Sendzimir Cluster Mill

The Sendzimir Cluster Mill is a cold rolling mill built to reduce hard, thin metal strip that ordinary four-high mills cannot handle. Its defining feature is a very small work roll, often 50 to 90 mm in diameter, supported by a cluster of progressively larger rolls. A small work roll lowers the contact area and the required separating force, so the mill can reduce stainless steel, silicon electrical steel and titanium strip down to a few hundredths of a millimetre. A small roll on its own would deflect and bend, so the 20-high roll cluster braces it from every side and passes the rolling load outward into the frame.

What a cluster mill rolls and why

Hard alloys work-harden quickly and need high reduction per coil, which drives up rolling force. On a conventional mill that force bends large work rolls and ruins gauge and flatness. The cluster arrangement breaks the problem into stages. The work roll only touches the strip; everything behind it exists to keep that roll straight and rigid. Because the work roll is small and replaceable, the mill rolls thin gauges, including foil, at high tension and high reduction without the roll deflection that limits a four-high stand.

The monobloc housing

The monobloc housing is the structural reason the cluster works. Instead of separate posts and caps bolted together, the frame is a single steel casting, the monobloc frame casting, with the backing saddle seats bored directly into it. The one-piece body is far stiffer than a built-up housing, so under 8 to 20 MN of rolling force the bores stay round and the roll axes stay parallel. End plates close the drive and operator ends, a housing cover retains the cluster, and the whole frame sits on the mill base plate. This rigidity is what lets the tiny work rolls survive the load.

The 20-high roll cluster

Loads pass from the strip outward through five rows. The two work rolls, usually tungsten carbide or hardened tool steel, sit against the strip. Behind them, four first intermediate rolls are driven and axially shiftable, the As-U rolls that set the broad crown. Six second intermediate rolls, some of them driven, carry the torque inward from the spindles. The outermost row is the eight backing bearing assemblies. Each is a backing bearing shaft riding on a row of bearing races separated by eccentric backing saddles, seated in the bored housing. The backing assemblies transmit the full rolling force into the frame over a wide footprint, which is how a 70 mm work roll can carry millions of newtons without bending. The cluster is the heart of the machine.

As-U-Roll crown and flatness control

Strip flatness depends on the shape of the roll gap across the width. The As-U-Roll crown system controls it by bending the backing shafts. Each backing shaft carries eccentric crown racks that rotate the backing saddles through crown adjustment shafts driven by individual crown servo motors. Rotating a saddle raises or lowers the shaft locally, bowing the backing assembly and changing the gap profile. The loop reads its target from the flatness measuring roll, a segmented roll whose shapemeter segments and pressure sensors measure strip tension across the width. The As-U controller compares that profile to target and adjusts the crown servos, giving the automatic flatness control that makes these mills suited to electrical steel and precision stainless.

Drive and high-tension coil handling

Torque enters through the drive train. The main drive motor, built from a stator assembly, rotor assembly and copper winding in a motor housing, feeds the gear distributor, which splits torque through gear pairs to four drive spindles turning the driven second intermediate rolls. Because Sendzimir mills are reversing, the coil handling line uses two tension reels, one each side, each with an expanding reel mandrel and a reel drive motor. The strip runs over deflector and bridle rolls under high tension, threaded by strip guides and monitored by a tensiometer. High strip tension reduces the rolling force needed for a given reduction, so tension control is part of the gauge strategy.

Coolant, hydraulics and control

The cluster runs flooded in low-viscosity rolling oil. The rolling oil system uses oil pumps, an oil tank, filters, spray headers with many nozzles, an oil cooler and a mist extractor. The roll gap is set by the hydraulic screwdown system, where gap cylinders driven through servo valves react against rolling force load cells and position sensors for automatic gauge control. Oil for the cylinders, crown system and reels comes from the hydraulic power unit, with its pumps, accumulators and valve manifold. The control system ties it together through the AGC board, the AFC loop, the drive control and the operator panel, reading encoders and pressure sensors across the mill.

Use and variants

Sendzimir mills dominate cold rolling of stainless steel sheet and strip, where the combination of small work rolls and tight flatness control gives consistent gauge on a hard material. They are the standard mill for grain-oriented and non-oriented silicon electrical steel, where flatness and thickness uniformity affect core loss. Narrow versions roll titanium and specialty alloys, and the thinnest gauges produce foil. Variants differ in width, number of stands and whether they run as standalone reversing mills or in tandem lines, but the 20-high cluster and monobloc frame remain the common pattern.