Sep 18, 2023

Repair of Refractory Materials in Heating Furnace Lining

Lining repair is a common item in heating furnace maintenance work. There are two main methods of repairing linings. One is to use the same refractory castable as the original lining for repair, and the other is to paste a certain thickness of refractory fiber felt. The construction method and quality requirements for repairing the lining with refractory concrete are the same as those for the new furnace lining. In addition, pretreatment of the repair surface needs to be done.

Construction Method of Repairing Lining with Refractory Castable

Commonly used for repairs of lightweight refractory castable linings. Before construction, materials must be prepared, a detailed understanding of the construction site, and construction tools must be cleaned. The specific pre-construction preparations are as follows.

• (1) Before construction, the repair scope should be reasonably determined based on the damage to the lining. Remove the failed furnace lining within the repair range to meet the pretreatment requirements for repair construction.
• (2) Containers and tools used for lining construction should be cleaned. Prevent lime, other cement, clay, and other impurities from mixing into the aggregate.
• (3) Ceramsite should be soaked for at least 12 hours before use, and excess moisture should be eliminated during use.
• (4) The parts of various pipe racks, casings, and other metal components (except insulation nails) buried in the lining should be coated with 0.5~1.0mm thick asphalt.
• (5) The construction site should be maintained between 10 and 25°C, and cooling or warming measures should be taken accordingly in summer or winter. After the curing is completed but not in the oven, the temperature should be kept above 5°C to prevent freezing damage to the lining.

The construction method of repairing the lining with refractory concrete can be carried out in the following three methods depending on the materials used.

1. Smearing method

During construction, the steel wire mesh must be filled with castable. There must be no holes and the concrete must be dense. When applying, spread the concrete and smooth it with a wooden trowel until the surface is rough. To prevent cracks, the castable surface cannot be calendered. This method is suitable for small-area lining repairs.

2. Spray coating method

The semi-dry method should be used for spraying, that is, the refractory material should be properly moistened with water and stirred evenly before adding it to the sprayer. When spraying, the material and water should be sprayed evenly and continuously, and there should be no dry material or flow on the spray surface. The nozzle should continuously move in a spiral manner to distribute coarse and fine particles evenly. Spraying should be carried out in sections and continuously, reaching the thickness at one time to avoid delamination. If the thickness cannot be reached at one time, layered spraying can be used, but the second layer must be sprayed before the initial setting of the previous layer of spray paint. When construction must be interrupted, diagonal stubble should be left at the joints. When construction continues, the joints must be cleaned and moistened with water. During spraying construction, the thickness of the spray coating should be checked at any time. The excessively thick parts should be shaved off, and the surface of the spray coating should not be smoothed. When spraying, a wooden box should be used to leave a test block at the spraying location to check its strength and bulk density. After construction, tap gently with a small hammer to check the density of the sprayed layer. If any holes or interlayers are found, they should be dug and repaired in time. This method is suitable for repairing or constructing new furnace linings in large areas with thick linings (greater than 50mm).

3. Mold pouring

The pouring and loading of the mold into the formwork should be done in layers, and the thickness of each layer should be 150~200mm. In order to prevent the delamination of light aggregate and cement during tamping, which increases the bulk density and affects the thermal conductivity, mechanical tamping should not be used. Manually tamped concrete must be dense and free of honeycombs and voids. When tamping, first tamp around the anchor pin, and then tamp it again with half a hammer, without over-tamping or missing tamping.

Pouring of refractory concrete is best done continuously. When construction must be interrupted, the joints should be “roughed” and covered tightly with plastic film. After 12 hours, pouring can be continued.

When pouring refractory concrete on top of the insulation block, prevent the upper insulation block from absorbing water. The best way is to paint a layer of asphalt on the insulation block, or you can lay a layer of plastic film. If plastic film is spread on a vertical surface, it should be fixed to prevent it from slipping. This method is also suitable for the repair of large-area, large-thickness vertical linings and the lining construction of new furnaces.

Refractory fiber paste repair method

The use of refractory fiber paste to repair the lining is a new method developed in recent years. It has the advantages of simple construction, no need for maintenance, and short oven and maintenance cycles.

When overhauling the lightweight heat-resistant concrete lining of the heating furnace, it was found that the surface of some linings was generally delaminated, powdered and peeled off, that is, the surface layer of the concrete lining lost its strength. The reason for this phenomenon may be the corrosion of the gas medium in the furnace. If you still use raw materials to repair it at this time, you will definitely make the same mistake again. The use of pasted refractory fiber felt is an effective method.

