**Casting and Forming of Aluminium Alloys**

**1** 

*Nigeria* 

**Aluminium Countergravity Casting –** 

*1Centre for Energy Research & Development, Obafemi Awolowo University, Ile-Ife, 2Department of Materials Science and Engineering, Obafemi Awolowo University, Ile-Ife,* 

Counter-gravity casting, also called vacuum casting, is a mould filling technique in which low pressure created inside a mould cavity, causes prevailing atmospheric pressure on the melt surface to bring about an upward or counter-gravity movement of the melt into the mould cavity. The process was patented in 1972 by Hitchiner Manufacturing (Lessiter & Kotzin, 2002) and different variants of the process had evolved over the years. Greanias & Mercer (1989) reported a novel valve system that could potentially increase throughput by allowing mould disengagement prior to solidification while Li *et al* (2007) have developed a multifunctional system aimed at aggregating different variations of the technology into a single equipment. The unique mould filling approach of the countergravity casting technique confers on it a set of unique advantages related to casting economics, defects elimination and attainment of net-shape in cast products. Such desirous attributes has ensured the growing importance of the technology, especially in power and automotive applications. A testament to the rising profile of this casting technique is its adoption in the production of a range of parts such as compressor wheels for turbo-chargers (TurboTech, 2011), automotive exhaust manifolds (Chandley, 1999) and a high-volume production (130,000 units/day) automotive engine

The growing importance of this casting technique in some metal casting sectors notwithstanding, there is scant awareness and interest in many mainstream casting spheres. This chapter thus seeks to present a technology overview of the countergravity casting technique. The shortcomings of conventional processes are highlighted alongside the unique advantages of the countergravity technique. Challenges of the countergravity technique are

The basic process steps for the vacuum casting process are presented as follows. In the diagram in figure 1, a preheated investment mould with an integrated down-sprue (fill

The sprue, with a conical-shaped intersection point with the rest of the mould, pokes through and sits in the conical depression of the lock-nut. The "square" fit of the two, depicted in figure 2, ensures a sealing of the flask interior from the external environment.

also presented with discussion of efforts and prospects for their redemption.

**2. Description of the countergravity casting process** 

pipe) is positioned in the moulding flask.

**1. Introduction** 

Rocker Arm (Lessiter, 2000).

**Potentials and Challenges** 

Bolaji Aremo1 and Mosobalaje O. Adeoye2
