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Mould plate coatings for the 21st centuryThe ceramic coating of slab caster moulds is realising significant benefits in terms of mould life, cast product shape and caster operating costs. It is now standard practice within Corus and is being trialled extensively worldwide. Similar benefits are now being seen on bloom machines, and trials are currently underway on a billet caster.

Corus Process Engineering (CPE) is heavily involved in the continuous casting plant enhancement,

development and refurbishment business worldwide, in particular the development of technologies and engineering advancements that improve the performance and operational efficiency of customers’ businesses.

Copper plate moulds in bloom, billet and slab casters have been at the forefront of the work. This paper charts the recent development and experience of coating mould plates with a ceramic material, Castcoat. It also highlights the advances made in the past two years, including extended performance and development into other applications of the coating. Corus was the first to utilise Castcoat and has been at the forefront of establishing the coating as a standard application to all its slab moulds. The following describes current Corus experience and highlights the growing use of the coating worldwide.

CASTCOAT TECHNOLOGYCastcoat is a hard ceramic coating that has been developed for use in steel industry applications, in particular for coating continuous caster copper mould plates. The background and history of mould copper plate technology and the development of coatings for them is well documented [1], including their application to all four faces of the mould, which is now commonplace. It is applied using a

Authors: Brian Stalker, Kevin Goode, David Preshaw and Charles M KayCorus Process Engineering and ASB Industries Inc

r Fig 1 Thermal spray coating

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conventional thermal spray coating process (see Figure 1). Early tests showed the coating had a low coefficient of friction, is inert to liquid steel and casting powders and has a negligible effect on mould heat transfer. Significant life improvements were achieved, accompanied by improved product shape. In operation the coating has been shown to achieve virtually zero wear. Initial trials were on the narrow face plates but, once proven, the same technology was applied to the broad faces and now these fully coated moulds are very common.

CORUS SLAB CASTER EXPERIENCETeesside Cast Products, UK Castcoat trials began at Teesside in 2001. In service, the ceramic coated slab mould life was, during the early trials, twice that of the conventional copper mould at 300,000t of steel cast. During this time little mould wear was evident and no detrimental effects were observed. Those early successes have now been translated into fully ceramic coated moulds being used as standard on both of Teesside’s twin-strand slab casters, a

r Fig 2 Teesside mould in mid campaign

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end, whether because of breakout or overcooling of the mould surface at the end of cast. By and large these minor defects do not affect the coating’s performance or that of the mould and the product produced, and can be left unattended and monitored between campaigns. Where these defects are substantial, and/or are in an area near to the meniscus, it may be necessary to effect a mid-campaign repair. CPE has, as a result, perfected a simple repair technique by specialist welding during a planned stoppage that has proved very successful and allowed the plates to achieve their full through-life potential, examples of which can be seen in Figure 5.

Strip Products, Ijmuiden, The Netherlands Several moulds have been equipped with Castcoat, including both broad and narrow faces, and one pair of narrow faces has achieved 895,000t of steel cast. This is, we believe, a

and since that time the service life has been increased to an aim removal time of 350,000t.

Figure 2 shows a Teesside mould in mid-campaign; Figure 3 is a composite picture of the variable side mould plate at the end of its useful life and prior to re-coating. It is interesting to note that the fixed side mould plate (see Figure 4) is in a much superior condition and could almost certainly go back into service. Matching a newly coated plate with a mid-campaign plate and the balancing implications is something that is under discussion, as it could further extend the mould plate through-life cost benefit. Even without developing such replacement techniques, the savings in mould maintenance costs alone are approaching 15%.

During operation minor mechanical damage does occur to the ceramic coating as a result of several factors, including dummy bar packing and/or while extracting a cold strand

r Fig 3 Variable side mould plate ready for strip and re-coating

r Fig 4 Fixed side mould plate ready for strip and re-coating

r Fig 5 Broad face plate repairs

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world record for a ceramic coated narrow face mould plate (see Figures 6 & 7).

These plates are still operational and so are establishing new records with every cast. Based on the performances achieved, Castcoat has been specified as the mould plate coating on the new moulds being supplied as part of the enhancement of Strip Products’ CGM21 caster from a curved to vertical-with-bending machine.

