Title of Invention

CASTING ROLLER FOR A DOUBLE ROLL CASTING PLANT

Abstract

A casting roller for a double roll casting plant that is subjected to temperature variations/fluctuations and high rolling pressures for the casting of strips close to the final dimensions, has a casing of an age-hardenable copper alloy comprising of - 0.4% to 2% by weight of cobalt, which can be partially replaced by nickel, 0.1% to 0.5% by weight of beryllium ; 0.03% to 0.5% by weight of ziroconium ; 0.005% to 0.1% by weight of magesium ; and, if necessary, maximum upto 0.15% by weight of at least one element selected from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest being copper, including impurities usually associated with the production and the processing of the alloys.

Full Text

The invention concerns a cast roller for a double roll casting plant. The universal goal, especially of the steel industry, is to cast wrought products as closely as possible to final dimensions, in order to economise on the hot and/or cold forming steps, has lead since about 1980 to a series of developments, for example in one- and two-roll continuous casting method. During these casting methods, very high surface temperatures arise on the water-cooled cylinders or rolls for the casting of alloy steels, nickel, copper as well as alloys, which can be hot rolled only with difficulty, in the casting-in zone of the melt. These lie, for example for the casting of an alloy steel close to the final dimensions, at 350 °C to 450 °C, in which the cast rolling casing is of a CuCrZr-material with an electrical conductivity of 48 Sm/mm2 and caloric conductivity of approximately 320 W/mK. Materials based on CuCrZr were previously used primarily for thermally high demanding continuously cast ingot moulds and casting wheels. The surface temperature is reduced to about 150 °C to 200 °C just before the casting-in zone for these materials by the cooling of the cast rollers cyclically for each rotation. On the other hand, it remains to a large extent constant at about 30 °C to 40 °C on the cooled rear side of the cast rollers during the rotation. The temperature gradient between the surface and the rear side in combination with the cyclical alteration of the surface temperature of the cast rollers cause thermal stresses in the surface area of the casing material. According to investigations of the fatigue behaviour on the previously used CuCrZr-material at different temperatures with a strain amplitude of ± 0.3 % and a frequency of 0.5 Hertz - these parameters correspond approximately to the rotational speed of the cast rollers of 30 RPM -, under most favourable conditions a life of 3000 cycles can be expected 2 before the formation of cracks for a maximum surface temperature, for example, of 400 °C, corresponding to a wall thickness of 25 mm above the water-cooling. Therefore, the cast rollers have to be reworked even after a relatively short operation time of about 100 minutes, for the purpose of remedying the surface cracks. Moreover, the life between the reworks is essentially dependent, among others, on the effectiveness of the lubricant/stripping agent at the casting surfaces, the constructional and process-required cooling as well as the casting rate. The casting machine must be stopped and the casting cycle interrupted for changing the cast rollers. A further disadvantage of the field-proven CuCrZr ingot mould material is the relatively low hardness of about 110 HBW to 130 HBW. But it is not possible to avoid the splashes from reaching the roller surface before the casting-in region in the case of a one- or two-roller continuous casting process. Then, the solidified steel particles are pressed into the relatively soft surfaces of the cast rollers, whereby the surface quality of the cast strips is considerably affected from about 1.5 mm to 4 mm thickness. Also, the lower electrical conductivity of a standard CuNiBe-alloy with an addition of up to 1 % niobium leads to a higher surface temperature in comparison to a CuCrZr-alloy. Since the electrical conductivity is approximately proportional to the caloric conductivity, the surface temperature in the casing of a cast roller made from CuNiBe-alloy is raised to about 540 °C in comparison to a cast roller with a casing of CuCrZr with a maximum temperature of 400 °C at the surface and 30 °C on the rear side. Although ternary CuNiBe- or CuCoBe-alloys have basically a Brinell hardness of above 200 HBW, however the electrical conductivity of the 3 standard wrought products out of these materials, like for example rods for the production of resistance welding electrodes or plates and strips for the production of springs or lead frames, reach at the most values lying in the range of 26 Sm/mm2 to about 32 Sm/mm2. Under optimum conditions, only a surface temperature of about 585 °C would be attained on the casing of a cast roller with these standard materials. Also, there are no indications that conductivity values of > 38 Sm/mm2 can be attained in combination with a minimum hardness of 200 HBW with the targeted selection of the alloy components for the CuCoBeZr-or CuNiBeZr-alloys, as fundamentally known from the US-patent Further, the use of an age-hardenable copper alloy consisting of 1.0 % to 2.6 % nickel that can be partially or totally replaced by cobalt, 0.1 % to 0.45 % beryllium, 0.05 % to 0.25 % zirconium as desired and, if necessary, maximum 0.15 % of at least one element from the group consisting of niobium, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest copper, including impurities associated with the production and the usual processing alloys, with a Brinell hardness of minimum 200 HBW and an electrical conductivity above 38 Sm/mm2 as material for the production of cast rollers and casting wheels is considered within the scope of EP 0 548 36 Bl, as per the state-of-art technology. Alloys with these compositions, like for example the alloys CuCo2Be0.5 or CuNi2Be0.5, have disadvantages of hot formability due to the relatively high alloying element contents. However, high degree of hot forming are necessary to achieve a fine-grained product with a grain size 4 large cast ingots of desired quality could be produced at very high expenditure, especially for large sized cast rollers; however hardly any industrial forming equipments are available to carry out a sufficiently high hot kneading for the re-crystallisation of the cast structure to a fine-grained structure with reasonable expenditure. The invention is based upon the task - starting from the state-of-the-art