US3405757A - Method and apparatus for continuous casting of metal between oppositely rotatable cooling rolls set generally one above the other - Google Patents

Description

Oct. 15, 1968 LQM. HARVEY ET AL 3,405,757

METHOD AND APPARATUS FOR CONTINUOUS CASTING OF METAL BETWEEN OPPOSITELY ROTATABLE COOLING ROLLS SET GENERALLY ONE ABOVE. THE OTHER Filed April 12, 1967 5 Sheets-Sheet 1 M l I g :6 -Qvmpaum and) FIG 1.

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L 50 M. HARVEY HERB RT HARVEY 6 01!!! M l/ARl/EY L IIVOEN C. HILL A TdRNEY Oct. 15,1968 LMH VEY ETAL 3,405,757

APPARAT METHOD AND US F0 ONTINUOUS CASTING OF METAL BETWEEN OPPO E ROTATABLE COOLING ROLLS SET GEN I ONE ABOVE THE OTHER Filed April 12, 1967 5 Sheets-Sheet 2 l/vrswraas. )7. Mam 5y as lwzy [R IV. Mwvsv 4/4/05 C, l/IM BWJW 3,405,757 STING OF METAL 5 Sheets-Sheet 3 A Ame-areas. Asa M Mel/Er A f/orng Oct. 15, 1968 M. HARVEY ET AL METHOD AND APPARATUS FOR CONTINUOUS CA BETWEEN OPPOSITELY ROTATABLE COOLING ROLLS SET GENERALLY ONE ABOVE THE OTHER Filed April 12, 1967 Oct. 15, 1968 L, HARVEY ET AL 3,405,757

METHOD AND APPARATUS FOR CONTINUOUS CASTING OF METAL BETWEEN OPPOSITELY ROTATABLE COOLING ROLLS SET GENERALLY ONE ABOVE THE OTHER Filed April 12, 1967 5 Sheets-Sheet 4 FIG. 2. .i/

WK/IL? '4 f arbey Oct. 15, 1968 L. M. HARVEY ET AL 3,405,757

METHOD AND APPARATUS FOR CONTINUOUS CASTING OF METAL BETWEEN OPPOSITELY ROTATABLE COOLING ROLLS SET GENERALLY ONE ABOVE THE OTHER 5 Sheets-Sheet Filed April 12, 1967 s y mr n W3 fl l W M a r A 5 5 2% 4 Y B M X f United States Patent 3,405,757 METHOD AND APPARATUS FOR CONTINUOUS CASTING OF METAL BETWEEN OPPOSITELY ROTATABLE COOLING ROLLS SET GENERALLY ONE ABOVE THE OTHER Leo M. Harvey, Los Angeles, Herbert Harvey, Palos Verdes Estates, Homer M. Harvey, Los Angeles, and

Linden C. Hill, Rolling Hills, Califl, assignors to Harvey Aluminum (Incorporated) Continuation-in-part of application Ser. No. 416,093 Dec. 4, 1964. This application Apr. 12, 1967, Ser. No. 633,668

16 Claims. (Cl. 164-87) ABSTRACT OF THE DISCLOSURE In the present invention metal sheet and plate substantially free of entrapped gases is cast between a pair of opposed cooling rolls disposed with the line between their centers inclined no more than about 23 from the vertical, the rolls preferably being one above the other. The molten metal to be cast is charged into a plenum chamber between the rolls through a nozzle spaced therefrom and complete solidification of molten metal is effected at a point within the chamber wherein the spacing between the rolls is from about 12 to 50 percent greater than the spacing at the roll nip.

This is a continuation-in-part application of co-pending United States patent application Ser. No. 416,093, filed Dec. 4, 1964, now abandoned.

