3. Materials and methods
The sunflower threshing unit (Fig. 1) operates on the
principle of axial flow movement of the material. The
threshing mechanism consisted of a threshing drum,
which rotates inside a two section concave. The concave
was made of steel plate, with an elliptical hole of 11 mm
by 60 mm. The distance between adjacent holes was
11 mm, and between the hole axes was 22 mm. The
concave clearance was fixed at about 35 mm, which had
proved satisfactory in the preliminary tests. The length
of the concave of the threshing unit was 096 m. To
determine the separation over the length of the threshing
drum, the concave was divided into six equal sections
by metal sheets underneath the concave. Sections 1 and
2 (feed and threshing section) covered the concave
over the length of the feed opening and threshing;
Sections 3–5 were the threshing, separating and conveying
sections, and Section 6 at the outlet section
separated the rest of the concave into two parts. Six
chutes were constructed underneath the concave to
collect the separated material from each section. A
plastic container was used to collect the material ejected
from the straw outlet.
Three threshing drums used were a peg tooth type
with an open threshing drum a peg tooth type with a
closed threshing drum and a rasp bar type (Fig. 2). The
peg tooth open threshing drum was constructed using 48
pegs arranged in four rows on the surface of the
threshing drum. The pegs were 50 mm in height and
were cut from a 19 mm by 19 mm mild steel square.
They were fixed on a drum with the help of nuts and
bolts in a helical arrangement. The distance between
each tooth was 60 mm. The diameter and length of