How Particle Properties, Moisture, Cohesion and Fluidization Behavior Affect Air Slide Conveying
Introduction
Air slide conveyor material compatibility depends primarily on whether a powder can be fluidized consistently by low-pressure air and then move under gravity.
Dry, fine powders such as cement, fly ash and raw meal are commonly conveyed by air slides, but material name alone is not enough to determine suitability. Moisture, particle size distribution, cohesion, bulk density, temperature and the tendency to agglomerate can significantly change how the same material behaves.
This guide explains which materials are generally suitable for air slide conveying, which require additional evaluation, and which are normally better handled by another conveying method.
Why Fluidization Determines Material Compatibility
A powder is suitable for air slide conveying only if air can pass through the material bed and reduce particle-to-particle resistance enough for the powder to flow under gravity.
This behavior is influenced by particle size distribution, moisture, cohesion, bulk density and material condition. Two powders with the same general name may therefore behave differently if their fineness, moisture or storage condition changes.
For a detailed explanation of the conveying mechanism, see Air Slide Conveyor Working Principle.
Air Slide Conveyor Material Compatibility Overview
| Material | General Suitability | Main Factors to Verify |
|---|---|---|
| Cement Powder | Generally suitable | Moisture, fineness, agglomeration and temperature |
| Fly Ash | Generally suitable | Fineness, moisture, bulk density and fluidization stability |
| Raw Meal | Generally suitable | Particle distribution, moisture and flow behavior |
| Slag Powder | Generally suitable when fine and dry | Fineness, moisture and abrasiveness |
| Limestone Powder | Generally suitable when sufficiently fine and dry | Particle size distribution and moisture |
| Lime Powder | Requires evaluation | Moisture sensitivity, cohesion, temperature and particle condition |
| Dry Gypsum Powder | Requires evaluation | Moisture, cohesion and tendency to cake |
| Other Fine Mineral Powders | Requires evaluation | Fluidization behavior, particle size, moisture and temperature |
| Coarse Aggregate or Clinker | Generally unsuitable | Large particles do not fluidize reliably |
| Wet or Sticky Powders | Generally unsuitable | Cohesion and buildup prevent stable fluidization |
Material compatibility should be evaluated from the actual powder condition rather than the material name alone. A dry cement powder may fluidize well, while the same material can become difficult to convey after moisture pickup, caking or prolonged storage.
Cement Powder
Cement is one of the most common materials handled by air slide conveyors because it is normally fine enough to fluidize effectively when kept dry.
The main factors to verify are:
✓ Moisture and tendency to cake
✓ Fineness and particle distribution
✓ Bulk density
✓ Material temperature
✓ Presence of hardened lumps or agglomerates
Cement that has absorbed moisture or contains hardened lumps may no longer behave like freely fluidizable powder. Where occasional agglomerates are present, upstream screening or lump breaking may be required before the material enters the air slide.
Fly Ash
Dry fly ash is generally suitable for air slide conveying because of its fine particle size and ability to become aerated.
However, fly ash characteristics can vary significantly depending on source, fineness, storage condition and moisture. Very fine powders may respond quickly to aeration, while compacted or moisture-affected fly ash may require closer evaluation of airflow and feeding conditions.
Do not assume that all fly ash behaves identically. The actual material condition should be considered before the conveyor configuration is finalized.
Lime Powder
Lime powder can be conveyed by an air slide in some applications, but its suitability should be evaluated more carefully than simply assuming that all fine lime products will fluidize in the same way.
Important factors include:
✓ Moisture sensitivity
✓ Cohesion and caking tendency
✓ Particle size distribution
✓ Material temperature
✓ Abrasiveness
✓ Storage condition
If the powder tends to cake, absorb moisture or form persistent agglomerates, stable fluidization may be difficult even when the nominal particle size appears suitable.
Raw Meal and Slag Powder
Dry raw meal is commonly compatible with air slide conveying when its particle size distribution and moisture allow stable fluidization.
Finely ground slag powder can also be suitable, but material fineness, moisture and abrasiveness should be checked before final equipment selection.
For both materials, suitability should be confirmed from the actual operating condition rather than assuming that all powder from the same process behaves identically.
Key Material Properties That Affect Air Slide Compatibility
Particle Size and Particle Distribution
Air slide conveyors are intended primarily for fine powders rather than coarse granules or lumps. However, there is no single particle-size limit that can be applied reliably to every material.
Fluidization behavior depends on particle size distribution, particle shape, density and cohesion together. Large particles, irregular granules or a high proportion of coarse material can reduce fluidization stability and increase the risk of settling or buildup.
Moisture and Cohesion
Moisture can increase cohesion between particles and reduce the ability of a powder to fluidize consistently.
