Patent Publication Number: US-11028643-B2

Title: Down the hole drilling machine and method for drilling rock

Description:
RELATED APPLICATION DATA 
     This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2018/064318 filed May 31, 2018 claiming priority to EP 17174126.7 filed Jun. 2, 2017. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a down the hole drilling machine comprising an impact device and especially to fluid conveyance inside the impact device. The drilling machine is provided with a reciprocating percussion piston, which is moved by controlling feeding an discharging pressurized fluid into an out of working chambers where working surfaces of the piston are located. The piston is configured to strike to a drill bit being connected directly to the drilling machine. 
     Further, the invention relates to a method for drilling rock. 
     Holes can be drilled in rock by means of various rock drilling machines. Drilling may be performed with a method combining percussions and rotation. Then the drilling is called percussive drilling. Further, percussive drilling may be classified according to whether an impact device is outside the drill hole or in the drill hole during the drilling. When the impact device is in the drill hole, the drilling is typically called down-the-hole drilling (DTH). Since the impact device is in the DTH drilling machine located inside the drill hole, structure of the impact device needs to be compact. 
     In the known DTH drilling machines efficiency of the impact devices are shown not to be satisfactory. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It is an object of this invention to provide a novel and improved drilling machine and a method for drilling rock. 
     An idea of the disclosed solution is that the impact device comprises a piston provided with a longitudinal central opening passing axially through the piston. Thus, the piston has a sleeve-like configuration. An outer shell of the sleeve-like piston is solid, which means that the piston is without any transverse through openings extending between an outer surface and an inner surface. Thereby the sleeve-like piston is not provided with openable and closable transverse control openings. Further, at least fluid passages for feeding or supplying pressurized fluid into a top working chamber and bottom working chamber are located inside the central opening of the piston. In summary, the present solution discloses an improved way for pressurized fluid routing in DTH drilling machines. 
     An advantage of the disclosed solution is that when the fluid is controlled into both working chambers by means of the mentioned fluid passages inside the central opening of the piston, then top and bottom working areas of the piston inside the working chambers may be maximized. Increased size of the working areas affected by pressurized fluid means that greater impact pulses can be produced. Thereby effectivity of the impact device may be increased without increasing outer dimensions of the impact device. In known impact devices the fluid routing system comprises fluid passages outside the piston, whereby they limit size of working areas of the piston. Further, when the piston has no cross holes the structure of the piston is robust and durable. 
     A further advantage is that, when the drilling machine is pneumatically operated this solution also ensures as great space as possible for the supplied air and its pneumatic expansion during the work cycle. 
     An idea of an embodiment is that in addition to the feed or supply fluid passages, the fluid passages for discharging the pressurized fluid out of the top and bottom working chambers are also located inside the central opening of the piston. In other words, both feeding and venting of both working chambers is done through a piston bore whereby there is no need for discharging channels arranged around the piston. Owing to this, the structure may be compact and the piston may have large working surface areas. Further, controlling of the discharge flows may be executed without any dedicated discharge control elements, such as control sleeves, which simplifies the structure. 
     An idea of an embodiment is that connections between the working chambers and the fluid feed passages inside the central opening of the piston are opened and closed by the movements of the sleeve-like piston provided with the solid outer shell. In other words, the feed flows to both working chambers are controlled by the position of the piston. Further, if the discharge flows of both working chambers are also routed through the central opening of the piston, then the position of the piston controls also the discharge flows. An advantage of this embodiment is that there is no need for any separate movable control sleeves or valves for controlling the feeding and discharging. This simplifies the structure. The piston having the solid-sleeve configuration provides itself the needed control for the work cycle of the impact device. 
