US 3036348 A
Descripción (El texto procesado por OCR puede contener errores)
May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS ll Sheets-Sheet 1 Filed March 17, 1958 77 4/42 4 ATTORNEYS MMHAZELEIT E/cHA/ w HA2??? Y amt:
INVENTORS 19055197 WILL flaw/14 s May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS l1 Sheets-Sheet 2 Filed March 17, 1958 wNM INVENTORS KOBE/F7 W/LL/AM HAZELETT k/CHAED HAZE/.577
BY anti Hm: fi s-d ATTORNEYS May 29, 1962 R. w. HAZELETT ETAL 4 METAL CASTING METHODS AND APPARATUS ll Sheets-Sheet 3 Filed March 17, 1958 May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS 11 Sheets-Sheet 4 Filed March 17, 1958 INVENTORS ATTORNEYS MNN NNN
May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS l1 Sheets-Sheet 5 Filed March 17, 1958 FIG. 5.
- INVENTORS ROBERT W/LL/AM HAZELET T lP/C/l/YPD HAZELEKT 5y new): Fi /M ATTORNEYS May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS l1 Sheets-Sheet 6 Filed March 17, 1958 FIG. 6.
L A I. w 5 L w d. w /l w I T A 07 Z 06 jW 2w f A 0 w w INVENTORS EET W/LL/AM 194421-1577 HARD HAZELETT BY awn/ WWW ATTORNEYS May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS Filed March 17, 1958 7 l1 Sheets-Sheet 7 FIQ. 8.
INVENTO ROBERT WALL/HM HHZELE IP/CHHED HHZELETT ATTORNEYS May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS l1 Sheets-Sheet 8 Filed March 17, 1958 INVENTORS RfiBE/PT VV/LL/AM HAZELETT 19/6 HHE'D HAZELETT B) a. 3, 7, &/ L
ATTORNEYS May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS ll Sheets-Sheet 9 Filed March 17, 1958 FIG. l2.
%:IIIIIIIII'II----I-------------II I II INVENTORS KOBE/PT W/LL/AM HHZELETT fi/(HHED HAZELETT AW 6442:; Mr Firm 7414 ATTORNEY-5' y 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL CASTING METHODS AND APPARATUS Filed March 17, 1958 11 Sheets-Sheet 10 Q Q g g R Q N "m 1 1 g i Q l gl L0 N a i i $1 m 9 l i i m LL 5 l i 1 I $3 i I 2 K 2 1 i '1 R Q w I! a N 1 v Hm. m
INVENTORS K055197 W/LL/HM HAZELETT lP/CHAEO HHZELETT BY a d}, lfm r ATTO R N EYs May 29, 1962 R. w. HAZELETT ETAL 3,036,348
METAL. CASTING METHODS AND APPARATUS ll Sheets-Sheet 11 Filed March 17, 1958 FIG. I?
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z v F United States Patent Hazelett, Rocky River, Ohio, assignors to Hazelett Strip-Casting Corporation, Fairfield, Conn.
Filed Mar. 17, 1958, Ser. No. 722,005
25 Claims. (Cl. 22-57.4)
This invention relates to machines and processes for casting metal strips directly from molten metal and more particularly for continuously casting metal strips between spaced parallel portions of a pair of flexible metal belts which are moved along with opposite surfaces of the strip being cast.
The invention is described as embodied in the structure and operation of a continuous strip-casting machine in which the molten metal is fed into a casting region between opposed parallel portions of a pair of moving flexible metal belts. The moving belts confine the molten metal between them and carry the molten metal along as it solidifies into a strip between them. Spaced rollers having narrow ridges support and drive the belts while holding them accurately positioned and aligned as they move along so as to produce metal strip of high quality and having good surface qualities. The vast quantities of heat liberated by the molten metal as it solidifies are withdrawn through the portions of the two belts which are adjacent to the metal being cast. This large amount of heat is withdrawn by cooling the reverse surfaces of the belts by means of rapidly moving substantially continuous films of liquid coolant travelling along against these surfaces.
It is an object of the present invention to provide methods and apparatus for continuously casting metal strip of high quality directly from molten metal.
It is an object of the present invention to provide methods and apparatus for continuously casting metal strip directly from molten metal enabling the operator quickly and easily to adjust for casting strip metal of various widths and thicknesses as may be desired.
Among the many advantages of the illustrative embodiment of the invention described herein are those resulting from the fact that the moving belts are accurately supported and steered while being maintained under high tension so as to produce metal strip smoothly and continuously of the desired width and thickness.
Advantageously, the carriages which carry the rollers for supporting the casting belts are mechanically isolated from the remainder of the machine so that any stresses or strains in the framework of the machine or in the reservoir tank or base of the machine cannot affect the quality of operation. Such stresses or strains in the framework of the machine may result from racking forces imposed during lifting or moving of the machine or may accumulate over long periods of time as a result of settling of a floor or foundation upon which the machine is standing. Nevertheless, the belt-supporting carriages will remain free of any such imposed forces enabling the belts to run along true courses with respect to each other so as to maintain high quality of product. This isolation of the carriages from the framework is provided by utilizing a three-point suspension for one of the carriages and aligning the other carriage with it. As shown the lower carriage is rigidly supported from the frame at two points but the third point of suspension can freely shift with respect to the frame. Also, the upper carriage is rigidly aligned with the lower carriage at two points while a third point of suspension for the upper carriage can freely shift with respect to the frame.
A particular feature of the support for the upper carriage is the use of a lever of the third-class. This lever 3,036,348 Patented May 29, 1962 has its fulcrum point located most remotely from the upper carriage itself. Thus, as the upper carriage is raised and lowered by the lever, the lever itself swings through only a small angle because of the remote location of the fulcrum point. As a result of this advantageous lever construction a substantially greater range of up and down movement of the upper carriage is obtained without increasing the clearance within the carriage itself. This enables the operator to open the machine up much wider than heretofore obtainable in a machine of comparable size. Moreover, this third-class lever construction enables wider belts to be used without introducing any increase in headroom requirement because the angle of swing for the lever is lessened, thus reducing clearance requirements for any given belt width.
Among the further many advantages of the methods and apparatus described herein as illustrative of the present invention are those resulting from the fact that they enable the moving casting belts to be supported from behind or backed-up at numerous closely spaced points along both faces of the casting region while also providing a tremendous cooling capacity. By virtue of the numerous closely-spaced support points the areas of the two belts are held precisely positioned in parallel planes as they move along through the casting region. Thus, a smooth and uniform supporting action is provided to both surfaces of the strip of molten metal as it solidifies. In this embodiment of the invention these numerous support points for each casting belt are provided by closely spaced parallel back-up rollers having relatively high narrow ridges or fins engaging the reverse surfaces of the belts. The film of liquid coolant travels at high speed along the reverse surface of each belt passing through the grooves between the ridges of the back-up rollers forming a substantially continuous high-speed layer. The liquid coolant is conveyed into position through numerous large capacity headers which are positioned back away from the reverse surface of each belt farther away than the plane of the axes of the back-up rollers. This construction advantageously enables the back-up rollers to be placed quite close together because the cooling headers are in a different plane, while also enabling large quantities of coolant to be conveyed to every desired point of both belts so as to provide tremendous cooling capacity over the full width and length of each belt. This construction enables large increases in width of continuous cast metal strip to be obtained.
