Patent Publication Number: US-6904980-B2

Title: Linerbolt removal tool

Description:
TECHNICAL FIELD 
     This invention relates to a linerbolt removing tool. 
     BACKGROUND OF THE INVENTION 
     A typical application of the present invention is in the removal of bolts from mining equipment, such as mills that utilise sacrificial segmented liners bolted to the internal casing of the mills which are regularly replaced during routine maintenance. Typically such mills may range in size from three meter to eleven meter in diameter and are lined with replaceable heavy steel segments attached internally to the mill casing by through bolting. In such applications the bolts become corroded and clearances between bolts and holes become compacted with ore fines. This results in difficult bolt removal at liner removal time. As a result the many bolts that are utilised to attach the liners to the mill shell: are often required to be freed manually by the use of large sledge-hammers. This is a difficult and time-consuming task that may result in injury to the workers. 
     While it is well known to use percussive devices such as jack-hammers and hydraulically powered hammers to provide repetitive impacts for many applications, they are not able to be manually guided into alignment with wall mounted bolts and other components. The applications of jack hammers are limited as the hammering effect produced by an electrically or pneumatically operated jack hammer does not provide the impact as would be provided by a sledge hammer, for example. 
     In known hammering devices capable of delivering such impacts, a high reaction force is produced which necessitates that such devices be carried by articulating machines or be rigidly attached to some support structure. This reduces their versatility and makes them unsuitable for many applications. Furthermore, it is difficult to quickly and accurately align such devices with the shank of a bolt or the like for effecting ready removal thereof. 
     International publication WO97/26116 by the present applicant describes a hydraulic linerbolt removal tool. The hydraulic tool essentially comprises a housing having a moil mounted at the forward end and a hydraulic piston assembly reciprocally moveable along the hammer axis between a striking position at which the piston assembly strikes the impact delivery member and a retracted position remote from the impact delivery member. A firing means is provided for hydraulically firing the piston assembly from its retracted position to its striking position under the control of actuating means. A reactive body assembly is moveable in the direction of the hammer axis by driving means towards the impact delivery member prior to operation of the firing means whereby the reactive body assembly may be energised by movement and subsequently decelerated to substantially absorb the reaction generated by firing the piston assembly. Recoil is thus reduced whereby the apparatus may be operated by hand with the apparatus being suspended about its centre of gravity at the work site. 
     This hydraulic apparatus requires a 2400 psi hydraulic supply. The apparatus also requires electronic control for timing purposes. The present applicant has determined that there is a need for linerbolt removing tools that are operable from a conventional compressed air supply. 
     SUMMARY OF INVENTION 
     With the foregoing in view, this invention in one aspect resides broadly in a pneumatically actuated linerbolt removing tool including:
         a housing;   a moil supported for reciprocal movement along a hammer axis by the housing;   an inertial body mounted for reciprocating movement in said housing along said hammer axis;   a piston assembly moveable within said inertial body along the hammer axis between a striking position at which the piston assembly strikes the moil and a retracted position remote from the moil,   a gas-charged accumulator adjacent said piston assembly and tending to urge said piston toward said moil;   working air supply means to a cylinder associated with said housing and adapted to urge a biasing piston on said inertial body relative to the housing and toward said moil, said inertial body being ported whereby said working air is supplied to a front face of said piston assembly to urge the piston assembly to a cocked position away from said moil and whereby said accumulator is in its compressed state; and   selectively operable porting means adapted to equalize pressure between said front face and a rear face of said piston whereby said piston accelerates forward under accumulator force to strike said moll while said inertial body accelerates away from said moil, said porting means being adapted to continuously allow transfer of air between said faces while in operation.       

     The moil is preferably constrained to move over a selected distance along the axis. The moil may be biased toward its rearward retracted position with the tool at rest. 
     The inertial body is preferably constrained to move along one or more guides associated with the housing. The cylinder associated with the body and receiving the supply air may cooperate with the biasing piston associated with the inertial body to provide at least a portion of this guidance. 
