Affecting Variables Order in Upper Sieve Return Loss

Wheat is the most important crop in Iran and plays main role in the food supply chain. But, its production is associated with high losses. Hence, efforts to increase the production yield by reducing wastes are concerned. Unfortunately, according to some researchers in this field, the combine harvesting loss in Iran is about 20% or higher. One of the ways concerning to loss reduction is separation of harvesting processes and providing a desired mathematical model for them by investing and measuring of important parameters in losses. Cleaning process is one of these processes which has more effect on combine harvester performance. The performance of a cleaning shoe is expressed in terms of (1) grain loss or cleaning efficiency, (2) grain dockage, and (3) cleaning capacity. Material feed rate, fan speed and degree of sieve opening are operation parameters which were used in combine design and evaluating of its performance. In order to evaluate the effect of these parameters on cleaning efficiency, an experiment was conducted in 3×3×3 factorial pattern with randomized blocks design. The independent variables in the experiment were material feed rate, degree of sieve opening and cleaning fan speed. The first two variables and B×C interaction effect had significant effect on cleaning efficiency (P<0.01). But, fan speed and other interaction effects of these variables were not significant. Grain loss increased when feed rate was increased and it decreased when degree of sieve opening was decreased. Multiple regressions were used to express the relation between the dependent and independent parameters. The most compatible model (in the scope of this study) for grain loss (y2) was: which x1, x2 and x3 determined the material feed rate, fan speed and degree of sieve opening, respectively and a0, a1, a2 and a3 were constants.