What is a refractory material?
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.
The purpose of a refractory material is to withstand the high temperatures required in furnaces, kilns, incinerators, power plants etc without contaminating other materials and to conserve heat in the area where it is needed.
Below is a list of the most common refractory materials:
1. High-Temperature 90% Alumina Refractory Castables Cement (Service Temperature 1750-1810 degrees)
2. Medium-Temperature 60% Alumina Refractory Castables Cement (Service Temperature 1600)
3. Refractory Mortar 90K
4. Refractory Fire Bricks 230*115*75mm both 40% Alumina and 70% Alumina
5. FONDU Cement
6. Insulating Cement BLACKYT (Paste Form) for joining insulating bricks
7. Insulating Cement BLACKYT (Powder Form)
8. Binder Cement (ACCOSET) for joining fire bricks
9. Chrome Magnesite Bricks
10. Chrome Magnesite Cement
11. Insulating Bricks
12. Taper Bricks – Side Arch; End Arch
13. Hearth Blocks – 600*300*115mm
14. All Consumables for Continuous Casting Machine
15. Silicon Manganese 60/14
16. Acid Resistant Tiles & Mortar – For Pickling Plants (Acid wash)
17. Heat Resistant Adhesives
18. Heat Resistant Sealants/ Silicone
These are heavy with low porosity but high mechanical strength. The most common form of dense refractories are firebricks. Made from hydrated aluminium silicates with small amounts of other elements, they are versatile and relatively cheap. Firebricks with a higher alumina content are able to perform at higher temperatures. Refractories with an alumina content of 99% are known as corundum and are used in processes at over 1500°C such as pouring steel, glassmaking, ash melting, incineration and moulds for casting super alloys.
Insulating refractories have a higher porosity making them less dense and with low thermal conductivity. This increases efficiency and reduces the amount of energy required for the process at hand.
These are supplied in unshaped form to be cast, rammed or gunned into place on site. Casting refractories are also known as refractory concretes and contain high alumina cement. They are used in the iron and steel industries in kiln cars, boilers and to cover the floor, doors, walls and other surface areas where high temperature processes take place. Insulating castables contain lightweight aggregates such as vermiculite. They are weaker than standard castables.
Plastic refractories are supplied in clay like blocks which can be cut to size and rammed into place. They are designed for repairs to brick or monolithic linings and are also used in ladles and launders.
Insulation firebricks are made from fireclays with added alumina, for its refractory properties, and organic filler which burns away during firing to leave a lightweight and porous brick. Bricks are graded according to the temperature level they can withstand and are used for lining furnaces and kilns or as secondary insulation, flue linings, in soaking pits and reactor chambers, among others.
Refractory ceramic fibre, also known as alumina silicate wool, is a form of high temperature insulation wool. Spun from a mix of melted aluminium dioxide and silicon dioxide, the fibres are made into blankets, paper, rope, board and block modules. Lightweight with low thermal conductivity and excellent thermal shock resistance, ceramic fibre products are used for insulation in boilers and kilns, on kiln cars, in the crowns of glass furnaces and around expansion joints, to create seals around furnace doors, and as lining for reforming and pyrolysis in the petrochemical industry.
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.
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.
There are various types of refractory cement in Kenya. Citizen Cooling Solution 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.
CIMENT FONDU® 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
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.
Another common refractory cement (fire 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
Applications of Maxheat K
Maxheat K fire 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.
3. Maxheat A
Maxheat A is a castable cement in Kenya suitable for high temperature applications. Just like Maxheat K, It is premixed with refractory compositions which can cast into any required shape and size. It is mostly preferred due to its high thermal and shock resistance.
MaxHeat K Specifications
Applications of Maxheat K
Just like Maxheat K fire cement in Kenya, Maxheat A 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. However, its service temperature is higher than that of Maxheat K.
Refractory cement is used for building brick or stone fireplaces, barbecues or other installations which are subjected to intense heat. While refractory cement is similar to standard cement in how it is mixed, it differs significantly from standard cement in the use of one ingredient. Rather than using Portland cement for a cementing agent in the mixture, refractory cement uses a compound called calcium aluminate instead. This provides the heat-resistant properties needed.
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.
Mortar, 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.
A fire brick is a block of refractory ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. 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 eg in a pizza oven after the fire has been taken out. Kiln bricks are made by firing a clay based composition in the kiln until it is partly vitrified, and for special purposes may also be glazed. Refractory bricks usually contain 30-40% alumina and the primary raw material is usually chamotte with other materials.
We have two types of fire bricks:
Our firebricks measure 230mm by 115mm by 75mm and are bauxite based.
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 Insulation 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.