     The accumulator may be formed as a substantially blind axial cylinder formed in the inertial body. There may be provided an integrally formed or assembled rearward piston portion adapted to close the open face of the accumulator bore. The accumulator may be gas charged external of the housing via a suitably valved charging tube to the inertial body which may include a flexible tube section to accommodate movement of the inertial body. 
     The means for providing working air to the front face of the piston assembly is preferably via a passage from through the biasing piston to an annular space which may port through a plurality of ports in the forward peripheral wall of the bore in which the piston assembly slides in the inertial body. By this means the pressure applied to the front face may remain constant while the air supply is connected, and the annular space may then accommodate a sleeve-type porting closure adapted to selectively open and close corresponding ports arranged about the periphery of the other end of the bore to equalize pressure on both faces of the piston assembly. 
     The preferred porting closure is preferably adapted to have a closely conformed sealing surface at each of its forward and rearward extents and the rearward sealing surface is adapted to selectively occlude and open the rearward ports by axial movement of the closure on a corresponding sealing surface on the inertial body. Between the forward and rearward sealing surfaces of the closure, there is preferably provided an annular space having a working surface and adapted to be supplied with a switchable air supply. The annular space may be divided into a pressurizable space controlled by said switchable air supply and a vented space. 
     On switching of the air supply to the pressurizable space, the porting closure moves forward to open the rearward ports thus allowing equalizing pressure to pass to the rear face of the piston assembly. There may be provided an overlapping vent between the rearward ports and the vented space and adapted, to be closed by the closure before the rearward ports are opened. 
     On equalization on both sides of the piston, the accumulator urges the piston into impact with the moil, reaction forces being borne by the relatively massive inertial body and thus isolated from the housing at the time of impact to be dissipated over the relaxation time of the heavier body. 
     When the switchable air is turned off, the static pressure of the air supply returns the components to their original positions. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical embodiment of the invention and wherein: 
         FIG. 1  is a longitudinal sectional view of a tool of the present invention; 
         FIGS. 2 and 3  illustrate the hammer mechanism of the apparatus of  FIG. 1 , in retracted and extended attitudes respectively; 
         FIG. 4  is a half section of the valve arrangement of the apparatus of  FIG. 1 , operably closed; and 
         FIG. 5  is a half section of the valve arrangement of the apparatus of  FIG. 1 , operably open. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1  to  5  depicts a linerbolt removing tool  1  adapted to be suspended by a length adjustable sling (not shown) supported about its centre of gravity by a mounted overhead carriage (not shown), in a similar manner to the prior art tool disclosed in International Patent Publication No. WO97/26116. Tool  1 , in a similar manner to the prior art tool, is readily pivoted about horizontal and vertical axes to align moil  2  with a bolt (not shown) to be removed from a mill casing (not shown). 
     An important feature of tool  1 , is the operation of hollow tube  3  and cylinder  4  which actuate, hammer body  5 . Air is supplied at relatively constant pressure and connected to a large reservoir. This ensures that the force at the end of hollow tube  3  is fairly constant. Cylinder  4  is anchored to the outer case  6 , which the operator holds. This means that although large recoil forces are acting upon the hammer body  5  during the firing cycle, the effect on the operator is a constant low force. 
     Hammer body  5  is mounted within case  6  via four linear bearings on two parallel rails. These allow hammer body  5  to freely move axially. In the forward rest position the face of end plate  7  rests against a rubber/steel buffer  8 . Compressed air is delivered to volume  9  of hammer body via port  10 . Hollow tube  3  acts as a bias piston inside cylinder  4  which is sealed. Compressed air is supplied to cylinder  4 , which in addition to supplying the needs of hammer body  5 , exerts a force on the end of hollow tube  3 . This force biasedly holds hammer body  5  in the forward position, and when hammer body  5  is fired, decelerates the body and returns it to the forward rest position. 
