A high resilience rubber screening media has helped a South American family-owned aggregates business to almost eliminate contamination and fines and increase its operational efficiency.
Santa Isabel Quarry has been in operation since 1959 and is part of Votorantim Cimentos, one of the largest business groups in Brazil. Located in Mogi das Cruzes, in Greater São Paulo, the quarry serves customers in the metropolitan region of the largest Brazilian city and provides aggregates for civil construction, major works and cement block producers. However, the company’s positive story was jeopardised in 2018.
Votorantim’s Santa Isabel Quarry faced two major challenges. In addition to the retraction in civil construction, the plant was having problems due to aggregate contamination and an above average presence of fines. Both had a negative impact on buyers’ perception of the final quality and on Santa Isabel’s sales. On the sand and gravel market, buyers prefer materials with controlled levels of contaminants and dust – that is, “cleaner” aggregates.
With the arrival of Votorantim Cimentos’ new regional manager Carlos José Barbosa Silva, the quarry began to implement operational changes, including training employees and addressing the main technical problem – the improvements needed in the aggregate screening process. Specialists from original equipment manufacturer Metso Outotec were invited to assess the operational efficiency of the screens. “We had already faced a similar problem at the Araçariguama Quarry and achieved good results with the solution presented,” Silva said. “The screens were retrofitted and the wire media was replaced with Metso Outotec’s high resilience rubber screening media.”
IMPROVED PERFORMANCE FROM SCREENING OPTIMISATION
The tests conducted at the Araçariguama Quarry plant were replicated at the Santa Isabel Quarry. “In Araçariguama, the tests involved simultaneous operation of two screens – one with wire media and another with rubber media,” Metso Outotec’s screening specialist André Rosa said. “When the media change-out was made, an analysis was performed in the quarry laboratory. We discovered that the use of rubber screening media nearly eliminated the final product contamination and reduced the presence of fines. Even with a smaller open area, the high resilience rubber media is much more efficient than the wire media.”
The tests played a decisive role in the selection of Metso Outotec as a partner for Araçariguama, and later for Santa Isabel.
While the screens alone were not the reason for the improved operational performance, the screen adjustments and the use of rubber media were considered key factors in the increased production quality. This is supported by an analysis of the end-user feedback. The quarry index of one complaint for every 37 thousand tonnes produced (2018) decreased to one complaint for every 700 thousand tonnes produced — an improvement of 20 times better than planned. The current assessment parameter is 10 times higher than the specified target of one complaint per 67 thousand tonnes. “It was a fantastic leap that surprised everyone. We didn’t miscalculate our goal. The results of the changes were significant,” Silva added.
The challenge of the above average presence of fines was addressed by optimising the screening solution. In addition, the main action to address the internal contamination – the unwanted mixture of different products – was training. Internal contamination was reduced by correcting the improper procedures of the loader operators that were moving products in both operating shifts. Mistakes in the transportation stage from the quarry to the customers – performed by third parties – were also corrected. The errors were identified, and the drivers were given the appropriate guidance.
However, the best indicator of success was the pricing. In July 2019, for example, the price of stone powder had been increased seven times in a row. The recovery of the price negotiated between local customers and the increase in production were complemented with an even bolder plan in 2020 – screening changes that allowed for the supply of an intermediary product between fine and medium gravel. It improved the quality of concrete block production with lower cement consumption and higher mechanical strength and visual quality.
“There is pent-up demand already being seen, but our production should be able to keep up by making screening adjustments,” Silva said. The executive added the quarry already takes a LEAN approach in operations, having increased its productivity by 4000 tonnes per employee from 2018 and 2019.
“Some of the buyers of our sand and fine gravel are concrete block producers, who have automated machines and demand a high homogeneity standard,” he said. “They were the first to observe the change in the quality and the appearance of our final product.”•
This article appears in the September issue of Quarry Magazine.