The coolant rushes in through these headers, and from the headers the coolant is accelerated toward the reverse surface of each belt by passing through narrow supply channels extending between the back-up rollers. From these narrow channels the liquid is further accelerated and propelled in jets travelling at high velocity with a grazing incidence angle toward the reverse surface of each belt so as to form and to maintain the substantially continuous, high-speed cooling films.
The casting region is inclined downwardly in the direction of travel of the strip being manufactured, for example, an angle lying in the range from 5 to 10 below the horizontal provides a system which works very Well, and an angle of 6 below the horizontal is the preferred value shown in this example, and the molten metal flows from a bath down at this angle into the casting region between the belts. As this molten metal progresses further and further down into the space between the casting belts it exerts a continuously increasing pressure on the front faces of the belts, trying to drive them apart, because of the liquid head which exists. Inasmuch as molten metals generally are far more dense than water, it will be appreciated that only just a few inches of height of molten metal will exert a substantial pressure due to the liquid head. This pressure of the metal as it travels down between the belts is advantageously overcome by crowding the back-up rollers progressively closer together toward the discharge end of the machine. Conversely, the progressive increase in space between the back-up rollers up toward the input end or bath region of the machine .is used to advantage to provide for additional amounts of cooling capacity upon the reverse surfaces of the belts near the input end, where the metal is hottest.
An additional advantage provided by the present embodiment of the invention is the relatively sharp edges on the ridges of the back-up rollers. These sharp ridges only engage very narrow portions of the reverse surface of the belts so as to expose as much of the belts as possible to the fast-moving cooling film. The edges of these ridges have a width relative to the thickness of the belt of not less than the belt thickness and not more than three times the belt thickness, and also they define an angle of not more than effectively 20 between sides for reasons explained in detail further on in the specification.
A further feature of this machine is the increase in visibility into the bath region resulting from bringing the upper belt down steeply toward the lower belt and then curving it around a substantial length of are on a nip roll at the entrance to the casting region. This wide opening of the bath region is enabled to be accomplished by virtue of the intense cooling which is directed onto the upper belt where it curves down under the nip roll. As seen in FIGURE 10 the nip roll is grooved and the nozzle ends of numerous coolant tubes are fitted down directly into the respective grooves and all are fed from a large capacity high pressure header so that a high velocity film is created against the inside surface of this belt as it bends around the nip roll.
In this example the liquid coolant is water to which a small quantity of rust inhibitors has been added. It will be appreciated that as the molten metal solidifies it releases its heat of fusion, which represents a large quantity of heat per unit volume of metal being cast. The resultant rate of transfer of heat from the solidifying metal through the thin casting belts into the film of coolant is so great that the 'molecules of water adjacent to the reverse surface of each belt tend to flash into steam, that is, they tend to boil almost at the very instant of coming into contact with the belt. During this instant of time in which any minute volume of water is being turned into steam at any spot on the surface of the belt a very great localized cooling action is provided to the belt adjacent to the point at which the steam is being formed.
However, as soon as a pinpoint of steam or a small bubble of steam is formed on the belt, then the presence of this steam would tend to prevent further water from coming into contact with this spot on the belt and thus reduce the cooling action. By virtue of the rapidly moving coolant film, any steam bubbles which form are immediately replaced by more water. Moreover, the grazing incidence of the high-speed jets of water tends to enhance the scrubbing away of steam bubbles. Also, these jets add fresh impetus to the moving film at many places so as to maintain the necessary high velocity and continuity to the film.
The theory which we use to explain this highly effective cooling action of the rapidly-moving and unconfined film of water is set forth hereafter, but we do not wish to be bound by this theory, because, regardless of the actual microscopic action involved, this example of our invention works quite satisfactorily. The theory is that the rapid growth and subsequent quick collapse of the many minute steam bubbles causes intense agitation of the layer of the water film which is in engagement with the belt. This intense agitation of the water at the surface of the belt causes the water to scour the belt surface between steam bubbles so that a large portion of the heat is transferred directly into the water and heat is also removed through the vaporization of the water into steam.
Thus, a highly advantageous method of cooling is provided in this example wherein a rapidly moving continuous film of water removes vast quantities of heat from a surface through the rapid formation and collapse of multitudes of minute steam bubbles. Some of this cooling action is provided by withdrawing heat to vaporize the cooling liquid and by immediately replacing this vapor with more liquid ready to be vaporized in the subsequent instant of time. We believe that even more of the heat is removed directly to the water by the vigorous agitation caused by the rapid growth and collapse of steam bubbles. In operation, the temperature of the casting belts is stabilized and maintained constant at a temperature not greatly in excess of 212 F., that is, not far above the boiling point of water at atmospheric pressure.
For further increasing the cooling action, the narrow coolant supply channels are shaped to provide scoops extending generally across the belt just ahead of the respective sets of jets. The edges of these scoops are sharpened and spaced only a small distance away from the surface of the belt. These scoops remove the outermost layers of the water, leaving a film of reduced thickness passing at high speed along the surface of the belt beneath the edge of the scoop. As the jets of liquid impinge on this thinner film they spread out and build up the film thickness to its original value while at the same time re-accelerating the film to its original velocity.
Advantageously, the liquid films are unconfined as they skim along at high speed against the surface of each casting belt, that is, their outer surfaces are exposed to the atmosphere. Thus, the pressure at the surface of the belt is also approximately equal to atmospheric pressure so that the water there will boil at approximately 212 F.
" This is in marked contrast to the use of a confined chamber or a water jacket through which water is forced under pressure which raises the boiling point and reduces velocity because of confinement.
In this illustrative embodiment the two main downstream rolls, that is, the two large rolls at the discharge end of the machine are grooved to provide multiple liquid channels. Thus, when the fast moving films of coolant reach these rolls they continue to scoot along the inside surface of the belt as it curves around the rolls. The liquid which flows around the lower downstream roll passes back harmlessly beneath the machine and falls into the reservoir tank beneath the machine. A special liquid catcher and gutter apparatus is positioned close to the upper downstream main roll so as to trap the liquid shooting out from between the belt and the grooves at the top of this roll, thus preventing this liquid from cascading back into the machine or from ricocheting onto the molten metal.
Among the further advantages of the machine described herein are those resulting from the fact that the steering action of the belts is accurate and is positive in action by skewing the axis of one of the main rolls at one end of each carriage with respect to the axis of the main roll at the opposite end of the carriage. Moreover, this skewing motion is readily and accurately produced and controlled in spite of the high tension in the casting belts which exerts a large force on these main rolls. The hearing at one end of each skewed roll is held fixed and the hearing at the other end is supported on a slide which is linked to an eccentric. By turning the eccentric this slide is caused to move as desired to control the position of the hearing.
A further advantage of the illustrative machine lies in the pour distributor for the molten metal which slows the passage of molten metal and spreads it out to the full width of the strip being cast. This pour distributor releases the molten metal slowly and uniformly across the full width of the strip and releases it beneath the surface of the molten metal already in the bath on the lower belt. Moreover, the air is completely excluded while the metal is slowed down and spread out beneath the surface of the bath with a minimum of turbulence. At the instant that the incoming molten metal is released its temperature, of course, is the hottest which must be withstood by the casting belts. Any turbulence present when this incoming metal reaches the lower belt greatly increases the localized rate of heat transfer into the lower belt and can readily overheat it causing it to warp. By releasing the incoming metal uniformly across the full width of the bath of molten metal a cushion of cooler metal is obtained preventing direct impact on the belt and preventing high turbulence at the instant of release.
