Patent Publication Number: US-7896109-B2

Title: Spacer ring for elastomeric seal

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to earth-boring rotary cone drill bits and in particular to a protective device for protecting the seal of the cone from damage due to debris. 
     2. Description of Related Art 
     Earth-boring bits of the type described herein include a bit body having at least one bearing pin, normally three, and a cone rotatably mounted to each bearing pin. Each cone includes cutting elements for engaging the earth formation as the bit body rotates. The bearing spaces between the cavity of the cone and the bearing pin are typically filled with a lubricant. A seal is located near the mouth of the cone cavity for the purpose of sealing lubricant from drilling fluid. 
     During typical drilling operations, debris, whether it originates from within the drill bit or from the bore hole, can find its way to the seal and cause wear, which in turn can eventually lead to the failure of the seal. One type of seal includes an elastomeric member having an inner diameter in sliding engagement with the bearing pin and an outer diameter that is normally in static engagement with the cone. This type of seal can form a nip area with the bearing pin and allows debris to accumulate near and migrate into the sealing interface. The accumulated debris can cause wear and leakage. In addition, drilling mud or fluid to remove cuttings are circulated at high velocity and can contribute to the degradation of seals. The drilling fluid can include abrasive cuttings which continuously erode the surfaces of the drill bit. 
     Another type of seal used in drill bits employs primary metal-to-metal face seals that are energized by an elastomeric ring. One type of seal assembly employs a secondary elastomeric seal exterior of the energizer ring to protect the primary seal. The secondary seal takes up precious space, and the assembly requires pressure compensation for the space between the two seals. 
     Other designs use an elastomeric ring that has a more wear-resistant elastomeric layer upon the inner diameter. The more wear-resistant layer may comprise a different elastomer, or it may be made up of a wear-resistant fabric. 
     Thus, there exists a need to provide an improved seal for a roller cone drill bit whereby wear and leakage may be minimized. 
     SUMMARY OF THE INVENTION 
     In this invention, a companion ring formed of porous material is positioned between the seal and a side surface of the seal area to prevent the incursion of drill cuttings to the drill bit. 
     In one aspect, an earth boring bit is provided having a bit body that includes a depending bearing pin. The bit includes a cone having a plurality of cutting elements for engaging a bore hole, wherein the cone includes a cavity that rotatably engages the bearing pin. The cone and the bearing pin include a seal area defined by two annular surfaces, one of which rotates relative to the other. The bit includes a seal that includes a forward side surface and a rearward side surface. The seal is positioned between the bearing pin and the cone cavity in sealing engagement with the annular surfaces of the seal area; and a companion ring abutting one of the side surfaces of the seal and positioned between the bearing pin and the cone cavity in non-sealing engagement with the annular surfaces of the seal area, wherein the companion ring is a permeable material. 
     In certain embodiments, the permeable material that includes a fluid compatible with the lubricant lubricating the interface between the bearing pin and the cone cavity. In certain other embodiments, the permeable material is impregnated with a fluid that is compatible with the lubricant lubricating the bearing pin. 
     In another aspect, an earth boring bit is provided that includes a bit body having a depending bearing pin, and a cone having a plurality of cutting elements for engaging a bore hole. The cone includes a cavity that rotatably engages the bearing pin. A groove having a forward side surface, a rearward side surface and a base is formed in the cavity of the cone, and includes a seal in the groove between the bearing pin and the cone. The seal includes a forward side surface and a rearward side surface and has an outer diameter that sealingly engages the base of the groove and an inner diameter that sealingly engages the bearing pin. At least one companion ring is adjacent to the side surface of the seal. The companion ring is formed of a permeable material. The height of the groove is greater than the combined height of the seal and the companion ring. 
     In certain embodiments, the permeable material is compatible with a lubricant operable for lubricating the interface between the bearing pin and the cone cavity. 
