Fiber Cement Sheet Machine

Overview

A fiber cement sheet machine forms flat boards and corrugated roofing sheet from a dilute slurry of Portland cement, ground silica, and reinforcing fiber. It works by the Hatschek process, which builds the sheet from many thin films rather than casting it in one pour. The Vat Section holds the slurry, a rotating screen in the Sieve Cylinder Section section picks a thin film of solids out of the vat, and the Felt Conveyor carries that film to the Format Roll Section. There the films wind up layer on layer until the sheet reaches its set thickness, and the Cutting and Transfer Section section cuts it to length. Flat board goes straight to curing, while sheet bound for roofing passes through the Corrugation Section section first. The whole line runs off a single Main Drive Train train and is sequenced by the Control Cabinet cabinet.

The reason the process uses thin films is strength. A cement film a fraction of a millimetre thick holds its fibers in the plane of the sheet, so the finished board resists bending far better than a cast slab of the same cement would. Building the sheet from stacked films also lets the operator set thickness by counting layers, which is why one machine makes a thin facade panel and a thick fire board on the same tooling.

The vat and sieve cylinders

Forming starts in the Vat Section. Two Slurry Vat tanks hold cement, silica, and fiber at a few percent solids, kept in suspension by a slow Vat Agitator driven through its Agitator Motor so the heavy cement does not settle out. A Headbox spreads incoming slurry across the full width, a Slurry Feed Pump keeps the vat topped up, and a Overflow Weir fixes the level while a Consistency Valve trims the solids returning from the recovery loop.

The Sieve Cylinder Section section sits in the vat. Each Cylinder Shell is a perforated drum wrapped in a fine Cylinder Screen of phosphor bronze mesh. As the drum turns through the slurry, water drains inward through the Cylinder Shaft and a thin film of cement and fiber stays caught on the screen. The End Spider end plates keep the drum open so the water has a clear path out. Each cylinder lays down one film, so a two-cylinder machine builds the sheet twice as fast as one.

The felt and dewatering

The Felt Conveyor takes the film off the cylinders. A Couch Roll presses the felt against the screen so the film transfers cleanly onto the Felt Belt, a woven polyester loop that runs the length of the machine on Guide Roll idlers under load from a Tension Roll. On its return run the felt passes the Felt Washing Shower shower, where a Wash Pump feeds water through the Shower Header and its Spray Nozzle jets to clear trapped cement, since a clogged felt picks up film unevenly.

While the film rides the felt it crosses the Vacuum Dewatering Section section. Three Suction Box units under the belt pull water through the film by suction from a Vacuum Pump driven by its Vacuum Pump Motor, with the drawn-off water split out in a Water Separator and the suction level set by a Vacuum Valve. Two Pressure Sensor units report the vacuum so the controller can hold dewatering steady as the felt ages. Taking water out here, before the format roll, sets how well the layers bond.

The format roll and cutting

The dewatered film reaches the Format Roll Section section, which is where the sheet actually builds. The felt wraps each film onto the Accumulator Roll, and a loaded Press Roll compacts each new layer onto the ones below so the laminate bonds into one body. A Thickness Gauge watches the wound sheet, and when it hits the target the wound mat is slit off the roll. A Doctor Blade then cleans the roll for the next sheet, and the Format Roll Frame lets the roll lift away as the diameter grows.

The released sheet runs into the Cutting and Transfer Section section. A Cross Cutter cuts the green sheet to length, two Edge Trimmer discs square the sides, and the Transfer Table moves it on. Because the green sheet is wet and fragile, a Vacuum Lifter with rubber Suction Cup heads on a Lifter Frame picks it up by the face rather than the edge, which would crack it.

Corrugation, drive, and control

Sheet meant for roofing goes to the Corrugation Section section while it is still soft. A Forming Press drives a profiled Forming Platen down through its Press Cylinder rams, pushing the green sheet into a Corrugating Mould that holds the wave shape while it cures. A Profile Template sets the pitch when profiles change, and the Mould Stacker racks loaded moulds for curing. Flat board skips this step and goes straight to stacking.

Every section turns together so the films register. The Main Drive Train train runs a Main Drive Motor through the Line Gearbox onto the Main Line Shaft, with Servo Motor units trimming individual sections. The Control Cabinet cabinet ties it together: a PLC holds the sequence and the level and speed loops, a Operator Panel panel sets recipe and thickness, and Variable Frequency Drive drives hold motor speeds.

Materials, curing, and use

The slurry is roughly Portland cement with ground silica and a few percent of cellulose pulp and PVA fiber for reinforcement. After forming, the green sheet cures one of two ways. Air-cured board sets at ambient temperature over weeks, while autoclaved board goes into a steam pressure vessel where the silica reacts with the cement to give a tougher, lower-density panel in hours. Fiber cement made this way is used for facade cladding, soffits, fire-rated wall board, flooring underlayment, and corrugated roofing. It took over much of the market once asbestos was banned, since the Hatschek machine runs the same way on cellulose and PVA fiber as it once did on asbestos, only with safer feedstock.