Note: Descriptions are shown in the official language in which they were submitted.
3 238896
HYDRODYNAMIC LUBRICANT SEAL FOR DRILL BITS
FIELD OF THE INVENTION
This invention relates generally to rotary cone
cutter type rock bits for drilling bores in hard earth or
rock formations and, more particularly, concerns a
hydrodynamically lubricated seal that greatly enhances seal
life during drilling operations. The lubricant seal
concept of this invention provides for the development of a
hydrodynamic lubricant film by a wedging action on the
lubricant side of the seal and substantially no
hydrodynamic activity on the mud side of the seal whereby
lubricant is hydrodynamically transferred from the
lubricant side across the seal interface to the mud side,
while simultaneously preventing the reverse to occur. The
seal provides for continuous flushing away of drilling
particles with hydrodynamically induced lubricant flow as
well as continuously providing a scraping activity to
prevent migration of particulate into the interface between
the sealing member and the relatively rotating and axially
movable surface of the drill bit against which it seals.
This seal design eliminates direct rubbing contact between
the surface o~ the elastomer lubricant seal and the metal
counterface of the rotary cone or the shaft, as the case
may be, by the presence of the lubricant film. The
presence of the lubricant film and the prevention of the
mud contaminants at the sealing interface is responsible
for extending the life of the lubricant seal well beyond
that of presently available seals.
1~3B896
BACKGROUND OF THE INVENTION
Although a number of different general types of
drill bits are provided for drilling earth formations, the
drill bit construction under consideration herein is
generally known as a rotary cone type rock bit. A drill
bit body structure is provided which is threadedly
connectable to drill pipe that is supported and rotated by
a drilling rig. The body structure of the drill bit
provides leg structures each having stub shafts or axles
which provide support for rotary cone type cutter elements
that cut away the formation as the drill bit is rotated.
Typically, the drill bit is provided with an internal
lubrication system having a quantity of fairly viscous
lubricant which is retained within the lubrication system
by means of sealing elements at each of the rotary cone
members. Although virtually all rotary cone type drill
bits incorporate lubricant seals, it is also well known
that these seals tend to wear rather rapidly because of the
harsh abrasive environment within which the drill bit
operates. The lubricant seal element of each of the rotary
cone cutters of the drill bit is subjected to drilling
fluid which contains fine abrasive particulate such as
bentonite and drill cuttings eroded from the formation
during drilling operations. The drilling fluid, typically
known as drilling mud, utilizes water and other liquid
materials as a carrier constituent for the solid
particulate of the drilling fluid.
A majority of the bearing failures in the drill
bits are preceded by failure of the seal which is intended
to keep the lubricant inside the bit. Seals are the
weakest link in the sealed lubrication systems currently
~L23B896
-- 3
being used in various drill bit designs. A drill bit seal
is expected to operate under a very harsh environment which
includes abrasive mud, high temperatures and complex
movement between the cutter cone and the axis of the shaft
that it is mounted on. These movements include axial play,
radial play, cone wobbling from side to side and a
combination of the above. As the bearing wear continues,
these radial and axial movements also continue to increase.
Associated with these complex cutter movements, it is
estimated that pressure fluctuations of high frequency and
magnitude reaching + 50 psi to + lOO psi or even greater
are encountered. This is due to the inability of the
pressure equalizing system to respond to these rapid
fluctuations. A good seal design must have the ability to
continue to perform its sealir.g function under the above
movements, pressure fluctuations, high temperature and the
abrasive mud environment with a low leakage rate and the
design must also provide an extended service life.
Several seal designs have been used by various
bit manufacturers which have gradually improved the seal
life over the years. One of the more widely used seal
designs at present is set forth in U. S. Patent
No. 3,397,927 of Hughes Tool Co. This particular seal
design employs an O-ring with a high initial interference
to accommodate the cone movements and yet have sufficient
compression available to compensate for the high magnitude
of abrasive wear that this seal is subjected to. Such a
seal operates under "brute force" approach, i. e. using
increased seal compression to prolong seal life; it is not
designed to operate under any definitive mechanism of
hydrodynamic lubrication and therefore allows a direct
contact between the elastomeric sealing surface against the
~2~8896
relatively rotating metal surface of the cone or shaft, as
the case may be. Because of the direct rubbing contact
between the seal and the metal surface, abrasive wear of
the elastomeric material takes place rather quickly. This
problem is further aggravated by the relative axial
movement that typically occurs between the seal and its
mating surface on the cone. There is a tendency for the
abrasive mud particles to be wedged under the sealing
interface due to this relative axial movement. This
wedging of the mud particles is caused by the gradually
converging shape of the O-ring cross-section outside the
contact width zone of the sealing surace. The net result
of the lack of a lubricant film and the ingress of the
abrasive mud particles at the sealing interface is that the
elastomeric material of the seal is subject to a high wear
rate, thus giving a relatively short seal life. A major
percentage of the initial compression of the O-ring seal is
thus used up in feeding elastomeric material to compensate
for the abrasive wear while maintaining a seal. In order
to prolong the seal life, softer elastomers and higher
initial compressions have been used.
Another problem associated with such seals is the
high rate of heat generation and a localized increase in
interfacial temperature of the seal. This is due to high
friction which occurs at the dynamic interface in the
absence of a lubricant film. High initial interference
further aggravates the situation, resulting in further
increase in seal temperature. The localized temperatures
under the seal interface are thus significantly higher than
the ambient environment, which results in a severe
reduction of seal life due to the blistering, scorching and
hardening of the seal material. Because the temperature
~238896
generated at the seal interface increases dramatically as
the rubbing speed is increased~ this seal is not suitable
for high bit speeds.
Another design that is described in U. S. Patent
No. 3,765,495 of G. W. Murphy Industries provides
competitively equivalent seal life through utilization of a
deeper oval cross-section seal to accomplish a larger
initial compression of the seal while maintaining a
percentage compression ratio of below 10 percent. This
seal design also operates with no lubrication at the
sealing interface and has well-rounded edges on both the
lubricant side and the mud side which results in wedging of
abrasive mud particles in the seal interface due to
relative axial motion. The life of this design is also
S relatively short and comparable to the high interference 0-
ring seal described earlier.
It is well-known that hydrodynamic lubrication
can dramatically improve the life of rotary shaft seals in
a clean environment. Prior art shows several designs of
elastomeric seals that operate on the basis of hydrodynamic
lubrication. By creating a hydrodynamic film thickness of
sufficient magnitude, a complete separation between the
asperities of the two rubbing surfaces (the elastomeric
surface of the seal and the metal surface of the rotating
part) can be achieved. This can provide a virtually wear-
free seal in a clean, lubricated environment. For example,
U. S. Patent Nos. 3,449,021; 2,867,462; 3,831,954;
2,571,500; 3,195,902; 2,647,770; and 3,272,521 deal with
slanted sealing surfaces between tubular members to create
hydrodynamic action. U. S. Patent No. 3,449,021
illustrates such a seal for use between relatively rotating
surfaces. Such designs, however, are not suitable for use
~;~3~3896
where an abrasive fluid medium is present as in well
drilling applications where the fluid is in intimate
contact with the seal due to the high level of agitation.
This i$ due to the tendency of these designs to also
promote a strong wedging activity on the mud side, forcing
abrasive mud particles from the mud side into the sealing
interface which creates very rapid wear due to abrasion and
re6ults in early failure of the seal. Thus, even though
these designs work successfully in a clean lubricated
environment, they are totally unsuitable for conditions
where the seal is exposed to the abrasive fluids, such as
drilling mud.
The characteristics of lubrication of
hydrodynamic seals have been studied by the inve:ntor and
reported in several articles. Kalsi, M.S. and G. A.
Fa~ekas, "Feasibility Study of a Slanted 'O-ring' as a High
Pressure Rotary Seal," ASME Paper No. 72-WA/DE-14 11972);
Kalsi, M.S., "Elastohydrodynamic Lubrication of Offset O-
Ring Rotary Seal," ASME Paper No. 80-C2/Lub-7 (1980) and in
a dissertation of the same title submitted to the
Uni-~ersity of ~louston in 1975. This study deals with the
fundamental lubrication principles for successful use of
the hydrodynamic seals in rotary shaft applications. These
studies were confined to O-ring cross-section seals
operating in clean lubricated environment.
An invention utilizing a slanted seal principle
for use in mud motors for drilling applications is
disclosed in U.S. Patent No. 4,484,753 of Monmohan Singh
Kalsi. This invention also employs the principles of
hydrodynamic lubrication in a rotary shaft seal and
successfully overcomes the application problems that are
prevelant ~ in mud motor
lZ3~3~396
applications. Specifically, the slanted mud motor seal is
designed to operate under high differential pressures
utilizing a differential area principle in conjunction with
hydrodynamic sealing principles to obtain extended life for
the application. It should be pointed out that the use of
such a seal in a drill bit application is not technically
feasible because of the severe dimensional constraints that
must be adhered to. Further, the complexity, bulk and high
cost involved with such a seal renders its use in drill bit
applications impractical. In drill bit applications, the
seal must be very compact, preferably fitting into the
dimensional constraint imposed by drill bit designs of the
current configuration. Seals of this nature must also
provide a very low leakage rate and a simple construction
to be practically implemented in drill bits. The drill bit
seal operates approximately under zero or relatively low
mean differential pressures, therefore, some of the
features used in mud motor seals to overcome the
difficulties imposed by high differential pressure sealing
are not necessary. Also, unlike in mud motor seals
described, one cannot rely on a high lubricant leakage rate
across the seal to prolong the seal life because of the
limited capacity of the pressure equalizing reservoir
commonly used in the drill bits. Therefore, this specific
application requires a seal that operates under a very low
leakage rate, yet prolongs the seal life. Another feature
that is required in the drill bit seals to successfully
extend their service li~e is to combat any tendency for
ingress of abrasive mud particles into the sealing
interface under relative axial motion between the seal and
the shaft or cone, as the case may be. This problem does
not exist in mud motor seals as the relatively rotating
1238896
members are substantially fixed in the axial direction with
respect to each other by a rigid bearing system. The
present invention describes a seal which successfully
overcomes the problems enumerated above for a rotary cone
drill bit.
SUMMARY OF THE INVENTION
From the standpoint of the basic concept, a
sealing element is provided which presents a different
geometry on the lubricant side where promotion of
hydrodynamic lubrication action is intended than the seal
geometry on the abrasive mud side where avoidance of any
hydrodynamic activity is desirable. The invention employs
a lubricant sealing element of generally circular form
having a hydrodynamic shape on the lubricant side defining
one or more waves, the amplitude and shape of which is
selected to create a desirable amount of hydrodynamic film
due to the relative rotation at the seal interface. On the
mud side of the sealing element, the geometry of the seal
can take a number of forms which substantially prevent any
hydrodynamic activity due to the relative motion between
the seal member and the corresponding rotating surface of
the drill bit cone or shaft. The geometry of the seal on
the mud side also successfully combats substantially any
wedging action of the abrasive mud particles due to the
relative axial movement between the dynamic surface of the
seal and the counterface of the shaft or the cone. In its
simplest form the seal c~n define a series of sinusoidal
waves on the lip exposed to the lubricant side and have a
planar annular cylindrical surface on the abrasive mud
side.
- 8a ~ ~238896
The invention in one aspect comprehends a seal
member establishing a seal between a relatively rotatable
housing and shaft, comprising a ring-like body of
resilient sealing material forming a sealed partition
between the housing and shaft and forming a lubricant
face, a contaminant face and at least one peripheral
sealing lip in relatively rotatable interference sealing
engagement with one of the housing and shaft and forming
static sealing engagement with the other of the housing
and shaft. The contaminant face is of such configuration
as to generate substantially no hydrodynamic lift of the
peripheral sealing lip responsive to relative rotational
movement of the contaminant face and contaminant. The
lubricant face has a tapered convoluted annular
configuration generating a hydrodynamic lift of the
peripheral sealing lip thus inducing minute migration of
lubricant from the lubricant face to the contaminant face
at the seal interface of the peripheral sealing lip and
said one of the housing and shaft.
The invention also pertains to a rotary cone type
drill bit having a cone support structure incorporating a
body structure forming a liquid lubricant supply and a
plurality of bit support legs, each leg having an axle
supporting a roller cone cutter element in rotatable
relation thereon. The improvement comprises a seal
chamber being defined cooperatively by the roller cone
cutter element and the cone support structure and being
formed in part by a circular relatively rotatably movable
sealing surface. A resilient circular hydrodynamic
- 8b - lZ38~96
sealing element is disposed about the axle and within the
seal chamber and maintains a seal between the roller cone
cutter element and the cone support structure and forms a
sealed partition establishing a drilling fluid interface
and a lubricant interface, the circular sealing element
establishing a sealing interface with the circular
rotatably movable sealing surface. The lubricant
interface is of a configuration acting cooperatively with
the liquid lubricant to hydrodynamically induce lubricant
wedging causing controlled unidirectional hydrodynamic
pumping of lubricant from the lubricant interface through
the sealing interface to the drilling fluid interface
responsive to rotation of the roller cone cutter element
about the axle for lubrication at the sealing interface
and for lubricant flushing of solid particulate from the
sealing interface. The drilling fluid interface is of a
configuration acting cooperatively with the drilling fluid
to induce substantially no hydrodynamic back feeding
drilling fluid pumping activity at the sealing interface
responsive to rotation of the roller cone cutter element
about the axle.
~Z38896
~ydrodynamic sealing has not heretofore been used
in drill bit applications because of the obvious problems
of contaminant intrusion at the seal interface. In other
non-drill bit seal applications, many hydrodynamic seal
designs try to promote lubrication of the sealing interface
from both the lubricant and the nonlubricant side of the
seal. It is a specific object of this invention to employ
hydrodynamic lubrication in drill bit seals and to promote
hydrodynamic activity only on the lubricant side and
substantially eliminate such activity on the mud side of
the seal. This seal design, therefore, does not try to
recapture any of the lubricant that is transferred from the
lubricant side to the nonlubricant or contaminant side as
is done in conventional hydrodynamically lubricated seals
of prior art relating to devices other than rotary cone
drill bits. The seal geometry thus utilized results in a
net lubricant flow from the lubricant side to the mud side.
The geometry of the wave-form on the lubricant side is
selected so as to create a film thickness of desirable
magnitude but still maintain a leakage rate as low as
possible and compatible with the reservoir volume available
in the pressure compensating lubricant reservoir system.
Unlike the seals being currently used in drill bits, this
bit design will experience a desirable and consistent
leakage rate throughout the operational life of the seal.
The current designs show virtually no leakage in the
beginning and, because of the lack of lubrication, have a
short life resulting in ~ sudden but high leakage rate at
failure.
On the mud side, the seal member presents a
substantially non-converging edge to contaminants such as
drilling fluid to prevent the drilling fluid from
lZ38B9~
-- 10 --
developing any degree of hydrodynamic lift as relative
rotation occurs between the sealing element and the surface
against which it seals. This non-converging shape also
prevents any hydrodynamic lifting activity during relative
axial motion between the seal and the cone or shaft.
Conventional O-ring cross-section presents
inclined converging surfaces to the drilling fluid and
therefore are subject to some degree of wedging action
permitting contaminant access to the sealing interface
during axial motion. In prior drill bits, the durometer of
the sealing material has been decreased to some degree and
the degree of seal compression has been controlled to
ensure against migration of contaminants between the
relatively rotating sealing surfaces. The present
invention, however, by virtue of the cross-sectional
configuration of the sealing member and its contaminant
interface/lubricant interface design, effectively prevents
migration of contaminants toward the lubricant interface
surfaces of the seal. At its lubricant interface, the
sealing element defines a surface forming at least one and
preferably a plurality of waves which may be in the form of
smooth sine waves or waves of differing design. The
sealing element on the lubricant side is formed to define
an undulating hydrodynamic geometry forming an inclined
surface as viewed in cross-section that cooperates with the
circular metal sealing surface of the cone or shaft to form
a hydrodynamic entrance zone of greater width toward the
lubricant chamber and gradually tapering to a minimal
dimension at the point of contact. The undulating surface
geometry establishes a seal contact width that varies
circumferentially dependent on that location of the seal
cross-section being considered. The gradually tapering
~!23~38~6
surface of the seal at its point of contact with the
relatively rotatable metal sealing surface of the roller
cone or shaft of the drill bit, as the case may be, defines
a merging radius to prevent or minimize any scraping
activity that might interfere with the flow of lubricant
film toward the mud side. As relative rotation occurs
between the seal member and the circular metal sealing
surface, the undulating design of the seal member at the
lubricant interface surface thereof causes development of
hydrodynamic lifting forces at the contact between the seal
and the relatively rotating sealing surface. These forces
cause slight lifting of the sealing material of the seal
from thé metal sealing surface and thus develop a minute
pumping activity causing an extremely small but definite
quantity of lubricant to migrate under hydrodynamic
influence from the lubricant interface of the seal member
toward the contaminant interface. This migration of
lubricant develops a flushing action to ensure continuous
removal of any abrasive particulate that might be present
near the contaminant interface of the seal. Also, the
separation caused by the introduction of a hydrodynamic
lubricant film at the seal interface of the seal with the
metal surface eliminates a direct rubbing contact and
associated wear. It also ensures continuous maintenance of
minimal friction between the sealing member and the metal
sealing surface and maintains a low temperature environment
to thus ensure enhanced operational life of the sealing
element. In fact, the fiIm of lubricant actually maintains
a minutely spaced relation between the elastomer material
of the seal and the metal sealing surface. These
cooperative features promote the development of a
hydrodynamic seal for rotary cone type rocX bits promoting
123~3~396
service life that is greatly enhanced in comparison to
similar rock bits being marketed at the present time,
This invention, though primarily designed for
enhancing the wear capabilities of rock bits, also has
application where rotary shafts are sealed with respect to
housings with either the housing or shaft being the rotary
member. This invention is also applicable when the sealing
members of rotary cone rock bits or rotary shafts are
composed of single piece elastomeric material or formed by
two or more seal forming elements that may be of different
material and which function in coordinated assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited
features, advantages and objects of the invention, as well
as others which will become apparent, are attained and can
be understood in detail, a more particular description of
the invention, briefly summarized above, may be had by
reference to the embsdiments thereof illustrated in the
appended drawings, which drawings form a part of this
specification. It is to be noted, however, ~hat the
appended drawings illustrate only typical embodiments of
this invention and are not to be considered limiting of its
scope, for the invention may admit to other equally
effective embodiments.
In the Drawings:
FIG. 1 is a partial sectional view of a rotary
cone type drill bit showing an end of one of the leg
portions of the body structure and illust~ating rotary
support and sealing of a rotary cone element in accordance
with the features of this invention.
l~3ass6
FIG. lA is a fragmentary sectional view of the
drill bit structure of FIG. l showing the sealing member
and related parts of the drill bit in greater detail.
FIG. lB is a fragmentary sectional view
representing an alternative embodiment of this invention
wherein the sealing member is rotatable along with the
rotatable member.
FIG. 2 is a linear diagram illustrating the
circumferentially developed configuration of the circular
sealing element of FIGS. l and 2 in conjunction with a
corresponding velocity diagram.
FIG. 3 is a circumferentially developed linear
representation of a circular sealing element in
diagrammatic form similar to that of FIG. 2 and
representing a modified embodiment of this invention.
FIGS. 4 through 8 are circumferentially developed
linear diagrams of circular sealing elements representing
other embodiments of the present invention.
FIG. 7A is a fragmentary cross-sectional
illustration and taken along line 7A-7A of FIG. 7 and
showing a hydrodynamic sealing element constructed of two
interrelated seal components.
FIG. 8A is a fragmentary cross-sectional
illustration similar to that of FIG. 7A, being taken along
line 8A-8A of FIG. 8, and showing a modified hydrodynamic
sealing element constructed of two interrelated seal
components of different nature.
FIG. 9 is a sectional view of the hydrodynamic
seal structure of FIGS. l and lA showing a hydrodynamic
surface of multiple sine-wave form.
'1 23~3~396
- 14 -
FIG. 10 is a sectional view of a circular sealing
element defining an abrupt scraping edge on the contaminant
side thereof.
FIG. 11 is a sectional view of a hydrodynamic
sealing element having multiple inclined hydrodynamic
grooves of alternating pattern formed therein, said sealing
element representing an alternative embodiment of this
invention.
DETAILED DESCRIPTION OF PREFERRED EM80DIMENT
Referring now to the drawings and first to FIG.
1, there is shown in the partial sectional view generally
at 10 the lower leg portion 12 of the body structure of a
rock bit. The leg structure 12 is formed to define a
lubricant passage 14 which is in communication with a
lubricant supply system of conventional nature. For
example, the lubricant supply system may conveniently take
the form shown in U. S. Patent 4,375,242, assigned to
Hughes Tool Co., or a lubricant supply system of any other
convenient form. The lubricant supply system does not
constitute any portion of the present invention except to
the extent that the hydrodynamic sealing member of the
present invention is intended to be employed in conjunction
with a drill bit having a lubricant supply system. The
lower end of the body leg 12 is provided with an extended
journal portion 16 about which is received a rotary cutter
element 18 which is typically referred to as a rotary cone
because of its generally conical configuration. The rotary
cutter is provided with a plurality of cutter inserts 20
such as are typically formed of tungsten carbide or other
suitable materials and which cut away the formation as the
drill bit is rotated by rotation of the drill pipe to which
~23~3896
it is connected. The rotary cutter cone and its cuttin
teeth may take any one of a number of suitable forms
without departing from the spirit and scope of this
invention.
The journal portion 16 of the leg 12 may consist
of a plurality of bearing systems which support the rotary
cutter element 18 and maintain it against separation from
the journal. The journal defines a ball bearing race 20
within which is received a plurality of ball bearing
elements 22. The rotary cutter element 18 also defines a
corresponding circular bearing race 24 registering with
race 20 and cooperating therewith to form a circular
channel within which the ball bearings are received. The
ball bearings provide for rotatable bearing support of the
cutter 18 and also serve to retain the rotary cone cutter
in assembly with the journal 16. The journal is provided
with a bearing insert bore 26 receiving a plug member 28
which forms a portion of the bearing race 20. During
assembly of the bit structure, the ball bearings are
inserted through passage 26 into the bearing race with the
rotary cutter element assembled to the journal in the
manner shown in FIG. 1. Thereafter, the plug member 28 is
positioned within the passage 26 and is secured in
immovable relation with the journal by means of a weld
connection 30 or by any other suitable means for plug
retention. As shown, the plug member 28 is provided with a
lubricant depression or groove 32 which is disposed in
registry with the lubricant passage 14 and a lubricant
branch passage 34. The lubricant branch passage conducts
lubricant to the bearing interface defined between hardened
cylindrical surfaces 36 of the rotary cone and 38 of the
journal, thus providing a film of lubricant between these
,
123~3891~
- 16 -
relatively movable cylindrical surfaces.
At the free extremity of the journal 16, a
hardened cylindrical journal surface is provided at 40
against which is positioned a bushing member 42 forming a
cylindrical bearing surface. The bushing 42 and the
journal bearing surfaces 36 and 38 cooperate with the ball
bearings 22 in the bearing race to prevent undue wobble of
the rotary cutter element 18 as it rotates relative to the
journal and responds to the loads induced by drilling. At
the free extremity of the journal 16 a planar bearing
surface is defined by hardened material 44 and an axial
bearing insert 46 supported within a bearing pocket 48 of
the rotary cutter 18 provides a bearing capability
resisting axial thrust forces.
Although a specific bearing and bushing
arrangement has been discussed for rotary bearing support
of the cutter element 18 relative to the journal 16, such
is not intended to be in any way limiting of the scope of
this invention. Other bearing and bushing support systems
and lubrication systems may be incorporated in conjunction
with the present invention without departing from the
spirit or scope thereof.
At the juncture of the rotary cutter element with
the depending leg portion of the drill bit, there is
typically provided a lubricant sealing element having the
capability of retaining lubricant for lubrication of the
bearing and bushing assembly and retarding migration of
contaminants, such as drilling mud, into the bearing and
bushing assembly. For example, U. S. Patent 3,866,695
illustrates such a circular sealing member at 23 in FIG. 2
and Reissue Patent 28,625 shows lubricant sealing members
lZ38~396
- 17 -
at 26 in FIG. 1 and 86 in FIG. 4. In accordance with the
present invention, as shown in Fig. 1, a circular sealing
element 50 is shown to be received within a circular seal
pocket 52 formed in the rotary cutter element 18. In the
alternative, the sealing element may be received within a
seal groove formed within the journal 16 within the
teachings of this invention or in a groove formed in the
cone as shown in Fig. lB. The journal member 16, at its
juncture with the depending leg portion 12 of the body
structure, forms a circular seat 54 for maintaining
stabilization of the sealing member 50. The sealing member
may be composed of any one of a number of suitable sealing
materials including elastomeric or rubber-like sealing
material and various polymeric sealing materials.
The sealing element 50 of FIGS. 1, lA, 2 and 9 is
of a novel design which successfully introduces a
hydrodynamic film of lubricant of a desired magnitude by
promoting a wedging action on the lubricant side of the
sealing member while preventing any such wedging action on
the contaminant or mud side. The cross-section of this
sealing element, as shown in FIGS. 1, lA and 2, has a lip
with sinusoidal contact shape on the lubricant side and a
straight line contact on the mud side when viewed in a
circumferentially developed representation of the contact
plane due to the abrupt contact of planar surface 64 with
the cylindrical surface 68 defined by the sharp corner 78.
The number and amplitude of sine waves on the lubricant
side of the sealing membe`r can be effectively varied to
achieve the desired magnitude and uniformity of
hydrodynamic lubricant film thickness. As shown in FIG. 2,
the relative velocity, "v," between the seal and the
rotating cutter element of the drill bit can be broken down
~238896
- 18 -
into a normal component, l'vn", and a tangential component,
"vt", with respect to the longitudinal direction of the
seal. The normal component vn in conjunction with a
gradually converging shape of the seal cross-section
defined by converging surfaces 68 and 82 on the lubricant
side as shown in FIG. lA, creates a lifting action of the
elastomeric sealing surface, thereby introducing a
hydrodynamic film of lubricant at the interface. The
tangential component vt promotes the transfer and
distribution of this lubricant film in a circumferential
direction of the seal. It should be noted that the
hydrodynamic lifting action is created by the presence of
the normal velocity component vn in conjunction with the
presence of a gradually converging shape of the seal.
Since the side of the seal that is exposed to the
contaminant-laden drilling mud is of planar configuration,
defining a perfect circle at sharp edge 78, no normal
component of velocity is generated on the mud side of the
seal due to the relative rotational velocity between the
seal and the rotary cutter element.
FIG. lA is a fragmentary cross-sectional
illustration showing drill bit and rotary cutter components
in assembly and with the sealing member 50 positioned
within the seal pocket 52. As shown, the journal portion
16 of the leg member 12 forms a cylindrical journal surface
56 and a circular planar surface 58 which are intersected
by a circular radiused surface 60. The surfaces 56, 58 and
60 cooperate to define the seal stabilizing receptacle 54
discussed in conjunction with FIG. 1. The sealing element
50 defines corresponding surfaces 62, 64 and 66 which
engage the appropriate stabilizing surfaces and thereby
ensure positive positioning of the sealing element during
123889~;
-- 19 --
operation of the drill bit. The rotary cutter element 18
defines a cylindrical sealing surface 68 and a planar
circular surface 70 which cooperate to define the circular
seal pocket or receptacle 52. The sealing element 50 forms
a circular sealing surface 72 which maintains sealing
engagement with surface 68 of the rotary cutter. The
sealing element 50 is maintained under sufficient
compression between surfaces 56 and 68 to thereby ensure
maintenance of the seal at the interface between surfaces
68 and 72 as well as surfaces 56 and 62 and to accommodate
wobble of the cutter.
As mentioned above, the sealing element 50
provides a scraping activity under relative axial motion to
ensure against migration of contaminants into the sealing
interface between surfaces 68 and 72. At the juncture of
the journal 16 with the leg portion 12 of the drill bit
body there is defined a planar surface 74. The inner end
surface 76 of the rotary cutter is of circular planar
configuration and spaced from surface 74 thereby permitting
access of contaminant laden liquid, such as drilling mud,
to the planar surface 64 of the seal member 50. To prevent
ingress of abrasive particulate into the sealing interface
between surface 72 of the seal member and surface 68 of the
rotary cutter, the seal member is provided with a scraping
characteristic that is developed by a sharp circular edge
or corner 78 which intersects the cylindrical surface 68 of
the rotary cutter at a sharp angle, e. g. 9O. It should
be borne in mind that th-e configuration of the sealing
element at the contaminant interface may be of any
configuration that develops substantially no hydrodynamic
activity. Instead of the 9O angular relationship shown at
corner 78, the angular relationship may be inclined as much
~Z38896
- 20 -
as about 45 in either direction, acute or obtuse, from the
annular corner without the risk of developing measurable
hydrodynamic lift. The acute angular relationship,
however, must be such that no significant wedging activity
occurs. Further, the contaminant interface may be of any
surface characteristic other than the planar surface shown
at 64 so long as it does not Aevelop hydrodynamic activity
responsive to relative rotary motion. It is important that
for any angle of the contaminant interface surface, a
gradually converging shape be avoided because such could
otherwise develop hydrodynamic activity on the mud side of
the lubricant seal. For example, one could employ a wave-
like geometry at the edge 78 similar to the wave-like shape
employed in the vicinity of the contact edge 51, provided
that the angle defined by the surface 64 with respect to
the surface 72 of the seal is sufficiently abrupt to
prevent development of any hydrodynamic activity.
Hydrodynamic theory shows that for a 90 angle at edge 78
the hydrodynamic film activity produced from the mud side
at the edge 78 is zero for any amplitude and number of
waves on the surface 64. Even for angles differing from
90, there is a minimum value of the angle for which the
; hydrodynami~ activity is essentially negligible for any
given rotational speed, lubricant viscosity, amplitude and
number of waves. For example, it is also possible to
employ a seal geometry which utilizes the same number and
amplitude of waves both on the mud side and the lubricant
side provided the seal c~oss-section defines a gradually
converging shape on the lubricant side as shown by surface
82 and a substantially abrupt angle at the edge 78 on the
mud side. This geometry will permit a uniform width of
contact as the contact suface undulates circumferentially.
~ 2~l3896
- 21 -
~t the opposite axial extremity of the circular
seal member 50, a planar surface 80 is defined which is
maintained in spaced relation with respect to planar
surface 70 of the rotary cutter. An angulated surface 82
is formed by the sealing member 50 which intersects
S cylindrical surface 72 and planar surface 80 of the sealing
member forming a gradually merging or converging radiused
edge 51. The angulated surface 82, though illustrated in
FIG. lA as being of generally conical configuration, may
take any suitable form, such a concave, convex, etc.,
without departing from the spirit and scope hereof. The
angulated surface 82 cooperates with cylindrical surface 68
to define a hydrodynamic lift area of the seal which
responds to lubricant movement relative thereto to develop
a lift-inducing force causing the cylindrical sealing
interface surface 72 to be lifted slightly from the
cylindrical sealing surface 68 by the hydrodynamic wedging
action caused by the velocity component Vn. Further, as is
evident from the linear diagrammatic view of FIG. 2, the
tapered hydrodynamic lift surface 82 is of variable
dimension along the circumferential length thereof, causing
the sealing surface 72 to also be of varying dimension
about the circumference of the seal. The intersection of
the angulated surface 82 with respect to the cylindrical
surface 72, as shown in FIG. 2, is in the form of a gently
curving sine wave having two cycles per revolution.
Fig. lB is a fragmentary sectional view
representing an alternative embodiment of this invention
wherein the sealing member is mounted in the rotatable
member thus establishing a dynamic sealing interface
against the stational journal. As shown in Fig. lB, the
sealing member 61 is retained within a circular seal groove
1238896
- 22 -
63 in member 65 and establishes a circular sealing lip 67
having relatively rotatable sealing engagement with
cylindrical sealing surface 69 of member 71. The
convoluted inclined surface 73 establishes intersection
with the sealing lip 67 at a radiused edge 75~ A scraping
edge 77 is formed at the intersection of the contaminant
face surface 79 with the sealing lip 67. The hydrodynamic
seal 61 functions in the same manner as described herein in
connection with seal member 50.
In addition to preventing hydrodynamic action on
the mud side during rotary motion, it is also necessary to
prevent such action during the relative axial motion. An
feature of this lubricant seal design is the detail of the
locali~ed geometry of the seal cross-section in the
vicinity of the contact between the cylindrical sealing
surface 68 of the rotary cutter on the mud side. As shown
in FIG. lA, the seal geometry on the mud side has a very
sharp, abrupt edge contact at 78, instead of a gradually
converging cross-sectional shape as shown on the lubricant
side. The lack of a gradually converging shape on the mud
side prevents any wedging of the abrasive mud particles
under the seal interface when the rotary cutter element is
subjected to an axial movement relative to the seal.
In fact, this square edge very effectively
functions as a scraper, to wipe the mating surface 68 of
the cutter element clean during such axial movement of the
cutter. Due to the positive hydrodynamic action created on
the lubricant side of the sealing element, there is a
definite quantity of lubricant leakage that is pumped out
across the seal interface at sealing surfaces 68 and 72
during the relative rotation between the sealing member and
the rotary cutter element. By proper selection of the
~238~396
- 23 -
amplitude and number of waves, this lubricant leakage can
be made small and consistent, but it is sufficient to
maintain the sealing interface flushed clean of any
abrasive particles. The number of sine waves defined at
the lubricant side of the sealing member and the amplitude
of such sine waves can be selected in the design to create
the desirable amount of hydrodynamic lubricant film as well
as the lubricant pumping action that takes place. The
lubricant reservoir is compatibly si~ed to have sufficient
capacity to provide a continuous flow of lubricant at the
seal interface during the expected service life of the
sealing element.
It should be pointed out that an abrupt scraping
edge geometry as described above integral to the seal on
the mud side as shown in Fig. 10 can be expected to provide
an improvement in the seal life even in seals having no
hydrodynamic lubrication activity on the lubricant side.
The scraping activity by itself be considered an
improvement in current seal designs. Fig. lO shows a
sealing element 79 having an abrupt scraping edge 81 on the
contaminant side which can be a square edge as shown or any
abrupt angular configuration capable of accomplishing
efficient scraping activity for removal of contaminant from
the sealing surface upon relative axial movement of the
seal and the sealing surface.
Another important advantage of employing a
hydrodynamically lubricated seal for sealing between
relatively rotatable su~faces is the low rate of heat
generation at the sealing interface and a more effective
heat transfer mechanism to keep the interfacial seal
temperatures low. A constant wiping action takes place
between the cone surface and the seal contact zone, which
~238896
- 24 -
more effectively transfers heat from the seal interface
into the main volume of the lubricant. It has been found
in controlled experiments by the inventor that this more
effective heat transfer mechanism and a much lower level of
heat generation is also responsible for extending the seal
life significantly as compared to the seal life of
conventional O-ring seals. In the conventional O-ring
seals, the interfacial temperatures can become much higher
than the bulk fluid temperatures surrounding the seal, and
can cause scorching and blistering of the elastomeric
surface of the seal member. This detrimental activity
hardens the elastomeric material which further accelerates
the abrasive wear process that diminishes the life of such
sealing elements. This problem becomes even more acute as
the rotational speeds are increased. Therefore, the use of
conventional O-ring sealing elements in the bit design
limits their use to relatively low-speed applications. The
hydrodynamically lubricated seal, on the other hand, has
been tested and found to perform successfully at speeds
much higher than those permitted by conventional O-ring
type seals. Excellent performance from such seals at
speeds well over l,OOO rpm has been obtained with
hydrodynamically lubricated seals of the size typical in
drill bits. This high speed compatability will permit the
use of the hydrodynamically lubricated bit seal design of
this invention in mud motor applications, which typically
operate at much higher rpm.
Since this seal design effectively prevents the
ingress of drilling mud at the seal interface and minimizes
any direct contact between the elastomer sealing member and
the dynamic metal surface, there is very little abrasion
encountered during operation of the seal. In long term
~238~96
- 25 -
tests, it has been found that the cross-section of the seal
changes by a negligible amount due to the combined effect
of abrasive wear and permanent set when tested under
significant differential pressures and high temperatures.
Therefore, this seal design requires very little initial
radial interference to compensate for wear, unlike in the
present 0-ring or oval cross-section drill bit seals which
require significant radial interference. The magnitude of
minimum interference that the seal is installed with should
simply exceed the radial cone movements and the above
negligible magnitude of wear. This is significantly in
contrast to the approach typically utilized in the previous
O-ring bit seals where an initial compression of 15~ to 20%
is regularly employed. A large percentage of that initial
compression is simply provided to compensate for the high
magnitude of abrasive wear present in O-ring sealing
elements of conventional design to thus obtain increased
seal service life. It should be pointed out that the
hydrodynamically lubricated seal design of this invention
also worXs very well with high initial squeeze although
such is not necessary for its proper functioning. This is
so because hydrodynamic film thickness is relatively
insensitive to initial squeeze pressure and differential
pressure of the system.
Several other variations of the basic
hydrodynamically lubricated seal design discussed above in
connection with FIGS. l, lA, lB and 2 are disclosed in
FIGS. 4 through 8A.
A circumferentially developed linear illustration
of a double lipped embodiment of this invention is
illustrated in FIG. 3 where a seal member illustrated
generally at 90 provides a design having certain advantages
~238896
- 26 -
over the seal design disclosed in conjunction with FIGS. l,
lA and 2. This design, utilizes a simple elastomeric seal
with a cross-section that promotes a complete hydrodynamic
lubrication of the main sealing lip from both sides. As
shown in this figure, the contact width of the seal is
divided into two contacting lips 92 and 94. The sealing
lip 94, being closest to the lubricant side 96 of the
sealing member, is provided with a sinusoidal form along
both of its axial edges A, B, C, D and E, F, G, H. The
second sealing lip 92 establishing the mud side 98 at the
abrupt scraping surface portion of the seal defines a
straight edge, N, O, P, Q. The areas of the seal width not
in contact with the rotating housing are shown crosshatched
in this figure, whereas the areas that are in contact are
left uncrosshatched. As in the hydrodynamically lubricated
seal design discussed in conjunction with FIGS. l, lA, lB
and 2, a hydrodynamic wedging action is present on the side
A, B, C, D of the main sealing lip 94 adjacent the
lubricant side of the seal established by surface 96. This
hydrodynamic pumping action transfers the lubricant to the
opposite side of this seal lip 94 across the edge E, F, G,
H. Thus, a pool of lubricant becomes trapped in the
recessed cavity lOO defined by the sides E, F, G, H and J,
K, L, M. This pool of lubricant creates an effective
hydrodynamic lubricating action on the opposite side, E, F,
G, H, of the first sealing lip 94. This results in the
generation of a complete hydrodynamic film at the interface
of the first sealing lip 94 from both sides. In other
words, hydrodynamic activity takes place that forces
lubricant back and forth between the lubricant side of the
sealing member and the sinusoidal recessed cavity lOO.
This pool of lubricant in the intermediate cavity also
3 Z3~3896
- 27 -
lubricates the side J, K, L, M of the second sealing lip
92. As in the first design described earlier, the farthest
side, N, 0, P, Q, of the seal exposed to mud or other such
contaminants is straight as defined by planar surface 98
and has an abrupt edge (instead of a convergent cross-
section~l shape), thus avoiding any wedging action of the
abrasive mud particles at the seal interface. The
advantage of this construction is that the first lip 94 is
very effectively hydrodynamically lubricated from both
sides and better isolated from the abrasive mud, thus
potentially prolonging its life even further. The sealing
lip 92 on the mud side of the drilling bit is also
hydrodynamically lubricated by a film of lubricant being
transferred from the sinusoidal cavity 100 across the
sealing interface toward the planar surface 98.
FIG. 4 is a linear r~presentation of a
hydrodynamic lubricant seal for drill bits, rotary shafts
and the like shown generally at 102 which presents a
circumferential sealing surface 104 intersected by an
abrupt surface 106 corresponding to surface 64 of FIG. lA.
Surface 106 is presented at the mud side of the sealing
element while the opposite surface 108 is presented at the
lubricant side of the seal. A gradually tapered
hydrodynamic lifting surface 110 is provided which defines
multiple wave forms of other than sine-like configuration.
These wave forms can take any suitable design configuration
promoting the character of hydrodynamic lifting and
lubricant pumping capabi~ity that is desired.
In FIG. 5, a similar linear diagram
representation of a hydrodynamic lubricant seal is provided
generally at 112 which forms a sealing surface 114
corresponding with surface 72 of FIG. lA, for engagement
~23~3B96
- 28 -
with the metal cylindrical sealing surface 68 of the rotary
cutter element 18. Seal member 112 defines an abrupt
surface116 at one axial extremity and a surface 118 at the
opposite axial extremity corresponding with surface 80 of
FIG. lA. A tapered hydrodynamic lift surface 120 is also
formed by the sealing element 112 which intersects the
cylindrical sealing surface 114 in a triangular
configuration defined by multiple straight intersecting
lines 122 formed by radiused edges.
In FIG. 6, a lubricant seal is shown generally at
124 which is of hybrid design incorporating some of the
features of the seal designs of both FIGS. 2 and 3. The
sealing element defines an abrupt surface 126 on the mud
side and an opposed surface 128 on the lubricant side~ A
hydrodynamic lift surface 130 is provided, intersecting
sealing surface 132 at a sinusoidal line 134 forming lip
136. At appropriate areas about the circumference of the
sealing element lubricant cavities 138 and 140 are defined
which receive lubricant material transferred from the
lubricant side of the sealing element. By virtue of flat
surfaces 142 and 144 and curved surfaces 146 and 148,
lubricant is transferred by hydrodynamic activity only
toward the lubricant side from the recesses 138 and 140.
In other locations along the periphery of the sealing
element, hydrodynamic activity develops the contaminant
flushing and lubricating activity described above in
connection with FIG. 2.
FIG. 7 disclose~ a sealing element illustrated
generally at 150 which defines a seal contact surface 152
and a hydrodynamic lift surface 154 similar to that
described in conjunction with FIG. 2. The sealing element
150, however, as shown in FIG. 7A, is composed of a seal
~8896
- 29 -
body 156 having a groove formed therein which receives an
0-rin~ type sealing element 158. The seal body and sealing
element may be composed of differing materials, if desired.
In FIG. 8, a sealing element is shown generally
at 160 having a seal body 162 and a seal ring 164 of
rectangular cross-section. Elements 162 and 164 cooperate
to define sealing lips 166 and 168, sealing lip 166 being
of sinusoidal form. The lip 168 is of circular form and
defines a circular edge at the intersection thereof with
the abrupt wiping surface 170 at the mud side of the seal.
A lubricant cavity 171 is defined between the sealing lips
166 and 168.
Where two or more sealing lips are defined, the
sealing lip on the mud side merely functions as a secondary
seal whose primary function is to act as a barrier to mud
ingress. As in the previous design, a positive pumping
action created by the hydrodynamic action constantly
maintains a minute quantity of fluid flow from the
lubricant reservoir to the intermediate cavity, and from
the intermediate cavity to the mud side. This keeps the
seal interface flushed clean of any abrasive particles and
maintains effective lubrication of the contact surfaces of
the seal and the rotary cutter.
Another advantage of the hydrodynamically
lubricated seal design is its ability to operate very
effectively even under the presence of high differential
pressures. Hydrodynamic seal designs have been extensively
tested with differentiaL pressures up to 1,000 psi with
virtually no wear. The high pressure fluctuations which
are normally encountered in the drill bit do not exceed
~ 100 psi. In conventional O-ring or similar seal designs,
these pressure fluctuations can increase the rate of wear.
3.Z3~896
- 30 -
The hydrodynamic seal design can effectively withstand
pressure fluctuations of this magnitude without squeezing
the hydrodynamic lubricant film out from the sealing
interface. In fact, it is possible to have some constant
positive pressure on the lubricant side with such seal
designs without any degradation of their service life.
This may be advantageous to the seal operation and can be
achieved by the use of a spring biasing means in the
pressure equalizing systems of various drilling bit designs
currently employed at the present time.
It has also been found that it is not necessary
to utilize low durometer elastomers to provide adequate
service life in hydrodynamic seals for drilling bits,
rotary shafts and the like. With the use of elastomers
having a hardness in the range of from 70 durometer to 85
durometer, the inventor has obtained long sealing life
without any significant evidence of abrasive wear. The
present seal design therefore functions equally well in
high initial squeeze or low initial squeeze environments.
The presence of lubricant film at the interface which
separates the seal surface from the metal surface
essentially eliminates abrasive wear action, thus making
the role played by durometer hardness a secondary one.
As can be appreciated from the description of the
hydrodynamically lubricated bit seal design set forth in
the drawings, the seal has a very simple and compact
configuration that overcomes all of the problems mentioned
earlie~ with respect to present seal designs, thus greatly
improving the performance, reliability and life of drilling
bit seals. The seal cross-section does not take up any
more axial space on the existing lug or cone geometries of
drilling bits than is required for lubricant seals of
lZ38896
conventional design and can therefore be easily installed
into the seal pockets of most of the present bit designs as
replacement seals. This is important, especially since the
life of the various components within the drilling bit is
very delicately balanced. Any reduction in the axial
length available for the journal bearing or roller bearings
employed in current rotary cone type drilling bits could
reduce the bearing life and, therefore, the overall useful
life of the bit. The hydrodynamic lubricant seal designs
proposed were developed keeping in mind the dimensional
constraints imposed by the current geometries of present
rotary cone drill bits. Hydrodynamic lubricant seals will
obviously provide significant increase in seal life without
decreasing the life of other components of the drill bit.
Even though several specific seal geometries are
discussed in detail herein, many other variations of the
seal geometries employing the basic principles and
teachings of this invention are possible. Moreover,
hydrodynamic sealing elements can be provided which
incorporate the beneficial advantages of a wide range of
materials, including the use of two or more materials for
the beneficial function thereof. It can also be
appreciated that, even though a simple, one-piece integral
seal construction is being employed in the proposed seal
designs, it is possible to accomplish the same function
with split or multiple piece designs. The dynamic sealing
surface can be selected to be either on the cone or against
the shaft by simply molding the hydrodynamic lip details on
the outside diameter or inside diameter of the seal while
maintaining all of the advantages of the invention
discussed earlier. The inverted seal is installed in such
a way that the hydrodynamic film takes place at the lug
~ 23~8g6
shaft rather than on the inside diameter of the drill bit
cone as discussed in the detailed description.
In Fig. 11 is shown a circular sealing element
172 defining a contaminant side 174~and a lubricant side
176. Multiple inclinded grooves 178 are formed in the
sealing element which intersects the lubricant face and the
inner or outer peripheral surface 180 as the case may be.
As shown, the included grooves are in oppositely directed
groups so that seal lubrication will be hydrodynamically
energized regardless of the direction of relative rotation.
The groove 178 pick up lubricant and the inclined surface
thereof provide a hydrodynamic wedging activity to create
hydrodynamic seal lift in similar manner as described
above. As before on the contaminant side a sharp scraping
edge is defined.
