Extrusion Technology Questions and Answers

Answer: C

The stages are I - Feeding, II - Kneading, III - Cooking, IV - Expansion.

In the extruder the raw material first enters and is conveyed at low temperature and pressure (feeding, I, the flat start of the curve). The screw then compresses and works it into a dough, raising temperature and pressure gently (kneading, II). Next, intense shear and barrel heat raise both steeply, gelatinizing the starch and denaturing proteins (cooking, III, ending at the peak just before the die). Finally the hot, pressurized melt leaves the die, the pressure drops suddenly and water flashes to steam, puffing the product (expansion, IV, the sharp fall).

Options putting cooking before kneading, or cooking first, do not fit the gradual-then-steep rise, and kneading cannot come before the material is fed.

Answer: C

The stages are I - Feeding, II - Kneading, III - Cooking, IV - Expansion.

In an extruder the material first enters the feed section, where it is merely conveyed and temperature and pressure stay low and flat (I). In the kneading (compression) section it is compacted and worked into a dough, so temperature and pressure begin to rise (II). In the cooking (metering) section intense shear and heat drive both to a maximum, gelatinising starch and denaturing protein (III). At the die the melt exits to atmospheric pressure, and the sudden drop lets superheated water flash to steam and expand the product (IV).

The other options place cooking before kneading or kneading before feeding, which contradicts the rising temperature and pressure profile.