DO YOU NEED TO IMPROVE POOR POWDER FLOW?

Bridging, blocking and powder segregation are the traditional powder handling challenges. Is your product quite sticky and poor flowing? Are you having trouble in getting it out of your containers? What methods are you deploying to free this powder? Over the years we have seen facilities where product has got stuck in the outlet of the container or hopper. In order to free the material, we have seen operators use mallets to thump the outside of the bin or rods to try to unblock the obstruction. Hammering the side of the equipment both distorts it and only leads to problems further down the track. Not exactly good manufacturing practice either. What has happened in the bin to cause this? There are commonly two such causes: rat-holing and bridging. Rat-holing happens when flow only takes place directly above the outlet of the container. Product at the sides gets held up and can cake or agglomorate. Once the central core is discharged, flow stops and the rest of the material remains stuck to the sides. This is when the mallets are deployed, to help create vibration and free the material. The sloping hopper/bin walls are not steep enough or low enough in friction for material to move, so instead the particles cling to the sides and themselves. This core flow means that particles can have a tendency to segregate, which means the blend becomes demixed. Yield is also poor as product sticks to the sides of the container. Bridging is when an arch-shaped block of powder forms above the outlet. It is caused when particles interlock and become cohesive. Initially product flows, but this quickly stops once the free material is discharged. At this point the container is usually opened from above and rodded. This of course can create a dusty environment and can sometimes be a very hazardous operation. What can be done? There are several options available to correct this problem. The first is to use the geometry and the material of the hopper to induce movement. Material flow is determined by a combination of the angle at the bottom of the hopper and the friction caused by the internal surface, so for instance a shallower angle could be used if the surface has low friction, or a rougher surface would need a steeper angle.

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