Abstract

A small-scale mobile jaw-crusher unit with a throughput of 1-1.5 tons of aggregates per hour has been designed, manufactured and tested at the Department of Chemical and Processing Engineering, University of Dar es Salaam. The equipment is aimed at reducing the drudgery and hardships faced by artisanal miners, mostly women, who spend long hours in quarrying sites excavating and crushing aggregates using manual tools. The aim was to design a low-cost unit powered by bicycle pedals however this objective was defeated by economic constraints like labor cost and product price, as well as, technical limitation of the human physique and stamina to sustain pedaling of heavy inertial flywheels required to overcome the actual load and intermittent shock-loads. Instead a simple air-cooled engine 2.94 kW was used causing a 25% increase in investment cost but had 6 fold improvement in productivity over bicycle power and 30 fold boost over manual tools like sledge hammer, pickaxe and crowbars previously used by miners. The crusher was successfully field tested for 3 months by Umoja ni Nguvu women group at Kunduchi Mtongani quarry site to crush 6-8” limestone rocks to aggregates of various sizes ½”, ¾” and 1” required for road and building construction of roads on the outskirts of Dar es Salaam city. Based on the field data and an investment cost of Tshe 3.5 million, a financial profitability analysis indicated that the crusher project has a daily net-inflow of Tshs 259 thousand and a pay-back period of two months. Since the unit requires low level of technical skills and is not capital intensive it is recommended for micro- and medium scale aggregates miners and can be deployed in peri-urban quarries or remote villages without electricity grid.

Key words: Jaw-crusher, size reduction, power requirement, small-scale mining.