In the conventional roll casting of metal sheet and plate, molten metal is introduced through a nozzle positioned below and contiguous to a pair of opposed rotating rolls disposed with the line between their centers lying along the horizontal, the resultant casting being discharged vertically upwardly (see United States Patent 2,790,216). In the start-up of this vertical casting apparatus, the nozzle and rolls are heated from ambient to the operating temperature by the initial charge of molten metal. Upon contact with the cold rolls, this initial charge prematurely solidifies forming a plug which throttles the metal flow and often jams the rolls.

To avoid premature solidification of the molten metal, it has been proposed to initially operate the rolls at speeds considerably above the optimum. The initial transfer of heat from the molten metal to the rolls cannot, however, be satisfactorily controlled by regulating their rotational speed; consequently, segments of the cast sheet are often discharged while still in a semi-fluid condition. In cases where the rolls are operated above the optimum speed, voids or so called hotspots appear in areas of the sheet which are not picked up by the rolls. At the other extreme, operation at roll speeds below the optimum may produce cold laps, the result being that power requirements increase sharply. As a result of these difiiculties in achieving optimum roll speeds, the product cast during the first ten to twenty minutes of operation is of little or no commercial value and considerable operating time is wasted. The use of such vertical casting apparatus, therefore, requires relatively long casting runs to be commercially feasible because any interruption in the process, for example, to adjust the spacing between the rolls, results in large down times and a waste of relatively large amounts of metal.

Moreover, in vertical casting where the molten metal flows from the nozzle upwardly through the roll nip, entrapped gases tend also to flow upwardly within the stream of metal and remain entrapped, leaving in the cast product undesired voids. It is, therefore, necessary in casting vertically to rigorously degas the molten metal before its introduction into the casting chamber.

3,405,757 Patented Oct. 15, 1968 To obviate the foregoing difficulties, it has been proposed to continuously cast between a pair of opposed rolls whose axis of rotation is situated in a plane inclined with reference to the horizontal (see Canadian Patent 619,- 491). The nozzle supplying molten metal to this apparatus is, however, maintained by means of an elastic seal in tight contact with the rolls to close off the plenum chamber therebetween. Since entrapped gases evolving from molten metal in the plenum chamber cannot escape therefrom, the metal used in this horizontal casting device must also be degassed.

Further, in this horizontal casting process, heat losses from the nozzle at the point of intimate contact with the roll surface cause the metal in the nozzle to freeze and block further flow of metal therethrough. This condition is found to exist even where the nOZZle is constructed of ceramic-like insulating materials such as that known by the trademark of Marinite. Additionally, the surface of the roll in contact with the nozzle is often injured thereby, the protective oxide coating on the roll surface being scratched, chipped, or otherwise deleteriously affected. As a result, the metal being cast often adheres and/or becomes welded to uncoated areas of the roll surface.

In the above described casting devices, pulsations of the liquid metal within the plenum chamber produce pronounced cross-banding on the surface of cast sheet. Where such cast sheet is to be anodized, it is therefore necessary to reroll the surface thereof to reduce the depth of these cross-bands.

It is therefore a principal object of the present invention to provide in a continuous casting process an improved method and apparatus for eliminating in the cast product undesired voids and other defects caused by entrapped gases within the molten metal.

Another object is to provide in the casting of sheet metal an improved apparatus which minimizes cross-banding on the cast sheet surface.

Still another object is to provide an improved continuous casting apparatus which can be started with ease to initially produce a high quality cast product.

Yet another object is to provide in a continuous casting operation an improved method of reaching more quickly the optimum operating temperature, thereby to achieve more rapidly steady state casting conditions.

A further object is to provide an improved method and apparatus of continuous casting wherein adhesion of molten metal to the rolls is minimized.

These and other objects and advantages will become apparent upon reference to the following description, drawings, and claims appended hereto.

