GIMBAL BEARING SYSTEM AND METHOD

BACKGROUND

Riser strings are often installed on offshore drilling platforms. Since a riser string is not yet supported at the wellhead and/or sea floor during installation, the riser string needs support to prevent or minimize potential damage. Axial shock loading is often encountered during installation of the riser string. Submerged current or other sea conditions manifest themselves as bending stresses within the riser string if a non-compliant support structure is utilized during assembly of the riser string.

To solve such problems, gimbal bearings are typically provided. A gimbal bearing is used to support the riser string during installation. A gimbal bearing accommodates axial shock loading of the riser string, while also mitigating bending stresses in the riser string by providing compliance for riser string cocking deflections. The extreme conditions and forces experienced by gimbal bearings lead to wear issues, and these wear issues tend to result in a short effective life for the gimbal bearing. Therefore, it is desirable to have gimbal bearings with increased lifespan and improved reliability. It is further desirable to have a gimbal bearing with features configured to provide an easy visual indication regarding a remaining life of the gimbal bearing.

SUMMARY

Aspects of the disclosure include embodiments of a gimbal bearing comprising: a top ring configured to encompass a riser string; a bottom ring configured to encompass a riser string; and at least one high capacity laminate (HCL) bearing positioned between and affixed to the top and bottom rings. Other aspects of the disclosure include embodiments of a gimbal bearing comprising: a top ring; a bottom ring; and a plurality of shim stack assemblies positioned between and affixed to the top and bottom rings; wherein the plurality of shim stack assemblies are spaced evenly about the circumference of the top and bottom rings. Still other aspects of the disclosure include embodiments of a gimbal bearing comprising two rings and a plurality of bonded shim packs positioned therebetween and affixed about the circumference of the rings.

Other aspects of the disclosure include embodiments of a method of forming a gimbal bearing for a riser string, comprising one or more of the following steps: forming a plurality of bonded shim packs with alternating layers of steel shims and elastomeric elements; affixing top and bottom interface members to each bonded shim pack to form a plurality of shim stack assemblies; and affixing the plurality of shim stack assemblies to a top ring and a bottom ring, with each shim stack assembly being positioned between the top ring and the bottom ring; wherein the plurality of shim pack assemblies may be spaced evenly about the circumference of the top and bottom rings. These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a gimbal bearing.

FIG. 2 illustrates an embodiment of a shim stack assembly for a gimbal bearing.

FIG. 3 illustrates an embodiment of a bonded shim pack for a gimbal bearing.

FIG. 4 illustrates an alternative embodiment of a gimbal bearing, in which the rings employ a clamshell design.

FIG. 5 illustrates an exploded view of a gimbal bearing having a clamshell (split) design.

FIGS. 6 and 7 illustrate cross-sectional views of an elastomeric mold bonded laminated bearing stack with multiple alternating layers of non-elastomeric shim member layers and elastomeric layers with an interior elastomer region having at least a first interior optical characteristic different than the exterior elastomer region.

FIGS. 8 and 9 illustrate interior and exterior elastomeric regions with the interior elastomeric composition having at least a first interior optical characteristic different than the exterior elastomeric composition, with the elastomeric region materials shown before they are bonded and cured into a marker layer.

FIG. 10 illustrates a spherical bearing with non-black colored elastomer on the outside exterior surface of two elastomeric shim member layers.

FIGS. 11-13 depict the results of fatigue tests illustrating optically distinguishable elastomeric crumbs expelled from the bearing's interior elastomeric region and persisting on the exterior surface of the bearing.

FIGS. 14 and 15 depict photographs of the results of fatigue tests illustrating optically distinguishable elastomeric crumbs expelled from the bearing's interior elastomeric region and persisting on the exterior surface of the bearing.

FIG. 16 illustrates a mold for bonding non-elastomeric shim members and elastomeric shim member layers together to provide an alternating laminated bearing stack. The mold having an elastomer transfer sprue proximate the interior elastomeric region.

FIG. 17 illustrates a mold for bonding non-elastomeric shim members and elastomeric shim member layers together to provide an alternating laminated bearing stack. The mold having elastomer transfer sprues proximate the exterior elastomeric region.

FIGS. 18-25 illustrate views of a wear-indicator equipped HCL bearing marker layer with an interior elastomer region having optical characteristics different than the exterior elastomer region.

FIG. 26 illustrates expelled elastomeric crumbs staying on the bearing when exposed to a forceful stream of water.

DETAILED DESCRIPTION

The present disclosure generally relates to gimbal bearings having at least one high capacity laminate (HCL) bearing positioned between two rings. Some embodiments might use a single HCL bearing between and securely affixed to the rings. For example, such embodiments might have a HCL bearing that is fully annular, perhaps spherical in design. More commonly, however, embodiments might use a plurality of HCL bearings positioned between and affixed to the two rings, with the HCL bearings evenly distributed circumferentially on their supporting rings. Each HCL bearing comprises a bonded shim pack, with each such bonded shim pack comprising an alternating series of shims and elastomeric elements bonded together. The HCL bearings provide designers additional options for tuning of axial and shear spring rates, thereby allowing for optimization of shock attenuation and cocking compliance bearing characteristics. Such gimbal bearing embodiments can be designed to have high compressive load carrying capacity while accommodating shear motion.

