Note: Descriptions are shown in the official language in which they were submitted.
g~
The present invention relates to a process for
manufacturing seamless metal tubes wherein hollow shells
produced by piercing billets are subjected to wall thick-
ness equalization and/or outside diameter adjustment.
Seamless metal tubes often involve problems of
wall eccentricity. In this regard, there are two types
of eccentricities, namely, eccentric wall eccentricity
- wherein the inside diameter and outside diameter
centers are not aligned - and symmetrical wall eccentri-
city - wherein the centers are aligned but both inside
and outside walls are eccentric in shape. These problems
are most prevalent when using a continuous elongating
mill such as a mandrel mill (for small diameter tubes of
1 to 6 inches) and a multi-stand pipe mill (for medium
diameter tubes of 6 to 16 inches).
It is therefore an object of the invention to
provide a process for manufacturing seamless metal tubes
by using a continuous elongating mill such as a mandrel
mill or a multi-stand pipe mill, or a single-stand type
elongator such as a plug mill or assel mill, wherein a
significant decrease in wall eccentricity ratio can be
achieved.
It is another object of the invention to
provide a process for manufacturing seamless metal
tubes which permits decreasing the number of sizes
of billets to be prepared as stock for tube manufactur-
ing and which can be developed into an integrated tube
manufacturing line so that continuous casted billets
are directly put in process for tube making.
It is a further object of the invention to
provide a process for manufacturing seamless metal
tubes which permits effective correction of wall
eccentricity or equalization of wall thickness even
if the ratio of wall thickness to outside diameter
(t/D) is as small as 5 ~ 15%.
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It is a still further object of the invention
to provide a process for manufacturing seamless metal
tubes wherein hollow shells, whether from a Mannesmann
piercer or from a press piercer, are corrected as to
their wall eccentricity, thus higher quality being
assured of the resulting finished tubes.
In accordance with a particular embodiment of
the invention, there is provided a process for manufac-
turing seamless metal tubes. The process includes the
step of subjecting a shell being worked to outside
diameter reduction by means of a cross roll type rotary
mill having three or four rolls arranged around a pass
line. The axes of the rolls are inclined or inclinable
so that the shaft ends on either side of the rolls stay
close to or stay away from the pass line. The axes are
inclined so that the shaft ends on either side of the
rolls face to the peripheral direction on one and the
same side of the shell being worked. The rotary mill is
operated in such a way that the roll axes are inclined
so that the shaft ends on the inlet side of the rolls
stay close to the pass line. Internal sizing tools are
not used.
In accordance with a further embodiment, there
is provided a process for manufacturing seamless metal
tubes. The process includes the step of subjecting a
shell being worked to outside diameter reduction by
means of a cross roll type rotary mill having three or
four rolls arranged around a pass line. The axes of the
rolls are inclined or inclinable so that the shaft ends
on either side of the rolls stay close to or stay away
from the pass line. The axes are inclined so that the
shaft ends on either side of the rolls face to the
peripheral direction on one and the same side of the
shell being worked. The rotary mill is operated in
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such a way -that the roll axes are inclined so that the
shaft ends on the inlet side of the rolls stay away
from the pass line. Internal sizing tools are not
used.
In accordance with a still further ernbodi-
ment, there is provided a process for manufacturing
seamless metal tubes comprising the step of subject-
ing a shell whose ratio of wall thickness to outside
diameter is between 5 to 20% to outside diameter
reduction by means of a cross roll type rotary mill
having three or four rolls arranged around a pass
line. The axes of the rolls are inclined or inclinable
so that the shaft ends on either side of the rolls stay
close to or stay away from the pass line. The axes are
inclined so that the shaft ends on either side of the
rolls face to the peripheral direction on one and the
same side of the shell being worked. The rotary rnill
is operated in such a way that the rolls are arranged
to have a feed angle ~ and a cross angle Y meeting the
following conditions without using internal sizing
tools: 0~ ~ ~ 14, -7~ y<7
In accordance with a still further embodiment
of the invention, a process for manufacturing seamless ~-
metal tubes comprises the step of subjecting a shell
whose ratio of wall thickness to outside diameter is
5 to 15% to outside diameter reduction by means of a
cross roll type rotary mill having three or four rolls
arranged around a pass line. The axes of the rolls are
inclined or inclinable so that the shaft ends on the
inlet side of the rolls stay away from, and those ends
on the outlet side stay close to, the pass line. The
a~es are inclined so that the shaft ends on either side
of the rolls face to the peripheral direction on one
and the same side of the shell being worked. The rotary
mill is operated in such a way that the rolls are
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,
arranged so as to have a feed angle ~ and a cross angle
y meeting the following conditions and without using
- internal sizing tools: 0 ~ ~ < 14, -7< y < 0.
