Spraying Construction Method of Rongsheng High Temperature Refractory Coatings

Refractory spray paint is used to spray new linings and can also be used to repair furnace pipes. Spraying construction method of Rongsheng high-temp refractory coating. It is an effective unshaped refractory material that is easy to construct, extends the service life of the kiln, and reduces the consumption of refractory materials. The material composition of refractory spray paint is basically similar to that of refractory castables of the same type. The difference is that the critical particle size of refractory aggregate is smaller, generally 3~5mm, and is constructed using spraying methods. The dosage of refractory powder, ultrafine powder, and binder is relatively large, generally 35~45%.

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Spraying Process of Refractory Coating

Spraying is carried out using a spray machine or spray gun. The material obtains considerable speed with the help of compressed air and is sprayed onto the sprayed surface through the nozzle, forming a strong spray layer. The key technologies of refractory spray coatings are mainly adhesion, bonding, strength, and sintering. This is also the basic characteristic that the material should have, otherwise the service life of the spray coating will be reduced. These characteristics are not only related to the quality of the material itself, but also affected by the spraying equipment, construction technology, and the state of the sprayed body.

The particles of refractory spray paint cannot be larger than 5mm. Because when it is larger than 5mm, the spray gun will be blocked and normal construction will not be possible. During construction, the refractory spray coating is sprayed 40-50mm into the pipe, and the spray coating can be quickly formed. Generally speaking, the rebound rate of refractory spray coatings produced by refractory spray coating manufacturers is 10%.

In refractory spray coatings, medium and fine particles can greatly improve the adhesion rate, but will increase peeling during drying. Coarse particles can make the repair layer more stable, but too many coarse particles will lead to a high rebound rate and increase the amount of material used. Therefore, the particle gradation must be reasonable and cannot exceed 5mm. Because it exceeds 5mm, the spray gun cannot spray. Reasonable gradation can best improve the construction and use performance of spray coatings.

High-Temperature Refractory Coatings

Refractory spray coatings are divided into light spray coatings and heavy spray coatings. The materials selected according to different use environments include corundum, high alumina, mullite, clay, SiC, magnesium, etc. Mainly used in hot blast furnaces, heating furnaces soaking furnaces, blast furnaces, flues and chimneys, etc. However, lightweight refractory spray coatings are relatively more expensive than heavy refractory spray coatings.

The density of heavy refractory spray paint is generally 1.6-1.8g/cm3. However, there are different requirements in different furnace pipelines. Especially the sintering machine pipes must be made much better than other parts. In other words, this part needs to use refractory spray paint with a density of 2.2g/cm3. Of course, the price of refractory spray paint for sintering machines will be much higher than that of refractory spray paint for other parts.

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What is Refractory Coating?

(1) Heavy refractory spray paint  

The bulk density of heavy refractory spray coatings is generally greater than 1.8g/cm3. Refractory aggregates and powders generally use aluminum silicate materials, with a critical particle size of 5 or 10 mm. Particle composition: 3~5mm is about 30%, 1~3mm is about 30%. Less than 1mm is about 40%. The binding agent is aluminate cement and water glass, plus additives. Generally, semi-dry method or false dry method is used for construction.

Main properties of heavy refractory castables. The medium temperature strength of CA-50 cement spray coating is reduced. However, water glass and phosphate spray coatings increase with the increase of heating temperature, and their bulk density is slightly lower than the same type of refractory castables produced by vibration molding.

In recent years, medium-heavy refractory spray coatings with a bulk density of 1.8~2.1g/cm3 have been developed. That is, on the basis of heavy materials, 3% to 6% expanded perlite or 5% to 20% porous light clinker is added. It is mainly used on the heat insulation layer of kilns and has good heat preservation effect.

(2)Lightweight refractory spray coating

There are many varieties of lightweight refractory spray coatings, mainly including clay, ceramsite, perlite and other refractory spray coatings. Lightweight refractory spray paint is mainly used for the thermal insulation layer of kilns, and can also be used for the working layer of tubular heating furnaces, flues and chimneys.

