The reheating furnace for steel rolling is used to heat metal materials or workpieces to the forging and rolling temperature. The furnace roof is an important part of this type of furnace. If any problem happens with the roof, it can lead not only to temperature loss and repairs but even production shutdowns.
After being used for a long time, the roof of a reheating furnace often suffers from repeated large-scale collapses. Repairs do not solve the problem, and issues like burning through the roof and flames leaking out frequently happen. In more serious cases, the furnace has to be shut down.
The furnace roof has a stepped structure with many sawtooth-shaped drops. Where the roof curve changes, there are many right angles or even sharp corners. During heating and cooling, these areas easily form stress points that lead to cracks and falling pieces.
The layout of anchor bricks is unreasonable. In some parts (like the center of the roof), the roof is thicker and heavier, but there are not enough anchor bricks. This makes it easier for cracks to expand and cause collapse.
The thickest part of the roof is at the sawtooth-shaped drop, which is the weakest point, yet there are no anchor bricks directly hanging here. This makes it very easy for this part to fall off badly.
The expansion joint design is not proper. The furnace roof is arched, with a span of 4480 mm. However, only horizontal expansion joints were left, and no vertical expansion joints. This caused irregular vertical cracks that usually go through the full thickness of the roof, leading to local collapse.
The insulation design is poor. Only a 65 mm thick layer of lightweight clay bricks was used. These bricks have high thermal conductivity and poor sealing, resulting in poor insulation.
The entire furnace roof was cast using high-strength, high-temperature castable. However, testing showed that this material has poor thermal shock resistance and high-temperature performance, which causes frequent roof failures and leads to overheating on the roof surface.
The flat-flame burners on the roof wear out quickly due to harsh working conditions. Poor mixing of fuel and air leads to bad combustion and low energy efficiency.
Change sharp corners on the furnace roof to rounded corners (R30°) to reduce stress and prevent cracking and falling when heating or cooling.
Add more anchor bricks in the thick central part of the roof and arrange them symmetrically across the roof to increase strength and reduce the chance of collapse.
Move the sawtooth-shaped drop forward by 232 mm and use longer anchor bricks in this area. After moving forward, these longer bricks can directly support the thickest part of the roof, improving strength and avoiding collapse.
Add 8 mm wide vertical expansion joints between two anchor bricks in the middle of the roof. This helps release stress from thermal expansion and contraction and prevents vertical cracking.
Use a composite insulation structure. Attach two layers of 20 mm thick ceramic fiber blanket with low thermal conductivity closely to the outer roof wall, then cover with a 65 mm thick layer of lightweight clay bricks.
Replace the high-strength castable with a reliable, fast-drying, anti-explosion self-flow castable. This material is especially suitable for arched furnace roofs. It flows and settles by gravity without vibration, preventing anchor bricks from being displaced or damaged. It has low porosity, excellent thermal shock resistance, and high strength at high temperatures.
Use energy-saving flat-flame burners. These burners have good flame shape, strong wall attachment, and allow full mixing of air and fuel. This improves combustion and heat transfer inside the furnace.
Conclusion
With these improvements, the roof of the reheating furnace no longer has failures, and its service life is extended. The energy efficiency has improved, especially due to the excellent performance of the self-flow castable. There are no more frequent collapses, meeting production needs and improving the working environment.