Other objects and novel features of the
invention will be apparent from the following descrip-
tion taken in connection with the accompanying drawings
wherein:
Fig. 1 is an illustration showing the sequence
of stages in the process according to the invention;
Fig. 2 is an explanatory view showing the
inclined disposition of rolls,
Fig. 3 is an illustrative representation
showing the sequence of stages embodying another aspect
of the process of the invention,
Figs. 4(a) and 4(b) are graphs showing the
effect of the invention,
Figs. 5(a) and 5~b) are graphical representa-
tions showing the effect of the invention where a
2-roll type rotary mill is used,
Fig. 6 is an illustrative representation
showing the sequence of stages embodying still another
aspect of the process of the invention,
Figs. 7(a) ? 7(b) and 7(c) are views illustra-
ting the roll arrangement in a wall thickness equalizer
having a positive cross angle ~toe angle),
Figs. 8(a), 8(b) and 8(c) are views showing
the roll arrangement in a wall thickness equalizer
having a negative cross angle,
Figs. 9 to 11, inclusive, are charts showing
pentagon deformation data based on experiments with
the process of the invention,
Figs. 12 and 13 are graphs showing observa-
tions based on experiments with the process of the
invention,
Fig. 14 is an illustration showing the
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sequence of manufacturing stages in conventional
Mannesmann mandrel mill process;
Fig. 15 is an explanatory view showing an
eccentric wall eccentricity;
Fig. 16 is an explanatory view showing a
symmetrical wall eccentricity;
Fig. 17 is an illustration showing the
sequence of manufacturing stages in conventional
Mannesmann plug mill process;
Fig. 18 is an illustration showing a tube
manufacturing line employing a multi-stand pipe mill;
and
Figs. 19 and 20 are photographic representa-
tions showing a pentagon-shaped angulous deformation
seen with a seamless steel tube.
Before discussing the invention herein, the
problems of the prior art will be described in greater
detail in association with Figures 14 to 18.
The manufacture of small diameter tubes, 1 -
6 in. in diameter, is conventionally carried out in a
manner as illustrated in Fig. 14. That is, round bar
stock or round billet 10 is heated to 1200 - 1250C in
a rotary hearth furnace 31, pierced by means of a
piercing mill 32 (e.g. Mannesmann piercer), and the
resulting hollow shell 11 is processed by a continuous
elongating mill 33 (e.g. a mandrel mill) into a semi-
finished pipe 12 having a wall thickness substantially
comparable to that of a finished tube. The semi-
finished tube 12 is then heated in a reheating furnace
(not shown) and sized by means of a stretch reducer 34
to the specified outside diameter. In conjunction with
outside diameter sizing, some wall thickness adjustment
is made to obtain the thickness of a finished tube.
Described above is a typical process for manufacture-of
small-diameter tubes on a mass-production line known as
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Mannesmann mandrel mill line. A study of wall eccen-
tricity occurrences under this process revealed that
eccentric wall eccentriclty in which, as Fig. 15
illustrates, the inside and outside diametral centers
do not agree with each other was found with hollow
shells ll from the piercer 32, the wall eccentricity
ratio ranging from 5% to 15%. With semi-finished
tubes 12 from the elongating mill 33, symmetrical wall
eccentricity in which, as Fig. 16 illustrates, the
inside and outside diametral centers are identical, was
found to have occurred in the range of 3 to 5% in terms
of wall eccentricity ratio~ this eccentricity being
added to the above said eccentric wall eccentricity.
The term "wall eccentricity ratio" referred to herein
is defined as [(Tmax - Tmin)/Tmean] x 100%, wherein
Tmax is maximum wall thickness of tube section, Tmin
is minimum wall thickness thereof, and Tmean is mean
wall thickness thereof.
No appreciable change was caused at the
stretch reducer 34. In effect, the wall eccentricity
caused at the piercer 32 was introduced into the
finished product substantially as it was. It was also
discovered that continuous elongating mill was in-
effective for the purpose of wall thickness equaliza-
tion and that especially where rolling reduction wasnot uniform in successive passes, some symmetrical
wall eccentricity was added to the initially caused
eccentricity.
In such Mannesmann mandrel mill process
there is sometimes provided a shell sizer between the
piercer 32 and the continuous elongating mill 33~ A
shell sizer comprises 5 to 7 stands of 2-roll or 3-roll
type, each having a grooved roll arranged in tandem.
Each hollow shell 11 is passed through the shell sizer
in the axial direction without rotation, so that its
outside diameter is reduced to the required outside
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diameter. It was primarily for the purpose of decreas-
ing the number of sizes of billets to be provided to
meet the specifications of various different finished
products that the shell sizer was introduced into the
Mannesmann mandrel mill process. Granting that only
one size of hollow shell i9 obtainable from one parti-
cular size of billet at the piercer 32, the provision
of a shell sizer makes it possible to obtain a plurality
of shell sizes. It follows that the shell sizer permits
simplification of billet sizes and furthers continuous
casting of billets. Even if such sizer is applied,
however, the wall eccentricity caused in the earlier
stage can hardly be corrected: only slight thickness
change takes place adjacent the roll flanges, and
there is little metal flow in the peripheral direction
of the shell.
In the manufacture of medium diameter tubes,
6 to 16 inches in diameter, a process known as Mannes-
mann plug mill process is often used which, as Fig. 17
illustrates, comprises a billet 10 heated in a heating
furnace 61 being pierced by a piercer 6~ into a hollow
shell 11, the shell being passed through a rotary
elongator 63 for inside diameter expansion or wall
thickness reduction, the resulting product being
delivered as such to a plug mill 64, then passed
throug~ a reeler 65 and a sizer 66 into a finished
product. Said rotary elongator 63 is such that a plug
is inserted into the hollow shell 11 to perform wall
thickness reduction in cooperation with opposed rolls
arranged in oblique relation to the shell 9 SO that
wall thic~ness reduction of hollow shell is performed
with outer and inner tools under controlled conditions
to permit positive metal flow in the peripheral direct-
ion for the correction of any wall eccentricity caused
at the earlier stage. Insofar as the plug mill process
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is concerned, there is no such problem of wall
eccentricity with medium diameter tubes as is the
case with Mannesmann mandrel process in the manu-
facture of small diameter tubes. Recently, however,
there is a growing tendency that a continuous type
elongator called "Multi-stand pipe mill", featuring
high reduction capacity and high efficiency, is used
in the manufacture of medium diameter tubes. Where
such mill is combined with the abovementioned piercer,
the manufacturing line consists of a heating furnace
71, a piercer 72, a multi~stand pipe mill 73 and a
sizer 74, as illustrated in Fig. 18. With such
simplified arrangement, one similar to that for small
diameter tube manufacturing, there is involved a
problem similar to the one noted with small diameter
tubes: that any wall eccentricity as caused at the
piercer 72 is carried into the finished product.
