The risk of segregation

Question

The result of mixing dry solid ingredients may be a definite pattern of particle segregation. This is due to differences in the physical properties of ingredients and the shape and surface characteristics of the mixer. 
Particle size may be the most important factor in causing this phenomenon. In general, the smaller and the more uniformly sized the ingredients are prepared, the more nearly they will approach random distribution during mixing. In many formulae, a decrease in particle size is necessary to attain a sufficient number of particles of an essential additive (vitamin, mineral, medication) for dispersion in each daily feed unit. This may require the particle size to be the diameter of dust, from 10 to 50 microns.
Certain ingredients are unstable in finely divided form and likely to acquire an electrostatic charge. The concentration of particles on a charged surface, roughness of the mixed and stickiness of oily and wet ingredients are factors in causing segregation when very small particles are mixed and when these are much smaller than the bulk of other ingredients.
Segregation or poor blending can have many implications, including:

Rejected product
Variable color, look or taste
Excessive blend times
Customer complaints
Erratic dosage 
Product or process delays
Inconsistent particle size
Poor quality control

Pelleting prevents the segregation of ingredients in a mixing, handling or feeding process. By feeding a pelleted feed, the animal is more apt to receive a totally mixed ration than one that has separated through these processes.

Enrique Diaz · Accepted Answer

Ingredients segregation is a problem that will directly affect the balancing on the formula and at the same time animal performance in the field.

Segregation takes place in the mixer and is caused mainly for excess or lack of mixing time. There are other factors that might be involved like bulk density of the ingredients, non-uniform particle size reduction, addition of liquids, sequence of ingredients during dosing and others.

Mixing time is the sum of dry time plus wet time mixing. Dry time is very short and includes the mixing of the ingredients without any liquid. The wet mixing time start when liquids are added into the mixer, this takes longer time than dry mixing.

Nowadays, we can find mixing time less than 2.5 minutes depending on the mixer configuration, specially in the shaft or shafts when we see twin shaft mixers. The most important parameter to control is the coefficient of variation which determine if the mixing time is the correct or if the ingredients have been mixed properly. This CV must be about 5% or less.

Thanks.
ED.

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The risk of segregation

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North American Renderers Association (NARA)