Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: Power Tong Cage Plate Lock System
FIELD OF THE INVENTION
[0001] This invention relates to the field of power tongs, in particular
improvements to
open-throated power tongs used in oil-field application.
BACKGROUND TO THE INVENTION
[0002] It is frequently necessary in oil field operations to connect or
disconnect lengths
of drill pipe which are threaded together at their joints. Power tongs replace
the old
system of wrapping a chain five or six times around drilling pipe and then
pulling on the
chain in order to make-up or to break a threaded joint in a string of oil well
drilling pipe.
Power tongs contain multiple assemblies nested within each other to engage
with the pipe
and force the pipe to turn. A typical power tong includes a mechanism for
gripping the
external surface of a first pipe section and then rotating this first pipe
section while the
adjacent pipe section, to which it is connected, is held stationary or rotated
in the opposite
direction.
[0003] The outer frame of an open-throated power tong is held stationary,
typically by
being chained to the oilrig. This frame has a C-shaped access opening to
receive pipe. In
use, a gate is swung across the opening to close the gap and make the frame
rigid. Some
examples of power tongs with various types of gates to close the outer frame
are US
6,279,426, US 6,058,811, US 5,144,868, and US 4,593,584. Inside the outer
frame are
sets of pivoting jaws contained within a geared, internal rotating ring, also
C-shaped.
This ring gear is forced to rotate through its geared outer periphery. The
interior surface
of the ring gear carries a camming surface which, as the ring gear rotates
with respect to
the jaws, causes the jaws to swing inwardly to engage with the drill pipe.
[0004] Typically, such a power tong assembly includes top and bottom plates,
cage
plates, that carry hinge pins for the jaws. These cage plates are carried in
turn by the
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ring gear and, when the jaws are locked up, rotates with the ring gear. Before
the jaws
lock up on the drill pipe, the top and bottom cage plates are marginally free
to rotate with
respect to the ring gear, causing the camming surface to advance the jaws for
engagement
with the drill pipe.
[0005] An outwardly-directed radial reaction force is required on the face of
the
camming surface of the ring gear in order for the rotational torque to be
developed. This
reaction force increases as the rotational torque requirement increases. The
more
rotational torque required, the greater the jaw pressure against the pipe and
the greater the
outwardly - directed force against the ring gears camming surface. This
reaction force
will tend to spread the ring gear open. Under previously used moderate torque
levels, the
rotating gear has been made of such sufficiently strong steel that this
tendency to spread
has been minimal. However, at extremely high torques, this tendency for
spreading of the
rotating gear increases. High torques are becoming increasingly common in the
industry.
[0006] To resist such spreading, open-throated power tongs typically include
containment rollers mounted either on each of the cage plates or within the
frame of the
tong to bear against and resist spreading of the ring gear. These containment
rollers are
expensive and, in some cases are approaching their strength limits . It has
therefore been
recognized that additional means to resist spreading of the ring gear are
needed.
[0007] In existing power tongs a door is pivotally connected to the tong frame
or body
adjacent a side of the open throat. This door is positioned to extend across
the open
throat when in the closed position, resisting the tendency for spreading to
occur across
the entire tong body.
[0008] US 5,904,075, asserts that it describes a method of reducing
transmission of
spreading forces to the ring gear. In this reference, portions of the jaws are
advanced into
a hooked connection to each other so that a portion of the spreading forces
developed by
the hinge pins of the jaws are absorbed through the jaw contacts rather than
being
focused exclusively on the pivot pins. By this arrangement the jaw pivot pins
are
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partially restrained against spreading by the hooked engagements extending
between the
jaws. This reduces the spreading forces that would otherwise be directed into
the cage
plate and ring gear.
[0009] The invention described in this patent helps to lower the outwardly -
directed
force acting on the ring gear by transmitting a portion of the load through
the cage plates.
But no support is provided to the cage plates to prevent such cage plates from
spreading.
