By Charles Ross and Son Company
Efficient mixing of viscous applications takes into consideration, among many other factors, viscosity and level of shear. It is common for batch materials to exhibit fluctuating rheology during different stages of mixing and demand varying shear intensity depending on ingredient additions or temperature limits. The appropriate mixing equipment must therefore have the ability to control flow pattern and fine tune shear input at any point of the mix cycle. Achieving this basic requirement is more straightforward in some applications than others, but even the complex ones can now be processed at better efficiencies due to new developments in high viscosity mixer designs.
The mixing equipment and applications discussed in this paper are based on the collective experience of Ross mixing experts. For over 150 years, Ross has partnered with thousands of companies making high viscosity products for almost all uses and applications. The aim of this paper is to provide a brief compilation of technical and practical information on high viscosity mixing and how specific process needs can be successfully met through the efficient use of specialty mixing equipment.
Anyone who has worked with materials over 100,000 cP knows that viscosity by and in itself presents a distinct mixing challenge. These products require sufficient torque and thorough agitation to achieve a homogenous state. In reality, this requirement is often compounded by other constraints such as the presence of shear- or heat-sensitive raw materials, hard-to-disperse fibers, powders that form tough agglomerates, fragile or abrasive components, highly volatile solvents, or batch material that is very sticky, dense, dilatant, etc. The suitable mixing system must typically tackle one or more of these issues in addition to the underlying rheology factor.
The complete spectrum of high viscosity mixers available to today's manufacturers vary widely in terms of mixing mechanism, agitator style, energy consumption, cost, etc. Some of these technologies are comparatively new and offer several advantages over older mixer designs which may be deemed as "standard equipment" for certain specific applications. At the same time, a number of these classic mixers remain to be the best at what they are known to do but have evolved and incorporated new features for improved efficiency, cleanability, maintenance, etc. From a business perspective, knowing which advances in mixing technology apply to your own process is a great opportunity for upgrading production lines, solving recurring problems, or increasing production with a quick return on investment and improved mechanical reliability.
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