Patent Publication Number: US-2022234151-A1

Title: Method for forming cutters

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     See Application Data Sheet. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
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     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC OR AS A TEXT FILE VIA THE OFFICE ELECTRONIC FILING SYSTEM (EFS-WEB) 
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     STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to polycrystalline diamond compact cutters on a drill bit. More particularly, the present invention relates to a method for forming cutters. The present invention relates to protecting the cutter during leaching to remove the metallic binder of the cutter body. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     Polycrystalline diamond compact (PDC) cutters are commonly used in drilling operations for oil and gas. PDC cutters are diamond tipped protrusions on a drill bit. The PDC cutters form the cutting surface of the drill bit with diamond, while the drill bit can be comprised of other materials. Drill bits were tipped with diamond for improved cutting efficiency through rock formations. Bonding diamond to metal is a challenge. 
     A basic PDC cutter is comprised of a diamond table made from diamond grit with binder and a substrate of another composite material, usually tungsten carbide, and metallic binder, usually cobalt. The diamond grit is sintered under high temperature and high pressure conditions, forming a layer as a diamond table bonded to the tungsten carbide or other substrate. The High Temperature-High Pressure (HT-HP) press can form the diamond table with a Cobalt or other Group VIII element as the catalyst binder, and the properties of the layer have been modified for various thicknesses, profiles, and patterns to affect the working life of the cutters. 
     The PDC cutter is further processed to withstand the downhole conditions of extreme pressures and high temperatures. Excessive heat, over 750 degrees Celsius, causes thermal expansion of the diamond-binder bond in the diamond table, causing changes to the integrity of the cutter. To reduce the susceptibility to high temperatures, the cutter is subjected to a leaching process, which removes metallic binder from the diamond table using acid. Selective leaching removes the binder, usually cobalt, in different percentages through the volume of the diamond table so that the cutter is resistant to thermal expansion. However, the selective leaching affects other properties of the cutter, such as fracture toughness. Even though the cutter is more resistant to thermal expansion, the cutter may be less tough. 
     Various patents have issued, and various applications have been published in the field of measuring PDC compact cutters. U.S. Patent Publication No. 2007/0169419A1, published on 26 Jul. 2007 for Davis et al, describes sonochemical leaching of polycrystalline diamond. U.S. Patent Publication No. 2012/0151847A1, published on 21 Jun. 2012 for Ladi et al, describes another type of leaching of polycrystalline diamond elements. U.S. Patent Publication No. 2013/0247478A1, published on 26 Sep. 2013 for Bellin et al, also discloses a leaching process. U.S. Patent Publication No. 2015/0014067A1, published on 15 Jan. 2015 for Muzzi et al, discloses another leaching process with cutter protection. 
     The prior art O-ring of the known methods is made of fluoroelastomers with good acid resistance, such as fluoroelastomer (FKM) or a copolymer of tetrafluoroethylene and propylene (FEPM). However, the sealing force of the prior art O-ring in acids at high temperatures cannot be maintained. The acid degrades the prior art O-ring over time, which results in the damage to substrate or insufficient removal of the metallic binder from the diamond table. The percentage of removing of cobalt from the diamond table or the pattern of removed cobalt is incomplete. Due to the manufacturing process, prior art PDC cutters can be made with low quality or even be fatally defective. 
     It is an object of the present invention to form a polycrystalline diamond compact (PDC) cutter. 
     It is an object of the present invention to increase the time and cost efficiency of forming a PDC cutter. 
     It is another object of the present invention to maintain the sealing force of an O-ring during the step of leaching when forming a PCD cutter for a drill bit. 
     It is still another object of the present invention to apply a protective layer to an O-ring during the step of leaching when forming a PCD cutter. 
     It is yet another object of the present invention to have less hardness reduction of a protected O-ring during the step of leaching conditions when forming a PCD cutter. 
     It is yet another object of the present invention to have less modulus reduction of a protected O-ring during the step of leaching conditions when forming a PCD cutter. 
