2. Design and development of stripper header
The locally made rice combine harvester manufactured
by Kasetpatana Manufacturing Company, Phitsanulok
province, northern Thailand, was selected for this study,
as it was found to be the most popular model in the
country. This combine harvester is a self-propelled machine
equipped with a cutter bar mechanism having
a cutting width of 3 m and a 108 kW diesel engine as the
prime mover (Fig. 1). Power was transmitted by V-belts
from the engine shaft to other components of the machine,
except for traction and header height control
which used a hydrostatic power transmission system. The
power from the traction shaft was further extended to
two independent hydraulic pumps (gear type) via double
chain couplings. Two low-speed, high-torque, radial piston
motors were selected to drive the sprocket wheel of
Fig. 1. Thai-made rice combine harvester equipped with cutter
bar mechanism Fig. 2. Mechanical transmission system of the stripping rotor
Table 2
Speci5cations of the Thai-made combine harvester with stripper header
Stripping width, mm 3000
Stripping rotor diameter, mm 540
Number of stripper rows 8
Number of teeth per row 71
Transmission system Hydraulic
Range of speed, min~1 600}800
Nose adjustment, mm 200
Power source, kW 108 (reconditioned Isuzu diesel engine)
Number of operators 2
Number of unskilled labourers 3
Forward speed, km h~1 3}7
the machine. The working speed of the machine was
varied from 3 to 6 km h~1 depending on the crop and
"eld conditions. An axial #ow thresher was used as
a threshing unit and the mechanism consisted of a pegtooth
cylinder which rotated inside a concave double
section. The locally made rice combine harvester equipped
with a cutter bar cut almost the whole rice plant
whereas the stripper header stripped only grains, leaving
most of the straw in the "eld.
Modi"cations of the rice combine harvester for "tting
a stripper header were carried out by removing the pick
up reel and cutter bar units of the machine. Three rubber
paddles (5 cm by 50 cm) were fabricated and attached to
the centre of the front auger which enabled it to convey
stripped material easily from both sides of the table auger
through the centre of the feeder conveyor. The feeder
conveyor was attached with rectangular rubber pieces
(5 cm by 35 cm) along the chain conveyor in order to
convey the stripped material into the threshing unit. The
power from the engine was transmitted to the stripping
rotor through a combination of pulleys and V-belts
(Fig. 2) or through a combination of hydraulic and
mechanical transmission system.
2.1. ¹he prototype stripper header
A stripper header was fabricated and mounted on
a Thai-made rice combine harvester and the performance
of the header was evaluated. The stripper header mainly
consisted of the stripping rotor, ba%e, hood, nose, front
auger and the hydraulic motor and pump which were used
to drive the stripping rotor. Design parameters of the stripping
rotor were based on the stripper rotor system developed
in theUK by Silsoe Research Institute. A summary
of the speci"cations of the stripper header is presented in
Table 2 and its main components are explained below.
The outer diameter of the stripper rotor was 450 mm.
Along the direction of rotor axis, a stripper rotor was
installed with eight rows of teeth, each row consisting of
71 teeth. The rotation of the stripping rotor was in the
reverse direction in relation to the ground wheel rotation
(Fig. 3). The stripping rotor speed was between 600 and
800 min~1 resulting in a peripheral speed of 17}22)7 m
s~1. They were essentially &V' shaped but with a 20 mm
circular recess at the base (Fig. 4). The height of the
stripping rotor could be adjusted from the operator's seat
using hydraulic means.
Fig. 3. Schematic diagram of the stripping rotor
Fig. 4. Proxle of stripping elements (all dimensions are in mm)
The prototype stripper header was "tted with local
industrial rubber teeth. This was because the imported
polyurethane was expensive and di$cult to obtain locally.
The cost of local rubber teeth was US$ 125 for a set
whereas a set of polyurethane stripper elements for the
stripper harvester cost about US$ 1000 and needed to be
imported from the UK. The performance of the local
rubber teeth was found to be satisfactory during "eld
testing in standing and lodged crop conditions.
The ba%e positioned behind the stripping rotor
prevented crop re-entry into the rotor. It was made of
3 mm thick sheet metal.
The metal hood, positioned in front of and above the
stripping rotor, de#ected the harvested material into the
front auger. The wall of the hood was made of 3 mm
thick sheet metal.
The nose determined the position of the crop during
harvesting. The position of the nose could be adjusted by
sliding it up or down the hood. The nose was held in
position by a pair of wing nuts, making adjustment easy.
The nose height could be adjusted up to a range of
200 mm.
The use of readily available materials and the
uncomplicated design enabled the stripper header to be
manufactured locally