Eddie McGee, technical director, Ajax Equipment discusses the merits of batch and continuous mixing and blending and considers the question: what are the advantages of switching from batch to continuous mixing?
Mixing and blending solids with more solids, pastes and liquids can be performed with either batch or continuous mixers. Batch mixing is the most common form of mixing and blending. It has the advantages of being well-understood, enables ease of quality monitoring and precise control of ingredient quantities. Critical factors in optimising batch mixing are the condition and size of the ingredients to ensure a consistent blending time, the shape of the mixing vessel and profile of the mixing paddle. The paddle's profile and movement should prevent any dead zones in the vessel where ingredients remain unmixed.
Batch mixing has various drawbacks. Whereas in principle, the mixing can be continued until such time as satisfactory homogeneity is achieved, the quality of some products can suffer from overworking. In addition, batch mixing is particularly prone to inconsistencies between batches caused by powder segregation during processing, changes in temperature, humidity, powder particle size and storage. It also tends to be labour intensive and introduces problems of flow, residue, stock accommodation and the matching of output with filling and packing operations. Moreover, any problems that may be found in batches are only detectable after the mixing process has been completed, which is then time consuming and expensive to correct. In addition, during post processing care has to be taken when discharging the batch mix to reduce the risk of desegregation as the mix is transferred to say a Big Bag or IBC for storage and distribution.
Continuous mixing allows process engineers to side step many of the problems encountered in batch processing. The continuous mixer comprises either a singe screw or two screws rotating in opposite directions; powders and other materials are mixed as they are driven along the short casing of the machine. Liquor additions can be made by way of sprays or drizzles, as appropriate, as the material moves through the mixer.
Batch and Continuous Mixing
Batch and Continuous mixing – when to switch?
Eddie McGee, technical director, Ajax Equipment discusses the merits of batch and continuous mixing and blending and considers the question: what are the advantages of switching from batch to continuous mixing?
Mixing and blending solids with more solids, pastes and liquids can be performed with either batch or continuous mixers. Batch mixing is the most common form of mixing and blending. It has the advantages of being well-understood, enables ease of quality monitoring and precise control of ingredient quantities. Critical factors in optimising batch mixing are the condition and size of the ingredients to ensure a consistent blending time, the shape of the mixing vessel and profile of the mixing paddle. The paddle's profile and movement should prevent any dead zones in the vessel where ingredients remain unmixed.
Batch mixing has various drawbacks. Whereas in principle, the mixing can be continued until such time as satisfactory homogeneity is achieved, the quality of some products can suffer from overworking. In addition, batch mixing is particularly prone to inconsistencies between batches caused by powder segregation during processing, changes in temperature, humidity, powder particle size and storage. It also tends to be labour intensive and introduces problems of flow, residue, stock accommodation and the matching of output with filling and packing operations. Moreover, any problems that may be found in batches are only detectable after the mixing process has been completed, which is then time consuming and expensive to correct. In addition, during post processing care has to be taken when discharging the batch mix to reduce the risk of desegregation as the mix is transferred to say a Big Bag or IBC for storage and distribution.
Continuous mixing allows process engineers to side step many of the problems encountered in batch processing. The continuous mixer comprises either a singe screw or two screws rotating in opposite directions; powders and other materials are mixed as they are driven along the short casing of the machine. Liquor additions can be made by way of sprays or drizzles, as appropriate, as the material moves through the mixer.
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