Background of the Invention Single-wheel continuous casting is a well-developed technology for the production of both pure metal (with trace elements) and alloy bars. te casting techniques and procedures employed for production of alloy bar are generally more complex for the following reasons: most alloying elements tend to harden the base metal, thereby making it more difficult to deform in hot working; some alloying elements tend to segregate during and after solidification, and this segregation is often localized in various parts of the bar cross section; the alloy melt requires careful monitoring and control of the furnace conditions and master-alloy additions; furnace cleaning to remove trace elements from previous runs can be a very tedious and expensive process requiring extensive flushing of the metal; and the large solidification range of alloys requires more careful control of the cooling rates to make sure the core of the bar is solidifie before excessive stresses are applied to it, and to obtain the optimal metallurgical structure.

The technology of choice to achieve a high-quality as-cast bar is the single wheel-casting process, which has been adopted to produce a wide range of alloys in aluminium and copper. Various vendors produce standard equipment with proprietary technology for the casting industry: Kvaerner Metals (former Davy-Clecim), Morgan, Hunter, Continuus Properzi, to name a few. A typical wheel-casting process utilizes a large casting wheel with a peripheral groove into which the metal is introduced through a specially shaped spout emanating from a tundish. The tundish is fed with metal from one or more holding and alloying furnaces, and the metal is previously degassed, filtered, and modifie in-line and laundered into the tundish with minimum turbulence. Dross skimming and careful melt temperature and chemical

composition monitoring is performed, and the metal is fed into hollow arcuate endless mold on the periphery of the moving casting wheel. The wheel rotation and cooling rates are critical to the quality of the produced bar and the repeatability of the process.

The casting wheel is hollow and also has cooling sprays internally that spray onto the underside of the peripheral groove-mold. The sides of the mold have sprays built onto manifolds and a cooling box is mounted atop the mold to cool the upper side of the mold (ive., the belt). The top surface of the mold is created by an endless steel or copper belt that is wrapped around the casting wheel. The copper belt has better heat conduction characteristics but needs to be replace more frequently than the steel belt.

In each of the above cooling zones, the cooling rates are carefully controlled by the flow rates of the water and pressures of the spray. The cooling rates, along with the melt superheat, pouring rate and casting wheel speed, control the solidification of the metal or alloy produced. In most cases, it is desirable to have a quiet and controlled feeding of the metal into the mold, though turbulence near the solidification front both enhances cooling rates and allows for grain shearing to produce a finer microstructure.

The casting wheel is usually made of a special copper alloy for aluminum casting and of steel for copper casting. The use of a copper wheel/steel band configuration implies that the upper part of the cast bar is in contact with the belt is hotter (due to lower thermal conductivity of the steel band), and hence the segregating elements tend to accumulate at the top and upper corner of the bar.

The cast bar usually has square, rectangular, trapezoidal or pentagonal cross- section. For some alloys it is recommended that the bar be scalped before entering into the rolling equipment, to remove the segregation zone which is formed during the continuous casting. This scalping process can require rather complex equipment, since the bar is hot (generally around 500°C for aluminum bar) and the scalping is carried out at high bar translation rates (at speeds up to 20 m/min). The bar usually has a cross-sectional area ranging from 1000 to 6000 square millimeters.

The wheel-casting process described above can produce only a limited number of bar shapes. In particular, the side of the bar which is formed at the belt generally must be flat. Subsequent working and/or machining is necessary to produce rods of

round or other, more complicated cross-section. Most commonly, such working comprises hot-rolling. However, hot-rolling cannot achieve a truly round rod, and in general cannot achieve fine dimensional tolerances. Alternatively, cold-rolling has been used after casting, but high reductions can not generally be achieved without cracking of the rod, limiting the utility of this method.

Summarv of the Invention In one aspect the invention provides a method for producing metal profiles having close dimensional tolerances. The method comprises continuously casting a metal bar by wheel-casting, hot-rolling the bar to produce a rod of a different cross- sectional area and shape, and cold-rolling the rod to achieve a selected final profile.

