friction of the moldblocks on the bars to drive the latter, 'and in that case the mold blocks would merely skid along the vbars. -Thepinch rolls.223,22l maybe tightened'down ontofthe bars by the adjusting screw233'tosecure ra powerfulfrictional grip thereon.

The pinch rolls 223, 221i thus cooperate y.with

' the castingmachine 221to perform the method'of' Bti continuous casting which forms the essence of' the Apresent invention. The method of vthe in vention consists of the steps of pouringmolten` metalinto a continuously traveling,-powerfdrivenz mold'which chills the metal into a solid`fbar,and then engaging vthe bar beyond the exitend of the mold, as by the pinch rolls 223, 224, and driving the same at a predetermined linear speed substantially corresponding to the speed at which thel mold is traveling, less the linear rate of thermal contraction of the cast bar between the point of solidication and the point of driving engagement by the pinch rolls. The bar is thus held back into the mold to an extent such that the metal in the hot-short zone is maintained substantially without tension, and at the same time, the bar is propelled beyond the exit end of the mold by the pinch rolls, entirely independent of the frictional engagement of the bar by the surfaces of the mold blocks.

As the bars leave the pinch rolls, they are engaged on their outer edges by two guide rolls 25!) (Figures 3 and 4) which are supported on a narrow shelf 25| projecting laterally outward from the supporting structure 8E) at the extreme end thereof.

Beyond the guide rolls 256, the bars pass through the flying shear cut-off 23, where they are automatically cut to predetermined lengths while continuing in motion. The flying shear cuto (best shown in Figures 1 and 3) is essentially a hydraulically operated shear mounted on a freely movable carriage that is adapted to travel with the bars while the latter are engaged by the shear blades. The construction and operation of the flying shear cut-off 28 is described in detail in my Patent No. 2,631,343, to which reference may be had.

The operation of the casting machine is believed to be self-evident from the foregoing description. When the machine is rst started up, the openings M3 in the box 35 through which molten metal flows into the spouts 36 are blocked off, and the furnace is tapped. Molten metal is allowed to iill the chambers t2 and 43, and to overflow through a notch 223 in the side of the box, running down a gutter 282 into pig molds,` until the launders 34 and box 35 have been thoroughly heated and the temperature of the metal in the box is right for casting. The passages 2l3 are then uncovered, and metal is allowed to ilow through the spouts 36 into the mold cavities. 'I'he mold cavities are usually plugged with a block so as to prevent the metal from flowing along the mold cavity until the latter has been lled. These blocks are carried through the machine on the front ends of the bars, and drop 01T when the bars push out of the machine at the exit end thereof. While the speed of the machine depends upon a number of variables, I have found that the most satisfactory operation for aluminum alloys is obtained with a chain speed of approximately 5 feet per minute.

While I have shown and described in considerable detail the preferred casting machine embodying the method of my invention, it will be understood that the method may be practiced by using other apparatus, and the present machine is merely illustrative.

I claim:

The method of continuously casting metal in bar form, comprising the steps of introducing molten metal into the entrance end of a continuously traveling, power driven mold, rapidly chilling the metal so as to solidify the same into a negrained metal bar, said bar being propelled by tractional engagement of the mold walls with the bar, and then engaging the bar beyond the exit end of said mold and positively driving the same at a linear speed substantially corresponding to the speed at which the mold is traveling, less the linear rate of thermal contraction of the cast bar between the point of solidication and the point of driving engagement, the tractive forceexerted on said bar beyond the exit end of said mold opposing and exceeding the tractive eiort of the mold walls, whereby the bar is held back into said mold to an extent such that the metal in the hotshort zone is maintained substantially without tension, and whereby said bar is propelled beyond the exit end of said mold independently of the frictional engagement of the bar by the surfaces of said mold.

JOSEPH L. HUNTER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,865,443 Perry et al July 5, 1932 1,870,406 Douteur Aug. 9, 1932 2,290,083 Webster July 14, 1942 2,565,959 Francis et al Aug. 28, 1951 2,590,311 Harter et al Mar. 25, 1952 FOREIGN PATENTS Number Country Date 273,311 Great Britain May 17, 1928

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