Mixers & Blenders
energy efficient as the initial ingredient separation is at a large scale compared with the simultaneous feed of components to a continuous mixer to present the ingredients in close proximity. Importantly, segregation processes that can occur in batch mixing and blending are normally far less of a problem in continuous systems, mainly because the cross-section of the flow channel is so reduced that there is little scope for segregation along the axis of flow.
up of sticky compounds, while making cleaning easier. The flexibility of the continuous mixer is further increased by the use of interchangeable mixing shafts, allowing the machine to be used for a wide range of products. To aid processing the continuous mixer body and / or the mixing augers can be temperature controlled, either heating or cooling product as required, in a way that is much more difficult with batch mixers. Where the process has to meet strict hygiene standards such as those found in the pharmaceutical industry, the mixer is fitted with quick release screw shafts and end plates or may have a clean-in-place option. These allow the screws to be quickly removed for cleaning and product changeover or to change between the different mixing forms. Critical factors for continuous mixers are the shaft arrangements, paddle and screw geometries, temperature, liquid addition and consistent ingredients feed. This latter factor is important. Screw feeders are generally used to ensure delivery of ingredients in a controlled manner into the mixer.
Switching to continuous manufacture
Many companies switch from batch to continuous manufacture to improve productivity and expand their product range. There will be some products that are unsuitable for batch mixing and blending. Moreover, batch mixing is a self-limiting factor on productivity, limited by the mass to mix, and loading and unloading times. Productivity increases will require a larger batch mixer. Continuous mixing, on the other hand, transforms manufacture from a disconnected, sequential operation involving intermediate storage, intermittent sampling and assessment and separate product quantities to a compact, continuous production flow line with minimum manual intervention. The relatively small size and flexibility of continuous mixers makes it easy to fit them into existing plant processes.
Continuous production, in which transfer of 'work in progress' is part of the production process and not simply the movement of intermediates between process stages, has many attractions for manufacturers. Stock inventory can be minimised at plant level and the process aligns with many associate processes, such as drying and packing, to allow the assembly of efficient and compact production lines. Avoiding inconsistencies that can arise from batch manufacture is a prime benefit of continuous mixing, but others include processing product that is more readily free flowing at a constant temperature and requires consistent ingredient distribution. Indeed some food products demand continuous production; spice mixes and health snack bars are just two examples. In these cases batch mixing is not
18 Solids & Bulk Handling • May 2010
www.solidsandbulk.co.uk
On-going advances in continuous mixing technology have removed many of the barriers to switching from batch to continuous mixing. Companies who had previously rejected change to continuous operation because of the demanding requirements of quality control and verification, can now take advantage of improvements in on-line measuring techniques and control technology. Industries such as the pharmaceutical industry are now employing continuous mixing as an alternative to batch mixing in some production situations. In conclusion, while batch processing is adequate for many products, process engineers should consider a switch to continuous mixing when wishing to increase plant throughput by continuous production. The mixing methodology should also be considered for those products that are difficult to process using batch mixing and are an on-going source of quality control problems.
For more information contact Ajax Equipment, on 01204 386723, email
sales@ajax.co.uk and web site:
www.ajax.co.uk
The compact mixing concept
At Powtech 2010 in Nuremberg, Germany, K-Tron and Dinnissen introduced a new variation of the Pandora End of Line Mixing System, especially suited for significantly reducing rework. The Pandora End of Line Mixing System, which is designed to feed up to a maximum of 10 (micro) ingredients very precisely into a compact Pegasus Paddle Mixer, where they are mixed extremely homogenously in a continuous process. Pandora End of Line Mixing is ideal for applications which require quick and easy changes in formulation without contamination or danger of segregation. An additional advantage is the low power consumption.
For more information visit:
www.ktron.com
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