Patent Publication Number: US-2015059977-A1

Title: Support fixture and cap for the acid etching of pcd cutting inserts

Description:
THE FIELD OF THE INVENTION 
     The present invention relates to acid etching of polycrystalline diamond compact cutting inserts. More specifically, the present invention relates to a support fixture and sealing cap for the acid etching of polycrystalline diamond (PCD) inserts used in drill bits and industrial cutters. 
     BACKGROUND 
     PCD inserts are used to form the cutting tips on underground drill bits, such as those used to drill oil and gas wells. Such inserts are cylindrical in nature, having a substrate which is typically sintered carbide and a layer of sintered polycrystalline diamond on an end of the cylinder. Multiple of such inserts are attached to drill bits as the PCD forms a durable cutting edge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  shows an etching system. 
         FIG. 2  shows a perspective view of a PCD drilling insert. 
         FIG. 3  shows a perspective view of an etching fixture. 
         FIG. 4  shows cross-sectional view of the etching fixture. 
         FIG. 5  shows a detailed view of a section of the etching fixture. 
         FIG. 6  shows another detailed view of a section of the etching fixture. 
         FIG. 7  shows a side view of the etching fixture. 
         FIG. 8  shows a bottom view of the etching fixture. 
         FIG. 9  shows a perspective view of a cap. 
         FIG. 10  shows a bottom view of the cap. 
         FIG. 11  shows a side view of the cap. 
         FIG. 12  shows a top view of the cap. 
         FIG. 13  shows a cross-sectional view of the cap. 
     
    
    
     It will be appreciated that the drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. The embodiments shown accomplish various aspects and objects of the invention. It is appreciated that it is not possible to clearly show each element and aspect of the invention in a single figure, and as such, multiple figures are presented to separately illustrate the various details of the invention in greater clarity. Similarly, not every embodiment need accomplish all advantages of the present invention. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention. 
     Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments or examples. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings are not necessarily drawn to scale. 
     While PCD cutting inserts provide a durable cutting edge, the solvent metal which occupies the interstitial spaces between the diamond crystals can cause degradation of the insert during use. In the sintered diamond layer, the diamond often accounts for about 85 to 95 percent of the PCD, and the remaining material is a metal which acts as a solvent for carbon and a catalyst for diamond formation while sintering the PCD. The fraction of solvent metal is sufficient to cause problems while using the PCD cutting insert. One problem is that the solvent metal expands more with temperature than diamond, and can cause cracking of the PCD layer as the cutting insert is used. Another limitation is that the solvent metal, being a solvent for carbon during the formation of diamond crystals, also acts as a carbon solvent for the degradation of the diamond at elevated temperatures. As such, the solvent metal remaining in the PCD causes the diamond to convert into carbon dioxide, carbon monoxide, or graphite at temperatures near 700 degrees Celsius. As such, it is desirable to remove the solvent metal from the PCD cutting inserts before use. The solvent metal may be etched from the PCD using a mixture of strong acids, such as hydrofluoric and nitric acids (HF and HNO 3 ). 
     Referring to  FIG. 1 , an example system for etching PCD cutting inserts is shown. The system may include an etching fixture  10  and a cap or lid  14  which are used to etch a PCD insert  18 . The PCD insert  18  is typically cylindrical and includes a sintered carbide body with a layer of sintered diamond on an end of the carbide body. The PCD insert  18  is inserted into the fixture  10  so that a portion of the diamond layer protrudes from the bottom of the fixture and the end of the PCD insert can be etched. A cap  14  is placed on the fixture  10  and the fixture  10  is placed into an etching tray  22 . The fixture  10  typically holds the bottom of the PCD insert  18  off of the surface of the etching tray  22  to facilitate etching the PCD insert. Typically, the tray  22  holds a number of fixtures for etching. 
     Concentrated acid  26  is placed into the etching tray  22  so that the acid  26  covers the bottom of the fixture  10  and the exposed bottom end of the PCD insert  18 . The acid  26  is kept at a desired temperature for a desired time period to etch metal from the sintered diamond PCD insert  18 . The inserts  18  may often be etched for a long period of time, and may sometimes be etched for a period of 5 to 10 days in order to remove the solvent metal from the sintered diamond to a desired depth. 
