ISSN 1068-798X, Russian Engineering Research, 2008, Vol. 28, No. 1, pp. 20–22. © Allerton Press, Inc., 2008. Original Russian Text © N.B. Abramova, 2008, published in Vestnik Mashinostroeniya, 2008, No. 1, pp. 23–24.

Manufacture of Mold Sleeves for Continuous-Casting Machines N. B. Abramova Orsk State Technical Institute DOI: 10.3103/S1068798X08010061

Economic progress demands more efficient production processes. However, the manufacture of mold sleeves for continuous-casting machines is characterized by low labor productivity, high cost, considerable expenditure of materials, and poor product quality. For decades now, the technological level of ferrous metallurgy has been judged in terms of the efficiency of continuous casting [1]. The mold is the key component of continuous-casting machines. The ingot is formed in the mold; as the metal solidifies, heat is transmitted through the mold; the product quality and casting productivity depend on the mold quality. In continuouscasting machines, the mold operates at temperatures of 293–863 K, in the presence of intense cyclic heat fluxes (heat-flux density up to 20 MW/m2), intense wear, cyclic thermodynamic stress, and corrosion. The working life of the mold is less than that of the other replaceable components. Mold malfunctions leads to production problems and shutdown, with a negative impact on the environment and on worker safety. Molds in which the working element is a sleeve are most widely used. The main benefits of sleeve-type molds are as follows: (1) the absence of junctions in the sleeve, which reduces snagging of the ingot casing; (2) rapid heat transfer, which permits faster casting of steel; (3) easy sleeve replacement. The sleeve requires a unique combination of chemical, thermophysical, physicomechanical, and other properties. Sleeve production is a complex technological problem. Many different processes are used for the manufacture of sleeve-type molds. Mold production in which the sleeve wall is soldered to the mold housing is of interest. The wall material must have higher oxygen affinity than the housing material [2]. A shortcoming of this method is that the strength of the wall–housing bond is low. Another approach is to use a chemically active liquid to form the wall. The liquid eats away the mold metal; the volume of metal removed is controlled by changing the liquid level relative to the mold [3]. This technology is effective for alloys with little inclination to form a passivating (and corrosion-inhibiting) film at the surface. It is environmentally hazardous.

Konkast has developed an explosive method of attaching the sleeve wall to the mold housing [4]. In the USA, the production of copper sleeves by welding the wall and housing has been developed [5]. This weld joint is the weak spot of the mold. Operational experience with molds of different design shows that molds with an integrated sleeve are most reliable. Leading non-Russian companies have introduced the production of sleeve-type molds of different shape and cross section. In particular, KM-Kabelmetal (Germany), a leading European manufacturer of such molds, produces round, square, rectangular, hexagonal, octagonal, and round profiles, as seen in the figure. In Russia, only molds of square and rectangular profile are produced, as summarized in the table. Sleeve-type molds are produced from rolled and drawn pipe of wall thickness >40 mm, length <300 mm, and diameter no more than 128 mm. For large molds, the use of thick-walled pipe is economically inexpedient, since less than 40% of the metal is utilized [1]. The manufacturing technology for the mold blanks significantly affects their physicomechanical properties. Cast copper has a large-grain structure. Under the Blanks for Mold Sleeves Blank Plate: hot-rolled with cut edge cold-rolled with cut edge hot-rolled with uncut edge cold-rolled with uncut edge Ingot: with uncut edge with cut edge Pipe: cold-rolled hot-rolled hot-drawn pressed 20

Material M2R, M1R M2R, MS (Ag), Cu + Cr + Zr Cu + Ag M2R, MS (Ag) M2R M1R M2R M1R M1F M1F

MANUFACTURE OF MOLD SLEEVES FOR CONTINUOUS-CASTING MACHINES

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(b)

(a)

(c)

(d)

(e)

KM-Kabelmetal bar molds: (a) round, square, and octagonal profile; (b, c) rectangular profile; (d, e) rail profile.

action of thermal stress, with a weak bond between the large grains, cracks form along the grain boundaries, even under relative small mechanical stress. The quality and productivity of the process may be improved by pressing (extension coefficient 4–6) the cast blank prior to reduction. The degree of deformation in reduction is 60–90%, and deformation rates of 250–1500 mm/min are employed in bulk stamping at 823–1063 K [6]. The quality of copper alloys may be increased by thermomechanical treatment, including quenching, deformation, aging, and repeated deformation with 50– 90% reduction [7]. According to the technology patented in the USA, the mold sleeve is made of copper alloy subjected to 15–40% cold deformation. The thermal conductivity of the alloy is 40–75% of that for pure copper. Besides copper, the alloy components are 0.18–0.4% Sn, RUSSIAN ENGINEERING RESEARCH

