Non-asbestos corrugated roofing sheet was made from cement, paper pulp, PVA fiber and other inorganic additives. Just with some simple raw materials but it is not easy to make good final sheet that requests exactly in proportion of raw materials, slurry and all process. So, how to make non-asbestos corrugated roofing sheet well?
To get the good final sheet, it has to go through eight basic stages.
Stage 1: Preparing raw material
Preparing materials in accordance with the ratio. PVA fiber (1 – 2 wt%), paper pulp (2 – 5 wt%), inorganic additives (5 – 10 wt%), cement (balance).
Stage 2: Pulp preparation
The first stage of the production is pulp preparation. Crushing kraft paper with water proportionally to convert to slurry.
Stage 3: PVA fiber preparation
After being pre-mixer, PVA fibers are fed into high-speed air stream to further separate single fibers to avoid clumping when mixed with the slurry. Then, the PVA fibers continue to be passed through pneumatic piping system and into the de-pressurizing chamber and then dropped into the vertical hydraulic mixer and dispersed into the slurry mix.
Stage 4: Two – component slurry preparation
Slurry - a component that is pumped quantitatively into the hydraulic vertical mixer. Here, water and cement are supplied quantitatively to create a two-component slurry. In this stage, the prepared additives silica fume and bentonite are also added according to the required material.
Stage 5: Three – component slurry preparation
Adding PVA to the two-component slurry to create a three-component slurry. After the homogeneity of the three-component slurry has been achieved, they are discharged into the turbo-mixer to continue mixing with the necessary additive components.
Stage 6: Green sheet forming process
The green sheet forming process is started from the rotary distributing mixer. Slurry mixture consists of paper pulp, PVA fiber, cement and together with a small percentage of additives to increase forming. All of this mixture is stored in the rotary distributing mixer to avoid any setting taking place and transferred into the green-sheet forming tank at a fixed rate at a certain time interval. The rotary distributing mixer will also add muddy water to the green-sheet forming tank to to maintain necessary water proportion in the mix. According to the principle of hydrostatic pressure and filtering a dilute suspension, the material is transferred on the cylindrical presses, one layered upon another. When the desired thickness is reached, the indicator light comes on, the worker uses the automatic cutter to detach the green sheet from the rotating cylinder sieve. The green sheet is then moved to the 1st conveyer belt, finishing the green sheet forming process.
Stage 7: Product forming process
After cutting the green sheet, it will be picked up and transferred into the 2nd conveyer belt. In these two conveyor belts, the green sheet will be cut by by the vertical and horizontal cutter. Once the specified size are achieved, the air-suction forming unit will picked-up and laid down onto the metal mould. At this point, the product forming process is over.
Stage 8: Product curing process
After the wave sheet is formed, it is moved to the steam curing chamber. The boiler will enhance the setting ability of the product. After 2.5 - 3 hours, the product reaches the required hardness and can be demoulded by automate stacker unit.
With only eight above basic stages, the fiber cement corrugated roofing sheet has been produced successfully. However, after that, the sheet should be properly cured to ensure the best quality, curing time should be 14 days before the day of loading.