US3797555A

US3797555A - Method for continuous casting of metal strips

Info

Publication number: US3797555A
Application number: US00207843A
Authority: US
Inventors: C English
Original assignee: Noranda Inc
Current assignee: Wolverine Tube Canada Inc
Priority date: 1971-09-30
Filing date: 1971-12-14
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19
Also published as: GB1385985A; FR2154440B1; SE397278B; DE2240795B2; DE2240795A1; FR2154440A1; CA936328A; BE787970A; BR7205737D0; JPS4841923A

Abstract

There is provided a method and an apparatus for continuous casting of metal strip. According to this new system, molten metal is introduced into a tundish which has at its bottom a downwardly projecting open ended graphite mould which is directly connected with the tundish. The tundish is preheated to maintain the molten metal at a desired temperature and the molten metal is allowed to flow from the tundish into the mould at a controlled rate. Cooling water is directly applied onto the lateral walls of the mould so as to solidify the metal therein and then it impinges directly onto the metal strip emerging from the mould. An intermittent withdrawing mechanism is used to withdraw the metal strip at speeds of up to and in excess of 30 in./min.

Description

United States Patent 1 English 7 v METHOD FOR CONTINUOUS CASTING OF METAL STRIPS Christopher John English, Hudson, Quebec, Canada [75] Inventor:

[73] Assignee: Noranda Mines Limited, Toronto, Ontario, Canada [22] Filed: Dec. 14, 1971 [21] Appl. No.2 207,843

[30] Foreign Application Priority Data Mar. 19, 1974 1/1955 Tarquinee et a1 164189 711970 Wertli 164/283 5 7.] ABSTRACT There is provided a method and an apparatus for continuous casting of metal strip. According to this new system, molten metal is introduced into a tundish which has at its bottom a downwardly projecting open ended graphite mould which is directly connected with the tundish. The tundish is preheated to maintain the molten metal at a desired temperature and the molten metal is allowed to flow from the tundish into the mould at a controlled rate. Cooling water is directly applied onto the lateral walls of the mould so as to solidify the metal therein and then it impinges directly onto the metal strip emerging from the mould. An intermittent withdrawing mechanism is used to withdraw the metal strip at speeds of up to and in excess of 30 in./min.

15 Claims, 3 Drawing Figures PAIENTEDHAR 1 9 m4 SHEU 1 0F 3 INVENTOR Christopher John English Arman-rs PATENTEDHAR19'974 3791.555

SHEET 2 OF 3 FIG.2

INVENTOR Christopher John Eng/15h l METHOD FOR CONTINUOUS CASTING OF METAL STRIPS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and an apparatus for continuously casting metal strip and particularly strips of copper and copper based alloys such as brass, bronze, nickel-silver, cupronickel and the like.

The invention is especially applicable to casting of thin metal strip, which can then be directly cold-rolled, at speeds up to and in excess of 30 in./min.

2. Description of the Prior Art The art of continuous casting is well known. Since the first U.S. Pat. No. 1,908 issued to George Escol Sellers on Dec. 17, l840, many patents and publications have appeared describing various aspects of continuous casting of metals.

For example, U.S. Pat. No. 2,740,177 of Apr. 3, 1956 to J .8. Smart Jr. relates to a continuous metal casting process for casting various shapes such as round ingots, tubular structures or rectangular shapes within a hot top mould provided with an indirect cooling.

It has been recognized, however, that strip metal casting has particular difficulties and that it is in a different category from casting of round and rectangular ingots. Continuous strip casting particularly requires a very effective and controllable cooling system which is extremely difficult to achieve. For example, U.S. Pat. No. 3,519,062 of July 7, 1970 to A..l. Wertli recognizes various difficulties of strip casting and suggests an apparatus having cooling and heating means for the mould of a very specific type. An even more recent U.S. Pat. of A.'J. Wertli, namely No. 3,542,119 of Nov. 24, l970, relates to another cooling device for continuous casting of strip metal. In most of the known cooling systems used for continuous strip casting, the cooling medium, e.g. water, is not applied directly to the surface of the mould but rather is contained in a metallic jacket in which the mould is encased. Thus, an extra resistance to heat transfer is introduced since water flow must cool the jacket wall which, in turn, must cool the mould wall. As it is impossible to eliminate an air gap between the jacket wall and the mould wall, the heat transfer rate in an indirectly cooled mould is substantially lower and less uniform than when the mould is cooled directly.