As mentioned above, the illustrative embodiment o the present invention enables much greater widths of metal strips to be continuously cast than have been made heretofore, and the casting belts are of much greater Width. However, the operator may, from time-to-time wish to cast a strip which is not as wide as the full width of the belts. This use of very wide belts, and particularly the casting of narrower strip on wider belts results in a condition which we call cold-framing of the belts. That is, the center portions are heated along the full length of the belts and expand from heating while their edges are cooler and do not expand so much. Because of this differential expansion across the belt width the center portions lose their tension and become slack compared with the taut edges. The tendency thus is to form scallops or flutes extending longitudinally along the center of the belts while the edges appear to form a fiat coldframe. For the purpose of preventing cold-framing by providing a lateral tension to the belts so as to maintain them fiat by stretching the belt edgewise, we find it to be advantageous to use very slightly reverse-crowned rolls at opposite ends. That is, the center portions of the rolls are of slightly less diameter than the ends. For example, with a belt 46 inches wide the ends of the main rolls may advantageously measure about 0.005 of an inch more in diameter than their centers. This reverse crown imposes an extreme tension on the very edges of the belt adjacent to the main rolls causing the two edges of the belt to bow out slightly away from each other so as to maintain the center under lateral tension so as to prevent formation of longitudinal scallops due to cold-framing.
Another advantage of this embodiment of the present invention is the added cooling of the downstream ends of the stationary dams Which is provided by coolant Wipers engaging the front surface of the upper band ahead of the point where it rubs against the cusps of the stationary dams.
In this specification and in the accompanying drawings are described and shown metal casting methods and apparatus embodying this invention and various modifications thereof are indicated, but it is to be understood that these are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the manner of applying the method and apparatus in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions for casting a particular metal or alloy.
The various features, aspects, and advantages of the present invention will be more fully understood from a consideration of the following description of continuous strip casting methods and apparatus incorporating the invention, considered in conjunction with the accompanying drawings, in which:
FIGURE 1 is a perspective view of a continuous stripcasting machine embodying the present invention as seen looking at the input end (molten bath region) of the machine from a position adjacent to the control panel, which is positioned near one corner of the reservoir tank for the cooling liquid. For convenience of illustration the box for the molten metal and the pour distributor which feeds the molten metal down into the bath region are omitted from this view.
FIGURE 2 is a perspective view of this machine as seen looking at the output end, and showing the control panel;
FIGURE 3 is a longitudinal elevational sectional view taken along a plane perpendicular to the axes of the various rolls and with parts shown partially broken away for clarity of illustration;
FIGURE 4 is a cross sectional view of the machine taken along the line 4-4 of FIGURE 3 looking toward the input end;
FIGURE 5 is a partial perspective View illustrating the three point suspension system for isolating the carriage support mechanism from any twisting or Warping stresses which may be imposed upon the tank or supporting framework when the whole machine is transported;
FIGURE 6 is an enlarged cross sectional view of one of the nozzle, scoop and gutter assemblies for cooling the upper belt shown in relation to the adjacent back-up rollers and showing the way in which a portion of the cooling liquid is removed by the scoop and is replaced by faster moving liquid to maintain a rapidly moving film of cooling liquid on the surface of the belt;
FIGURE 7 is a partial perspective view of the upper part of the gutter assembly, shown partially broken away and in section;
FIGURE 8 is an enlarged elevational and sectional view of the two end portions of one of the back-up rollers, illustrating the configuration of the narrow ridges along its length in detail and showing the bearing sockets;
FIGURE 9 is a further enlargement of the ridges on one of the back-up rollers showing the relationship of edge thickness to belt thickness and edge angle limitation;
FIGURE 10 is an enlarged perspective view of the bath region as seen looking down and forwardly showing the lateral position adjustment mechanism for the stationary and moving edge dams, the cooling wiper sponges for the stationary dams, and with portions of the upper and lower belts shown cut away to reveal the grooved nip roll which guides the upper belt down into the molten metal bath. This figure shows the header for cooling the bend of the upper belt as it curves under the nip roll, this header having nozzles fitting down into the grooves of the nip roll, and also shows the relationship of the molten metal to the moving and stationary edge dams and to the pour distributor;
FIGURE 11 is an enlarged partial sectional view on the same scale as FIGURE 9 and showing the configuration of the grooves in the surfaces of the two main downstream rolls (one for the upper belt and one for the lower belt). These grooves allow the fast-moving cooling liquid to flow away from the casting region by shooting along the inside surfaces of the casting belts, and going halfway on around these rolls;
FIGURE 12 is an enlarged sectional view of the upper downstream roll and of the adjacent catcher and gutter assembly for catching and removing the cooling liquid which shoots out above the top of the roll along the inner surface of the upper belt after rushing up and around from beneath the roll;
FIGURES 13A and B are diagrammatic exaggerated views of the lower belt illustrating the method and operation of the belt steering mechanism;
FIGURE 14 is an elevational view of the lower carriage belt steering mechanism which operates by moving one of the bearing pillow blocks of the lower upstream pulley so as to skew very slightly the axis of the pulley for steering the belt;
FIGURE 15 is a partially cut away cross sectional view taken generally along the line 1515 of FIGURE 14 looking toward the left and showing details of the steering mechanism;
FIGURE 16 is a perspective view showing the construction of one of the moving side dams and the way in which the end connections are made;
FIGURE 17 is a side elevational sectional view of the pour distributor for the molten metal;
FIGURE 18 is a top view, with portions shown broken away to reveal features of this pour distributor;
FIGURE 19 is an enlarged longitudinal sectional view of the tip of one of the nozzle tubes which wraps around the lower upstream roll; and
FIGURE 20 is an enlarged sectional view taken along the line 20-20 of FIGURE showing the way in which the wrap-around nozzle tubes nest in the grooves of the roll.
General Description of Strip Casting Methods and Apparatus In this example, as shown in FIGURES 3 and 17, the molten metal is supplied from a pouring box 2 made from heat insulating material, as will be described in detail further below. The rate at which the metal is fed down through an outlet 4 in the bottom is controlled by the operator by adjustment of a tapered stopper 6 carried on a vertical threaded rod 8 which is screwed through a support bar 10. This arrangement for pouring from the bottom of the metal supply 11 leaves any particles of slag or oxidized metal floating on the surface of the supply remaining in the pour box. As the metal flows down along the numerous narrow distribution grooves 12 in the distributor plate 14 its velocity is controlled by friction with the walls of the numerous grooves while the atmosphere is excluded by a distributor cover 16' and by a front bafiie 17 forming a transverse distribution channel 18. The incoming metal flows from this channel by passing forward under the front bafile 17 and is smoothly and uniformly released beneath the surface of the existing molten pool or bath B, which is maintained during operation and is seen most clearly in FIGURES 10 and 17.
