Monolithic Refractories...

Monolithic Refractories  Monolithic refractory is the name normally given to all unshaped refractory products, the word monolithic coming from the word monolith meaning ‘big stone’. Monolithic refractories are special mixes or blends of dry granular or cohesive plastic materials used to form virtually joint free linings. They are unshaped refractory products which are installed as some form of suspension that ultimately harden to form a solid mass. Most monolithic formulations consist of large refractory particulates (an aggregate), fine filler materials (which fill the inter particle voids) and a binder phase (that gels the particulates together in the green state). Monolithic refractories represent a wide range of mineral compositions and vary greatly in their physical and chemical properties. Some are low in refractoriness while others approach high purity brick compositions in their ability to withstand severe environments. Monolithic refractories are replacing the conventional type fired refractories at a much faster rate in many applications including those of industrial furnaces. Monolithic refractories are used to advantage over brick construction in different type of furnaces. Their use promotes quick installation, avoid delays for the manufacture of special brick shapes. Use of monolithics frequently eliminates difficult brick laying tasks, which may be accompanied with weakness in construction. They are of major importance in the maintenance of furnaces because substantial repairs can be made with a minimum loss of time and, in some cases, even during operations. Under certain conditions, monolithic linings of the same composition as firebrick provide better insulation, lower permeability and improved resistance to the spalling effects of thermal shock. With little or no preparation, monolithic refractories can be applied to form monolithic or joint free furnace linings in new constructions or to repair existing refractory lining. Other major advantages of monolithic refractory linings are as follows. It...

Refractory castables

Refractory castables Refractory castables comprise a large and diverse group of materials in the family of monolithic (shapeless) refractories. Their use has grown significantly in the past 30 years. Progressing from simple mixes, refractory castables today comprise some very complex and technical formulations, finding use in a variety of very  demanding and severe applications. Refractory castables are premixed combinations of refractory aggregates, matrix components or modifiers, bonding agents, and admixtures (Fig 1). They are mixed with a liquid (usually water) at the point of installation and vibrated, poured, pumped, or pneumatically shot into place to form a refractory shape or structure that becomes rigid because of hydraulic or chemical setting. The majority of refractory castables use calcium aluminate cement as the bonding agent though in recent years other bonding agents have also been developed. All castables have refractory aggregates and matrix components which allow their use to temperatures up to 1850 deg C. Fig 1 Components of refractory castables  Refractory castables are classified in several ways. The primary classification is based on chemistry which separates the refractory castables based on alumina and alumino-silicate aggregates from the castables based on basic refractory oxides such as magnesite and dolomite. Also this division is fundamental in that different bonding agents are utilized in each category. Alumina and alumino-silicate refractory castables are further classified in several ways based on the attributes such as chemistry and/or mineralogy, alumina content/refractoriness ( super duty, 60 % alumina etc.), mineral base ( mullite, fused silica etc.), density/thermal insulating value (dense, medium weight, light weight/insulating etc.),  cement content ( conventional, low cement, and ultra low cement etc.), and flow/placement characteristics (vibrating, casting, free flow, shotcrete etc.). The proportions of each components (refractory aggregates, matrix components, bonding agents, and admixtures) used in the refractory...