Patent Grant
8020638
Not Applicable.
Not Applicable.
1. Field of the Invention
The invention relates generally to seal assemblies for sealing between a rotating and a static member. In one particular aspect, the invention relates to seals for rolling cone bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. In a more particular aspect, the invention relates to seals that are employed to seal and protect the bearing surfaces between a rolling cone cutter and the journal shaft on which it rotates.
2. Background of the Invention
An earth-boring drill bit is typically mounted on the lower end of a drill string. With weight applied to the drill string, the drill string is rotated such that the bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone.
A typical earth-boring bit includes one or more rotatable cone cutters. The cone cutters roll and slide upon the bottom of the borehole as the drillstring and bit are rotated, the cone cutters thereby engaging and disintegrating the formation material in their path. The rotatable cone cutters may be described as generally conical in shape and are therefore referred to as rolling cones.
Rolling cone bits typically include a bit body with a plurality of journal segment legs. The rolling cones are mounted on bearing pin shafts (also called journal shafts or pins) that extend downwardly and inwardly from the journal segment legs. As the bit is rotated, each cone cutter is caused to rotate on its respective journal shaft as the cone contacts the bottom of the borehole. The borehole is formed as the action of the cone cutters removes chips of formation material (“cuttings” or “drilled solids”) which are carried upward and out of the borehole by the flow of drilling fluid which is pumped downwardly through the drill pipe and out of the bit. Liquid drilling fluid is normally used for oil and gas well drilling, whereas compressed air is generally used as the drilling fluid in mining operations.
Seals are positioned in glands formed between the rolling cones and their journal shafts to prevent lubricant from escaping from around the bearing surfaces and to prevent the cutting-laden, abrasive drilling fluid from entering between the cone and the shaft and damaging the bearing surfaces. When cuttings and/or abrasives are conveyed into the seal gland, they tend to adhere to the gland and/or seal component surfaces, and may cause deformation, damage and/or slippage of the seal components. Moreover, the cuttings can accelerate abrasive wear of all seal components and of the bearing surfaces.
In oil and gas drilling, the cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed before reaching the targeted formation. This is the case because each time the drill bit wears out or fails as a borehole is being drilled, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section by section in order to replace the bit. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section by section. The amount of time required to make a round trip for replacing a bit is essentially lost from drilling operations. As is thus obvious, this process, known as a “trip” of the drill string, requires considerable time, effort and expense. It is therefore advantageous to maximize the service life of a drill bit. Accordingly, it is always desirable to employ drill bits that will be durable enough to drill for a substantial period of time with acceptable rate of penetration (ROP).
The durability of a bit and the length of time that a drill bit may be employed before it must be changed depend upon numerous factors. Importantly, the seals must function for substantial periods under extremely harsh downhole conditions. The type and effectiveness of the seals greatly impact bit life and thus, are critical to the success of a particular bit design.
One cause of bit failure arises from the severe wear or damage that may occur to the bearings on which the cone cutters are mounted. These bearings can be friction bearings (also referred to as journal bearings) or roller type bearings, and are typically subjected to high drilling loads, high hydrostatic pressures, and high temperatures.
As previously mentioned, the bearing surfaces in typical bits are lubricated. Seals between the journal shaft and the rotating cone mounted to the journal shaft serve to retain lubricant within the bit and prevent cutting-laden and abrasive drilling fluid from passing to the bit bearings. The seal is typically in the form of a ring disposed between the journal shaft and the rotating cone mounted to the journal shaft. Further, the seal typically includes a dynamic seal surface placed in rotating contact against the journal shaft surface, and a static seal surface that engages the rotating cone. In other words, this conventional seal rotates along with the cone relative to the journal shaft. Although the bit will experience severe and changing loading, as well as a wide range of different temperature and pressure conditions, the dynamic and static seal surfaces must nevertheless remain sealingly engaged in order to prevent the lubricant from escaping and/or cuttings from entering the lubricated areas, and should perform these duties throughout the life of the bit's cutting structure.
A variety of seal types are known in the art. These include O-ring type seals made of rubber or other elastomeric material. The service life of bits equipped with such elastomeric seals is generally limited by the ability of the seal material to maintain sealing engagement at each dynamic and static seal surface while withstanding the different temperature and pressure conditions at each dynamic and static seal surface.
The conditions at the dynamic seal surface of the seal are often more harsh than the conditions at the static seal surface. This is typically the case because the relative motion at the dynamic seal surface often results in increased friction, increased temperatures, increased abrasion, and increased wear. Consequently, failure of most conventional seals occurs at the dynamic seal surface that dynamically engages the journal shaft. Failure of the seal at the journal shaft surface may undesirably provide a relatively direct path for entrance of cutting-laden drilling fluid into the inner workings of the rock bit.
Internal pressures within rock bits are caused by the elevated temperatures that occur within a bit during operation, as well as the elevated temperature of the downhole environment. In some deep hole drilling applications, internal rock bit temperatures can go as high as 300° F. and beyond. During any drilling operation the pressure of drilling mud external the rock bit may be higher than 10,000 psi (˜68 MPa). This pressure is typically equalized within a bit by the pressure compensation subassembly, so that the annular seal has substantially equivalent pressure acting on both the mud side (i.e., the side of the annular seal positioned adjacent the bit external environment) and the bearing side (i.e., the side of the annular seal positioned distal the external environment and adjacent the bit bearing) of the seal. This pressure equalization is important for purposes of maintaining proper seal positioning within the seal gland in the bit.
