Surface Miners – Power with Precision

Vermeer is in a good position as an equipment engineering-focussed company, being both privately owned and debt free.  Outside of its home manufacturing plant in Pella, Iowa, the company also has a factory near Beijing, as well as direct-owned offices/locations in the Netherlands, Australia, Brazil and Singapore; as well as 73 other international dealerships. In terms of the its overall product range, its HDD line-up for trenchless construction represents the most significant part of the business in revenue terms, however, the importance of the mining market is increasing.

Efficiency at the Pella site has been increased significantly in recent years with the adoption of lean manufacturing techniques. One of the points emphasised by the company is the strength of its engineering competency inhouse.  The Vermeer engineering teams are located on the factory floor itself, so they have constant communication with the manufacturing teams. While components such as engines, tracks, cylinders, radiators and pumps are outsourced, the core of the machine manufacture including areas such as fuel tanks, cabs, frame and steel body are very much retained. This allows flexibility when it comes to new designs and alteration of existing designs. Current customers also get priority over future customers wherever possible.

Terrain Leveler development

The surface miners fall under the so-called Specialty Excavation group and evolved from Rock Trenching work in the 1970s with the current line developing out of the T555 model.  The evolution from rock trenching is still evident in the design, in that the current Terrain Leveler machines can cut vertical highwalls at the margins of surface mines.

The initial surface miner model was the T1055, which initially had four cutting discs working in a “bottom-up” cutting design.  However, the final design settled on had a top down cutting method and a patented tilting cutting drum with multiple cutting teeth arranged in a staggered pattern.

A key decision was also to move the cutting drum from the middle or front to the rear of the machine, meaning that the tracks are not driving over and compressing the cut material. The forward motion of the drum and top down method also helps to propel the machine forward, and sees the teeth more easily push through the material. The method also allows for final product flexibility – a lower travel speed allows greater cutting depth to be achieved as well as a smaller particle size, with the opposite true of faster operation. Larger gaps between cutting teeth where the material allows it produces higher tonnage capacity.

The mining market itself commenced in 2001, when Vermeer began working with US Gypsum on surface mining possibilities, and another Italian quarry customer asked for a machine to help them avoid drilling and blasting in parts of their operation. The first new T1255 machine was used in a limestone operation in the Dominican Republic. A specialist mining engineering group led by Jim Hutchins subsequently converted all the known operational parameters of the machine from depth and width of cut to detailed operational costs into a template model, from which a customer, after inputting details about the material to be cut and required production rate, can calculate total fixed and variable costs per hour and ultimately cost per tonne. This means decision on whether a mine is suitable for precision surface mining can be made at an early stage, and if the decision is positive, this is often verified through trialling a machine at the mine-site – and according to Vermeer the reality almost always matches the data predicted by the model. In addition, Vermeer purchased a range of rock testing lab equipment; along with developing its own series of tests; to much more accurately measure material parameters as well as to take into account ore variability. In general, the more representative samples a customer can provide, the better.

Direct loading or cut to ground

A key difference between the Vermeer concept and the Wirtgen concept is that the Vermeer machines do not have a conveyor attached for simultaneous truck loading, which could be regarded as the “conventional” surface miner set up. The Vermeer team looked in depth at this issue back in the early 2000s and concluded that the direct dump option was preferable for several reasons. Principally, Vermeer argues that truck efficiency is lowered by their queuing behind the surface miner, which also increases overall relative fuel consumption versus more consistent speeds. It also argues that accurate loading of trucks using this method is difficult and that trucks are often under filled; the trucks themselves being capable of moving more material than the surface miner can provide.

It is also argued that with most mines having ore variability requiring regular changes to cutting speed with a resulting change in tonnes per hour; that it is very difficult to predict the number of trucks needed or more accurately, the number that can be effectively utilised. It was therefore concluded that omitting a built in loading tool/conveyor was the better option.

With the direct dump or “cutting to ground” design, wheel loaders are normally used to load trucks after the surface miners have completed excavation of an area. In some cases, dozers may be used to blend or stockpile material prior to truck loading allowing added flexibility, while scrapers represent another loading option. In the future, combining surface miner operations with shiftable conveyors could represent another take on the IPCC concept.

