US3364979A

US3364979A - Continuous casting machine

Info

Publication number: US3364979A
Application number: US459202A
Authority: US
Inventors: Carton Jean
Original assignee: Compagnie Francaise Thomson Houston SA
Current assignee: Compagnie Francaise Thomson Houston SA
Priority date: 1964-06-09
Filing date: 1965-05-27
Publication date: 1968-01-23
Anticipated expiration: 1985-01-23
Also published as: ES313942A1; BE665050A; GB1107054A; AT254417B; US3478810A; FR1434123A; NL6507140A; DE1483546A1; OA01744A; CH430959A

Description

Jan. 23, 1968 J. CARTON CONTINUOUS CASTING MACHINE 7 Sheets-Sheet 1 Filed May 27, 1965 Jan. 23, 1968 CONTINUOUS CASTING MACHINE J. CARTON 7 Sheets-Sheet 2 J. CARTON CONTINUOUS CASTING MACHINE Jan. 23, 1968 7 Sheets-Sheet 5 Filed May 27, 1965 Jan. 23, 1968 Filed May 27, 1965 J. CARTON CONTINUOUS CASTING MACHINE 7 Sheets-Sheet 4 Jan.23,1968 J. CARTON 3,364,979

CONTINUOUS CASTING MACHINE Filed May 27, 1965 7 Sheets-Sheet 5 Jan. 23, 1968 J. CARTON 3,364,979

CONTINUOUS CASTING MACHINE Filed May 27, 1965 7 Sheets-Sheet '7 United States Patent 3,364,979 CONTINUOUS CASTING MACHINE Jean Carton, Paris, France, assignor to Compagnie Francaise Thomson-Houston, Paris, France, a corporation of France Filed May 27, 1965, Ser. No. 459,202 Claims priority, application France, June 9, 1964, 977,539, Patent 1,434,123 14 Claims. (Cl. 164154) ABSTRACT (3F THE DISCLGSURE A continuous copper casting machine comprising a centerless annular ingot mold (2) having a massive head (24) with a casting groove (4) in its top and a long slender cooling flange (26) depending from the center of the head. The mold is supported with the lower end of its cooling flange resting freely on a centerless annular support (28) mounted on rollers (52) and driven in rotation through roller (60). Annular walls (38, 40) upstanding from support (28) define an annular trough in which a body of cooling liquid is formed to a controlled depth in which the cooling flange (26) of the mold (2) is immersed. Molten copper is poured into the casting from tundish (12) and solid copper rod is continuously extracted from the groove at (16) and directly passed to ahot-rolling mill (20), FIGURE 1.

This invention relates to the continuous casting of metals in the form of elongated elements or rods of indefinite length and uniform cross section. The invention is more especially concerned with the continuous casting of non-ferrous metals, particularly copper, into rods capable of being directly hot-rolled and processed (e.g. drawn) into wire, strip and other metal products progressively as they solidify.

In conventional copper Wire-drawing plants in which wire is produced for the electrical and related industries, the usual procedure is to start operations with copper castings known as Wire-bars, which are thick oblong bars of rectangular cross section. Such wire-bars may he, say, about 1.3 meters long and may weigh from 60 to 140 kilograms. These are first heated to a temperature in the range of BOO-900 C. and hot-rolled into rod stock of from 6 to 12 millimeters diameter. This may require up to twenty rolling passes or more. The hot-rolled rod, after cleaning and pickling, is passed to the wire-drawing machines where it is reduced to its desiredfinal diameter which may range anywhere from some millimeters to the order of one hundredth of a millimeter in size.

It would be extremely advantageous if the copper could be cast not as separate bars, but instead in the form of a continuous rod capable of being passed directly as it solidifies from the casting apparatus to the initial processing stage such as hot-rolling mill. This would at a stroke eliminate one or more reheating furnaces (as required to reheat the wire-bars to hot-rolling temperature) and almost all of the large and expensive rolling mills used at present in order to reduce the wire-bars to the dimensions at which they can be fed to the wire drawing mills. The saving in space, equipment, labour and energy would be immense.

There have been many proposals in the prior art to provide continuous casting equipment for non-ferrous metals which would make such type of operation feasible. Certain of these proposals have taken the form of a largeradius casting wheel, supported for rotation about its axis (e.g. vertical), and formed with an annular casting groove in its rim. As the wheel rotates, a stream of molten metal is continuously poured into the casting groove at one point of its circular path, and the solidified metal rod is continuously withdrawn from the groove at another point of the path.

Although the principle involved in such a continuous casting system is sound, practical results have not come up to expectations, and the actual operation of such systems has been found too unrealiable and unsatisfactory for general industrial purposes, in spite of the very important advantages pointed out above, which the use of such systems would otherwise afiord.

The chief ditficulties encountered have concerned the thermal conditions in the system. The molten copper is poured into the casting groove at a temperature of say 1150 -C. It must be completely solidified at its point of emergence from the groove, about three quarters of a circumference beyond the pouring point. However, it must not be allowed to solidify too far ahead of its point of emergence since otherwise it could not be pulled out from its arcuate shape in the groove to a straight condition without cracking. The optimal temperature range at which the copper rod should be extracted in order to be passed directly to a hot-rolling mill, is 800 C. surface temperature and not more than 900 C. core temperature. The maintenance of these conditions requires energetic cooling as well as precise thermal control near the casting groove and around the periphery of the casting wheel. At the same time it is important that the thermal expansion-contraction eflects caused by the sharp temperature gradients inherent in such an apparatus shall not set ilp damaging stresses in the annular mold, nor tend to distort the casting groove and affect the uniformity of the cross section of the continuous cast rod.

