Refractory castables types

Like MgO-MA refractories, AI2O3-MA refractories are prepared as shaped bricks or monolithic castables. In recent years, extensive research and development work on AI2O3-MA castables had led to their use in many areas such as steel-making ladles. Two AI2O3-MA castable types are used AI2O3-MgO castables and AI2O3-spinel castables. In the former, MgO is added to alumina-based castables to form in-situ spinel, and in the latter, preformed synthetic MA spinel is used instead of MgO. Due to the difference in the spinel used, these two kinds of castable show different microstructures, properties, and performances. 

Alumina and alumino-silicate refractory castables may further be classified or typed in many ways. The American Society for Testing and Materials (ASTM) classifies alumina and alumino-silicate refractory castables in a very simplistic and general classification (3) that is a useful initial guide. In reality, refractory castables are typed or classified by a combination of the attributes listed in Table 1. 

To complete the refractory castable formulation, various types of additives ... 

The category of refractory castables classified as dense castables represents a large and diverse group consisting of conventional-type castables and the various categories of advanced products. For the refractory user, the differences in the types of advanced castable are important to understand since dense refractory castables are used as structural components in furnaces and kilns, as primary lin-... 

Because of the many types of advanced castables on the market today and due to the specialized development of many of these materials for specific uses, it is harder to characterize their strength development. The refractory manufacturer has less leeway in development of most dense conventional castables since they are viewed more or less as a commodity product (every manufacturer makes similar products) in the marketplace, and price dictates formulation constraints. This is sometimes true for low end (superduty, 50% alumina) advanced castable types in the low- and ultralow-cement classifications. However, application and performance criteria can and do call for the development and use of premium castables where the use of expensive formulations and exotic modifiers can modify physical properties and characteristics such as strength in specific temperature ranges that correspond to the anticipated service condition. 

For the past 30 years, refractory technologists have significantly improved refractory castable formulations, widening both the types of castables and the installation methods available. The improvement in their physical properties and characteristics have enabled castables to gain in market share and application at the expense of other types of refractories. In a recent report, an industrial market research firm predicted that castables would see the best sales growth in the refractory market over the next 5 years due to superior performance character-... 

Chemically Bonded Castables. These refractory castables contain one or more chemical bonds. After the addition of water or a suitable mixing liquid and an intensive mixing, they start setting mostly due to a neutralization process. By this it should be stressed that a clear differentiation between a chemically bonded castable and a deflocculated one of the NCC type is hardly possible. This can be also traced back to the fact that the nature of bonds has not been investigated in detail, respectively classified, so far. 

Plastic Refractory Materials. The product group is demonstrably the oldest monolithic material. It was developed in the United States as pliable firebrick in 1914, and for a long period it was used as the standard material for the front installation of many types of furnaces (3). (The refractory castable was developed at a later stage a first patent application in the United States was registered in 1923.)... 

Inside and outside vibrators are used for compaction. The consistency of the castable requires special consideration if using outside vibrators. The refractory castable should never be adjusted to suit the vibrator. The vibrator must always be regulated in regard to the type of castable and the wall thickness. For example, MCC- and LCC-type castables often have a viscous consistency, which can be changed by adding more liquid. This will enable the user to install the castables with less suitable equipment, but in the end the user will also run the risk that the expected properties of the castables will not be achieved. 

These correlations are typical for all regular refractory castables. The final strength will depend on the type of refractory castable in other words, on the type of aggregate, grain structure, cement type, water-to-cement ratio, and installation technique. 

Table 12 lists properties of eight different industrial refractory castables and gives a comparison between RC- and MCC-type castables. Chamotte (A 1 -I- A 2), flint clay (B 1 - - B 2), flint clay/fused brown alumina (Cl -I- C 2), and tabular alumina (D 1 - - D 2) were selected to serve as examples of the raw material... 

Insulation - The steel shell of the stack is lined for its entire length with monolithic type castable refractory. 

For pure thermal insulation in very clean atmospheres, insulating refractories may be used. These types of refractories are normally very lightweight and can be purchased as brick shapes, as castables or refractory concretes, and as ceramic fiber. 

Other binary aluminates include magnesium spinels that are used extensively as castable refractory ceramics. Lithium aluminates are used, potentially, in fuel cells and as materials for new types of nuclear reactors. Again, these applications reflect the refractory nature of aluminates and their chemical resistance. 

This reactor section containing the fluidized bed is 28 inches od and 15 inches id. The insulation lining is 4 inches of Type 1620-K fire brick (Babcock and Wilcox Co.) and 2 inches of Plicast Tuff-Mix castable refractory (Plibrico Co.). The height of this section is 8 ft. Above the fluidized bed section, the reactor diameter expands to 35 inches od and 22 inches id. This particle-disengaging chamber is 4 ft high and is lined in the same manner as the fluidized bed section. 

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