Method and apparatus for making a hydrocyclone separation chamber

An elongate tubular member with a seamless frusto-conical interior wall surface having a selected taper angle of typically 5.degree. or less which is formed from a metal tubular member of ductile material and circular wall cylinder configuration by the process of sequentially expanding contiguous length segments of the ductile tubular member to an interior frusto-conical wall configuration. The process involves inserting the tubular member into a female die member which defines an interior frusto-conical surface with a selected cone angle of typically 10.degree. or less with the tubular member coaxially aligned with the die member interior surface. Contiguous length segment of the ductile tubular member are sequentially expanded into conforming engagement with the wall surface of the die member wherein the expansion of each length segment selected for expansion to frusto-conical configuration is achieved by application of hydraulic pressure to the interior of the tubular member at a pressure level which exceeds the yield strength of the ductile metal material. Each selected length segment of the tubular member is also of a length predetermined with respect to the taper angle and the ductility and wall thickness of the ductile metal tubular member such that the hydraulic pressure does not exceed the tensile strength of the tubular member. After each sequential expansion, the tubular member is annealed.

FIELD OF THE INVENTION 
This invention relates to a manufacturing process and a separation chamber 
obtained by the process of forming an elongated tube member having a 
seamless frusto-conical interior wall surface from a cylindrical member of 
circular cross section where the formed tube member provides a separation 
chamber for hydrocyclones. 
1. Background of the Invention 
Hydrocyclones are an effective, simple and relatively low maintenance 
apparatus for centrifugally separating constituents of a mixture based on 
density of the constituents. Most hydrocyclones in present day use are 
designed for removing a more dense dispersion from a continuous phase. 
They do this by creating a vortex within the hydrocyclone body, which 
causes the dispersion to migrate radially outwards towards the walls, 
leaving a dispersion depleted continuous phase near the axis of the 
hydrocyclone. In recent years, development work has been directed towards 
separation of liquid/liquid mixtures using a hydrocyclone. An industry 
problem that has lead to this development occurs in oil production. In a 
typical oil well production operation, the amount of produced water 
increases as an oil field matures. In some operations, the bulk of the 
volume of produced fluids may be water. Although there may be no direct 
economic incentive, recent tightening of government regulations in various 
parts of the world regarding the amount of oil in discharged waters has 
increased interest in improving and optimizing oily water separators. 
This problem is particularly acute on offshore production platforms. There, 
the size and weight limitations on separation equipment limit the 
available options. Furthermore, on floating offshore platforms, the 
movement of the platform may affect the performance of some traditional 
types of separating equipment. The most traditional scheme utilized for 
cleanup of oily water on offshore platforms includes a weir type primary 
separator which allows the oily water to stand for a period of time such 
that free oil can accumulate at the top thereof and pass over a weir. The 
cleaner stream is then drawn off from the primary separator and directed 
to a flotation-type secondary separator. The flotation-type secondary 
separator is very large, on the order of the size of a large room, and is 
motion sensitive. As offshore fields mature and the volume of water 
production becomes greater and greater, traditional systems like the one 
just described become less and less practical. 
In recent years, the use of hydrocyclone separators has been investigated 
and has proven to be a successful solution to the problem outlines above. 
