1. The core advantage of ceramic sand as ladle filler sand
Spherical particle structure
Excellent fluidity: small friction between spherical particles, high filling density (bulk density 1.6-2.0 g/cm³), can quickly form a uniform sand layer, and drainage is smoother when pouring.
Strong anti-permeability: the tightly packed structure can effectively block the penetration of molten steel and reduce the risk of sintering.
High refractoriness and thermal stability
Refractory ≥ 1750°C (Al₂O₃ content 50-90%), can withstand high temperature erosion of molten steel (1600°C).
Low thermal expansion coefficient (0.5-1.0×10⁻⁶/°C), stable volume at high temperature, not easy to crack.
Chemical inertness
Strong resistance to erosion of molten steel and slag (especially suitable for complex steel grades such as high oxygen steel and stainless steel).
No harmful substances (such as hexavalent chromium) are released, and the environmental protection is better than chromium ore sand.
2. Application steps of ceramic sand as drainage sand
1. Raw material selection and pretreatment
Particle size control:
The particle size of ceramic sand sand is usually 0.2-1.0mm, and the recommended grading is:
Coarse particles (0.7-1.0mm) account for 40%
Medium particles (0.4-0.7mm) account for 30%
Fine particles (0.2-0.4mm) account for 30%
To balance fluidity and anti-permeability.
Drying treatment:
Before use, it needs to be dried at 200-300°C for 2-3 hours to remove adsorbed moisture and prevent explosion when molten steel is poured.
2. Mixing and preparation (optional)
Additive optimization:
Add 1-2% graphite powder: improve lubricity and reduce friction between sand layer and molten steel.
Add 0.5-1% borax: reduce sintering temperature, promote moderate bonding of sand layer at high temperature, and prevent premature collapse.
Mixing uniformity:
Use a twin-shaft mixer to mix for 5-10 minutes to ensure uniform distribution of additives.
3. Filling the ladle nozzle
Filling method:
Inject sand into the ladle bottom nozzle (such as sliding nozzle or long nozzle) through pneumatic conveying equipment. The filling height is usually 150-250mm, and slight vibration compaction is required.
Layer design:
For large ladles, layered filling can be performed:
Lower layer (contacting molten steel): fine-grained gemstone sand (0.2-0.4mm) to enhance sealing.
Upper layer: coarse-grained gemstone sand (0.7-1.0mm) to ensure drainage speed.
4. High-temperature pre-sintering (key step)
Pre-sintering process:
Pre-sintering at 1000-1200°C for 30-60 minutes to slightly melt the surface of the sand particles to form a “micro-glaze layer”, which not only maintains the independence of the particles, but also enhances the overall structural strength to prevent the sand layer from collapsing due to molten steel impact.
5. Ladle pouring
Drainage mechanism:
Under the static pressure of molten steel, the bottom of the sand layer is heated and softened, and the pearl sand flows out with the molten steel by its own fluidity to form a stable flow channel.
Flow rate adjustment:
By adjusting the particle size ratio (the higher the proportion of coarse particles, the faster the flow rate), the initial molten steel flow rate is controlled to avoid turbulent slag.
III. Key points
Particle size management
It is forbidden to use ultra-fine powder with a particle size of less than 0.1mm, which is easy to cause slab blockage.
Regularly screen and remove the debris generated during use (the number of cycles is recommended to be ≤3 times).
Environmental adaptability
High oxygen steel: It is necessary to test the stability of ceramic sand sand in an oxidizing atmosphere (Al₂O₃ content ≥70% is safer).
Vacuum refining (VD/VOD): The low volatility of ceramic sand sand is suitable for vacuum environment, but the pre-burning temperature needs to be increased to 1300°C.
Cost control
The unit price of ceramic sand sand is relatively high (about usd500/ton). The cost can be reduced by mixing it with cheap sand (such as quartz sand) at a ratio of 7:3, but the fluidity of the mixed sand must meet the standard.
