Browsing by Author "CHIN, TS"

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EFFECT OF ARC PLASMA-HEATING ON THE AIR POCKET FORMATION DURING THE PLANAR FLOW CASTING
(1991)
WANG, WK
;
KUO, CT
;
CHIN, TS
;
機械工程學系
;
Department of Mechanical Engineering
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.
EFFECT OF MELT TEMPERATURE ON THE FORMATION OF AIR POCKETS DURING SPLAT QUENCHING
(1992-03-15)
WANG, WK
;
KUO, CT
;
CHIN, TS
;
機械工程學系
;
Department of Mechanical Engineering
The effect of melt temperature on the formation of air pockets at the contact surface of the ribbons was studied. An alloy with a melting point slightly higher than room temperature (320 K) was used and was heated to 353, 573 and 773 K, respectively, to investigate the thermal effect of the melt temperature on the gas. Under high casting velocity (20 m s-1) and extremely low melting temperature (353 K), the air pockets were slender and parallel to the casting direction. The liquid melts with a higher casting temperature (773 K) induced coarse air pockets at various casting velocities, and the air pockets were coarser than those induced by the pressure of the gas boundary layer only. The heat flow analysis showed that the local pressure of the entrapped gas, built up by the thermal effect and assuming constant volume, is far greater than the pressure by the gas-boundary layer effect. Thus the thermal effect of the liquid melt should be taken into account in the formation of air pockets during splat quenching.