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0−0.22% Mg, 0.3–0.7% Si, 0.45–0.25% Ni, 0.02– 015% Li, and 0.02–0.15% Ag [8]. Analysis of literature data shows that there has been virtually no Russian research into the manufacture of sleeve-type molds from cast blanks. The forged sleeves for continuous-casting machines in operation at various Russian plants, such as Orsk Nonferrous-Metal Treatment Plant, are made in the USA. The life of these sleeves is 3–4 times that of Russian sleeves. The blank employed is a one-piece pipe of wall thickness 100 mm. Russian specialists remain unfamiliar with the manufacturing technology for mold sleeves employed in the United States. Given the lack of information on the manufacture of mold sleeves by non-Russian manufacturers, we need to create analogous processes manufacturing competitive products in Russia. There has been intensive development of the mold system (its design, the material, the surface coating, and 2008

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the operating conditions). Refinement of the geometry and internal lining of the mold cavity will ultimately improve the casting rate and product quality. The main approach to improving mold sleeves is to optimize the shape and design of the working components and to organize the external factors on the cast metal (the ingot-cooling rate, the amplitude of mold oscillation, etc.) so as to increase product quality, intensify the thermal processes, and improve the overall economic performance [4]. The factors shaping improvements in sleeve design and manufacture are as follows: (1) the need for constant adjustment of the range of cast steels in accordance with customer requirements and market conditions; (2) the need to modernize existing continuous-casting machines, so that they remain competitive; (3) the need to design the mold so as to compensate for various properties of the steel and alloys, such as shrinkage. Coating the working surface of the sleeve with special materials extends its life and improves the quality of the cast steel. Nickel coatings of various thicknesses are widely used, and chrome coatings are sometimes employed. It is less common to use multilayer coatings, coatings in individual zones, or sprayed metal coatings. The coatings may be made of chromium, nickel, cobalt, graphite, fluorocarbon resin, and aluminum dioxide on a nickel–iron substrate. Europa Metall I-LMI has extended the life of mold sleeves from 1000 to 2000 melts by applying a preliminary nickel coating (thickness 1–2 mm) and a final chrome coating (thickness 0.05 mm) to the internal surface of the mold. For melts with a high heat flux, the nickel coating is of thickness 1 mm at the beginning of the sleeve and 2 mm at the end, in order to reduce the ingot–sleeve friction. Experiments with tungsten carbide, chromium carbide, and mixed nickel and chromium carbides have proven successful. In many cases, the internal surface of the mold is made from metal– ceramic alloy, with an external layer of copper. A promising approach to increasing the effectiveness of heat transfer is to apply relief in the form of a regular system of spherical craters to the external mold surface. Research shows that the heat-transfer coefficient is increased here by 60–80% relative to a smooth

surface. This is better than for methods based on surfaces with artificial roughness. The presence of fins at the external mold surface increases the heat transfer. The design and manufacture of finned molds has been developed at the ORMETO-YuUMZ plant, Analysis of the manufacturing technology, design, and operational characteristics of molds shows that the most reliable include a casing in the form of a copper sleeve made by bulk stamping. CONCLUSIONS The design and operational characteristics of the mold largely determine the performance of continuouscasting machines. The cost of the final product depends on the working life of the mold. The factors determining the mold life are its material and the manufacturing technology. Sleeves made from copper alloys with 0.08–0.12% Ag and 0.06–0.012% P are highly competitive. However, Russian manufacturers do not produce thickwalled pipe made from alloys that contain silver. Analysis of possible alternatives shows that the most promising approaching is to manufacture the molds from cast blanks by bulk stamping. At the ORMETO-YuUMZ plant (Orsk), an experimental batch of molds has been manufactured from oxygen-free copper produced in an ELP-30 electronbeam furnace. Research shows that the physicomechanical properties of the blank are high. In particular, the hardness of forged pipe is 20% higher than for rolled pipe, with corresponding increase in the moldís working life. This technology has been patented. REFERENCES 1. Parshin, V.M., Casting and Rolling Complexes for Competitive Manufacturing, Stal’, 1999, no. 6, pp. 26–28. 2. Japanese Patent 21093. 3. British Patent 1035843. 4. Gankin, V.B., Sivak, B.A., Nikolaev, G.I., et al., SleeveType Molds of High-Speed Continuous Bar-Casting Machines, Tyazh. Mashinostr., 1997, no. 5, pp. 19–22. 5. US Patent 3646799. 6. USSR Inventorís Certificate 749931. 7. USSR Inventorís Certificate 357263. 8. US Patent 3988176.

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