     In removing the solvent metal from the sintered diamond with acid, it is typically necessary to protect the insert substrate from the acid, as it is not desirable to etch or erode the substrate. The fixture  10  provides a sharp delineation between etched and non-etched diamond, allowing the diamond to be etched more consistently and allowing the diamond layer to be etched to a level closer to the substrate. It is also necessary to protect the substrate of the PCD insert from acid vapors while etching the diamond layer. Since the acid  26  is strong, corrosive acid vapors are typically present in the etching tray. 
     The cap  14  is installed on the top of the fixture  10  and seals against the top of the fixture  10  to prevent liquid and vapors from entering the interior of the fixture and etching the insert  18 . The cap  14  creates a slight positive pressure within the fixture  10  when installed on the fixture. The positive pressure helps keep the acid from leaking into the fixture and provides an additional measure of safety in etching the PCD inserts. 
     The fixture  10  and the cap  14  may be injection molded, significantly reducing the cost of the fixture and cap. The fixture  10  is typically a thermoplastic polymer and the cap  14  is typically a thermoplastic elastomer. By reducing the cost of the fixture, the fixture may simply be discarded after use rather than cleaning the fixture for reuse. 
       FIG. 2  shows a typical PCD cutter insert  18 . The insert  18  includes a substrate  30  and a PCD layer  34 . As discussed, the substrate  30  is typically sintered carbide, which is a sintered mixture of metal carbides and metals. The PCD layer  34  is typically sintered diamond and may include about 85 to 95 percent diamond crystals and the remainder an appropriate solvent catalyst metal which is active in sintering diamond at high temperature and pressure. The insert  18  is typically a cylindrical shape, and includes a circular cross section and flat ends. The PCD layer  34  is typically a round disk shape and is bonded to an end of the substrate  30 . 
     The insert  18  is typically about 0.5 inches in diameter and about 0.75 inches in length. The substrate  30  may be about 0.5 inches in diameter and about 0.6 inches in length. The PCD layer  34  may be about 0.5 inches in diameter and between about 0.1 and 0.2 inches in length. The insert  18  may be made in somewhat larger or smaller sizes to fit different sizes of cutting drills. The insert  18  is often manufactured by sintering the carbide and metal substrate  30  and the diamond and metal PCD layer  34  at high temperature and pressure to create a sintered structure having the layers and construction shown. The insert  18  is typically then ground to final dimensions. 
     PCD inserts  18  may commonly be 13, 16 or 19 millimeters in diameter. This application primarily discusses the 13 mm diameter insert as an example. Other sizes of inserts  18  would use a correspondingly sized fixture  10 , with similar clearance or interference in the fit. The 13 millimeter insert may be casually referred to herein as a one half inch insert, since 13 mm is 0.512 inches in diameter. 
     Turning now to  FIG. 3 , a perspective view of the fixture  10  is shown. The fixture  10  has a body  50  which is generally cylindrical, and has a bore  54  therethrough and a base  58  formed at the bottom thereof. The bore  54  is sized to receive a PCD insert  18 . As there are different diameters of PCD inserts, different diameters/sizes of fixtures  10  are made. The base  58  may extend radially outwardly from the bottom of the body  50 . A plurality of feet  62  extend downwardly from the base  58 . The feet  62  elevate the base  58  and the diamond face of the insert  18  which is being etched to raise these off of the bottom of the etching tray  22  and allow for better circulation of the acid  26  around the PCD insert  18 . Using a structure such as feet  62  to elevate the PCD insert  18  off of the tray  22  improves the etching of the insert. 
       FIG. 4  shows a cross-sectional view of the fixture body  50 . As shown, the bore  54  may be made with two sections of different diameter. As shown, the top portion  54   a  of the bore (approximately the top half) is a few hundredths of an inch larger in diameter than an insert  18 , and for this example, may have an inside diameter of about 0.533 inches. The top portion  54   a  may be between 1 and 4 hundredths of an inch larger in diameter than the insert  18 . The lower portion  54   b  of the bore (approximately the lower half) may be smaller in diameter than the top portion  54   a  and larger in diameter than the insert  18 . The lower portion  54   b  may be between about 5 thousandths of an inch and a few hundredths of an inch larger in diameter than the insert  18 , and may be about one hundredth of an inch larger in diameter than the insert  18 . For this example, the lower portion  54   b  of the bore  54  may have a diameter of about 0.525 inches. Having a bore  54  with these relative diameters allows an insert  18  to easily be placed within the fixture body  50  while keeping the insert aligned within the body. 
