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Our journey through Zanardi Fonderie’s production plant continues and in this video we will observe the ancient melting and casting process of the cast iron jets, a process which is still evolving today.
In our previous video, we started with the design offices all the way to the coupling of the two green sand half moulds, ready to host the liquid cast iron.
Today we will discover the process of melting and casting of the cast iron.
Zanardi Fonderie plant has 3 electric induction melting furnaces operating at mains frequency with a capacity of about 28 tons and an installed power of 3,300 KW each.
The ovens are loaded by vibrating loading platforms located in the rear part, while the liquid basic pig iron is poured from the front part of the oven which had been previously tipped.
The filling materials used to realise the liquid-based cast iron bath(I don’t think it’s the correct definition) are mostly:
- Pig iron
- Steel scraps
- Scraps of previous castings
All these materials are stored in different compartments found in the raw material park and are transported to the loading wagons by an electromagnet equipped with a load cell semi-automatically maneuvered by the operator.
In order to achieve a suitable chemical composition of the base cast iron, in addition to the three materials mentioned above, graphite, silicon carbide, silicon iron, copper, manganese iron, molybdenum iron can be loaded manually by foundry operators (Cure Oven Operators) ; this activity is necessary to get closer to the final cast iron composition.
During the preparation phase of the base cast iron which precedes the pouring phase from the treatment ladle (or transport phase and within which the spheroidization reaction will take place), it is best practice to take samples from the bath to carry out the thermal analysis and obtain the samples for the chemical analysis, in order to monitor the conditions and the composition of the bath, if necessary, make corrections to reach the required target. The temperature in the oven is also monitored by an immersion thermocouple probe. The temperature must be constantly monitored, since after pouring the molten metal into the treatment ladle it will decrease during the transport phase (which includes spheroidization reaction, further ladle slag and pouring) from the ovens to the casting line.
As anticipated, to transport the liquid cast iron, from the melting furnaces to the casting line, a ladle is used. It has a capacity of 3,000 kg, inside which the spheroidization reaction takes place by adding suitable ferroalloys (Fe-Si- Mg iron-silicon-magnesium, Ni-Mg nickel-magnesium). The ladle, maneuvered by a crane, before hosting the liquid base cast iron, passes through a loading station where spheroidizing alloys and corrective materials for the composition are introduced (for example correction ferroalloys such as Fe-Si Ferro- Silicon, pure metals such as Cu Copper and Ni Nickel); this is necessary to reach the optimal conditions to obtain the spheroidization reaction and the chemical composition of the final cast iron.
During the pouring, the (very violent) spheroidization reaction begins inside the treatment ladle, which enables the formation and growth of graphite particles in a spheroidal shape rather than lamellar shape when solidifying.
Before pouring the liquid cast iron from the treatment ladle to the casting one, it is necessary to carry out a second ladle slag removal since the spheroidization reaction produces a certain quantity of waste.
To produce graphite cast iron, it is necessary to implement various strategies intended to inhibit the formation of cementite in each area of the casting to be produced. A very effective but complex intervention consists in intervening on the chemical composition using elements called "graphitizing" such as silicon.
Another type of intervention on the nucleation mechanisms, more effective even if delicate, consists of introducing heterogeneous preferential nucleation sites of graphite into the liquid cast iron. This is the process known by the name of inoculation which enables to eliminate the formation of cementite in thin areas of the cast iron and to control and make the type and distribution of the graphite particles homogeneous within the casting and therefore its mechanical characteristics.
During the pouring phase of the liquid cast iron into the casting ladle, a first inoculation is carried out, called pre-inoculation; in this process, inoculants based on FeSi (Iron-Silicon) are added to the liquid cast iron, which allow the formation of nucleuses around which the formation of graphite nodules will take place.
In addition to the practice of inoculation, the proportion of metal presence in some chemical elements also plays an important role in the nucleation state.
