The Gerdau group is the largest metal recycler in the Americas and has four operations in Brazil that transform scrap as part of steel production. Usina Riograndense is the largest of the four operations and faced the challenge of optimizing the operation of its crusher, technically known as a shredder. The focus of this optimization was to make the change from conventional grates – the shredder's metal, fixed component – to double grates. The goal? To extend the operating life of grates and other cast components and reduce the time it takes to changeover these elements. Both goals were achieved in a two-way effort between the company and its technology partner, Metso.
The adoption of double grates is truly an unprecedented initiative in South America; the pilot project started in July 2017 and was completed earlier this year. Due to the change in the component, Gerdau decided to research new configurations for hammer operations, the main cutting element of the shredder. These devices cut the scrap by striking it against anvils inside a crushing chamber, which could now be reconfigured with the change to double grates.
The Riograndense pilot was completed at the beginning of 2018 and produced a 30% gain in the operating life of the grates. Using conventional components, the shredder recycled about 180 thousand tons of scrap before being shut down for the changeover process. With the double grates, the unit was able to process 230 thousand tons. The same gain was extended to three other casts used in the shredder. The process was also improved in terms of the removal and changeover of the double grates. In this case, the total time – which used to take a week with conventional grates – was reduced by 40%.
Maintenance time was reduced by 40%
The change in technology also reduced the unit's downtime, with the removal of the double grates taking a day and a half to complete, as compared to the previously used conventional technology, which took three days. Furthermore, installations that normally require another three days, could now be completed in two. "This is a critical, high-exposure operation. The longer it takes; the more risks the teams will be exposed to. Therefore, reducing the time of exposure means increasing safety for the professionals involved," says André Stefenon, Improvement Facilitator at Gerdau.
The expert explains that Gerdau is still studying other indirect gains in relation to the increase in operational life of the 30 hammers installed in the shredder. According to André, the change allows the hammers to be reconfigured due to factors such as the geometry of the double grates. "We don't have complete data on this, but we will be able to evaluate it when the process is extended to the other units", he adds. The 30% gain in the operational life of the double grates is extended to another three cast components.
With the success of the pilot project, Gerdau Riograndense is already operating its shredder with a new set of double grates, and the unit now serves as a point of reference for the units at Araçariguama (São Paulo) and Cosigua (Rio de Janeiro). Both units have already acquired the new Metso components, which will be installed in the first half of the year. The third unit that uses a shredder is at Recife, where the changeover to double grates has also been greenlit.
This project involved the Brazilian team and support from the United States
The adoption of double grates at Gerdau's scrap recycling units was also the result of Gerdau's technical relationship with Metso, whose Brazilian team participated in the project with support from the North American subsidiary. "There was project alignment with our team in Texas, which also provided us with the existing designs from North America plants," explains João Pensa, Recycling Technical Management for Metso South America. He points out that Metso was responsible for the installation of the four Gerdau shredders between 1990 and 2010.
Pensa highlighted two direct gains as a result of the double grates. "As the name suggests, they are duplicate parts which thus leads to a longer operational life. The pieces are heavier and sturdier and warp less than a single piece", he explains. The second advantage, according to Pensa, is that the hammers wear homogeneously, unlike the projects with single grates, where the configuration of the pieces leads to positions where the wear is greater.
*Metso Outotec was formed July 1, 2020 when Metso and Outotec merged into one company. This case study has been written prior to the merger under the old company name.