Effect of shell thickness and firing temperature on properties of modified ceramic shell for precision casting of Al-Si alloys

Abstract

Precision casting also known as 'investment casting' is an important manufacturing process used to produce precision castings. In this process, very fine ingredients are used to prepare the ceramic slurry so as to develop the ceramic shell with smooth internal surface. These fine ingredients reduce shell's permeability, leading to porosity defects on the cast part. In the present investigation, an attempt has been made to enhance the permeability of the ceramic shell by mixing fine needle coke and ABS powders to the inner coat and the outer coat slurries respectively. After firing, fine needle coke and ABS powders got burnt and left some micropores and macropores respectively inside the shell. These pores improved the shell's permeability to a considerable extent. The modified shells were used to cast Al-Si alloy. The ceramic shell modified with fine needle coke and ABS powder also possessed improved porosity, surface roughness and hardness of castings.