Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/10—Wear protectors; Centralising devices, e.g. stabilisers
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B1/00—Percussion drilling
  • E21B1/38—Hammer piston type, i.e. in which the tool bit or anvil is hit by an impulse member

Definitions

• the present invention relates to a rock drilling element for percussive rock drilling, a drill string and a method of transferring impact energy in a drill string according to the preambles of the independent claims.
• Drilling straight holes to locate the explosives at the right place with good spacing and burden has always been considered as a must in the industry of drilling. It is quite easy to drill a straight hole with a down-the-hole machine whose percussion piston is located immediately on top of the drill bit. It is more difficult to ensure a straight hole with a top hammer machine where the percussion piston hits a drill string, including from 1 to 10 rods.
• Drill rods are somewhat flexible, which basic specification allows them to drill through difficult rock at an acceptable deviation, but also with reasonable low fatigue stresses in the body and the connecting ends. This feature allows the drill rods to achieve a good service life and grants to the top hammer drilling a low cost per drilled meter.
• the difficulty starts when the commonly achieved deviations are no longer tolerated. A better location of the explosives inside the rock body becomes compulsory. A better location of the explosives will also allow decrease of the amount of explosives per ton of blasted rock and can lead to substantial savings in explosives and in secondary breaking.
• Many means to improve the hole straightness with top hammer drilling have been developed over the years. The two most common means are: guide bits and guide tubes. Guide bits are provided with up to 6 or 8 splines on the external part of the skirt. The splines are the means to improve the guiding inside the drilled hole, but they inevitably wear out, by far earlier than the carbide buttons crushing the rock into cuttings. After some while, the drill bit is still able to drill, but the guiding means have vanished.
• Guide tubes such as disclosed in U.S. Patent No. 6,681 ,875, have external diameters close to the drill bit diameter.
• the very high rigidity of the guide tube tends to keep the drill bit straight in line.
• the penetration rate slows down by 10 to 20 %.
• a guide tube does not withstand the percussion power over a long period of time and inevitably breaks at the connection to the drill bit, or forces the upper rod connected to it to break.
• the resulting drilling costs are usually considered as excessive, and guide tubes are not well accepted in the field.
• Other common guide systems have short splines that wear out quickly, and the expected improvement in guiding the drill bit becomes very quickly ineffective.
• One object of the present invention is to provide a drill string having an efficient and long lasting guide means.
• Another object of the present invention is to provide a rock drilling element that avoids over-stressing of the thread joint connecting to the drill string.
• Still another object of the present invention is to provide a rock drilling element designed with a relatively low linear weight for a high efficiency of the shock wave transmission.
• FIG. 1A schematically shows a prior art drill string during transmission of a shock wave.
• Figs. 1 B and 1C schematically show two prior art drill string equipments during transmission of a shock wave.
• Fig. 2A schematically shows a drill string according to the present invention in an exploded, cross-sectional view comprising an extension rod, a guide rod and a drill bit.
• Fig. 2B schematically shows the guide rod according to the present invention shown in Fig. 2A.
• Fig. 3 schematically shows a drill string comprising a guide rod according to the present invention during transmission of a shock wave.
• Fig. 4A schematically shows an alternative drill string according to the present invention in an exploded, cross-sectional view having an extension rod, an alternative guide rod and a drill bit.
• Fig. 4B schematically shows the guide rod according to the present invention shown in Fig. 4A.
• Fig. 5 schematically shows the alternative drill string during transmission of a shock wave.
• the basic idea for the guide rod or rock drilling element 10 according to the present invention is to avoid at best any stress concentration at a thread joint, which inevitably occurs with the heavy guide tubes as experienced in prior art solutions such as U.S. Patent No. 6,681 ,875.
• the stress concentration in a conventional guide tube is depicted in Fig. 1 A, and inevitably leads to an early breakage inside the thread joint 5 between drill rod 1 and the guide tube 2.
• the early breakage has three specific origins, namely compressive shock waves, torsional waves and static bending stresses.
• Figs. 1 B and 1C schematically show two prior art drill string equipments during transmission of a shock wave.
• the piston impacts on a shank adapter connected to an extension rod.
• a shock wave is i.a. dependent on the shape and length L of the piston.
