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Metallurgy

Better quality

Unicamp and steel mill partnership design plasma torch to improve steel quality

Aruy MarottaIngot equipment at Villares: stable temperatureAruy Marotta

The production line at Villares Metals, in Sumaré, metropolitan area of Campinas, held an experiment last year that was the triumph of a research project that began in the late nineties and that aimed at improving the quality of the steel produced in Brazil. A plasma torch capable of generating very high temperatures, transforming electric energy into heat transported by a gas, was tested at the company’s steel mill, in order to delay the steel’s cooling process during the phase in which the newly molten metal is cast into continuous ingots.

Experiments in other countries show that the plasma torch can be used in a continuous ingot casting equipment to improve steel quality. It stabilizes the temperature inside the equipment’s intermediary reservoir, or distributor. A stable temperature in this process, which takes about two hours, leads to producing steel with a lower risk of forming ceramic fragments, which can happen when the metal cools down. It also prevents the segregation of alloys, which can occur when the metal is overheated. Without using plasma, overheating is required to keep the steel from hardening within the distributor.

This technology is used in steel mills in developed countries, and any firm that wants to use it in Brazil has to purchase the know-how abroad. The experiment’s success showed that one can install a plasma torch in a steel production line without having to hire an international company specialized in this technology, which should cheapen the costs, says Aruy Marotta, coordinator of the project and researcher of the Plasma Physics and Technology Group (GFTP) at the Gleb Wataghin Institute of Physics (IFGW) of Unicamp. Celso Barbosa, Technology, Research and Development manager at Villares Metals, highlights the improvements the plasma torch can provide. We are interested in this technology because it will allow us to improve the production of high-alloy special steel, such as the kind used in engine valves and in the aircraft industry, he says. We expect that with the improvement in mechanical resistance, it will be possible, for example, to decrease the degree of steel lamination (thinner and with the same hardness), he affirms.

The plasma torches work as a sort of resistance capable of producing extremely high temperatures, of up to 70 thousand degrees Celsius. In the torch, plasma is generated when an electric arch is formed; this is akin to an ongoing lightning bolt. It is caused by running a current through ionized gas – formed by ions (atoms with electrons lost or gained). Some of the advantages of the plasma torch are its high efficiency in converting electric energy into thermal energy – as much as 95% – and the possibility of using it with any type of gas. Unlike combustion, thermal energy does not depend on gas flow; there is a quick response and very high power density, resulting in more efficient equipment, says Marotta. Plasma torches have been used since the 1960’s in steel mills to cut, weld or cast. They are also essential so that metal and ceramic layers are deposited – aviation turbines are coated with ceramic surfaces using this technology. In the last two years, plasma torches have gained importance in the processes of destroying toxic waste and synthesizing new nanometric material.

The project arose because the sector needed it. A letter sent in 1997 by ABM, the Brazilian Metal and Metallurgy Association, to professor Cecília Zavaglia from the Mechanical Engineering College of Unicamp, was practically a summons to the institution’s researchers, whose studies might lead to competitive gains for the sector. Professor Marotta submitted a group of three projects on the use of thermal plasma, but ABM’s potential interest was not realized. Convinced that his project could be of interest to the sector, Marotta submitted his project to Villares Metal in more specific terms and asked whether they were interested in taking part in FAPESP’s Pite program (Partnering for Technological Innovation Research). The partnership, set up in 1998, depended on the construction of the Industrial Plasma Laboratory (LPI) of Unicamp, which only became ready in 2001, thanks to the funding provided by Finep, CNPq, Unicamp and especially FAPESP. ?A unique structure was built over the course of a decade for research and development of plasma technologies that are very interesting for Brazilian industry, says Marotta.

Aruy Marotta Industrial interest: mechanical resistanceAruy Marotta

Belarus
The initial research stage (1999 to 2001), was based in Belarus, an Eastern European country and former Soviet Republic, at the Heat and Mass Transfer Institute (HMTI) labs. Marotta, a pioneer in this line of research in the country, had established a productive collaboration in the mid eighties with researchers from the former Soviet Union, where he studied. This connection caused several Soviet researchers to help drive the Brazilian partnership, resulting in significant scientific and technological exchange.
The project’s second stage, conducted at Unicamp, took place from 2001 to 2003, with the development at LPI of a plasma source with 500 kVA power, plasma torches and related equipment – made for the Pite project with Villares. The last stage included assembling and testing the entire plasma system on the Villares Metals production line. However, when the project was approaching its conclusion, the company decided to postpone its implementation, as it would demand heavy investment in changing the plant’s configuration. “We hope to implement this stage as of 2012”, says Celso Barbosa, of Villares Metals. While the project was developed, the Brazilian company, which used to belong to the Villares family, was sold to the Spanish group Sidenor. It is currently held by the Austrian multinational Böhler-Uddeholn. The company has only one continuous ingot casting machine in industrial production. For this reason, the system was installed and tested under real operation conditions, but outside the production line, using the same three-ton liquid steel distributor.

“Despite postponing the implementation, Villares evaluates that the project was technologically successful. It is a industrial technology project on a huge scale. It was a major challenge to develop it and transfer it out of Unicamp’s laboratories and into the pilot plant”, says Barbosa. “The implementation and operation of a plasma torch developed by a Brazilian team, in a large industry had never been done before in the country”, says Aruy Marotta.

Marotta and his team currently work at the LPI on a project of the Innovative Research Program for Very Small and Small Companies (Pipe), with the company Siderol, in the recycling of fast steel found in the sludge of the tools industry. This steel, which has significant added value because of its alloy elements, is currently disposed of as waste. In a plasma oven, the steel is separated from the sludge that contains oil and abrasive ceramic. This project is a further development of the technology created in the Pite program. “It is extremely important to continue and further develop LPI’s activities, with the creation of human resources and new technology for Brazilian industry”, says the researcher.

The project
Application of plasma torches in ironwork processes (nº 98/03353-0); Type Pite – Partnering for Technological Innovation Research; Coordinator Aruy Marotta – Physics Institute – Unicamp; Investment R$ 371,403.00 (Villares) R$ 310,500.00 and US$ 305,000.00 (FAPESP)

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