     These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The method for forming cutters includes setting a back cap into a pod so as to form an assembly with a pod cavity and applying a protective layer on an O-ring so as to form a protected O-ring. The protected O-ring is placed around a cutter body having a substrate section and diamond section with a metallic binder. The method includes inserting the cutter body into the pod cavity so as to seal the substrate section within the pod. An end portion of the diamond section extends outward from the pod. The method also includes leaching the metallic binder through the end portion of the diamond section for at least one day or 1-3 days at 60 degrees Celsius or higher so as to form a polycrystalline diamond compact cutter from the cutter body. The protected O-ring seals the substrate section from the leaching conditions, such as strong acids. The protected O-ring becomes an exposed O-ring in the step of leaching, having a hardness reduction relative to the protected O-ring and a modulus reduction relative to the protected O-ring. The hardness reduction and the modulus reduction of the exposed O-ring are less than the hardness reduction and the modulus reduction than an exposed unprotected O-ring, that is, an O-ring without the protective layer of the invention. The exposed O-ring can maintain a sealing force to protect the substrate for at least one day or 1-3 days, while achieving the target profile of the diamond table during that one day or 1-3 days. 
     In one embodiment, the step of applying the protective layer is coating a poly (para-xylene) on the O-ring so as to form a coated layer as the protective layer. 
     In another embodiment, the step of applying the protective layer is coating a fluoropolymer on the O-ring so as to form a fluoro-coated layer as the protective layer. The step of coating the fluropolymer includes applying the fluoropolymer by liquid suspension on a surface of the O-ring, drying the fluoro-coated layer, and heating the fluoro-coated layer and the O-ring to form the protected O-ring. Alternatively, the step of coating the fluropolymer includes melt-coating the fluoropolymer on the O-ring. 
     In still another embodiment, the step of applying the protective layer is fluorinating a surface of the O-ring so as to form a fluorination layer as the protective layer. 
     In yet another embodiment, the step of applying the protective layer is encapsulating the O-ring with an encapsulated fluoropolymer so as to form an encapsulated layer as the protective layer. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional view of an assembly for manufacturing cutters according to the present invention. 
         FIG. 2  is an elevation view of the assembly of  FIG. 1 . 
         FIG. 3  is a perspective view of the assembly of  FIG. 1 . 
         FIG. 4  is an elevation view of the polycrystalline diamond compact cutter from the cutter body after the step of leaching. 
         FIG. 5  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the coated layer as the protective layer of the present invention. 
         FIG. 6  is a graph illustration of Modulus Reduction for O-rings according to the embodiment of the coated layer as the protective layer of the present invention. 
         FIG. 7  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the fluorinated layer as the protective layer of the present invention. 
         FIG. 8  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the encapsulated layer as the protective layer of the present invention. 
         FIG. 9  is a graph illustration of Modulus Reduction for O-rings according to the embodiment of the encapsulated layer as the protective layer of the present invention. 
         FIGS. 10A, 10B, 11A, 11B, 12A, 12B, 13A and 13B  show photographs of embodiments of the O-ring being comprised of FKM and specific embodiments of PFA and FEB as the encapsulated fluoropolymer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a protective layer for an O-ring to withstand the exposure to high strength acidic conditions and high temperatures while maintaining sufficient sealing force in a method of forming a PDC cutter. Protecting the O-ring from degradation by a protective layer must be balanced against increasing hardness reduction. The additional complications are the elevated temperature conditions and reduced time of exposure. Being able to withstand the acid for longer periods of time still must accommodate the time needed to seal for leaching. The present invention is a method that applies a layer to the O-ring that adds protection from acid at higher temperatures, while still being able to seal for the time needed for leaching metallic binder from the diamond table. The method maintains enough hardness and modulus for sufficient sealing force against the cutter body for the needed time in the high strength acidic and high temperature conditions. 
       FIG. 1  shows a cross-sectional view of an assembly  10  for manufacturing cutters.  FIG. 2  is an elevation view of the assembly  10  of  FIG. 1 , and  FIG. 3  is a perspective view of the assembly  10  of  FIG. 1 . The method of the present invention includes setting a back cap  12  into a pod  14  so as to form the assembly  10  with a pod cavity  16 . The pod  14  can be comprised of at least one of polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), ethylenetetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidenefluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), and ethylene chlorotrifluoroethylene (ECTFE). 
