TAILIEUCHUNG - Foseco Ferrous Foundryman's Handbook Part 3

Tham khảo tài liệu 'foseco ferrous foundryman's handbook part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 4 Melting cast irons Introduction Iron foundries require metal of controlled composition and temperature supplied at a rate sufficient to match the varying demands of the moulding line. The metallic charge to be melted consists usually of foundry returns iron scrap steel scrap and pig iron with alloying additions such as ferrosilicon. The charge is usually melted in a cupola or in an electric induction furnace. Gas-fired or oil-fired rotary furnaces can also be used but their use is less common. Cupola melting The cupola Fig. is the classical iron melting unit and is still the most widely used primary melting unit for iron production due to its simplicity reliability and the flexibility in the quality of charge materials that can be used because some refining of undesirable elements such as zinc and lead can be achieved. While the cupola is an efficient primary melting unit it does not adapt easily to varying demands nor is it an efficient furnace for superheating iron. For this reason it is often used in conjunction with an electric duplexing furnace. The simplest form is the cold blast cupola which uses ambient temperature air to burn the coke fuel. The metal temperature that can be achieved is normally from 1350 to 1450 C but higher temperatures can be achieved through the use of divided blast as in Fig. or oxygen enrichment. The refractory linings of cold blast cupolas have a short life of less than 24 hours so cupolas are operated in pairs each used alternately while the other is re-lined. In hot blast cupolas Fig. the exhaust gases are used to preheat the blast to 400-600 C reducing coke consumption and increasing the iron temperature to more than 1500 C. They may be liningless or use long life refractories giving an operating campaign life of several weeks. Cokeless cupolas Fig. have been developed in which the fuel is gas or oil with the charge supported on a bed of semi-permanent refractory spheres. They have advantages of reduced .

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