Zanardi Fonderie’s casting line is an automatic system composed of an unheated pressure casting ladle, also called cold ladle, a nozzle for regulating the flow during casting and a control and supervision equipment with PLC and dedicated casting software. Let’s see in detail the various components.
In our previous video, we started with the design offices all the way to the coupling of the two green sand half moulds, ready to host the liquid cast iron.
Today we will discover the process of melting and casting of the cast iron.
Zanardi Fonderie plant has 3 electric induction melting furnaces operating at mains frequency with a capacity of about 28 tons and an installed power of 3,300 KW each.
The ovens are loaded by vibrating loading platforms located in the rear part, while the liquid basic pig iron is poured from the front part of the oven which had been previously tipped.
The filling materials used to realise the liquid-based cast iron bath(I don’t think it’s the correct definition) are mostly:
- Pig iron
- Steel scraps
- Scraps of previous castings
All these materials are stored in different compartments found in the raw material park and are transported to the loading wagons by an electromagnet equipped with a load cell semi-automatically maneuvered by the operator.
In order to achieve a suitable chemical composition of the base cast iron, in addition to the three materials mentioned above, graphite, silicon carbide, silicon iron, copper, manganese iron, molybdenum iron can be loaded manually by foundry operators (Cure Oven Operators) ; this activity is necessary to get closer to the final cast iron composition.
During the preparation phase of the base cast iron which precedes the pouring phase from the treatment ladle (or transport phase and within which the spheroidization reaction will take place), it is best practice to take samples from the bath to carry out the thermal analysis and obtain the samples for the chemical analysis, in order to monitor the conditions and the composition of the bath, if necessary, make corrections to reach the required target. The temperature in the oven is also monitored by an immersion thermocouple probe. The temperature must be constantly monitored, since after pouring the molten metal into the treatment ladle it will decrease during the transport phase (which includes spheroidization reaction, further ladle slag and pouring) from the ovens to the casting line.
As anticipated, to transport the liquid cast iron, from the melting furnaces to the casting line, a ladle is used. It has a capacity of 3,000 kg, inside which the spheroidization reaction takes place by adding suitable ferroalloys (Fe-Si- Mg iron-silicon-magnesium, Ni-Mg nickel-magnesium). The ladle, maneuvered by a crane, before hosting the liquid base cast iron, passes through a loading station where spheroidizing alloys and corrective materials for the composition are introduced (for example correction ferroalloys such as Fe-Si Ferro- Silicon, pure metals such as Cu Copper and Ni Nickel); this is necessary to reach the optimal conditions to obtain the spheroidization reaction and the chemical composition of the final cast iron.
During the pouring, the (very violent) spheroidization reaction begins inside the treatment ladle, which enables the formation and growth of graphite particles in a spheroidal shape rather than lamellar shape when solidifying.
Before pouring the liquid cast iron from the treatment ladle to the casting one, it is necessary to carry out a second ladle slag removal since the spheroidization reaction produces a certain quantity of waste.
To produce graphite cast iron, it is necessary to implement various strategies intended to inhibit the formation of cementite in each area of the casting to be produced. A very effective but complex intervention consists in intervening on the chemical composition using elements called "graphitizing" such as silicon.
Another type of intervention on the nucleation mechanisms, more effective even if delicate, consists of introducing heterogeneous preferential nucleation sites of graphite into the liquid cast iron. This is the process known by the name of inoculation which enables to eliminate the formation of cementite in thin areas of the cast iron and to control and make the type and distribution of the graphite particles homogeneous within the casting and therefore its mechanical characteristics.
During the pouring phase of the liquid cast iron into the casting ladle, a first inoculation is carried out, called pre-inoculation; in this process, inoculants based on FeSi (Iron-Silicon) are added to the liquid cast iron, which allow the formation of nucleuses around which the formation of graphite nodules will take place.
In addition to the practice of inoculation, the proportion of metal presence in some chemical elements also plays an important role in the nucleation state.
