System upgrade and performance optimization of a sunflower seed Detacher unit

Oilseeds after cereals ranked at second place as human’s food sources. Among them, sunflower is one of the main oilseed for cultivation. Because of increasing demand rate for edible oil import, it is necessary to avoid any grain loss during harvesting and processing of oilseeds. In some sunflower fields, mechanical harvesting is hardly done by combines due to difficulty for movement as well as the small-cultivated area. Then, manual harvesting and processing of sunflower heads and grains are appropriate and most used field operations. Detachments of grains from heads is a tedious work and labor-intensive operation. Also, form medical and ergonomic point of views it makes physical problem for workers. All commercial equipment thrash field dried sunflower heads, entirely. Therefore, some wastes are produced at preharvest (in field), threshing and separation processes. Some research have been conducted to adjust combine to decrease grain losses. Cylinder rotational speed and type, distance between cylinder and concave, heads moisture content and threshing unit feed rate were such adjustment. However, none of the detached grains from head without head threshing. On the other hand, losses to about ‎‏46% during harvesting the ‎sunflowers with the combine, a partially mechanized approach for grain detachment was chosen in this study. ‎

To do this an existing sunflower seed detacher unit (Jahani, 2014) was equipped with cleaning unit. In addition, the unit efficiency was improved by optimizing the device settings. This device consisted of a feeding conveyor belt, two series detacher cylinder with 8 cm rubber fingers covered all through their peripherals in segregated patterns, cleaning unit, two electric motor and deriving mechanism (belt and pulley). Cleaning unit comprised an axial flow fan and an inclined guide canal for grain movement. Fan was selected in such a way that separate the gross waste materials mixed with grain, detached from heads by laboratory test using a terminal velocity test rig. Slope and material of canal was determined by laboratory trials using a test rig to measure sliding coefficient of grain batches. For evaluating the unit performance, laboratory experiment was carried out at four levels of rotational speed of the detacher cylinders (300, 450, 510 and 600 rpm) and four levels of grain moisture content (7, 15, 20 and 27% db) in three replications. Cylinder rotational speed and feeding belt speed were selected based on Janani’s research results. Feeding belt speeds were adjusted in such a way that the speed ration of linear velocity of cylinders to feeding belt were constant and about 72.2 as reported by Jahani (2014). Moisture content levels were considered based on harvesting, processing and storage conditions of sunflower grains. Raw data were used to compute percentage of seed detachment, percentage of separation and grain fracture percentage.

ANOVA revealed that main factors of cylinders rotational speed and moisture contents and their interaction significantly affected percentage of separation (p < 0.01). Increasing in moisture content reduced the amount of detached grains from head due to flexibility of grains at higher moisture content and damping impact of rubber fingers. In addition, it was reported that lower moisture content produced lower adhesive force between grain outer surface and the pod. On the hand, increasing in rotational speed increased the amount of detached seed because of impact of rubber fingers and stored kinetic energy in shelled grains. The most detaching was obtained at 600 rpm and 5% moisture content. The rotational speed and grain moisture content and their interaction significantly (p < 0.01) affected percentage of fractured grains. Moisture content had more share for grain failure than rotational speed. Higher fracture was observed at lower moisture contents and higher cylinder speeds, so that it was around 6.4% at 600 rpm and 7% moisture. According to the results, cleaning was affected by moisture content alone and higher percentage took place at lower moisture contents because of lighter produced wastes. Overall, considering all above aforementioned indices, cylinder rotational speed of 600 rpm and grain moisture content of 20 % was the appropriate adjustment set for grain detaching. In such adjustment, detachment rate was as high as 94.6 %, grain fracture was limited to 0.27 %, cleaning was 68 % and the output capacity of the machine of 268 kgh-1 was achieved. More adjustment on fan speed is required to increase the rate of cleaning to approach hundred percent of cleanness.