As previously discussed, typical hydrocyclones are concerned with 
separating solids and fluids such as air. In these operations the disperse 
phase is heavier than the continuous phase, and therefore the disperse 
phase is centrifugally moved to the walls of the hydrocyclone leaving the 
continuous phase as a central vortex. On the other hand, when treating 
oil/water mixtures, nearly all oils are less dense than water and 
therefore when oil contaminated water is passed through a hydrocyclone, 
the radial acceleration of the vortex causes the oil droplets to migrate 
towards the hydrocyclone axis at the center of the vortex, leaving 
oil-free water near the walls of the hydrocyclone. This, therefore, puts 
different constraints upon the design of the hydrocyclone. Whereas, in a 
gas/solid separation, with a more dense dispersion, the majority of the 
continuous phase is removed through a vortex in the upstream end wall of 
the hydrocyclone as the overflow. The separated dispersion leaves with a 
small part of the continuous phase from the wall boundary layer in the 
underflow. When the dispersion is the less dense phase, the underflow 
becomes the greater proportion of the total throughput (90 to 99%) while 
the overflow (removing the dispersion from the hydrocyclone axis), is much 
reduced. Also, the more dense constituent upon reaching the hydrocyclone 
wall is held there in a relatively stable wall boundary layer, but the 
less dense dispersion that forms a core along the hydrocyclone axis has no 
such constraint and relies entirely upon the favorable internal flow 
structure for its stability and removal from the hydrocyclone without 
further disruption. With an oil dispersion in water, the density 
difference is relatively small (less than 10% that of most solids 
encountered) and, therefore, the design must not only produce regions of 
very fast spin to promote separation, but also be designed to avoid 
breakup of the oil droplets in regions of high shear. With these 
constraints in mind, the design of an efficient hydrocyclone for oily 
water separation, although perhaps superficially similar to the case of 
the hydrocyclone for the more dense dispersion, is essentially different 
in its requirements, leading to a rather different geometry. 
One such difference in geometry is the provision of an elongated separation 
chamber having a continuous taper at a relatively small angle from the 
hydrocyclone axis. The shape of such a chamber is in the form of an 
elongated frustoconical chamber which forms a volume of revolution about 
the central axis of the hydrocyclone chamber. 
One technique for manufacturing such an elongated structure has been to 
form the chamber in two halves and weld the chamber along a longitudinal 
seam. Another technique is to shape multiple longitudinal sections which 
are connected end to end. It must be remembered, however, that in an 
oil/water hydrocyclone, one of the design requirements is that the mixture 
not be subjected to shear forces within the hydrocyclone chamber. Any 
shearing of droplets of the dispersed phase will cause an emulsion of oil 
and water which is counterproductive to the separation process. Therefore, 
it is desirable to remove the problem of having an elongated seam or a 
circumferential seam to deal with in the construction of such a chamber. 
It is difficult when bonding metal surfaces, such as by welding, to 
totally eliminate any residual deformity in the mated surfaces so as to 
provide a smooth wall in the hydrocyclone. The use of the techniques just 
described for making hydrocyclones is also time consuming, and therefore 
expensive. In order to achieve the desired results outlined above, a 
swaging process was tried to form these elongated frusto-conical 
separation chambers. One problem encountered was that of removing the 
swaging die from the chamber after the forming operation. The low angle of 
attack combined with the elongated configuration of the separation chamber 
provides so much friction between the die and the formed part that removal 
of the die from the expanded product is a problem. 
It is therefore an object of the present invention to provide a new and 
improved process for forming an elongated frusto-conical member having a 
small angle of taper. 
Various forms of industrial and scientific equipment also can require the 
utilization of a relatively long tubular member having an interior surface 
of frusto-conical configuration. For forming relatively long thin-walled 
tubular metallic members with frusto-conical wall interiors with smaller 
diameters and under 10.degree. taper angle it is not practical nor 
feasible to machine a single long tubular member with frusto-conical 
interior wall or to fabricate a plurality of small lengths of tubular 
members and attach these in end-to-end coaxial relationship by welding. 
Machining processes are not accurate and many times not possible with 
taper angles under 10.degree. (included angle) so that the resulting 
product is usually not a tubular member with a true frusto-conical 
interior surface. Where short lengths of tubular members are welded end to 
end, the heat from welding distorts the cross sectional shape to something 
other than true circular form. Similarly, longitudinal welds of 
semi-formed tubular members are egg shaped in cross section. 
As discussed above, hydrocyclone vortex separators for oil/gas mixtures 
employ elongated, relatively small diameter tube members where a tube 
member has a frusto-conical interior wall surface with a cone angle of 
less than ten degrees. Such separators are used in the oil industry for 
separating oil and water from well fluid mixtures of oil and water. The 
separators require numerous vertically or horizontally arranged tube 
members each with an interior frustoconical surface having a small angle 
of taper, such as in the range of 3.degree. to 5.degree. or less. A 
typical hydrocyclone separator tube may include such a tapered section 
with, for example, a length of approximately 67 centimeters and a 
frusto-conical interior with an interior diameter of 3.5 cm at its entry 
end and 1.7 cm at the exit end. The separation of fluids, which is 
effected by cyclonic spiralling motion of the fluid mixture through the 
tube member, requires a true or smooth frusto-conical interior wall 
surface for efficient operation. Since the machining or casting of a tube 
member with such a wall surface is presently impractical for economic and 
efficiency reasons and is likely to result in imperfections or grooves in 
the surface, there is a need for a more practical and efficient method of 
forming long tube members with interior frusto-conical wall surfaces, 
particularly for hydrocyclone separator tubes. 
