Hydraulic drills hammer through with new designs, tougher materials.
Major step-changes in hard-rock drilling technology can be counted on one hand: the introduction of pneumatic drills to replace sledge-hammers; the realization that water is essential for keeping down dust during drilling; and the replacement of air power by hydraulic energy. To put that into perspective, manpower dominated drilling up to the mid-1800s, when the first pneumatic drill designs appeared. The realization that dust generated by mechanized dry drilling is a major health hazard took a further 50 years or so to materialize, but from then on, through the first half of the 20th century, pneumatic drilling was king.
Essentially, a post-World War II development, the application of hydraulic technology to industrial settings marked another milestone, although it was some time before the concept moved into mining. According to Atlas Copco, the company introduced its first hydraulic drill--the COP 1038--to mark its centenary in 1973. Development had begun in the 1960s, it added, noting that although the early designs proved not to be as effective as hoped, it was clear that the concept had major potential.
Of course, Atlas Copco did not have the field to itself; other companies were also working on the concept. Hannu Paasonen, one of the team members involved at Tamrock at that time, recalled for E&MJ that the company had introduced its own hydraulic rock drill in 1974; he himself later designed the first units produced by Doofor, another Finnish company.
And in the U.S., companies such as Gardner Denver had also recognized the opportunity for improving drilling efficiency with hydraulic power, building on the experience gained over much of the 20th century with its pneumatic drills.
Today, hydraulic drills are the machines of choice for a significant proportion of mining companies and contractors around the world. Obviously they carry with them different requirements in terms of maintenance and consumables. They offer the major benefit of not having to rely on extensive pipe ranges for their power source, with electric-driven pumps bringing added advantages in terms of reduced noise and improved ventilation quality. Above all, rigs carrying hydraulic drills, whether for development or production, are more flexible in use.
In order to get a better understanding of how hydraulic drilling technology for underground applications has developed over recent years, and some of the key issues associated with its application, E&MJ asked some of the world's major suppliers for their insights. Respondents were Kalle Kuusento, managing director of Doofor; Morgan Kanflod, Atlas Copco's product portfolio manager for underground rock drills; Sandvik product manager Anssi Kouhia; and Joe Patterson, vice-president for marketing at U.S.-based TEI Rock Drills.
Looking Back a Decade
E&MJ's first question to the industry experts asked for their perspective on the major developments in hydraulic drill technology over the past 10 years.
"The focus has been on improved availability and allowing longer periods between servicing," said Atlas Copco's Kanflod. "This has helped customers to increase productivity and reduce their costs. Further improvements in penetration rate have also been achieved by increasing the rock-drill frequency."
Doofor's Kuusento looked at drill internals. "We have made improvements in the valve function in our rock drills in order to reduce 'lost flow' of hydraulic oil and to reduce cavitation to almost zero," he said.
Sandvik's Kouhia also focused on internal design, as well as noting that the introduction of high-frequency drilling has led to greater efficiency. "Cavitation erosion has been eliminated through the use of highly sophisticated CFD simulation," he stated, "and there have been major improvements in mechanical reliability due to state-of-the-art in-house 3-D dynamic FEM simulation tools."
TEI's Patterson considered that the main developments have mostly involved the design of larger versions of older drifters, although, "TEI has one of the few new concepts in percussion drilling during the past 15 years," he claimed. "Our patented Automatic Stroke Adjustment, or ASA, reduces the power and frequency of the piston when the drifter is not fully engaged with the rock. In mining, this technology greatly reduces wear on the drill tooling by not allowing the drifter to 'dry fire' during operation."
E&MJ then asked about the materials used in drill construction, and what the experts considered the most important advances that have been made. Kanflod looked at one of a drill's key components--the piston. "Corrosion-resistant and generally more durable impact pistons have been introduced over recent years," he said. "Atlas Copco puts a lot of effort into finding the correct hardening of its pistons and other steel components."
"High-quality steel is the most important ingredient to a successful drifter," Patterson added. "In the United States and Europe, we have access to documented quality steel, so the drifters most widely used around the world come from these areas. Advances in plastics for seals and bearings have also increased the life of these wear parts as well as reducing the cost."
