Design, development and evaluation of a size grading machine for onion

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.