Scrape off the powdery layer on the original lining surface and roughly level it. Large cracks and peeling areas are hand-painted with raw materials, and then a layer of refractory fiber felt is pasted. The thickness of the paste should be determined through calculation, but it should not affect the heating of the furnace tube surface. This composite structure of ceramic fiber felt is vertically attached. The vertical ceramic fiber felt is cut by machine according to the required thickness and tied into bundles.

Before pasting, clean the flattened lining to remove any floating material. When pasting, start from the root of the wall and paste it from bottom to top. Use a paint brush to spread the adhesive on the furnace wall and the ceramic fiber bundle strips respectively, and apply it fully. Then attach the ceramic fiber bundle strips and compact them with your hands. If there is water on the furnace wall or top, the ceramic fibers will not be able to stick to it.

The adhesive should have properties such as high-temperature resistance, strong adhesion, lightweight, and the ability to cure at room temperature. Currently, commonly used adhesive types include:

• (1) Water glass: pulp waste liquid = 1:1 plus 10% clay clinker powder and a small amount of clay powder.
• (2) Aluminum silicate adhesive.
• (3) Methylcellulose.
• (4) Aluminum phosphate adhesive, phosphoric acid: aluminum hydroxide = 8:1.

For example, adding masonry powder to the adhesive to make it into a paste, and adding some MgO can make it stronger at room temperature.

Rongsheng refractory material manufacturers can provide customers with comprehensive refractory material services. Extend the service life of refractory lining materials in high-temperature industrial kilns and reduce the number of furnace shutdowns and repairs. Design and construction of refractory solutions for insulation layers, and turnkey projects of refractory lining materials for high-temperature industrial furnaces. If you are in need of purchasing heating furnace lining refractory materials, refractory brick linings, or unshaped refractory linings, please contact us. Get free quotes and samples.

Sep 18, 2023

RS Monolithic Refractories for Delivery

Sep 1, 2023

AZS Fused Zirconia Corundum Brick Fused Brick – Refractory Brick for Glass Kiln

Fused zirconia corundum brick is a high-quality, high-temperature performance refractory material, mainly made of zirconia and alumina through arc melting. The adobe has the characteristics of high density, high hardness, high heat resistance, corrosion resistance, etc., and has good use effects in high temperature and chemical erosion environments. Zirconia corundum bricks are refractory bricks made of industrial alumina and zircon sand. According to the manufacturing process, zirconium corundum bricks can be divided into two types: fused zirconium corundum bricks and fired zirconium corundum bricks.

Properties and Characteristics of Zirconium Corundum Bricks

Fused zirconia corundum bricks are commonly known as white iron bricks, also known as corundum-deleyite bricks. The main chemical composition is Al2O3 50% to 70%, ZrO2 20% to 40%, and the rest is SiO2. The main mineral composition is baddeleyite (ZrO2), corundum (α-Al2O3) and glass phase. Baddeleyite crystallizes to form the backbone of the brick body, ZrO2 has a high melting point (2715°C), has good chemical stability, and has strong corrosion resistance to acidic and alkaline media, especially glass liquid.

physical properties

Fused zirconia corundum bricks have some excellent physical properties, which make them work well in high-temperature and chemically erosive environments. The following will introduce its main physical performance indicators:

density and hardness

The density of fused zirconia corundum bricks is generally between 35.6-4.2 g/cm3, which is a high-density material. At the same time, its hardness is very high, usually above 9.0 Mohs, which is three times that of steel. This means that it can also maintain good wear resistance under high temperatures and strong acid and alkali environments.

heat resistance

The heat resistance of fused zirconia corundum brick is also one of its main physical properties. The material can withstand very high temperatures, generally above 2200. This enables it to operate at high temperatures for a long time without deformation, cracking, etc.

Corrosion resistance

The corrosion resistance of fused zirconia corundum bricks is also excellent, mainly due to their good chemical stability and oxidation resistance. Fused zirconia corundum bricks have good corrosion resistance in corrosive environments such as acid and alkali, high temperature, and humidity, which makes them able to withstand more severe working conditions during production.

Preparation Process of Fused Zirconia Corundum Brick

The preparation process of fused zirconia corundum bricks is relatively complicated. It is necessary to select high-quality zirconia and alumina raw materials and mix them evenly. Next, the mixture is poured into an electric furnace for high-temperature electric fusion to form solid adobes. The electric melting furnace usually inserts two electrodes into the furnace body at the same time, generates high temperature through the electric arc in the furnace, heats the raw materials to a molten state, and forms a hard adobe after melting.