The attainment of the results just enumerated comprise chief objects of this invention.

According to an important feature of the invention, the rim of the casting wheel or annular ingot mold has a cross sectional shape whichincludes a massive head portion with an upwardly-open casting groove therein, and a relatively long and slender flange or cooling fin of tapered shape depending from the head portion. Further, the annular mold is centreless, that is, free from any web, spokes, arms or the like radially inward of the rim, so that said rim with the casting groove therein is free to expand in an uninhibited manner circumferentially. This centreless annular mold is supported for rotation about an ideal axis which is generally vertical, and for this purpose said mold is made to rest with the lower end of its depending cooling fin freely engaging under gravity the flat top of an annular supporting member, which is driven in rotation by suitable means such as rollers. For cooling the mold, there are provided walls defining an annular trough on the top of the supporting member, containing a body of cooling liquid, generally water, in which said cooling fin is immersed.

The annular supporting member preferably also is in the form of a centreless ring, e.g. of cast steel, and is supported and driven so as to be freely expansible relative to its stationary support structure, whereas the copper casting wheel is in turn freely expansible relative to the annular cast-steel supporting member.

With such an arrangement it has been found possible to exercise highly precise control over the temperature of the metal in the casting groove by simply varying the depth of the body of water in the trough in which the cooling flange or fin of the annular mold is immersed.

The annular mold is preferably made of copper for maximum conduction of heat, and its slender tapered fin provides a path for the rapid dissipation of heat from the casting groove to the surrounding Water.

At the same time the relatively much more massive head, in which the casting groove is formed, possesses easily and accurately the body of cooling liquid in the trough. f The provision for free independent expansion of the continuous casting retains a thermal inertia and thus stabilizes the temperature of the metal in the casting groove, resulting in a steady, continuous decrease in temperature around the circumference from the point at which the moltenmetal is poured to the a point at which the solid rod is withdrawn. The final temperature of the metal at this point of withdrawal can be adiusted as by varying the depth of steel or cast iron annular supporting member and the copper annular mold prevents darn-aging distortion to the parts of the casting machine and ensures that the uniform undistorted cross section throughout.

Owing to the accurate temperature control achievable with the improved continuous casting machine it becomes possible to feed the cast rod directly as it solidifies and is stripped out of the casting groove, to a hot rolling mill thus eliminating an intermediate reheating step.

The various objects and novel features of the invention will become apparent from the ensuing description of an exemplary embodiment selected by way of illustration but not of limitation and with reference to the accompanying drawings wherein:

FIG. 1 is a perspective view, somewhat simplified, of the main parts of an improved continuous copper casting machine; 7

FIG. 2 is a larger-scale View in perspective and in section generally on line 11-11 of FIG. 1 further showillustrated in FIG. 1;

ing certain additional parts not FIG. 3 is a cross sectional view showing in detail a preferred contour used for the annular casting mold;

FIG. 4 is a cross section, generally on the line IV-IV of FIG. 1, on an enlarged scale;

FIG. 5 is a small-scale schematic plan view of the machine and shows in phantom the positions assumed by the casting wheel and other parts at elevated casting temperature, the displacements from the full-line positions being considerably exaggerated for clarity;

FIG. 6 is a large-scale perspective View of the extractor device associated with the casting wheel;

FIG. 7 is a large-scale fragmentary view in cross section of. the casting groove and casting therein and illustrates a heat-isolating coating lining the walls of the groove, in exaggerated form;

FIG. 8 is a partial view on a scale larger than that of FIG. 1, showing the casting wheel and its supporting means in cross section and the ladle and feeder tank in elevation together with the movable mounting means for the feeder tank.

The continuous copper casting machine illustrated includes as an essential component a revolving annular ingot mold or casting wheel 2 supported for rotation in the direction indicated by the arrow A in FIG. 1 in a generally horizontal plane, through means later described. As will be apparent from the large-scale cross sectional views of FIGS. 2, 3, 4, 6, 8, the annular mold 2 is formed in its upper surface with an annular casting groove 4.

Near the annular mold 2 there is positioned a conventional casting ladle 6 containing a body of molten metal, in this instance copper, supplied thereto at a suitable casting temperature from an appropriate melting furnace not shown. The ladle '6 is supported on a frame generally designated 8 by way of the horizontally aligned pivots 10 for rotation about a horizontal rocking axis, whereby the molten contents of ladle 6 can be poured into a regulating feeder tank or tundish 12 which is sup ported from frame 8 in a position such that a bottom outlet orifice of tundish -12 directly overlies at all times a point of the casting groove 4 in the annular mold 2. The supporting means for tundish or feeder tank 12 will be later described in detail. The molten metal can thus 4,. be made to flow as a regular uniform-rate stream the casting groove 4, and as the casting wheel 2 revolves, a charge of molten metal isthus continuously deposited into the casting groove. 1

The metal thus deposited into the casting groove 4 rather rapidly cools and solidifies as it is carried around- .with the revolving mold 2, so that at a point situated some three fourths of a circumference or so beyond the point at which the stream of molten metal is poured, the metal has solidified. At or shortly beyond the point of solidification, the continuous solid copper rod is stripped from the casting groove t by means of an extractor device generally designated 16 and later described in detail. Essentially this extractor device consists of a stationary ramp or wedging member inserted into the groove 4 so as to lift the solidified metal rod out of the groove.

