Extrusion process development

Profiles, was recently opened to make plastic lumber profiles using a proprietary, continuous-extrusion process developed in-house. 

Two notable methods to produce microcellular foams include gas supersaturation in combination with an extrusion process developed by MIT/Trexel [84-86] and the continuous extrusion process by Dow [87,88]. Super-insulating materials are made by the encapsulation of a filler material inside a barrier film, aluminum foil, or metallized film. These materials exhibit 5-7 times the R-value of typical nonvacuum insulating materials depending on vacuum level and barrier and filler type. Uses for these VIPs (vacuum insulation panels) include refrigeration and controlled-temperature shipping containers. 

Figure 16.4. Extrusion process developed by Monsanto for recycling carpet waste [63],...

Exemplarily, Figure 18 shows the process parameters of a pharmaceutical melt extrusion process developed on a corotating twin-screw extruder. 

Fused deposition modeling (FDM) is an extrusion process developed by Stratasys. Parts are built up in layers from extruded plastic strands. In principle, the FDM process is suitable for all materials that can be melted and extruded. Plastics such as ABS, ABSi, PC-ABS, PC, PC-ISO, and PPSF are typical of the materials used. The material for extrusion must be in filament form, with a circular cross-section and a diameter between 1 and 2 mm. The initial data in 3D CAD form are generally converted to SLA format, and this data is used to create 2D cross-sections as slices through the part to be produced. Although the material solidifies very quickly, structures made of support material are needed for cantilever structures. These supporting structures are subsequently easy to remove. Filaments of different materials are needed for the part and the supporting structure. Drive rollers carry the two filaments to an electrically heated plastifier, where the filaments are heated to just below melting temperature (Fig. 7.3). 

Continuous Solvent—Extrusion Process. A schematic for a typical continuous process, widely used for making solvent propellant for cannons, is shown in Figure 7. This continuous process produces ca 1100 metric tons of single-base propellant per month at the U.S. Army Ammunition Plant (Radford, Virginia). Continuous processes have also been developed for double- and triple-base propellants and for stick as well as granular geometries. A principal aspect of these processes has been the extensive use of single- and double-screw extmders instead of the presses used in the batch process. 

There are a number of techniques that are used to measure polymer viscosity. For extrusion processes, capillary rheometers and cone and plate rheometers are the most commonly used devices. Both devices allow the rheologist to simultaneously measure the shear rate and the shear stress so that the viscosity may he calculated. These instruments and the analysis of the data are presented in the next sections. Only the minimum necessary mathematical development will he presented. The mathematical derivations are provided in Appendix A3. A more complete development of all pertinent rheological measurement functions for these rheometers are found elsewhere [9]. 

Performing numerical simulations of the extrusion process requires that the shear viscosity be available as a function of shear rate and temperature over the operating conditions of the process. Many models have been developed, and the best model for a particular application will depend on the rheological response of the resin and the operating conditions of the process. In other words, the model must provide an acceptable viscosity for the shear rates and temperatures of the process. The simple models presented here include the power law. Cross, and Carreau models. An excellent description of a broad range of models was presented previously by Tadmor and Gogos [4]. 

This appendix contains the detailed development for the equations that are presented in Chapter 3. Full understanding of these developments is not required for detailed analysis and troubleshooting of the extrusion process. They are presented here for those who desire a deep understanding of the mathematics involved with the screw rotation analysis. Some of the equations and figures are duplicated in this appendix for clarity. The nomenclature used here is consistent with that used earlier. The reader is directed to Chapter 3 for nomenclature. 

Details are given of extrusion and thermoforming lines developed by Italproducts for the manufacture of PP foam containers. The extrusion process using high melt strength PP and chemical blowing agents is described and results are presented of thermoformability studies. 

Hot Extrusion of Shells. A modification of the Ugine-Sejournet hot extrusion process (using glass as lubricant) is used by Scaife Company of Oakmont, Pennsylvania. In this process a complete shell (such as 4.2 inch) can be produced in one piece from a simple billet. Important features of the development are in the substitution of readily available billet stock for seamless steel tubing, a critical material in times of war. Another feature of this process is that it requires about 25% less steel Refs Ordnance, 38, 753 (1954) 2) Iron Age... 

The most important materials developed are nanocomposites and nanotubes. Fabrication of the first nanocomposites was inspired by nature (biomineralisation). Nanocomposites based on nanoclays and plastics are seen as ideal materials for improved barrier properties against oxygen, water, carbon dioxide and volatiles [37]. This makes them in particular suitable for retaining flavours in foods. The technology is rather straightforward using commercially available nanoclays and extrusion processing. 

History. The cast double-base process was developed under U.S. Government auspices during World War II, the initial work being done by Kincaid and Shuey (7). The process filled a need for rocket charges significantly larger than those conveniently made by the then existing extrusion processes. 

The potential volume involved and our assessment of the property benefit of Celcon in the application were sufficient to justify a lab program whose objective was to develop a polymer or modify the extrusion process so that Celcon would extrude at comparable or faster speeds than the material being used. After some nine months of effort an extrusion die was designed that permitted extrusion speeds of 450 feet per minute while making tubing with the tolerance specifications established by the customer. The foregoing is an example of a type of process development work described in the preceding paper. 

The success of epoxy syntactic foams is associated with the development of the extrusion process for materials containing glass microspheres. Large articles and profiles with dimensions as large as 6 x9 m2 can be made this way (See also Sect. 7). 

When the rheometer is retrofitted with a single-screw extruder one can measure rheological properties and extrusion processing characteristics to differentiate lot-to-lot variance of polymer stocks. It also enables the process engineer to simulate a production line in the laboratory and to develop processing guidelines. 

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