Method of and roll stand for diagonal rolling of tubes

In a method and a roll stand for diagonal rolling of medium or thin-walled tube ingots, an inner mandrel rod is held at an inlet side and controllably axially displaceably relative to rolls. In order to avoid a funnel-shaped expansion at the tube ingot end, the rolling product during rolling is rolled in a constriction of the mandrel rod and thereby obtains a thickened wall forming a support of the tube ingot wall against the expansion.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of and a roll stand for diagonal 
rolling of tubes. 
Various methods are known for diagonal rolling of tubes or tube ingots. 
Such diagonal rolling processes are performed for example on rolling 
devices identified as diagonal rolling mechanism, assel rolling mill, 
diescher rolling mill, planetary skew rolling mill, cone skew rolling 
mill, etc. When such devices are utilized for rolling medium or 
thin-walled rolling ingots, or in other words such which have a 
diameter/wall thickness ratio of approximately greater than 10:1, problems 
arise during rolling of the rear rolling ingot ends as considered in the 
rolling direction. During the rolling process they expand in a 
funnel-shaped manner in a radial direction, which leads to rolling errors 
and to jamming of the tube ingot ends in the caliber opening of the roll 
stand. The reason for this disadvantageous expansion is that during the 
progressing rolling process the support of the rolling ingot wall against 
the expansion due to the not yet rolled and therefore still thick-walled 
rear part of the rolling ingot progressively reduces and finally 
disappears. 
For avoiding such an expansion of the tube ingot ends, it was proposed in 
the German patent document DE-PS 38 23 135 to reduce the outer diameter 
and/or the wall thickness of the tube ingot end before it is inserted in 
the caliber opening of the diagonal roll stand. In this known process an 
additional working step must be performed with respect to the rolling 
ingot ends and an additional device is needed which is suitable for 
reducing the tube ingot ends before the diagonal rolling itself. 
Contrary to this, in accordance with the solution proposed in the German 
document DE-OS 15 27 750 the tube ingot ends are provided with a greater 
wall thickness. This is obtained in that during the diagonal rolling the 
rolls are displaced from one another in a radial direction when the tube 
ingot ends come into proximity to the rolls. The adjustment of the rolls 
required for this must be performed however precisely, which includes 
substantial difficulties and high expenses. This means that in addition to 
the rolls, also extensive bearing inserts and guiding elements or in other 
words many parts must be also adjusted synchronously and with a high 
accuracy to maintain the required roll tolerances. This involves further 
difficulties that the parts to be displaced have high weight and they are 
loaded during adjustment with great working forces, since the adjustment 
must be performed during the rolling. Moreover, it is necessary to perform 
the adjustment fast, so that the tube ingot ends with a thickened wall are 
maintained as brief as possible, which involves a substantial loss since 
later they are separated and must be scrubbed. Furthermore, the known 
processes cannot be utilized with planetary diagonal roll stands since 
there the rolls are supporting in a rotor which rotates with a high speed 
and therefore fast radial adjustment of the rolls during the rolling 
process is not possible. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
and a roll stand for diagonal rolling of tubes, which avoids the 
disadvantages of the prior art. 
The invention starts from a known method of diagonal rolling of medium and 
thin-walled tube ingots, in which a mandrel rod retained at the inlet side 
in an axially displaceable way is introduced into a tube ingot and 
subsequently both are introduced into a caliber opening formed by rolls 
and eventually guiding means, and during the rolling are displaced 
axially, wherein rearwardly as considered in a rolling direction a short 
tube ingot end is rolled with a thickened wall. 
The objective of the invention is to provide a method and a diagonal roll 
stand in which the above disadvantages are eliminated and in which with 
low expenses rolling errors and operational disturbances are eliminated by 
reliably expanding tube ingot ends. 
This objective is achieved in that the rolling product of the rear tube 
ingot end is rolled in a constriction of the controlled axially displacing 
mandrel rod and thereby is provided with a thickened wall. 
