Hammers strike the balance in drilling
01 JUNE 2002
Jukka Naapuri, a Dubai-based sales manager with Sandvik Tamrock Middle East ( UAE), elaborates on the various drill hammers offered by the company and how they have been designed with particular attention to meet market demands.
Today's customer looks for superior performance in bench drilling: fast penetration, high availability, high hole quality with long drill steel service life - whether the rock is hard, soft, abrasive or fractured.
Each bench drilling task is a challenge. Different worksites require different hole diameters and lengths, depending on work arrangements and rock conditions.
Optimal energy transmission in percussive drilling is a key element for efficient and economical bench drilling.
Sandvik Tamrock of Finland offers a wide range of hydraulic top hammer and down-the-hole drills for bench drilling in construction, quarrying and mining.
This range of drills provides a solution for each drilling task where hole diameter, hole depth, drill steels and drilling power are in balance, resulting in top performance and drilling economy.
Hydraulic top hammer
Hydraulic top hammer drilling is the most modern of the percussive drilling methods used in bench drilling. Hydraulics offers specific advantages in the transmission of forces and energy. The rotary and linear movement can be accomplished with a high degree of precision and applicability. With the introduction of hydraulic rock drills, large strides have been taken in automation and mechanisation in terms of performance, safety and working environment.
The percussion energy produced in the rock drill by the piston is transmitted to the rock through drill steels. The piston is accelerated to a certain speed before it strikes the shank adaptor. The kinetic energy is transmitted through rods to the bit in the form of a compressive shock wave, which travels along the steel at a speed of 5,000 m/s. When the shock wave reaches the bit, rock is broken by the crushing effect, through the penetration of the bit.
The rock drills percussive energy derives from the pressure and flow of hydraulic oil. Various combinations of pressure and flow can be selected to provide the required energy per blow and blow frequency. Hydraulic rock drills are designed to operate at pressures ranging from 90 to 250 bar.
An important design variation concerns the mechanism which regulates the flow of oil to reciprocate the piston in the cylinder. In a typical design operated at low pressure, a distributor - in a form of a sleeve valve - surrounding the piston opens and closes ports to the front and rear chambers. The advantages of this design are short flow channels, low flow losses and low leakage due to long sealing lengths. There are only two moving parts, the piston and the sleeve valve.
Revolutionary crawler drills
The Ranger hydraulic crawler drills are Tamrock's response to the global needs of the quarrying and mining industry for performance and total drilling economy. This track drill range outclasses all other manufacturers in power, versatility, operator comfort and reliability. The Rangers are self-contained bench drills, for drilling 51 to 115 mm diameter holes on benches up to 25 m, using R32, T38, T45 and T51 series extension drill steels.
The drilling capacity of Rangers is boosted by the revolving superstructure, which allows the operator move the boom through a 120 degrees arc, giving these drills a vertical drilling coverage up to 17.6 sq m. Because the boom and feed assembly is counter-balanced by the crosswise rear-mounted engine and power pack, these drills are inherently more stable even in the roughest terrain. While the FOPS/ROPS operator's cabin turns with the superstructure and boom, for the first time, operators are offered a better visibility over drilling. The new low-noise cabin offers plenty of space and a high level of comfort. A single joystick provides direct and stepless control over the whole drilling process.
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Table 1 |
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Table 1 shows the properties of Ranger hydraulic top hammer crawler drills for quarries, mines and construction. All three Ranger models - 500, 600 and 700 - are powered by Caterpillar 3116 series diesel engines. Two variable displace pumps and two gear pumps are directly driven while the air compressor is belt driven. Tamrock's straightforward and robust hydraulic technology will ensure the operators stay in schedule.
The Pantera range of heavy-duty hydraulic crawler drills targets production costs in quarrying and open-pit mining. It offers best value in bench drilling of 89 to 140 mm diameter blastholes, by combining high production rates with best hole quality. Panteras are designed to use 51 mm and 60 mm diameter extension drill steels. These heavy rock tools provide high bending resistance, enabling the use of maximum kinetic power for drilling large and straight holes fast, without compromising drill steel service life.
|
Table 2 |
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Table 2 shows the characteristics of Pantera hydraulic top hammer crawler drills for quarries and open-pit mines.