However, in some cases, an unchecked differential pressure may arise and exert an undesired pressure force on the seal in an axial direction within the seal gland within which it is seated. The direction that the seal is urged depends on whether the bit external or internal pressure is controlling, which will depend on the particular bit design, drilling application and operating conditions. In situations where the bit external pressure is controlling, the annular seal will be forced inwardly within the seal gland in an axial direction along the journal axis. In situations where the bit internal pressure is controlling, the annular seal will be forced axially outwardly within the seal gland towards the bit external environment. In either case, if a sufficient pressure differential exists between the internal and external pressures, a sidewall portion of the seal may be urged and extruded into a clearance or groove extending from the seal gland that is formed between the cone and journal shaft. The portions of the seal that extrude into the clearance or groove adjacent the seal gland may become pinched between the rotating cone and static journal shaft, potentially leading to “nibbling” and/or excessive wear or damage to the seal. Due to the relative movement and harsher conditions encountered at dynamic seals, portions of the seal proximal dynamic seal surfaces are especially susceptible to undesirable extrusion and nibbling.
The internal temperatures within the drill bit, especially the temperature of sealing surfaces that engage seals between the journal shaft and the rotating cone mounted to the journal shaft, can impact the performance, wear, and lifetime of such seals within the drill bit. For instance, temperatures in excess of 250° to 300° F. may result in undesirable breakdown of elastomeric seals. In addition, higher seal temperatures generally cause the seal to expand. The expansion of the seal may result in increased engagement, friction, and wear at the dynamic seal surface, which in turn further increase the seals temperatures. This viscous cycle may result in relatively quick temperature increases in the seal, rapid wear of the seal, and eventually failure of the seal. In addition, excessive temperatures may result in undesirable breakdown in lubricant flowing between the journal shaft and rolling cone mounted to the journal shaft.
In many conventional multi-seal arrangements, a primary seal and a secondary seal are disposed proximal one another between the journal shaft and the rotating count mounted to the journal shaft. Traditionally, both the primary seal and secondary seal are oriented with their dynamic seal surface engaging the journal shaft. As previously described, heat generation and temperatures at dynamic seal surfaces are generally greater than static seal surfaces. By positioning the dynamic seal surfaces of both the primary and secondary seals adjacent one another against the journal shaft, the temperature of the journal shaft proximal the dynamic seal surfaces may increase beyond the desirable operating temperature range. The increased temperature of the journal shaft may lead to premature breakdown and/or failure of the primary and/or secondary seal.
It is therefore desirable that a new, durable and long lasting seal assembly be devised, one including long life, relative insensitivity to high temperatures and pressures, and enhanced protection of dynamic seal surfaces, but one that is not as susceptible to damage caused by extrusion and nibbling.
Accordingly, to provide a drill bit with better performance and longer life, and thus to lower the drilling costs incurred in the recovery of oil and other valuable resources, it would be desirable to provide a seal that has the potential to provide longer life than conventional elastomeric seals. Preferably, such seals would provide a bit that will drill with acceptable ROP for longer periods so as to increase bit life and increase in footage drilled as compared to bits employing conventional seals.
In accordance with at least one embodiment of the invention, a seal assembly for sealing between a journal shaft and a rotating cone cutter of a drill bit comprises a seal gland positioned between the journal shaft and the cone cutter. The seal gland comprises an annular recess that includes a sealing surface. In addition, the seal assembly comprises an annular seal body disposed about the journal shaft within the annular recess. The seal body comprises a dynamic sealing surface at its outer diameter D1 that forms a dynamic seal with the sealing surface of the recess and a static sealing surface at its inner diameter D2 that forms a static seal with an outer bearing surface of the journal shaft.
In accordance with another embodiment of the invention, a drill bit for drilling through earthen formations comprises a bit body including an extending journal shaft having an outer bearing surface. In addition, the drill bit comprises a rolling cone cutter rotatably mounted on the journal shaft. The rolling cone cutter includes an inner bearing surface adjacent the outer bearing surface of the journal shaft. Further, the drill bit comprises a first seal assembly positioned between the rolling cone cutter and the journal shaft. The first seal assembly comprises a first annular recess including a sealing surface formed in the inner bearing surface of the rolling cone cutter. Moreover, the first seal assembly comprises a first annular seal body positioned around the journal shaft within the first annular recess. The first annular seal body comprises a radially outer dynamic sealing surface that sealingly engages the sealing surface of the first annular recess and a radially inner static sealing surface that sealingly engages the outer bearing surface of the journal shaft.
In accordance with another embodiment of the invention, a method for sealing between a journal shaft and a rotating cone cutter of a drill bit comprises forming an annular recess in an inner surface of the cone cutter, wherein the recess includes a sealing surface. In addition, the method comprises disposing an annular seal body about the journal shaft within the recess. The annular seal body comprises a radially outer sealing surface that sealingly engages the sealing surface of the recess and a radially inner sealing surface that sealingly engages an outer surface of the journal shaft. Further, the method comprises applying a torque T1 to the seal body at the interface of the outer sealing surface of the seal body and the sealing surface of the recess. Still further, the method comprises applying a torque T2 to the seal body at the interface of the inner sealing surface of the seal body and the outer surface of the journal shaft, wherein T2 is greater than T1.
Embodiments described herein thus comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings.
For a more detailed description of the preferred embodiments of the present invention, reference will now be made to the accompanying drawings, wherein:
The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.
Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness.
In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other or intermediate devices and connections.
Referring now to
It is to be understood that seal assemblies are described herein with respect to a three cone bit for purposes of example only, and that the seal assemblies described herein may be employed in single cone bits, as well as in bits having two or more cones. Likewise, the seal assemblies described herein may have application beyond drill bits, and may be used wherever a seal is required to seal between a shaft and a rotatable member mounted on the shaft.
