Productivity and Product Quality in Continuous Casting Machine Jun25

Productivity and Product Quality in Continuous Casting Machine...

Productivity and Product Quality in Continuous Casting Machine Continuous casting is the process by which liquid steel is solidified into a semifinished steel product (billet, bloom, or slab etc.) for subsequent rolling in the hot rolling mills. Continuous casting of liquid steel was introduced for commercial application in 1950s. In the relatively short time span since the introduction of continuous casting for the commercial application, the process has evolved with a wide variety of new process developments directed towards achieving improved productivity and superior product quality. These developments include new design concepts of continuous casting machines, metallurgical practices, and the application of process control and automation by computer systems. The main driving force behind these developments has been the recognition that substantial improvement in the yield and energy savings are possible which have a dramatic effect on operating cost. Through these developments, it has been possible to achieve major quality improvements of the continuous cast product.  Present day continuous casting machines produce cast steel products having quality which is fully equivalent to and exceeds that of products produced from ingot steel. Modern continuous casting machines efficiently produce essentially all grades of steels, including the highest qualities for critical applications. Productivity improvement The two methods to improve the productivity of the continuous casting process include improving the continuous casting machine throughput (tons/hour) and net-working ratio. The through put of the continuous casting machine is improved by increasing the casting speed as well as by increasing the cross sectional area, while the net- working ratio is improved by decreasing the casting machine down time. The casting speed of the continuous casting machine is limited by several different phenomena as given below. A high casting speed results in a significant increase in the flow velocity of the...

Secondary Cooling Technology in Continuous Casting Process Jul31

Secondary Cooling Technology in Continuous Casting Process...

Secondary Cooling Technology in Continuous Casting Process  A wide range of steel grades ranging from ultra low carbon (ULC) and low carbon grades to high carbon and different grades of special steels are required to be cast in continuous casting machine (CCM). The casting of these grades is to be achieved while maximizing CCM output. Consistent production of prime quality cast steel product requires increased operational and maintenance flexibility in the CCM for maintaining optimum casting parameters can be maintained. This flexibility is needed both for every element as well as control system of CCM. While the strand is continuously withdrawn at the casting speed, solidification of steel continues beneath the mould through the different zones of cooling having a series of water sprays. The secondary cooling system consists of these different zones, each responsible for a segment of controlled cooling of the solidifying strand as it progresses through the CCM. The sprayed medium is either water or a combination of air and water (mist spray cooling). Mist spray cooling provides the following advantages. Uniform cooling Less water requirement Reduced surface cracking Product quality in a CCM is considerably influenced by temperature variations during strand cooling in secondary cooling zone. Hence secondary cooling zone has a very important function for the maintenance of a correct temperature parameter and is crucial to the quality of the cast steel product. Since the quality of steel depends on the behavior of the surface temperature and the solidification of steel front in time, it is to a large extent defined by the intensity of the water sprays. Improper cooling conditions can have detrimental impact on stress distribution in solidified shell. First of all, overcooling can lead to the formation of cracks. Moreover, there must be a smooth transition...

Role of Mould in Continuous Casting of Steel May21

Role of Mould in Continuous Casting of Steel...

Role of Mould in Continuous Casting of Steel  Moulds play an important role in the process of continuous casting of liquid steel. They are the heart of the continuous casting process. In the process of continuous casting, liquid steel is poured from the tundish into the casting mould through the submerged entry nozzle (SEN) immersed in the liquid steel. The moulds are water cooled. Solidification of liquid begins in the mould by indirect cooling. The cooling process in the mould is known as primary cooling process. In the mould, a thin shell of steel next to the mould walls solidifies before the middle section. This is called a strand and leaves the base of the mould into a spray chamber. The bulk of liquid steel within the walls of the strand is still molten. The strand is immediately supported by closely spaced, water cooled rollers which support the walls of the strand against the ferrostatic pressure of the still solidifying liquid steel within the strand. To increase the rate of solidification, the strand is sprayed with large amounts of water as it passes through the spray chamber. This is the secondary cooling process. Final solidification of the strand may take place after the strand has left the spray chamber. The function of continuous casting mould is to receive the liquid steel and guarantee a rapid heat transfer to the cooling water to enable quick solidification. The liquid steel, when leaving the mould, must exhibit a just thick enough outer shell to prevent it from splashing over the continuous casting machine parts. The mould is to serve this function. After the mould further cooling of the steel strand is done through the faster direct cooling with the help of the direct water sprays. Solidification arises from the dynamic...

Tundish Metallurgy May08

Tundish Metallurgy

Tundish Metallurgy To transfer liquid steel from a teeming ladle to the continuous casting machine mould, an intermediate vessel, called a tundish, is used. Tundish is a rectangular big end up, refractory lined vessel, which may have a refractory lined lid on the top. The tundish bottom has one or more nozzle port(s) with slide gate(s) or stopper rod(s) for controlling the flow of liquid steel. Tundish is often divided into two sections namely (i) an inlet section, which generally has a pour box and where liquid steel is fed from the steel teeming ladle, and (ii) an outlet section from which liquid steel is fed into the continuous casting machine mould(s). Various flow control devices, such as dams, weirs, baffles with holes, etc., may be arranged along the length of the tundish. Longer path is preferred to prolong residence time of liquid steel to promote floatation of macro inclusions. Important tundish metallurgy elements of a tundish are shown in Fig 1. Fig 1 Important tundish metallurgy elements of a tundish The continuous casting tundish serves as a buffer and links the discontinuous process of the secondary steel making in the ladle with the continuous casting process in the mould. It acts as a reservoir during the ladle change periods and continues to supply liquid steel to the mould when incoming liquid steel is stopped, making sequential casting by a number of ladles possible. The main causes for inclusion formation and contamination of the liquid steel include reoxidation of the liquid steel by air and carried over oxidizing ladle slag, entrainment of tundish and ladle slag, and emulsification of these slags into the liquid steel. These inclusions must be floated out of the liquid steel during its flow through the tundish before being teemed...

Basics of Continuous Casting of Steel Jan25

Basics of Continuous Casting of Steel...

Basics of Continuous Casting of Steel Continuous casting is the process whereby liquid steel is solidified into a semi finished product for subsequent rolling in the finish rolling mills. Continuous casting of steel was conceived and patented in 1865 by Sir Henry Bessemer, but it could not be commercialized because of problems related to engineering and equipment. After solving these problems, continuous casting of steel was introduced commercially in 1950s and around 1475 million tons of continuous cast steel was produced globally in 2012. Continuous casting has replaced several steps during steel making process such as ingot casting, mould stripping, heating in soaking pits, and primary rolling with one operation. Continuous casting of steel has helped to achieve improved yield, quality, productivity and cost efficiency. The principle of continuous casting is shown in Fig. 1. Fig 1 Principle of continuous casting Referring to Fig 1, Liquid steel in the steel teeming ladle (1) from the secondary steel making unit is taken to the continuous casting machine. The ladle is raised onto a turret that rotates the ladle into the casting position above the tundish (3). Liquid steel flows out of the ladle into the tundish, and then into a water-cooled copper mould (5). Solidification begins in the mould, and continues through the roll support (6) and the turning zone (7).  The continuous cast strand is then straightened, torch-cut, and then discharged for intermediate storage or hot charged for finished rolling. Depending on the product end use, various shapes are cast. In conventional continuous casting machines these are slabs, blooms or billets. In recent years, the melting, casting, and rolling processes have been linked while casting a shape that substantially conforms to the finished product. These near net shape cast sections are usually applied to beams...