This difficulty may be overcome by providing a rotary
elongator between the piercer and the multi-stand pipe
mill 73. Indeed, such arrangement is adopted in a
known process wherein square bloom is used as stock
and wherein a press piercing mill is used in place
of an ordinary type piercer. This arrangement, however,
has an economical disadvantage that there are present
two different elongators, that is, rotary elongator and
multi-stand pipe mill, which fact is unfavorable from
the standpoint of equipment investment efficiency.
The invention herein will now be described in
association with Figures 1 to 13.
First, a basic application of the process of
the present invention to the Mannesmann mandrel process
will be explained. According to one basic aspect of the
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invention, the process includes a stage wherin rolling
operation is carried out by means of a 3-roll or 4-roll
type rotary mill to reduce the outside diameter of the
hollow shell without any internal sizing tool being used.
The purpose of the stage is primarily to correct wall
eccentricity or equalize wall thickness. Generally,the
stage precedes the operation of above said elongating mill
whose main function is wall thickness reduction.
The process of wall eccentricity correctingby the
rotary mill is such that shells are rolled as they are
fed while being rotated,'whereby positive metal flow
in the peripheral direction takes place despite of the
absence of internal sizing tools.
Fig. 1 shows the sequence of stages in the process
of the present invention, as used in the manufactu~e
of small diameter tubes. A round billet 10 is heated to
1200 - 1250C in a rotary hearth type heating furnace 1,
then pierced by a piercer 2 into a hollow shell 11. The
hollow shell is then passed through a 3-roll type rotary
mill 3 (hereinafter referred to as "wall-thickness equal-
izer") which has no such internal sizing tool as plug,
mand'rel bar or the like. The ~all-thickness equalizer 3,
as stated above, has no internal sizing tool; its primary
object is to reduce the outside diameter of the hollow
shell 11 so as to correct wall eccentricity. Essentially
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lt 1~ a rolllng mill ha~ing 3 rolls o~ truncated cone
or barrel shape arranged i~ obllque relation to the a~is
o~ the hollow shell. In conilguration, it i~ slmilar to
a 3-roll type piercer or asYel mill ~rom whlch th~ plug
or mandrel bar, as the ca~e may b~ ha~ been removed.
The e~pression ~arranged in oblique relatlon" used
herein mean~ that the roll~ are arranged in such a ~ay
that their re~pective a~es are lnclined at a~ equal angl~
relativc to th~ condition oi their being parallel to the
a~ls o~ tha hollow ~hall and in the tangentlal dlr~ctlon
o~ a virtual circle (shown by an alternate lon~ and two-
~hort-dashec line in Fig. 2) cent~red at the a~l~ of th4
~hell 7 all the roll i a~ in th~ same directlon. The
inclined roll arrangement 18 shown in a dlrection per-
pendlcular to the direotlon oi ahcll ieed ln Fig. l, andin the dlrection Or shell ~eed in ~lg. 2. The angle at
whlch each roll i8 incllned i8 re*~rrcd to a~ ~eed angls"
hereina~ter,
~he wall thickness equallzer 3 perrorms 5 - 50 % diameter
20 reductlon. Correction Or the wall eccentrlcl t~ takes
place in tha cour~e o~ the dlameter reductio~ operation,
The ~hell ll' ~rom the equalizer 3 18 then ~ed to th~
mandrel mill 4 where it i8 subJected to wall ~hick-
ne~s reduction to b~ made into a ~emi-fini~hed tube 12
havlng a wall thic~nes~ almo3t comparable to that o~
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a flnished tube. A~ter heated in a reheating furnace
(not shownj, the semi-~inished tube 12 i8 pas~ed through
a reducing mill 5 for sizing into a ~ini~hed size.
Fi~. 3 illustrRtes the sequence o~ Rtages in the
process o~ the inventlon, a~ used ln the marlufacture
o~ medlum diameter tubes.~ The stages o~ up to wall eccen-
tricity correc$in~, namely~ heating ~urnace 1, piercing
mill 2 and wall-thiclmess equalizer 3, are same a~ those
in the case o~ ~all-dlameter t~be making.'A
hollow ~hell 11' from the equali,~er 3 i~ fed to a multi-
stand pipe mill 6 ~or workl~ into a semi-~ini3hed ~be
12 havin~ a wall ~hickne~3 almost ~qual to th3t of a
fini~hed tube.~ A~ter heated ln a reheating furn~ce (not
~hown), the ~emi-fini~hed tube 12 i9 pa~sed through a
sizer 7 in whioh it i8 worked ko the specified size.
Th~ two embodiment~ described above, both employ a con-
tinuous type elongator ~uch as r~ drel mill or multi-
stand pipe mill, as the case may be, This lnvention,
however, m~y be equally applied to a t~e makin6 : ~
line employin~ a sin~le-~tand elongator ~uch as plug mill
or th~ like, ~'or this purpo~e, the line may comprise a
rotary piercer, a wall-thic~ness equaIizer, a rota~y
clGngator, a plug mill, a reeler, and a sizer; or a
press pisrclng mill, a wall-thick:nes~ equalizerL a rotary
elon~ator, a plug mill, a reeler, and a ~izer.
