The Hatschek Process for Fiber Cement Sheets

The Hatschek process makes fiber cement sheets the way a cylinder paper machine makes board. Rotating sieve cylinders in vats of dilute cement-fiber slurry each pick up a thin film, an endless felt collects the films, vacuum boxes remove water, and a forming roll winds layer upon layer until the sheet reaches its thickness. The wet sheet is then cut off, pressed if required, and cured.

It is the oldest sheet-forming method for fiber cement and still the most common one (Global Cement, Cement Boards 101). This article explains how a Hatschek machine works part by part, how the number of layers relates to board thickness, what the felt does, and how the process compares with flow-on forming, the main alternative for new board plants.

Where the Hatschek Process Came From

Ludwig Hatschek, an Austrian industrialist and inventor, solved the problem of binding asbestos fibers with Portland cement in 1900 and was granted Austrian patent 5970 for his production method in 1901; “Eternit” was protected as the name of the sheets (Neue Deutsche Biographie). The process applies the principle of the cylinder machine used in paper and board making: cement sheets are formed from thin, dewatered layers.

The machine outlived the fiber it was designed for. Asbestos was replaced by refined cellulose pulp and, in air-cured products, by synthetic fibers such as PVA. In Australia, asbestos-free sheets were in commercial production by May 1981 (Ni, 1995). Today’s standards are written for non-asbestos products: ASTM C1186 does not apply to asbestos-cement sheets (ASTM C1186), and EN 12467 defines a designation for sheets made with non-asbestos technology (EN 12467). Fiber choice matters to the process, as explained below, but the machine principle is unchanged.

How a Hatschek Machine Works, Step by Step

1. Slurry preparation. Cement, silica or limestone, refined cellulose pulp and water are mixed into a very dilute slurry, about 7–10% solids by weight (Ni, 1995).
2. Film formation in the vats. Several vats are placed in a row along the machine. In each one, a sieve cylinder covered with fine wire mesh rotates partly submerged. Water drains through the mesh into the cylinder, and the fibers and fine particles build up on its surface as a thin film. The fibers act as the filter that holds the cement on the mesh.
3. Transfer to the felt. An endless felt runs over the tops of the cylinders. Pressed against each cylinder by a roll, the felt lifts off the film. After passing all the vats, the felt carries a combined ply of several films (Ni, 1995).
4. Vacuum dewatering. The felt carries the ply over vacuum (suction) boxes, which remove most of the remaining water (Ni, 1995).
5. Winding on the forming roll. The ply is transferred to a steel forming roll, also called the accumulator or making roll, and compressed by pressure rolls in contact with it (Ni, 1995). Each revolution adds another ply.
6. Cutting off the sheet. When the target thickness is reached, the accumulated sheet is cut across the roll and taken off onto a conveyor (Redco, US 10,144,150).
7. Felt return. The felt is washed and conditioned on its return run so that it picks up the next films evenly.

After the machine, the green sheet goes on to trimming, stacking, optional pressing and air or autoclave curing. Those later steps are covered in Fiber Cement Board Manufacturing Process.

Main Parts of a Hatschek Sheet Machine

The number of vats varies. A Redco patent illustrates four rotating sieve drums (Redco, US 10,144,150); a Nichiha patent example uses three cylinders (Nichiha, US 8,043,461). More vats add more film per revolution and therefore more output per roll turn, at the cost of a longer, more complex machine.

The felt: the consumable that runs the machine

The felt is the part operators talk about most, because its condition shows up directly in the sheet. A patent on felts for forming fiber cement describes a woven base fabric with a fibrous batt layer on top and often underneath. The batt helps the felt pick up slurry from the vats, and the felt then carries the wet web over suction boxes, which draw water out through it (US 9,415,564).

Three things follow for a plant:

• The felt has to stay open. Fine cement and silica gradually clog it. Washing and conditioning on the return run keep drainage steady. When drainage falls, the machine must slow down or the sheets come off wetter and weaker.
• The felt wears. Abrasive slurry and suction boxes wear the batt and base fabric, and felts are replaced on a schedule. Felt changes are planned downtime, so ask how long a change takes on the machine offered and how many spare felts are included.
• The felt sets surface quality. A worn or marked felt leaves its pattern on the sheet face, which then needs more sanding.

Layers, Forming Roll and Sheet Thickness

A Hatschek sheet is a laminate. Each vat contributes one thin film per revolution, and the forming roll keeps turning until enough plies have built up.

Patent literature describes individual films of 0.1–0.6 mm (Redco, US 10,144,150). A Nichiha patent gives a worked example: three cylinders each form a 0.4 mm film, so each revolution adds a 1.2 mm ply; ten revolutions give a 12 mm sheet with 30 layers in total, and five revolutions give a 6 mm sheet (Nichiha, US 8,043,461).

Two practical conclusions follow.

• Thicker boards cut output. At a given machine speed, a 12 mm board takes twice as many revolutions as a 6 mm board. A line’s output in m² per year has to be stated for a specific thickness mix.
• Sheet length is set by the roll. The sheet is cut across the forming roll, so the raw length depends on the roll circumference. Sheet width is set by the cylinder and felt width. Check that the raw sheet size suits the finished sizes you plan to sell, with a trim allowance.

Fiber Orientation and the Bond Between Layers

Because each film is formed on a rotating cylinder and drawn along by a moving felt, fibers tend to line up in the machine direction. The board is therefore stronger lengthwise than across. CSIRO research on a 6 mm Australian sheet measured dry flexural strength of about 19.2 MPa in the machine direction and 13.5 MPa across it (Ni, 1995). Product tests must cover both directions, and fixing details for long boards should take the difference into account.

