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The wrong construction method will also affect the service life of the dry ramming material in the furnace bottom.
Dec 08, 2018

At present, the working layer of high-power and ultra-high-power electric furnaces is generally constructed of dry magnesium ramming material, which is made of high-iron high-calcium synthetic magnesia and electrolyzed magnesia as aggregate to synthesize magnesia and fused magnesia. The sand is used as a fine powder with a critical particle size of 5~6mm. It is made of C2F (dicalcium ferrite) as a sintering aid in synthetic magnesia. It is made of multi-stage ingredients without adding any binder. Through strong beating construction, the density after construction is guaranteed, and it can be sintered into a solid whole at an appropriate temperature, and its life is several times higher than that of the previous knotting and brick laying methods. Under normal circumstances, the use of dry ramming material can reach more than 300 furnaces at one time, and can be extended to 500~600 furnaces by heat repair, which not only reduces the number of furnace shutdowns, but also significantly reduces the consumption of refractory materials per ton of steel.


A construction preparation


Clean up foreign matter such as permanent residue, dust, iron wire, and plastic cloth. Calculate the knot size, the actual knot thickness is equal to the required knot thickness multiplied by 1.09, and prepare a sufficient amount of ramming material according to the construction furnace slope and furnace bottom size requirements. Check the ramming material for any debris and moisture after the incoming material. The sundries should be cleaned up, the damp materials should not be used, and the knotting equipment such as the smashing machine and the wind smashing should be prepared.


B Construction method


After shovel the shovel with iron shovel, use the foot to remove the air. After the steadiness, insert the steel into the material and shake it repeatedly. Then use the foot to further practise. The thickness of each layer of the ramming material is 150~200mm. It is advisable to beat it three times in a spiral from the periphery to the center with a knotting device.


The method of checking the quality of knotting is usually to place a round steel with a diameter of 5 mm on the ramming layer and press it under a pressure of 10 kg, the depth of which is not more than 30 mm. When the construction is on site, the steel can be inserted with force, and the depth should not exceed 30mm.


The method of knotting the slope is the same as that of the bottom of the furnace. First, use the foot to be solid, and then beaten with a knotting device. The maximum angle between the slope and the bottom of the furnace is not more than 40°. Prevent rolling or slumping due to too much slope of the furnace slope.


In the place where the steel taps such as the tapping bricks and the furnace door are agitated, it should be strongly beaten and appropriately thickened to extend the service life of the refractory materials in these damaged parts as much as possible.


After the completion of the fight, the 5~10mm thick steel plate is covered on the ramming material to prevent the shape of the bottom of the furnace from being damaged when the scrap is loaded or the scrap steel is inserted into the ramming layer, causing hidden troubles of steel leakage. If steel is not produced in time, 100~200mm thick lime is added to the iron plate to prevent hydration of the ramming material.


C new furnace smelting operation requirements


Magnesium-calcium-iron-synthesis sand dry mash has obtained knotted bulk density after construction in strict accordance with construction technical requirements. In order to ensure that the dry slag can be sintered into a solid whole during the smelting process, it can enhance the resistance to molten steel erosion and slag corrosion resistance. The smelting operation of the first furnace of the new furnace is crucial. The specific operation can be carried out as follows:


Loading scrap steel: Select high-quality scrap steel with low C and Si content. It is best to use shearing material or small block material. The number of loading should be one more than that of normal smelting. When loading, the hopper should be as close as possible to the bottom of the furnace to avoid oversize. The block material is loaded into the bottom of the furnace; each time the feed is melted by about 80%, and the feed is re-applied; after all the feeds are melted, the temperature is slowly raised to over 16001, and should be kept for more than 30 minutes.


Smelting speed: The smelting time of the first furnace is required to be 2~3 times of the normal smelting time. The low-speed gear should be used as much as possible in the power transmission operation, and the oil-oxygen gun or carbon-oxygen gun is not allowed to be used for melting.


Deflating: After the scrap is completely melted, the operator should arrange 2 deflation opportunities for at least 30 minutes each time the pumping system is insufficiently pumped. At the same time of deflation, pay attention to the heat preservation and shake the furnace to the tapping position. The ramming material around the tapping port is sufficiently sintered.


Oxygen blowing operation: When the molten steel composition does not meet the requirements in the later stage of smelting, it is often necessary to use oxygen blowing measures. However, it is more advantageous to use the oxygen blowing tube in the oxygen blowing operation. The depth of the inserted steel is generally about 100~150mm, and the insertion angle is generally At around 30°, the operating time is as short as possible; it prevents damage to the ramming material at the bottom of the furnace due to the large amount of blowing and the angle of blowing oxygen.


Smelting temperature and time: The first furnace smelting temperature is as high as possible, and the time is more than 2~3 times of the normal smelting time, which is beneficial to the sufficient sintering of the bottom ramming material. When the steel is tapped, a certain amount of molten steel should be left at the bottom of the furnace. The steel stay should be used to protect the bottom of the furnace. At the same time, the whole smelting process should pay attention to avoid the violent boiling of the molten steel and wash the bottom of the furnace.


D Electric furnace dry materials use precautions


(1) The residual steel and residue at the bottom of the furnace must be cleaned up, otherwise it is easy to produce new and old materials to be stratified. During use, the ramming material may be turned upside down, thus affecting the service life.


(2) When knotting and smashing, it must be strictly operated according to the construction requirements to ensure the compactness of the ramming material. Otherwise, the smashing material will be seriously contracted during use, and a large number of cracks will cause spalling, resulting in a decrease in life.


(3) The first furnace smelting is very important. When blowing oxygen decarburization, the oxygen blowing tube must not be inserted too deeply, otherwise it will easily cause the bottom of the furnace to turn up and produce a large pit.


(4) When the first furnace is smelted, the bottom of the furnace can be covered with a layer of lime, which not only avoids the scrap steel directly smashing the bottom of the furnace, but also prevents hydration of the ramming material and can form slag early.


(5) When a large pit appears at the bottom of the furnace, the residual steel and residue in the pit must be cleaned and then repaired with ramming material. If there is a little steel in the pit that is not clean, add some lime or dolomite to the molten steel, and use the iron shovel to clean the dolomite together with the molten steel. Otherwise, the interlayer will be formed in the pit when the bottom of the furnace is repaired, which will affect the repairing effect.


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