     In another aspect, an earth boring bit is provided that includes a bit body having a depending bearing pin and a cone having a plurality of cutting elements for engaging a bore hole. The cone has a cavity that rotatably engages the bearing pin, and the cone and the bearing pin have a seal area defined by two annular surfaces, one of which rotates relative to the other. The bit includes an elastomeric seal having a forward side surface, a rearward side surface and is positioned between the bearing pin and the cone cavity in sealing engagement with the annular surfaces of the seal area. The bit includes a first companion ring abutting the forward side surface of the seal and positioned between the bearing pin and the cone cavity in non-sealing engagement with the annular surfaces of the seal area, wherein the first companion ring is foam material. The bit also includes a second companion ring abutting the rearward side surface of the seal and positioned between the bearing pin and the cone cavity in non-sealing engagement with the annular surfaces of the seal area, wherein the second companion ring is felt material. 
     In another aspect a method of sealing drilling fluid from lubricant in an earth boring drill bit having a cone rotatably mounted on a bearing pin for engaging a borehole is provided that includes the steps of providing a seal area between the cone and the bearing pin defined by two annular surfaces, one of which rotates relative to the other. A seal that includes a forward side surface, a rearward side surface, at least one dynamic seal surface and a least one static seal surface and a companion ring are located between the annular surfaces. The companion ring includes a porous material and is in non-sealing engagement with the seal are. The method further includes rotating the cone on the bearing pin within a borehole and sealing drilling fluid in the borehole from lubricant with a dynamic seal surface of the seal and companion ring, and blocking at least a portion of any drilling fluid or debris that contacts the companion ring from migrating past the companion ring. 
     In certain embodiments, the companion ring is impregnated with a fluid that is compatible with the lubricant lubricating the bearing pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross sectional view of a roller cone drill bit having a seal in accordance with one embodiment of the invention. 
         FIG. 2  is a partial cross sectional view of a seal in accordance with one embodiment of the invention. 
         FIG. 3  is a cross sectional view of another seal in accordance with another embodiment of the invention. 
         FIG. 4  is a cross sectional view of another seal in accordance with another embodiment of the invention. 
         FIG. 5  is a cross sectional view of another seal in accordance with another embodiment of the invention. 
         FIG. 6  is a cross sectional view of a seal in accordance with another embodiment of the invention. 
         FIG. 7  is a cross sectional view of another seal in accordance with another embodiment of the invention. 
         FIG. 8  is a cross sectional view of the inner diameter of a seal in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the drill bit has a bit body  11  that includes at least one bit leg  13 . In certain embodiments, the body  11  includes three bit legs  13 . A bearing pin  15  depends downward and forward from each bit leg  13  toward the axis of rotation of the bit. A cone  17  has a cavity  19  that slides over bearing pin  15 , allowing cone  17  to rotate relative to bearing pin  15 . Cone  17  has a plurality of cutting elements  21  on its exterior. Cutting elements  21  may be tungsten carbide inserts pressed into mating holes, or cutting elements  21  may comprise teeth integrally machined from the body of cone  17 . Cone  17  is held on bearing pin  15  by a locking element, which in one embodiment can include a plurality of balls  23  located in mating annular grooves of bearing pin  15  in cone cavity  19 . 
     A lubricant passage  25  extends through each bit leg  13  from a compensator  27  to the bearing spaces within cavity  19 . A seal  29  is provided to seal lubricant within the bearing spaces. Compensator  27  reduces the pressure differential across seal  29 , which is exposed to borehole pressure on its rearward side and lubricant pressure on its forward side. The surfaces between the bearing pin  15  and the cone  17  are lubricated by grease. The grease fills the regions adjacent to the bearing surfaces and fills various interconnected passageways. The bit includes a grease reservoir, including a pressure compensation subassembly  27  and a lubricant cavity  25 , which is connected to the ball passageway by a lubricant passageway. The grease is retained in the bearing structure and the various passageways by means of seal assembly  29 . Additionally, seal  29  prevents drilled cuttings and drilling fluid from passing the seal and washing out the lubricant and damaging the bearing surfaces. In certain embodiments, companion ring  41  is in non-sealing engagement with the seal area. 