In another aspect, the invention provides another method for producing metal profiles having close dimensional tolerances. This method comprises continuously casting a metal bar by wheel-casting, hot-rolling the bar to produce a rod of a different cross-sectional area and shape, extruding the rod to further change the cross- sectional area and shape, and cold-rolling the extruded rod to achieve a selected final profile.

In either of these aspects, the bar may be scalped after casting, and may be heated before hot-rolling. In some embodiments, the hot-rolling comprises an in-line heat treatment. Heat treatments may also be applied after the hot-rolling step or before or after the cold-rolling step. These heat treatments may comprise aging or solutionizing the rod. The rod may be finished by stretching, cutting, machining, or final dimensioning after cold-rolling. The rod may comprise aluminum, copper, magnesium, or their alloys. If the rod is aluminum, the hot-rolling may be performed at a temperature of 350°C-600°C, or more preferably of 450°C-550°C. The cold- rolling may be performed at a temperature of 25 °C-350 °C for an aluminum rod, and may comprise reducing the cross-sectional area of the rod by an amount less than 70%. Dimensional tolerances of 0.001 mm can be achieved for some alloys. A very large number of final cross-sections can be produced, including circular, notched circular, semicircular, oval, triangular, square, rectangular, cross-shaped, and L- shaped.

In a related aspect, the invention comprises metal rod produced by these methods.

In a further aspect, the invention comprises systems for producing metal profiles. These systems include a wheel-casting apparats which produces continuously cast metal bar, a hot-rolling apparats which transforms the bar into a shaped rod of a different cross-sectional area and shape, and a cold-rolling apparats which shapes the rod into a selected profile. There may also be included an extrusion apparats, which reshapes the rod produced by the hot rolling mill before it is fed into the cold rolling mill.

The term"bar,"as it is used herein, refers to an elongated shape whose cross- section is one which can be produced by casting, while the term"rod"refers to an elongated shape whose cross-section can be produced by rolling. A"rod"will usually have a curved cross-section (e. g., circular or oval), especially as it emerges from a hot-rolling apparats, but the use of the word"rod"does not preclude other cross- sectional shapes such as square, rectangular, or triangular.

Brief Description of the Drain The invention is described with reference to the several figures of the drawing, in which, Figures la and lb portray the process steps of two embodiments of the invention; Figure 2 portrays selected rod cross-sections which can be achieved by the methods of the invention; Figure 3 portrays a wheel casting machine which can be employed in the practice of the invention; Figure 4 portrays a hot-rolling mill which can be employed in the practice of the invention; Figure 5 portrays a cold-rolling mill which can be employed in the practice of the invention; Figure 6 portrays a frictional extrusion apparats which can be employed in some embodiments of the invention; and

Figure 7 portrays the cross-section of the aluminum profile described in Example 1.

Detailed Description The invention comprises a method of producing shaped metal rod to close tolerances starting with liquid metal. Because the standard tooling which is readily available for the practice of this method is typically made of steel, the method is most useful in producing rod compose of metals which have melting points below that of steel, such as aluminum, copper, magnesium, and their alloys. Flow charts illustrating the process steps of the invention are shown in Figures la and lb. In these two Figures, optional steps of the invention are shown by boxes with rounded corner.

In the embodiment illustrated in Figure la, liquid metal is cast into a bar shape by wheel casting 10. Preferably, this step is accomplished in a continuous manner with closed-loop control over the starting melt conditions, cooling rates in the casting and deformation system, and exit bar temperature. The as-cast bar may be scalped 12 to remove any segregated phases, oxides and accumulated debris from the bar top and sides. The bar is then hot-rolled 14. The hot-rolling step 14 may optionally include pre-heating the bar to a suitable rolling temperature. This step produces a rod of a different cross-sectional area and shape, and preferably reduces or eliminates shrinkage porosity from the casting step. It may be desirable to heat-treat 18 the rod at this point, for example to solutionize alloying phases before the next step. Finally, the rod is cold-rolled 20 to produce the desired profile shape, in continuous or discrete lengths. The cold-rolling 20 can be performed either in-line with the casting 10 and hot-rolling 14 operations, or in a separate line. The latter gives great flexibility in scheduling various alloy casting runs for an industrial plant, and may facilitate cleaning the rod before cold-rolling. The use of separate lines also permits better control of the process and allows different line speeds to be utilized.

