The following is an introduction to threading and alloy casting.
(1) Withdrawal time. As the smelting process continues, more and more molten iron accumulates in the furnace. A large amount of molten iron with strong conductivity accumulates in the furnace, which causes the electrode to rise and makes it difficult to operate. Therefore, in order to ensure the normal course of the smelting process, it is necessary to open the iron drainage hole at regular intervals and to discharge a large amount of molten iron accumulated in the furnace in a timely manner. Short tap intervals and longer retraction times facilitate electrode insertion. However, longer retraction times result in greater heat loss and casting losses. Therefore, the appropriate diversion time should be determined according to the furnace capacity and the heat grade. Generally, the lower the silicon content of ferrosilicon, the longer it takes to tack. For example, when smelting 75% ferrosilicon in an electric furnace with a capacity of 10000~30000 kVA, 4~5 furnaces are tapped in 8 hours. When smelting 75% ferrosilicon in an electric furnace of 180()~9000 kVA-A, 3~4 furnaces are listened to in 8 hours.
(2) Preparatory work before tapping. Before tapping, it is necessary to prepare all the tools for opening and locking the furnace eye, as well as check the ladle for compliance with the requirements. Prepare the balls for the cement slurry. The closure materials are mainly coke powder (electrode paste), water and a small amount of graphite powder mixed into conical balls of sludge that can be joined together. The dirt balls are appropriately sized.
(3) Plugging the threaded hole. As a result of the leaching of high-temperature molten iron, oxidation and ablation of air, the threaded hole is very easy to damage. Practice shows that the service life of the threaded hole often determines the service life of the furnace body. In order to extend the life of the furnace body, it is necessary to use and maintain the threaded hole correctly.
When threading, round steel should be used to remove residues near the hole, beat off the dirt balls around the furnace eye, clean the threading trough, and then open the furnace eye with round steel at the upper end of the furnace eye centerline. If the furnace eye is difficult to open, it can be opened with a burner. If it is not possible to open the eye, it can be opened with oxygen. When opening a new furnace eyelet, oxygen can be used to open the furnace eyelet. When using round steel or a burner to tamper the furnace eye, it is strictly forbidden to tamper or burn indiscriminately, especially tamper or burn randomly below the center line of the furnace eye, otherwise it will cause holes in the furnace eye, destroy the shape of the furnace eye, which is small inside and large outside, which will make it difficult to clog the eyes.
(4) Iron tapping and slag removal. During the iron tapping process, the furnace eye will automatically expand due to the erosion of molten iron. Therefore, when the furnace eye is just opened, especially when a new furnace is just opened, the furnace eye should not be opened too much, otherwise the flow pressure will be too great, the slag will be difficult to remove, and the iron ladle can be easily damaged. If the temperature of molten iron is too highjuice, and the flow pressure is too high, the power should be reduced, and the furnace eye should be opened smaller. Usually, when molten iron covers the bottom of the ladle or reaches 1/3 of the ladle, the furnace eye is gradually enlarged by round steel.
Once the furnace eye is opened, the electrode should be inserted gradually, depending on the outflow of molten iron and the load. The electrode at the outlet mouth should remain as stationary as possible at the early stage of pig iron removal, and at a later stage it can be gradually inserted. When the molten iron flows out, if the flow pressure is too great, it can be shut off with round steel with rake head; If the flow pressure is too low, use round steel to pierce the furnace eye. For large stoves, use a ladle. When tapping cast iron, in order to prevent the surface melt from solidifying, it is necessary to constantly add coke powder to maintain heat.
During the layering process, more slag must be removed. The amount of slag in a ferrosilicon furnace can reach 2-4% of the alloy weight. When the furnace is in good condition, its thickness is about 300mm with iron. After the eye of the old furnace is clogged at a late stage, the excess of the external mouth is about 200 mm.
The sealing of the eye eliminates the loss of the furnace lining and wellhead during cutting. In addition, attention should be paid to the repair of the flow channel. The ladle in which the molten iron is stored is built of mud bricks and coated with mud mixed with refractory clay and coke powder to facilitate the removal of slag. The ladle must be dried with hot slag before use.
(6) Alloy casting. After the molten iron is briefly solidified in the ladle, a small amount of slag on the molten iron is scraped off, a graphite rod is added to block the slag, and then the molten iron is poured into the black iron ingot mold. In a trough-shaped cast iron mold for small electric furnaces, molten iron is usually poured directly. Before pouring the ingot, the mold should be cleaned and kept dry. In order to avoid ferrosilicon sticking to the ingot mold, the iron ingot in the furnace should be cooled with water after extraction, and the graphite powder or lime milk slurry should be applied to the ingot mold in a hot state. The finished ferrosilicon should be placed flat at the impact point of the molten iron flow head.
During pouring, the appropriate temperature and pouring speed should be controlled. The casting speed should be based on the principle of no molten iron splashing. The corresponding casting temperature is usually 100-200°C higher than the melting point of ferrosilicon. In order to make the sample representative and overcome the unevenness of the ladle composition, sampling should be carried out at the early, middle and late stages of casting.
