Bulk Material Testing - Powder Caking

Overview

Why Powder Caking Testing?

Caking occurs when particles agglomerate and form solid lumps or masses.

Caking is usually undesirable, resulting in customer complaints, rejected product, and additional processing steps needed to delump the material.

Though caking commonly occurs with many packaged powders, it can also occur in poorly designed silos, hoppers, and other equipment that allows material stagnation. Preventing caking can be difficult if factors contributing to these problems are not well understood.

Caked material within a drum.

This brown sugar shows caking.

Lumpy, caked material.

Caking within a sulfur stockpile.

Caking within a salt stockpile.

Factors

Powder Caking Key Factors

Key factors affecting caking are intrinsic properties and environmental conditions.

Intrinsic properties

Particle size, distribution and shape
Moisture content and migration
Chemical composition/impurities
Particle hardness, surface chemistry

Environmental conditions

Temperature (constant, cycle)
Storage at rest
Consolidating pressure
Relative humidity

Knowing the caking behavior of your material under representative conditions will allow equipment designers to develop strategies for necessary process changes or storage and handling features that either solve or prevent costly powder caking problems.

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Challenge

Powder Caking Tests

The tests below can be run to determine the cause of powder caking, particle agglomeration, or clumping. Representative environmental conditions are important.

Direct shear strength: effect of pressure, temperature, moisture, chemistry, particle size or shape, and time at rest
Moisture sorption/desorption: effect of water vapor uptake (hygroscopicity)
Morphology: observation of particle shape and size using microscope
Surface energy: characterization of bulk solid’s surface

Results

Powder Caking Test Results

The powder caking results are presented in a report which contains:

Overview of caking test method and complete results
Qualitative observations of unique caking behavior
Conclusions and recommendations to avoid powder caking

After completion of the caking tests, we will review the report with you, answer any questions, and discuss interpretation of the results. Common solutions for powder caking can involve storage vessel modifications, powder cooling or heating, and use of anti-caking flow agents.

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