Cold-rolling step 20 produces a rod which exhibits superior mechanical properties, close dimensional tolerances, and can take various complex shapes that normally would require rather complex molds if produced directly by casting.

(Figure 2 illustrates some achievable cross-sectional profiles according to the methods of the invention).

After cold-rolling 20, the rod may be subjected to various finishing processes 24, such as heat-treatment. If the rod is compose of a heat-treatable aluminum alloy, it may be subjected to an aging heat treatment 22 to further improve its mechanical properties. It may also be stretched to straighten it, cut, and/or machine, for example to improve dimensional tolerance.

In the embodiment illustrated in Figure lb, the first step is again wheel casting 26 of liquid metal into a bar shape. This bar may optionally be scalped 28 to remove any segregated phases, oxides and accumulated debris from the bar top and sides. The bar is then hot-rolled 30, and may also be heat-treated 32, for example to solutionize alloying elements. The solutionizing step may be combine with the hot- rolling step by careful control of the temperature of the rolls and lubricant.

The rod is then extruded 34 to change its cross-sectional area and optionally to form a preprofile shape. This process usually increases the cross-section of the rod, and preferably comprises frictional extrusion. The extrusion step 34 may be performed either in-line with continuous casting 26, or in a separate line. This step may be followed by solutionizing or other heat treatments 36, and possibly also by cutting the rod into lengths 3 8 for further processing. Finally, the rod is cold-rolled 40 to produce the desired profile shape, in continuous or discrete lengths. The cold- rolling 40 can be performed either in-line with the extrusion operation 34, or in a separate line. If the cold-rolling 40 is performed in a separate line, it is sometimes found convenient to cut the rod 3 8 before cold-working, but this step may be performed either on continuous or discrete lengths of rod.

Once cold-rolled, the rod can be subjected to various finishing processes as described above. These can include heat-treatment 42, such as an aging treatment for an aluminum alloy, and various mechanical finishing processes 44 such as cutting, stretching, machining, and final dimensioning.

In both of these embodiments, the first step of the process of the invention is continuous wheel casting of the metal bar. Wheel casting is a technique well-known in the art, and is described in many handbooks, including the ASM Handbook, Vol.

15 (Casting), pages 314-315, which is incorporated herein by reference. A typical wheel-casting machine is illustrated in Figure 3. Referring to that drawing, liquid metal is placed in a tundish 50, and deposited through a pouring spout 52 onto a

casting wheel 54. The wheel is desirably compose of steel, with a copper rim 56, having a central endless groove (not shown). A band or belt 58 is held against the rim 56, and travels therewith as the wheel 54 is rotated (clockwise, in the illustrated embodiment). The band 58 is usually made of steel, but when producing some difficult-to-cast alloys, it may be found advantageous to make the band out of copper or other materials. The band 58 and the groove in the rim 56 together form the mold in which the liquid metal solidifies. The band and wheel are cooled by water sprays 60. The liquid metal solidifies as it travels with the turning wheel and band, emerging as completed casting 62. A typical cross-section of a completed casting is shown in Section A-A. Optionally, an aftercooler 64 may be provided to cool the bar before emergence from the caster.

If the bar is compose of an alloy, it may experience significant segregation associated with directional solidification (usually from the wheel 54 to the belt 58).

Upon emergence from the wheel caster, it may be scalped to remove some of the segregated material. Usually, the sides of the cast bar which have been in contact with the band 58 are removed in this step, although it will be apparent to those skilled in the art that it may be more advantageous to scalp other areas of the bar in certain casting configurations and alloy systems. Preferably, the milling depth of the scalper is ajustable to accommodate varying segregation depths, which are dependent upon the alloy type. Typical segregation depths are between 1 and 5 mm. At both sides of the bar material from 0.1 up to 3 mm can be removed, as dictated by the needs of the particular embodiment.

In order to facilitate economical further processing of the chips produced during scalping, it is important to avoid any contamination of the chips with cutting oil or mulsion. Therefore a dry cutting with diamond tools is recommended. All chips must be removed from the surface, to avoid chips being rolled into the material, resulting in surface defects or breaks in the final product.

