Study on Carbon Deposition and Coil Breakdown Mechanism of Medium Frequency Coreless Induction Furnace

The medium frequency coreless induction furnace has gradually replaced the cupola in cast iron melting. However, induction coils at the bottom 1-6 turns can experience issues posing production and resulting safety risks. A kind of coil interturn breakdown failure caused by black attachment has occurred in our engineering practices. To explain the attaching and breakdown mechanism, an experimental investigation and detailed analysis of physical and chemical processes are performed. SEM, EDS and Fourier transform infrared spectrum results show that the attachment is primarily composed of free carbon, with a mass and atomic fraction of 62 and 71%, respectively. There were no C-H bonds in the powdered black attachment. The redox reactions of SiO2 and C, hydrogen and disproportionation reactions of CO and the ionization reactions of H2O contribute to the C transfers. The physical isolation of the Isoplan board, which prevents the mixture of CO, CO2, H-2, H2O, and O-2 from diffusing, causes C deposited only on the coil surface. The conductive carbon deposition in a moisture environment reduces the insulation degree of interturns and generates high-voltage discharge between adjacent coils. According to the findings, three improvement strategies are proposed and validated: (1) drilling holes in the Isoplan board; (2) unplugging the silicate insulating cloth in the lining sintering; and (3) as new lining is put into service, silicon steel sheets are prioritized for use as furnace charge.