Screw flight depth

Figure 7.8 Screw diameters and screw flight depths of three-zone screws.

Max. screw speed = 100 rev/min, screw diameter — 40 mm flight depth (metering zone) = 3 mm. 

The size of flight radii on the screw channel is important for the proper performance of a single-screw extruder. The specifications of the flight radii are commonly made using a combination of personal experience and guidelines [16] from the Society of the Plastics Industry, Inc. (SPl). These guidelines state unless otherwise specified the root radius will not be less than one-half of the flight depth up to... 

Geometric variables screw or inner barrel diameter D, axial screw length L, channel depth h, and clearance between the screw flight and the barrel 5... 

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... 

Transition Zone-. It is the section, also called the compression zone, of a screw between the feed zone and metering zone in which the flight depth decreases in the direction of discharge. In this zone the plastics starts in both solid and molten state with target to have all molten upon leaving this zone. 

In the flight depths illustrated in Figure 12.12, a distinction is made between standard screws and shallow-flight screws. Shallow-flight screws pick up less material and, as a result, the residence time is the plasticizing unit is shortened. This can be advantageous when utilizing thermally sensitive additives, such as colorants, or when the part production rate is a small compared with extruder capacity. 

Figure 6.12 Features of a typical extrusion screw. Key L= screw length, D = diameter, h = initial flight depth, hi = final flight depth. L/D = length/diameter ratio, h/hl = compression ratio.

D. The channel depth ratio varies from less than 2 to 4. The compression ratio, CR, has been defined as a ratio of the screw flight volume... 

The change in flight depth along the screw (i.e., the ratio of the solids metering channel depth to the melt pump channel depth) is known as the... 

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