     A small rib  66  is formed at the bottom of the bore  54 . The rib  66  seals against an insert  18  which is pressed through the top of the bore  54 , through the lower end of the bore  54  and past the rib  66  by a desired amount. 
       FIG. 5  and  FIG. 6  show detailed views of the rib  66 . The rib  66  extends approximately 0.03 inches into the bore  54 , making the diameter of the bore  54  at the rib  66  approximately 0.495 inches. The rib thus forms an interference fit with a 0.512 inch diameter PCD drill insert. It is currently preferred to have a rib  66  which is between about 0.01 inches and 0.04 inches smaller in diameter than the insert  18 , and which may be about 0.02 inches smaller than the insert  18 . In loading the fixture  10 , an insert  18  is placed into the bore  54  with the diamond layer  34  facing down and the insert  18  is pressed through the rib  66  so that the insert  18  extends past the rib  66 . When an insert  18  is pressed into the body  50 , the rib  66  seals against the insert. As shown in  FIG. 5 , the rib  66  may have a radiused upper portion  66   a  which transitions into a lower sealing portion  66   b . The upper portion of the rib  66  may taper and may gradually transition between the bore  54  and the sealing portion of the rib. The upper portion and lower portion may both be between about 0.01 and 0.03 inches in height, and have a protrusion into the bore  54  as discussed. 
     As shown in additional detail in  FIG. 6 , the rib  66  may have an upper portion  66   a  which transitions from the bore  54  to a lower sealing portion  66   b . The sealing portion  66   b  protrudes into the bore  54  as discussed above to create an interference fit between about 0.01 and 0.03 inches with the insert. The upper transition portion  66   a  and the lower sealing portion  66   b  may both between about 0.01 and 0.03 inches in height. The rib  66  may also have a smaller secondary rib  66   c  extending outwardly (i.e. inwardly) from the lower portion  66   b  and further into the bore  54 . The secondary rib  66   c  may typically between about 0.001 and 0.01 inches in both height and width (protrusion into the bore  54 ), and preferably may be about 0.003 inches in height and protrusion into the bore. 
     The upper transition region  66   a  helps the insert move smoothly past the rib  66  without causing damage. The lower sealing region  66   b  presses against the insert  18  to seal against the insert. The secondary rib  66   c , if used, provides a more easily deformable section of material to the sealing rib  66  and can improve the effectiveness and reliability of the sealing rib  66 . 
     Different etching conditions such as time or temperature may affect the inner size of the rib  66 , requiring the rib to be larger or smaller in size. Thus, the interior diameter defined by the rib  66  may be a few hundredths of an inch larger or smaller. Typically, a similar amount of interference is used between the rib  66  and different sizes of inserts  18 , such as a 16 or 19 millimeter insert. That is to say that the difference in size between the inner diameter of the rib  66  and the outer diameter of the insert  18  may be approximately the same. Advantageously, the fixture  10  may be adapted to receive 16 or 19 millimeter diameter inserts by changing the diameter of the body  50  while leaving the diameter of the base  58  and location of the feet  62  the same. This allows the use of the same loading and processing equipment for different insert sizes. 
       FIG. 7  shows a side view of the fixture body  50  with an insert  18  loaded therein. The insert  18  is placed into the top of the bore  54  and pressed downwardly past the rib  66 . A simple pressing jig can be made which contacts the bottom of the base  58  and which allows the insert  18  to move downwardly past the base  58  a predetermined distance before stopping the insert. This allows the insert  18  to be easily and repeatably loaded into the fixture body  50 . The fixture  10  achieves a significant time savings in loading the insert  18  as well as providing a much more accurate and repeatable loading and etching process. The improved accuracy and repeatability of loading and etching allows the diamond layer  34  to be etched closer to the substrate  30 . This improves the performance of the etched insert  18 . 
