Rotary extruders

By far practically all extruders use screws in their plasticators to melt the plastics. However ram, over a century popular melting system, is used to process plastics that cannot be melted by a screw. The ram devices are essentially batch devices, and although it is possible to achieve a constant output by sequentially operating two or more rams, the method is of virtually no importance for practically all TPs. The ram is used for processing plastics that come close to not being meltable. Another possibility is the rotary extruder, a device in which rotating... 

Figure 7 (A) Gravity-feed rotary extruder (B) close-up showing the extrusion zone (C) operating principle of gravity-feed extruder. (Courtesy of Niro Pharma Systems.)...

The turbo-tray dryer can handle materials from thick slurries [1 million (N s)/m (100,000 cP) and over] to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter-press cakes are granulated before feeding. Thixotropic materials are red directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-ffowing after one revolution. 

Basic types of extruders include axial end plate, radial screen, rotary cyhnder or gear, and ram or piston. For a review, see Newton [Powder Technology Pharmaceutical Processes, Chuha et al. (eds.), Elsevier, 391 (1994).]... 

USATHAMA) completed a trial burn of explosive, contaminated soil in a rotary kiln (Noland, 1984). Soil contaminated from red and pink water lagoons was successfully burned. A transportable rotary kiln yrstem was set up. The technology by Therm-All, Inc., had been used in industry for destruction of solid wastes. The normal screw feed system was not used, due to fear of a soil explosion during the extruded plug feed process. Therefore, the soil was placed in combustible buckets and individually fed by a ram into the incinerator. The feed rate was 300 to 400 Ib/hr and the operational temperature was 1200° to 1600°F in the kiln and 1600° to 2000°F in the secondary chamber. 

Rotary valves have been specified for the receivers of the vacuum pneumatic conveying systems (RV-601 and RV-602) and for the feeders (RV-40 1) and receivers (RV-501) of the positive-pressure system transferring powder from the dryers to the extruders. Perry72 gives some recommended sizes for rotary valves. The power required by all these valves will probably not exceed 2 kw and will be ignored. 

To a 500 g sample of acidic, dealuminized mordenite (CBV-20A from PQ Corporation, 1.5 mm diameter extrudates that had been calcined at 540 °C, overnight) was added a solution of 33 ml of 48% HF in 1633 ml of distilled water, and the mix cooled in ice, stirred on a rotary evaporator overnight, then filtered to recover the extruded solids. The extrudates were further washed with distilled water, dried in vacuo at 100 °C, and then calcined at 540 °C, overnight. Analyses of the treated mordenite showed 1.2% fluoride, 0.49 meq/g acidity. Samples were charged to the reactive distillation unit either as 20/40 mesh granules, or as ca. 1.5 mm extrudates. 

Reverse-phase evaporation in a nitrogen atmosphere was used to prepare lipids. A lipid film previously formed was redissolved in diethyl ether and an aqueous phase containing the dyebath components added to the phospholipid solution. The resulting two-phase system was sonicated at 70 W and 5 °C for 3 minutes to obtain an emulsion. The solvent was removed at 20 °C by rotary evaporation under vacuum, the material forming a viscous gel and then an aqueous solution. The vesicle suspension was extruded through a polycarbonate membrane to obtain a uniform size distribution (400 nm). 

Examples A, O-rings for rotary and static applications (43) B, extruded items such as hose, tube, and solid splicable stock C, fuel hose for low temperature service (—57°C) and coated fabric for collapsible fuel storage tanks (40, 45) D, biomedical applications such as soft denture liners (48) and blood compatible parts E, lip seals (42) F, shock absorption and vibration damping mounts, (Photograph courtesy of the Firestone Tire... 

Very soft doughs that are not suitable for rotary moulding are extruded onto a belt to produce strips of dough. These dough strips can then be guillotined before or after baking. 

Fig. 12. Tentative flow curves of low-density polyethylene with MFI = 2.0 g/10 min extruded at 170 °C through channels with a two-angle ellipse Wber cross section with a length of 50 (a), 75 (b), and 100 (c) mm with reciprocating-rotary vibration of the element in the zone upstream of the inlet to the channel (according to the diagram given in Fig. 9) ...

Fig. 6.21 A rotary-sector slider pad extruder. [Reprinted by permission from R. F. Westover, A Hydrodynamic Screwless Extruder Soc. Plastics Eng. J., 1473 (1962).]...

Screw extruders are also used, however, to produce pelleted materials, either as a final product or for further processing, in the food, ceramics, chemical and other industries. Many orifices in a die plate form a multiplicity of extruded rods which are cut into pellets by rotary cutter blades. The extrusion operation is frequently the final step in a sequence of processes which may include binder/lubricant addition, mixing, heating, cooling or vacuum degassing. 

Figure 7,2 (1) In-line high-speed sheet extruder feeding a rotary thermoformer and (2) view of the thermoforming drum (courtesy of Welex/lrwin)...

Mechanical movement action in a die is used to extrude these different profiles such as tubing or strapping with varying wall thicknesses or perforated wall. It is usually accomplished by converting rotary motion to a linear motion that is used to move or oscillate the mandrel. For certain profiles, such as the perforated tubing, the orifice exit would include a perforated section usually on the mandrel. 

Oscillating kneader extruder, based on a single helical screw blade which in addition to its rotary... 

For Saffil alumina fiber, aluminum oxychloride [Al2(OH)jCI] is mixed with a medium molecular weight polymer such as 2wt% polyvinyl alcohol. The aqueous phase contains an oxide sol and an organic polymer. The sol is extruded as filaments into a coagulating (or precipitating) bath in which the extruded shape gels. The gelled fiber is then dried and calcined to produce the final oxide fiber. This solution is slowly evaporated in a rotary evaporator imtil a viscosity... 

---