Moisture Migration Analysis | Powder Caking Analysis

Overview

Moisture Migration & Caking Analysis

Caking results when particles agglomerate and form solid lumps or masses. Typically caking is 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. Key factors affecting caking are intrinsic properties and environmental conditions. Caking induced by moisture is the most common cause.

Modeling Moisture Migration and Caking is an efficient way to test conditions rapidly without having to stop production or wait for expensive stoppages due to agglomeration.

Crystals lumping together and building a bridge, leading to caking of the material.

Caking of powdered material.

Issues

Why is Caking a Problem?

When bulk solids agglomerate or lump due to the formation of strong bonds between the particles, it’s usually a problem.
Awareness may not occur until it causes operating difficulties. Common customer complaints include:

“Sometimes the product flows well, and at other times it doesn’t. The competitor’s product always flows well.”
“Some bulk bags are caked so hard that we cannot not unload the material; we have to break them up by ramming them against a wall.”
“Some bulk containers are taking excessive time to unload. This is costing us too much money.”
“Some batches are full of agglomerates that don’t dissolve.”

Why does material Cake?

Moisture Migration

Moisture migration due to temperature gradients can produce localized high levels of moisture inside product bags to cause caking. This is the process where moisture from relatively hot sections of the bulk bag migrates to cooler areas.

Temperature Variations in Shipping Containers

Wide Temperature gradients can be imposed on bagged products during transport, either by diurnal changes in environment or when the product is packed out hot and put into the warehouse to cool. During transportation in ship containers, there could be great variation of ambient temperature between day and night near landmasses (e.g. in port). In addition to the air temperature, solar heating can exacerbate the temperature variations.

Moisture Migration & Caking Analysis Challenges

Permeation of moisture from ambient through the plastic bag liner can also produce sufficiently high moisture content for caking during prolonged storage in a warehouse or during transport inside containers. Chemical reactions (ex: dehydration) can also liberate water inside the bagged product to cause caking during storage.