The compression ratio should be between 3:1 and 3.5:1 (Fig. 1). The flight depths themselves depend on the screw diameter D and on the melt viscosity.
Barrier screws are used especially for a constant output. Gentler melting and constant transport of the melt in a narrow output range are possible here.
The screw clearance (radial clearance between the screw and the barrel) should be 0.1-0.2 mm to minimize leakage.
Shear sections at 22-25 D are recommended for screws with a diameter of 90-150 mm.
Screen pack sizes of 400-3600 mesh/cm² are usually essential for the required pressure build-up and good melt homogeneity.
The processing temperature is 270 to 290°C for Ultramid® A grades (PA 66 grades), 240 to 270°C for Ultramid® B grades (PA 6 grades) and 210 to 260°C for Ultramid® C grades (PA 6/66 grades), depending on the product and the process. Appropriately powerful heater bands and drives (e.g. 10 kW heater power and 60 kW drive power for an extruder with a screw diameter of 60 mm), with precise controllers for screw barrels, adapters and dies are required. The best temperatures for a particular production must be determined by trials. Lubrication and nucleation have no significant effect on the resulting melt temperature.