Factors affecting the service life of refractory materials used in electric furnace roofs

The electric furnace roof is a spherical structure with electrode holes and exhaust holes. The outer ring is the main furnace roof, and the central triangular area is called the small furnace cover (triangle area), which is removable during charging. The electric furnace smelting process is complex, and the prefabricated parts in the triangle area are used in an extremely harsh environment. They are mainly affected by factors such as arc radiation, rapid cooling and heating, chemical corrosion, high-speed airflow impact wear, and structural design.

The main factors affecting the service life of the small furnace cover of the electric furnace

Arc Radiation

The arc generated by the electrodes during electric furnace smelting can reach temperatures exceeding 3000°C, causing severe melting damage to the working surface of the small furnace roof. During the arc starting phase, the arc is exposed above the charge and close to the furnace roof, resulting in strong heat radiation. The longer the arc and the greater the power, the more severe the thermal shock to the furnace roof, leading to rapid damage to the furnace roof. Steel mills typically use low-power supply during arc starting to control the arc length; during the drilling phase, the voltage and current are gradually increased to protect the furnace roof.

Sudden Cooling and Heating

Operations such as arc heating, tapping, and furnace roof removal and charging result in rapid temperature fluctuations, generating thermal stress that can cause spalling of the furnace roof working surface and is a major cause of refractory damage.

Dust Removal System Exhaust

The high-speed airflow generated by the dust removal system impacts the working surface of the furnace roof, causing wear. If the exhaust is insufficient, flue gas and flames escape through the gaps between the electrode holes. Long-term erosion can cause the electrode holes to expand. When the main furnace roof is spherical or curved, the small furnace roof is prone to arc erosion. The flue should be cleaned regularly to prevent blockage and ensure dust removal effect.

Chemical Attack

Steam and slag splash onto the furnace cover surface, where the acidic components react with the refractory material and penetrate, forming a metamorphic layer. Sudden temperature changes cause the metamorphic layer to flake off due to thermal stress, and the new surface is further eroded, creating a cycle of damage. It is recommended to maintain a distance of at least 1.5 meters between the molten pool surface and the small furnace cover to reduce splashing and chemical attack.

Hot Metal Intake Ratio

Steamed iron contains high silicon and sulfur contents. Under oxidizing conditions, it generates acidic substances such as silicon oxide and a small amount of sulfur oxide, which intensify chemical attack on the small furnace cover. The higher the hot metal intake ratio, the more severe the attack.

Electrode Water Spray

Spraying electrode water reduces electrode wear and cools the area around the electrode hole, mitigating high-temperature melting losses. Failure to implement this measure can lead to hole enlargement and accelerated damage.

Impact of Replaceable Water Cooling Ring Leakage

Water leaks in the water cooling ring evaporate and are discharged with the flue gas. Minor leaks have minimal impact. However, severe leaks can cause large steel sprays or explosions, necessitating early replacement of the welding ring. This process requires the removal of the furnace roof, which causes the small furnace roof to experience rapid cooling and heating, significantly shortening its lifespan. In some cases, it is forced to be discarded due to cooling cracking or excessively thin lining, artificially shortening its lifespan. Therefore, preventing water leakage in the water cooling ring is critical to ensuring stable furnace roof operation.

Influence of the Furnace Roof Structure

Flat-top furnace roofs are prone to loosening, collapse, and even three-hole interconnections due to cracking in the ribs under their own weight, necessitating early replacement. A domed roof structure can close cracks under its own weight, preventing loosening and extending its service life. Overall, the domed roof structure is superior to the flat roof structure.

Foamy Slag Production Technology

Foamy slag is required in the later stages of smelting to cover the molten steel surface, bury the arc, reduce arc exposure, and minimize heat radiation to the small furnace roof and melt loss. A well-produced foamy slag helps extend the lifespan of the furnace roof. There are two main methods for slag production: one is to generate carbon monoxide from carbon in the molten steel in an oxidizing atmosphere to form foamy slag; the other is to inject carbon pulverized carbon and oxygen through a carbon-oxygen lance at the furnace door, or to manually add carbon pulverized carbon to produce slag. Requirements for Refractory Materials for Furnace Roofs

To withstand rapid cooling and heating conditions, furnace roof refractory materials must possess excellent thermal shock resistance. They must also exhibit good slag resistance against slag splashing and acidic corrosion. Furthermore, to prevent cracking, loosening, or collapse, the material must possess strong integrity and a solid structure.