The continuous rod 18 thus extracted is shown as being fed directly to the rolls of a conventional hot rolling mill 2i). i

The reference 22 designates a sprayer device, schematically shown, positioned to overlie the groove 4 in the are I thereof beyond the extracting station 16 and ahead of the casting station 14; and serving to spray a suitable lubricant composition into the empty casting groove as later described in greater detail. I 1 a a The annular ingot mold 2 is formed with a cross sectional contour clearly shown in FIG. 3 as including a relatively massive upper head part 24 in which thecasting groove 4 is formed, and a relatively thin, downwardly tapered circumferential flange 26 extending downward from the head 24. y

A supporting and cooling assembly for the annular mold 2 is shown as comprising an annular support member 28 which may be a steel or iron casting and has the general cross sectional shape of an inverted channel. Secured to the fiat upper surface of the member 28 are a series of supporting blocks or shims 30 which extend radially across the annular upper surface of member 28 and are spaced. circumferentially. around that surface. The blocks 30 have flat upper surfaces over a major intermediate portion of their extent, and tap er down at their ends as shown at 32. The annular mold 2 is supported on the shims 30 atop the member 28 under its own weight, with the lower end surface of flange 26 resting upon the flat upper surfaces of the shims 30 substantially centrally thereof. To prevent appreciable circumferential displacements of the mold 2 relative to the supporting member 28, one or more radially extending key elements such as the one shown at 34' in FIG. 2 are secured to the upper surface of member 28 in'addition to the shims 30, and project upwardly into a complementary notch 36 formed in the lower end part of the flange 26 of the the upper surface'of member 28. At the same time, the

ingot mold 2 remains at all times connected for bodily rotation with its supporting member 28 as the latter is driven in rotation through means to he later described.

An annular trough for a cooling liquid is defined atop the supporting member 28 and around the flange 26 of the ingot mold by a pair of

annular walls

38 and 40 made of steel strip, 'aifixed to the vertical sides of the supporting member 28 and projecting upwardly thereabove. The trough thus defined contains a body of cooling liquid, such as water substantially free from mineral salts capable of depositing as scale over the side surfaces of flange 26 and interferring with heat transfer. Means are provided for maintaining the level of cooling water 46 in the trough at a constant, adjustable height, and include a feed pipe 42 and a discharge pipe 44 supported at stationary posiinto 5 tions through means not shown and having their ends bent as shown to project downwardly into opposite sides of the trough. The feed pipe 42 may be connected to a constant-delivery pump, not shown, and discharge pipe 44 may be similarly connected to a pump, not shown, which will operate whenever the level of the water 45 reaches up to the end orifice of the pipe 44. Means including a sealed mechanism casing 47 and handwheel 49 are provided for adjusting the vertical position of discharge pipe 44 thereby to maintain the level of the liquid at a correspondin position. It will be understood that any suitable means other than those just described may be provided for maintaining the level of the cooling liquid 46 in the trough at an adjustable elevation. It will be noted that the water delivered by the feed pipe 42 rapidly fills the bottom of the trough on both sides of the cooling flange 26 of the ingot mold owing to the gaps provided beneath said flange between the circumferentially spaced supporting shims 30 and that the response to any readjustment of the water level is very rapid especially owing to the fact that the trough is revolving whereas the

pipes

42, 44 are stationary. Moreover, owing to the extremely effective heat transfer present between the flange 26 of the ingot mold and the surrounding water, the degree of control thus obtained over the temperature in the ingot mold 2 is etficient, sensitive, and precise. Thus in one specific process later described in detail, a change of one centimeter in the hei ht of the water level 46 in the trough was found to produce a consistent variation of about 50 C. in the temperature of the metal in the ingot mold.

Desirably, the water level 46 in the trough may be automatically regulated to maintain the output temperature of the casting at a prescribed value. For this purpose there is schematically indicated in FIG. 1 a temperature sensing member 51 such as a thermocouple contacting a side of the rod 18 as it issues from the casting groove beyond extractor 16. The output conductors. 53 of temperature senser 51 provide the electrical signal input to a conventional SEI'VO-IllOiOI unit 55 which may include an amplifier and reversible motor operating the handwheel 49 through a. drive connection schematically indicated at 57 so as to raise or lowe the outlet pipe 44. Thus when the electric signal from temperature senser 51 present on conductors 53 indicates an increase in the temperature of the casting above a prescribed upper limit servomotor 55 will act to raise outlet pipe and thus increase the depth of the body of cooling Water in the trough, while in case of a drop in the sensed temperature below a prescribed lower limit the motor 55 will act to lower pipe 44.

It will he observed that while the shims 30 constitute a convenient means of providing the necessary liquid passages over the surface of the bottom of the trough across the flange 25 to ensure the establishment of the requisite hydrostatic balance in the body of liquid on both sides of said flange, other means may be used for this purpose, such as by providing circumferentilaly spaced cutouts in the lower edge of the flange 26.

It is frequently desirable to cause the casting and solidification of the cast metal to proceed under controlled atmosphere conditions, such as in an inert or reducing gas, or water vapor. For this purpose, an annular hood 48 of inverted channel shape in crosssection, is suspended from stationary overhead structure 49 as by means of the suspension rings t} and hooks or other means. The sides of the annular channel-shaped hood 48 project downward into the body of water 46 in the cooling trough thereby defining a gastight annular tunnel surrounding the ingot mold 2 and the metal cast in the casting groove 4. It will be understood that the stationary hood 48 may be provided with suitable apertures, not shown, for the pouring of the stream of molten metal from tank 12 into the groove and for the withdrawal of the solid continuous rod 18. In operation the cooling water 46 heated by the flange 26 of the ingot mold generates considerable amounts of steam which displace the air from the interior of the hood 48 and inexpensively provide a desirable nonoxidizing atmosphere for casting copper and other metals. If desired however, means may be connected with the hood 48 for circulating some other desired atmosphere through it, such as an inert gas. In yet other cases, the hood 48 may be removed entirely and the whole process carried out in free atmosphere.

