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Materials Engineering

In the mouth of the furnace, new steelworks

Precision instrument and a new generation of refractory concrete arrive to improve the efficiency of steel making and to maintain the competitiveness of the country in this sector

EDUARDO CESARA partnership between the Federal University of São Carlos (UFSCar) and the company Alcoa Alumínio has resulted in the creation of an unprecedented instrument: the concrete rheometer. The piece of equipment is designed to measure of the degree of quality and the reactions between raw materials used in the formation of refractory concrete, applied to the linings of furnaces and equipment for the production of iron and steel. These concretes are made with low cement content and high content of alumina, a by-product in the aluminum industry which is very resistant to high temperatures.

The rheometer was developed through a thematic project on advanced refractory concretes financed by FAPESP and coordinated by Victor Carlos Pandolfelli, of the Department of Materials Engineering (Dema) of UFSCar. The project opened up a line of study that has already produced ten master’s dissertations and seven doctorate theses, as well as a book that can serve as a source of consultation in materials courses. It was also responsible for the registration of three patents. One for the rheometer itself, another for the software Particle Size Designer, which defines and analyzes the particulate materials used in the concretes. Launched on the 23rd of October by Alcoa, the software costs R$ 800,00 and total of the sales income will go to UFScar. It also contributed towards the goal of the third patent: a generation of cement refractory material with low levels of water in their preparation and greater mechanical resistance at high temperature.

The rheometer and other pieces of equipment and developed processes comes at a good time. In 2000, the world production of steel was of 847 million tons. The current demand of the steel mills is for refractory concretes that are more and more resistant and durable. Therefore, the competitive differential must be in performance and the added value of the material, and not just in productivity. A forecast and a consensus of opinion: the less efficient steel mills will close down. This has already been going on in the USA.

The challenge of the steel industry is to lower costs and raise performance. For this to happen, the refractory blocks aredecisive as well as the technologies that have sprung up over the last few years to raise efficiency. “The refractory blocks used today”, says Pandolfelli, “are a sophisticated class of material, whose conception and projection of their microstructure goes well beyond the classic combination of raw materials in order to obtain an improved component”. The steel mills are right about wanting to change the old refractory bricks for a covering of refractory concrete: “With the bricks many more man hours were spent because they were laid by hand, one by one. The refractory concrete uses a much faster machine, doesn’t need the different brick shapes to build up the furnace and doesn’t leave joints at which a corrosion process can begin.”

It is forecast that by 2007, 100% of the high temperature-furnaces and other installations of the Brazilian steel making industry will be using refractory concrete. Today they account for 60% of the refractory material used in the sector, which has an annual turnover of some US$ 350 million. The quality of the refractory material reveals itself in its resistance to temperatures in the transformation of the iron ore into pig iron and steel, which get as hot as 1,600º C. Three decades ago, the consumption of refractory bricks by the Brazilian steel making industry was at 30 kilograms (kg) per ton of steel produced. Today, this relationship is at 9 kg per ton, close to what is considered to be excellent, which is 7 kg per ton. The more efficient and under control the steel making process becomes, the less it consumes refractory material.

For this reason, Brazilian steel making has become more competitive. However, in order to maintain this standard, and even to improve upon it, the gap for carrying out studies and experimentation is narrowing: it is necessary to master and shortly afterwards apply the forms of knowledge that are more and more specific. It is in this context, in the Pandolfelli’s opinion, that the rheometer can make a difference. It plays a fundamental role in the production pumpable refractory concrete, produced as mixtures in the location of the steel works themselves and taken in through a hose pipe, under pressure, to be the coating of the high temperature blast furnace.

New times
The rheometer measures the torque (turning force) necessary for the mixing of the concrete under different conditions, simulating the industrial pumping. It also indicates the pH (acidity/alkalinity) and the temperature, according to the reactions as they occur. Thus, the instrument allows the simulation the demands to which the concrete will be submitted, from the moment at which its components are mixed until their application. The engineer Carlos Pagliosa, today working with the company Magnesita, the largest Brazilian manufacturer of refractory material, was one of the first to work with professor Pandolfelli as a post graduate student in the development of concrete pumps.

