In an industry renowned for its low return on investment, selecting the most efficient mining machine is crucial to the profitability, and productivity, of the mine. On the surface, this could be considered straightforward. Earth movers above ground have no restrictions on their size and, when it comes to choosing bucket capacity, payload size and the most fuel-efficient design, the sky’s the limit.
It’s a slightly different story, however, when machines are taken underground. In order to achieve the same productivity as on the surface, underground machines must be cleverly designed to incorporate the necessary production functions, as well as the added features essential for the underground environment.
Machine size is restricted due to the narrow working spaces and rock conditions. The salty, damp and corrosive environment places added pressure on machines to work efficiently and to capacity and, precious production hours can be lost in the long commute from the entrance to the working face. In short, machines underground have to work harder for their keep than their surface counterparts.
But there are machines built to withstand the harsh conditions underground. A load haul dumper (LHD) is the specialised machine used to scoop material, which is then dumped into haul trucks ready to be taken to the surface. With the capability to scoop between three and 15t in one pass, these are no lightweight machines. Their core function is to get material underground to transport, safely, quickly and efficiently. Descending to depths of up to 2,500m and climbing inclines of up to 11.5 degrees, these vehicles are the Olympians of their field.
One size doesn’t fit all
Mine owners have to weigh up several considerations when in the market for an underground machine. Perhaps the first and foremost is the question of diesel or electric machines. While the demand for diesel still outstrips that of electric models, there has been rising interest in electric loaders and trucks in recent years.
Electric machines tend to be used mainly in mass mining methods such as block and panel caving. The major advantages of electric machines are their running and energy costs which are considerably lower than diesels. Electric machines run at 95 per cent eficiency whereas only 30 per cent of the fuel’s energy in a diesel motor is used in loading and tramming operations, with the rest lost as heat.
Electric models are not without their issues however. They are run by power from a cable, attached to power supply, which reels on and off as the vehicle moves. For that reason, they can be less _ exible than diesels. Plus, as well as the obvious risks of damage to the cable as it travels through the tunnels’ twists and bumps, the reel must also have a large diameter to help preserve the life of the cable. And while an electric machine can be considered to be more cost effective than a diesel, this is only true if the infrastructure to run power to the machine is readily available. To install it at brown_ eld sites can be a complicated and expensive process.
The increasing cost of oil and gas, as well as the ventilation issues that inevitably come with running a diesel engine underground, has no doubt played a part in the rising popularity of electric machines.
Environmental concerns, legislation on emissions, health and safety, air quality and ventilation are placing more restrictions on diesel engines. Mines need a lot of ventilation to keep diesel machines underground cool as well as removing harmful gasses. Plus, diluting emissions of carbon particles and noxious gasses caused by burning fuel underground can account for as much as 40 per cent of the electricity costs of underground mining operations.
Recent and upcoming regulations demand a reduction in polluting emissions from mining vehicles and the industry has to respond.
Casper Swart, global product line manager at Atlas Copco explains, "We are currently repairing and retro fitting our diesel engines to meet Tier 3 emission standards. Tier 4 standards will be phased in by 2014. All these modifications have an impact on the size of machines. Engines have to be cleaner, but cleaner engines often means installing bigger components to machines which obviously brings other challenges."
Ryan Lipic of Mining Technologies International (MTI), agrees. "It can be challenging and time consuming," he says, "because legislation is not consistent from country to country. Standards in the US, for example, are more stringent than in Canada but we obviously have to meet all the standards to be able to operate in those countries.
"While actual manufacture of a loader typically takes around six months, it takes two to three years to take a product from paper to market. This is largely due to all the testing that we have to go through as well as ensuring it complies with all the necessary legislation."
A partnership approach
The size, type and capacity of machines used in a mine will often depend on the application so a certain amount of collaboration exists between manufacturer and operator in the development and production of underground machines. "Much of the conversation would be around the application of the mine and the infrastructure", says Swart. "There are mines, mostly copper, with tunnels measuring 4.5m by 4.5m, and you have bigger, mostly iron mines, which have tunnels of 6m by 6m where you can use a far bigger carrying capacity vehicle with a higher profile.
"Then there’s a platinum mine that requires low profile vehicles because their tunnels are 5m by 1.8m. Plus we need to know what kind of infrastructure is available so we can provide the customer with the appropriate solution.
"Whatever the size of tunnel or application of mine, the objective remains the same – to fit the biggest carrying capacity in the smallest envelope. This is essential for maximum productivity."
The pairing of loader and truck plays a huge part in productivity. For example, if a smaller loader is paired with a large truck, it would take many more passes to fill the truck. This results in heavy wear on the loader as well as a waste of valuable production time to get it filled.
By the same token, a smaller truck being filled by a loader with a large bucket capacity runs the risk of being overloaded, thus increasing maintenance costs of the truck. The general rule is that three is the ideal number of passes for optimum productivity – so a truck will take three loads from the correct sized loader until it’s at capacity. Most manufacturers promote and produce their underground loaders and trucks so they complement each other in this way.
Reaching new heights
The industry has evolved massively as technology has become more advanced. The increase in the use of LHD automation is one trend that has had an impact on the industry. Without the restrictions that having a human operator in the cab places on underground operations, machines are able to significantly increase productivity levels.
Full or partial automation can mean reduced manning costs, fewer loaders in production and ensure a continuous production process.