Indirect cooling of strip material complicates the control of heat transfer from the liquid metal and may result in an insufficient cooling rate to produce metal strip at satisfactory industrial speeds. For this reason, production rates have been mostly limited to approximately 12 in./min. and the width of the cast material to about 12 in. at the most.

Moreover, because of metallurgical and mechanical considerations, copper and copper alloy strips, to be cold-rolled must have a maximum thickness of about one-half in. and certainly not over a thickness of,1 in. Thus, at a thickness of about one-half in., a copper alloy coil of 500 lbs/in. width corresponds to a length of 280 ft. A strip of this length may be produced by semi-continuous casting of a long, thick section which is then hot-rolled to about one-half in. thickness, or by welding together shorter lengths hot-rolled from statically cast thick strips. The first alternative requires a large capital investment and correspondingly high opcrating costs, while the welding process is unsuitable from the viewpoint of quality control and operating costs.

Because of high production rates associated with modern strip processing equipment, there is, an increasing demand for large coils of strip stock. For example, in the years between 1965 and 1970 the required weight has increased from about to 500 lb/in. of width of the coil and there is every indication that this trend will continue.

SUMMARY OF THE INVENTION The present invention provides a solution to the above limitations of the hitherto existing methods and apparatuses by introducing a novel concept to continuous metal casting of strips, which enables high production speeds in excess of 30 in./min. of strips as thin as onehalf in. or less and as wide as 30 in. or more. This corresponds to production rates in excess of 7,000 lbs/hr. In the case of copper and copper based alloys, such strips are suitable for cold-rolling with or without intermediate annealing and have a very smooth surface and generally an excellent metal structure which has not been achieved, up to now, by continuous casting on industrial scale.

Basically, the method according to the present invention for continuously casting metal strips comprises pouring molten metal into a tundish which is provided at its bottom with a downwardly projected open-ended mould made of non-wetting material, the upper end of this mould being directly connected with the bottom of the tundish, preheating this tundish to maintain the molten metal at a predetermined temperature, feeding the molten metal from the tundish into the mould, applying a cooling liquid directly onto the lateral walls of the mould so as to solidify the metal in the mould, withdrawing the solidified metal strip in a predetermined stop and start sequence from the mould and allowing the cooling liquid to impinge directly onto the metal strip emerging at the bottom end of the mould.

As mentioned above, the mould should be made of a non-wettable material with respect to the metal. This material should also be refractory and heat-conducting and the preferred material is graphite. Preferably, the mould projects vertically from the tundish and has an opening or cavity of a width substantially corresponding to the thickness of the metal strip to be cast and of a length substantially correspondimg to the width of said strip. Generally, in a preferred embodiment, the mould will have a cavity from about one-half to l in. wide and up to about 30 in. long. The height of the mould will preferably be such that the residence time of the metal in the mould is between 2 and 8 seconds. Very short moulds of about 4 in. in height are suitable although longer moulds may also be used.

The cooling liquid which is normally water is applied onto the lateral walls of the mould at such level as to leave a pool of molten metal above the solidification level in the mould such that the turbulence created by the flow of metal into the tundish is dampened and a quiescent layer of molten metal is maintained at the solidification level in the mould. Thus, the section of the mould above the level at which cooling water is applied becomes a hot-top section while that below said level becomes a cold section. This pool of molten metal normally corresponds to about 4 to 6 times the width of the mould above the solidification level.

The feed rate ofliquid metal from the tundish is controlled by the rate of withdrawal of the cast strip. The rate of flow of the cooling liquid onto the walls of the mould and then onto the metal strip emerging therefrom, is controlled to provide the necessary rate of extraction of sensible and latent heat from the molten metal so that the perimeter of the metal strip in the mould is solidified and made strong enough to be handled by a withdrawing mechanism below said mould. The effective withdrawal rate is normally adjusted to a speed of between and 60 in./min., and preferably between and 30 in./min.

This method is particularly advantageous for continuously casting metal strips of copper or copper based alloys which can be cold-rolled. Such strips will usually be about one-half in. thick and up to about 30 in. wide.