The critical particle size of refractory aggregate for lightweight refractory spray paint is 5mm. The particle gradation is: 3~5mm, about 19%~30%. 0.6~3mm is about 8%~14%. 0.088~0.60mm is about 30%~40%, and less than 0.088mm is about 25%~35%.

The main properties of lightweight refractory spray coatings. During the spraying construction process of refractory spray paint, the original particle gradation will be greatly changed due to the rebound and scattering of refractory aggregates and the splashing of refractory powder. Therefore, when the aggregate size requirements of the refractory spray coating are certain, in order to make the aggregate gradation of the actual spray coating meet the requirements, the original gradation before spraying must be adjusted to meet the requirements after spraying.

Spraying construction of Rongsheng Refractory Spray Coating

Before spraying paint, test spraying should be carried out in accordance with the construction instructions provided by the manufacturer for the brand of spray paint. To determine the appropriate parameters, such as wind pressure, water pressure, etc.

Several commonly used spray coatings

• (1) When spraying clay materials at room temperature, the aggregate particle size should be below 3.5mm. When the spray paint lacks viscosity, 2% clay should be added to improve its construction performance.
• (2) When spraying high-aluminum materials at room temperature, additives should be added to prevent falling and increase the density of reinforced metal parts.
• (3) When lightweight insulation materials are used for spraying, lightweight aggregates with higher strength should be used, and appropriate amounts of asbestos and clay should be added. Aggregates with low strength, brittle under pressure and friction, or elastic aggregates are not suitable for spraying. The volume density of lightweight thermal insulation spray paint should be between 0.7~1.3t/m3.

Reinforcement metal parts

Spraying construction must be reinforced with metal supports. Metal supports should have the characteristics of simple shape, small size, and reliable performance. Generally, it should be made of round steel.

When the thickness of the spray coating is 35~75mm, metal mesh should be used for reinforcement. The diameter of the metal mesh is Φ3.2~4.2mm, and the mesh size should be 1.5 times the thickness of the spray coating. And it is fixed on the furnace wall by welding, binding, and crimping.

When the spray thickness is more than 100mm, round steel of 4~8mm should be used to make V-shaped or Y-shaped metal parts and welded to the furnace shell.

The installation distance of metal parts: the side wall part should be 3 times the thickness of the spray coating, and the top part should be 1.5~1.8 times the thickness of the spray coating. The distance from the front end of the metal anchor to the surface of the spray coating should be 50mm for the side wall and 25~30mm for the ceiling.

Process inspection before spraying

The following process inspections should be carried out before spraying refractory spray paint:

• (1) Before spraying, the installation position, spacing size, and welding quality of the metal supports should be checked and cleaned.
• (2) When there is a fixed steel wire mesh on the support frame, check whether the anchoring quality of the steel wire mesh meets the requirements. The upper, lower, left, and right sides of the steel wire should overlap one grid. The overlap shall not exceed three layers and the fasteners shall be oriented toward the non-working layer.
• (3) Check the sprayed surface. There should be no floating rust, dust accumulation, oil stains, or water immersion on the sprayed surface.

Spraying operations and adjustments

Refractory spray paint is sprayed onto the sprayed surface with a spray gun. Materials constructed by spraying are called refractory spray paint. Spraying is carried out using spray machines and spray guns. The refractory spray paint uses compressed air or mechanical pressure in the pipeline to obtain sufficient pressure and flow rate. Spray onto the sprayed surface through the nozzle to form a solid spray layer.

The spraying methods of refractory spray coatings are divided into three categories: wet method, dry method, and flame method. When constructing refractory spray coatings, appropriate construction plans for high-temperature coatings and refractory coatings can be specified based on actual working conditions. To extend the service life of the kiln lining.

How to Choose Honeycomb Ceramic Regenerator?

In recent years, honeycomb regenerative furnaces have developed very rapidly. Since the regenerator can be miniaturized and integrated with the burner, and each burner maintains its independence, it becomes a regenerative burner. It truly achieves extreme waste heat recovery and ultra-low NOX emissions. The energy-saving effect brought by regenerative combustion technology is very obvious. It can absorb the heat of high-temperature flue gas to the maximum extent and avoid heat waste. Honeycomb ceramic regenerator is the key and core component of regenerative high-temperature combustion technology.