Referring to
It is to be understood that the terms “radial” and “radially” define positions and/or movement relative to, and substantially perpendicular to, the central axis (e.g., axis 90) of a rolling cone cutter (e.g., cone 14). Further, the terms “axial” and “axially” define positions and/or movement relative to, and substantially parallel to, the central axis (e.g., axis 90) of a rolling cone cutter (e.g., cone 14). For instance, the y-axis illustrated in
Referring still to
Journal shaft 18 includes a bearing surface 42 that is substantially concentric to bearing surface 30 of cone 14. In some regions where bearing surfaces 30, 42 do not contact each other, a clearance groove or passage 33 may form therebetween. Bearing surface 42 includes a groove 32 for receiving locking balls 37. A ball passageway 36 intersects groove 32 and forms a means by which locking balls 37 are placed into cone 14 during assembly. Locking balls 37 retain cone 14 on journal shaft 18. After locking balls 37 are in place, a ball retainer 39 is inserted through ball passageway 36 and an end plug 38 is welded or otherwise secured to close off the ball passageway 36.
Journal shaft 18 further includes a reduced diameter portion 47 and end-surface 44. Bearing surface 42 of journal shaft 18 and bearing surface 30 of cone 14 may include cylindrical inlays 48, 49, respectively, that are disposed in grooves formed in the respective parts for reducing friction, such inlays being made, for example, of aluminum bronze alloys. A nose bushing 45 is disposed about reduced diameter portion 47 of journal shaft 18. Cone 14 is disposed over pin 18 with nose button 46 positioned between end-surface 44 and end portion 31 of central bore 28.
Seal assembly 50, shown schematically in
The bearing structure described and shown
Bearing surfaces 30, 42 of cone 14 and journal shaft 18, respectively, are lubricated by grease. The grease is applied so as to fill the regions adjacent to the bearing surfaces and to fill various interconnected passageways such that, upon bit assembly, air is essentially excluded from the interior of the bit. The bit includes a grease reservoir 19, including a pressure compensation subassembly 29 and a lubricant cavity 20, which is connected to the ball passageway 36 by lubricant passageway 21. The grease is retained in bit 10, the bearing structure, and the various passageways, including diagonal passageway 35 and passageways 21, 36, by means of seal assembly 50. Likewise, seal assembly 50 prevents drilled cuttings and abrasive drilling fluid external to bit 10 from passing seal assembly 50 and washing out the lubricant and potentially damaging the bearing surfaces.
Referring now to
Annular seal body 60 is retained within a seal gland 51, generally comprising an annular recess 34 in cone 14. Recess 34 includes a sealing surface 52 and a pair of annular surfaces 53 extending between bearing surface 30 of cone 14 and sealing surface 52. In this embodiment, sealing surface 52 is cylindrical and faces journal shaft 18, and thus, may be referred to as a cylindrical shaft-facing surface. Further, in this embodiment, annular surfaces 53 are generally planar and substantially parallel, however, in other embodiments, annular surfaces may be non-parallel and/or non-planar. Each annular surface 53 intersects sealing surface 52 to form an annular corner 57. Further, each annular surface 53 intersects bearing surface 30 to form an annular corner 58. In this embodiment, annular surfaces 53 of recess 34 are substantially parallel and generally perpendicular to cone axis 90. As best shown in
Referring still to
In this embodiment, seal sidewalls 65 do not contact annular surfaces 53 of recess 34, resulting in a void or gap G between seal sidewalls 65 and annular surfaces 53. In particular, referring briefly to
As best shown in
Similarly, lubricant 95 within bit 10 may move toward seal assembly 50 the clearance groove or passage 33 between bearing surfaces 30, 42 generally in the general direction of arrows 96. Lubricant 95 that reaches seal body 60 will generally reside between sidewall 65 furthest from backface 22 and annular surface 53 nearest backface 22 (i.e., between the leftmost sidewall 65 and the leftmost annular surface 53 in
Referring now to
Referring now to FIGS. 4 and 6A-6C, to assemble bit 10, seal body 60 is first positioned within recess 34 of cone 14 in its undeformed state (
Stretching of seal body 60 around journal shaft 18 and radial compression of seal body 60 within seal gland 51 may tend to deform seal body 60. For instance, in this embodiment where seal body 60 has a generally rectangular cross-section in its undeformed state prior to assembly, radial compression of seal body 60 causes seal sidewalls 65 to slightly bulge outward. For reasons explained below, although seal sidewalls 65 may bulge outward, at least one seal sidewall 65 preferably does not contact an annular surface 53 of recess 34 when seal assembly 50 is fully assembled. Instead, seal body 60 and seal gland 51 are shaped and dimensioned such that a gap G exists between at least one seal sidewall 65 and annular surface 53. In some embodiments, such as those shown in
It should be appreciated that radial compression of seal body 60 within seal gland 51 (i.e., between journal shaft 18 and sealing surface 52) energizes seal assembly 50, meaning that it tends to bias outer sealing surface 61 firmly towards sealing surface 52 of recess 34, and it tends to bias inner sealing surface 62 firmly towards bearing surface 42.