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Next, the e~ect o~ the proce~s according to thel~vention will be e~plalned on the ba~is o~ concrete
e~amples. ~`igs. 4 ~a~ snd 4 ~b) are graphs ~howing
observation data on the wall eccentricity correcting
effec-t of a 3-roll type wall-thickne~s equalizer ln
accordance with the inv~ntion. ~igs. 5 (a) and 5 (b)
are graph~ ~howing data of ~imilar nature observed with
a ~-roll type rotary mill for comparison purposes. The
data presented in ~igs. 4 (a) and 4 (b) relate to the
results observed with a 3-roll type equalizer hav~ng a
feed angle of 6, wher~as the data in ~'ig8. 5 (a) and
5 (b) relate to the re~ults observed with a 2-roll type
rotary mill having a ~eed angle oY 8. I~ thc ~raphs D
outside-diameter reduction ratio is given on the abscls~a,
and ¢orrection ratio o~ ~all eccentricit~
max. thicknes~ - min. thickn~ 100 % )
mean thickne~
on the ordinate. The wall eccentricity ratio ~ith respect
to each hollow ~hell 11' prior to being fed to tho equal-
izer or rotary mill, a~ the case may be, iB u3ed ~s a
parameter.
In Figs. 4 (a) and 5 (a), data given relate to
re~ults with respect to ~hells wherein t/D (wall thickne~s/
outside diam~ter) i~ 20 %, and data in ~igs. 4 (b) and
5 (b) relate to result~ with re~pect to ~hells, ~1D 10
It i~ apparent Yrom the~e graph~ that thc 3-roll type
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wall thickness equalizer and 2-roll type rotary mill,
both have positive effects in improving wall eccentricity.
Furthermore, it is clear that the freater the outside-
diameter reduction ratio, the more significant is the
effect of correction of wall eccentricity ; similarly, the
greater the shell wall eccentricity and the higher the wall
thickness to diameter ratio (t/D), the more remarkable
is the effect of correction of wall eccentricity. It is also
noted that the 3-roll wall~thickness equalizer according to
the invention is more effective than the 2-roll rotary
mill. Where the latter mill is used, its effect in
correcting wall eccentricity ratio is relatively small if
t/D is 10 %; and no significant effect is obtainable
unless outside-diameter reduction ratio is increased up
to 50 % or so. However, increasing the outside-diameter
reduction ratio to 50 % is undesirable in many way~:
smooth roll contact relative to the shell may be
hindered; wrinkles may tend to develop in the shell
interior: the billet diameter is required to be about
double the diameter of the shell at the outlet end of
the rotary mill, which fact would make it difficult to
provide a heating furnace of a suitable design, parti-
cularly in view of a substantially heavier load on the
hearth; and not economical, From a practical point of
view, therefore, it is not advisable to apply a 2-roll
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type rotary mill as a wall-thickness equalizer.
Table 1 presents comparative da-ta on billet diameter,
tube outside diameter, and wall thickness at various
stages in the process of the invention and at those in
conventional Mannesmann mandrel mill process.
Table 1
In mm
. . . ._ _
Wall thickness Mandrel
Process Billet Piercer .
~ equallzer mill
._ .
Invention 205~ 205~x42.5t 186~x45.2t 1S~x30t
_ . ~
. Conventional 186~ 186~x42.5t 158~x30t
. . _ .
Fifty samples were taken of tubes from mandrel mill
stage in each process and examined as to wall-eccentric-
ity ratio. Whereas the eccentrici-ty ratio was 12 % with
tubes manufactured under the conventional process, tubes
from the process of the invention showed considerable
improvement, with an eccentricity ratio of 5 % only.
As can be readily seen from this comparison, the
concept of the present invention, when applied to the
Mannesmann process, permits a significant decrease o~
shell wall eccentricity in the course of seamless metal
tube making. This means less section deviation in
the finished tube and better-quality seamless me~al
tube. Moreover, as compared with rotary elongator,
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the wall-thickness equalizer is more simple in construc-
tion, cost less, and requires less space. The process
of the invention ha~ an added advantage that outside-
diameter reduction is carried out concurrently with wall
eccentricity correcting, which fact makes it possible to
decrease the number of diameter sizes of billet3 to be
supplied to meet various different specifications and
thus to establish suitable production lines for continuous
billet casting.
Now, the inventors found out some new problems when
they were experimenting on the process of the present
invention under various conditions to ascertain its
effects. One is that, as may be seen from the comparison
of Fig. ~ (a) with Fig. 4 (b), where t/D is rather small
(e.g. S - 15 %), the extent of wall eccentricity correc-
tion achievable is fairly small, if the outside-diameter
reduction ratio is small. Another problem is that on the
tail portion of tubes of reduced shells there is
often caused a so-calLed pentagon formation, that is, the
section configuration i5 deformed into a pentagon ~hape,
as shown in Figs. 19 and 20. The smaller the t/D, the
more noticeable the phenomenon is. This means that it
i8 impossible to compensate insufficient correction of
wall eccentricity in the case of the t/D ratio being
small by increasing outside-diameter reduction ratio.