     The “valve function” will now be described.  FIGS. 2 and 4  show hammer body  5  with hammer piston  11  retracted in a charged position. In this state valve sleeve  12  is retracted against buffer  13 . A series of radial ports  14  are covered by sleeve  12  preventing pressurised air from volume  9  entering space  15  behind piston  11 . The space  16  in front of piston  11  is connected to pressurised volume  9  via a series of radial ports  17 . Space  15  behind piston  11  is vented to atmosphere via ports  19  and  20 . The differential pressure across piston  11  holds it in the retracted position against the pressure  29  of nitrogen charged accumulator  22 . 
     The pilot line  21  is vented to atmosphere through the trigger valve  30 . This places the volume  26  in front of seal ring  23  at atmospheric pressure. Volume  27  behind the seal ring  23  is also vented to atmosphere via port  20 . The outside of sleeve  12  is at system pressure. The cross-sectional area of the front of sleeve  12  is greater than the cross-sectional area of the rear of sleeve  12 ; this results in an unbalanced force keeping the sleeve  12  in the retracted position. 
     When the operator presses the trigger valve  30  the volume  26  in front of the seal ring  23  is pressurized. This causes valve sleeve  12  to move towards cushion  28  (refer FIGS.  3  and  5 ). As it moves, port  19  is covered and radial: ports  14  are uncovered. The space  15  behind the piston  11  is no longer vented to atmosphere but is pressurised by the system pressure in volume  9 . The pressure across piston  11  is now balanced and the pressure  29  of the nitrogen gas in accumulator  22  acting on the rear of piston  11  accelerates it forward. As piston  11  travels forward, the gas in front of the piston in space  16  vents through radial ports  17  into volume  9 , and fills space  15  created by advancing piston  11  via radial ports  14 . 
     When trigger valve  30  is released, sleeve valve  12  retracts covering radial ports  14  and uncovering port  19 . This vents space  15  behind piston  11  to atmosphere, causing piston  11  to retract as described above. 
     The valve operation described above ensures that the pressure drop across piston  11  is minimised during firing; this is due to the fact that large volumes of gas do not need to be vented to atmosphere during the firing cycle. 
     The firing of piston  11  will now be described. Piston  11  is supported in two bronze glands  35  and  36  and is sealed against sleeve  37  creating the two spaces (volumes)  16  and  15 . The rear of piston  11  extends into pressurized accumulator  22 . A piston cap  38  is mounted on the rear of piston  11 . A seal  24  prevents gas entering the space between piston  11  and piston cap  38 . 
     As piston  11  and piston cap  38  accelerate forward under the force of the accumulator gas pressure  29  acting on the rear of piston cap  38 , a point is reached where the piston cap  38  comes into contact with the gland  35 . As piston  11  continues to travel forward a vacuum is drawn between the piston cap  38  and piston  11 . The piston  11  is now no longer being accelerated by the nitrogen gas filled volume  29  in accumulator  22  but is being retarded slightly by the vacuum. The piston  11  travels at a nearly constant velocity for a short period after the impact of piston cap  38 . It is during this period of constant velocity that piston  11  strikes moil  2 . This period of constant velocity is necessary as the distance from piston  11  to moil  2  may change from one fire to the next, due to the angle of operation and the other variables. Once piston  11  has struck moil  2  its forward motion is halted and it remains at rest until the trigger valve  30  is released initiating the retraction cycle. If piston  11  was still being acted upon by accumulator pressure  29  at the moment of impacting moil  2 , the piston  11  would continue to push on moil  2  after impact and create a variable recoiling force which would be felt by the operator. If for some reason piston  11  does not strike moil  2  during this period of constant velocity, it continues forward until the leading edge of piston  11  begins to cover radial ports  17 . The air occupying space  16  then begins to compress decelerating piston  11 . The piston  11  will eventually entirely cover radial ports  17  and the enclosed volume will bring piston  11  to a complete rest. The piston buffer  40  is shaped to match the internal profile of piston  11 ′ to ensure that the enclosed volume  16  is minimised during the cushioning process. A larger volume would result in piston  11  not coming to rest before reaching the end of its travel. 
     The velocity of piston  11  when retracting is considerably less than when it is firing therefore a similar but somewhat smaller cushion is provided at the end of the retraction stroke. 
     It is to be understood that the above has been given by way of illustrative embodiment of the invention, all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as described herein.