Drilling production holes requires a highly stable crawler drill. Rock-steady penetration rate is achieved through sturdy undercarriage construction, heavy-duty booms and cylinder-rope feeds. Pantera joystick controls provide direct and stepless control over drilling. Percussion power follows feed resistance to allow optimal settings in all rock conditions.
Panteras are equipped with Ergo Pro cabins for best working environment for the operator. High production rates are ensured by low noise level (below 80 dBA), excellent comfort, visibility and easy-to-use joysticks for superior drilling control.
DTH drills
Down-the-hole (DTH) drills utilise compressed air power in percussive drilling more efficiently than conventional pneumatic top hammer drills. A DTH hammer follows behind the bit into the hole and therefore little percussion energy is dissipated in pipe joints. The penetration rate is constant regardless of hole depth. As the piston blows are transmitted directly to the bit, the drill string can be made considerably lighter as it merely imparts rotation to the bit and acts as an air passage to the hammer. A comparatively large diameter drill pipe lessens the annular area between the pipe and wall of the hole, improving flushing of holes. Drilling accuracy is good. The exhaust air of the hammer works as the flushing medium and is led through the drill bit.
The noise level with DTH drills is lower since the hammer follows the bit into the hole. This helps muffle the noise generated by the piston striking the bit, the exhaust air from the hammer and the ringing pipe noises. With hydraulic rotation heads noise hardly exists.
Sandvik has put considerable investment into developing DTH drills in the past years, and BPI down-the-hole drills are designed for drilling 85 to 152 mm diameter holes in construction, quarrying and mining industries.
These light to medium heavy self-contained DTH drills are equipped with FOPS/ROPS operator's cabins, advanced drilling control systems, automatic pipe changers and rugged telescopic or single section booms for maximum performance. Onboard air compressors, low centre of gravity and powerful oscillating crawler bases ensure maximum onsite mobility.
BPI drills are fitted with silenced power packs comprising of diesel engine, hydraulic pumps and air compressor. They are known for their rugged designs and are particularly suited for drilling difficult rock formations, for precision drilling and toe holes.
The main advantages of DTH over top hammer drills are:
The current trend is towards higher pressures since the percussion mechanism is limited by the diameter of the DTH hammer. DTH hammer manufacturers are also focusing on more efficient ways of using the air when it arrives in the hammer, to achieve greater impact power and higher penetration rates at both high and low air pressures.
The future
The future is in hydraulic top hammer drills, which are growing more advanced as users are demanding better controls, cabin comfort and safety while tighter regulations are cutting noise, exhaust and dust emission levels. Instrumentation expands with operator needs. New systems are available, which give quarry and mine operators the chance to measure drill productivity and quality of holes.
At the other end of the scale, rock tool technology has been improved giving straighter holes, longer drill steel service life and allow the transmission of higher kinetic power into rock for maximum penetration rates. However, each drilling site is different. Moreover, with the appearance of more sophisticated and powerful drilling equipment, the basic theories of rock drilling mechanics have become crucial economic factors in achieving savings in machinery, equipment and explosives.
Drilling controls: The need for more efficient rock drilling has led to the use of ever more powerful drills and further mechanisation. Mechanisation, again, has brought new elements between the driller and the rock drill. All information from the operator has to be processed and transmitted to the components through a control system.
The reliable, user-friendly hydraulic control system allows high drilling performance without compromising on drill steel economy. Percussion power automatically follows rock conditions and the feed resistance, so underfeeding is avoided.
Proportionally controlled collaring with an optimised feed-percussion ratio gives a maximised penetration rate with high drill steel service life and minimum drill steel cost. On the other hand, knowledge of how to select and take advantage of electronics in control systems, is important.
Operator performance: Operators perform better with the new low-noise FOPS/ROPS operator cabins (noise level below 80 dBA) which offers plenty of space and a high level of comfort. Single joysticks provide direct and stepless control over the whole drilling process. Ease of drilling can further be boosted by the use of a revolving drill superstructure, which allows the operator to move the boom through a 120 degrees arc. While the operator's cabin turns with the superstructure and boom, for the first time the operators are offered a better visibility over drilling.
