Problems of engineering design and production of screws in counter-rotating twin-screw extruders
Polimery 2002, No 6, 441
Sequence of basic steps required during conceptual design of twin-screw plasticizing systems has been presented (Fig. 2). Bibliographic data allowed analysis of intermeshing flows to be performed and their effect on the plasticizing process was determined. Results of investigating the axial and frontal screw outline were presented, confirming changeability of the screw outline course in different cross-sections along screw axis. Change in the angle of flight flank inclination along the screw zone (β) requires appropriate change in the channel width, b, along this zone to maintain the existing intermeshing gap (Fig. 3.). Also, in zones where the screw helix angles exceed 35o and difference of helix angles > 15o, suitable erihancing of side inter-screw gap or scarfing of the flight edges are required to attain its appropriate minimum value (> 0.5 mm). Gap between the interacting screws varies at different locations of the flank surface of the flights — e.g. is higher in axial cross-section as compared with the piane perpendicular to flight inclination on the pitch diameter of screws (Fig. 11). Shape of the side intermeshing gap should be approximately rhomboidal (Fig. 3), i.e. the difference of the side inter-screw gap (Sb max. - Sb min.) should be from 0.1 to 0.3 mm, to maintain mass flowing through the gap along is width, he, under approximately identical shearing rate.
Keywords: counter-rotating twin-screw extruders, engineering design, selection of intermeshing gap, technology limitations