     An idea of an embodiment is that the impact device comprises a feed tube arranged inside the central opening of the piston. The feed tube arranged coaxially inside the sleeve-like piston is for controlling fluid flows of the impact device. The feed tube is a two-part structure comprising an outer feed tube and an inner feed tube. The outer feed tube is supported to an axial bore of the piston and the inner feed tube is arranged inside the outer feed tube. In other words, the feed tube is a double wall structure providing the structure with additional axial fluid passages inside the central opening of the piston. Thus, an advantage of the disclosed double feed tube is that the structure may comprise several fluid passages. There may be fluid passages between the piston and the outer feed tube, between the outer feed tube and the inner feed tube, and further, inside the inner feed tube. 
     An idea of an embodiment is that inside the central opening is the feed tube as is disclosed in the previous embodiment. The feed tube is an immobile element relative to the casing. Since the fluid flows are controlled by the movements of the piston, there is no need to move the feed tube in accordance with the work cycle. 
     An idea of an embodiment is that inside the central opening of the piston is the feed tube disclosed above. Contrary to the previous embodiment the feed tube is arranged axially movably relative to the casing. An advantage of this solution is that timing of opening and closing of fluid passages may be adjusted by adjusting axial position of the at least one of the tubes of the feed tube. Thereby it is possible to provide the drilling machine with an asymmetric timing feature for the fluid routing, for example. The axial position of the feed tube may be adjusted by means of adjusting screws, for example. 
     An idea of an embodiment is that the fluid routing inside the impact device is executed without the above disclosed features of the double wall system or double tube structure. In this alternative solution inside the central opening of the piston may be two or more separate axial fluid channels for executing the fluid supply and discharge separately. 
     An idea of an embodiment is that the impact device comprises two separate feed tubes arranged inside the central opening of the piston. The feed tubes are not arranged coaxially inside the sleeve-like piston. One feed tube is for the upper working chamber and the other feed tube is for the lower working chamber. Thus, there are separate parallel feed tubes for controlling fluid flows of the impact device. This embodiment is an alternative to one single coaxial feed tube. 
     An idea of an embodiment is that inside the central opening of the piston is a feed tube comprising an outer feed tube and an inner feed tube arranged inside the outer feed tube. The double wall feed tube provides the structure inside the piston with three axial passages. Inside the inner feed tube is a discharge passage whereby the discharging of the fluid from at least the top working chamber is configured to be executed via the discharge passage. Between the outer feed tube and the inner feed tube is a feed passage, which is connected to the inlet port at a top end and is provided with constant fluid supply during the working cycle of the impact device. And further, between the outer tube and the piston is a top feed passage for conveying fluid from the feed passage to the top working chamber and being opened and closed by the piston for controlling the working cycle. According to an idea of a further embodiment also the bottom working chamber is discharged via the discharge passage of the inner feed tube. 
     An idea of an embodiment is that inside the central opening of the piston is the feed tube comprising the above disclosed double wall or double tube structure. The inner feed tube is arranged to extend axially to the drill bit. The bottom end of the inner tube is arranged inside a central opening or bore of the drill bit. Between the inner feed tube and the drill bit may be fluid tight connection. The fluid flow discharged via the inner passage of the inner feed tube may flow through the bore of the drill bit out of the impact device. The bore of the drill bit is in fluid connection with at least one flushing channel extending to a bottom face of the drill bit. An advantage of this embodiment is that the inner feed tube provides the impact device with a convenient and compact fluid path. 
     An idea of an embodiment is that the feed tube comprises at least one transverse discharging opening at the top part of the feed tube and passing through the inner tube and the outer tube for discharging the top working chamber to the axial discharge passage when being opened by the piston. 
     An idea of an embodiment is that at the bottom end portion of the drilling machine is a bottom sleeve surrounding the bottom end portion of the piston and the top end portion of the drill bit. The bottom sleeve comprises fluid passages allowing fluid connection from the bottom working chamber to at least one discharging channel passing the drill bit and directing the discharged fluid to sides of the drill bit. The bottom sleeve is connected immovably to the casing of the drilling machine. By means of the bottom sleeve, suitable fluid passages may be easily arranged at the end structure of the impact device. The mentioned fluid connection for discharging the bottom working chamber is controlled by the axial movements of the piston. 