• the shock wave has an irregular shape with high maximum amplitude peak A.
• the shock wave has a rectangular shape with constant amplitude A.
• the length 2L of each shock wave is however always two times the length L of the piston.
• Fig. 1A shows the transmission and reflection of an incident shock wave 4A delivered by a drilling machine piston.
• the shock wave in Fig. 1 A is for illustrative purposes based on a shock wave as shown in Fig. 1C.
• a drill rod 1 partly shown at the left-hand side of Fig. 1 A, is tightly threaded to the female end of a guide tube 2 via the thread joint 5.
• a drill bit 3 is connected to the other end of the guide tube, and the drill bit is pressed against the rock to be drilled.
• the shock wave 4A shown in its entire length, which means twice the length of the impact piston, travels along the rod 1 towards the right- hand side of Fig. 1 A.
• the incident shock wave 4A is supposed to travel through the thread joint 5 without any reflected wave; such an assumption is only made for sake of discussion.
• a heavier thread joint with partial reflection when the shock wave impacts on it, would slightly decrease the stress level of the shock wave transmitted further to the guide tube 3, and slightly increase the stress level in the male thread, but would not basically change the explanation.
• a heavy joint would just enhance by a few percent the problem to be described.
• the incident shock wave 4A is split into a transmitted wave 4C traveling through the tube 2 and a reflected wave 4B of same length traveling back towards the drilling machine.
• the more or less dense hatching reflects the stress amplitude in both transmitted 4C and reflected 4B waves.
• the shock wave is defined by its stress level and the pulse length.
• a high stress level typically 200 MPa
• a dense hatching at time t -1 before the wave abuts on the heavier tube 2.
• the stress level is slightly lower, and thus the hatching is less dense after the wave travels into the tube section.
• the reflected wave 4B is depicted by a very loose hatching, inclined in another direction as a symbol of a wave traveling towards the left-hand side in Fig. 1A.
• the reflected shock wave 4B is additive to the incident shock wave 4A, and therefore the stress level (shown by density of hatching) is maximum.
• the first half (50 %) of the incident shock wave 4A is transmitted and reflected.
• the incident shock wave 4A travels to the right and the length of the rod subjected to high stress level is shorter than before.
• the transmitted wave 4C traveling to the drill bit now abuts on the rock.
• the reactions at the drill bit 3 are very variable, depending on the drill bit weight and rock hardness. It is assumed that the drill bit of same linear mass as the tube section is used, and that the rock to be hard enough to withstand the drill bit motion and bit pressure. A second reflected compressive shock wave will then be initiated.
• the reflected wave 4B is completed and travels to the left- hand side towards the drilling machine.
• Fig. 1 A shows a triangle depicting position and time for the overlap between incident and reflected waves.
• the resulting stress level is 240 MPa.
• the 240 MPa stress level would develop in a regular rod-to-rod thread joint not shown, at a drilling machine with a 44 % higher energy per impact (E), as a result of the formula:
• the conventional drill string cannot withstand a 44 % increase in energy per impact.
• the thread joint between drill rod and guide tube, subjected to a 44 % higher stress, has proven to be the weak point of the drill string.
• the fatigue cracks usually develop in the thread joint 5, and more precisely in the male thread, limiting the life of the two components to the range of 800 to 2500 drilled meters.
• a standard rod-to-rod thread joint is able to drill from 10 000 to 20 000 drilled meters. Such rod and guide tube lives are commonly recorded on jobsites.
• the object of the present invention is to avoid the higher stress level that currently occurs in any thread joint between the drill rod and the guide rod.
• the guide rod 10 comprises an elongated first or slender portion 10A with a substantially cylindrical basic shape of a diameter D1 and a length L1 and a second or guide portion 10B with a substantially cylindrical basic shape of a diameter D2 and a length L2.
• the guide rod further comprises a first or upper end 11 defined by a preferably welded-on sleeve or female portion 12 and a second or lower end 13 defined by a spigot or male portion 14.
• the spigot 14 has a substantially cylindrical external thread 15 and the sleeve 12 has a substantially cylindrical internal female thread 16.
• the first portion 10A has an outer diameter D1 approximately equal to the major diameter of the female thread 16.
• the female thread 16 is provided in a recess in the sleeve having an abutment surface or bottom 18.