Another very advantageous aspect of the present invention is obtained in the casting of strips of copper alloys which contain a constituent which has an appreciable vapour pressure at the point of solidification, as for example brasses or tin bronzes. Considerable difficulties are associated with casting of such alloys because of metal volatilisation resulting in a tightly adherent film which condenses on the mould surface thus welding the casting to the mould and causing surface tearing and mould erosion. According to the present invention, this problem is solved by controlling the flow of cooling water onto the surface of the mould so as to maintain the temperature at the solidification level within the mould in the range of or above the melting point of the constituent which has an appreciable vapour pressure. This is done by embedding thermocouples at predetermined points into the wall of the mould and measuring the temperature at these points with relation to the rate of flow of the cooling water. In such circumstances, the zinc or tin constituents which are deposited will not act as an adhesive but rather as a lubricant helping in the overall casting operation and producing remarkably smooth casting with no visible deterioration in the mould surface over long periods of operation. Thus, in the case of brasses the temperature at the solidification level at the inner wall surface of the mould is maintained at about 400 to 600C, which is close to the melting point of zinc at 420C. In case of tin bronzes, the temperature is maintained at about 200 to 400C, tin having a melting point of 232C. This is another unobvious and advantageous aspect of the present invention. It should be noted, of course, that in the case of metals which form an oxide which is not reducible by carbon monoxide normally present in the gap between the casting and the mould wall, a neutral or reducing atmosphere should be introduced into said gap to prevent oxidation of the metallic vapour.

. the lateral walls of the mould at a controlled rate and so that it will flow on the walls and will then directly impinge onto the metal strip emerging at the bottom end of the mould; and means for withdrawing the metal strip from the mould at a predetermined stop and start sequence.

The bottom of the tundish may have a layer of highly conductive refractory material to bring the very top of the mould to a temperature close to that of the preheated tundish. The mould is preferably made of graphite and usually projects vertically from the tundish. The opening or cavity in the mould is preferably about onehalfin. to 1 in. wide and up to 30 in. long and the mould is about 4 to 8 in. in height in its preferred embodiment. The mould may also be removably connected with the bottom of the tundish.

It has also been found that in its particularly preferred design, the mould would have a thin wall upper section and a laterally bulging and downwardly tapering lower section onto which cooling water is applied. This lower section also acts as a reinforcing means for the mould, which prevents it from bulging inwards due to the steep temperature gradient which is produced by cooling. If this design is not used, then the mould should preferably be reinforced or provided with means to counteract the forces generated by this temperature gradient across the mould wall at the solidification level, which forces may otherwise cause the mould to bulge inwards.

The means for applying cooling liquid or water onto the lateral walls of the mould will usually include a number of water conduits within enclosed chambers on each side of the mould, from which the cooling water is adapted to flow onto the lateral walls of the mould at predetermined levels and thereafter to impinge from each side wall directly onto the metal strip emerging from the mould. The rate of water flow on each side of the mould is closely controlled to achieve desired cooling characteristics.

The means for withdrawing the metal strip usually comprises the stop and start withdrawing mechanism which is generally known in the art. The apparatus may also be provided with a mould floating arrangement so that the mould may have the desired flexibility during the withdrawal of the metal strip and thereby avoid possible breakage through misalignment or the like.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be desribed with reference to the appended drawings in which:

FIG. 1 is a generally perspective view of the arrangement according to the present invention with some portions being represented in section so as to show more clearly the characteristic features of the novel method and apparatus.

FIG. 2 is a vertical section view of the arrangement representing the method and apparatus according to a preferred embodiment of the present invention.

FIG. 3 is a comparative illustration of the structure of continuously cast strip made according to prior art and made according to the present invention in the case of leaded a/B brass.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 and 2, there is provided according to this invention a mould 5 the upper section 6 of which is connected with the bottom of the tundish 10 in such a manner that there is produced direct communication between the two and so that molten metal 11 can flow directly from the tundish into the mould 5.

The molten metal may simply be poured into the tundish or introduced by a down spout as shown in H0. 2. The tundish may also be enclosed within an insulated wall 16 for better control of the temperature and preheated or heated to a desired temperature by burners 12, 13. A drain hole 14 is also normally provided for draining the metal out of the tundish when the casting is terminated. The bottom section 17 of the tundish will usually be made of a highly conductive refractive material so that the temperature of the upper part 6 of the mould may be brought as close as possible to that of the preheated tundish. The term tundish signifies here any desired type of reservoir for the molten metal, many of which are known in the art.

