Internal bubbling process

V. Sidiropoulos and J. Vlachopoulos, Numerical Study of Internal Bubble Cooling in Film Blowing, Int. Polym. Process., 16, 48-53, (2001). 

The properties of the film are determined by the blow-up ratio and the speed. The blow-up ratio is the ratio between the diameter of the final tube of film and that of the die. The internal air pressure that expands the tube into the bubble is typically supplied through a port into the mandrel, the interior part of the die. Once the process is running steadily, little air is usually lost, so make-up requirements are small. When internal bubble cooling is used, air is constantly being exchanged inside the bubble. 

The strong interdependence of process variables is another aspect of the process that requires a high level of operator skill and has led to extensive advancements in measurement and control techniques. There are many process variables - screw speed, nip speed, internal bubble air volume, and cooling rate (frost-line height) - that influence bubble geometry and, as a result, film properties. An adjustment to any one... 

Fig. 4. Blown film process, quench air ring, and internal bubble cooling.

In industrial practice, cooling of the blown film is enhanced from the outside by an annular air jet, which fiows from an air ring (see Fig. 9.20) attached very close to the die and/or the inside by a process called internal bubble cooling (IBC). Note that the air jet usually hits the film... 

The processing conditions for all bubbles depicted in Figure 5 are summarized in Table 1. Note that for all cases the freeze line height is about 0.18 m. The bubbles with no neck (1-2, 4-5) were described by the Eq. 1 in [8] whereas the description of the bubble with a neck height (3), has been modeled by Eqs. 25 and 27 in [8]. The corresponding compliances summarized in the Table 2 were determined from the measured internal bubble pressure for the individual processing conditions summarized in Table 1. 

The general charac teristics of the main types of reac tors—batch and continuous—are clear. Batch processes are suited to small production rates, to long reaction times, or to reactions where they may have superior selectivity, as in some polymerizations. They are conducted in tanks with stirring of the contents bv internal impellers, gas bubbles, or pumparound. Temperature controf is with internal surfaces or jackets, reflux condensers, or pumparound through an exchanger. 

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