• the slender portion 10A outer diameter D1 is approximately equal to the major diameter of said thread 16.
• the length L1 can be defined as the distance from the bottom 18 to the closest position where the guide portion 10B has a full diameter D2.
• the length L1 is greater than the length of the piston used in the drilling machine, i.e. at least 500 mm.
• the length L2 can be defined as the distance between the ends of the guide portion 10B, which ends have full diameters D2.
• the guide portion diameter D2 is 105-250 % of the slender portion 10A diameter.
• the guide portion 10B is maximum 250% of the slender portion 10A.
• a flushing channel which is generally depicted 19 extends internally of the guide rod 10, through which a flush medium, usually air or water, is transferred.
• the through-going flush channel 19 is provided to lead flush medium to the rock drill bit 3 for percussive top hammer drilling. This channel is suitably centrally positioned in the guide rod.
• the slender portion 10A and the guide portion 10B are preferably essentially cylindrical.
• a first shoulder 25 and a second shoulder 26 border the cylindrical part of the slender portion 1OA at respective axial ends thereof.
• the first shoulder 25 is provided in the vicinity of the female thread 16.
• Fig. 3 shows the transmission of a shock wave similar to Fig. 1 A with identical shock wave transfer and reflection, applied to drill string according to the present invention comprising the guide rod 10 according to the present invention.
• the guide rod 10 includes a sufficiently long slender rod section 10A, defined in such a way that the thread joint 5 is definitely located outside of the triangle where incident 4A and reflected 4B shock waves overlap.
• the thread joint 5 is subjected to the incident shock wave 4A, similar to any thread joint between two standard rods.
• the incident shock wave 4A has already ended and the stress level is close to zero. This feature occurs before the reflected shock wave 4B reaches the thread joint 5 in opposite direction.
• the basic idea for the guide rod 10 according to the present invention is to keep the end part or the part of the guide rod facing away from the drill bit 3 as identical as possible to the drill rod 1 connected to it, and therefore to avoid the negative influence of a 105 % to 150 % heavier linear mass of the conventional guide tube, enhancing locally compressive, rotation and bending stresses.
• this slender portion 10A of the guide rod 10 should have a length equal to or preferably longer than the impact piston, which means the length of the slender portion 10A should be at least 500 mm.
• This slender portion 10A simultaneously smoothens the torque pulses and the bending stresses before those are conveyed towards the thread joint 5 and conveyed into the very sensitive male thread of the rod 1 connected to it.
• the guide portion 1OB of the guide rod is a tubular section acting as a bearing in contact with the hole wall to improve the guidance of the drill bit 3.
• the major reason for defining a tubular section instead of for example six long splines is deducted from field experience, that is guide tubes are considered to be less aggressive in overburden drilling and in soft rock drilling, while six splines may deteriorate the wall and drive the hole to collapse.
• This second portion 10B is preferably carburized or heat-treated, to withstand high wear because of heavy friction against abrasive rock, to a surface hardness between 48HRC and
• the second portion 10B may comprise external shallow splines in order to increase the flushing area and simultaneously decrease the clearance between splines and hole wall, for an improved guidance.
• the method according to the present invention for transferring impact energy from a top hammer unit to a drill bit can be summarized as follows.
• the top hammer unit has a piston that provides shock waves 4A.
• Each shock wave has a length 2L.
• the method comprises the steps of:
• a drill string comprising one or more extension rods 1 or extension tubes, a rock drilling element 10 as defined above, and a drill bit 3 or one or more guide tubes connected to a drill bit 3,
• the second portion 10B can in addition be altered in length, in order to optimize the shock wave transmission to the drill bit and to the rock.
• An alternative guide rod 10' according to the present invention is shown in Figs. 4A, 4B and 5. Contrary to our previous description, the drill bit 3 linear mass is often not equal to the tube linear mass. The drill bit 3 is much heavier, and so is the thread joint from the second portion 1OB to the drill bit 3. Because of this observation, more energy is reflected backwards to the drilling machine and not transferred to the rock.
• Figs. 4A and 4B schematically show an alternative drill string according to the present invention and an alternative guide rod 10' according to the present invention, respectively, wherein like numerals depict like features as in the previously described embodiment.
