Refractory castables

High purity CA cements are primarily used as binders for high strength refractory castables to form linings up to about 1.0 m thick, as, for example, in iron blast furnaces. Since the 1970s, large monolithic precast CAC castable shapes have found increased usage in a variety of specialty fired shapes that are too expensive to be inventoried. 

Other common refractory forms include setter tile and kiln furniture, fusion-cast shapes, cast and hand-molded refractories, insulating refractories. castables and gunning mixes, plastic refractories and ramming mixes, mortars, composite refractories, and refractory coatings,... 

Used with appropriate refractory aggregates, calcium aluminate cements may be used to make refractory castables having applications in the steel and other heat-using industries. Cements made from bauxite may thus be used at hot face temperatures up to 1350 C. White calcium aluminate cements, which are low in iron and higher in alumina, can be used with appropriate aggregates to make castables similarly resistant up to 2000°C. 

Refractory castables have good resistance to thermal shock. 

Catalyst-carrier lines. Catalyst-carrier lines as large as 105 in. in diameter are used (271). To provide wear resistance, these pipes are ordinarily lined with refractory castable cement reinforced by steel mesh which is welded directly to the inside of the line. In midget fluid units, however, alloy-steel carrier lines may be used in direct contact with the catalyst, because the small size of the lines makes it difficult to install internal insulation (237). Counterweights are used to help support long carrier lines, and shock absorbers have been employed in order to minimize vibration or jiggling (20). 

Granular refractories (castables, mouldables, mortars, etc.) serve for the construction of monolithic kiln and furnace linings, for hot and cold repairs, as mortars for the joining of bricks, etc. Essentially, they are mixtures of refractory granular materials with inorganic binders which provide strengthening in situ . 

Studart, A.R. etal.. Selection of dispersants for high-alumina zero-cement refractory castables, 7. Eur. Ceram. Soc., 23, 997, 2003. 

One very important niche application for calcium aluminate (cements) is as refractory castables. Key to the success of calcium aluminates in this application are their refractory properties that contrast with those of Portland cements. Although Portland cement maintains good strength when heated, reactive components (CaO) are liberated and can absorb moisture from the atmosphere when cooled, causing expansion and deterioration of, for example, kiln linings. CACs are not much susceptible and can be used to form monolithic castables and refractory cements [28, 29],... 

S. Mukhopadhyay, et al., In situ spinel bonded refractory castable in relation to co-precipitation and sol-gel derived spinel forming agents. Ceram. Int. 29(8), 857-868 (2003). 

Calcium aluminate cements are examples of conventional refractory castables. Development of low, ultralow cement, no-cement pumpables, and self-flow castables has increased the applications of monolithics [42], Steel-reinforced refractories (SFRR) are used in applications that include ferrous and nonferrous metal production and processing, petroleum refining, cement rotary kilns, boilers, and incinerators. Steel fibers are added to refractory concretes to improve resistance to cracking and spalling in applications of heavy thermal cycling and thermal shock loads. 

Permeability is the material property that most influences the drying process of refractory castables [43—45]. The permeability of compressible fluids flowing through rigid and homogeneous porous media is described by the Forchheimer equation, which includes a quadratic term for the flow rate q. For small changes in pressure, the Forchheimer s equation leads to Darcy s law ... 

R.E. Moore, J.D. Smith, and T.P. Sander, Dewatering monolithic refractory castables experimental and practical experience, Proc. UNITECR 97, 1997, pp. 573-583. 

T. Richter, and D. McIntyre, Novel form free installation method for refractory castables, Refract. Appl. News 6(4) 3-5 (2001). 

ASTM C860 Standard Practice for Determining the Consistency of Refractory Castable Using the Ball-in-Hand Test, April 2000. 

Tabi 9-7C. Characteristics of Hiqh-temperature Insulation. Classification op Refractory Castables (Refractory aggregates plus hydraulic cement)... 

British Ceramic Research Assoc., Thermomechanical Behavior of Refractory Castable Linings, Technical Note No. 320, March 1981. 

The white calcium aluminate cements, with special aggregate (for example corundum) can be used for production of refractory concretes resistant even up to 2,000 °C (Super Secar 250). Refractory castables have also good resistance to thermal shock. 

ASTM C-974 Preparing test specimens from basic refractory castable products by casting... 

Cokilite. A refractory castable based on silicon nitride. 

Coning and Quartering. A method of obtaining a random sample of a powder by pouring it out to form a cone, which is then divided into four by two diametral cuts . One quarter is selected, and the process may be repeated. Consistency. The flow or mechanical displacement properties of cements, mortars and refractory castables. See... 

Seating Block. A block of fireclay refractory, shaped to support a boiler. Secar. Trade-name a pure calcium aluminate cement, suitable for use in making special refractory castables or shapes, made by Lafarge Aluminous Cement Co. Ltd. It is available in two grades the purer (Secar 250) contains 70-72% AI2O3, 26-29% CaO, 1% SiOz and 1% Fc203. 

Slurry infiltrated fibrous castable (SIFCA). A refractory castable containing up to 16% steel fibres. The fibres are filled into the mould first, followed by a fine-grained castable, this approach overcoming previous difficulties of mixing and placing which limited the fibre content to c. 2 vol%... 

A multi-legged refractory brick arch capped with refractory castable, used in some vertical shaft preheaters in cement manufacture. 

Vibrating Table. A table which oscillates rapidly to remove air and compact a refractory castable placed on it. Vibro-casting. Pouring concrete into a mould, and densifying by vibration. 

Castables are more convenient refractories than bricks at this time. The main principles for the structure of corrosion refractories (castables and bricks) that are resistant to A1 are low porosity (< 13-15%) and low gas permeability (<0.4—0.5 pm ), while most pores are smaller than 3—4 pm. 

Out of all the unshaped refractory material subdivisions, refractory castables are the most important. These are produced as dense or insulating materials. Formerly, these were made as mixtures of aggregates and calcium aluminate cements. After continuous improvement, they are produced on a very high technical level today. Because of their varieties, they are further classified as follows. 

Methods of Mixing and Installation of Different Refractory Castables... 

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