pouring molten material onto refractory materials

Refractory, Definition, Types, Materials and Applications, a Guide

Refractory materials are used in some high-intensity and highly industrial applications, requiring robust protective materials. These applications range from furnaces and kilns to incinerators, and even reactors. They’re used to make crucibles and similar uses like moulds for casting glass, metals and for flame retardent and heat deflecting surfaces even as high temperature as rocket launching structures. Here we’re going to explore a number of aspects that make up these materials and their uses.

But first, there are main definitions, but let’s give a quick answer on exactly what these materials are...

What are Refractory Minerals?

The definition would be minerals or synthetic, inorganic crystalline materials that have a high degree melting point. During exposure to high temperatures, they are resistant to deformation and to any softening. Refractories are classified as either acid, basic, or neutral.

But what are these materials? Ok, first let's go through what we deal with in our product range, that will hopefully give you some idea on the subject, and some confidence that we know what we're talking about.

African Pergmatite deal with the type of base materials you'd find in most refractory products. Most notably the following products listed below...

Coal Dust

Among lots of other applications across many types of industries, coal dust is used in the manufacturing of refractory bricks.

Refractory Chrome Flour

Used in the production of chrome magnesite bricks by way of a Refractory Cement Mix, these bricks are then used in the construction of certain furnaces and kilns.

Refractory Chrome Sand

Used in the production of chrome magnesite bricks, these bricks are most commonly used in the construction of certain types of furnaces and kilns.

Glass Powder

Glass Powder is widely used in the foundry industry as a formulation in fluxes and in the manufacture of tundish liners. A tundish acts as a reservoir and a distribution channel in the continuous casting of Steels (CC).

These materials are usually referred to as non-metallic materials which have specific characteristics - which allow them to be used in high-temperature environments. Let’s take a further look at these heat resistant materials in general...

Refractory made products like bricks and tiles

What Are the Classifications of Refractory?

The chemicals in this material are mostly classified by their oxide compounds, the type of element is grouped according to where is appears in the periodic table.

Most oxide compounds of elements based on the left-hand side of the periodic table consist of basic characteristics, while those on the right hand have more acidic characteristics. Those in the middle simply have what called neutral characteristics.

These materials are classified by two factors. One is their chemical properties and the other is their physical properties.

In physical classification they’re usually grouped according to the following criteria or appearance…

Shaped refractory such as the factory brick or insulating fire brick
Unshaped or monolithic refractory. Eg mortar, castable, or lightweight castable, plastic, gunning mixes, ramming mixes, spraying and coating mixes
Fibrous refractory material - such as ceramic fiber

On the chemical side of classification, it is grouped into basic, acidic or neutral. These also follow the characteristics outlined in the periodic table mentioned previously.

So silica, for example, would be classed as acidic, while, magnesium-based compounds would be classed as a basic class. Alumina content, for example, would form a neutral type.

Shaped Refractory

Here are some examples based on their appearance classification.

● Fireclay.
● Silica brick
● High alumina
● Magnesite
● Chromite
● Zirconia
Various base substances within these example categories might be coal dust, refractory chrome, refractory chrome sand, and glass powder.

With these substances, there are variations within each type, so if we take the typical example of fire brick, these are broken down into 5 sub-groups of classification based on their refractoriness. Namely:

● Super Duty (PCE 33)
● High Duty (PCE 31)
● Medium Duty )PCE 29)
● Low Duty (PCE 15)
● Semi Silica (S10, > 72%)

These are related to the softening temperature of the material. So, therefore, based on these criteria, these are recommended in low-temperature environments. Typical scenarios for this might be…

● Calciner
● Cyclone
● Inlet Zones
● Coolers in Cement Kilns
● Backup lining in steel and glass applications

There are other criteria applied to these materials too, such as classifications by service temperature and bulk density and other variable temperatures such as thermal conductivity, load-bearing, and insulating properties.

Pouring molten material into refractory moulds made with iron chromite

Fibrous Refractory Materials

Quite simply, these materials usually take the form of boards and in some cases pliable blankets. They typically provide high-temperature insulating materials. Fire blankets are one common example of a fibrous application.

Unshaped or Monolithic Refractory Materials

These materials are normally classified by their application use. This could be a mortar, casting, gunning, ramming, and others use.

Refractory mortar, for example, is made up of fine particles of heat resistant materials which are used as a binding material, used in binding bricks.

