Sand grinding in an AAC Raw Material Processing System should produce slurry that is reactive enough for autoclaving, stable enough for accurate dosing, and fluid enough for reliable transfer. The finest possible grind is not automatically the best. Excessive grinding can increase power consumption and slurry viscosity, while insufficient grinding can leave a coarse fraction that settles quickly and reacts less readily during hydrothermal curing.

A useful assessment therefore connects particle size distribution, solids concentration, and slurry flow behavior to the performance of the complete production line. Mill discharge quality matters, but so does the condition of the slurry when it reaches the mixer after storage and transfer. A grinding specification is only meaningful if it supports consistent casting, cutting, and finished-product performance.

Particle size affects both silica reaction and slurry handling

In sand-based autoclaved aerated concrete production, grinding exposes more surface area on silica-bearing particles. During autoclaving, silica reacts with calcium-bearing constituents to form calcium silicate hydrates, including strength-giving tobermorite under suitable process conditions. Smaller particles generally provide more accessible reaction surface, but the result also depends on sand mineralogy, the mix formulation, and the curing cycle.

This distinction matters when comparing sand sources. Two sands with similar total silica content can behave differently because their quartz content, impurities, and grindability differ. Matching a particle size specification does not, by itself, establish equivalent suitability for AAC production.

The coarse end of the distribution deserves particular attention. A slurry can have an acceptable average particle size while still containing a significant coarse fraction. Those particles tend to settle faster and may react less completely within the available autoclaving cycle. Their effect on finished strength depends on the formulation and curing conditions; grinding alone cannot predict the outcome.

At the other end, a larger proportion of very fine particles increases surface area and can raise water demand and viscosity at a given solids concentration. Particle packing also matters: a well-balanced distribution may flow better than a narrower distribution at the same solids content. This is why a single fineness result cannot fully describe slurry quality.

The practical target is a repeatable particle size distribution that supports the established recipe and production cycle. A lower average particle size is useful only when its process benefits justify the extra energy and any change in handling behavior.

Solids concentration determines what the fineness result means

Wet grinding couples size reduction with water addition. Changing the sand-to-water ratio changes the slurry flowing through the mill, the conditions of grinding, and the amount of water subsequently carried into the AAC mixer. Fineness and concentration therefore need to be assessed together.

A dilute slurry may be easy to pump, yet it introduces more water for each unit of dry sand delivered. Unless the batching system compensates, the total mix water changes. That can alter casting consistency, expansion behavior, and the development of sufficient green strength for cutting.

A concentrated slurry reduces the water carried with the sand, but increasing concentration can make mixing and transfer more demanding. As solids concentration rises, interactions between particles become stronger. The resulting viscosity increase can be substantial, particularly when the slurry contains many fine particles or clay-bearing impurities.

There is no universal concentration that suits every sand, mill, storage arrangement, and AAC recipe. The operating range should allow stable grinding, reliable agitation, and predictable dosing while remaining compatible with the total batch water balance.

Density is a useful operating signal, but it is not a complete quality measurement. Converting slurry density into solids concentration requires an appropriate solids-density assumption, and entrained air can distort the reading. Periodic gravimetric measurements—determining solids content from the wet sample mass and its dried residue—provide a reference for checking routine density measurements.

The distinction becomes important when dosing by volume. The same delivered slurry volume can contain different masses of dry sand if concentration fluctuates. Even mass-based slurry dosing needs concentration information to determine how much sand and water enter the batch.

Grinding equipment must be assessed at a defined slurry quality

Wet ball mills are commonly used for AAC sand preparation. Their performance depends on the interaction of feed size, sand hardness, grinding media, mill speed, solids concentration, and residence time. A quoted throughput has limited value unless the feed conditions and required discharge quality are also defined.

Increasing feed rate can increase output while leaving less opportunity for size reduction. Adding water may improve flow through the mill, but it also changes concentration and residence conditions. Neither adjustment should be judged solely by tonnes processed per hour.

Grinding media condition is another source of gradual variation. Media wear changes the charge and its ability to break particles. Where different media sizes are used, their balance influences the treatment of coarse feed and finer material. Liners and discharge components also affect mill behavior as they wear. A setting that produced acceptable slurry earlier may no longer produce the same distribution.

Feed preparation can reduce this variability. Large changes in incoming sand size place a different load on the mill, while debris can disrupt feeding or damage equipment. Consistent feeding and suitable upstream screening help the mill operate within a controllable range.

