Slitting Line, Cold Rolling and Pickling Line Automation

A slitting line runs in this order: coil car and uncoiler, straightener and head shear, slitter head (circular knives on upper and lower arbors), scrap winders for edge trim, loop pit, separator discs and tension stand (felt pads or tension rolls), recoiler (expanding mandrel) and coil unloading car. The slitter head sets line speed; the uncoiler holds back tension on the strip and the recoiler applies its own tension after the tension stand.

The loop pit lets strips between the slitter and recoiler run at different lengths: edge strips elongate slightly differently from centre strips, and the difference is absorbed by the depth of the loops hanging in the pit. Loop level in the pit is read by ultrasonic or photocell sensors and the speed difference between slitter and recoiler is set from this level. On lines without a loop pit (drag mode) the slitter turns freely and the strip is pulled by the recoiler; this layout needs care with knife marks and edge quality on thin strip.

On the recoiler, motor speed drops as coil diameter grows; tension is held by motor torque from diameter calculation or by back tension from the tension stand. On the uncoiler, torque is reduced with diameter to give the same back tension as the coil shrinks; on heavy coils the uncoiler motor regenerates and energy is fed back to the mains or a common DC bus. Slowing down at coil head and tail is done from coil diameter and remaining length calculation.

On a cold rolling line the strip is reduced between work rolls; on reversing mills the strip passes back and forth between two coilers, one acting as uncoiler and the other as recoiler on each pass. The mill main drive is the speed reference, and entry and exit tensions are part of thickness control. On a pickling line the strip runs through acid tanks at constant speed; entry and exit accumulators keep the process section running during coil changes and welding, and bridles separate tension between sections.

In the ONX architecture the slitter is the line speed reference; the uncoiler and recoiler run in tension mode with diameter calculation and torque control, and loop level corrects the speed difference between recoiler and slitter. Control runs in CODESYS; diameter calculation, inertia compensation and tension ramps are sent to every drive in the same cycle. Scrap winders turn in ratio to line speed with limited torque.

On heavy coils high-power AC drives are used for uncoiler and recoiler, with a regenerative supply or common DC bus where needed; on DC motor lines DC drive replacement is an option. Coil data, strip layout and tension recipes are managed from the screen; coil head and tail slowdown is automatic from remaining length calculation.

The architecture on this page is built on the diameter calculation, torque control and drive platform ONX Control uses in winder tension control, accumulator and cut-to-length applications. We work out your line layout and tension needs together in a meeting.

A typical picture on slitting lines: DC motor uncoiler and recoiler, a recoiler whose tension the operator sets with a potentiometer, coils that loosen or telescope as they grow and a loop level watched by hand. In a retrofit the knife arbors, loop pit and mandrels are kept; drives are renewed or moved to AC and tension is held automatically from diameter calculation.