The means for rotatably supporting the assembly including the annular mold 2 and its supporting and cooling means, will now be described. The rotatable supporting means are shown as including three pairs of rollers 52 angularly equispaced around the circumference of the annular structure as shown in FIGS. 1, 4 and 5. Each pair of rollers 52 comprises two aligned,

frustoconical rollers

52a and 52b freely rotatable on a common generally horizontal shaft 54 and having their peripheral surfaces defining a common conical surface. The two rollers 52:: and 52b of each pair are engaged by the lower end surfaces of the outer and inner walls 28a and 28b respectively, of the channel-shaped supporting member 28. It will be noted that said walls 28a and 28b are bevelcut to unequal lengths so as to conform to the common conical surface defined by the rollers 52:: and 521).

With each pair of rollers 52 there is associated a roller 56 freely rotatable on a vertical shaft 58 and engaging the outer vertical surface of the radially inner wall 28b of the member 23. The horizontal shaft 54 and the vertical shaft 58 of each of the three sets of three supporting rollers described may be supported from a common fixed frame structure of suitable character, not shown. It will be noted that the arrangement described provides for the rotational support of the entire annular structure about an ideal axis of revolution without having to materialize such axis physically as a shaft. The steel annular support member 28 is thu allowed to expand circumferentially with temperature, and in so doing its flanges 28a and 28b will shift radially over the

rollers

52a and 52b. The rollers being separately rotatable about their common shaft 54, the contact thereof with the respective flanges 23a and 23b is substantially slip-free.

The supporting structure (not shown) for the

shafts

54 and 58 of the three sets of supporting and centering

rollers

52 and 56 may be so arranged that the entire annular assembly is supported in a substantially horizontal plane for rotation about a vertical axis. However, if desired said supporting structure may be so arranged that said annular assembly is supported in a general plane tilted to the horizontal, in a direction away from the casting station at which the molten metal stream pours into the casting groove 4 of ingot mold 2, thereby opposing any tendency to backflow of the molten metal as it enters the groove 4 with a tangential component in the direction of arrow A as earlier described. It is found in some cases that if the metal is allowed to flow back and upstream from its point of injection along the groove 4, as may tend to occur in the absence of the aforementioned tilt imparted to the annular ingot-mold 2 and its supporting assembly, the uniformity of the cross sectional dimensions of the cast metal bar is disturbed. The said general tilt successfully eliminates this defect and may thereby improve the quality of the final product. A preferred range for the angle of tilt with respect to the horizontal plane is found to be from about 10 to about 20.

cans are provided for imparting rotation to the annular assembly comprising support 28 and the ingot mold 2 resting upon it. As shown in the drawings the cylindrical vertical surface of the radially inner wall 28b of the annular member 28 is engaged by a friction roller 60 secured on the vertically projecting shaft of a suitable motor 64 mounted on the fixed frame structure. Directly opposite to the point of engagement of radially inner wall 28b by drive roller 60, the outer surface of the radially outer wall 28a of annular member 28 is engaged by a backing roller 66. Roller 66 is mounted for free rotation by a compression spring 74 thereby urging the backing roller 66 into resilient pressure engagement with the wall 28a and urging wall 28b against drive roller 60. The backing pressure exerted by roller 66 is made adjustable through displacement of a movable abutment member, not shown, abutting the rear end of spring 74 and preferably comprising a screw and nut device supported from the frame member 72.

The drive arrangement thus described is simple and efficient, and at the same time permits free circumferential or radial expansion of the annular supporting member 28 with temperature, owing to the virtually point character of the areas of engagement between said member and the respective drive and

backing rollers

60, 66. Thus, at high temperatures the steel annular member 28 expands radially to assume the form shown (in an exaggerated manner) in- FIG. in broken lines, in which the radially inner surface of member 28 no longer vengages the centering rollers 56 but still rides freely on the supporting rollers 52 as earlier explained.

The extractor device generally designated 16 in FIG. 1 will now be described in greater detail with reference to FIG. 6. As known per se and as indicated earlier herein,

the extractor device 16 includes a wedge-shaped member 7 6 of such transverse dimension as to be freely insertable into the bottom of the casting groove 4, and having an upper surface tapering down into the direction of movement of the ingot mold 2 indicated by arrow A. The larger end of the wedge member 76 is pivoted on a transverse horizontal shaft 78. The shaft 78 is mounted on suitable supporting structure, not shown, which is gennerally stationary but permits sufficient freedom of motion for said shaft 78 to allow the lifter member 76 to remain properly positioned within the groove 4 regardless of thermal expansion and contraction of the annular ingot mold 2.

It is also noted that the feeder tank or tundish 12 while being mounted in a generally stationary manner from the frame 8 as earlier indicated, is arranged to be capable of freely following the displacements of the casting groove 4 as the ingot mold 2 expands and contracts with changes in temperature.

