The effect of superimposing longitudinal and transverse oscillations on the die section at the exit of an extruder is examined. Longitudinal oscillations ranged from 0 to 30 mm in amplitude, and frequencies varied between 0 and 50 Hz. Transverse vibrations varied from 0 to 0.35 rad in amplitude and from 0 to 50 Hz in frequency. Experiments were performed in two types of extruders: a horizontal Brabender Plasticorder and a vertical Scamia both with similar characteristics of 7 Kw power output and 7.105 Pa maximum pressure. The polymers used were high and low density polyethylene and polystyrene. The overall effect of the oscillations is to increase the mechanical properties of the extrudate as well as to reduce the pressure drop in the die section. This pressure reduction results in a considerable saving of the total power consumption per unit weight of extrudate. Within a given range of amplitude‐frequency of oscillations, overall power savings of up to 25% are possible with respect to the stationary mode. Furthermore, the total flow rate through the die is enhanced by the vibrations and the die swell is diminished.

A capillary-type viscometer was used in a twin-screw extruder to measure the apparent viscosity of cooked-extruded wheat-flour dough with various ingredients: lecithin, palm oil, sucrose, whey, sodium chloride, and bran. The effects of concentration of these ingredients on dough rheology and physical properties of extrudates (apparent density, expansion ratios, mechanical, and crispness properties) were measured. The role of ingredients was discussed in terms of their physico-chemical effect on biopolymer conversion. The correlations between apparent viscosity of dough and physical properties of extrudates were developed.

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