Note: Descriptions are shown in the official language in which they were submitted.
~L2753L98
ROTOR OF A SCRE~V HYDRAULIC D0~iNHOLE MO~OR,
ETHOD FO~ ITS PROnUCTI0~ A DEVICE FOR
CARRYING ~ E INTO EFFECT
l'he present invention relates to drilling equip-
ment and more sp~cifically7 to one of tho major units
of screw hydraulic downhole motors applicable for
drillin~ oil and gas wells, viz., the rotor of a
screw hydraulic downhole motor, and to a method for
producing said rotor.
Modern progress in well-drilling technigues usin~
screw hy~raulic downhole motors is aimed at the provi-
sion of' drilling machines incorporating multi-lobe
rotors that feature high torque on the output sha~`t ~
and a reduced rotation freguency thereof. ~rhis enables
one to apply up-to-date low-speed high-torgue rolling-
cutter drilling bits with oil-filled bearing asse~bly,
and drilling bits with polyclystal diamond inserts,
which impose stricter reguirements on the ability
of a downhole motor to operate und~r heavy axial thrust
and at high torq~e.
Known in the art presently is a downhole motor
with a multi-lobe rotor made as a solid metallic
multiple-thread screw, whereln tho number o~ starts
of the helical surface (helical teeth) is in excess
of unity (cf. USSR Inventorls Certi~icate No.926,209,
Int.C1. E 21B 4/02, published on ;/iay 7, 19~
'l'h~ rotor is accommodated inside a st~tor f'~atur-
75~98
ing an inn~r multiple-thread helical surface, wherein
the number o~ starts is in excess o~ that o~ the rotor
by unity; said helical sur~ace is moulded on the lin-
ing made o~ a resilient material, such as rubber pasted
to the inner sur~ace o~` the stator ~rame. The rotor
axis is o~fset with respect to the skator axis which
aligns with the motor axis, by the amount of eccentri-
city equal to half the length o~` the rotor and stator
teeth, while the ratio of the axial pitch of the rotor
helical teeth to the exial pitch of the stator helical
teeth equals the ratio between the number o~ teeth
on said motor components. When the rotor teeth e~ge
the stator teeth, spaces are formed, opening to the
rotor top portion and closing over the length of the
helix lead. ~'ihen drilling mud is injected into tha
screw hydraulic downhole motor from daglight surface
along the drill string to the bottom end of ~hich
the screw hydraulic downhole motor is connected, tho
rotor of the motor perfor~s planetary motion, while
the rotor axis rotates about the stator axis in counter-
clockwise direction at an angular velocity ~1' and
the rotor itsel~ rotates about its own axis in cloock-
wise direction at an angular velocity ~ 2 The magnitude
o~ the angular velocity ~1 is equal to that o~ the
angular velocity ~2 multiplied by the numb~r of L~otor
teeth, while the centriI`u~al ~orce acting on the rotor
75~98
i5 proportio~al to its mass and to the square of the
angular velocity CJl
However, lar~e mass of a solid rotor and high
magnitude of the an~ular velocity ~1 at which rotates
the rotor re~ult in high centrifugal forces arisin~
during the operation of' the motor. These forces inducs
vigorous transverse vibrations which affect adversely
the durability o~ the rotor, stator, hinge joints, as
well as of the threaded joints of the motor and the
drill string.
'~he multi-lobe rotor of the aforediscussed motor
is manu~actured by virtue of ~ear hobbin~, i.e., outt-
ing with a ~etal-cutting tool called the hob. ~he
method is an expensive one, suffers from an inadequate
productivity, failq to provide hi~h guality o~ rotor
teeth surface finish and involves sophisticated and
costly metal-cutting machinery and tools. Further-
more, resort should be made'to polishing or grinding
of the rotor working surfaces to improve the guality of
surface finish, which is a complicated technoligica
task on accou~t of i~tricate co~figuration of the
rotor and its long overall length.
I~ addition, it is due to a g~r~at length of the
multi-lobe rotor that the cutting lips o~ a hob gro~
worn in the course of rotor machining, which affects
badly the accuracy o~' the finished product.