2. Prior Patent Art 
U.S. Pat. No. 4,544,486, inventor Noel Carroll, issued Oct. 1, 1985, shows 
expansion chamber geometry in accordance with this invention. 
U.S. Pat. No. 4,764,287, inventors Derek Colman and Martin Thew, issued 
Aug. 16, 1988. 
U.S. Pat. No. 4,849,107, inventors Derek Colman and Martin Thew, issued 
Jul. 18, 1989, shows curved wall hydrocyclones which would be applicable 
to the forming process. 
SUMMARY OF THE INVENTION 
The invention relates to a process for forming an elongated metal tubular 
frusto-conical member ("tube member") with a seamless frusto-conical 
interior wall surface having a taper angle of 5.degree. or less 
(10.degree. included angle for a conical surface) from a tubular member of 
circular cylinder wall configuration and to a product formed by such 
process. 
The frusto-conical wall interior in a metal tubular frusto-conical member 
is incrementally formed in steps from an elongated metal tubular member of 
ductile material with a circular cylinder wall configuration. The ductile 
metal tubular member is first disposed end first into a female die member. 
The female die member has a first length or portion with an interior 
frusto-conical wall surface with a cone angle of 10.degree. or less and 
the remaining length is cylindrical but with a larger internal diameter 
than the outer diameter of the ductile metal tubular member. The ductile 
metal tubular member is also disposed in coaxial alignment with the axis 
of the female die member thereby defining a frusto-conical annular space 
with a diverging conical surface of the die member relative to the outer 
cylindrical surface of the ductile metal tubular member. Liquid under 
pressure is applied to the interior of the tubular member to apply 
sufficient force to deform the wall of the tubular member to the inner 
wall of the die member yet less than the force required to rupture the 
wall of the tubular member. The tubular member is then removed and 
annealed to return the tubular member to its normal metallurgical 
condition. The annealed partially formed tubular member is then inserted 
into a die member which has the first length of frusto-conical wall 
surface and has a second length of frusto-conical wall surface for a 
second expansion and annealing. Successive lengths of a tubular member can 
be deformed by additional steps so that a continuous full length seamless 
interior conically shaped surface is formed. 
In short, an elongated metal tubular frusto-conical member with 
frusto-conical interior wall surface is formed by sequentially and 
separately expanding interior contiguous length segments or lengthwise 
extending selected portions of the ductile metal tubular member into 
conforming engagement with the interior wall surfaces of female die 
members with successively arranged length segments. The expansion of each 
selected ductile metal length segment of a tube member into conforming 
engagement with an interior frusto-conical wall of a female die member is 
obtained by an application of hydraulic pressure to a selected interior 
length segment of the tubular member at a pressure level which exceeds the 
yield strength of the ductile material of the length segment of tubular 
member while the radial expansion of the remainder of the tube member is 
restricted. Each length segment of the ductile tubular member which is 
selected for expansion to frusto-conical configuration is of a length 
predetermined with respect to the taper angle, the ductility and wall 
thickness of the tubular member and relative to the hydraulic pressure 
level so that the tensile strength of each selected length segment is not 
exceeded. After each sequential expansion of a length segment the tube 
member is annealed. 
In the present invention, a hydrocyclone separator tube is formed for use 
in separating lighter and heavier weight components of a liquid mixture 
where the tube has an interior, seamless frusto-conical wall surface about 
a central axis with a cone angle for receiving a radial input of a liquid 
mixture at its larger open end and for containing a spiraling forward 
fluid flow over a length of said tubular member so that heavier weight 
component of the liquid mixture is centrifugally moved outwardly toward 
the interior wall surface and a lighter weight component of the liquid is 
forced inwardly toward said central axis thereby separating the mixture 
into lighter weight components and heavier weight components. 
