Process of continues casting machine (CCM) . Types of CCM

Continuous Casting Machines and their Types

Continuous casting (CC) is a process of producing an infinite solid strand from liquid steel by continuously solidifying it as it moves through a CC machine. It is the predominant process route in a modern steel plant which links steelmaking with hot rolling of steel. In the CC machine, the liquid steel is solidified into a semi-finished steel product for subsequent rolling in the hot rolling mill. The basic operation of the CC machine is to convert liquid steel of a given composition into a strand of desired shape and size through a group of operations.

Continuous casting is distinguished from other solidification processes by its ‘steady state’ appearance. That is, the liquid steel freezes against the mould walls and is withdrawn from the bottom of the mould at a rate which keeps the solid / liquid interface at a constant position with time, relative to an outside observer. Major types of continuous casting machines are given in Fig 1.

Fig 1 Major types of continuous casting machines

In the CC machine as shown in Fig 1, liquid steel flows from a ladle, through a tundish into the water cooled mould made of copper.  Liquid steel is protected from exposure to air by a slag cover over each vessel and by ceramic nozzles between vessels. Once in the mould, the liquid steel solidifies against the mould walls to form a solid shell. Drive rolls lower in the CC machine continuously withdraw the shell from the mould at a rate or ‘casting speed’ which matches the flow of incoming liquid metal, so the process ideally runs in steady state. Below mould exit, the solidifying steel shell acts as a container to support the remaining liquid. Rolls support the steel to minimize bulging due to the ferrostatic pressure. Water and air mist sprays in secondary cooling zone cool the surface of the strand between rolls to maintain its surface temperature until the liquid core is solid. After the centre is completely solid (at the ‘metallurgical length’) the strand is cut into desired length of the cast product.

Cross-sections of the cast product can be rectangular, for later rolling into plate or sheet, square for rolling into long products (rounds, rebars, angles, channels, tees, and beams etc.) , circular for wire and seamless pipes, ‘dog-bone’ or ‘beam blank’ shapes for ‘I’ or ‘H’ beams, and even thin strip, rod, and other products.