Learn factors influencing electric furnace roof service life

The furnace roof of the electric furnace is a spherical structure with electrode holes and smoke exhaust holes. The outer ring part is called the main furnace cover, and the middle part is called the small furnace cover (also known as the triangle area). The furnace cover can be removed when charging. The electric furnace smelting process is extremely complicated, and the conditions for the use of prefabricated parts in the triangular area are very harsh. The life of the electric furnace cover is mainly affected by the combined effects of electrode arc radiation, rapid cooling and rapid heating, chemical erosion of molten steel and slag, impact wear of high-speed airflow formed during dust removal, and unreasonable structure of the furnace cover.

Water cooled EAF roof factors for influencing life

1. Arc Radiation

During electric furnace smelting, the arc temperature generated by the electrode discharge is as high as 3000 ℃, and the working surface of the small furnace cover is severely melted. In the arc starting stage, the arc is exposed above the charge, close to the furnace top, and the heat radiation is large. The longer the arc is, the greater the power, the greater the radiant heat to the furnace top, and the faster the furnace top is damaged. Generally, steel mills require low-level power transmission to control the arc length during arc starting; large voltage and high current power supply is gradually used in the process of well penetration, all to protect the furnace cover.

2. Rapid cooling and rapid heating

Arc heating, tapping and rotation of the furnace cover to the outside of the furnace for charging cause rapid cooling and rapid heating, which in turn causes thermal stress on the furnace cover to cause the working face to peel off.

3. Dust removal system suction

The impact wear of the working surface of the furnace cover caused by the high-speed airflow formed by the dust extraction of the dust removal system. When the pulling force is insufficient, most of the flue gas and flame generated by the melting of scrap steel escape from the gap between the electrode and the electrode hole, and the long-term violent scouring of the air flow causes the electrode hole to expand seriously. When the main furnace cover has a spherical or arc-shaped structure, the working surface of the small furnace cover will be eroded in an arc shape. For this reason, the operator should regularly clean the debris in the flue of the dust removal system to avoid blockage of the flue and affect the dust removal effect.

4. Chemical attack

The molten steel and slag are sprayed onto the working face of the furnace cover, and some chemical components in it react with the working face and penetrate into the interior of the working face to form a metamorphic layer. The thermal stress generated when the temperature changes suddenly promotes the peeling off of the metamorphic layer, and then forms a new working surface and suffers cyclic damage. The higher the distance between the molten pool level and the working surface of the small furnace cover, the smaller the splash effect and the smaller the chemical erosion effect. The height is generally above 1.5m.

5. Hot metal mixing ratio

The molten iron contains high silicon and sulfur, and it is easy to form acidic substances such as silicon oxide and a small amount of sulfur oxide in an oxidizing atmosphere, which aggravates the damage to the small furnace cover. The higher the proportion of molten iron added, the greater the impact.

6. Electrode spray water

The use of spray water on the electrode not only reduces the consumption of the electrode, but also reduces the temperature around the electrode hole, thereby suppressing the high temperature melting loss to a certain extent. If this measure is not adopted, the damage of the electrode hole will be aggravated, which is mainly manifested as hole reaming.

7. The effect of water leakage of the replaceable water cooling ring

The replaceable water-cooling ring has water leakage in many steel mills: when the water leaks, the water is quickly vaporized and extracted with the flue gas, which has little effect on the small furnace cover. However, serious water leakage may lead to a large molten steel spray or a furnace explosion accident. In order to prevent this accident, the water cooling ring is often replaced and welded in advance. At the same time, the small furnace cover is hoisted down, and then re-welded and then hung up for use. At this time, the metamorphic layer of the working face is severely quenched and heated, which will greatly reduce the life of the small furnace cover. Sometimes, when the small furnace cover is seriously cracked or the lining is thin in the cooling state, the user will turn it over, which artificially limits the service life of the small furnace cover. Therefore, preventing the leakage of the replaceable water cooling ring is the primary task of the steel mill.

8. The influence of the furnace cover structure

Under the action of its own weight, the flat-top structure furnace cover is prone to loosening and slumping due to the cracking of the ribs between the electrode holes without external support, and even three electrode holes are connected to form a large hole, which eventually leads to the replacement of the furnace cover. If it is a vault structure, even if there are cracks, the cracks will be squeezed tightly under the action of the furnace cover's own weight, which will not cause loosening and can prolong the life of the furnace cover. Therefore, the furnace cover of the vault structure is better in use than the flat roof structure.

9. Technical level of foaming slag

In the later stage of electric furnace smelting, foam slag needs to be made. The foam slag covers the molten steel surface and buryes the electrode arc, which not only improves the thermal efficiency, but also has less arc exposure and less melting damage to the working surface of the small furnace cover. influences. There are two ways to make foamed slag. One is to use molten steel containing a large amount of carbon, and in an oxidizing atmosphere, carbon monoxide can be automatically formed through the slag to form foamed slag; the other method is more commonly used, using carbon at the furnace door. The oxygen lance sprays carbon powder and oxygen to generate carbon monoxide and passes through the slag to form foamed slag.

EAF roof refractory materials requirements

Arc heating, tapping and rotation of the furnace cover to the outside of the furnace cause rapid cooling and rapid heating, which requires good thermal shock resistance of the refractory material for the electric furnace cover. Due to the splash of molten steel and slag and the erosion of the furnace cover by acidic substances such as silicon oxide and a small amount of sulfur oxide, the refractory material is required to have good slag resistance to high-temperature slag; the furnace cover is under the action of its own weight, due to the ribs between the electrode holes Cracking, it is easy to cause loosening and slump without external support.