Typically, a gimbal bearing is positioned about a riser string. The top ring of the gimbal bearing is attached to a spider, while the bottom ring is attached to a rotary table. The common means of attachment is removable, for example using bolts. Specific bolt patterns for attachment can be customized to suit the specific project.

FIG. 1 shows an embodiment of a gimbal bearing 100 in more detail. The gimbal bearing 100 has top ring 102, bottom ring 104, and a plurality of HCL bearings 106. Top ring 102 is operable to encompass a riser string and interface with a spider. Top ring 102 interface with the spider is through an end-customer defined set of bolts and bolt holes (not shown). Bottom ring 104 also is configured to encompass riser string and interface with a rotary table. Bottom ring 104 interface with rotary table is also through an end-customer defined set of bolts and bolt holes (not shown). HCL bearings 106 are positioned between and affixed to top ring 102 and bottom ring 104. While the HCL bearings 106 of many embodiments are directly affixed to top ring 102 and bottom ring 104, in other embodiments the HCL bearings 106 may be indirectly affixed. Top ring 102 and bottom ring 104 are shown as circular members with a passage 108 therethrough. However in other embodiments, top ring 102 and/or bottom ring 104 may comprise any shape having a passage 108 therethrough. Passage 108 provides a path for the riser string through the gimbal bearing 100, with the gimbal bearing 100 encompassing the riser string. The gimbal bearing 100 includes at least three HCL bearings 106. The number of HCL bearings 106 depends on the specific design needs of the project. FIG. 1 illustrates gimbal bearing 100 having eight HCL bearings 106, for example.

In the embodiment of FIG. 1, the plurality of HCL bearings 106 are spaced evenly about the circumference of top ring 102 and bottom ring 104. Top ends 110 of each HCL bearing 106 are spaced evenly about the circumference of top ring 102, and bottom ends 112 of each HCL bearing 106 are spaced evenly about the circumference of bottom ring 104. Top ring 102 of FIG. 1 has a diameter 114 (or width) that is smaller than the diameter 116 of bottom ring 104, such that the HCL bearings 106 angles inward as extending upward from bottom ring 104 towards top ring 102. Angle α is based upon the specific needs of the project, and may be customized accordingly. In FIG. 1, angle α ranges between zero (0) degrees and forty-five (45) degrees. In another embodiment, in which the top ring 102 and bottom ring 104 are about the same size, HCL bearings may have an angle of zero (0) degrees extending from bottom ring 104 to top ring 102. In alternative embodiments, the HCL bearings may be composed of chevron shaped shims and elastomeric elements to further decrease torsional shear motions and thereby decrease buckling risks.

Top ring 102 and bottom ring 104 are formed of a material of sufficient strength to withstand all normal operating loads without detrimental permanent deformation and to be able to withstand extreme and survival loads without rupturing. Top ring 102 and bottom ring 104 may be formed of steel or some other similarly strong material. In one example, top ring 102 and bottom ring 104 are formed of 4130 Alloy Steel.

The HCL bearings 106 of FIG. 1 have alternating layers of shims 118 and elastomeric elements 120 bonded together. The shims 118 and elastomeric elements 120 allow for the accommodation of cocking motions while providing the axial stiffness required for static and shock loads without damage and survival loads without leading to failure of the bearing. The shims 118 might be formed of a metallic or other relatively stiff material. In FIG. 1, by way of example, the shims 118 can be formed of steel, such as 4130 Alloy Steel; and the elastomeric elements 120 may comprise natural rubber and/or nitrile. The bonding of different materials forms the laminate structure of the HCL bearings 106, and the use of multiple layers of at least two different materials may provide for improved fatigue characteristics. The HCL bearings 106 of FIG. 1 each have about 1-52 steel shims 118 in alternating configuration with about 2-51 elastomeric elements 120. This range is a suggested range, but its upper limits are theoretically much higher. The number of alternating layers of shims 118 and elastomeric elements 120 in the design are determined by the spring rates desired in the compression axis and shear axes directions and the stresses and strains imparted to the elastomeric elements 120 in operation. The alternating steel shims 118 and elastomeric elements 120 of FIG. 1 are bonded using adhesive. The adhesive of the embodiment of FIG. 1 has sufficient strength so that any failure in the high capacity laminate bearing would occur in the elastomeric element 120 and not the adhesive. For example, a heat activated adhesive might be applied in the mold, with heat then being applied to bond the materials together into an integral HCL bearing 106. Chemlock® is an example of an adhesive that might be used in the HCL bearings 106 of FIG. 1.

