At present, the working layer of high-power and ultra-high-power electric furnaces is generally constructed with magnesia dry ramming material. The working layer uses refractory materials to directly contact molten steel and slag, and directly bear high-temperature thermal load and corrosion of molten slag, and erosion of molten steel and steel scrap. Mechanical impact and oxidation and reduction operations at high temperatures in the furnace cause molten slag to penetrate into the bottom of the furnace, resulting in thinning of the bottom of the furnace. In the discontinuous operation, the dicalcium silicate in the slag absorbs moisture in the atmosphere and collapses and falls off, reducing the durability of the material and affecting its service life.
Common dry ramming materials use high-iron, high-calcium synthetic magnesia and fused magnesia as aggregates, synthetic magnesia and fused magnesia as fine powder, with a critical particle size of 5-6mm, and synthetic magnesia with C2F (Dicalcium ferrite) is used as a sintering aid without adding any binding agent, and it is made with multi-level ingredients. Through strong ramming construction, the density after construction can be guaranteed, and it can be sintered into a solid whole at an appropriate temperature, and its life span is several times longer than the previous knotting and bricklaying methods. The dry ramming material used in the intermediate frequency furnace has higher quality requirements. Some scholars have studied the use of fused corundum, white corundum, tabular corundum, and magnesia as granular materials, and fine magnesia powder and corundum powder as powder. High-temperature burning accelerator, boric acid as an admixture, mix various raw materials uniformly and adjust the particle gradation to make dry ramming material.
Before the construction of the electric furnace bottom dry ramming material, attention should be paid to clean up the permanent layer residue, dust, iron wire, plastic cloth and other foreign objects. 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 size of the construction furnace slope and furnace bottom. After the incoming material, check whether the ramming material has debris and damp, the debris should be cleaned up, and the damp material should not be used, and prepare knotting equipment such as rammers and pneumatic picks.
The specific construction steps can refer to the following scheme:
After shoveling the material flat with a shovel, step on it firmly with your foot to remove the air, insert the steel drill into the material and shake it repeatedly, then use your foot to further solidify, the construction thickness of each layer of ramming material should be 150~200mm , And then use a knotting tool to repeatedly beat it 3 times in a spiral shape from the periphery to the center.
The method to check the quality of knots is usually to put a round steel with a diameter of 5mm on the ramming layer and press it down with a pressure of 10kg, and its depth does not exceed 30mm. Steel brazing can be inserted forcefully during site construction, and its depth should not exceed 30mm.
The method of knotting the furnace slope is the same as that of the furnace bottom. First, use your feet firmly and then use the knotting appliance to ramming. The maximum angle between the furnace slope and the furnace bottom does not exceed 40°. Prevent rolling or collapse due to the furnace slope is too large.
Place bricks at the tap hole, furnace door and other places where molten steel is agitated and scour severely should be rammed strongly and can be appropriately thickened to extend the service life of the refractory materials in these damaged parts as much as possible.
After beating, cover the ramming material with 5~10mm thick thin steel plate to prevent the shape of the furnace bottom from being damaged or the waste steel penetrating the ramming material layer when loading the scrap steel, which may cause the hidden danger of steel leakage. If steel cannot be made in time, 100~200mm thick lime should be placed on the iron plate to prevent hydration of the ramming material.
When knotting the ramming material, it must be operated strictly according to the construction requirements to ensure the compactness of the ramming material, otherwise it will cause serious shrinkage of the ramming material during use, resulting in a large number of cracks and spalling, resulting in a decrease in life. The first furnace is very important for smelting, and the oxygen blowing pipe must not be inserted too deep during oxygen blowing and decarburization, otherwise it will easily cause the furnace bottom ramming material to turn up and produce big pits. During the smelting of the first furnace, the bottom of the furnace can be covered with a layer of lime, which not only prevents the scrap steel from directly hitting the bottom of the furnace, but also prevents hydration of the ramming material and can form slag earlier.
Under normal circumstances, the one-time life of dry ramming material can reach more than 300 furnaces, and it can be extended to 500~600 furnaces through hot repair, and even some products on the market can reach more than 600 furnaces.
After the electric furnace bottom ramming material is used for a certain period of time, due to various reasons, the electric furnace bottom will be damaged to different degrees. Therefore, the furnace lining should be repaired according to the damage of the furnace lining.
(1) Hot repair is carried out every certain period in the smelting, but after each furnace steel is finished, attention must be paid to the dynamics of the furnace bottom, and the pit must be repaired when the depth is greater than 150mm.
(2) Before repairing, use oxygen (immediately after the steel and slag are removed) to purge the repaired surface to completely remove the residual steel residue in this part.
(3) Lift in the ramming material until it falls above the part to be repaired, and move the crane to make the distribution reasonable.
(4) Lift into iron blocks or other heavy objects to compact.
(5) It should be emphasized that if the furnace bottom and furnace slope are hot repaired on a large area, in order to ensure the service life after repair, shorten the number of repairs, and reduce the consumption of steel per ton of dry ramming, the first furnace steel after hot repair can refer to ” The new furnace smelting operation requires “smelting.”