       FIG. 8  shows a bottom view of the fixture body  50 , showing the placement of the feet  62 .  FIGS. 7 and 8  illustrate how the fixture body  50  keeps the diamond layer  18  off of the bottom of the etching tray  22 , and allows better circulation of acid around the etched face of the diamond layer  18 . This allows for more consistent etching of the diamond layer  18 . 
     The fixture  10  may be formed from a plastic such as polypropylene, polyethylene, polyvinylidene fluoride, polytetraflouroethylene, and mixtures thereof. Other suitable plastics are Liquid Crystal Polymer (LCP) or PolyEtherKetone (PEK). A suitable material is C3350 TR polypropylene co-polymer. 
       FIGS. 9 through 13  show the cap  14 .  FIG. 9  shows a perspective view of the cap  14 .  FIG. 10  shows a bottom view of the cap  14 .  FIG. 11  shows a side view of the cap  14 .  FIG. 12  shows a top view of the cap  14 .  FIG. 13  shows a cross-sectional view of the cap  14 . The cap  14  is used to seal the top of the fixture  10  and to protect certain parts of the insert  18  such as the insert substrate  30  during the etching process. As discussed, it is typically not desirable to etch the substrate  30 . During the etching process, the concentrated acid  26  forms acid vapors. The etching tray  22  is typically used with a lid to contain the acid  26  and protect the acid bath from contaminants. As a result, a corrosive environment of acid vapors exists in the etching tray  22  around the fixtures  10 . The cap  14  particularly keeps acid vapors out of the etching fixture  10  during extended etching processes. 
     The top of the fixture  10  may form a circular wall defined by a smooth round (cylindrical) outer surface, a flat upper surface, and the round interior bore  54 . An example fixture  10  may have a round upper wall which is about 0.05 inches (1.25 mm) thick. The cap  14  is designed to fit over the top of the fixture  10 , and may engage the bore  54 , the outer surface of the body  50 , and the top of the fixture body  50 . The cap  14  may be formed from a thermo plastic elastomer. 
     The cap  14  has a lower surface  70 , a generally cylindrical sidewall  74 , and an upper surface  78 . A groove  82  is formed in the lower surface  70 . The groove  82  extends upwardly into the lower surface  70  of the cap. The edges of the groove may define a cylindrical center plug  84  and an outer circumferential band  88 . The groove  82  fits over the upper wall of the fixture  10  and the cylindrical plug  84  engages the bore  54  while the outer circumferential band  88  engages the outside of the body  50 . The groove  82  may also engage the top of the insert  10 . The upper surface  78  of the cap  14  may include a recessed center portion  86  located inside of the cylindrical plug  84 . The recessed center portion  86  of the top  78  of the cap  14  may allow a relatively uniform thickness of material to be formed above and to the sides of the groove  82 , as is visible in  FIG. 13 . Thus, the bottom  70 , outer side wall  74 , top  78 , and inner side wall  90  may all be approximately the same thickness. An example cap  14  may be about 0.05 inches thick around the groove (i.e. the bottom  70 , outer side wall  74 , top  78 , and inner side wall  90 ). The cap  14  may include a shoulder ridge  94  which extends laterally out from the outer side wall  74 . The lateral shoulder ridge  94  may increase the sealing pressure of the cap  14  against the outside of the fixture  10 . 
     The groove  82  may be formed with internal sealing ridges which assist in sealing between the cap  14  and the fixture  10 . These ridges are particularly visible in  FIG. 13 . A first set of ridges  98  may be formed on inside side wall of the groove  82 . The cap  14  may include 3 inside sealing ridges  98 . These inside ridges  98  may be angled downwardly such that the lower flank of the ridge is more steeply inclined (more perpendicular to the groove  82 ) and the upper flank of the ridge is less steeply inclined than the lower flank of the groove. Additionally, a relatively flat section which is generally parallel to the groove  82  may separate adjacent ridges  98 . 