     Referring to  FIG. 2 , one embodiment of an improved seal is provided. Seal  29  is located within seal groove  31  formed in cone cavity  19 . Seal groove  31  is perpendicular to the axis  16  of bearing pin  15  and includes a cylindrical base  34  and parallel flat side walls, which include a forward side surface  36  of the seal groove and a rearward side surface  38  of the seal groove. Seal groove  31  is located a short distance within cavity  19 . Cone  17  has a back face  33  that surrounds the mouth of cavity  19 . Companion ring  41  is located within seal groove  31  between seal  29  and forward side surface  36  of the seal groove. In certain embodiments, companion ring  41  provides positional stability for the seal  29 , thereby restricting or preventing axial movement of the seal within the seal groove  31 . 
     Seal  29  can include an elastomeric ring having an outer diameter  35  and an inner diameter  37 . In certain embodiments, the outer diameter  35  and inner diameter  37  of the seal  29  are generally cylindrical. In certain embodiments, forward side surface  39  and rearward side surface  40  of seal  29  are generally flat. In other embodiments, the forward side surface  39  and rearward side surface  40  of seal  29  have a generally round profile. Other shapes for seal  29  are also feasible. While  FIG. 2  generally shows a high aspect ratio seal and corresponding companion ring, it is understood that in other embodiments a seal having a substantially round cross section may also be used. 
     Companion ring  41  is a porous material forming a ring having an outer diameter  49  that contacts seal groove base  34  and an inner diameter  51  that contacts bearing pin  15 . In certain embodiments, outer diameter surface  49  and inner diameter surface  51  are generally cylindrical. In other embodiments, outer diameter surface  49  and inner diameter surface  51  are generally straight when viewed in cross-section. In certain embodiments, forward side surface  53  of companion ring  41  and rearward side surface  55  of companion ring are generally straight. In certain embodiments, forward side surface  53  of companion ring  41  and rearward side surface  55  of companion ring are generally arcuate. In certain embodiments, the height of companion ring  41  between forward side surface  53  and rearward side surface  55  is less than the height of seal  29 . In certain embodiments, the height of companion ring  41  is less than the distance between the outer diameter of the companion ring  49  and the inner diameter of the companion ring  51 . Generally, the companion ring  41  is disposed between the bearing pin  15  and the seal groove base  34  without forming a seal. In certain embodiments, rearward side surface  55  of the companion ring  41  and seal forward side surface  39  abut each other. The height of seal groove  31  can be greater than the height of companion ring  41  and seal  29 . In certain embodiments, companion ring  41  does not exert lateral force to seal  29 . 
     In certain embodiments, the companion ring is permeable to liquids. In certain embodiments, the companion ring  41  is a porous material includes a liquid that is compatible and/or miscible with the lubricant or grease that is used to lubricate the interface between the bearing pin  15  and the cone cavity  19 . As used herein, compatible means that the liquid does not interfere, disrupt, harm or diminish the performance of the lubricant. The companion ring  41  may be soaked or impregnated with a fluid compatible with the rock bit grease, such as for example, but not limited to, calcium complex containing rock bit grease, lithium complex containing rock bit grease, and the like, as well as perfluoropolyether and perfluoroalkylpolyether lubricants, such as for example, the Krytox® lubricants manufactured by DuPont, and the like. In certain embodiments, the porous material is permeable to a liquid miscible with the grease or lubricant used to lubricate the interface between the bearing pin  15  and the cone  19 . Preferably, the companion ring  41  is soaked or impregnated prior to installation. Preferably, companion ring  41  comprises a material that is chemically and thermally stable. In certain embodiments, companion ring  41  can be made from a variety of materials, including but not limited to, fibrous materials, polyethylene microfibers, polypropylene microfibers, polyester, fiberglass materials, polyesters, polyethylene terephthalate/polypropylene composite materials, and the like. In certain embodiments, companion ring  41  can be made from air filter media of various densities. In certain preferred embodiments, companion ring  41  is deformable. In certain embodiments the companion ring material can absorb up to at least three times its weight of a fluid compatible with the lubricant. In certain other embodiments, the companion ring material can absorb at least  6  times its weight of a fluid compatible with the lubricant. In certain preferred embodiments, the companion ring is a foam material. In certain embodiments, when the companion ring is impregnated with a fluid compatible with the lubricant, a closed cell foam material may be preferred. In certain embodiments, it is anticipated that a closed cell foam material may break and release the impregnated fluid, when subjected to an increased pressure. In certain embodiments, when the companion ring is soaked with a fluid compatible with the lubricant, an open cell foam material may be preferred. 
