Die swell ratio

Table 13.2 Die-swell ratio as a function of mean residence time in the capillary0 for the three polymers shown in Table 13.1 [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning , Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

This composition contains abont 90 to 60 pbw of a PP block copolymer and abont 10 to 40 pbw of a PE. The block copolymer contains abont 99 to 90 wt.% of a crystalline PP and abont 1 to 10 wt.% of an amorphons ethylene/alpha-olefm copolymer and has a melt flow rate of about 2 to 15 g/10 min and a die swell ratio, measured by a capillary rheometer, of at least 1.7. Foamed materials containing a fine and uniform foam are obtained from this composition. 

The variation of die swell ratio De/D (where De and D are the diameters of the extrudates and die) of virgin PP, untreated and treated composites is represented in Table 9.5 [74]. It is evident that the swell ratio of the virgin matrix decreased with the incorporation of fibers. This is probably attributed to the distribution of fibers within the PP matrix which results in stress transfer from matrix to the fiber, thereby retarding the elastic recovery of the material [75]. Furthermore, the treated composites displayed a lesser die swell, thus confirming enhanced fiber-matrix adhesive strength. However, the swell ratio increased with the shear rate, which is probably due to the decrease of normal stress and elastic recovery at low shear rates. 

Table 9.5 Die swell ratio of virgin PP, untreated and treated PP/sisal composites at 30% fiber loading [74].

Die swell ratio is defined as the ratio of the diameter of the extrudate to the diameter of the capillary die (see Fig. 10 in Section 3.6). The inerease in diameter can be expressed as a percentage of die diameter. Whether the measurements are at room temperature or test temperature is also part of the definition. Die swell can be measured using capillary rheometers from either measurement of diameter after the cooling of a piece of extrudate of specified length or by noncontact optical or photographic means of the hot extrudate as it issues from the die. 

FIGURE 3.82 Measurement of swelling of die extrudate. Die swell ratio=BM. 

If the die swell ratios in thickness and dicumferential directions are 1.S0 and 1.23, reqiectivety, find the final dimensions and velocity of the extrudate. 

When producing carbon fibers from pitch, a critical processing parameter is the viscosity of the pitch, which is extremely dependent on the spinning temperature. If pitch was a truly Newtonian fluid, the viscosity would be independent of shear rate, attaining its value almost instantaneously. It would be expected that the ratio of the hot filament diameter to the orifice diameter (die swell ratio) would be less than 1.1 and the molten fluid would not climb the stirring rod (the so called Weissenberg effect) [228]. 

Sample Glass Fiber (%) Shear Rate (see" ) Die Swell Ratio... 

Die-swell ratio (extrudate-swelling ratio) n. In extrusion, particularly in extruding par-isons for blow molding, the ratio of the outer parison diameter or parison wall thickness to, respectively, the outer diameter of the parison die or the die gap. The ratio is affected by the polymer type, its temperature, the die geometry, and the extrusion rate. Some writers have defined the die-swell ratio as the ratio of the cross section of the extrudate shortly after emergence to that of the die opening. 

Figure 13. Die swell ratio vs. shear rate for styrene copolymers filled with different loading volumes of carbon black (constant l /D ratio of 10) [44].

In blow molding, the die swell ratio is the ratio of the outer parison diameter (or parison thickness) to the outer diameter of the die (or die gap). Die swell ratio is influenced by polymer type, head construction, land length, extrusion speed, and temperature. 

Die swell ratio and melt shear modulus exhibit melt viscoelasticity. 

Fig. 9-12 Die swell ratio as a function of temperature for acrylonitrile-butadiene-styrene (ABS) and high-density polyethylene (HDPE) [4].

Little has been published on the effect of Reynolds number on extrudate swell of liquids from fully three-dimensional dies. However, its effect on two-dimensional extrudate swell of a Newtonian fluid has been well characterized [1-4]. The influence of Reynolds number on the final die swell ratio for both planar jets (i.e., the thickness of the extrudate divided by the width of the channel) and axisymmetric jets (i.e., the diameter of the jet divided by that of the tube) are summarized in Fig. 1. In both cases, swell is greater than 1 for low Reynolds numbers but decreases to values less than 1 at high Reynolds numbers. As Reynolds number approaches infinity, the die swell ratios for the axisymmetric and planar jets approach the asymptotic values of /3/2 and 5/6, respectively [5,6]. 

Die-Swell Ratio n (extrudate-swelling ratio) In extrusion, particularly in extruding parisons for blow... 

Figure 8.31 Dependences of viscosity and die swell ratio of PS/EPDM (80/20) blends melt on ultrasonic intensity at different screw speeds [103].

Pressure, p.s.i. Shear stress, (dyn cm ) xl0 t Shear rate, s t Average density, g cm t Mass flow rate, g min Die swell ratio Extrudate appearance... 

FIG. 47 Die swell ratio (B) of HDPE (Marlex 6009) as a function of apparent shear rate (O) constant pressure (A) constant speed. (From Ref. 72.)... 

The first die swell theory was presented by Tanner (1970) to compute the die swell ratio for given material properties. The die swell ratio was calculated for a very long die (length-to-diameter ratio approaching infinity) and was formulated using the normal stress difference and shear stress at the wall. 

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