Repair of billet copper mould tube

Abstract: The problems affecting the maintenance quality of billet molds were analyzed and solutions were proposed.

Keywords: billet mold; maintenance; quality

With the development of continuous casting technology and the continuous increase in slab output, the online service life of continuous casting molds has been continuously extended, which has put forward higher requirements for the maintenance quality of mold equipment. Issues such as the accuracy of the copper mould tube water seam and the arc accuracy of the foot rollers have received widespread attention. However, in actual work, there are still some problems that cannot be ignored. The existence of these problems has adverse effects on the high efficiency and long life of the copper mould tube.

1 Analysis of billet copper mould tube problems

(1)Scale film on the surface of the copper mould tube steel tube and its impact: Under high temperature conditions and when the water quality is unstable, a thin scale film will easily form on the four sides of the cooling water on the copper tube wall. There is no scale film on the corner surface (because the corner is two-dimensionally cooled, an air gap is formed before the face, and the heat transfer is slow, so the scale film is not easily formed on the corner). This kind of situation is not easy to attract attention during maintenance operations. Through 11 sets of square deformation (the billet produces rhombus deformation, the unique shape defects of the square billet, the reason for the rhombus deformation is often accompanied by the occurrence of internal cracks, the billet with severe rhombus deformation cannot be rolled, and the pass pattern cannot be bitten) ) Inspection of the copper mould tubes revealed that there was scale film on the surface of the copper tubes of 8 copper mould tubes, accounting for more than 75%. This kind of scale film is quite harmful, directly leading to an increase in thermal resistance, a decrease in heat flow, uneven cooling around the area, and easy to cause a peeling accident.

(2) Mold shell corrosion and impact: Billet continuous casting machines usually have the capability of casting billets with several cross-sections. When a certain size of copper mould tube is used, other sizes of copper mould tubes are usually stored for use after they have been repaired. It is common to store them for 1 to 2 months, or even for more than half a year (slab copper mould tubes also have similar problems). Once such a copper mould tube with a long storage period is put into use, quality problems will easily occur in the cast slab. In severe cases, large fracture-like cracks will appear on the surface of the cast slab, causing steel leakage accidents. When this type of copper mould tube is disassembled, it can be seen that there is a lot of oxide scale in the inner cavity. Due to long-term use, the inner cavity surface of the shell is severely corroded, forming a massive oxide scale. When reused, it will be washed by cooling water with a pressure of 0.8~1.1MPa, and the peeling oxide scale will block the water seams and pollute the water quality. This leads to uneven cooling or low cooling intensity within a certain period of time, causing the billet shell to fail to reach a safe thickness after it leaves the mold. Cracks will occur when entering the guide roller or the straightening roller, resulting in billet quality or steel leakage accidents.

(3) Deformation and influence of the copper tube after the copper mould tube is assembled: Since the copper tube is a molded part, it is easy to neglect to re-test the copper tube after the copper mould tube is assembled (especially the new copper tube). When the 130 billet copper mould tube of a steel plant was put into use, there were many problems with squareness. After searching for the problem, the inner cavity of the copper tubes after repair and assembly in 6 batches within 30 days was tested for a ratio of copper tube deformation greater than 0.3mm. : The first batch 45%; the second batch 40%; the third batch 35%; the fourth batch 43%; the fifth batch 38%; the sixth batch 45%. It can be seen from the inspection that the rate of copper pipe deformation exceeding 0.3mm is relatively high. Using a dial indicator, it can be seen that the largest deformation is at the lower sealing flange. Due to the eccentricity of some of the crystallizer copper tubes after assembly, when the lower sealing flange was installed, the copper tube was forcibly extruded and corrected, causing the inverse taper of the copper tube to suddenly change at the extrusion point. On-site use tracking found that when the deformation of the copper pipe is above 0.3mm, the resistance to drawing increases and the wear of the lower cavity of the copper pipe increases, resulting in an increased chance of stripping and steel leakage.

2 Methods to improve the quality of billet mold maintenance

(1) After taking out the copper tube from the copper mould tube, wipe the surface with white paper. If there is scale, use fine sandpaper to wipe it instead. In particular, the upper end of the copper pipe should be wiped carefully in the area 350mm downward. If the scale film is not easy to be wiped off, a portable cloth grinder can be used to polish it to ensure good thermal conductivity of the copper pipe.

(2) Before a copper mould tube stored for a long time is put into use, it must be disassembled, the oxide scale removed, and blown with compressed air to keep the inner cavity of the copper mould tube shell clean.

(3) After the copper mould tube is assembled, the taper of the inner cavity of the copper tube needs to be checked twice. If the deformation exceeds 0.3mm, it must be reassembled. If necessary, metal processing must be performed to correct the center. In addition, seals with soft texture can be used to reduce the extrusion force on the copper pipe and control the deformation within 0.3mm.

3 Conclusion

Paying attention to maintenance details and improving maintenance quality are important guarantees for the efficient and long-life use of the copper mould tube, and are the key to stable and high output of the continuous casting machine.

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