A method and apparatus are disclosed for processing extrudable materials in such a way as to apply a controlled and predetermined degree of shear force to the materials.
Typically, an extruder apparatus comprises a housing (1) having first and second screws (8,7) mounted therein for rotation on a common axis, the arrangement being such that longitudinal thrust forces exerted by the first screw (6) are at least partially compensated by corresponding forces generated by the second screw (7), inlet means for introducing material to be processed into the housing and a shear generating device (59,60) located between said screws, said device including a restriction through which material is forced from said housing (1) to exit from said housing (1).
The restriction is preferably an annular gap (61,62) formed by a sleeve fixed relatively to the housing and a shaft (57,58) portion which extends into the sleeve.