technology - to produce a cast roller as component of a double roll casting plant, which can be exposed readily to temperature variations/fluctuations and high rolling pressures for a long time for the casting of strips close to the final dimensions from nonferrous metals. The instant invention solves the task by providing a casing of an age-hardenable copper alloy of a defined composition on the casting roller for a double roll casting plant that is subjected to temperature variations and high roller pressure for the casting of strips close to the final dimension. The instant invention provides a casting roller for a double roll casting plant that is subjected to temperature variations/fluctuations and high rolling pressures for the casting of strips close to the final dimensions, wherein said roller has a casing of an age-hardenable copper alloy comprising of - 0.4% to 2% by weight of cobalt, which can be partially replaced by nickel ; 0.1% to 0.5% by weight of beryllium ; 0.03% to 0.5% by weight of ziroconium ; 0.005% to 0.1% by weight of magesium ; and, if necessary, maximum upto 0.15% by weight of at least one element selected from the group 5 consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest being copper, including impurities usually associated with the production and the processing of the alloys. On the one hand, a still sufficient hardenability of the material is ensured for the attainment of a higher strength, hardness and conductivity by the use of a CuCoBeZr (Mg)-alloy with an already mentioned low graded Co- and Be-content. On the other hand, only low degrees of hot forming are required for the complete re-crystallization of the cast structure and conversion to a fine-grained structure with sufficient plasticity. Thanks to a cast roller of this type produced as component of a double roll casting plant, it is possible to increase the speed for casting of a strip from a nonferrous metal, especially out of aluminium or an aluminium alloy, by more than double as against that of a roller arrangement equipped with unalloyed steel jackets. Besides, a markedly improved surface quality of the cast strip is achieved. A considerably longer life of the mould is also ensured. The cast roller can be formed as a hollow cylinder; that is, inherently rigid without core. The surface coming in contact with the casting strips can nevertheless also be component of a casing with a core, especially a steel core. Then the casing can be shrunk on such a core as a carrier, HiP-processed, or mounted and then mechanically clamped. 6 Further it can be thought of that, for the use of a casing, this can be formed as single- or multi-layered. The enveloping surface of the cast roller can be cylindrical or be designed with a bomb-shape in order to compensate bending due to rolling, if necessary. A further improvement of the mechanical properties of the mould, especially an increase of the tensile strength, can be achieved advantageously by the cooper alloy containing 0.03 % to 0.35 % zirconium and 0.005 % to 0.05 % magnesium. According to a further embodiment, the copper alloy contains a proportion of It is further advantageous if the ratio of cobalt to beryllium lies between 2 and 15 in the copper alloy of the casing. Especially, this ratio of cobalt to beryllium amounts to 2.2 to 5. As per the invention it is permissible to have copper alloy containing up to 0.6 % nickel, besides cobalt. Further improvements of the mechanical properties of the mould can be achieved if, the copper alloy contains up to maximum 0.15 % of at least one element from the group comprising niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. The mould is produced advantageously through the processing steps of casting, hot forming, solution annealing at 850 °C to 980 °C, cold forming up to 30 % as well as hardening at 400 °C to 550 °C within a period of 2 to 32 h, whereby it has a maximum average grain size of 1.5 mm as per ASTM E 112, a hardness of minimum 170 HBW and an electrical conductivity of minimum 26 Sm/mm2. It is especially advantageous if the mould, exhibits in the hardened condition an average grain size of 30 µm to 500 µm as per ASTM E 112, 7 a hardness of minimum 185 HBW, a conductivity between 30 and 36 Sm/mm2, a 0.2 % proof stress of minimum 450 Mpa and a breaking elongation of minimum 12 %. If the casing is provided with a coaling, which reduces the diathermancy or equalises the heat flow, the product-quality of the strip cast out of a nonferrous metal, however especially out of aluminium or an aluminium alloy, can be improved still further. The coating, selected on the basis of the operational behaviour of the casing out of a copper alloy with especially an aluminium strip, is formed as follows. An adhesion layer is formed at the beginning of a casting and rolling process from the combination of copper with aluminium on the surface of the casing, then aluminium penetrates into the copper surface during the further course of the casting process and forms a stable, robust diffusion layer there, whose thickness and property are essentially determined by the casting rate and cooling conditions. This improves the surface quality of the aluminium strip and consequently the product quality is markedly improved. The life of the casing can be increased still further by providing it with a diathermancy reducing coating having high surface hardness. The surface of the cast roller can be made smooth. This finish can be achieved especially by rolling. By this, compressive stresses are induced in the shell, which enable an additional resistance against crack formation and crack progress to increase the life of the cast roller. Further the surface of the cast roller can be textured. A texturing can occur for example by machining, rumbling, erosion or sandblasting. 