Annular swell

TABLE 7.1 Description of Resins Studied in Annular Swell... 

If bentonite pellets or chips are to be used instead of grout, the bentonite pellets can be placed in shallow wells (within 15.0 m of ground surface) by pouring them through the annular space from above in much the same manner as the filter pack is placed. If this installation procedure is chosen, sufficient potable water must be added in conjunction with the bentonite to hydrate the individual pieces. Hydration causes the pieces to swell and form a highly impermeable seal. 

This is another ramification of incomplete response of polymers, because the experimental time is smaller than the relaxation time of the system of macromolecules. As expected, weld lines are mechanically weak and have optical properties that differ from those of the bulk, making them visible. Furthermore, they result in film or tube gauge nonuniformities, probably because of the different degree of swelling of the melt in the neighborhood of the weld line. They also induce cross-machine pressure nonuniformities. To overcome these problems, basic cross-head die designs (Fig. 12.42) have been devised in which the mandrel is mechanically attached to the die body in such a way that obstacles are not presented to the flow in the annular region. 

Fig. 14.25 Schematic parison die designs (a) convergent (b) divergent, and (c) straight. [Reprinted by permission from A. Gracia-Rejon, R. W. DiRaddo, and M. E. Ryan, Effect of Die Geometry and Flow Characteristics on Viscoelastic Annular Die Swell, J. Non-Newt. Fluid Mech., 60, 107-128 (1995).]...

N. Orbey and J. M. Dealy, Isothermal Swell of Extrudate from Annular Dies Effects of Die Geometry, Flow Rate, and Resin Characteristics, Polym. Eng. Sci., 24, 511-518 (1984). 

Y. Otsuki, T. Kajiwara, and K. Funatsu, Numerical Simulations of Annular Extradate Swell Using Various Types of Viscoelastic Models, Polym. Eng. Sci., 39, 1969-1981 (1999). 

Otsuki Y, Kajiwara T and Funatsu K (1997) Numerical simulations of annular extrudate swell of polymer melts. Polym Eng Sci 37 1171-81. 

In the film blowing process where a continuous stable parison is blown from an annular die, it is crucial that the molten polymer exhibits certain elastic extensional properties and it is here that the viscoelastic nature of the polymer is beneficial.If, however, the manufacturer is concerned with profile and surface finish of an extrudate, viscoelastic effects of the polymer may well present difficulties. Both die swell and most polymer extrusion instabilities are linked to viscoelastic effects and as such different levels of viscoelasticity give rise to different extrusion characteristics. 

The melt parison is extruded from an annular die. The wall thickness of the parison depends both on the annular gap setting and on the shear rate of the melt in the die. The melt will swell after the parison exits from the die and the die swell Increases with increasing shear rate. The die swell is also a function of the temperature, the type of polymer, and its elastic melt properties. Usually the shear rate in the die varies from 10 to as high as 700 s . As a rule of thumb one uses a die land length 8 times the annular gap. The parison should normally not be blown up beyond 3 1 (i.e., bottle parison diameter). 

Pulled elbow does not require manipulation under anaesthesia. The forearm is flexed and supi-nated. Often this results in a gratifying pop and the child resumes normal activity. If this manoeuvre is unsuccessful, simply resting the arm in a sling will allow swelling in the annular ligament to subside and the radial head will reduce within 2-3 days. 

At the present time, the CABRI-FAST international programme is still continuing. In this programme the behaviour of annular fuel cladded with the improved (low swelling) dad material 15-15 Tis (CW 15 -15 Ti) is studied under slow ramp and TUCOP conditions. 

In order to capture the time evolution of die swell, some empirical equations have been proposed for annular die geometries. The diameter (B,) and thickness swell (B2) are made time dependent via an exponential function by including a characteristic time (p. This leads to expressions of the form ... 

Answer Both are equally Important - an increase in the Panellit pressure may be due to an obstruction downstream in the annular space in the tube, to oiling vapor" lock, or to swelling of a fuel slug. A decrease in pressure may result from a plugging of the front crossheader or venturi screens, or a tube leak. Any of these conditions represents a potential hazard to the reactor. 

Annular die swell is equal to the (thickness of melt index strand - die diameter)/die diameter. 

The weight and diameter of the parison is controlled by the geometry of the annular die opening and the resin being extruded. As the molten polymer is extruded through the die, it swells to a thickness and diameter that is greater than the dimensions of the die opening. The amount of swell is dictated by a complex relationship between the internal shape of the die and the viscoelastic properties of the polymer. 

Annular extrudate swell is important for parison formation in blow molding. Finite element calculations and comparison to experiment, together with calculations and measurements of blown bottle thickness, are in... 

Oibey, N. and Dealy, I. M., Isothermal swell of extrudate from annular dies. Effects of die geometry, fbw rate, and resin cliaractmstics, Pofym. Eng. ScL, 24,511-518 (1984). 

Figure 5.4.3 compares Ni and Wz as determined from total thrust in the cone and plate to values obtained from the pressure distribution. Figure 6.2.13 and Table 6.2.2 compare N from cone and plate to extrudate swell. Figures 6.3.4,6.3.6, and 6.3.7 do the same for N determined by exit pressure and hole pressure. These comparisons helped us to decide which mediods were reliable and over what range of measurement The same ccndd be said of the normal stress comparisons made for axial annular and tangential annular flow in Figure 6.4.2. 

Figure 4.14 Simulation of extrudate swell from tapered annular dies for an HDPE melt. Memo7 phenomena are present manifested in enhanced swelling from converging dies. Viscoelastic simulations with the K-BKZ integral model (Eq. (4.12)) [66].

Luo, X.L. and Mitsoulis, E. (1989) Memory phenomena in extrudate swell simulations from annular dies. J. Rheol., 33,1307-1327. 

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