US3478810A

US3478810A - Continuous copper wire-making process

Info

Publication number: US3478810A
Application number: US684105A
Authority: US
Inventors: Jean Carton
Original assignee: Compagnie Francaise Thomson Houston SA
Current assignee: Compagnie Francaise Thomson Houston SA
Priority date: 1964-06-09
Filing date: 1967-11-20
Publication date: 1969-11-18
Anticipated expiration: 1986-11-18
Also published as: CH430959A; DE1483546A1; GB1107054A; US3364979A; BE665050A; ES313942A1; AT254417B; NL6507140A; FR1434123A; OA01744A

Description

6 J. CARTON I CONTINUOUS COPPER WIRE-MAKING PROCESS '7 Sheets-Sheet 1 Original Filed May 27, 1965 NOV. 18, J C ON CONTINUOUS COPPER WIRE-MAKING PROCESS Original Filed May 27, 1965 7 Sheets-Sheet 2 fit 2 4B I 40' "'2 47 A 30 P36. 74 as I Nov. 18, 1969 J. CARTON A 3,478,810

CONTINUOUS COPPER WIRE-MAKINQPROCESS Original Filed May 27, 1965 7 Sheets-Sheet a Nov. 18,1969 J, CARTON 3,478,810

1 CONTINUOUS COPPER WIRE-MAKING PROCESS Original Filed May 27, 1965 z g F 3 38 25* 46 f za i 28 28b 52a 52b W '7 Sheets-Sl'ieet 4 Nov. 18, 1969 J CARTON CONTINUOUS COPPER WIRE-MAKING PROCESS 7 Sheets-Sheet Original Filed May 27, 1965 Nov. 18, 1969 JQCARTON CONTINUOUS COPPER WIRE-MAKING PROCESS- Original Filed May 27, 1965- 7 Sheets-Sheet 6 Nov, 18, 1969 J. CARTON 3,478,810

CONTINUOUS COPPER WIRE-MAKING PROCESS I Original Filed May 27, 1965 '7 Sheets-Sheet '7 United States Patent 7 Int. Cl. B22d11/06, /04

US. Cl. 164-87 4 Claims ABSTRACT OF THE DISCLOSURE Molten copper from ladle 6 is continuously poured into a casting groove formed in upper surface of centerless revolving annular ingot mold 2 and solidified cast rod is extracted from groove at extractor 16 and continuously passed through hot rolling mill 20 to form a wire rod. The temperature of the process is precisely regulated by

servos

51, 53, 55, 57, 47, 44, through control of depth of cooling water in annular trough surmounting revolving annular support 28 on which the ingot mold 2 rests by way of a long slender cooling fin depending from massive head of ingot mold and immersed in said cooling water. FIGURE 1.

CROSS-REFERENCES This application is a division of my copending US. patent application Ser. No. 459,202, filed May 27, 1965, now Patent No. 3,364,979 issued Jan. 23, 1968.

BACKGROUND OF THE INVENTION This invention relates to a continuous process of casting and hot-rolling copper. A basic object of the invention is to provide an improved method whereby copper is continuously processed from the molten phase to the condition of a continuous, hot-rolled wire-rod capable in turn of being continuously drawn into copper wire of any desired diameter.

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 be, 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 800-900 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 desired final 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, labor 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.

Patented Nov. 18, 1969 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 unreliable and unsatisfactory for general industrial purposes, in spite ofthe very important advantages pointed out above, which the use 0 such systems would otherwise afford.

The chief difiiculties 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 to 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 effects caused by the sharp temperature gradients inherent in such an apparatus shall not set up 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.