The bar emerges from the caster (and optional milling step) at a relatively high fraction of its melting point, typically on the order of 0.8 Tm (surface temperature). It is then continuously hot-rolled. A typical hot-rolling mill is illustrated in Figure 4.

The path of the cast bar is indicated by dashed line 68. A typical mill comprises a number of vertical stands 70 and horizontal stands 72. The hot-rolling apparats also

frequently inclues a cooling unit 74, which guarantees consistent heat-treatment of the hot-rolled rod.

The profile of the rod may be substantially changed from that of the as-cast bar in this step. While close dimensional tolerances cannot be achieved by hot-rolling (typical tolerances are on the order of 0.2-0.4 mm), the rod can be formed in a preprofile shape similar to the desired final profile. For many final profiles, the most convenient rod shape after the hot-rolling step is an approximately circula cross- section, but many other shapes are possible.

For alloyed rod, a low entry temperature to a hot-rolling step can cause excessive load on the roll bearings. If the rod is not sufficiently hot upon exit from the casting (and optional scalping) steps, it may be preheated before entering the rolling mill. For most aluminum alloys, the entry temperature into the hot-rolling mill should be in the range of 350°C-600°C, and preferably in the range of 450°C-550°C (all temperatures refer to the surface temperature of the bar). The rolling mill is usually 10-20 stands, and is commonly 2-high (although 3-roll systems are also commercially available) with circula, oval, hexagonal, or triangula milled surfaces that impart shape and dimensions to the rod. As is normal practice in lines containing rolling apparats, the rolls may be periodically rotated from stand to stand for edge compensation.

It is preferred that the rolling mill be cooled, for example by an mulsion coolant, which may also serve as a lubricant. The mulsion coolant acts to avoid overheating of the rolls and sticking of the material to the rolls. By controlling the flow and pressure of the mulsion lubricant, a thermomechanical heat treatment can be done in line, which guarantees homogeneous and reproducible product properties.

After rolling the rod can be quenched, preferably with water or mulsion oil.

This process maintins alloying elements in solution, and/or cools the material to a sufficiently low temperature to avoid inhomogeneous properties of the material after coiling. If it is desired to coil the rod for easier handling, this can be done onto roll type (e. g. with horizontal axes) or basket-type twin-drum coilers.

After the hot-rolling, the worked rod is cold-rolled. A typical cold-rolling mill which can be used for this step is illustrated in Figure 5. The rod from a continuos casting and hot-rolling line can be transferred in line to a cold-rolling mill or

transferred in coils. Profiles with a maximum dimension below 50 mm, and more preferably below 30 mm, can be cold-rolled immediately; larger profiles are preferably subject first to the extrusion process described below.

In the embodiment illustrated in Figure 5, the cold rolling mill consists of both driven and non-drive rolling stands. The material is taken from vertical coil pay-off unit 80, and passes first through feeding rollers 82 and an inlet device 84. It then encounters non-drive calibration rolls 86.

The material then reaches driven vertical rolling stand 88 and horizontal rolling stand 90. It passes through a traction/dancer control 92, reaching another set of calibration rolls 94. Four-roll profile rolling stand 96 is driven, and is followed by another set of calibration rolls 98. Finally, the material passes over a swinging tension arm 100 to enter the horizontal spooler 102.

The first (usually 2 to 4) driven stands 88 and 90 are preferably two-roll rolling stands independently driven to allow a maximum flexibility of reduction per rolling step depending on the complexity of the profile and the type of alloy. The last (usually 1 to 2) driven stands 96 are preferably four-roll stands, two horizontal and two vertical rolls in the same plane. Typical area reductions in these stands vary from 1 % up to 40%, depending on alloy type and profile form, and are preferably in the range of 5%-25%. Non-drive two roll stands (usually 4 to 8) are preferably installe in front 86, in between 94 and at the end 98 of the rolling mill and act as calibration stands for subsequent reduction stands. Typical area reductions in these stands vary from 1 % up to 15%, and are preferably in the range of 2%-8%.

The driven stands are preferably lubricated and cooled with an mulsion or oil.

The flow, pressure, and temperature of the lubricant may be controlled in order to obtain the exact desired deformation temperature in each deformation step and to guarantee the optimal final microstructure of the profiles.