From the bath B the molten metal is carried into the casting region formed between the opposed surfaces of upper and lower flexible casting belts 20 and 22, respectively, and generally indicated at C (please see FIGURE 3). These casting belts are formed of flexible and heat resistant sheet metal having a relatively high tensile strength, for example, conventional cold-rolled low-carbon sheet steel having its ends welded together with both surfaces at the weld being ground smooth and flush to form a continuous wide band or belt having a smooth outer or front surface operates very well. The belts are relatively wide and thin, for example, of the order of 46 inches in width and, for example, having a thickness lying in the range from 0.015 to 0.035 of an inch. This illustrative system operates very well with belts having a thickness of 0.025 of an inch. The two belts are supported and driven by means of upper and lower carriages, generally indicated at U and L, respectively.
These two casting belts are driven at the same linear speed, and their adjacent portions move away from the bath region downwardly at a small angle from horizontal, for example, an angle in the range from 5 to 10 operates highly satisfactorily. In this particular example, 6 is described as the preferred value which is found to be optimum for aluminum and aluminum alloys. During operation these belts are held under a high tension, for example, such as 10,000 to 12,000 pounds of tension force are exerted by the main end rolls on each belt for a belt 46 inches wide, as shown. The belts are supported, that is, backed up" so that their opposed front surfaces are held planar and uniformly spaced over the length of the casting region C. The molten metal is solidified between the casting belts by withdrawing heat through them by means of liquid coolant 24 (FIGURES 1 and 2) supplied into numerous nozzle and header assemblies 23 and 25 from a reservoir tank 26 extending beneath the machine.
As shown in FIGURE 2, the liquid coolant 24 is drawn from the reservoir 26 through a large conduit 27 feeding to a large capacity centrifugal pump (not shown), for example, such as a double-suction, single stage centrifugal Gould pump having a capacity of 3,000 gallons per minute and driven by a 75 horsepower motor. This liquid is returned through a flexible coupling conduit 29 to a coolant supply main 31 (please see FIGURES l and 4) which extends along the rear of the machine and feeds coolant into the various nozzle and header assemblies 23 and 25 and also to other headers as explained in detail further below. Because of the large quantities of coolant being pumped, it is desirable to avoid any sharp bends in the conduit or supply main. The pump is positioned as close to the side of the tank 26 as convenient and then a large radius sweeping curve feeds up in the flexible coupling 29.
It will be appreciated that with this system the metal strip solidifies without application of any pressure except that which is caused by the vertical head of molten metal which results from the difference in elevation of the surface of the bath B and the point down in the casting region C at which the solidification occurs. A smooth continuous solid strip of metal of high quality is discharged from the right end of the machine.
By virtue of the fact that the metal strip is directly formed without any working" of the metal such as would occur during the formation of strip by rolling down from ingots, a very soft high quality strip is produced. When the metal being cast is aluminum or aluminum alloy or other conventional electrical conductor material, such as copper or electrical brass, the resulting soft strip provides a product of very high conductivity as may be desired for electrical installations, because of the absence of work-hardening of the strip product. Also, the softness of the metal strip product lends itself very well for use in applications requiring substantial amounts of reduction in thickness by multiple rolling operations 1 because this strip is so soft and can be cast so thin that multiple annealing steps are avoided. For example, aluminum foil 0.003 of an inch thick can be rolled down from a cast strip /2 inch thick formed by these methods and apparatus with only one annealing operation being required during the rolling down of the foil. Aluminum or aluminum alloy strip cast by these methods and ap paratus is highly adapted for forming foil suitable for building insulation or the thinner foil used for packaging purposes. When it is desired to obtain strip of increased strength and hardness, the machine is adjusted to cast a thicker strip than the final product requires, and then this oversize strip is readily rolled down to the desired size and hardness.
As will be explained in detail, the upper carriage U can be raised further away from the lower carriage or lowered down closer to the lower carriage so as to cast strips of various thickness. The width of the strip being cast is determined by the spacing between a pair of moving side dams 28 and 30 which run between the respective edges of the casting belts in the casting region (please see also FIGURE 4) and also is determined by the spacing between a pair of stationary side dams 32 and 34 (please see FIGURE 10) in the bath region which are associated with the respective moving side dams 28 and 30. This spacing between these sets of dams is readily adjusted so as to change the width of cast strip, as explained in detail further below.
Laterally Adjustable Moving and Stationary Edge Dams As will be noted particularly clearly in FIGURES l, 3, and 10 the lower belt 22 has a planar area at the input (left) end of the machine which is held taut in true alignment with the portion of the lower belt in the casting region C. The incoming molten metal from the distribution channel 18 feeds into the molten bath B which is supported on this forwardly extending portion of the lower belt.
In order to prevent the pool B from spilling over the edges of the lower belt and to retain the molten metal in the casting region C between the belts, there are provided two sets of interengaging moving and stationary edge dams. The two moving dams 28 and 30 are positioned so that they continuously run along down into the casting region C engaging the front surfaces of both belts in the casting region. The moving dams provide a tight seal against leakage of the molten metal at either edge of the strip being cast so as to define the exact width of strip desired. These two moving dams are identical in construction and each is in the form of an endless loop which is somewhat longer than the lower belt 22. Both moving dams hang down freely beneath the lower carriage L during their return trip back to the input end of the machine.
In this example (please see FIGURE 16), the moving dams 28 and 30 are formed by numerous small blocks 36 of hard, heat-resistant metal, for example, cold-rolled carbon steel, which are strung in end-to-end relationship onto a metal strap 38. The edges of this strap 34: engage in opposite sides of T-shaped slots 39 which advantageously expose most of the width of the strap to view so that it can be readily inspected from time-to-time to check for flexure cracks. In order to provide for ease in assembly, the ends of the strap 38 have holes 40 and are connected together by machine screws 41 engaging in a pair of threaded sockets 42 in the top of the T-shaped slot in one of the blocks.
As seen in FIGURES 1 and 10, the full height of the moving dams is exposed to the molten metal along both edges of the molten bath B. These moving dams confine the metal while at the same time they provide a continuous movement along both sides of the pool B so as to prevent any excessive solidification or freezing up of the metal at the edges. This continuous motion of the two dams 28 and 38 together with the continuous motion of the lower belt and the 6 forward-downward pitch of the machine all co-operate in feeding the metal smoothly into the casting region before any substantial build up of solid metal can occur along the edges or bottom surface of the bath B.
Although it is possible to operate this machine with a shallow pool B, it is preferable not to do so for reasons which will be explained now. A shallow pool is one which has a depth less than the height of the moving dams 28 and 30. Thus, with a shallow pool the molten metal would not engage the upper belt until a point is reached down in the casting region beyond the arcuate portion of the upper belt where it curves down under the upper-belt curving guide means 44, shown here as a grooved nip roll. In effect, this curving guide means 44 defines the entrance to the casting region. When a shallow pool is used the molten metal does not come into engagement with the upper belt 20 until after the entrance to the casting region has been passed. The difficulty with a shallow pool arrangement is that a slim triangular wedge-shaped space exists above the upper surface of the molten metal and the front surface of the upper belt as they converge. This tends to trap air and gases between the upper surface of the molten strip and the upper belt and to draw the trapped gases further down into the casting region, thus causing an undesirable, rough, cracked top surface to form on the strip product resulting from trapped gas and consequent irregular cooling.
