Dispersing: Simple in Theory – Difficult in Practice?
The function of the Rotor-Stator-System by construction depends on the narrow gap between rotor and stator. In general, both parts (the rotating and the static part) are equipped with toothed geometries. Due to the given geometries, the shear gradient is maintained constant and almost independent from the viscosity of the liquid.
In practice, the production of a suspension is sometimes quite difficult. All types of machines mentioned above, are installed directly into a vessel or lowered into the vessel by the means of a lift. Normally the basic liquid is filled into the vessel and the raw materials are added simply be pouring them onto the surface of the liquid.
What to Expect of Powder Bulk Products
Powders have a rather large specific surface, in extreme cases (e.g. for fine pigments, nano powders, or silica acids) it calculates to about 300,000 m²/kg of powder. In most production scenarios, several kilogramms of these powders are added directly onto the surface of the liquid. The liquid only has an area of a few square meters so it soon becomes obvious that there is an adverse relation between the surface of powder and the surface of liquid. The result is that individual particles will not be wetted, only the agglomerates and aggregates become roughly wetted.
How Adding a Liquid Can Help
The powder floats on top of the surface and an intensive mixing effect has to be applied to wet all the particles. When a dissolver is used, a Vortex builds up in the liquid and besides the powder air is brought into the product as well.
Very often, different raw materials have to be dispersed into a liquid, creating a high work load for the handling of the different packing systems such as bags, barrels and containers that have to be moved and emptied.
Some of the used products tend to stick, so a powder wetting unit can help. Learn, how to achieve an efficient dispersing of sticky products on page 3!
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