• the alternative guide rod 10' comprises the advantages of the guide rod 10 and thus has a slender portion 10A' and a guide portion 10B'.
• the major difference from the guide rod 10 is that the length L2' of the guide portion 10B' has been reduced.
• the length L1 ' of the slender portion 10A' is greater than the length of the piston used in the drilling machine, i.e. at least 500 mm.
• the alternative guide rod 10' further has a possibility to provide some more energy to the rock through the second portion 10B' of the guide rod 10' and the drill bit 3 considered as a whole.
• the overall length of the second portion 10B' and the drill bit 3 is designed as substantially half of the length of the piston of the drilling machine, which means that their overall length is substantially one quarter of the incident shock wave 4A.
• the first half of the shock wave 4A creates a first level of stress in the guide portion plus bit assembly, while the second half of the shock wave further increases the first level of stress to a higher value.
• the enhanced stress level is then able to push the carbide buttons some further into the rock. This process can improve in fact the overall energy transfer to the rock and the overall efficiency.
• the ideal length for the guide portion 10B' plus bit 3 is theoretically substantially equal to half of the piston length.
• optimization by finite element analysis shows that the overall guide portion plus bit length should be approximately one third of the piston length. This value is only an indication considering the finite element analysis being the only way to optimize the shock wave transfer to the rock while considering the true mass distribution along the tube and bit.
• shock wave transmission is not compulsory.
• a somewhat or even a much longer guide portion for improved guiding inside the hole can be designed to solve different drilling situations. For example, when the straightness of the hole is of a higher priority than the penetration rate.
• Such a guide rod would still take advantage of the lower compression stresses, more even rotation stresses and more even bending stresses in the thread joint 5 that will highly benefit the drill string life.
• Such a guide rod 10 and 10' is designed to accept conventional drill bits with a skirt and a female thread.
• the drill bit 3 can have either a standard skirt or a guide skirt.
• a guide rod according to the present invention preferably has a peripheral contact (also called shoulder contact) between the guide rod 10, 10' and the drill bit 3.
• a peripheral contact also called shoulder contact
• the major reason for having the shoulder contact around a large thread is to provide the shock energy precisely where it is going to be useful at the peripheral buttons of the drill bit.
• the drill bit 3 can alternatively be designed with a male threaded spigot to be inserted inside the guide rod having a corresponding female thread.
• a carburized guide portion able to withstand high wear can in this context be the sole means for guiding inside the hole, such that the drill bit 3 needs no integral guiding devices.
• the guide rod has been shown up to now with a bit directly connected to it. It is also possible to use the guide rod as an intermediate element connecting together two drill string sections of different cross-sectional area (in mm 2 ) or linear mass (in kg/m). For example, a 60 mm drill rod delivers the impact pulses to the guide rod, which in turn is connected to one or more guide tubes with heavier linear mass. The drill bit 3 is finally connected to the last guide tube.
• the drill string of rods could alternatively be a string of drill tubes wherein the guide rod 10, 10' then is replaced by a guide tube of similar geometry but with greater dimensions.
• a guide tube should be essentially identical to the drill tubes in its upper end, and have a larger and heavier tube at its lower end to suit the drill bit diameter.
• the present invention proposes a guide rod where the thread joint is moved away from the unfavorable reflection area.

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• Engineering & Computer Science (AREA)
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• Geology (AREA)
• Mining & Mineral Resources (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Earth Drilling (AREA)

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• 2005
  • 2005-05-09 SE SE0501054A patent/SE531017C2/sv not_active IP Right Cessation
• 2006
  • 2006-05-03 WO PCT/SE2006/000536 patent/WO2006121386A1/en active Application Filing
  • 2006-05-03 EP EP06733391A patent/EP1882078A1/de not_active Withdrawn
  • 2006-05-03 RU RU2007145427/03A patent/RU2007145427A/ru unknown
  • 2006-05-03 US US11/919,793 patent/US20090065224A1/en not_active Abandoned
  • 2006-05-03 CA CA002606120A patent/CA2606120A1/en not_active Abandoned
  • 2006-05-03 KR KR1020077026052A patent/KR20080013901A/ko not_active Application Discontinuation
• 2007
  • 2007-11-02 ZA ZA200709487A patent/ZA200709487B/xx unknown

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