Additive manufacturing processes material extrusion

Continuous polymerization n. In polymer manufacture, linkage of the various stages of polymerization so that materials flow without interruption from the addition of raw materials to delivery of the finished polymer from the system. Extrusion as film, chip or fiber may be linked to a continuous polymerization line. Because there is no break in the process while the transition from low molecular weight to high occurs, multiple stage reaction vessels may be required and accurate process control is critical. 

Since the presence of moisture can result in porosity in processed material, this can be removed by pre-drying the additive before processing, downstream melt devolatilisation, for example during extrusion of profile, or by use of low moisture content filler, available from some manufacturers. 

Fabrication. Processes for fabricating solid fuel pellets from a variety of feedstocks, particulady RDF, wood, and wood and agricultural residues, have been developed. The pellets are manufactured by extrusion and other techniques and, in some cases, a binding agent such as a thermoplastic resin is incorporated during fabrication. The fabricated products are reported to be more uniform in combustion characteristics than the raw biomass. Depending on the composition of the additives in the pelletized fuel, the heat of combustion can be higher or lower than that of the unpelletized material. 

The cost of manufacturing thermoformed, polystyrene foam sheet parts is less dependent on raw material cost than other extrusion processes. This is largely due to the combined effects of additional energy costs required to operate two extruders, heat removal requirements in the secondary extruder, cost of pelletizing (densifying) regrind and the relatively low output of the process for the equipment scale and cost. Typical cost factors for the manufacture of thermoformed polystyrene foam sheet products include raw materials 35%, labor 27%, sales and administration 16%, depreciation 8%, utilities 7% and other 7%. 

In addition, process schemes for manufacturing laminated inhibited films by co-extrusion are presented in Fig. 2.11. Working volumes of extruders 1 for processing polymer materials (A, B, C) are connected with extrusion head body 2. The head is fitted with several annular slots that form, on blowing, a multilayered hose 3. Two-ply films can be formed from the same [7] or two different (Fig. 2.11a) polymers. Three-layered films can, correspondingly, incorporate two (Fig. 2.11b) or three different (Fig. 2.11c) polymer materials. 

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