For him, the new times imposed the use of multi-functional and adequate products to a process of faster installation, as the system of concrete pumping is. “It was necessary to treat the refractory concretes as high technology products. In this context, the new products could no longer be generated by empirical concepts and we went on towards computerized modeling and the development of specific equipment.” says Pagliosa.

The partnership of UFSCar with the Alcoa Company – which is responsible for 25% of the production of aluminum in the country – was born some ten years ago, and since then the company has invested US$ 650,000 in various partnership projects. “With the rheometer, the company hopes to differentiate itself by giving to the market an instrument for the evaluation of quality of the raw materials themselves”, says he chemist Jorge Gallo, who heads the company’s research and carries out the coordination with UFSCar, at the same time as he develops his doctorate within the thematic project.

Less effort
The resources invested by the Alcoa Company in UFSCar supports necessities that FAPESP funding cannot fulfill, such as the expansion of the physical space in the university. Consequently, with resources from the company, a 900 m2 unit was built in which is located the various pieces of equipment as well as where the group involved in this project works. An example of the benefits that accrued to Alcoa through the partnership occurred during the first quarter of the year when it reformed one of its alumina (roasting) furnaces. “It’s a routine operation that occurs once every two years. But this time it was different”, explains Jorge Gallo. “We formed a group with people from the company, from the Dema-UFSCar and the refractory supplier, Magnesita.

Then together, under the orientation of professor Pandolfelli, we were able to steer the work with much more knowledge. We estimate that this will allow us to increase the time space between stopping the equipment for maintenance, which, if confirmed, will represent a considerable reduction in our costs.”The project also contributed to the company Cerâmica Saffran of Betim (MG) become a pioneer in the use of national technology for the development of pumpable refractory concrete, including for the repair of steel making equipment. Together with the team from the UFScar, the company managed to improve the performance of the channels in which the molten metal runs towards the high temperature blast furnaces. The use of the rheometer led to the development of the refractory concrete used in these channels.

The company also saved development time and costs with industrial testing, which are expensive because they involve a minimum quantity of up to 2 tons of material. Consequently, the experience of the Saffran Company, founded in 1954, was important in proving the efficiency of the rheometer. Whilst the Brazilian refractory concrete market placed their bets firmly on machinery and imported technology, the Saffran Company found its own way together with the UFSCar.

Marcelo Guerra, a research engineer with the company explained: “Our new concrete is pumped with such efficiency that it allows for the applied product to have a better quality and performance. Since we don’t have to apply any vibration – necessary for the older system of pumping, so that the concrete would flow with greater ease -, we reduced by two thirds the operation time. For example, a furnace of some 200 tons consumes 72 hours of vibration application. For the same volume, we now carry out the same operation in 20 hours”.

Household conception
Pagliosa, whose doctorate thesis focused on pumpable concretes, adds: “The development of the technology of pumpable concretes by Saffran was carried out in the company itself, with the support from the team of the thematic FAPESP project. It wasn’t something developed from within the company that migrated to the university. The product concept was done together by the company and the UFSCar, and the evaluation tests of the product with the rheometer and the technical discussions were fundamental for the success of the development as a whole.”

Among other results of the thematic project, professor Pandolfelli highlights another five pieces of equipment that were built during the last four years – some of them still under test, for possible patent requests. The team that was involved received nine awards and has had 71 scientific papers published in specialist magazines both here and abroad. These are results that well exemplify our current generation of science and its application”, completes the coordinator Pandolfelli.

The project
Systematic Study of the Development of Advanced Refractory Concretes (nº 97/01114-5); Modality Thematic Project; Coordinator Victor Carlos Pandolfelli – UFSCar; Investment R$ 525,877.47 and US$ 456,438.54