When choosing the right drilling technique for drill-and-blast operations at open-pit mines or quarries, miners and drillers need to consider blasthole diameter range and ground characteristics.

One of the methods in question is rotary drilling, which is the principal practice used for large-diameter (9in/299mm or greater) blastholes, particularly in hard rock, due to its cost-efficiency in these conditions. Rotary drilling is typically the preferred method for production drilling where feasible due to its overall low costs of operation. Tab Siegrist, product line manager – surface drills at Sandvik Mining, says: “Most of our mining customers can do little to influence the price of their product, so they stay competitive by controlling and reducing cost per tonne.”

Other methods commonly used for blasthole applications are down-the-hole (DTH) and top-hammer drilling, and rotary drills are generally capable of both the rotary and DTH techniques.

Matthew Inge, Atlas Copco’s product manager for mid-range blasthole, explains: “The primary difference between rotary drilling and other methods is the absence of percussion. In most rotary applications, the preferred bit is the tri-cone bit, which relies on crushing and spalling the rock. This is accomplished through transferring downforce, known as pulldown, to the bit while rotating in order to drive the carbides into the rock as the three cones rotate around their respective axes.”

As a result, these larger tri-cone bits can take advantage of heavier pulldown loads and rotation torque to power through hard rock.

Inge adds: “Rotation is provided by a hydraulic or electric motor-driven gearbox (called a rotary head) that moves up and down the tower via a feed system. Feed systems utilise cables, chains or rack-and pinion mechanisms driven by hydraulic cylinders, hydraulic motors or electric motors.”

Each drilling method naturally comes with its advantages and limitations. When it comes to the choice between rotary and DTH, Jim Peterson, applications engineer for Cat Surface Drills, comments: “Drill manufacturers simply do not have the compressed-air packages to operate DTH hammers larger than 8in (20.3cm) and retain the productivity advantage that the DTH method normally has in really hard rock. So by default, rotary drilling is used for the large-hole drill-and-blast programmes.”

In addition, Brian Fox, vice-president product management, surface mining division at Joy Global, cautions: “Smaller tri-cone bits become more limited in smaller diameters in hard material, and cannot keep up with DTH, which are very effective from the 6-9in (152-229mm) range.”

Rudgormash concludes: “In our opinion, rotary drilling is the most universal method to make a blasthole when mining. It gives an opportunity to mine minerals with various mechanical characteristics and of different hardness; it is therefore used more often than others.”

Design features

Over recent years, when designing rotary blasthole rigs, manufacturers have placed increased emphasis on the personnel that operates and supports the drill. Enhancements to safety, ergonomics, user-friendliness, serviceability and productivity are all at the top of the list.

“Drill rigs have incorporated more operator safety features, more diverse machine self-diagnostics and improved automation of repetitive functions in the drilling cycle,” lists Peterson.

Sandvik Mining’s new, ‘next-generation’ DR461i, which is a diesel-powered, self-propelled, crawler-mounted and automation-ready blasthole drill, includes safety enhancements such as autonomous pipe handling, above-the-deck bit change, additional walkways, hand railings and safety interlocks. The drill was also designed to fully comply with safety standards such as Mining Design Guidelines (MDG) for mobile and transportable equipment in mines, Earth Moving Equipment Safety Roundtable (EMESRT) design philosophies and CE conformity marking.

Atlas Copco has also been involved with EMESRT since 2010, implementing their principal design philosophies across its Pit Viper fleet.

In addition to safety, ergonomic operator cabs help create a productive work environment. Ken Stapylton, vice-president of surface drilling at Sandvik Mining, explains that when Sandvik started to design the DR461i, it took a close look at the previous DR460 cab and identified ways to improve comfort and functionality for the operator. For example, the windows on the cab have been designed with an outward 5° tilt, reducing glare from the sun light when it hits the window, helping with visibility and keeping the temperature down in the cab.

Siegrist adds: “Our just-released DR461i rotary drill has attracted a lot of attention with its improved safety features, advanced control systems and scalable automation. This model provides improved penetration rates increasing production, with lower costs with such advancements as our compressor management system (CMS).”

