The effects of screw configuration on the screw fill degree and special mechanical energy in twin-screw extruder for high-moisture texturised defatted soybean meal

• Effects of screw element type, length, location on SFD and SME were studied.
• The more flow restricting ability, the higher SFD and SME.
• Increasing reverse kneading element length increased SFD and SME.
• Increasing reverse kneading element space or element-die distance reduced SME.
• Locating the element at high viscosity position increased SME.

To control the mechanical energy output by adjusting the screw configuration during soybean protein extrusion texturisation, the relationship between the screw configuration and the special mechanical energy was investigated. Different types of screw elements, element lengths and positions were designed and configured, while the other parameters were kept unchanged. The screw fill degree and specific mechanical energy output were detected. The results demonstrate that when the helix angle of conveying elements turns from forward (45°) to reverse (−37.5°), the disc width of the kneading elements decreases from 7.5 mm to 5 mm, and when the disc stagger angle turns from forward (45°) and forward (90°) to reverse (−45°), the screw fill degree and specific mechanical energy increase. When the length of the reverse kneading element increases, the screw fill degree and specific mechanical energy increase. When the distance between the reversing knead element and the die increases or the element space between the reversing knead element increases, the specific mechanical energy appears to decrease. Thus, the elements with reverse helix or stagger angles, narrow kneading disc, long length and flow-restricting ability increase the screw fill degree and induce high special mechanical energy. The special mechanical energy increases when the reverse kneading element is located at the screw position where the material viscosity is relatively high during extrusion.