~ nother screw hydraulic ~lownhole motor ~nown in
~ 75~8
-- 4
the present state o1 t~ie art comprises a LlolloY~ multi-
lobe rotor. .~or the ~urpose of joining~ with a cardan
or ~ flexible sna~t, the rotor is ri~idly connected 9 by
virtue of a threa~ed join-t, to -the union coupling (cf.
a textbook "~crew hydraulic downhole motors for
-vlell drillin~' by ~ Gusman et al., ;,loscow, ~Tedra i;H,
19~1, pp. 1~5-1~8 (in iius~ian). 'l~he rotor
i~ question is hollow-centred by removal of the metal
~`rom ~he central portion thereof either by virtue of
a centre hole ~irilled in the rotor or througn the use
ol ~ thick-~alled pipe shell.
f~his ma~es it possible to reduce to some extent
the centrifu~al forcas applied to the rotor, tnus lo~ier-
in~ the dynamics of tran5verse oscillations both of
the rotor and of the motor as a whole. However~ a con-
sid0rabLe mass OL` ~etàl remains in the bulk of the ro-
tor teeth in th~ peripheral portion thereof, with the
result that hi~h centrifugal forces arise durin~ the
motor operation, which af~ect adversely the motor du
rability.
oreover, joining the rotox with a cardan or a
flexible shaft through a coupling incorporating threaded
joints is unreliablg, sinc~ such joints are likely to
disen~a~e under the action of danymic forces resulting
f'rom motor op~ration~
L'he helical teeth o~ the rotor of`-the ~otor unaer
~ ~ 75 ~
considerattion are also pro~uced by the ~ear-hobbing
technique which suffers from the disadvanta~es men-
tioned above.
Furthermore, provision o~ a solid rotor or a rotor
made from a thick-~valled pipe lea~s to high consumo-
tion OI` stainless steel. i,!otors incorporatin~ the
ai'oredescribed rotor ~eature relatively low ef~iciency
and power output, since ~,reat mechanical losses occur
~urin~ operation Yor the stator rubber to self-heat.
'here is ~nown more productive an~ ef~`ici~nt
;Dethod for m~Kin~ the sin~le-lobe rotor of the i.luano
scr~w oump (cf. US ~atent i~o. ~4~4,011 l~ational Patent
ClassiYication 103-117, published on March ~, 1949).
~ he method consists in de~orming a tube blank on
a formative helical surface by virtue of a fluid pres-
sure applied to said tube blankO
i~he method is carried into ef~`ect through a device
comprising a housin~ ~hich accom~odates a ~ormin~
element with the formative surface, the tube blank
being situated inside said ~orming element.
'~ne formative helical sur~ace is situated on the
inner sur~'ace o~ the formin~ e1elnent which serves at
the same time as the aousin~ and has a number of
axial joints. A ~luid pressure is built up in the
bore (or hollow space) oL the tube blan~ located
inslde the ~orminO element ~rovi~e~l ~!Jith seals. i~le
proeess o~ ~`or~in~ the rotor of a sin~Jle-scL~ 3U(,ip
~75~
_ 6
is carried out in a number of sta~es, each bein~ ~ollow-
ed by extracting the tube blan~ from the forming ele-
ment for annealing with a view to reducing the hard-
ness of` the blani~ and relieving internal stresses ~he-
rein .
The aforediscussed method and the device forcarrying it into ef~ect suf~er from too low quality of
the rotor outer surface on ~Ihich there ar~ marks left
by the joint surface of the forming element, eliminati-
on of said marks involving additional machining of the
rotor outside surface using special eguipment.
Another disadvantage o~ said method and device
resides in a sophisticated process for making the inner
surfaces of the split forming element, as well as a
complicated procedure OI` bringing the ~ormative helical
surfaces in coincidence in the jointing planes. '~he
disadvantages mani~est themselves more conspicuously
when makin~ rotors featuring hi~h length-to-diameter
ratio, thus rendering impossible the production of
multi-lobe rotors by the method described above.
One more disad~anta~e inherent in the aforemention-
ed known method is the necessity to apply high hydro-
static fluid pr~ssure, since -the pipe blank undergoes
considerable tensile deformation. '~his, in turn, ac-
counts for high sp~cific power consumption o the pro-
cess.
