Mould electromagnetic stirrer (M-EMS) coil assembly for billet and round bloom casting

01

Choose inside-mould or outside-mould mounting

Kishore Windwell, an EMS coil maker, classes stirrers by position along the strand as mould (M-EMS), strand (S-EMS) and final (F-EMS) stirrers, and lists four mould arrangements: inside the mould using mould water (2–8 Hz), inside the mould water jacket with a separate clean-water circuit (2–8 Hz), outside the mould with separate cooling water, which makes copper tube changes simple and suits a wide range of sections (2–5 Hz), and an inner-cooling type that can go inside or outside the mould (1–6 Hz). [1]

The same maker describes the inside-mould type on mould water as convenient and low in cost, the clean-water version as compact and long-lived, and the inner-cooling type as giving an even field but with higher magnetic leakage, strict cooling-water quality requirements and higher operating cost. [1]

Section size and mould copper both matter. In a round-bloom study with a stirrer of 1,010 mm inner diameter, 1,510 mm outer diameter and 300 mm height, at 280 A and 2 Hz, reducing the section from Φ650 to Φ550 mm moved the strand surface farther from the coil while the copper tube stayed 29 mm thick, and the maximum electromagnetic force fell from 440.0 to 227.4 N/m³; at Φ450 and Φ350 mm, with 25 mm copper, the force rose again. [3] With the stirrer and a smaller strand off-centre (eccentric stirring), the outer-arc side received more force than the inner-arc side, by 143.1 N/m³ at Φ350 mm and 6.6 N/m³ at Φ550 mm. [3] Editorial note: give the supplier every section and copper thickness you will cast through the same stirrer, and ask for the force at each.

Give the supplier the caster type and radius, every section size, mould copper thickness, mounting position (inside water jacket or outside the mould), available cooling water and its quality, power supply, required frequency and current range, stirring mode (continuous or alternating), and the steel grades and quality targets.

02

Set the current and frequency range

In a 200 mm × 200 mm square billet study with a stirrer of 12 coil packages on a toroidal core, varying the current from 0 to 500 A showed the lowest carbon segregation at 300 A, and segregation rose with frequency between 3 and 5 Hz; 3 Hz with 300 A was the best setting found, and the maximum tangential steel velocity was 0.19, 0.31 and 0.38 m/s at 100, 300 and 500 A. [2]

In the round-bloom study, three pairs of windings in twelve coil rows carried three-phase current 120° apart; the maximum electromagnetic force rose from 151 N/m³ at 180 A to 367 N/m³ at 280 A and 2,163 N/m³ at 680 A, and measured flux density at the centre fell as frequency rose while measured torque peaked near 2 Hz. [3] Editorial calculation: from 280 A to 680 A the current rises 2.43 times and the force 5.89 times, close to the square of the current ratio (5.90).

Editorial note: because flux density and stirring torque move in opposite directions over part of the frequency range, ask the supplier for measured torque (or force) against frequency at your section, not flux density alone.

03

Four round-bloom sections served by one stirrer

The round-bloom study modelled one stirrer (1,010 mm bore, 300 mm high) on a caster with a 660 mm effective mould length casting four sections, each with its own copper tube, speed and mould water. [3]

The authors attribute the dip at Φ550 mm to the combined effect of the thicker copper tube's magnetic shielding and the field's decay in air, and conclude that, of the four, the Φ650 mm section has the highest efficiency in converting electromagnetic energy into kinetic energy. [3] Editorial note: if a stirrer must serve more than one section, ask the supplier for the force at each one with its own copper thickness, not only at the design section.

04

Data for a mould stirrer enquiry

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

Caster: [billet, bloom or round bloom; radius]
Sections: [all sizes; mould copper thickness]
Mounting: [inside water jacket or outside mould]
Power: [current range; frequency range; supply]
Stirring: [continuous or alternating]
Cooling: [mould water or clean water; quality]
Steel: [grades; quality targets]
Documents: [torque vs frequency; reference casters]

See manufacturer records Send an enquiry through CNFX