It is preferable to use a pool B as shown in FIGURE which has a depth just before the entrance to the casting region which is greater than the height of the moving dams 28 and 30 being used so that the upper surface of the molten metal engages the upper belt as it curves down under the nip roll 44. As indicated by the dash-and-dot line 46 the horizontal upper surface of the pool B extends up above the moving dams onto the inner faces of the stationary dams 32 and 34. By virtue of this added height to the pool B, the molten metal fills the entire entrance to the casting region. Also, this height of the pool B provides a slight head so as to assure that the molten metal firmly presses against the upper belt just before and during its entrance into the casting region C. As a result, the
upper surface of the cast strip is formed smooth and of high quality.
The operator in observing the pool B has a view corresponding to that seen in FKGURE 10. He makes sure that the depth of the pool B is continuously maintained up against the stationary dam at the level 46 and accordingly adjusts the feed stopper 6.
In order to guide the moving dams, each of the stationary clams has its inner face flush with the inner face of the associated moving dam and has a guide shoe 48 bearing against the inner surface of its associatedmoving darn. As shown, the guide shoe 48 is formed by a plate of steel secured by screws 50 flush against the inner surface of the stationary dam 32. The guide 48 extends down close to the lower belt 22 just forward of the bath B, and
' its forward end is flared out at 52 to guide smoothly the blocks of the moving dam.
Each of the stationary dams is wider than the moving dam as seen most clearly from the section taken in FIGURE 10 through the set of moving and stationary dams 30 and 34, with the outer edge of the stationary dam projecting out beyond the outer face of the moving dam. In order to resist the outward pressure exerted by the molten bath on the moving dams and to prevent the moving dams from spreading apart from each other as they progress down into the casting region due to the increasing head of molten metal, a long guide bar 54 is secured beneath the overhanging edge of the stationary dam 34. This guide bar 54 extends down along the outer face of the moving dam 30 a substantial distance below the entrance to the casting region. As shown the guide bar 54 and a corresponding one (not shown) for the moving dam 28 each extend for at least 20% of the length of the casting region.
For purposes of providing additional guidance for the moving dams 28 and 30 before they arrive at the guide shoes 48 and the guide bars 54, a rigid leg 56 (please see FIGURES 3 and 10) is secured by screws 57 to each of the stationary dams and extends down to hold a pair of lead guides 58 and 59. Thus, whatever may be the laterally adjusted positions of the stationary dams 32 and 34, the moving dams are controlled by the stationary dams, being positively guided and held thereby in the desired positions.
As mentioned previously, one of the advantages of the present methods and apparatus is the ease with which adjustment is made to produce strips of different widths. The upper ends of the .stationary dams 32 and 34 are adjustably held by a pair of clamps 60 and 62, respectively; Each clamp includes a pair of grooved slides 64, as indicated in FIGURE 10, which run along lateral ways 66 formed by the opposite edges of the upper flange of an I-beam 65. These ways 66 are machined so as to be square edged and truly parallel. To lock these clamps in position, the operator tightens the clamping screws 67 which are anchored in the edges of a vertical bracket 68 having a pair of slots 69 in its upper end so as to permit vertical adjustment of the free end of the stationary dam which is locked to these slots by clamping bolts 70 (as shown'also in FIGURE 1).
Cooling means are provided for each of the stationary dams 32 and 34. As shown in FIGURE 10, this cooling is provided by an internal passageway 72 for coolant. The coolant is fed'into the passageway 72, through a flexible inlet hose 73 connected to a nipple projecting from the outside edge of the dam ahead of the molten pool B and is fed out through another flexible hose 74 near the place where the stationary dam engages the upper belt 22. This coolant is supplied from the main 31 and the return through the hoses 74 is dumped back into the tank 26.
Coolant Applicators on Upper Belt for Cooling Cusps of Stationary Dams As will be appreciated, the, stationary .dams 32 and 34 ride on top of their associated moving dams 28 and 30 so as to retain the molten pool. In order to. provide a tight seal against the upper belt as it curves down under the nip roll 44, the downstream end of each stationary dam has a cylindrical concave saddle 75 (please see FIG- URE ending at a sharp cusp 76 (please see FIGURE 3) which projects inward under the curve of the upper belt ending at a point where the upper belt converges against the top of the moving dam.
In cases where the saddle 7'5 and cusp 76 may tend to overheat, and also to provide lubrication where the saddle 75 rubs against the curve of the upper belt, a pair of coolant applicators 78 (FIGURE 10) rub against the upper belt ahead of the position where it meets the stationary dam. These applicators are of porous sponge or felt material and are fed coolant at a very slow rate through feed tubes 79 so as to form a series of very small droplets of coolant which ride down onto the saddle 75. The lateral position of these applicators is adjusted to correspond with that of the stationary dams.
Methods and Apparatus for Cooling the Casting Belts by Creating and Maintaining a Substantially Continuous Fast Moving Coolant Film As mentioned in the introductory portion of the specification, the molten metal solidifies between the upper and lower belts and 22. During this solidification tremendous quantities of heat are liberated per unit weight of strip being cast because, in addition to cooling the molten metal down to its freezing point, its heat of fusion must be removed as it solidifies, and then cooled further before discharge from between the belts.
In order to give the reader an impression of relative size it is noted that in this example the total distance in FIGURE 3 from the point beneath the nip roll 44 at which the upper belt 22 first straightens out after passing under this roll over to the point beneath the upper downstream main roll 78 at which the upper belt first begins to curve .up around this roll is 4 feet and 1 inch. The total distance from the point at which the lower belt 20 first straightens out after passing around the lower upstream roll .80 over to the point at which the lower belt begins curving down around the lower downstream roll 82 is a total distance of 6 .feet 5 inches.
In order to provide tremendous cooling capacity to these planar portions of the belts, substantially continuous high speed films of coolant are created and maintained flowing along at high speed against their respective reverse surfaces. Each of these high-speed coolant films is created and maintained by a sequence of nozzle and header assemblies 23 and 25 working in conjunction with scoops for the purpose of increasing the cooling action. There are a sequence of four substantially identical nozzle-and-header assemblies 25 for cooling the upper belt and also a first nozzle-and-header assembly 23 which is similar to those at 25, except that it does not have an associated scoop. There are a sequence of seven assemblies 25 preceded by two assemblies 23 for cooling the lower belt.
In FIGURE 6, which is drawn to a scale of exactly three-quarters of actual size is shown an upper nozzleand-header assembly. For convenience of reference, the one actually shown in FIGURE 6 is the one which appears in FIGURE 4. It is the middle nozzle-and-header assembly .(please see FIGURE 3) for the upper belt, and is indicated by the number'25'. A high-speed film 83 of unconfined liquid coolant is shown in FIGURE 6 travelling along the reverse surface of the upper belt. A similar unconfined film of coolant 84 is travelling along the reverse surfaceof the lower .belt. a
In this example, the coolant 24 in the reservoir tank 26 is water to which a suitable rust inhibitor, such as-sodium chromate has been added in a concentration of 6.7 ounces per 100 gallons of water. The reservoir tank 26 holds 1,200 gallons of water in normal usage, for example, in casting aluminum or aluminum alloys.
These high-speed water films are enabled to be substantially continuous by virtue of the fact that the back-up rollers 86 only touch the reverse surfaces of the belts at quite-widely spaced points where numerous relatively high, thin ridges 87 provide a knife-edge-like contact with the belt. These high, thin ridges on the back-up rollers are illustrated generally in FIGURE 4, and an idea of their precise configuration can be obtained by glancing at FIGURES 8 and 9.. The many advantages of this particular configuration of the knife-edge ridges on the backup rollers will be described in detail further below.