75~3
-- 7
It is a primary and essential object of the inven-
tion to pro~ide a rotor of a screw hydraulic downhole
~ motor for drilling wells~ and a method and a davice f`or
its production, which would make it possible, due to
constructional features of the rotor, to improve out-
put power characteristics oX the motor, reduce .~ricti-
on loss and increase rotor production eXficiency.
The essence oX the invention resides in that the
rotor of a 5crew hydraulic downhole motor made as a
multiple-thread sclew having the number o~ teeth on
th~ helical surface exceedin~ unity and ri~idly connect-
ed to a union couplin~, according to the invention~ is
substantially hollow and features substantially cons-
tant wall thickness, whils the ratio of the length of
the rotor cross-sectional outside contour to the length
of a circle circumscribed around said contour is 5ub-
stantially within 0.9 and 1.05.
Such a constructional arrangement oX the rotor
makes it possible to improve the output power characte-
ristics OI the motor, reduce transverse vibrations, add
. to the strength oX the rotor with respect to the torgue
applied thereto and bending load imposed thereon, dec-
rease the rotor mass and its specific metal content,
cut down stainless steel consumption, and better the
guality oX its manufacture.
'iihe essence of a method for the rotor production
5~
resides in that a tubular blank is subjected to defor-
mation on the formative surface by virtu~ of a fluid
pressure and in that, according to the invention, the
forming element ~lnos~3 outside surface is in ~act the
formative sur~ace 9 iS placed inside the tubular blank,
while the fluid pressure is applied to the outside
sur~`ace of the tubular blank.
This enables one to attain high quality of the
rotor helical surface, reduce power and labour consump
tion for its manufacture, cut down production ~ime
and -thus obtain a rotor featuring improved technical
characteristics, higher quality of surface finish and
precision, which makes it possible to minimize fric-
tion loss and improve oubput power charac-teristics of
a motor incorporating the rotor of the present i wen-
tion.
On some occasions it is expedient that the form-
in~: process of a tubular blank be carried ouk in two
stages, at the first of which the tubular blank is
given the shape of a helical polyhedron with rounded-off
vertices, featuring the diameter of a circumscribed cir-
cle drawn therearound somewhat in excess o~ the diame-
ter of a circumscribed circle drawn around a finished
rotor, and the number of faces is equal to the num-
ber of threads (or starts) of the rotor helical sur-
face, whereas at the second stage the rotor helical
.X75
surface is forrned finall~.
~ his enables one to avoid metal wrinkling during
the forming process of a tubular blank and ensure ex-
cellent workmanship, hi~h ~imensional accuracy and
trueness of ~eometrical shape.
It is expedient that before exerting pressure on
the tubular blank a union coupling recessed on its
outside sur~ace be inserted into said blank, and the
latter be forced a~ainst the surface o~ the union
coupling concurrentlg with the formation of the rotor
helical surface, thus making the ~lank fast in the
rotor.
: This makes it possible to cut down the time spent
for producbion of` a rotor with a union coupling due to
simultaneous (combined) formin~ of the rotor helical
orking~ surface and securing o~ the union coupling in
the rotor. Besides, there ~ provided higher reliabi-
lity and pressure-tightness of the joint of the rotor
with said coupling~
'rhe essence of a device for makin~ said rotor by
~he r~ethod set ~orth hereiabefore consists in that it
comprises a housi~g which accorrlmodate~ a fo~ing
element having a formative sur~ace, wherein, according
to the invention, the forming elernent is in~talled
inside the housing on centring bushings, while the
~; ;ormative Sur~aGe is ~rovided on the formin~ element
.~ .
:
75~
-- 10
outside surface 9 and tAe centring bushes have fitting
areas adapted for the tubular blank ends to fit tightly
thereon.
'~his provides ~or reliable location o~` the forming
element with respect to the housing and tubular blank
and production of a rotor having high-quality outside
workin~ surface, as well as simplifies the manufacture
of the forming element.
It is expedient that each centring bushing be pro
vide~ ~vith a projection adjacent to its ~ittin~ area and
adapted for tne tubular blank set on said ~itting area,
to rest against, and that ~aid projection have an a~-
nular groove whose width is substantially equal to the
thicknes~ of the tubular blank, said groove being
adapted for a seal to accommodate.
This provides for reliable ori6inal hermetic seal-
ing of the high-pressure chamber of the device before
be~innin~ the process of deformation of a tubular blank
on the fritting ar~9 of the centrin~ bushings, as well
as makes it possible to attain more reliable operation
of the rotor manufacturi~ device.
It becom~s necessary, on some occasions, that the
formin~ element should be replaceable in the housing
and that a preforming element be provided for preli-
~inary formatio~, made as a helical polyhedron with
rounded-off vertices, featurin~ the diameter of its
, ,~
,:,
~7S~
: circumscribed circl~ so~ewhat in excess of the diameter
of a circumscribed circle of the forming element for fi-
nishing formation, the number of the ~aces of said poly-
hedron being egual to the numoer of threads on the
rotor helical surface.
~his makes it possible to prevent wrinkling on
the rotor working surfaces and provide high quality oX
said surfaces, high dimensional accurac~ and trueness
of geometric shape.
.- In what follows the invention is illustrated b~ a
detailed description of a specific embodiment thereof
with reference to the accompanying drawin~s, wherein:
FIG. 1 is a schematic, partly longitudinal section-
al view of a screw hydraulic downhole motor for drill-
ing oil and gas wells, incorporating the rotor, accord-
ing to the invontion;
FIG. 2 is a cross-sectional view of the motor,
taken along the line II-II; !
`~ FIG. 3 is a longitudinal-section view o~ the rotor,
according to the invention;
FIG. 4 is a cross-sectional view of the rotor,
: tak~n aIong the lin~ IV-IV;
FIG. 5 is a cross-sectional vi~w of the rotor,
ta~en ~long the line V-V;
FIG. ~ is a longitudinal-sectional view of a devics
for making the rotor, according to the invention;
. . .
.;275
-- 12
FIG. 7 is a cross-sectional ~iew of a devico for
makin~ the rotor, taken along the line VII-VII;
FIG. 8 is a cross-sectional view of the forming
cores for preli~inary and finishing Yorming process;
and
~ IG. 9 is a fra~mentary longitudinal-scctional
view of a de~ice for making the rotor with simultaneous
forcinK of a union coupling.
A rotor 1 is in effect one of the major compo-
nents of a downhole motor (FIG. 1); it i5 made as a
multiple-thread screw havin~r external helical teeth 2,
the number OL threacLs (teeth) on the helical surface
bein~ in excess of unity. r~he rotor 1 is accommodated
ins~de a stator 3 which is provided with a lining 4
made of such a resilient material as rubber. '~he lin-
ing 4 has an inside helical surface which Yorms he-
lical teeth 5 the number of which exceeds the number
of teeth on the rotlor 1 by unity. An axl~ l (F~g. 2)
of th~ rotor 1 is offset with respect to an axis 2
of the stator 3 by an amount 7e ~ of eccentricity. The
rotor 1 (EIG. 1) is associated with a shaft 6 of a
bearing unit 7 of the motor throu~h a flexible shaft 6
or a cardan shaft (not shown). '~he bearing unit 7
comprises axial and radial bcarings (not shown) adapt-
ed to take up bottom-hole loads. Connected to the
lower encL of the shaft 6 of the bearing unit 7 is a
`:
' ~ '
'' ~ `
~.27~ 8
- 1 3
,
rock destruction tool 9. '~he stator 3 of the-motor is
connected, through an adaptor lO, to thc lower ~nd of
a drill string 11.
The rotor 1 (~IGS 3, 4) , according to the inven-
tion, is a hollow structure 9 comprising a tubular
shell 12 (housing) and a union couplin~ 13 (FIG. 3)
rigidly h~ld to said.shell and adaptod for assoclation
with the flexible shaft 8 (FIG. 1). ~he union coupli~g13
(FIG. 3) is provided with el~m~nts 14 ~or connecting
the flexible sha~t8~ e.g.~threadS~ though some alter-
natives may be resorted to, such as welding, joinin~ by
m~ans of cones, etc.
It is a preferable method of holding the union
couplin~ 13 to th~ tubular sh~ll 12 by forcing the
latter against the shaped outside Sur~aGe o~ ths union
coupling 13, wherein r~cessss 15 are provid~d by the
method described below. ~h~ recesses 15 may be 9haped
as radial blind holes, longitudinal or cross slots or
~lats, annular or helical ~rooves, or a~ combinations
ther~o~. It is important that projections 16 that aro
established on the inner ~urface of the tubular shell 12
as a result of forcing the terminal portion of th~ tubu-
lar shell 12 against the shaped outsido sur~aco o~ th~
union couplin~ 13, should interact with th~ recesses 15
o~ the union coupling 13 so as to transmit the torquo
and axial :load.
75~
14
Shown as an exa~ple in FIGS 3 and 5 i9 -the re-
cess 15 shaped as an annular groove having a diameter
dl and bein~ eccentrical with respect to an outside
cylindrical surface 17 of the union coupling 13.
'~he ratio of the lengtn of an outside contour 18
of the cross-section of the rotor 1 to the length of a
circle 19 circumscribed around said contour, is sub-
stantially within 0.9 and 1.05~ ~hen said ratio is
below 0.9, other things being egual, this-results in
adve~sely affected output power characteristics of
the screw motor as to the torque developed and ths
output power (due to a reduced number of rotor threads)7
in reduced torsional and bending stren~th of the
hollow rotor9 as well as in d~teriorated quality of
rotor manufacture by the method and device proposed
herein and described in detail beloW, due to wrinkl-
ing on the rotor surface and d~parture ~rom true geo-
metric shape of the rotor.
ihen said ratio exceeds 1 05 this results in re-
duced efficiency of the motor (du~ to an increased num-
ber of the rotor threads), in affected torsional and
bendin~ strength of the rotor, and in some difficul-
ties encountered in the manufacture of the rotor accord-
in~ to the m~thod and devico proposed in this inv~n~
tion and described in detail her~inbelow, due to con-
siderably incr~eased values o~ working pressure, as
,. . . .
.-- .
~, , .
" ~IL,275~L~8
- 15
well as on account o~ hig~ pow0r consumption of the
rotor production procoss.
Th~ rotor disclosed in this invention operat~s as
follows. Wh~ drilling mud is ~ed from dayli~ht sur-
facc along-the drill string 11 (FIG. 1), the rotor 1
is urged to rotat~, under the actlon of an unbala~ced
fluid pressure applied to its lateral helical surface,
thus rolling ov~r the teeth of the stator 3. The tor-
gue and axial (thrust) load developed on the rotor as
a result, are transmitted to the sha~t 6 o~ the bearing
unit 7 through the flexible shaft 8 connected to th~
rotor 1 through the union coupling 13. Further on ro-
tation ~rom the shaft 6 of the beari~g unit 7 is trans-
lated to the rock destruction tool 9.
~ he rotor o~ a SCL ew hydraulic downhole motor des-
cribed above is manufactured as follows. ~ ~`orming
element having an outer ~`ormative surface shaped as a
multiple-tnread helisal sur~ace, is placed in a tubular
blank that has preliminarily b~0n machined on its
outside sur~ac~ to a reguired guality of surface
finish (e.g. , by grinding~ polishin~, etc.). There-
upon the ends o~` the tubular blank are herm0tically
s~aled with respect to the forming element, at the
same time mutually centre-ali~ning the tubular bla~k
and the forming olement, and a pressur~ o~ such a
fluid as, e.g., mineral oil is applied to the outside
. .
. ~ . ,.
-`
~75
-- 16
surface of the tubular blanX. Under the effect of
said fluid pressure the tubular blank loses stability
and ~ets defor~ed cross-sectionally, with the re~lt
that the blank becomes snug against the formative sur-
face of the forming element, thus acquiring the requir-
ed geometric shape of a multi-lobe rotor of a screw
hydraulic downhole motor~ In some cases, particularly
with a great length of the rotor teeth and their low
number, the rproce~s of forming the rotor teeth by
the aforedescribed method is expedient to carry out
in two stages. At the first stage the tubular blank
is subjected to partial deformation for an incomplete
tooth lengt~l, thus imparting to it the shape o~ a he-
lical polyhedron with rounded-off vertices, while at
the second stage the rotor helical surface is finish-
formed. In this case a guality helical surface free
from wrinkles and other departures from true geomet-
ric shape is obtained at the first stage due to a re-
duced amount of radial deformation. ~he first sta~e of
the process may be conducted at a reduced fluid pres-
sure, since that stage is aimed at overcoming the
stability of the tubular blank cylindrical shape and
preforming a helical surface having the same number o~
th~eads and the same helix lead as in the finished
rotor. '~he tubular blank obtained at the first stage
as a helical polyhedron is subjected to final forming ~;
- ~ ~75:~g~3
-- 17
to establish the helical surface of the rotor, by the
same method, i.e., by applying a ~lu~pressure to the
outside surface of the tubular olank inside which the
forming element is placed.
On many occasions an optimum method for making the
rotor is the one, wherein the process for forming a
helical surface on the rotor proceeds simultaneously
with the joining of its tubular shell 12 with the
union coupling 134 ~0 this end there is inserted in
the interior of the tubular blank before its ~orcing b~
the fluid pressure, t~e union coupling 13 whose outside
surfaca is made profiled or shaped, that is, is provided
-vith recesses having this or that form, e.g., radial
blind holes, longitudinal cros~ slots or flats, annular
or helical grooves, or any combinations thereof. iuhen
forcing the terminal portion o~ the rotor tubular
shell, projections are formed on the shell inner sur-
face, which are adapted to interact with the recesses
in the union coupling, thus making it possible t-o
impart the torque and axial forces developed on the
rotor tubular shell, to the union cou~ling and further
on to the ~lexible shaft.
The aforedescribed method for producing a rotor
of a screw hydraulic downhole motor can be carried into
~; effect with the aid of ~ device shown in FIG. 6 in a
longitudinal section, and in FIG. 7, in a c~oss-section.
:
~ 275~
- 18
'l'he device comprises a thick-walled tubular housing 20
which accommodates a formin~ element 21 cenkre-aligned
with the housing 20 by means OI` centring bushings 22, 22'
(FIG. 6). ~he outside ~ormative surface of the forming
element 21 is shaped as helical teeth 23 having the
same hand o~ helix and helix lead as the rotor being
manufactured, whereas the cross-sectional dimension o~
the forming element 21 is equidistant with respect to
the rotor cross-sectional outside contour. 'The amount
of equidistance equals the thickness ~ (FIG~ 4) of
the wall of a tubular biank 24. Fitting areas 25 are
provided on the outside sur~ace of the centring bus-
shings 22 (FIG. 6), on which the end portions of the
tubular blank 24 are fitted. I
The centring bushings 22, 22' are provided with
seals 26, 26' located at the places of contact o~ said
bushing~ with the hous~ng 20. ~he af`oresaid seals are
in the form o~ e.g. 9 rubber 0-rings.
'~he centring bushing 22 has a projection adjacent
to the fitting area 25 and having an end annular
groove 27, which receives a seal 28 ~ade of rubber or
any other elastic material. ~he width of the groove
is substantially equal to the thic~ness ~ of the
tubular blank 24. The tubular blan~ 24 is located on
the fitting areas 25 (only one of these being shown in
the FIGUR~) of the centring bushings 22, 22' in such a
75~L3~3
-- 19
manner that the ends of the blank 24 rest against the
~aces of the seals with some axial tension applied to
the rubber. Axial holding of the tubular blank 24, the
centring bushings 22, 22~ with the ~eals 28 (only one
of these being shown in FIGUR~), and the forming ele-
ment 21 is by means of the inside faces 29 of circular
nuts 30 (only one of' these being shown) turned onto the
end threads of the housing 20.
A chamber 31 is established between -the outside
surface oY the tubular blank 24 and the inside surface
of the housing 20 for a fluid under pressure to feed~
~orts 32 and 33 are provided in the housing 20-for
the purpose.
