U.S. patent application number 11/771814 was filed with the patent office on 2008-01-31 for power tong having cam followers with sliding contact surfaces.
Invention is credited to Murray KATHAN.
Application Number | 20080022811 11/771814 |
Document ID | / |
Family ID | 38984805 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080022811 |
Kind Code |
A1 |
KATHAN; Murray |
January 31, 2008 |
POWER TONG HAVING CAM FOLLOWERS WITH SLIDING CONTACT SURFACES
Abstract
In a pivoting-jaw power tong having a rotary gear with
substantially linear camming surfaces and pivoting jaw members with
cam followers for engagement with the camming surfaces upon
rotation of the rotary gear relative to the jaw members, each cam
follower has at least one contact surface configured for sliding
engagement with a primary camming surface. The provision of sliding
contact surfaces reduces contact pressures between the cam
followers and the camming surfaces, thus reducing wear. The cam
followers may be formed integrally with the jaw members, but
preferably will be rollers which can swivel relative to their
respective jaw members to facilitate substantially uniform sliding
contract between the cam follower contact surfaces and the camming
surfaces of the rotary gear. In alternative embodiments, the
camming surfaces may have a slight concave curvature, with the cam
followers' contact surfaces being correspondingly convexly
curved.
Inventors: |
KATHAN; Murray; (Gibbons,
CA) |
Correspondence
Address: |
DONALD V. TOMKINS;C/O TOMKINS LAW OFFICE
740, 10150 - 100 STREET
EDMONTON
AB
T5J 0P6
CA
|
Family ID: |
38984805 |
Appl. No.: |
11/771814 |
Filed: |
June 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60806409 |
Jun 30, 2006 |
|
|
|
Current U.S.
Class: |
81/57.18 ;
81/57.15 |
Current CPC
Class: |
E21B 19/164
20130101 |
Class at
Publication: |
081/057.18 ;
081/057.15 |
International
Class: |
E21B 19/16 20060101
E21B019/16 |
Claims
1. A power tong having: (a) a gear housing defining a central
space, and a perimeter opening into said space; and (b) a pair of
opposing jaw members disposed within said central space, each jaw
member having; b.1 a pivot end, a free end, an inner side, and an
outer side, with said pivot end pivotably mounted to the gear
housing, and said free end oriented toward said perimeter opening;
b.2 a pair of dies associated with said inner side; and b.3 a cam
follower associated with said outer side; (c) a rotary gear
rotatably mounted within the gear housing, and having: c.1 a
circular perimeter with a plurality of gear teeth; c.2 an inner
surface defining a central space large enough to enclose said jaw
members; and c.3 a throat opening in said perimeter; wherein said
inner surface defines: (d) a pair of opposed neutral recesses; and
(e) a first pair of opposing primary camming surfaces, each
extending substantially linearly in a first direction away from an
associated one of the recesses; and wherein: (f) the radial
distance from the axis of rotation of the rotary gear to a point on
any primary camming surface decreases substantially linearly with
increased distance from the associated recess; and (g) each cam
follower has at least one contact surface configured for sliding
engagement with a primary camming surface.
2. The power tong of claim 1, further comprising a second pair of
opposing primary camming surfaces, each extending substantially
linearly in a second direction away from an associated one of the
recesses.
3. The power tong of claim 1 wherein the cam followers are
rollers.
4. The power tong of claim 3, further comprising bias means
associated with each roller, said bias means being adapted to a
facilitate orientation of the cam follower's at least one contact
surface with a selected primary camming surface.
5. The power tong of claim 1 wherein the cam followers are
protuberances formed integrally with their associated jaw
members.
6. The power tong of claim 1 wherein each primary camming surface
is concavely curved, and the contact surface of each cam follower
is convexly curved to allow substantially uniform sliding
engagement with a corresponding primary camming surface.
7. In a power tong having: (a) a rotary gear defining substantially
linear camming surfaces; and (b) a pair of pivoting jaw members
each having a cam follower for engagement with one of said camming
surfaces upon rotation of the rotary gear relative to the jaw
members; the improvement comprising the provision of each cam
follower with at least one contact surface configured for sliding
engagement with a primary camming surface.
8. The improvement of claim 7 wherein the cam followers are
rollers.
9. The improvement of claim 8, further comprising the provision of
bias means associated with each roller, said bias means being
adapted to facilitate orientation of the cam follower's at least
one contact surface with a selected primary camming surface.
10. The improvement of claim 7, wherein each primary camming
surface is concavely curved, and the contact surface of each cam
follower is convexly curved to allow substantially uniform sliding
engagement with a corresponding primary camming surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit, pursuant to 35 U.S.C.
119(e), of U.S. Provisional Application No. 60/806,409, filed on
Jun. 30, 2006, and said provisional application is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates in general to power tongs for
gripping oilfield tubulars to facilitate make-up or break-out of
threaded connections between tubulars. In particular, the invention
relates to pivoting-jaw power tongs having rotary gears with
improved camming surface geometry.
BACKGROUND OF THE INVENTION
[0003] Power tongs are well known in the field of drilling and
servicing oil and gas wells. Drill pipe and production tubing are
typically provided in the form of round steel pipe (commonly
referred to as tubulars) with threaded ends for connecting tubulars
into a drill string or a production string, depending on the
operation being conducted. The term "make-up" is commonly used to
refer to the process of connecting tubulars to each other (i.e.,
"making up" a threaded connection), and the term "break-out" refers
to the process of disconnecting tubulars (i.e., "breaking out" a
threaded connection). Well drilling and well servicing involve both
make-up and break-out functions, for a variety of purposes well
known in the field.
[0004] Make-up or break-out of a threaded joint requires that the
tubular on each side of the joint be firmly gripped so that the
tubulars can be contra-rotated relative to each other, either
clockwise or counterclockwise, to make up or break out the joint as
desired. This gripping function is commonly carried out using a
power tong in each of the tubulars. Power tongs typically have
either sliding jaw assemblies or pivoting jaw assemblies, and the
present invention is particularly referable to the pivoting-jaw
type. There are numerous known types or models of pivoting-jaw
power tongs, but they generally have the common features of a
partial-circle (or "C-shaped") rotary gear, the internal surface of
which defines a camming surface, and a jaw assembly disposed inside
the rotary gear and having two or more cam followers that ride
against the camming surface of the rotary gear. The cam followers
may be in the form of rollers which turn around suitable axles or
pivot pins, or they may be formed integrally with the jaws. The jaw
assembly has several (typically four) dies--i.e., elements which
are toothed or otherwise adapted for grippingly engaging the
circumferential outer surface of a tubular member by effectively
biting into the steel surface of the tubular when forced against
the tubular. The geometry of the camming surface is adapted such
that when the rotary gear is rotated around the jaw assembly,
either clockwise or counterclockwise away from a neutral position,
the dies are used into gripping contact with the outer surface of
the tubular. When the tubulars on each side of the joint have been
thus engaged by respective power tongs, the tongs may be rotated
relative to each other in the desired mode, thus making up or
breaking out the joint as desired.
[0005] One example of a prior art pivoting-jaw power tong is
disclosed in Canadian Patent No. 1,125,737 issued on Jun. 15, 1982
to Farr et al. (and corresponding to U.S. Pat. No. 4,350,062). As
with typical pivoting-jaw power tongs, the camming surface of the
Farr device includes a pair of opposed recesses (or neutral zones)
such that when the rotary gear is rotated to a neutral position
wherein when each cam follower has moved into one of the recesses,
the jaws spread apart so as to allow the jaws to receive a tubular.
On either side of each recess, the camming surface has a
circularly-curved primary camming surface. These primary camming
surfaces are configured such that when the rotary gear is rotated
in either direction away from the neutral position, each jaw is
rotated inward. As rotation of the rotary gear increases, the jaws
close on the tubular, causing the dies to bite into the tubular.
When the tubular is firmly gripped by the dies, the tubular can be
rotated so as to be connected to or disconnected from (as the case
may be) another tubular.
[0006] The primary camming surfaces of the Farr device have
different curvature radii on either side of each recess, and this
is considered to have certain advantages over typical prior art
pivoting-jaw power tongs in which the same curvature radius is used
for all of the primary camming surfaces. However, it has been
observed that power tongs with circular primary camming surfaces
are prone to reduced effectiveness as the dies, pins, rollers,
and/or camming surfaces become worn. In such circumstances, the
force with which the dies are urged against the surface of the
tubular is not uniform, so the dies grip the tubular with variable
effectiveness, and in the worst case a die may grip the tubular
with little or no effectiveness at all. In such cases only three of
the dies will be effectively gripping the tubular instead of four,
and this condition tends to causing warping and/or marking of the
tubular. This tends to be particular problem for the dies located
near the pivot points of the jaws.
[0007] U.S. Pat. No. 6,988,428 (Kathan) discloses an improved
pivoting-jaw power tong with enhanced capability for reliable and
effective gripping engagement of tubular members in cases where
dies, pins, rollers, and/or camming surfaces are worn. In the
pivoting-jaw power tong of U.S. Pat. No. 6,988,428, the primary
camming surfaces of the rotary gear have a novel geometry. Each
primary camming surface has a substantially linear configuration,
rather than a circularly-curved configuration. More specifically,
each primary camming surface is oriented so as to form an acute
angle with a radial line extending from the rotary gear to the
point where the primary camming surface meets its corresponding
neutral recess. By virtue of this geometric configuration, the
radial distance to a point on any of the primary camming surfaces
reduces, in substantially linear fashion, with increased distance
away from the neutral recess. Therefore, increased rotation of the
ring gear in either direction away from the neutral position will
cause both jaws to rotate further inward, thus increasing the force
that the dies on the free ends of the jaws will exert on a tubular
being engaged by the apparatus.
[0008] When using a power tong having such linearly-configured
primary camming surfaces, the dies will engage the tubular with
considerably increased uniformity and effectiveness, even when the
dies, pins, cam followers (e.g., rollers), and/or camming surfaces
are worn. In prior art power tongs with curved camming surfaces
(such as in the Farr reference), there is a relatively small "sweet
spot" or optimal contact zone on the camming surface corresponding
to each cam follower such that each die will exert maximum gripping
force on the tubular when the cam followers are at their
corresponding sweet spots. This works well when the apparatus is
new, without any wear to the various components. All of the cam
followers will hit their sweet spots at the same time (i.e., when
the rotary gear is in a specific optimal position), because the
distance from the rotary gear's center of rotation to the sweet
spot is the same for all of the cam followers, the distance from
the center of rotation to the face of the cam followers is
constant, and the distance from the center of rotation to the die
contact surfaces is constant.
[0009] Continued use of the power tong inevitably results in wear
to the components, however, and a certain amount of "play" develops
in the mechanism. This causes changes in the geometrical
relationship between the com followers, dies, and/or camming
surfaces, such that the cam follower can no longer hit their sweet
spots at the came time. In effect, one or more of the sweet spots
become shifted to a different position on the camming surface
because of the wear, and the geometric relationship between the
sweet spots no longer coincides precisely with the geometric
relationship between the cam followers. Even small amounts of play
can thus result in reduced gripping force being applied to the
tubular at one or more of the dies, such that the tubular is not
gripped uniformly.
[0010] This undesirable condition cannot be effectively remedied by
further rotation of the rotary gear, because the tangential angle
between the cam followers and the camming surfaces (which may be
referred to as the "tangential contact angle") changes as the cam
followers move away from their sweet spots or optimal contact zones
on the camming surfaces, due to the fact that the camming surfaces
are curved. However, when substantially linear camming surfaces are
used, the tangential contact angle will be substantially the same
for all cam followers regardless of the position of the rotary
gear, and will not be materially altered by normal operational wear
to the various components of the power tong.
[0011] In the power tong of U.S. Pat. No. 6,988,428, the linear
camming surfaces are oriented such that the radial distance from
the center of rotation to the camming surface decreases in
substantially linear fashion as the camming surfaces propagate away
from the neutral recesses in the camming surfaces. By virtue of
this camming surface geometry, rotation of the rotary gear in
either direction away from the neutral position results in a
linearly progressive reduction of the distance from the center of
rotation of the points where the cam followers contact the camming
surfaces, with the rate of reduction varying in proportion to the
angular displacement of the rotary gear, regardless of how far the
cam followers may be displaced away from the neutral recesses.
[0012] The use of such linear camming surfaces results in a much
larger sweet spot corresponding to each cam follower. This camming
surface geometry allows the power tong to automatically adjust for
wear in the mechanism such that the contact force between the cam
followers and the camming surfaces--and, therefore, the gripping
force applied by the dies to the tubular--will be substantially
constant at all locations.
BRIEF SUMMARY OF THE INVENTION
[0013] The invention has found that the effectiveness of the power
tong of U.S. Pat. No. 6,988,428 can be enhanced by using beveled
cam followers, so as to provide a substantially flat contact area
when a cam follower is brought into contact with one of the linear
camming surfaces. This geometry has the effect of significantly
reducing the contact pressure between the cam follower and the
camming surface, as compared to the typical case in known power
tongs where the cam follower is a circular roller or has a curved
profile. In such cases, the contact area between the cam follower
and the camming surface will be comparatively small, in the nature
of a concentrated point load or line load. In the present
invention, however, both contact surfaces are substantially flat or
planar, and substantially parallel to each other. Accordingly, for
a given force being transferred perpendicularly across the contact
area, the contract pressure will be considerably less than it would
be in prior art tongs where the same force is applied much like a
concentrated point load or linear load.
[0014] The use of substantially flat cam follower surfaces can
reduce or even eliminate localized deformations in the camming
surfaces and the cam followers. The high contact pressures
resulting from the use of round or roller-type cam followers cam
cause localized plastic deformation of the surficial layers of
metal in the contact zones of each of these elements, possibly
causing the formation of grooves or ruts in the camming surfaces
and/or wear in the cam followers. These undesirable effects can
over time result in the need for increased rotation of the rotary
gear in order to develop satisfactory gripping forces between the
dies and a pipe joint being made up or broken out with the power
tong.
[0015] Accordingly, the present invention may be described in
general terms as an improvement for a power tong with linear or
substantially linear camming surfaces, with the improvement
comprising a cam follower having one or more substantially flat
contact surfaces configured and oriented to coma into sliding and
substantially uniform contact with one of the linear camming
surfaces. Preferably the cam follower will be developed so as to
have two such substantially flat contact surfaces, oriented such
that the cam follower will come into sliding and substantially
uniform contact with one of the linear camming surfaces regardless
of which direction the rotary gear is being turned (i.e., whether
for purposes of make-up or break-out).
[0016] The one or more substantially flat contact surfaces can be
provided in a cam follower that is formed integrally with a power
tong jaw. In such cases, the angular orientation of the flat
contact surfaces will typically be selected so as to optimize the
uniformity of contact with their corresponding linear camming
surfaces under maximum load conditions.
[0017] Alternatively, the one or more substantially flat contact
surfaces can be provided in the roller of a roller-type cam
follower that is rotatably mounted to a power tong jaw. In this
embodiment, the roller can rotate to accommodate the slight changes
in the angular relationship between the jaws and their
corresponding linear camming surfaces as the rotary gear turns.
This results in automatic adjustment of the substantially flat
contact surfaces of the cam followers such that they will be in
optimally uniform contact with the corresponding linear camming
surfaces, despite angular movements of the jaws.
[0018] The substantially flat contact surfaces of the cam followers
may be coated or laminated with a material that facilitates
sliding, while also being capable of withstanding, without
excessive deformation, the compressive stress acting over the
contact area with the linear camming surfaces.
[0019] As will be appreciated from the preceding discussion, the
term "linear camming surface", as used in this patent
specification, is not to be constructed as requiring perfectly
planar camming surfaces, but are to be interpreted as covering
substantially linear camming surfaces as well. Similarly,
references to "flat cam follower surfaces" are to be interpreted as
covering substantially flat cam follower surfaces, rather than
being limited to perfectly planar cam follower surfaces.
[0020] In alternative embodiments of the invention, the camming
surfaces may have a slight concave curvature, with the cam follower
surfaces having a corresponding convex curvature to facilitate
sliding and substantially uniform contact with the curved camming
surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the present invention will now be described
with reference to the accompanying figures, in which numerical
references denote like parts, and in which:
[0022] FIG. 1 is an isometric view of a prior art power tong in
accordance with U.S. Pat. No. 6,988,428, shown with the rotary gear
in the neutral position such that a tubular can pass through the
throat opening when the hinged doors have been opened.
[0023] FIG. 2 is a perspective view of the prior art rotary gear of
the power tong of FIG. 1.
[0024] FIG. 3 is a plan view of the prior art rotary gear pf FIG.
2.
[0025] FIG. 4 is an enlarged plan view of the prior art rotary gear
of FIG. 2, illustrating the geometric configuration of the camming
surfaces.
[0026] FIG. 5 is a plan view of the rotary gear and pivoting jaws
of the prior art power tong of FIG. 1, shown with the rotary gear
in the open position in which a tubular can pass through the throat
of the rotary gear and into position between the pivoting jaws.
[0027] FIG. 6 is a plan view of the prior art rotary gear and
pivoting jaws as in FIG. 5, shown with the rotary gear rotated
counterclockwise from the neutral position with a tubular
positioned inside the pivoting jaws, and with the jaws' dies
beginning to engage and the tubular.
[0028] FIG. 7 is a plan view of the prior art rotary gear and
pivoting jaws as in FIG. 5, shown with the rotary gear rotated
further counterclockwise, with the front pair of dies securely
engaging and gripping the tubular.
[0029] FIG. 8 is a plan view of the rotary gear and pivoting jaws
generally similar to those shown in FIGS. 5, 6, and 7, but with
each cam follower having flat-surfaced sliding contact surfaces in
accordance with one embodiment of the present invention.
[0030] FIG. 9 is a plan view of a rotary gear with pivoting jaws
having roller-type cam followers with sliding camming surfaces in
accordance with an alternative embodiment of the invention, shown
with the rear pair of dies beginning to engage a tubular.
[0031] FIG. 10 is a plan view of the rotary gear and pivoting jaws
as in FIG. 9, shown with the rotary gear rotated clockwise relative
to FIG. 9, with all dies securely engaging and gripping the
tubular.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
1. Prior Art Power Tong
[0032] FIG. 1 generally illustrates an assembled prior art power
tong 10 in accordance with U.S. Pat. No. 6,988,428. With the
exception of the configuration of the camming surfaces of the
rotary gear (which is not visible in FIG. 1), the construction of
power tong 10 is largely similar to known power tongs. A
generally-C-shaped gear housing 12 has doors 14 which can be swung
open about hinge points 18 using handles 16 (as indicated by the
broken arrows in FIG. 1) so as to provide an opening into a central
space 19 within gear housing 12. A pair of jaw members 20
(typically of generally arcuate shape) are pivotably mounted within
gear housing 12. As shown in FIG. 5, each jaw member 20 has a pivot
end 20A, a free end 20B, an inner side 20C disposed toward central
space 19, and an outer side 20D. The pivot end 20A of each jaw
member 20 is pivotably mounted to gear housing 12 by means of a
pivot pin 22, at a point opposite the opening into central space
19. Dies 30, for grippingly engaging a tubular, are mounted on the
inner sides 20C of each member 20 near each end thereof. Additional
features of jaw members 20 are shown in FIGS. 5, 6, and 7, and
described in greater detail further on in this specification.
[0033] Disposed within gear housing 12 (but not shown in FIG. 1) is
a generally C-shaped rotary gear 40, exemplary embodiments of which
are is illustrated in FIGS. 2-7. Rotary gear 40 has a circular
perimeter with a plurality of gear teeth 41. Rotary gear 40 also
has an inner surface 42 which encloses a central space 48 of
sufficient size to enclose jaw members 20 without interference. The
perimeter of rotary gear 40 is interrupted by a throat opening 46
which provides access to central space 48. Rotary gear 40 is
mounted within gear housing 12 so as to surround jaw members 20 (as
best seen in FIGS. 5-7), and so as to be rotated within gear
housing 12 about center axis C of rotary gear 40. The power tong 10
includes means for rotating rotary gear 40, and such means may be
of any suitable type well known in the field of the invention. For
exemplary purposes, FIG. 1 illustrated power tong 10 with hydraulic
actuation means 100, comprising a hydraulic motor 110 which rotates
a pinion gear (not shown) that engages gear teeth 41 so as to
rotate rotary gear 40 clockwise or counterclockwise as desired, by
means of hydraulic valve control levers 112. Hydraulic lines 114
lead from hydraulic actuation means 100 to a hydraulic pump (not
shown) associated with the drilling rig or service rig on which
power tong 10 is being used. FIG. 1 also illustrates a lifting ring
120 of a type that may be used for suspending power tong 10 from
the rig's hoist.
[0034] The three-dimensional configuration of rotary gear 40 is
illustrated in FIG. 2. As shown in plan view in FIG. 3, inner
surface 42 is of a generally circular configuration, but includes
several geometrically distinct portions. If rotary gear 40 as
illustrated in FIG. 3 is analogized to a clock face, with throat
opening 46 at approximately six o'clock, a first neutral recess 43A
is formed in inner surface 42 at approximately nine o'clock, and a
second neutral recess 43B is formed in inner surface 42 at
approximately three o'clock. The purpose of these neutral recesses
will be explained later in this document.
[0035] First neutral recess 43A is contiguous with inner surface 42
at points W and X, and second neutral recess 43B is contiguous with
inner surface 42 at points Y and Z. Inner surface 42 includes
substantially linear (i.e., substantially planar) primary camming
surfaces 44W, 44X, 44Y, and 44Z which propagate away from
transition points W, X, Y, and Z respectively, as shown in FIG. 3.
Primary camming surfaces 44W, 44X, 44Y, and 44Z are indicated in
FIG. 3 as having lengths L.sub.W, L.sub.X, L.sub.Y, and L.sub.Z
respectively. The magnitude of these lengths will be dependent on
the particular requirements of a given power tong 10.
[0036] The geometric characteristics of primary camming surfaces
44W, 44X, 44Y, and 44Z are illustrated in FIG. 4. A radial line R
extending from center axis C to transition point W, X, Y, or Z will
form an acute angle (A.sub.W, A.sub.X, A.sub.Y, or A.sub.Z) with
the corresponding primary camming surface 44W, 44X, 44Y, or 44Z. By
virtue of this geometric characteristic, the radial distance from
center axis C to a point on a given primary camming surface
decreases in substantially linear fashion according to the distance
away from the corresponding transition point. Acute angles A.sub.W,
A.sub.X, A.sub.Y, or A.sub.Z will typically be between eighty and
ninety degrees, but the precise magnitude of these angles will be
determined to suit the particular requirements of a given
application (including, for example, the size of tubular T on which
the power tong 10 is to be used).
[0037] FIGS. 5, 6, and 7 illustrate rotary gear 40 with jaw members
20 disposed within central space 48, and within gear housing 12
(the components of which are omitted from FIGS. 5, 6, and 7 for
clarity). As previously mentioned, the pivot end 20A of each jaw
member 20 pivots about a pivot pin 22 mounted to gear housing 12 at
a point generally opposite throat opening 46. Each jaw member 20
has a cam-following element (or cam follower) 24 associated with
outer side 20D. In the embodiments shown in FIGS. 5, 6, and 7, cam
followers 24 are provided in the form of protuberances formed
integrally with jaw members 20. Alternatively, cam followers 24 may
be in the form of rollers rotatably mounted to their corresponding
jaw members 20 using suitable axles or pivot pins. In any event,
jaw members 20, cam followers 24, inner surface 42, and neutral
recesses 43A and 43B are configured and arranged such that jaw
members 20 can pivot outward into an open position (as illustrated
in FIG. 5) in which each cam follower 24 is disposed within a
corresponding neutral recess (43A or 43B), and in which a tubular T
can pass through throat opening 46 of rotary gear 40 into central
space 48, and so as to be substantially concentric with center axis
C of rotary gear 40.
[0038] The basic operation of the prior art power tong 10 of U.S.
Pat. No. 6,988,428 may be understood with reference to FIGS. 6 and
7. In FIG. 6, with a tubular T positioned between jaw members 20,
rotary gear 40 has been rotated counterclockwise (as indicated by
the curved arrows) relative to jaw members 20 (and relative to gear
housing 12). The rotation of rotary gear 40 has forced cam
followers 24 out if their corresponding neutral recesses 43A and
43B, such that they engage opposing primary camming surfaces
44.sub.W and 44.sub.Z. As a result, the free ends 20B of jaw
members 20 have rotated inward to the point that dies 30A and 30B
have begun to engage the cylindrical outer surface of tubular T.
Because primary camming surfaces 44.sub.W and 44.sub.Z are of
linear (or planar) configuration as previously described, further
counterclockwise rotation of rotary gear 40 causes further inward
rotation of jaw members 20 such that dies 30A and 30B bite into
tubular T as shown in FIG. 7. Tubular T is thus securely gripped by
jaw members 20, thereby facilitating rotation of tubular T relative
to an adjoining tubular.
[0039] In similar fashion, clockwise rotation of rotary gear 40
(from the open position) would cause cam followers 24 to engage
opposing linear primary camming surfaces 44.sub.X and 44.sub.Y.
[0040] In the embodiment described above, inner surface 42 of
rotary gear 40 defines linear primary camming surfaces adjacent to
each neutral recess. Alternative embodiments may have only one
opposing pair of linear primary camming surfaces (i.e., 44.sub.W
and 44.sub.Z, or 44.sub.X and 44.sub.Y), with the other opposing
pair of camming surfaces being of a different configuration (e.g.,
curved).
2. Power Tong Having Cam Followers with Sliding Contact
Surfaces
[0041] The present invention may be understood with reference to
FIG. 8, which illustrates a rotary gear 40 and pivoting jaw members
20 largely similar to those of the prior art power tong shown in
FIGS. 5, 6, and 7. In accordance with the present invention,
however, each jaw member 20 incorporates a cam follower 240 with a
first substantially flat sliding contact surface 250 and a second
substantially flat sliding contact surface 260. The first sliding
contact surface 250 are oriented to come into sliding and
substantially uniform contact with linear primary camming surfaces
44.sub.W and 44.sub.Z when rotary gear 40 is being turned
counterclockwise relative to jaw members 20 (as in FIG. 8), and
second sliding contact surfaces 260 are oriented to come into
sliding and substantially uniform contact with linear primary
camming surfaces 44.sub.X and 44.sub.Y when rotary gear 40 is being
turned clockwise relative to jaw members 20.
