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Continuous Casting in Steelmaking: How the Process, Equipment, and Caster Selection Work<\/strong><\/p>\n

Continuous casting is the process that transforms molten steel directly into solid billets, blooms and slabs in a single uninterrupted strand, replacing the ingot route that dominated steelmaking before the 1950s. It now represents more than 90 % of the world’s crude steel \u2014 over 500 million tonnes a year, as quantified by the University of Illinois Continuous Casting Consortium<\/a> \u2014 and defines the interface between liquid metal and every downstream rolling, forging and machining process in a modern steelmaking plant equipment<\/a> line.<\/p>\n

This guide is aimed at plant engineers, EPC procurement people and operators who are considering a new caster or retrofit; it discusses the seven-stage process, the major components, the forms of cast product, the implications against ingot casting, the materials which can be cast and a Caster Selection Matrix related to plant capacity. A brief future outlook section discusses the direction of the technology as steel moves toward decarbonisation.<\/p>\n

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Quick Specs<\/h3>\n\n\n\n\n\n\n\n\n\n\n
Process Type<\/td>\nStrand casting (continuous solidification, steady-state)<\/td>\n<\/tr>\n
Casting Speed (steel)<\/td>\n1\u20138 m\/min (billet up to 4 m\/min, slab around 1.4 m\/min)<\/td>\n<\/tr>\n
Casting Speed (aluminium DC)<\/td>\n0.03\u20130.1 m\/min<\/td>\n<\/tr>\n
Output Forms<\/td>\nBillet (<200 mm sq) \u00b7 Bloom (>200\u00d7200 mm) \u00b7 Slab (180\u2013250 \u00d7 500\u20132200 mm) \u00b7 Round (140\u2013500 mm) \u00b7 Strip (2\u20135 mm)<\/td>\n<\/tr>\n
Mold Shell at Exit<\/td>\n6\u201320 mm<\/td>\n<\/tr>\n
Metallurgical Length<\/td>\n10\u201340 m (steel curved caster)<\/td>\n<\/tr>\n
Global Adoption<\/td>\n>90 % of crude steel \u00b7 ~500 Mt\/yr (steel) + 20 Mt (Al) + 1 Mt (Cu)<\/td>\n<\/tr>\n
Reference Standards<\/td>\nASTM A788, EN 10084, AISI\/SAE grade specifications<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

What Is Continuous Casting?<\/h2>\n

\"What<\/p>\n

Continuous casting, also known as strand casting, is a steady-state process by which molten metal solidifies against a water-cooled mould while the partially solidified strand is withdrawn from the bottom of the mould at a matching rate. Liquid metal enters at the top while a solid section emerges at the bottom, and the run continues until the steel input is interrupted \u2014 typically a tundish-by-tundish sequence that can last anywhere from one hour to several weeks.<\/p>\n

Continuous casting replaced the older route whereby molten steel was teemed into individual ingot moulds, kicked out, reheated in soaking pits and broken down through a primary rolling mill. Sir Henry Bessemer patented the working of casting between two counter-rotating rollers in 1857, but the major innovation to make it commercially active in the steel industry was Junghans’s 1934 invention of vertical mould oscillation with the “negative strip” principle, which prevents the solidifying shell from sticking onto the mould walls. Steel mills adopted the technology widely through the 1960s, and continuous casting surpassed the conventional ingot route in tonnage during the mid-1980s.<\/p>\n

Today, continuous casting is the default route in almost every modern integrated mill and electric-arc-furnace mini-mill. Aluminium and copper are also continually cast, though the dominant aluminium format is a semi-continuous direct-chill (DC) machine as a continuous strand.<\/p>\n

How Continuous Casting Works: From Ladle to Cut Strand<\/h2>\n

\"How<\/p>\n

A modern steel caster operates as a fluid pipeline. Liquid metal enters the top of the machine in a teemed ladle, exits as a cooled strand at the bottom, and is cropped into manageable lengths \u2014 all while a downstream rolling mill schedules its own draft passes around the caster’s withdrawal rate.<\/p>\n