To achieve the foregoing objects, it has been surprisingly discovered that metal sheet and plate, substantially free of voids and entrapped gases, can be successfully cast between a pair of spaced rolls set generally one above the other with the line between their centers inclined from the vertical no more than about 23, preferably between about 0 and 15 more preferably between about 0 and 5 provided there is a substantial clearance between the rolls and the nozzle through which molten metal is introduced. By continuously casting in this manner, it was unexpectedly found that dissolved and entrapped gases rise upwardly through the liquid metal in the plenum chamber and escane through the clearance between the nozzle and the rolls.

In practice, the outer surface of the upper nozzle block is spaced from the upper roll a distance of at least 0.007 inch, the spacing desirably being between about 0.007 and 0.04, preferably between about 0.007 and 0.002, more preferably between about 0.01 and 0.015 inch. The spacing between the nozzle and the rolls not only facilitates removal of entrapped gases escaping from the "ice molten metal, but also prevents scratching, chipping or other injury to the oxide coating formed on the roll surface. By maintaining this oxide coating intact without bringing the nozzle into contact therewith as in the prior art, it has been found that adhesion and/or welding of molten metal to the rolls is inhibited.

The molten metal or other fusable material to be cast is supplied to the plenum chamber through a hollow ejector or nozzle having beveled or slanted outer walls which conform in contour to the roll surfaces. The outer wall of the nozzle should conform closely to the arcuate surface of the rolls to prevent back flow of metal between the nozzle tip and the rolls, the spacing therebetween being preferably at least about 0.007 inch. This clearance not only minimizes heat transfer between the nozzle blocks and the rolls, but also permits the escape from the plenum chamber of gases which would otherwise remain entrapped in the metal.

A suitable nozzle for use herein comprises a pair of complementary nozzle blocks which define a conduit. The type of material to be used in constructing the nozzle blocks depends in large part upon the type of metal to be cast, a satisfactory nozzle for casting aluminum being constructed of a ceramic-like material comprising diatomaceous silica, asbestos fiber, and a binder as described in United States Patent 2,326,516. Also suitable are other ceramic or ceramic-like materials which are inert to the metal being cast and are not wetted thereby.

Among the various metals which can be continuously cast by the present process are, for example, aluminum, copper, lead, zinc, magnesium, tin, silver, brass, bronze, zirconium, and the alloys thereof, and other similar malleable and ductile metals and alloys. Also suitable are admixtures of metals which do not alloy, as well as mixtures of metals which form intermetallic compounds. Utilizing the present process, higher melting point metals and alloys, such as steel, can also be successfully cast by merely increasing the rate of cooling and employing high temperature resistance ceramic nozzles.

As an additional safeguard in minimizing the starting period, the nozzle blocks are preheated to remove any absorbed moisture. In practice, it is preferred to preheat the nozzle to a temperature slightly above the optimum operating temperature. For example, in casting aluminum and the alloys thereof, the nozzle is preferably heated to from about 1,l00 to l,325, preferably from about 1,200 to 1,300 F. Although any fluid medium which remains inert and stable at these temperatures can be used, it is preferred to employ a dry gaseous medium, such as air, nitrogen, carbon dioxide, argon, or mixtures thereof. When hot air is used, it is preferred to blow it onto and/ or through the nozzle for about twenty to sixty minutes before operation commences.

Either before or optionally after the nozzle is preheated to a suitable temperature, the rolls are turned at between about 12 and 26, more preferably between about 16 and 22, and particularly at 18 inches per minute of exposed roll surface, coolant being circulated through the rolls to lower the skin temperature thereof below about 80, preferably between about 0 and 70", more preferably between about 50 and 60 F.

To eliminate the start-up problems of the prior art devices, a barrier means is disposed at the roll exit to close off the plenum chamber and prevent the flow of unsolidified metal therefrom. A suitable barrier means can comprise, for example, a plug formed from a flat metal plate, the plug being inserted between the rolls a distance of from about /2 to 1, preferably about of an inch beyond the roll nip. The leading edge of the otherwise semi-fluid cast sheet is solidified upon contact with the plug and operation at a reduced speed can begin thereafter.