[0010] There remains a need for a power tong system that includes cage plates
that are
better able to resist spreading themselves as well as provide support for the
ring gear to
resist expansion when exposed to the large amounts of torque developed in
modern
power tongs.
[0011] The invention in its general form will first be described, and then its
implementation in terms of specific embodiments will be detailed with
reference to the
drawings following hereafter. These embodiments are intended to demonstrate
the
principle of the invention, and the manner of its implementation. The
invention in its
broadest and more specific forrns will then be further described, and defined,
in each of
the individual claims which conclude this Specification.
SUMMARY OF THE INVENTION
[0012] According to one aspect of the invention, a cage plate locking means is
provided for spanning across the open throat of the cage plate to strengthen
the cage plate
from spreading under high loads. The locking means essentially 'closes' the
cage plate
mouth allowing higher radial forces to be supported within the cage plate and
ring gear
assembly. The cage plate locking mechanism opens to allow pipe to be inserted,
but when
closed, 'locks' and rotates with the cage plate.
[0013] In a preferred embodiment a power tong for rotating a pipe to make up
or break
up a threaded joint comprises a tong body having an open throat therein, a
ring gear
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rotatably supported by the tong body, twin cage plates rotationally mounted
with respect
to the ring gear on opposite sides of the ring gear. The cage plates are free
to rotate with
respect to the ring gear, but are constrained to maintain a center of rotation
substantially
corresponding to the center of the ring gear. According to this preferred
embodiment of
the invention, a cage plate locking means is connected to each cage plate
adjacent a side
of the open throat in the cage plate to extend across the open throat when
locked in a
closed position and to expose the open throat of the power tong when in an
opened
position to enable the power tong to be moved laterally on or off the pipe.
[0014] In one embodiment the cage plate locking means includes a pair of
linking arms
each respectively connected to the outer faces of the top and bottom cage
plates.
Optionally, these linking arms may be connected by a joining bar or other
means to be
swung in unison. When swung into their locking position, each of the locking
arms
engages with a pin protruding from the outer surface of the respective cage
plates.
[0015] Actuation means, optionally in the form of a hydraulic cylinder seated
on the
frame of the power tong, may swing the locking arms between open and closed
positions.
[0016] The cage plate locking means of the invention provides support to the
cage
plates, resisting expansion of the cage plates about the open throat formed
therein. The
cage plates of the invention are also mounted to the ring gear preferably
through a
friction-minimizing ring and track coupling. This coupling enables the cage
plate to
supply support to the ring gear, thereby absorbing part of the spreading
forces that would
otherwise be applied to the ring gear. By reducing the tendency for an
expansion of the
cage plate to occur, the cage plates in a power tong according to the
invention are better
able to support the ring gear against expansion.
[0017] The foregoing summarizes the principal features of the invention and
some of
its optional aspects. The invention may be further understood by the
description of the
preferred embodiments, in conjunction with the drawings, which now follow.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 is a top view of the power tong with the cage plate lock
system in the
closed position.
[0019] Figure 2 is a side view of the power tong from Figure 1.
[0020] Figure 3 is a perspective view of the power tong with the cage plate
lock system
in the open position.
[0021] Figure 4 is an isometric side view of the power tong showing the rail
and groove
connection between the cage plates and the ring gear.
[0022] Figure 5 is a chart showing the relationship between mouth displacement
and
torque.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] As shown in Figures 1-4, the power tong 10, includes a tong body 12, a
ring
gear 14, and a pair of cage plates 16 having an open throat portion 19.
Secured to each
cage plate 16 is the cage plate lock system 18.
