Introduction
Magnesia ramming mix is an unshaped refractory material composed primarily of magnesia sand (MgO), supplemented with binders and additives, and compacted through manual or mechanical ramming. With a typical MgO content ≥85%, it exhibits excellent resistance to alkaline slag corrosion, making it ideal for high-temperature, strongly alkaline smelting environments.
The magnesia ramming mix is formulated by blending magnesia sand (aggregate) and magnesia powder (fines) in specific proportions, combined with a binder to achieve a certain density. Its key thermal properties include:
Melting point: 2825°C
Thermal conductivity: 45 W/(m·K)
Coefficient of thermal expansion: 14 × 10⁻⁶ /°C
Heat capacity at 1500 K: 53.6 J/mol
These properties confer exceptional thermal shock resistance.
Advantage
High Temperature Resistance
Refractoriness ≥2000°C, capable of withstanding molten metal and slag at 1600–1800°C.
Slag Erosion Resistance
Exhibits strong resistance to alkaline slags (e.g., CaO, FeO), outperforming ordinary refractory bricks.
Construction Plasticity
Available in granular or mud form, it can fill complex-shaped gaps via ramming or vibration, ensuring good sealing.
Volume Stability
Minimal volume change at high temperatures, excellent thermal shock resistance, and low susceptibility to cracking or spalling.
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Raw Materials
Magnesia-based Materials
Magnesia sand: The core raw material of magnesia ramming mix, primarily composed of magnesium oxide (MgO). Classified by production process and purity:
Sintered magnesia: Produced via high-temperature sintering (1600–2000°C), featuring high density and slag resistance. Commonly used in critical refractory applications.
Electrofused magnesia: Formed by cooling after electrofusion melting, with ultra-high purity (MgO ≥98%), perfect crystallization, and superior erosion and high-temperature resistance. Suitable for harsh environments (e.g., ladle slag lines, blast furnace shells).
Light-burned magnesia powder: Derived from magnesite calcined at low temperature (700–900°C), exhibiting high reactivity. Often used as binders or to modify matrix properties.
Binders
Chemical binders:
Magnesium salt binders: For example, magnesium chloride or sulfate solutions, which react with magnesia sand to form hydrated magnesium salts (e.g., Mg(OH)₂), providing room-temperature strength.
Resin binders: Organic binders such as phenolic resins that cure upon heating, enhancing the plasticity of the ramming mix and improving high-temperature strength. Ideal for rapid-molding scenarios.
Physical binders: For example, water glass (sodium silicate solution), which forms bonds via water evaporation. Used in environmentally sensitive applications.
Additives
Sintering aids: Such as SiO₂ and Al₂O₃, which promote sintering to improve material density and slag resistance.
Anti-slag agents: Such as spinel (MgAl₂O₄) and zircon (ZrSiO₄), enhancing slag erosion resistance, especially in alkaline slag environments.
Plasticizers: Such as bentonite and organic polymers, improving the workability of the ramming mix for easier on-site compaction.
Anti-explosion agents: For example, aluminum powder, which reacts with water during baking to generate hydrogen gas, preventing coating spalling caused by rapid moisture evaporation.
Physical and Chemical Specifications
|
Item |
QD-1 |
QD-2 |
QD-3 |
QD-4 |
QD-5 |
|
MgO% ≥ |
80 |
76 |
88 |
90 |
58 |
|
Cr2O3% ≥ |
|
|
|
1 |
16 |
|
CaO% |
6~9 |
12~16 |
|
|
|
|
Fe2O3% |
3~6 |
3~6 |
|
4 |
|
|
SiO2% ≤ |
2.0 |
2.0 |
5.0 |
2.0 |
1.8 |
|
Grain Size(mm) |
0~6 |
0~6 |
0~5 |
0~5 |
0~5 |
|
Application |
EAF Bottom |
EAF Bottom |
Metallurgical Furnace Bottom |
Furnace Bottom/Mouth/Tap Hole |
RH Furnace Bottom |
|
Bonding Method |
Ceramic Bonding |
Ceramic Bonding |
Chemical and Ceramic Bonding |
Chemical and Ceramic Bonding |
Chemical and Ceramic Bonding |
Process
Pre-treatment
Remove oil, rust, and impurities from the construction surface by sandblasting or mechanical grinding.
Inspect ramming tools (e.g., ramming hammer, vibrator) to ensure proper operation.
Batching and Mixing
Blend magnesia sand, binders (e.g., water glass, resin), and additives according to the specified recipe.
Dry mix for at least 15 minutes to ensure material uniformity; sieve to remove lumps if necessary.
Ramming and Molding
Construct in layers, controlling each layer's thickness at 50–100 mm using mechanical ramming or vibratory compaction.
Maintain a ramming density ≥2.8 g/cm³ to ensure no voids or loose areas.
Curing and Baking
Cure naturally for 24–72 hours (adjusted based on binder type).
For high-temperature kilns, bake according to the prescribed heating curve (initially 10–20°C/h, then 30–50°C/h) to remove moisture and complete binder curing.
Application
Iron and Steel Metallurgy
Converters and electric furnaces: Used for furnace bottom and wall ramming layers, withstanding scouring from molten steel and alkaline slags at 1600–1700°C.
Steel ladles: Ramming construction in the slag line area extends service life to over 100 heats (compared to ~60 heats for conventional brick linings).
Non-Ferrous Metal Smelting
Nickel and copper smelting furnaces: Bottom and wall linings resist erosion from high-nickel slags, matte, and other strongly alkaline melts.
Other High-Temperature Industries
Cement kiln firing zones: Used to replace magnesia-chromite bricks, capable of withstanding CaO-based clinker slag erosion at 1450–1600°C while reducing chromium pollution.
Glass kiln regenerators: Prevent penetration of glass melt vapors and maintain heat exchange efficiency.
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