     An idea of an embodiment is that the drilling machine is a pneumatically operable device and the fluid is pressurized gas. 
     An idea of an embodiment is that the drilling machine and the impact device is a hydraulically operated device. The device may be used by means of pressurized water, for example. 
     The above disclosed embodiments and their features may be combined. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Some embodiments of the invention will be explained in greater detail in the attached drawings, in which 
         FIG. 1  shows schematically a rock drilling rig provided with a DTH rock drilling machine, 
         FIG. 2  shows schematically a DTH drilling machine at a bottom of a drill hole, 
         FIGS. 3 and 4  show schematically two different cross-sectional views of a DTH drilling machine, 
         FIG. 5  shows schematically and enlarged a cross sectional view of part of the drilling machine of  FIGS. 3 and 4 , 
         FIG. 6  shows schematically timing of discharge of a bottom chamber and utilization of a bottom sleeve, 
         FIG. 7  shows schematically an alternative discharging of the bottom chamber trough an axial passage of an inner feed tube, 
         FIG. 8  shows schematically an inner feed tube allowing discharge of a top working chamber and a bottom working chamber trough an inner axial passage, 
         FIG. 9  shows schematically an inner feed tube suitable for impact devices of  FIGS. 3-5  wherein only the top working chamber is discharged through the inner axial passage, 
         FIG. 10  shows schematically an outer feed tube and  FIG. 11  is a cross section D-D of  FIG. 10 , 
         FIG. 12  shows schematically a piston of an impact device of  FIGS. 3-5  and  FIG. 13  is a cross-sectional view of the sleeve-like piston of  FIG. 12 , 
         FIGS. 14-16  show schematically cross-sectional views of possible alternative sleeve-like pistons and axial fluid passages inside central openings of the pistons, 
         FIG. 17  shows schematically a cross-sectional view of the top end of the impact device when the piston is in a top feed timing position, and 
         FIG. 18  shows schematically a cross-sectional view of the top end of the impact device when the piston is in a top vent timing position. 
     
    
    
     In the figures, some embodiments of the invention are shown simplified for the sake of clarity. Like reference numerals refer to like parts in the figures. 
     DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows a rock drilling rig  1  that comprises a movable carrier  2  provided with a drilling boom  3 . The boom  3  is provided with a rock drilling unit  4  comprising a feed beam  5 , a feed device  6  and a rotation unit  7 . The rotation unit  7  may comprise a gear system and one or more rotating motors. The rotation unit  7  may be supported to a carriage  8  with which it is movably supported to the feed beam  5 . The rotation unit  7  may be provided with drilling equipment  9  which may comprise one or more drilling tubes  10  connected to each other, and a DTH drilling machine  11  at an outermost end of the drilling equipment  9 . The DTH drilling machine  11  is located in the drilled bore hole  12  during the drilling. 
       FIG. 2  shows that the DTH drilling machine  11  comprises an impact device  13 . The impact device  13  is at the opposite end of the drilling equipment  9  in relation to the rotation unit  7 . During drilling, a drill bit  14  is connected directly to the impact device  13 , whereby percussions P generated by the impact device  13  are transmitted to the drill bit  14 . The drilling equipment  9  is rotating around its longitudinal axis in direction R by means of the rotation unit  7  shown in  FIG. 1  and, at the same, the rotation unit  7  and the drilling equipment  9  connected to it are fed with feed force F in the drilling direction A by means of the feed device  6 . Then, the drill bit  14  breaks rock due to the effect of the rotation R, the feed force F and the percussion P. Pressurized fluid is fed from a pressure source PS to the drilling machine  11  through the drilling tubes  10 . The pressurized fluid may be compressed air and the pressure source PS may be a compressor. The pressure fluid is directed to influence to working surfaces of a percussion piston of the drilling machine and to cause the piston to move in a reciprocating manner and to strike against impact surface of the drill bit. After being utilized in working cycle of the drilling machine  11  pressurized air is allowed to discharge form the drilling machine  11  and to thereby provide flushing for the drill bit  14 . Further, the discharged air pushes drilled rock material out of the drill hole in an annular space between the drill hole and the drilling equipment  9 . 
