Surface Miners

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Open pit mining is among mankind's largest manufacturing and process-intensive operations. With huge investments in land, mining permits, human resources and equipment, mining companies are constantly analyzing their processes for improved production and safety. As a result of this pursuit, mining has historically unearthed new technologies that not only benefited their bottom line, but has benefited other industries including site and heavy highway construction.

Open pit or surface mining, including strip mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit (the overburden) is removed. This is the opposite of underground mining in which the overlying rock is left in place, and the minerals are removed through shafts or tunnels.

Surface mining began in the midsixteenth century and is practiced throughout the world, although the majority of surface mining occurs in North America. It gained popularity throughout the 20th century, and is now the predominant form of mining in coal beds such as those in Appalachia and America's Midwest.

In most forms of surface mining, heavy equipment is used to first remove the overburden. Next, huge machines, such as dragline excavators, mining shovels and bucket wheel excavators extract the mineral. The overburden and mineral removal is traditionally preceded by drilling, blasting and depending on the blast fragmentation, possibly crushing.

Traditional Mining Workflow
In order to fracture the overburden and the desired minerals, holes are drilled per a blast hole design. The blast hole design is prepared by an engineer who strategically places and angles the drill holes for optimal fragmentation and blast direction. Blast hole design is a specialized science in its own right. Typically, the engineer's hole patterns are marked on the ground to guide large drill rig operators. This can be challenging if not impossible at night or in adverse weather conditions. Positioning via 3D drilling systems is gaining in popularity. The blast hole design file is loaded into the 3D drilling system to provide guidance for hole pattern placement, angle and depth. (Read more about the benefits of 3D Drilling at http://www.machinecontrolonline.com/randy-noland/2723-3d-drillingsystems-features-a-benefits)

Once the holes are drilled (see Fig 1), demolitions experts load the holes with prescribed explosives. As you can imagine, safety is of critical concern and the site must be cleared for the blast. (See Fig 2) The support system to store explosives, explosive vehicles to carry explosives and accessories are extensive and highly regulated (additional expense).

After the blast, the material is assessed and if proper fragmentation was not achieved, additional crushing is required. The material is then loaded by a shovel, dragline or wheel loader into trucks for hauling. (See Fig 3)

Enter the Surface Miner
In the pursuit of process refinement, the surface miner is becoming a popular machine choice for many operations. First, lets take a brief look at its origin.

Development of surface miners was begun in the 1970s, was continued into the early 1980s, and marks a new paradigm in surface mining systems. The design concept for the surface miner is based on the milling principle and in a reverse of technology contribution, owes its origin to the road milling machines which cuts the old road surface for road construction. Since the 1990s, surface miners have gained in popularity with improved design of the cutting drum and higher machine power. This has enabled the users to excavate rock and other minerals with competitive cost and eco-friendliness. Viability of a mining project rests upon the appropriate selection of an excavation system right from the planning stage.

Basic Concept
The surface miner uses a drum to mill or excavate the material. Different manufacturers place the drums in different locations on the machine, i.e. the middle, the front, etc and use different methods for powering the drums. Also, the shape, composition and arrangement of the bits on the drum vary amongst manufactures and applications.

The operating method of surface miners resembles that of cold milling machines. A special cutting drum cuts and crushes the material. Drum location, bit shape, composition and arrangement vary between manufacturers and applications. Robust conveyor systems then load the material on dumpers or discharge it to the side of the miner. Alternatively, the material can also be deposited as a windrow between the miner's crawler tracks. This is valuable when there are not enough trucks available for loading the material from the conveyor belt.A highly precise automatic leveling system maintains the cutting depth. This highly accurate method enables useful minerals, coal or limestone to be mined selectively and with high purity.

Benefits
There are several benefits of using a surface miner depending on the application. The primary benefits are that drilling, blasting, crushing and loading are replaced by a single machine and single process. These machines can run 24 hours per day without the coordination of the drill-blast process. There are some areas where blasting is prohibited thus surface miners may be the only choice.

In some regions, active mining must be setback 30-50' from high-walls due to blasting. This results in a significant amount of unavailable minerals. Surface miners can provide greater exploitation of a mine's resources.

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 crushing systems, savings that can continue well past the primary crushing stage.

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 valuable­but not compatible­the 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.

CO2 Emission savings are another potential benefit especially in this era of carbon cap and trade. Increased production with less machines all support this potential.

3D Machine Control and Positioning
Precision surface mining is a great candidate for utilizing high accuracy GPS technology and two-way data communication. An engineer is able to 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.

Surface miners can offer a flat, level bench via their leveling system. 3D machine control can also assist with keeping the cutting drum steady at a desired elevation. Site connectivity features could include production rates, volumes, idle time, service time, as well as fuel consumption. This information, among others, can be streamed back to a central fleet management system for analysis, reporting and historical playback.

Autonomous/SemiAutonomous Mining
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.

Conclusion
Higher mineral prices and demand along with stricter environmental regulations are driving mining operations to explore new methods for extracting their minerals. Surface miners offer some mining applications a simple, precision and cost effective solution. These systems are also candidates for 3D machine control and site connectivity and offer strong future potential for driving tomorrow's autonomous mines. MC

Randy Noland is the Managing Editor and Cofounder of Machine Control Magazine.

References (PDF contains clickable URLs)
Montrie, Chad (2003). To Save the Land and People: A History of Opposition to Surface Coal Mining in Appalachia. United States: The University of North Carolina Press. pp. 17. ISBN 0-8078-2765-7.

Blasthole Drilling in Open Pit Mining-- Third edition 2012

3D Drilling­Features and Benefits

Predicting "cuttability" with surface miners­A rockmass classification approach. Dey, K., Ghose, A.K.bNational Institute of Technology, Rourkela, 769008 Indian School of Mines University, Dhanbad Journal of Mines, Metals and Fuels Volume 56, Issue 5-6, May 2008, Pages 85-91

Large Surface Miners-Applications and Cost Calculations

Wirtgen Surface Miners

Welcome to Tenova Takraf

Videos References For Surface Miners
Vermeer Surface Miners at work

Iron Ore Mining in Australia--Wirtgen 4200 SM

Lignite Mining in the USA-- Wirtgen 4200 SM

A 1.127Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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