Hausherr’s largest rotary drill, equipped with its latest design features, the HBM 160, has a newly developed falling-object protective structures (FOPS) proofed cab, with all operating elements for the main functions integrated in the new multifunction joysticks and in the armrests of the air-sprung and heated driver's seat. It can be rotated by 270° for entry and for driving or drilling operation, so that all operating and monitoring instruments can always be reached and read by the operator from a comfortable sitting position. Its new control concept makes operation easier while simplifying monitoring and fault diagnosis. The operating and service display can be used to select and show the machine status, operating information or fault messages.

A new technological advancement that Caterpillar is progressively rolling out is CANbus control systems on its drills, which enable automation of different segments of the drilling cycle. Peterson says: “Years of field development have resulted in an algorithm to replicate human interaction with the drill. The system directs the auto-drilling mode as a standalone feature or as an integrated part of the autonomy package. This also enables optimal consumables life.

“Drill productivity tends to parallel operator experience. By providing more intuitive automation, the average productivity is increased and hole quality is improved. Further, this reduces or eliminates short holes, over-drilled holes and incorrectly placed holes.”

The Sandvik DR461i also runs off the CANbus system on the drill, while its graphical user interface (GUI) system acts like a production-monitoring and rig health-monitoring system in one.

Joy Global’s P&H 285XPC large diesel drill was released in February 2014. It offers more pulldown, rotary torque and air volume for faster drilling of 10-5/8in to 12-1/4in (270mm to 311mm) holes. Fox notes: “It includes the Universal Drill Cab, which is common to all new P&H drills. The cab offers outstanding visibility and operator comfort. A powerful crawler system offers two-speed propelling, with a maximum speed of 3.06km/h.”

However, the 320XPC large electric drill is the most popular P&H model. Fox says: “It has been derived from a successful line of drills starting with the Gardner-Denver GD120, and continues to be a rugged, reliable, low-cost machine.”

Rudgormash Co produces rotary blasthole drill rigs with electric or diesel drives and hole diameters of 160-311mm. This equipment is supplied to customers in Russia, the Commonwealth of Independent States and other countries globally. Since 1965 Rudgormash has produced and supplied more than 3,500 drill rigs to its customers, and there are currently over 1,000 Rudgormash drills in operation at open-pit mines. The company states that for the last few years its engineers and mine specialists have changed some of the drill-rig parameters to enhance the competitiveness of the machines. The manufacturing technology of its crawler mounting and mast frame has been changed completely. The drill rigs are equipped with Bosch Rexroth mobile hydraulics and compressors made by leading OEMs. The design of Rudgormash’s drill rigs has greatly changed recently due to the use of modern high-quality materials and components from leading Russian and foreign manufacturers. These alterations in design are also the result of new engineering and manufacturing methods. The appliance of modern information technologies, such as computers, controllers and CANbus signal transmission, for the automation of drill rigs has also had an impact. The basic Rudgormash SBSH-250MNA-32 drill rig has been upgraded to improve its reliability, working efficiency and technical characteristics, and to enhance its competitiveness in foreign markets. The variety of modifications available has been substantially extended. The company says that all design and technological alterations to the drill have been tested and proved effective in continuous operation conditions in different mines. Rudgormash says that the SBSH-250MNA-32 is the most popular drill in its product line. The company is currently assembling the 1,565th such drill rig, and states that its popularity can be explained by the enduring reliability of its basic parts and components.

 

Customer requests

When it comes to the key features from the customer’s point of view, systems that reduce the cost of operating the drill are at the top of the wish list as the price of commodities such as iron ore, coal, gold and copper are depressed from prior levels. Rig manufacturers are thus focusing on increasing the productivity of their drills.

Siegrist says: “Cost-saving systems such as Sandvik's Compressor Management System (CMS) can really delivery dramatic cost reductions of up to 35% in fuel alone, before you consider extended engine and compressor life.”

In addition, customers are keeping an eye on energy costs, while looking for drills that can perform multiple tasks.

