Comparison of service life before and after reformation of steel rolling heating furnace roof

Steel rolling heating furnace is an industrial furnace that heats materials or workpiece metal products to the forging temperature. The furnace roof is an important part of the steel rolling furnace. Therefore, if there is a problem with the furnace roof of some steelmaking enterprises, it will not only bring about Cool down and repair, or even discontinue production.

First of all, we can be sure that after long-term use of the steel rolling heating furnace, the furnace roof will collapse in large areas for many times, and it will not help after repairing. Frequently, the furnace roof may be burnt through and the flames may go outside, causing the company to be forced to cool down and repair. For more serious cases, stop the furnace directly, and the outer surface temperature of the heating section and the soaking section of the heating furnace is high, with an average of 230°C, and the local temperature is as high as 300°C.

Problems with the stove top

1. The top curve of the heating furnace is a multi-stage choke type, (as shown in the figure below), there are many zigzag depressions. The changes in the top curve are mostly right angles, and some parts are acute angles. When the temperature is raised and lowered, it is easy to cause a right angle. , Stress concentration at acute angles causes cracking and shedding.

2. Anchor brick refractory brick layout is unreasonable. Some parts (the central area of ​​the furnace roof) have a thicker furnace roof and heavy weight, but there are relatively few anchor bricks, which makes the furnace roof easier to fall off after cracks occur.

3. The zigzag depression of the furnace roof is the thick refractory material of the furnace roof, which is the weak link of the furnace roof, but it is directly hung without anchoring bricks, which makes the furnace roof easy to fall off. The collapse is serious.

4. The setting of the furnace roof expansion joint is unreasonable. The cross section of the roof of the heating furnace is bow-shaped, and the roof span is 4480mm. However, the original furnace roof only has horizontal expansion joints and no longitudinal expansion joints, which leads to multiple irregular longitudinal cracks in the furnace roof. The depth of the cracks generally penetrates the entire thickness of the furnace roof, which makes the furnace roof prone to local collapse.

5. The design of the furnace roof insulation layer is unreasonable, only a layer of 65mm thick light clay bricks, which have high thermal conductivity, not tightly sealed, and poor heat insulation effect.

6. ​​The top of the furnace is casted with high-temperature and high-strength castables. The product has been researched and found that its high-temperature strength, thermal shock stability and other high-temperature performance are not good, causing the furnace roof to frequently fall off, causing the temperature of the outer wall of the furnace roof to exceed the standard.

7. The flat flame burner on the top of the furnace will accelerate its damage due to the bad use conditions, insufficient fuel and air mixing, poor combustion quality, and poor energy-saving effect.

Optimization solution:

1. Change the right and acute angles of the furnace roof to R30 ° rounded corners to reduce cracking and falling off caused by stress concentration during heating and cooling. (as shown in picture 2)

Reasonably arrange the anchor bricks, add an anchor brick in the central part of the furnace roof that is thicker and easy to fall off, and distribute it symmetrically along the furnace roof to increase the strength of the furnace roof and reduce the probability of falling off at the central part of the furnace roof.

2. Move the “sawtooth” down part of the furnace top 232mm forward as a whole, and use extended anchor bricks at the down part. After the “saw-tooth” type is pressed down and moved forward, the elongated anchor bricks directly act on the thick part of the furnace roof at the pressed part, which improves the overall strength of the pressed part of the furnace roof and avoids collapse here.

3. Add a longitudinal expansion joint with a width of 8mm between the two adjacent anchor bricks in the middle of the furnace roof to relieve the stress concentration of the refractory material on the furnace roof during cooling shrinkage and heating expansion, and avoid longitudinal cracks.

4. The furnace roof adopts a composite thermal insulation structure, which is closely attached to the outer wall of the furnace roof. It is covered with two layers of aluminum silicate fiber blankets with low thermal conductivity and a thickness of 20mm, and a layer of light clay bricks with a thickness of 65mm is laid on the outer layer. .

5. Use reliable self-flowing, quick-drying, explosion-proof castables instead of high-temperature and high-strength castables. This castable is particularly suitable for the pouring of bow-shaped furnace tops. It can use its own gravity to flow out without vibration to achieve compaction. To prevent the anchoring brick from being deflected or broken by vibration. At the same time, the castable has low porosity, good thermal shock stability, good high-temperature strength, and excellent high-temperature performance.

6. Choose a more energy-saving flat flame burner. This burner has a good airflow expansion shape, good wall attachment effect, uniform fuel and air mixing, and full combustion, which can effectively strengthen the heat transfer process in the furnace and increase the radiant heat transfer.

Through the trial, the top of the steel rolling heating furnace not only cleared the fault, but also prolonged the service life, achieving the purpose of energy saving and consumption reduction. In particular, the use of self-flowing castables is very delicate, stable performance, and no frequent shedding occurs again. Meet the needs of production, thus also improve the working environment.