Precision engineering group, Horne, has successfully tested its Levelok E-Brake, the world’s only emergency mine cage braking system to comply with the Ontario safety standard on both wooden and steel shaft guides. All other Ontario-compliant emergency braking systems are designed to work on wooden shaft guides only.
Formally launched in 2010 after development in South Africa lasting more than two decades, Horne last year installed two Levelok E-Brake systems at Peñoles’ Fresnillo mine in Mexico, a third this year at Ivanhoe Mines’ Oyu Tolgoi Shaft Number One in Mongolia, and a fourth at the underground vaults of the Hutchinson facility in Canada.
Despite the product’s South African origins, sales of this Ontario-compliant system are ironically not expected into South Africa, where SABS standards applied to the mine rope are sufficiently strict to preclude any possibility of failure. For the South African market, Horne’s standard Levelok system delivers chairing only, whereby clamps hold the cage steady during load transfer, then gradually release their grip at a controlled rate to allow smooth take-up of rope stretch.
For all other countries, though, E-brake is a dual purpose product, delivering a safe stop under emergency conditions as well as the standard chairing function needed at shaft stations. Under failed rope conditions, a valve on E-Brake’s hydraulic accumulator automatically opens to force hydraulic fluid under regulated pressure from the accumulator to the clamps, activating them and bringing the cage to a safe halt. The accumulator recharges to full pressure each time the cage is stopped at a shaft station.
Three features make E-Brake unique. First, careful regulation of emergency hydraulic fluid release allows the cage to decelerate without injury to a human load as the stop is controlled. Second, the system works equally safely on both wooden and steel shaft guides. No other system in the world can effect a controlled cage deceleration on the steel guides currently replacing wooden equivalents in modern mines. Third, E-Brake has been formally tested and proven in working mine environments.
Horne Group managing director André du Preez explained that prior to E-Brake’s development, mines with steel shaft guides had turned to duplicate drum winders and duplicate ropes to meet emergency regulations. “The steady move away from wooden shaft guides caused problems meeting the safety requirements of an emergency stop, but many countries allow the omission of an emergency braking system if the mine installed multiple ropes. So, of course, that is what they did,” he said. “This is a very expensive option, and arguably not safe at all because there is no control over the rate of deceleration when the cage reaches the end of the second rope. It just stops, and this can kill people and will definitely injure them. In China and Russia, the law requires an emergency braking system irrespective of the number of ropes installed.”
Internationally applicable standards for safely stopping a cage under emergency conditions (known as the Ontario standard) specify deceleration of between 0,8 and 2 g when the cage is fully loaded. “The problem is that cage deceleration tends to increase with lighter loads,” continued du Preez. “Therefore a braking system can meet the Ontario standard, which is a full-man standard, but cause serious injury if the cage is carrying just one or two people, because the rate of deceleration is too high for the human body to withstand.
After fully developing the product, Horne carried out live testing of Levelok E-Brake at the Stainless Steel Technology exhibition in Sudbury, Canada, where a consulting engineer monitored the test cage under full man load and also with a load of just a single person. Deceleration using E-Brake fell within the Ontario limits with a test load equivalent to a single man standing in the cage. The test structure at Sudbury comprised a tower with a height of 20 metres, fitted with steel guides, and equipped with a cage 10 metres high.
“The consulting engineer was sceptical, and cleared the test site around the tower of all personnel, expecting a failed stop with potentially life-threatening consequences,” du Preez recalled. “Instead, the test was successful. We are now negotiating purchase of land to put up our own testing tower and develop the product further,” he concluded.
For more information contact André du Preez, Horne Group, +27 (0)11 974 1004, [email protected], www.horne-group.com
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