In another embodiment of the invention, a stream of refrigerated gas is used during start-up as a barrier means to chill and solidify the leading edge of the cast sheet.

4 a A high pressure curtain of the refrigerated gas at a temperature preferably below 0 F. is directed over the full length of the roll nip, the leading edge of the initial surge of molten metal being solidified as when a solid plug is employed.

In still another embodiment, the leading edge of the cast plate during start-up is completely solidified by circulating a supercooled liquid through the bottom roll. Upon contact with the cold lower roll, the initial charge of molten metal is solidified and stratifies, building up in thickness until a solid metal plug reaches the top roll. This and other described barrier means all serve to form a plug at the exit between the rolls and to confine molten metal within the plenum chamber during start-up, thus preventing discharge thereof before cast sheet is completely solidified.

In other continuous casting devices employed heretofore, rolling of completely solidified metal often results in adhesion and/or Welding of cast sheet to the roll surface. Additionally, the dendrites formed during solidification are often fractured by rolling, the resultant cast sheet being non-homogeneous and resembling a laminate. These and other deleterious effects of rolling are obviated in the present process by reducing the thickness of completely solidified metal to from about 15 to 50, preferably from about 25 to 45, more preferably from about 33 to 40, and particularly 36 percent.

According to the present invention, coolin of the rolls and metal in contact therewith is controlled to effect complete solidification at a point within the chamber wherein the spacing between the rolls is from about 12 to 50, preferably from about 14 to 40, more preferably from about 18 to 20 percent greater than the spacing at the roll nip.

The nozzle .is preferably spaced from the roll nip a distance sufficient to facilitate solidification as well as the desired amount of rolling. For example, with conventional two foot diameter steel rolls spaced 0.5 inch apart at the nip, the tip of the lower nozzle block is positioned from about 0.75 to 1.5, preferably about 1.37 inches from the roll nip, the optimum spacing being routinely determined by measuring the rate of heat transfer to the roll at any given roll speed.

In another embodiment, deleterious cross-banding on the surface of sheet cast in the prior art devices is minimized by the use of an improved nozzle of the present invention. conventionally, the tip of the upper and lower nozzle blocks lie in a plane parallel to the plane between the roll centers, this symmetry in the system being thought necessary to effect uniform fiow in and to the plenum chamber. It was, therefore, unexpected to find that by shortening the tip of the upper nozzle block from about & to /4, preferably about inch, cross-banding on both the upper and lower surfaces of cast sheet is inhibited.

Without being bound by an explanation of the mechanism by which the nozzle of the present invention improves surface characteristics of cast sheet, it is believed that the frequency and amplitude of liquid metal pulsations in the plenum chamber are dampened with the result that the sheet cast is relatively free of cross-bands.

This invention is illustrated further in several typically preferred embodiments in the accompanying drawings in which:

FIG. 1 is a perspective view of a preferred horizontal casting device of the present invention, illustrating schematically an entire casting installation with auxiliary apparatus used in supplying molten metal thereto;

FIG. 2 is a sectional view taken through lines 22 of an apparatus similar to that of FIG. 1, showing the observation reservoir, position of the nozzle and a preferred roll construction being inclined with reference to the horizontal;

FIG. 3 is a detailed fragmentary view of the casting chamber of FIGS. 1 and 2, illustrating particularly the solidification of metal between the rolls and the spacing of the nozzle therefrom;

, FIG. 4 is a plan view in partial section along lines 4 -4 of FIG. 2, showing the relative position of the nozzle blocks with respect to the rolls;

FIG. 5 is an enlarged fragmentary cross section of one end of the plenum chamber, showing the lateral expansion of the cast sheet therein;

FIGS. 6 and 7 are enlarged sectional views, taken through lines 6-6 and 7--7, respectively, of FIG. 1, of preferred apparatus used 'in supplying molten metal to the nozzle;

FIGS. 8, 9, and are enlarged sectional views of the plenum chamber defined by the rolls and nozzle, and illustrating the pulsations in the liquid metal stream during operation.