During the preparation process, special attention needs to be paid to controlling the conditions such as atmosphere and temperature in the furnace to maintain the uniformity of the melt and the stability of the chemical composition. In addition, the baking and processing of Adobe is also an important link affecting product quality, which is directly related to the physical performance parameters such as density and hardness of Adobe.

Application Field of Zirconium Corundum Brick

Fused zirconia corundum bricks are widely used in the industrial field, especially where high-quality, high-performance refractory materials are required in high-temperature and chemically aggressive environments. The following will introduce its application fields in detail from several aspects:

glass melting furnace

In glass melting furnaces, fused zirconia corundum bricks are usually used as important parts such as the upper pool wall, small furnace flat wall, small furnace stack, tongue wall, and parapet. This is because a glass melting furnace is a high-temperature, high alkalinity, highly corrosive environment that requires the use of high-quality refractory materials that can withstand long periods of operation. The fused zirconia corundum brick not only has excellent heat resistance and corrosion resistance but also can maintain good physical stability, ensuring the smooth progress of the glass production process.

Application of Fused Zirconia Corundum Brick in Glass Furnace

Fused zirconia corundum bricks are used in industrial furnaces such as glass-melting furnaces. The parts used in the glass melting furnace are the masonry of the upper pool wall, the small furnace flat wall, the small furnace stack, the tongue wall, and the parapet. The following problems should be paid attention to in the use of fused zirconia corundum bricks:

① Irregular changes in thermal expansion. The expansion curve of the fused zirconia corundum brick has an abnormal section near 1000°C. Its internal ZrO2 crystal undergoes reversible crystal transformation and has a large volume change. Therefore, bricks containing ZrO2 should not be used in places where the temperature often fluctuates sharply around 1000 °C. When baking the kiln, the temperature change should not be too large at 900-1150 °C. Generally, it cannot exceed 15°C/h, and a steady temperature rise is required. Some parts need to be protected from cold wind and need to be protected by other bricks to prevent bursting.

②Shrinkage cavity. During pouring molding, shrinkage cavities often appear at the gate, where the brick body has more pores and poor density. Therefore, when building the wall of the glass melting tank, the shrinkage cavity is all directed towards the inner direction of the kiln. If the sprue is facing outward, when the brick body is corroded to a very thin thickness, it will cause a glass liquid leakage accident. When used in the upper flame space of the pool kiln, the service life is very long, and the problem of glass liquid running out will not occur. Therefore, the spout is used outwards to prolong the service life.

③ eutectic. Fused zirconia corundum bricks are built in contact with clay bricks, and the eutectic phenomenon will occur at a high temperature of 1300 °C. Therefore, when choosing refractory materials, it should be avoided to contact the two refractory materials with serious eutectic phenomenon for masonry. If the silica brick is under the fused zirconia corundum brick, it is most susceptible to erosion by the fused zirconia corundum brick.

Sintered zirconium corundum bricks are also known as ceramic-bonded aluminum-silicon-zirconium bricks. Compared with fused zirconia corundum bricks, the chemical composition of sintered zirconia corundum bricks is similar. However, it has the advantages of no carbon, low content of glass phase, uniform structure, no shrinkage cavity, good thermal shock stability, and corrosion resistance.

Metallurgical equipment

Fused zirconia corundum bricks are also widely used in metallurgical equipment, especially in the iron and steel industry. For example, high-quality, high-performance refractory materials are required in equipment such as blast furnace interiors, converter interiors, heating furnaces, and dryers. Fused zirconia corundum bricks just meet this requirement.

aerospace equipment

Fused zirconia corundum bricks are also more and more widely used in aerospace equipment. For example, in high-temperature components such as engine nozzles and combustion chambers, high-quality ceramic materials are required to withstand high temperature, high pressure, and severe airflow erosion. The fused zirconia corundum brick has excellent heat resistance and corrosion resistance, making it one of the ideal materials for these components.

AZS Bricks Fused Zirconia Corundum Brick Fused Bricks

With the increasing demand for high-quality refractory materials, the market prospect of fused zirconia corundum bricks is also becoming brighter. Especially in the fields of glass, metallurgy, aerospace, and other fields, the application prospect is very bright. zirconium bricks series, Fused zirconia corundum brick is an excellent refractory material with high density, high hardness, high heat resistance, and corrosion resistance. It is widely used in industrial production. The preparation of fused zirconia corundum bricks requires fine control in multiple steps to ensure their excellent physical properties. Buy High-Quality AZS-Fused Zirconia Corundum Bricks Fused Bricks – Refractory Bricks for Glass Kiln, Contact us to Get a Free Quote.