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How to Choose the Honeycomb Ceramic Regenerator?

The selection of a honeycomb ceramic regenerator is very critical. Improper selection will cause blockage, burning, collapse, and other phenomena during use, causing the furnace temperature to rise slowly, failing to reach the temperature, and in serious cases causing furnace shutdown accidents. It affects production and increases gas consumption.

Therefore, when selecting a honeycomb body, in addition to considering the rapid cooling and rapid heating resistance of the honeycomb ceramic regenerator, load softening temperature, compressive strength, thermal expansion coefficient thermal shock resistance, and other indicators. The heat release characteristics of the honeycomb ceramic regenerator also need to be considered. It is necessary to select a honeycomb ceramic regenerator made of materials with a large specific surface area, large blackness, large heat capacity, and fast thermal conductivity. In this way, the honeycomb ceramic heat storage body absorbs and releases heat faster and more, and can effectively absorb the heat of the flue gas. Significantly increase the preheating temperature of gas and air, increase the combustion temperature of the heating furnace, and achieve the purpose of reducing gas consumption.

Silicon Carbide Honeycomb Ceramic Regenerator

The silicon carbide honeycomb ceramic regenerator is an improvement based on the formula of the corundum-mullite honeycomb ceramic regenerator. A certain amount of high-purity silicon carbide is added to improve the performance of the original honeycomb ceramic regenerator. Silicon carbide honeycomb ceramic regenerator combines the advantages of silicon carbide, zirconium chromium corundum, and other materials. It has the characteristics of good antioxidant, slag resistance, high-temperature resistance, high blackness, and fast thermal conductivity. Its high-temperature strength can be maintained up to 1600°C, making it the material with the best high-temperature strength among ceramic materials. Due to its fast thermal conductivity and high blackness, it has better energy-saving properties than a corundum-mullite honeycomb ceramic regenerator. According to relevant customer usage statistics, the use of silicon carbide honeycomb ceramic regenerators can significantly reduce the exhaust temperature of exhaust gas and reduce gas energy consumption by more than 5-10% compared with other honeycomb ceramic regenerators. Silicon carbide honeycomb ceramic regenerator is mainly used as the heat exchange medium for high-temperature regenerative industrial kilns above 1250°C.

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Large Holes and Big Eyes Honeycomb Ceramic Regenerator

The hole shapes of honeycomb ceramic regenerators often include square holes, round holes, hexagonal holes, etc., and the hole spacing is usually between 3-6mm. Among them, the hexagonal hole surface layout is more uniform and the structure is more stable. It is currently the most commonly used hole type. In addition to matching the medium pressure, flow rate, burner combustion capacity, and other factors, the selection of hole type and aperture should also pay attention to the actual medium quality conditions. For exhaust gas with high dust content, the hole diameter and wall thickness should be appropriately increased. Choose a honeycomb ceramic regenerator with large holes and large eyes to reduce the clogging and corrosion hazards caused to the honeycomb ceramic regenerator.

The honeycomb ceramic regenerator with large holes and large eyes is mainly used to deal with the harsh working environment of some industrial furnaces and the high dust content in the flue gas. During use, the small holes of the honeycomb ceramic regenerator often become blocked. After the small holes of the honeycomb ceramic regenerator are blocked, not only will its heat storage and smoke exhaust performance be significantly reduced. It also causes smoke exhaust and uneven heating of the honeycomb ceramic heat storage body, which is prone to cracks and aggravates its damage. In regenerative industrial furnaces with harsh working environments and high dust content in flue gas, the use of honeycomb ceramic regenerators with large holes and large eyes can effectively avoid clogging the small holes of conventional honeycomb ceramic regenerators.

