Best dry powder mixer for your application - Mixer buying guide

1. The Best Mixer is...

There is quite a large variety of technology and design for bulk solids / powder mixing. Thus defining a BEST type of mixer can only be done relatively to the application. One mixer design can be perfectly adapted to a given situation but will not perform well in another application in terms of mixing time and / or homogeneity achieved.

This page is a selection guide for powder mixers aiming at helping the reader define the best design for his particular application. It reviews different mixing purposes commonly found in industry according to the throughput required, the type of mixing to perform, the kind and proportion of ingredients to mix...etc...

2. Choice criteria

How to chose well your powder dry mixing equipment ?

2.1 Capacity

2.1.1 Small scale operations

Not all industries are huge ! It is sometimes necessary to have a rather manual but yet very flexible process in order to perform some contract manufacturing, produce personalized batches or even to produce a preblend within the factory  that will then be used by a bigger line.

For this type of process, mixers such as...

Drum blenders
V blenders
Bin blenders

... are usually a good choice. Their size is flexible, they can stand-alone inside a production area and provide reasonably good mixing performance for free flowing powders. For the simpler design, the absence of agitator makes their cleaning easy and will therefore facilitate changeovers which are usually very frequent in small, flexible manufacturing lines.

2.1.2 Large scale operations

For high capacity lines, the mixer has to be integrated inside a fully automated system allowing to reduce the batching time or even consider a continuous mixing process. The mixing time must be short to ensure a high capacity, therefore such mixers cannot rely only on diffusive mechanisms like drum or bin blenders, but must have agitation tools to provide convective and, to different levels, shear mixing.

For this type of process, consider mixers such as...

Ribbon blenders
Double shaft paddle mixers
Shear mixers

2.2 Mixing of products having a tendency to segregate

The more the mix ingredients are different in size and density, the harder they will be to mix and the more they will tend to segregate. Rotating mixers may then be limited in such situations and mixers with an agitation tool will typically show better performance. However the mixture may segregate in the process steps following mixing that is why it is important to have the mixer as close as possible to the final process step and avoid free fall, conveying...etc... Continuous mixers may offer interesting advantages to this regard.

For this type of mixtures, usual advices is to consider :

Ribbon blenders... to some extent
Double shaft paddle mixers
Shear mixers
Continuous mixers if required to reduce segregation after mixing

2.3 Mixing of products having a tendency to agglomerate

Powders may have the tendency to agglomerate, in order to have a good mixing, it is important to have a mixer design that can break the lumps. Rotating mixers are typically very gentle and will not deagglomerate although some design exist with agitators or small high shear mixers for this purpose. Such design may however come to the expense of the ease of access to the mixer and of the simplicity of the machine.

Shear mixers and to a lesser extent double shaft paddle mixers or ribbon blenders will allow to break some lumps that may be present in the ingredients or forming during mixing. In general, such phenomena will mainly happen if few percents of liquid is sprayed during the mixing, to granulate the mixture or bring flavors for example. In case the percentage of liquid is high, those mixers must be equipped with deagglomerators, small high shear mixers, that allow to break agglomerates and ensure a satisfactory homogeneity.

When ingredients tend to agglomerate, the recommended mixers are :

Double shaft paddle mixers
Shear mixers

Note that Ribbon blenders may be sufficient for lumps very easy to break

When adding liquid, the following types can be used :

• Shear mixers - Ploughsare with deagglomerators

• Double shaft Paddle mixers with deagglomerators

2.4 Mixing of micro ingredients

When having to dose micro ingredients, which means a minimum of <1% to 0.1% of the formulation, only high efficiency mixers should be used if the ingredient has not been preblended. It means that...

Double shaft paddle mixers batch or continuous
Shear mixers

... are recommended.

Other kind of mixers can be used if the ingredients have been preblended.