Behaviour of Grain Separation in Thai Transverse Axial Threshing Units for Chainat 1 Rice Variety

A transverse axial threshing unit is widely used in self-propelled combine harvesters in Thailand and the ASEAN region. The grain separating behaviour of this threshing unit affects the performance of the threshing unit and cleaning unit. This study aims to find out the behaviour of grain separation in a Thai transverse axial flow threshing unit. The concave rod clearance was chosen as the test medium, as this significantly affects the behaviour of grain separation and Chainat 1 rice variety was chosen for test. The results show that 70-80% of grain were separated from the straw, and then fell through the lower concave of the feeding zone into the cleaning unit; whilst the rest were threshed in the separation zone. The purity of grain input into the cleaning unit was quite steady in the feeding zone, although the grain purity in the separation zone decreased as the length of the separation zone increased. The cumulative straws increased linearly during the feeding zone, as they increased exponentially in the separation zone. In contrast, the cumulative undeveloped kernels and other contaminants increased linearly when the length of the separation zone also increased.