The continuous casting installation shown in FIG. 1 includes a melt supply means indicated generally as F, a pair of opposed roll means R, nozzle means N, melt control means C, guide means G, product reel P, speed control means S governing the take-up of cast sheet CS on reel P, and preheating means D.

The melt supply means F comprises a gas fired melt furnace 5 and a holding reservoir 10 with a trough or conduit 6 extending therebetween. The pig, scrap, and/ or alloying materials are heated in the refractory lined vessel 9 of furnace 5 to the desired temperature, preferably somewhat above their melting point. The resultant molten metal passes through tap 5 and valve 7 located in the wall of furnace 5 (FIG. 6), and then through refractory lined trough 6 into reservoir 10 where it is maintained above its melting point. As shown in FIG. 6, a removable wedged shaped partition 6" acts as a valve and separates section 6 from moveable section 6' which is hingedly connected to and extends through opening 7 in reservoir 10. After molten metal from furnace 5 flows through trough 6 into reservoir 10, partition 6" is removed, section 6' is swung out of opening 7 and a movably insulated panel 8 is swung into position to close hole 7'.

The metal in reservoir 10 is supplied as needed through tap 11 into float box 47 and then to laterally extending refractory lined trough or run 12 (FIG. 7). After the liquid metal is cooled to a temperature slightly above its melting point, it is passed to wall 17, through opening 18 therein, and into channel 13 defined by flat parallel walls 14 and 15 of nozzle blocks and 36, respectively, the walls 16 of refractory end members 37, all of which are held in position by members 39 (FIGS. 2, 4, and 5). The upper nozzle block 35 is preferably positioned slightly below the level of molten metal in trough 12 and channel 13 preferably extends across the transverse length of rolls R. The outer concave surface of complementary nozzle blocks 35 and 36, preferably conform in contour to roll faces 20, orifice extending up to plane a spaced rearward of plane b which extends between the roll axe-s (FIG. 3).

Preferably, the rolls are disposed on adjustable parallel axes which extend transversely of the plane of sheet being cast. Although any conventional cylindrical roll can be used, it is preferred to employ 24 inch diameter rolls of steel or beryllium copper having a polished exterior face 20 with a micro finish of (32) or smoother. In operation, the confronting faces 20 move forwardly in the same direction at a predetermined speed as selectively con- 6 trolled by a variable speed drive 21. Within each of the rolls are passages through which cooling water or any other non-corrosive liquid is circulated to carryaway absorbed heat, the coolant then being recirculated through cooler 23 and back through pump 22 into the rolls.

During periods of interrupted operation, nozzles of ceramic-like material, such as Marinite, tend to absorb moisture which can cause bubbles within the molten stream of metal. Before operation commences, a preheating means D is preferably employed to remove absorbed moisture from the nozzle. Suitable means for preheating the nozzle comprise a compressed air supply means indicated generally at 25 and a compressor 26 which can deliver compressed air at a pressure of, for example, p.s.i.g. After removal of moisture from the compressed air in separator 27, resultant dry compressed gas is passed to storage reservoir 28. Shortly before start-up, valve 29 is opened and compressed air is passed through conduit 31 and coils 32 within flue 33 where it is heated to elevated temperatures, such as, 1700 F. by gas fueled heater 30. The high temperature compressed gas is then passed from coil 32 through line 34, cover 24 of trough 12 into and through nozzle N (FIG. 1).

The size of plenum chamber 0 (FIGS. 4 and 5) is determined by the spacing between the rolls and also by the distance between the forward edge of the nozzle blocks and the roll nip lying along plane 12. As molten metal issues through opening 18 into channel 13, it is immediately spread outwardly over the width of channel 13 by means of veins or projections 38 extending inwardly from walls 14 and 15 (FIG. 4).

