Flight clearance

Figure 7.4 Schematic of the modified free helix extruder with a barrel diameter of 58 mm and a flight clearance of 0.1 mm [5]...

The double integral represents the nonzero terms of the dissipation rate tensor as adapted by Middleman [61] and Bernhardt and McKelvey for adiabatic extrusion [62]. The nontensorial approach was adopted by Tadmor and Klein in their classical text on extrusion [9]. In essence these are the nonzero terms of the dissipation rate tensor when it is applied to the boundary of the fluid at the solid-fluid interface. In the following development this historic analysis was adopted for energy dissipation for a rotating screw. In this case the velocities Ui are evaluated at the screw surface s and calculated in relation to screw rotation theory. The work in the flight clearance was previously described in the literature [9]. The shear... 

Rowell and Finlayson described leakage flow through the flight clearance as flow between two parallel plates [7]. The rate of energy dissipation between the flight lands and the barrel wall is given by Eq. 7.82. This dissipation is considered to be the same as that for barrel rotation, and it is provided in the literature [9]. 

Mixing and Melting Performance as a Function of Flight Clearance... 

Klein, I., The Effect of Flight Clearance on the Performance of Plasticating Extruders, SPE ANTEC Tech. Papers, 20, 237 (1974)... 

Lead length, flight width, and flight clearance were 203.2, 23.9, and 0.20 mm, respectively, in all sections of the screw. A 28.7 mm diameter screw cooling hole was drilled in the shank end of the screw, and it extended 3.8 diameters into the feed section. The first 2.5 diameters of the screw were inside a water-cooied feed casing. The specific rotationai rate of the first-stage metering section was caicuiated at 20 kg/(h-rpm). 

Due to the high cost of replacing the feed casing and the lack of direct evidence that the ledge and large flight clearance were the root cause of the reduced rate, an alternative experiment needed to be developed that simulated the process. Without these data plant personnel were unwilling to replace expensive components and incur downtime based on indirect evidence. 

Table 12.7 Ledge Sizes and Flight Clearances in the Feed Casing for the 63.5 mm Diameter Laboratory Solids-Conveying Device...

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