Large, more powerful track-mounted units offer options for small to medium size mining operations
By Simon Walker, European Editor
To be fair, crushers do not often hit the headlines. Hidden away in some dark cavern, or masked by ranks of tires and gabions along a pit bench, it is hard for a crusher to compete with the higher visibility of a new truck fleet or drill rig. Yet an effective crusher is a key component of any mineral-production system, paving the way for all of the subsequent stages of extraction technology. The crusher goes down, and the mine marks time.
One of the fundamental processes in mineral recovery, rock breaking absorbs progressively greater energy inputs as size reduction proceeds. Even primary crushing is energy-intensive, with the optimum relationship between blasting fragmentation, crushing capacity and concentrator throughput liable to change over time with altering orebody characteristics.
The number of different crushing concepts available has expanded slowly over time, such that today’s mine operator has a wider range of choices than his predecessors did. The traditional jaw crusher and gyratory still dominate in primary-crushing applications, of course, while the choice for secondary reduction now encompasses technologies such as high-pressure grinding rolls as an alternative to cone or other crushers. The required characteristics of the end product often govern the selection of crusher technology, with vertical-shaft impact machines having made significant inroads into the market for certain applications.
Reliability is clearly the name of the game; no operation can afford to be without its crushing capacity other than for routine maintenance and the replacement of wear parts. This is heavy-duty engineering at its peak, whether the machine involved is stationary, semi-mobile or fully capable of being maneuvered to wherever it is required. Indeed, the introduction of successful mobile crushing plants revolutionized the way in which some surface mines, and in particular quarries, have been designed and are operated.
As with many aspects of today’s mining-equipment supply chain, relatively few manufacturers supply the bulk of the market for crushing equipment. Each offers a comprehensive range of systems, with design improvements mainly focusing on reducing energy usage while maintaining a unit’s output characteristics to meet the requirements of later processing stages.
New Mines Need New Crushers
With mine-development programs seemingly little affected by the global economic slowdown, there has been a steady stream of news from the major manufacturers about new crushing installations. Some are for completely new mines while others, such as the two semi-mobile units recently installed at Boliden’s Aitik copper mine in northern Sweden, have been commissioned as part of capacity expansions.
Supplied by Sandvik, both units have a capacity of 8,000 t/h. At the heart of each is a gyratory crusher that takes run-of-mine ore and reduces it to minus-400 mm for belt transport to the intermediate stockpile that in turn provides the concentrator feed.
As noted in the October edition of E&MJ (pp.100–101), only one of the new crushers has been sited within the existing Aitik pit, where it is providing additional capacity to the original in-pit unit. The other has been built on surface, where it can crush run-of-mine ore from the new Salmijärvi satellite pit, before also feeding its output to the intermediate ore stockpile.
Other recent crusher orders that have either been fulfilled or are in the process of supply by Sandvik include a primary gyratory unit for Tata Steel in India and six cone crushers for Areva’s Trekkopje uranium project in Namibia.
Earlier this year, Sandvik reported on the installation of its first CG820 gyratory crusher at Tata Steel’s Noamundi mine in the Indian state of Jharkand. Ordered as a replacement for an existing crusher, the new unit is capable of handling minus-1,200 mm run-of-mine ore at a throughput rate of 3,500 t/h. The new crusher is part of a larger, $40-million investment in a new materials-handling system that will allow the mine, which has been in production since 1925, to increase its output for Tata’s Jamshedpur steelworks.
Meanwhile, the six CH880 cone crushers Sandvik is supplying to Trekkopje will be used to process 100,000 t/d of uranium-bearing ore once the operation is at full capacity in 2012. Run-of-mine ore will be crushed initially in a mobile primary crusher, then conveyed to two of the cone crushers for secondary breaking. Output from these will be fed to the other four Sandvik units, running as tertiary crushers, which will produce minus-38 mm material for either agglomerating or placing directly on to heap-leach pads. French state-owned nuclear company Areva acquired Trekkopje when it spent $2.5 billion in buying the former owner, UraMin, in 2007. The operation is planned to produce around 3,000 t/y of uranium once it is in full production, using leaching technology on low-grade, calcrete-hosted ore.
Mobility Offers Cost Advantages
The concept of mobility for crushers dates back some 30 years or more, with the realization it is sometimes simpler and more cost-effective to take the crusher to the rock rather than the other way round. Still, “mobility” can mean different things in different situations, and just because a crusher is described as being mobile or semi-mobile does not necessary mean it will be moved on anything like a regular basis.