[0024] As can be seen in Figures 1 and 3, the cage plate lock system 18
further includes
a pair of locking arms 20. Each of the locking arms 20 is respectively
rotatably secured
at one end to the outer surface of a cage plate 16 as shown in the form of a
securing pin
21. The locking arms 20 are free to rotate between the closed position seen in
Figures 1
and 2, and the open position shown in Figure 3. At the other end of each
locking arm 20
is a hook member 22, which is dimensioned and positioned to removably engage
with a
pin 24 positioned on the outer surface of the cage plate 16, on the opposite
side of the
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open throat 19. Once the locking arms 20 of this locking system 18 are
engaged, they
serve to secure the cage plates 16 against expansion under high torques.
[0025] As can be best seen in Figure 3, a joining bar 28 connects between each
locking
arm 20, to allow the top and bottom locking arms 20 to be moved as one
complete
system. Actuation means, shown in the form of a hydraulic cylinder 26 is
seated on the
frame 12 of the power tong and coupled to at least one of the linked locking
arms 20 to
swing the locking arms 20 between open and closed positions. Optionally, a
handle 27
may also be attached to the locking arms 20 to carry out this function.
[0026] A gate 30 is connected to the tong body 12 and is able to rotate from
an open to
a closed position, to allow a pipe (not shown) to enter through the open
throat 19, and
then be secured inside. The gate 30 serves to prevent spreading of the tong
body 12.
The cage locking arms 20 of the plate lock system 18 are attached to the cage
plates 16 so
that, upon disengagement, the joining bar 28 is able to swing clear of the
path of the
throat 19, resting against gate 30 when it is fully open, as shown in Figure
3.
[0027] When in use the door 30 and the cage plate lock system 18 are in the
open
position, a pipe with a threaded joint needed to make up or break up may be
placed
within the open throat 19 of the power tong 10. Once the pipe is placed
inside, the gate
30 and the cage plate lock system 18 are then rotated and secured in the
closed position
seen in Figure 1.
[0028] The cage plates 16 are coupled to the ring gear 14 through a friction-
minimizing
groove 32 and rail 33 arrangement. As shown in Figure 4, the groove 32 is
formed in the
top surface of the ring gear 14, and a track or rail 33 protrudes into the
groove 32 from an
adjacent cage plate 16. This configuration may be reversed with the groove 32
being
present in the cage plate 16 etc. In order to minimize friction, the ring or
rail 33 may be
made of a different material, e.g. brass or bronze, that has a reduced
tendency to
frictionally engage with the steel sides of the groove. Alternately, one or
the other of the
cage plates 16 or ring gear 14 may carry rollers that engage against a surface
carried by
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the other part. Through this coupling, the cage plates 16 provide support for
the ring gear
14, absorbing part of the spreading forces that would otherwise be applied to
the ring gear
14.
[0029] Accordingly, the use of the locking means 18 to constrain expansion of
the cage
plates 16 provides an indirect means for supporting the ring gear 14 against
expansion.
[0030] The throat 19 of the ring gear 14 in a power tong 10 actually widens
under high
torque to a measurable degree. Figure 5 compares a prior art power tong
without a cage
plate locking system 18 with the power tong in accordance with the invention.
While not
based upon actual measurements, Figure 5 shows a projection of the general
direction of
the effect of the cage plate locking means 18, as described herein. With
higher radial
forces the mouth of a conventional cage plate/retaining gear assembly
continues to spread
in an essentially linear fashion with torque. With the invention present, this
trend is
arrested after it is only partially developed. This permits a power tong 10 to
be used
under higher torque conditions.
[0031] The invention has the alternate advantage of allowing the use of a
lighter ie.
thinner, cage plate 16 and/or a lighter ring gear 14 for a given torque than
would
otherwise be employed.
CONCLUSION
[0032] The foregoing has constituted a description of specific embodiments
showing
how the invention may be applied and put into use. These embodiments are only
exemplary. The invention in its broadest, and more specific aspects, is
further described
and defined in the claims which now follow.
[0033] These claims, and the language used therein, are to be understood in
terms of
~
the variants of the invention which have been described. They are not to be
restricted to
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such variants, but are to be read as covering the full scope of the invention
as is implicit
within the invention and the disclosure that has been provided herein.
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