The most commonly used spheroidizers in industry are magnesium, re and calcium. Magnesium has the strongest spheroidizing ability, but its boiling point is much lower than that of molten iron. When magnesium is used as spheroidizing agent, its vaporization is serious, its absorption rate is low, and it lacks economy and safety. In industry, magnesium is not used as spheroidizing agent alone, but ferrosilicon magnesium alloy or rare earth ferrosilicon magnesium alloy is used as spheroidizing agent. The boiling point of Cerium in rare earth is 1400 ° C, the spheroidization reaction is stable, and the anti-interference ability is strong, but cerium is expensive, and the spheroidization effect is not as good as magnesium, so it can be used in the production of large section ductile iron under certain conditions; heavy rare earth is mostly used in large section ductile iron, and the spheroidization reaction is stable, and the anti-aging ability is strong, and the anti-aging ability of yttrium based heavy rare earth is better than that of cerium based light rare earth. The boiling point of calcium is 1487 ° C, the effect is stable, but the spheroidizing ability is weak, the addition amount is usually large, and it is easy to oxidize and difficult to store, which limits the use of calcium.
(1) Charging method: the advantages of this spheroidizing process do not require much skill for workers, and excellent castings can be obtained by strictly abiding by the casting process requirements; however, the combustion of magnesium in this process leads to a large amount of burning loss of spheroidizing agent in molten iron, which reduces the absorption rate of magnesium (about 30% – 50%), and pollutes the workshop environment.
(2) Pressure magnesium addition method: the temperature before spheroidization is 1350 ° C? At 1400 ° C, the sulfur content of the original molten iron is less than 0.1%, pure magnesium or pure magnesium with rare earth ferrosilicon alloy is selected, and the process is generally suitable for treating more than 3T. The cover package and the package for pressure magnesium method must be tightly fitted and sealed. The spheroidizing process needs to strictly control the temperature of molten iron treatment, and the operation requirements are strict, so its application is limited.
(3) In mold spheroidizing treatment: the mechanical properties are higher than ordinary spheroidizing treatment process, the magnesium absorption rate is higher (can reach more than 80%), the spheroidizing and inoculation decline are improved, the working conditions are improved, etc.; however, the requirements for the composition of molten iron are strict, the sulfur content is less than 0.008%, each casting needs to be tested for spheroidizing rate, and the production control requirements are high.
(4) Wire feeding method: in 1976, Japan developed the feeder wire process, also known as core wire injection method The core wire process equipment is composed of core wire, wire feeder and pipe. 20% – 30% Mg + L% – 2% Ca + 40% Si + Fe is used as spheroidizing agent, and the core wire diameter is 13mm. Wire feeding spheroidizing process has the following characteristics: ① magnesium absorption rate is 40% – 50%; ② the tendency to reduce casting defects; ③ good working environment; ④ digital and remote management can be realized; ⑤ suitable for various batch production.
In addition, the spheroidization process also includes the subcontract method, magnesium spraying method and so on.