The upper portion 6 of mould 5 is directly connected with the bottom part of the tundish so as to allow molten metal 11 to be fed into the mould. At the very top of this upper portion 6 of the mould there may be provided a seal 8 to produce a slightly tapering effect and facilitate the flow of metal as well as to prevent the molten metal from penetrating into the mould-tundish interface. Thermocouples 9 may also be provided to check the temperature at various levels within the mould and, if necessary, adjust it in a desired manner.

Mould 6 may be supported at its lower end by any desired means, but in the case of the present embodiment metal slabs 18 and 19 are used for this purpose. Slab l8 presses by one of its side ends against a portion of the mould wall and rests at the other end on another slab 19 which is used to support the whole arrangement. Below slab 18 there is provided a chamber 22 into which cooling water is introduced through water pipes 23. From this chamber 22 the cooling water flows through channel 24 towards and against the walls of the lower portion 7 of the mould and then impinges directly onto the metal strip 25 emerging from the mould. The water flow to each lateral side of the mould is separately controlled to provide optimum heat transfer rate for each side of the cast strip. A sealing gasket may be provided between slab l8 and the wall of the mould portion 7 to avoid penetration of water into the gap that may exist therebetween. Metal strip is then withdrawn in a predetermined sequence by

rolls

26 and 27.

As shown in FIG. 1, slab 19 may itself be supported on a pair of mould floating members 28 which, in this case, consist of two members 29, 30 provided with a groove therebetween in which ball bearings 31 are inserted so that member 29 may move in the directions shown by the small double arrow and thereby provide mould 5 with a desired flexibiity if it is budged one way or the other due to misalignment or the like. This mould floating arrangement is desirable to increase the life of the mould and the quality of the cast.

The floating arrangement 28 may itself be positioned on a platform 32 which is provided at each corner with posts 33 held on the floor or on the supporting member 34 as the case may be.

Due to the fact that the mould is non-lubricated, the withdrawal by

rolls

26, 27 must be of a stop and start type which is also called intermittent withdrawal. llt is well known that in order to withdraw the casting from a non-lubricated mould it is necessary to minimize the contact between the mould and the casting during the withdrawal step. According to the present invention this is accomplished by stopping the casting for long enough to allow the frozen skin to progress towards the feed end of the mould for a distance about equal to the subsequent withdrawal amplitude. The arrest plus advance cycle times are normally between about 2 and 8 seconds. Due to the fact that the skin of the casting detaches itself from the mould wall almost immediately after freezing, the need for lubrication is eliminated and the only requirement is for a nonwetting mould material, which is impermeable to the coolant.

Due to the direct cooling used according to the present invention, the very rapid chilling effect results in a fine microstructure which introduces a remarkably uniform distribution of alloying constituents and secondary and tertiary phases. FIG. 3 illustrates this very fine and uniform structure by comparing leaded a/B brass continuously cast according to a known method with indirect cooling and at rates of 10 in./min. shown at A, with leaded cit/,8 brass cast according to the present invention at a rate of 24 in./min. shown at B. Each specimen has been magnified 400 times. The coarse grain size and islands of ,8 phase are easily seen at A together with small lead particles in the form of small drops which are clearly present in this photographic representation, while at B, the fine grain and distribution of B phase without the visible presence of lead particles is clearly demonstrated. This very fine and uniform structure of the strip metal produced according to the present invention combined with the geometry of a thin strip, enables very short heat treatments to be used to change the properties of alloys such as high tin bronze, a/B brass and nickel silver where the as-cast structure may not be suitable for cold-rolling. The result of this quality is that continuous in-line heat treatment processes immediately subsequent to the casting operation are technically feasible. This is a distinct advantage since it is well known that continuous annealing allows better quality control of the entire length of the strip.

The invention will now be further described in the following non-limitative example.

EXAM PLE:

One-hundred twenty-five lbs of /30 cartridge brass slitter scrap were charged into a KW, 4,000 cycle induction furnace. The charge was melted and stabilized at a temperature of l,O20C. Concurrently, the tundish section of the apparatus and the feeding launder were preheated with propane gas burners to a temperature of l',l00C.