“Mines often have complex orebodies with varying rock hardness, and being able to switch the drilling method and tooling with a control in the cab allows the customer the flexibility of choosing the best drilling system for that particular bench or row of holes. Having both a DTH- and rotary- enabled drill, pre-loaded with both tool sets, has a major impact on productivity and better fragmentation options in the overall planning of operations,” explains Peterson.

Joy Global has identified increased customer interest in semi- or fully automated systems that provide mine operators with production and machine health data as well as GPS positioning. These types of control systems may be used to improve drilling accuracy, but they can also improve safety by allowing remote operation and moving the operator away from high faces. The company is currently exploring and developing technology that can lead to autonomous operation of its own P&H drills.

Fox says: “Automation continues to be a big request from our customer base, but reliable operation and strong product support remain critical to getting tonnes on the ground. Rapid access to drill information to help track productivity and troubleshoot machine problems is increasingly important to mining companies as they implement increasingly sophisticated fleet-management systems.”

Atlas Copco says its Pit Viper fleet enables automation to provide higher levels of productivity, safety and efficiency, with onboard operator-assist functions such as AutoDrill, AutoLevel and hole-navigation systems delivering repeatable and predictable results. Carrying these functions over to tele-remote operations, single and multi-drill solutions increase the effects seen with the onboard functions. “Culminating with the future autonomous Pit Viper, Atlas Copco has a field trial showing tangible results in each of these three categories: safety, productivity and efficiency,” adds Inge.

Trends

According to Sandvik Mining, the drilling market is split between those wanting more technology and those who want to keep the drills simple to work on and maintain as they are the first step in the mining process.

However, drills continue to become more automated each year. The rate of change is accelerating as positioning and networking technology develops in other industries, opening the possibility of satellite positioning of drills and drill spacing; recent drills are increasing the use of GPS hole location, automated functions and drill-data interface into mine-planning systems.

Fox says: “We can take advantage of new, more reliable, off-the-shelf solutions rather than developing systems in-house over multi-year periods.”

Overall, the future of drilling is autonomous. All drill manufacturers are heading towards autonomous operation, and have achieved various stages of progress.

Fox adds: “Remote operation of multiple machines will yield outstanding benefits in terms of increased utilisation and improved safety. Beyond the machine control, we must leverage the data generated in the drilling process to determine the geology in order to drive changes in the blast design. By getting the blast right, all downstream activities (especially loading and crushing) will improve.”

Further advancements in automation and tele-remote operation will also get the operator out of the pit and open up the possibility of having more than one drill per operator. There will be no need for an operator cab as all controls will be remote, keeping operators out of the pit. In addition, cost-effective autonomous drilling of an entire bench will be possible with the push of one button.

Siegrist comments: “The key advantages are keeping operators out of the pit, and delivering lower costs with less operator damage and longer life of components.”

In addition, the three-dimensional modelling with simulation of functions and system analysis are allowing ideas to be tested virtually before they are actually built. This improves the time to develop new innovations and allows new concepts to be virtually verified, reducing the cost and time of testing.

Rotary drills on site

Cat MD6420B

At Glencore’s Ravensworth coal mine in New South Wales, Australia, two new Cat MD6420B rotary drills have been cutting their teeth on the overburden for the last 12 months. Their production results are in, and according to Caterpillar, their engine hours are well above the industry’s ‘good’ rating of 5,000 engine hours per year and even beyond the industry’s ‘excellent’ rating of 6,000 engine hours per year. The first unit, #112 (aka Judy) has achieved a record level 6,876 hours in her first year and #113 (John) has come in at 7,006 hours in his.

The table shows that the mean times between failure are 33.5 and 38.2 hours for the two drills, and the average repair durations are 1.9 and 2.3 hours. Mining managers’ expectations are about 6 hours.
Here is a complete picture of all the ratings for drill performance:

Rating	Judy	John	Industry avg. approximations
Engine hours per year	6,876	7,006	5,000
Mean time between failures	33.5	38.2	25
Mean time to repair	2.3	1.9	6

According to Andrew Elbourn, Caterpillar product-support representative for drills, “what this means is that the MD6420B is a low-maintenance drill overall. It self-monitors and diagnoses issues, which drives low mean time to repair (MTTR). The performance of these drills has been incredible. They just keep drilling.”

