As the use of refractory castables becomes increasingly widespread, there are indeed certain methods and techniques for selecting the appropriate material type and specifications.
Refractory castables are classified as neutral, acidic, or alkaline, and are further distinguished as heavy-duty or lightweight. Heavy-duty refractory castables are generally used for the working layer, while lightweight castables are used in the insulation layer to provide thermal insulation.
For neutral high-alumina refractory castables, the specific grade of castable to be used is determined based on the temperature and erosion conditions of the furnace lining. If the temperature is below 1200°C, clay castables are sufficient; if the temperature exceeds 1250°C, high-alumina castables must be selected. If the operating temperature exceeds 1350°C, corundum refractory castables should be selected. In cases of extreme erosion, chromium corundum castables should be chosen, and for severe wear, wear-resistant refractory castables should be used. Neutral materials have a shelf life of 6 months; it is essential to store the raw materials and binders separately.
1. Use acid-resistant castables in acidic atmospheres
For castables used in acidic atmospheres, acid-resistant castables should be selected. These castables are available with two types of binders: water glass and phosphoric acid. In acidic atmospheres where temperatures do not exceed 1250°C, water glass-bonded acid-resistant castables are sufficient; if temperatures are higher, phosphoric acid-bonded acid-resistant castables should be chosen.
2. Select magnesium-based refractory castables for use in alkaline atmospheres
For castables used in alkaline atmospheres, magnesium-based refractory castables should be selected. For applications involving erosion and wear, magnesium-aluminum-based refractory castables or magnesium-chromium-based castables should be chosen. If temperatures are excessively high, high-density magnesium-based castables or those with a high magnesium content should be used. However, special care must be taken when storing magnesium-based castables; they must not be stored outdoors, as they must not come into contact with water, otherwise they will powderize.
3. Use lightweight refractory castable for the insulation layer
If castable refractories are used for the insulation layer, the choice depends on the temperature. For low temperatures, standard lightweight insulating castables are sufficient. If temperatures are too high, lightweight high-alumina castables or lightweight castables containing alumina hollow spheres should be used as the insulation layer. Care must also be taken when storing lightweight castables; they must not be stored together with highly corrosive materials, as this could damage them.
4. Since the furnace shell has low thermal requirements, a double-layer insulation design is used to address this
If the furnace shell has low weight requirements, a double-layer insulation system should be used, consisting of ceramic fiber followed by lightweight insulating castable, or ceramic fiber blocks can be used directly. However, if there are weight requirements for the insulation area, an insulation layer with a density of 0.6–0.8 should be used. For flue ducts where insulating castable is applied directly to the working layer, a lightweight castable with a density of 1.3–1.5 should be selected for the lining. For corrosive atmospheres, lightweight acid-resistant castable should be selected for the lining.
In summary, regardless of the type of refractory castable chosen, the selection must be based on the specific application, lining atmosphere, and temperature conditions.
More details about refractory castables
What are refractory castables?
Refractory castables are unshaped refractory materials that can be mixed on-site with water and cast into virtually any form. They consist of carefully graded refractory aggregates, hydraulic or chemical binders, and performance-enhancing additives.
What is the difference between castable refractory and fire brick?
Firebricks are commonly used as the cooking surface and can withstand temperatures of up to 2,000°F. Ceramic fiber insulation is used to insulate the oven and reduce heat loss. Castable refractory cement is used for the oven dome and can withstand temperatures of up to 3,000°F.
What is refractory in casting?
Refractory is a very important component in economically successful melting of cast iron. Refractory is used to line the furnace or any other vessel used for melting or holding of the molten metal.
How to use castable refractory?
To use castable refractory cement correctly, you must follow five critical stages: surface preparation, accurate mixing, proper installation, controlled curing, and staged drying/heating. Each stage directly affects the final strength, thermal stability, and service life of the refractory lining.