Zanardi Fonderie’s casting line is an automatic system composed of an unheated pressure casting ladle, also called cold ladle, a nozzle for regulating the flow during casting and a control and supervision equipment with PLC and dedicated casting software. Let’s see in detail the various components.
The metal inside the main room is kept in a modified atmosphere using nitrogen and forced to rise inside a canal, exposed to atmospheric pressure, at the end of which is placed the nozzle, which acts as a regulating valve for the control of the liquid cast iron flow when filling the bracket below. The casting ladle has a maximum capacity of 4,500 kg and is equipped with cameras to control that the nozzle opens to let the liquid cast iron flow.
During the casting phase, a second inoculation, called post-inoculation, is carried out directly on the liquid cast iron flow immediately before entering the earth mould; unlike the pre-inoculation, this second inoculation is much more efficient as the liquid cast iron is already at a good level of nucleation and furthermore the particles constituting the post-inoculant are finer, a characteristic that facilitates its dissolution.
The whole process is automatic and supervised by the operator in the casting cabin (caster), who keeps under control the flow of liquid cast iron, the amount of inoculant introduced and any anomalies that may occur in order to prevent possible interruptions in the process and guarantee the metallurgical quality of the cast iron produced.
During the casting process, the operators carry out various analysis on the quality of the final cast iron, as well as the micrographic control of the ladle specimens, necessary to evaluate the shape of the graphite and the efficiency of the spheroidization treatment, the control of the chemical and thermal analysis.
Once the brackets have been cast, they move forward along the line to allow the liquid cast iron cluster to cool and solidify.
During the solidification phase, the material is subject to phase transitions; for example, in case we have a hypoeutectic spheroidal cast iron, the solidification phase begins around 1.170 °, with the formation of primary austenite in the form of dendrite. With the progress of solidification they will grow and enrich the liquid cast iron around them with carbon, at this point, in the carbon over-saturated liquid are created the conditions for the precipitation of graphite nodules between the branches of the dendrites(figure 8a - later stage). Over time these nodules will then be enveloped by the dendrites themselves.
Then follows the precipitation of graphite and eutectic austenite (figure 8b) with divorced increase effect.
Once the cast iron jet is solidified, the earth mold containing the solid cluster is extracted from the brackets. Subsequently the extracted mould will continue its journey along the cooling line until it will be possible to shatter it and to extract the group below the temperature of the last transformation around 730°.
During this cooling phase, , the austenite is over saturated with carbon; therefore the excess of carbon inside the austenite will be rejected by migrating towards the graphite nodules. Austenite begins to decompose in ferrite creating a ring around the graphite spheroids; the reaction proceed due to the diffusion of the carbon through the ferrite shell. If the cooling phase is quickly enough, the carbon is will not spread further through the ferrite shell, thus allowing the birth of perlite within the residual austenite and forming the classic bull’s-eye structure.
The perlite formation process is favored by the presence of elements called "perlitizing", such as copper. The microstructure of perlite is made up of lamellar ferrite and cementite.
The cluster, which is now in the air and still partially covered with earth, continues to advance inside a rotary vacuum-drum filter; through the rotary motion impressed and the injection of water it is possible to remove all of the soil residues and to cool down the cluster to room temperature, making it suitable for handling. After passing the rotating drum, in correspondence with an intermediate station called ACME 1, operators equipped with a hydraulic wedge perform a first phase of feeders removal, i.e. they dismember the groups by separating the jets from the nozzles (casting system and fuel supply). Then jets and nozzles enter the sandblaster for the final cleaning, to exit at the station called ACME2 where other operators equipped with a hydraulic wedge complete the phase of feeders removal. In addition to these operations, the operators also carry out a first visual check on the castings, separating imperfect ones if necessary; they also pick up some castings in order to conduct statistical hardness analysis and to take specimens for micrographic examination. Finally, thanks vibrating conveyors, the castings reach a first storage area in metal boxes from where they will then advance to the next stages of the process, while any waste and ends up in the raw materials park to be recycled.