Steel-caster flow runs through six physical stages:<\/p>\n

    \n
  1. Ladle and turret \u2014 a teemed ladle sits on a rotating two-position turret directly above the caster. One ladle feeds the cast while the next is prepared “off-cast”, switched in when the first is empty. This handover is what gives continuous casting its name: the strand never stops while ladles change.<\/li>\n
  2. Tundish \u2014 molten material flows through a refractory shroud into the tundish reservoir, lined with disposable tundish boards that can be easily replaced. This buffer evens out flow surges into each mould and lets oxide inclusions float into the slag layer for cleaner metal.<\/li>\n
  3. Submerged entry nozzle (SEN) and mould \u2014 metal leaves the tundish through another refractory shroud and enters a water-cooled copper mould 0.5 to 2 metres deep. The copper mould oscillates vertically \u2014 or slightly off-vertical on a curved path \u2014 to keep the shell from sticking to the walls; a thin layer of mould powder melts on contact with the steel meniscus, lubricating the gap and trapping any remaining inclusions.<\/li>\n
  4. Primary cooling and shell formation \u2014 inside the mould, a 6 to 20 mm shell quickly forms against the copper wall while the casting interior stays liquid. The strand exits the mould bottom into a spray chamber.<\/li>\n
  5. Secondary cooling \u2014 water sprays and water-cooled rollers extract surface heat as the strand passes through the spray chamber. Rolls must be precisely aligned, as they also resist the ferrostatic pressure of the still-molten core.<\/li>\n
  6. Straightening and cropping \u2014 on a curved-apron casting machine, straightening rollers bend the partially solid strand back to a horizontal axis. Once the casting has reached its metallurgical length (10 to 40 m for steel), the strand is cut into slabs, blooms, or billets by mechanical shears or oxyacetylene torches.<\/li>\n<\/ol>\n
    \n

    \ud83d\udcd0 Engineering Note<\/strong><\/p>\n

    A modern steel caster runs at 1 to 8 m\/min, with billet machines at the upper end (typically around 4 m\/min) and conventional slab machines around 1.4 m\/min. Casting speed is governed by the allowable liquid-core length: if the strand exits the mould before a sufficient shell forms, ferrostatic pressure causes a breakout. Withdrawal rate, mould water flow and spray-chamber cooling are coordinated by a programmable logic controller drawing on electromagnetic level sensors at the tundish and mould, plus thermal sensors along the strand path.<\/p>\n<\/div>\n

    What Is the Step-by-Step Process of Continuous Casting?<\/h3>\n

    A six-step sequence captures the shortest practical answer: tap molten steel into a ladle, transfer to a tundish above the caster, feed through a submerged entry nozzle into a water-cooled copper mould, allow primary solidification of the shell while the mould oscillates, withdraw the strand through secondary cooling sprays and support rolls, then straighten and cut to length. Each handover is buffered by the previous reservoir so the strand itself never stops moving while it is in steady state. Engineers at the University of Illinois Continuous Casting Consortium describe the steady-state condition as one in which the solid\u2013liquid interface holds a constant position in the mould frame of reference, which is what distinguishes continuous casting processes from every other casting method.<\/p>\n

    Continuous Casting Machine: Key Components<\/h2>\n

    Each station on a continuous casting machine carries a distinct technical role and a distinct service-life envelope. Plant audits and turnaround planning typically work down this list.<\/p>\n

    \n\n\n\n\n\n\n\n\n\n\n\n\n\n
    Component<\/th>\nFunction<\/th>\nMaterial \/ Service Life<\/th>\n<\/tr>\n<\/thead>\n
    Ladle & turret<\/strong><\/td>\nBuffer between EAF\/BOF and caster; supports handover<\/td>\nRefractory-lined; preheated before each cast<\/td>\n<\/tr>\n
    Tundish<\/strong><\/td>\nReservoir, flow regulator, inclusion separator<\/td>\nDisposable working lining (tundish boards) replaced per heat sequence<\/td>\n<\/tr>\n
    Submerged entry nozzle (SEN)<\/strong><\/td>\nDelivers metal below the slag layer to prevent re-oxidation<\/td>\nRefractory ceramic; replaceable per sequence; alignment is a leading breakout cause<\/td>\n<\/tr>\n
    Copper mould<\/strong><\/td>\nPrimary heat extraction; forms the solid shell<\/td>\nCr-plated copper plates: industry-reported 100\u2013150 heats; Ni-plated: ~300 heats<\/td>\n<\/tr>\n
    Mould oscillator<\/strong><\/td>\nVertical oscillation prevents shell sticking (“negative strip” interval)<\/td>\nHydraulic or mechanical drive; periodic inspection of bearings and stroke<\/td>\n<\/tr>\n
    Mould powder feed<\/strong><\/td>\nLubricates strand\u2013mould gap; absorbs alumina inclusions<\/td>\nSynthetic flux specific to steel grade; consumable per cast<\/td>\n<\/tr>\n
    Secondary cooling spray<\/strong><\/td>\nWater mist removes heat below mould exit<\/td>\nNozzles map zone-by-zone to grade-specific cooling curves<\/td>\n<\/tr>\n
    Support & withdrawal rolls<\/strong><\/td>\nResist ferrostatic pressure; pull strand at casting speed<\/td>\nClosely spaced; alignment controls bulge and internal cracks<\/td>\n<\/tr>\n
    Straighteners & torch cutter<\/strong><\/td>\nBend strand to horizontal; cut to length<\/td>\nHydraulic straightener rolls; oxyacetylene or plasma torch<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

