Design and fabrication of a coffee hulling machine.

Abstract

Coffee is one of the most important cash crops grown across the world and a major source of export earnings. Coffee hulling is the removal of what is left of the fruit from the bean, whether it is the crumbly parchment skin of wet-processed coffee, the parchment skin and dried mucilage of semi-dry-processed coffee, or the entire dry, leathery fruit covering of the dry-processed coffee. The simplest traditional methods of hulling parchment coffee (seeds) involve the use of pestle and mortar and a sack and pestle. However, these methods are of low hulling and cleaning efficiency, cause over breakage of the coffee beans and are also labor intensive The purpose of this project was to design and construct a coffee hulling machine for helping coffee farmers improve on the quality of their coffee beans through reducing breakages which yield high market prices hence improving their economic wellbeing The method of primary processing of coffee is a vital determinant of quality and price. Wet processing method produces higher quality beans but is very laborious. A motorized coffee hulling machine was designed, fabricated and tested to assist coffee farmers to hull coffee easily and cheaply. The hulling machine consist of a hopper, hulling drum, a blowing fan, cleaning unit, belts and pulleys, a reciprocating screen, a shaft, Power source, Outlet for hulled coffee beans and coffee husks and the frame. The design philosophy is to use rubber beaters to achieve sufficient impact force that can break the hull of green parchment coffee and detach the beans through impact and shearing forces caused by rubber beaters. The beaters arranged around the circumference of a hollow pipe rotates with relatively high speed to achieve sufficient impact force and also move the broken materials against the concave to release the beans from the hulls. The performance tests carried out on the constructed machine showed an efficiency of 90% with an output capacity of 120kg/hr. This machine can be produced in local small machine shops existing in coffee producing areas in Uganda.