Materials that normally flow well when dry may become sticky, form agglomerates or block the conveying surface after absorbing moisture. The acceptable moisture level therefore depends on the specific powder and operating conditions rather than a universal percentage.
Bulk Density
Bulk density affects conveying capacity and system sizing, but density alone does not determine whether a powder is compatible with an air slide.
Two powders with similar bulk density may have very different fluidization behavior because of differences in particle size, cohesion, moisture and permeability.
Flowability and Agglomeration
A powder that forms persistent lumps, cakes during storage or bridges at feeding points may not enter the air slide in a uniform condition.
Compatibility therefore depends not only on how the powder behaves while aerated, but also on whether it can be fed consistently into the conveyor.
Material Temperature
Material temperature should be checked because it affects the suitability of the air slide fabric, sealing materials and other components.
High-temperature applications require confirmation that the selected fabric and equipment materials are suitable for the actual operating temperature.
Abrasiveness
Abrasive powders may increase wear on chute surfaces, the fabric support plate and transfer points.
Abrasiveness does not automatically make a material unsuitable for air slide conveying, but it should be considered when selecting materials of construction and maintenance intervals.
Suitable, Conditional or Unsuitable: How to Judge a Powder
A practical material compatibility assessment can be divided into three categories:
Generally Suitable
The powder is dry, fine, non-sticky and fluidizes consistently under low-pressure air.
Typical examples include dry cement, fly ash, raw meal and some finely ground mineral powders.
Requires Evaluation
The powder is fine enough for air slide conveying but has characteristics that may affect fluidization, such as moisture sensitivity, high cohesion, elevated temperature, abrasiveness or variable particle distribution.
Examples may include lime powder, gypsum powder and some process-specific mineral powders.
Generally Unsuitable
The material contains large granules or lumps, is wet or sticky, strongly cohesive, or cannot be fluidized reliably by low-pressure air.
In these cases, another conveying method may be more appropriate. For applications where mechanical conveying may be required, see Air Slide Conveyor vs Screw Conveyor.
What to Check Before Confirming Material Compatibility
Before confirming air slide conveyor material compatibility, collect the following information about the actual powder condition:
✓ Material name
✓ Bulk density
✓ Particle size or fineness
✓ Moisture content
✓ Material temperature
✓ Flowability or tendency to cake
✓ Presence of lumps or coarse particles
✓ Previous fluidization or aeration behavior, if known
When material behavior is uncertain, representative powder testing or operating experience is more reliable than selecting equipment from a generic material name alone. For general reference on bulk-solids flow-property testing, see ASTM D6128 – Shear Testing of Bulk Solids Using the Jenike Shear Tester.
For detailed conveyor sizing after material suitability has been confirmed, see the Air Slide Conveyor Selection Guide.
Air Slide Conveyor Material Compatibility FAQs
What types of materials are generally suitable for air slide conveyors?
Dry, fine and fluidizable powders such as cement, fly ash, raw meal and some finely ground mineral powders are generally suitable. Actual compatibility depends on the powder condition and fluidization behavior.
Is there a maximum particle size for air slide conveying?
There is no single particle-size limit that applies to every powder. Suitability depends on particle size distribution, shape, density, cohesion and the ability of the material bed to fluidize consistently.
How does moisture affect air slide conveyor material compatibility?
Moisture can increase particle cohesion, promote caking and reduce stable fluidization. The acceptable moisture level depends on the specific material and process conditions rather than one universal percentage.
Can lime powder be conveyed by an air slide conveyor?
It can be suitable in some applications, but moisture sensitivity, cohesion, temperature, particle condition and fluidization behavior should be evaluated before the system is selected.
Are coarse or lumpy materials suitable for an air slide conveyor?
Generally no. Air slides are intended for fluidizable powders rather than coarse aggregates, clinker lumps or other large particles. These materials normally require another conveying method.
Conclusion
Air slide conveyor material compatibility is determined by actual powder behavior rather than material name alone. Dryness, particle distribution, cohesion, fluidization, bulk density, temperature and agglomeration tendency should be considered together.
Cement, fly ash, raw meal and many fine mineral powders are commonly suitable, while moisture-sensitive, strongly cohesive, coarse or lumpy materials require more careful evaluation or a different conveying method.
Once material suitability is confirmed, conveyor width, capacity, slope, airflow and layout can be evaluated separately during the equipment selection stage.
Need Help Evaluating Your Powder?
Send LVRUI your material name, bulk density, particle size or fineness, moisture, temperature and any known flow or caking characteristics.
Based on this information, LVRUI can first evaluate whether the material is generally suitable for air slide conveying. If suitable, conveying capacity, distance, available elevation difference, air supply and equipment configuration can then be reviewed for preliminary selection.
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