Vent Port Configuration

In addition to the undercut, the vent port is often offset from the vertical, again to minimize the chance of polymer scraping off at the leading edge of the vent port. The length of the vent port is usually 0.5 to 1.5 D and the width about 0.25 to 0.75 D. Another vent port geometry is shown in Fig. 8.50(b). 

this geometry minimizes the chance of polymer melt being scraped off at the leading edge of the vent port. 

Another interesting vent port design is shown in Fig. 8.50(c). 

In this design, the feed port is combined with the vent port. The volatiles are removed through the annular space between the feed pipe and the feed port housing. The system is used in conjunction with a vacuum feed hopper as described by 

Franzkoch [21], Such a system allows devolatilization to occur in the feed hopper section of the extruder. This type of devolatilization is successfully used with powders, particularly when the material in the hopper can be heated. The vacuum feed hopper system and some of the problems associated with it are discussed in Section 3.4. Hopper devolatilization of pellets is generally unsuccessful because the larger particle size reduces the surface area and thus the devolatilization effectiveness, as discussed in Section 5.4.1. 

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The extruder barrel configuration (i.e., feed position, vent port position, etc.) is maintained... 

Fig. 8. MVX basic configuration. Key a, inlet hopper with pusher b, mixing chamber c, vent port d, extruder screw e, reverse port to empty screw. Farrel Bridge Ltd, 1987.

Fig. 2-4. Typical batch reactor configuration. pH is controlled by a combination pH electrode and automatic buret connected to an autotitrator a syringe sampler allows for removal of a subsample of suspension an addition port permits injection of solute an inert gas is bubbled through the suspension by means of a gas dispersion tube and the system is vented through a gas trap a thermometer allows for temperature monitoring and the suspension is mixed with an overhead stirrer.

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