According to the herein-proposed metaod, when the
rotor is manufactured in two stages, the forming ele-
ment 21 (FIG. 8) is made replaceable. A formin~
element 21l for preliminary forming is made as a helic-
al polyhedron having the cross-sectional shape o~ a
polygon with rounded-off vertices and features a
reduced length hl of helical teeth and an increased
outside dia~neter d2 as ompared with respective di
mensions h3 and d3 of the forming element 21 for
~inish-for~ing. FIG. 8 represents the superposed
cross-sectional contours of ~he forming elements 21'
and 21 for preliminary and finish forming respecti-
vely.
~7S3L9~3
~ 20
The device is assembled and operates as follows.
~he forming element 21 is :inserted in the tubular
blank 24 that has preliminarily been machined on its
outside surface to a quality of sur~ace ~inish requir-
ed t`or the rotor (e.g., by grinding, polishing, etc.).
~he centring bushing 22' is set on one end of the
forming element 21, simultaneously engaging the end
portion of the tubular blank 24 with the fitting area
of the centring bushing 22'. Then the ~orming ele-
ment 21 with the tubular blank 24 and one of the
centring bushings 22, 22' is placed in the housing 20.
Next the other centring bushing 22 is set on the free
end of the forming element 21, simultaneously bring-
ing its fitting area into the tubular blank 24, and
the outside surface o~ the centrin~ bushings 22, into
the hou.~ ng 20. '~hereupon the thus-assembled compo-
nents are held in place in the housing 20 by means of
nuts 30 until the ends of the tubular blank 24 are some-
what forced into the bulk o~ the rubber seals 28. 'llhen
a fluid, e.g., a mineral oil is ~ed to the chamber 31
of the device through the port 32 of the housing 20
to expell air from the chamber 31 through the port 33.
~s soon as oil appears ~rom the port 33~ the latter
is shut with a cock (omitted i~ the ~rawlng). As the
feed ~f the ~luid continues the cylindrical tubular
bla~k is liable to lose its stability under the effect
of externally applied pressure, thus becoming forced
~.~75~98
- 21
against the formative helical sur~`aces of' the forming
element 21, whereby the rotor helical teeth are formed
on the outside surface of the tubular blank 24. The
seals 26 establish pressure-tightness in the joint
clearances between the housing 20 and the centring
bushings 22 (and egually the bushing 22~), while the
clearances between the centring bushings 22, 22' and
the tubular blank 24 are pressure-tightened at the
initial instant due to the fact that the ends of the
tubular blank 24 are somewhat forced into the rubber
seals 28. As the fluid pressure in the chamber 31 rises
and deformation of the tubular blank 24 progresses, the
clearances between the t~bular blank 24 and the fitting
areas ~5 of the centring bushings 22, 22' a~e pressure-
tightened by virtue of hydraulic forcing of the tubular
blank 24 against said fitting areas.
On completion OL' the aeformation process applied
to the tubular blank 24, which is judged by a rapid
fluid pressure rise, the pressure is relieved, the
device is disassembled and the forming element 21 is
removed from the tubular shell of the rotor.
~ IG. 9 illustrates an embodiment of the method for
making the rotor of a screw hydraulid downhole motor
with a simultaneouS pressing-in of the union coupling 13.
According to said embodiment, one end of the forming
element 21 is located in the housing ~0 by means of
., ,
~"~d75~L98
- 22
a centring bushing 3~ which accommodates the union
coupling 13 whose outside surface serves as the ~itting
area ~or the tubular blank ~4 and is provided with the
recess 15 shaped as an eccentric groove. 'l'he process
of forming the rotor helical sur~ace proceeds con-
currently with the Eorci~g o~ the union coupling, with
the result that a projection is formed on the tubular
shell inner sur~ace, The projection engages the recess 15
of the union coupling 13 and is adapted to interact
therewith when transmitting the torgue and axial load.
It is due to the forclng o~ the tubular blank 24 against
the outside surface o~ the union coupling 13 under the
e~fect of high fluid pressure that hermetic sealing
of the joint is attained.
The aforedescribed invention is e~ficiently appli-
cable for the proYision o~ high-torque screw h~draulic
downhole motors for drilling oil and gas wells, such
motors featuring improved output power and performance
characteristics.