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RTO Incinerator Honeycomb Ceramic Regenerator

The honeycomb ceramic regenerator of the RTO incinerator has the characteristics of high softening temperature under load, small expansion coefficient, strong resistance to rapid cooling and rapid heating, and long service life. The basic principle of an RTO incinerator is to oxidize organic waste gas at high temperatures (>760℃) to generate CO2 and H2O. The use of honeycomb ceramic regenerators can maximize the recovery and reuse of heat energy, with a heat recovery rate greater than 95%. The geometric characteristics of the RTO honeycomb ceramic regenerator are generally made into columnar regenerators with dimensions of 150mm×150mm×150mm and 150mm×150mm×300mm and are integrated into the RTO regenerator. The number of holes in the cross-section of a piece of packing that airflow passes through is called the hole density, also expressed by the number of holes per square inch (CSI). Usually from 13×13 (number of holes 169) to 60×60 (number of holes 3600).

The greater the hole density, the larger the surface area per unit volume, which can provide a larger heat transfer area and thereby improve the heat transfer efficiency. The organic waste gas is heated to above 760°C, causing the VOC in the waste gas to oxidize and decompose into carbon dioxide and water. The high-temperature gas generated by oxidation flows through the special ceramic heat storage body, causing the ceramic body to heat up and “storage heat”. This “heat storage” is used to preheat the subsequent incoming organic waste gas. This saves fuel consumption for exhaust gas heating.

The honeycomb ceramic regenerator of the RTO incinerator should be divided into two or more zones or chambers. Each regenerator goes through the procedures of “heat storage-heat release-cleaning” in turn, starting over and over again and working continuously. After the regenerator “releases heat”, part of the clean exhaust gas that has been processed should be introduced immediately, and the regenerator should be cleaned to ensure that the VOC removal rate is above 95%. Only after cleaning is completed can the “heat storage” program be entered.

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Honeycomb ceramic regenerator is the key material of regenerative industrial kilns, and it is the heat exchange medium of regenerative industrial kilns. The honeycomb ceramic regenerator absorbs and stores the heat from the waste gas in the industrial kiln, and then uses the stored heat to heat the air and fuel. This not only increases the calorific value of the fuel, lowers the emission temperature of exhaust gas, and saves energy, but also reduces the emissions of CO2 and NOX, which is helpful for environmental protection. The cross-sectional holes of honeycomb ceramic regenerators mainly have square, regular hexagonal, and circular three-hole structures. Moreover, the pores are straight channel structures that are parallel to each other. This structure greatly reduces the resistance of the pores to flow through and greatly improves the single-hole volume heat transfer efficiency of the honeycomb ceramic regenerator. The main materials of the honeycomb ceramic regenerator of the RTO incinerator are dense cordierite, high alumina, corundum mullite, chromium corundum, zirconium corundum, silicon carbide, etc. Contact us for a free quote.

Corundum Castable that is Resistant to High Temperatures and Slag Erosion

Corundum castable is a high-grade castable in a series of unshaped refractory materials. It has a stable crystal structure has more stable performance in high-temperature sintering processes, and is suitable for use in high-temperature areas lined with various kilns. Corundum castable that is resistant to high temperatures and slag erosion. Refractory castables made of this material can better reflect its fire resistance and wear resistance at high temperatures. Its thermal shock resistance can also achieve better performance at high temperatures, and its performance is reliable and reliable during high-temperature operation of the kiln.

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High-Grade Corundum Castable

Corundum castable is used in high-temperature parts of industrial kilns between 1400℃ and 1650℃. It is produced using bauxite clinker and corundum with an aluminum content of more than 90% as aggregate, using micro-powder technology and pure calcium aluminate cement. This kind of corundum refractory castable has high strength, high volume density, and strong high-temperature stability. Used in high-temperature parts of industrial kiln linings, it has strong resistance to slag erosion, wear resistance, and high-temperature gas erosion resistance.

Performance Characteristics of Corundum Castables

Corundum castables have high-energy effects of high temperature resistance and corrosion resistance, and can still maintain stable performance under long-term use. It can be combined with silicon carbide, mullite, andalusite, sillimanite, etc. to make composite refractory castables. It can be used in high-temperature furnace lining parts in different atmospheres.

The high-temperature main crystal phase of corundum castable is corundum refractory castable. It is a refractory castable prepared with special high-alumina bauxite clinker or fused brown corundum as aggregate, adding refractory powder, pure calcium aluminate cement binder, silica powder, and admixtures. Usually, the pouring method is used for construction. It can be cast into a complete lining, or prefabricated blocks of castable materials customized by the manufacturer can be spliced on-site for use.