Joseph Bontje, marketing representative at Caterpillar says safety is the key driver behind the move towards automation. "There are many instances underground when it’s not safe to have an operator in the cab," he explains, "so being able to control and monitor machines safely from above ground is critical to operations. Caterpillar’s command system is a safe and production solution to having human operators underground. When the safety issue is removed, you can really optimise production."
But while technology has played a major part in increasing productivity, reducing costs and improving safety, so too have customers’ expectations grown.
Mine owners are looking for the same gadgetry, functionality and capacity that are on surface vehicles – GPS, mapping and localization to name a few. They want to know what the machine is doing in real time – fuel usage, how much muck is being moved, errors in handling, etc. These are essential pieces of information that, when put together, help the owner work out ways to reduce the cost per tonne.
Manufacturers are constantly looking for ways to incorporate these features into machines already crammed with the standard requirements for health, safety and optimum production as well as innovative ways of being more efficient with fuel. How much further they are able to develop, enhance and improve remains to be seen.
Manufacturing in a global market
Competition is this specialist market is fierce and manufacturers have to work hard to carve their niche. The following organisations are by no means an exhaustive list of the players in the LHD market:
Atlas Copco, based in Sweden, has been providing industrial productivity solutions above and below ground since 1873. Their range of LHDs comprises 13 machines, which includes the Scooptram range of six diesel and three electric loaders, as well as the Minetruck range of underground trucks. The smallest of the Sooptram range, the Scooptram ST2D has a 3.6metric tonnetramming capacity for smaller sized operations, particularly in narrow vein mines.
The largest, Scooptram ST1520 is a 15t LHD for large underground operations. Its low profile means that it can be used in tunnel where the work height is as low as 2.7m. The latest addition to the range of Scooptram underground loaders – the Scooptram ST7 – has a tramming capacity of 6.8t, articulated steering and an oscillating rear axle. It is powered by a clean burning, 193 hp 6.7 litre Cummins Tier 3 engine and benefits from traction control to increased loading performance and improved tyre life. Of the future, Swart says "We are constantly striving to meet our customers’ needs and we have a few exciting products in the pipeline that we hope will continue to do just that."
GHH Fahrzeuge’s product line for underground operations features diesel and electric loaders and diesel trucks as well as niche super low profile loaders for more niche markets, including Russia, Africa and China. They offer a ‘plain technology’ option for customers wanting a simple solution as well as high tech versions with more sophisticated features. Their loaders transport payloads of between three and 20t, while dump trucks have loading capacities of 15 to 55t. Four wheel drive and articulated swivel hinge are standard features.
GHH’s new generation of electric loaders – the LF-10HE, LF-14HE and LF-20HE – are equipped with the GHH-designed Efficient DriveSystem (EDS). EDS is a revolutionary brand new hydrostatic drive line concept. Its advantages include fuel consumption savings, less wear for tyres and brake, highest brake out force and easy handling in one system. The special, active cable drum device helps extend the lifetime of the cable.
Christian Riedel, product manager, says "Not only are our EDS loaders suitable for applications where adaptation for ventilation isn’t possible, but they provide increased comfort for the operator and a smooth drive".
MTI’s LT series loaders range includes the LT-70, the LT- 350, the LT-650, the LT-1050 and the LT 1150. Their latest addition, the LT1650 is their largest loader to date and has an 11 yard bucket capacity. There are plans in the works to develop an even larger truck with a 14 yard bucket.
In addition, MTI built the world’s first hybrid diesel electric loader which can operate with low decibel levels and near zero emissions. Its electric motor is powerful enough to perform the tasks of a diesel loader. While running on diesel, it charges its battery for the electric motor, eliminating the need to be stopped to recharge.
Noxious gas emissions are reduced by between 40 per cent to 70 per cent, and combined with a high efficiency particulate filter, enables a decrease in breathable combustible dust emissions of 95 per cent.
In addition, these decreases could result in a 20 per cent to 40 per cent reduction in the energy required to ventilate a mine. Their DT Series four wheel drive trucks range from 7t to 30t. They offer EPA and MSHA certified engines to provide cleanest air possible, as well as an optional automated lubrication system.
Caterpillar’s best sellers are driven by geography and geology. Their smallest loader, the R1300G, and truck, the AD30, are designed for high production in smaller underground mining applications such as those in South America. The biggest machines, the R2900G loader and the AD60 truck, are suited to the larger operations of Australian mines. Caterpillar’s underground loaders have payload capacities ranging from 6.8t to 20t with bucket sizes ranging from 2.4m3 to 11.6m3 based on machine and application. Truck capacity ranges from 30t to 60t; body sizes from 11.3m3 to 36.6m3. Sandvik offers a range of LHDs, which includes small models designed for narrow vein and low profile applications, mid sized – for wide variety of mining applications as well as construction tunneling, and high capacity LHDs for mass mining applications. Their diesel and electric loaders have tramming capacities ranging from 1 tonne to 25 tonnes. Three separate low-profile models: the LH205L-M, LH208L and LH209L operate in low profile mining operations with the LH205L-M able to work in back heights as low as 1.6.m.
Sandvik’s trucks range from the TH320 with a 20t payload capacity, to the TH680, a side-tipping, 80t truck for horizontal underground hauling. All models with payloads from 15 to 60t are designed to operate fully loaded on long spiral gradients of up to 20 per cent high speeds
