Bridging
In bulk material technology, bridging refers to the formation of a stable material structure across a container opening or outlet.
What happens when bridging occurs?
The particles support each other, "locking" together to form a kind of bridge. Although sufficient material remains in the container, this bridge prevents a consistent flow of bulk material, and can even stop the flow entirely.
Bridging occurs particularly with cohesive or poor-flowing bulk materials and can significantly impair the continuous supply of material to a feeder.
How does bridging occur?
Whether a bulk material tends to form bridges depends on the interaction of various material and process conditions. Factors that play a role include particle size and shape, moisture, compaction, and the flowability of the material, among others. Fine or cohesive powders, for example, can exhibit stronger binding forces between individual particles, allowing them to form stable structures.
The container's design also plays an important role. The container walls' geometry and inclination as well as the outlet's size and shape affect how reliably bulk material can flow.
Why is bridging problematic in feeding?
A feeder can only work consistently if it is reliably supplied with material. If a bridge restricts or completely interrupts the material flow, this can result in feed rate fluctuations or a break-off of the material supply.
To avoid bridging, container geometry, feeder, and bulk material properties must be coordinated. Depending on the application, agitators in the feeder or separate discharge aids or bin activators for the upstream storage container, for example, can help ensure a reliable material flow.
Preventing bridging contributes significantly to a consistent material flow and a reliable feeding process.