The disadvantageous and undesired expansion of the rear tube ingot end is 
thereby avoided, in that the wall reduction at the tube ingot end is 
avoided and at the tube ingot end a thick-walled support is provided. In 
contrast to the known method, the wall thickening at the tube ingot end is 
produced not by providing a greater outer diameter, but instead by 
reducing the inner diameter of the tube ingot within a short end portion. 
No additional working step is required for this purpose and also no 
additional device, but instead a tube ingot end which has a thickened wall 
is provided during the diagonal rolling by tools of the diagonal roll 
stand which are involved in the rolling process anyway. This saves working 
time and additional investment cost. Moreover, in the inventive method it 
is not required to adjust the rolls, their extensive bearing inserts and 
eventually available guiding means in the radial direction when the tube 
ingot end runs into the caliber opening. The high multiple expenses for 
precise fast adjustment of the rolls and the guiding means can be thereby 
dispensed with. Only conventional adjusting devices are needed. Further, 
the inventive method can be used for all diagonal rolling processes, in 
which a mandrel rod is used as an inner tool. This is true also for the 
planetary diagonal rolling since in the inventive rolling method no radial 
adjustment of the rolls is needed. 
With the controlled axial displacement of the mandrel rod during the 
rolling process, it is possible to position its constriction relative to 
the tube ingot end and to the rolls so that the tube ingot end with the 
supporting thickened wall is sufficiently long but remains as short as 
possible and thereby the material loss during separation of the tube ingot 
end with the thickened wall is retained low. The controlled axial 
displacement of the mandrel rod can be performed in the inventive method 
so that neither the movement direction, nor the movement speed of the 
mandrel rod is changed, which is advantageous for maintaining narrow 
tolerances of the wall thickness. Despite the fact that the speed and the 
movement direction remain as identical as possible, the mandrel rod is 
moved so that the tube ingot end together with the constriction of the 
mandrel rod run into the caliber opening and the tube ingot end is rolled 
in the region of the constriction of the mandrel rod. 
In accordance with a further embodiment of the inventive method, the 
mandrel rod after the tube ingot end with the thickened wall passes the 
caliber opening, is pulled back to the inlet side and the tube ingot is 
stripped from the mandrel rod. The tube ingot during pulling back of the 
mandrel rod can be retained by a stripping element at the outlet side. 
This provision is recommended first of all for diagonal roll stands, such 
as for assel or diescher roll stands, in which the tube ingot is rotated 
during the rolling around its longitudinal axis. Contrary to this, it is 
also possible during pulling back of the mandrel rod to retain the rolling 
ingot by a subsequently arranged device for further machining of the tube 
ingot at the outlet side. This is recommended in particular for a 
planetary diagonal roll stand in which the rolling ingot during the 
rolling process is not rotated around its longitudinal axis and as a 
result their size or length reducing roll train can be arranged in a 
straight line and with a short distance directly after it so that it then 
engages the tube ingot and holds it back when the mandrel rod of the 
planetary diagonal roll stand is pulled back. 
After finishing the diagonal rolling, the short tube ingot end with the 
thickened wall is no longer needed as a support and means against the 
undesired expansion of the tube ingot end. There is then the possibility 
to separate the tube ingot end with the thickened wall after passing the 
caliber opening from the tube ingot and later remove the remaining tube 
ingot from mandrel rod. Another possibility resides in that the tube ingot 
end with the thickened wall after stripping of the tube ingot from the 
mandrel rod can be expanded by a conical longitudinal portion of the 
mandrel rod and stripped from the remaining tube ingot from the mandrel 
rod. The further possibility is however especially advantageous, in 
accordance with which the tube ingot end with the thickened wall is 
expanded both by a conical longitudinal portion of the mandrel rod as well 
as by round zones of the rolls to a greater inner diameter than the outer 
diameter of the mandrel rod and rolls from the constriction of the mandrel 
rod. The latter mentioned possibility is therefore especially advantageous 
since first the tube ingot end with the thickened wall which serves as a 
support is rolled by the mandrel rod and the end of the rolling process, 
and thereby a separation of the tube ingot end in the region of the 
diagonal roll stand is avoided. 