FIG. 2 illustrates an exemplary embodiment of an HCL bearing 106. The HCL bearing 106 includes a bonded shim pack 122 and some means for affixing the bonded shim pack 122 to the top ring 102 and bottom ring 104. For example, the HCL bearing 106 of FIG. 2 is a shim stack assembly 123 comprising a bonded shim pack 122 with a top interface member 124 and a bottom interface member 126. The bonded shim pack 122 has two ends on its longitudinal body, a top end 128 and a bottom end 130. An interface member corresponds to each end of the bonded shim pack 122, and serves to attach the bonded shim pack 122 to the top ring 102 and bottom ring 104. As illustrated, the interface members 124, 126 each have two attachment faces, for example a ring attachment face 132 operable to interface with the corresponding ring and a bonded shim pack attachment face 134 angled to orient the bonded shim pack 122 between the top ring 102 and the bottom ring 104. In FIG. 2 for example, the longitudinal centerline axis CL of each bonded shim pack 122 may extend perpendicular to the planar bonded shim pack attachment face 134 of the corresponding interface member. Each interface member of FIG. 2 has a wedge shape, with the ring attachment face 132 positioned to minimize shear/bending loads from bolted joints, and with the bonded shim pack attachment face 134 oriented based on the angle a of the HCL bearing 106.

Each interface member 124, 126 is bonded to a corresponding end of the corresponding bonded shim pack 122. For example, each interface member is bonded with adhesive to the corresponding end of the bonded shim pack 122. Each interface member 124, 126 is also operable to be affixed to the corresponding top and bottom ring 102, 104. In embodiments, each top interface member 124 is removably attached (for example, by bolting) to the top ring 102, while each bottom interface member 126 is removably attached to the bottom ring 104. The use of removable attachment means provides a modular design that can simplify refurbishment and allow retrofitting of existing gimbal bearings with high capacity laminate bearings. In alternative embodiments, however, the interface members might be permanently affixed to the rings, or even formed as part of the rings. The interface members 124, 126 are formed of material sufficiently strong and durable so that any failure in the gimbal bearing 100 is likely to occur in the bonded shim pack 122, rather than the interface. The interface members 124, 126 of FIG. 2 may be formed of 4130 alloy steel, for example. The attachment of the interface member to the rings is also sufficiently strong and durable so that any failure would be likely to occur in the elastomeric elements 120 of the bonded shim pack 122.

A bonded shim pack 122 embodiment is shown in FIG. 3. The bonded shim pack 122 has a plurality of steel shims 118 and a plurality of elastomeric elements 120. The shims 118 and elastomeric elements 120 are joined into an integral bonded shim pack 122 via adhesive. The adhesive generally would have sufficient strength and durability so that any failure would be likely to occur in the elastomeric element 120 rather than the adhesive bond. The steel shims 118 and elastomeric elements 120 are arranged in alternating layers. In FIG. 3, the steel shims 118 form the ends of each bonded shim pack 122, for attachment to the interface members 124, 126. The elastomeric elements 120 have specific spring rate and damping characteristics suitable for the application and sufficient material strength to withstand the stresses imparted to the bonded shim pack 122. The shims 118 have sufficient material strength to withstand the stresses imparted to the bonded shim pack 122, while providing a surface on which adhesive may be applied and cured to provide greater adhesion strength to the metal than the tear strength of the elastomeric element 120. The shims 118 should also have a stiffness much higher than the elastomeric elements 120 to prevent the elastomer from deflecting at the interface between elastomeric element 120 and shim 118. In FIG. 3, the elastomeric elements 120 comprise natural rubber, and the shims are steel, such as 4130 Alloy Steel.

Typical ranges for the steel shims 118 might be from about 0.125 to 0.375 inches in thickness 136, while typical ranges for the elastomeric elements 120 might be from about 0.05 to 1 inches in thickness 138. The steel shims 118 generally have a width or diameter 140 that is slightly greater than the width or diameter 142 of the elastomeric elements 120. This accounts for bulging of the elastomeric elements 120 when loaded. The shapes and sizes of the shims 118 and elastomeric elements 120 are sized to meet the static and dynamic requirements of the riser string in question. The steel shims 118 of a bonded shim pack 122 might all be the same material and size, and the elastomeric elements 120 of the bonded shim pack 122 might all be the same material and size. In other embodiments, however, designers might use steel shims 118 and/or elastomeric elements 120 with varying sizes and materials in order to fine tune the characteristics of the HCL bearings 106. For example, one or more of the elastomeric elements 120 of an HCL bearing 106 may not have the same spring value (rate). The number of shims and elastomeric elements can also vary to allow for tuning of the HCL bearing 106 characteristics.

The bonded shim pack 122 of FIG. 3 may distribute bulge strain to prevent excessive stresses in the elastomeric elements 120 at bulging points. The steel shims 118 modify strain in the elastomeric elements 120, increasing allowable stress. This in turn may lead to a longer life for the gimbal bearing 100. The steel shims 118 also reinforce the elastomeric elements 120, for example improving their ability to withstand buckling. Additionally, the use of HCL bearings 106, such as those with bonded shim packs 122, may allow embodiments to be fine-tuned with respect to axial and cocking stiffness of the gimbal bearing 100 while minimizing elastomer strains. Designers may create gimbal bearings 100 with high compressive stiffness, for example 283-2,264 kip/in, and low shear stiffness, for example 14-100 kip-ft/deg. Designers may also be able to independently tune the axial and shear spring rates, to allow for optimization of shock attenuation and cocking compliance characteristics of the various gimbal bearing 100 embodiments. The characteristics of the gimbal bearing 100 embodiments can be tuned based on one or more of the following: selection of materials for the HCL bearings 106 and rings 102, 104; the size, shape, orientation, and number of HCL bearings 106; and material, number, and size of shims 118 and elastomeric elements 120.

