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Basic knowledge of refractory materials

Nov 08, 2023

1. What is refractory material?

Refractory materials refer to inorganic non-metallic materials that can meet the requirements for use in high-temperature environments. They have certain high-temperature mechanical properties and good volume stability, and are essential materials for various high-temperature equipment.

2. What are the types of refractory materials?

According to the chemical properties of its main components, it is divided into three categories: acidic, neutral, and alkaline. According to refractory materials, they are divided into ordinary high acid and special high acid (refractory degrees are 1580-1770℃, 1770-2000℃, 2000℃ respectively). They can also be classified according to firing method, porosity and other methods.

3. What does the structural performance of refractory materials mean?

Refers to its porosity, water absorption, air permeability, pore size distribution, volume density, true density, etc. They are important indicators for evaluating the quality of refractory materials.

 

4. Explanation of terms

(1) Thermal expansion: refers to the length change of refractory products during the heating process. It is expressed in two ways: linear expansion rate and linear expansion coefficient.

(2) Thermal conductivity: refers to the heat passing through the unit area of the sample at unit temperature and unit time.

(3) Fire resistance strength: refers to the ultimate load that unit area can withstand at a certain temperature.

(4) Bending strength: refers to the ultimate breaking ability of the sample unit when it withstands bending moment.

(5) Refractory resistance: refers to the ability of refractory materials to resist high temperature and melt when there is no load.

(6) Load softening temperature: refers to the temperature that occurs when refractory products are continuously heated and subjected to a constant load.

(7) Unshaped refractory materials: refers to refractory materials with an indefinite shape formed by a certain gradation of aggregates and powders, binders and admixtures and can be used directly without high-temperature firing.

(8) Refractory castables: refers to unshaped refractories that are constructed using the castable method and can be hardened without heating.

(9) Refractory spray material: refers to unshaped refractory materials used to repair thermal equipment using spray construction methods.

(10) Alkaline refractory products: refers to refractory products with magnesium oxide and calcium oxide as important ingredients.

(11) Insulating refractory materials: refers to the ultimate load that refractory materials can withstand per unit area at a certain temperature.

(12) Re-firing change rate: refers to the residual expansion and contraction caused by the fired refractory products being heated to a specified temperature again, kept warm for a certain period of time, and cooled to room temperature.

(13) Thermal shock resistance: refers to the ability of refractory materials to resist slag erosion and erosion at high temperatures.

 

5. Basic requirements for refractory materials used in rotary kilns

(1) Requires high refractoriness;

(2) Requires high thermal strength, compression resistance at high temperatures, and flexural strength;

(3) Requires high resistance to chemical attack and high wear resistance;

(4) High thermal shock resistance is required;

(5) The shape and size are required to be within the allowable range to facilitate masonry construction;

(6) The fired bricks require easy hanging of the kiln skin;

(7) Requires lower thermal conductivity and thermal expansion coefficient.

6. What are the general regulations for castable construction?

Before construction of castable materials, the following inspections should be strictly carried out:

(1) Check the factory date and quality certificate of the product, and confirm whether it has failed through inspection and testing;

(2) Check whether the formwork support meets the requirements to reserve expansion joints;

(3) Check the appearance and cleanliness of the equipment to be injected;

(4) Check the condition of construction machines and tools, and vibrating tools and other spare parts must be in good condition;

(5) Check the type, size, layout and welding quality of anchors;

(6) Check the surrounding refractory insulation layer’s measures to prevent water loss of castables;

(7) Check the construction water and measuring tools, and consider the construction environment (winter, summer);

(8) Make sure there is no power outage during construction. Once the construction is not interrupted, the formwork used must have sufficient strength, good rigidity, no deformation, no segmentation, and no leakage of grout. The steel formwork and wooden formwork must be painted with waterproofing agent, and reused molds must be first It can be used after cleaning and painting. The amount of water added should be strictly controlled. Sufficient time should be allowed for stirring and vibration. Expansion joints should be reserved reasonably. The maintenance time should not meet the requirements.

 

7. General procedures for laying bricks in rotary kiln

(1) Select refractory bricks and classify them according to different masonry methods and sizes;

(2) Conduct a comprehensive inspection of the four walls of the kiln shell to ensure that the steel plate of the kiln body is clean, remove corroded slopes, and clean the dust and slag on the inner wall;

(3) When laying out the lines in the kiln, the longitudinal reference line should be parallel to the axial centerline of the kiln. One line should be placed every 1.5m around the perimeter, and one line should be placed every 10m towards the base line. Do the above work before proceeding with the final laying.

8. Basic requirements for bricklaying in the kiln

(1) The brick lining is close to the shell; (2) The bricks are closely connected to each other; (3) The brick seams are straight; (4) The intersection is accurate; (5) The brick locking rate; (6) The position is not correct; (7) The bricks are not in position. Drooping and emptying. It is necessary to ensure that the brick lining and the kiln body are reliably concentric during the operation of the kiln. The stress in the brick lining should be evenly distributed on the entire lining and brick lining. At the welds and twisted parts of the kiln, homogeneous fire mixing can be used to compensate for the maximum The thickness shall not exceed 8mm and shall not be supplemented by steel plates or castables. The circumferential seam deviation is allowed to be ≤2mm per meter and shall not exceed three pieces (locking brick area). Each type of locking brick shall not exceed 2 pieces.

9. What are the common problems that often occur in rotary kiln masonry construction?

Mainly include inversion of large and small heads, drawing lots, mixing, dislocation, tilt, uneven gray joints, climbing, off-center, heavy joints, through joints, voids, rough joints, serpentine bends, masonry bulges, missing corners and blocked corners. wait.

10. What are the performance properties of refractory materials?

Mainly refers to the refractory material's refractoriness, load softening temperature, re-firing change rate, earthquake resistance, slag resistance, acid resistance, alkali resistance, oxidation resistance, hydration resistance, and erosion resistance.

11. Analyze the main reasons for the red kiln’s reversal

(1) Operation reasons: a. The kiln skin is not hung well; b. Local overheating and deformation; c. Improper adjustment of combustion; d. The bricks are thin; e. Local high temperature or over-burning.

(2) Mechanical reasons: a. The central area of the cylinder is not straight, causing brick displacement; b. Inner wall welds, etc.; c. Local cylinder deformation.

(3) Others: a. The quality of the kiln lining is poor; b. Frequent.

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