EXPERIMENTAL STUDY ON ALTERNATIVE TECHNIQUES FOR IMPROVEMENTS IN CERAMIC SHELL USED IN IN VESTMENT CASTING TO MANUFACTURE TRUNNION PIN

Abstract

Permeability of the ceramic shell plays an important role to let the gases (from the molten metal and the air that is present in the shell) to escape during pouring. These gases if not escaped can cause holes on the surface of the casting which leads to poor surface finish. Present work focuses on increasing the permeability without decreasing the strength of the shell. Addition of Iodine (I) crystals to the ceramic slurry for the first two coats (inner layers) and fme silica sand for further coats (outer layers) with aluminum as basic refractory powder and ethyl silicate as liquid binder will increase the thickness and green strength. In the de-waxing process Iodine evaporates at 160 C leaving holes in the inner part of the shell and silica sand creates gaps in the outer part after firing increasing the permeability. In relation to WRD projects a cylindrical die which was available and has a resemblance to trunnion pin constituting one of the crucial components of radial gate has been used to conduct the experimental study to improve the surface finish. We know, as the surface finish increases, friction decreases, keeping in mind this basic principle, new techniques to manufacture the trunnion pin which posse's good surface finish is required. This will assure safety in operation and increases reliability of the radial gate and importance of safety is well established and hence this experimental study on alternative techniques is necessary for improvements in ceramic shell used in investment casting to manufacture trunnion pin. In order to check the permeability of the ceramic shell the study has been done by using SEM (Scanning Electron Microscope) after preparing the ceramic shell in the lab.