Nodularization treatment is always a tricky phase in the cast iron production process: molten metal weight, temperature, chemistry, physical behavior of the iron etc. Everything contributes to modifying the yield of the treatment. The Cored Wire Injection (CWI) process is well known to have many advantages compared to traditional treatment methods like sandwich, tundish, or in-mold.
CORED WIRE FEATURES
The internal powder may be a mixture or alloy. In the first case, Mg is present as pure metal and, due to its low boiling temperature (approx. 1100°C) and low density, the reaction is average more violent than the alloy one. In the case of alloy wire, which is the usual spheroidizing alloy FeSiMg (also containing other elements typical of spheroidizing alloys, such as rare-earth elements, Ca, Al, etc.) crushed to a finer granulometry, the reaction is usually calmer and on average more performing than mix, since its boiling temperature and density are generally higher.
Itaca CoredWire contains Mg percentages ranging from 16% to 25% (or even higher in the case of applications and requirements). The choice depends on the size of the treatment ladle and the amount of cast iron to be processed: smaller ladles imply smaller amounts of tapped metal, so it is preferable to opt for a wire containing 16% Mg, while as the size of the ladle and the amount of metal to be treated increases, one moves accordingly to wires containing 21% or 25% Mg.
The outer diameter of the ITACA CoredWire can change. Diameters of 9 mm, 13 mm, or 16 mm are available. The choice of diameter also depends on the size of the ladle and the amount of metal to be processed. The larger the diameter of the wire, the greater the amount of core present inside it (measured in g/m).
The data are purely indicative based on Proservice‘s experience, whose technicians will be on hand to assist you in choosing the most suitable cabin and cored wire for your melting process.
ITACA CoredWire SPHEROIDIZATION PROCESS
The introduction of ITACA CoredWire into the liquid metal is carried out using special treatment stations called ITACA Wire.
Thanks to ITACA Wire station, it is possible to automatically add the correct amount of magnesium based on the analysis of the base cast iron, the temperature of the ladle cast iron, and the amount of tapped cast iron, which can vary depending on the average stirrup weight. The performance of Mg treatment will also depend on the correct wire introduction speed and the choice of wire. Treatment with wire allows the cast iron to be pre-conditioned more effectively before spheroidization treatment by adding ITACA Inoc 5600H directly into the ladle before tapping from the melting or holding furnace. The treatment performance also depends on the fume extraction system and the coupling of the ladle with the station cover.
ITACA Wire stations are studied and designed according to the melting process, layout, and cycle time, with the aim of making the spheroidization treatment as efficient as possible.
The factors that most influence spheroidization treatment with cored wire are:
- sulfur content in cast iron base;
- the geometry of the treatment ladle;
- type and quantity of cored wire;
- cored wire insertion speed;
- tapping or treatment temperature;
- quantity of metal tapped or treated.
KEY FACTORS OF THE PROCESS
As far as the geometry of the treatment ladle is concerned, ladles developed in height rather than circumference should be preferred. A very effective geometry specifically designed for ITACA CoredWire treatments is to have a height-to-diameter ratio of 2:1. This is because, as already explained for the case of ITACA Imag alloys, during the spheroidization reaction the magnesium vaporizes, developing gas bubbles which obviously tend to move upwards and escape from the metal; therefore, the greater the distance the bubbles have to travel, the longer they remain inside the liquid metal.
Another feature affecting the geometry of the treatment ladle, and one that depends more on the amount of metal tapped normally based on the demand of the pouring line, is the height of the free liquid metal coat relative to the bottom of the ladle (liquid column) and the ladle lid (free volume). According to Proservice‘s experience, the liquid column should be at least 500 mm, while the free volume should be at least 400-450 mm.
SPEED OF ITACA Wire INSERTION
The insertion speed of ITACA CoredWire is highly dependent on the height of the liquid column and, like all spheroidization treatments, on the temperature of the metal. Generally, the insertion speed is between 15 m/min and 40 m/min, but there may be cases of higher speeds.
To avoid lengthening the treatment time too much, a trick is to insert more than one wire at the same time (for example: on the treatment of 80 meters of wire, instead of taking 4 minutes to insert just 1 wire at a speed of 20 m/min, you can opt for 2 wires to halve the treatment time while maintaining the same treatment speed). However, the insertion speed should be chosen so that the reaction takes place as close as possible to the bottom of the ladle, avoiding the possibility of it occurring in a central or even superficial area and the wire folding up at the bottom of the ladle and consequently rising to the surface.
The choice of the optimal wire insertion speed not only helps to improve the yield of the spheroidization treatment but also reduces the production of slag during the treatment itself, thus the risk of the castings related to it (inclusions, dross, blowholes, etc).
An absolute innovation that characterizes ItacaWire is the compensation of the insertion speed to avoid incorrect treatments or discrepancies with the target. Using sensors installed in the feeders, the system constantly monitors the injection speed, calculates the yield of the process, and makes the appropriate adjustments, if necessary, modifying the process itself in real time.
Another important issue is the way in which ITACA CoredWire enters the ladle: in ITACA Wire systems, it is introduced as perpendicularly as possible to the liquid metal, so that it cannot enter curved and thus rest along the walls of the ladle.