Refurbishing continuous casting moulds (figure 1) made of silver-alloyed copper or chromium-zirconium-alloyed copper by coating, preferably with nickel, is state-of-the-art technology today. This technique not only improves the surface quality of the cast slabs but - what may be even more important - also reduces the running costs for moulds as a result of the extended mould life. However, this technique has not been there for ever. Actually, Evertz was the first company in the world to succeed in electroplating nickel onto copper plates, in the downstream hot mill had become obsolete. Additionally, it was soon recognized that electroplating also resulted in a significant increase in the working life of the mould plates. Initially, manufacturers (OEMs) of copper mould plates had massively opposed the new coating technology since they feared losing revenues and market shares. But this resistance tumed out to be unsustainable. Steel mill operators soon recognized that galvanic plating of copper mould plates provided extremely positive and benefical effects. initially for the mould of a single-strand circular-arc slab caster in Germany, back in the mid-1970s. This measure led to a significant improvement in the surface quality of the continuously cast slabs. So called star cracks, which previous- Egon Evertz KG, Solingen, Germany ly had occurred in certain steel grades, became a thing of the past. Removal of Conta scarfing effort - prior to rolling the slabs In the early 1980s, following the initial success, Evertz developed a onepiece mould made up of electrodeposited layers, mainly for use in billet casters. The mould is either made entirely of copper or has an additional inner nickel coating, which increases the mould life by reducing damage caused by the dummy bar. The respective European Patent No. 0125509 was applied for on Apri113, 1984, published on November 21, 1984 and finally granted on September 9, 1987. This is just one of over 30 patents held by the Evertz Group for inventions associated with continuous casting technology, primarily casting moulds. Since, Evertz has established two refurbishing centres for copper moulds, one in Langenfeld, Germany, and one in Middletown, Ohio, USA. The latter is operated by Evertz Technology Service - a subsidiary of the Evertz Group. lt is equipped with three ten-axes Klopp CNC milling machines and has recently made another technological breakthrough: After intermediate machining (repair) in the mechanical workshop, a full face nickel re-coated mould was put back into service, reaching a record service life of 544 heats in the thin slab caster of the Flat Roll Division of Steel Dynamics, Inc. in Butler, Indiana, USA. Furthermore, a new service life record of 627 heats has been reached by using a coated mould in a thin slab caster of Nucor Crawfordsville, Indiana. Previously, mould plates used to be repaired mechanically on milling machines several times during their life time to remove the cracks created during casting. Each time during this procedure, copper material is being removed, leading to the plate becoming thinner and thinner. The procedure can be repeated several times, but only until a critical thickness of the mould has been reached. At that point, the plate must be scrapped. A few years ago, Evertz further developed the above described technology of electrodepositing coating layers onto a one-piece tube mould and used it for copper-onto-copper electroplating of base plates for slab moulds. This technique fully compensates the thickness reduction of the plate resulting from machining, leading to a significant increase in plate life time and the associated cost reductions. The mould plate lives much longer before the plate finally has to be scrapped. Actually, the plate is potentially everlasting. Hence, in theory, the everlasting mould was born. This newly developed copper-to-copper coating solution for slab mould plates has already been successfully used in German and North American continuous casting plants. Figure 2 shows a sample of a bending test of such an electroplated copper layer including a nickel coating as the basis for the everlasting mould.
MPT-International (Metallurgical Plant and Technology) October 2013
