The ductile iron pipe is poured and melted in an intermediate frequency induction furnace. The temperature does not need to be too high. The furnace can be released when the temperature reaches 1480 ℃. The molten iron should stay in the ladle for a period of time for sedation. Depending on the size of the workpiece, it can be poured between 1380 ～1410 ℃ . The furnace lining can be acidic or alkaline. The proportioning, knotting, drying and sintering of the furnace lining are all carried out according to conventional processes.
The charging is generally carried out in the normal order. Firstly, refractory iron alloys such as gray pig iron and ferro-molybdenum are loaded into the bottom of the furnace, and then the scrap steel is loaded according to the principle of tight bottom and loose top. The melting temperature of high chromium cast iron is higher than that of ordinary cast iron, about 1200 ℃, and the firing temperature is about 1500 ℃. Medium frequency induction electric furnace is used for smelting.
After the metal charge is completely melted and the temperature is raised to 1480 ℃ for deoxidation, ferromanganese, ferrosilicon and aluminum are added for deoxidation. The power of the electric furnace is adjusted to a large power for melting. Because the smelting loss of Cr is relatively large ( about 5% to 15%) , the ferrochrome should be added later, usually after the scrap steel is completely melted, the roasted red ferrochrome is added.
Because ductile iron pipe fittings use flexible joints, the construction operation is more convenient, which can improve construction efficiency, improve construction conditions, and reduce construction costs. Moreover, most of the interfaces are connected by aprons, which is easy to operate, shorten the construction period and reduce the construction cost.
Ductile iron pipe fittings can withstand high water supply pressure, resist external loads and adapt to changes in geological conditions. The pipe has the advantages of high strength, good toughness, corrosion resistance, easy installation of flexible interfaces, strong earthquake resistance, and low labor intensity. It can be applied to geology. In poor locations and crossing highways, no additional processing of steel pipes is required, and coupled with strong corrosion resistance, it can be applied to coastal and saline-alkali areas. It is widely used in underground pipeline engineering.