T1655 development and delivery

Based on discussions with Fortescue Metals Group (FMG) and assessment of the wider potential future market, a series of targets were set for the new machine. Wirtgen already had a large machine, the 4200SM, so the company knew what it had to achieve to compete in terms of performance. Previously developed machines, including the 112 t T1255, had a chain drive, but for the new 182 t T1655, a direct cylinder drive was chosen to achieve higher production rates of 4,000 t/h and higher.  Vermeer argues that this machine is helping to shift the boundaries of where surface mining ceases to be economic versus drill and blast. In general, a single T1655 is capable of the same production as three T1255 machines.

Operator cab elevation is an attribute of the T1655 allowing better visibility and maintenance access

The T1655 has two engines; effectively doubling up the single engine in the T1255. This option was chosen versus having one very large engine, as is much cheaper as well as simpler from a component supply standpoint, both for Vermeer and for the customer. The smaller engines also have a much shorter delivery time.  The two engines feed power into one gearbox, meaning all available horsepower can be consumed and the level of load control means it is virtually impossible to “hot stop” one of the engines.

The direct drive concept was tested on a modified T1255 at a gypsum operation in Oklahoma. As a result, an original design for the T1655 with a direct drive and 950 hp weight was altered to a 1,200 hp machine with direct drive.

A complication in Pella was that Vermeer did not have a facility large enough in terms of vertical clearance, to build the new machine. A new $8 million facility was built as a result, with a higher clearance, larger floor area and high hoist crane capacity. The floor also had to be made of concrete to allow for the 410,000 lb machine weight. The switch to direct drive also made the machine wider. The T1655 is shipped in five pieces with a separate container of parts – as within the US there is a 150,000 lb road transport restriction.

Once in Australia the miner is assembled complete at the Vermeer yard close to Perth airport; and transported complete to the FMG site; as the same road transport restrictions do not apply. The facility in Perth is connected to the home factory and the minesite by satellite and sends real time machine performance data back to Pella for analysis.

The T1655 in detail

At 182 t, the T1655 is significantly larger than its predecessor, the T1255 Terrain Leveler. It stands 5.2 m high from ground to the top of the cab at full extension. Its length spans 13.4 m and its width is 6.4 m. The T1655 is designed specifically for precision surface mining, a process that allows mine operators to selectively extract mineral seams in surface mining applications. Operators can also influence material sizing – producing consistent-sized material in a uniform configuration so minerals can be handled more efficiently than product produced by drilling and blasting. The uniform product size allows more efficient settings on secondary and tertiary crushing systems. The particle size produced is fairly consistent but the slower the drum is rotated, there is a corresponding torque increase.

The T1655 is the newest generation of Terrain Leveler, modelled after the Vermeer Commander series of tough track trenchers but with specific technology for seamless operation. An important feature contributing to the ease of operation is the TEC Plus display, which allows the T1655 to communicate with the various control modules situated throughout the machine, as well as the engine. The TEC Plus display allows the operator to easily monitor and control machine functions and improves the onboard diagnostic capabilities.

Crawler dozers moving into position to stockpile ROM ore for loading into trucks

Vermeer also designed several enhancements to the cab for operator comfort. An air-ride suspension system provides a smoother, more comfortable and quieter ride for the operator in the typically harsh environment of a mining operation. The enclosed cab features a filtered air system, dual heating/cooling systems, sound attenuating foam, as well as dual full suspension seats for optimum operator comfort and training. Not only does the cab elevate to a maximum height of 17 ft, it also expands out an additional 58.4 cm for enhanced visibility. The cab is designed to be a structure in itself and meets the standards of a roll over protection structure (ROPS). The T1655 cab elevation also gives easier access to maintenance points. The cab is lowered during machine transport or relocation in order to give a better centre of gravity.

The productivity of the T1655 centres on the direct drive drum with the drive motors attached directly to the cutter drum as stated. This not only improves cutter drum efficiency, but it also reduces wear costs associated with chain, sprocket or belt transmissions. The cutter drum is located on the rear of the machine. This, and the machine’s low centre of gravity, provides ample traction and keeps the T1655 balanced and stable. The cutter drum has a patented tilt feature that allows it to tilt 5° in either direction for a smooth excavated area. Ultimately it is planned that the direct drive T1655 will operate in a team of miners as the high tonnage production machine, with ancillary chain drive T1255 machines still used at mine boundaries, such as to create vertical highwalls. The chain drive is more expensive to maintain due to servicing sprockets etc. Some 85-90% of mining occurs away from these boundary areas.

