Billet Casting Process Flow
The ladle with refined molten steel is transported to the rotary table. After the rotary table rotates to the pouring position, the molten steel is injected into the tundish, which then distributes the molten steel to each crystallizer through the nozzle. The mold is one of the core pieces of equipment of the continuous casting machine, which enables the casting to form and rapidly solidify and crystallize. The tension leveler and the crystallization vibration device work together to pull out the castings in the mold, and cut them into slabs of a certain length after cooling and electromagnetic stirring. The whole process is called the billet casting process flow.
Main Equipment of Billet Casting Process Flow
Ladle Turret
The ladle turret is a device set above the casting position of the continuous casting machine to carry the ladle span and support the ladle for casting. It is composed of six parts: base, slewing arm, driving device, slewing support, accident drive control system, lubrication system and anchor.
Tundish
Tundish is a refractory container used in short-process steelmaking. First, it receives molten steel poured from the ladle, and then distributes it to each mold through the tundish nozzle.
Crystallizer
In continuous casting, vacuum suction casting, unidirectional crystallization and other casting methods, it is a special metal mold that makes castings form and rapidly solidify and crystallize. Mold is one of the core equipment of continuous casting machines, which directly affects the quality of the continuous casting slabs.
Tension Leveler
In the continuous casting process, the speed control of the casting roll is one of the three key technologies of the continuous casting machine. The speed control level of the casting roll directly affects the output and quality of the continuous casting slab, and the performance of the motor drive device of the casting roll plays an important role in it.
Electromagnetic Stirrer
The essence of electromagnetic stirring (EMS) is to strengthen the movement of molten steel by means of the electromagnetic force induced in the liquid phase cavity of the slab. Specifically, the alternating magnetic field excited by the agitator penetrates into the molten steel of the casting slab, where the current is induced. The induced current interacts with the local magnetic field to generate electromagnetic force, which is a volume force acting on the volume element of molten steel, thus promoting the movement of molten steel.
Cooling Nozzle
The cooling nozzle has the characteristics of a simple structure and uniform spray. According to the requirements of the spray area, many nozzles can be installed on the header. When the nozzles are evenly arranged, it can ensure that the sprays cross each other and overlap slightly so that the entire header can spray evenly; It is mainly applicable to continuous casting machines, blooming, and various mechanical equipment requiring flat spray cooling.
Flame Cutting Machine
The flame-cutting machine is also called oxygen cutting, and a cutting nozzle with an appropriate aperture is installed according to the thickness of the steel plate to be cut.
Preparation of Molten Steel for Billet Casting Process Flow
1. Temperature Requirements for Continuous Casting Molten Steel:
Hazards of High Molten Steel Temperature:
① The billet shell of the crystallizer is thin and easy to break out;
② The rapid erosion of refractory materials is easy to lead to out-of-control billet casting process flow and reduces the casting safety;
③ The addition of non-metallic inclusions affects the internal quality of the slab;
④ The columnar crystal of the casting slab is developed;
⑤ The central segregation is aggravated, and the centerline crack is easy to occur.
Hazards of Low Molten Steel Temperature:
① It is easy to block the nozzle and interrupt the casting;
② The continuous casting surface is easy to produce blisters, slag inclusions, cracks, and other defects;
③ Nonmetallic inclusions are not easy to float, which affects the internal quality of the slab.
2. Temperature Control of Molten Steel in Ladle:
The tapping temperature shall be strictly controlled according to the steel grade to make it change in a narrow range; Secondly, the temperature drop from tapping, ladle, ladle transportation, and the whole billet casting process flow of entering the tundish shall be minimized.
In actual production, measures shall be taken to adjust the temperature of molten steel in the ladle:
1) Ladle argon blowing temperature regulation;
2) Add scrap steel for temperature regulation;
3) Technology of heating molten steel in a ladle;
4) Thermal insulation of ladle.
Temperature Control of Molten Steel in Tundish
1. Determination of Casting Temperature
The casting temperature refers to the temperature of molten steel in the tundish. Generally, a furnace of molten steel needs to be measured three times in the tundish, that is, 5min after the start of casting, 5min in the middle of casting and 5min before the end of casting. The average of the three temperatures is considered the average casting temperature.
The determination of casting temperature can be expressed by the following formula (also called target casting temperature):
T=TL+△T。
2. Liquidus Temperature of Billet Casting Process Flow:
The temperature at which solidification begins is the basis for determining the casting temperature. The calculation formula is recommended:
T=1536-{78[%C]+7.6[%Si]+4.9[%Mn]+34[%P]+30[%S]+5.0[%Cu]+3.1[%Ni]+1.3[%Cr]+3.6[%Al]+2.0[%Mo]+2.0[%V]+18[%Ti]}
3. Determination of Molten Steel Superheat
The superheat degree of molten steel is mainly determined according to the quality requirements and casting performance of the billet.
4. Determination of Tapping Temperature
The molten steel goes through five temperature drop processes from tapping to entering the tundish:
△ T total=△ T1+△ T2+△ T3+△ T4+△ T5 △ T1 temperature drop during tapping;
△ T2 temperature drop of molten steel during transportation and standing (1.0~1.5 ℃/min);
△ Temperature drop during T3 ladle refining (6-10 ℃/min);
△ Temperature drop of molten steel after T4 refining when it is standing and transported to the continuous casting platform (5 ～ 1.2 ℃/min);
△ Temperature drop of T5 molten steel injected into the tundish from the ladle.
T tapping=T pouring+△ T total
Controlling tapping temperature is the first prerequisite to ensure the target casting temperature. The specific tapping temperature shall be determined according to the process route of each steel grade based on the investigation of the temperature drop law of each steel plant.