The seamless wall surface of the tube is formed by sequential controlled 
radial expansions of sequential sections of a tubular member to 
sequentially tapered wall surfaces in die members with annealing of the 
tubular member between such sequential expansions. 
Yet another aspect of the invention resides in forming a hydrocyclone 
separation chamber for separating liquid/liquid mixtures in an elongated 
frusto-conical shaped separation chamber having a cone angle less than 
10.degree. and wherein the separation chamber has a seamless wall surface 
formed by sequential controlled radial expansions of sequential sections 
of a tubular member into tapered wall surfaces in die members with 
annealing of the tubular member between such sequential expansions.

DETAILED DESCRIPTION OF THE INVENTION 
Referring more particularly to the drawings, there is shown in vertical 
cross section an assembly of die members 11 arranged in a vertical stack 
on a base member 12 to provide a female die assembly 14. The die members 
11 and the base member 12 each have an outer cylindrical surface 
configuration and each of the members 11 and 12 is provided with an 
upstanding annular lip flange 15 and each of the members 11 and 12, except 
for the base member 12 are provided with an outer annular groove 16 at a 
lower surface for accommodating the upstanding annular lip flange 15 of 
the next adjacent member on which it is superposed. Each die member 11 is 
formed with a central axial opening which is machined therein to define a 
frusto-conical surface with a taper angle of 3.degree. and an axial 
dimension of 6.1 inches, or approximately 15.75 cm. The frusto-conical 
surfaces in the several die members 11 are formed such that the longest 
diameter of the frusto-conical surface of each die member 11 corresponds 
to the smallest diameter of the frusto-conical surface of the next lower 
die member 11 whereby, in coaxial alignment, a uniform frusto-conical 
surface 20 with over-all length of 31 inches, approximately 78.75 cm, is 
defined by the die members 11. The base member 12 is also provided with a 
central axial opening 21 which, when the assembled die members 11 are 
supported by the base 12 is coaxially aligned with the axial openings of 
the members 11. The axial opening 21 is defined below a concave annular 
surface 22 having a largest diameter at the opening in its upper surface 
which conforms to the diameter of the frusto-conical wall surface of the 
next adjacent die member 11 superposed thereon. The wall surface defining 
the axial cylindrically shaped opening 21 preferably is about the same as 
the diameter of the frusto-conical wall surface 23 in the uppermost die 
member 11 at its upper opening in the upper surface of the die member 11. 
A hydraulic press 30 is located at the upper end of the die members 11. The 
press 30 includes a piston-cylinder assembly with a hydraulic cylinder 31 
and a piston 32 in a chamber 33. The press 30 is adapted for use with the 
female die assembly 14 (see FIG. 2). Accordingly, the lower end of the 
cylinder 31 is formed by an annular surface including an annular 
peripheral groove 34 and conforming in configuration to the upper surface 
of the upper most die member 11. The cylinder chamber 33 of the cylinder 
31 is formed at its lower end, with internal threads 36 in a cylindrical 
bore section thereof which communicates with a larger diameter portion 
accommodating the piston 32. The threads 36 of the hydraulic press 30 are 
adapted to receive the threaded end of a ductile metal tubular member 38 
from which an elongate frusto-conical tube member may be formed in 
accordance with the invention. 
As shown in FIG. 1, the ductile metal tubular member 38 is attached be a 
threaded connection at its upper end to the press 30 and the lower end is 
disposed within the female die assembly 14. An O-ring 35 or other suitable 
seal means establishes a fluid-tight seal between the cylinder 31 and 
tubular member 38. The length of the tubular member 38 is such that a 
small portion of the lower end of the tubular member is snugly received in 
the cylindrical bore section 21 of the base 12. Also, at its lower end, 
the tubular member 38 is closed by a cap member 39 which may be welded or 
otherwise rigidly joined thereto. 