Referring now to
In addition, reactive forces 71 give rise to frictional forces 73 acting on seal body 60 at the interface of surfaces 61, 52 that tend to resist relative motion therebetween. In other words, frictional forces 73 seek to maintain static engagement of surfaces 61, 52. Thus, as cone 14 rotates about journal shaft 18 generally in the direction of arrow 75, frictional forces 73 act on seal body 60 in the same direction as the rotation of cone 14, and seek to maintain static engagement of seal body 60 and cone 14 as cone 14 rotates. Although only the frictional forces 73 acting on seal body 60 at the interface of surfaces 61, 52 are illustrated in
The interference fit between journal shaft 18 and seal body 60 as well as the compression of seal body 60 within seal gland 51 results in generally equal and opposite radial reactive forces 72 at the interface between inner sealing surface 62 and bearing surface 42 of journal shaft 18. Reactive forces 72 tend to urge inner sealing surface 62 and bearing surface 42 towards each other, resulting in the sealing engagement between surfaces 62, 42 at inner seal 64. In addition, reactive forces 72 give rise to frictional forces 74 acting on seal body 60 at the interface of surfaces 62, 42 that tend to resist relative motion therebetween. In other words, frictional forces 74 seek to maintain static engagement of surfaces 62, 42. Thus, as cone 14 rotates about journal shaft 18 generally in the direction of arrow 75, frictional forces 74 act on seal body 60 opposite to direction of rotation of cone 14, and seek to resist the rotation of seal body 60 relative to journal shaft 18. Although only the frictional forces 74 acting on seal body 60 at the interface of surfaces 62, 42 are illustrated in
Without being limited by theory, in general, the magnitude of frictional forces 73, 74 depend on (a) the magnitude of the reactive forces acting in the radial direction (i.e., substantially normal to the interfacing surfaces), and (b) the coefficient of friction at the interface. It should be understood that the coefficient of friction at the interface is at least partially dependent upon the material composition of the interfacing surfaces and the textures of the interfacing surfaces (e.g., the coefficient of friction at the interface of bearing surface 42 and inner sealing surface 62 depends on the material composition of bearing surface 42 and inner sealing surface 62 and the textures of bearing surface 42 and inner sealing surface 62).
Since frictional forces 73, 74 act at a radial distance from axis 90 of journal shaft 18 (
In the embodiments described herein, torque T2 is preferably maintained to be greater than torque T1, and thus, outer seal 63 may be referred to as dynamic seal 63 and inner seal 64 may be referred to as static seal 64. Likewise, in such cases, outer sealing surface 61 may be referred to as dynamic sealing surface 61 and inner sealing surface 62 may be referred to as static sealing surface 62.
As previously described, reactive forces 71, 72 give rise to torques T1, T2 acting on seal body 60. Reactive forces 71 result substantially from the compression of seal body 60 within seal gland 51. However, reactive forces 72 result from the compression of seal body 60 within seal gland 51 as well as the interference fit between seal body 60 and journal shaft 18. Thus, by design, reactive forces 72 are greater than reactive forces 71, thereby enabling torque T2 acting on seal body 60 at inner sealing surface 62 to be greater than torque T1 acting on seal body 60 at outer sealing surface 63, even after taking account for differences in the radial distances at which torques T1, T2 act. Thus, in the embodiments described above, static engagement between inner sealing surface 62 and bearing surface 42 is maintained, at least in part, by an interference fit between seal body 60 and journal shaft 18.
It should be appreciated that by varying the inner diameter D1 and the outer diameter D2 Of seal body 60, reactive forces 71, 72 and torques T1, T2 may be adjusted and controlled as desired. For instance, in an exemplary embodiment, the radial difference (D3−D1)/2 between journal shaft 18 and seal body 60, when seal body 60 is in its undeformed state, preferably ranges from 0.010 inch to 0.060 inch, and more preferably ranges from 0.020 inch to 0.050 inch. Further, in the exemplary embodiment, the radial difference (D4−D2)/2 between sealing surface 52 and seal body 60, when seal body 60 is in its undeformed state, preferably ranges from 0.005 inch to 0.030 inch, and more preferably ranges from 0.010 inch to 0.02 inch.
Referring briefly to
Although seal body 60 and recess 34 are each shown as having a rectangular cross-section, it should be appreciated that seal body 60 and/or recess 34 may have other suitable cross-sectional shapes, such as circular, oval, triangular, or trapezoidal, as examples. In
Referring to
Referring to
Lastly, referring to
In each embodiment illustrated in
Seal body 60 preferably comprises an elastomeric material such as fluoroelastomers including those available under the trade name Advanta manufactured by DuPont, carboxylated elastomers such as carboxylated nitrites, highly saturated nitrile (HISN) elastomers, nitrile-butadiene rubber (HBR), highly saturated nitrile-butadiene rubber (HNBR) and the like. It is to be understood that the HNBR material set forth in the example, and the HSN materials described above, are only examples of elastomeric materials useful for making an embodiment of annular seal body (e.g., seal body 60) according to the present invention, and that other elastomeric materials made from different chemical compounds and/or different amounts of such chemical compounds may also be used.
Suitable elastomeric materials have a modulus of elasticity at 100 percent elongation of from about 500 to 2,000 psi (˜3 to 14 MPa), a minimum tensile strength of from about 1,000 to 7,000 psi (˜6 to 50 MPa), elongation of from 100 to 500 percent, die C tear strength of at least 100 lb/in. (1.8 kilogram/millimeter), durometer hardness Shore A in the range of from about 60 to 95, and a compression set after 70 hours at 100° C. of less than about 18 percent, and preferably less than about 16 percent. A preferred elastomeric material is a proprietary HSN manufactured by Smith International, Inc., under the product name HSN-8A. A material having these properties will provide the desired degree of wear resistance, abrasion resistance, friction resistance, and temperature stability to provide sufficient seal performance at seals 63, 64 under operating condition. In addition, materials with these or similar properties will provide seal body 60 with a desired degree of deflection so as to provide enhanced sealing under extreme operating conditions.
