Expansion joints in refractory brickwork may be arranged either in a concentrated pattern or a distributed pattern, but in both cases they must meet the total expansion allowance required by the design. Concentrated expansion joints can be further divided into staggered expansion joints and keyed expansion joints.
A staggered expansion joint means that the expansion joints in each brick course are staggered between the upper and lower courses. A keyed expansion joint means that the expansion joints in different inner and outer brick layers are offset from each other, as shown in Figure 2-1.
Concentrated expansion joints divide the total expansion allowance of the brickwork into several larger joints. In general, each joint should be 10–20 mm wide, with a spacing of 2–3 m.
Distributed expansion joints keep the total expansion allowance unchanged, but arrange more joints with smaller widths along the brick length, width, or thickness direction.
During refractory brick installation, the following points should be considered when setting expansion joints:
The following are examples of expansion joint locations and installation methods for different parts of refractory brickwork.
In furnace wall brickwork, expansion joints in the inner and outer layers made of different refractory bricks should be arranged as keyed joints, so that they do not connect directly with each other. Between upper and lower brick courses, the joints should be arranged in a staggered pattern, as shown in Figure 2-2a and Figure 2-2b.
In general, one expansion joint is arranged every 2 m, but the joint should avoid burners, openings, arch doors, and similar areas on the furnace wall.
For curved walls, the expansion allowance is usually provided by leaving a gap between the circular brickwork and the outer shell instead of arranging a conventional expansion joint. The gap is then filled with refractory mortar or insulating material.
This is because when circular brickwork is heated, it expands in the circumferential and radial direction. To prevent damage to the steel structure and fixed brickwork, the filler material can be compressed to absorb the expansion of the lining. See Figure 2-2c.
For furnace arch roofs, through expansion joints are generally left at both ends. When arranging these joints, not only the longitudinal expansion of the arch roof should be considered, but also the upward expansion of the furnace walls at both ends.
When the arch roof length is greater than 5 m, expansion joints should be arranged not only at both ends, but also in the middle of the arch roof in sections according to its total length. The expansion joint in the arch roof should be covered with a flat-laid brick course, as shown in Figure 2-2d.
For suspended roofs, expansion joints are usually arranged on the side and bottom of the brick rows near the side walls, and the joints are filled with asbestos rope, as shown in Figure 2-2e. The expansion joint left at the back of the first row of transverse arch bricks should be treated in the same way as the side joint.
For arch roofs dry-laid with silica bricks, 1–2 mm thick cardboard should be inserted into the radial joints every 3–5 bricks to compensate for thermal expansion.
When building furnace bottoms with magnesia bricks or magnesia-chrome bricks, one expansion joint with a thickness of 2–3 mm should be arranged every 3–4 bricks.
Inside the joint, 2–3 sheets of 1 mm thick cardboard can be inserted. Another method is to place one sheet of 1 mm thick cardboard in each brick joint.
The arrangement method for expansion joints in pipe linings is shown in Figure 2-2f.
The transverse expansion joints allow the lining to expand along the length direction, while the circumferential joints allow expansion along the diameter direction.
When metal components are embedded in refractory brickwork, expansion joints should be arranged between the metal components and the surrounding brickwork. This allows the metal components to expand freely when heated.
The method of arranging expansion joints in boiler furnace walls and the refractory brick walls around the furnace is shown in Figure 2-3. For partition walls or flame baffle walls inside the furnace, it is generally suitable for them to extend 90–95 mm into the wall.
To prevent air from entering the furnace or furnace gas from escaping, the expansion joints must be tightly filled with asbestos rope. For easier filling, the asbestos rope should be suspended above the joint before bricklaying, so that it can be compressed into place during masonry construction.
The asbestos rope used in expansion joints should be soaked in thin refractory slurry in advance. If the expansion joint width is 20 mm, asbestos rope with a diameter of 25 mm should be used for filling.
Expansion joints around tubes, steam drums, and other metal components inside boiler furnace walls are shown in Figure 2-4.
For tubes inside the wall, asbestos rope with a diameter of 10–20 mm must be wrapped around the tube to form the expansion joint. For castings inside the wall, 10–15 mm thick asbestos board should be used as the filler material around the support strips. For the steam drum inside the wall, a circular arch should be built around the circumference of the steam drum, and 25 mm diameter asbestos rope should be filled between the steam drum and the arch.
To ensure the correct thickness and position of expansion joints, templates should be used as the reference during construction.
The inside of the expansion joint must be kept clean. Therefore, during bricklaying, the reserved expansion joint should be filled with cardboard or properly sized wooden strips to prevent debris from falling into the joint.
Expansion joints in industrial furnace refractory brickwork have received increasing attention. In the past, serious damage has occurred due to insufficient expansion joint width or incorrect joint arrangement. Typical problems include furnace gas leakage, molten steel leakage, collapse of brickwork, deformation or cracking of steel structures, and even forced furnace shutdown for repair.
As a result, many improvements have been made to expansion joint design. For example, the original staggered expansion joint has been improved into a sliding expansion joint.
A sliding expansion joint changes the staggering method from every brick course to every 4–5 courses. At the staggered position of the brickwork, oiled cardboard is used as a separation layer, without refractory mortar. The joint is then filled with refractory fiber, as shown in Figure 2-5.
The main advantage of a sliding expansion joint is that when the brickwork expands under high-temperature conditions, it reduces the friction caused by staggered bricks and lowers the resistance caused by uneven masonry construction. This makes expansion and contraction easier.
At the same time, because there is no refractory mortar at the staggered position, the brickwork on both sides of the expansion joint can slide more freely.
In addition, refractory fiber filled in the sliding joint can help prevent flame penetration through the brickwork. When the masonry expands, the refractory fiber is compressed. Even if it cannot fully fill the expanded space, it can still provide refractory performance, thermal insulation, and sealing function.