The T1655 has dual hydrostatic tracks for independent rotation in either direction. The machine can quickly reposition up to 360° in either direction for the next cut. The load control feature allows the machine to automatically adjust ground speed to use full engine horsepower, thus making the machine more productive. This provides a stable ground drive speed for maximum productivity in varying conditions. The T1655 features two Cat C18 ACERT engines for a total of 1,200 hp. The dual engine configuration provides power to a common pump drive so that each engine provides power equally to the machine; however, if one engine is not operational, the machine is still able to function on a single engine. A 3,028.3 litre fuel tank provides 13.2 hours of continuous operation at maximum horsepower.

The company works with Kennametal for the supply of cutting teeth; and as with other mining machines that use cutting such as longwalls and roadheaders, the key is to changeout the teeth before the main carbide steel tooth wears out and the wear encroaches onto the adaptor, requiring more time consuming and costly repair. The tooth pattern on the drum (which on average is run at 25 to 28 rpm) varies from mine to mine – at Christmas Creek there is a tooth cutting rock about every two inches. To some extent the operator can start to feel wear on the teeth through a loss of production performance. For safety, the drum can be raised or lowered remotely for teeth changeout as well as rotated.

The angles of the teeth are greater at the drum edges, as at this point the teeth have to cut wide of the drum itself. Wear rates are highest either side of the drum centre. At FMG Christmas Creek, the T1655 machines achieve about 25 bcm per pick or 75 t.

Broadening horizons

T1255 machines have already been used in Australia by contractor HWE at the BHP Billiton Yandi iron ore operation, where the surface miners excavated bands of soft cap rock that could not be blasted due to their being close to the water table. This is an example of where surface miners can be utilised in conjunction with a mainly drill and blast mine, because of water issues, or proximity to urban areas, or to mine more precisely with a neater highwall at the margins of a pit. Several major bauxite operations are close to urban areas, and have been using crawler dozers to rip material, but are potential candidates for the successful use of surface miners.  Diamond (kimberlite) and uranium operations also represent potential markets and discussions with potential customers are ongoing.

The Christmas Creek OPF showing the reclaimer in the background

The key order came in October 2011 when FMG ordered an additional 15 machines, a combination of 8 T1255 and 7 T1655 miners.  From the T1655 standpoint, this meant that development of the machine could be completed more rapidly; but it was an important point that FMG had to commit to the cutting to ground concept. As it stands, FMG Christmas Creek has both Vermeer and Wirtgen miners, but both are used for cutting to ground, even though the Wirtgen machines are equipped to direct load. At Cloud Break, Wirtgen miners are still used to direct load trucks.

Shipping the assembled T1655 from Perth to FMG Christmas Creek

The T1655 itself was never actually tested in the US due to the lack of a suitable test site – this was done at a location in Western Australia near Bindoon after the first machine was shipped. As with any completely new machine there were some design issues, the main one being refining the cab suspension, though this was quickly resolved and less modification/customisation was required than expected. The cab is distinctive in having two full operator seats to assist in training, unlike the T1255 which has a fold down second seat.

At the time of the IM visit to FMG Christmas Creek in June 2012, there was one T1655 at the mine site, one at the dealer yard and the other five on order with a scheduled delivery time of one every two months. One of the new machines will be at the MINExpo show in Las Vegas prior to it being shipped to Christmas Creek after the exhibition.

Precision surface mining

Using the Vermeer Terrain Leveler allows the mine to make a layered cut at a desired depth.  Cutting dimensions can be very accurately controlled in 2D and 3D space. Laser guidance is used for 2D grade control such as drum tilting as it is low cost and relatively simple, while for machine positioning, a Trimble based high precision GPS is used. In the future, the machine design and the mine method make it very amenable first to remote control and ultimately autonomous operation, due to surface mining being a relatively repeatable process when compared to conventional mining. It also avoids the stop/start nature of drill and blast.

Chain drive on T1255

“Today’s mineral prices are driving mine operators to explore new methods to extract mineral seams,” says Mark Cooper, Senior Director of Specialty Excavation for Vermeer. “In Australia, operators must follow a 10 m setback from a highwall for blasting. That’s 10 m of material and a significant amount of money that they just leave. Mines can’t afford to leave these deposits behind, based on today’s market prices.”

A patented drum tilt system allows the operator to control grade in both the lateral and longitudinal directions and the unit can dig up to 27 in deep and 144 in wide in a single pass.