The ductile tubular member 38 is preferably stainless steel characterized 
by a yield strength of approximately 30,000 p.s.i., however depending on a 
particular intended application, other ductile metal materials 
characterized by other yield strengths can be employed. The end cap 39 is 
of a material such as carbon steel alloy or titanium with a yield strength 
which not only exceeds the yield strength of the ductile tubular member 38 
but also its tensile strength. The hydraulic press 30 is designed with a 
capability of delivering hydraulic pressures throughout a wide range of 
pressures up to as much as 80,000 p.s.i. 
In accordance with the present invention, a length segment of the ductile 
tubular member 38 adjacent to the press 30 is first selected for radial 
expansion into conforming engagement with the adjacent interior 
frusto-conical wall surface of the female die assembly 14. An application 
of hydraulic pressure to the interior of the ductile tubular member 38 
which exceeds the yield strength of the tubular member 38 will effect its 
radial expansion throughout its length if not restrained. If the radial 
expansion exceeds the tensile strength, the tubular member will burst or 
rupture. To avoid a rupture of the tubular member 38, the hydraulic 
pressure applied by the press 30 must not expand the tubular member to the 
point that the tensile or burst strength of the tubular member 38 is 
exceeded. Accordingly, the length segment of the tubular member 38 
selected for expansion by a first application of hydraulic pressure, is 
predetermined in length with respect to the ductility, the wall thickness 
of the tubular member 38 and the particular taper angle of the interior 
wall surface of the die member 14. This may have to be empirically 
determined in some instances. In FIG. 1, this selected length segment 38' 
extends along a length 38a of the die member which corresponds to 
approximately one-third of the total length of the interior wall surface 
20 of the die assembly 14. However, to preclude the possibility of a 
rupture of the tubular member 38 because of excessive expansion, it is 
necessary to restrict the radial expansion of the remaining length 38" of 
the tubular member 38. 
For the purpose of restricting the radial expansion of the remaining length 
38" of the tubular member, a carbon steel sleeve member 40 is inserted 
into the female die assembly 14 from the lower end thereof during the 
assembly of the apparatus before the base 12 is connected. The sleeve 
member 40 has a length 38b which is equal to or slightly less than the 
length of the remaining unselected length segment 38" of the ductile 
tubular member 38 and is provided with an exterior tapered wall surface 39 
which conforms to the frusto-conical die wall surface 20 along the length 
of the sleeve member 40. (See FIG. 5). The sleeve member 40 is also 
provided with a central axial cylindrical opening 41 with an inner 
diameter which is slightly greater than the external diameter of the outer 
wall 42 of the unexpanded ductile tubular member 38 and the annular space 
43 (see FIG. 5) allows a uniform radial expansion of the sleeved portion 
of the tubular member 38 to a limited extent, the limited extent being 
that amount of radial expansion which can occur without same time as the 
length segment 38' is being deformed under pressure (enlarged) to the 
length segment 38a of the wall surface 20 of the die assembly 14, the 
remaining length 38" of the tubular member 38 in the length 38b of the 
sleeve member 40 is expanded radially to a limited extent to the 
cylindrical wall 41. As shown in FIG. 6, the length segment 38' of the 
tubular member which extends downwardly through the length 38b of the 
sleeve die 40 is reduced in wall thickness and expanded to conform to the 
taper of the wall 20 of the die assembly 14. The length segment 38" of 
tubular member 38 in the length segment 38b of the die sleeve 40 is 
radially expanded to conform to the die wall 41. The cylindrical wall of 
the length segment 38" of the tubular member is reduced in wall thickness 
due to the radial expansion. As is obvious, the wall thickness of the 
tubular member 38 should be sufficient to permit expansion over the entire 
desired expansion length of the tubular member 38. 
After the first expansion of the length segment 38' of the tubular member 
38, the base 12, the die members 11 and the sleeve member 40 are 
disassembled from around the tubular member 38. The tubular member 38 is 
then disconnected from the press 30 so that the partially expanded tubular 
member 38 can be subjected to an annealing process which includes heating 
to a temperature of approximately 1800.degree. F. (982.22.degree. C.) and 
then air cooled whereby the stress and brittleness induced in the metal by 
the expansion process are relieved and the partially formed tubular member 
is in its original metallurgical condition. 
