A laboratory threshing unit was constructed utilising a standard tangential feed ("conventional") combine cylinder, concave, beater and transition grate. This unit was used to study the phenomenon of corn cob break-up and its effect on the performance of the threshing unit. It was found that the degree of corn cob break-up was affected by cylinder peripheral speed, cylinder-concave clearance and hybrid cultivar. Within the hybrid cultivars used, increased cob break-up was associated with decreased shelling efficiency and concave separation efficiency. / The possibility of reducing kernel damage and increasing concave separation efficiency by changing some of the concave design parameters was investigated. A mathematical model of the tangential feed threshing unit was developed and used to investigate the effect of the concave design parameters. Experimental data indicated that kernel damage may be reduced by at least 24 per cent and concave separation efficiency increased by at least 38 per cent.

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