       FIG. 2  indicates by an arrow TE an upper end or top end of the drilling machine  11  and by an arrow BE a lower end or bottom end of the drilling machine. 
       FIGS. 3 and 4  disclose a DTH drilling machine  11  and its impact device  13 . The cross-sections are shown at differing points in  FIGS. 3 and 4 . The drilling machine comprises an elongated casing  15 , which may be a sleeve-like frame piece. At a top end TE of the casing  15  is a connection piece  16  by means of which the drilling machine  11  can be connected to a drill tube. The connection piece  16  may comprise threaded connecting surfaces  17 . In connection with the connection piece  16  is an inlet port  18  for feeding pressurized fluid to the impact device  13 . The inlet port  18  may comprise valve means  18   a , which allow feeding of fluid towards the impact device but prevent flow in an opposite direction. The impact device  13  comprises a piston  19  which is arranged to be moved in a reciprocating manner during its work cycle. At a bottom end BE of the piston is an impact surface ISA arranged to strike an impact surface ISB at a top end of a drill bit  14 . As can be noted, the piston  19  is a sleeve-like piece comprising an outer surface supported against an inner surface of the casing, and an inner surface defining a central opening  20 . The piston  19  is without any transverse channels or openings and only comprises the central opening  20  extending from end to end. The central opening  20  is utilized for conveying pressure fluid from the inlet port  18  to a top working chamber  21  and to a bottom working chamber  22 . Thus, there is no need for feed fluid passages around the piston  19 . The piston  19  has a top working surface  23  which is affected by the pressure prevailing in the top working chamber  21  and is defined by diameters D 1  and D 2 , wherein D 1  is outer diameter of the piston and D 2  is diameter of the central opening at the top end. At the bottom end of the piston is a bottom working surface  24  defined by diameters D 1  and D 3 , wherein D 3  is diameter of central opening at the bottom end. 
     Inside the central opening  20  may be a feed tube  25  for conducting the fluid flows. The feed tube  25  may extend from the inlet port  18  to the drill bit  14 . The feed tube  25  may comprise an outer feed tube  25   a  supported to the central opening  20 , and an inner feed tube  25   b  arranged inside the outer feed tube  25   a . The two feed tube components  25   a ,  25   b  provide the feed tube  25  with double wall structure and may create three axial fluid passages inside the central opening  20  of the piston  19 . Then a fluid passage  26  may be formed between the piston  19  and the outer feed tube  25   a , a fluid passage  27  may be between the outer feed tube  25   a  and the inner feed tube  25   b , and further, inside the inner feed tube  25   b  is a fluid passage  28 . Furthermore, inside the piston  19  is a top feed chamber  29 , which is limited radially by the outer feed tube  25   a . The top feed chamber  29  is in continuous fluid connection to top working chamber  21  by means of axial fluid passages  30  of the outer feed tube  25   a.    
     At the inlet port  18  is a pressure space  31  wherein prevails substantially constant pressure. The pressure space  31  is in constant fluid connection with a fluid passage  27  and a fluid space  32 . Thus, between the outer feed tube  25   a  and the inner feed tube  25   b  prevails constant fluid pressure, which may be conveyed to the working chambers  21  and  22  in accordance with movement of the piston  19 . 
     The feed tubes  25   a ,  25   b  are arranged immovably relative to each other and typically the entire feed tube  25  is arrange immovably relative to the casing  15 . Then the piston  19  moves relative to the feed tube  25  and opens and closes transverse openings of the outer feed tube  25   a  and the inner feed tube  25   b . The movement of the piston  19  also opens and closes axial connection between the fluid space  32  and the bottom working chamber  22  as will be disclosed below. 