Furthermore, it is advantageous when the rear tube ingot end is prevented 
by a shoulder-like projection from a further displacement on the mandrel 
rod against the roll direction over the rear end of the constriction. This 
ensures a reliable feed of the rolling product at the beginning of the 
rolling process and prevents an excessive displacement of the rolling 
product on the mandrel rod against the rolling direction. 
It is also an object of the present invention to provide a diagonal roll 
stand for performing the inventive method, with a mandrel rod which is 
held at an inlet side and is controllably axially displaceable during the 
rolling. Moreover, it is immaterial what is the design of the diagonal 
rolling stand. In accordance with the present invention, the mandrel rod 
of the diagonal roll stand is provided in the region of its rear 
longitudinal portion as considered in the rolling direction, with a 
constriction for receiving the rolling product and therefore for rolling a 
tube ingot end with a thickened wall. It is recommended to select the 
diameter of the constriction so that with the same position of the rolls 
and in some cases of the guiding means, the roll ingot end obtains such a 
thickened wall and thereby such a sufficient support that no 
disadvantageous funnel-shaped expansion of the tube ingot end occurs. The 
thicker the wall of the tube ingot end, the lower is the tendency for 
expansion. On the other hand, for the reasons of efficiency the low 
thickening of the tube ingot end must be selected as small as possible and 
the diameter of the constriction must be selected as great as possible, so 
that the wall thickness is sufficient for preventing a significant 
expansion. 
The mandrel rod in accordance with the present invention can be provided 
with a conical longitudinal portion in the region of each front 
transition, as considered in the rolling direction, between the 
constriction and the main parts of the mandrel rod. Such a conical 
longitudinal portion of the mandrel rod at this location can be used for 
expanding the tube ingot end with its inwardly directed wall thickening so 
that it can be easily stripped over the main part of the mandrel rod. For 
expansion, in many cases it is sufficient to use the pulling back force of 
the mandrel rod relative to the tube ingot which is retained always with 
corresponding means. A ring-shaped bead with a substantially greater outer 
diameter of the conically shaped front transition to the main part of the 
mandrel rod provides for somewhat greater expansion so that a stretching 
of the mandrel rod during the pulling back and stripping of the tube ingot 
can be avoided. 
In accordance with a further feature of the present invention, the mandrel 
rod in the region of its front transition between the constriction and the 
main part of the mandrel rod, is provided with a small, preferably 
partition-like rim of a greater diameter than the main part of the mandrel 
rod. With such a partition-like rim, it is possible to provide during 
rolling of the wall of the tube ingot a notch at a location shortly before 
the tube ingot end with the thickened wall in a peripheral direction, so 
that this notch leads to breaking of the tube ingot end with the thickened 
wall from the main part of the tube ingot when the mandrel rod is pulled 
back against the holding force of a subsequent device acting on the tube 
ingot, for example a subsequently arranged length reducing roll train. The 
short tube ingot end which remains on the mandrel rod can be removed by a 
stripper or in another manner from the mandrel rod before it is inserted 
into the next tube ingot. 
It is advantageous when a retractable and expansible stripping element is 
provided at the outlet end behind the rolls in the roll line. This however 
can be dispensed with when a conical longitudinal portion between the 
constriction and the main part of the mandrel rod can cooperate by a 
longitudinal displacement of the mandrel rod with the rolls in particular 
the round zones of the rolls, and in this way the tube ingot end with the 
thickened wall can be rolled at the end of the rolling process and the 
forwardly moving tube ingot longitudinal portion is engaged by a 
subsequently arranged device. 
