Development of an extrusion system for Bori and force characteristics of its batter during extrusion

An extrusion system with intermittent discharge mechanism has been developed for preparing conical shaped nuggets (bori, a traditional Indian product) from semi-solid pulse batter. The system is comprised of a barrel and plunger, a piston and a receiving tray. All operates in synchronized manner with gear and chain drive mechanism to discharge an array of nuggets one after another on the receiving tray with the manual rotation of a handle. The speed of the plunger inside the barrel could be regulated by using interchangeable lead screws having different pitches.Irrespective of the speed (displacement/time) of the plunger inside the barrel continuous operation of the extrusion showed a constant force (steady state) zone followed by an increasing trend. However, the length of this zone (duration) decreased with the increase in either speed of the plunger or L/D ratio of the extruder die. Average extrusion force at the steady state region varied from 3.9 to 5.9 N, 5.7 to 8.1 N and 9.9 to 14.8 N for L/D ratio of 2/12, 2/10 and 2/8, respectively for plunger speeds from 1.67 to 5.00 mm/s. At the same plunger speed, the force–time profile for discontinuous (intermittent) extrusion showed similar trend to that of continuous extrusion, however, the levels of (peak values) forces were higher for the former, for the entire range of plunger displacement. For a particular set of operation uniform product formation was ensured from the least variation of the diameter of the discharged nuggets over the respective mean values. Whole extrusion system requires 45 watts for formation of array of nuggets.