Abstract:
A method for testing thermal fatigue resistance of a shear cutter includes: engaging the shear cutter with a rotating target cylinder; moving the shear cutter along the rotating target cylinder until the shear cutter is heated to a threshold temperature; cooling the shear cutter in response to heating of the shear cutter to the threshold temperature; and repeating the heating and cooling of the shear cutter.

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
       [0001]    The present disclosure generally relates to thermomechanical testing of shear cutters. 
       Description of the Related Art 
       [0002]    U.S. Pat. No. 8,453,497 discloses a fixture for holding a cutter for a vertical turret lathe including a block with a blind hole. A cutter with an indenter on its distal end may be secured within the hole such that a portion of the indenter comprises a positive rake angle. A method for testing cutters may comprise securing a cutter on a fixture of a vertical turret lathe which has a cutting material positioned adjacent the cutter. The cutting material may be rotated around a rotational axis at a constant rotational velocity. The fixture may be urged laterally such that the cutter progressively moves towards a periphery of the cutting material. The rotational velocity may be decreased as the cutter moves laterally to maintain a relative constant linear velocity between the cutting material and the cutter. 
         [0003]    U.S. Pat. No. 9,222,350 discloses a cutting element for an earth-boring drilling tool and its method of making. The cutting element may include a substrate, a superhard layer, and a sensing element. The superhard layer may be bonded to the substrate along an interface. The superhard layer may have a working surface opposite the interface and an outer peripheral surface. The outer peripheral surface may extend between the working surface and the interface. The sensing element may comprise at least a part of the superhard layer. 
         [0004]    U.S. Pat. App. Pub. No. 2011/0148021 discloses a target cylinder and a method for fabricating the target cylinder. The target cylinder includes a first end, a second end, and a sidewall extending from the first end to the second end. At least one of the second end and the sidewall is an exposed portion that makes contact with a superhard component to determine at least one property of the superhard component. The exposed portion comprises at least one soft material and at least one hard material that is interveningly positioned between or within the soft material in a predetermined and repeatable pattern. In one embodiment, the differential of the unconfined compressive strength between the hard material and the soft material ranges from about 1,000 psi to about 60,000 psi. 
         [0005]    U.S. Pat. App. Pub. No. 2013/0067985 discloses a method and apparatus for testing the abrasive wear resistance of PDC cutters or other superhard materials. The method includes obtaining a first cutter having a first substrate and a first cutting table coupled thereto and obtaining a second cutter having a second substrate and a second cutting table coupled thereto. The method also includes positioning a surface of the first cutting table in contact with a surface of the second cutting table. The method also includes rotating at least one of the first cutters and the second cutters where at least a portion of the first and/or second cutting tables is removed. The method includes determining the amount of first and/or second cutting table removed. The apparatus includes a first holder coupled to the first cutter and a second holder coupled to the second cutter, where at least one holder rotates circumferentially. 
         [0006]    U.S. Pat. App. Pub. No. 2013/0239652 discloses a target cylinder, a method for testing a superhard component thereon, and a method for selecting an untested component for use in field applications. The target cylinder includes a first end, a second end, and a side wall extending from the first end to the second end. At least one of the second end and the sidewall is an exposed portion that makes contact with the superhard component to determine at least one property of the superhard component. The target cylinder is formed from a first material evenly distributed throughout a second material. Upon testing superhard components at one or more impact frequencies, untested superhard components are selected based upon field anticipated impact frequencies. 
         [0007]    U.S. Pat. App. Pub. No. 2014/0250973 discloses a system and a method of testing a superabrasive cutter. The system of testing a superabrasive cutter may include a spinning wheel holding the superabrasive cutter; a rock feeding into a rotation of the superabrasive cutter on the spinning wheel; and a plurality of sensors operably attaching to the spinning wheel and the rock to detect properties of the superabrasive cutter. The method of testing a superabrasive cutter may include steps of attaching a superabrasive cutter to a spinning wheel; moving a rock into a rotation of the superabrasive cutter on the spinning wheel; and communicably coupling a first sensor to the superabrasive cutter. 
         [0008]    U.S. Pat. App. Pub. No. 2015/0075252 discloses methods and techniques for determining wear abrasion resistance of superhard components, such as cutters used in down-hole drilling tools. The methods and techniques produce an efficiency ratio of a superhard component through data obtained from a vertical turret lathe test. The efficiency ratio is the ratio between the volume of a target cylinder removed by the superhard component during the vertical turret lathe test and the normal force applied onto the superhard component by the target cylinder. The efficiency ratio is indicative of the energy efficiency of the superhard component. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    The present disclosure generally relates to thermomechanical testing of shear cutters. In one embodiment, a method for testing thermal fatigue resistance of a shear cutter includes: engaging the shear cutter with a rotating target cylinder; moving the shear cutter along the rotating target cylinder until the shear cutter is heated to a threshold temperature; cooling the shear cutter in response to heating of the shear cutter to the threshold temperature; and repeating the heating and cooling of the shear cutter. 