Then the mandrel rod at the rear end of the constriction as considered in 
the rolling direction is provided with a shoulder-like projection, it is 
recommended to select its outer diameter greater than the inner diameter 
of the tube ingot. In accordance with a further embodiment of the 
invention, the outer diameter of the shoulder-like projection can be 
greater than the inscribed circle of the caliber opening. The latter is 
possible since the mandrel rod is not guided with its rear end and the 
shoulder-like projection provided on it through the caliber opening. At 
the beginning of the rolling process, the shoulder-like projection ensures 
that the tube ingot is reliably moved into the caliber opening by the 
receiving table when the inner diameter of the inserted tube ingot before 
the rolling is substantially greater than the outer diameter of the 
mandrel rod. The tube ingot can be always moved only to the shoulder 
shaped projection on the mandrel rod, and then the tube ingot is 
positively guided by the axially driven mandrel rod into the caliber 
opening. 
When during insertion of the tube ingot into the caliber opening, the tube 
ingot end abuts against the shoulder shaped projection of the mandrel rod, 
the mandrel rod during the rolling process passes through the caliber 
opening with acceleration because of the feeding action of the rolls which 
acts through the rolling product also on the mandrel rod in the region of 
the caliber opening in the rolling direction. This accelerated passage 
ends when the tube ingot end abuts against the shoulder shaped projection 
of the mandrel rod. The rolls try to displace the mandrel rod in the 
rolling direction through the rolling product relative to the tube ingot 
end, which however can no longer be performed since the mandrel rod is 
supported through its shoulder shaped projection at the tube ingot end 
which is located before the caliber opening. Only together with the 
advancement of the tube ingot end, the mandrel rod can move then and so 
further in the rolling direction before a predetermined fixed end position 
shortly before the rolls, without contacting the shoulder shaped 
projection of the rolls. In this position of the mandrel rod which is 
fixedly held in the axial direction, the rear tube ingot end which is 
rolled in the constriction and therefore wall-thickened can be rolled out 
of the constriction through the conical longitudinal portion at the front 
transition between the constriction and the main part of the mandrel rod, 
and in particular by cooperation of the round zones of the rolls, with the 
conical longitudinal portion of the mandrel rod. The roll tube end is 
released from the shoulder shaped projection and rolled through as the 
front longitudinal portion of the tube ingot through the caliber opening. 
When the tube ingot is engaged at the outlet end for example by a 
subsequent device for further machining, the mandrel rod can be pulled 
back to the inlet side and is available for insertion into the next tube 
ingot or into the next hollow block, and in some cases after a cooling and 
lubricating step at the inlet side. 
The above described operation allows a fast and continuous rolling product 
sequence and thereby a high productivity, and also a direct arrangement of 
the devices for further machining of the tube ingot at a short distance 
after the diagonal roll stand, which is not space consuming but instead 
saves an intermediate warming thereby investment and operational costs 
required for it. This is true first of all for the combination of a 
planetary diagonal roll stand and a length reducing roll train or a size 
roll train. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows schematically a diagonal roll stand 1 with two rolls, in which 
of course, another number and type of rolls can be utilized as well. 
Moreover, guiding elements such as guiding shoes, guiding discs and 
similar elements can be provided as well known in diagonal roll stands. 
The diagonal roll stand 1 can also be formed as a planetary diagonal roll 
stand. The drive of the roll stand is not shown since it can be of any 
type. A hollow block or a tube ingot 4 is supplied by a transverse 
transporting means 3 into the roll line and in particular at an inlet side 
between the diagonal roll stand 1 and the mandrel rod 5 which is pulled 
back from the diagonal roll stand 1. The mandrel rod 5 and a coupled shaft 
rod 6 which extends it can be controllably displaced in an axial direction 
by means of a motor 7 inside a guide 8 by a mandrel rod abutment 9. 
FIG. 2 shows the diagonal roll stand 1 of FIG. 1 but with the forwardly 
displaced mandrel rod 5, the shaft rod 6 and the mandrel rod abutment 9. 
