Steel Slitting Line Product

Overview

A steel slitting line takes a wide coil (600–1,600 mm) and uses rotating shear blades to cut it into multiple narrower coils of exact width. This is the workhorse of flat-rolled steel distribution: a single coil of hot-rolled strip arrives in 5–10 tonne reels, and the slitter converts it into 4–7 narrower coils, each suitable for customer use in stamping dies, tube mills, or further downstream processing. The line runs continuously at 10–80 m/min, is synchronized across the uncoiler, knife head, and recoilers, and produces coils with virtually no edge scrap (the width tolerance is ±1 mm).

The incoming wide coil mounts on the Motorized Uncoiler and feeds through the Strip Tensioner which maintains constant strip tension. The strip then passes under a rotating Rotary Slitter Head Assembly that has 5–8 Rotary Knife Blade blades arranged side by side, each separated by a Spacer Ring to set the final coil widths. The blades shear the strip into narrow coils as it moves, and each coil winds onto its own Recoiler Mandrel on the exit side. When a coil reaches full diameter (typically 500–1,000 kg), the Coil Ejector removes it and the next coil begins winding.

Rotary knife design and cutting mechanics

The cutting action is a continuous shear between the rotating Rotary Knife Blade and a stationary backup blade (or sometimes a second rotating blade), passing through the moving strip. The knife speed is typically 400–600 rpm at a 10–50 m/min strip speed, so the knife has a peripheral velocity several times the strip speed — this creates a slicing action rather than a pure shear, reducing chatter and producing a clean edge. The knife blade is tungsten-carbide or high-speed steel hardened to 60–65 HRC; edge life is 500–3,000 tonnes before resharpening becomes necessary.

The Slitter Head Drive Motor is a separate high-speed motor (1,500–3,000 rpm input) coupled through a gearbox to the Knife Spindle at the desired blade speed. The slitter head float is supported by a Thrust Bearing to handle the cumulative side load of multiple cuts. The Spacer Ring are precision-ground rings slipped onto the spindle between Knife Holder Cartridge cartridges; they set the exact distance between adjacent blades and therefore the width of each output coil. Changing the coil widths requires swapping spacer rings — a 30-minute job done during coil change intervals.

Synchronization and tension control

The entire line is electronically synchronized. The PLC Control Cabinet PLC reads the Tension Dancer Arm position (via a Pressure Sensor) and adjusts the Uncoiler Motor speed to maintain constant tension. The uncoiler slitting-line-motor-controller is a closed-loop DC drive or VFD that modulates motor power to track the setpoint. If the coil diameter shrinks suddenly (indicating a sudden tension rise), the uncoiler backs off; if tension drops, it speeds up. This feedback loop is fast enough to handle diameter changes as the large coil unwinds down to scrap-spool size.

The Main Drive Motor VFD ramps the line speed up and down under PLC command, and the Knife Motor VFD slews the blade speed proportionally so the shear angle and cut quality stay constant. Each Recoiler Servo Motor is a servo motor with its own encoder; the PLC software winds each coil at a speed proportional to the input strip speed, ensuring even tension and avoiding side-slip.

Recoiling and coil building

The output coils are wound onto Recoiler Mandrel stations on the far end of the line. Each mandrel is driven by its own slitting-line-recoiler-servo-motor (an induction motor with feedback) at a variable speed proportional to coil diameter. A growing coil increases in outside diameter, so the surface speed of the mandrel must rise to maintain constant line speed; the servo ramp-up is automatic under PLC command.

The recoiler mandrel is tapered (like the uncoiler) so that finished coils can be slid off axially. When a coil reaches setpoint diameter (often 1.2 m or 800–1,000 kg), the Recoiler Holding Brake holds the mandrel, the Coil Ejector extends (usually pneumatic cones that push radially), and the finished coil slides onto a collection table. The ejector retracts, the brake releases, and the empty mandrel restarts winding the next coil.

Edge trim and scrap handling

The outboard edges of the original wide coil — areas beyond the outermost knife blade — form trim scrap that falls into a bin beneath the line. Some machines have an auxiliary scrap coil recoiler that winds the trim (2–5 % of input width) for sale as mill scrap. The trim is typically discarded or sold to a scrap dealer; it contains no contamination because it is fresh from the same coil as the product.

Material-specific considerations

Mild steel (< 200 MPa) cuts cleanly at all speeds. High-strength grades (HSLA, 300–550 MPa) and stainless steel (304, 430) demand slower speeds (≤ 40 m/min) and sharper blades (regrind every 500–1,000 tonnes). Aluminium (1100 H14, 3105 H14) is non-ferrous and cannot use electromagnetic tension feedback (load cells are mandatory); the line also runs faster (50–80 m/min). Coated steels (galvanized, pre-painted) dull the blades faster; blade life drops to 300–500 tonnes, but the coating is preserved without edge spalling.

Changeover and setup

Changing coil widths (moving from one product to another) requires swapping the Spacer Ring and reprogramming the recoiler servo targets in the HMI Touchpanel. This takes 1–3 hours depending on complexity. The new spacers are measured and installed on a separate prep bench, and the line is run at slow speed to confirm edge alignment before ramping to production speed. The knife blades themselves are site-changed every 3–6 months depending on throughput and material hardness — typically done in-place on a Saturday or Sunday.