The Extru-Technician, Summer 2017
Summer 2017 5 the potential to add or subtract value to the process In some cases these other steps can have a catastrophic impact A good example would be extruding small feeds without adequate grinding No extrusion system has the ability to deal with oversized particles fouling the die Extruder con guration temperature time in processing and other factors should be stable from batch to batch and moment to moment to create an end product with the necessary attributes This involves getting the extrusion process up and running and on spec as quickly as possible Should unstable conditions arise technicians must know how to recognize pellets that are off spec and be empowered to divert them when necessary This creates a stable predictable manufacturing process Formulation considerations Their effect on physical properties Ingredients in uence the physical properties in a variety of ways but not all of them are easy to predict or account for Binders play a critical role in creating the right physical properties for aquafeed They serve as the glue that holds pellets together contributing to cohesiveness and durability But they provide their own challenges The primary binder used in aquafeed is starch which has great holding power but is prone to expansion during the extrusion process This means more air in the nal product a useful result when your goal is to reduce density for oating feeds But starch can make it dif cult to achieve the high densities necessary for sinking feeds or the high protein high fat content needed in nutrient dense diets See sidebar on ADT to learn about minimizing expansion in the extrusion process Fish meal is slowly being replaced by other protein sources for sustainability and cost reasons These proteins behave differently leading to new challenges Advanced Densi cation Technology creates more dense pellets Because extruders operate at higher moisture contents and higher temperatures than steam pelleting systems they offer the potential to more thoroughly cook and plasticize raw materials into very durable pellets that resist disintegration Unfortunately the typical extrusion parameters that in uence good water stability also promote expansion This can be a challenge in producing sinking feeds Extru Tech has developed Advanced Densi cation Technology ADT to address these issues ADT components are designed to create heat and shear in the initial stage of the extruder rather than at the die This allows the nal stage at the die to focus on densifying and forming pellets minimizing expansion ADT has three main design features that build on the basic elements of an advanced extrusion system The mid barrel valve MBV More ef cient non conical nal screw geometry Die designs focused on capacity and densi cation In traditional extrusion systems the die performs two major functions It restricts ow which increases cook via mechanical energy sheer and retention and it facilitates the formation of pellets An Extru Tech ADT equipped extruder uses the mid barrel valve to move shear and retention to the initial segments of the extruder long before it reaches the die The mid barrel valve creates a more substantial contrast between zones than a traditional segmented barrel extruder with steam locks lobe locks or interrupted ight elements Because the die no longer needs to accomplish signi cant cooking its open area and hole geometry can be designed for making more dense pellets at increasing open area for much higher rates
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