         [0010]    In another embodiment, a method for testing thermal fatigue resistance of a shear cutter includes: engaging the shear cutter with a rotating target cylinder; moving the shear cutter along the rotating target cylinder without coolant, thereby heating the shear cutter; cooling the shear cutter after heating the shear cutter for a period of time; and repeating the heating and cooling of the shear cutter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
           [0012]      FIG. 1  illustrates commencement of a thermomechanical vertical turret lathe (VTL) test by engagement of a shear cutter with a target cylinder, according to one embodiment of the present disclosure. 
           [0013]      FIG. 2A  is an enlargement of a portion of  FIG. 1 .  FIG. 2B  illustrates engagement of the shear cutter with the target cylinder. 
           [0014]      FIG. 3  illustrates a heating cycle of the test. 
           [0015]      FIG. 4  illustrates the end of the heating cycle. 
           [0016]      FIG. 5  illustrates a cooling cycle of the test. 
           [0017]      FIG. 6  illustrates results of tests performed on a plurality of shear cutters. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  illustrates commencement of a thermomechanical vertical turret lathe (VTL) test by engagement of a shear cutter  1  with a target cylinder  2 , according to one embodiment of the present disclosure. To prepare for commencement of the test, the shear cutter  1  may be mounted to a head  3  of the VTL  4 . The VTL  4  may include the head  3 , a track  5 , a plunger  6 , a runner  7 , a turntable  8 , a cooling system  9 , a programmable logic controller (PLC)  10 , and a frame  11 . 
         [0019]    The track  5  and turntable  8  may be mounted to the frame  11 . The runner  7  may be transversely movable along the track  5  by operation of a track actuator (not shown), such as a rack and pinion. The rack may extend along the track  5  and the pinion motor may be mounted to the runner  7 . The pinion motor may be operated by the PLC  10  via a control line. The plunger  6  may be a piston and cylinder assembly having an upper end connected to the runner  7  and a lower end connected to the head  3 . The plunger  6  may be operated by the PLC via a control line to raise and lower the head  3  relative to the turntable  8 . Each of the track actuator and the plunger  6  may also include a position sensor in communication with the PLC  10 . The target cylinder  2  may be mounted on the turntable  8 . The turntable  8  may include a motor (not shown) for rotating the target cylinder  2  relative to the head  3 . The turntable  8  may also include a tachometer (not shown) in communication with the PLC  10 . The target cylinder  2  may be made from hard natural rock, such as granite, marble, or sandstone. 
         [0020]    Alternatively, the target cylinder  2  may be a synthetic composite having a matrix of concrete and plates of hard natural rock or synthetic ceramic disposed about the matrix in a pattern. The concrete may include cement, such as Portland cement, reinforced with quartzite sand. Alternatively, the rock or ceramic may be dispersed throughout the cement as large particles. 
         [0021]    The cooling system  9  may include a reservoir  12 , a pump  13 , a nozzle  14 , and a plurality of fluid conduits. The reservoir  12  and pump  13  may be mounted to the frame  11  and the nozzle  14  may be mounted to the head  3  or the plunger  6 . A supply conduit may connect the reservoir  12  to an inlet of the pump  13  and a discharge conduit may connect an outlet of the pump to the nozzle  14 . The discharge conduit may be flexible, such as a hose, to accommodate movement of the head  3  relative to the runner  7  and movement of the runner  7  relative to the frame  11 . A quantity of coolant  15  may be disposed in the reservoir  12 . The coolant  15  may be a liquid, such as water. The nozzle  14  may be disposed in proximity to the mounted shear cutter  1  and aimed thereat to spray coolant  15  onto the shear cutter  1 . The PLC  10  may be in communication with the pump  13  via a control line for selectively activating and deactivating the pump. 
         [0022]    Alternatively, the nozzle  14  may be mounted to the frame  11 . Alternatively, the nozzle  14  may be aimed to spray the coolant onto the target cylinder  2  instead of onto the shear cutter  1 , thereby indirectly cooling the shear cutter  1 . Alternatively, the reservoir  12  may be omitted, the coolant  15  may be air instead of water, and the cooling system  9  may include a compressor instead of the pump  13 . Alternatively, the coolant  15  may be oil and the turntable  8  may have a sump and a recycle pump for returning the oil to the reservoir  12 . 
