The flow of liquid steel from ladle to tundish is controlled by the use of a sliding gate valve. This valve consists of three refractory plates, two fixed and one free which can be moved horizontally by means of a hydraulic unit. Due to the low pressure generated in the sliding gate plates due to the venturi effect effective shrouding by means of argon gas is normally employed to prevent air pickup and inclusion formation.
It can be a generic rotary or linear type.
Material Selection
The well block is usually made up of Alumina magnesia spinel mix(sometimes Alumina-zirconia). The upper nozzle is made from Alumina-Carbon mix(High purity tabular white fused alumina and 94% graphite) and will contain antioxidants(like Al, Si) in the range of 3-8% to protect the carbon.
Slide gate plates are made of Alumina-Zirconia-carbon mix(high quality tabular or white fused alumina and 94% graphite).It usually contains 5-8 % carbon and carbon bonded plates(high fired in a reducing atmosphere) are preferred over resin bonded plates for their superior performance. Usually, zirconia is added as a fused alumina-zirconia or fused mullite zirconia material in order to prevent zirconia phase change issues.Anti-oxidants(like Al, Si) in the range of 3-8% are added to prevent the loss of carbon.
The ladle lower nozzle is usually made up of alumina-carbon mix(high purity tabular or white fused alumina and 94% graphite).Antioxidants(like Al, Si) in the range of 3-8% are added to prevent the loss of carbon.
The Ca ppm level in the steel is to be controlled and kept below 30ppm to prevent the calcium wear effects. The wear effect increases exponentially above 35 ppm. The wear increases with longer casting duration. Aggressive ladle lancing erodes the plates and too frequent and long gate stroke is to be avoided to prevent fin formation in steel.
The ladle slide gate arrangement
Three Plate system: The typical ladle slide gate system comprises of well block where the upper nozzle sits, top slide gate plate, middle movable plate, the lower plate, and collector nozzle.
© Metal world insight