[0042] FIGS. 9 and 10 illustrate an alternative embodiment of the
present invention (for simplicity, gear teeth 41 of rotary gear 40
are not shown in FIGS. 9 and 10). In the embodiment of FIGS. 9 and
10, each jaw member 120 has a roller-type cam follower 130,
rotatably or swivellably mounted to the jaw member 120 by means of
a swivel pin 132. Each roller-type cam follower 130 has a first
substantially flat contact surface 150 and a second substantially
flat sliding contact surface 160. First siding contact surfaces 150
are oriented to come into sliding and substantially uniform contact
with linear primary camming surfaces 44.sub.W and 44.sub.Z when
rotary gear 40 is being turned counterclockwise relative to jaw
members 120, and second contact surfaces 160 are oriented to come
into sliding and substantially uniform contact with linear primary
camming surfaces 44.sub.X and 44.sub.Y when rotary gear 40 is being
turned clockwise relative to jaw members 120 (as in FIGS. 9 and
10).
[0043] In FIG. 9, a tubular T has been positioned between jaw
members 120, and rotary gear 40 has been rotated clockwise such
that first contact surfaces 150 of roller-type cam followers 130
have begun to slide counterclockwise along corresponding primary
camming surfaces 44.sub.X and 44.sub.Y, and such that rear dies 30A
of jaw members 120 have begun to grippingly engage tubular T. In
the embodiment shown in FIG. 9, each jaw member 120 has an
additional die 30C disposed between front and rear dies 30A and
30B, to enhance overall gripping effectiveness of the power tong.
However, the inclusion of central dies 30C is not essential to the
present invention, and in fact the number and configuration of the
dies are entirely incidental to the invention.
[0044] In FIG. 10, rotary gear 40 has been rotated further
clockwise such that the first substantially flat sliding contact
surface 150 of such roller-type cam followers 130 now fully and
slidingly engages either of primary camming surfaces 44.sub.X and
44.sub.Y. As shown, cam followers 130 have moved further
counterclockwise along primary camming surfaces 44.sub.X and
44.sub.Y such that, due to the geometric characteristics of primary
camming surfaces 44.sub.X and 44.sub.Y as previously described, all
of the dies 30A, 30B, and 30C have come into secure gripping
engagement with tubular T.
[0045] Roller-type cam followers 130 may optionally be mounted to
jaw members 120 in association with biasing means such as a spring
(not shown), to orient first and second sliding contact surfaces
150 and 160 for optimal engagement with primary camming surfaces
44.sub.X, 44.sub.Y, 44.sub.W, and 44.sub.Z as the case may be,
depending on the direction of rotation of rotary gear 40. In
alternative embodiments, each roller-type cam follower 130 could
have only a single sliding contact surface, with biasing means
provided to orient the single sliding contact surface for
engagement with primary camming surface 44.sub.X, 44.sub.Y,
44.sub.W, or 44.sub.Z as the case may be.
[0046] As previously discussed, primary camming surfaces 44.sub.X,
44.sub.Y, 44.sub.W, and 44.sub.Z may have a slight concave
curvature, with first and second contact surfaces 150 and 160 being
correspondingly curved for sliding and substantially uniform
contact with curved primary camming surfaces 44.sub.X, 44.sub.Y,
44.sub.W, and 44.sub.Z. In such alternative embodiments, primary
camming surfaces 44.sub.X, 44.sub.Y, 44.sub.W, and 44.sub.Z will
retain essentially the same geometric characteristics as described
in the context of substantially linear primary camming surfaces
with reference to FIG. 4, but with acute angles A.sub.W, A.sub.X,
A.sub.Y, and A.sub.Z being formed with reference to chord lines
between the beginning and end points of the corresponding curved
primary camming surface 44W, 44X, 44Y, or 44Z. The radial distance
from center axis C to a point on a given primary camming surface
will still decrease in substantially linear fashion according to
the distance away from the corresponding transition point, in spite
of the slight curvature of the primary camming surfaces.
[0047] It will be readily appreciated by those skilled in the art
that various modifications of the present invention may be devised
without departing from the essential concept of the invention, and
all such modifications are intended to come within the scope of the
present invention.
[0048] In this patent document, the word "comprising" is used in
its non-limiting sense to mean that items following that word are
included, but items not specifically mentioned are not excluded. A
reference to an element by the indefinite article "a" does not
exclude the possibility that more than one of the element is
present, unless the context clearly requires that there be one and
only one such element.
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