One of the leading developers of truly mobile crushers, the Finnish company Lokomo, was swallowed up by what is now today’s Metso Minerals, which is still actively developing its mobile crushing technology. While the Lokotrack concept has largely been confined to quarrying and smaller metal-mining operations up to now, Metso now reports it has succeeded in breaking in to the high-volume mining market as well.
Production of iron ore at the Samarco joint venture of between Vale and BHP Billiton is set for some 40 million mt this year, with 24 million mt of concentrate being used as pellet feed. Located in hilly terrain in Brazil’s Minas Gerais state, the operation already used conveyor transport for coarse-screened run-of-mine ore, so replacing the existing loading system with a Lokotrack and Lokolink conveyor presented fewer problems than would have been the case had a completely different method of transport been needed.
With a throughput of 2,000 t/h, the Lokotrack crusher has proved to have cut ore-haulage costs by nearly one-half, Metso reports, with the company now looking for other applications for its mobile crusher units in high-volume metal mines.
In a more conventional application, the German company Hazemag & EPR reported recently on the successful installation of the first semi-mobile impact roll-crusher plant. Supplied to the Austrian cement company, Zementwerk Leube, the unit is designed to handle up to 600 t/h of limestone, reducing quarry rock from minus-1,200 mm to a minus-250 mm product with a minimal proportion of fines.
The layout of the crusher unit means that neither a bench edge nor a loading ramp is needed for the wheel loaders that feed rock into its hopper, so the machine can be moved quickly without the need for special site preparation, Hazemag notes. The feed conveyor to the crusher also acts as a primary screen, allowing material smaller than 120 mm to bypass the crusher completely. Crushed rock is removed by conveyor for secondary crushing to the correct sizing for cement-plant feed.
Hazemag’s primary impact roll crushers are designed to handle medium-hard rock such as limestone, gypsum and coal. Fully electric-powered, they are also designed to be moved using a wheel loader, so have no need for any auxiliary diesel engine or drive system for their tracks.
In September, Atlas Copco announced its acquisition of Hartl Anlagenbau, the Austrian manufacturer of mobile crushers and screeners. The acquisition was covered in more detail in the October edition of E&MJ (p. 92), but to summarize, Atlas Copco Powercrusher now offers a wide range of track-mounted mobile jaw, impact and cone crushers, with crushing capacities ranging from 200 to 500 t/h.
Optimizing Crusher Control
Whatever the type and configuration, crushers have an exceedingly hard task to perform and, in consequence, also experience significant wear. Maintaining a consistent output over time therefore requires compensation for this wear, until the stage is reached that replacement of wear parts is needed and the unit can be reverted to its original setting.
The idea, of course, is to keep the crusher running at optimum performance throughout each wear cycle, with researchers at Chalmers University of Technology in Sweden having devised control systems that, they say, can achieve this. Authors from the university presented four papers on various aspects of crusher control and breakage performance at the Comminution ‘10 conference, held in Cape Town in April this year, with other papers presented elsewhere in the recent past.
In their paper, Optimization of Crushing Stage Using On-Line Speed Regulation on Cone Crushers, presented at the 14th International Mineral Processing Conference in Beijing in 2008, Erik Hulthén and Dr. Magnus Evertsson reported on their development of an algorithm for the improved control of cone crushers, based not only on the crusher drive speed but also on an optimized product output.
As Hulthén and Evertsson noted, control systems are already widely used for cone-crusher settings to compensate for wear and to protect the crusher. While the eccentric speed affects the particle-size distribution of the product and the crusher’s capacity, until recently changes to the crusher speed could only be made by changing drive-pulley configurations, which can involve considerable downtime.
Now, however, the use of a frequency converter means continuous adjustments can be made to a crusher’s speed, and this input, together with data acquired from sources such as mass-flow sensors, can be used to ensure the crusher’s performance is optimized on a minute-by-minute basis.
These authors tested the algorithm they had developed on a 350,000-t/y crusher at an aggregates plant at Ludden in central Sweden. Using a computer that could communicate with the frequency controller on the crusher drive, retrieve data from four mass-flow meters, and interact with the crusher operator, the system was able to improve the output of the unit by more than 4%. While this was the key parameter from an economic point of view, even more importantly from a maintenance perspective was the increase achieved in the crusher liner lifetime, at 27% longer than when the crusher was being run conventionally. Hulthén and Evertsson pointed out that since an operator cannot monitor the optimum crusher speed continuously, the use of a control algorithm clearly offers a significant improvement.