         [0023]    Also in preparation for commencement of the test, one or more parameters  16  may be input to the PLC  10 . The parameters  16  may include depth of cut (DOC)  16   d , a temperature threshold (Max Temp)  16   t , and/or cooling time (Cool Time). Additional parameters may include a surface speed (Surf Speed) the turntable  8  and/or a speed of the runner  7  (Run Speed). The threshold temperature  16   t  may range between eight hundred and thirteen hundred degrees Celsius. During testing, the PLC  10  may utilize measurements from the position sensor of the track actuator and may adjust an angular speed of the turntable motor so that the target cylinder rotates at a constant surface speed relative to the shear cutter. The surface speed may range between three hundred and six hundred fifty feet per minute (ninety-one and one hundred ninety-eight meters per minute). 
         [0024]      FIG. 2A  is an enlargement of a portion of  FIG. 1 .  FIG. 2B  illustrates engagement of the shear cutter  1  with the target cylinder  2 . Referring also to  FIG. 1 , the head  3  may include one or more sensors in communication with the PLC  10  via a data cable for monitoring the test. The PLC  10  may include a memory unit (not shown) for recording measurements from the sensors and a cycle count. The sensors may include a load cell  17  and a thermometer, such as a thermocouple  18 . The load cell  17  may be mounted to the head  3  for measuring force  22  exerted by the plunger  6  onto the shear cutter  1  and/or reaction force (not shown) exerted by the target cylinder  2  onto the shear cutter. The shear cutter  1  may be mounted to a pocket formed in the head  3 , such as by a clamp  19 . The pocket may be lined with a thermally insulating material  3   n , such as a ceramic, such as alumina. The thermally insulating material  3   n  may obstruct heat transfer from the shear cutter  1  to the head  3  during a heating cycle of the test. The pocket may be configured such that the cutter  1  engages the target cylinder  2  at a positive back rake angle. 
         [0025]    The shear cutter  1  may include a cutting table  1   t  attached to a cylindrical substrate  1   s . The cutting table  1   t  may be circular and the substrate  1   s  may be a circular cylinder. The cutting table  1   t  may be made from a superhard material, such as polycrystalline diamond (PCD), attached to a hard substrate, such as a cermet, thereby forming a compact, such as a polycrystalline diamond compact (PDC). The cermet may be a cemented carbide, such a group VIIIB metal-carbide, such as cobalt-tungsten carbide. The cutting table  1   t  may have an interface with the substrate  1   s  and a cutting face opposite to the interface. The cutting table  1   t  may be non-treated or thermally stable. 
         [0026]    Alternatively, the shear cutter  1  may be oval. Alternatively, the superhard material may be cubic boron nitride or impregnated diamond. 
         [0027]    The clamp  19  may include a threaded fastener  19   f  screwed into the head  3 , a yoke  19   y  disposed onto the fastener, and a nut  19   n  for securing the yoke onto the fastener. The clamp  19  may further include a pad  19   p  disposed between the yoke  19   y  and the shear cutter  1  for evenly distributing a clamping force along the cutting table it. The pad  19   p  may be made from a thermally insulating material to obstruct heat transfer from the shear cutter  1  to the yoke  19   y  during the heating cycle. 
         [0028]    The thermocouple  18  may include a contact  18   c , a pair of sensing wires  18   s , a junction  18   j , and a pair of lead wires arranged together in a cable. The contact  18   c  may be mounted to the pad  19   p , such as by soldering, brazing, or interference fit therein. As the nut  19   n  is being screwed onto the fastener  19   f , the yoke  19   y  may be advanced toward the cutting table  1   t  until the contact  18   c  is pressed firmly into thermal engagement with the cutting table. A first end of the sensing wires  18   s  may be secured to the contact  18   c  and the sensing wires may extend through an opening formed in the pad  19   p  and a passage formed in the yoke  19   y . The junction  18   j  may be mounted on a surface of the yoke opposite to the cutting table it, such as by one or more fasteners. The junction  18   j  may connect each second end of the sensing wires  18   s  to an end of a respective lead wire. The thermocouple  18  may further include a reference temperature sensor (not shown) disposed in the junction  18   j  and a reference wire may also be arranged in the cable with the lead wires. The cable may extend to the PLC  10 . 
         [0029]    Alternatively, the contact  18   c  may be mounted to a surface of the yoke  19   y  facing the cutting table  1   t , such as by soldering or brazing, and the contact may extend through an opening formed in the pad  19   p . Alternatively, the shear cutter  1  may be brazed into the pocket and the contact  18   c  may be brazed or soldered onto the cutting table  1   t . Alternatively, the contact  18   c  may be mounted to the substrate  1   s  instead of the cutting table  1   c.    
         [0030]    Once the preparations have been completed, the test may begin. The turntable  8  may be activated to rotate the target cylinder  2 . The PLC  10  may operate the track actuator to position the shear cutter  1  into alignment with an outer surface of the target cylinder  2 . The PLC  10  may then activate the pump  13  so that coolant  15  is sprayed onto the shear cutter  1 . The PLC  10  may then operate the plunger  6  to lower the head  3  until the shear cutter  1  engages the outer surface of the target cylinder  2 . The PLC  10  may continue to operate the plunger  6  to press the shear cutter into the target cylinder until the DOC  16   d  is reached. 
