What are the Insulation Refractory Raw Materials?

The main purpose of heat-insulating refractories made of heat-insulating refractory raw materials is to reduce the heat dissipation of high-temperature kilns, reduce the weight of the kiln body, and reduce the external temperature of the kiln body. Insulation refractories play a vital role in high-temperature kilns and are generally used in conjunction with heavy refractories. Forming a multi-layer composite structure can effectively improve the service life of the kiln, and at the same time save energy and protect the environment.

Thermal Insulation Refractory Raw Materials for Thermal Insulation Refractories

1. Hollow ball

Hollow sphere refers to melting alumina or zirconia and other raw materials into a liquid state, blowing the high-temperature molten liquid into small droplets with compressed air, and forming hollow spheres under the action of surface tension and centrifugal force. The common materials are alumina hollow balls, zirconia hollow balls, etc. Hollow balls of these materials are widely used in refractory materials and can be used to produce hollow ball bricks and thermal insulation castables. Because the hollow spheres of these materials have high purity, low impurity content, high strength, and low thermal conductivity. Therefore, it is generally used to produce high-grade thermal insulation materials, which have good high-temperature performance and thermal insulation performance, and can also be in direct contact with flames.

Hollow Ball

2. Floating beads

Floating beads refer to the hollow microspheres of fly ash that can float on the water surface, which are separated from the coal powder ash discharged from the pulverized coal combustion furnace, and are mostly off-white. The chemical composition of floating beads fluctuates greatly, which is closely related to the composition of coal powder. The particle size is usually between 20-250μm, the specific surface area is 3000-3200cm2/g, and the bulk density is generally 250-400kg/m3. Floating beads are generally used in thermal insulation castables, because of their high cylinder compressive strength and low thermal conductivity. Therefore, the purpose of introducing it is mainly to improve the strength of the thermal insulation castable and reduce the thermal conductivity.

Floating Beads

3. Diatomaceous earth

Diatomaceous earth is a siliceous sedimentary rock of biological origin. The size of a diatom frustule is about 5-400μm, contains a large number of tiny pores, and the porosity reaches more than 80%, so it has excellent heat insulation performance. The bulk density is an important standard to measure the quality of diatomite, the smaller the bulk density, the better the quality. Diatomaceous earth is commonly used in the production of diatomite bricks and has good thermal insulation properties. But the use temperature should not be higher than 900°C, otherwise, the silicon dioxide in the diatomite will be transformed into cristobalite and lose its thermal insulation performance. In addition, diatomaceous earth can also be used as a filler in amorphous materials.

Diatomaceous Earth

4. Perlite

Perlite is acidic lava from a volcanic eruption, which expands at a high temperature of 1180-1350°C to form expanded perlite rich in closed and open pores, and the expansion multiple is more than 7-30 times. The bulk density of expanded perlite is small, generally, between 40-200kg/m3, the thermal conductivity is extremely low, the safe use temperature is below 800°C, and it has certain fire resistance. Therefore, expanded perlite is widely used in thermal insulation refractory materials. It is used in a very large amount in thermal insulation castables, mainly to reduce the thermal conductivity of thermal insulation materials. At the same time, massively expanded perlite can provide a certain strength, and is widely used in the petrochemical industry for kiln and pipeline insulation. In addition, expanded perlite is also used to make some shaped products.

5. Ceramsite

Ceramsite is a spherical porous material made of low melting point clay, shale, fly ash or coal gangue as raw materials and calcined. It has a smooth and hard surface, a honeycomb-like interior, low thermal conductivity, and high strength. It is a high-quality artificial lightweight raw material and is mainly used as aggregate in thermal insulation refractory castables.

6. Vermiculite

Vermiculite is a typical layered silicate mineral composed of biotite, phlogopite, and other minerals. Its chemical composition fluctuates widely, mainly depending on the composition of the mica. Vermiculite has the characteristics of thermal expansion, which makes it used in the field of refractory materials. When the vermiculite is heated to 200°C, it begins to expand in volume, and the bulk density decreases to 600-900 kg/m3. After complete burning, the bulk density can be reduced to 100-130 kg/m3. The thermal conductivity is also small and has good thermal insulation performance. The maximum service temperature of vermiculite can reach 1100°C, so it can be introduced in the form of granules or fine powder, and it can be made into vermiculite bricks or thermal insulation castables and applied to places with slightly higher temperatures.

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Gas Powered Furnaces

Compared to the industrial ovens, Industrial furnaces are enclosed structures that generate high heating temperatures in the heat chambers on metals and materials of high melting points. Natural gas furnaces are economical that create a high heat by burning propane or natural gas to generate heat used for high temperature applications. Heat transmission is by radiation from the wall of the furnace chamber that is heated. Various industries that find these furnaces suitable are glass manufacturers, ceramic firing, metal hardening, brazing, sintering, carburizing, stress relieving and solution treatment. These furnaces are multi-utility equipment that find wide application and are available in various types and configurations.

Features of the high temperature gas fired furnace are worth considering. Distribution of temperature is even and uniform. Initial operating costs are quite economical, as this eliminates the costly electrical heating elements. Operational hazards reduced by well-developed modern safeguard systems and overheating also is controlled by protecting safeties. Rugged in construction normally with stainless steel adequately refractory lined, this has flexibility by offering wide range of operation.

Centrifugal blowers used to give a steady airflow pressure and the modulated burner system offers a constant gas-air mix ratio for ideal firing by automatic sequence control that regulates the industrial variable speed centrifugal blower also. Refractory lined doors manually operate either by hand or by pedal and are spring loaded to ease opening or closing using minimum effort.

High induced sparks ignite the gas-air mixture to establish flame sensing which the photocell disconnects the supply to spark-plugs while the flame continues with modulated intensity by the sequence controls. The temperature is maintained to constant levels by this automation, either by regulated supply of combustion mixture or by having different burners all of which are controlled automatically by sequence controllers. Thus, steady temperature is maintained throughout the furnace all the time of operation.

The fire-box or the combustion chamber is made of a metal casing to retain the form but cannot withstand the temperature. So refractory lining is given by alumina, which provides longer service life than the soft fire bricks used for insulation refractory purpose. Refractory clay that could be cat to the required form gives the furnace the necessary insulation against high temperature, thereby enhancing the efficiency of the furnace.

Gas furnaces are mechanically very simple and are best for melting operations. They are easy to install and operate at the same time very reliable. Depending on the availability of the gas, this furnace becomes ideal with its cost effectiveness. Automation makes the operation easier and the production of heat is substantial making the melting process faster. Loss of metal avoided because of the crucibles that protect exposure of metals to direct flame avoiding extra oxidation.

Nevertheless, the temperature of the metal in the furnace cannot be regulated precisely as the gas overshoots the metal temperature in melting process and allow metal temperature to drop below the desired pouring limit. The gas fired crucible furnace is also not accurate in keeping the temperature.

To circumvent these limitations gas-electric dual energy crucible furnace is evolved that quickly melts the metal in the crucible and the temperature is maintained precisely. Thus, these hybrid furnaces became very popular as they are economical and are available in sizes to the requirement of the user.

 

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