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Product Features of Corundum Castables

• (1) High compressive strength and strong lining stability at high temperatures.
• (2) The volume density is high, and the overall lining has strong resistance to slag erosion and permeability.
• (3) Strong resistance to erosion by solid particles, dust, and high-temperature gases.
• (4) Low mechanical wear resistance.
• (5) Not affected by reducing gases such as H2 and CO.

Corundum Castable Product Uses

The use temperature of corundum castable is 1600-1700℃, and it is mainly used as lining material for various high-temperature kilns and high-temperature structures. Such as the outer lining of the impregnation tube of the molten steel vacuum degassing device, the lining of the spray metallurgy, and the argon-blowing integral spray gun. The lining body of the electric furnace top triangular area and the LF furnace cover. High-temperature wear-resistant lining for catalytic cracking reactors in the petrochemical industry. High-temperature wear-resistant lining for circulating fluidized beds and power plant boilers.

How to Improve the High-Temperature Slag Corrosion Resistance of Corundum Castables?

The development trend of dense refractory castables requires the calcium aluminate cement content to be reduced as much as possible while maintaining good green strength and high-temperature mechanical properties. The key technology is to increase the packing density between particles. The above purpose can be effectively achieved by adding micron powder, submicron powder, or even nano-alumina powder. The reasons are:

• 1) Reduce the CaO content in the castable and reduce the low melting phase generated at high temperatures. It can significantly improve the high-temperature mechanical properties of castables.
• 2) Promote sintering at medium temperature and increase the medium temperature strength of castables.
• 3) Reduce the total amount of water added and increase the density of the castable.

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In terms of comprehensive cost performance, the role of alumina micropowder cannot be ignored. Its particle morphology, size, particle size distribution and specific surface area will have a great impact on the performance of the castable. In particular, the particle size distribution plays an important role in filling the pores between aggregates and increasing the packing density. Research has found that using composite micropowders with different particle size distributions can significantly increase the packing density. Reducing water consumption is beneficial to mechanical properties such as high-temperature flexural resistance and post-thermal shock strength. Li Wenping studied the influence of alumina powder particle size on the properties of castables. It was found that as the particle size of the micropowder decreases, the flowability and setting time of the castables both show an increasing trend.

More importantly, alumina micro-powder can promote the formation reaction of the CA6 phase of calcium aluminate cement at high temperatures, thereby significantly improving the high-temperature properties of castables. Pinto et al. found that the particle size of alumina powder decreased. It can nearly double the flexural strength of castables containing 1% (mass fraction) CAC cement and promote the formation of the CA6 phase. Auvray et al. discovered the optimization of alumina micro-powder and the in-situ generation of CA6. Ceramic bonding can be formed in the castable, which significantly improves the high-temperature elastic modulus of the castable. Specifically,

• 1) As the alumina fine powder content increases and the corundum fine powder content decreases, the normal temperature performance and high-temperature performance of the castable samples after heat treatment at different temperatures are improved to varying degrees. After being treated at 1600°C, the normal temperature flexural strength, normal temperature elastic modulus, and elastic modulus at 1400°C can be increased by 53.9%, 47.9%, and 40.4% respectively.
• 2) Adding too much micro powder is detrimental to the thermal shock stability of the castable. The more the amount of alumina powder is added, the residual flexural strength retention rate of the sample after thermal shock decreases with the increase in the amount of alumina powder. After three water-cooling thermal shocks, the residual flexural strength retention rate of the material decreased from 18.45% to 11.97%.
• 3) As the content of aluminum oxide powder increases, the slag erosion resistance of the castable gradually increases, and the thickness of the permeable layer decreases from 2.9mm to 2.1mm. The higher content of micro-powder will make the pore diameter of the castable smaller, promote the interpenetration and bonding of plate-like CA6 in the original layer, and make the matrix bonding closer. It is beneficial to improve the slag resistance performance of castables.

To purchase high-quality corundum castable refractory lining materials, please contact us.