###### Abstract  
Sunflower threshing is one of the most interesting field processes for making the sunflower ready for seed handling, drying, cleaning and oil extraction. One of the biggest problems observed during the sunflower threshing process is the accumulation of threshed crop on the first third of the threshing roller and passing off some unthereshed parts of sunflower heads. To solve the aforementioned problem and optimize the efficiency of the sunflower threshing process, this research was focused on devising and testing a sunflower threshing machine with a close threshing box system equipped with a screw conveyor that evenly distributed the feedstock of sunflower heads on the entire length of the threshing roller. The machine was tested to assess the seed damage rate, unthereshed seed percentage, threshing efficiency, machine productivity, power requirements and specific energy consumption. The evaluation was done under different roller rotational speeds (150, 200, 250 and 300 rpm) and feeding rates (600, 700, 800 and 900 kg/h). The obtained results revealed that the threshing evaluation parameters were affected significantly by the roller rotational speed and feeding rate. The threshing efficiency was observed to rise with the rise in the roller rotational speed, and it also rose with the increasing feed rate up to 800 kg/h and then started to descend. The unthereshed seed percentage decreased with the increase in the roller rotational speed for all feed rates, and it decreased with the increasing feed rate up to 800 kg/h and then started to increase at the higher feed rates. The damaged seed percentage, power requirement and machine productivity increased with the increase of the roller speed and feed rate. The Buckingham \(\pi\) theorem was followed to find an equation to predict the threshing efficiency, resulting in an equation with an R\({}^{2}\) value of 0.9309. With elimination of the blockage problem and better threshing efficiency, this machine could be a good choice for small- to medium-sized sunflower farms. stationary threshed machines; axial flow thresher; screw conveyor; sunflower thresher; performance efficiency +
Footnote †: journal: Applied Sciences  
10 June 2021  
Accepted: 6 July 2021  
Subfigurethreshing machines to thresh sunflower heads, resulting in seeds damages amounting to more than 4-10% and seed losses of 3-13%, while some threshers resulted in grain losses of 20-35% [4]. The main purposes of mechanized sunflower threshing are to replace reduced manual labor efforts to thresh sunflower in fields, reduce threshing time, raise the quality of threshed seed and increase threshing efficiency. Productivity, threshing efficiency, broken seeds, grain loss, power consumption, cleaning efficiency and specific energy are the indicators for a thresher's performance [5]. In Ref. [6], it was made clear that the sunflower threshing process is affected directly by the feed rate, roller speed, concave clearance and thresher type. The seed loss percentage may reach 6% in the threshing or striking process [7]. The untraditional methods of threshing sunflowers depend upon striking, friction and concurrent striking with friction [8]. The authors of [9] made and tested a rubbing thresher machine to thresh flax and sunflower crops. The performance of the rubbing threshing machine was estimated at different threshing roller speeds, threshing belt linear speeds and concave clearances. The data showed that for the two crops, the threshing efficiency increased with the increase in the roller speed, and it decreased with the increase in the concave clearance. Furthermore, the authors of [10] assessed several typical sunflower thresher machines, with the axial flow design being used. Their study indicated that it is better to thresh sunflower at a cylinder revolving speed of 6.5 m/s with a head feeding rate of 1500-2000 kg/h at a seed moisture content of 30% (\(w/w\)). The authors of [11] developed a test bench thresher for sunflower heads, applying fundamental techniques used for seed threshers.