Casting alloys must be melted first, then injected into the molds and cooled to the characteristics of the castings, making the casting industry the only industry in the large machinery industry to use the smelting furnace.The annual production of castings in China is about 50 million tons, which means that the foundry industry melts 83 million tons of alloy liquid every year. Therefore, the importance of smelting furnace to the foundry industry is self-evident.Different alloys need different smelting furnaces for smelting. As the production of cast steel only accounts for about 10%, non-ferrous alloys are less than 20%, and the proportion of cast iron is more than 70% both in the world and in China, more attention has been paid to the development and selection of cast iron smelting furnaces.
China is the first country in the world to use ore to smelt pig iron.The largest iron castings in history, such as the Pending Ding weighing 413 kg in 513 BC, the Pujin Tieoxu weighing 45 t in 724 A.D., the Cangzhou Tielion weighing 40 t in 953 A.D., and the Dangyang Iron Tower weighing 27 t in 1061 A.D., are all cast in China, which also proves that China has long mastered the shaft furnace smelting equipment with blowers.However, due to the feudal system being self-contained and not keeping up with the industrial revolution of the times, the melting of cast iron in modern China remained at the level of three furnaces and scoops.The first cold air cupola in the world was invented by John Wilkison in 1794 in the United Kingdom. The first cupola in China was installed by Dalian Iron Worker in 1907.In 1895, the electric arc furnace was invented by Heoult, France, for the smelting of cast steel. It was later used in the production of cast iron to increase the temperature of the molten iron, to use iron chips and to produce alloy cast iron.
In 1953 FAW built the plant to produce piston rings by melting alloy cast iron in electric arc furnace. In 1960s, GM, Ford and other companies built a new foundry to mass produce cast iron in large-tonnage electric arc furnace.The induction furnace was invented in 1921 in the United States, but it was only widely used in the 1970s after the thyristor was invented in 1957.At that time, it was the first time in China that large quantities of cast iron were melted by power frequency induction electric furnace.Therefore, it can be said that the cupola was mostly used in the melting of cast iron before 1960s in the world, while the cupola was mostly used in China in the early 1990s.
Subsequently, the improvement and development of induction furnaces, especially the requirement for flexibility in production, completely replaced electric arc furnaces in the smelting of cast iron and small and medium-sized cupolas in cast iron foundries.In developed western industrialized countries, because there are few small foundry enterprises and environmental protection is paid more attention, the conversion and transformation of smelting furnace is based on flexibility, quality and cost.But there are many differences in our country: from 1990s onwards, up to now, 8 million tons of centrifugal cast nodular iron pipes and pipe fittings are mostly produced by the original blast furnace pig iron manufacturer using the “short process” advanced process, i.e. using the dual smelting of blast furnace liquid iron and coreless induction furnace to provide molten iron, unlike most foreign cast pipe enterprises using the cupola-coreless induction furnace dual smelting.Process can reduce production costs; the proportion of small and medium-sized foundry enterprises in China is high; they used cupola smelting in the past, especially all cupolas do not have effective dust removal devices installed, resulting in serious environmental pollution; the Ministry of Industry and Information Technology of China, with the support of China Foundry Association, has implemented the “Foundry Access” and “Foundry Enterprise Specifications”, and vigorously implemented the action to safeguard the blue sky to promote environmental pollution.This has led a large number of small and medium-sized foundries to shut down operations or replace cupolas with induction furnaces.Therefore, by 2016, the smelting proportion of cupola in China has decreased to less than 36%, and it has continued to decrease in recent years, which is quite different from that of cupola and induction electric furnace in foreign countries which account for 50% respectively.