Dense refractory bricks

Firebricks are refractory products with an Al₂O₃ content of up to 50%.

They are manufactured from low-iron clays and pre-fired grog granules and are normally fired at temperatures of up to 1,300°C. Due to their relatively low gross densities, these grades exhibit significantly better thermal insulating properties. These properties make them suitable for use as brick linings for incineration plants operating at process temperatures of up to around 1,400°C, as permanent linings for metallurgical vessels and as an inexpensive lining variant for basic thermal applications.

The addition of phosphate to refractory clay products serves to inhibit the penetration of alkali compounds and increases resistance to infiltration by aluminium.

Dense firebricks, so-called „super duties“, are made of selected refractory clays and grog granules making pre-firing at high firing temperatures possible. This increases their high-temperature durability compared to standard grades and makes them largely resistant to CO atmospheres. This makes them ideally suited to applications where CO attack is expected, e. g. the brick backing of pig iron transport ladles.

HIGH-ALUMINA BRICKS with 60% Al₂O₃ are usually made of andalusite as the main raw material blended with other Al₂O₃- SiO₂ refractory raw materials as necessary in order to achieve the desired properties.

When converted into mullite at high process temperatures, andalusite exhibits a controllable increase in volume that works to counteract thermal shrinkage of the brick matrix and makes the grade suitable for use at high temperatures. Phosphate additives have both an infiltration-inhibiting effect and improve other properties too, such as wear resistance and general toughness.

High-alumina bricks at around 80% Al₂O₃ can be produced from a variety of different high-quality raw materials and therefore have a correspondingly wide range of properties and applications.

In principle, the average composition is close to that of the mineral mullite (approx. 72 % Al₂O₃, approx. 28 % SiO₂) in order to take advantage of its refractory properties (melting point 1,800 °C). The individual properties of the products are therefore predominantly determined by the raw materials used and their secondary components.

The raw materials can be alumina-enriched andalusite, bauxite, pre-fired mullite, tabular alumina or corundum and suitable mixtures thereof. These materials are used, for example, for the linings of incineration plants, to line vessels in metallurgy or corrosion-resistant undercasting frames for steel ingot casting, but also as high-quality kiln furniture.

High-alumina bricks containing between 85 and 99.5% Al₂O₃ are designed for specific requirements and therefore manufactured from raw materials with an especially high Al₂O₃ content.

These can be alumina-enriched bauxites, sintered or fused mullites, tabular aluminas or fused corundums. The high alumina content means they can withstand high temperatures, usually in combination with demanding thermo-mechanical and thermo-chemical environments, such as strongly reducing atmospheres, contact reactions with metals or melts as well as media containing fluorine.

The range of applications is correspondingly diverse and includes in carbon black reactors, in the hydrocarbon processing industry, as high quality feeding channels for ingot casting, environments exposed to media containing hydrofluoric acid or as high-quality kiln furniture. Grades with a high phosphate content are resistant to aluminium melts and inhibit so-called corundum formation.

Chromium oxide bricks are a product group composed of corundum or andalusite and chromium oxide pigment.

The high corrosion resistance of CR₂O₃ to aggressive media is why these products are predominantly used in hazardous waste incineration plants. Specific properties, such as thermal shock resistance, are tailored through the addition of selected additives.

High-temperature fired bricks based on partially stabilised ZrO₂ exhibit high-end properties with respect to temperature resistance (> 2,200°C) and are used for extreme high-temperature applications e.g. carbon black reactors.

As the ZrO₂ content increases towards a majority ZrO₂-based brick, these materials exhibit increased resistance to aggressive glass melts. The addition of zircon to aluminosilicate-based bricks results in increased resistance to alkalis.

High-alumina bricks with carbon are generally used in metallurgical vessels for transporting or processing pig iron, e.g. torpedo, pipe or converter-filling ladles.

The base raw materials are andalusite, bauxite or high-quality fused corundum. The primary carbon carrier is graphite that is bound using synthetic resin.

The bricks are manufactured either without extra additives or with the addition of SiC to form ASC bricks for high demanding zones. A special variant produced with the addition of magnesia (AMC) is suitable for use in steel ladle impact zones, for example.

SiC bricks are extremely versatile due to their high mechanical toughness, wear resistance, high thermal conductivity and good thermal shock resistance.

SiC products are resistant to non-ferrous metal melts, such as zinc, aluminium, copper and lead, and find use in such plants. The formation of a protective layer means that SiC grades withstand oxidation well.

What makes the reaction-bound bricks product group unique is that the binder phase is formed during the reaction firing. This allows bricks based on a variety of raw materials and different nitride compounds to be offered. Their outstanding physical and thermo-mechanical properties and very high resistance to chemical attack afford this product group its special status.

Examples of application for SiC-based products are the non-ferrous metals industry, acid-resistant construction sector and applications in general involving high levels of mechanical wear, for corundum-based materials, in the bosh of blast furnaces, in cupola furnaces and, depending on design, certain areas of iron and steel manufacturing plants.