After the initial expansion of the tubular member 38 provides the tubular 
member 38 with a predetermined length segment 38' of expanded section with 
a frusto-conical configuration and a smooth interior frusto-conical wall 
surface, a portion of the next contiguous length segment 38" of the 
tubular member 38 (see FIG. 6) is expanded to a frusto-conical wall 
configuration by following the steps of expansion described above to 
obtain a greater length of frusto-conical section. 
A second expansion of the tubular member 38 is illustrated in FIG. 2 
wherein a second carbon steel sleeve 50 having a length 38c is inserted 
into the die member 14. The sleeve 50 serves to limit the radial expansion 
of a lower portion of the tubular length segment 38" while an intermediate 
length segment is expanded. For this second expansion operation a second 
or intermediate length segment of the tubular member 38 contiguous to the 
first frusto-conical expanded length segment 38' is selected for expansion 
into conforming engagement with the interior wall of the die member 14. 
This second length segment of the tubular member 38 is of a length 
predetermined with reference to the ductility and wall thickness of the 
tubular member 38 and the taper angle of the frusto-conical wall surface 
of the die member 14 in the same manner followed for determining the 
length of the first length segment 38' of the tubular member 38 which was 
selected for a frusto-conical expansion. The carbon steel sleeve 50, 
required for the second expansion is shorter in length but similar to the 
form of the sleeve 40 with the shorter length 38 c corresponding to the 
remaining length of tubular member 38 to be precluded from a 
frusto-conical expansion. The sleeve 50 is also provided with an inner 
diameter which is somewhat greater than the outer diameter of the sleeve 
40 to allow a further limited radial expansion of the sleeved portion of 
the tubular member 38 to cylindrical configuration without incurring a 
wall rupture. The application of hydraulic pressure to the interior of the 
tube member 38 to effect its second expansion, is also selected to be at a 
level which exceeds the yield strength of the metal but not the tensile 
strength of the tubular member 38. After the second expansion, the base 
12, the die members 11 and the sleeve 50 are disassembled and the tubular 
member 38 disconnected from the press 30. As previously done, following 
the first expansion, the tubular member 38 is subjected to an annealing 
and air cooling process. 
It will therefore be seen that by sequentially expanding contiguous length 
segments of the ductile tubular member 38 into conforming engagement with 
the frusto-conical wall surface of the female die members 11 and the use 
of sleeves, in the manner described above, it is possible to shape the 
entire length of the tubular member 38 to smooth surface frusto-conical 
configuration with a small taper angle. 
The results of a third expansion of the tubular member 38 is shown in FIG. 
3 obtained by following the same sequence of steps as described for the 
first two expansions but wherein it was not necessary to use a sleeve 
since no further portion of the tubular member 38 was desired for 
frusto-conical expansion. It is to be noted that the portion of the 
tubular member 38 received in the base 12 is gradually expanded by each 
application of hydraulic pressure to ultimately conforming engagement with 
the concave surface of the base opening 21. 
It will therefore be appreciated that a unique process for forming a 
tubular member with a seamless smooth frusto-conical interior wall surface 
and a unique product formed by such a process is described herein. The 
angle of taper in a product formed in accordance with the invention could 
be as large as 7.degree. depending on the ductility and tensile strength 
of the cylindrical metal tubular member selected for expansion. The 
sequence of expansions to obtain a desired length of frusto-conical member 
may be of almost any number so long as an expansion does not exceed the 
tensile strength of the material. 
A particularly useful application for the member having an elongated 
frusto-conical interior wall surface fabricated in accordance with the 
invention, is a hydrocyclone separator tube incorporated in vortex type 
fluid separators. Such a tube 60 is shown in FIG. 4, wherein the 
frusto-conical tubular member in its final form as shown in FIG. 3 may be 
used. Typically, the threaded end of the expanded tubular member 38 and 
the end portion thereof which is received in the base 12 are cut-off such 
that the remaining portion is provided with a smooth frusto-conical 
interior. As shown in FIG. 4, this portion may be welded at its narrow end 
to a cylindrical tubular member 61 and at its wider end to a tubular 
adapter member 62 having flanged ends and a larger interior frusto-conical 
surface which can be machined therein. In operation of such a tube 60 as a 
vortex separator, a mixture of fluids such as an oil-water mixture of well 
fluids is delivered by spiral injection into the larger end of the tube 
60. The spiraling liquid creates large centrifugal forces which migrate 
oil to the central axis of the tube and the oil is subjected to a back 
pressure which creates a reverse axial flow and oil exits from the larger 
end of the tube while water is discharged through the small end of the 
tube to effect the separation and delivery of oil from one end of the 
tube. 