Continuous casting and hot-rolling processes have heretofore been proposed for the production of aluminum strip, using a casting drum rotatable about a horizontal axis and having a flat casting groove formed in its periphery, with an endless chain-like covering member cooperating with the casting groove on the down-going side of the drum from an upper casting point to a bottom point of extraction. The thermal problems involved in-the casting of copper are much more critical and diflicult of solution than are those encountered with aluminum because of the much higher melting temperature of copper, 1083 C. as against 658 C. Even disregarding this fundamental difference in the nature of the metals involved, the process just referred to would be totally unsuitable for the production of wire-rod, no matter how the shape of the casting groove is modified, because the chain-like cover member required in that process would impose unacceptable surface conditions on the resulting cast rod, rendering the rod incapable of being drawn into satisfactory wire products.

SUMMARY OF THE INVENTION An object of this invention is to cast and hot-roll copper stock in a continuous, non-stop process without the necessity of any intermediate reheating step, thereby greatly to simplify, expedite and reduce the cost of wiredrawing operations. An object is to produce a continu ously cast copper rod having rounded edges and a surface condition as well as temperature throughout its'cross section such that the cast rod can be continuously passed as cast to a hot-rolling mill and thence to wire "drawing mills to produce high-quality copper wire for the electrical industries.

I have found that, contrary to a belief that has been widespread in the industry for many years, the continuous fully' accomplished provided it is possible to establish and maintain the critical temperature conditions noted above, in a stable way throughout the casting step and ahead of the ensuing hot-rolling step. Means for achieving this result have been disclosed in conjunction with a particular embodiment of a continuous copper casting machine in my parent application, and the present process will accordingly be disclosed by way of example with reference to that construction of casting machine. The casting ma- "chine'of the parent application comprises a centerless annular ingot mold revolving about a vertical axis and ineluding in cross section a massive head and a long slender cooling fin depending therefrom. A casting groove of generally trapezoidal section is formed in the upper surface of the massive head portion of the annular ingot mold.

Molten copper is continuously poured into the casting groove at one point and the solidified cast rod is extracted from the groove at another point spaced circumferentially :beyond the pouring point. The temperature of the process is precisely regulated by servo-mechanism through control of the depth of a body of cooling water in an annular trough in which said cooling fin is immersed, the trough =rol1ing mill arranged a short distance aside from the revolving casting assembly. Under these conditions, it is found that a satisfactory wire-rod can be produced under very economical conditions.

The above machine is illustrated in the accompanying ='drawings, in which:

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

; FIG. 2 is a larger-scale view in perspective and in section generally on line II-II of FIG. 1 further showing certain additional parts not illustrated in FIG. 1;

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 IVIV .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 sec- :tion 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 sca e 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.

I -.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 beapparent 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 ins ance pp pp ed here o at a sui able 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 tang or tundish 12 which is supported 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 be made to flow as a regular uniform-rate stream into the casting groove 4, and as the casting wheel 2 revolves a charge of molten metal is thus continuously deposited into the casting groove.

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 4 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 20.

The reference 22 designates a sprayer device, schematically shown, positioned to overlie the groove 4 in the arc 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.

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 the casting groove 4 is formed, and a relatively thin, downwardly tapered circumeferential flange 26 extending downward from the head 24.

A supporting and coding 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 flat 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 fiat upper surfaces over a major intermediate portion of their extent, and taper down at their ends as shown at 32. The annular mold 2 is supported on the shims 30 atop 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 mold.

With the supporting arrangement thus described, it will be understood that the annular ingot mold 2 is free to expand and contract circumferentially, the lower end surface of its flange 26 then shifting radially outward or inward across the supporting surfaces of shims 30 upon 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 be 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, affixed 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 interfering 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 positions through means not shown and having their ends bent as shown to project downwardly int-o 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 46 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 corresponding 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 readadjustment 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 efficient, sensitive, and precise. Thus in one specific process later described in detail, a change of one centimeter in the height of the water level 46 in the trough' was found to produce a consistent variation of about 50 C. in the temperature of the metalin the ingot mold.

