Screw length/diameter

The screw length/diameter ratio, L/D is maintained around 16 1 to 24 1 ... 

Typical extruder dimensions include a screw length/diameter ratio of 20 or less for melt extruders, with standard diameters varying from 20 mm (0.75 in) to 600 mm (24 in). They... 

The copolymers are used in the manufacture of filaments. These may be extruded from steam-heated extruders with a screw compression ratio of 5 1 and a length/diameter of 10 1. The filaments are extruded downwards (about 40 at a time) into a quench bath and then round drawing rollers which cause a three- to four-fold extension of the filaments and an increase in strength from about 10000 to 36 000 Ibf/in (70-250 MPa). The filaments are used for deck chair fabrics, car... 

In a particular extruder screw the channel depth is 2.4 mm, the screw diameter is 50 mm, the screw speed is 100 rev/min, the flight angle is 17° 42 and the pressure varies linearly over the screw length of 1000 mm from zero at entry to 20 MN/m at the die entry. Estimate... 

Abbreviation for length/diameter ratio, commonly used to describe machine barrels and screws. 

For square pitched screws, Ls = Ds, and the flights are all perpendicular to the screw axis. Extruder screws range from 25 to 150 mm in diameter, with screw lengths typically of 25 to 30 screw diameters. They rotate at speeds from 50 to 150 rpm, and deliver melt at rates from 10 to 1000 kg/h with pressures up to 40 MN/m. ... 

In its simplest form, the ratio of screw diameter is the basis for scaling. The ratio of the large diameter D2 of the large scale unit to the small diameter Z>i of the lab unit is represented by the lower case d as shown in Table 4. The primary scaling variables are channel depth H, screw length L, helix angle cj), and screw speed N. The ratio of the primary variables of the two scales is then expressed as a power of the screw diameter ratio, d. 

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... 

A twin screw extruder with a diameter of 32 mm has a clearance of s=0.15 mm between the screw and barrel. The screw is double-flighted. At a throughput of 50 kg/h (density p = 1000 kg/m3), a speed of 300rpm, and a melt-containing screw length of 1S/D=10, the return flow fraction results in ... 

Extruders may be classified conveniently using a three-figure system—for example, 1-60-24—where the first number states how many screws the machine has, the second gives the diameter of the screw in millimetres, and the third the effective length of the screw as a multiple of the diameter. In a 1-60-24 there would be a single screw of diameter 60 mm and length 24 diameters. 

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