Asbestos Cement Sheet Making Machine

 

I. Main Production Raw Materials of Asbestos Cement Sheet Making Machine

1. Curing Materials:

Cement: Mainly uses ordinary Portland cement (OPC), requiring stable quality and high grade (such as P.O 42.5 or higher). It is the basis for the strength of the tile body. Sometimes, a small amount of high-alumina cement or fast-setting cement is added to adjust the setting time or early strength.

Siliceous Materials: Quartz sand or silica sand. Provide a framework, increase hardness and wear resistance, and reduce shrinkage. The particle size (usually fineness modulus around 1.8-2.2) and clay content need to be strictly controlled.

Active Mineral Additives: Such as fly ash, silica fume. Partially replace cement to reduce costs, improve workability, and enhance later strength and durability (volcanic ash effect).

2. Reinforcing Fibers (Non-Carbon Fiber):

Cellulose Fiber: Comes from chemical pulp or mechanical pulp (such as bleached coniferous wood pulp). The most commonly used alternative fiber, providing good dispersion, initial wet strength, and certain ultimate strength. The cost is relatively low.

Synthetic Fibers:

Polyvinyl alcohol fiber: High strength, high elastic modulus, good alkali resistance, is an important reinforcing material for high-performance tiles.

Polypropylene fiber/Polyethylene fiber: Low cost, mainly provides crack resistance (crack resistance effect), with relatively small contribution to ultimate strength.

Aramid fiber: High strength, high modulus, high temperature resistance, used in special high-performance products, with high cost.

Mineral Fiber: Basalt fiber (high temperature resistance, corrosion resistance, high strength), glass fiber (requires alkali coating, AR-Glass). The application is gradually increasing.

3. Water: Meets the standard for concrete mixing water. It is a necessary medium for forming the cement paste and undergoing hydration reactions.

4. Additives (Small amount but crucial):

Dispersants/Retarding Agents: Improve the fluidity of the slurry, reduce the water-cement ratio, and enhance density and strength. Commonly used are high-efficiency polycarboxylate retarding agents.

Early Strength Agents: Accelerate cement hydration, increase early demolding strength.

Retarding Agents: Used when it is necessary to extend the operation time.

Defoaming Agents: Reduce the bubbles introduced during mixing and molding, improve product density.

Waterproof Agents/Hydrophobic Agents: Improve the waterproof performance of the finished product (sometimes applied in surface treatment or coating).

Paints: Used when producing colored tiles, using inorganic pigments (such as iron oxide series) that are resistant to alkali.

 

 

II. Core Production Process Flow

The mainstream production methods for fiber cement tiles are "wet spinning method" and "sheeting method". The wet spinning method has lower equipment investment and a simpler process, making it the mainstream for domestic small and medium-sized enterprises; the sheeting method has a higher degree of automation and produces products with more uniform and stable performance, making it suitable for large-scale production. The following will provide a detailed explanation using the wet spinning method as an example:

1. Raw material storage and pre-treatment:

Cement and sand are stored in silos.

The sand needs to be dried (to control moisture) and sieved (to control particle size).

Fibers (such as pulp) may need to be unpacked, shredded or pulped (mixed with water in a pulping machine to form a uniform pulp).

Additives are prepared according to the formula.

2. Ingredients and Mixing:

According to the precise recipe proportions, pour the cement, treated sand, fiber pulp (or dry fibers), water, and various additives into a high-speed mixer.

Mixing is a crucial step, requiring:

High shear force: Ensure that the fibers are fully dispersed without clumping.

Uniformity: Form a uniform, stable, and moderately fluid slurry.

Control the water-cement ratio: Keep it as low as possible while ensuring fluidity to enhance the product's strength.

Transfer the mixed slurry to a storage tank or directly supply it to the molding machine.

3. Forming (Core of the Slurry Flow Method):

Forming machine: The core equipment consists of a continuously rotating blanket (a flat filter cloth) and a vacuum dehydration box below.

Slurry tank: The slurry flows (or overflows) uniformly from the slurry tank onto the continuously running blanket.

Initial dehydration: The slurry naturally dehydrates on the blanket due to gravity, forming a layer of wet material.

Vacuum dehydration: The wet material layer follows the blanket to the top of the vacuum box. Under the suction effect of vacuum, a large amount of water and air are quickly removed, and the material layer is compressed, forming a continuous wet brick with a certain initial strength. Vacuum degree and dehydration time are key control parameters.

Gathering/Layering: According to the thickness requirements of the brick, the blanket will cycle multiple times (usually 2-4 layers), and the new material layer is superimposed on the partially dehydrated bottom layer. Through the pressure of the blanket and vacuum, it is tightly laminated together to form an overall wet piece.

Trimming/Cutting edges: The edges of the wet piece may be trimmed by rotating cutting blades to ensure uniform width.

Cross-cutting: The continuous wet bricks pass through an automatic cross-cutting machine and are cut into single pieces of wet bricks according to the set length. The cutting methods include rotating saw blades or steel wire cutting.

4. Piling and Pre-Curing:

The individual wet tile blanks cut off are automatically stacked on the curing tray (cold steel).

The stacking height is determined by the tile type and strength.

The wet tile blanks, along with the tray, are sent to the pre-curing area (usually a static room with controllable temperature and humidity). At this stage:

The cement begins to undergo initial hydration.

The moisture distribution within the tile blanks becomes more uniform.

A certain initial strength (the "demolding strength") is achieved, allowing for demolding within 8-12 hours. After being stacked indoors for a few days, they can be shipped out or moved outdoors.

5. Demolding, Drying and Post-Treatment of Asbestos Cement Sheet Making Machine:

Demolding: After the curing process is completed, the tiles are removed from the support board.

Drying/Natural Curing: The tiles after steam curing contain a small amount of residual moisture. They need to be naturally dried in a well-ventilated area or a drying room for a period of time (from a few days to a week) to reach a balanced moisture content and further improve stability.

Surface Treatment (Optional):

Surface Coating: Spray or roll apply acrylic, silicone or fluorocarbon coatings to provide color, enhance waterproofing, resistance to stains and aesthetic appeal.

Surface Etching: Before forming or curing, use a patterned roller to imprint wood-like or stone-like textures.

Polishing/Inspection: Check the appearance, dimensions, for any cracks or other defects, and make necessary adjustments (such as grinding off burrs).

Packaging and Storage: Qualified products are packed according to specifications. Usually, they are bundled or stacked on pallets and stored in a dry warehouse awaiting shipment.

 

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