There are two types of mortar, heat setting mortar which is heated up to 1000 degrees centigrade to create a bond in the bricks, and the other is air setting mortar which is chemically bonded and hardens at room temperature. This second type of mortar is used more in applications needing load bearing such as kilns, towers, stacks, roofs, etc.

So there are two physical types of mortar, dry mix or ready mix. The mortar is mixed with dry mix mortar before applying, whereas wet mix is ready to use upon opening.

Another familiar type is castable. The uses of castable applications are that it can be applied to difficult and complex areas. There are five groups of castable

● General Castable
● Low Cement Castable
● Ultra-Low Cement Castable
● No Cement Castable (especially used for organic binding)
● Insulating Castable (low Heat Loss Applications)

Castable material is carefully selected based on its variable characteristics, depending on the application it is needed for. These criteria would typically depend on characteristics such as…

● Refractoriness
● Resistance to Abrasion
● Strength
● Load-Bearing Capabilities
● Thermal Conductivity
● Thermal Shock Resistance
● Chemical Resistance

Other types of refractory materials are often named after their specific applications and are usually selected based on their specific application needs.

Type of RefractoryApplication
Gunning MixFor applications requiring gunning machines for applying the material
Ramming MixWidely used in the base of electric arc furnaces
Spraying MixFor spraying applications with special spraying machines
Coating Materials Where coating methods are involved in the application
Patching MixManual patching work
PlasticSemi-wet and ready-mix applications for reparation uses in steel industries

Typical Applications for these Materials

Refractory Bricks Applications
We provide the materials to create specific shaped and custom bricks.

Refractory Lining Applications
Often used in blast furnaces and cement rotary kilns, using shaped and unshaped materials.

Boiler Refractory Applications
As the name suggests, these are used in heat retention for boiler applications. Again using fibrous materials.

Kilns in which refractory bricks are used

Refractories in Consumer Applications

We mentioned fire blankets already, but other common forms of low-level refractory material use that consumers will be able to relate to would be examples like the basic fire bricks that are used to insulate around ovens and kilns.

For those that have a fireplace within their homes, it’s very likely that the bricks and possibly the mortar around your fireplace would be made using these materials.

The types of materials used in consumer goods that have been made using these materials would be those where materials have been shaped or reformed. A good example of this would be glass bottles, where special heat treatment is applied within a glass manufacturing plant.

African Pegmatite Refractory Materials

Typical examples of refractories that we provide for industrial use are as follows...

Chrome Flour

Used in the making of blends for ladle sand and nozzle sand. Also used in making a variety of bricks. Chrome flour is used in the production of chrome magnesite refractory bricks, these kind of bricks are are mostly used in the construction of certain types of furnaces and kilns. It has a highly corrosion-resistant nature to it which prolongs the life of the kiln. Chrome flour is also used to produce magnesia chrome refractories. These types of refractories are used in non-ferrous metals like copper, lead, and even zinc.

In stainless steel production environments, filler sand - made with chrome flour, prevents molten steel from settling inside any tap holes and solidifying. The chrome flour refractory allows this solution to be effective at high temperatures with long processing times.

Chrome Sand

Used in making blends for ladle sand and nozzle sand. Also used in making bricks. Due to its highly corrosion-resistant nature, chrome sand is also used to produce magnesia chrome refractories. magnesia chrome refractories are used in non-ferrous metals like copper, lead, and zinc.

Fller sand made with chrome sand also prevents molten steel from settling inside tap holes and solidifying (like chrome Flour). And chrome sand also allows this solution to be effective at higher temperatures with long processing times.

Coal Dust

Used in the production of bricks. Refractory bricks have many uses around the world, across many industries, uses include open hearth furnaces, electric arc furnaces, metallurgy furnaces, cement rotary kilns, as well as glass kilns. Coal dust provides the thermal insulation necessary for these bricks to perform as needed.

Glass Powder

Glass Powder in varying granular grades is widely used in the foundry industry as a formulation in fluxes and in the manufacture of tundish liners. A tundish acts as a reservoir and a distribution channel in the continuous casting of Steels (CC).

Plus other specialist materials.

Conclusion

We hope this has been useful in helping you to understand what these type of materials are and their typical uses. At African Pegmatite we provide the base refractory materials used in all these applications. If you’d like to know more then contact us, we will be happy to discuss your material requirements.