Design Criteria of an Inclined Draper Separator for Cleaning Decorticated Groundnut

Abstract

This study focused on establishing design criteria for an inclined draper separator for cleaning decorticated groundnut. Inclined draper separators utilise differences in size, shape, and surface characteristics between groundnut kernels and shell particles for separation. However, previously reported studies have largely been descriptive, with deck angle and belt speed presented as operating values that performed satisfactorily rather than as parameters derived from explicit design criteria. This limits the transferability of the reported information to other crops or belt materials. In the present study, quantitative design criteria for an inclined draper separator were developed and subsequently incorporated into a functional prototype. Three criteria were derived from the measured physical properties of groundnut (cv. Kadiri-9) at a moisture content of 13.36%: (i) a friction angle range for selection of the deck inclination, bounded by the rolling angle of groundnut kernels and the sliding angle of shell particles; (ii) a limiting belt speed, requiring the belt speed to remain below the downslope rolling velocity of the kernels; and (iii) a monolayer loading criterion based on the available deck area. For the groundnut velvet belt combination, the friction angle range was 17°–27°, representing a narrow operating window of 10°, with corresponding kinetic and static coefficients of friction of 0.306 and 0.510, respectively. The downslope rolling velocity of the kernels was zero at the lower limit, indicating that separation cannot occur at this inclination irrespective of belt speed, whereas velocities of 1.40 and 1.98 m s⁻¹ were obtained at deck inclinations of 22° and 27°, respectively. The actual material loading was 9–53 times lower than the estimated monolayer capacity of 6.01 kg m⁻². The developed machine completely covered the identified friction angle range and operated at belt speeds corresponding to 40.3–116.7 rpm, while requiring less than 12 W of power compared with the assumed human power limit of 75 W. Among the three criteria, the friction angle range was identified as the actual design determining criterion, as both its limiting boundaries were encountered during operation. In contrast, the belt speed and loading criteria reached only 39.3% and 10.4% of their respective limits and therefore served primarily as verification criteria. Consequently, application of the proposed design approach to another seed or belt material requires only the repetition of the two relevant inclination measurements.