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48 / January 2020 powderbulk.com AVOID OVERMIXING: HOW TO ENSURE MIX QUALITY AND OPTIMAL CYCLE TIME Although there are a variety of different factors that affect bulk solids mixing and blending, some issues are common and one is overmixing. This article explains the risks of overmixing and offers simple tips to help achieve the most optimal mix cycle for your application. Ashley Bester-Barnett, Eirich Machines prepackaged macaroni and cheese mix are just a couple examples of consumer expectations for product consis- tency. Consumer standards must be met, at a minimum, and preferably exceeded, to maintain marketplace suc- cess. This requires mixing cycle optimization. Agglomeration. Depending on the environment, bulk raw materials might be stored in silos, hoppers, drums, or bulk bags. Nonetheless, moisture has a way of making an unexpected and uninvited appearance even in the most controlled environments. Regardless of storage method, humidity is a factor that every manufacturer must mitigate as much as possible. When moisture is present, prolonged mixing times will act as a catalyst to spark reactions between mix components or draw the moisture to particle surfaces. This causes adhesion in the material, as well as with storage vessel walls and mixing agitators, which can lead to agglom- I n the world of bulk solids mixing technologies, the one constant every application must avoid is overmixing. Whether pharmaceuticals or powdered chicken-broth base, prolonged mixing can degrade essential compo- nents in a mix, decrease end-product quality, and — in the worst cases — create triboelectric effects throughout the material, leaving it electrically charged. Energy-efficiency and consistency also are important considerations. Achieving high material throughput with less energy input helps a processing operation stay competitive in today's world of lean manufacturing. But this means more than just quicker batch times. Refined mixing cycle times optimize the processing quality standard. More important, batch mixing repeatability shouldn't depend on an operator but instead on the robust consistency of the technology in place. Overmixing risks There are many risks associated with overmixing. A few of the most common include: Demixing. Defined as "the unintended segrega- tion of materials within a substance," demixing has a higher probability the longer the mixing cycle. The probability of demixing is even higher in mixtures of components with varying bulk densities because of gravity's influence. Heavier materials will undoubtedly sink to the lowest region of a vessel or mixture, which negates the possibility of homogeneity (an ideal mix- ture) over time. While there may be quality tolerances where this wouldn't be a problem, in industries such as pharmaceuticals where active ingredients must be time-released into specific parts of the digestive system for instance (think intestine rather than stomach), mix consistency is critical. Consumer demand also matters. The same nut-to- fruit ratio in each trail mix package or consistent color in FIGURE 1 A simple visual streak test shows that nail enamel and pigment weren't evenly dispersed in the mixing process.

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