Development of a multi-commodity hammer mill for small-scale milling operation

Abstract Size reduction is essential in agricultural commodities for efficient feed utilization in animal consumption. Oyster shells and corn (including charcoal) are some of the common feed ingredients in poultry production in the Philippines which requires a maximum of 1,100 N (average 606 N) force and 280 N (average 151.2 N) force, respectively, to break. One of the common machines used in the size reduction of agricultural commodities for animal feed is the hammer mill. Common hammer design of hammer mills is a strong, hard, and thin steel vertically oriented (90°) which is attached to a shaft that utilizes mostly impact, shear, and attrition forces when it collides with the commodity. The study aimed to design and evaluate the performance of the three-rotor hammer mill machine with slanted hammers (45°) to increase the impact forces during milling. Finite element analysis (FEA) was used to aid the design of the hammers and computer-aided drafting (CAD) was used in the drawing of the machine. Results of the performance evaluation showed that a 90°-45°-90° hammer design and arrangement is the most advantageous in milling oyster, corn, and charcoal when operating at a hammer speed of 2,450 RPM and fan speed of 4,295 RPM with an air inflow of 4.5 m/s and air outflow of 6.0 m/s. The machine has a noise level of 94.7 dB and an electrical energy consumption of 1,173 watts. The milling capacity of the machine is 29.57 kg/hr for oyster shell, 13.52 kg/hr for corn, and 62.51 kg/hr for charcoal with particle size output of 3.00 mm, 4.47 mm, and 1.07 mm, respectively. The cost analysis of the machine revealed a break-even point (BEP) of 46,090 kg/yr for milling oyster shell, 9566 kg/yr for milling corn, and 55793 kg/yr for milling charcoal with an operating cost of ₱2.44/kg, ₱5.33/kg and ₱1.15/kg, respectively.