In addition, to maintain the desired properties of seal body 60 at the pressure and temperature conditions that prevail in a rock bit, to inhibit leakage of the lubricating grease across seal assembly 50, and for a long useful life, seal body 60 preferably comprises a material or coating that is resistant to crude oil and other chemical compositions found within oil wells, have a high heat and abrasion resistance, have low rubbing friction, and not be readily deformed under the pressure and temperature conditions in a well which could allow leakage of the grease from within bit 10 or drilling mud into bit 10.
As previously described, most conventional seal assemblies in rolling cone bits for preventing leakage of lubricant and entrance of drilling fluid include an O-ring type seal that is intended to dynamically seal with the journal shaft of the bit and statically seal with the rolling cone that rotates about the journal shaft. In contrast to most conventional seal assemblies, embodiments of seal assembly 50 described herein include a seal body 60 having a dynamic sealing surface 61 at its outer diameter D1 that forms a dynamic seal 63 with cone 14, and a static sealing surface 62 at its inner diameter D2 that forms static seal 64 with journal shaft 18. Orientation of dynamic sealing surface 61 at the outer diameter D1 of seal body 60 and static sealing surface 61 at the inner diameter D2 of seal body 60 offers the potential for several benefits over conventional rolling cone drill bit seals as are described in the paragraphs to follow.
As previously described, since dynamic sealing surfaces and dynamic seals typically encounter increased abrasion, wear, and temperature conditions as compared to static sealing surfaces and static seals, dynamic sealing surfaces and dynamic seals are generally more susceptible to premature breakdown and failure than static sealing surfaces and static seals. Referring to
Referring still to
Referring still to
Likewise, within recess 34, drilling fluid 91 will also have its highest tangential velocity and lowest pressure adjacent sealing surface 52 proximal corner 57 and dynamic seal 63. Thus, drilling fluid 91 may have a tendency to flow towards this relatively lower pressure region within recess 34. However, the pressure of lubricant 95 within drill bit 10 is controlled by pressure compensation subassembly 29 (
To the contrary, in most conventional rolling cone drill bit seals, the dynamic seal is located at the inner diameter of the seal body against the journal shaft, and the static seal are located at the outer diameter of the seal body against the rolling cone. Since the dynamic seal is located at lesser radial distance than the static seal, the lubricant will tend to flow to the lower pressure region adjacent the static seal and away from the region where it is needed most, adjacent the dynamic seal.
Although embodiments of seal body 60 previously described comprised a single material, preferably an elastomeric material, it should be appreciated that a single seal body may comprise two or more different materials having different hardnesses, wear resistances, durabilities, etc. Such a seal body comprising more than one material may be referred to herein as a “multi-part seal body” or a “composite seal body.”
As previously described, different portions of a seal body (e.g., seal body 60) experience different operating conditions. For instance, the dynamic sealing surfaces of a seal body are generally subjected to harsher operating conditions that other regions of the seal body. In particular, dynamic sealing surfaces are subjected to a higher degree of wear and heat from rotation against cone surfaces or journal surfaces. Additionally, dynamic sealing surfaces are subjected to a highly abrasive environment of drilling fluid and hostile chemicals. For at least these reasons, a seal body formed from a single type of material may not necessarily be perfectly suited to meet the operating conditions at the different regions of the seal body (e.g., the dynamic sealing surface, the static sealing surface, etc.) Although simpler and less expensive to manufacture, a seal body made of a single type of material may represent a compromise between meeting the operating conditions at different portions of the seal. Such a compromise may result in premature failure of the seal body. However, the use of a multi-part seal body enables the customization of the material composition and material properties at different regions of the seal body, thereby offering the potential for a seal body with improved operational capabilities and an enhanced operational life.
Referring now to
In this embodiment, multi-part seal body 460 includes an outer radial portion 460a made of a first material 466, a middle portion 460b made of a second material 467, and an inner radial portion 460c made of a third martial 468. During use, outer sealing surface 461 of outer radial portion 460a is intended to engage sealing surface 452 and form an outer dynamic seal 463 therebetween. Similarly, inner sealing surface 462 of inner radial portion 460c is intended to engage journal shaft bearing surface 442 and form an inner static seal 464 therebetween.
The composition of first material 466, second material 467, and third material 468 may be selected as desired. Any two or more of first material 466, second material 467, or third material 468 may comprise the same or different materials.
Outer sealing surface 461 forms outer dynamic seal 463, and thus, first material 466 preferably comprises a relatively harder, more wear resistant material having a relatively low coefficient of friction and capable of operating at relatively higher temperatures. In addition, inner sealing surface 462 forms inner static seal 464, and thus, third material 468 may comprise a material that is softer, i.e., lower durometer hardness, having a higher coefficient of friction than first material 466. However, since inner sealing surface 462 may rotate relative to journal shaft bearing surface 442 on occasion, third material 468 preferably comprises a relatively harder, more wear resistant material having a relatively low coefficient of friction and capable of operating at relatively higher temperatures. Middle portion 460b preferably biases outer sealing surface 461 towards sealing surface 463 and biases inner sealing surface 462 towards journal shaft bearing surface 442. Thus, second material 467 preferably comprises a relatively softer, i.e., low durometer hardness, rubber or elastomeric material capable of serving as an energizer that urges dynamic sealing surface 461 towards sealing surface 452 and urges static sealing surface 462 towards journal shaft bearing surface 442, thereby producing a sufficient amount of contact pressure between surfaces 461, 452 and between surfaces 462, 442.
