Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The production of seamless tubing is a well known and
well developed art. In general, however, the economical production
of seamless tubing requires enormous capital investments and, as
a result, conventional techniques are economically satisfactory
only where tonnage requirements are quite large. Nevertheless,
in many areas of the world, particularly the developing countries,
there is a significant need for seamless tube production facilities
suitable for operation under relatively moderate tonnage production
; rates In the past, this need typically has been met with one of
two production systems, referred to herein for convenience as the
push bench system and the extrusion press system. In the push /;
bench system, heated square billets, typically about one meter
in length, are introduced into a piercing press, in which the
square billet is compressed into a round cross section and pierced
axially to form a hollow shell, closed at one end. The pierced
shell is then introduced into a three-roll Assel-type elongator,
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achieving an elongation of approximately two to one. From the
Assel elongator, the shell is processed in a push bench, in which
a mandrel is introduced into the shell, which still has a closed
~ end, and the mandrel and shell are pushed through a series of roll
stands, to effect a further elongation (approximately six to one)
of the shell. The mandrel and shell are then processed in a reel-
ing mill, which serves ~o round up the shell and loosen the mandrel.
`~ After removal of the mandrel, the closed end of the shell is cut
off. Where further elongation is desired, the shell is reheated
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and processed ln a conventional stretch reducing mill, for a
further elongation of about three to one.
In the push bench system, overall elongation of the
original square billet can be as much as thirty-nine to one,
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-', 30 through the stretch reducing mill. Maximum production is about
- four pieces per minute. While the overall elongation is satisfac-
tory, as is the overall production rate, the push bench system
involves rather excessive crop losses, because of the removal of
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the closed end of the shell after the reelin~ step. Moreover,
the system involves a substantially higher capital investment than
the system o~ the invention, to be described.
In the extrusion press system, the square billet is
processed firs~ in the piercing press, as in the p~sh bench system.
However, the closed end of the billet is cut o~f before further
processing. The open-ended shell is then introduced into an
` extrusion press, which achieves an elongation of about ten to one.
The tail end extremity of the extruded shell is cropped off as
it leaves the press. After the extrusion press, the shell is re-
heated and further processed in a conventional stretch reducing
mill, providing an additional elongation of about three to one.
The overall elongation, from billet form through the stretch re-
ducing mill is approximately thirty-three to one, with production
being limited to approximately two pieces per minute.
- In addition to higher capital investment costs, the
extrusion press system involves substantial crop losses, because
of the need for cropping operations following both the piercing
- press and extrusion press operations.
Pursuant to the present invention, an improved method
is provided for the production of seamless ~ubing in moderate
tonnage requirements, which is not only less costly in terms of
capital investmen~ requirements, but is also significantly superior
~; in operating capabilities to the prior art systems described above.
More particularly, the invention provides a production procedure
and system which, notwithstanding a lower capital investment re-
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quirement as compared to the above, is at least equal to the better
of the above described systems in terms of production capacity,
and is superior to both of the prior art systems in other important
respects, particularly with respect to improved product quality,
lower crop losses and lower tooling expense. Moreover, ~he proce-
dure of the invention admits of additional significant improvements
to be incorporated, without major equipment changes, as improved
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acilities become available and economic conditions become more
favorable.
In accordance with the invention, the initial, generally
square billet is processed in a piercing press, to produce a hollow,
closed end shell. The pierced shell is then processed in a piercing-
type elongator, which may be either a three-roll or a two-roll type.
In either case, the shell is elongated approximately three or four
to one in the piercing-type elonga~or. Additionally, as the closed
end o~ the pierced shell reaches the piercing mandrel o the
elongator, the closed end of the shell is pierced without loss of
material. In the procedure of the invention, the pierced shell is
now processed in a conventional mandrel mill, which provides Eurther
elongation of about three to one. Desirably, although the capacity
of a mandrel mill to elongate is considerably greater than three
; to one, the mandrel mill is operated at about that level of
elongation, in order to accommodate the use of mandrels of ordinary, ~
low-strength mandrel bars, which typically would be available in a -
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developing country. As and when high strength mandrel bars become
available, and/or the economics of the process admitted of the
importation of such bars, greater amounts of eIongation could
be carried out in the mandrel mill.
After processing in the mandrel mill, the shell is
stripped from the mandrel bar and reheated, after which it is
processed in a conventional stretch reducing mill for a further
three to one elongation. Overall, the elongation is up to approxi-
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mately thirty-nine to one, with a production rate o~ about -Eour
` pieces per minute. While comparing closely an elongation and
production rate to the push bendh process, the procedure of the
invention involves significantly lower initial equipment costs,
provides for a product of significantly higher quality, and achieves
a higher yield of usable product in relation to the starting mate-
' rial, because of the limitation of crop losses. In the procedure
.~ of the invention, crop loss is involved only at the stretch
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reducing mill, which is a loss common to the other systems as well.
