Fire mouth castable: the guardian of the 'throat' of high-temperature kilns

What is burner castable?

Fire mouth castable is a special unshaped refractory material specially used for industrial kiln burners, kiln mouth and other high heat load parts. It directly faces flame impact and high-temperature material erosion, and is a key barrier to protect the "throat" of the kiln.

How bad is the fire mouth? Taking the cement rotary kiln as an example, the burner not only has to withstand the impact of high-temperature flames above 1700°C, but also the chemical erosion of clinker slag and the thermal shock test of rapid cooling and rapid heating. Ordinary refractory materials may crack, peel or even burn through in a few months under such working conditions, but high-quality burner castables can extend the service life by 2-3 times.

Core performance requirements of burner castables

A good fire mouth castable needs to be qualified and meet the standards in the following dimensions:

1. High refractoriness

This is the most basic requirement. The burner temperatures of different kilns vary greatly, and the material selection must match the actual working conditions.

Recommended materials for typical usage temperatures in application scenarios

Cement rotary kiln kiln mouth 1400-1700℃ corundum-silicon carbide

Aluminum melting furnace burner 1000-1650℃ corundum-mullite

Biomass boiler burner 1000-1500℃ corundum/silicon carbide

2. Excellent thermal shock resistance

The fire mouth often experiences a "heating-cooling" cycle, so the material must have good thermal shock resistance, otherwise it will crack due to thermal stress. Taking Shengyuan"s burner castables as an example, its 1100°C water-cooled thermal shock stability can reach more than 25 times, which means it can withstand repeated temperature shocks without peeling off.

3. High strength and erosion resistance

The scouring power of high-temperature flames is very strong, and the burner castables need to have sufficient high-temperature flexural strength. For example, the 1400°C high-temperature flexural strength of some burner castables can exceed 10MPa, which can effectively resist the mechanical wear of high-speed air flow.

4. Resistant to chemical attack

The burner also faces various chemical attacks such as slag, alkali vapor, acid gas, etc. The material selection needs to match the working conditions in a targeted manner.

Main types and application scenarios of burner castables

The working conditions of the burner of different kilns are different, and the material selection is also clearly distinguished.

Corundum-silicon carbide burner castable

Suitable for use in cement rotary kiln kiln mouth, burner and other parts. Typical indicators: Al₂O₃≥85%, SiC content 10-20%, its service temperature can reach 1700℃. The addition of silicon carbide significantly improves the material"s thermal shock resistance and alkali corrosion resistance.

Corundum-mullite fire mouth castable

Suitable for use in aluminum melting furnaces, regenerative burners, etc. The Al₂O₃ content is generally between 65-80%, and the use temperature is 1500-1650℃. This type of material has a dense volume and small porosity, and can resist the erosion of flue gas in acid and alkali atmosphere without peeling or bursting.

Corundum burner castable

Suitable for use in occasions with high purity requirements, such as high-purity aluminum smelting burners. The Al₂O₃ content can reach more than 90%, and the service temperature can reach 1790℃. It has the characteristics of high purity, high strength, erosion resistance and good thermal shock stability.

The correct construction method of fire mouth castables

If you choose the right materials, it will be "in vain" if the construction is not in place. The following are the key control points for the construction of fire mouth castables.

1. Strictly control the amount of water added

Excessive water addition by construction workers in order to "work well" is the most common reason why the strength of castables does not meet the standard. The amount of water added must be strictly controlled in accordance with the manufacturer"s instructions. Generally, the recommended water amount for burner castables is between 5-6.5%. Adding too much water will significantly increase porosity and reduce strength and erosion resistance.

2. Thermal expansion treatment of anchors

The castable material fell off in pieces, and a large part of the reason was the anchors. The thermal expansion of metal anchors will "crack" the castable, so the anchors must be compensated for expansion, such as painting the head with asphalt or putting a plastic cap on it.

3. Stir and vibrate thoroughly

Be sure to use a forced mixer and mix for no less than 5 minutes. After pouring into the mold frame, you should immediately use a vibrator to vibrate in layers. The height of each layer should not exceed 300mm. After seeing the slurry on the surface, slowly pull out the vibrator to avoid cavities.

4. Curing and baking

After the castable construction is completed, sufficient curing time is required to allow the material to fully solidify. After that, you must bake according to the principle of "slow heating and constant temperature" to completely drain out free water and crystal water to avoid bursting when used at high temperatures. Winter construction also requires anti-freezing measures.

Conclusion

The performance and service life of the burner castable directly determine the operation rate of the kiln and the production cost of the enterprise. Choosing the right materials, controlling the construction, and standardizing the baking, none of these three links will work.

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