First material 466 forming outer radial portion 460a and dynamic sealing surface 461 preferably comprises a wear resistant rubber or elastomeric material having a durometer Shore A hardness measurement in the range of from about 75 to 95, and more preferably greater than about 80, a modulus of elasticity at 100 percent elongation of in the range of from about 700 to 2,000 psi, (˜4 to 14 MPa) elongation of from about 100 to 400 percent, a tensile strength of in the range of from about 1,500 and 4,000 psi (˜10 to 28 MPa), and a compression set after 70 hours at 100° C. in the range of from about 8 to 18 percent. A material having these properties will provide the desired degree of wear resistance, abrasion resistance, friction resistance, and temperature stability to provide enhanced seal performance at the dynamic seal surface under operating conditions, thereby extending the service life of the rock bit.
Harder rubber or elastomeric materials are preferred to form the dynamic sealing surface (e.g., dynamic sealing surface 461) because they are also more stable under high temperature conditions, generally have a lower coefficient of friction, and minimizes stick slip, thereby resulting in less wear and less heat generation at the dynamic surface of the seal.
Other suitable materials useful for forming outer radial portion 460a and dynamic sealing surface 461 include so called self-lubricating rubber or elastomeric compounds that include one or more lubricant additive(s) to provide enhanced properties of wear and friction resistance along the surface of the dynamic seal. Suitable lubricant additives include, without limitation, polytetrafluoroethylene (PTFE), graphite flake, hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and other known fluoropolymeric, dry, or polymeric lubricants and mixtures thereof. The lubricant additive is used to provide an added degree of low friction and wear resistance to the elastomeric component of the composite material that is placed in contact with a rotating surface. A preferred lubricant additive is hBN manufactured by Advanced Ceramics identified as Grade HCP, having an average particle size in the range of from about five to ten micrometers. hBN is a preferred lubricant additive because it provides a superior degree of lubrication when placed in contact with steel without producing harmful, e.g., abrasive, side effects to the journal or cone.
A particularly preferred HSN elastomer (HSN-8A) useful for forming the dynamic seal surface has a durometer Shore A hardness measurement in the range of from about 77-84, a modulus of elasticity at 100 percent elongation of in the range of from about 800 to 1300 psi (˜5,500 to 8,700 kPa), elongation in the range of from about 150 to 400 percent, a tensile strength in the range of from about 1,000 to 4,500 psi (˜7,000 to 31,000 kPa), and a compression set after 70 hours at 100° C. of less than about 18 percent.
Since static sealing surface 462 may occasionally rotate relative to journal shaft bearing surface 442, third material 468 forming inner radial portion 460c and static sealing surface 462 also preferably comprise a wear resistant rubber or elastomeric material similar to those disclosed above with reference to first material 466.
Second material 467 forming middle portion 460b preferably comprises a rubber or elastomeric material such as nitrile and HSN elastomers that have a durometer Shore A hardness measurement in the range of from about 60 to 80, and preferably less than about 75, a modulus of elasticity at 100 percent elongation of between about 400 to 750 psi (˜2,700 to 5,000 kPa), elongation of from about 200 to 1,000 percent, a minimum tensile strength of from about 1,000 to 4,000 psi (˜7,000 to 28,000 kPa), and a compression set after 70 hours at 100° C. the range of from about 5 to 18 percent. A material having such properties forms a seal surface that provides a desired degree of deflection and biasing action to provide enhanced seal performance at static sealing surface 462 and dynamic sealing surface 461 under operating conditions, thereby extending the service life of the rock bit.
A preferred rubber or elastomeric material for use in forming middle portion 460b is HSN that has a durometer Shore A hardness measurement in the range of from about 73 to 78, a modulus of elasticity at 100 percent elongation of between about 500 to 600 psi (˜3,500 to 4,200 kPa), elongation of from about 300 to 400 percent, a minimum tensile strength of approximately 4,000 psi (˜27,000 kPa), and a compression set after 70 hours at 100° C. of approximately 14 percent.
Although multi-part seal body 460 illustrated in
In the embodiments described herein that include a seal body comprising two or more materials, the materials may be coupled by any suitable method to form a unitary seal body. Examples of suitable methods include, without limitation, bonding the materials together by an adhesive or chemical bond, molding or melting the materials together, or combinations thereof.
As an alternative to, or in addition to, wear resistant rubber or elastomeric materials, in some embodiments, one or more surfaces of the seal body (e.g., seal body 60) may comprise a non-elastomeric wear resistant and/or temperature resistant layer. Such layers may be especially beneficial for use on dynamic sealing surfaces that typically experience greater wear, abrasion, and temperatures than other regions of the seal body.
Referring now to
As with seal body 460 previously described (
Non-elastomeric materials suitable for first material 366 forming dynamic sealing surface 461 are preferably in the form of fibers known to have good properties of wear resistance and/or temperature resistance. Example polymeric materials include polyester fiber, cotton fiber, aromatic polyamides (Aramids) such as those sold under the trade name Kevlar by E.I. DuPont de Nemours and Co. of Wilmington, Del., polybenzimidazole (PBI) fiber, poly m-phenylene isophthalamide fiber such as those sold under the trade name Nomex by E.I. DuPont de Nemours and Co. of Wilmington, Del., asbestos fiber, and mixtures or blends thereof. The fibers can be: (1) used in their independent state, e.g., as a random arrangement of fibers distributed within an elastomeric constituent of the seal; (2) combined in a random or unordered an-angement to form a felt sheet; (3) combined in an ordered or non-random arrangement to form a sheet; or (4) combined into threads and woven into a fabric to form a fabric sheet. When fabricated into sheet form, the fibers can be arranged to provide a desired tensile strength in one or more desired direction to meet particular application demands. Additionally, the same or differently oriented fabric sheets can be stacked upon one another to meet certain performance characteristics, e.g., the sheets can be ordered and stacked to provide properties of improved wear resistance in a particular direction.