For this purpose, as illustrated in FIG. 8, the feeder tank or tundish 12 is secured on a truck 80 movable on a bracket 82 secured to a side of the ladle structure 6 and projecting above the casting wheel 2. The truck is provided with rollers 84 riding on rails 86 attached to the horizontal top of the bracket 82 in a direction radial to the casting wheel. A pivot shaft 88 projecting vertically downward from the truck 80 has a follower roller 90 pivoted to its lower end so as tobe engageable with the cylindrical inner surface of the casting wheel 2. The follower roller 90 is biassed into engagement with the casting wheel 2 by means here shown as a compression spring 92 having its ends engaging suitable seating surfaces on the bracket 82 and truck 80*. Instead of a spring a counterweight may be used as the biassing means. The arrangement is such that when follower roller 90 is engaging the rim of the annular casting member 2 as shown, the pouring outlet 94 of the feeder tank is positioned substantially centrally of the casting groove 4. It will be evident that with this arrangement, the stream of molten metal will be properly delivered into the casting groove regardless of any distortions of the casting member 2 and its supporting member 28 due to temperature variations.

Important features of this invention relate tothe construction of the ingot mold 2 and to the cross sectional contour imparted to it, and these features will now be described in detail with especial reference to FIG. 3. As earlier indicated, the upper rim or head part of the cross section of the ingot mold is relatively massive. This is necessary in order to impart the desired dimensional and thermal stability to the casting groove 4 therein and to the ingot mold as a whole. Desirably, said rim or head part 24 is approximately octagonal in outer contour (disregarding the groove 4). In contrast to the massive rim or head part 24, the flange 26 must be relatively long and slender in order to achieve the desired rapid rate.

of heat transfer between the ingot mold 2 and the surrounding cooling water medium. It will be noted that the rim 24 is heated by direct contact with the hot metal in groove 4 whereas flange 26 is cooled through contact with the cooling water. This results in alarge degree of differential expansion therebetween with changes in temperature, the massive head part 24 expanding to a greater degree than the flange 26. To allow for this,

differential expansion and prevent damaging strains being set up and the occurrence of dimensional distortion in the casting groove and hence in the cast product, the

cross sectional contour of the annular ingot mold 2 is conically angled to the general axis of symmetry of the annular mold, in a downward-outward sense. That is,

considering in FIG. 3 the axis of symmetry AA'of the v general cross sectional outline of the annular ingotmold 2 as above defined, this axis AA is tilted downwardly away from the central axis of revolution of the annular mold, indicated at OO. In yet other words, the surface of revolution generated by the symmetry axis AA of the cross sectional outline about the symmetry axis 00 of the entire ingot mold isna cone whose apex lies above the general plane of the ingot mold. In this manner it will be understood that'when the ingot mold as a whole is heated to its average overall working temperature, the increased radial and circumferential expansion of the hot massive upper part 24 over that of the cool flange 26, causes the annular ingot mold member 210 distort in such a way that its cross sectional contour is bodily rotated in a sense (clockwise in FIG. 3) that tends to bring the symmetry axis AA of said contour into parallelism with the symmetry axis 00 of the annular ingot mold member 2.

It can be shown that the proper value to be imparted to the cone angle formed between the two above-defined axes AA and O0 in the cold condition of the ingot mold is given approximately by the relation 2hE T in radians) (1) where R is the mean radius of the annular ingot' mold member, it its total height or depth dimension, 0: is the linear thermal expansion coefficient of the mold. material, and AT is the difference between the mean temperatures in the rim or head 24 and flange 26 during a casting process. Obviously the correct value to be selectedfor depends on the overall size and cross sectional dimensions of the ingot mold, the material from whichit is made and the temperature conditions applied during trated in FIG. 3 the bottom wall of the casting groove 4 is slanted downward in a radially inward direction i.e.

towards the centre axis 00 of the annular mold, relative to the cross sectional contour of the mold as defined above. The slant angle, which is relatively small, is indicated as 0 in FIG. 3. In other words, considering now the symmetry axis BB of the casting groove 4 as distinct from the symmetry axis AA of the outer cross sectional contour of the ingot mold previously considered, then said axis BB (which is normal to the bottom surface 100 of the groove), forms an angle 9 with respect to the axis AA, this angle being directed in the same sense as is the angle :1: formed by axis AA withrespect to axis 00.

Consequently it will be clear that the axis BB forms an angle (+0) to the general axis of symmetry of the annular mold. The reason for thus slanting the bottom of the casting groove is, essentially, to provide compensation for centrifugal force.

That is, the molten metal initially poured into the casting groove at 14 is highly fluid, and the centrifugal force created by the rotation of the mold about its centre axis 00 therefore causes the free upper surface of the metal in the groove 4 to slant upwardly in the radially outward direction, away from centre axis 00. Should the molten metal be allowed to solidify in this configuration without special precautions, the resulting casting would have an asymmetrical cross sectional contour in which the top and bottom surfaces would not be parallel. By slanting the bottom surface of the casting groove 4 as indicated, this efiect of centrifugal force can be compensated and a substantially truly symmetrical casting can be obtained.

It can be shown that the proper value to be imparted to the slant angle 0 between the two above-defined axes BB and AA is given approximately by the relation 0=Rw /g (0 in radians) (2) where R, as before, represents the mean radius of the annular mold, w is the angular velocity of the revolving mold in radians per second, and g is the acceleration of gravity. For most practical conditions a suitable angular range for the angle 0 is approximately from 1 to 3". For the specific case of the practical example to be disclosed herein, the value of 6 is about 140.

