Electroslag (melting casting) is a kind of secondary refining technology, which is a comprehensive metallurgical casting process combining secondary refining of molten steel with directional solidification.The principle is that the current [TJC STEEL]passes through the liquid slag pool slag heat resistance, the metal electrode melts, the molten metal collects into the molten drop, drops through the slag layer into the metal molten pool, and then crystallizes in the water-cooled crystallizer to solidify into ingots.

 

Technology Development:

ESR is the refining process of casting or forging steel smelted in open - hearth furnace, converter, arc furnace or induction furnace into electrodes for secondary remelting by slag resistance heat.The principle of this refining method was first proposed by R.K.Hopkins in the 1940s.Then the Soviet Union and the United States [TJC STEEL]established electroslag furnaces for industrial production.In the mid-1960s, electroslag remelting developed rapidly in The Soviet Union, Western Europe and the United States due to the development of aviation, aerospace, electronics, atomic energy and other industries.The products include: high quality alloy steel, high temperature alloy, precision alloy, corrosion resistant alloy and aluminum, copper, titanium, silver and other non-ferrous metal alloys.In 1980, the world's production capacity of electroslag remelting steel exceeded 1.2 million tons.

 

Working Process:

Molten slag is contained in a copper water-cooled crystallizer and one end of the consumable electrode is inserted into the slag.Consumable electrode, slag pool, metal melting pool, steel ingot and bottom water tank form circuit through short wire and transformer.In the process of electrification, joule heat is released from the slag pool, and the consumable extreme end is gradually melted, and the molten metal is gathered into droplets, which pass through the slag pool and fall into the crystallizer, forming a [TJC STEEL]metal melting pool, which is cooled by water and quickly solidified into ingots.During the droplet formation stage at the end of the electrode and the droplet dropping through the slag pool, the steel and slag are in full contact, and the non-metallic inclusion in the steel is absorbed by the slag.The harmful elements (sulfur, lead, antimony, bismuth, tin) in steel can be effectively removed by steel-slag reaction and high-temperature gasification.The reoxidation of liquid metal is basically avoided under the cover of slag pool.Because it is melted, refined and [TJC STEEL]solidified in a copper water-cooled crystallizer, the pollution of steel by refractory materials is eliminated.Before the ingot solidifies, there are metal melting pool and slag pool on the upper end of the ingot, which play the role of heat preservation and retraction to ensure the densification of the ingot.The rising slag pool forms a thin slag shell on the inner wall of the mold, which not only makes the surface of the ingot smooth, but also acts as insulation and heat insulation, so that more heat is transferred to the lower part, which is conducive to the directional crystallization of the ingot from the bottom up.Because of the above reasons, the quality and performance of the steel ingots produced by electroslag remelting are improved, the plasticity and impact toughness of alloy steel are enhanced at low temperature, room temperature [TJC STEEL]and high temperature, and the service life of steel is prolonged.

 

Equipment:

Electroslag equipment is simple, less investment and lower production cost.The disadvantage of electroslag remelting is that the power consumption is high, and the general slag contains CaF2 more. In the remelting process, the environment is polluted, so dust removal and fluoride removal devices must be set up.

 

The Biggest Furnace:

In April 1980, a 200-ton electroslag furnace was successfully trial-produced in Shanghai Heavy machinery Plant.It is the largest electroslag remelting furnace in China and the largest in the world.

The construction of large electroslag furnace is an important project.The whole project is led and organized by Deputy chief engineer Lin Zongtang. Professor Zhu Jou of Beijing Iron and Steel Institute is the consultant. Shanghai Heavy Machinery Plant and Beijing Iron and Steel Institute jointly develop and develop the project.Remelting process and workshop design by Liu Chunlin;The electroslag remelting equipment is[TJC STEEL] designed by Huangfu Gems;High and low voltage electrical design by Su Ye and Tan Heirloom;The civil and utility parts are designed by Shanghai Electromechanical Design And Research Institute.From November 1972 to December 1974, liu Chunlin and Liu Haihong, a teacher from Beijing Iron and Steel Institute, led the experimental team to carry out a number of tests in Shanghai Heavy plant and relevant factories successively, in order to determine the design parameters of electroslag furnace equipment, remelting and drawing process parameters.This three-phase three-rocker double-pole tandem type large electroslag furnace consists of three small racks arranged in an equilateral triangle arrangement.Each small rack has a column 18 meters high.The bottom of the three columns is fixed on the foundation, and the middle and top are connected by curved beams to form the electroslag furnace body.A 2.8 m diameter copper lined steel shell water cooled crystallizer is arranged on the middle curved beam.The upper part of each column is equipped with rocker arms which can move up and down and rotate from left to right through the transmission device.One end of the rocker arm is equipped with an electrode clamping mechanism, which can clamp two electrodes which are insulated[TJC STEEL] from each other and connected in series.Six electrodes are suspended from the three rocker arms.Each of the two electrodes is supplied by a single-phase transformer.In this way, the six electrodes form a three-phase bipolar series circuit.The electrodes are 500 mm in diameter and weigh about 5 tons each.The lower part of the crystallizer is equipped with an electric flat car with water-cooled bottom plate, which can carry a load of up to 300 tons.Flat cars are placed on a movable platform that can move up and down along three columns.Before remelting [TJC STEEL]begins, the movable platform rises so that the water-cooled bottom plate seals the lower part of the mold, and then slag and remelting electrodes are made in the mold.Six steel electrodes are remelted at the same time, and after a certain period of time the electrodes are remelted, the three rocker arms are replaced by new electrodes alternately, so that a large electroslag ingot can be smelted.With the remelting of the steel electrode, the slag liquid level of the mold rises continuously, and after reaching a certain height, the ingot-drawing operation is carried out, that is, the water-cooled bottom plate is lowered slowly while the slag liquid level rises, so as to obtain a large electroslag ingot with a certain length and required tonnage.After the ingots are made, the platform descends and the ingots are drawn out of the mould. An electric flat car carries the ingots along the track and out of the oven.

This electroslag furnace has the following characteristics: bipolar series power supply, can reduce the loop induction, improve the electric power factor;Three-phase power supply is adopted, which is beneficial to voltage balance of external network.Three rocker arms rotate electrodes and remelting large ingot with small cross section electrode is helpful to control the segregation of electrode components.Long ingot can be remelted with short crystallizer by using ingot drawing operation.

In 1982, the forging made from remelting ingots passed the national appraisal and agreed to use this electroslag furnace to produce ingots for first-grade safety pressure vessels for China's first nuclear power station -- Qinshan 300mw [TJC STEEL]nuclear power station.Then all the large electroslag ingots needed for evaporators and regulators of nuclear power plants are provided.The two largest electroslag ingots weigh 205 tons and 207 tons respectively.

This electroslag furnace was then used to remelte large electroslag ingots for thermal forging and chemical containers.The large electroslag ingots produced by it have been appraised by the state, which show that the electroslag steel has high purity, uniform composition, good performance and excellent toughness.Thus it opens a new way for the manufacture of high quality large forgings in China.