In FIGURE 6 the water film 83 is shown coming into the drawing from the left at quite a high speed as indicated by the long arrow 88. However this film is already beginning to slow down to such a speed as to provide less than adequate cooling. The reason that the film is slowing down is the skin friction exerted by the surface of the belt as well as the minute pinpoint bubbles of steam which are continuously forming adjacent to the surface of the belt and must be instantaneously scrubbed away. As will be seen from FIGURE 3, the water film 83 will have skidded along the surface of the belt 20 a distance of more than six inches after having received its most-recent impetus from the numerous nozzles 90 r of the preceding nozzle-and-header assembly 25 before reaching the sharp leading edge 91 of a scoop 92 which is an integral part of the assembly 25.
The purpose of this scoop 92 is to remove the outermost layers of the fast-moving water film while allowing a film 93 of reduced thickness to continue skidding along the belt. This thinner film 93 has less inertia than the original thicker film 83, and thus it is easier to re-accelerate as it again receives impetus from the next set of nozzles 90 of the assembly 25'. As shown, the leading edge 91 of the scoop extends across substantially the entire width of the belt and this edge 91 is positioned a uniform distance from the reverse surface of the belt so as to leave a reduced film 93 of the desired thickness and speed. For example, in this embodiment of the invention the spacing between the reverse surface of the belt and the scoop edge 91 is a distance of exactly of an inch. In order to provide clearance for the continuing film 93, the leading edge 91 is closer to the belt than is the remainder of the undersurface '94 of the assembly 25.
It is important to note that there is an abrupt steplike break in the continuity of the undersurface of the scoop just behind the edge 91. This abrupt change in spacing at 95 has a function of breaking the suction" between the fast-moving film 93 and the undersurface of the scoop. Its purpose is to enable the continuing high-speed film 93 to break away abruptly and cleanly from the undersurface of the scoop. This abrupt change 95 is positioned as closely behind the edge 91 as possible while still providing the desired structural strength in the edge portion of the scoop. Behind this abrupt change 95 the undersurface 94 recedes farther from the fast-moving film 93 so as to provide extra clearance. In this example, the very first portion 97 of the undersurface of the scoop immediately behind the edge continues back parallel with the belt surface for a distance of of an inch to provide the necessary structural strength, and then at 95 the undersurface abruptly moves away from the belt.
It is not desirable to have this first portion 97 of the undersurface 94 recede away from the belt because the film of coolant would then tend to cling to the receding undersurface of the scoop and would slow down. That is, if the undersurface 97 should recede significantly from the belt, then an expanding wedge-shaped region would be formed between belt and undersurface 97. The liquid passing under the edge 91 and entering this expanding region would be slowed down as it increased in thickness so as to fill up the increasing size of the region. In effect, then, should the undersurface 97 recede significantly from the belt surface the result would be to produce a confined-type of flow, whereas the optimum cooling, as
explained, is provided by an unconfined fast-moving film.- Having the undersurface 97 recede significantly is unde sirable because it would tend to slow the film 93 down toward the minimum velocity required for proper cooling and also is undesirable because it would tend to build up the thickness of the film 93, making it too diflicult to reaccelerate.
By virtue of the abrupt change in spacing at '95, the film 93 is enabled to break away cleanly from the undersurface of the scoop. And this film 93 then continues on at high speed at the desired reduced thickness, which is adapted for ready re-acceleration. The minimum change in spacing required at 95 to assure that the film 93 will break cleanly away from and remain away from the undersurface of the scoop depends to some extent upon the total width of the belt and upon the total extent of the undersurface 94, because the undersurface 94 tends to create a suction effect between itself and the nearby fast-moving film 93, and also depends upon the amount of extra clearance provided at 99 along the rear edge of the header assembly.
In any event, the abrupt change in spacing at 95 should be at least of an inch, and in this particular example we find that a change in spacing of no less than A of an inch is desirable. The total spacing at 99 between the belt and the undersurface 94 is no less than 7 of an inch in this example.
In order to re-create a. moving film of the desired thickness and reaccelerated to the desired high speed, all of the various nozzles 90 are aimed to eject jets of water 96 at grazing incidence so that the ejected water hugs the surface of the belt and skids along it in a way which is most effective for producing tremendous cooling capacity by instantaneously scrubbing away steam bubbles as they are formed and immediately replacing with more water instantaneously ready to be boiled.
It has been found important to assure that the angle of the bores 98 of these nozzles 90 is set properly, for maintaining the continuity of the fast-moving films 83 and 84 and for producing a scrubbing action of the films all along the surfaces of the belts near the bath region and near the casting region.
When the angle a is increased above the oncoming jets 96 penetrate clear through the reduced film 93 and they consequently strike too hard against the surface of the belt so that they bounce or ricochet off from the belt with resultant loss of cooling and failure to produce a continuous scrubbing action over the entire belt surface. As a result, the angle on should be no more than 10. If the liquid jets are aimed too closely parallel to the surface of the belt, then the cooling effectiveness of the jets is diminished due to the fact that they strike the surface of the film at a point too far from the preceding scoop and too close to the succeeding scoop. These jets 96 are spaced laterally one inch apart, and as they strike into the reduced film, as shown in FIGURE 6, they add impetus to the film and spread out laterally, building up the film thickness and producing a scrubbing action across the full width of the belt.
We find that the best results under all conditions of operation are obtained by using an angle a of approximately 6, that is, within one degree either side of 6". In this particular example, the angle a is precisely 6, which is the optimum angle for cooling a cold-rolled lowcarbon steel casting belt 0.025 -of an inch thick when casting aluminum or aluminum alloys using nozzle assemblies as described herein.
As mentioned before, the molecules of water immediately adjacent to the reverse surface of each casting belt .fiash into steam bubbles almost instantaneously upon coming in contact with the belt. We explain the highly effective cooling action of these fast-moving unconfined films 83 and 84 in part by the theory that the many minute 14 steam bubbles which are continuously exploding into existence at the surface of the casting belt tend to create intense localized turbulence by hurling adjacent molecules of water into contact with the belt, and then almost immediately the steam bubbles are swept away and replaced by more water ready to boil.
In order to increase further the cooling capacity, the reverse surfaces of these two belts can be roughened slightly so as to increase the turbulence in the layer of molecules of the cooling film immediately adjacent to the belt. For example, a suitable roughening can be produced by scouring the reverse surface of each belt with a course emory cloth using a circular motion. Alternatively, the reverse surfaces of the belts can be roughened by sand blasting with a finer grit, that is, using a gr-it capable of passing through a fine mesh screen having at least 25 lines per inch. Also, the minute peaks and valleys on the reverse surface of the belt enhance the cooling action by providing many points on the surface at which the steam bubbles can form readily.