The casting groove 4 has substantially straight side surfaces 102 which diverge slightly in the upward direction symmetrically to the opposite sides of the groove symmetry axis BB, in order to facilitate withdrawal of the solidified casting from the groove. This angle of divergence or taper may be of the order of 2 on each side, as here indicated. The sides 102 of the casting groove connect with the bottom 100 of it by way of rounded corners, as shown, the radius at each corner being preferably about 2 mm. This radius is substantially the same as the radius assumed due to surface tension at the lines of contact of the upper free surface of the molten metal with the sides 102 of the casting groove. As a result there is produced a casting in which the cross sectional contour is a trapezoid having equally rounded corners.

Prior to the casting operations, the inner surfaces of the casting groove 4 are coated with a thin layer of a suitable heat-insulating and refractory substance, such as any of various silicates, aluminates or bentonite. This coating has the dual function of preventing overheating of the mold and over-cooling of the metal, and the coating thickness is determined by test to obtain optimum temperature conditions in the casting at the point of its extraction from the casting groove. In the case of the copper castings here considered, these optimum conditions are such that the cast rod as it is withdrawn at the extraction station 16 is fully solidified to the core, and is still at a surface temperature not substantially less than about 800 C. (a suitable range of temperatures throughout the cross section of the trapezoidal rod is from 800 to 900 C). In these conditions the continuous rod as it issues from the ingot mold can be directly passed through the hot-rolling mill 20 without having to be reheated, with considerable advantage to the overall economy of the process.

A generally suitable range of thicknesses for the heatinsulating lining just mentioned is from 0.1 to 0.5 millimeter. It has been found however that for best results the thickness of this lining, as indicated at 104 in FIG. 7, is preferably not uniform, but is somewhat greater in the upper or outer parts of the groove sides 102 and then 7 tapers down to a uniform value along the bottom surface of the groove. This precaution serves to oppose a tendency to a premature cooling of the metal as it first contacts the side walls 102 and consequent defects such as cracks in the casting. Alternatively, a similar result can be obtained by imparting to the groove sidewalls an incurvated contour somewhat as indicated in dotted lines at 102 in FIG. 7. In this figure, reference 106 indicates the cast metal in the groove 4.

Over the heat isolating coating 104 just described, there is provided a thin film of lubricant such as colloidal graphite, serving to prevent adhesion of the solidified metal to the underlying surface. This lubricant coating is applied continuously during the casting process, as already indicated, by means of the sprayer unit 22. in the casting groove 4 in the empty arcuate segment thereof between the extractor station 16 and the pouring station 14. The rate of delivery of the sprayer 22 is adjusted to coat the inner surfaces of the groove 4 with a thin film which may be of the order of a few hundredths of one millimeter in depth.

In a specific embodiment of the invention now to be described in detail by way of example, the annular ingot mold 2 had a mean radius R=l,400 mm. as measured from the centre axis 00 to the centre of the casting groove 4. The vertical dimension of the mold was h= mm. The cross sectional shape of the mold was substantially as shown in FIG. 3, the groove 4 being about 22 mm. deep and formed and dimensioned to provide a finished rod having a trapezoidal cross section 13.5 mm. in altitude and 13.5 mm. average width. The conical angle in the cold condition of the mold was 2, and the slant angle 9 of the groove bottom 100 to the symmetry axis AA of the cross section was 140. The head portion 24 was 55 mm. thick and the flange 26 tapered down from 30 mm. to 10 mm. over a length of 70 mm.

The annular mold 2 was rotated from motor 64 through drive roller 60 at a uniform angular rate of 4.32 r.p.m., or w=0.452 rad/ sec. The linear velocity V of withdrawal of the continuous cast rod was therefore V=Rw or :38 meters/minute, and the casting output was about 3.7 metric tons per hour.

The cooling system described was operated to maintain a body of water between 30 and 70 mm. deep in the annular trough surrounding the cooling flange 26. Under these conditions it was found that the metal in the casting groove 4 cooled at a rate such that the rod emerging at extractor station 16 had just solidified to the core but its surface temperature was still somewhat above 800 C. The rod was seen to possess a highly regular trapezoidal cross section, with its top and bottom surfaces substantially parallel. The cross section was strictly uniform throughout the length of the rod, about 600 meters for a one-ton copper melt. The crystal structure of the casting was excellent, fine-grained and free from oxidation, occlusions, cracks, blow-holes and other defects.

As this rod emerged continuously from the extracting station 16 at a temperature in the range of 800 to 900 C., it was immediately fed through the hot rolling mill 20 in which it was converted to a round rod or wire 10 mm. in diameter. This was then fed continuously to the conventional wire-drawing mills in which it was drawn to various standard gauges.

During test runs, measurements were taken with thermocouple probes to determine the temperatures in various parts of the annular mold. It was found that the mean temperature within the massive head portion 24 of the cross section was T C. and that in the cooling flange 26 was T =6 2 C. Thus the temperature differential AT=88 C. Substituting this value into Equation 1 given above, and further putting R=l.4, h=0.l2 and e=l.7 l0 (the linear expansion coefiicient for copper), there is found =0.035 radian, or 2, the selected value indicated above. Measurements showed that during the casting process the flange 26 effectively assumed under the differential expansion effect earlier explained a substantially upright position parallel to the centre axis 00 of the annular mold.

the desired overall compensation both for differential expansion and for centrifugal effects as earlier explained. Inadequate control over thermal conditions in prior-art continuous casting machines of'the class to which the invention relates has been responsible for many and serious difficulties which have heretofore prevented continuous casting processes from gaining wide acceptance in the field of non-ferrous metallurgy, particularly though not exclusively copper wire-drawing plants. These difficulties have included temperature instability. That is, it was not found practicable to cool the annular mold with the efficiency and uniformity required to create and maintain a steady, continuously decreasing temperature gradient around the circumference of the mold all the way from the molten metal pouring station to the extracting station, as would be essential if the temperature of the casting at its point of extraction was to be accurately maintained within its critical range. This range (800- 900 C; for copper) is critical for several reasons as earlier indicated. The cast rod must have solidified to the core before it can be extracted, yet it must not have solidified too far ahead of its point of extraction since in such case it would set in a curved state owing to the curvature of the annular mold, and it would then tend to crack as it is straightened out by extractor 16. Also, the rod should preferably be at a temperature where it can be directly hot-rolled without reheating.