Preferred non-elastomeric polymeric materials suitable for first material 366 forming dynamic sealing surface 461 include those having a softening point higher than about 350° F., and having a tensile strength of greater than about 10,000 psi (˜68 MPa). Other non-elastomeric materials suitable for use in forming one or more portion of a seal body include those that display properties of high-temperature stability and endurance, wear resistance, and have a coefficient of friction similar to those polymeric materials specifically mentioned above.
Although non-elastomeric wear resistant and temperature resistant layers may be particularly beneficial to dynamic sealing surfaces, it should be appreciated that such wear resistant materials may also provide benefits at static sealing surfaces that may rotate on occasion or may rotate upon failure.
In the embodiments described above, the static engagement between the inner sealing surface (e.g., inner sealing surface 62) of the seal body (e.g., seal body 60) and the journal shaft bearing surface (e.g., bearing surface 42) is maintained, at least in part, by an interference fit between the seal body and the journal shaft. However, other methods may also be employed to enhance the likelihood of static engagement between the inner sealing surface and the journal shaft bearing surface and dynamic engagement between the outer sealing surface and the sealing surface (e.g., sealing surface 52) of the recess (e.g., recess 34).
Referring to
Seal assembly 550 operates substantially the same as seal assembly 50 previously described. However, in this embodiment, seal body 560 is maintained static relative to journal shaft 518 via a bond 599. Specifically, bond 599 fixes inner sealing surface 562 of seal body 560 with bearing surface 542 of journal shaft 518. Consequently, a static seal 464 is formed at the interface of inner sealing surface 562 and bearing surface 542, and a dynamic seal 563 is formed at the interface of outer sealing surface 561 and sealing surface 552 of recess 543. Thus, bond 599 may be used to maintain a static seal 464 between the inner sealing surface 562 of seal body 560 and bearing surface 542 of journal shaft. It should be understood that bond 599 may be used as an alternative to an interference fit between seal body 560 and journal shaft 518, or in addition to an interference fit between seal body 560 and journal shaft 518.
Bond 599 may be formed by any suitable method. For instance, a bonding agent may be employed to form bond 599 between surfaces 562, 542. The bonding agent may be applied to bearing surface 542 opposite recess 534 prior to assembly. Alternatively, the bonding agent may be applied to inner sealing surface 562 or provided as an additive in seal body 560 at inner sealing surface 562 prior to assembly. Following assembly, the bonding agent may be activated to form a fixed bond 599 between surfaces 562, 564. For instance, the bonding agent may be heat and/or pressure activated such that following assembly of seal assembly 550, the application of heat and/or pressure to the bonding agent causes the bonding agent to form a fixed connection or bond between surfaces 562, 542.
In general, the bonding agent employed to form bond 599 is preferably suitable for bonding the materials employed at inner sealing surface 562 and bearing surface 542. In embodiments where inner sealing surface 562 comprises an elastomer and journal shaft 518 comprises a metal or metal alloy, the bonding agent preferably comprises a phenolic resin (e.g., novolac type, resol types, etc.), a phenolic resin/chlorinated polymer combination, silanes, or the like. In some embodiments, additional ingredients or slurries may be added to the bonding agent to enhance the mechanical strength of the bond.
Referring now to
Referring still to
By increasing the contact surface area and footprint Fi between inner sealing surface 662 and bearing surface 642, flange 667 offers the potential to increase frictional forces acting at the interface of surfaces 662, 642. Consequently, flange 667 may provide an additional, or alternative means, to maintain inner sealing surface 662 of seal body 660 static relative to bearing surface 642. Since axially extending flange 667 increases the surface area of inner sealing surface 662 of seal body 660, flange 667 may be described as increasing the “footprint” of inner sealing surface 662.
In this embodiment, space to accommodate flange 667 is provided by an annular recess 674 adjacent recess 634. Without sufficient space to accommodate flange 667, nibbling of flange 667 between the rotating cone bearing surface 630 and the static journal shaft bearing surface 642 may occur.
Referring now to
In addition, in the embodiment illustrated in
By engaging sealing surface 752 of recess 734 with peak 770, a reduced portion of radially outer portion 760a of seal body 760 contacts sealing surface 752 as compared to the embodiment illustrated in
Seal bodies including a radially inner static sealing surface that sealingly engages a journal shaft and a radially outer dynamic sealing surface that sealingly engages a cone cutter may be employed in multi-seal arrangements to achieve one or more of the benefits described above. Referring now to
Primary seal assembly 150 generally includes a multi-part seal body 160 retained within a seal gland 151, generally comprising an annular recess 134 in cone 114. Recess 134 includes a sealing surface 152 and two annular surfaces 153 extending between cone bearing surface 130 and sealing surface 152. Each annular surface 153 intersects sealing surface 152 to form an annular corner 157. Further, each annular surface 153 intersects bearing surface 130 to form an annular corner 158. Seal gland 151 is further defined by cylindrical bearing surface 142 of journal shaft 118.
Referring still to
Outer sealing surface 161 engages sealing surface 152 of recess 134 to form a radially outer seal 163. Inner sealing surface 162 engages journal shaft bearing surface 142 of journal shaft 118 to form an inner seal 164.