Direct drive on the T1655

Precision surface mining produces a smooth floor that can minimise wear and tear on mine trucks and loaders, especially on machines with rubber tyres. This can also allow the use of offroad trucks in place of mine trucks in many cases.

Producing small-sized material in a uniform configuration allows minerals to be handled more efficiently than product produced by drilling and blasting. The uniform product size also allows more efficient settings on secondary and tertiary crushing systems, savings that can continue well past the primary crushing stage.

New and worn Kennametal tooth as used on the T1655

Where the desired minerals are in thin layers, precision surface mining can follow the layers and help prevent unwanted mixing of materials.  Since it is entirely possible that all layers are economically valuable – but not compatible – the ability to separate them through precision surface mining provides benefits over drilling and blasting. Precision surface mining allows this process to be closely controlled so that almost all available products are recovered, resulting in a product of higher quality and value.

“We’re looking at somebody digging with a garden shovel versus somebody cutting out pieces with knives,” says Cooper. “It’s just a different way of approaching mining. Vermeer believes we can offer mines the ability to chase smaller seams and product located in corners that current methods don’t allow mines to go after economically.”

In hardness terms the Vermeer T1255 and T1655 can handle rock of up to 300 MPa, with the hardest material encountered at FMG in the region of 250 Mpa. But hardness is not necessarily the key factor – some hard material may fracture easily due to having natural bedding/joints etc, whereas some softer material can prove harder to actually break.

Working conditions are also important, especially a smooth working floor, as the process is much more efficient where the miner can repeatedly make the same cuts in a similar manner to ploughing a field. Wet weather does not have an effect on machine performance per se but does affect the cut product

Trimble GPS antenna on T1655

Precision surface mining also gives mine operators the ability to react quickly by increasing mine production in a short period of time. The capital costs to expand or open a mine are significant, and can require up to three years of planning and installation before the mine is operational.

“An iron ore mine in Australia recently purchased T1255 Terrain Leveler Surface Excavation Mining (SEM) units and portable crushers to quickly increase mine capacity, in order to chase spot prices in the market,” says Cooper. “Precision surface mining gives mines this type of flexibility. Since the Terrain Leveler SEM is a production machine, the mine was up and running in a matter of months versus years.”

Precision surface mining going forward will be able to more effectively use high GPS technology and two-way data communication.  An engineer could create a mine plan in the office and send the data to the Terrain Leveler.  The operator can then pull the plan up on the screen and go to work based on the new mine plan that is displayed.

Cloudbreak and Christmas Creek

Located in the heart of the Pilbara, the Chichester Hub is made up of Fortescue’s flagship mine Cloudbreak, and the second mine Christmas Creek. Together, the two mines currently produce 55 Mt/y and will ramp up to a targeted 95 Mt/y in 2013. Only Chichester Hub uses surface miners, with the future Solomon Hub to employ conventional mining – this is mainly due to it having deeper ore with more variable thicknesses. Christmas Creek itself would not actually be economic were it not for precision surface mining – as drilling and blasting the ore would cause too much dilution.

Fortescue’s first minesite, Cloudbreak currently mines and processes ore at a rate of around 40 Mt/y. More than 2,000 people work an eight days on, six days off roster at the site which has been in full operation since May 2008. The horizontal nature of the deposits at Cloudbreak called for a new mining approach to that used at other mines which operate on vertical deposits of ore. Overburden removal is done using conventional blast, truck and shovel methods while Wirtgen surface miners cut and load the ore into trucks for transport to the run of mine stockpiles.

Screening, crushing and desand plants at the Cloudbreak ore processing facility prepare and refine the product before the ore is stockpiled ahead of transport to port. The train loadout facility at Cloudbreak is capable of feeding 16,000 t/h to the iron ore trains.

Mining began at Christmas Creek, 50 km to the east of Cloudbreak, in May 2009, and within the next two years, major expansion projects had been undertaken to increase the capacity of Fortescue’s second mine. During the first phase of the Christmas Creek expansion, a new ore processing facility was constructed and successfully wet commissioned in March 2011.  The ore processing facility is now operating at its targeted capacity of approximately 18 Mt/y.  The expansion also saw a 50 km extension to the existing Port Hedland to Cloudbreak rail line to transport the ore from Christmas Creek to Cloudbreak and Port Hedland. Work is also complete on a 1,600 bed permanent operations village to house the growing Christmas Creek workforce.