In the invention, the requisite temperature stability and consequent precise control over the temperature of the casting at its point of extraction is achieved mainly through the feature that the cross sectional shape of the annular mold includes two sections differing radically in their geometric and physical characteristics: a relatively massive head or rim portion having the casting groove formed in it, and a slender cooling fin integrally depending from the head and immersed a controllable depth in cooling water. The cooling fin assures efiicient dissipation of heat from the casting groove to the cooling medium at a controllable rate, while the massive head owing to its large moment of inertia imparts thermal as well as dimensional stability to the casting groove and the molten metal therein. The thermal inertia of the head section surrounding the casting groove ensures that the temperature in the casting groove will at no time tend to change abruptly but will present a steady, continuously decreasing gradient all the way from the pouring station to the extracting station, so that the final temperature of the casting at the extracting station remains always perfectly well determined and fully controllable.

Another class of difiiculties present in conventional continuous casting systems of the type specified has resided in the occurrence of deformations both in theparts of the casting machine itself and in the casting, as a result of differential expansion effects. These difficulties have been eliminated in the invention through the construction of the revolving annular mold as a generally horizontal, centreless annulus capable of free and uninhibited circumferential expansion without distorting the cross section of the casting groove. Furthermore, since the centreless annular mold of the invention is preferably made of copper for optimal conduction of heat through its cooling 'fin as explained in the foregoing paragraph, it is contemplated that the mold is supported and driven by resting under its own weight upon an annular supporting member of cast steel, with provision for free expansion of the copper mold and steel supporting annulus independently of one another, thereby preserving the feature of free circumferential expansibility of the copper mold, and with further provision for driving the supporting annulus 12 and mold in bodily rotation without interfering with the free expansibility. of either annular part.

Various modifications may be made in the specific embodiment described and shown without departing from the scope of the invention. The cross sectional shape of the annular mold may be altered, especially as regards the cross section of the casting groove therein, while preserving the main geometric characteristics.

Various ancillary devices of generally conventional character may be associated with the casting machine.

Thus suitable guiding means and draft tension-control arrangements may be interposed between the extracting station 16 and the hot-rolling stand 20, and may serve-to impart a controllable retarding force to the rod 18. as it issues from the extractor.

Servo-mechanism of conventional type may be provided for automatically controlling the rateat which molten metal is poured from the feeder tank'12, and/ or the rate of rotation of the casting wheel 2 from drive motor 64, in order to regulate the vertical dimension of the continuous cast rod. Such servo-mechanism may be tied in with the servo means earlier described herein for controlling the depth of cooling water in the trough.

What I claim is: I

1. A continuous metal casting machine comprising:

an annular casting member in the form of a circumferential-ly continuously integral centreless rim positioned in a generally horizontal plane and havinga cross-sectional contour including a massive head POI".

tion with an upwardly-open casting groove therein and a cooling fin portion depending from the head portion; said cooling fin portion comprising a relatively long and slender flange of a material having high heat conductivity extending front a substantially central area of the undersurface of said head portion; means mounting the casting member for centreless rotation about a generally vertical ideal central axis, of rotation, said mounting means comprising a supporting member having a generally flattop and means driving said supporting member in rotation about said generally vertical axis, the casting member resting upon, the supporting member with the lower end of said flange of the depending cooling fin freely engaging said flat top so as to be driven in rotation circumferentially with the supporting member while being freely movable radially with respect thereto under forces of differential thermal expansion and contraction; means for retaining a body of cooling liquid atop the supporting member in which said cooling fin portion of the casting member is immersed with both outer sides of said flange being contacted by the liquid; and

means for pouring molten metal into the casting groove at one point of its rotational path and means forextracting a continuous casting from the groove at another point of its path.

2. A continuous casting machine comprising:

an annular casting member in the form of a centreless rim positioned in a generally horizontal plane and having a cross-sectional contour including a massive head portion with an upwardly open casting groove therein and a relatively long and slender cooling flange portion depending therefrom;

an annular trough means disposed coaxially with and under said casting member with the lower end of said 13 means for pouring molten metal into the casting groove at one point of its rotational path and means for extracting a continuous casting from the groove at another point of its path; whereby said massive head portion with molten metal in the groove thereof will undergo in operation considerably greater thermal expansion than said slender cooling flange immersed in the cooling liquid and the casting member will consequently be distorted so that said head portion thereof is rotated radially outward relative to the cooling flange portion; and said casting member being formed so that the crosssectional contour thereof at ordinary temperature has an axis of symmetry inclined to said axis of rotation in a downward-outward direction an angular amount such as to cancel said distortion and render said cross sectional contour substantially vertical under casting temperature conditions. 3. A casting machine as defined in claim 2, wherein said casting groove has a generally flat bottom wall slanting at a small angle downward in the radially inward direction relative to said cross sectional contour.

4. A casting machine as defined in claim 3, wherein the casting groove has a generally trapezoidal cross sectional contour with side walls diverging upward from perpendicnlars to said bottom wall.

