The grinding operations of corn cobs using two different local manufactured hammer mills namely: Aamagro (mill A), and El-Gohary (mill E) were evaluated and compared to be used as an ingredient in feedstuffs for animal and poultry farms. The field experiments were carried out at Sakha Agricultural Research Station, Kafrelsheikh Governorate, Egypt during the year of 2015. These experiments were deduced to evaluate and compare the performance of the investigated hammer mills under the effects of

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... hree feeding rate levels (0.2, 0.4 and 0.6ton/h), four rotor speed levels (1200, 1500, 1800 and 2100rpm), and two screen hole diameter levels (9 and 14mm) using corn cobs. The performances of both machines were evaluated in terms of: fineness degree (particle size distribution), machine productivity, power requirements, specific energy consumption, and machinery unit cost. The results revealed that, the optimum operating conditions for both A and E mills were obtained at rotor speed of 2100rpm, cobs feed rate of 0.2 ton/h and 9mm screen hole diameter. Whereas, under these conditions the maximum percentages of fine milled cobs (1.7-≤1.18mm) of were 63.71 and 53.16% for A and E mills, respectively. Also, mill productivity of 0.185 and 0.146ton/h, power requirements of 2.245 and 3.076kW and specific energy consumption of 12.134 and 21.065kW.h/ton were determined under the optimal operating conditions for A and E mills, respectively. Moreover, the estimated machinery unit cost for mill E was about 1.124 times that of mill A.