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What is worse, as the rolling speed becomes
higher, pentagon formation extends over a larger length,
and therefore, incorporating a wall thickness equalizing
mill into the manufacturing line may lead to the
5 lowering of production efficiency. Thus it became appar- -
ent that overcoming such deformation difficulty is of
extreme importance in order that the scope of application
of the invention may be extended even to cases where ths
t/D ratio is small and if the invention can be put in
practice effectively and without lowering production
efficiency. And the inventors discovered that the dif-
ficulty could be overcome by employing a cross-type rotary
mill. Accordingly, a more practical form of the inven-
tion comprises the step of subjecting shells being worked
to outside-diameter reduction by means of a cross roll-type
rotary mill ~or a cross-type rotary mi~l) having 3 or 4
rolls arranged around a passline, the axes of which rolls
are inclinable so that the shaft ends on either side of
the rolls may stay close to or stay away from the yass
line and so that said sha~ ends may face to the peripheral
direction on one and same side of the shell being worked,
and without employing internal sizing tools.
An example of the process of tha invention using
a crossroll-type rotary mill having 3 rolls is explained
hereinbelow. In Fig. 6 there is shown an example wherein
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a cross roll-type rotary mill is used in a Mannesmann plug
mill line.
Round billet 10 is heated to 1200 - 1250C, for
example, in a heating furnace 1 of rotary hearth type,
The billet 10 is then pierced by a piercing mill 2
(Mannesmann piercer) into a hollow shell 11, which is
then passed through a cross roll-type rotary mill 3
(hereinafter referred to as "wall-thickness equalizer")
which is not provided with any internal sizing tool such
as plug or Mandrèl bar. The wall-thickness equalizer 3,
designed for correcting wall eccentricity of hollow -
shell 11, is essentially a rotary mill having 3 rolls 31
(only 2 rolls shown in Fig. 6) of a circular truncated
cone type, each having a gorge portion at a location about
half way in the direction of its axis, and has no internal
sizing tool, as above mentioned. The rolls ~ay be of
barrel shape instead of truncated cohe.
The hollow shell 11 is subjected, at the thickness
equalizer 3, to outside-diameter reduetion, during whieh
operation it concurrently has its wall eccentricity
corrected, and the so worked shell 11' i8 then fed to
a plug mill 8, where ik is subj.ected to elongation for
wall thickness rsduction, whereby it is made into a
semi-finished tube 12 having a wall thickness substantially
eomparable to that of a finished tube. After subjeeted
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to reeling by means of a reeler 9, the semi-finished
tube 9 is passed through a sizer 7 in which it is sized
to finished size.
Concretely, some aspects of the configuration of the
wall-thickness e~alizer are shown in Figs. 7 (a), 7 (b)
and 7 (c). Fig. 7 (a) is a front elevation showing
relative positions of rolls 31 which constitute a rolling
mill as wall-thickness equalizer 3,as seen from the inlet
side of the mill~ Fig. 7 (b) is a sectional view taken
along the lines I - I in Fig. 7 (a). Fig. 7 (c) is a
side view taken on the line lI - II in Fig. 7 (a). Each
roll 31 has a gorge portion 31a abouthalf way in the
axial direction. The gorge 31a forms the boundary between
the front portion (inlet side) and the rear portion (outlet
side) of each ro]l. The front portion is gradually reduced
in diameter toward the front shaft jend, and the rear portion
is grad~ally enlarged in diameter toward the rear shaft
end. Thus, the roll is shaped like a circular truncated
cone, and has an inlet surface 31b and an outlet surface
31c, The rolls 31 are arranged around a pass lins X - X
for shell 11 (pass line X - X corresponds to shell axis)
in such a way that their centers, each represented by an
intersection point O between an axis line Y - Y and a
plane including the gorge 31a (said intersection point
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~g68~
to be hereinafter referred to as roll center), are
positioned at equal spacing on a plane crossing at
right angle with the pass line X - X, with their
respective inlet surface 31b side portions disposed
on the inlet side in the direction of flow of shells 11.
The axes ~ - Y of the rolls 31, as seen from Fig. 7 (b),
are inclined at an angle y (hereinafter referred to as -
cross angle) relative to the pass line X - X so that their
shaft ends on the same side, as viewed on a plane, that
is, the front-side (inlet side) shaft ends approach
toward the pass line X - X. The inclined arrangement of
the rolls 31 is in same manner as shown in Figs. 1 and 2.
That is, their front shaft ends face to the peripheral
direction on one and same side (clockwise) of shell 11
as shown in side elevation in Fig. 7 (a), being inclined
at feed angle ~ as shown in Fig. 7 (c). The rolls 31 are
connected to a drive source not shown, being driven to
rotate in same direction. Shell 11 fed between the rolls
31 is moved in the axial direction while being rotated
around the axis line. In other words, shell 11 is sub-
jected to outside-diameter reduction while being screwed
forward, whereby its wall eccentricity is corrected.
Fig~ 8 shows another example of wall-thickness
equalizer 3. I~ Fig. 8 (a) it is illustrated in front
elevation as seen from the inlet side of the miil.