Q 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 aside of .the'ro'd 18 as it issues from the casting groove beyond extractor 16. The output conductors 53 of temperature senser 5 1 provide the electrical signal input to a conventional servomotor uriit 55 which may include anamplifier and reversible motor operating the handwheel 49 through a drive connection schematically indicated at.57. so as to raise or lower the outlet pipe 44. Thus when the electric. signal from temperature senser 51 present on con- .ductOIS 53 indicates an increase in the temperature of the casting above a prescribed upper limit servomotor 55 will act to raise outlet pipe 44 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 be 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 26 to ensure the establishment of'the requisite hydrostaticbalance in the body of liquid on both sides of said flange, othe'rm'eans may be used for that purpose,

"suclf-as"by'providing circumferentially spaced cutoutsin the 'lower 'edg'eof the flange 26. It i'sfrequentIy desirable to cause the casting and solidification of the" castmetal to "proceed under'controlled atmos here conditions, such as in an inertor reducing gas, 'or waterwapor. F-or'this purpose fan annular h'ood '48 of-invert'ed channel shape in cross-section, is suspended from stationary overhead structure 49 as by means of the suspension rings 50 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 gas-tight 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 non-oxidizing 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 in 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 equi-spaced around the circumference of the annular structure as shown in FIGS. 1, 4 and 5. Each pair of rollers 52 comprises two aligned, frusto-

conical rollers

52a and 52b freely rotatable on a common generally horizontal shaft 54 and having their peripheral surfaces defining a common conial surface. The two

rollers

52a 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 beveled out to unequal lengths so as to conform to the common conical surface defined by the

rollers

52a and 52b.

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 28. 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 comm-on 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 thus 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

28a and 28b 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'.

1 Means 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 28d of annular member 28 is engaged by a backing roller 66. Roller 66 is mounted for free rotation about a vertical axis between the arms 68 of a fork or clevis member which arms are horizontally slidable in apertures 70 formed therefor in a fixed upstanding support 72. The rear end of clevis 68 is pressed forward 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 7 2.

The drive arrangement thus described is simple and eflicient, 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 engages 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 76 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 an transverse horizontal shaft 78. The shaft 78 is mounted on suitable supporting structure, not shown, which is generally 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 to 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 to be engageable with the cylindrical inner surface of the casting wheel 2. The follower roller 90 is biased 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 biasing 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 casting machine relate to the construction of the ingot mold 2 and to the crosssectional 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 a large 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 comically 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 general cross-sectional outline of the annular ingot mold 2 as above defined, this axis AA is tilted downwardly away from the central axis of revolution of the annular mold, indicated at 00. In yet other words, the surface of revolution generated by the symmetryaxis AA of the cross-sectional outline about the symmetry axis 00 of the entire ingot mold is a 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 over-all 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 2 to 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 where R is the mean radius of the annular ingot mold member, h its total height or depth dimension, on 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 selected for depends on the over-all size and cross-sectional dimensions of the ingot mold, the material from which it is made and the temperature conditions applied during casting. However, for most practical purposes it can be indicated that a suitable angular range for the angle 4: is approximately from 1 to 4. For the specific case of the practical example to be disclosed presently, the value of is about 2.

According to a further feature of the annular casting mold illustrated in FIG. 3 the bottom wall of the casting groove 4 is slanted downward in the radially inward direction i.e. towards the center axis 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 0 with respect to the axis AA, this angle being directed in the same sense as is the angle formed by axis AA with respect to axis 00. Consequentially it will be clear that the axis BB forms an angle (+0) to the general axis of symmetry 00 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 center 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 center 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 effect 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 g (01nrad1ans) (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 0 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 over-all 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 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 into 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 casting machine now to be described in detail by way of example, the annular ingot mold 2 had a mean radius R: 1,400 mm. as measured from the center axis 00 to the center 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 as in the cold condition of the mold was 2, and the slant angle 0 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 driver 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 rod emerging at extraction 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, occulsions, cracks, blowholes 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 11 mean temperature within the massive head portion 24 of the cross section was T =l50 C. and that in the cooling flange 26 was T :62 C. Thus the temperature differential AT=88 C. Substituting this value into Equation 1 given above, and further putting R=1.4, h=0.l2 and a=l.7 l" (the linear expansion coefficient 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 center axis 00 of the annular mold.