As we have observed, the casting process is extremely complex, with several steps that must be perfectly synchronized to obtain a process without setbacks / slowdowns.
In the next video we will discover all the processes and procedures that are carried out after the casting of the cast iron casting.
During the casting phase, a second inoculation, called post-inoculation, is carried out directly on the liquid cast iron flow immediately before entering the earth mould; unlike the pre-inoculation, this second inoculation is much more efficient as the liquid cast iron is already at a good level of nucleation and furthermore the particles constituting the post-inoculant are finer, a characteristic that facilitates its dissolution.
The whole process is automatic and supervised by the operator in the casting cabin (caster), who keeps under control the flow of liquid cast iron, the amount of inoculant introduced and any anomalies that may occur in order to prevent possible interruptions in the process and guarantee the metallurgical quality of the cast iron produced.
During the casting process, the operators carry out various analysis on the quality of the final cast iron, as well as the micrographic control of the ladle specimens, necessary to evaluate the shape of the graphite and the efficiency of the spheroidization treatment, the control of the chemical and thermal analysis.
Once the brackets have been cast, they move forward along the line to allow the liquid cast iron cluster to cool and solidify.
During the solidification phase, the material is subject to phase transitions; for example, in case we have a hypoeutectic spheroidal cast iron, the solidification phase begins around 1.170 °, with the formation of primary austenite in the form of dendrite. With the progress of solidification they will grow and enrich the liquid cast iron around them with carbon, at this point, in the carbon over-saturated liquid are created the conditions for the precipitation of graphite nodules between the branches of the dendrites(figure 8a - later stage). Over time these nodules will then be enveloped by the dendrites themselves.
Then follows the precipitation of graphite and eutectic austenite (figure 8b) with divorced increase effect.
Once the cast iron jet is solidified, the earth mold containing the solid cluster is extracted from the brackets. Subsequently the extracted mould will continue its journey along the cooling line until it will be possible to shatter it and to extract the group below the temperature of the last transformation around 730°.
During this cooling phase, , the austenite is over saturated with carbon; therefore the excess of carbon inside the austenite will be rejected by migrating towards the graphite nodules. Austenite begins to decompose in ferrite creating a ring around the graphite spheroids; the reaction proceed due to the diffusion of the carbon through the ferrite shell. If the cooling phase is quickly enough, the carbon is will not spread further through the ferrite shell, thus allowing the birth of perlite within the residual austenite and forming the classic bull’s-eye structure.
The perlite formation process is favored by the presence of elements called "perlitizing", such as copper. The microstructure of perlite is made up of lamellar ferrite and cementite.
The cluster, which is now in the air and still partially covered with earth, continues to advance inside a rotary vacuum-drum filter; through the rotary motion impressed and the injection of water it is possible to remove all of the soil residues and to cool down the cluster to room temperature, making it suitable for handling. After passing the rotating drum, in correspondence with an intermediate station called ACME 1, operators equipped with a hydraulic wedge perform a first phase of feeders removal, i.e. they dismember the groups by separating the jets from the nozzles (casting system and fuel supply). Then jets and nozzles enter the sandblaster for the final cleaning, to exit at the station called ACME2 where other operators equipped with a hydraulic wedge complete the phase of feeders removal. In addition to these operations, the operators also carry out a first visual check on the castings, separating imperfect ones if necessary; they also pick up some castings in order to conduct statistical hardness analysis and to take specimens for micrographic examination. Finally, thanks vibrating conveyors, the castings reach a first storage area in metal boxes from where they will then advance to the next stages of the process, while any waste and ends up in the raw materials park to be recycled.
As we have observed, the casting process is extremely complex, with several steps that must be perfectly synchronized to obtain a process without setbacks / slowdowns.
In the next video we will discover all the processes and procedures that are carried out after the casting of the cast iron casting.