To eliminate contact in the plenum chamber between semi-solid and/or solid metal being rolled and the end members 37, wall 16 at plane a forms shoulder 41 with a beveled or concave wall 42 extending to end face 43 of the nozzle blocks. The outwardly stepped shoulders 41 of end member 37 extend between planes a and b to completely close off the ends of the plenum chamber c, the constant rolling and expanding edge of solidified metal therein being out of contact with face 42 of shoulder 41 (FIGS. 4 and 5).

In the casting of A inch thick sheet aluminum, for example, wall 42 is inclined from about 25 to 50 with respect to wall 16, the juncture between walls 42, 43 recessed from wall 16 a depth of from about /s to inch. As shown in FIG. 5, the transition of molten metal a to the solid state e, as indicated by the strippled area, together with rolling causes lateral expansion of the cast sheet in the plenum chamber.

The amount of rolling (percent reduction in thickness of cast sheet) is primarily controlled by the cooling capacity of the rolls and the spacing between the nozzle orifice 40 and the roll nip, i.e., the perpendicular distance between planes a and b. With a pair of rolls having a given diameter and a cooling capacity, the amount of rolling can be controlled by adjusting the spacing of nozzle N from the nip and the roll speed.

Where metals having a sharp melting point are being cast, the exact point at which solidification occurs in chamber c can be easily controlled. However, in the casting of alloys having wide melting points, more accurate control of the cooling rate and roll speed is necessary. Satisfactory operation can be achieved, for example, using the operating conditions as shown in Table I below.

TABLE I.-CASTING OF INCH THICK SHEET BETWEEN A PAIR OF TWO FOOT DIAMETER WATER COOLED ROLLS Spacing between Melting point Temperature Cooling rate of Rollin Metal cast" nozzle orifice range of metal, of metal in rolls, B.t.u. per Roll surface reduaigfi iii and roll mp, F. nozzle, F. min. per inches speed, inch/min. thickness of inches of width solidified metal) 1100 Al alloy 1. 25 1, 190-1, 215 1, 260-1, 290 290-319 38-44 40-44 2014 A1 alloy 1. 00 950-1, 180 1, 270-1, 290 246-268 28-32 30-34 5005 A] alloy 1. 1, -1, 205 1, 270-1, 300 263-287 30-35 34-40 5052 A1 alloy 1. 06 1, 100-1, 200 1, 260-1, 280 253-268 30-32 32-36 003 A1al1 y 1. 25 rum-1,210 1, are-1,300 258-308 32-40 40-44 Editi fhlloying compositions described in Standard for Aluminum Mill Products, published by The Aluminum Association, 9th

Preferably, the pressure of liquid metal entering chamber c is just sufiicient to raise the level of the metal to a point X on face 20 of the roll, i.e., the meniscus between the upper roll and nozzle nip (FIG. 8). As surface 20 f the rolls moves forwardly, the layer of solidified metal in contact with face 20 and forward of the meniscus is pulled toward the nip causing the point of tangency X to also move forwardly (FIGS. 9 and 10). At the same time, the point of tangency X between the meniscus and the lower roll face correspondingly moves forward. When the tension on the meniscus produced by the forward movement of face exceeds the surface tension of the metal, the meniscus ruptures and metal flows back to point X.

As described above, these pulsations in the liquid metal which cause cross-banding can be minimized by employing an upper nozzle block whose tip is recessed from about to inch rearward of the tip of the lower nozzle block. Preferably, the tip of lower nozzle block 36 lying along plane a is forward of upper nozzle block a distance of about A inch.

