How Does an AAC Block Production Line Transform Raw Materials into Finished Products?

Stage 1: Raw Material Preparation as the Quality Foundation

Quality in an AAC production line is determined before the mixer is ever filled. Particle size distribution, chemical activity, and dosing consistency at this stage set the ceiling for everything that follows.

Siliceous Material Grinding

Fly ash or sand provides the silica source. Grinding fineness directly affects the reactivity of the mix and the final strength development.

• Target fineness: 200 to 300 mesh.
• Residue on sieve: less than 15 percent.
• Ball mill energy consumption is a major operating cost and should be evaluated against throughput and fineness targets.

Calcium Material Preparation

Quicklime is crushed and ground to an active, consistent powder. CaO content should be controlled at 85 percent or higher. Variations in lime activity shift the foaming window and cause density fluctuation across the production batch.

Aluminum Agent Dosing

The aluminum-based foaming agent is used in very small quantities, but its dosing precision is critical. A deviation of plus or minus 0.1 percent can move the finished density outside specification. In a well-designed AAC block plant, the aluminum dosing circuit is isolated, temperature-controlled, and verified by weight feedback.

Iron Removal and Material Handling

Magnetic separation with a removal rate of 99 percent protects mills, pumps, and cutting wires from metallic debris. Inconsistent feeding from the raw material yard creates downstream batching errors that no control system can fully correct.

Stage 2: Batching and Mixing Under Precision Discipline

Batching is where the theoretical mix design meets real material behavior. Small errors in weighing or sequencing produce large errors in the final product. A disciplined AAC block production line treats batching as a controlled process, not a manual loading operation.

PLC-Controlled Automatic Weighing

Modern AAC production lines use PLC-controlled weighing systems with an accuracy standard of plus or minus 0.3 percent. This applies to silica material, lime, cement, gypsum, aluminum agent, and water. Each scale should have independent calibration records and automatic compensation for material buildup.

Slurry Temperature Control

Pouring temperature is typically controlled between 40 and 45 degrees Celsius. This range supports uniform gas formation and consistent setting behavior. If the slurry is too cold, foaming is slow and uneven. If it is too hot, the mix can set before the gas reaction is complete.

Mixing Time and Uniformity

Mixing time must be long enough to disperse the aluminum agent uniformly, but not so long that the reaction begins inside the mixer. In practice, the mixing cycle is defined by the reactivity of the lime and the volume of the batch.

Consequences of Loose Batching Discipline

• Density variation between batches increases.
• Rejection rates rise at the cutting and autoclave stages.
• Autoclave cycle times become inconsistent, wasting steam.

Stage 3: Pouring, Foaming, and Pre-Curing Variables That Decide the Outcome

After mixing, the slurry is poured into molds where the foaming reaction and initial setting occur. This is a time-sensitive stage with narrow operating windows.

The Foaming Reaction

The aluminum agent reacts in the alkaline slurry and generates gas bubbles. These bubbles expand the mixture to several times its original volume and create the porous structure that defines autoclaved aerated concrete. The reaction rate depends on temperature, alkalinity, and the fineness of the aluminum agent.

Pre-Curing Time Window

The green body must reach sufficient hardness before it can be demolded and cut. The pre-curing window is a balance:

• If the body is demolded too early, it lacks strength and collapses or deforms.
• If it is demolded too late, the body becomes too hard and can block or overload the cutting station.

Ambient Temperature and Humidity

Workshop temperature and relative humidity affect surface drying and hardness development. In cold climates, pre-curing rooms may require heating. In hot and dry conditions, surface moisture loss can cause crusting that interferes with cutting quality.

Practical Control Points

• Record the pouring temperature for every mold.
• Monitor the rise height of the foaming mix.
• Use a penetration test or hardness probe before demolding.
• Maintain a stable pre-curing environment rather than relying on operator judgment.

Stage 4: Cutting Precision That Determines Yield

Cutting converts the large green body into blocks of final dimensions. The accuracy of this stage directly affects material yield, autoclave loading efficiency, and the amount of recyclable waste.

Longitudinal and Cross Cutting

Modern AAC block production lines use a combination of longitudinal and cross cutting. The green body first passes through vertical wire cutting, then through horizontal wire cutting. Each axis must be independently controlled so that dimensional tolerances remain within plus or minus 1 millimeter.

Cutting Wire Management

Wire tension, wear, and replacement intervals are critical. A worn wire produces wider kerfs, increases waste, and can leave rough surfaces. Scheduled replacement based on production volume is more reliable than replacement based on visual inspection alone.

Waste Recovery

Cutting generates green waste that can be returned to the mixer. A well-designed recovery system can reuse up to 95 percent of this material, reducing raw material consumption and disposal costs.

Stage 5: Autoclave Curing and the Final Transformation

Autoclave curing is the stage where the green body becomes a finished AAC product. The pressure and temperature profile determines crystalline structure, strength, and dimensional stability.

Pressure and Temperature Curve

Typical autoclaving conditions are 1.2 MPa saturated steam pressure and approximately 188 degrees Celsius. The cycle has three phases:

• Pressure rise: Gradual increase to avoid thermal shock and cracking.
• Constant pressure: The period during which calcium silicate hydrates form and strength develops.
• Pressure release: Controlled reduction to prevent rapid expansion and internal stress.

Energy Optimization

Steam consumption is one of the largest operating costs in an autoclaved aerated concrete production line. Heat exchangers that recover waste steam can return up to 70 percent of the energy to the next cycle, reducing boiler load and overall energy cost.

Common Autoclave Defects

• Cracking from too-fast pressure rise.
• Incomplete strength development from insufficient constant-pressure time.
• Surface damage from rapid pressure release.

Stage 6: Finished Product Handling, Inspection, and Packaging

After autoclaving, the product must be separated, inspected, and prepared for transport. Rough handling at this stage can damage edges and corners, turning a technically sound product into a rejected one.

Separation and Lifting

Because AAC blocks are autoclaved in large cakes, they must be separated into individual blocks. A cake splitting machine and finished product lifting equipment work together to separate the layers without shock loading. The synchronization of these two systems determines edge quality.

Inspection Standards

Packaging and Edge Protection

Packaging protects the product during storage and transport. Edge protectors, strapping tension, and pallet stability should be specified so that the product arrives at the construction site without chipping. For export orders, moisture protection may also be required.