The terminology ‘mixing’ and ‘blending’ is often grouped together as the same process, technically they are slightly different. The process of blending is the homogenous distribution of differing materials and is usually a relatively gentle process.
This involves, either solid-solid mixing or the mixing of bulk solids with small quantities of liquid. Whereas mixing is usually a more aggressive process involving the combining of materials through the beating or stirring of the contents within a static vessel.
Agglomerators can be included under the description of mixing and blending as the agglomeration process involves the creation of granules from powders through the addition of liquids. In certain circumstances some mixers can also operate as agglomerators and dryers as well.
In an industrial setting blending, often takes place in Double Cone and Vee blenders that gently tumble their contents over and over. Rotating Drum blenders, fountain blenders and low speed ribbon and paddle mixers can also be used for blending too.
Mixing can be achieved by using high speed rotating ribbon blades, ploughshare blades or orbiting vertical screws.
‘No-dead pocket’ valves with contoured outlets are essential when the entire contents must be fully mixed, otherwise there is a possibility that some unmixed material will discharge from the mixer each time it is unloaded leading to quality control issues.
Blenders that tumble do not suffer this characteristic as the mixture is all funnelled to the outlet. Ribbon mixers, paddle mixers and blenders also can have the ability to mix the ingredients gently so that they do not damage delicate products.
Ploughshare mixers, on the other hand, are ideal for mixtures that need to be beaten together or where colourings or other coatings need to be smeared over the entire surface of other materials. Both mixers and blenders can accommodate the addition of liquids to form pastes or slurries and both can be jacketed for heating or cooling their contents during the process.
Mixing in static vessels can either be batch based or used on a continuous process, whereas tumbling blenders are purely batch machines. Mixers and blenders can have heated jackets or have warmed, dried air passing through them so that they become dryers or reactor vessels.
It is the aim of all mixer and blender manufacturers to achieve a homogenous mix in the shortest possible time and then to discharge it without any segregation during the process. Such aims have resulted in a multiplicity of variations on traditional mixer and blender types plus a host of inventive, proprietary mixer and blender designs.
Besides machines that are dedicated to mixing, there are storage silos that mix materials: these are called Live Bins or Fountain Blenders.
They use screws, spirals internal baffles and air to continuously recirculate material during storage. Agglomerators fluidise powders so that they can be wetted and combined to form larger particles or granules. The controls associated with the powder flow, fluidisation and liquid injection offer the options of varying particle size, shape and density according to requirements.
Allied to mixing and blending are sieves, screens, separators, sifters and shakers, as well as classifiers which reverse the process of mixing and are used to separate products either in size, weight, material type etc and can be used for all materials.
Such equipment may be used for QA sampling or production in batches or continuous processes. Because of the very broad applications spectrum, the science of particle separation and classification requires very specialised knowledge of the product characteristics as well as the entire process.
Robust screens to progressively separate quarried minerals, for example from coarse aggregates to fines, obviously require a very different approach to the sieving of delicate pharmaceutical materials.
Again, difficult materials may adhere or agglomerate requiring techniques such as ultrasonics to enable successful sieving and accurate size classification. Diverse products such as zinc, powder coatings, gypsum or rice meal need expert treatment.
As can be seen there are many differing processes under the global heading of mixing and blending, sieving this is where SHAPA can help, with its members many years of expertise through operating and providing solutions for mixing and blending and sieving processes you can be assured that SHAPA members have the right solution for your process.
A quick visit to the Equipment Finder section on the SHAPA website www.shapa.co.uk will guide you through the different choices ensuring you have the right solution for your process needs.
For more information and assistance with all your solids and bulk handling requirements, visit the SHAPA website at www.shapa.co.uk or email your requirements to [email protected] where our members will be happy to help.