Screw extruder for the production of an expanded dry feed for foodstuff

A screw extruder for the production of an expanded dry feed or foodstuff, comprising:

• a stationary casing having an inner wall defining an axially extending bore;
• a screw mounted for rotation within said casing;
• the latter and said screw defining a push zone, a filling and transport zone, a compression zone and a final zone;
• said casing have a lateral filler opening at the beginning of said transport zone, and further having an outlet at one end thereof;
• said screw includes an end portion near said outlet, said end portion having the shape of a cone, said bore in the casing having an end portion surrounding said end portion of the screw and also having the shape of a cone, said casing and said screw extending in said push zone beyond said filler opening over a distance equal to at least one pitch length of said screw in a direction opposite to said outlet;
• said screw being sealed with respect to said casing at the end of said push zone;
• said filler opening being positioned at a distance of said compression zone which is at least equal to one pitch length of said screw;
• said casing having spaced-apart internal grooves extending in the longitudinal direction, said grooves having in cross-section the shape of a rectangular trapezium including a radially extending rectangular edge and a bevelled edge, said rectangular edge being the front edge and said bevelled edge being the rear edge when seen in the direction of rotation of said screw.