The second weak point of any laminate is the bond between layers. Calcium silicate board patents treat interlaminar strength as a controlled property; one requires an interlaminar peeling strength of at least 3% of the flexural strength (Ask Corp., US 5,851,354). Good bonding comes from even dewatering, adequate pressure on the forming roll and, for dense products, pressing of the stacked sheets.

Hatschek vs Flow-On Forming

Flow-on forming is the main alternative for flat sheets. Instead of picking up films from vats, the machine applies the slurry directly and continuously onto the moving felt, dewaters it by suction and winds it onto the forming roll (Nichiha, US 8,043,461). Flow-on processes were developed as an alternative to Hatschek for producing fiber cement sheets (US 2018/0036908).

On the board lines we supply, flow-on forming is the more common choice for new plants. The equipment is simpler, energy and running costs are lower, it is more tolerant of raw material variation, and it uses less water. Hatschek forming remains a sound choice where a producer wants the fine laminated structure and has experience running it. For 8–10 million m² a year, our reference designs use a twin-roll board machine.

A third wet process, the Magnani process, uses a much thicker slurry, about 50% solids, which flows directly onto a felt conveyor over many vacuum boxes. It is used mainly for corrugated sheets and pipes rather than flat boards (Ni, 1995).

Choosing a Forming Process for a New Fiber Cement Plant

The forming machine should follow from the product plan, not the other way round. Work through these questions with each supplier:

1. Which boards, which thicknesses? Thin flat sheets, thick facade boards, or both. The thickness mix decides output per machine.
2. Which curing route? Air-cured boards with PVA, or autoclaved boards with ground silica. This changes fiber selection and how the slurry drains.
3. Which standard? EN 12467 category and class, or ASTM C1186 type and grade. Strength in both directions and the bond between layers are tested.
4. Which raw materials? Local cement, sand and the pulp grade you can buy reliably. Run tests on them before the machine is chosen.
5. How much water is available, and how will white water be treated?

We recommend a forming process after reviewing your products and raw materials, and both machines are available.

FAQ

What is the Hatschek process?

A wet sheet-forming process for fiber cement, patented by Ludwig Hatschek in Austria at the start of the 20th century. Sieve cylinders in vats of dilute slurry form thin films, which a felt collects and carries over vacuum boxes to a forming roll. The roll winds plies until the sheet reaches thickness; the sheet is then cut off and cured.

How many layers does a Hatschek fiber cement sheet have?

It depends on the number of vats, the film thickness and the board thickness. Patents describe films of 0.1–0.6 mm. In a Nichiha example, three 0.4 mm films make a 1.2 mm ply per revolution, so a 12 mm sheet has 30 films from ten revolutions. Thicker boards need more revolutions.

What is the felt on a Hatschek machine?

An endless woven fabric with a fibrous batt layer. It runs over the sieve cylinders, picks up the films, and carries them over suction boxes that draw out water before the ply reaches the forming roll. Felts wear and clog, so they are washed continuously and replaced periodically. Their condition affects drainage, machine speed and surface quality.

Is the Hatschek process better than flow-on?

Neither is better for every plant. Hatschek is the established process and builds a finely laminated sheet from many thin films. Flow-on is simpler, uses less water and, on the lines we supply, tolerates more raw material variation, which is why most of our board lines use it. The right choice depends on products, raw materials and operating experience.

Can calcium silicate board be made on a Hatschek machine?

Yes. Patents for calcium silicate board name the Hatschek sheet machine as a standard forming method. The slurry is based on lime, ground silica and cellulose fiber instead of cement, and the sheets must then be autoclaved so that lime and silica react. See Calcium Silicate Board Manufacturing Process.

Planning a Fiber Cement Board Line?

Both Hatschek and flow-on board machines are offered on our fiber cement board production line, with pressing, autoclaving and finishing for 3, 5 or 8–10 million m² a year. Our calcium silicate insulation plant setup guide covers a different product, insulation board and pipe sections, but its planning steps from raw material tests onward are a useful reference.

Sources

• Neue Deutsche Biographie, “Hatschek, Ludwig” (Deutsche Biographie): https://www.deutsche-biographie.de/sfz28130.html
• A. Saunders and E. Davidson, “Cement Boards 101”, Global Cement Magazine, December 2013: https://globalcement.com/magazine/articles/825-cement-boards-101
• Y. Ni, Natural Fibre Reinforced Cement Composites, PhD thesis, Victoria University of Technology / CSIRO Division of Forest Products, 1995: https://vu-9.eprints-hosting.org/15654/1/Ni_1995compressed.pdf
• Redco NV, US 10,144,150 B2, Hatschek process for the production of fiber cement plates: https://patents.google.com/patent/US10144150
• Nichiha Corp., US 8,043,461 B2, Method for manufacturing fiber reinforced cement board: https://patents.google.com/patent/US8043461B2/en
• US 9,415,564 B2, Felt for forming fiber cement articles and related methods: https://patents.google.com/patent/US9415564
• US 2018/0036908 A1, Process and apparatus for making a fiber cement sheet: https://patents.justia.com/patent/20180036908
• Ask Corp., US 5,851,354 A, Method of manufacturing calcium silicate board: https://patents.google.com/patent/US5851354A/en
• ASTM International, ASTM C1186-26 Standard Specification for Flat Fiber-Cement Sheets: https://store.astm.org/c1186-26.html
• CEN, EN 12467:2012+A2:2018 Fibre-cement flat sheets – Product specification and test methods (SIST adoption listing): https://iteh.es/catalog/standards/sist/e6248861-5e94-4617-a934-1a3c85c01195/sist-en-12467-2013a2-2018