Kemi Cracks a Problem
When this Nordic underground chromite producer needed more power to break boulders in the stopes, it found a solution literally in its backyard
By Kyran Casteel, European Editor
“When we blast our stopes it sometimes happens that large boulders break loose from weaker rock types in the ground surrounding the charged volume, falling either during or after blasting. Any boulder more than one meter in diameter is not only too big for the crusher but also very difficult to handle, because no loader able to operate in this size of stope can move or roll, let alone carry such large boulders. They must therefore be broken up for loading, the options being drilling and blasting or fracture by hydraulic breaker.
“But it’s always hard to organize drilling for blasting, sometimes just plain impossible, on account of the risk of collapse in a freshly blasted stope. Even if drilling is safe, someone then has to do the charging, again in a very hazardous environment. The alternative is to bring in a large hydraulic breaker mounted on a loader and split up the boulders, using remote control when necessary. In theory this is very safe and does not require so much reorganization of the operations undertaken by the other machines working in the stope. One man can solve the whole problem in very short time.”
In practice things are a little bit harder, explained Saari. “First, the boulder to be broken is usually very big. Typical diameters can be from 2 to 6 meters. So, every time a breaker is needed, the job is very tough and extremely hard work for the loader/hammer combination. Our Toro 1250/Rammer G90 combination has been doing the job quite well, but the hurry and the heat produced by weaknesses in the auxiliary hydraulics for the breaker makes the machine very vulnerable. Any significant stoppages for maintenance work or fixing break-downs quickly cause problems for production planning: a stope with just one of the larger oversize boulders is out of production until the 1250/G90 machine is available to break up the stope-accessblocking boulder. Clearly then, we needed at the least a machine to back up the much-in-demand 1250/G90. And the bigger this machine could be the more effective it would be—any loader that could fit in the mine accesses could not be too big.
“As it happened, we did have in our fleet one almost new Sandvik Toro 0011 loader, acquired as a spare unit available to maintain production levels in the event of a loading capacity problem. Although this loader was not factored in to either our normal production plans or our routine maintenance budget it was clocking up quite a few hours hauling backfill to the stopes and other auxiliary jobs. The fact it was new, large and easy to handle made it just too popular. We needed a consistent and budgeted application with a limited number of operators responsible for the machine.”
Here was an opportunity “to kill two birds with one stone” noted Saari, “providing the extra breaker power and capacity we needed and making more efficient use of the 0011 loader. The boulder breaking job would frequently benefit from the bigger, harder hitting machine. The Toro 0011 was the biggest underground diesel-powered loader on the market and it should be possible to modify the machine in such a way that the breaker attachment could be quickly interchanged with the standard bucket for production loading and haulage.”
We Did it Our Way
“Toward the end of 2007, with these things in mind, Mine Manager Jyrki Salmi and I, together with our respective groups, agreed to start an internal study of how to convert a really big but otherwise standard loader to a special rock breaking machine,” said Saar. “We quickly reviewed the options, concluding that a one-off machine would not be a very tempting project for the loader manufacturer, especially given the risks involved in developing a machine that had never been built before—at least as far as we knew. So if we wanted such a machine in the near future, we would have to do the engineering ourselves.
“We contacted Marakon, a company based near the Sandvik Mining & Construction breakers operation in Lahti, and told them about our plans. As a result we received an offer for a hammer and zoom unit and ordered a Sandvik BR 4510 tunnel-hammer (previously the G100) and an EC 80 zoom designed especially for the 0011 loader’s boom geometry. At the same time, Jarkko and I in underground maintenance designed a way to operate the hammer using the 0011 loader’s variable-flow hydraulics with minimal losses and heat production. Our heat challenges on the 1250/G90 machine were so etched in our memory that the main idea in designing the 0011 hammerhydraulics system was to try to avoid any heat sources and all restrictions.”
During the design process, “we decided to skip the traditional directional valve/auxiliary hydraulics design and developed our own ideas. In our version, the hammer is directly fed from the main hydraulics with one no-loss, non-restrictive on/off valve. Instead of throttling down the flow using restrictions such as a proportional valve, we were able to use the double-pump configuration on the 0011 to modify the loader so we would be able to adjust the pump flow suitably for the hammer. By so doing we could open wide the flow from the pump to the hammer. In designing the direct pump system and adjustment of the flow during the breaking operation, we took advice on techniques for overriding the CAN-bus system from Sandvik’s loader factory at Turku. As it was impossible to make prototypes or carry out extensive tests we had to hope our simulations had eliminated any major potential problems. All that remained now was a rather nervewracking wait for the hammer, zoom and hydraulic parts to arrive.”
The hammer and zoom arrived in the Summer of 2008, according to Saari. “By autumn, the machine was ready to run. From the first test the machine has worked perfectly and at the moment is being used for production. The only additions made since the test run are camera installations for extra visibility.”