DESIGN, CONSTRUCTION AND EVALUATION OF IMPACT HAMMER MILL FOR LIMESTONE CRUSHING FOR ACIDIC SOIL

Abstract

Soil acidity becomes a serious threat to crop production in most highlands of Ethiopia particularly in Western parts of Oromia. Frequent tillage, removal of crop residues and mono-cropping and heavy rainfall contributes to soil acidification by leaching of cations. Agricultural limestone raises soil pH and reduces solubility of potentially toxic elements such as hydrogen, aluminum (Al3+) and manganese (Mn) at optimum nutrient uptake by crops. In an effort to alleviate the problems associated with soil acidity, a motorized agricultural limestone crusher was designed and fabricated. The prototype of limestone crusher machine has a feed table, hammer plate, concave sieve, discharge chute, and supporting frame. Pertinent physical and mechanical properties of the limestone revealed that the mean major, intermediate and minor diameters for the limestone before crush were 42.27, 35.49 and 28.09 mm, respectively. The mean geometric diameter, arithmetic diameter, bulk densities, moisture content for the limestone were found to be 33.89 mm, 35.28 mm, 2088 kg/m3 and 3.871%, respectively. Performance of the prototype hammer mill machine, in terms of crushing capacity (kg/h), crushing efficiency (%), Mean particle size (mm), fuel consumption (ml/kg) or energy consumption (wh/kg) was evaluated. Tests were carried out at engine speeds of 540, 720, 900 rpm, screen hole diameter of 2, 4, 6 mm and feed rates of 3.50, 7.00, 10.50 kg/min. The maximum crushing capacity of 630.32 kg/hr was recorded when the engine speed was 900 rpm, the screen hole diameter 6mm and the feed rate 10.50 kg/min whereas the minimum crushing capacity of 65.623 kg/h was observed when the hammer mill speed was 540 rpm, screen hole diameter 2 mm and feed rate 3.50 kg/min. The mean consumed energy ranged from 15.47 to 149.16 Wh/kg with hammer rotor speed of 540 to 900 rpm, screen hole diameter of 2 to 6 mm and the feeding rate of 3.5 to 10.5 kg/min. The mean particle size ranged from 0.121 to 0.448 mm with hammer rotor speed of 540 to 900 rpm, screen holes diameter of 2 to 6 mm and the feeding rate of 3.5 to 10.5 kg/min. It could be noticed that the lowest values of mean particle size were obtained at engine speed of 900 rpm, screen hole diameter of 2 mm and feed rate of 10.5 kg/min.