Winnowing is the process of separating grain from a mixture of grain and chaff in an air stream created artificially or naturally. Separation is achieved by allowing the air stream to pass through the mixture falling vertically downward direction. The grain being the heavier material gets deposited almost at the place of dropping, whereas the lighter material (chaff) is blown away to a greater distance. The winnowing operation which is very common in India is done on the threshing floor where all harvested crops are stacked in bundles. Usually one or more persons pour the threshed material with a basket from slightly above their own height. For effective cleaning, they shake the basket while pouring the mixture against the positive direction of air stream.
When the natural wind velocity is not adequate, artificial means are employed to create sufficiently strong air blast. Winnowing fans are either manually operated or mechanically powered. Manually, operated fans of various types are available for use in India. Most often, the hand operated or pedal operated winnowing fans are used by farmers. In either case, the fan blades create a steady blast of air at the front side of the fan. One or more workers standing on the front side can drop the threshed material for effective separation. Thus winnowing is one of the challenging task in paddy cultivation.
A motorized version of the winnower is available in the market which runs on 1 HP electric motor, and comes at around Rs. 30,000/-. But this machine is not economical for small-medium scale paddy farmers. After analyzing various issues, the main need regarding winnowing was identified as development of a low cost paddy winnower.
Keeping in view of the above few facts, Mitraniketan has developed a low cost Paddy Winnower which runs on domestic fans. After conducting field trials, the technology was proven insufficient.
Under core support project, the existing low cost design was further modified for wide usage. The developed machine consists of feeding hopper at the top to regulate and control the flow of threshed paddy; an integrated fan to blast air to separate the straw, chaff and other impurities from grain. Two separate outlets were provided that facilitates grading of the paddy grains.
The most notable modification is the introduction of vibrating system, which facilitates proper feeding of grains into the machine. The system consists of a eccentrically loaded rotating leaf strategically placed in the path of air flow. This leaf rotates due to the air vortex created by the winnowing fan. Since the size of the vibrating fan is small compared to that of the blower, the energy absorbed will be less. Since the vibrating system is provided as a separate unit with appropriate dampers, it will not cause any damage to the fan or the essential structure of the machine, but creates enough vibration to facilitate smoother flow of grain from the hopper to the drum.