As shown in FIGURE 6, the film 83' is moving so fast that the portion of the coolant which is caught on the upper surface of the scoop 92 curves up along the scoop and shoots at high speed up along the upright front wall of the header and nozzle assembly 25 and is trapped in a gutter 102. This gutter has a relatively narrow intake passageway 104 passing upwardly between first and second spaced walls 106 and 108, respectively, and the lower edge of the wall 106 fits down behind a lip 107 which extends along the top of the header wall 100. As the liquid travels upwardly along the inner surface of the wall 106 it is deflected back overhead at 109* by an inclined portion 110 and then curves over further and engages a series of slanted and inclined deflectors 112 (please also see FIGURE 7) secured to the top 114 of the gutter. As shown in FIGURE 7 these deflectors are all slanted at an angle of 30 with respect to the onrushing liquid so as to propel the liquid toward the discharge end of the gutter. Also, these deflectors are inclined at an angle of 45 to the top 114 thus trapping the liquid and preventing it from splashing down away from the deflectors. Thus, the liquid is deflected and travels diagonally down the back wall 116 of the gutter as indicated by the arrows 117 into the trough 118 at the bottom of the gutter.
A pair of angle braces 120 and 122 serve to stiffen the front wall 108 and prevent the liquid in the trough from splashing up and interfering with the incoming liquid 109. These angle braces are secured in place by pairs of rivets 124 which also secure the walls 106 and 108 firmly in position against small channel-shaped or U- shaped spacers 126. These rivets 124 and U-spacers 126 do not interfere with the flow of liquid up the passageway 104 because they are fairly small and relatively widely spaced as indicated in FIGURE 7, and the liquid is able to pass up between the two sides of these spacers.
The front ends of these gutters 102 are covered with rectangular plates 125, as seen in FIGURES l and 2 as well as in FIGURE 6, but'the rear ends, toward which the flow 117 is directed, are wide open. The spent coolant cascades out of the rear ends of these gutters, falling down into the reservoir tank as indicated by the arrow 127 in FIGURE 4.
As seen in FIGURE 3, the lower nozzle and header assemblies 25 also have associated gutters. The coolant travelling down from the respective scoops forms sheets of liquid shooting directly down into four larger gutters 128, 129, 130, and 131, respectively. These gutters are shaped to fit around the various braces within the lower carriage L. The first gutter 128 catches the coolant from the first two units 25, the second gutter 129 serves the third and fourth units 25,,and the third gutter 130 serves the fifth'andsixth units 25, while the last gutter 131 serves the seventh unit 25. These four lower gutters also direct the spent coolant over to the rear of the machine as indicated by the arrow 132 in FIGURE 4.
It is preferable to have the upper belt somewhat wider than the lower belt as shown in FIGURE 4. For example, in a machine for casting strip up to 40 inches in width the upper belt is 46 inches wide and the lower belt is 44 inches wide, thus providing 1 inch of overhang of the upper belt on each side. This is desirable in case any drops of coolant fall off from the upper surface of the upper belt. Because of the overhang any drops of coolant completely miss the lower belt and thus they are prevented from falling onto the upper surface of the lower belt where they might run in and hit the molten metal. The extra width of the upper belt advantageously shields the front (upper) surface of the lower belt from the coolant.
In order to supply a large quantity of coolant across the full width and length of each casting belt, the coolant 24 in the supply main 31 (please see FIGURE 4) is fed out through connections 133 and 134 which are canted along the main 31 in the direction of flow so as to aid the flow. From these connections 133 and 134 the coolant passes through sections of flexible high pressure hose 135 and 136, respectively, which feed into horizontal supply pipes 131 and 138 connected onto the ends of the respective header and nozzle msemblies or 23, as the case may be.
As shown in FIGURE 6, the nozzle and header assemblies, such as the assembly 25 include an integral extruded body 140 which is integrally attached to one of the horizontal supply pipes, such as the pipe 137. The upper portion of this extruded body forms a header 142 preferably having a cross sectional area at least fourtimes the sum total of the areas of the individual nozzle bores 98 so as to supply a large quantity of coolant to all of the nozzles without undue loss of pressure.
In order to bring the back-up rollers close together, the large header 142 is positioned up farther away from the belt than is the plane of the axes of the back-up rolls. A narrow tapering channel 144 extends down from the header 142 between the front wall 100 and a rear wall 146. The coolant progressively accelerates in passing down through this channel 144 and then curves around a streamlined ridge 148 and further accelerates into the bores of the closely-spaced nozzles 90. The inner ends of these nozzles are of reduced diameter and are threaded so as to screw into openings 150 spaced uniformly along the lower edge of the wall 146 beneath the flow-directing ridge 148.
In this example all of the nozzles 90 along each of the assemblies 23 and 25 are spaced one inch apart on centers. For a machine having a capacity for casting strip 40 inches wide there are 39 or 40 nozzles on the respective units 23 and 25. The reason that the number varies from 39 to 40 is that it is desirable to stagger the lateral position of these nozzles from unit to unit so that the nozzles do not all lie along the same longitudinal lines of the belts, thus producing a more uniform fastmoving film of coolant. This staggering is accomplished most conveniently by slightly shifting the lateral positions of the successive units 23 and 25. If necessary, because of the nearness of the edge of the belt, an end nozzle may be omitted from one or two of the shifted units and the opening plugged up.
As mentioned previously, the pressure exerted by the molten metal increases progressively down in the casting region C due to the head of metal. In order to counterbalance this pressure on the upper belt 20, the back-up rollers 86 (please see FIGURE 3) are set closer together near the center and discharge end of the casting region. For example, in this machine the longitudinal spacing between the axis of the nip roll 44 and the axis of the first upper back-up roller 86 is 6% 16 inches, and then the spacing to the axis of the second back-up roller is 6 /8 inches; The spacing between the axes of the second and third back-up rollers 86 is 4 inches, and a similar spacing is used for the succeeding five upper rollers 86.
In order to provide greater cooling capacity near the input end the sets of nozzles 90 are positioned more closely than they are further down along the belts. The first upper nozzle and header unit 23 does not include any scoop because the coolant film at this region has not built up to such thickness as to require thinning down before re-acceleration by the, first set of nozzles 90. From the tips of the first set of nozzles 90 the coolant film only travels 3% inches before reaching the edge 91 of the first scoop and then continues on for a total of only 6 /2 inches to the tips of the second set of nozzles 90. Thereafter, along the upper belt the spacing from nozzle tip to succeeding scoop is 6% inches and from nozzle tip to succeeding nozzle tip is 9inches.
For the lower belt in this example, the longitudinal spacing between the axis of the lower upstream roll and the axis of the first back-up roller 86 is 9% inches. Then the spacing between the axes of the next five back-up rollers is 6 inches, and thereafter the spacing is 4 /2 inches corresponding to that for the upper rollers. Throughout the middle and lower portion of the casting region the axisof each lower back-up roller is longitudinally positioned mid-way between the axes of the upper back-up rollers and vice versa. It has been found that this sym metrically staggered arrangement of the back-up rollers 86 is most effective for producing uniformly high quality cast strip.
In order to provide the greatest cooling capacity beneath the bath region B, there are two coolantfilm accelerating nozzle assemblies 23 with their nozzle tips spaced longitudinally 6 inches, followed by three assemblies 25 whose nozzle tips are also spaced 6 inches along the belt. Further on down under the casting region the nozzle and scoop spacing corresponds to that for the upper belt. For the first three lower scoops, which are located directly under the bath at the position requiring maximum cooling, the distance between them and the tips of the preceding nozzles is only inches, less than for any of the upper scoops. Also, several sets of these lower nozzles have somewhat increased bores so as to apply a larger impulse to the film and increase the scrubbing action directly under the bath, where the most rapid formation of steam bubbles occurs.
