Analysis of Casting Defects in Steel Foundry by Computerized Simulations (CAE) - A New Approach along with some Industrial Case Studies

摘要

This study reports an in house experience of the occurrence of different types of casting defects and its scientific analysis by computerized simulation techniques supported by industrial case studies. The main two categories of defects viz. solidification related defects like hot tear, shrinkage and porosity defects etc. and flow related defects like sand inclusions, sand burn in, cold shut, air entrapment etc. are discussed here along with simulation results and practical case studies. Casting simulation helps visualize mould filling and casting solidification; predict-related defects like cold shut, shrinkage porosity and hot spots; and optimize the casting design to achieve the desired quality with high yield. We know that in steel castings contraction takes place during solidification and hot tears are initiated at a temperature within the solidification range of the alloys that is some time before the solidus temperature is reached. Further opening and extension of tear can however occur at lower temperature due to continuing lower contractions. Generally two conditions are necessary for hot tearing. a) There must be resistance to contractions. b) There must be variable temperature gradients within the casting section. The low collapsibility of cores/ mould materials, higher percentage of sulphur and phosphorous, excessive large feeders used, improper design of castings i.e. wide variations in wall thicknesses can cause hot tears in steel castings are discussed here along with simulation results. This paper also investigates the formation of shrinkage defects in bogie castings by simulation methods. The Simulation software is used to calculate the material property data required by the casting simulation package Auto Cast-X and Adstefan V2011, Hitachi make. The effect of alloying contents on materials properties and the subsequent influence on casting behaviour are investigated through computer simulation of feedability and prediction of the shrinkage defect formation in Bogie castings. This paper shows the sand burn in and sand fusion defects in the Indian Bogie items like Bolster- centre pivot casting has been analyzed here by simulation software and practical case studies. Sands due to high temperature of molten metal or low refractoriness of base sands, or due to poor quality of bentonite or high moisture of processed sands, or soft moulds or improper or no painting of moulds fuse at the casting surface and stick to the surface is called rough surface finish of the castings. Lastly this paper highlights some of the cold shut related problems and air entrapment defects in Bogie items -side frame and bolster castings along with CAE Simulation analysis and results. This study also shows that after taking remedial measures how the simulation results validate.