What are Refractory Materials?
Refractory material is any material that has an unusually high melting point and that maintains its structural properties at very high temperatures.
Composed principally of ceramics, refractories are employed in great quantities in the metallurgical, glassmaking, and ceramics industries, where they are formed into a variety of shapes to line the interiors of furnaces, kilns, and other devices that process materials at high temperatures.
Below is a list of the most common refractory materials:
Castable refractory products are non-metallic materials that have chemical and physical properties used for creating heat-resistant structures that retain and insulate. Due to their high resistance to heat and thermal shock, you can use castable refractory cements and other products to build kilns and furnaces. Refractory castables can be used to create the monolithic linings within all types of furnaces and kilns. They can be further classified into the following sub-categories: conventional, low iron, low cement, and insulating for installation either by gunning or manually. There is a wide variety of raw materials that refractory castables are derived from, including chamotte, andalusite, bauxite, mullite, corundum, tabular alumina, silicon carbide, and both perlite and vermiculite can be used for insulation purposes.
i. CONVENTIONAL DENSE REFRACTORIES
Conventional dense castables are created with high alumina cement, and can withstand temperatures from 1300oC to 1800oC. These refractory castables are great for common furnace applications, burner blocks, speciality muffle furnaces and boiler work. Resistance is a key quality that varies with the choice of materials, resulting in abrasion, thermal shock and slag attack. Casting and gunning techniques are the method of installing the materials. For the ease of castable placement, gunning materials and water are combined together at the gunning equipment’s nozzle. This is a great method of placement for bulk materials, in cases when circumstances make formwork overly time consuming or simply impractical. In general, the method of installation will depend on cost and accessibility.
Another product that we supply is the castable refractories that are low density. These insulating castables pose very low thermal conductivity and are utilized for either high temperature face work or when used for a backup lining, which is found behind dense castables or brick work. Here, the insulating castables are able to decrease the lining’s overall density or the cold face temperature. Their strength, which ranges from low to medium, is based on the fact that their density is low and is the main reason that they are not resistant to abrasion. They are most suitable where they do not have to stand up to much wear and tear.
iii. LOW CEMENT
This type of refractory castable is prepared with a lower amount of cement than the standard dense castable is normally created with. Low cement castable refractories fluctuate in alumina content, which provides exceptional physical properties, including low porosity, great abrasion properties and high vigour. These products will commonly necessitate installation that is controlled, however, the big advantage of low cement castables is that they are easily pumped into position, and some may not require vibration, because they are free flowing.
Refractory Cement / Mortars
There are various types of refractory cement in Kenya. Insulation World Kenya Limited supplies the 3 main types refractory cement in Kenya. These are Fondu Cement, Maxheat K and Maxheat A. The three types of cement are classified according to their alumina content which determines the range of temperature which they can withstand.
i) Max50/ Fondu Cement
Max50/ Fondu Cement is a calcium aluminate-based hydraulic binder and contains calcium silicates, as opposed to Portland Cements. Its has the properties of high early strength and good refractoriness.
Fondu Cement Properties
- High temperature resistance (up to 1000°C)
- Has 3 to 30 minutes setting
- Corrosion Resistance (pH ≥ 4)
- Suitable in very temperatures (-10°C)
- Quick activity resumption (activities can be resumed after 6 hours
Fondu Cement Applications
Fondu cement in Kenya is applied in various places such as incinerator walls, fences, barbecues fire drill areas, sewage and wastewater systems, seaside projects, ovens, industrial floors, agricultural buildings, lintels, sealing hinges etc.
ii) Refractory Castable Maxheat K
Another common refractory cement in Kenya is Maxheat K. It is premixed refractory compositions which can cast into any require shape and size. It is mostly preferred due to its high thermal and shock resistance.
MaxHeat K Specifications
- Material: – Refractory Castable
- Service Temperature: – 1600°C
- Type: – 56% Min – 60% Max Alumina Dense castable
- Nature of Bond: – Hydraulic
- Installation: – Vibration Casting
- Maximum Grain Size: – 5 mm
- Water required for casting: – 11 to 12.5%
Applications of Maxheat K
Maxheat K refractory castable cement in Kenya is applicable in General purpose uses, Blast furnace, Foundries, Forge furnace, Tunnel kilns, Heat treatment furnace car tops, Electro phosphorus furnace, Sock pit cover construction etc.
iii) Refractory Mortar/ Fire Cement
Refractory mortar is a specially engineered mixture of sand, calcium aluminate, cement, and fireclay. It is used to lay firebrick in places that are exposed to extremely high temperature. The refractory mortar is utilized only to build fire places and shall not be applied on hot faces.
