The Solids Conveying Device at Dow

The solids conveying device at Dow was built from a standard 63.5 mm diameter extruder. It was built by replacing the standard barrel with a short barrel, providing an L/D ratio of 4.5. The feed hopper casing had an effective barrel length of 1.9 diameters and was water cooled. The feed opening was 1.5 diameters in length  

An LDPE resin was used for this study. The resin had a melt index of 2.0 dg/min (2.16 kg, 190 °C) and a solid density of 0.922 g/cmT The shear viscosity was reported previously [37] thermal properties are provided in Chapter 4 bulk density as a function of temperature and pressure is provided in Fig. 4.4 and the coefficients of dynamic friction are provided in Appendix A5. The lateral stress ratio was measured at 0.7 [38] using the device shown in Fig. 4.8. 

The effect of channel depth on solids conveying rate is shown in Fig. 5.26 for screw and barrel temperatures of 75 and 125 °C, respectively, and at a screw speed of 50 rpm. At zero discharge pressure, the solids conveying rates were nearly proportional to the depth of the screw channel (or cross-sectional area perpendicular to the flight). For example, the conveying rates were 91 and 125 kg/h for the 8.89 and 11.1 mm deep screws, respectively. For these screws, the cross-sectional areas perpendicular to the flights were calculated at 420 and 530 mm an area increase of 

The solids conveying data indicate that two competing factors are controlling the rates. The rate reduction caused by a decrease in the cross-sectional area perpendicular to the flight for the large-radii screw is the most obvious factor. As the radii of the flights are increased, the area perpendicular to the flight tip decreases and 

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Figure 5.20 Photographs of the solids conveying device at Dow a) full view of the device, and b) the pressure discharge unit. Pellets were discharged through an annular opening between the discharge (matched) plate and the torpedo...

Table A5.1 Channel Dimensions for the Shallow and Deep Screws for the 63.5 mm Diameter, 4.5 L/D Solids Conveying Device at Dow...

Table 5.1 Experimental Solids Conveying Rates (Fig 5.24) as a Function of Discharge Pressure at a Screw Speed of 50 rpm and Barrel and Screw Temperatures of 75 °C for the LDPE Resin. Data were Collected Using the Shallow Screw for the Dow Solids Conveying Device...

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