Referring now to FIGS. 7 and 8, another form of the invention is 
illustrated. In FIG. 7, a die assembly 70 is illustrated wherein the die 
assembly is arranged with a first cylindrically shaped length segment 72, 
an intermediate frusto-conical length segment 74 with the desired taper 
angle and a second cylindrically shaped length segment 76. It is desired 
to form a tubular member 78 with adjoining sections where one length is 
substantially cylindrical such as section 61 of FIG. 4 and where the 
adjoining length is frusto-conical such as section 60 of FIG. 4. 
In the forming process as described herein it is sometimes difficult to 
remove the deformed tubular member from straight cylindrical die sections. 
For that reason the cylindrical sections can have a slight taper relief to 
ease removal of the tubular member. 
Where it is desired to maintain the cylindrical tubular shape, a closely 
sized cylindrically shaped bar member 80 is inserted into the bore 82 of 
the tubular section 61 to be maintained. At the upper end of the bar 
member 80 is a sealing means 88 such as a poly pack which provides a 
pressure seal. The pressure seal means 88 prevents the protected tubular 
section 61 from receiving pressure and thus protects against expansion to 
the bore of the die assembly which makes it difficult to remove the 
tubular member. As shown in FIG. 7, a tubular member 78 is threadedly 
connected with the lower die member 84 and the press member 86. The bar 
member 80 and the sealing means 88 are disposed in the section 61 to be 
maintained cylindrical. Adjacent to the portion 76 of the die assembly 
containing the section 61 of the tubular member is a first frusto-conical 
section 74 in the die assembly with included angle of 10.degree. or less. 
Above the frusto-conical section 74 is a cylindrical section 72 which may 
have a slight taper for ease of removal. As described heretofore, 
hydraulic pressure is applied to the interior of the tubular member 78 to 
deform the tubular member to the frusto-conical section 74 and to the 
cylindrical section 72 of the die assembly. The sealing means 88 prevents 
enlargement of the section 61. After the first deformation, the tubular 
member is removed from the die assembly and annealed to return the tubular 
member to its initial metallurgical condition. 
A second length segment is formed in the tubular member 78 in a second die 
assembly where a portion of the cylindrical section 72 is replaced with a 
die section 72' having a continuing taper with the die section 74. The 
tubular member 78 has the previously formed length segment 78' which is 
received in the die section 74. The tubular member 78 is disposed in a 
tapered die bore 83 which extends to a cylindrical bore 85. Upon the 
application of hydraulic pressure the tubular member conforms to the die 
bores 83 and 85. The tubular member is removed and annealed. 
The final section is formed in a third die assembly which has a taper to 
continue the taper configuration of the die bore 83. The final section is 
formed and annealed as described herein with respect to FIGS. 7 and 8. 
While the description has been of formation of a frusto-conical interior 
surface in three separate operations and an included cone angle of 
10.degree. or less it will be apparent that the number of operations 
required is a function of the metal ductility and metallurgical 
characteristics, the wall thickness, the length of taper and the angle of 
the taper. While an angle of 10.degree. of less is referred to herein, the 
method is applicable to larger angles, however larger angles permit the 
formation of an interior seamless frusto-conical surface by machining and 
other mechanical processes. 
It is to be understood that the foregoing description of a preferred 
embodiment of the invention has been presented for purposes of 
illustration and description and is not intended to limit the invention to 
precise form disclosed. For example, the die member assembly can be formed 
from various numbers and sizes of individual sections and these can be 
provided with any of a wide variety of interlocking means. Accordingly, it 
is to be appreciated that various changes may be made by those skilled in 
the art without departing from the spirit of the invention.