Thin Slab Casting

Thin slab casting aims at to cast slabs of thicknesses less than 100 mm, say around 60 to 80 mm. The objective is to integrate caster, reheating furnace and hot strip mill to increase the productivity. A slab of cross section 1500mm x 80mm would require melt flow rate 3.78 tons/min at 4.5 m/min casting speed. Since the mould size is smaller turbulence in the mould increases which results in entrapment of mould flux on surface causing surface defects.

Use of funnel shaped mould with enlarged cross section at the meniscus is one remedy. Electro-magnetic brakes are very effective in parallel moulds.

Development of liquid core reduction is one such technology that has helped thin slab casting development. Solid ingot with liquid core is subjected to on-line rolling. This brings the following advantages;

• Rolling can be eliminated
• Improved internal quality in term of segregation
  
  

Thin slab caster can be integrated with EAF units and hence mini steel plants are using thin slab casting to produce hot strips with lower segregation, finer grain size and higher strength

Near Net shape casting

The conventional methods of producing metallic strips and sheets require the casting of large ingots which are subsequently hot rolled and cold rolled to final thickness. Several unit operations like ingot soaking, slabbing mill, intermediate annealing, pickling are required to produce the strips. An alternate to this route is the near net shape casting or direct strip casting. In this technology strips are cast close to the final desired thickness and thus many of the unit operations in the conventional technology can be eliminated.
The near net shape casting units are classified into four categories, namely

• Thin slab caster producing 20mm to 70mm thick slabs of cross section 20mm to70mm X 1000mm to 2000mm which could be fed directly into the finishing stands of the hot strip mill without any conditioning
  
  
• The thick strp caster producing 10mm to 20mm thick strips which may need some limited rolling for metallurgical reasons.
  
  
• Strip casters producing strips less than 10mm thickness which is sent directly to the cold strip mil
  
  
• The thin strip or foil caster with a thickness of approximately 20 to 500µm thickness and upto 300 mm wide.