However, there is no crop loss prior to the stretch reducing mill,
as there is in the above described prior art systems. The system
accommodates significant upgrading at a future time, with minimum
changes in the basic installation.
For a better understanding of the above and other
features and advantages of the invention, reference should be made
to the following detailed descrip~ion of an illustrated embodiment,
and to the accompanying drawing.
The single figure o the drawing is a highly simplified
and schematic 1OW sheet diagram of a seamless tube production
procedure according to the invention.
Referring now to the drawing, the reference numeral 10
designates generally a metal billet which forms the starting
material for the seamless tube process of the invention. Typically,
the billet 10 is the product of a continuous casting operation,
and is generally square in cross section, although preferably with
generously rounded corners. By way of e~ample only, a typical
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billet may have cross sectional dimensions of approximately 140
x 140 ~m and an overall length of about 730 mm. The corners of
the precast billet typically might be radiused at about 27 mm.
In another typical example, the starting billet might have cross
sectional dimensions of 165 x 165 mm, with corners radiused at
32 mm, and an overall length of about 832 mm. Of course, these
specific dimensions are illustrative only and do not in any way
limit the invention.
The billets are first introduced successively into a
rotary or other suitable hea~ing furnace, in which they are brought
up to a temperature appropriate for the subsequent operations.
Typically, this may be a temperature of for example 1100-1200 C.
The heated billet is next introduced into a piercing
:r' press 12, which may be of a standard, conventional type as for
. example that made commercially available by Schloemann AG, of
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Duesseldorf, Germany. The piercing press includes a cylindrical
container 13, provided with a bottom sleeve and bo~tom plunger
14, 15, together forming the bottom structure of the container.
The press is also provided with a compression ram 16 and piercing
ram 17. The piercing press, which may be vertically oriented,
is arranged to receive the billet 10, seated against the bottom
structure 14, lS. Initially, both the compression ram 16 and
piercing ram 17 are forced into the container 13, compressing
the billet 10 and forming it into the cylindrical shape of the
interior of the container 13. By way of e~ample, the 140 mm billet
may be compressed into a cylindrical billet of 180 mm in diameter,
while a 165 mm square billet may be compressed into a cylindrical
billet of 210 mm in diameter, the billet diameter being desirably
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only slightly larger than the maximum (diagonal) dimensions of the
rounded-corner billet. The compression ram 16 is then backed off
slightly and the piercing ram 17 is driven axially through the
center of the billet, to a point near the distant end of the billet.
When the piercing ram is withdrawn, the biIlet is in the form of
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a closed end tubular shell. In this respect, the piercing ram
~ 20 desirably is stopped approximately 20-25 mm from the bottom of
,l the piercing press, leaving the pierced shell with a bottom wall
of approximately that dimension, as reflected in the drawing.
In the course of the piercing press operation, there
; may be a slight elongation in the billet 10, depending upon the
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specific geometry of the press and the billet. In this respect,
~, in compressing the billet into the cylindrical shape of the con-
-; tainer, the billet will tend to become shorter in length, to a
degree which depends somewhat upon the initial roundness of the
corners of the square billet. On the other hand, the displacement
of metal involved in the travel of the piercing ram 17 will cause
the billet to elongate. These two factors are somewhat mutually
- compensating, and the elongation factor in the piercing press may
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range from slightly less than 1.0, where particularly high quality
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is sought for, to as high as about 1.25, in cases where a somewhat
les~er degree of precision in concen~ricity may be tolerated. In
general, and for the purposes of this description, the elongation
factor in the piercing press may be considered as approximately
1Ø By way of typical example, the initial 140 mm square billet
may leave the piercing press with an outside diameter of about
180 mm, a cylindrical wall thickness o~ about 45 mm, and a length
of about 715 mm.
Immediately after being removed from the piercing press,
the billet 10, now in the form of a closed end tubular shell 18,
is inserted into a piercing-type elongator, generally designated
by the numeral 19. The elongator may be either of a two-roll or
three-roll type but in either case includes two or more barrel-
type working rollers 20 disposed at a shallow angle to the axis
of the tube and a piercing-type mandrel plug 21 mounted on a fixed
mandrel bar 22. In general, the piercing-type elongator functions
in the manner of a so-called No. 2 piercing mill, in a more conven-
tional seamless tubing process. By way of example, U.S. Patent No.
1,808,957 is generally illustrative of a two-roll piercing-type
elongator.
