EFFECTS OF OPERATING SPEED AND SCREEN DIAMETERS ON THE EFFICIENCY OF A HAMMER MILL.

Abstract

A hammer mill was developed for pulverizing dried yam. The machine was evaluated using screens of different sizes (1.5mm and 5.0mm) and different operating speeds (650 rpm and 1300rpm) to ascertain effects of these parameters on the machine output efficiency, capacity and fineness of the end-products. Four replicate samples were prepared namely: A – [5.0mm ø screen, 650rpm
speed], B – [1.5mm ø screen, 650rpm speed], C – [1.5mm ø screen, 1300rpm speed] and D – [5.0mm ø screen, 1300rpm speed] respectively. The end-products were subjected to sieve analysis; the following inferences were drawn: (i) D is most time efficient with operational time of 8.10sec for 10Kg of dried yam, followed by C (8.60sec), A (9.15sec) and B (9.40sec) respectively for same mass of test material; this shows that higher operational speed and screen size enhanced the milling time.(ii) The output efficiency (%) are in the order: C (81.50%), B (79.40%), D (77.10%) and A (73.39%) respectively; best output efficiency was achieved at higher speed cum small screen hole diameter.(iii) Also that the operational speed and screen hole diameter affects the machine output capacity, as shown: D (74.07 Kg/hr), C (69.77 Kg/hr), A (65.57 Kg/hr), and B (63.83Kg/hr) in decreasing order respectively and fineness modulus: A (0.88), D (0.84), B (0.75) and C (0.62) in increasing order respectively. Therefore, a suitable operational speed and screen size was
ascertained and recommended for the optimum efficiency of the hammer mill.