The construction details and operation of a modified cereal huller that can operate as a thresher to remove Prosopis seed from pods, described by Flynt and Morton (1969), are presented below. To facilitate application, the original English units have been converted to their approximate equivalents in the metric units.
Construction details
The basic units of the thresher is a cereal huller powered with a ¼-horse-power (93,200-watt) electric motor. The abrasive cylinder and brushes used for hulling the cereals are removed, and the brushes are replaced with two discs and spacers. Three ¼-inch (0.635-centimeter) square steel bars, 1½ inches (3.81 centimeters) long, are welded to each disc. These discs are rotated within the threshing chamber at 1,750 revolutions per minute.
The screen, which forms the periphery of the threshing chamber, is made from sheet metal 1/16-inch (0.159 centimeter) thick, 18 inches (45.7 centimeters) long, and 2½ inches (6.35 centimeters) wide. It is curved in a circle, with the ends welded together so that it fits into the space provided for the conventional screens.
As shown in the diagram, one-half of the screen is perforated with 5/16-inch (0.794-centimeter) holes (Section A in the diagram). These holes permit the seed to leave the threshing chamber as they are released from the endocarp, but they are not large enough to permit the intact endocarp containing the seed to pass. Five slots, (Section B in the diagram) 3½ inches (8.89 centimeters) long and 1/8-inch (0.318-centimeter) wide, are cut parallel to the length of the screen so that the broken endocarp tissue can leave the threshing chamber.
A 2-by-2½ inch (5.08-by-6.35 centimeter) piece of Number 30 grit sand paper is attached to the nonperforated portion of the screen (Section C). This abrasive surface wears away the spongy mesocarp and the edges of the endocarp tissues surrounding the seed. Three ¼-inch (0.635-centimeter) square steel bars (Section D), ½-inch (1.27 centimeters) long are welded to the screen between the holes and the slots. A slot 3/4-by-1½ inches (1.90-by-3.81 centimeters), is cut in the screen to permit the pods to be released in case too many are fed into the threshing chamber.
Threshing Screen. A. 5/16-inch holes; B. 1/8 by 3-1/2-inch slots; C. Number 30 grit sandpaper; D. 1/4-inch square steel bars.
Source: Flynt and Morton 1969.
Operation of thresher
Pods are dried in an oven at 44°C for 24 hours, after which they are broken into 1-inch (2.54-centimeter) segments. The segments are placed in a hopper, from which they are uniformly fed into the threshing chamber. The pods are further broken down by the rotating and stationary bars, and the pericarp tissue is eroded by the sandpaper. When the endocarp has been broken, the seed is released from the threshing chamber through the 5/16-inch (0.794-centimeter) holes and the endocarp through the 1/8-inch (0.318-centimeter) wide slots. All of the seed and the pericarp tissues pass into a small two-screen, wind cleaner, where most of the seed is separated from the pericarp. A small gravity separator removes the endocarp tissues, which are of the same size as the seed.
The pods should be dry for maximum results. When the pods are wet, the hygroscopic pericarp tissue is deposited on the interior of the device.
With this modified cereal thresher, 1 bushel (0.0352 cubic meters) of Prosopis pods can be threshed in 1½ hours. Approximately 160 hours would be required to thresh an equivalent amount by hand.
