FEED TECHNOLOGY UPDATE - AquaFeed.com

EXTRUSIONTwin Screw ExtruderTwin screw cooking extruders(Figure 1) have typicallyfound limited utility in theproduction of feeds. A majordrawback of these extrudersis their high capitalinvestment cost and theirrelatively higher cost ofmaintenance and operation.The capital equipment costof a co-rotating twin screwextruder is 1.5 to 2 timesthe cost of a state-of-the-artsingle screw extruder withcomparable hourly productioncapacity.Because of the increased costs, only thosefeed products with strong value added potentialare processed via the twin screw extruder.Specific product characteristics or processingrequirements where twin screw extrusionsystems have found applications are asfollows:• Ultra-high fat feeds (above 17 percentinternal fat)• Products which have high levels of freshmeat or other high moisture slurries(above 35 percent).• Uniform shape/size product (portionedfoods)• Ultra-small products (0.6 to 2.0 mm diameterproducts)• Co-extruded products (complex pet foodtreats)C2 2 TX ExtruderThe C2 2 TX (conical co-rotating twin screwextruder) is the most recent extrusion systemintroduced to the feed industry (Figure2). The C2 2 TX’s conical design allows forpositive compression in the barrel and reducespossibility of back feeding.Positive compression yields an efficientmanner of imparting mechanical energy intoFigure 2: Conical Co-rotating Twin Screw Extruderthe extrudate.The conical design of the C2 2 TXcauses thematerial to be kneaded and sheared alongthe screw profile. In traditional twin screwextruders, the melt is kneaded and shearedby shear locks, mixing lobes, or cut-flightscrew elements. This “profile kneading”eliminates the need for special screws andlocks to provide the appropriate cooking.Extruder shafts and screws can be machinedfrom a single piece of steel, resultingin lower manufacturing costs. Maintenanceand down time are also reduced, because ascrew profile change is not needed for eachdifferent product.Tools for Extrusion FlexibilityNo matter which of these extruder designsis used, the availability of a wide range ofextrusion add-ons and tools available todaycan assist in maximizing extruder flexibilityand efficiency. Obviously, some standardoptions for extruder flexibility have alwaysbeen available, such as variable speed maindrive motors.More recently though, features and toolshave been specifically designed to improveextrusion process optimization. A list of theitems covered in this article includes the