Williams S. Ebhota

Centrifugal casting technique baseline knowledge, applications, and processing parameters: overview

Abstract The increasing need for materials with light weight, high resistance to corrosion and wear, toughness and strength, machinability, high thermal capacity etc. for various applications is unending. This demand has continued to stretch the exploitation and manipulation of various functionally graded materials (FGMs) and their production methods. This study explores one of the FGM production processes called the centrifugal casting technique (CCT). The centrifugal casting process has several potential advantages over traditional casting methods. This study provides information regarding the basic functionally graded production methods and their applications and also discusses categories of CCT, evolution and process parameters.

Design basics of a small hydro turbine plant for capacity building in sub-Saharan Africa

This paper presents a simplified design considerations for a propeller hydro-turbine, including tabulated relevant mathematical expressions of operating parameters. In the design calculation, a 2.5 m head and 0.183 m3/s flow rate were used as river data for power of 2.61 kW. A four-blade propeller with an outer diameter of 0.226 m and a hub diameter of 0.079 m was considered suitable for the low head application. Dimensionless performance parameters for various power (2–10 kW) and flow rate (0.2–0.6 m3/s) were evaluated (using constant head and rotational speed), the results were tabulated and graphs plotted. The static axial force on the blade and hub analysis was carried out and results shown satisfactory performance of aluminum 6061-T6 alloy as the blade material. Popularisation of small hydro power (SHP) design and production technology in sub-Saharan Africa through domestic capacity building will accelerate local fabrication of SHP plants and components. The study recommends that the design process be based on available materials and manufacturing facilities. The provision of SHP for rural areas, industrial estates and standalone electrification will provoke commercial and industrial activities in sub-Saharan Africa. This will consequently raise the productivity and the standard of living of the people.

Design and Processing of Bimetallic Aluminum Alloys by Sequential Casting Technique

Sequential casting is a facile and fairly new technique to produce functionally graded materials (FGMs) and components by controlled mold filling process. In the present investigation, functionally graded bimetallic aluminum alloys are produced by sequential gravity casting using A390–A319 and A390–A6061 alloy combinations. The control in pouring time between two melts has shown a significant effect on the quality and nature of interface bonding. The microstructure reveals good interface miscibility achieved through diffusion bonding between the alloys. A higher hardness of 160 BHN in the A390 region is obtained in both sequential cast systems, and a minimum value of 105 and 91 BHN is observed in the A319 and A6061 regions, respectively. The tensile and compression strength for A390–A319 are 337 and 490 MPa, whereas for A390–A6061, they are 364 and 401 MPa, respectively, which are significantly higher compared with the standard values of the base alloys, which confirms strong interface bonding. The A390 region shows higher wear resistance compared with other regions of the sequential cast system. The process described in this study is a potential and efficient approach to create good bonding between two different aluminum alloys to develop advanced functional and structural materials.

Electricity insufficiency in Africa: A product of inadequate manufacturing capacity

Energy availability is fundamental and crucial for human survival and for national economic development. Energy consumption per capita of a country or region is a measure of quality of life and industrialisation of a country or region. This to certain extent explains why energy consumption is higher in technologically developed countries than the developing ones. Africa is faced with chronic power problems and this stalls her economic growth, in spite of availability of vast natural resources in the region. The number of Africans without access to modern energy is over 600 million and the projected year of adequate power accessibility in Africa is 2080. This study shows that the main hindrances to access to power in Africa are insufficient continental collective effort, inadequate application of academic based research findings, inadequate manufacturing infrastructure and overdependence on foreign technology, insufficient human capacity development and the high cost of power projects in the region. The study went further to identify small hydropower plant (SHP) technology capacity building to facilitate domestication, establishment of regional energy research institutions, transformation of research findings into real products, and adoption of Asian developing countries’ energy development approach as formidable ways of tackling power problems and power sustainability in Africa.

Facilitating greater energy access in rural and remote areas of sub-Saharan Africa: Small hydropower

Flowing water has hydraulic energy that can be transformed into electrical energy, sub-Saharan Africa has an abundance of hydro resources that are untapped. In this study, various barriers limiting the use of small hydropower to tap the abundant hydro potentials for power generation are discussed. These barriers include insufficient fund; lack of adequate manufacturing infrastructure; lack of adequate power generation and distribution policies; inaccurate hydrological data; insufficient human and power infrastructure capacities; and inadequate domestic and regional participation in design and manufacture of small hydropower component devices and systems. This study sees hydro as a cleaner energy source and small hydropower as the best power system for rural and remote areas and for stand-alone electrification. For power sustainability in the region, public–private partnership, domestication of small hydropower technologies and less reliance on foreign technologies and international support are key factors.

Functionally graded metal matrix composite by centrifugal casting technique mathematical correlation

The functionally graded materials (FGMs) solidification process has complicated movement phenomena of fluid, solute and heat. These phenomena control the segregation of particles in a molten matrix, interactions of particles with a solidification front and the integration of particles in the solidifying matrix. The desired particle distribution in a solidified component can be achieved by manipulating the time of solidification and this makes the study of particle motion during solidification important. This study involved analysis of particle/matrix configuration, solid/liquid interface shape within the vicinity of the particle, thermal conductivity and the pushing/engulfment transition. An overview of the mathematical models of centrifugal casting of FGMs is presented and these include forces acting on the particle; melt particle and solid/liquid interface forces; composite thermal conductivity; heat-transfer coefficient composites; volume fraction resolution; and, particle matrix field temperature configuration.

Improving the surface properties of a Pelton turbine bucket via centrifugal casting technique

This study examines the possibility of fabricating a complex, non-cylindrical, Pelton turbine bucket by centrifugal casting technique. Oil hardening non-shrinking die steel material was selected for the permanent mould production, machined with computer numerical control and heat treated to a hardness of 432 BHN. Aluminium alloys, A390 and A390-5%Mg, were considered as the Pelton turbine bucket materials, cast and characterised. The effects of centrifugal casting technique and thermal treatment on the mechanical properties and corrosion resistance of A390 and A390-5%Mg alloys were studied. A hardness of 150 BHN (maximum) was recorded near the inner surface of the bucket and 157 BHN (maximum) was recorded at the outer periphery of the cylindrical cast. It was observed that A390-5%Mg by gravity casting shows higher corrosion resistance than the A390 alloy. Furthermore, the specimen from the outer zone of the circular cast shows a higher corrosion resistance than the specimen from the inner periphery.