The complete charge was then poured into the tundish via the connecting launder over a period of approximately l5 seconds. As soon as the molten metal level in the tundish reached 2 in. above the entrance to the hot-top, the withdrawal of the starting bar was commenced at an amplitude of approximately one-fourth in. at an average withdrawal speed of 24 in./min. followed by an arrest period bringing the net casting speed to approximately 15 in./min. The instantaneous withdrawal speed was steadily increased over 'a period of approximately 30 seconds to give a final net withdrawal speed of 24 in./min.

To provide an indication of the temperatures in the hot-top, thermocouples were embedded l in. and 2% in. below the entrance and it was noted that the temperatures stabilized at 970C and 900C respectively once the final net withdrawal speed had been reached.

A cast strip in. wide by one-half in. thick by 70 in. long was produced which was rolled down to 0.020 in. following the commercial mill schedule for this alloy. Deep drawing tests indicated less than one-half percent earing, and it was concluded that from the production processing point of view the properties of the continuously cast strip were as good or better as the best produced by conventional means.

Subsequently, the following alloys were successfully cast and rolled using the same procedure with suitable adjustments to the pouring temperatures and rolling schedules: deoxidized low phosphorous copper, common bronze, red brass, yellow brass, leaded yellow brass, substantially pure copper and aluminum zinc alloys.

Summarizing, therefore, the continuous casting process according to the present invention consists of feeding molten metal from a preheated tundish into a bottomless mould at a rate controlled by the speed of withdrawal of the cast strip and applying a heat extraction system to the mould and below the mould on the cast strip in order to solidify the perimeter of the strip and render it strong enough to be handled by the withdrawing stop-start mechanism.

For a stable operation, the rate of extraction of sensible and latent heat from the molten metal should be substantially equal to the rate of heat transfer to the cooling system. Moreover, as the metallurgical structure of a metal or alloy is sensitive to the freezing rate of the casting, a homogeneous structure requires uniform and stable heat transfer rate around the perimeter of the mould. For this reason, it is provided according to a preferred embodiment of the present invention that at the level ofinitial solidification in the mould, the liquid metal be fairly quiescent and at a generally uniform temperature. This condition is accomplished by feeding the casting mould from a hot-top of molten metal large enough to dampen out the turbulence generated by the feeding stream. The tundish is heated and the temperature of the molten feed metal is controlled so that the required conditions of quiescence and uniform temperature at the solidification level in the mould are obtained.

The arrangement of the tundish and the mould as directly communicating vessels does not allow the introduction of lubricants at the top of the mould and for this reason a stop and start mechanism such as described above is required to withdraw the solidified casting without seizure to an unlubricated mould wall.

Having obtained a condition of uniform heat input,

a uniform and stable heat withdrawal system is desirable to obtain a thermal balance and maintain the level of solidification constant during the continuous formation of the casting. This may be accomplished by locating the insulated hot-top section which is heated by the incoming stream of molten metal directly adjacent to the cooled mould section so that the resulting steep thermal gradient locates the solidification front. By applying the coolant directly to the mould surface at a velocity sufficiently high to prevent film boiling on the outer surface of the mould, a highly effective cooling system is provided which results in the formation of a uniform and adequately strong shell around the inner perimeter of the mould. As soon as this shell is strong enough to contain the liquid pressure from the molten metal head it shrinks away from the mould wall and a gap is formed. In order to complete solidification or heat extraction throughout the casting, the water stream is directed against the surface of the strip as it emerges from the mould. This effective and intense cooling applied both to the mould and the emerging strip allows for a very short residence time in the mould, typically 2 to 5 seconds and consequently a very short mould can be used for a given casting speed. Although the invention is not limited to short moulds, such short moulds are preferred in accordance with this invention because they have a number of important advantages both from a metallurgical and mechanical standpoints. The short residence time between the retraction of the solidified skin from the mould face and its exposure to the direct secondary cooling substantially reduces the problem of remelting the cast skin and of metal volatilization which may occur within the air gap. Reheating of the cast skin resulting from a long residence time in the air gap of a long mould can result in significant volatilization of alloying elements such as zinc and tin whose vapour pressure at the temperatures prevailing in this area are quite high; this not only affects the alloy composition of the skin, but may also result in metal condensation on the mould wall which may eventually fill the gap produced by the shrinkage and weld to the emerging casting. This usually eitherstops the casting process altogether or damages both the mould and the casting surface. To avoid this, it is also possible according to the present invention to regulate the temperature at the solidification level of the mould so that it is about the same or higher than the melting point of such alloying elements. In this way, they tend to act as a lubricant rather than an adhesive. It should also be noted that reheating of the already solidified shell may result in the formation of sub-surface porosity and allied defects. This is obviated according to the present invention by the use of a short mould and intense cooling.

