SAND CASTING EQUIPMENT.

The spheroidization grade of ordinary ductile iron castings should reach above grade 4 (spheroidization rate 70%), and the spheroidization rate achieved by the general foundry is about 85%. In recent years, with the development of ductile iron production, especially in the wind power casting production and casting quality requirements of the industry, the requirement of spheroidization level to reach level 2, that is, spheroidization rate to reach more than 90%. By analyzing and improving the spheroidization and inoculation process originally used in QT400-15 as well as spheroidizing agent and inoculation agent, Xinyuanzhu Group achieves the spheroidization rate of nodular cast iron above 90%.

1. Influence of major elements on spheroidization rate
C, Si: C can promote graphitization, reduce the tendency of white mouth, but (C) high amount will make CE too high and easy to produce graphite floating, generally controlled at 3.7%~3.9%. Si can strengthen graphitization ability and eliminate cementite. When Si is added as an inoculant, the supercooling capacity of molten iron can be greatly reduced. In order to improve the inoculation effect, the amount of (Si) in the original iron solution decreased from 1.3% ~1.5% to 0.8%~1.2%, and the amount of (Si) was controlled at 2.60%~3.00%
Mn: During crystallization, Mn increases the supercooling tendency of cast iron and promotes the formation of carbides (FeMn) 3C. During the eutectoid transition, Mn reduces the eutectoid transition temperature, stabilizes and refine the pearlite. Mn has no significant effect on spheroidization rate. Due to the influence of raw materials, general control (Mn) <0.30%
P: When (P) <0.05%, it is difficult to form phosphorous eutectic, which has little effect on the spheroidization rate of nodular iron.
S: S is an anti-spheroidizing element. In the spheroidizing reaction, S consumes Mg and RE in the spheroidizing agent, hinders graphitization and reduces the spheroidizing rate. Sulfide slag will return sulfur before the solidification of molten iron, consume spheroidized elements again, accelerate the decline of spheroidization, and further affect the spheroidization rate. In order to achieve a high spheroidization rate, the amount of (S) of the original iron solution should be reduced to less than 0.02%.

2. Improvement measures
Raw materials shall be cast iron, scrap steel without rust or less rust and return charge; Desulphurization of the original iron solution by adding soda ash (Na2CO3); Fusco 390 pretreatment agent was used to predeoxidize in the package. Fosco spheroidizing agent was used for spheroidizing treatment. Silicon carbide and ferrosilicon were used for joint inoculation.
2.1 Desulfurization treatment
When the burden melting, sampling analysis of chemical composition, when the amount of (S) is higher than 0.02% to be desulfurized treatment.
The principle of soda desulfurization is as follows: put a certain amount of soda in the casting ladle and stir it with the iron liquid flow. The soda is decomposed at high temperature. The reaction formula is Na2CO3=Na2O+CO2↑ : the generated Na2O is combined with the sulfurization in the iron liquid to produce Na2S, (Na2O) +[FeS]= (Na2S) + (FeO). The decomposition of CO2 from Na2CO3 resulted in violent agitation of iron solution, which promoted the desulfurization process. The pure alkali slag is easy to flow and float up quickly. The desulfurization reaction time is very short. After desulfurization, the slag should be scraped in time, otherwise the sulfur will return.
2.2 Predeoxidization, spheroidization and inoculation
Fusco 390 pretreatment agent in the package plays a role of pre-deoxidization, at the same time increase graphite nucleation core, increase the number of graphite spheres per unit area, but also can improve the absorption rate of Mg, greatly improve the anti-recession ability, improve the spheroidization rate. Fusco inoculant contained (Si) =60%~70%, (Ca) =0.4%~2.0%, (Ba) =7%~11%, and Ba could prolong the effective inoculation time.
Choose a brand as an NODALLOY7RE, the omega (Si) = 40% ~ 50%, omega (Mg) = 7.0% ~ 8.0%, omega (RE) = 0.3% ~ 1.0%, omega (Ca) = 1.5% ~ 2.5%, omega (Al) < 1.0%. Because the iron liquid after desulfurization and pre-deoxidization treatment, iron liquid consumption of spheroidizing agent element greatly reduced, so the selection of (RE) low amount of spheroidizing agent, to reduce RE to the deterioration of the shape of spherical graphite; The spheroidizing elements are mainly Mg; Ca and Al can play a role in strengthening inoculation. The combined inoculation treatment of silicon carbide and ferrosilicon is adopted. The melting point of silicon carbide is around 1600℃, and graphite crystal nucleus is added during solidification.

3. Conclusion When the spheroidization rate of ferrite nodular cast iron is more than 90%, the following measures can be adopted
3.1 select high quality charge to reduce anti-spheroidizing elements in charge.
3.2 The low amount of (RE) spheroidizing agent was used to reduce the deterioration effect of RE on the shape of spherical graphite.
3.3 The amount of (S) of the original iron solution shall be less than 0.020%, so as to reduce the consumption of spheroidizing agent, especially the consumption of spheroidizing elements consumed by sulfur secondary back to sulfide slag.
3.4 Predeoxidize iron liquid, increase the number of graphite balls per unit area, improve the spheroidization rate, greatly improve the anti-decay ability, and extend the effective incubation time.
3.5 Reduce the amount of (Si) in the original iron solution, increase the amount of spheroidizing agent, inoculant and various pretreatment agents, strengthen inoculant treatment.

Xinyuanzhu Group is a China Casting Supplier, specializing in the production of Ductile iron Castings, Pig Iron Gray iron Casting, Steel Casting and Brass Casting. We can carry out bulk Casting production according to the Casting drawings. We welcome customers to visit and inspect the factory.