5. A continuous casting machine comprising: an annular casting member in the form of a circumferentially continuously integral centreless rim having a massive head portion with an upwardly-open annular casting groove formed in the top thereof and a relatively long and slender annular cooling flange depending from a substantially central area of said massive head portion at least said flange being made of a material having high heat conductivity;

annular trough means disposed coaxially with and under the casting member with the lower end of the cooling flange resting on a bottom surface of the trough; means for delivering cooling liquid into the trough at one point and withdrawing liquid from the trough at another point, including means for varying the depth of the body of liquid in the trough, said liquid contacting both outer side surfaces of said cooling flange;

means for bodily rotating the trough means and casting member about a generally vertical ideal central axis of rotation;

means for pouring molten metal into the casting groove at one point of its rotational path and means for extracting a continuous casting from the groove at another point of its path;

means for sensing the temperature of the casting adjacent said last point; and

servo-means connected with the temperature sensing means and connected with the depth varying means to increase the depth of cooling liquid when the sensed temperature rises and decrease said depth when the sensed temperature decreases.

6. A continuous casting machine comprising:

an annular casting member in the form of a circumferentially continuously integral centreless rim having an annular upwardly-open casting groove in the top thereof and a cooling flange portion depending from a substantially central area of said massive head portion at least said flange being made of a material having high heat conductivity;

annular trough means underlying the casting member generally coaxially therewith with the lower end of the flange portion resting on a bottom of the trough means;

generally stationary inlet pipe means positioned to deliver cooling liquid into the trough at at least one point of its rotational path, said liquid contacting both outer side surfaces of said cooling flange;

generally stationary outlet pipe means positioned to withdraw liquid from the trough at at least one point of said path; and

means for pouring molten metal into the casting groove at one point of its rotational path and means for extracting a continuous casting from the groove at another point of its path.

7. A casting machine as defined in claim 6, wherein said outlet pipe means is arranged to have an end thereof dipping into the trough from the top thereof, an extractor =pump connected with another end thereof, and means for vertically displacing said outlet pipe means for varying the level of cooling liquid in the trough means.

8. A continuous casting machine comprising:

an annular casting member in the form of a circumferentially continuously integral centreless rim having a massive head portion with an annular upwardlyopen casting groove in the top thereof and an annular cooling flange depending from a substantially central area of said massive head portion at least said flange being made of a material having high heat conductivity;

means mounting the casting member for centreless rotation about a generally vertical ideal central axis of rotation, said mounting means comprising an annular supporting member having a generally flat top upon which the lower end of the cooling flange rests freely under gravity whereby the casting member is circumferentially rotatable with the supporting member while being freely movable radially thereof under forces of differential thermal expansionand contraction;

a driving roller engaging one peripheral side surface of the annular supporting member and a backing roller engaging an opposite peripheral side surface of the supporting member in radial alignment with the driving roller and motor means for rotating the dirving roller to rotate the supporting and casting members about said axis while permitting free circumferential expansion of the supporting member;

means defining an annular trough atop the supporting member for containing a body of cooling liquid in which said cooling flange is immersed with both outer side surfaces thereof contacted by the liquid;

means for pouring molten liquid into the casting groove at one point of its rotational path and means for extracting a continuous casting from the groove at another point of its path.

9. A casting machine as defined in claim 8, wherein the supporting member has an undersurface which is frustoconical with respect to said axis of rotation, and a plurality of circumferentially spaced supporting idler rollers engaged by said undersurface and having their axes generally radial with respect to said axis of rotation.

19. A casting machine as defined in claim 8, including a plurality of circ-umferentially spaced positioning idler rollers engaging an inner one of said peripheral side surfaces of the annular supporting member when said member is under ordinary temperature conditions.

11. A continuous casting machine comprising:

annular trough means underlying the casting member generally coaXially therewith with the lower end of the flange freely resting under gravity on a bottom surface of the trough;

means defining flow passages over said bottom surface between the opposite sides of said flange to allow free establishment of hydrostatic balance across the flange in a body of cooling liquid present in the trough said liquid contacting both outer side surfaces of said flange;

means for delivering cooling liquid into the trough at one point and withdrawing liquid from the trough at another point for providing said body of liquid in the trough;

means for rotating the trough means and thereby rotating the casting member while enabling free relative expansion of the casting member with respect to the trough means;

means for pouring molten metal into the casting groove 1 at one point of its rotational path and means for withdrawing a continuous casting from the groove at another point of the path;

and means for varying the hydrostatic level of the body of liquid in the trough so as to maintain a prescribed temperature in said casting as it issues from the casting groove.

12. A machine as defined in claim 11 wherein said metal is copper and said groove has substantially uniform cross-sectional dimensions.

erally horizontal plane is tilted from the true. horizontal plane at a relatively small downward angle away from said metal pouring means in the direction of rotation of the casting member.

14. A machine as defined in claim 8, wherein said casting member is made of copper and said supporting member is made of steel.

References Cited UNITED STATES PATENTS 7 359,348 3/1887 Daniels 164-268 368,817 8/1887 Daniels 164278 405,914 6/1889 Schutlz 164-276 2,659,949 11/1953 Properzi .164278 3,284,859 11/1966 Conlon etal 164 -259 1,902,559 3/1933 Kemp 164 348 I FOREIGN PATENTS 125,883 6/1928 Switzerland. 528,359 7/1956 Canada.

J. SPENCER OVERHOLSER, Primal) Examiner.

R. D. BALDWIN, Assistant Examiner.

13. A machine as defined in claim 1, wherein said gen- 25