Screw channel width

W Width of flow channel screw channel width (6.3-2)... 

The helix angle and the channel widths at the screw core or root are designated with a subscript c, and they are calculated as follows ... 

Wc channel width perpendicular to flight at the screw core Wgr width of the grooves in a grooved barrel... 

Figure 7.1 Extruder screw transformation a) schematic of a screw inside a barrel, and b) an unwrapped channel showing the transformation with the helical length Z and the channel width W. The screw is shown moving and the barrel is stationary...

Figure 7.7 Schematic of a screw channel perpendicular to the flight edge showing the width of the channel and the depth of the channel...

Eqs. 7.22 and 7.24 represent the velocities due to screw rotation for the observer in Fig. 7.9, which corresponds to the laboratory observation. Eq. 7.25 is equivalent to Eq. 7.24 for a solution that does not incorporate the effect of channel width on the z-direction velocity. For a wide channel it is the z velocity expected at the center of the channel where x = FK/2 and is generally considered to hold across the whole channel. The laboratory and transformed velocities will predict very different shear rates in the channel, as will be shown in the section below relating to energy dissipation and temperature estimation. Finally, it is emphasized that as a consequence of this simplified screw rotation theory, the rotation-induced flow in the channel is reduced to two components x-direction flow, which pushes the fluid toward the outlet, and z-direction flow, which tends to carry the fluid back to the inlet. Equations 7.26 and 7.27 are the velocities for pressure-driven flow and are only a function of the screw geometry, viscosity, and pressure gradient. 

The Tj, factors correct for the non-Newtonian shear rheology effects that occur in the channel. The parameters that are used in the correction correlation include rheological and geometric factors power law index (n), aspect ratio of the channel [H/W], the ratio of the channel width to the screw diameter (W/Df), and the number of flight starts (p). 

In polymer extrnsion, show that, for a single-flighted screw, the channel width is related to the inner barrel diameter by W = tvDs sinO. Clearly state any assnmptions yon make. 

Since we are scaling the system with the same material, we can assume that the material parameters remain constant, and for simplicity, we assume that the heater temperature remains the same. In addition, we will fix our geometry to a standard square pitch screw ( =17.65°) and therefore, a channel width proportional to the diameter. Hence, the parameters to be determined are D2, h2 and n2. 

Devolatilizing Screw Extruder A 150-mm-diameter, square-pitched, single-flighted screw extruder, with screw channel depth of 25 mm and 20-mm flight width is used to devolatilize a 1000-kg/h stream with 0.78-g/cm3 density at 200° C and 125 torr. (a) At what frequency of screw rotation will the channel be 30% or less full (b) With water injection, if density is halved by formation of 1-mm bubbles, how much surface area (per meter length) is created (c) How does... 

We now take the drag and pressure flow terms in Eq. 9.2-5 and substitute the relevant numerical values. We assume a square pitched screw, neglecting the difference between mean and barrel surface helix angle, and neglecting shape factors and flight clearance. We further assume that flight width is 10% of the barrel diameter. We can make these simplifying assumptions because, at this point, we only wish to select the barrel diameter and the screw speed. The channel width can be expressed in terms of the screw diameter as follows ... 

Fig. 2 Geometrical diagram of an extruder screw 1) diameter of the barrel (Db) inside diameter of the barrel 2) channel depth (H) distance from screw roots to barrel inner surface 3) flight clearance (c5f) the distance in between the flight and the barrel inner surface 4) channel width (ff(r)) distance in between two neighboring flights and 5) helix angle (6r) angle formed in between the flight and the direction perpendicular to the screw axis.

---