Metalurgia

WIRE FEEDING TECHNIQUE



GENERAL INFORMATION 2

HOW TO FEED CORED WIRE 3

CALCIUM TREATMENT 4











GENERAL INFORMATION


Wire feeding is a modern means to improve various properties of steel. Therefore it is mainly used in the processes of secondary metallurgy and in continuous casting of steel. Wire feeding technology has become an important element whenprecise treatment and fine adjustment of the chemistry of molten metal is required.
Wires are applied into the molten metal by means of a special wire feeding machine.
Aluminium for steel deoxidation and alloying is used in form of solid wire whereas other materials are added to steel in form of cored wires. Cored wire is a two-component wire, consisting of a steel sheath and a powder filler. Bymeans of a filler the cored wire acts on molten metal in order to modify the properties of final product.
Depending on the type of filler, the wire can be used for deoxidation, refining, microalloying, modification of non-metallic inclusions etc.

Compared with traditional methods of introducing lumpy materials or powdered agents into molten metal the wire has the following advantages:

*higher efficiency and low consumption of alloys;

* lower losses by burning up or evaporation;

* lower energy losses;

* lower turbulence of liquid metal;

* relatively low investment cost;

* good adaptability for various production processes;

* high accuracy of dosing;

* possibility of long storing of easy oxidising and/or hygroscopic materials.


The table belowpresents the list of elements for the introduction of which into the molten metal the wire injection technique is advantageous:


|LOW DENSITY |Ca, Mg, C, B, Si, S, Al, Se |
|LOW MELTING POINT |S, Se, Pb, Bi, Mg, Al, Ce, Ca |
|HIGH VAPOUR PRESSURE|Mg, Ca, Se, Te |
|STRONG AFFINITY TO O2 |Ca, Mg, Ce, Zr, Al, Al, Ti, Si, Nb |
|TOXIC OR TOXIC FUMES |Pb, Se, Te |


HOW TO FEED CORED WIRE


Depending on the location of chosen for the wire feeding, different equipment’s andsettings are possible. In case of space limitations the following solutions are available:


* fixing the wire feeding machine in inclined or vertical position;


* designing of a tube guide with proper geometry - up to three bends maximally;


* using flipping wire coils which are placed close to the feeder or at a certain distance from it.


Attention has to be given to design ofthe wire guide. The main points are:


* its finishing part has to be vertical - minimum on 0.6 meter length minimum - to assure straightening and good penetration of the wire in the metal bath;


* its internal diameter has to be related to the wire diameter, i.e.

- about 25 mm for wire diameters 12 - 18 mm;
- about 13 mm for wire diameters 5 - 9 mm;

* guide bends areto be smooth with approximately 1 meter radius;


* the distance between guide end and steel meniscus has to be as short as possible - 0.5 meter preferably.


The guide end has to be placed above the ladle away from the argon plume. In case of big ladles - over 150 ton - soft stirring for homogenisation, inclusion flotation and dilution of introduced alloy may be applied during wirefeeding.

There is no theoretical model for predicting precisely the time needed for the wire to deliver addition into liquid steel. Different phenomena take part in the process:


* freezing of slag and steel at the surface of wire;


* heating and melting of steel sheath;


* heating and phase transformation of added alloy.


One has also to take into account the kinetics of the...