Investment Casting under vacuum suction with Flyash as filler - Property Evaluation and Comparision with the Conventional Casting

摘要

The requirement of precision investment casting has shown a great promise with regard to casting excellence for the aerospace and defence applications. In the present study, an indigenously developed Investment casting process (using Ethyl Silicate or preferably Silica sol as Binder) was used to make the castings of LM25 (BS1490) alloy. The investment castings were made under two conditions namely, normal filling i.e., gravity pouring and vacuum suction filling. Since the later process was a new method, it is appearent that the feeder requirement for making sound Investment casting becomes very important. Hence the feeder need for 10, 15, 20 and 25 mm diameter cylindrical castings was taken up in this study. The feeder variable was the modulus ratio. The modulus ratio was varified from 0.8 to 1.2 insteps of 0.2. The basis of evaluating the feeder effectiveness was the tensile property and the porosity. These results were further compared with normally filled Investment castings of indentical section size and shape. The results of Investigation show that the strength of Investment castings were inversely related to the casting size and a modulus ratio of one was most suitable. The hardness values of vacuum filled investment castings are higher than that of the normally filled investment castings. Investment castings made by vacuum suction filling method had higher tensile strength than that of the normally filled investment castings. The microstructure of vacuum suction filled investment castings exhibit high amount of precipitation of Al-Zn-Mg secondary phase.