These two authors followed this up with a further presentation, Two Variable Real-Time Algorithm for Cone Crusher Control, at the 15th IMPC, held in Brisbane in September. Here, they showed not only was their previously developed algorithm even more effective than their earlier results had indicated, but a newly developed so-called “loaf” algorithm performed even better. The 400,000-t/y plant on which their tests had been performed consisted of a Nordberg HP4 tertiary cone crusher, with a 16–70-mm feed size and recirculation of any product material larger than 22 mm.
No fewer than 10 mass-flow meters were used as inputs, as well as frequency-converter data, with the algorithm providing a 6.9% improvement in crusher throughput over conventional manual control. And, while this particular implementation was focused on the production of sized aggregate, it provides food for thought for other applications where, for instance, better control of crushing could lead to reduced energy requirements for both crushing and subsequent grinding stages in ore processing.
Safety Drives New Crusher Design
In a paper presented at this year’s SME annual meeting, held in Phoenix, authors from crusher manufacturer FLSmidth and two aggregates producers reported on how improved safety and maintenance accessibility considerations had driven the design of the latest generation of gyratory primary crushers. In their paper Safety and Maintenance Centered Design of Primary Crushers, Solomon, Maio and Herber described the development of FLSmidth’s “top-service” concept, by which the task of stripping out key components of a gyratory crusher, such as the drive eccentric, has been made simpler and safer.
Four key achievements claimed for the system are a big reduction in the risk of maintenance personnel falling while working on a crusher, the elimination of overhead work and work underneath suspended loads, and a significant reduction in the exposure of crews to falling objects. There have also been some major improvements in the time needed for maintenance, the authors stated, with the downtime needed to replace a crusher eccentric having been slashed from around 24 hr to as little as four. This, they added, has a knock-on effect on regular maintenance, since preventive work can be carried out much more quickly, and with less impact on plant throughout, than with conventional bottom-service crusher designs.
Better, more regular preventive maintenance in turn helps reduce the risk of breakdown, not only in components directly involved with the crusher drive, but within the wider crusher structure as well.
Further improvements of the new design include readily interchangeable pistons in the hydraulic support system, while the eccentric design used means that out-of-balance forces can be markedly reduced. Not having to make provision for access at the bottom of the crusher also offers the potential for lower overall crusher-station heights, with less costly yet stronger discharge bins also feasible, the authors concluded.
As one of them noted at the end of the paper, his company had decided to install one of the top-service crushers because it offers improved safety for maintenance personnel, faster maintenance, lower overall construction costs and, importantly, the design changes posed little operational risk in terms of operating performance.
Gradual Evolution Continues
In October, the Australian-based manufacturer of mining and quarrying equipment, Screening and Crushing Solutions (SCS), unveiled what it claims is the world’s largest-ever mobile cone crusher. Weighing 135 t, the company’s TC1885 offers what it describes as a very high-capacity mobile solution for mining and quarrying applications, with an output capacity of around 1,000 t/h of crushed rock.
“Profitability in mobile crushing relies on higher crushing capacity, with fewer machines,” said SCS’s Sales and Marketing Manager Brian Court. “In the crushing industry, bigger is usually better. A mobile crushing unit can be placed right at the rock face where it is needed. The TC1885 can be moved around a mining operation, depending on where it is needed the most. This can help eliminate costly double-handling of material. Processing at the rock-face will save mining companies a great deal of money on fuel and equipment costs, and significantly lower the cost of production per ton of rock.”
The TC1885 is powered by a 650-kW (875-hp) Caterpillar engine. The closed-side setting can vary from 65 mm down to 15 mm, with available feed openings ranging from 180 mm up to 500 mm.
The fact that this machine came through SCS’s 15 years of experience in crusher technology serves to highlight the gradual evolutionary process that is continuing within the crusher-supply industry. Remember the first semi-mobile in-pit crushers only came into service in the mid-1980s; today, few new open-pits opt for anything else.
Clearly, the choice of crusher goes hand-in-hand with the engineering design of the mine, be it open-pit or underground, and the crushing capacity required. Maybe before long, with tire and fuel costs climbing, fully mobile crushing will become an option for serious consideration.