8 These types of measures can purposefully influence the heat transfer coefficient. Finally, a material with a lower calorific conductivity compared to the calorific conductivity of copper can be embedded in the recesses formed by the texturing. A material of that type can, besides a metallic material- especially nickel or a nickel alloy, also be a ceramic material. Such a type of filling of the recesses formed by a texturing in the surface of the cast roller results in creation of a good surface quality and thus ensuring an enduring influence on the calorific conductivity. The invention is explained in detail below. Based on the seven alloys for the casing of a cast roller (alloys A to G) and three alloys for comparison (H to J), it is shown how critical the composition is to achieve the desired combination of properties. All alloys were molten in a crucible furnace and cast into round ingots of same form. The composition in percentage by weight is given in the following Table 1. The addition of magnesium serves for the pre-deoxidation of the melt and the zirconium addition operates positively on the hot-plasticity. Table 1 Alloy Co (%) Ni (%) Be (%) Zr (%) Mg (%) Cu (%) A 0.68 0.20 0.20 0.03 Rest B 1.0 0.22 0.22 0.03 Rest C 1.4 0.20 0.18 0.02 Rest D 0.65 0.29 0.21 0.04 Rest 9 E 1.0 - 0.31 0.24 0.01 Rest F 1.4 - 0.28 0.29 0.03 Rest G 1.0 0.1 0.22 0.16 0.03 Rest H - 1.7 0.27 0.16 - Rest I 2.1 - 0.55 0.24 - Rest J - 1.4 0.54 0.20 - Rest The alloys were subsequently pressed to flat bars with a low pressing ratio (= cross-section of the ingots / cross-section of the pressing bar) of 5.6:1 on an extruder at 950 °C. Thereafter, the alloys were subject to a minimum 30 minute solution heat treatment above 850 °C followed by a water quenching and subsequently hardened for 4 to 32 h in the temperature range between 400 °C and 550 °C. The combinations of properties shown in the Table 2 below were achieved. Table 2 Alloy Rm Mpa Rpo.2 Mpa A% HBW 2.5 187.5 el. cond. Sm/mm2 Grain size mm A 694 492 21 207 36.8 0.09-0.025 B 675 486 18 207 32.8 0.09-0.018 C 651 495 18 211 30.0 0.045-0.013 D 707 501 19 207 31.4 0.09-0.025 E 735 505 19 229 33.6 0.045-0.018 F 735 520 19 224 32.3 0.09-0.025 G 696 513 18 213 33.5 0.065-0.018 10 H 688 556 10 202 41.0 2-3 I 784 541 11 229 30.3 1.5-3 J 645 510 4 198 30.9 4-6 Rm = Tensile strength Rp0.2 = 0.2 % proof stress A = Breaking elongation HBW = Brinell hardness As can be seen from the combination of properties, the alloys as per the invention achieve, especially for the production of a casing of a cast roller, the re-crystallised fine-grained structure with the relevant desired high breaking elongation. The reference alloys H to J have a grain size of over 1.5 mm, because of which the plasticity of the material is reduced. An additional increase in strength can be achieved by cold forming before hardening. In the following Table 3, combination of properties are again given for the alloys A to J, which are attained by solution heat treatment of the pressed material for minimum 30 minutes at above 850 °C followed by water quenching, 10 % to 15 % cold rolling (cross sectional reduction) and finally hardening for 2 to 32 hours in the temperature range between 400 °C and 550 °C. 11 Table 3 Alloy Rm Mpa Rp0.2Mpa A% HBW 2.5 187.5 el. cond. Sm/mm2 Grain size mm A 688 532 20 211 36.7 0.13-0.025 B 679 534 18 207 34.6 0.045-0.018 C 741 600 17 227 34.4 0.065-0.018 D 690 537 21 207 32.6 0.065-0.025 E 735 576 19 230 34.7 0.045-0.018 F 741 600 17 227 34.4 0.13-0.025 G 695 591 15 224 33.0 0.18-0.035 H 751 689 9 202 40.9 2-4 I 836 712 10 229 31.0 2-3 J 726 651 6 198 31.5 3-6 The alloys A to G as per the invention once again show higher breakage elongation and a grain size below 0.5 mm, while the reference alloys H to J have a coarse grain with a grain size above 1.5 mm and lower breakage elongation values. Consequently, these copper alloys have definite processing advantages for the production of casings, especially for larger cast rollers of double roll casting plants, whereby it is possible to produce a fine-grained end product with optimum basic properties for the range of application. 12 WE CLAIM : 1. A casting roller for a double roll casting plant that is subjected to temperature variations/fluctuations and high rolling pressures for the casting of strips close to the final dimensions, wherein said roller has a casing of an age-hardenable copper alloy comprising of - 0.4% to 2% by weight of cobalt, which can be partially replaced by nickel; 0.1% to 0.5% by weight of beryllium ; 0.03% to 0.5% by weight of ziroconium ; 0.005% to 0.1% by weight of magesium ; and, if necessary, maximum upto 0.15% by weight of at least one element selected from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest being copper, including impurities usually associated with the production and the processing of the alloys. 2. Casting roller as claimed in claim 1, wherein the copper alloy contains 0.03% to 0.35% zirconium and 0.005% to 0.05% magnesium. 3. Casting roller as claimed in claim 1 or 2, wherein the copper alloy contains less than 1.0% cobalt, 0.15% to 0.3% beryllium and 0.15% to 0.3% zirconium. 4. Casting roller as claimed in claim 1 or 3, wherein the ratio of cobalt to beryllium in the copper alloy amounts to between 2 and 15. 13 5. Casting roller as claimed in claim 4, wherein the ratio of cobalt to beryllium in the copper alloy amounts to between 2.2 and 5. 6. Casting roller as claimed in any one of claims 1 to 5, wherein the copper alloy contains, besides cobalt, upto 0.6% nickel. 7. Casting roller as claimed in any one of claims 1 to 6, wherein the copper alloy contains maximum up to 0.15% of at least one element selected from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. 8. Casting roller as claimed in any one of claims 1 to 7, wherein the casing is produced by the steps of casting hot forming, solution heat treatment at 850°C to 980°C, cold forming up to 30% as well as hardening at 400°C to 550°C within a period of 4 to 32 hours and has a maximum average grain size of 1.5 mm as per ASTM E 112, a hardness of minimum 170 HBW and an electrical conductivity of minimum 26 Sm/mm2 9. Casting roller as claimed in claim 8, wherein the casting exhibits in the hardened condition, an average grain size of 30 urn to 500 urn as per ASTM E 112, a hardness of minimum 185 HBW, a conductivity of between 30 and 36 Sm/mm2, a 0.2 % proof stress of minimum 450 Mpa and a breaking elongation of minimum 12%. 14 10. Casting roller as claimed in any one of claims 1 to 9, wherein the casing is provided with a diathermancy reducing coating, such as herein described. 11. Casting roller as claimed in claim 10, wherein the coating has a high surface hardness such as herein described. 12. Casting roller as claimed in any one of claims 1 to 11, wherein the surface comprises a smooth surface. 13. Casting roller as claimed in any one of claims 1 to 11, wherein the surface comprises a texturised surface. 14. Casting roller as claimed in claim 13, wherein a material with a lower thermal conductivity compared to the thermal conductivity of copper is embedded in the recesses formed by the texturing. 15 -16- 15. A casting roller for a double roll casting plant, substantially as herein described and as illustrated in the foregoing examples.