Where a classification and return circuit is included, coarse material can be returned for further grinding. Its benefit depends on the separation performance and circulating load. A classifier adds pumps, controls, maintenance, and power demand; it should earn its place through a demonstrated improvement in useful capacity or slurry consistency.

Energy comparisons should use energy per tonne of dry sand processed to the agreed quality. Comparing power per tonne of wet slurry can make a more dilute operation appear efficient simply because it handles more water.

Storage and transfer can undo a good grinding result

Acceptable mill discharge does not guarantee acceptable mixer feed. During storage, coarse particles can settle, while fine particles may form a concentrated sediment that is difficult to redistribute. Agitation must maintain sufficient uniformity across the tank, including near the bottom and around the withdrawal point.

An agitator running continuously is not proof that the tank is homogeneous. Tank geometry, liquid level, impeller arrangement, and slurry properties determine where circulation reaches. Poorly mixed zones can remain even when the surface appears active.

Sampling location can conceal this problem. A sample from the upper part of a tank may suggest low solids concentration, while the pump draws denser slurry near the bottom. Comparing samples from defined locations, together with a sample from the delivery line, helps establish whether storage changes the material being dosed.

Pumpability also needs a more useful definition than “the slurry flows.” A suitable slurry should transfer at the required rate without excessive pressure, unstable flow, or progressive blockage. Abrasive wear in pumps and valves can change delivery performance, while deposits in pipes can increase resistance.

Storage time and shutdown conditions belong in the assessment. A slurry that transfers reliably during continuous production may be difficult to restart after an extended stop. The tank and transfer arrangement should support sediment redistribution and an orderly restart under the intended operating schedule.

Trace casting problems through the complete batch

Sand slurry influences the water balance and rheology of the fresh AAC mix. These affect how evenly ingredients disperse and how the mix accommodates gas generated by the aluminum reaction. A change in grinding may therefore appear downstream as altered rise behavior, segregation, or a different time to reach cutting readiness.

Those symptoms are not specific to sand grinding. Lime reactivity, cement properties, aluminum dosing, return slurry, and mixing temperature can produce similar changes. Adjusting mill operation in response to every casting problem risks adding another source of variation.

A stronger diagnosis follows the material through the process. Compare feed sand, mill discharge, storage slurry, and mixer delivery, then relate the measurements to the corresponding batch records. Tracking residence times is necessary: the slurry sampled at the mill now may not be the slurry used in the current casting batch.

Define acceptance criteria through measurable conditions

A technical specification for an AAC Raw Material Processing System should connect output capacity to slurry quality at agreed operating conditions. “Fine grinding” and “uniform slurry” are too broad to support a useful equipment comparison or acceptance test.

The specification should define the incoming sand, required dry-solids throughput, particle size criteria, solids concentration range, and sampling point. It should also state whether the guarantee applies at mill discharge or at delivery to the mixer. These locations answer different questions about system performance.

Measurement methods need equal attention. Wet sieve residue describes material retained above a selected opening; laser diffraction provides a broader particle size distribution. Their results are not interchangeable. Sample preparation, dispersion, and instrument settings should remain consistent so that a reported change reflects the process rather than the test method.

A viscosity result also requires context. Slurries can respond differently at different shear rates, temperatures, and measurement times. Reporting only a viscosity number, without the measurement conditions, makes comparison unreliable.

Product standards establish requirements for finished AAC, but they do not automatically provide a universal sand-slurry fineness or concentration target. Those process limits should be linked to a validated formulation and operating cycle.

An acceptance trial should consequently address several connected conditions:

• Required throughput while meeting the agreed slurry size distribution and concentration.
• Specific grinding energy under those same conditions.
• Uniformity after the intended storage period and reliable delivery to the mixer.
• Stable batching, casting, cutting, and finished-product results using the designated recipe.

Changing sand source, water quality, or return-slurry proportion may require adjustment of the operating window. Return slurry carries water and solids of its own, so its contribution should be included in the batch balance rather than treated as neutral dilution.

When comparing line suppliers, including Shandong Hongfa Scientific Industrial & Trading Co., Ltd., which manufactures AAC production lines, request the grinding and slurry-handling proposal against the same raw-material description and acceptance conditions. This makes differences in capacity, energy use, storage design, and process control easier to assess.

Begin with the sand source and the production recipe, then establish the slurry characteristics that allow that recipe to run consistently. Select and control the grinding system around those requirements. That sequence gives fineness a practical purpose: dependable material delivery and predictable AAC production.