Smith - 2003 - Rice origin, history, technology, and production

Rice Harvesting 525
■Í
Figure 4.1.26. Axial-flow and rotary thresfiers have been around for over two centuries, but what the IRRI team was
able to achieve in some developing countries was to popularize an axial design that was well matched to small-area
farming conditions and that could be fabricated locally at modest cost. This is a portable unit at work in a Sri Lankan
rice field. (Photo by G. R. Quick.)
rotor by means of magnets and induction sensors. The straw may trayel from 4 to 11
times around the rotor (Gum m ert et al., 1992). Considerations o f straw flow led to
a Vietnamese design which utilizes fewer teeth and can thresh rice bundles that are
dripping wet from flooded fields. By 1990, government people estimated that there
were 1000 thresher manufacturers in the Mekong Delta o f Vietnam alone and that
they had built over 50,000 units. Following the popularization o f power threshers
in the Mekong, Vietnam joined the top three rice-exporting nations, with m ost o f
Vietnam’s export grain com ing from the Mekong Delta (Hien, 1991) (Figure 4.1.27).
Ú
Throw-in Threshers That Chop the Straw for Stockfeed
M any farmers in South Asia want cereal straw— wheat straw in particular— ^to be
chopped up fine for use as animal feed. In some seasons, chopped wheat straw has
almost as much value as the grain. Indian threshers achieve a simultaneous threshing
and straw-chopping action: All o f the crop material is forced through the concave
and the rotor is equipped with chopping blades similar to those on a hamm er mill.
Often, a fan is mounted integrally on the rotor axle to provide the air blast for the
cleaning system underneath the concave, along with heavy flywheels to maintain the
m om entum required for chopping.
Where wheat and paddy are grown in rotation, such as in Egypt, parts o f China,
and in India, farmers need threshers capable o f use in either crop with a minim um
o f modification (Figure 4.1.28). An adapted thresher with a set o f adjustable louvers
inside the cover o f the thresher drum can be fixed at 90“ to the rotor axis and the
straw outlet blanked out for tlireshing wheat in the beater mode. W ith this A.U. Khan
design, for threshing paddy the louvers are set at 75° to the rotor axis and the straw
outlet door opened for separated straw discharge (Quick, 1998b).