     In certain embodiments, as shown in  FIG. 3 , companion ring  41  can be composed of two materials of varying density that are bonded together. In alternate embodiments, the companion ring can be formed by two separate unbonded materials. The companion ring first material  70  can be a porous and/or absorbent material and the companion ring second material  72  can be more dense than the companion ring first material  72 . In certain embodiments, the companion ring second material  72  can be less permeable to a lubricant compatible liquid than the companion ring first material  70 . As noted previously, both the first and second materials can be soaked or impregnated with fluid compatible with the grease used to lubricate the interface between bearing pin  15  and the interior cavity of cone  19 . Preferably, the companion ring  41  is soaked or impregnated prior to installation. In certain embodiments, the companion ring second material  72  is substantially denser than the companion ring first material  70 . In certain other embodiments, the companion ring first material  70  is soaked with a fluid compatible with the lubricant or grease used to lubricate the interface between bearing pin  15  and cone cavity  19  and the companion ring second material  72  is not soaked with a fluid compatible with the grease used to lubricate the interface between bearing pin  15  and cone cavity  19 . In certain embodiments, less porous second material  72  is substantially denser than the companion ring first material  70 , and blocks drilling fluids and/or cuttings from migrating to the interface between bearing pin  15  and cone cavity  19 . In certain embodiments, the height of companion ring  41  and the height of the seal  29  are less than the height of seal groove  31 . 
     In certain other embodiments, as shown in  FIG. 4 , companion ring  41  can be positioned between rearward side surface  40  of seal  29  and rearward side surface  38  of seal groove  31 . Placement of the companion ring  41  between rearward side surface  40  of seal  29  and the rearward side surface  38  of seal groove  31  allows the companion ring to function as a debris trap and filter. As noted previously, in certain embodiments, companion ring  41  can be soaked or impregnated with a lubricant or grease compatible fluid. In certain other embodiments, the companion ring  41  is not soaked or impregnated prior to installation. In certain embodiments, the heights of companion ring  41  and the height of seal  29  are less than the height of seal groove  31 . 
     In other embodiments, as shown in  FIG. 5 , two companion rings can be employed. First companion ring  41  can be positioned between forward side surface  39  of seal  29  and forward side surface  36  of seal groove  31 , and second companion ring  74  can be positioned between rearward side surface  40  of seal  29  and rearward side surface  38  of seal groove  31 . In certain embodiments, the heights of companion rings  41  and  74  and the height of seal  29  are less than the height of seal groove  31 . In certain preferred embodiments, first companion ring  41  is soaked or impregnated with a fluid compatible with the lubricant prior to installation and second companion ring  74  is not soaked or impregnated prior to installation. In certain preferred embodiments, first companion ring  41  is a foam material and second companion ring  74  is a felt material. 
     In certain embodiments, as shown in  FIG. 6 , companion ring  41  can include layered structure. The layered structure can include a high density core  80  that is positioned between two low density layers  78  and  82 , respectively. In certain embodiments, the high density material can be resistant to absorbing liquids. In certain embodiments, the high density material can be less porous than the low density material. In certain embodiments, the high density material can be resistant to aqueous based materials, such as for example, aqueous based drilling fluids. In certain embodiments, first low density layer  78  and second low density layer  82  are different materials. In certain other embodiments, first low density layer  78  and second low density layer  82  can be the same materials. 
