Production Technology of Cored Wire Used for Liquid Metal Treatment in Steel Plants: Part Two

Genesis of CW

Before the advent of CW, the traditional method of LMT was in practice, which was not only uneconomical but also suffering from several inadequacies like high rate of additive consumption with high dissolution time and also low additive yield & reproducibility. These problems were encountered because of poor additive penetration deep in melt due to their low density, thermal instability, and entrapment in slag.

Besides this, the toxic metals like S, Te, Se, and Pb etc. when charged in ladle, used to generate toxic vapors. Subsequently penetration of additives briquettes in LM became more difficult due to an increase in ladle capacities in steel mills and to meet the above challenges, efforts were made by investigators in search of a viable alternative methods, till such time when it was conceived that; “If an additive powder encapsulated in a steel tube is quickly injected into the ladle, the momentary survival of steel tube in LM can help additive to reach deep inside the metal pool safely” and after release the additives start moving from bottom towards the top of ladle.

Because of high surface area of powder it makes intimate contact with LM and improves the performance of the additive. This simple but innovative concept was the genesis of LMT with CW. To materialize the above concept of additive charging, CW-mill, CW-additives and CW-injection machines were developed. Some patents relevant to these developments along with their titles are chronologically given in Table 2, as reference.

Table 2: List of patents

From the list of patent it may be seen that:

1) Initially inventions were made to improve the techniques of LMT.

2) There after, the focus was aimed on the creation of a technique, by which the additive could be penetrated deep inside the metal pool.

3) Subsequently it was realized that the coil penetration should be controllable enough for precise release of additives in liquid metal, irrespective of the ladle capacity & depth. Furthermore, it was also noticed that the voids between additive particles carry air (oxygen) and cause local oxidation. To counter the above deficiencies the metallurgy of the steel jacket, chemistry of additives & CW injection machines were improved. The solid core and doped additives were introduced, to counter the effect of entrapped air.

4) In the quest for enhancing the survival of the CW jacket for little more time under high temperature, thermal insulation on the outer surface of the coil and co-centric tubes were developed. Similarly to achieve better CW performances, variations in coil diameters, sheath thickness & seam lock formations were tried but these developments gradually raised the inventory of CW.

5) To reduce the inventories and to improve the performances, stranded and higher diameter CW, multifunctional additives, and high speed multiple wire feeding machines were developed.

By Dr Pradeep K. Maitra
dipalyconsultants@hotmail.com