Kuusento said, "Different kinds of treatments and coatings have become more popular in rock drill technology. However, proper design still remains the key element in making a fast-penetrating rock drill with a good service life."
Kouhia also looked at steel specifications. "Special steels are now used more often," he said. "In some cases, these steels are so hard that separate heat treatment is not needed, and there have been advances in alloying, coating and heat-treatment technology to extend component life for critical drilling conditions.
"Material purity has been a key issue for percussive parts because of their ultra high-cycle fatigue requirements, and the next big thing will be 3-D printing for hollow and complex parts," he added.
Improving Equipment Reliability
What have manufacturers done to improve hydraulic drill equipment reliability? Kuusento said that Doofor has used computer-aided design from the beginning. "In the past 10 years, Doofor has minimized friction inside its drills to ensure that the most vital components achieve a good lifespan," he explained.
"It is also of paramount importance to make sure that end users know how to use their drills correctly, to use the proper, high-quality hydraulic oils and to make sure that there is sufficient shank lubrication when operating the drill."
"There is no other secret to reliability than hard work and experience," said Kanflod. "You have to understand failures that happened in previous generations of rock drills, and work hard to improve the issues that occurred. Some problems can be solved within the existing rock-drill family, while others can only be solved with the design of a new generation of drills."
Patterson addressed the technical side of manufacturing in this context. "CINC machining has brought a consistency to drifter manufacture that has helped improve reliability and quality," he said. "Most manufacturers have many years of experience with drifters that cannot be duplicated by a startup company. This experience of what will, and what will not work, helps improve reliability.
"And, of course, new innovation such as TEI's automatic stroke control is a tremendous improvement over drifters that can only deliver 100% power, 100% of the time."
Sandvik is "always aiming to improve maintenance intervals," said Kouhia. "Drills are simpler and materials are selected very carefully. Advances in simulation technology have allowed us to analyze and reduce hotspot stresses, which has significantly improved the life expectancy for those parts with the highest loadings. In addition, better oil filtering and cooling keep oil temperatures in the optimum range, and there have also been improvements in hose technology that have helped reduce the number of broken hoses, and allow better routing around the machine.
When asked what performance improvements users can expect to achieve by switching from pneumatic drilling to hydraulic, Patterson said, "pneumatic drifters are used mostly in third-world countries and countries with large fuel subsidies. Anyone will tell you that a hydraulic drifter drills twice as fast for half the fuel cost. It takes twice as much fuel to turn screws in an air compressor as a hydraulic pump." "Hydraulic drifters hit 3,500-6,000 blows per minute," he said. "An old pneumatic drifter is lucky to get 1,700 blows per minute. And finally, no company has designed a new pneumatic drifter in more than 25 years. Old technology ... really old technology." Kuusento: "The most important thing is the fuel savings. One can get a very high drilling speed compared to pneumatic drilling with the same engine."
Kanflod agreed and said: "There is a huge improvement in energy efficiency when switching from pneumatic equipment to hydraulic. The drilling speed is improved, which of course boosts customers' productivity, and there is also a noticeable reduction in drill-steel costs going from pneumatic to hydraulic rock drills."
Kouhia: "Reliability is better where high-power drilling is needed. Pistons and tools last longer because of the design of hydraulic drill components, while hydraulic systems can use rock recoil stabilization--which is very difficult or impossible to use with air-activated hammers."
The fluid used in hydraulic systems is a critical aspect in achieving good results with them. All too often, fluids can be contaminated by water or dirt by poor storage, while maintenance issues can lead to filters not being changed as regularly as they should be. What should mining companies do to make sure that the fluids that they use are kept free from contamination?
Patterson: "Use high-pressure hydraulic filters on all of the pressure lines to the drifter. They never do this, and mining companies always pay the price for ignoring such a simple solution."
Kanflod: "Preventive maintenance, including filter changes, is one of the first steps. Continuous filtration of the hydraulic oil through kidney filtration systems is also something from which we see good results, removing not only particles but water as well. Finally, cleanliness during service and overhaul of the rock drill is most important; it doesn't matter how good your filtration system is if you leave contamination inside the rock drill during service."