Documents:

00603-cal-2002-abstract.pdf

00603-cal-2002-claims.pdf

00603-cal-2002-correspondence-1.pdf

00603-cal-2002-correspondence-2.pdf

00603-cal-2002-description(complete).pdf

00603-cal-2002-form-1.pdf

00603-cal-2002-form-19.pdf

00603-cal-2002-form-2.pdf

00603-cal-2002-form-3.pdf

00603-cal-2002-form-5.pdf

00603-cal-2002-gpa.pdf

00603-cal-2002-letters patent.pdf

00603-cal-2002-priority document.pdf

603-cal-2002-granted-abstract.pdf

603-cal-2002-granted-acceptance publication.pdf

603-cal-2002-granted-claims.pdf

603-cal-2002-granted-correspondence.pdf

603-cal-2002-granted-description (complete).pdf

603-cal-2002-granted-form 1.pdf

603-cal-2002-granted-form 19.pdf

603-cal-2002-granted-form 2.pdf

603-cal-2002-granted-form 3.pdf

603-cal-2002-granted-form 5.pdf

603-cal-2002-granted-gpa.pdf

603-cal-2002-granted-letter patent.pdf

603-cal-2002-granted-priority document.pdf

603-cal-2002-granted-reply to examination report.pdf

603-cal-2002-granted-specification.pdf

603-cal-2002-granted-translated copy of priority document.pdf