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...

Production Process for Shaped Refractories Feb03

Production Process for Shaped Refractories...

Production Process for Shaped Refractories Refractory products can be shaped (formed) or shapeless (monolithics/castables).  They can be made of acidic, neutral, basic or composite materials. The materials used for the production of refractories may or may not contain additives. Further shaped refractories can be made in several shapes and are usually called refractory bricks. Typical production flow used in the process of the production of refractories is given in Fig 1. Fig 1 Typical flow in the production process for refractories  Shapeless refractories are normally dispatched from the refractory manufacturing plant not as a refractory but as refractory materials which become refractory only after it undergoes mixing, forming, aging, drying, and preheating etc. at the site of use. This means that in case of shapeless refractories, a part of the process in the manufacture of shaped refractories shifts to site of use. The fundamentals of refractory bricks manufacturing have not changed over time. However, technological advancements have made contemporary brick plants substantially more efficient and have improved the overall quality of the products. The manufacture of these refractories is based on knowing which combination of chemical compounds and minerals will give the produced refractories its needed properties such as refractoriness, thermal stability, corrosion resistance, thermal expansion, and other important qualities. A more complete knowledge of raw materials and their properties, better control of firing, improved kiln designs used for firing of green refractories and more advanced mechanization have all contributed to the advancement of the refractory brick industry. The technical objectives of manufacture of a given refractory are to obtain its properties and performance for an intended application. For fulfilling these objectives, the basic components of the refractory manufacture consist of proper selection of raw materials, processing methods, and maintenance of technological parameters during...