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TABLETING 65


up to more than 50kg/h, at L.B. Bohle by standard a screw diameter of 25mm and a length of 20 x D is applied, but this is fl exible to the specifi c process demands. Virtually an infi nite number


of diff erent screw confi gurations is conceivable by combining diff erent types of elements, which results in granules of diff erent characteristics. Porosity, compactibility, granule size, etc. are subject to this infl uence. Conveying elements are used to convey the material through the barrel with minimal input of shear energy. T e pitch of the elements can also be varied, to alter the conveyed mass per screw-revolution. Kneading elements are thin discs or longer blocks. T e imparted shear energy increases and the conveying capacity decreases with an increasing advanced angle of the kneading zone. An intermediate between these two extremes is represented by distributive fl ow elements,


which feature conveying capacity as well as shear energy. T e ratio of inner and outer diameter of the screw elements infl uences the amount of material that can be transported and thus the maximum possible fi ll-level of the TSG. T e fi ll-level depends on the feed-rates of the material, the screw geometry and the screw-speed, which is another important factor to be varied. T e introduction of liquid


into the process is of major importance and the accuracy and precision of this sub-process has to be ensured. T e liquid can be pure water, a binder solution or an organic solvent, depending on the formulation and the desired granulation mechanism. Within the BCG, a pressurised pump is employed to deliver the liquid in a pulsation-free way, even at lowest feeding rates or viscosities >1 Pas. T e application of openings smaller than 0.5mm prevents a blockage of the nozzles through bypassing powder, guarantees process stability


and prevents the creation of huge and lumpy granule- nuclei due to the generated small liquid droplets. T ereby, wetting uniformity of the whole mass and the granulation of even hydrophobic powders becomes easily feasible. T e fl exibility


of TSG and ease of adopting the process make it a perfect and versatile tool for the continuous production of granules during R&D and production phases, and thus can be a door opener into the world of continuous manufacturing.


The BCG is characterised by a small footprint and a wide throughput range


Dr Robin Meier is manager Scientific Operations at L.B. Bohle www.lbbohle.com


www.scientistlive.com


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