Each driven and non driven rolling stand is desirably equipped with a motorized roll adjustment system with a digital control system, to guarantee an optimal and reproducible setting of the rolls.

The speed of the cold rolling mill is typically around 300 m/min, and this speed is practically independent of the profile size or type. The rolling mill is preferably equipped with a accurate layer-wound take-up system 102, which enables

the profiles to be coiled on wooden or steel spools with a product weight up to 3500 kg or more. For typical aluminum alloy profiles, dimensional tolerances of 0.001 mm are easily achieved, and tolerances as low as 0.0005 mm have been attained.

A run-out table with automatic flying shear may be installe to produce straight length profiles up to 20 meter unit length. A stretching bench may also be installe. Some alloys require a heat treatment (e. g., aging or homogenizing) after the cold rolling which can be done in a separate furnace treatment. Such heat treatment will almost inevitably cause some distortion of the profiles; a final dimensioning step is therefore recommended after heat treatment, in order to maintain dimensional tolerances.

For profiles with a dimension about 30 mm, the continuous cast and hot-rolled rod may be transferred to an extrusion line, where the rod is continuously extruded into larger sections (preferably by frictional extrusion), typically up to 100 mm diameter, or, depending upon the end profile shape, into a shaped pre-profile. In preferred embodiments employing an extrusion step, the hot-rolling shapes the rod into an approximately circular profile, which is the preferred shape for most commercially available extruders. A frictional extrusion apparats is illustrated in Figure 6; this apparats is described in U. S. Patent No. 5,167,138, incorporated herein by reference. The apparats comprises a wheel 104, a shoe 106, an abutment 108, an extrusion chamber 110, and a die 112. Material enters the extruder at point 114, and the rotation of the wheel in the direction of the arrow pulls the material upward against the abutment 108. The frictional heat and pressure so generated cause the material to flow into the extrusion chamber 110, which is maintained at a constant temperature by heat exchangers 116. Finally, the material exits through the die 112, whose shape determines the cross-section of the extruded rod. The apparats of Figure 6 is given for exemplary purposes; other extruders may be used in the practice of the invention. For example, the extrusion chamber 110 and heat exchangers 116 may not be necessary for some alloys, and may be eliminated. Extruders which work by processes other than frictional extrusion are also contemplated within the scope of the invention.

The extrusion line may be either in-line or separate from the hot-rolling line.

The frictional extrusion apparats is preferably equipped with a run-out table,

including the facilities for controlled cooling (e. g. , by air, forced air, or water) of the extruded profile. This enables the required temper of the material to be obtained, and may also aid in maintaining the temper of the input material after extrusion. The extruded profiles may be continuously transferred to the cold-rolling line, where they are further processed into the final product according to the above described techniques.

Examples Example 1-Aluminum alloy 1350 triangularprofile Aluminum 1350 alloy, whose composition is detailed in Table 1, was cast and formed into a triangular profile using the methods of the invention. Fe 0.12% si 0.08% Mg 0.004% Mn 0.001% Cr <0.001% Ti 0.010% V <0.001% B 0.007% Cu 0.001% Pb 0.001% Zn 0.004% Na 0.001% Al balance Table 1 The alloy was continuously cast into a trapezoidal shape with a cross-sectional area of 3600 mm2. Hot rolling was then carried out at a temperature of 520 °C, to give <BR> <BR> the rod a round cross-sectional shape, with a diameter of 18.2 mm i 40. mm. The rod was cooled to room temperature before cold rolling. Mechanical properties of one length of hot-rolled rod were determined experimentally; the rod had an ultimate

tensile strength (UTS) of 91 N/mm2, and an elongation of 18%. Vickers hardness was 25-30.

The rod was then cold-rolled to achieve the triangula profile depicted in Figure 7. The final profile had a height of 12.460 mm and a width of 16.401 mm, with a dimensional tolerance of 0.001 mm. The cross-sectional area was 142.8 mm2.

Mechanical testing of the profile gave a UTS of 128 N/mm2, and an elongation of 6%. Vickers hardness of the profile was 39-47.

Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein.

It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

What is claimed is: