U.S. patent application number 10/601505 was filed with the patent office on 2004-02-19 for dlc coating for earth-boring bit bearings.
Invention is credited to Dick, Aaron J., Lin, Chih C..
Application Number | 20040031625 10/601505 |
Document ID | / |
Family ID | 40099560 |
Filed Date | 2004-02-19 |
United States Patent
Application |
20040031625 |
Kind Code |
A1 |
Lin, Chih C. ; et
al. |
February 19, 2004 |
DLC coating for earth-boring bit bearings
Abstract
An earth-boring bit has a bearing member having a DLC coating.
The bearing member locates between a bearing pin and a cone of the
bit. The bearing member may be a thrust washer or a bearing sleeve.
The DLC coating is diamond-like carbon that may be coated by
different processes onto bearing member.
Inventors: |
Lin, Chih C.; (Spring,
TX) ; Dick, Aaron J.; (Houston, TX) |
Correspondence
Address: |
James E. Bradley
BRACEWELL & PATTERSON, LLP
P.O. Box 61389
Houston
TX
77208-1389
US
|
Family ID: |
40099560 |
Appl. No.: |
10/601505 |
Filed: |
June 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10601505 |
Jun 23, 2003 |
|
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10223533 |
Aug 19, 2002 |
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Current U.S.
Class: |
175/371 ;
384/95 |
Current CPC
Class: |
F16C 2206/04 20130101;
E21B 10/25 20130101; F16C 2352/00 20130101; F16C 33/043 20130101;
F16J 15/3496 20130101 |
Class at
Publication: |
175/371 ;
384/95 |
International
Class: |
E21B 010/22 |
Claims
1. An earth-boring bit, comprising: a bit body; a cantilevered
bearing pin depending from the bit body; a cone mounted for
rotation on the bearing pin; and a bearing surface between the cone
and the bearing pin, the bearing surface having a DLC coating
formed thereon.
2. The bit according to claim 1, wherein the DLC coating has a
thickness in the range from 1 to 10 micrometers.
3. The bit according to claim 1, wherein the DLC coating has a
thickness in the range from 2 to 5 micrometers.
4. The bit according to claim 1, wherein the DLC coating has a
thickness in the range from 2 to 3 micrometers.
5. The bit according to claim 1, wherein the DLC coating has a
Knoop Scale hardness in the range from 2000 to 5000.
6. The bit according to claim 1, wherein the DLC coating is of
carbon with a mixture of sp3 and sp2 bonds between atoms of the
carbon.
7. The bit according to claim 1, wherein the DLC coating is formed
of amorphous and hydrogenated amorphous carbon.
8. The bit according to claim 1, wherein the DLC coating is doped
with an alloying element from the group consisting essentially of
silicon, boron and boron nitride and a refractory metallic element
from the group consisting essentially of tantalum, titanium,
tungsten, niobium and zirconium.
9. The bit according to claim 1, further comprising a thrust washer
located between a thrust shoulder of the bearing pin and the cone,
the bearing surface containing the DLC coating being on at least
one side of the thrust washer.
10. The bit according to claim 1, further comprising a sleeve
located between the bearing pin and the cone, the bearing surface
containing the DLC coating being on at least one side of the
sleeve.
11. The bit according to claim 1, further comprising a thrust
washer located between a thrust shoulder formed on the bearing pin
and the cone, and a sleeve located between the bearing pin and the
cone, the bearing surface containing the DLC coating being on at
least one side of the thrust washer and on at least one side of the
sleeve.
12. The bit according to claim 1, wherein the bearing surface
having the DLC coating is formed on a journal surface of the
bearing pin.
13. The bit according to claim 1, wherein the bearing surface
having the DLC coating is formed within a cavity of the cone.
14. An earth-boring bit, comprising: a bit body; a cantilevered
bearing pin depending from the bit body, the bearing pin having a
thrust shoulder that is in a plane perpendicular to the axis of the
bearing pin; a cone mounted for rotation on the bearing pin, the
cone having a thrust shoulder facing toward the thrust shoulder of
the bearing pin; and a thrust washer located between and in
engagement with the thrust shoulders of the bearing pin and the
cone, the thrust washer having a DLC coating formed thereon on at
least one side.
15. The bit according to claim 14, wherein the DLC coating is
formed on both sides of the thrust washer.
16. The bit according to claim 14, wherein the thrust shoulder of
the bearing pin contains an inlay of a hard wear resistant
material.
17. The bit according to claim 14, wherein the thrust shoulder of
the bearing pin has a DLC coating formed thereon.
18. The bit according to claim 14, wherein the coating is of carbon
with a mixture of sp3 and sp2 bonds between atoms of the
carbon.
19. The bit according to claim 14, wherein the coating is formed of
amorphous and hydrogenated amorphous carbon.
20. The bit according to claim 14, wherein the DLC coating is doped
with an alloying element from the group consisting essentially of
silicon, boron and boron nitride and a refractory metallic element
from the group consisting essentially of tantalum, titanium,
tungsten, niobium and zirconium.
21. An earth-boring bit, comprising: a bit body; a cantilevered
bearing pin depending from the bit body; a cone mounted for
rotation on the bearing pin; and a sleeve located between the
bearing pin and a cavity in the cone and having a DLC coating
formed thereon that is on at least one side.
22. The bit according to claim 21, wherein the DLC coating is on
both sides of the sleeve.
23. The bit according to claim 21, wherein the bearing pin also
contains a DLC coating.
24. The bit according to claim 21, wherein the cavity of the cone
also contains a DLC coating.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This invention is a continuation-in-part of application Ser.
No. 10/223,533, filed Aug. 19, 2002.
FIELD OF THE INVENTION
[0002] This invention relates in general to earth-boring bits,
especially the bearings for earth-boring bits of the rolling cone
variety. More particularly, the invention relates to coatings on
the bearings for enhancing wear resistance.
BACKGROUND INFORMATION
[0003] In drilling boreholes in earthen formations by the rotary
method, earth-boring bits typically employ at least one rolling
cone cutter, rotatably mounted thereon. The bit is secured to the
lower end of a drillstring that is rotated from the surface or by
downhole motors. The cutters mounted on the bit roll and slide upon
the bottom of the borehole as the drillstring is rotated, thereby
engaging and disintegrating the formation material. The rolling
cutters are provided with teeth that are forced to penetrate and
gouge the bottom of the borehole by weight from the
drillstring.
[0004] As the cutters roll and slide along the bottom of the
borehole, the cutters, and the shafts on which they are rotatably
mounted, are subjected to large static loads from the weight on the
bit, and large transient or shock loads encountered as the cutters
roll and slide along the uneven surface of the bottom of the
borehole. Thus, most earth-boring bits are provided with
precision-formed journal bearings and bearing surfaces, as well as
sealed lubrication systems to increase drilling life of bits. The
lubrication systems typically are sealed to avoid lubricant loss
and to prevent contamination of the bearings by foreign matter such
as abrasive particles encountered in the borehole. A pressure
compensator system minimizes pressure differential across the seal
so that the lubricant pressure is equal to or slightly greater than
the hydrostatic pressure in the annular space between the bit and
the sidewall of the borehole.
[0005] The bearing surfaces include a thrust shoulder formed on the
bearing pin perpendicular to the axis of the bearing pin. A mating
thrust shoulder is formed in the cavity of the cone. A partially
cylindrical journal bearing surface is formed around part of the
bearing pin for engaging a mating surface in the cavity of the
cone. In the past, inlays of a hard material, such as Stellite,
have been placed on the thrust shoulder and on the journal bearing
surface. Also, a hardened ring has been mounted in the cavity of
the cone for engaging the inlay on the journal bearing surface.
[0006] Very hard, wear-resistant layers and coatings have been
developed for a variety of purposes, such as those employing
diamond. These coatings, however, generally need to be applied at
high temperatures and high pressures and are applied after the
steel member has been hardened. If the high temperatures exceed the
lowest transformation temperature of the steel member, such as the
temperature at which the steel member has been tempered, this would
adversely affect the properties of the seal member.
[0007] U.S. Pat. No. 6,209,185 to Scott discloses applying a
diamond layer to a substrate, then attaching the diamond layer to a
rigid seal ring. This avoids having to heat the hardened ring
beyond its lowest transformation temperature, but it does require
attachment by brazing, epoxy or the like. U.S. Pat. No. 6,045,029
to Scott discloses forming a diamond layer directly on a rigid seal
ring by a process that is accomplished at a temperature lower than
the lowest transformation temperature of the metal of the seal
ring. This may be done in an amorphic diamond process or by forming
the diamond layer separately and attaching it to the rigid ring of
the seal.
SUMMARY OF THE INVENTION
[0008] In this invention, rather than a diamond coating, a
diamond-like coating (DLC) is applied. A DLC coating is a form of
meta-stable amorphous carbon or hydrocarbon polymer with properties
very similar to those of diamond. It is a vapor deposited carbon
coating with a mixture of sp3 and sp2 bonds between the carbon
atoms and could be doped with one or more alloying elements such as
silicon, boron, boron nitride, and one ore more refractory metallic
elements, such as tantalum, titanium, tungsten, niobium or
zirconium. The designation sp3 refers to the tetrahedral bond of
carbon in diamond, while the designation sp2 is the type of bond in
graphite. As DLC has a certain percentage of both, the hardness is
less than diamond and between diamond and graphite.
[0009] The DLC coating is applied to the seal face of a bearing
member after it has been hardened and tempered. It is applied at a
temperature lower than the lowest transformation temperature so as
to not detrimentally affect the dimensions or hardness of the
substrate body of the thrust member. In one process, it is
performed by the decomposition of a carbon and hydrogen compound,
such as acetylene, in the presence of a plasma. The process is
carried out until the coating has a thickness in the range from
about 1 to 10 micrometers. The Knoop scale hardness is in the range
from 2,000 to 5,000.
[0010] In one embodiment, the bearing member that has the DLC
coating comprises a thrust washer that locates between the thrust
shoulders of the bearing pin and the cone. Also, the bearing sleeve
that fits in the cone and engages the bearing pin preferably
contains a DLC coating on at least one side. In the first
embodiment, the bearing pin thrust shoulder and journal bearing
surface have inlays of a hard, wear resistant material such as
Stellite. In an alternate embodiment, the DLC coating is also
applied to the bearing pin thrust shoulder and journal bearing
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a sectional view of a portion of an earth-boring
bit constructed in accordance with this invention.
[0012] FIG. 2 is a perspective view of a journal bearing sleeve of
the bit of FIG. 1.
[0013] FIG. 3 is a perspective view of a thrust washer of the bit
of FIG. 1.
[0014] FIG. 4 is a schematic sectional view of a portion of the
thrust washer of FIG. 3.
[0015] FIG. 5 is a side view of part of a bearing pin of an
alternate embodiment.
[0016] FIG. 6 is a graph illustrating a thrust wear test.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Referring to FIG. 1, bit 11 has at least one bit leg 13 and
normally three. Each bit leg 13 has a bearing pin 15 that extends
downward and inward toward an axis of rotation of bit 11. Bearing
pin 15 has a cylindrical nose 17 on an inner end that is of lesser
diameter than remaining portions of bearing pin 15. An inward
facing annular thrust shoulder 19 surrounds nose 17. Thrust
shoulder 19 is located in a plane perpendicular to an axis of
bearing pin 15. In this embodiment, thrust shoulder 19 optionally
has an inlay 21 of a hard, wear resistant material, such as
Stellite. Similarly nose 17 may have an inlay 23 of the same wear
resistant material on its cylindrical exterior.
[0018] Bearing pin 15 has a partially cylindrical journal bearing
surface 25 that extends around its lower side. In this embodiment,
an optional inlay 27 of a hard wear resistant material, such as
Stellite, is located in journal bearing surface 25. Since the
thrust imposed on bit 11 is downward, inlay 27 does not extend to
the upper side of bearing pin 15. Inlays 21 and 23 could be omitted
if desired. A lubricant passage 29 extends through bit leg 13 and
bearing pin 15 to the upper side of bearing pin 15. A pressure
compensator (not shown) supplies pressurized lubricant to passage
29.
[0019] A cutter or cone 31 mounts rotatably to bearing pin 15. Cone
31 has a plurality of teeth 33 on its exterior. FIG. 1 shows teeth
33 from all three cones 31 of bit 11 rotated into a single plane.
Teeth 33 may be hard metal inserts pressed into mating holes in the
body of cone 31, as shown. Alternately, they may be steel teeth
milled into the exterior of cone 31.
[0020] Cone 31 has a central cavity 35 for rotatably mounting on
bearing pin 15. Cavity 35 has a thrust shoulder 37 that is
perpendicular to the axis of cone 31 for mating with bearing pin
thrust shoulder 19. A thrust washer 39 is located between thrust
shoulders 19 and 37. In the preferred embodiment, thrust washer 39
is not fixed to either thrust shoulder 19 or 37, although it could
be brazed or welded to one of the shoulders 19 or 37.
[0021] A bearing sleeve 41 is located in the cavity of cone 31 in
this embodiment to serve as part of a seal assembly. As shown in
FIG. 2, bearing sleeve 41 preferably does not extend entirely 360
degrees, rather has a gap or slit on its upper side. Bearing sleeve
41 rotates with cone 31 and slidingly engages journal bearing inlay
47 in this embodiment. A retainer ring 43 extends around cavity 35
in engagement with a retaining groove 45 to hold cone 31 on bearing
pin 15. Another type of retainer uses balls. A seal assembly 47
seals the outer end of cavity 35 to bearing pin 15.
[0022] Thrust washer 39 and bearing sleeve 41 are preferably formed
of a hardened ferrous metal selected from the group consisting
essentially of iron with cobalt and alloys thereof, such as
stainless steel or Stellite. The material of thrust washer 39 and
bearing sleeve 41 has a lowest transformation temperature, which is
considered to be a temperature at which the metal at least
partially loses its properties as a hardened metal.
[0023] As illustrated in FIG. 4, a coating 49 of DLC material is
applied to at least one of the faces, preferably both, of thrust
washer 39. The thickness of coating 49 is greatly exaggerated in
FIG. 4. A similar DLC coating is optionally applied to the inner
diameter of bearing sleeve 41. As discussed above, DLC, or
diamond-like carbon, is a form of meta-stable amorphous carbon or
hydrocarbon compound with properties very similar to those of
diamond. Being amorphous, there are no grain boundaries. DLC
coating is a carbon coating with a mixture of sp3 and sp2 bonds
between the carbon atoms. The sp3 bond is a tetrahedral bond of
carbon that forms diamond. The sp2 bond is of a type that forms
graphite. Technically, the sp3 bond means that the carbon
reconfigures one s-orbit and three p-orbits to form four identical
orbits in a tetrahedral configuration for bonding to the next
carbon atom. The sp2 bond is the hybridization of one s and two
p-orbits to three sp2 orbits, which are planar. DLC has a certain
percentage of both types of bonds, thus the hardness is between
diamond and graphite. The proportions of sp2 and sp3 can be varied.
In addition to carbon, there is a certain amount of hydrogen in the
DLC coatings. The hydrogen content comes from the process gas used,
since normally DLC coatings are deposited by the decomposition of a
carbon and hydrogen compound. One acceptable compound is acetylene.
Also, the DLC coating may be doped with one or more alloying
elements such as silicon, boron, boron nitride and one or more
refractory metallic elements, such as tantalum, titanium, tungsten,
niobium or zirconium.
[0024] Thrust washer 39 and bearing sleeve 41 are first hardened,
tempered and formed to the desired dimensions. Portions of thrust
washer 39 and bearing sleeve 41 that are not to be coated are
masked off. One process to apply the DLC coating comprises
depositing material from an RF (radio frequency) plasma, sustained
in hydrocarbon gases, onto negatively biased thrust washer 39 and
bearing sleeve 41. In this process, referred to as plasma assisted
chemical vapor deposition or PACVD, thrust washer 39 and bearing
sleeve 41 are heated by an electron current to a temperature below
their lowest transformation temperatures. Electrons from the
electron current are attracted to the exposed portions of thrust
washer 39 and bearing sleeve 41 from a plasma beam in the center of
the chamber. After heating, the exposed portions are etched by
argon ion bombardment. For this etching process, thrust washer 39
and bearing sleeve 41 are biased to a negative potential to attract
argon ions from a plasma source. This process cleans the exposed
surfaces by etching.
[0025] Afterward, one or more metallic interlayers, usually
chromium, is applied from a sputter source such as a chromium
target. Sputtering is a similar process to etching, but a bias
voltage is applied to the chromium target of several hundred volts.
The exposed surfaces of thrust washer 39 and bearing sleeve 41
serve as a negative electrode. Material is removed from the
chromium target surface by the impact of argon ions. This material
condenses on the exposed surfaces. The metallic interlayer is used
to increase adhesion and could be formed of other metals such as
titanium.
[0026] After the interlayer is laid, acetylene is introduced and a
plasma is ignited between the exposed surfaces of thrust washer 39
and bearing sleeve 41 and the chamber walls. The acetylene
decomposes to form carbon atoms that coat the exposed surfaces on
the metallic interlayer with DLC. DLC coatings are insulating, thus
the plasma for the DLC cannot be a DC plasma, but must be an AC
plasma. Typically an RF plasma is used. After coating, thrust
washer 39 and bearing sleeve 41 are cooled before venting the
chamber. During the entire coating process, the temperature will be
maintained below the lowest transformation temperature of thrust
washer 39 and bearing sleeve 41.
[0027] In addition to the process described above, other processes
are suitable, including primary ion beam deposition of carbon items
(IBD). Another process that may be suitable is sputter deposition
of carbon with or without bombardment by an intense flux of ions
(physical vapor deposition). Another technique is based on closed
field unbalanced magnetron sputter ion plating combined with plasma
assisted chemical vapor deposition. The deposition is carried out
at approximately 200.degree. C. in a closed field unbalanced
magnetron sputter ion plating system.
[0028] DLC coating 49 preferably has a thickness in the range from
1 to 10 micrometers, preferably 2 to 5 micrometers and, even more
specifically, 2 to 3 micrometers. The hardness is in the range from
2,000 from 5,000 Knoop, thus not as hard as diamond. Once the
coatings are formed on thrust washer 39 and thrust washer 41, these
members are installed in cone cavity 35. Cutter or cone 31 is
installed on bearing pin 15 in a conventional manner.
[0029] Laboratory tests have been conducted to demonstrate the
performance of the coating. First, thrust washer pressure-velocity
tests were carried out. In one test, an uncoated stainless steel
440C thrust washer ran against a mating surface that was coated
with DLC to a thickness of 2 to 3 micrometers. This pressure
velocity tests showed that the DLC coating more than doubled the
load carrying capacity of the component. The average load at the
pressure velocity limit for the standard was 1.6 million Newtons
millimeter per second, while the DLC coating had an average load at
the pressure velocity limit of greater than 4.3 million Newtons
millimeter per second.
[0030] Then, a wear test was carried out to demonstrate the wear
resistance of the DLC coating. The results are shown in FIG. 6. The
designation TWI top and low refers to two thrust washers rotated
against one another, with one of the thrust washers having a DLC
coating and the other being uncoated 440C stainless steel. When
rotated against one another, the TWI thrust washers exhibited very
little weight loss after a two-hour test interrupted at 30 minute
intervals (1800 seconds) to make a weight loss measurement. The
other specimens, designated TW2, had both top and bottom washers of
440C stainless steel without any DLC coatings. The bottom or lower
thrust washer wore significantly during the two-hour test.
[0031] In the embodiment of FIG. 5, bearing pin 51 does not have a
thrust shoulder inlay 21 or journal bearing inlay 27 as in FIG. 1.
Instead, a DLC coating 53 is directly applied to the journal
bearing of bearing pin 51. A DLC coating 55 is directly applied to
the thrust shoulder of bearing pin 51. DLC coatings 53, 55 are
applied in the same manner as described above and replace inlays 21
and 27. Thrust washer 39 (FIG. 1) preferably has a DLC coating as
previously described and slidingly engages thrust shoulder DLC
coating 55. The DLC coatings 41 and 55 are thus in sliding
engagement with each other. Alternately, the DLC coatings could be
in the cavity of the cone and on bearing pin 51, and thrust washer
39 could be conventional without DLC coatings.
[0032] As additional alternates, bearing sleeve 41 (FIG. 1) may
have a DLC coating on its inner diameter as previously described
that slidingly engages DLC coating 53. As an another alternate
embodiment, a DLC coating could be applied to the outer diameter of
bearing sleeve 41 and to the inner diameter of the cavity in cone
31 (FIG. 1). In this arrangement, bearing sleeve 41 would be
rotatable relative to cone 31. In such case, bearing sleeve 41
could either have DLC coatings on both sides or no DLC coatings at
all.
[0033] The invention has significant advantages. The DLC coating is
applied in a process that does not detract from the properties of
the substrate. The DLC coating exhibits high wear resistance, with
the graphite component in the DLC coating enhancing
lubrication.
[0034] While the invention has been shown in only two of its forms,
it should be apparent to those skilled in the art that it is not so
limited but is susceptible to various changes without departing
from the scope of the invention.
* * * * *