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~96~
of ~hell~. Fig. 8 (b) is a section taken along the
line~ III ln Fig. 8 (a). Fig. 8 (c) i8 a side
view taken on the line IV - IV in Fig. 8 (a). In tho
wall-thickne~s equalizer 3 ~hown~ rolls 41 each ha~ a
gorgo 41a about centrally in the a~ial direction. Each
roll 41 con~i~ts o~ front and rear portlons, wlth the
gorge 41a batween. The iront portlon i~ ~radually e~-
panded in d1ameter toward the front ~haft end, and the
rear portion is gradually reduced in diameter toward the
rear 3haft end. Each roll 41 i~ shaped like a circular
truncated cone and ha~ an lnle~ ~urface 41b and an out-
let ~ur~ace 41c. The roll~ 41 are 80 arranged that the
inlet surface (41b) slde i~ positioned on the upper
~tream s1de o~ ~low of shelle 11, with a cro~ angle
set at ~ and a feed angle at ~. ~he inclination in the
peripheral direction, i.~ ed an~le ~ is get 80 that
the rear ~haft end 18 in clockwl~e direction. Wherea~
the cros~ angle ~ for roll~ 31 in Figs~ 7 (a) - 7 (c~,
a~ can be clearly seen from Plg. 7 (b), is ~et in ~uch
a way that the inlet ~ur~aco 3~b o~ each roll ~
relatively alose to the pa~ line X - X ~or shell 11,
th~ cross angle ~ for the roll~ 41 shown in Fig~. 8 (a) -
8 (c), as is clear from Fig. 8 (b)g is in reverse rela-
t~on to that in Fig. 7 (b). The angle in the iorm~r
ca~e i~ hereina~ter re~errad to ae po~itlve angle
- 20 -
6~6
(y>O), and the one in the latter case as negativs
angle (y<O). -
Experiments were made on a 3-ro~l cross roll-type
rotary mill ~9 the one shown in Figs. 7 (a)-tc) and 8(a)-(c)
by employing same in subjecting shells to outside-diameter
reduction, without using internal ~izing tools such
as mandrel, plug and the like. The results o~ these
experiment~ are explained below.
For rolls in th~ rotary mill, truncated-cone-shaped
rolls, each 180 mm in barrel length and 200 mm in diameter
at gorge, were used, with feed angle designed in 3
different ways and cro~s angle in 6 different way~.
Pentagon formation occurrences were axamined with respect
to various different combinationsO Samplo shells were
used in 5 varieties in the outside diameter range of
80 mm - 100 mm. Diameter reduction ratio was set at
20 %, and roll speed at 200 r.p.m.
The expsriment re~ults arb presented in Figs. 9, 10
and 11, in which mark O denotes no pentagon formation
and ~ denotes pentagon~shaped angulou~ deformation
occurred.
As can be seen from Figs.9~ 10 and 11, cro~s angle
y-faed angle ~ combination3 in roll arrangement have
con~iderable bearing upon pentagon formation control.
For such control purpose, it is found mo~t sffective
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to ha~e: ~ ~eed angle~5 ~et relatively amall; ~ cro3s
angle ~ set small in the positive angle range; and ~
cros~ angle ~ set relatiYely large in abaolute terma ii
given negative angle value. By setting ~eed angle ~
relatlvely small is meant that acrewing pitch ln rolling
i8 small and further that ~hell rotation specd in the
roll-shell contact zone iB lncreased. Thu~, it can be
said that smaller pitch o~ shell 3crewing and higher
~hell rotation 3peed are ~ectivc ~or the purpo~e o~
post-roll1ng pentagon~ ormation control.
Setting po~itive cros~ angle ~ relati~ely 8mall or
setting negative cros3 angle ~ relatively large al~o
means that ~hell screwing pitch is ~mall and that shell
rotation speed 18 increasedO From the viewpoint o~
pent~gon ~formation co~trol, howe~er, it i~ more e~Pective
to chango croa3 angle ~ than to ¢hange ~eed an~le ~.
The ~act that ~etting ~ and ~ valu~8 relatively
small (where ~ ~ O, ~etting relati~ely large) i5 ei~eotiv~
a~ such ig a~sumed to ba attributable to th~ follo~ing
rea~on~: ~3 a re3ult o~ these mea~ure~, screwlng pitch
b~comes ~maller and ~hell rotation speed i~ increa~ed.
Thus, various portion3 oi the ~hell are sub~ected to
diameter reducing actioa of th~ rolls more time~.
Moreover, time per tur~ of actlon become~ ~hort. Cvn8e-
quently, wall thickness i8 e~ective~y reduced i~ a
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~L5968~
smooth flow over the entire area.
~heoretically, it may be considered that abo~e
described feed and cross angle roll setting a~ preven-
tive measures against pentagon formation i9 applicable
to 2-roll rotary mill having no internal sizing tool and
in which roll axes are inclined relatiYe to the pass
line, for the purpose o~ preventing angulous deformation
whlch present substantially triangular configuratio~ aR
often observed typically in ~he case of diameter reducing
for shells, t/D 5 - 15~ Where a 2-roll t~pe rotary mill
i8 used, however~ expectable wall eccentricity cor~
rectio~ effect is absolutel~ ~mall; therefore, any effect
sufficient to ~ustify the cost of equipment may not be
obtained.
Referring to diameter reduction operation where a
3-roll cross roll-type rotary milllas above desGribed i8
used as ~ wall-thick~ess equalizer~, without usin~
internal sizing tools, experiments were made on th~
relation between correctio~ ratio of wa~l ecce~tricit~ a~d
feed and cross angle set~ing~ and rfor rolls. Results
o~ the ~xperiments are explained below. ~or the purpose
o~ the cross roll-type rotary mill., rolls of the s~me ~peci-
ficatio3 a~ used in the earlier me~tioned experi-
ments were used. Sample shells u~ed were of the follow-
ing descriptions; t/D 10 ~, 5 ~iæes within outer diameter
. , :
range of 80 mm - 100 mm; wall eccentricity ratios 10 %,
20 %, and 30 ~. The samples were subjected to rolling
at rotation speed of 200 r.p.~. The results are graphi-
cally shown in Fig. 12, in which abscissa deno-tes feed
angle 3 and ordinate denotes correction ratio of wall
eccentricity (~).