       FIG. 4  is an elevation view of the polycrystalline diamond compact cutter  40  from the cutter body  30  after the step of leaching.  FIG. 4  also shows an elevation view of the exposed O-ring  42 . In the present invention, the method includes applying a protective layer  22  on the O-ring  20  so as to form a protected O-ring. The O-ring can be comprised of at least one of nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), Ethylene-propylene diene monomer (EPDM), Epichlorohydrin (ECO), Polyacrylic rubber (ACM), Fluorosilicone rubber (FVMQ), Fluoroelastomers (FKM), Copolymer of tetrafluoroethylene and propylene (FEPM), perfluoroelastomer (FFKM), and Silicone rubber. The protected O-ring undergoes the step of leaching so as form the exposed O-ring  42 . 
       FIGS. 1-3  show the steps of placing the protected O-ring around a cutter body  30 .  FIGS. 1-4  show the cutter body being comprised of a substrate section  32  and diamond section  34  being comprised of a metallic binder  36 . The substrate section  32  can be tungsten carbide, and the metallic binder  36  can be cobalt. Then, the cutter body  30  is inserted into the pod cavity  16  so as to seal the substrate section  32  within the pod  14  of  FIGS. 1-2 . 
     The diamond section  34  is comprised of an end portion  38  extending outward from the pod  14 . The end portion  38  is sealed to the substrate section  32  by the protected O-ring. In the present invention, the method includes leaching the metallic binder  36  through the end portion  38  of the diamond section  34 . Strong acids, such as HF, HNO 3 , H 2 SO 4 , or hydrogen peroxide, or the combination of two or more of the chemicals, can be used to remove the metallic binder  36  from cutter body  30  in the step of leaching. The O-ring  20  as the protected O-ring isolates the substrate section  32  from the strong acid. The integrity of the substrate section  32  is maintained to prevent a fatally flawed cutter. 
     Again, protection from acid damage is not the only functionality of the present invention. The total process time depends on the solution bath conditions, including acid strength and temperature, and the seal of the substrate section  32  must be maintained for the total process time. In the present invention, the step of leaching is for at least one day or 1-3 days at 60 degrees Celsius or higher so as to form a polycrystalline diamond compact cutter  40  from the cutter body  30  in  FIG. 4 . Any target profile of the diamond section  34  or diamond table can be achieved at this elevated temperature and during the time period for the percentage and distribution of remaining metallic binder  36  to be set in the diamond section  34 . The present invention removes the metallic binder  36  in the designated thickness of the diamond table or diamond section  34  of the PDC cutter  40  with damage to the substrate section  32 . The PDC cutter  40  of the present invention has more consistent quality and higher quality because the target profile of the diamond table can be achieved before failure of the protected O-ring. There is no premature stoppage of the leaching step of the prior art for preserving the protection of the substrate section. 
       FIG. 4  also shows the exposed O-ring  42  from the protected O-ring and initial O-ring  20  from the method of the present invention. The exposed O-ring  42  has a hardness reduction relative to the protected O-ring and a modulus reduction relative to the protected O-ring. The exposed O-ring  42  avoids a fatally device PDC cutter by maintaining the seal of the exposed O-ring  42  on the cutter body  30 . In particular, the exposed O-ring  42  has a hardness reduction less than a hardness reduction of an exposed unprotected O-ring, that is, an O-ring without the protective layer of the present invention, relative to an unprotected O-ring. The exposed O-ring  42  also has a modulus reduction less than a modulus reduction of the exposed unprotected O-ring relative to the unprotected O-ring. 
     In one embodiment of the present invention, the step of applying the protective layer  22  is comprised of the steps of: coating a poly (para-xylene) on the O-ring  20  so as to form a coated layer as the protective layer  22 . The coated layer can have a thickness of at least 1 micrometer or a range of 1-5 micrometers. In the present invention, the poly (para-xylene) is comprised of at least one of a group consisting of: 
     
       
         
         
             
             
         
       
     
     In an embodiment of the coated layer as the protective layer  22 , the step of leaching the metallic binder is for 1-3 days at 60 degrees Celsius or higher, and the exposed O-ring has a hardness reduction of less than 20% as shown in  FIG. 5 .  FIG. 5  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the coated layer as the protective layer  22 .  FIG. 5  shows the O-ring  20  being comprised of FKM and specific embodiments of Coating (b) and Coating (c). 