The closed end shell 18, which is the input to the
piercing-type elongator, is both significantly elongated and re-
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duced in its wall thickness, in passing through the working rollsof the elongator. Upon passing through the piercing-type
eLongator, such billet having an outside diameter after piercing
of 180 mm, desirably will continue to have an outside diameter of -
about 180 mm, but its wall thickness will be significantly reduced ;
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. to, for example, somewhere in the range of 11.5 mm to 15.2 mm, ~; `
; depending upon the ultimate product objectives. Elongation of the
billet in the piercing-type elongator will average somewhere around
- three to one, being somewhat less (about 2.5 to 1) for the heavier
;; walled tubes, and somewhat greater (3.25 to 1) for the lighter
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walled tubes.
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In the case of a 165 mm square billet, for example, the
billet may leave the piercing press with a diameter of about 210
mm, a wall thickness of about 53 mm and a leng~h of about 822 mm.
After passing through a two-roll elongator, such a billet may have
a typical outside diameter of about 206 mm, a wall thickness,
depending on ultimate product objec~ives, ranging from about 16.5
mm to about 22.3 mm. The elongation factor in the latter example
may range from around a minimum of 2.1 to l, ~or heavier walled
tubes, to a maximum of around 2.8 to 1, for thin walled ~ubes.
In general, elongation o~ the pierced billet in the piercing-type
elongator may range from ebout 2 to about 4 to 1.
One of the advantages o~ the process, which is derived
from the use at this stage of a piercing-type elongator, is the
improved concentricity of the inner and outer walls of the tube.
Because the piercing-type elongator has a relatively gradual de-
forming action on the tubular shell, and is in contact with it
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' over a relatively substantial increment of time, there is a
tendency to maintain substantial precision in tube wall concentric-
` ity. Indeed, initial eccentricities introduced in the piercing
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?~' 20 press can be corrected for to a rather significan~ extent in the
,i piercing-type elongator. Thus, in the piercing-type elongator,
the rolls and mandrel plug may be in contact with the shel1 over a
; linear extent of as much as ten inches, as compared to perhaps
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~ only an inch on the Assel-type elongator. In the two-roll pierc-
- ing-type elongator, the tubular shell is guided by arcuate mill
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shoes located between the working rolls. In the three-roll pierc-
ing-type eIongator, the rolls themselves are arranged to perform
a guiding function of the mill shoes in the two-roll elongator.
In either case, a significant improvement in the control over
concentricity is provided at a critical stage of the process.
As the closed end shell 18 completes its passagP through
;~ the elongator 19, the closed end 23 is pierced by the mandrel 21
and becomes part of the tubular shell. This avoids the need for
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cropping off the tail end of the shell and results in an overall
improved yield from the process.
After completion of processing in the piercing-type
elongator, the shell is passed directly to a mandrel mill 24,
which consists of a plurality of roll stands 25, of which eight
such stands might be considered typical. In the mandrel mill,
the tubular shell is reduced in outside diameter and wall thickness,
and is significantly elongated. By way of example, the initial 140
mm billet may be reduced in outside diameter in the mandrel mill
from about 180 mm to about 137 mm. Wall thickness, in the case of
a thin walled tube received from the elongator, may be reduced from
about 11.5 mm to about ~ mm; in the case of the heavier walled
tubing, wall thiclcness may be reduced in the mandrel mill from
about 15.2 mm to about 7.7 mm. Overall elongation of the billet
in the mandrel mill typically may range from about 2.5, in the case
of heavier walled tubing, to about 3.6, in the case of lighter
walled tubing and in general may range from about 2 to about 4 to 1.
; In the case of the example 165 mm billet, outside diameter may be
.~ reduced in the mandrel mill from about 206 mm to about 165 mm.
For lighter walled tubing, wall thickness reduction may typically
be from about 16.5 mm to about 6.0 mm; for heavier walled tubing, ~-
~reduction may be from about 21.7 mm to about 11.2 mm. Overall
elongation may range from about 3.3 mm, for thin walled tubing,
; to around 2.3 mm, for heavier walled tubing.
The construction and operation of the mandrel mill may
be substantially conventional. The several roll stands are driven -
at appropriate speeds, and the tubular shell-27 is driven through
the mill with a mandrel bar 26. The mandrel, preferably of the
full floating type, is initially inserted within the shell and is
of a length greater than the elongated length of the shell after
passing through the mill. Such mandrel mills, are commercially
available from sources as Aetna-Standard Engineering Co.. Ellwood
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City. Pa.
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The performance of the process, overall, is carried out
in such manner that the elongation achieved in the mandrel mill is
less than four to one, which is considerably less than the theoreti-
cal elongation capability of the mandrel mill. This is done
purposefully, so that the mandrel bars 26 may be formed out of
ordinary steel. In order to achieve greater levels o~ performance
in the mandrel mill, in terms of greater elongation, it would be
necessary to utili~e mandrel bars of special alloy construc~ions.