Correction ratio of wall eccentricity referred to
herein is expressed by the following formula:
Wall eccentricity Wall eccentricity
Correction ratio of ratio of shell - ratio of product
wall eccentricity ~ x 100 %
- Wall eccentricity ratlo of shell
As can be clearly noted from the graph, in order to
improve correction ratio of wall eccentricity, it is most
effective to have: ~ feed angle ~ set relatively small;
~ cross angle y set small in the positive angle range;
and ~ cross angle y set relatively large in absolute
terms if given negative angle value. All this agrees
with data on pentagon formation control as based on the
experimental results presented in FigS. 9, 10,and 11.
Wall thickness is gradually transferred in the peripheral
direction little by little over many times. That iS9
thickness transfer from thick portion to thin portion in
the peripheral direction is selectively accomplished, and
thus wall eccentricity is corrected.
If feed angle ~ is set relatively small, with
cross angle y set, on the negative angle side, relatively
' : . ' :
~ 6
llarge in absolute terms, correction ratio:!l of wall eccent-,-
ricity of more 60 % can be obtained. ~his stands in a
striking contrast with the fact that where a 2- roll
t,ype ro~ary mill in w~lich roll axes are inclined
relative to the pass line but do not cro~s with it is
employed as a thickness equalizer, a correction ratio
obtain~ble may be at most 20 % or so. ~he fact that a
correction ration o~ as high as 60 % is obtainable mean~
that an eccentricity ratio of 30 % with a shell can be
reduced to 12 ~; that in the case of a shell with an
eccentricit~ ratio of 20 ~, the ratio can be redu¢ed
to 8 %; and if the eccentricity ratio is 10 %t it ca~
be reduced to 4 %.
Next, where diameter reduction,operation is r.arried
out by means of above ~aid ~-roll cross roll-type rotar~
mill and without employin internal sizing tools ? the
relation~ between rollin~ ~peed and feed and cross angle
settings~ and ~ for rolls will be e.xplained on the
~asis of experimental data. Used roll~s were of the
same dimen~ions as earlier mentioned. Sample shell~
of the following de.scription were used: t/D 10 ~, outside
diameter 90 mm, wall thick~ess 9.0 mm. ~he ~hells were
~ub~ected to outside-diameter reductio~ u~der thess
conditions: reductio~ ratio 20 %, rotation velo~ity
200 r.p.m. ~he result~ aro graphed in Fig. 13, wherei~
`: :
- 2~ -
' ' ', ' :
the abqcissa denotes feed angle ~ and the ordinate
denoteq rolling speedO
As is clear from the graph, in order to increase
rolling qpeed, it is deRirable to have: ~ feed angla
~ set relatively large; ~ cro~s angle ~ set relatively
small in absolute terms, if it i~ given a negative value;
and ~ cross angle ~ 1 if on the posi~ive side, set
relatively large in absolute terms.
It is ~oted that the above described conditions for
increasing rolling spaed are in complete disagreeme~t
with the earlier mentio~ed condition~ for preventing
pentagon formation or for improving corection ration of
wall eccentricit~
~his i8 quite natural since the conditions for th~ latter
purpose~ are largely related with the matter of reducing the
screwing pitch for shells~ If empha~is i~ placed on met~l -
tube quality only, rolling speed may well be sacri~iced.
As a ma~ter o~ practice, however, when incorporati~g
a 3-roll cross roll-type rotary mill~ as a thickne~
equalizer, into a manu~acturing proce~s for seamle~s
metal tubes, the matter o~ efficiency balance is of
great importance, e~pecially where a high-p~o~cti~i~y
metal ~ube making process i~ ussd. ~he presence of ~ :
significant unbalance between such rotary mill ~nd
existing rolling mills at ad~acent ~tage~ for example,
piercer and plug milll may often make such
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introduotion impracticable. ~herefore, in setting up
a 3-roll cross roll-type rotary mill as above described,
prudant consideration must be given to productivity
as well as pentagon formation control and wall eccen-
tricity correction so that setup conditions may be
determined ~rom a standpoint of overall requirements.
By way of exampl~, preferred setup condition~ are
presented below.
i) ~asicall~, roll setup conditions for cro~s roll-type
rotary mill should be ~uch that feed angle~ i9 set
as small as feasi~le, with cross angle~~~et a3 large
aspossible in ab~olute terms on the negative angle
side. Decrea~s~ in productivit~ due to use of ~maller
feed a~gle ~ may be prevented preferabl~ by increasing
rotation speed of rolls as much as possible.
ii) It i~ to be notsd~ however, that an exoe~si~e i~crease
oY rotation s~eed of rolls may ofton be a cau~o of
trouble and un~esirable from the st~dpaint of safat~,
and further that it may more or less have a nogative
effect on pentagon formation control and wall ecc8~-
tricity correction. ~herefore, when setting cro~s
angle o~ the positive angle side, it is ~esirable to
set feed angle ~ at as small a value a~ possible and
to compensate any decrease in productivity
re~ulting therefrom by ~ettinB cross angle rel~tively
_ 27 -
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large. It is also desirable that when setting cross
angle ~ on the negative angle side, as large a value
in absolute terms as feasible should be used and that
any decrease in productivity due thereto should be
compensated by setting feed angle as large as possible.
iii) If there is no problem of productivity
balance with thickness equalizer in tube manufacturing
process, it is desirable that feed angle ~ is set as
small as possible, with cross angle y set on the
negative angle side as large as possible in absolute
terms, whereby greater pentagon formation control and
correction effect of wall eccentricity may be obtained.
