Determination of the critical drop height and critical flow velocity of aluminum alloy (AL-91% Mg-8% Fe-0.4% Zn-0.2%) in gravity sand casting

Abstract

Casting is a manufacturing process in which molten metal is poured through the gating system to fill the mould cavity where it solidifies. Variations in casting parameters by different researchers have led to significant variations in casting guidelines, which have forced Foundry Engineers to carry out a number of trial-and-error runs to create guidelines based on their own experience. These variations in guidelines have led to defects occurring in casting during the mould filling process. This work aimed at determining the critical drop height and critical flow velocity of a certain molten aluminum alloy as it flow down the mould sprue in gravity sand casting. The continuity equation was used to describe the velocity distribution of the aluminum alloy as it flows down the sprue. The mathematical tool used in this research is the finite element method. It involves the discretization of the domain of interest into smaller finite elements. The weak form of the governing equation was obtained and integrated over the domain of interest. The results obtained, established the critical flow velocity of aluminum alloy, down the sprue, as 2.565 × 103 mm/s and the critical drop height as 377mm. Results obtained were compared with literature and were also used to produce various casts, it was observed that casts produced, using sprue height below the critical drop height obtained prevented casting defects, while at sprue height above the critical drop height, the danger of casting defects could not be avoided.

Keywords

• Critical drop height
• Critical velocity
• Gravity sand casting
• Finite element method
• Sprue

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