Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
`~ 1085377
The present invention relate~ to a casing tong, in
particular a tong for turning borehole casings, which
comprises an enclosure with an axial opening and a
radially recessed portion adapted to the casing outside
diameter as well as a gear rim inside said enclosure which
i~ rotatable under the action of a drive means, said gear
rim being provided with a corresponding radially recessed
portion and with cams having associated gripping jaws
which are universally movably arranged on suitable holding
elements,
The use of oasing tongs of the type described above
requires high gripping or clamping forces to sorew pipes
into and/or out of engagement with one another. Tongs
that have been used in the past employ very flat curvatures
of the cams which convert the peripheral forces of the drive
means into gripping or clamping force. Besides the
existence of substantially radial forces which are very
unfavourable to the tong and which may result in undesired
expansion thereof, there is another drawback involved in
that the magnitude of forces would cause sub~tantial
penetration oi the blades into the casing pipe material
90 that after elimination of contaot forces said blades
are prevented from clearing the pipe wall by turning the
gear rim in the opposite direction. A reversal of the
direction of rotation after screwing would force the pipe
to rotate to the opposite direction so that the screwed
joint i~ loo~ened again. Even more difficult is to
separate the clamping blades from the pipe or casing after
an un~crewing operation. The pressure applied to the
ca~ing wall by the gripping or clamping jaws i9 increased
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until the unscrewing process has been initiated. A~ter
complete separation of the oa~in~ pipe from it~ ~onnector
it is very difficult and may even be impossible to detac~
the gripping jaws from the unscrewed casing section by
reversing the direction o~ rotation, since there is no
longer any countertorque. Trials with steeper cams
~howed that the contact force~ were too low. A makeshift
was therefore adopted in practice in that unscrewing was
done in two 6teps of which the first was to initiate the
unscrewing operation and was stopped immediately on having
achieved such initiation ~or refitting the tong, and the
second was to carry out the remainder of the unscrewing
operation with reduced gripping or clamping forces involved,
~he bite of the tong bladee into the casing pipe material
is all the heavier, the flatter are the cams oi the gear
rim, the reasons being that as the tongs grip there i9
simultaneously a con~iderable peripheral distance being
traversed which entails a tangentially directed cut into
- the ca~ing pipe material. The application oi high forces
by flat cams moreover results in a resilient deiormation
of the mating parts, i,e, of olamping jaw guide rollers
and cams. This resilient deformation partioularly
contributes to the fact that separating the clamping blades
on termination of a working cycle is extremely di~iicult.
It is an objeat of the present invention, therefore,
to provide a oasing tong of the type described above
wherein the gripping or clamping Jaws thereof can be
readily freed irom the casing pipes after both a screw-
ing and an unsorewine operation, In particular, the
ioroe~ prêvailing between the cams and the guide rollers
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moving along the curved faces thereof are minimized
so that the material will not be exposed to ~uch loads
as would entail resilient deformation.
According to the present invention thi~ problem is
solved in that lever means to increase the clamping or
gripping force are used between the clamping or gripping
jaws and the holding elements thereof and that each cam
iB provided with a shallow-curve centering face and a
substantially steeper-curve clamping face, Contact
force~ can be very advantageously increased in that the
clamping or gripping force is applied unilaterally, i,e,
via one clamping or gripping jaw at a time while the
opposite jaw only serves as reaction element. This
permits the clamping face to be provided with an even
steeper slope so that there is a rapid increase of clamp-
ing force and the gripping jaws engage into the casing
materials in a virtually radial orientation. It is for
this purpose that the centering face is subdivided into
a shallow-slope centering portion and a circular concen-
trically extsnding retainer portion. ~he lever means
are provided in the form of one-armed lever~ to simplify
construction, They are pivoted to the outer extremities
of a substantially semicircular gripping jaw carrier and
on their iree ends carry guide rollers adapted to move
along the curved ¢entering and clamping face~ of the cams,
with the pivot attachment of said gripping jaws to the
lever~ being dispo~ed between the pivotal axes of the guide
rollere and the pivotal axes of the lever mean~ at the
extremitiee of the gripping jaw carrier,
It ha~ ~urprisingly been found that steeper cams,
the u~ of which i~ pr~ctic~ble due to provision of
~orce-increasing lever arms and introduction o~ clamping
force via only one of the gripping jaws, permit to
disengage the tong from the casing without difficulties
even in the absence of countertorque. No resilient
deformation can be caused of the cams and guide rollers
due specifically to the use o~ steeper clamping faces,