Kuusento: "It is important to make sure that the oil filters are in good condition, and it is a good idea to have a filter on both the pressure and return side of the drill. Operators can train their staff to remember that whenever they open a hydraulic drill for maintenance, the risk of foreign particles entering the drill must be minimized by a high level of cleanliness."
Kouhia summarized this advice as: "Store hydraulic fluids properly, and strictly follow oil suppliers' recommendations. Regular oil analysis and preventative maintenance are key to good performance."
Following on from this, they were asked what the manufacturers recognize as being the most common mistakes that mining companies make when using and maintaining hydraulic drilling systems, and what advice can they give to help them in this respect. "Hydraulic fluids lose viscosity over time and should be changed at the intervals recommended by the oil supplier," said Kuusento. "If a major overhaul is done on a drill jumbo, the hydraulic oils are not always changed, which is a big mistake."
"We do see companies using components and parts for too long without any service," said Kouhia. "Some use the wrong type of oils, while there may not be any proper maintenance facilities or tools. Maintenance training can be poor, and this leads to contamination occurring when critical components are overhauled. If hoses break, dirt can get in if the hoses are not flushed properly."
Patterson: "Only open drifters in a clean room, and have a spare drifter to exchange with the one that requires maintenance. Cleanliness is next to godliness as far as hydraulics are concerned."
Kanflod: "Using the wrong settings for a specific application, a common problem we see is that operators use a 'standard' setting for all different conditions and rock drills. Another thing is not carrying out preventive maintenance according to our recommendations; this can affect rock-drill lifespan and availability of the equipment.
"One way of solving both of these problems is to follow the settings documents and maintenance instructions for our rock drills and rotation units; this will improve their performance and increase their availability."
Designed for Simpler Maintenance
Following on from these thoughts, E&MJ then asked how manufacturers can make their drills easier for users to maintain, given that the mining industry is often short of skilled mechanics who specialize in hydraulic equipment.
"We need to use fewer parts and to provide good maintenance instructions," Kouhia suggested, "with the opportunity for regular training at our production and distribution facilities. The use of service kits with simple instructions will also help, while we need to design drills that are appropriate for different customer groups."
Kuusento agreed: "Manufacturers should give easy-to-follow pictorial maintenance manuals in written and video format," he said. "Doofor drifters are not too difficult to maintain and we provide our dealers, OEM customers and end users with proper training."
Kanflod: "We can make the user's life a little bit easier by designing more reliable equipment that doesn't need to be serviced as often. We also need to differentiate clearly between daily
maintenance that can be done on-site, and bigger overhauls that need to be done in a workshop. Service points must be easily accessible, and hoses need to be protected from accidental and unnecessary wear to give longer hose life."
Patterson: "This is a difficult question, as there is no substitute for skilled labor. At TEI we take this issue very seriously. We hold schools for drilling, hydraulics, and drifter rebuilding to help our customers stay working and profitable. Any manufacturer that is not actively training their customers will have serious consequences in the future," he cautioned.
Which Way Now?
Finally, E&MJ asked about the key developments that the experts expect to see in hydraulic drilling technology in the next five years. All of them mentioned improvements in drilling efficiency, lower energy input, and increased maintenance intervals, all of which will help users cut their overall drilling costs. From Atlas Copco, Kanflod singled out rock-drill reliability as being important, with the need to reduce unscheduled downtime so that better use can be made of automation and remotely operated drilling to increase safety and productivity.
Kuusento: "Doofor is continuing product development to create faster rock drills and make service intervals longer. Better manufacturing methods will lead to lower spare-parts pricing for users."
Patterson: "Drifters used underground will be engineered better so that smaller, lighter drifters will give the same output power as the ones used today. This will allow the same amount of rock removal with smaller equipment and lower fuel consumption."
Kouhia predicted the use of higher-frequency rock drills, not necessarily with more power, but that are able to achieve better drilling efficiency. "Digital hydraulics are coming, with advances in control systems, auto-functions, sensor-based boom navigation and underground GPS," he said. "These are all turning the game more and more toward the use of electronics and computers."