Another advantage of the short mould is that as the cooled section is short, both the cold and hot sections may comprise a total depth of approximately 4 to 6 in. Consequently, the heat storage capacity of the mould itself is far less than in existing processes and devices which, because of the inefficiency of the indirect cooling systems used, require moulds at least 8 to 12 in. long. Although the thermal capacity of the mould does not affect the heat extraction rate during the casting process, it is extremely important during starting. At the start, molten metal is fed into a mould, which is necessarily colder than during the casting process, and I sticking to the mould wall it has to be very carefully withdrawn to avoid rupture. Consequently start-up difficulties are magnified as the mould length is increased.

For the above-mentioned reasons, it is preferred to use short moulds in accordance with the present invention. Thus, the length of semi frozen metal which has to be extracted at the start is much less and starting sensibility is considerably reduced. A still further advantage of the short mould is that since the surface temper ature gradient below the level of solidification is necessarily steep, it is possible to locate the perimeter of the solidification profile (liquid-solid interface) and to reinforce the mould at this level to counteract the expansion forces due to the thermal gradient across the mould wall. This characteristic of the process reduces the required amount of subsequent overhauling necessary to produce a flat uniform strip suitable for coldrolling. However, a particularly suitable design of the mould is such as illustrated in the drawings and described above, where the upper portion of the mould is thin walled and straight while the lower portion thereof has a laterally bulging and downwardly tapering thick wall. This mould being made of graphite, the thick wall is sufficiently conductive not to affect the cooling while at the same time it is sufficiently strong to prevent any substantial dishing of the mould and generally provides a very strong and satisfactory mould for this type of operation.

It should, of course, be understood that the invention is not limited to the specifically defined and exemplified embodiments but that many modifications obvious to those skilled in the art can be made without departing from the spirit of the invention and the scope of the following claims.

I claim:

l. A hot-top mould casting method for continuously casting metal strips suitable for cold rolling, which method comprises the steps of: introducing molten metal into a tundish which is provided at its bottom with a downwardly projecting, open-ended, elongated mould made of non-wetting, heat conducting material, the upper end of said mould being directly connected with the bottom of the tundish; preheating said tundish to maintain the molten metal at a predetermined temperature; feeding said molten metal from the tundish into the mould; applying a cooling liquid directly onto the lateral walls of the mould so as to produce a steep temperature gradient between an upper hot-top section of said mould and a lower cold section of said mould and thereby solidify said metal in said mould in strip form; withdrawing the solidified metal strip in a predetermined stop and start sequence from said mould; and allowing said cooling liquid to impinge directly onto the metal strip emerging at the bottom of the mould.

2. Method as claimed in claim 1, in which the open ended mould into which molten metal is fed is a hot-top mould made of graphite and projecting vertically from said tundish, the opening in said mould being such as to cast metal strips about one-half to 1 inch thick and up to about 30 inches wide.

3. Method as claimed in claim 2, in which said mould is of such height that the residence time of the metal in the mould is between 2 and 8 seconds.

4. Method as claimed in claim 1, in which the cooling liquid is water and it is applied onto the lateral walls of the mould at such level as to leave a pool of molten metal above the solidification level in the mould such that turbulence is dampened and a quiescent layer of molten metal is maintained at the solidification level in the mould, and the section of the mould above the level at which cooling water is applied becomes the hot-top section while that below said level becomes the cold section.

5. Method as claimed in claim 4 in which the depth of said pool of molten metal corresponds to about 4 to 6 times the width of the mould, above the solidification level.

