This paper introduces the defects existing in the current production process of the copper mould tube inlet and return pipes of billet continuous casting machines, and explains the obvious effects achieved after the transformation, which reduces the consumption of spare parts and reduces the accident rate.
Keywords: billet continuous caster; copper mould tube;copper mould tube water inlet and return pipeline
In the steelmaking process, the billet cooling device of the billet continuous casting machine includes two parts: a copper mould tube cooling device and a secondary cooling chamber cooling device. When the continuous casting billet reaches the copper mould tube in a liquid state, only 10% to 20% of the molten steel has solidified. About 80% to 90% of the molten steel in the casting billet has not yet solidified. The continuous casting billet leaving the copper mould tube solidifies into a thin shell. , the shell thickness is generally 8mm ~ 15mm. The inside of the cast slab is still filled with high-temperature molten steel. In order to continue solidifying the cast slab during production, a multi-section water spray zone is set up from the mold outlet to the tension and leveling machine, that is, the secondary cooling chamber cooling zone. The foot roll cooling zone is the first stage of secondary cooling after the continuous cast slab leaves the copper mould tube. Steel breakouts generally occur in this section, which shows how important the cooling of the slab in the mold is.
Equipment and process conditions
The No. 1 steel rolling mill of Tonghua Iron and Steel Co., Ltd. has three 240-ton converters, three LF refining furnaces, two thin slab continuous casters, and two eight-machine eight-strand billet continuous casters. The main types of steel produced include carbon structural steel, high-quality carbon structural steel, alloy structural steel, low-alloy high-strength steel, etc. Among them, 45 steel, welding rod steel H08A, amorphous steel TGF07, high-strength earthquake-resistant steel bars HRB400-500E, Q275B, and SAE1008B have mass production capabilities. Among them, the form of the billet continuous caster is a full-arc billet continuous caster with a radius of 9000m. The cross-sectional dimensions of the cast billet are 120×120mm and 160×160mm. The number of continuous caster streams: eight machines and eight streams. The casting mode: Fully protective cast. The schematic diagram of the full arc billet continuous casting machine is shown in Figure 1.
Working principle of copper mould tube cooling device
Working principle of copper mould tube
During production, the purpose of vibrating the mold up and down is, on the one hand, to prevent the continuous casting billet from bonding with the copper wall of the mold during the solidification process, and to avoid accidents such as billet shell cracking or steel leakage. On the other hand, during the vibration process of the copper mould tube, the protective slag on the copper wall of the copper mould tube penetrated, changing the original lubrication conditions. It reduces the adhesion between the high-temperature solidification shell of the continuous casting billet and the copper wall of the mold and reduces the frictional resistance of the billet drawing, thereby improving the surface quality of the continuous casting billet.
Working principle of copper mould tube cooling water
The main function of the copper mould tube cooling water is to take away the heat released by the shell formed by the solidification of liquid steel in the copper mould tube . The cooling water enters from the water inlet pipe at the lower part of the copper mould tube, flows around the copper mould tube at high speed, takes away the heat released by the shell, and then flows out from the water outlet pipe at the upper part of the copper mould tube. The amount of crystallizer cooling water is mainly considered from the two aspects of preventing steel breakage and reducing surface defects of the cast slab. If the water volume is too large, cracks will occur in the continuous casting billet due to excessive water volume; if the water volume is too small, the cooling capacity of the continuous casting billet will be insufficient, resulting in leakage due to the shell being too thin.
Analysis of problems before water inlet pipeline modification
The copper mould tube is installed on the copper mould tube vibration stand, and the motor drives the reducer, eccentric device, leaf spring and linkage mechanism to achieve uniform sinusoidal motion of the crystallizer. The metal hose is installed between the vibrating table body pipeline and the water supply pipeline. As shown in Figure 2, a schematic diagram of the metal hose at the water inlet of the copper mould tube before modification. The reason why this position cannot be connected with a hard pipe is because the stress cannot be eliminated when the vibrating table makes a reciprocating curved motion. In addition to the connection function, the installation of metal hoses is mainly for stress relief. However, when the vibrating cylinder makes non-sinusoidal motion, the position of the metal hose pressure head at the water inlet of the copper mould tube and the middle position of the metal hose will bend back and forth and rub, resulting in hose leakage, pipe explosion, etc., seriously affecting production. A total of 16 metal hoses are installed on site as shown in the picture below. On average, leakage accidents occur every month, and an average of 2-3 pipes are replaced every month. Due to frequent accidents here, it not only increases the workload of workers, but also seriously restricts production.
Water inlet pipeline renovation design plan and usage results
According to the limitations of the installation location of the metal hose on site, the following modifications were made to the pipe. As shown in Figure 3, the schematic diagram of the connection form after the transformation. This form mainly involves cutting off the hard pipe elbow of the cooling water supply pipeline and the pipe elbow of the vibration table body and then welding the flange. Install two series-connected shock absorber throats between the two flanges, and install a length-adjusting short pipe between the two shock absorber throats. The reason why two shock absorber throats are installed in series is that one shock absorber throat can only slow down the stress generated during the curved motion of the vibrating table, but cannot completely eliminate it. Resulting in damage to a single shock absorber throat.
After adopting this connection method, the occurrence of leakage accidents here is basically eliminated. There were no leaks there in the year since the change. Within a year the place is essentially maintenance-free. It greatly reduces the consumption of spare parts, reduces the labor intensity of workers, and ensures the smooth progress of production.