Performance Evaluation of the Cutter Unit of A Straw Chopper

A prototype of a straw chopper, equipped with a discharge system was designed and fabricated in the Department of Mechanics of Agricultural Machinery, University of Tehran, Karaj, Iran. To test for the effective performance of the machine, the effects of such parameters as: drum speed (at three levels of: 400, 540, and 800 rpm), screen size (at two levels: 2.5 and 4 cm), and number of blades on each flange (4 and 8 blades), on power requirement for particle size reduction, chopping capacity, and straw particle size distribution were investigated. Based on the results, with increase in drum speed, power requirement as well as threshing capacity increased. There was no significant difference observed between drum speeds of 540 and 800 rpm as regards particle size distribution, while a speed of 400 rpm resulted in longer particles, therefore a drum speed range of 540 to 800 rpm was recommended. With decrease in screen opening's size, the power requirement increased while the threshing capacity decreasing. Screen size of 2.5 cm led to finer particles. With an increase in the number of blades on each flange, the power requirement decreased while the threshing capacity increasing. Since there was no significant difference observed between the number of the two sets of blades as regards particle size distribution, it is recommended that 8 blades be installed on each flange. The power requirement can thus be reduced and the cutting capacity increased.