Crawler drills have traditionally been designed using boxed shapes. Experience has shown, however, that equipment designs reflect on contractors' image and may improve their success in project awards. In work sites proud drill operators perform better, too. The latest crawler drill generations incorporate industrial designs applied in today's product ranges of leading manufacturers of earthmoving equipment.
Monitoring production: Measurement systems allow drill penetration rates to be closely monitored and shift production can be accurately tracked. This is particularly important for calculating the total cost per drilled metre in quarrying or mining. The information can then be used to predict drill production and helps in scheduling work. In addition, drill penetration rates can be used for identifying rock types and determining the explosive loading required.
Tamrock Integrated Measurement System (TIM) collects and stores data from purpose-built sensors mounted all over the drill and are capable of monitoring a vast range of drilling parameters. They measure feed tilt, feed swing and rock drill movements (feed rate, penetration rate). The data is converted into digital impulses which are processed by an onboard computer. TIM software (developed and patented by Tamrock) calculates values and shows the required information on an easy-to-read digital display. This system can be used to position the drill's boom and feed accurately in three dimensions, while the conventional systems work only in two axes. The operators can use a fixed point in a quarry or a mine as a reference and then work from this when setting up the rig for each hole.
Engines: Drill rig engine suppliers are targeting to meet the demand for high output, low fuel consumption and clean running engines with their latest generations. Advances in electronic management systems and engine design has led to better fuel economy, power increases, while stronger components have brought increase in engine durability. The fuel issue is highly important with end users, as a 5 per cent saving in consumption for a 250 kW output engine can save around $5,000 in fuel per year.
Electronic control modules keep watch over engine functions such as timing, fuel temperature, engine oil temperature and oil pressure. They ensure peak performance at all times and highlight any abnormal conditions that could lead to faults if left unattended. Electronic control monitors also allow engine manufacturers to tailor engine's performance to suit a specific work cycle.
Rock tools: High efficiency in rock drilling can only be achieved by making maximum use of the input energy for optimum breaking performance in the rock. The basic objective is to arrive at a balanced drilling system that perfectly transmits the impact from the rock drill, through drill string and bit into the rock. While the type of rock cannot be influenced, the choice of rock drilling tools can. To achieve optimum drilling economy, the important factors are:
Several types of straight-hole rock drilling tools can offer a solution for maximised hole straightness, optimised drilling patterns and tolerance of a wide range of rock types. Long-hole bench drilling with these tools in various configurations confirm that a 2 per cent margin for hole deflection can be achieved.
Fitting out the drill with MF extension rods and retrac bits is a popular first step. The long body of the retrac bit that has a diameter only slightly smaller than the bit head gives the bit good guidance, while the longer body has cutting edges at the rear to help the bit backwards if blockages occur. MF-rods have been developed to optimise energy transmission. Featuring male and female thread connections, these rods eliminate the need of coupling sleeves. Energy losses in the joints are reduced and the string as a whole operates as a more balanced and stiff unit.
Drilling precision can further be improved by using a guide tube as the first rod in a MF-rod drill string. The guide tube has almost the same diameter as the bit front, which increases stiffness of the string and is less likely to deviate. Hole straightness is comparable to DTH drilling. To optimise the entire drill string for accurate drilling of long holes, a guide bit can be used at the front. Optimum guidance can be achieved thanks to the long skirt wings along the steel body, separated by grooves to allow easy passage of flushing air and drill cuttings.
A system that optimises energy transfer and withstands the impact forces from the most powerful hydraulic top hammer rock drills in the 22 to 28 kW range, was recently introduced in the 102 to 152 mm bench drilling. While reducing the drill's workload by minimising the drill string weight, the 60 mm diameter Sandvik Sixty rods feature optimised energy transfer and flushing performance for optimal cost-effective large diameter top hammer drilling.
|
Table 1 |
Table 1 shows the properties of Ranger hydraulic top hammer crawler drills for quarries, mines and construction. All three Ranger models - 500, 600 and 700 - are powered by Caterpillar 3116 series diesel engines. Two variable displace pumps and two gear pumps are directly driven while the air compressor is belt driven. Tamrock's straightforward and robust hydraulic technology will ensure the operators stay in schedule.