In operation, tap 11 is opened and melt control means C maintains a constant level of molten metal in float box 47 slightly above the elevation of orifice 40, preferably at an elevation of about /2 to 1 /2 inches above orifice 40 (FIG. 2). Melt control means C comprises valve element insertable into tap 11 and float 46 to position the valve element 45. As the level of metal drops in fioat box 47, a two-way limit switch 48 actuates a pressure operated motor 49 which moves valve element 45 into a predetermined position. As shown in FIG. 7, valve element 45 is only partially opened restricting the normal fiow of metal through tap 11. The limit switch 48 also 'actuates solenoid valves 48' and 48" to regulate the position of valve element 45 and control the level of liquid metal in the reservoir. Adjustable stops 49' and 49" are preferably incorporated in the cylinder of motor 49 to preset the position of valve element 45.

To better control the temperature of molten metal initially charged, a first portion of the metal can be diverted to stand-by reservoir 50 until the bulk temperature thereof is slightly 'above the melting point. Preferably, there is inserted in line 12 an observation reservoir 51 which incorporates valve plate 52 or 52 for diverting flow into standby reservoir 50. Valve plate 52 can be opened to permit flow through run 12 and channel 13 into plenum chamber 0.

To prevent discharge from the rolls of unsolidified metal, plug 55 is inserted between the roll nip, see FIG. 2. Plug 55 preferably comprises a inch thick plate having a flat face 56 adapted to engage the forwardly disposed end faces 43 of end members and the leading edge of the sheet. The plug 55 is preferably held in place until the plenum chamber is completely filled whereupon operation of the rolls is begun and the cast sheet CS moves forward with the plug. Often, the leading edge of the sheet becomes welded to the plug in which case it is necessary to jolt the plug to disengage it from the sheet. During startup, the rolls R are preferably turned at a relatively low speed until the cooling rate of the rolls can be adjusted to solidify a greater amount of metal in the plenum chamber.

To enhance the traction between the roll face 20 and the surface of cast sheet, a magnesium oxide film may optionally be sprayed onto the roll surface during operation as shown in FIG. 1. In the casting of aluminum, however, an aluminum oxide coating is formed on the roll surface which satisfactorily provides the needed traction.

The cast sheet issuing from the rolls is passed over horizontally disposed guide means G, speed control means S and onto product reel P as shown in FIG. 1. The guide means G comprises one or more supporting members 60 and retaining members 61 which preferably comprise a pair of rolls. In the event sheet is cast at an angle inclined with reference to the vertical, it is preferable to space guide means G a distance from the rolls sufficient to prevent excessive bending of the freshly cast sheet.

A speed control means S preferably comprises a Vertically shiftable support member 65, means 66 which urges the support member 65 into supporting engagement with cast sheet, and speed governing means 67 sensitive to the vertical shifting of member 65 and also controlling the speed of product reel P. Support member 65 which preferably comprises a roll extending transversely beneath the cast sheet is shiftably carried by a vertically moveable carriage 70, means 66 being shown as an air cylinder and piston unit that urges the roll member 65 into supporting engagement with cast sheet. As shown, speed governing means 67 comprises cam 71 and a cam follower 72 which is positioned vertically by movement of roll member 65. Product reel P is provided with suitable linkage 68 to variable drive member 69 to control take-up speed thereof and minimize buckling of cast sheet.

Speed control means S synchronizes the rotational speed of product reel P to the rate at which cast sheet issues from rolls R thereby to minimize tension or slack in the cast sheet traveling over guide means G. As an accessory to the method and apparatus herein, a knife 75 is provided at or adjacent the product reel P to sever cast sheet as circumstances demand.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What we claim is:

1. In a process of continuously casting and rolling sheet metal in a plenum chamber formed between a nozzle and a pair of oppositely rotating spaced rolls, the steps comprising:

(a) introducing molten metal into the chamber through a nozzle spaced from rolls set generally one above the other with a line between their centers inclined from the vertical no more than about 23 and (b) cooling the molten metal at a rate sufficient to affect its complete solidification at a point within the chamber wherein the spacing between the rolls is from about 12 to 50 percent greater than the spacing at the roll nip.