Various embodiments allow for fine control of individual layer shear moduli, thus more evenly distributing elastomer strain rates. Such embodiments may have prolonged life expectancy, for example at least five times that of conventional gimbal bearings. While embodiments may be designed or fine-tuned to handle a wide array of loads and motion conditions, the gimbal bearing 100 in the present embodiment has a maximum axial loading of about 800-3000 kips and maximum cocking angle of about 6 degrees or, in other embodiments, about 10 degrees. Of course, these design features are based on current riser string characteristics, and could change in the future based on changes to the riser string designs and/or specific customer requirements. Stiffness of the gimbal bearing 100 embodiments can be chosen to optimize shock attenuation while minimizing bulge/shear strain. An embodiment might have an axial stiffness of about 283 kip/in, for example. Embodiments are fully scalable, however, with the range of loads and sizes scalable up as wells are drilled deeper. In some embodiments, independent fine tuning of axial and shear spring rates can be performed by varying the number of steel shims 118 or changing the shape factor of individual elastomeric elements 120. As used herein, shape factor is the ratio of loaded surface area to the bulge area.

In some embodiments, one or more of the elastomeric elements 120 of the bonded shim pack 122 comprise a marker layer. Such a marker layer might simplify inspection, making wear easier to detect. The elastomeric elements 120 of the bonded shim packs can be formed so that the outer surface of the elastomeric element is one color, while an inner layer of elastomeric element, located beneath the outer surface layer, is another color. The inner layer may be termed a marker layer, and might be a color that highly contrasts with the color of the outer surface layer. Such an approach simplifies inspection, since as the elastomer degrades the surface layer crumbles to reveal the inner layer with the contrasting color. The use of marker layer in elastomeric elements 120 can be particularly effective at detecting wear for the gimbal bearing 100 as a whole, since gimbal bearings 100 are typically designed so that failure or wear will first occur in the elastomeric elements 120.

Though described in circular terms for ease of understanding, the marker layer may be any shaped elastomeric element 120 having an interior element that is optically distinguishable from the exterior elastomeric element. In this embodiment, the elastomeric element 120 has at least two optically distinguishable rings, with the outer ring being an elastomeric element that is dark in color, preferably carbon black or a carbon black substitute, and the inner ring being an elastomeric element that is optically different in color from the outer ring. The optically different color could be any distinguishable color, such as the non-limiting examples of yellow, orange, or some other brightly distinguishable color. So in this embodiment, the inner ring serves as the marker layer. In other embodiments, at least a third innermost ring of an elastomeric element may also be used, thereby positioning the marker layer between the innermost ring and the outer ring. Such an at least third innermost ring could have yet another distinguishable color, different than that of the outer ring and/or the first inner ring, perhaps allowing it to serve as an additional marker layer. By including additional rings (typically with different colors), more detailed wear information may be readily gathered during inspection. An exemplary elastomeric element might have any number of rings, with the number being determined by the end use. Typically, at least one of the one or more marker layers would be positioned at a depth level within the elastomeric element to indicate wear requiring replacement while still within a safety margin (e.g. at a safe level before mechanical failure of the elastomeric element).

As the HCL bearing 106 wears, the one or more marker layers may be viewed through any cracks that may form in the elastomeric element, or through any debris that may fall therefrom. The marker layer provides an optically detectable area of the HCL bearing 106 for determining wear thereof. The optically detectable element is in the form of visually viewing the marker layer through a crack, or by viewing small debris from the marker layer in and about the HCL bearing 106.

FIG. 4 illustrates yet another embodiment of a gimbal bearing 100. In FIG. 4, the top ring 102 and bottom ring 104 each are split, for example in halves along split-line 144, but are operable to be joined into an integrated whole for encompassing the riser string. For example, the halves might be joined using bolts (not shown) or other means to securely join the split halves. Such a split design can be termed a clamshell design. As shown in FIG. 5, the split top ring 102 and bottom ring 104 each comprise overlapping linking elements 150 at the split-line 144, and one or more bolts securely join each set of corresponding overlapping linking elements 150. In other words, the gimbal bearing 100 of FIG. 4 is operable to open and separate about the split-line 144 in the rings, but is also operable to close and securely encompass the riser string during installation. The gimbal bearing 100 of FIG. 4 can be removably secured in a closed position, for example using one or more bolts in proximity to the split-line 144. Opening the clamshell gimbal bearing 100 facilitates removal of the gimbal bearing 100 once the riser string is installed. FIG. 4 also illustrates a bottom ring 104 fitted with lifting points 146. For example, the lifting points 146 could be eyebolts which accommodate hooks for lifting the gimbal bearing 100 into position. The lifting points 146 shown in this embodiment as located on the bottom ring 104 so that installation loads may not pass through the HCL bearings 106. So for example, in FIG. 4 the lifting points 146 are positioned on the upper surface 148 of the bottom ring 104. Other positions for lifting points 146 are possible in other embodiments, however.

According to one embodiment, a method of forming a gimbal bearing embodiment for a riser string comprises the following steps: forming a plurality of bonded shim packs 122 with alternating layers of steel shims 118 and elastomeric elements 120; affixing a top interface member 124 and a bottom interface member 126 to each bonded shim pack 122 to form a plurality of shim stack assemblies 123; and affixing the plurality of shim stack assemblies 123 to a top ring 102 and a bottom ring 104, with each shim stack assembly 123 positioned between the top ring 102 and the bottom ring 104. The plurality of shim stack assemblies 123 are spaced evenly about the circumference of the top ring 102 and bottom ring 104. Forming bonded shim packs 122 comprises laminating alternating layers of steel shims 118 and elastomeric elements 120 using an adhesive. In some embodiments, the adhesive is heat activated, with adhesive applied and heat activated in a mold. Sequential bonding, for example using structural adhesive, can be employed. The alternating layers of elastomeric elements 120 may vary in spring value, allowing for fine tuning of the gimbal bearing 100 characteristics.

Each set of top and bottom interface members 124 and 126 can be affixed to the corresponding bonded shim pack 122 using shear bosses, bolts, bonding adhesives, combinations thereof, or other means, and then the shim stack assembly 123 can be affixed to the top ring 102 and bottom ring 104 at corresponding locations. In this embodiment, the top and bottom interface members 124, 126 are removably affixed to the top 102 and bottom rings 104 using bolts to allow for a modular design that simplify repair. In other embodiments, however, the interface members are permanently attached to the rings using adhesive or welding. Gimbal bearings with a clamshell design have top ring 102 and bottom ring 104 with clamshell configuration, such that the rings split in half but are operable to be joined into an integrated whole that can encompass the riser string. The riser string would typically be inserted through the rings of the gimbal bearing 100 without opening the rings, but the top ring 102 and bottom ring 104 could be opened to allow for removal of the gimbal bearing 100 once installation of the riser string is complete. The clamshell top ring 102 and bottom ring 104 would be opened to allow for removal of the gimbal bearing 100 from the riser string. The top ring 102 interfaces with a spider element, while the bottom ring 104 interfaces with a rotary table.

FIGS. 6 and 7 show an alternative embodiment of an HCL bearing 200 that is substantially similar to HCL bearing 106 but with a primary difference being that the HCL bearing 200 generally comprises curved components to form a cylindrical and/or spherical bearing profile. Even though the figures depict various embodiments of an HCL bearing 200 suitable for use in gimbal bearing 100 and/or other gimbal bearings, the described embodiments and use of HCL bearing 200 may be suitable in any application in which bearings experiencing repetitive relative motion between two members as described herein are utilized. For example, the HCL bearing 200 described herein is suitable for installation and use in water environment applications and non-water environment applications.

HCL bearing 200 comprises a mold bonded laminate bearing stack 202. Bearing stack 202 includes a first end 204, a second end 206, and longitudinal axis 208 between first and second ends, 204 and 206, respectively.

Bearing 200 connects a first member 210 and a second member 212. In some embodiments, the first member 210 and the second member may generally comprise the top ring 102 and the bottom ring 104, respectively. The design of bearing 200 accommodates repetitive relative motion between first member 210 and second member 212. For example, under operational conditions bearing 200 may experience repetitive compressive load 214 shown in the directions indicated by arrows between first member 210 and second member 212. Compressive load 214 may be in the same direction as longitudinal axis 208. Bearing 200 may also experience a repetitive alternating shear load 216 that may be nonparallel to said longitudinal axis 208. Upon degradation of bearing 200 due to the compressive loads 214 and shear loads 216, a fracture 218 may form in marker layer 220 and generates a plurality of crumbs 222 of first inner material comprising a first elastomeric composition 224. Crumbs 222 are detectable at an exterior surface 226 of said bearing stack 202.

As shown in FIGS. 6, 7 and 10, bearing stack 202 includes alternating layers of elastomeric material layers 228 and non-elastomeric shim material layers 230. FIGS. 6 and 7 depict cross-sectional views of the alternating layers of elastomeric material layers 228 and non-elastomeric shim material layers 230 of bearing stack 202.

Elastomeric material layer 228 and non-elastomeric shim material layer 230 are concentrically arranged about longitudinal axis 208 with each elastomeric material layer 228 sandwiched between at least two non-elastomeric shim material layers 230 as depicted in FIGS. 6 and 7. Referring to FIGS. 6 and 7, first end 204 of bearing stack 202 is a non-elastomeric shim material layer 230 and second end 206 of bearing stack 202 is also a non-elastomeric shim material layer 230.

In bearing stack 202 at least one elastomeric material layer 228 functions as a marker layer 220. Marker layer 220 can be seen in FIGS. 8, 9, 10, and 18-25. Marker layer 220 is configured to indicate wear or fatigue of bearing 200. Marker layer 220 is made up of a first elastomeric composition 224 and a second elastomeric composition 232. For example, first elastomeric composition 224 and second elastomeric composition 232 may include different ingredients such as different rubber composition ingredients and/or different optical characteristic ingredients or may be the same rubber composition ingredients but include different optical ingredients. As a result, first elastomeric composition 224 and second elastomeric composition 232 are different. In some embodiments, the exterior surface 226 of bearing stack 202 has a substantially similar appearance to second elastomeric composition 232. In other embodiments, for example, as shown in FIG. 10, exterior surface 226 of marker layers 220 may have a different appearance than exterior surface 226 of other elastomeric material layers 228.

First elastomeric composition 224 includes a first optical characteristic ingredient. First elastomeric composition 224 defines an interior elastomeric region 236. A second elastomeric composition 232, having a second optical characteristic ingredient, defines an exterior elastomeric region 234 which envelops interior elastomeric region 236. Typically, exterior elastomeric region 234 and first elastomeric composition 224 will have a coplanar and concentric relationship such that the interior and exterior elastomeric regions 236 and 234, respectively, are centered about the bearing center axis 208 or longitudinal axis 208. With reference to FIGS. 18B, 24B, and 25B, a single elastomeric composition forms elastomeric material layers 228 that are not marker layer 220. Typically, the single elastomeric composition is second elastomeric composition 232.

Marker layer 220, as shown in FIG. 18A, has a radius r defined from a center 238 of elastomeric material layer 228. Referring to FIGS. 9, 18A and 19A, interior elastomeric region 236 and exterior elastomeric region 234 of marker layer 220 have a combined radius of r. Exterior elastomeric region 234 extends outward from the perimeter of interior elastomeric region 236 a distance d up to the perimeter of marker layer 220. Distance d of exterior elastomeric region 234 is in the range of 0.01 r to 0.5 r. In other embodiments d is in the range of 0.02 r to 0.3 r. Interior elastomeric region 236 has a radius of q, where interior elastomeric region 236 is r−d (r minus d).

The dimensions of r, q, and d are predetermined based on the end-use application of bearing 200. For example, the dimensions r, q, and d are sized and calibrated based on desired service life for bearing 200 and other parameters set based on historical testing or performance characteristics for the intended end-use application or environment of bearing 200. Interior elastomer region 236 cannot be seen upon initial installation of bearing 200 in bearing location 240 or when bearing stack 202 is removed from the mold. Preferably, interior elastomer region 236 is located a predetermined distance from exterior surface 226 of bearing stack 202 with the distance based on the calibration established by the replacement criteria for bearing 200.

The intended end-use environment of bearing stack 202 and any historical or known instances where bearing 200 first typically experiences wear or fatigue will determine the placement of marker layer 220 within bearing stack 202. When positioned within a predetermined layer within bearing stack 202 corresponding to the likely point of initial failure for the particular use of bearing 200, marker layer 220 will evidence fatigue in the form of a, crack, fissure, and/or fracture 218. As fracture 218 extends from exterior surface 226 of bearing stack 202 inward toward the bearing center or toward the interior elastomeric region 236 due to torsion experienced by bearing 200, fracture 218 evidences the approaching failure of bearing stack 202 by producing a plurality of detectable elastomeric crumbs 222 of the first elastomeric composition 224. Crumbs 222 are expelled through fracture 218 to exterior surface 226. Crumbs 222 are sticky and may be configured to persist on exterior surface 226.

FIGS. 11, 12, and 13 depict the results of torsional fatigue tests illustrating distinguishable elastomeric crumbs 222 expelled from interior elastomeric region 236 of bearing 200 and persisting on exterior surface 226.

FIGS. 14 and 15 depict the results of crumbs 222 of a first elastomeric composition 224 deposited on a second elastomeric composition 232, wherein the colors of the first and second elastomeric compositions are different from each other in both figures.

Upon fracture 218 reaching interior elastomeric region 236, crumbs 222 having a different appearance, for example a different color than exterior elastomer region 234, or a different optical characteristic ingredient, will collect and persist within fracture 218 and/or on exterior surface 226 of bearing stack 202. The presence of the different colored crumbs or change in appearance of crumbs 222 when exposed to an inspection fluid or exposed to ultraviolet light provide an indication of wear that fracture 218 has a reached a certain depth of bearing 200, and thus indicates bearing 200 has met or is near its predetermined service-life replacement criteria.

For example, the spherical bearing 200 depicted in FIG. 10, includes two marker layers 220 that are colored differently than the other elastomeric material layers 228 of bearing stack 202. In this embodiment, the two marker layers 220, have a yellow colored elastomer exterior elastomer region 234 and exterior surface 226 and include a black interior elastomeric region 236 therein (not depicted). In this example, marker layers 220 are selected to be positioned in the fifth and sixth elastomer layer (counting down bearing stack 202 from second end 206). The fifth and sixth elastomer layers were selected based on historical studies and testing which showed that layers five and six are prone to degradation and that elastomeric damage should be expected to develop at these locations first. As a result, when bearing 200 begins to degrade, a fracture 218 forms and extends toward interior elastomeric region 236. Upon reaching the interior elastomeric region 236, black crumbs 222 from interior elastomeric region 236 may accumulate on the yellow colored exterior elastomer region 234 and exterior surface 226 of layers five and six and thus, provide a wear-indication to an observer based on the difference in color on bearing stack 202. In this example, distance d of exterior elastomer region 234 was ⅜ inch, approximately between 10% to 25% of the combined radius r.