With a maximum bit load force of 42,000kg and three different mast lengths to choose from, the MD6420B can drill holes as large as 311mm (12.25 in) in diameter and as deep as 74.4m – making it suitable for high-production drilling in hard- or soft-rock applications. The rotary drill features heavy-duty structures, rugged components, a comfortable cab, convenient service access and many other attributes that reduce cycle time, improve productivity and lower ownership costs.

One example is the new operating system. The MD6420B has advanced controls and technology, such as the control system that is ECM/CANbus, fully electronic with a state-of-the-art user interface. Drill monitoring and diagnostics are displayed on a large touch-screen panel. History files detailing machine performance and health are downloadable. Advanced automation features include: Auto-Level, Auto-Drill, Auto-Mast and Virtual Stops in upper and lower head positions.

The control system also includes real-time machine health monitoring and built-in diagnostic tools that contribute to strategic service and maintenance planning.

Glencore's Ravensworth North mine site is in the Hunter Valley of New South Wales and uses Cat equipment almost exclusively. The mine equipment is supported by the regional Cat dealer, Westrac, under a maintenance-and-repair contract. Drills now operating at Ravensworth include two MD6420B’s, one MD6420A, two MD6290’s and one SK40. 

Glencore is one of the world’s largest global diversified natural-resource companies and a major producer and marketer of more than 90 commodities. Its operations comprise over 150 mining and metallurgical sites, oil production assets and agricultural facilities.

Atlas Copco Pit Viper 311

Atlas Copco’s Mining and Construction Magazine recently reported that the latest member of Atlas Copco’s blasthole PV-310 rotary drill-rig range – the Pit Viper 311 – has successfully completed a six-month field test at a copper mine in the southwestern region of the US.

The prototype PV-311 went into service at the mine with the focus on co-operation between mine personnel and Atlas Copco engineers to test modifications that would help increase productivity and efficiency.

The PV-311 drilled 255mm- and 317mm-diameter holes – the largest hole this rig can drill – on benches 15m high. The 255mm holes were drilled to a depth of 17m with 2m of subdrill, while the 317mm holes were drilled to a depth of 20m with 3m of subdrill.

Five different drill patterns were used depending on the location of the test in the pit. The rig typically completed 35 to 40 holes amounting to 365m drilled in a 12-hour shift. The average availability was 90–95%. The rock encountered in the mine is typical of most copper applications, not homogeneous and with a compressive strength around 250–300Mpa.

Atlas Copco Secoroc Tricone/DTH bits were used with each bit lasting 2.5–3 days. The prototype rig was subsequently purchased by the mine. Maureen Bohac, product manager for large blasthole drills at Atlas Copco, says: “The PV-311 had no trouble managing rough conditions while consistently hitting its targeted depth and maximising the quality of the hole drilled.

“One of the contributing factors was that the PV-311 is designed so that the bits are changed above the rig’s deck, even while single-pass drilling a 20m deep hole. This enabled the operators to focus on making and breaking the pipe connections each time.

“In addition, this prototype included our optional hydraulic clutch, which is designed to reduce fuel consumption during non-drilling operations and this had a big impact. Another factor that influenced fuel efficiency was the autodrill functionality of the rig control system.”

Fuel efficiency was approximately 20% better than other rigs on the site. On top of this, the PV-311’s quiet and comfortable cab proved to be especially appreciated by the operators.

“The new cab on the PV-310 series is one of the things operators are most excited about,” continues Bohac. “The cab has a fully adjustable and elevated chair with joystick and cab controls and an excellent view with larger windows and mirrors, well placed so the operator can see what’s going on at ground level and in front of the rig.”

The PV-311 is now production drilling at mines on three continents in applications including copper, coal and iron.

This is an extended version of an article that ran in the April 2015 issue of GeoDrilling International