    The mould copper plate is the highest-attrition component on a steel caster. Industry tracking from caster maintenance providers shows campaign life depends primarily on the coating: chromium-plated plates typically run 100\u2013150 heats before reconditioning, while nickel-plated plates can reach roughly 300 heats. Replacement cost and lost tonnage during a mould swap are why coating selection and oscillation tuning carry capital-grade weight in plant operating budgets. Modern casters also use computational fluid dynamics on the tundish and mould to predict turbulence, slag entrapment and shell-thickness profiles before a steel grade is committed to a campaign. These integrated control systems and casting processes are now standard on tier-1 European and Asian plants.<\/p>\n

    To plan a complete equipment package \u2014 including matching the caster to upstream EAF or BOF capacity, refractory consumption and mould-yard logistics \u2014 you can configure your steel plant equipment<\/a> with our steelmaking-line selector.<\/p>\n

    Cast Product Types: Billet, Bloom, Slab, Round, and Strip<\/h2>\n

    \"Cast<\/p>\n

    The caster is dimensioned around the section it casts, and the section is dictated by the downstream rolling mill. Five families dominate steel and metal plants worldwide.<\/p>\n

    \n\n\n\n\n\n\n\n\n\n\n\n
    Cast Form<\/th>\nTypical Cross-Section<\/th>\nLength<\/th>\nDownstream Use<\/th>\n<\/tr>\n<\/thead>\n
    Billet<\/strong><\/td>\n<200 mm square (typically 130\u2013200 mm)<\/td>\nup to 12 m<\/td>\nLong products: rebar, wire rod, rails, angles, bars<\/td>\n<\/tr>\n
    Bloom<\/strong><\/td>\n>200\u00d7200 mm, up to 400\u00d7600 mm<\/td>\n4\u201310 m<\/td>\nHeavy sections, large bars, forging stock<\/td>\n<\/tr>\n
    Slab (conventional)<\/strong><\/td>\n100\u20131600 mm wide \u00d7 180\u2013250 mm thick<\/td>\nup to 12 m<\/td>\nHot-rolled coil, plate, automotive sheet<\/td>\n<\/tr>\n
    Slab (thin \/ wide \/ thick)<\/strong><\/td>\nThin 40\u2013110 mm \u00b7 Wide up to 3250\u00d7150 mm \u00b7 Thick up to 2200\u00d7450 mm<\/td>\nup to 12 m<\/td>\nCSP-line hot strip; plate mill heavy plate<\/td>\n<\/tr>\n
    Round<\/strong><\/td>\n140 or 500 mm diameter<\/td>\ncut to order<\/td>\nTube and pipe stock, ring rolling, large forgings<\/td>\n<\/tr>\n
    Beam blank<\/strong><\/td>\n1048\u00d7450 mm or 438\u00d7381 mm (I-beam profile)<\/td>\ncut to order<\/td>\nDirect rolling to structural I- and H-beams<\/td>\n<\/tr>\n
    Strip (direct cast)<\/strong><\/td>\n2\u20135 mm \u00d7 760\u20131330 mm<\/td>\ncoil<\/td>\nNear-net-shape hot-rolled coil bypassing reheat<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

    Choosing the cast section is therefore choosing the rolling investment. Billet casters fit long-product mini-mills, slab casters fit hot-strip and plate mills, and beam-blank casters fit structural-section mills that would otherwise rely on heavy bloom-rolling chains.<\/p>\n

    Continuous Casting vs Ingot Casting: Why the Industry Switched<\/h2>\n

    \"Continuous<\/p>\n

    Before the 1960s, steel was teemed into stationary ingot moulds, demoulded after solidification, soaked in reheating pits and broken down on a primary rolling mill before reaching the finishing trains. Continuous casting eliminates the demoulding, soaking-pit and primary breakdown steps in one move \u2014 and that is the structural reason the industry switched.<\/p>\n

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    \n

    \u2714 Advantages of Continuous Casting<\/strong><\/p>\n