Abstract:
Improvement of quality and value addition of agricultural produces has gained higher concern in recent times in Sri Lanka due to
creation of new opportunities for sale of agricultural commodities in open market at competitive prices. Grading according to the
sizes is an important value adding technique for most agricultural products. And also the price of the many agricultural products
varies significantly according to their uniformity in size. Uniformity in size not only makes the produce more attractive to
consumers but also improve its processing qualities. At present, size grading of most agricultural crops including big onion are
carried out manually by crop collectors, whole sellers and retail sellers, most of farmers market their products without any
grading. In Sri Lanka, persons engaging in post-harvest crop handling such as collectors, whole sellers, retail sellers, and farmers
have less chance to use high technical and costly grading technique. And also local market survey reported, retail market price of
the big onion bulbs are significantly varied according to its size. Hence, this research study attempted to design and development
of a low cost size grading machine for size grading of big onion bulbs. Size grading machine was fabricated by cast iron and
PVC tube and It was designed for grading of onion bulbs into three sizes i.e. small (φ< 4 cm), medium (4 < φ < 6cm) and large (φ
> 6cm). Grading machine was also fabricated to operate either by manual or electric motor. The machine was tested for grading
efficiency/quality accordingly, machine performance was optimized. Optimized machine adjustments for its maximum
performance were 3oinclined angle of the grading cylinder against horizontal axis and 15 rpm rotating speed of the grading
cylinder. Maximum grading qualities/efficiencies under optimized machine adjustments for small, medium and large sizes were
reported 84.47%, 93.46% and 90.14 respectively. The capacity of the grading machine was 630 kg/hour under the optimized
operational conditions.
