EFFECT OF ARC PLASMA-HEATING ON THE AIR POCKET FORMATION DURING THE PLANAR FLOW CASTING

Air pockets have long been an unsatisfactory feature of the planar flow casting (PFC) process, which is a potential method for manufacturing thin strip. In this study, heating the gas on the wheel surface upstream of the puddle by means of an arc plasma was used to improve the puddle stability and inhibit air pocket formation. It was found that in the plasma heating region air pockets were almost invisible microscopically and the polishing tracks on the wheel surface were well-duplicated on the wheel side contact surface of the cast ribbon, while in the unheated regions a conventional air pocket characteristic was observed. This fact confirms that the thermal expansion of the gas in the converging contact angle, which builds up a local high pressure region at the melt/substrate interface, lifts up the melt and enhances the gas entrapment. Arc plasma heating reduces the temperature difference, hence the pressure build-up. The increase in temperature and pressure of the gas at the melt/substrate interface was calculated to confirm its role in air pocket formation. The plasma heating can improve wheel side contact thereby increasing the cooling rate of the ribbon during casting.