Barrel wall

A schematic of a continuous bulk SAN polymerization process is shown in Figure 4 (90). The monomers are continuously fed into a screw reactor where copolymerization is carried out at 150°C to 73% conversion in 55 min. Heat of polymerization is removed through cooling of both the screw and the barrel walls. The polymeric melt is removed and fed to the devolatilizer to remove unreacted monomers under reduced pressure (4 kPa or 30 mm Hg) and high temperature (220°C). The final product is claimed to contain less than 0.7% volatiles. Two devolatilizers in series are found to yield a better quaUty product as well as better operational control (91,92). 

In the Reclaimator, a high pressure extmder, fiber-free mbber is heated to 175—205°C with oils and other ingredients. High pressure and shear between the mbber mixture and the extmder barrel walls effectively devulcanize the mixture in one to three minutes. In the Lancaster-Banbury method, high temperature, pressure, and shear are appHed to the mbber in a batch process that is otherwise similar to the Reclaimator process. In another high pressure process, scrap mbber is devulcanized at 5.5—6.9 MPa (54—68 atm) for ca five minutes. The product is milled, baled, or pelletized as in other processes. 

Hence a barrel wall thickness of 10 mm would be appropriate. 

Capacity reduction of the twin-screw compressor is effected by a sliding block covering part of the barrel wall, which permits gas to... 

Twin-screw extruders that contain two internal rotating screws that press material against heated barrel walls and forces the resulting molten mass through a restriction die which aligns the mass in the direction of... 

Table 8 shows large differences in bio-stabilization time. The reason is the thickness and thermo-conduction of the barrel wall which caused heat losing. Ahn s research has proven that the wall conduction accounted to 62% of the heat loss [13]. Two-layer insulation wall is therefore suggested. One more reason is the waste amount which was used, 18 kg/barrel. This weight is maybe not yet in optimal volume with the barrel. It may have resulted in inefficient microorganism activity. 

Fig. 5. Schematic representation of a screw channel that is partially filled with liquid. Mass transfer occurs from the film on the barrel wall and the surface of the nip.

For the ideal case of smooth, continuous films on the barrel wall and a vertical interface with no curvature, the following expressions are true ... 

Equation (35) predicts that the mass transfer coefficient increases with increases in the screw speed and the number of parallel channels on the screw. The explanation for this is rather simple and is related to the fact that each time the film on the barrel wall is regenerated and the surface of the nip is renewed, a uniform concentration profile is reestablished, which means that the driving force for mass transfer is maximized. Since the instantaneous mass transfer rate decreases with time, mass transfer rates can be maximized by keeping the exposure time as short as possible, and... 

Molar flux of volatile component in wiped film on barrel wall... 

Zj helical length of the channel at the barrel wall z(r) helical length of the channel at radial position r Zf, helical length of the metering channel at the barrel wall melt density of the fluid 7 average shear rate in the channel... 

A mechanical clearance between the top of the screw flight and the barrel wall helix angle at the barrel 6c helix angle at the screw core 6 r) helix angle at radial position r... 

Several of the most commonly used resins were studied at a screw and barrel temperature of 35 °C. As previously discussed, this temperature condition is comparable to the conditions in the feed casing or Section 1. This is just the start of solids conveying as conveying continues into Section 2 where the inside barrel wall temperatures are considerably higher. In order to visualize the contrast between the six different polymers tested, the solids conveying rates as a function of discharge pressure for these select resins are presented in Fig. 5.14. 

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