Hydraulic Rigs Reloaded
Last December, Atlas Copco announced the worldwide availability of
its "reloaded" single- or twin-boom Boomer M development jumbo, now equipped with the COP 1838FID+ rock drill. Described by the company as being "a favorite workhorse in underground mining and tunneling," the machine now has a range of enhancements that make it stronger, cleaner, safer and easier to operate, Atlas Copco claimed.
Product Manager Johan Jonsson said at the time: "The use of contractors in the mining industry is becoming increasingly common, and these companies have told us they need extremely robust drill rigs for drilling in tougher environments, and preferably rigs that can be used for more than one application. In response, we have further developed the new Boomer M series. These rigs are now much stronger and more powerful, and can be used for face drilling as well as rock bolting."
The Boomer M also incorporates several new design features that help to extend service intervals, Atlas Copco stated. A new filtration system keeps lubrication air and hydraulic oil free from water and fine particles. This improves the air and oil quality, which in turn prolongs the life of the hydraulic components and rock drills.
Available in a number of versions, the COP1838 family of hydraulic drifters is designed for drilling holes from 38 mm to 89 mm in diameter (1.5-3.5 in.), with the new generation of these drills offering service intervals 50% longer than the previous models in the range.
The company noted that the COP 1838 has a dual-dampening system to dissipate shock waves away from the rock, establishing the best possible contact between the drill bit and the rock. This allows transmission of the maximum power for crushing, while keeping the drill string threads tightly secured. The design also includes three accumulators to level out pressure peaks in the system, maximizing component life, the company said.
TEI was an Early Starter
Joe Patterson told E&MJ that the company began manufacturing its first hydraulic drills when the new owners of Gardner Denver--for which his father was chief engineer--moved production from Colorado to the east coast of the U.S. in 1981. While the company now focuses more on the construction industry than mining on account of its greater demand stability, TEI works with mining-sector OEMs and end-users who want to change drifter brands on their jumbos.
The company's newest hydraulic drifter, the TE1000, was designed to incorporate its ASA percussion system with the high torque of its RDS1000 rotary drill. The ASA only allows the percussion unit to operate at full force when the drill tools are engaged; when hitting a void or not having enough down pressure, the ASA automatically reduces the energy and frequency of the piston. The high frequency and smooth operation of the percussion system is accomplished by using three nitrogen-charged accumulators that level out pressure peaks in the hydraulic system, ensuring maximum life for drifter parts internally as well as maximum tool life externally.
According to Patterson, TEI's smaller TE260 and TE160HT drills are very popular for roof bolting, while the 7.4-kW TE260 is also widely used in South Africa on rail-mounted, narrow-vein jumbos that were introduced to the market in 2012. The manufacturer, mining contractor JIC Mining Services, designed the twin-boom Mantis rig to fill the gap between handheld jacklegs and big production jumbos. TEI has delivered more than 70 drill units for this application alone, with Mantis jumbos having proved popular for development in both gold and platinum mines in the country.
Doofor Supplies Several Markets
According to Kalle Kuusento, Doofor produces hydraulic drifters ranging in power output from 5 kW to 22 kW for general excavation, mining and bolting. It has been supplying its equipment to OEMs worldwide since 1993, and since 2010 has been working with Scandinavian Pile Driving (SPD) on the development of drill masts that can be mounted on hydraulic excavators and cranes.
Kuusento told E&MJ that SPD's MD33 mast equipped with the Doofor DF530S drill has been designed as a good combination for mobile bolt drilling. The Doofor DF530S is an updated version of the DF500-series of drifters, with a new control valve to minimize bypass flow and to create a high percussion frequency of 90 Hz. Doofor claims that the DF530S can save up to 20% on hydraulic oil flow compared to the previous version, as well as being more resistant to pressure variations from the drilling platform.
By Simon Walker, European Editor
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|Title Annotation:||UNDERGROUND DRILLING|
|Publication:||E&MJ - Engineering & Mining Journal|
|Date:||Apr 1, 2015|
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