Corundum Ramming Material for Filling Around Ladle Base Bricks and Tundish Water Nozzle

In recent years, due to the need to smelt clean steel, the residence time of molten steel in the ladle and tundish has been extended, which has put forward new requirements for refractory materials for steelmaking. In order to improve the service life of the refractory materials in the working layer, the ladle generally adopts the replacement of the nozzle seat bricks and the breathable seat bricks, and the digging and repairing of the ladle bottom to improve the service life. The tundish adopts the replacement of the nozzle to improve the service life. At present, the commonly used refractory materials for filling around the ladle seat bricks and the tundish nozzle are plastics. However, the plastic itself has relatively more pores, the material is low-grade, the slag resistance is poor, and there are great safety hazards during use. For this reason, the steel plant requires that the plastic be replaced with ramming materials with excellent performance. According to the analysis of the use and function of the ramming materials, the improved ramming materials should have the following properties:

It does not need to be stirred and used directly on site.
It can be stored for a long enough time to facilitate on-site use at any time.
The strength is appropriate, which is convenient for digging and repairing the seat bricks, and can fix the seat bricks to ensure safe use.
Good slag resistance.
The ramming material has good bonding with the upper working layer.

Based on the above ideas, this work developed corundum ramming materials for filling around ladle seat bricks and tundish water inlets that meet the requirements of steel mills.

Design of corundum ramming material for filling

The selection of raw materials and particle grading of ramming material will directly affect its construction performance and use performance. At present, the plastic material of the steel ladle in use is a high aluminum system, and the working layer castable is a corundum spinel system. Considering the cost and performance of the ramming material, after comprehensive consideration, it is finally determined to use corundum ramming material.

Brown corundum and white corundum have high volume density, low water absorption rate, and certain reaction inertness. Using them as aggregates is beneficial to the slag resistance and strength of the ramming material. Alumina powder has a fine particle size and can fill the micropores between aggregates and improve the organizational structure of the material. At the same time, it can react with the binder and silica powder in the ramming material at a lower temperature to improve the density, strength, and corrosion resistance of the material. Adding an appropriate amount of silica powder can generate an appropriate amount of low-melting-point phase in the ramming material at medium and high temperatures, so that the material has a certain creep property, which is very beneficial for absorbing stress and making the organization dense. It can reduce the residual expansion and high temperature expansion of the ramming material. Some of the currently used ramming materials do not use a binder, while some only add a small amount of flux.

The corundum ramming material developed this time must not contain a binder that hardens at room temperature, and needs to produce a strong bond during the heating process after tamping. The comparison of the particle size composition on the physical properties of the ramming material, the natural stacking of the ramming material, and the construction and operation conditions of the ramming material ultimately determined that the critical particle size of the corundum ramming material is 5mm. The particle size composition is: 35% large particles, 25% medium particles, and 40% fine powder.

Configuration of corundum ramming material for filling

The main raw materials are brown corundum, white corundum, alumina powder, silica fume, etc.

In addition to the main raw materials, there are also additives such as plasticizers, retarders, expanders, binders, etc. At the same time, in order to ensure that the ramming material produces moderate sintering strength during use, a small amount of sintering aid is added to the ramming material. By comparing the compressive strength of samples with different amounts of binders and sintering aids, the amount of binders and sintering aids added is determined.

After a certain amount of material is prepared according to the designed ratio and mixed evenly, it is rammed into a strip sample of 40mm×40mm×160mm and a crucible sample with an outer size of 70mm×70mm×70mm and an inner hole size of φ430/20mm×40mm. Natural curing for 24 hours, then curing in an oven at 110℃ for 24 hours, and demolding. Some of the dried strip samples were heat treated at 1000 and 1550℃ for 3h, and the heating permanent line change rate, flexural strength and compressive strength were tested. The dried crucible samples were taken for static crucible method test, 20g of ladle slag was added, and after heat treatment at 1600℃ for 3h, the crucible was cut along the axis, the penetration area was measured, and the penetration index (penetration area ÷ original crucible hole center cross-sectional area) × 100% was calculated.

Performance of corundum ramming material for filling

① Combination with working layer

The ramming material is used to tie a knot at the bottom of the mold, and the ladle bottom working layer castable is directly poured on it. After heat treatment at 110℃ for 24h and 1550℃ for 3h, the combination of the ladle bottom castable and the ramming material is observed. It can be seen that the combination of the two materials is good after heat treatment under different conditions, and no stratification or separation occurs.

② Slag resistance

According to calculation, the slag penetration resistance index of the working layer castable is 112%, and the slag penetration resistance index of the ramming material is 115%, which are similar. As a filling material around the seat brick, the slag resistance of the developed ramming material meets the requirements.

③ Storage time

The storage time of the ramming material should be controlled to be more than 30d as much as possible. In this experiment, the storage time of the ramming material is mainly adjusted by adjusting the type of retarder and its addition amount. The results show that the best effect is to use two retarders in a certain proportion.

Industrial application of corundum ramming material for filling

At present, corundum ramming material for filling has been used normally in the area around the water inlet of a steel plant instead of the original plastic material. The storage time of the normally supplied ramming material can reach more than two months. The ramming material has good on-site construction performance, is easy to disassemble, and its performance can fully meet the requirements of the steel plant. The next step will be to use it around the water inlet bricks and breathable bricks of the ladle.

Rongsheng Refractory Castable Manufacturer

Brown corundum, white corundum, alumina powder, and silica powder are the main raw materials. A reasonable particle ratio is adopted, and appropriate types and quantities of binders, plasticizers, expanders, sintering aids and retarders are added. A corundum ramming material with long storage time, good combination with the bottom working layer castable, and excellent slag resistance has been developed. The developed ramming material has been successfully used in steel plants, meeting the on-site needs for the use of ramming materials.