Billet Casting Process

The process is that liquid steel is poured into the continuous casting machine, and the slab is directly obtained after condensation and cutting, which is called the billet casting process for short. It is a process between steelmaking and rolling. The billet produced by continuous casting is the raw material for the hot rolling plants to produce various products. Continuous casting is one of the most critical technologies in the development of the iron and steel industry in the 20th century. Its appearance has fundamentally changed the mold casting and blooming process that has dominated for a century. The development of continuous casting technology has improved the mechanization and automation level of the steelmaking production process, which has greatly increased the steel production capacity and has become the main means for the steel industry to reduce production costs and improve competitiveness.

Brief History of Billet Casting Process

The development of the billet casting process can be roughly divided into four stages

① 1840-1930 was the enlightenment stage of the thought of continuous casting of molten metal. In 1840, G.E. Cyrus of the United States obtained a patent for continuous lead casting; In 1857, German R.M. Dylan proposed continuous casting equipment similar to the modern continuous casting machine, including an open mold, liquid metal injection, secondary cooling section, dummy bar, and billet cutting device.

② 1940~1949, the development stage of continuous casting characteristic technology of steel. The representative is S Jonathans. Vibrating water-cooled mold, submerged nozzle, mold powder, and other technologies were used on the test caster, which laid a foundation for the modern continuous casting machine.

③ From 1950 to 1976, the traditional continuous casting technology was mature. More than 5000 patents related to continuous casting have appeared.

④ Since the 1980s, the optimization development of conventional continuous casting technology and the development and application of near net shape continuous casting technology have been on the stage. The continuous casting ratio is rising, the caster operation rate, productivity, billet quality, casting speed, and the number of continuous casting furnaces are growing, the casting varieties are expanding, the production cost is decreasing, and the continuous casting process of cast steel completely replaces mold casting.

Advantage

Compared with the die casting process, the billet casting process has the following advantages: it simplifies the process flow of casting billet production, saves 40% of the process infrastructure investment, reduces 30% of the floor area, saves 40% of the operation cost, and reduces 15% of the refractory consumption; The metal yield is increased by 8%~14%; To reduce energy consumption and produce 1 ton of qualified billet can save 400~1200 megajoules of energy consumption.

Continuous Casting Ratio

The proportion of qualified continuous casting billet output to the total output of qualified continuous casting billet and qualified steel ingot is an important indicator of the comprehensive level of a country's steel industry, and also a measure of a country's steel competitiveness. In the 1990s, the continuous casting ratio in many industrial developed countries approached or reached 100%. In 2000, the continuous casting ratios of Japan and the European Community were 97.3% and 96.3% respectively, followed by the United States. Noncontinuous casting products in these countries are limited to die casting and special steel. Since 2010, the continuous casting ratio in China is higher than 99%.

Model of Continuous Casting Machine

There are many types of continuous casting machines.

① It is classified into the vertical continuous caster, vertical bending continuous caster, arc continuous caster, horizontal continuous caster, and wheel continuous caster according to the casting pattern of the continuous caster.

② There are square billet continuous casting machines according to the section of casting billet, and the section is less than or equal to 150mm × 150 mm is called billet, and larger than 200 mm × 200mm is called bloom; Slab continuous casting machine, the slab thickness is more than 120mm, and its width thickness ratio is generally more than 3; Rectangular billet caster, with rectangular billet section; Round billet continuous caster, with a round section and a diameter of 60-400mm; Profiled billet continuous casting machine, casting profiled section, such as I-beam; Thin slab caster, casting section (50-90) mm × (900 ～ 1680) mm; Thin strip continuous casting machine, which produces 2~5mm thick thin strips.

③ Single strand, double strand, or multi-strand continuous casting machines can be classified according to the number of strand streams that can be cast by the continuous casting machine in a common ladle; On one continuous casting machine, a square/slab compound continuous casting machine that can cast both slabs and several streams of billets at the same time according to production requirements.

④ In order to distinguish the steel grades that can be cast by the continuous casting machine, some of them are crowned with a special steel billet continuous casting machine or stainless steel slab continuous casting machine in front of the casting machine to show the difference from the ordinary steel continuous casting machine.

Near Net Shape Continuous Casting Process

The technology of making the section size of continuous casting billet as close as possible to the final section size of steel under the condition of ensuring the performance of steel. The technologies that have been developed and applied include thin slab continuous casting, thin strip continuous casting, beam blank continuous casting, etc.

① Thin slab continuous casting technology. In June 1989, the first compact hot strip production process (CSP) production line adopting thin slab continuous casting technology was put into production in Nucor. By 2012, 62 thin slab continuous casting and rolling production lines had been put into production worldwide. There are also thin slab continuous casters with different technologies, such as the online hot strip production process (ISP), which have been successfully used in production.

The mature thin billet casting process and rolling production processes include the CSP process, ISP process, flexible thin slab rolling process (FTSR), continuous slab direct rolling process (CONTROL), Sumitomo continuous casting and rolling process (QSP), thin slab production technology (TSP), Angang strip continuous casting and rolling process (ASP), endless continuous casting and rolling process (ESP).

② Thin strip continuous casting technology. It is another innovation in continuous casting technology to cast molten steel directly into strip billet (<10mm) and produce thin strip products without hot rolling or slightly hot rolling as finished products or as cold rolling billets. It has the advantages of simplifying processes, reducing investment, saving energy, good quality of finished products, and good environmental protection.

③ Beam blanks continuous casting technology. Shaped billet refers to the continuous casting billet with complex cross-sections except for square billet, slab, round billet, and rectangular billet, mainly in the form of an H-shaped billet. In the early 1960s, the beam blanks continuous casting technology developed by the Steelmaking Department of the British Iron and Steel Association was first industrially produced in Algoma Corporation in Canada, and the world's first H-beam billet production line was built in May 1968. Since then, Japan, the United States, Luxembourg, and China have also built production lines. 

The structure of a beam blank caster is basically the same as that of a square (rectangular) billet caster, with the main difference being the shape of the inner cavity of the mold and the distribution and layout of the backup rolls in the secondary cooling zone. The support guide section of the beam blank caster shall effectively support the H-shaped billet to prevent bulging deformation. When the beam blank is just pulled out of the mold, the shell is thin and easy to bulge, so the roll diameter and roll pitch of foot roll and the first groups of backup rolls in the secondary cooling zone should be as small as possible, and the layout of each group of backup rolls should be as close to the shape of the beam blank as possible. At the lower part of the secondary cooling zone of the continuous casting machine, because the cooling conditions at both ends of the profile blank wing plate are good and almost completely solidified, the four backup rolls at both ends of the side wing can be canceled.

The beam production process is formed by the compact arrangement of steelmaking, refining, beam caster, and rolling mill in beam continuous casting technology. Compared with the traditional square billet cold charging process, the process can save investment, reduce energy consumption, simplify operation, improve yield, and reduce the amount of rolling processing.

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