         [0031]      FIG. 3  illustrates a heating cycle of the test. Once the shear cutter  1  has penetrated the target cylinder to the DOC  16   d , the PLC  10  may lock the plunger  6  and may deactivate the pump  13 , thereby halting the flow of coolant  15  and beginning the heating cycle. The PLC  10  may then operate the track actuator to move the head  3  and mounted shear cutter  1  radially inward along a top of the target cylinder  2  as the target cylinder rotates relative thereto. The cutter  1  may shear material from the target cylinder  2  and heat may be generated by the cutting, thereby increasing a temperature  20  of the cutting table  1   t.    
         [0032]      FIG. 4  illustrates the end of the heating cycle. During the heating cycle, the PLC  10  may monitor the thermocouple  18  and compare the measured temperature  20  to the threshold temperature at a sampling frequency, such as once per second. The heating cycle may continue until the temperature  20  increases to the threshold temperature  16   t . The PLC  10  may record the temperature measurements in the memory unit. The PLC  10  may also sample measurements from the load cell  17  and record these measurements in the memory unit at the sampling frequency. 
         [0033]      FIG. 5  illustrates a cooling cycle of the test. Once the PLC  10  detects that the threshold temperature  16   t  has been reached, the PLC may reactivate the pump  13 , thereby spraying the coolant  15  onto the hot shear cutter  1 . The PLC  10  may operate the pump  13  for a period of time equal to the cooling time and then the PLC may deactivate the pump. The cooling time may be selected to quench the hot shear cutter  1  to a cold temperature  21 , such as less than or equal to one-half, one-third, one-fourth, or one-eighth of the threshold temperature  16   t . The PLC  10  may also sample temperature and load cell measurements and record the measurements in the memory unit at the sampling frequency during the cooling cycle. The cutter  1  may remain in engagement with the target cylinder  2  during the cooling cycle. The PLC  10  may halt operation of the track actuator to facilitate cooling. 
         [0034]    Alternatively, the cold temperature  21  may be input to the PLC  10  instead of the cooling time and the PLC  10  may utilize the thermocouple  18  to determine when to terminate the cooling cycle. Alternatively, the pump  13  may be operated during the heating cycle but at a reduced flow rate relative to the cooling cycle. Alternatively, a heating time may be input to the PLC  10  instead of a threshold temperature and the heating cycle may be performed for the heating time regardless of the cutter temperature. Alternatively, the PLC  10  may maintain operation of the track actuator during the cooling cycle. 
         [0035]    Once the shear cutter  1  has reached the inner periphery of the target cylinder  2 , the PLC  10  may operate the plunger  6  to raise the head  3  and the cutter  1  from the target cylinder  2 , move the head and cutter back into alignment with the outer surface of the target cylinder, and operate the plunger to lower the head and cutter into engagement with the target cylinder and further advance the cutter into the target cylinder by the DOC  16   d    
         [0036]    Alternatively once the shear cutter  1  has reached the inner periphery of the target cylinder  2 , the PLC  10  may halt the track actuator, unlock the plunger  6 , and operate the plunger to further advance the cutter into the target cylinder by the DOC  16   d . The PLC  10  may then reverse operation of the track actuator to move the shear cutter  1  radially inward along the target cylinder  2 . 
         [0037]      FIG. 6  illustrates results of tests performed on a plurality of shear cutters. Once the cooling cycle has completed, the heating and cooling cycles may be repeated until the cutter  1  fails. Cutter failure may be detected by the PLC  10  monitoring the load cell measurements during the test. A rapid decrease in the load cell measurements may indicate fracture of the cutting table  1   t . Once failure of the cutting table  1   t  has been detected, the PLC  10  may record the number of test cycles endured by the shear cutter  1  and terminate the test. One test cycle may include one heating cycle and one cooling cycle. The test may be performed on other types of cutters and the test results may be used to compare the types of cutters for selection to install the optimum type on a drill bit. The type of cutters enduring the most number of test cycles may be deemed to have the greatest thermal fatigue resistance. 
         [0038]    Alternatively, a plurality of cutters from each type may be tested and an average from each type may be used to compare the different types. Alternatively, the test may be performed on cutters of the same or similar type but from different batches to ensure quality. 
         [0039]    Advantageously, the present invention may more accurately simulate drilling than the prior art discussed above due to thermal fatigue exerted on a drill bit by drilling stoppages to add joints/stands of drill pipe to the drill string. 
         [0040]    While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope of the invention is determined by the claims that follow.