01. Factors affecting the quality of tundish repair
1. Loose tundish wall The loose casting tundish wall is mainly reflected in the contact position between the tundish wall and the bottom of the tundish. The loose tundish wall is manifested in two forms: one is that it extends longitudinally from the tundish wall to form an irregular surface; the other is that slender powder falls off to form a "slit shape".
There are two reasons for looseness: one is that the binder volatilizes, causing the overall bonding strength to decrease, especially the outermost; the other is that the fine powder containing resin does not wrap the particles, which eventually causes easy slag. Mixing borosilicate glass powder with phenolic resin and applying it to magnesium dry materials can better improve the low-temperature baking strength and medium-temperature strength of dry materials.
According to the on-site situation, the reasons for the low quality of casting tundish repair are: 1) The tundish material is unreasonable. The current tundish binder ratio is low, and there is a phenomenon of concentrated material distribution during repair, which makes the large-particle magnesia sand in the dry material easy to segregate. 2) The vibration time of the tire is long. At present, 4 motors are used for the tundish tire. In order to increase the density of the slag line, the vibration time is 15 minutes. Although the volume density of the dry material in the tundish is increased, the aggregate and powder of the lower dry material are easily separated, and the dry material is prone to "bridge" phenomenon, causing the wall of the package to be loose.
2. Cracks on the package wall
The package wall at the head of the tundish has horizontal lines. The thickness of the dry material at this position is 110 mm, and the crack depth is 40 mm. The main reason is: the current release agent is applied once, the thickness is only 0.1-0.2 mm, and the application is uneven, causing the dry material to adhere to the tire, and the dry material cracks after the tire is lifted. The tire mold generates stress concentration during the lifting process, which in turn causes surface cracks. 3. The shape of the upper nozzle does not meet the requirements
The current repair package operation procedures only require that there should be no debris in the nozzle. During operation, workers only use waste woven bags to plug the nozzle. There is no unified standard, let alone a reasonable mold, which often causes debris to remain in the nozzle, and the shape of the upper nozzle is irregular.
02. Application effect
The quality of the tundish repair is improved from the aspects of optimizing the composition of the tundish dry material, standardizing the material distribution operation, optimizing the vibration and baking process, using the release agent reasonably, and designing the foam plug for the special nozzle of the tundish. At present, the qualified rate of the continuous casting tundish repair has increased from 92.5% to 99.6%, which has improved the safety of the tundish, improved the anti-stripping and anti-permeability of the working layer dry material, improved the uniformity of the dry material distribution, and improved the density of the dry material. The erosion of the working layer has been significantly improved, and the large surface erosion of the working layer has been reduced from the original erosion of 30 mm in 20 hours to the current erosion of 25 mm in 24 hours, which has greatly improved the service life of the tundish and met the production requirements. Inspection of the improved tundish revealed that the strength of the dry material in the lower part of the tundish was significantly improved, and there was no phenomenon of loose material falling due to insufficient strength. Problems such as loose and cracked tundish walls have been solved.
