Effects of shot sleeve wave reflection on air entrapment in pressure die casting processes

摘要

The flow in the short sleeve of pressure die casting macines is analyzed using a model that is basedon shallow-water approximation and taking into account the effects of wave rflection against the end wall of the sleeve. The governing equations are solved numerically using the method of characteristics and a finite-difference grid based on the method of charac eristics and a finite-difference grid based on the inverse marching method. The results of the model for wave profiles, the optimum values of the parameters characterizing the law of plunger motion, and the volume of air remaining in the shot sleeve at the instant at which the molten metal reaches the gate to the die caviy, are compared with numerical results obtained from a finite-element code, which solve the two-dimensional momentum and mass conservation equations, taking into account non-hydrostatic and viscuous effects. Although it has been found that the shallow-water model does not provide a very accurate estimation of the mass of entrapped air in the shot sleeve, it describes reasonably well the influence of the acceleration parameters and the initial filling fraction on the entrapped air mass, and can be of help in choosing operating conditions that reduce air entrapment while keeping the shot sellve filling time as low as required.