     In the embodiment of the coated layer as the protective layer  22 , the step of leaching the metallic binder is for 1-3 days at 60 degrees Celsius or higher, and the exposed O-ring has a modulus reduction of less than 90% as shown in  FIG. 6 . The method of the present invention includes the exposed O-ring  42  having both the hardness reduction of less than 20% and the modulus reduction of less than 90%. In an alternate embodiment, the step of leaching the metallic binder is one day at 60 degrees Celsius or higher, wherein the exposed O-ring has a modulus reduction less than 60% as shown in  FIG. 6 .  FIG. 6  is a graph illustration of Modulus Reduction for O-rings according to the embodiment of the coated layer as the protective layer  22 .  FIG. 6  shows the O-ring  20  being comprised of FKM and specific embodiments of Coating (b) and Coating (c), similar to  FIG. 5 . The exposed O-ring  42  has both hardness and elasticity to seal the substrate section, while remaining intact against the highly acidic and high temperature conditions to effectively leach the diamond table as needed for high quality reliable cutters. The present invention identifies a time window so that many types of cutters and many patterns of diamond tables can be manufactured with quality and reliability. 
     In another embodiment of the present invention, the step of applying the protective layer  22  is comprised of the steps of: coating a fluoropolymer on the O-ring  20  so as to form a fluoro-coated layer as the protective layer  22 . The fluoro-coated layer can have a thickness of greater than 1 micron or a range of 1-5 micrometers. In the present invention, the fluoropolymer is comprised of at least one of a group consisting of: polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), ethylenetetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidenefluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), and ethylene chlorotrifluoroethylene (ECTFE). 
     The step of coating the fluropolymer is comprised of the steps of: applying the fluoropolymer by liquid suspension on a surface of the O-ring  20 , drying the fluoro-coated layer so as to remove water, and heating the fluoro-coated layer and the O-ring  20  so as to form the protected O-ring. Alternatively, the step of coating the fluropolymer is comprised of melt-coating the fluoropolymer on the O-ring  20 . 
     In still another embodiment of the present invention, the step of applying the protective layer  22  is comprised of the steps of: fluorinating a surface of the O-ring  22  so as to form a fluorination layer as the protective layer  22 . The fluorination layer can have a thickness of greater than 2 micrometers or a range of 2-4 micrometers. In one embodiment of the fluorinated layer as the protective layer  22 , the step of leaching the metallic binder is 1-3 days at 60 degrees Celsius or higher, and the exposed O-ring has a hardness reduction relative to the protected O-ring less than 20% as shown in  FIG. 7 .  FIG. 7  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the fluorinated layer as the protective layer  22 .  FIG. 7  shows the O-ring  20  being comprised of FKM and specific embodiments of fluorinated layer at 2 micrometer thickness and 5 micrometer thickness. 
     In yet another embodiment of the present invention, the step of applying the protective layer is comprised of the steps of: encapsulating the O-ring  20  with an encapsulating fluoropolymer so as to form an encapsulated layer as the protective layer  22 . The encapsulated layer can have a thickness with a range of 1-20 micrometers. In the present invention, the encapsulated fluoropolymer is comprised of at least one of a group consisting of: polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), ethylenetetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidenefluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), and ethylene chlorotrifluoroethylene (ECTFE). 
     In one embodiment of the encapsulated layer as the protective layer  22 , the step of leaching the metallic binder is 1-3 days at 60 degrees Celsius or higher, and the exposed O-ring has a hardness reduction relative to the protected O-ring less than 5%.  FIG. 8  is a graph illustration of Hardness Reduction for O-rings according to the embodiment of the encapsulated layer as the protective layer  22 .  FIG. 8  shows the O-ring  20  being comprised of FKM and specific embodiments of PFA and FEB as the encapsulated fluoropolymer. 
