Secondary-cooling spray chamber structure and foot-roller support for continuous casters

01

Support the strand under the mould with the foot-roller hanger

Androsenko and co-authors at Nosov Magnitogorsk State Technical University describe the foot-roller unit of a billet caster's secondary cooling zone: a base attached to the bottom plate of the mould, angle-section support brackets with two rows of holes for roller assemblies on axes and plain bearings, brackets set to the caster's basic radius, and the cooling nozzles attached to the base with water supplied between the rollers. Rollers in contact with hot metal take cyclic thermal stresses and mechanical load from the ferrostatic pressure of liquid steel, leading to wear, cracking and sometimes breakage. [1]

They report breakouts between the mould and the foot-roller unit and name roller spacing (mould to first line, first to second line, second line to the first bending roll) among the main design causes. Replacing two roller lines with three on the same base and brackets reduced calculated total deformation of billet and hanger by 30% and equivalent stress by 38%: von Mises stress fell from 8.5062 MPa to 5.2872 MPa and billet deformation from 2.5277 µm to 1.792 µm. The rebuilt hanger had its roller necks clad by a friction method to resist wear. [1]

The same paper notes that roller diameters grow in downstream sections as the shell thickens, that frames with foot rollers on all four sides are used against bulging along the slab edges, and that water consumption when casting killed steel is 0.4 to 1.0 m³/t at withdrawal speeds of 1.0–1.4 m/min. [1]

Editorial note: ask the supplier for the roll pitch from the mould exit through the first lines, the roll diameter and bearing type, and the stress check of the hanger, not only the frame drawing.

Send the cast sections and casting speed range, caster radius, mould type and bottom-plate interface, number of foot-roller lines and roll pitch, roll diameter and bearing type, chamber length and number of zones, enclosure material and panel thickness, access doors, steam exhaust and drain connections, and the plant's discharge limits.

02

Size the chamber for each zone's flow, pressure and heat

Marius and Erika Ardelean of the Hunedoara Faculty of Engineering describe the secondary area as spraying water under pressure that penetrates the steam layer on the strand, taking the surface from 1,200–1,300 °C at the mould exit to 700–900 °C at the end of the secondary area. They give, as a general figure, that the secondary area covers over 30 up to 50% of the liquid core length and is divided into individually controlled sub-areas. [2]

Their plant measurements show the water the chamber must drain: on 240 × 270 mm blooms at 8.6–10.7 bar the three areas took up to 81, 100 and 112 l/min; on Ø150 mm rounds at 8.2–8.6 bar up to 60, 84 and 73 l/min. [2] Editorial calculation: the bloom maximum is 81 + 100 + 112 = 293 l/min, about 17.6 m³/h per strand.

Editorial calculation, cross-checking with the Magnitogorsk range and assuming a steel density of 7.8 t/m³: a Ø150 mm strand at 1.2 m/min carries about 0.0177 m² × 1.2 m/min × 7.8 t/m³ ≈ 0.165 t/min, so 0.4–1.0 m³/t corresponds to roughly 66–165 l/min, the same order as the 41–84 l/min per area measured at Hunedoara. [1] [2]

03

Mount the nozzles on the frame for each zone

In the foot-roller unit described from Magnitogorsk, the cooling nozzles are attached to the same base that carries the roller brackets, and the water is supplied between the rollers; the brackets themselves are set to the caster's basic radius. [1] The Hunedoara authors note that nozzle spray angle, the distances between nozzles and the water pressure are regulated so that a steady or almost steady temperature is kept around the strand periphery, with water or a water-air mixture as the coolant. [2]

Editorial note: on the chamber structure this means nozzle mountings that follow the caster radius between roll lines and can be adjusted for angle and distance; ask for a drawing of nozzle positions relative to the rolls for the smallest and largest section, and for how a nozzle is changed without dismantling the roll frame. Nozzle types, sizes and turndown belong to the spray-zone specification rather than the structure.

04

Plan for the water that leaves the chamber

Under 40 CFR 420 subpart F, which applies to discharges from the continuous casting of molten steel through water-cooled moulds, US EPA's BPT limits are 0.0780 kg of TSS and 0.0234 kg of oil and grease per 1,000 kg of product as a daily maximum, 0.0260 and 0.0078 kg as 30-day averages, with pH 6.0–9.0. BAT limits for lead are 0.0000939 kg and for zinc 0.000141 kg per 1,000 kg as daily maxima. [3]

Editorial calculation: for a caster producing 1,000 t a day, the BPT daily maximum allows 78 kg of TSS and 23.4 kg of oil and grease in the discharge. Chamber drains and the downstream scale pit and filters are therefore part of the order boundary even when the chamber itself is bought as a structure.

05

What the chamber frame has to carry and hold

The structure items below follow from the foot-roller, chamber and water data above; values are cited where a source gives them.

06

Send the strand, structure and water data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Strand: [sections; speed range; caster radius]
Foot rollers: [lines; pitch; roll diameter; bearings]
Chamber: [length; zones; material; panel thickness; doors]
Water: [maximum flow per strand; drain connections]
Steam: [exhaust connection]
Discharge: [scale pit; filters; limits]

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