How to deal with the fine calcium carbonate powder whose bulk density changes a lot in your calcium carbonate powder packing machine?
Bulk density variations can be caused by a variety of factors. Please consider the following factors when you choose a fine powder packing machine.
First of all, if a material is compressible, like most fine powders are, then the level of pressure on the material can induce density variability. For example, fine confectionary sugar is packed at the bottom of the package, while at the top it remains quite fluffy.
Secondly, a fine material can be subject to aeration, and some materials, like fumed silica, can retain air for several hours. If the fine calcium carbonate is aerated at all from the use of flow aids, like Solimar-type air pads, then this can induce a large bulk density change from a compacted state to an aerated state where the material could behave like a liquid. Though the flow aid can be helpful in overcoming bridging problems in a converging hopper, the material could then flow like a liquid causing other processing issues.
Third, the flow pattern for the material in the hopper, along with the requisite flow problems, can induce bulk density variability. You indicate that the product “hangs in the hopper”, which means the material likely discharges in a funnel flow pattern. With funnel flow and fine powders that are cohesive, ratholing can result, yielding flow through a small central channel of stagnant material in the hopper. The powder moving through this small channel can remain quite aerated and flow like a liquid with large swings in bulk density as more deaerated material makes its way in to the moving stream. Furthermore, if the rathole forms and then collapses, this is a common manner in which density will vary quite dramatically with a fine powder.
It is important to know the flow pattern of material within the hopper; if mass flow, then ratholing is not possible and no stagnant regions exist. If funnel flow, many scenarios, as discussed above, can lead to powder density variability. The key will be to run flow tests on your powder to understand what the flow pattern is in the hopper, then to understand what flow obstructions could result. Also, knowing the material’s compressibility and permeability (resistance to air flow) will help to resolve the density variability issues.
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