Another advantage is that the gripping jaw blades
traverse only very minor peripheral distances on the
cn~ing ~o that the casing or pipe material undergoes
deformation to only a negligible degree only, ~he
necessary clamping or gripping force leads to no further
casing or pipe deiormation~
. Another essential advantage is that the steeper-curve
clamping faces suppress development of a radial force of
such magnitude as might bend or force the tong open,
A considerable portion of the driving force remains :
tangential so as to protect the gear rim from deflection,
The gripping or olamping force proper is accommodated by
the carrier directly holding the gripping jaws and thus
- kept away from the gear rim,
Fitting and removal of conventional radially-retractable
tong~ i9 difficult and time wasting, The tong must be
forced against the casing until ~he jaws have concentric-
qlly gripped or engaged the casing, Due to provision
of a short centering curved face which then changes over
into a holding or retaining curved face, the gripping
jaws are ad~usted into centering position after a minor
rotational movement of the gear rim, This means that
the tong automatically keep~ to the casing, though in
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1085377
the absence of any driving contact therewith, so that the casing is
still freely movable to a minor degree in the tong. It is no longer
possible after screwed engagement for the tong to come off the casing
since, following their release, the gripping jaws of the tong initially
remain in centering position, which means that the tong arrests the
casing in said position and the jaw blades are only disengaged out of
contact with the casing material. ~ue to the fact that the cams are
disposed in a symmetrically opposed relation and engage the guide
rollers of the lever means in such a way that the guide rollers of none
lever moves on the centering curved face, and the guide roller of the
lever opposite thereto necessarily moves on the clamping face, the
peripheral force is converted into clamping force via only one of the
levers during the clamping operation. The force of reaction is applied
as backup force by the opposite gripping jaw and the associated
clamping lever. This permits the use of an optimal, i.e. substantially
steep, clamping face which results in a substantially radial clamping
force of the gripping jaws as desired. By reversing the direction of
rotation of the tong, the gripping jaws can easily be released from the
pipe without the necessity of applying a countertorque.
Following upon the above discussion, the invention provides
in one broad aspect an apparatus for rotating a tubular member,
comprising a housing having a radially recessed opening for receiving
the tubular member; a latch for closing off the radially recessed
opening during operation of the apparatus, said latch being pivotally
secured to the housing on one side of the radially recessed opening; a
latch power means for actuating the latch connected to the latch; guide
discs mounted within the housing, said guide discs having a radially
recessed opening for receiving the tubular member corresponding to the
radially recessed opening of the housing; a gear rim mounted inside
said radially recessed opening in said housing and rotatable under the
action of a drive means, said gear rim having an interior wall and a -
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1085377
radially recessed opening for receiving the tubular member
corresponding to the radially recessed openings of the housing and of
the guide discs; a power drive means for driving the gear rim, said
power drive means being secured to the exterior of the housing; a first
and a second multi-faceted cam mounted within the gear rim in axially
staggered positions with respect to the axis of the apparatus; a
substantially crescent-shaped carrier member mounted within the gear
rim, and having a first end and a second end, said carrier member being
rotatable within the gear rim and along the cams; a first lever arm
pivotally secured to the first end of the carrier member; a second
lever arm pivotally secured to the second end of the carrier member; a
first gripping jaw for gripping the tubular member, said jaw pivotally
secured to the first lever arm; a second gripping jaw for gripping the
tubular member, said jaw pivotally secured to the second lever arm; a :~
first guide roller rotatably mounted to the first lever arm so that it
moves on the faces of the first multi-faceted cam for actuating the
first gripping jaw; and a second guide roller rotatably mounted to the :~
second lever arm so that it moves on the faces of the second
multi-faceted cam for actuating the second gripping jaw.
In a further embodimene, the multi-faceted cams are disposed
on substantially opposite sides of the axis of the apparatus, said cams
having three faces formed on the surface thereof, a centering face, a
holding face, and a clamping face, the holding face being shaped in the
form of a circular arc oriented concentrically to the axis of the
apparatus, the centering face sloping gently away from one end of the
holding face to the edge of the radially recessed opening of the gear
rim, and the clamping face sloping abruptly from the other end of
holding face to the interior wall of the gear rim, said cams being
axially staggered with respect to the gear rim and the axis of the
apparatus and disposed symmetrically with respect to the axis of the
apparatus.
