Extrusion techniques Nozzles

On the process side, techniques like the fluid bed method, extrusion, coacervation, the submerged nozzle process and molecular inclusion have gained importance within the last 10-15 years [1-3, 7]. 

FIGURE 9.3 Different droplet production processes by dripping and jet break-up techniques, (a) Simple dripping, (b) electrostatic extrusion, (c) coaxial flow, (d) vibrating nozzle, (e) jet cutting, and (f) spinning disk atomization. 

There are several nozzle extrusion methods for production of microbeads or microcapsules with entrapped cells, namely, simple dripping, concentric air jet, electrostatic droplet generation, rotating atomizers, and vibrating nozzle technique. AU merits and disadvantages of these techniques were... 

Fused deposition modeling (FDM) is a technique that builds plastic objects by extmsion of a polymer-wax filament through a nozzle (Fig. 6.52). A modification of the technique, referred to as fused deposition of ceramics (FDC), has been developed to create ceramic components from particle-filled polymer filaments (73). Ceramic-polymer mixtures used in FDC are similar to those described earlier for injection molding of ceramics. The mixture is first extmded to form filaments with a diameter of 2 mm, after which the spooled filaments are fed into a computer-controlled extrusion head. Extrusion of the plastic mixture through a nozzle is used to form the object layer by layer. Subsequent processing steps follow those described for injection molded bodies. 

The largest installed base of AM techniques is based upon material extrusion. Material-extrusion machines work by forcing material through a nozzle in a controlled manner to build up a structure. The build material is usually a polymer filament that is extruded through a heated nozzle—an automated version of the hot-glue gun used for arts and crafts. After a layer of material is deposited by the nozzle onto a platform, the platform either moves down or the nozzle moves up, and then a new layer of material is deposited. 

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