Strip Products, Port Talbot, UK By using Castcoat it has been possible to replace the CuCrZr base material with plain CuAg, achieving net savings in annual copper costs of 30%.

CORUS SLAB CASTER SUMMARYCastcoat is now the standard slab mould plate coating on all four mould faces at Corus. Table 1 lists the applications and typical life improvements achieved.

SLAB CASTER APPLICATIONS WORLDWIDEStainless steel casters The use of Castcoat has typically shown a 6-10 times improvement in mould service life over CuCrZn copper plates. This step change has not only

created increased caster availability and reduced mould maintenance costs, but has also resulted in improvements in surface quality on selected grades that were particularly susceptible to off-corner wide side cracks that had to be stripe scarfed. The level of scarfing has reduce dramatically and is thought to be as a result of the improved integrity and management of narrow face taper, with little or no wear occurring on the narrow faces.

Thin slab casters Early success was achieved with Castcoat applied to the narrow faces of thin slab caster moulds, particularly in North America, leading to significant increases in narrow plate lives. It is now also firmly established as a practical alternative on thin slab caster broad face plates. This now applies to funnel shaped moulds that are being trialled.

CPE supplies to several North American customers and has a USA coating base which allows an improved service to be provided. This facility became fully operational in 2006 and confirms North America as a world leader in the use of such technologies. Figure 8 shows a newly coated thin slab caster broad face mould plate.

Growth markets, such as Russia and Eastern Europe,

Plant life Mould operational Maximum mould life (tonnes) life improvementTeesside No.1 > 350,000 x 4Teesside No.2 > 350,000 x 4Port Talbot No.1 > 230,000 x 2.5Port Talbot No.2 > 150,000 x 2Port Talbot No.3 Narrow face only –Scunthorpe No.1 New installation –Ijmuiden DSP New installation –Ijmuiden CGM 21 narrow face > 620,000 x 3 Ijmuiden CGM 21 complete mould > 440,000 x 2 Ijmuiden CGM 21 vertical New installation

r Table 1 Castcoat slab caster applications at Corus

r Fig 6 Corus Ijmuiden narrow face plate after 438kt r Fig 7 Corus Ijmuiden narrow face plate after >500kt

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Bloom casters Corus Engineering Steels’ Aldwarke, UK plant operates a twin-strand large bloom caster (560 x 400mm). All four faces of a mould were coated with Castcoat and, following several months of operation, it is now in the final stages of evaluation. At the time of writing the mould had achieved 80,000t of steel cast – already three times Aldwarke’s previous best – and even though the trial mould operation is ongoing, Aldwarke is already convinced of its suitability and benefit to its operation and have ordered the whole mould fleet to be coated with Castcoat (see Figures 9 & 10).

In addition to the benefits of increased mould life and caster availability, there have been product quality advantages resulting from minimal wear, leading to maintenance of mould plate taper for much longer periods and preventing premature mould removal.

Previously, with the conventional mould there would be a significant loss of taper after approximately 200 heats (~16,000t of steel per mould) leading to longitudinal corner cracking of the bloom. Mould taper is now sustained throughout the mould campaign. There has also been a general improvement in overall bloom surface quality that has yet to be fully evaluated and quantified.

As a result of these trials Corus Scunthorpe Works conducted a trial on its six-strand bloom machine, casting sections from 230 x 283mm up to 305 x 483mm for a variety of applications. This has achieved a life of four times the previous chrome plated mould. As a result, Scunthorpe has ordered more moulds to be Castcoated.

On large bloom machines, based on conventionally designed plate type moulds, standard coating application methods can be used. This is not the case on smaller tube type moulds, but it is expected that the financial equipment savings generated by adopting tube moulds may well be negated by using a plate type mould with Castcoat, leading to annual mould cost savings.

r Fig 8 Example of a newly coated thin slab caster mould plate r Fig 9 Corus Aldwarke bloom mould after first

campaign

r Fig 10 Aldwarke mould after first campaign

are also embracing Castcoat in their desire to be cost and quality competitive. Table 2 indicates an up-to-date reference list of Castcoat users.