     In certain embodiments, the porous media of the companion ring positioned between seal  29  and lubricant passage  25  functions in a manner such that the porous media retains and provides additional lubrication to the sliding surface between bearing pin  15  and seal  29 . In certain embodiments, the movement of bearing pin  15  relative to cone cavity  19  causes an amount of grease to be squeezed from companion ring  41 . 
     In certain embodiments, the interior surfaces of cone cavity  19  and bearing pin  15  can be coated with a wear resistant material, such as for example, tungsten, tungsten carbide, silicon carbide, hard facing or a like material or process. In certain embodiments, the companion ring  41  is a material that is wear resistant, or resistant to the movement of the cone cavity relative to the bearing pin. 
     In certain embodiments, the companion ring is a material that is compressible. In certain other embodiments, the companion ring may have a non uniform thickness. 
     In certain embodiments, companion ring  41  is an open cell permeable material. In other embodiments, companion ring  41  is a closed cell permeable material. In certain embodiments, companion ring  41  can be a closed cell material and the inner diameter of the companion ring that contacts the surface of bearing pin  15  may include a textured surface. 
     Referring to  FIG. 7 , an embodiment of an improved seal is provided. Seal  29  is an o-ring having a substantially round cross-section located within seal groove  31  formed in cone cavity  19 . Seal groove  31  is perpendicular to the axis of bearing pin  15  and includes a cylindrical base  34  and parallel flat side walls, which include a forward side surface  36  of the seal groove and a rearward side surface  38  of the seal groove. Seal groove  31  is located a short distance within cavity  19 . Cone  17  has a back face  33  that surrounds the mouth of cavity  19 . A first companion ring  41  is located within seal groove  31  between seal  29  and forward side surface  36  of the seal groove. Seal  29  can include an elastomeric ring having an outer diameter  35  and an inner diameter  37 . As seal  29  is substantially round, it includes a curved forward side surface  39  and a curved rearward side surface  40 . 
     First companion ring  41  is a porous material forming ring having an outer diameter  49  that contacts seal groove base  34  and an inner diameter  51  that contacts bearing pin  15 . In certain embodiments, outer diameter surface  49  and inner diameter surface  51  are generally cylindrical. In other embodiments, outer diameter surface  49  and inner diameter surface  51  are generally straight when viewed in cross-section. Forward side surface  53  of companion ring  41  is generally flat. Rearward side surface  55  of companion ring  41  follows the curvature of the side of seal  29  and is generally curved for mating contact. In certain embodiments, the height of companion ring  41  between forward side surface  53  and rearward side surface  55  is less than the height of seal  29 . In certain embodiments, the height of companion ring  41  is less than the distance between the outer diameter of companion ring  41  and inner diameter of companion ring  41 . In certain embodiments, first companion ring  41  is permeable to a fluid compatible with the lubricant. First companion ring  41  preferably does not sealingly engage seal groove base  34  and bearing pin  15 . In certain embodiments, first companion ring  41  is soaked or impregnated with a fluid compatible with the lubricant lubricating the bearing pin  15  prior to installation. 
     Optionally, a second companion ring  83  formed of a porous material and having an outer diameter  84  that contacts seal groove base  34  and an inner diameter  86  that contacts bearing pin  15 . In certain embodiments, outer diameter surface  84  and inner diameter surface  86  are generally cylindrical. In other embodiments, outer diameter surface  84  and inner diameter surface  86  are generally straight. In yet other embodiments, outer diameter surface  84  and inner diameter surface  86  are generally arcuate. Forward side surface  88  of second companion ring  83  follows the curvature of the side of seal  29  and is generally curved. Rearward side surface  90  of second companion ring  83  is generally flat. In certain embodiments, the height of second companion ring  83  between forward side surface  88  and rearward side surface  90  is less than the height of seal  29 . In certain embodiments, the height of second companion ring  83  is less than the distance between outer diameter  84  of the second companion ring and inner diameter  86  of the companion ring. In certain embodiments, the second companion ring  83  is permeable to a fluid compatible with the lubricant. Preferably, first companion ring  41  and second companion ring  83  do not form a sealing engagement with seal groove base  34  and bearing pin  15 . In certain embodiments, second companion ring  83  is not soaked or impregnated with a fluid compatible with the lubricant lubricating the bearing pin  15  prior to installation. 