In general, such bars are not readily available in developing
countries and would have to be imported at great cost, adding
significantly to the initial investment in the mill and also to
the levels of operating expense. It is to be recognized, however,
` that in those areas in which high alloy mandrel bars are readily
and economically available, and/or whenever in the future such
bars may become readily and economically available, the process
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of the invention envisions utilizing the mandrel mill at greater
elongation capacities.
Following processing in the mandrel mill, the now highly
elongated tubular shells 28 may be reheated in a furnace 29 and
then processed further in a conventional stretch reducing mill 30
to achieve further elongation and further reduc~ion in wall thick-
ness and outside diameter. To greatest advantage, the stretch
reducing mill is operated generally in accordance with the Pozsgay
United States Patent No. 4,002,048, assigned to Aetna-Standard
Engineering Co. of Ellwood City, Pa.. The Pozsgay patent describes
an advantageous technique for operation of the stretch reducing
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:mill in a manner to minimize crop losses at the ends of the shell.
~: In a general sense, processing of the shell in a stretch.
reducing mill is common to the push bench process and the extru-
-30 sion process, previously described, excluding, of course, the
reduced crop losses resulting from following o the Pozsgay patent
procedures. When processing the 140 mm square billet pursuant
- to the invention, the final outside diameter of the tubing may
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be reduced, from the incoming diameter o~ about 137 mm, to, for
example, anywhere from about 40 mm to about 108 mm, depending
upon intended utilization. Wall thickness may range from about
3.2 mm, for the small diameter tubing, to about 4.5 mm, for the
larger diameter tubing. In the case of the 165 mm billet,
finished tubing O.D. may range from about 48 mm to about 159 m~,
with wall thicknesses ranging from a minimum o about 5.7 mm to
a maximum of about 12.5 mm. It is of course understood that all
of the foregoing dimensional examples are intended only to be
illustrative and typical, and are not in any way to be considered
as limiting the scope o~ the invention.
The present invention represen~s a significant advance
over the prior art in terms of substantially improved performance
` coupled with lower capital costs and lower operating costs. Thus,
in the push bench process, while rates of production compare rather
c~osely with those from the process of the invention, initial
capital requirements are significantly greater. Moreover, whlle
quality of production from the push bench system is reasonably
good, it is not as high as is attainable in the process of the :~
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present invention, because of the ability of the piercing-type
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elongator to maintain and even improve upon concentricity of the
, tubular shell. In the case of the extrusion process, not only ~ -
; is initial capital expense high, but quality cf production is
well below that achieved with the process of the invention.
In addition to the foregoing, the process of the invention ~
, is outstanding in terms of minimal crop losses. In the process -
of the invention, crop losses occur only after processing in the
- stretch reducing mill (and even these can be minimized significantly
.
by proceeding in accordance with the beforementioned Pozsgay Patent
No. 4,002,048). In the push bench and extrusion processes, crop
losses occur at earlier stages in the process, and ~hese are
particularly significant because of the lower elongation of the
tube sheIl at these upstream stages of the process. In the push ~
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bench process, crop loss occurs after the push bench operation, in
addition to a~ter the stretch reducing mill. In the extrusion
process, crop losses are experienced at thr~e stages. ~After the
piercing press, after the extrusion, and again after the stretch
r~ducing mill.
All things considered, the process of the invention
represents a significant improvement over known techniques for
the low capacity production of seamless tubing.
One o the particularly significant ad~antages of the
p~esent invention resides in the fact that, as and when cylindri-
cal billets become available to the mill -- a ~easonable future
expectation -- the piercing press and its operation may be entirely
eliminated, and the piercing-type elongator can be utilized to
perform the first stage of the process. In other words, the
cylindrical billet, utilized as the starting unit, may be both
-~ initially picrced and significantly elongated in the piercing-type
elongator. The pierced billet is then processed in the mandrel
mill and stretch reducing mill as described. Thus, the process
of the invention is capable of significant upgrading in the future,
` 20 both in terms of eliminating the billet piercing press, upon the
availability of cylindrical billets, and by significantly increasing
the capability of the mandrel mill, upon the ready availability
of high alloy mandrel bars. Such capacity for future upgrading
add significantly to the overall attractiveness of the process.
Thusj the invention includes the process of making
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seamless metal tubing from a generally rectangular billet, which
comprises heating the billet, compressing the billet longitudinally
- while confining it cross sectionally, to form a generally cylindric- `
al body whose diameter is not significantly in excess of the
diagonal dimension of the generally rectangular billet and, in
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conjunction therewith at least substantially piercing said billet
- axially to form a tubular billet shell, elongating and reducing
the wall thickness of said tubular billet shell by piercing-type
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elongating procedures, to form an elongated tubular shell of from
about two to about four times the length of the billet shell,
and thereafter, further elongating said elongated tubular shell
by mandrel mill procedures, to form a further elongated tubular
shell of from about two to about four times the length of the
elongated tubular shell.
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