     In another embodiment of the encapsulated layer as the protective layer  22 , the step of leaching the metallic binder is for 1-3 days at 60 degrees Celsius or higher, and the exposed O-ring has a modulus reduction relative to the protected O-ring less than 20% as shown in  FIG. 9 . The method of the present invention includes the exposed O-ring  42  having both the hardness reduction of less than 5% and the modulus reduction of less than 20%.  FIG. 9  is a graph illustration of Modulus Reduction for O-rings according to the embodiment of the encapsulated layer as the protective layer  22 .  FIG. 9  shows the O-ring  20  being comprised of FKM and specific embodiments of PFA and FEB as the encapsulated fluoropolymer, similar to  FIG. 8 . 
     The embodiment of the encapsulated layer as the protective layer  22  further identifies a critical range. With less than 1 day (24 hours) at 100 degrees Celsius and the acidic conditions in the step of leaching, there is a failure which renders the exposed O-ring nonfunctional. Similar to  FIGS. 8-9 ,  FIGS. 10A, 10B, 11A, 11B, 12A, 12B, 13A and 13B  show photographs of the O-ring  20  being comprised of FKM and specific embodiments of PFA and FEB as the encapsulated fluoropolymer, respectively.  FIG. 10A and 10B  show the FKM O-ring with PFA encapsulated layer and the FKM O-ring with FEB encapsulated layer respectively as protected O-rings without any leaching.  FIGS. 11A and 11B  show the FKM O-ring with PFA encapsulated layer and the FKM O-ring with FEB encapsulated layer respectively after leaching conditions in acid 6 hours at 100 degrees Celsius. There are noticeable cracks in the O-ring, even as the encapsulated layer is maintained.  FIGS. 12A and 12B  also show the FKM O-ring with PFA encapsulated layer and the FKM O-ring with FEB encapsulated layer respectively after leaching conditions in acid 24 hours at 100 degrees Celsius. There are noticeable cracks in the O-ring, even as the encapsulated layer is maintained. 
     However,  FIGS. 13A and 13B  show the FKM O-ring with PFA encapsulated layer and the FKM O-ring with FEB encapsulated layer respectively after leaching conditions in acid 72 hours at 100 degrees Celsius. The O-rings are both intact, and the corresponding encapsulated layers are maintained. The removal from leaching conditions appears to affect the shorter exposure, while the threshold to maintain the O-ring is between 1-3 days. 
     The present invention is a method for forming a polycrystalline diamond compact (PDC) cutter for a drill bit. In the prior art processes, the step of leaching can take up to 21 days in order to achieve the target profile of the diamond table. There are extensive time and costs for this weeks-long process. When previously compensating for these short-comings, the acids are stronger to reduce the time needed to achieve the target profile. However, these acids damage the substrate of the cutter such that the PDC cutter would have a higher chance of fatal defects. O-rings were used to protect the substrate, but the O-ring were still reactive to the strong acids in the leaching process. In order to preserve the O-ring and consequently, the substrate, the step of leaching was too short to achieve the target profile. The method of the present invention provides steps to identify a time window for forming cost efficient high quality and reliable PDC cutters. The method includes applying a protective layer to the O-ring so as to form a protected O-ring, while also increasing the temperature of the step of leaching beyond the prior art and determining a time window for sealing with sufficient hardness and elasticity in the highly acidic and high temperature conditions. Beyond applying a protective layer to withstand the strong acid of the step of leaching, the present invention elevates temperature and identifies the time window. The method maintains the sealing force of an O-ring during the step of leaching when forming a PCD cutter for a drill bit. There is a hardness reduction of a protected O-ring during the step of leaching conditions when forming a PCD cutter. There is a modulus reduction of a protected O-ring during the step of leaching conditions when forming a PCD cutter. The hardness reduction and modulus reduction determine a time window of manufacturing a high quality and reliable cutter because the substrate section remains sealed under the highly acidic and high temperature conditions. Additionally, the amount of hardness reduction and the amount of modulus reduction set time in the acid and temperature conditions of the step of leaching to achieve the target profile with consistency and reliability. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention.