GB2153882A - Copper-based spinodal alloy bearings - Google Patents

Abstract

This invention relates to the use of copper-based spinodal alloys, for example, copper-nickel-tin alloys, for bearing surfaces 125 formed between a journal shaft 130 and a roller cutter cone 118 of a sealed bearing rock bit. <IMAGE>

Description

SPECIFICATION Copper-based spinodal alloy bearings This invention pertains to heavy-duty, friction type bearings and to rotary rock bits incorporating such bearings.

The bearings of roller cone rock bits typically carry heavy loads (up to 40,000 pounds), plus intense and continual shock loads during bit operation. Relative sliding velocities between the cone bearing surface and its associated journal bearing run from fifty to as much as five hundred surface feet per minute. Lubrication is typically limited to self-contained non-circulating grease and bit operating temperatures, run between 150 and 400 Fahrenheit.

In the past, many materials and material systems have been used in the production of friction bearings for roller cone rock bits.

U.S. Patent No. 3,721,307, for instance, specifies the use of beryllium copper in a rock bit bearing. Porous steel bearings produced from powdered metal and containing lubricants, such as graphite, in their interstices are described in U.S. Patent No. 4,105,263.

Bearings wherein the steel members are treated to produce a special surface are also well known in the art. For example, U.S.

Patent No. 4,012,238 describes a treatment involving the combined use of boronizing and carburizing to produce a hardened "case" which is used as a bearing surface. U.S.

Patent No. 3,995,917 describes the use of aluminium bronze in the production of a rock bit friction bearing. Tungsten carbides have also been used, as have stellite and other hard materials which are applied by metallurgical hardfacing methods.

The useful life expectancy of these various systems varies according to the particular drilling conditions under which they are used but are typically about 100 hours. Depending upon these conditions, lifetimes of from 20 hours to about 1 50 hours are common.

A small family of highly specialized alloys, called copper-based spinodal alloys, developed in an art remote to either bearings or especially roller cone rock bits, have been discovered to possess physical properties advantageous to the production of rock bit friction bearings. Spinodal alloys, in most cases, exhibit an anomaly in their phase diagram called a miscibility gap. Within the very narrow temperature range of the gap, atomic ordering takes place within the existing crystal lattice structure. The resulting two-phase structure is stable at temperatures significantly below the gap. A cast or wrought material is first solution heat treated, permitting partial or full homogenization and annealing of the material, followed by a high-speed quench to freeze the fine grain structure.Subsequently, the material is age-hardened by raising the material to a temperature within the miscibility gap. A chemical segregation takes place called "spinodal decomposition" wherein two new phases form, of similar crystallographic structure but of different composition.

An intermediate cold-working stage is sometimes introduced between the initial homogenization step and the final age-hardening to increase the dislocation density of the alloy.

Spinodal decomposition does not change the crystal structure of the lattice; hence there are no changes in part dimensions during this process. So processed, spinodal alloys offer high levels of tensile strength, elastic limit, resistance to stress relaxation and fatigue strength.

It has been discovered that copper-based spinodal alloys exhibit tribological properties that facilitate their application in lubricated, as well as non-lubricated, bearing applications as will become evident from the text of this disclosure. The primary family of copperbased spinodal alloys that have performed in a superior manner in our testing are coppernickel-tin type spinodal alloys. These alloys consist primarily of copper containing nickel in an amount of from 2 to 20 percent by weight and tin in an amount of from 2 to 8 percent by weight. The preferred compositions are: 1) copper with 10 percent nickel and 8 percent tin and 2) copper with 1 5 percent nickel and 8 percent tin. Other spinodal alloys within the range of compositions could be used for similar superior bearing properties.

Other families of copper-based spinodal alloys where the nickel and/or tin are replaced by elements such as chromium or iron also peform as spinodal bearings. The preferred compositions are: 1) copper with 2 to 20 percent by weight of nickel and 2 to 8 percent by weight of chromium; 2) copper with 2 to 20 percent by weight of nickel and 2 to 8 percent by weight of iron; 3) copper with 2 to 20 percent by weight of chromium and 2 to 8 percent by weight of tin; and 4) copper with 2 to 20 percent by weight of iron and 2 to 8 percent by weight of tin.

Copper-nickel-tin spinodal alloys that contain one or more additional elements such as iron, zinc, niobium, magnesium, zirconium, chromium or aluminium in total amount(s) not to exceed 1 5 percent by weight, would perform in a superior manner in bearing tests.

Small additions of lead and/or sulfur to improve the lubricity and machinability of the disclosed copper-based spinodal alloys perform suitably in such bearings.

Copper-nickel-tin spinodal alloys, hereafter abbreviated as Cu-Ni-Sn type spinodal alloys, were developed by Bell Telephone Laboratories to provide a material of unusually high strength, simulultaneously with a material which for many years could resist corrosion and erosion in a marine or submarine environment.

A series of United States patents relating to the making and processing of Cu-Ni-Sn type spinodal alloys have been assigned to Bell Telephone Laboratories. Those patents of particular interest include the following: No.

3,937,638 (METHOD FOR TREATING COP PER-NICKEL-TIN ALLOY COMPOSITIONS AND PRODUCTS PRODUCED THEREFROM), No. 4,052,204 (QUATERNARY SPINODAL COPPER ALLOYS), No. 4,090,890 (METHOD FOR MAKING COPPER-NICKEL-TIN STRIP MATERIAL) and No. 4,142,918 (METHOD FOR MAKING FINE-GRAINED Cu-Ni-Sn AL LOYS).

None of the above patents suggest the use of these spinodal alloys for bearing applications. More importantly, none of the above patents suggest the use of these spinodal alloys as bearing materials for roller cone rock bits, a particularly harsh environment for any type of bearing material.

The singular most unique feature of the Cu Ni-Sn spinodal alloys shows up during the aging process. Tensile strength and ductility, normally mutually exclusive properties, are both very high after aging. The degree to which the tensile strength is increased in aging is highly dependent upon the degree of cold-working to which the material is subjected after its solution treatment. The tensile strength can go as high as 200,000 pounds per square inch. Surprisingly, during this process, very little of the ductility is lost.

In a comprehensive comparative program of laboratory testing on standard bearings, the Cu-Ni-Sn spinodal candidates performed favorably above the beryllium copper candidate.

The heat treatment schedules typically used to induce spinodal decomposition of the Cu Ni-Sn alloys were as follows. Cast or wrought materials were first solution heat treated between 725 and 825 Centigrade for 30 to 120 minutes to homogenize the alloys, followed by water quenching. The alloys were then aged between 350 and 425 Centigrade for between 3 to 5 hours to spinodally decompose the alloys, rendering materials of high hardness and high ductility.

An advantage of the use of Cu-Ni-Sn spinodal alloys is superior ductility. For example, beryllium copper has a hardness of about 38 Rockwell C (HRC), about the same as the Cu Ni-Sn spinodal alloys, but the spinodal materials are much more ductile parameter that is highly desirable in bearing materials.

In addition, beryllium copper is more susceptible to stress corrosion cracking and corrosion-related failures than the Cu-Ni-Sn spinodal alloys. Such environments are commonly found in drill bit applications, such as, chlorides, sulfates, silicates, etc. These corrosive environments (abrasion, adhesion and corrosion) combined accelerate corrosive wear and shorten the life of the bearing.

These types of tribological failures have been shown to be directly attributable to the ductility and toughness of any kind of bearing material.

Being less ductile, beryllium copper is also more susceptible to surface cracking and galling.

Cu-Ni-Sn spinodal alloys exhibit superior elongation properties as well as greater ductility and toughness. The materials also have excellent resistance to applied stresses, thereby controlling erosion, cracking, etc.

Cu-Ni-Sn type spinodal materials, therefore, have a particular application in rotary cone rock bits. The rock bit bodies are generally fabricated from metal with at least one leg depending from the bit body. A journal shaft depends from the leg. A metal roller cutter cone is adapted to be rotatively secured to the journal shaft. A bearing material is disposed between the journal and the roller cutter. The bearing material comprises copper-nickel-tin type spinodal alloys.

A three cone rock bit embodying the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of the three cone rock bit; Figure 2 is a partially broken away cross section of one leg of the rock bit of Fig. 1, illustrating the roller cone mounted to a journal bearing with a lubrication system communicating with the bearing surfaces defined between the journal bearing and the cone; Figure 3 is a partially broken away leg of a rock bit, illustrating a journal bearing shaft and a cone mounted to the shaft with a metallurgically bonded layer of Cu-Ni-Sn spinodal alloy in the bearing surfaces defined by the cone; Figure 4 is a graph comparing the Cu-Ni-Sn spinodal alloy with aluminium bronze and beryllium copper commonly utilized in the rock bit art; ; Figure 5 is a partially broken away cross section of another embodiment of the present invention, illustrating a sleeve of Cu-Ni-Sn spinodal alloy material pressed in a recessed cavity in the cone, the spinodal pressed-in sleeve acting as a bearing against the journal shaft; Figure 6 is a partially broken away cross section of still another embodiment of the present invention wherein a cylindrical ring of Cu-Ni-Sn spinodal material is pressed into a cavity in the cone, the inner surface of the spinodal material acting as a bearing surface against the bearing surfaces formed by the journal bearing; Figure 7 is yet another embodiment of the present invention wherein a cylindrical floating ring of Cu-Ni-Sn spinodal alloy material is placed between a journal bearing and a bearing surface formed in the rotary cone; and Figure 8 is still another embodiment of the present invention wherein a floating ring of Cu-Ni-Sn spinodal alloy material is positioned between a bearing surface formed in the cone and a bearing surface formed on the journal.

With reference to Fig. 1, a roller cone rock bit, generally designated as 10, is depicted. A bit body 1 2 defines a pin end 16, adapted to receive drill segments (not shown) that make up a typical drillstring in a drilling operation.

A series of legs 14 depend from the bit body 1 2. Each of the legs 14 support a roller cone, generally designated as 1 8. A multiplicity of cutter type elements 20 are strategically positioned on the cones to describe a specific cutting pattern in a borehole during bit operation. The types of cutters illustrated in Fig. 1 are tungsten carbide inserts that are pressed into drilled holes in the cone body. One or more nozzles 22 are positioned in the bit body 1 2 to pass drilling mud into the borehole bottom through each of the nozzles. A grease reservoir system, generally designated as 24, provides a reservoir of lubricant 52 to the sealed bearings formed between the cones 1 8 and their respective journals 30.

With reference now to Fig. 2, one of the sectioned legs 1 4 illustrates the lubrication reservoir system 24. The system includes a pressure compensator boot 50 to accommodate for differential pressures between the outside of the bit and the internal bearing surfaces of the bit. The reservoir system includes a channel 54 to direct lubricant from the reservoir to the bearings defined between the cone and the journal. The leg 1 4 terminates in a shirttail portion 1 5 (shown in both Figs. 1 and 2). A journal, generally designated as 30, is cantilevered from the leg 14 toward the centre of the bit. A ball race 40, transverse to the axis of the journal 30, is so positioned to register with a complementary ball race 21, formed in the cutter cone 18.A multiplicity of cone retention balls 42 are inserted through a ball hole 44. The ball hole is drilled from the outside shirttail portion 1 5 through the journal 30 to intersect the ball race 40. When the ball race 40 is filled with the balls 42, a ball plug 46 is then inserted in the ball hole 44 and secured by a welded cap 47. A relief portion 48 is formed in the ball plug 46 to admit lubricant from the grease reservoir chamber 52 to bearing surface formed between the journal and the cone.

In Fig. 2, the journal 30 has a channel 34 in the journal bearing surface 32. The bottom or load side of the journal 30 is filled with a hard-facing material 36 (for example, a stellite material). The upper portion of the channel 34 is left as a grease reservoir space 38 to provide a supply of lubricant to the bearing surfaces.

The cone, generally designated as 18, has an internal cavity 1 9 that serves as a cone bearing surface. A spindle bearing surface 26 is further formed within the cone 18 to complement a spindle bearing 33 that extends from the end of the journal bearing. The cone is, for example, fabricated from a metal, such as steel. The cone surface is machined and drilled to accept a multiplicity of, for example, tungsten carbide inserts 20 that are interference fitted within the drilled holes in the cone. The surface of the cone could, however, be machined to form equidistantly spaced milled teeth that form the cutting edge of each of the cones. A seal gland 27 may, for example, be cut into the entrance of the bearing surfaces in the cone 18, the seal gland being so configured to accept an O-ring type seal 28.The O-ring forms a seal between the seal gland 27 and the journal bearing 34.

Any type of seal may, however, be utilized without departing from the intent of the invention. A circumferential groove 23 is formed within the bearing surface 1 9 of cone 18, the groove generally registering with the groove 34 in journal 30. The groove 23 is subsequently filled with a Cu-Ni-Sn spinodal material which is metallurgically bonded within the annular groove 23 within cone 18. The spinodal material, as heretofore stated, provides a good bearing surface after machining that is both tough and ductile to enhance the logevity of the rock bit as it works in a borehole. The machined spinodal bearing surface runs against, for example, the hard stellite material 36 that is metallurgically bonded within the groove 34 in the journal.The rock bit, as it works in a borehole, exerts pressure to the loaded side of the journal, thus contacting the spinodal bearing material bonded to the cone against the hardened surface 36 within the load side of journal 30.

Another bearing surface 37, known as a "snoochie", is formed in the journal 30. The snoochie surface provides an in-thrust bearing surface that mates with a complementary surface 39 formed in the cone cavity. Although it is not illustrated, it would be obvious to use a spinodal material such as Cu-Ni-Sn alloy on the snoochie bearing surface formed on the journal or the complementary thrust bearing surface in the cone without departing from the teachings of this invention.

With reference now to Fig. 3, another embodiment of the present invention is depicted wherein the journal, generally designated as 130, is dependent from a leg 114. The bearing surface 132, however, lacks a circumferential annular groove in the journal as depicted in Fig. 2. The journal is machined to provide a bearing surface 1 32 in the parent material of the leg. The cone 11 8 has an annular groove 123, machined in the bearing surfaces 119, the groove being filled with a Cu-Ni-Sn spinodal alloy material 1 25 in the same manner as was done with the cone of Fig. 2. The spinodal material is subsequently machined and provides a primary bearing surface for the bearing 1 32 of journal 1 32.

Journal bearing 1 30 has a spindle 1 33 extending from the thrust bearing end 1 37 (snoochie) of the journal. A spindle bearing surface 1 34 runs against complementary bearing surface 1 26 in cone 118. Either the spindle or the cone could have a channel filled with a Cu-Ni-Sn spinodal material 1 25 to provide a superior bearing surface between the spindle and the cone. A series of cone retention balls 142 are confined within ball races 140/121 in journal 130 and cone 118.

A similar ball plug 146 is housed within a ball plug hole 144 and held in place with a welded cap 147 in shirttail 11 5. A seal 1 28 prevents leakage of lubricant from the bearing surfaces defined between the journal and the cone.

Turning now to Fig. 4, the chart illustrated depicts the tensile strength and ductility of three different bearing type materials. For example, in the first column, aluminium bronze has a tensile strength of 7,000 kg/cm2 (100KS1) and a ductility of 1%. Beryllium copper shows a tenstile strength of 14,000 kg/cm2 (200KSI) with a 1 % ductility factor while the Cu-Ni-Sn spinodal alloy material has a tensile strength of 13,400 kg/cm2 (190KSI) with a 4% ducility factor. Clearly then, the Cu-Ni-Sn spinodal alloy material has a greater than or substantially equal tensile strength when compared to aluminium bronze or beryllium copper-with a much higher ductility factor than either, which is advantageous when used as a bearing material, especially in the rock bit art.

Turning now to still a different embodiment, illustrated in Fig. 5, a spinodal material (such as Cu-Ni-Sn) is formed in a hollow right cylinder and generally designated as 225. The cylinder of spinodal material 225 is pressed into an annular recess 223, formed in cone 218. The journal 230 has a channel 234 formed in the journal 30 of Fig. 2. The loaded side 236 of the journal is filled with a hard metal. The unloaded side 238 of the channel 234 provides a grease reservoir for the bearings formed between the journal and the cone. Again, the cone is retained on the journal by a series of cone retention balls 242 that track within races 221 and 240, formed between the cone and the journal. A ball plug 246 secures the balls within their track.The internal diameter 226 of the ring of spinodal material 225 is machined with appropriate bearing tolerances to conform to the bearing surface 232 of the journal 230. In the embodiment shown in Fig. 5, the spinodal material 225 may be pressed or interference fitted within a complementary channel 223 formed in the cone without metallurgically bonding the ring of spinodal material within the cone.

Fig. 6 is yet another embodiment wherein a similar ring of spinodal material, such as Cu Ni-Sn alloy and generally designated as 324, is pressed within a complementary channel 323 in cone 318. The difference between Fig.

6 and Fig. 5 is that the journal 330 is machined from the basic material of the leg 314 (without the circular track 234, shown in Fig. 5). The inner machine bearing surface 326 in the spinodal material 325 runs against a complementary machined bearing surface 331 of the journal 330. A spindle 333 extends from the end of the journal 330 and mates within a complementary annular recess formed in cone 318. Again, an O-ring 328 is housed within a seal gland 327 formed in the cone 318. The seal acts to retain lubricant within the bearing surfaces formed between the journal and the cone.

Figs. 7 and 8 depict still different embodiments of the present invention. Fig. 7 illustrates a journal bearing 430 with a circumferential groove formed on the surface of the journal, the groove having the hardfacing material on the loaded side of the groove 436 with the open or unloaded side of the groove 438 acting as a lubricant reservoir as heretofore mentioned. A cylindrical floating bearing ring, generally designated as 424, is fabricated from Cu-Ni-Sn spinodal material 425.

The inner and outer bearing surfaces 426 and 427 are so machined to act as bearing surfaces between the journal bearing 431 and the cone bearing 41 9. The ring of spinodal material 425 now acts as a floating ring between the journal and the cone. By utilizing a floating ring of spindal material, the slip speeds (surface feet per minute) between the cone and the journal are divided by the bearing surfaces 426 and 427 of the ring of spinodal material. Thus, the surface feet per minute is halved between a journal bearing surface and a cone bearing surface when compared to a conventional bearing between a journal and a cone. A series of cone retention balls 442 are nested within ball bearing races 440 in the cone and a similar race by means heretofore described. Again, an O-ring 428 is confined within a seal gland 429 in the cone 418.

Finally, Fig. 8 depicts a floating ring, generally designated as 524. The ring of a Cu-Ni Sn spinodal material 525 floats between a journal bearing 530 and a cone 518. Again, both the inner cylindrical surface 526 and the outer cylindrical surface 527 of the spinodal material 525 acts as a bearing surface between the journal bearing surface 531, formed of the basic material of the journal 530. The hardfacing is absent from the configuration as illustrated in Fig. 8. The cone, again, is being retained by a series of balls 554 within ball races formed between the cone and the journal.

It would be obvious to press or metallurgically bond a ring of Cu-Ni-Sn spinodal material to the journal bearing shafts of Figs. 3, 6 and 8.

It would additionally be obvious to provide the Cu-Ni-Sn spinodal bearing material to both the cone recess and the journal without departing from the teachings of this invention.

Claims (7)

1. A rotary cone rock bit comprising: a rock bit body, at least one leg depending from said body, a journal shaft on said leg, a roller cutter cone adapted to be rotatively secured to said journal shaft, and a bearing material disposed between said journal and said roller cutter, said bearing material consisting essentially of copper-based spinodal alloys.

2. A bit as set forth in Claim 1, wherein said bearing material is metallurgically bonded to bearing surfaces formed within said cone.

3. A bit as set forth in Claim 2, including a circumferential groove in a bearing surface formed by said shaft, said groove being transverse to an axis of said shaft, a portion of said groove being filled with a hardfacing metal for acting as a bearing when said cone bearing surface is loaded against said shaft bearing surface during rock bit operation.

4. A bit as set forth in any one of Claims 1 to 3, wherein said bearing material is formed in a cylindrical ring, said ring being interference fitted within a complementary cavity formed in said roller cutter, an inner surface of said cylindrical ring forming a bearing surface for said journal shaft.

5. A bit as set forth in Claim 1, wherein said bearing material is formed in a cylindrical ring, said ring being so dimensioned to float between said journal shaft and said roller cutter, the inner and outer surfaces of said floating ring serving as bearing surfaces adjacent complementary bearing surfaces formed by said journal and said roller cutter.

6. A bit as set forth in Claim 1 or in Claim 2, wherein said bearing material is formed in a cylindrical ring, said ring being so dimensioned to float between said journal shaft and said roller cutter, the inner and outer surfaces of said floating ring serving as bearing surfaces adjacent complementary bearing surface formed by said journal and said roller cutter cone.

6. A bit as set forth in Claim 5, wherein the inner bearing surface of said floating ring bears against said journal shaft, said shaft having a circumferential groove in said shaft bearing surface, said groove being transverse to an axis of said shaft, a portion of said groove being filled with a metal harder than the metal of said shaft for acting as a bearing when said roller cutter and said floating ring is loaded against said hard metal surface during rock bit operation.

7. A bit as set forth in any preceding Claim, wherein said copper-based spinodal alloy comprises 2 to 20 percent by weight nickel and 2 to 8 percent by weight tin.

8. A bit as set forth in any one of Claims 1 to 6, wherein said copper-based spinodal alloys consist essentially of copper-nickel-tin.

9. A bit as set forth in Claim 8, where said copper-nickel-tin spinodal alloy consists essentially of copper having about 1 5 percent by weight nickel and about 8 percent by weight tin.

10. A bit as set forth in Claim 8, wherein said copper-nickel-tin spinodal alloy consists essentially of copper having about 10 percent by weight nickel and about 8 percent by weight tin.

11. A bit as set forth in any one of Claims 8 to 10, wherein said copper-nickel-tin spinodal alloy contains about 1 percent by weight sulfur.

1 2. A bit as set forth in any one of Claims 8 to 10, wherein said copper nickel-tin spinodal alloy contains about 1 percent by weight lead.

1 3. A bit as set forth in Claim 8, wherein said copper nickel-tin spinodal alloy contains a fourth metal selected from the group consisting of iron, zinc, niobium, magnesium, zirconium, chromium, aluminium.

14. A bit as set forth in Claim 13, wherein said copper-nickel-tin spinodal alloy contains up to 1 5 percent by weight of said fourth metal.

1 5. A bit as set forth in any one of claims 1 to 6, wherein said copper-based spinodal alloys consist essentially of copper-nickelchromium.

16. A bit as set forth in Claim 15, wherein said copper-based spinodal alloy comprises 2 to 20 percent by weight nickel and 2 to 8 percent by weight chromium.

1

7. A bit as set forth in any one of Claims 1 to 6, wherein said copper-based spinodal alloys consist essentially of copper-nickel-iron.

18. A bit as set forth in Claim 17, wherein said copper-based spinodal alloy comprises 2 to 20 percent by weight nickel and 2 to 8 percent by weight iron.

1 9. A bit as set forth in any one of Claims 1 to 6, wherein said copper-based spinodal alloy consists essentially of copper-chromiumtin.

20. A bit as set forth in Claim 19, wherein said copper-based spinodal alloy comprises 2 to 20 percent by weight chromium and 2 to 8 percent by weight tin.

21. A bit as set forth in any one of Claims 1 to 6, wherein said copper-based spinodal alloys consist essentially of copper-iron-tin.

22. A bit as set forth in Claim 21, wherein said copper-based spinodal alloy comprises 2 to 20 percent by weight iron and 2 to 8 percent by weight tin.

23. A rotary cone rock bit substantially as hereinbefore described, with reference to Figs.

1 to 4 or any one of Figs. 5 to 8 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1, 2 and 5 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:- Claims 3, 4 and 6 to 23 above have been re-numbered as 4, 5 and 7 to 24 and their appendancies corrected.

1. A rotary cone rock bit comprising: a rock bit body, at least one leg depending from said body, a journal shaft on said leg, a roller cutter cone adapted to be rotatively secured to said journal shaft, and a bearing material disposed between said journal and said roller cutter cone, said bearing material consisting essentially of copper-based spinodal alloys.

2. A sealed bearing rotary cone rock bit comprising: a rock bit body, at least one leg depending from said body, a journal shaft on said leg, a roller cutter cone adapted to be rotatively secured to said journal shaft, and bearing surfaces formed by said journal and said cone, one of said bearing surfaces having a bearing material disposed thereon, said bearing material consisting of copper-based spinodal alloys, the other of said bearing surfaces being formed of a material harder than said spinodal alloys.

3. A bit as set forth in Claim 1 or in Claim 2, wherein said bearing material is metallurgically bonded to a cavity formed by said cone, said material forming bearing surfaces within said roller cutter cone.