       FIG. 5  discloses a situation wherein the piston  19  is moved to its right most position and is at an impact point. Then the top end of the piston  19  opens fluid connection from the top working chamber  21  through the transverse openings  33  of the feed tube  25  to the fluid passage of the inner feed tube  25   b . Thereby the top working chamber  21  is discharged through the fluid passage  28  arranged inside the central opening  20  of the piston. The openings  33  are formed of aligned openings  33   a  and  33   b  of the inner and outer feed tubes  25   a ,  25   b . The inner fluid passage  28  of the inner feed tube  25   b  extends to a central bore  14   a  of the drill bit  14  whereby the top chamber  21  is discharged through the drill bit. 
       FIG. 5  further discloses that when the piston  19  moves in the impact direction A towards the impact point, then a fluid connection  34  opens between a control shoulder  35  and a bottom end portion  36  of the central opening  20  of the piston  19 . The pressure fluid may then flow from the fluid space  32  to the bottom working chamber  22  since the fluid space  32  is constantly connected to the inlet port  18 . This way feeding of the bottom chamber  22  is executed by means of fluid passages arranged inside the central bore  20  of the piston  19 . 
     As disclosed above, the top working chamber  21  is discharged through the fluid passage  28  and the bottom working chamber  22  is pressurized. Pressure affecting to the bottom working surfaces  24  causes the piston  19  to move towards the return direction B. As the piston  19  moves toward the top end TE, then the control shoulder  35  closes the fluid connection  34 . The bottom chamber  22  becomes then a closed pressure space inside which the pressurized fluid may expand, in case the used fluid is pressure air. The expanding fluid in the bottom chamber  22  forces the piston  19  to move in the return direction B and then the top end of the piston  19  closes connection to the transverse openings  33  whereby the top chamber  21  becomes a closed space. The piston  19  continues its movement in the return direction B and the bottom end of the piston  19  opens a discharge passage  37   b  through which the bottom chamber  22  is discharged via a passage  38   b  and through the side of the drill bit. However, the piston  19  moves still in the return direction B and a shoulder  40  opens passages  41  between the fluid passage  27  and the top feed chamber  29 . The top feed chamber  29  is then connected to the feed pressure. The same pressure prevails also in the top working chamber  21 , since the top feed chamber  29  and the top working chamber  21  are in continuous fluid connection through the axial fluid passages  30 . Then top dead point of the piston  19  is reached and movement direction of the piston  19  is changed towards the impact direction A. When the piston  19  moves in the impact direction A the shoulder  40  closes the passages  41  and the top working chamber  21  becomes a closed pressure space inside which the fed fluid expands. The movement of the piston  19  causes the top end of the piston to close discharge connection from the bottom working chamber  22  to the fluid passage  37   b . The piston continues its movement in the impact direction A and the top end of the piston  19  opens the transverse openings  33  and thereby allow the top working chamber  21  to be discharged to the fluid passage  28  inside the inner feed tube  25   b . When the piston continues its movement the end portion  36  of the central opening passes the control shoulder  34  and opens the fluid passage  34  for feeding fluid to the bottom working chamber  22 . The piston  19  impacts the drill bit  14  and the work cycle may continue in a similar manner. 
       FIG. 6  discloses in detail the discharge of the bottom chamber  22 . The fluid passages  37   b  and  38   b  are located in a bottom sleeve  42 . The bottom sleeve  42  surrounds the bottom end portion of the piston  19  and the top end portion of the drill bit  14 . The fluid passages  37   b  and  38   b  direct the discharging fluid flow to sides of the drill bit  14 . When the piston  19  moves in the return direction B an edge  43  of the piston  19  opens the discharge connection. 