As depicted in FIGS. 20A and 24B, annular bearings or bearings having a hollow center, r is defined from the centerline of the marker layer 220.

In some embodiments marker layer 220 further includes a third elastomeric composition 242 as shown in FIGS. 25A and 25B. The third elastomeric composition 242 defines a second interior elastomeric region 244 concentric about longitudinal axis 208. As used herein, second interior elastomeric region 244 may also be referred to as third elastomeric region 244. The third elastomeric composition 242 has a third optical characteristic ingredient. The third elastomeric composition 242 may be compositionally and/or optically different than first and second elastomeric compositions, 224, and 232, respectively. The third elastomeric region 244 is proximate to and enveloped by first interior elastomeric region 236. As previously discussed, first interior elastomeric region 236 is enveloped by exterior elastomeric region 234. All regions are concentric and coplanar.

As shown in FIG. 25A, marker layer 220 has a combined radius r of the first and second interior elastomeric regions 236 and 244, respectively, and outer exterior elastomeric region 234. As shown in FIG. 25A, exterior region 234 extends from the outer perimeter of the combined interior elastomeric region a distance d. The first interior elastomeric region 236 extends a distance of q2 and the innermost second interior elastomeric region 244 extends distance q1. For example, in embodiments having this configuration, the first interior elastomeric region 242 provides a first indication of the first depth range fracture 218 has reached within bearing 200 and the second interior elastomeric region 244 provides a second indication of the second depth range fracture 218 progressed within bearing 200.

The first, second, and third elastomeric compositions, 224, 232, and 242, respectively, are typically based on diene rubber, preferably natural rubber, polyisoprene, polybutadiene, styrene butadiene and blends thereof. The elastomers are formulated to be non-optically similar and compatible so they can be cured together as one elastomeric shim layer, and also distinct, either under human visible light or other electromagnetic spectrum wavelengths such as under ultraviolet light.

For example, one elastomeric composition may be reinforced with carbon black and another by precipitated or fumed silica as a carbon black substitute. When using silica as a carbon black substitute, it is preferred to include a silane coupling agent to increase the interaction between the silica and the polymer. The silica-reinforced elastomer composition may be colored by adding either organic or inorganic pigments or dyes, activated dyes.

The elastomeric compositions are provided with optically different characteristics via optical characteristic ingredients such as made white, rust brown red, and/or green through the addition of titanium dioxide, red iron oxide, and chromium oxide or with green phthalocyanine, respectively. In some embodiments pigments or dyes, including fluorescent pigment dyes are used to achieve visually distinct elastomeric compositions. In other embodiments, the dyes or pigments are water-soluble and activated by an inspection fluid. Other embodiments may use combinations of the above described embodiments.

An example of a distinguishable optical characteristic ingredient includes a water soluble form of fluorescein (called sodium fluorescein or uranine yellow). Sodium fluorescein is not soluble in the elastomer rubber but is readily soluble in water. When exposed to water, sodium fluorescein produces an intense yellow-green color. Sodium fluorescein and other compounds having similar properties may be included in first elastomeric composition 224 of marker layer 220 when bearing 200 is installed in a water environment.

The inclusion of sodium fluorescein in the interior elastomeric region 236 provides a visual or optical indication of fracture 218 depth when the elastomeric crumbs 222 or the fracture 218 itself is exposed to water and turns the water yellow. Expelled interior crumbs 222 may be inspected by water activation by exposing the expelled elastomeric crumbs 222 to water (as shown in FIG. 26), such as with water flushing, water spray, or wiping with a wet material, or installation of bearing 200 in a water environment. It should be appreciated that whatever optical characteristic ingredient that is used within elastomeric material layer 228 not be soluble in the elastomer rubber during the mold and curing process.

Below are examples of optically and/or visually distinguishable rubber elastomers with different distinguishable optical characteristic ingredients:

Optical Character color

Black with

Yellow

Black
Red
White
Yellow
Green
Indicator

Ingredient
—
—
—
—
—
—

Natural rubber
60.0
60.0
60.0
60.0
60.0
60.0

Polybutadiene
30.0
30.0
30.0
30.0
30.0
30.0

rubber

Styrene butadiene
10.0
10.0
10.0
10.0
10.0
10.0

rubber

Aromatic oil
5.0
5.0
5.0
5.0
5.0
5.0

Stearic acid
2.0
2.0
2.0
2.0
2.0
2.0

Zinc oxide
5.0
5.0
5.0
5.0
5.0
5.0

Sulfur
1.8
1.8
1.8
1.8
1.8
1.8

CBTS
1.2
1.2
1.2
1.2
1.2
1.2

(accelerator)

Si-69 Silane
—
5.0
5.0
5.0
5.0
—

N330 carbon
45.0
—
—
—
—
45.0

black

Hi-Sil 233 silica
—
40.0
40.0
40.0
40.0
—

Titanium dioxide
—
8.0
5.0
2.0
5.0
—

Red iron oxide
—
—
1.0
—
—
—

Chromium Green
—
—
—
—
2.0
—

oxide

Yellow 2555
—
—
—
2.5
—
—

pigment

Sodium
—
—
—
—
—
5.0

fluorescein

As shown in FIGS. 6, 7, 18-21, 24B and 25B, elastomeric material layer 228 has a thickness t. Thickness t is defined in the same direction as the longitudinal axis 208 for bearing a compressive between non-elastomeric shim material layers 230. Elastomeric material layer 228 also has an exterior surface bulge area BA and a bonded elastomeric interface load area LA. Interface load area LA corresponds to the bond interface between the elastomeric material layer 228 and non-elastomeric shim material layer 230. For example, as shown in FIG. 22B, elastomeric material layer 228 has a thickness t in the same direction as longitudinal axis 208 with load area LA as the interface bond between elastomeric material layer 228 and non-elastomeric shim material layers 230′ and 230″.