In general, the limitations of cross angle y
and feed angle ~ by which the better effect of the
present invention is obtained are as follows:
0 ~ ~ < 14
-7< ~ < 7
The upper limits of cross angle y and feed
angle ~ are those values below which remarkable effects
of both equalizing wall eccentricity and controlling
pentagon formation may be obtained. The lower limit
of cross angle y is decided so that both the mechanical
contact of roll spindle and shell, and extraordinary
vibration of shell itself are prevented.
If cross angle y is negative and its absolute
term exceeds a threshold value, a shell starts vibrating
to cause heavy noise which should be prevented.
The process described above is not only
applicable to Mannesmann mandrel line, but also is
applicable for the purpose of correcting spiral wall
eccentricity occurring in Mannesmann mandrel mill,
Mannesmann multi-stand pipe mill, Mannesmann assel
mill and Mannesmann pilger mill lines and/or for the
purpose of correcting parallel eccentricity developed
in Ugine-Sejournet extrusion and ~hrhardt push bench
~L~5~
reducing lines. Naturally, it is applicable to a tube
manufacturing line employing a press piercer instead
of a Mannesmann piercer.
For the purpose of applying the process of the
invention to various lines referred to above, the
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following layouts are recommended.
(1) In Mannesmann mandrel mill line (heating furnace
Mannesmann piercer + mandrel mill + reheating furnace~
stretch reducer), a wall-thickness equalizer is provided
preferably on -the outlet side of Mannesmann piercer or,
depending upon conditions, on the outlet side of mandrel
mill for correcting wall eccectricity. In this case,
wall eccecn-tricity correction or wall thickness equali-
zation may be effected with shells in a thin wall
range such as t/D 5 - 15 %.
(2) In Mannesmann plug mill line ( heating furnace~
Mannesmann piercer + rotary elongator ~ plug mill +
reeler ~ sizer), wall eccentricity-correcting or wall
thickness equalizing operation is carried out desirably
on the outlet side of Mannesmann pirrcer or, depending
upon conditions, on the outlet side;of plug mill,.
In the case whe~e piercing ratio at Mannesmann piercer
is substantially large, rotarj elongator may be omitted.
(3) In Mannssmann multi-stand pipe mill line ( heating
furnace ~ Mannesmann piercer ~ rotary elongator ~
multi-stand pipe mill ~ reheating furnace ~ sizer),
wall eccentricity correcting or wall thickness equalizing
operation i8 carried out desirably on the outlet side
of piercer or of rotary
elongator or, depending uponconditions, on outlet
side of multi-stand pipe mill.
; (4) In ~annesmann assel mill line (heating furnace
- 29 _
~,
Mannesmann piercer ) assel mill > reheating furnace ~ ~
sizer ~ rotary æizer) , eccentricity correction or wall
thickness equalization is carried out preferably on the
outlet side of Mannesmann piercer or, depending upon condi-
tions, on the outlet side of assel mill. Where piercing
ratio at Mannesmann piërcer i9 substantially large, assel
mill may be omitted.
(5) In Mannesmann pilger mill line (heating furnace )
Mannesmann piercer ~ pilger mill ~ sizer), eccentricity
correction or wall thicknesæ equalization is carried out
preferably on outlet side of Mannesmann piercer or, depend-
ing upon conditions, on the outlet side of pilger mill.
(6) In Ugine-Sejournet extrusion line (heating furnace
vertical press ~ horizontal press) , wall eccentricity
correction or wall thickness equalization operation is
carried out preferably on the outlet side of the vertical
press, but depending upon conditions, such operation may
be carried out on the outlet side of horizontal press.
(7) In Ehrhardt push bench reducing line ( heating
furnace ~ E~hrhardt vertical press ~ push bench), wall
eccectrity correction or wall thickneæs equalization i~
carried out preferably on the outlet side of Ehrhardt
vertical press, but may be carried out on the outlet æide
of bench depending upon conditions.
It is noted that avove described exAmples relate to
.
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ca~ses wl-ere ~ 3-roll cross roll-t~pe rotary mill is employed
as a t~ickness equalizer. However, the process of the
present invention is also applica~le where a 4-roll cross
roll- type rotary mill is used. In this case, greater
correctio~ effect may be obtained. ~his can be readily
anticipated from the fact that rolling pressure is dis-
tributed over 4 rolls. According to the inventors'
estimation, where ~ is on the ~egative angle side and
i3 relatively small, a correctio~ ratio of wall eccantricit~
of 9O ~ or morè may be attained~ ~rom the viewpoint
of construction, a 4-roll cross roll-type rotary mill can
be obtained only by increasing the number of roll~ arranged
around pass line from aboYe said three to four. However,
4- rolls make the arrangement complicated, and therefore,
it i8 desirable that 2 of the 4 rolls ~mployed as dri~e
rolls and the other 2 as idle rolls.
As described above, the process of the invention
employs a 3~xoll or 4-roll cross~type rotary mill as a
wall-thickness equali~er; and b~ ~ub~ecting shells to
wall-diameter reduction and withoùt using internal
~izing tools such as mandrel ber and plug, extremely
good ¢orrection effe~t-can be!~btai~od-w~hout-a~
deformatio~ such as pentagon formatio~ cau~ed to
~hells, and without rolling ~peed being sacrificed.
In add~tio~ by effecting wall eoce~tricit~ co~reotion
,
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with respect to shells, section deviation of finished
product can be notably.~decreased, which means improved
product qualit~. Further, as a pr~mary effect of
diameter reduction, the number of sizes of billets as
materials for tube making can be reduced.
32
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