       FIG. 7  discloses an alternative solution which is without the bottom sleeve of  FIGS. 3-6 . In  FIG. 7  the bottom working chamber  22  is discharged via the discharge passage  28  of the inner feed tube  25   b . Thus, in this solution both working chambers  21 ,  22  are discharged to the central bore  14   a  of the drill bit  14 . When the piston  19  moves in the return direction B, then an edge  44  opens transverse openings  45 , which are locating at the bottom end of the inner tube  25   b . A control shoulder  35  closes fluid connection between a top feed chamber  29  and the bottom work chamber  22  before the discharge. 
       FIG. 8  discloses an inner feed tube  25   b  comprising transverse openings  33   b  for the discharge of top working chamber and transverse openings  45  for the discharge of bottom working chambers. The openings  33   b  and  45  are located at grooves  46 ,  47  of enlargements  48 ,  49 . The grooves  46 ,  47  connect fluid spaces on both sides of the enlargements  48 ,  49 . At the bottom end BE of the inner feed tube  25   b  may be an end part  50 , which may be connected fluid tightly to a central bore  14   b  of a drill bit  14 . 
       FIG. 9  discloses an inner feed tube  25   b  suitable for impact devices of  FIGS. 3-5  wherein only the top working chamber is discharged through an inner axial passage  28 . The inner feed tube comprises transverse openings  33   b  for connecting the top working chamber and the passage  28 . The inner feed tube also comprises a control shoulder  35  and an end part  50 . 
       FIGS. 10 and 11  disclose an outer feed tube  25   a . The outer feed tube  25   a  comprises an enlargement  51  at its longitudinal middle section. Several axial passages  30  pass through the enlargement  51  and connect pressure space on opposite sides of the enlargement  51 . Further, the enlargement  51  comprises several transverse discharge openings  33   a  and feed openings  41  passing through the sleeve-like structure. Inside the outer tube  25   a  is a central space  52  inside which the inner feed tube may be arranged. 
       FIGS. 12 and 13  disclose the sleeve-like piston  19 . Between an outer surface  53  and an inner surface  54  are no holes or transverse apertures whereby the piston has a solid outer core. Inside the piston  19  is the central opening  20  inside which axial fluid passages and feed tubes may be arranged. Since the reciprocating movement of the piston  19  is configured to control the work cycle of the impact device, the piston  19  is provided with edges  40 ,  55 ,  56  and  57  or control surfaces for opening and closing the fluid passages, as it is disclosed above. 
       FIGS. 14-16  disclose some alternative sleeve-like pistons  19  and axial fluid paths Fp 1 -Fp 3  inside central openings  20  of the pistons  19 . The  FIGS. 14-16  are strongly simplified for improving clarity. In  FIG. 14  inside the central opening  20  is one feed tube  25 , whereby two fluid paths Fp 1  and Fp 2  is formed. In  FIG. 15  there are two separate feed tubes Ft 1  and Ft 2  and their fluid paths Fp 1  and Fp 2 . Further, in  FIG. 16  one single feed tube  25  comprises two internal flow paths Fp 1  and Fp 2 . 
       FIG. 17  discloses a portion of the impact device at the top end TE and in situation when the piston  19  is moving in the return direction B and the edge  40  opens connection to the feed passage  41  so that fluid can flow from the axial passage  27  to the top feed chamber  20 . Since the top feed chamber  20  and the top working chamber  21  are connected by means of axial channels  30  shown in  FIGS. 4 and 10 , the same pressure will prevail in both spaces  20 ,  21  after the passage  41  is opened. 
       FIG. 18  discloses a portion of the impact device at the top end TE top end of the impact device, and in situation when the piston  19  is moving in the impact direction A. Then the edge  55  or control surface opens transverse fluid passage  33  form the top working chamber  21  to the discharge passage  28 , whereby the top working chamber  21  is discharged through the inner feed tube  25   b.    
     The drawings and the related description are only intended to illustrate the idea of the invention. Details of the invention may vary within the scope of the claims.