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853~7
An embodiment of the present invention given by way of
example is hereinafter described with reference to the accompanying
schematic drawings in which:
Fig. 1 is a plan view of the casing tong;
Fig. 2 shows the gripping jaws with jaw carrier and gear rim
with cam means in neutral
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1085377
position, the top half of the figure
showing the tong during introduction
o-f the casing, and the bottom half show-
ing the ca~ing already swung into
position between the gripping jaws;
Fig. 3 shows a centered casing;
Fig. 4 shows a casing clamped in place between
the gripping jaws; and
Fig. 5 also shows a casing clamped in place, but
turned in opposite direction.
The plan view of the complete apparatus seen in Fig.
1 shows an enclosure 1 with holding and guide disks 2
to afford guiding action and to retain a gear rim 5
(Figs. 2 to 5) disposed therein to operate gripping jaws
3 and 4. These gripping jaws 3 and 4 encompass a
casing 6 to be centered and to be screw connected or
di~connected to and/or from extension means, A radially
reces~ed position 7 permits the tong to be pluced aroun~
the casing 6 and/or to remove it therefrom after the
ôperation has been completed. This reoessed position 7
is closed off by means of a latch type flap 8 which is
mechanically, hydraulically or pneumatically operable
with a means 9 and which connects the enclosure portions
separated by said rece~s 7 in a positive and form-fitting
manner, A hydraulic drive means 10 i8 used to operate
the gear rim (not ~hown) in Fig, 1,
Identical parts are raferred to by identical refer-
enca numerals in the figures, The gear rim 5 carries
cams 12 and 13 which are disposed in a symmetrical
relation to the centerline of the recessed portion 11.
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Each o~ said cams i~ provided with a curved centering
face 12a and/or 13a, a curved center-position holding
face 12b and/or 13b and a curved cla~ping face 12c
and/or 13c, Levers 15 and 16 are pivotably secured to
a ~ubstantially crescent-shaped carrier i4, The
respective pivot points on the gripping jaw carrier 14
are designated by the reference numeral 17. ~he levers
15 and 16 carry guide rollers 18 and 19 at their free
ends, and also support the gripping jaws 3 and 4 $itted
with clamping or gripping blades 20, Levers 15 and 16 - .
are one-armed levers, which means that the respective
pivot point 2i of said gripping jaws ~ and 4 is disposed
intermediate the guide rollers 18 and 19 and the respect- ~ ~:
ive pivot 17 of the levers at the gripping jaw carrier
14, ~ :
As can be seen from Figs, 3 to 5, the gripping jaw 3
is functionally as~ociated with oam 13 via guide roller
i8, and guide roller 19 can only engage cam 12 because
the rollers and their associated cams are axially ~taggered,
Fig, 3, $or instance, shows a centering operation via
gripping jaw 4,
The associated roller 19 initially engaged the center- -
ing $ace 12a o~ cam 12, which means it was displaced
radially inward until it reached the holding face 12b, ~.
and was retained in this position, By further turning
- the gear rim 5 in the direction oi~ the arrow, i,e,
clockwi~e, the guide roller 18 o$ gripping jaw 3 i9
moved to the curved olamping $aoe l~c. ~his operation
i8 particularly ¢lear from Fig, 4, The oams are hence
. in ~uoh relative arrangement that one o$ the gripping
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108~3~7
jaws is always retained in centered position by one of
the holding races and thus serves as a reaction element
to provide the backpressure or reaction ~orce necessary
for the clamping pressure of the opposite gripping jaw
to build up. As can be seen from Fig. 5, after reversal
the guide roller 18 move~ along the holding face 13b
oi cam 13, while guide roller 19 has entered the curved
olamping face 12c o~ cam 12 to thereby make the lever
16 exert the required pressure to the gripping jaw 4,
iOThe figuree of the drawings show that the curved
clamping ~ace~ of cams 12 and 13 are provided with a
steep ~lope so that the necassary clamping or gripping
iorce is obtained with only minor peripheral movements
of the gear rim involved, and with the gripping jaws
only having to make ex~remely small peripheral movements
during each clamping or gripping oper,ation, This tendency ~-
is considerably increased due to provision o~ levers 15
and 16.