The tube ingot 4 is already rolled and extends at the outlet side from the 
diagonal roll stand 1. The mandrel rod 5 in a further course of the 
rolling process is moved substantially in the rolling direction X and then 
after ending of the rolling process is pulled back to the inlet side to 
the position shown in FIG. 1. 
FIG. 3 shows the mandrel rod 3 on an enlarged scale and in particular its 
rear longitudinal portion as considered in the rolling direction X, 
shortly before the not shown shaft rod 5. The mandrel rod 5 has in this 
region a constriction 10. In order to show that other types of diagonal 
roll stands 1 can be utilized, FIG. 3 shows in contrast to FIGS. 1 and 2 a 
roll 2 which is substantially frustoconical. Since two or more rolls 2 
distributed over the periphery of the tube ingot 4 can be provided, and 
the other rolls 2 are located not in the shown section plane, the other 
rolls 2 are not shown in FIG. 3. A reduction zone 2a of the roll 2 reduces 
the outer diameter of the tube ingot 4 and a smoothing zone 2b determines 
together with the outer surface 15 of the mandrel rod 5 the new wall 
thickness of the tube ingot 4. The inner and outer surfaces of the tube 
ingot 4 are therefore smoothened. A round zone 2c imparts to the tube 
ingot 4 a shape which is circular in the cross-section. In FIG. 2 the rear 
tube ingot end 4a is rolled and the rolling product at this location is 
rolled in the constriction 10 of the mandrel rod 5 when with the same roll 
position it obtains a substantially thicker wall than the preceding 
longitudinal portion of the tube ingot 4. Since the mandrel rod 5 in a 
further course of the rolling process is moved only a piece in the rolling 
direction X through the caliber opening formed by the rolls 2, a 
constriction 10 with the rear tube ingot end 4a' and its thickened wall 
moves to the outer side of the diagonal roll stand 1 and therefore during 
the whole rolling process can support the forwardly arranged longitudinal 
portion of the tube ingot 4 with a thinner wall, which prevents a 
funnel-shaped radial expansion. 
FIG. 4 shows how the rear tube ingot end 4a looks after ending of the 
rolling process. It is located at the outlet side of the diagonal roll 
stand 1 behind the rolls 2. A longitudinal portion 11 is located between 
the constriction 10 and the main part of the mandrel rod 5 and is formed 
conically. When the mandrel rod 5 driven by the motor 7 in FIG. 1 is 
pulled back and therefore the tube ingot 4 is fixedly held at the outlet 
side, the conical longitudinal portion 11 expands the rear tube ingot end 
4a so that the tube ingot 4 can be stripped from the mandrel rod 5. 
FIGS. 5-8 show possibilities through wear of the outer surface 15 of the 
mandrel rod 5 by the rear tube ingot end 4a can be avoided. As can be seen 
from FIG. 4, in this embodiment example a conical longitudinal portion 11 
is provided in the region of the front transition as considered in the 
rolling direction, between the constriction and the main part of the 
mandrel rod 5. A cutter-like rim 12 is located in the region of this 
longitudinal portion 11 and has a greater diameter than the main part of 
the mandrel rod 5. During pressing of the cutter-like rim 12 through the 
caliber opening a notch is rolled in the tube ingot 4 shortly before the 
rear tube ingot end 4a, so that the wall thickness at this location of the 
tube ingot 4 is very thin. With corresponding dimensioning of the 
cutter-like rim 12 relative to the caliber opening formed by the rolls 2, 
the notch 13 can be so deep that when a sufficient pulling load occurs in 
this region for example due to fixing or further movement of the tube 
ingot 4 and pulling back of the mandrel rod 5, the rear tube ingot end 4a 
is torn off as shown in FIG. 6. The tube ingot 4 can be then easily 
separated from the mandrel rod 5, while the rear tube ingot end 4a is 
first retained on the mandrel rod 5 and at a later time is separated from 
it. This can be performed by suitable and known means, such as for example 
a stripping element either at the inlet side or at the outlet side of the 
diagonal roll stand 1. 