2. Process as defined by claim 1, wherein the rolls are disposed with the line between their centers inclined from the vertical between about 0 and 15, and the nozzle is spaced a distance of at least 0.007 inch from the rolls.

3. Process as defined by claim 1, wherein the rolls are disposed with the line between their centers inclined from the vertical between about 0 and 5, the nozzle being spaced from the rolls a distance of between about 0.01

' and 0.015 inch.

4. Process as defined by claim 1, wherein the rolls are set with one squarely above the other to affect horizontal casting, the nozzle being spaced from the rolls a distance of between about 0.007 and 0.04 inch.

5. Process as defined by claim 2, wherein the cooling in step (b) is controlled to affect complete solidification at a point within the chamber wherein the spacing between the rolls is from about 14 to 40 percent greater than the spacing at the roll nip.

6. Process as defined by claim 1, wherein the cooling in step (b) is controlled to affect complete solidification at a point within the chamber wherein the spacing between the rolls is from about 18 to 20 percent greater than the spacing at the roll nip.

7. Process as defined by claim 1, wherein during startup of the process a barrier means is inserted between the rolls to close off the plenum chamber and completely solidify the leading edge of resultant cast sheet.

8. Process as defined by claim 1, wherein the metal cast is selected from the group consisting of aluminum,

lead, zinc, magnesium, tin, copper, silver, brass, bronze, zinconium, and the alloys thereof.

9. Process as defined by claim 1, wherein the metal cast is aluminum or the alloys thereof.

10. Process as defined by claim 1, wherein molten metal in step (a) is introduced into the chamber through a nozzle whose upper tip is recessed rearward of its lower tip to inhibit cross-banding on the surface of cast sheet.

11. Apparatus for use in the continuous casting of sheet metal, said apparatus comprising in combination: a pair of oppositely rotatable spaced roll means set generally one above the other, nozzle means through which molten metal is supplied to a plenum chamber between the roll means, and refrigeration means in the roll means for removing sufiicient heat from molten metal in the plenum chamber to effect complete solidification thereof at a point within the chamber wherein the spacing between the rolls is from about 12 to 50 percent greater than the spacing at the roll nip, said nozzle means being spaced with sufiicient clearance from the roll means to permit escape from the plenum chamber of entrapped gases evolved from the molten metal.

12. Apparatus as defined by claim 11, wherein a line between the centers of the roll means is inclined from the vertical no more than about 23, and the nozzle is spaced from the roll means a distance of at least about 0.007 inch.

13. Apparatus as defined by claim 11, wherein a line between the centers of the roll means is inclined from the vertical between about and 15, and the nozzle is spaced from the roll means a distance of between about 0.007 and 0.002 inch.

14. Apparatus as defined by claim 11, wherein a line between the centers of the roll means is inclined from the vertical between about 0 and 5, and the nozzle is spaced from the roll means a distance of between about 0.01 and 0.015 inch.

15. Apparatus as defined by claim 11, wherein one of the pair of roll means is situated squarely above the other to affect horizontal casting, and the nozzle means is spaced a distance from the roll means of between about 0.007 and 0.04 inch.

16. Apparatus as defined by claim 11, wherein an upper tip of said nozzle means is recessed rearwardly of its lower tip, thereby to inhibit pulsations of liquid metal in the plenum chamber.

References Cited UNITED STATES PATENTS 379,096 3/1888 Brooke 164-277 1,903,897 4/1933 Harris l64-277 2,693,012 11/1954 Harris et al 16487 2,790,216 4/1957 Hunter 164277 XR FOREIGN PATENTS 106,520 l/ 1939 Australia.

897,412 5/ 1962 Great Britain.

OTHER REFERENCES Modern Metals, Continuous Casting, vol. 20, No. 2, March 1964, TS200.M7, Pp. -46.

J. SPENCER OVERHOLSER, Primary Examiner.

S. ANNEAR, Assistant Egtqgniuer.

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