6. Method as claimed in claim 1, in which the rate of feeding of said molten metal from the tundish into the mould is controlled by the rate of withdrawal of the solidified metal strip, and the rate of flow of the cooling liquid onto the walls of the mould and then onto the metal strip emerging therefrom is controlled to provide the necessary rate of extraction of sensible and latent heat from the molten metal so that the perimeter of the metal strip in the mould is solidified and made strong enough to be handled by a withdrawing mechanism below said mould.

7. Method as claimed in claim 6, in which the effective rate of withdrawal is adjusted to a speed of between 10 and in./min. I

8. A hot-top mould casting method for continuously casting metal strips of copper or copper based alloys which are suitable for cold rolling, which method comprises the steps of: introducing molten copper or copper based alloys into a tundish which is provided at its bottom with a downwardly projecting vertical openended graphite mould, the upper end of said mould being directly connected with the bottom of the tundish; preheating said tundish to maintain the molten copper or copper based alloys at a predetermined temperature; feeding said molten copper or copper based alloys from the tundish into the open-ended mould; applying cooling water directly onto the lateral walls of the mould so as to produce a steep temperature gradient between an upper hot-top section of the mould and a lower cold section of said mould and thereby uniformly solidify said copper or copper based alloys in said mould in strip form; withdrawing the solidified strip of copper or copper based alloys in a predetermined stop and start sequence from said mould; and allowing said cooling water to impinge directly onto the strip emerging at the bottom of the mould.

9. Method as claimed in claim 8, in which the opening in said mould is such as to cast strips of about onehalf inch thick and up to about 30 inches wide and the height of said mould is such as to achieve a residence time of the metal-in the mould of about 2-5 seconds.

10. Method as claimed in claim 8, in which the cooling water is applied onto the lateral walls of the mould at such level as to leave a pool of molten metal above the solidification level in the mould which corresponds to about 4-6 times the width of the mould, whereby turbulence is dampened and a quiescent layer of molten metal is maintained at the solidification level in the mould and the section of the mould above the level at which cooling water is applied is the hot-top section while that below said level is the cold section.

11. Methodas claimed in claim 8, in which the rate of feeding of the molten copper or copper based alloys suitable for cold rolling from the tundish into the mould is controlled by the rate of withdrawal of the solidified metal strip and the rate of flow of the cooling liquid onto the mould walls and then onto the metal strip emerging therefrom is controlled to provide the necessary rate of extraction of sensible and latent heat from the molten copper or copper based alloys so that the perimeter of the metal strip in the mould is solidified and made strong enough to be handled by a withdrawing mechanism below said mould, said withdrawing mechanism being adjusted to withdraw the metal strip at an effective speed of between 15 and 30 in./min.

12. A method for continuously casting metal strips of copper alloys suitable for cold rolling which contain a constituent which has an appreciable vapour pressure at the point of solidification, which method comprises introducing molten alloys into a tundish which is provided at its bottom with a downwardly projecting vertical open ended graphite mould, the upper end of said mould being directly connected with the bottom of the tundish, preheating said tundish to maintain the molten alloys at a predetermined temperature, feeding said molten alloys from the tundish into the open ended mould, applying cooling water directly onto the lateral walls of the mould so as to solidify said alloys at a predetermined level in said mould and controlling the flow of said cooling water so as to maintain the temperature at the solidification level in the mould at least equal to about the melting point of said constituent, withdrawing the solidified strip ofv the alloy in a predetermined stop and start sequence from said mould, and allowing said cooling water to impinge directly onto the strip emerging at the bottom of the mould.

13. Method according to claim 12, for casting brasses, in which the flow of said cooling water is controlled to maintain the temperature at the solidification level at the-inner wall surface of the mould at about 400-600C,

14. Method according to claim 12, for casting in bronzes, in which the flow of said cooling water is controlled to maintain the temperature at the solidification level at the inner wall surface of the mould at about 200400C.

15. In a method for continuously casting metal strips suitable for direct cold rolling and in a hot-top mould wherein molten metal is introduced into and maintained in its molten state by a heated tundish which is provided at its bottom with a downwardly projecting, open-ended, mould made of non-wetting, heat conducting material, wherein the upper end of the mould is directly connected with the bottom of the tundish, wherein the molten metal is fed directly from the tundish into the mould, and wherein the solidified metal is withdrawn from the mould in a predetermined stop and start sequence, the improvement comprising the steps of applying a cooling liquid directly onto the lateral walls of the mould so as to produce a steep temperature gradient between an upper hot-top section of the mould and a lower cold section of the mould and thereby uniformly solidifying the metal in the mould, and allowing the cooling liquid to impinge directly onto the metal strip emerging at the bottom of the mould.