Work is well underway on the second phase of expansion as part of the Chichester Hub expansion. During the 2011 December quarter, a product reclaimer at Christmas Creek was commissioned enabling significant reductions in the train loading times. Commissioning of the first stage of the Chichester Hub expansion is now complete and construction of the next stage, including a second ore processing facility, has already begun. Synergies will be achieved at Christmas Creek through the sharing of stock yards and the train loader together with brownfield expansion of the water and power facilities.

During the 2011 December quarter significant progress was made on the ore processing facility in the erection of primary steel. Foundation works for a remote crushing hub and overland conveyor system were largely completed and early mining works have commenced in two areas in preparation for mine ramp up.  The contract for a new Christmas Creek airstrip was awarded and construction of the airstrip’s earthworks, runway and facilities began in January 2012.

The second expansion phase, known as Christmas Creek Phase 2 Expansion, has a $1.1 billion project budget.  First ore through the new ore processing facility (OPF) is targeted in September 2012, with the ramp up to a combined Christmas Creek total run rate of 50 Mt/y planned for the December quarter of 2012.  Key achievements to date include the completion of foundation works for the second OPF with significant progress made in the assembly of steel and installation of equipment in the crushing and screening buildings.  Concrete works for a remote crushing hub were substantially completed earlier this year and formation of the ROM access ramps was completed prior to the delivery of the primary crusher. Installation of the overland conveyer system is well underway with modules expected to arrive early in the June 2012 quarter. Almost all of the major equipment has now been delivered and installed on site including the two scrubbers, cone crushers, wet and dry screens, clarifier and the first of the motor control centres.

The power station expansion remains on target and the new Christmas Creek airstrip is progressing on schedule.  Major roads have been completed and good progress is being made with other bulk earthworks for miscellaneous infrastructure.

The mining contracts for the second phase of Christmas Creek are currently being negotiated in parallel to the start of early mining works in two areas in preparation for mine ramp up.  Extensive plans are in place for the delivery of heavy mobile equipment to meet the ramp up requirements. The new T1655s are a key part of this and a new covered surface miner maintenance shop was under construction at the time of IM’s visit.

A group of three surface miners operates together in a group, mining an average area of width 83 m and length of 325 m; with a total area per miner of 27,083 m2. The strip ratio is about 5:1 waste to ore; with the downstream OPF, mainly consisting of milling and cycloning to remove silica and manganese. The ore is then railed some 290 km to Port Hedland for shipping, with each train hauling some 130,000t. Normally five trains a day leave for Port Hedland.

In its current planned ramp up, FMG will ultimately use 32 surface miners in all across the Chichester Hub – made up of 16 Wirtgen 4200SMs, nine Vermeer T1255s and seven Vermeer T1655s. WA Surface Mining and UEA are used as contractors at the mine but mainly supply operators only, with FMG owning and maintaining the machines.

The development rate for the T1655 was very quick from prototype to testing, and it was only three months into testing and 1,000 hours of test operation that FMG made a commitment to the seven machines. Ultimately the T1655s are for the longest open pits to provide the maximum productivity possible – these strips as stated are typically about 325 m but can be up to 800 m long. Both the T1655 and 4200SM are used, and both “cut to ground”, with ore dozed to a ROM pile and loaded into trucks. For shorter hauls, Caterpillar 777, 789 trucks are used, with highway bulk trucks used for longer hauls of over 5 km to reduce tyre wear. The overburden fleet consists mainly of MT3700/4400AC electric drive trucks and Caterpillar 793s. New Komatsu 930 trucks have also been ordered for Christmas Creek.

Overburden removal is conducted with conventional drill and blast mining, with Downer EDI and Ausdrill contracted to do the work; with ore mining carried out by FMG itself but with some contracted operators. NRW also conducts some of the ore removal. By contrast, Cloud Break is an owner operator mine only.

Christmas Creek has five main pits, all mined simultaneously. The iron ore seam average 1 m in thickness and tends to be quite shallow at only about 4.5 m beneath the upper waste horizon. One T1655 surface miner is capable of mining over 200,000 t of material per day. The mine geologists get the crawler dozers to stockpile the mined material based on grade.  The ore is loaded into the trucks by wheel loader and dumped at the processing plant (OPF), again based on grade. These ordered “fingers” of ore are then blended based on customer requirements. Some higher grade ore is trucked to Cloudbreak in order to blend it with their lower grade material. IM