     A second set of ridges  102  may be formed on the outside wall of the groove  82 . The cap  14  may include 3 outside ridges. The outside sealing ridges  102  may also be angled downwardly and be formed with a lower flank which is more steeply inclined (more perpendicular to the groove  82 ) and an upper flank which is less steeply inclined than the lower flank of the groove. The outside ridges  102  may also be formed with a relatively flat section between adjacent ridges. The lower flanks of the inside ridges  98  and the outside ridges  102  may be formed at approximately a 60 degree angle relative to the side of groove  82 . The upper flanks of the inside ridges  98  and the outside ridges  102  may be formed at approximately a 30 degree angle relative to the side of the groove  82 . A third set of ridges  106  may be formed on the top of the groove  82 . The cap  14  may include two of these upper sealing ridges  106 . 
     An example cap may provide a groove  82  which is about 0.05 inches wide and about 0.2 inches tall. The inner ridges  98  and outer ridges  102  may be about 0.015 inches tall and about 0.03 inches wide at the base. A flat area about 0.02 inches wide may be located between the ridges  98 ,  102 . The upper ridges  106  may be about 0.01 inches tall. The upper ridges may be about 0.01 inches wide at the base and have a space of about 0.01 inches between the upper ridges  106 . 
     In one example, a fixture  10  for a nominal  16  mm insert  18  may have an bore  54  with a top portion  54   a  which is 0.628 inches in diameter (15.95 mm) and a bottom portion  54   b  which is 0.618 inches in diameter (15.7 mm). The outer diameter of the top of the body  50  may be 0.728 inches in diameter (18.49 mm). The cap  14  may have inner ridges  98  with an outer diameter of 0.632 inches (16.05 mm) and outer ridges  102  which are 0.722 inches (18.35 mm) in diameter. The inner ridges  98  may be about 0.004 inches (0.1 mm) larger in diameter than the top portion  54   a  of the bore  54 . The outer ridges  102  may be about 0.006 inches (0.15 mm) smaller in diameter than the outside of the top of the body  50 . The inner ridges  98  may be between 0.002 inches (0.05 mm) and 0.01 inches (0.25 mm) larger in diameter than the top portion  54   a  of the bore  54 . The outer ridges  102  may be between 0.002 inches (0.05 mm) and 0.015 inches (0.6 mm) smaller in diameter than the outside of the top part of the body  50 . 
       FIG. 14  shows a cross-sectional view of the fixture  10  and cap  14  ready for etching an insert  18 . The fixture  10  has a PCD insert  18  which has been loaded into the body  50  by pressing the insert  18  down through the rib  66  to expose a desired length of the sintered diamond layer  34 . After pressing the insert  18  into place, a cap  14  is pressed onto the top of the body  50 . The cap  14  extends downwardly into the bore approximately 0.2 inches. The cap  14  has a slight interference fit with the bore  54  and the outside of the body  50 , sealing against the bore  54  and body  50  as it is pushed into place. As such, inserting the cap compresses the air in the bore  54  and the air in the groove  82  and causes a positive pressure to be formed inside of the bore  54  and groove  82 . This positive pressure helps to keep the etching acid and acid vapors out of the bore  54  while etching the insert  18 , further reducing the risk of leakage. 
     The shoulder ridge  94  of the cap  14  extends outwardly beyond the body  50  of the fixture  10  and forms a lifting flange which makes it easier to move the fixtures  10  into and out of the etching tray  22 . 
     One significant advantage of the fixture  10  is that the boundary between etched and non-etched portions of the diamond layer  18  can be precisely controlled. The rib  66  forms a sharp delineation between etched and non-etched diamond compact. The precise control of the etching boundary allows the insert  18  to be mounted into the fixture  10  with a greater amount of the diamond layer  18  exposed, improving the temperature stability and useful life of the etched insert. 
     Another significant advantage of the fixture  10  is the reduction of leaks during etching. Prior art etching devices have had a failure rate of between 2 and 5 percent. The present fixture  10  has experienced a failure rate of less than one percent. The reduction of the failure rate is significant because of the cost associated with producing the inserts  10  and the time and cost of etching the inserts. The thermoplastic elastomer cap  14  has provided a significant benefit in the etching process as it provides a reliable seal against acid and acid vapors and protects the insert substrate  30  from damage during the etching process. 
     There is thus disclosed an improved etching fixture for PCD drill inserts. The above description of illustrated examples of the present invention, including what is described in the Abstract, are not intended to be exhaustive or to be limitation to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various changes may be made to the present invention without departing from the scope of the claims.