Substituting into relation (2) the values R=1.4,

the selected value indicated. The fact that the finished casting had truly parallel top and bottom surfaces was proof that the angular values selected for the cross-sectional contour of the ingot mold substantially ensured the desired over-all 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 difiiculties 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 curve 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 casting machine, 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 eflicient 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 extraction station, so that the final temperature of the casting at the extracting station remains always perfectly well determined and fully controllable.

Another class of difficulties present in conventional continuous casting systems of the type specified has resided in the occurrenc of deformations both in the parts of the casting machine itself and in the casting, as a re- 12 sult of differential expansion effects. These difliculties have been eliminated in the invention through the construction of the revolving annular moldwas a generally horizontal, centerless annulus capable of 'free and uninhibited circumferential expansion without distorting the cross-section of the casting groove. Furthermore, since the centerless 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 expansibilty of the copper mold, and with further provision for driving the supporting annulus and mold in bodily rotation without interferring 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 rate at 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 is claimed is: 1. A copper wire-making process comprising the steps of:

providing an annular casting groove of an annular casting member in the form of a circumferentially continuously centerless rim positioned in a generally horizontal plane, said rim having a massive upper portion and a cooling flange of a material having high heat conductivity which is radially thinner than and depends from said upper portion; immersing said cooling flange in an annular body of cooling liquid having a surface incompletely covered by said casting member, with both outer sides of said flange being contacted by the liquid;

continuously supplying liquid to and removing liquid from said annular body of liquid;

rotating said casting member about a generally vertical axis of revolution with said cooling flange immersed in the liquid;

continuously pouring a stream of molten copper into said groove;

continuously extracting a rod of solidified copper from said groove at a point spaced circumferentially therealong beyond the pouring point; and

regulating the supply of liquid in said annular body of liquid to continuously withdraw heat from said casting groove at a precisely controlled rate such that said copper rod at the point of extraction is solidified to the core while still having a surface temperature somewhat higher than a predetermined copper hotrolling temperature.

' 2. The process defined in claim 1, wherein said copper rod at its point of extraction has a temperature substantially within the range of from 800 to 900 C. throug out its cross-section.

3. In a copper wire-making process the steps comprismg:

providing an annular casting groove formed in an upper surface of a centerless annular casting member, said member being made of a material which is a good conductor of heat and having a massive upper portion and a downwardly tapered radially thinner cooling flange depending from a substantially central area of said massive upper portion;

immersing said flange in an annular body of cooling liquid having a surface incompletely covered by said casting member, with both outer sides of said flange being contacted by the liquid;

rotating said centerless annular casting member about a generally vertical axis of revolution with said flange immersed in the liquid;

continuously pouring a stream of molten copper into said groove;

continuously withdrawing heat from said copper in said groove;

continuously extracting a rod of solidified copper from said groove at a point spaced circumferentially beyond said pouring point;

sensing the surface temperature of said copper rod near the point of extraction thereof; and

varying the depth of said body of cooling liquid in dependency on the sensed temperature so as to maintain said extraction temperature within a prescribed range.

4. The process defined in claim 3, including the steps References Cited UNITED STATES PATENTS 368,817 8/1887 Daniels 164-278 2,710,433 6/1955 Properzi l64270 X 3,279,000 10/1966 Cofer et al. l64l54 X 3,284,859 11/1966 Conlon et al 164283 X FOREIGN PATENTS 735,035 8/1932 France.

I. SPENCER OVERHOLSER, Primary Examiner ROBERT D. BALDWIN, Assistant Examiner