The Pantera range of heavy-duty hydraulic crawler drills targets production costs in quarrying and open-pit mining. It offers best value in bench drilling of 89 to 140 mm diameter blastholes, by combining high production rates with best hole quality. Panteras are designed to use 51 mm and 60 mm diameter extension drill steels. These heavy rock tools provide high bending resistance, enabling the use of maximum kinetic power for drilling large and straight holes fast, without compromising drill steel service life.
|
Table 2 |
Table 2 shows the characteristics of Pantera hydraulic top hammer crawler drills for quarries and open-pit mines.
Drilling production holes requires a highly stable crawler drill. Rock-steady penetration rate is achieved through sturdy undercarriage construction, heavy-duty booms and cylinder-rope feeds. Pantera joystick controls provide direct and stepless control over drilling. Percussion power follows feed resistance to allow optimal settings in all rock conditions.
Panteras are equipped with Ergo Pro cabins for best working environment for the operator. High production rates are ensured by low noise level (below 80 dBA), excellent comfort, visibility and easy-to-use joysticks for superior drilling control.
DTH drills
Down-the-hole (DTH) drills utilise compressed air power in percussive drilling more efficiently than conventional pneumatic top hammer drills. A DTH hammer follows behind the bit into the hole and therefore little percussion energy is dissipated in pipe joints. The penetration rate is constant regardless of hole depth. As the piston blows are transmitted directly to the bit, the drill string can be made considerably lighter as it merely imparts rotation to the bit and acts as an air passage to the hammer. A comparatively large diameter drill pipe lessens the annular area between the pipe and wall of the hole, improving flushing of holes. Drilling accuracy is good. The exhaust air of the hammer works as the flushing medium and is led through the drill bit.
The noise level with DTH drills is lower since the hammer follows the bit into the hole. This helps muffle the noise generated by the piston striking the bit, the exhaust air from the hammer and the ringing pipe noises. With hydraulic rotation heads noise hardly exists.
Sandvik has put considerable investment into developing DTH drills in the past years, and BPI down-the-hole drills are designed for drilling 85 to 152 mm diameter holes in construction, quarrying and mining industries.
These light to medium heavy self-contained DTH drills are equipped with FOPS/ROPS operator's cabins, advanced drilling control systems, automatic pipe changers and rugged telescopic or single section booms for maximum performance. Onboard air compressors, low centre of gravity and powerful oscillating crawler bases ensure maximum onsite mobility.
BPI drills are fitted with silenced power packs comprising of diesel engine, hydraulic pumps and air compressor. They are known for their rugged designs and are particularly suited for drilling difficult rock formations, for precision drilling and toe holes.
The main advantages of DTH over top hammer drills are:
The current trend is towards higher pressures since the percussion mechanism is limited by the diameter of the DTH hammer. DTH hammer manufacturers are also focusing on more efficient ways of using the air when it arrives in the hammer, to achieve greater impact power and higher penetration rates at both high and low air pressures.
The future
The future is in hydraulic top hammer drills, which are growing more advanced as users are demanding better controls, cabin comfort and safety while tighter regulations are cutting noise, exhaust and dust emission levels. Instrumentation expands with operator needs. New systems are available, which give quarry and mine operators the chance to measure drill productivity and quality of holes.
At the other end of the scale, rock tool technology has been improved giving straighter holes, longer drill steel service life and allow the transmission of higher kinetic power into rock for maximum penetration rates. However, each drilling site is different. Moreover, with the appearance of more sophisticated and powerful drilling equipment, the basic theories of rock drilling mechanics have become crucial economic factors in achieving savings in machinery, equipment and explosives.
Drilling controls: The need for more efficient rock drilling has led to the use of ever more powerful drills and further mechanisation. Mechanisation, again, has brought new elements between the driller and the rock drill. All information from the operator has to be processed and transmitted to the components through a control system.
The reliable, user-friendly hydraulic control system allows high drilling performance without compromising on drill steel economy. Percussion power automatically follows rock conditions and the feed resistance, so underfeeding is avoided.
Proportionally controlled collaring with an optimised feed-percussion ratio gives a maximised penetration rate with high drill steel service life and minimum drill steel cost. On the other hand, knowledge of how to select and take advantage of electronics in control systems, is important.
