Formation mechanism and improved remedy of thermal property of cold shut surface defects in Vortex Flow Meters: Numerical simulation and experimental verification in investment casting of 316 L stainless steel

Abstract

The purpose of this study aims to investigate the leading causes of CS (Cold Shut) defects in VFM (Vortex Flow Meters) of intricate geometric configuration and propose improvement strategies to leverage the thermal property in the vicinity of thin-walled regions, such as insulation-enhanced uniformly distributed temperature via ceramic core embedment. First, penetrant testing reveals whether the defect is a penetrating-type defect. Second, several extensive material characterization techniques such as optical microscopy (OM), energy-dispersive X-ray spectroscopy (EDS) analysis, and charge-coupled device (CCD) were employed to provide deeper insights into the formation and morphology of defects. Third, numerical simulations and experimental verifications were utilized to further analyze the causes of CS defects in vortex flowmeters. Fourth, effective preventive measures were designed after identifying the causes of defects, which involved using ceramic cores to replace the shell at deep and thin-walled locations. A virtual thermo-dynamic sensor (VTDS) was used to analyze the temperature distribution in the area before and after the installation of ceramic cores. The results indicate that the temperature in the defect area increased by >40 degrees during the filling period from 2.5 s to 5 s. Additionally, adequate thermal uniformity was achieved through the high thermal conductivity of the ceramic material, thereby reducing the cooling rate and the coefficient of kinematic viscosity in that area, leading to improved fluidity of the molten iron. Ultimately, the occurrence rate of CS defects decreased from 42.6 % to 0 %.