Powder Mixer homogeneity

What is homogeneity for a powder mixture ?
How to calculate the homogeneity of a mix ?
How to get a good mix ?

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Section summary
1. Definition
2. Loading sequence
3. Mixing speed at loading

Powder Mixing (main page)
# Types of mixers
# Mixing mechanisms
# Mixing time
# Mixing speed
# Mixing volume
# Mixing power
#Mixer loading # Discharge time
# Froude Number
# Coefficient of Variation
# Homogeneity
# Tracer
# Segregation / demixing
# Tip speed
# Sampling
# ATEX speed
# Mixer Bearing seals
# Mixer discharge valve

1. Definition

The use of a mixer is to obtain a mixtures of different components (or a single material but with different properties) that has the same composition at any point. For such a mixture, a good homogeneity has been reached.

Reaching a good homogeneity in an industrial mixer is less obvious than it seems. It

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.

3. Mixing speed at loading

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.

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