CONTINUOUS DEVELOPMENTSlab casters Continual evaluation of Castcoat and customers’ developing needs has led to the trialling of various formulations of the coating and methods of application. For instance, Castcoat 2 was developed and is now standard within Corus, which tailors the coating thickness to suit the actual mould wear pattern.

The driver behind the development was the requirement to coat a mould central divider on the Port Talbot Works Jumbo/combination slab caster. The mould divider is inserted into the mould to cast twin narrow slabs and is water cooled, but with a fixed taper that does not change with slab width. This imposes significant loads on the lower half of the divider in certain width ranges, leading to accelerated wear and the need to prematurely remove the mould to change a divider. The use of Castcoat has allowed the mould to remain in service up to three times longer than with a conventional CuCrZn copper divider.

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ACKNOWLEDGEMENTSThe authors would like to thank the Castcoat Users’ Forum for their help and assistance in the development and proving of the benefits of the ceramic mould. Without their contribution and sharing of plant experiences this paper would not have been possible. The authors would also like to thank the senior management of the various steel companies involved for their support and guidance, and in particular Corus Group, who has been instrumental in pushing the boundaries and extending the applications of Castcoat. MS

REFERENCE[1]B Stalker & B Allcock, ‘Improvements in Continuous Casting Mould technology – the First Fully Ceramic Coated Moulds.’ In AISTech04, USA, September 2004

Brian Stalker, Kevin Goode and David Preshaw are with Corus Process Engineering, Workington, UK; Charles M Kay is with ASB Industries Inc, Barberton, Ohio, USA.

CONTACT: brian.stalker@corusgroup.com

Billet casters This is the next mould challenge, where tube type designs are universally adopted. However, the same argument can be made for billet moulds as for smaller bloom moulds, described above, and a trial is now underway on a plate-type design 142 x 300mm billet mould at the Corus pilot plant caster at Teesside R&D Centre, UK. The benefits on billet casters could eclipse those seen on slab casters because mould tubes are viewed almost as a consumable, with a significant annual cost. Additionally, there are many more billet casters around the world than slab casters.

Mould foot rolls The first trials with coated foot rolls are underway at Corus Engineering Steel’s Aldwarke plant. A full four-roll set was installed in early 2006. Two rolls were coated with a parallel plain application and two with a diamond pattern to assist in the shedding of mould powder (see Figure 11). The results are eagerly awaited.

SUMMARYCorus Process Engineering was the first organisation to introduce ceramic coatings to caster copper moulds and has continued to lead the field in innovation and performance, bringing extended benefits to existing customers and adding new ones by tailoring the application to their specific requirements.

The need for increased mould life was the main driver, however, additional operational benefits have now been established, such as improved product quality for stainless steel producers and lowering of other operating costs. Improvements in the coating are pushing the limits for slab producers towards 0.5Mt per mould, with repair techniques underpinning those gains.

Now, applications on slab funnel moulds and bloom moulds are a reality – and a distinct possibility on billet moulds and foot rolls.

Plant Country Machine Plate type Maximum mould type life improvementPOSCO Pohang Works South Korea Thick slab Narrow faces x 2.5Arcelor Sidmar No.2 Belgium Thick slab Full mould x 2Arcelor Sidmar No.1 Belgium Thick slab Narrow faces OngoingMittal Steel Ostrava Czech Republic Thick slab Narrow faces OngoingUSS Kosice Slovakia Thick slab Narrow faces OngoingAlgoma DSP Canada Thick slab Narrow faces x 6Nucor Hertford USA Thick slab Narrow faces x 6Nucor Decatur USA Thick slab Full mould x 2Nucor Decatur USA Thick slab Narrow faces OngoingNucor Tuscaloosa USA Medium slab Narrow faces x 4.5Hadeed Saudi Arabia Thick slab Narrow faces x 3SSAB Lulea Sweden Thick slab Broad faces OngoingSeverstal Russia Thick slab Narrow faces Ongoing

r Table 2 Castcoat users worldwide

r Fig 11 Aldwarke Castcoat mould and foot rolls

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