Operator performance: Operators perform better with the new low-noise FOPS/ROPS operator cabins (noise level below 80 dBA) which offers plenty of space and a high level of comfort. Single joysticks provide direct and stepless control over the whole drilling process. Ease of drilling can further be boosted by the use of a revolving drill superstructure, which allows the operator to move the boom through a 120 degrees arc. While the operator's cabin turns with the superstructure and boom, for the first time the operators are offered a better visibility over drilling.
Crawler drills have traditionally been designed using boxed shapes. Experience has shown, however, that equipment designs reflect on contractors' image and may improve their success in project awards. In work sites proud drill operators perform better, too. The latest crawler drill generations incorporate industrial designs applied in today's product ranges of leading manufacturers of earthmoving equipment.
Monitoring production: Measurement systems allow drill penetration rates to be closely monitored and shift production can be accurately tracked. This is particularly important for calculating the total cost per drilled metre in quarrying or mining. The information can then be used to predict drill production and helps in scheduling work. In addition, drill penetration rates can be used for identifying rock types and determining the explosive loading required.
Tamrock Integrated Measurement System (TIM) collects and stores data from purpose-built sensors mounted all over the drill and are capable of monitoring a vast range of drilling parameters. They measure feed tilt, feed swing and rock drill movements (feed rate, penetration rate). The data is converted into digital impulses which are processed by an onboard computer. TIM software (developed and patented by Tamrock) calculates values and shows the required information on an easy-to-read digital display. This system can be used to position the drill's boom and feed accurately in three dimensions, while the conventional systems work only in two axes. The operators can use a fixed point in a quarry or a mine as a reference and then work from this when setting up the rig for each hole.
Engines: Drill rig engine suppliers are targeting to meet the demand for high output, low fuel consumption and clean running engines with their latest generations. Advances in electronic management systems and engine design has led to better fuel economy, power increases, while stronger components have brought increase in engine durability. The fuel issue is highly important with end users, as a 5 per cent saving in consumption for a 250 kW output engine can save around $5,000 in fuel per year.
Electronic control modules keep watch over engine functions such as timing, fuel temperature, engine oil temperature and oil pressure. They ensure peak performance at all times and highlight any abnormal conditions that could lead to faults if left unattended. Electronic control monitors also allow engine manufacturers to tailor engine's performance to suit a specific work cycle.
Rock tools: High efficiency in rock drilling can only be achieved by making maximum use of the input energy for optimum breaking performance in the rock. The basic objective is to arrive at a balanced drilling system that perfectly transmits the impact from the rock drill, through drill string and bit into the rock. While the type of rock cannot be influenced, the choice of rock drilling tools can. To achieve optimum drilling economy, the important factors are:
Several types of straight-hole rock drilling tools can offer a solution for maximised hole straightness, optimised drilling patterns and tolerance of a wide range of rock types. Long-hole bench drilling with these tools in various configurations confirm that a 2 per cent margin for hole deflection can be achieved.
Fitting out the drill with MF extension rods and retrac bits is a popular first step. The long body of the retrac bit that has a diameter only slightly smaller than the bit head gives the bit good guidance, while the longer body has cutting edges at the rear to help the bit backwards if blockages occur. MF-rods have been developed to optimise energy transmission. Featuring male and female thread connections, these rods eliminate the need of coupling sleeves. Energy losses in the joints are reduced and the string as a whole operates as a more balanced and stiff unit.
Drilling precision can further be improved by using a guide tube as the first rod in a MF-rod drill string. The guide tube has almost the same diameter as the bit front, which increases stiffness of the string and is less likely to deviate. Hole straightness is comparable to DTH drilling. To optimise the entire drill string for accurate drilling of long holes, a guide bit can be used at the front. Optimum guidance can be achieved thanks to the long skirt wings along the steel body, separated by grooves to allow easy passage of flushing air and drill cuttings.
A system that optimises energy transfer and withstands the impact forces from the most powerful hydraulic top hammer rock drills in the 22 to 28 kW range, was recently introduced in the 102 to 152 mm bench drilling. While reducing the drill's workload by minimising the drill string weight, the 60 mm diameter Sandvik Sixty rods feature optimised energy transfer and flushing performance for optimal cost-effective large diameter top hammer drilling.