     In certain embodiments, companion ring  41  supplies grease or other lubricant to the seal, such as for example, when the seal begins to wear. In certain embodiments, companion ring  83  prevents drill cuttings and drilling fluids, such as for example, aqueous or non-aqueous based drilling muds, from entering the cone cavity. In certain embodiments companion ring  83  prevents drill cuttings and drilling fluids from contacting the seal. In certain embodiments, first companion ring  41  is a foam material and second companion ring  83  is a felt material. In certain embodiments, first companion ring  41  is a felt material and second companion ring  83  is a foam material. In other embodiments, first companion ring  41  and second companion ring  83  are a felt material. In certain embodiments, first companion ring  41  and second companion ring  83  are a foam material. 
     In certain embodiments, the seal may include notch or recess in either the forward or rearward side surface adjacent to companion ring forward side surface adapted to matingly receive a pin or tab positioned on the adjacent side surface of companion ring. The mating engagement of notch or recess with pin or tab on the companion ring allows for the seal and companion ring to be coupled to one another. Alternatively, the notch or recess can be located on the forward side surface of the companion ring and the pin or tab can be located on the rearward side surface of the seal. 
     In certain embodiments, the seals can be formed entirely from a single elastomeric material. In other embodiments, the seal body can be formed of one material and the seal surfaces contacting either the bearing pin or the cone cavity can be a different material. 
     A variety of different surface textures can be employed on companion ring  41 . In certain embodiments, as shown in  FIG. 8 , companion ring  41  can include one or more undulating or wavy ridges that traverse inner diameter surface  51  of companion ring  41 . In other embodiments, the outer diameter of companion ring  41  can include a textured surface. In yet other embodiments, both inner  51  and outer  49  diameters of companion ring  41  can include a textured surface. The undulating wavy textured surface can apply varying pressure in the circumferential direction at the inner diameter of seal  29 . In certain embodiments, the textured or wavy surface has a height of less than about 400 microns. In certain embodiments, the textured or wavy surface has a height is between about 100 and 400 microns. In certain embodiments, textured surface  43  is in sliding engagement with the bearing pin and the waviness generates pumping action to lubricate the inner diameter surface  37  of the seal  29 . 
     In certain embodiments, companion ring  41  has a height less than the height of seal  29 . In certain embodiments, companion ring  41  does not create a seal with bearing pin  15 , but instead provides a surface that prevents the unwanted migration of debris into the seal, but allows the passage of fluid. In certain embodiments, textured surface blocks the passage of debris. In other embodiments, textured surface traps debris. In yet other embodiments, textured surface  3  promotes hydrodynamic lubrication of the fluid. 
     In certain embodiments, as shown in  FIG. 2 , outer diameter  35  of seal  29  and outer diameter  49  of companion ring  41  are approximately equivalent. In certain other embodiments, inner diameter  37  of seal  29  and inner diameter  51  of companion ring  41  are approximately equivalent. 
     Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope and spirit of the invention. Accordingly, the exemplary embodiments of the invention described herein are set forth without any loss of generality to, and without imposing limitations thereon, the present invention. 
     As used herein, optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur. 
     As used herein, recitation of the term about and approximately with respect to a range of values should be interpreted to include both the upper and lower end of the recited range. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 
     As used in the specification and claims, the singular form “a”, “an” and “the” may include plural references, unless the context clearly dictates the singular form. 
     Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations thereon, the claimed invention. 
     Throughout this application, where patents or publications are referenced, the disclosures of these references in their entireties are intended to be incorporated by reference into this application, in order to more fully describe the state of the art to which the invention pertains, except when these reference contradict the statements made herein.