Monolithic Linings

Refractories may be preformed, ie, shaped, or formed and installed on-site, ie, specialties. Iimovations in placement and vessel constmction has led to a greater emphasis on specialty refractory products. Castables, gunning mixes, and plastic and ramming mixes are used either for repair or for complete new constmction of what is known as monolithic linings. The tendency to use monolithics instead of constmctions using shaped products has been steadily increasing. As of the mid-1990s, monolithic installations are as common as conventional shaped product constmction. 

Clay fuses at from 2800 tit 3200T. tl53fi to 1760 0 the uppet limit being for flint clay and the lower for the plastic form which, due to its cc-mcming qualities, is especially valuable in fire-brick manufacture, Red brick is not suitable for refractory service, nor is insulating brick. There are several fire-clay furnace cements on the market that arc adaptable to monolithic lining. The standard sire of fire-brick and insulating brick is 9 inches by 4i inches by 2i inches 122.9 by 11.4 by 6.4 centimeters). 

Refractory flaws can also be caused by the frequency of temperature cycling, the rate of temperature drop, and the amount of temperature drop, which can lead to thermal shock or structural flaws from thermal expansion differences. Where monolithic linings are used, anchors attach the refractory material to the shell. Those anchors can experience failure from mechanical stresses, metal fatigue, or corrosion, leading to gaps between the refractory shell and the lining. Any gap impacts heat transfer and can initiate other types of refractory failure, such as slag corrosion because of heat buildup at those sites. 

Unless the steel deck is rigidly supported, it will flex under loading, causing the brick or monolithic lining to crack. 

The basic manufacturing operation is calcining the raw material to obtain the dead-burned magnesite which may be used directly for making monolithic linings, or serves as intermediate product in the manufacture of bricks. It has to be sufficiently dense and water resistant. 

Mcdifler, in glass structure, 59, 62 Modulus of elasticity, see elasticity modulus Molar volume, 82—83 Molybdenum silicide, 345, 346, 416 Monolithic lining, 391 Monticell ite, 240 Monfmorillonite, 33 Mullife, 38-42, 232, 372 in porcelain, 304—306 refractories, 373 Multi-chamber kiln, 298—299... 

Fireclay refractories are divided into several groups according to their properties and quality. The main criteria are refractoriness, AI2O3 content, porosity and strength. The complex of properties then determines the field of application. In addition to shaped ware, granular fireclay mixes are also manufactured for the preparation of mortars in furnace construction, for repairs or for monolithic linings. 

Every refractory has a limited service temperature, or maximum temperature. Above these temperatures brick linings are used. The cutoff of refractory in lieu of brick is about 1800°F. Bricks have the capacity to seal and return to shape after heating without spalling. Sohd monolithic linings do not. In addition, bricks can be made in thicker sections than can be cast from refractory. 

The cracks formed in monolithic linings above these temperatures are too severe for the material to recover. In the early day of FCC units, the regenerators and reactors were brick lined, like furnaces, because the technology of gunnited and cast linings was not capable of withstanding the service. Brick linings are still utilized in a variety of applications. Shapes are available to conform to cylindrical shapes of containers most commonly used in these vessels and equipment... 

Vib-cast materials must be cast with an internal form that must be removed later. This is costly but necessary. The materials are cast with very little water so must be vibrated during casting to remove air bubbles to ensure a monolithic lining without voids. This material has been perfected as an alternative to dual component systems without the inherent weaknesses of the dual component system, that is, the loss of biscuits due to vibration and wear. 

Key-in. To undercut all or part of the surrounding sound refractory to provide a physical key for the repair to a monolithic lining. 

Monolithic linings are a relatively recent development and consist of unshaped refractory products [3]. There are two basic types of monolithic linings castable refractory and plastic refractory. 

Incinerators used for the disposal of municipal waste rely heavily on various monolithic linings. In the primary combustion chamber, the entrance section is lined with an abrasion-resistant castable. The main section is usually lined with a high-alumina plastic gurmed material, which is backed with an insulating castable. The ducting that connects the primary and secondary combustion chambers is lined with a dense castable material, and so is the secondary chamber. The ducting that connects the dust collectors to the stack is made from an acid-resistant castable. 

A variety of doloma-based monolithic materials are designed to be used in conjunction with brick, and also monolithic lining materials or for maintaining and patching vessel linings. 

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