In order to provide the desired cooling for a machine capable of casting strip up to 40 inches in width, we find it desirable to use a header passageway 142 which is at least 2 /2 inches in diameter, thus providing a cross sectional area of at least 4.8 square inches. This is at least four times the sum total of the cross sectional areas of the individual nozzle bores 98 along the length of the header. The nozzle bores are larger for the first few nozzle and header assemblies 23 and 25 which cool the portions of the belts adjacent to the bath region B for the purpose of providing additional cooling capacity near this region. For example, the first upper unit 23 has stainless steel nozzles with bores 0.18 of an inch in diameter, thus providing a total bore area of slightly more than 1 square inch when using 40 nozzles spaced 1 inch on centers along the header. The first four header assemblies 23 and 25 for the lower belt also have nozzle bores of 0.18 of an inch in diameter. The remaining assemblies 25 for both belts have a bore of 0.15 of an inch, thus providing a total nozzle bore area per assembly of slightly more than 0.7 square inch.
We find that the water cooling films 83 and 84 on the belts adjacent to the bath region B have at least the following minimum velocity values, respectively, as measured in terms of impact pressure, i.e. velocity head by means of a Pitot tube and a pressure gauge, when casting Minimum Velocity Head in Films 83 and 84 Adjacent to Casting Region in Pounds Per Square Inch Minimum Veloeity Head in Films 83 and 84 Adjacent to Bath Region B in Pounds Per Square Inch Approximate Pouring Temperature, F.
Material Coolant Tubes Fitting Into the Grooves of Belt-Guiding Means and Wrapping Partially Around Rolls As discussed in the preceding section fast-moving coolant films 83 and 84 are utilized to provide a large cooling capacity. In order to apply the film 83 to the portion of the upper belt 20 which passes underneath the curved guide means 44, a plurality of closely spaced grooves 152 (please see FIGURES 3, 10, and 17) are provided. A large header 154 extends across the width of the upper belt closely adjacent to the curved guide means 44 and close to the steeply inclined portion of the upper belt above the bath region. For example, this header 154- has an internal diameter of 3 inches and is connected at one end to the supply main 31 by a large hose 156 as seen in FIGURE 1. The front end of the header 154 is held in position in a hole 157 in the frame of the upper assembly U. A plurality of nozzle tubes 158 having an internal diameter of 0.18 of an inch curve down from this header with their ends fitting into the grooves. The intake ends of these nozzle tubes are chamfered as shown at 159 in FIGURE 17 and their free ends are stabilized in position by a brace 160 extending between them just above the point where the ends of the nozzles enter the grooves. As shown these nozzle tubes are no more than 3 inches in length and they are spaced of an inch on centers along the header 154, with a total of 109 of them being used to cool fully the 40 inches of casting width. Thus, a fast, effective film of coolant shoots down along the inner surface of the belt underneath the nip roll 44 and is accelerated and thickened by the first nozzle assembly 23. Then a portion of this film is scooped off by the first scoop of the second nozzle assembly 25 so as to reduce the film thickness before it is re-accelerated.
It is important to note that the edges of the ridges of the nip roll 44 engaging the belt are of an inch wide (0.0625) and these ridges are spaced of an inch apart. This ridge width and spacing is desirable in order to give adequate support to the upper belt as it curves around this roll 44, because of the thinness of the belt and the high tension of 10,000 to 12,000 pounds under which it is operated. If the ridges on the nip roll are made much thinner than this or are spaced much. farther apart, then the belt will tend to scallop as it pulls against the ridges under the high tension being used. As mentioned above, we have found that it is usually desirable to use ridges which are no more than three times the thickness of the belt, for reasons discussed in detail below so as to assure adequate cooling. It will be appreciated that this figure of 0.0625 of an inch meets this criterion when using a belt of 0.025 thickness.
In order to apply a film 84 to the lower belt 22 commencing at a point closely adjacent to the roll 80, a large capacity header 162 is provided having a cross sectional area of at least square inches connected to a plurality of wrap-around tubes 164 nesting snugly in grooves 165 of the roll 80, as seen in FIGURE 20*. These wraparound tubes have an internal diameter of at least 0.375 of an inch so as to avoid excessive pressure drop along their length and have nozzles with bores of 0.25 of an inch formed by short lengths of tube 166 secured into the ends as shown in FIGURE 19. The purpose of. these restricting nozzles 166 is to give .the liquid jets 167 (FIGURE 10) a high discharge velocity. Advantageously, these jets 167 create a high-velocity of coolant on the inner surface of the belt 22 while the belt is still curving around the roll and just before it tangentially leaves the roll. It will be appreciated that these wrap-around tubes do extend around a substantial portion of the perimeter of the roll 80, and in this example they pass more than one-half of the way around it.
The ridges 168 (FIGURE 20) between the grooves are spaced A2 inch on centers and are of an inch wide at their edges, being formed without sharp corners which might tend to cut the belt. A total of 85 of these wrap-around tubes 164 spaced /2 inch on centers are used so as to assure adequate cooling of the belt in the area adjacent to the incoming molten metal in a machine having a casting capacity up to 40 inches in width.
As shown in FIGURE 3, this cooling film under the bath region is accelerated by the first nozzle assembly 23 and is re-accelerated by the second nozzle assembly 23 and then the thickness of this film is reduced by the scoop of the third nozzle assembly 25 before it is again re-accelerated.
Grooved Downstream Rolls to Accommodate Fast-Mov- Around the Downstream Rolls As shown in FIGURES 3, 11 and 12, the upper and lower downstream rolls 78 and 82 have peripheral ridges 170 which provide grooves to accommodate the fastmoving coolant film by allowing it to continue on around them. Also, the presence of this fast-moving film on the inner surfaces of the belts prevents the development of any hot spot on the belts as they begin to curve around these rolls. As shown in FIGURE 11, which is drawn exactly to scale twice full size, these ridges 170 are spaced /2 inch on centers and have edges engaging the belt which are of an inch in width. There are a total of 85 grooves 171 provided on the rolls 78 and 82 for a machine having a casting-width capacity of 40 inches. These grooves are /8 of an inch deep. In forming these ridges, their corners 172 are rounded slightly with a fine file to avoid undue sharpness.
Because of the larger diameter of the rolls 78, 80 and 82 compared with the nip roll 44, we have found that a ridge spacing of /2 an inch is highly satisfactory.
Coolant Catcher for Upper Downstream Roll As shown in FIGURE 12, the coolant which shoots up around the upper downstream roll 78 is caught by means of a catcher generally indicated at 174 having a scoop edge 176 lightly scraping against the underside of the belt 20. Thus, the coolant travels into the catcher 174 along the underside of its top panel 178 and is prevented from rebounding out of the catcher by a pair of inclined bai'fies 179 and 180 which trap the liquid as indicated by the various flow arrows. As the liquid rebounds from the back wall 181 it strikes the underside of these batlies 179 and 180 and is deflected down into the gutters 182 and 184, which open out toward the rear of the machine as generally indicated in FIG- URE 4 by the flow arrow 127. In case any drops of coolant cling to the belt after passing the scoop 176 they are caught on the top panel 1'78 which has an upturned trough 182 along its back edge.
Citas de patentes