Preventing Flow Stoppages in Powder Handling Processes
By Robert G. McGregor, Ametek Brookfield Engineering |
Predicting powder flow behavior is important to successful solids-handling processes. Provided here is a review of shear-cell testing and how the technique can be used to predict arching, ratholing and other behaviors
The phrases “failure to discharge” and “erratic flow in the hopper” are sometimes heard from frustrated production-floor workers when powder processes start to misbehave. Taking corrective action for these types of problems may involve shutting down the process to investigate the root cause. Ideally, processors would identify suspect powders prior to processing, thereby avoiding costly downtime. Traditional methods for predicting flow behavior — flow cup, angle of repose and tap tests — are giving way to shear-cell testing, which measures inter-particle sliding friction, as well as powder-to-hopper wall interfacial friction. This article explains the science behind shear-cell measurements. Predictions for density-compaction ratio, potential arching dimension or rathole diameter, and design requirements for hopper half angle to achieve mass flow are reviewed.
Types of powder flow behavior
Figure 1 illustrates two common flow types. “Core flow” is the default discharge pattern experienced on the…
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