Batch Mixer loading
In which sequence to load materials in a mixer ? At which speed ... ?
How to optimize the loading sequence of a batch mixer
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Coefficient of Variation
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Loading a mixer should be the most trivial operation in the whole mixing cycle... but as often in bulk solids processing, it is not. Indeed, the way the components will be loaded in a mixer will have an effect on the performances of the mixer.
2. Loading sequence
The important rule to apply is NEVER to load 1st in the mixer the small ingredients, like flavors, active principles, pigments... Indeed, those small ingredients can actually lie in dead area difficult more the mixer to disperse, like the small gap in between the agitator and the mixer housing. If a good mix can be reached, it will be after a longer than required mixing time.
The best is to load in sandwich the small ingredients in between 2 layers of major ingredients. The distance towards each area of the mixer will be optimized. For efficient mixers, it is also generally acceptable to load the small ingredients on the top, which may have some interest to optimize the cycle time of the powder / bulk solids mixer.
Loading in layers with a symetric spreading in the mixer is also recommended, particularly for tumblers for which the mixing time can be increased a lot if the materials are loaded by sections .
3. Mixing speed at loading
For mixers with an agitator (ribbon, paddle, ploughshare...) it is recommended to run the mixer at low speed ("ATEX speed") when loading the mixer. It helps to even the product in the mixer, allows to optimize the load, make a kind of premix and avoids to stall the agitator if it were to start on the mixer already full of product.
The mixer should be equipped with a filter to allow for the air exchange required when introducing a large amount of solids to the mixer during loading. Loading should indeed be done as quick as possible to optimize the cycle and the flow of product should not be hampered by a slight overpressure in the mixer, in case a filter is not present, undersized or clogged.
4. Optimization of the loading of a dry-mixer
From the observations above, some recommendations can be drawn in order to improve the cycle time of a mixing operation by loading quicker and promoting a short mixing time :
 Dealing with powder blending problems. Muzzio, Powder Bulk Engineering, 2018
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