Elastomeric material layer 228 also has a shape factor SF with 0.1<SF<60, preferably with SF=LA/BA and 0.25≦SF≦50. Preferably the interior elastomeric region 236 bonded interface load area compared to the total LA is between 25% to 98% of the total LA, preferably 50% to 96% of the total LA.

As depicted in FIGS. 16 and 17, bearing stack 202 is formed by mold-bonding non-elastomeric shim material layers 230 and elastomeric material layers 228, wherein elastomeric material layers 228 are cured inside mold 246. Elastomeric transfer sprue 248, shown in FIG. 16, is proximate to interior elastomeric region 236 such that the additional elastomer appears optically similar to the interior elastomeric composition 224. FIG. 17 depicts transfer sprues 248 proximate to exterior elastomeric region 234 and the additional elastomer added to the mold 246 appears optically similar to exterior second elastomeric composition 232. FIGS. 16 and 17 illustrate the transfer sprues 248 for forming the alternating layers of bearing stack 202.

Also included is a method for identifying and detecting fatigue in bearing 200. The method utilizes bearing 200 and bearing stack 202 described above. The method includes inspecting a bearing 200 for an indication of fatigue.

Upon fatigue of bearing 200, fracture 218 extends from an exterior perimeter of marker layer 220 toward interior elastomeric region 236 and generates a plurality of crumbs 222 of the first elastomeric composition 224. In embodiments having two interior elastomeric regions, fracture 218 extends toward both interior elastomeric region 236 and second interior elastomeric region 244.

The step of detecting fatigue includes inspecting bearing 200 from a distance, e.g. not in direct contact with bearing 200, by visual inspection, or through use of a stimulus, for example exposing bearing 200 to stimulus in the electromagnetic spectrum, for example, such as shining ultraviolet light thereon. Other forms of inspection may include causing a stream of inspection fluid, such as water to contact bearing 200. An indication of fatigue includes crumbs 222 of first elastomeric composition 224 collecting on exterior surface 226 of bearing 200. A further indication of monitoring the depth of fatigue or wearing within bearing 200 is provided by the difference observed in crumbs 222 of first elastomeric composition 224 as well as crumbs 222 of third elastomeric composition 242. Another indication of monitoring depth of fatigue or wearing within bearing 200 is provided by the difference observed in appearance when a fluorescent ingredient is used in first elastomeric composition 224 and/or third elastomeric composition 242. When an ultraviolet light is shined on bearing 200, if fracture 218 has reached interior elastomeric region 236, the fluorescent ingredient will fluoresce.

As previously discussed, the first, second, and third elastomeric compositions 224, 232, and 242, respectively, may be compositionally different and/or optically different. For example, first, second, and third elastomeric compositions can be different by each having different rubber compositions, different colors, and/or first and third elastomeric compositions can be optically different by including a fluorescent ingredient reactive to ultraviolet light, and/or a water-soluble dye, such that upon exposure to an inspection fluid, the water soluble dye causes the inspection fluid to change colors. As a result of the different visual or optical ingredients used, first, second, and third elastomeric compositions 224, 232, and 242 are different compositionally. The method of detecting fatigue in bearing 200 is also a method of monitoring fracture 218 depth within bearing 200.

Referring now to FIG. 26, in some embodiment, the crumbs 222 are sticky and persist on the outer surface of the HCL bearing 200 and are therefore capable of providing a persistent visual indicator of wear. FIG. 26 shows that crumbs 222 stay on the HCL bearing 200 in spite of a forceful stream of water.

In some embodiments, one or more of the HCL bearing 200 features disclosed in FIGS. 6-26 may be incorporated into a gimbal bearing, such as, but not limited to, gimbal bearing 100. Accordingly, this disclosure contemplates a gimbal bearing comprising at least one HCL bearing comprising elastomeric materials selected to selectively visually indicate wear of the gimbal bearing, such as, but not limited to, fatigue and/or fracture of the HCL bearing. It will be appreciated that one or more of the HCL bearing 200 features may be incorporated into one or more of the HCL bearings 106 while substantially maintaining the general shape and/or profile of the gimbal bearing of FIGS. 1-5. Further, in some embodiments, the elastomeric compositions of an HCL bearing comprising one or more of the HCL bearing 200 features may comprise primarily natural rubber, natural rubber mixtures, and/or elastomeric materials selected to selectively visually indicate wear as described above.

Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.

GIMBAL BEARING SYSTEM AND METHOD

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