Web Sheeting Machine

Overview

A web sheeting machine, often just called a sheeter, cuts a continuously moving web of paper, board, film, or laminate into flat sheets of a set length and stacks them. It bridges the gap between roll-fed converting, where material is made and printed in long webs, and sheet-fed processes, where the next machine, such as a die cutter, folder, or printing press, needs flat sheets. The sheeter unwinds the roll, meters the web to length, crops it with a rotating knife, slows the cut pieces so they overlap, and piles them into a neat stack. When the web carries a printed image, the machine cuts to register so every sheet shows the print in the same place.

The web runs from the Unwind Stand through the Feed and Registration section to the Rotary Cutting Head, then over the Overlap Conveyor to the Sheet Stacker. The Drive System phases the knife to the web, and the Control System sets sheet length and counts.

Unwinding and feeding

The roll mounts on the Unwind Stand, gripped by a Unwind Air Shaft with a Unwind Brake holding payoff tension and a Tension Dancer absorbing tension swings. A Edge Guide keeps the web centered. The web then enters the Feed and Registration section, where a pair of driven Pull Roll rolls, clamped by Nip Cylinder loading, meter the web forward at a controlled speed. A Web Encoder measures exactly how much web has passed so the controller knows when a full sheet length has fed. The metering accuracy of this section sets the sheet-length accuracy of the whole machine.

Cutting to length

The Rotary Cutting Head crops the moving web without stopping it. A Knife Cylinder carries a helical Rotary Blade that sweeps past a stationary Bed Knife once per revolution, shearing the web like a long rotary scissor. Because the web never stops, the knife cylinder speed is matched to the web so the blade meets the web at the cut line with no tearing. Sheet length is set by the ratio of knife speed to web speed: run the knife slightly faster or slower and the cut length changes. For printed work a Phase Adjuster shifts the cut position so it lands on the print mark rather than at a fixed mechanical interval, keeping every sheet in register with its image.

Slowing and overlapping

Sheets leave the cutter at full web speed, which is too fast to pile cleanly, so the Overlap Conveyor slows them and lays them in a shingle. A perforated Vacuum Belt, running slower than the web, holds each cut sheet down by suction from a Vacuum Box fed by a Vacuum Fan, so the trailing edge of one sheet rides over the leading edge of the next. Conveyor Roll rolls support and drive the belt. This overlap, or shingle, lets the sheets arrive at the stacker gently and squared, instead of slamming in at line speed.

Registration and accuracy

Cut accuracy depends on two things working together: how precisely the Feed and Registration meters the web, and how well the cut is phased to it. The Web Encoder tells the controller the exact web travel, and for plain stock the knife is simply timed to crop at the set length. For printed stock the Register Mark Sensor reads a register mark on the web and the controller nudges the knife phase through the Phase Adjuster so the cut falls at the same point on every repeat. Without register tracking, small variations in print repeat length would slowly walk the cut across the image.

Stacking, drive, and use

Slowed, overlapped sheets reach the Sheet Stacker, where a Front Stop gate halts each sheet at the pile front and side Jogger guides square them. The Stack Table lowers steadily, driven by a Servo Motor, so the drop height stays constant as the pile grows, and a Batch Kicker inserts a tab to mark counted batches. The Drive System uses several servo axes through Servo Drive amplifiers and a Gearbox Housing to phase the knife to the web, and the Control System system, built on a Machine Controller and an HMI, holds length recipes, counts sheets, and stops on a jam or web break. Sheeters serve commercial print finishing, folding-carton plants, and flexible-packaging converting, anywhere roll stock has to become sheet stock. Larger plants run twin-knife or duplex sheeters that combine several webs or cut at higher speed. The choice of knife geometry follows the material: a helical Rotary Blade gives a smooth shearing cut on paper and board, while harder films and laminates need a keener edge and a closer set against the Bed Knife to avoid drawing the web rather than cutting it. The Vacuum Belt slowdown is tuned to the sheet length and speed, because too little overlap lets sheets arrive unsquared and too much causes them to ride up over the Front Stop instead of dropping cleanly onto the pile.