To transfer finished melt steel from a ladle to mould in a continuous casting process, an intermediate vessel is used which is called tundish. The role of tundish is to deliver the molten metal to the moulds evenly and at a designed throughput rate and temperature without causing contamination by inclusions. Inclusion float out, slag vortexing, till end slab volume and residual metal in tundish are a strong function of tundish hydrodynamics. Tundish design as well as flow control devices / modifiers are known to have strong influence on tundish hydrodynamics.
Now-a-days refractory makers are offering customized refractory solution. The new age tundish refractories facilitate temperature homogenization, removal of macro-inclusion, prevention of nozzle clogging etc. inside tundish. To streamline the flow and compress turbulence inside tundish various Flow Control Devices (FCD) are being used in place of traditional FCDs or tundish furniture like Dams, Weirs, Charge Pads, and Side Wall Pads etc. The next generation FCDs are popularly known as Tundish Flow Modifier (TFM), Tundish Flow Optimizer (TFO) etc. are precast refractory shapes made of Ultra Low Cement Castables (ULCC) having 85 - 90% alumina.
One of the major functions of steel making tundish is to enhance inclusion floatability and thereby, produce clean steel. For the removal of inclusion through floatation, wall adhesion and agglomeration the flow patterns inside the tundish play an important role, which in turn is a function of tundish design. Melt flow in any given tundish can be favourably altered by incorporating suitable tundish flow modifiers (TFM) and/or changing the design of the tundish. The flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel.
The interior of tundish flow modifiers or flow optimizers as you say it, are designed in such a way that incoming steel gets a churning effect which results into inclusion flotation and subsequent absorption at the tundish powder level. Tundish argon diffusers are also being used to reduce inclusion in steel.
Eventually, it is tundish design from the viewpoint of metal flow and appropriate selection of refractory materials with their right positioning inside tundish that holds the key to the success of subsequent operations in steel making.