USING COMPUTER SIMULATION TO IDENTIFY DEFECTS FORMATION IN STEEL CASTINGS OF SHUT-OFF VALVES CASTED WITH LOST FOAM PROCESS

Processy litʹâ, 2021, Tom 145, №3 p. 53-60

Abstract

UDK 621.74.046:004.942

Received 02.08.2021

The results of computer simulation of the technological process of making a steel casting “Valve body DN80 PN40” produced with lost foam casting process are presented. The simulation is carried out using the Flow-3D Cast program to determine defects that can be formed in a casting during thermal decomposition of polystyrene foam pattern. The features of the Flow-3D Cast software product are analyzed for adequacy of the modeling results and their compliance with a field test. It is determined that the base of the calculation is the average speed of the metal front calculated through the heat transfer coefficient between metal and polystyrene foam, with the foam pattern described as a constant temperature barrier. It is determined that the prediction algorithm of surface defects in Flow-3D Cast consists of the initial values of the formation of oxide, which is proportional to the surface area and time of interaction, meanwhile the model does not take into account such phenomena as an oxide film that adheres to the walls of the form and the foam decomposition products that escape through a porous sand form. The mechanism of surface defects formation was investigated and explained by the physical model of the interaction of liquid metal with polystyrene foam. The results of “valve body DN80 PN40”casting simulation using Flow-3D Cast is presented with two variants of the gating system, the kinetics of the mould filling in the presence of polystyrene foam pattern and the surface defect formation probability is investigated. The optimal variant of the gating system is determined, namely the metal should be fed to the casting from below by means of three gates - in the flange and the middle part of the body, which eliminates the formation of “stagnation zones” at the meeting points of melt flows. It has been verified that the computer simulation system Flow-3D CAST allows to identify the places of folds formation and other defects associated with foam and foam degradation products entrapment.