Claims

1. A hot-top mould casting method for continuously casting metal strips suitable for cold rolling, which method comprises the steps of: introducing molten metal into a tundish which is provided at its bottom with a downwardly projecting, open-ended, elongated mould made of non-wetting, heat conducting material, the upper end of said mould being directly connected with the bottom of the tundish; preheating said tundish to maintain the molten metal at a predetermined temperature; feeding said molten metal from the tundish into the mould; applying a cooling liquid directly onto the lateral walls of the mould so as to produce a steep temperature gradient between an upper hot-top section of said mould and a lower cold section of said mould and thereby solidify said metal in said mould in strip form; withdrawing the solidified metal strip in a predetermined stop and start sequence from said mould; and allowing said cooling liquid to impinge directly onto the metal strip emerging at the bottom of the mould.

7. Method as claimed in claim 6, in which the effective rate of withdrawal is adjusted to a speed of between 10 and 60 in./min.

8. A hot-top mould casting method for continuously casting metal strips of copper or copper based alloys which are suitable for cold rolling, which method comprises the steps of: introducing molten copper or copper based alloys into a tundish which is provided at its bottom with a downwardly projecting vertical open-ended graphite mould, the upper end of said mould being directly connected with the bottom of the tundish; preheating said tundish to maintain the molten copper or copper based alloys at a predetermined temperature; feeding said molten copper or copper based alloys from the tundish into the open-ended mould; applying cooling water directly onto the lateral walls of the mould so as to produce a steep temperature gradient between an upper hot-top section of the mould and a lower cold section of said mould and thereby uniformly solidify said copper or copper based alloys in said mould in strip form; withdrawing the solidified strip of copper or copper based alloys in a predetermined stop and start sequence from said mould; and allowing said cooling water to impinge directly onto the strip emerging at the bottom of the mould.

9. Method as claimed in claim 8, in which the opening in said mould is such as to cast strips of about one-half inch thick and up to about 30 inches wide and the height of said mould is such as to achieve a residence time of the metal in the mould of about 2-5 seconds.

11. Method as claimed in claim 8, in which the rate of feeding of the molten copper or copper based alloys suitable for cold rolling from the tundish into the mould is controlled by the rate of withdrawal of the solidified metal strip and the rate of flow of the cooling liquid onto the mould walls and then onto the metal strip emerging therefrom is controlled to provide the necessary rate of extraction of sensible and latent heat from the molten copper or copper based alloys so that the perimeter of the metal strip in the mould is solidified and made strong enough to be handled by a withDrawing mechanism below said mould, said withdrawing mechanism being adjusted to withdraw the metal strip at an effective speed of between 15 and 30 in./min.

12. A method for continuously casting metal strips of copper alloys suitable for cold rolling which contain a constituent which has an appreciable vapour pressure at the point of solidification, which method comprises introducing molten alloys into a tundish which is provided at its bottom with a downwardly projecting vertical open ended graphite mould, the upper end of said mould being directly connected with the bottom of the tundish, preheating said tundish to maintain the molten alloys at a predetermined temperature, feeding said molten alloys from the tundish into the open ended mould, applying cooling water directly onto the lateral walls of the mould so as to solidify said alloys at a predetermined level in said mould and controlling the flow of said cooling water so as to maintain the temperature at the solidification level in the mould at least equal to about the melting point of said constituent, withdrawing the solidified strip of the alloy in a predetermined stop and start sequence from said mould, and allowing said cooling water to impinge directly onto the strip emerging at the bottom of the mould.

13. Method according to claim 12, for casting brasses, in which the flow of said cooling water is controlled to maintain the temperature at the solidification level at the inner wall surface of the mould at about 400*-600*C.

14. Method according to claim 12, for casting in bronzes, in which the flow of said cooling water is controlled to maintain the temperature at the solidification level at the inner wall surface of the mould at about 200*-400*C.