Refractory mortar cement , which is a mixture of water, cement, and sand, has a higher water-to cement ratio than concrete. It has a thicker consistency which makes it a great adhesive and bonding agent for bricks and tiles. Mortar mix can be used for construction and repair of brick, block, and stone for barbecues, pillars, walls, tuck-pointing mortar joints, and planters.
Refractory fire bricks
A refractory brick is designed mainly to withstand high heat, but should also usually have a low thermal conductivity to save energy. Usually dense bricks are used in applications with extreme mechanical, chemical, or thermal stresses, such as the inside of a wood-fired kiln or a furnace, which is subject to abrasion from wood, fluxing from ash or slag, and high temperatures. Dense refractory bricks have a high thermal mass which is sometimes a useful property in that they will retain heat.
Firebricks are the most common form of dense refractories. They are usually made from hydrated aluminium silicates and small amounts of pother elements.
Firebricks/refractory bricks are one of our main refractory material used mainly in steel mills, boiler houses, lining furnaces, kilns, fireboxes, ovens, fireplaces and other related applications.
We have two types of fire bricks:
- 40% Alumina Fire Brick-
- 70% Alumina Fire Bricks
Our firebricks measure 230mm by 115mm by 75mm and are bauxite based.
A fire brick is a block of refractory ceramic material used in furnaces, kilns, , and . Refractory bricks usually contain 30-40% alumina and the primary raw material is usually chamotte with other materials. The maximum service temperature increases with increasing alumina content and kiln bricks can be obtained with an alumina content of 80% and above.
Less dense refractory bricks (Insulating Fire Bricks)
In other, less harsh situations, such as a natural gas fired kiln, more porous bricks are a better choice, usually referred to as Insulating bricks . They are weaker, but they are much lighter, easier to form, and insulate far better than dense bricks. In this case they have a low thermal mass and so cannot be used to store heat. Insulation bricks have a better thermal shock resistance than dense firebricks but the main disadvantage is their low strength. The insulation property of these bricks usually comes from perlite or vermiculite. As with the dense refractory bricks there is a range of grades corresponding to different maximum service temperatures. The most common is Grade 23 – 1260oC.
Zirconia refractories useful as high temperature construction materials for furnaces and kilns because of its very high strength at room temperature. The thermal conductivity of zirconia refractories is much lower than most of other refractories, because of that it is used as a high temperature insulating refractory. Since it is not easily wetted by molten glass and because of its low reaction with molten glass, Zirconia refractories are one of the main refractory material for glass furnaces.
Zircon Refractory Bricks
Zircon Refractory Bricks are produced from natural zircon. Their main advantages are good slagging resistance, high load softening temperature, high performance to wear and good thermal shock stability. Zircon Refractory Bricks are mainly used for;
- Melting pools of Glass furnaces
- Regenerative chambers of Glass furnaces
- Solution erosion area in chemical industry furnaces
- Metallurgy kilns
Zircon bricks are mainly used in the glass industry. They are installed as lining for working ends and feeder channels in melting tanks.
Consequently, zircon refractories are only installed in the lower bottom courses of the melting tank with lower temperatures if soda – lime glass is being produced.
In addition, zircon refractories have an important function as separation layer between silica and fusion cast materials in order to prevent contact reactions.
In the glass industry bricks out of zircon and corundum are installed occasionally. Such bricks have higher corrosion resistance against glass than pure zircon and are also installed in glass contact areas or in the superstructure of glass melting tanks.
The Zircon – corundum materials are also advantageous for hot repair work due to their more favorable thermal shock resistance in comparison to the fusion cast materials usually installed.
Refractory mixes on a corundum –zircon base are often installed in bottoms of glass melting tanks as a monolithic bottom layer for the upper paving course out of fusion cast bottom plates.
Zircon bricks has a very high melting point of 2700˚C. Zircon bricks is a highly refractory material with good resistance to corrosion.