Method and apparatus for producing fully cooked extrudates with significantly reduced specific mechanical energy inputs

A twin screw extruder comprising:

• an elongated barrel presenting a material inlet and a material outlet;
• a restricted orifice die positioned adjacent said material outlet;
• and
• a screw assembly situated within said barrel and comprising—
• first and second elongated, axially rotatable screws each having an elongated shaft with outwardly extending helical flighting along the length of each shaft, the flighting of each shaft being intermeshed with the flighting of the other shaft,
• the flighting of each of the first and second shafts presenting a pair of axially spaced apart sections of short pitch length, and an intermediate section having a pitch length greater than the pitch lengths of either of said short pitch length sections,
• the flighting of said intermeshed intermediate sections having an axial gap distance therebetween of from about 0.1-0.4 inches.

A twin screw extruder comprising:

• an elongated barrel presenting a material inlet and a material outlet;
• a restricted orifice die positioned adjacent said material outlet;
• and
• a screw assembly situated within said barrel and comprising—
• first and second elongated, axially rotatable screws each having an elongated shaft with outwardly extending helical flighting along the length of each shaft, the flighting of each shaft being intermeshed with the flighting of the other shaft,
• the flighting of each of the first and second shafts presenting a pair of axially spaced apart sections of short pitch length, and an intermediate section having a pitch length greater than the pitch lengths of either of said short pitch length sections,
• the ratio of the pitch length of said intermediate section to the pitch lengths of either of said first and second sections being from about 1-7.

A twin screw extruder comprising:

• an elongated barrel presenting a material inlet and a material outlet;
• a restricted orifice die positioned adjacent said material outlet;
• and
• a screw assembly situated within said barrel and comprising—
• first and second elongated, axially rotatable screws each having an elongated shaft with outwardly extending helical flighting along the length of each shaft, the flighting of each shaft being intermeshed with the flighting of the other shaft,
• the flighting of each of the first and second shafts presenting a pair of axially spaced apart sections of short pitch length, and an intermediate section having a pitch length greater than the pitch lengths of either of said short pitch length sections,
• the ratio of said long pitch length to the flight depth ratio in the long pitch length section is from about 0.4-0.9.