In addition, multi-part seal body 160 includes a radially outer portion 160a comprising a first material 166, a middle portion 160b comprising a second material 167, and a radially inner portion 160c comprising a third material 168. First material 166 and third material 168 preferably comprise wear resistant materials as previously described. In some embodiments, first material 166 and/or third material 168 may comprise a non-elastomeric wear resistant material. Second material 167 preferably comprises an elastomeric material capable of biasing sealing surface 161, 162 towards surfaces 152, 142, respectively.
Likewise, secondary seal assembly 250 generally includes a multi-part seal body 260 retained within a seal gland 251, generally comprising an annular recess 234 in cone 114. Recess 234 includes a sealing surface 252 and two annular surfaces 253 extending between cone bearing surface 130 and sealing surface 252. Each annular surface 253 intersects sealing surface 252 to form an annular corner 257. Further, each annular surface 253 intersects bearing surface 130 to form an annular corner 158. Seal gland 251 is further defined by cylindrical journal shaft bearing surface 142 of journal shaft 118.
Referring still to
Outer sealing surface 261 engages sealing surface 252 of recess 234 to form a radially outer seal 263. Inner sealing surface 262 engages journal shaft bearing surface 242 of journal shaft 118 to form an inner seal 264.
Similar to seal body 160, multi-part seal body 260 includes a radially outer portion 260a comprising a first material 266, a middle portion 260b comprising a second material 267, and a radially inner portion 260c comprising a third material 268. First material 266 and third material 268 preferably comprise wear resistant materials as previously described. In some embodiments, first material 266 and/or third material 268 may comprise a non-elastomeric wear resistant material. Second material 267 preferably comprises an elastomeric material capable of biasing sealing surface 261, 262 towards surfaces 252, 242, respectively.
Seal assembly 200 may be referred to as a multi-seal assembly 200 since it includes more than one seal body (e.g., seal bodies 160, 260).
Cutting-laden, abrasive drilling fluid 91 will tend to enter via the clearance or groove between the drill bit leg and rolling cone backface as previously described with reference to
As desired, primary seal assembly 150 and/or secondary seal assembly 250 may be configured to form a static seal at inner seal 164, 264 and a dynamic seal at outer seal 163, 263 in accordance with embodiments of the present invention. For instance, in the embodiment illustrated in
In general, dynamic seals generate more thermal energy than static seals. This is due primarily to heat generated by friction resulting from rotation against cone surfaces (e.g., sealing surface 152) or journal surfaces (e.g., journal shaft bearing surface 42). Consequently, temperatures at dynamic seals and regions adjacent dynamic seals tend to be higher than temperatures at static seals and regions adjacent static seals. Heat generation, and resulting temperatures, adjacent sealing surfaces are preferably controlled to improve drill bit performance and life. For instance, temperatures in excess of about 250° to 300° F. may lead to premature breakdown and failure of elastomeric seal bodies. Temperature increases may also cause seal bodies (e.g., seal body 160, seal body 260) to expand, potentially increasing engagement with the recess (e.g., recess 134, recess 234) within which they are disposed. Such increases in engagement between the seal body and the recess from expansion may result in undesirable increases in frictional forces and further temperature increases. In addition, excessive journal shaft temperatures may lead to premature breakdown and failure of the lubricating grease that flows between the rolling cone cutter and the journal shaft.
Excessive heat generation and temperatures may especially be a concern in conventional multi-seal arrangements in which adjacent seal assemblies include seal bodies each having a dynamic sealing surfaces at their inner diameter dynamically engaging the journal shaft. In such cases, the heat generated by the relatively close dynamic seals tends to increase the temperature of the journal shaft more than a single dynamic seal would alone. However, by configuring adjacent seal assemblies such that one seal body forms a dynamic seal at its inner diameter with the journal shaft, while the other seal body forms a static seal at its inner diameter with the journal shaft, embodiments described herein offer the potential to improve heat distribution in multi-seal arrangements.
For instance, to enhance temperature distribution in multi-seal arrangement 200, adjacent seal bodies 160, 260 preferably do not each have dynamic inner seals 164, 264 or dynamic outer seals 162, 262. Rather, if primary seal assembly 150 includes a seal body 160 having a dynamic inner seal 162, it is preferred that adjacent secondary seal assembly 250 include a seal body 260 having a static inner seal 262, or vice versa.
Although seal bodies 160, 260 are each shown as comprising three materials, it should be appreciated that seal bodies 160, 260 may each comprise one or more materials. Further, seal bodies 160, 260 may each comprise the same or different materials.
Although seal assembly 50 illustrated in
In the manner described, embodiments of the seal assemblies, drill bits, and methods of sealing between two rotating bodies described herein offer the potential to provide several improvements over prior art seals. In particular, by positioning the dynamic sealing surface of the seal body at the outer diameter of the seal body within a recess, embodiments described herein offer the potential to increase the resistance to the flow of cutting-laden drilling fluid to the dynamic seal, to reduce the likelihood of extrusion and nibbling of the seal body, and improve the lubrication of the dynamic seal while restricting leakage of drill bit lubricant. In addition, in multi-seal arrangements, by forming a dynamic seal at the inner diameter of the primary seal assembly and a static seal at the inner diameter of the secondary seal assembly, or vice versa, embodiments described herein may beneficially reduce journal shaft temperatures. Consequently, one or more of the potential benefits offered by embodiments of the present invention may result in longer periods of time between seal body failure, improved drill bit lubrication, and improved drill bit life.
While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
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