Insulation Refractory Bricks...

Insulation Refractory Bricks  Insulating refractory brick (IRB) is the term used for heat insulating bricks and  covers those heat insulating materials which are applied up to 1000 deg C. IRBs are often mistakenly referred to as rear insulation materials. These bricks are assigned to the group of lightweight refractory bricks and are manufactured on the basis of naturally occurring lightweight raw materials. IRB is a class of brick, which consists of highly porous fireclay or kaolin. IRBs are lightweight, low in thermal conductivity, and yet sufficiently resistant to temperature to be used successfully on the hot side of the furnace wall, thus permitting thin walls of low thermal conductivity and low heat content. The low heat content is particularly important in saving fuel and time on heating up, allows rapid changes in temperature to be made, and permits rapid cooling. IRB is characterized by the presence of large amount of porosity in it. The pores are mostly closed pores. The presence of porosity decreases the thermal conductivity of the insulating bricks. IRBs  were developed in the 1930s, and they were the predominant form of insulation until the development of insulating castable and fiber refractories. There are two types of bricks namely (i) bricks based on clay and gypsum using the burnout of sawdust to create high porosity (and thereby provide better insulating value), and (ii) bricks based on lightweight aggregate and clays. Like all alumina-silica brick, IRBs have a duty rating (service limit). Over the years, IRBs have been made in a variety of ways, such as mixing of organic matter with clay and later burning it out to form pores; or a bubble structure incorporated in the clay-water mixture which is later preserved in the fired brick. IRBs are characterized by the presence...

Basic Shaped Refractories...

Basic Shaped Refractories  Basic shaped refractories are those refractories which have resistance to corrosive reactions with chemically basic slags, dusts and fumes at elevated temperatures. They are both MgO and CaO based refractories or in combination between them or in combination between MgO and Cr2O3. These refractories belong to MgO- CaO equilibrium system as shown in Fig 1. Fig 1 MgO-CaO equilibrium system  Broadly basic refractories falls into one of the following five compositional categories (Fig 2). Products based on dead burned magnesite (DBM) or magnesia. These products are known as magnesite bricks. Products based on DBM or magnesia in combination with chrome containing materials such as chrome ore. Chrome containing magnesite bricks with about 5 % to 15 % Cr2O3 are known as magnesite chrome bricks while those with 15 % to 30 % chromium are called chrome magnesite bricks. DBM or magnesia in combination with spinel. In these basic bricks magnesia-rich spinel (MgO.Al2O3) replaces chrome ore. These bricks are called magnesite spinel bricks. DBM or magnesia in combination with carbon. These bricks are known as magnesite carbon bricks. Dolomitic products. These bricks are known as sintered dolomite bricks. Fig 2 Categories of basic shaped refractories based on composition  Basic refractories are characterized by an extremely high refractoriness and good resistance to basic slags. Compared to fireclay bricks they do not have glassy phase. These refractories have low resistance both to thermal shocks and creep at temperatures close to 1500 deg C. The chemical-physical characteristics together with a very high thermal capacity and thermal conductivity make basic refractories ideal refractories for steel making processes. Hence basic refractories received increased importance with the introduction of basic oxygen steel making process. One of the more important types of magnesite bricks are those which have low...

Tundish and its role in Continuous Casting Sep28

Tundish and its role in Continuous Casting...

Tundish and its role in Continuous Casting Continuous casting of steel is a widely used process and an important step in the production of steel. The share of continuously cast steel around the world has increased significantly in the last 35 years or so. Presently this share is above 95 percent. However, concurrent with this increase in production levels, there are stringent quality requirements that have become crucial in the face of progressively increasing throughputs of continuous casting machines and larger dimensions of the cast products. In the process of continuous casting, to transfer liquid steel from a steel teeming ladle to the mould, an intermediate vessel, called a tundish, is used. A tundish is a rectangular big end up refractory lined open container which may have a refractory lined cover on the top. The tundish bottom has one or more holes with slide gate(s) or stopper rod(s) for controlling the metal flow. It is used to feed liquid steel into the copper moulds of a continuous casting machine, so as to avoid splashing and give a smoother flow. The tundish being a reservoir of the liquid steel ensures the feed of the liquid steel to the continuous casting machine during the change of steel ladles, thus acting as a buffer of liquid steel. It smoothens out flow, regulates steel feed to the mould and cleans the metal. Metallic remains left inside a tundish are known as tundish skulls and need to be removed, typically by mechanical means (scraping, cutting). Scrap recovered in this way is ordinarily recycled in the steelmaking process. The tundish is required to deliver the liquid steel to the moulds evenly and at a designed throughput rate and temperature without causing contamination by inclusions. The number of moulds is normally 1 to 2...