Design and construction of a small scale maize hammer mill.

Abstract

Maize (Zea mays L) is one of the world's important cereal crops and a major staple food in East Africa. In addition to it being an important animal feed, it's also a source of income. Milling of maize grain into flour and other bi-products such as bran is an important process in increasing food security as well as increasing the shelf life. Maize flour is used to prepare porridge and a paste called posho, highly consumed in institutions, prisons and food vending businesses. Maize flour also supports the local brewery industry, where flour is fermented to produce local brews. However, the maize milling technologies especially the maize hammer mills that exist have not been efficient enough to cope up with such increasing demands of maize flour. Parameters that affect their efficiency include: thickness of the hammers, the mill clearance, and moisture content of the grains, drum rotational speed and capacity of the mill. Poor design of such parameters leads to high power consumption during the milling process. The aim of this study is to design a maize hammer mill operating at an optimum speed with a mill clearance and hammer weight that will reduce power consumption and increase the efficiency of the mill. Designing and constructing of the various components of the maize hammer mill determining the appropriate angle of repose of maize grits, a suitable gate size for the hopper, determining the pneumatic pressure developed by the blower to convey the flour to the cyclone and analyzing forces acting on the components to prevent failure of the mill during operation. Force analysis led to selection of proper materials to withstand the forces to avoid failure. Engineering drawings of the various components of the hammer mill were designed before the hammer mill was constructed and assembled. The performance of the hammer mill after construction was evaluated taking into consideration hammer mill capacity, efficiency and power requirement. The obtained results reveal that it is recommended to operate the hammer mill at a rotational speed of about 3500 rpm, grain moisture content of 13%, mill clearance of 5mm and hammer thickness of 3mm to produce fine milled corn and decrease coarse milled corn. Therefore, it is recommended that, this maize hammer mill should be manufactured and popularized for adoption in Uganda and will help reduce power consumption as well as increase profits to the maize millers.