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How do high speed dispersers work?

April 10, 2013

A high speed disperser is quite a sought after industrial contraption in the present day and age. Widely used across the globe for the manufacture of or as a contributor in the process of manufacture of adhesives, sealants, batteries, electronics, chemicals, cosmetics, food, glass, cement, certain ceramics and metals, ink, paint, pharmaceutical and medical products, plastics, synthetics, and practically all items of everyday use that are manufactured as emulsions or colloids – meaning a symbiotic existence of two or more mutually insoluble substances (solid-liquid, liquid-liquid, or even solid-solid) in a suspended state.

The processes involved in the production of these commodities may be categorized (based on the physical state of the ingredients) as wet mixing, dry mixing, blending or milling. A typical disperser is comprised of a combination of a vertical shaft and a blade shaped like a disc that rotates when subjected to a very high shear force. The speed at which this blade rotates is usually as high as 5000 feet per minute. As a result of this centrifugal movement that generates a radial flow of the ingredient particles inside the stationary mixing container. These particles are pulled towards the sharp edges of the blades and are thus torn into several more particles that are much smaller in size. Simultaneously, these particles are dispersed into the liquid medium they are to be blended in.

To judge the consistency of the dispersed medium, the centipoise is used as a unit. It measures the dynamic viscosity of a liquid, which is essentially the amount of force that would be required in order to move one layer of the liquid in question with respect to another liquid, the latter being taken as the standard or base value for the same. This base liquid is usually distilled water, for which the value of dynamic viscosity is about 1 centipoise at a temperature of 21 degrees Celsius (or 70 degrees Fahrenheit).

To get a general idea of what a highly viscous liquid means in practical terms, it may be noted that the viscosities of honey, molasses and lard are 2000, 5000 and 100000 centipoise respectively. To synthesize a liquid of viscosity up to 50000 centipoise, a high speed disperser is quite adequate. For higher viscosities, however, a multi shaft mixer may have to be introduced. This mechanism, when used in conjunction with the disperser, can support the manufacture of liquids measuring several hundred centipoise in viscosity.

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