In contrast to FIG. 6, the notch 13 in FIG. 7 is less deep so that the rear 
tube ingot end 4a is not torn off when the tube ingot 4 is pulled from the 
mandrel rod 5 for example by a subsequently arranged device for further 
machining as considered in the rolling direction X. The inner tube ingot 
end 4a is however expanded by the conical longitudinal portion 11, 
obtaining by the rounded rim 12a a greater inner diameter than the outer 
diameter of the main part of the mandrel rod 5 (FIG. 8), so that its outer 
surface 15 during stripping of the tube ingot 4 is fined. 
While FIG. 3 shows rolling of the rolling product in the constriction 10 of 
the mandrel rod 5 and thereby the formation of the thickened rear tube 
ingot end 4a, FIG. 9 shows the increase of the inner diameter of the rear 
tube ingot end 4a at the end of the rolling process, so as to facilitate 
stripping of the tube ingot 4 from the mandrel rod 5 and to avoid damaging 
of the outer surface 15 of the mandrel rod. The mandrel rod 5 which in its 
position in which it is displaced the farthest and is firmly held at the 
inlet side via the mandrel rod 5 and the mandrel rod abutment 9 with the 
stopped motor 7. This can be recognized from the shoulder-like projection 
14, which the mandrel rod 5 has at its rear end of the constriction 10 as 
considered in the rolling direction X- The outer diameter of the shoulder 
shaped projection 14 is substantially greater than the inner diameter of 
the hollow block or the tube ingot 4, so that its rear end can be 
displaced at any time points farther on the mandrel rod 5. 
Due to the greater outer diameter of the shoulder shaped projection 14, the 
mandrel rod 5 must be held in the shown position so that the shoulder 
shaped projection 14 does not contact the rolls 2 as shown in FIG. 9. It 
can be clearly recognized from the drawing that the rear tube ingot end 4a 
with its connecting piece 4b obtains due to the unchanged position of the 
rolls 2, in particular their reduction and smoothing zones 2a and 2b, 
substantially the same outer diameter as the front longitudinal portion of 
the tube ingot 4. The thicker wall on the connecting piece 4b of the rear 
tube ingot end 4a is thinner and the inner surface of the tube ingot 4 is 
released from the mandrel rod 5. The situation during rolling of the rear 
tube ingot end 4a is shown with thick solid lines, and the constriction 10 
of the mandrel rod 5 is located completely in the region of the roll 2. 
The produced substantially thickened rear tube ingot end 4a is released 
from the outer surface 15 of the mandrel rod 5, since the round zone 2c of 
the rolls 2 together with the conical longitudinal portion 11 of the 
mandrel rod 5 provide an expansion. 
Broken lines identify in FIG. 9 such situation which is produced during 
rolling of the greater part of the tube ingot 4. The constriction 10, the 
conical longitudinal portion 11, and the shoulder-like projection 14 are 
located not in the region of rolls 2, but instead at portion of the main 
part of the mandrel rod 5 and its outer surface 15. Since the outer 
diameter of the outer surface 15 is greater than that of the constriction 
10, a substantially smaller wall thickness of the tube ingot 4 is produced 
with unchanged position of the roll 2, whose inner surface is released in 
the front region from the outer surface 15 of the mandrel rod 5. This can 
also lead to a substantially greater outer diameter of the tube ingot 4 
relative to its wall-thickened rear tube ingot end 4a. 
The tube ingot can be held at an outlet side during pulling back of the 
mandrel rod, by a subsequently arranged device for a further machining of 
the tube ingot at the outlet side. The tube ingot end with the thickened 
wall is separated from the tube ingot after passing the caliber opening, 
and later the separated tube ingot end and the remaining tube ingot 
portion are removed from the mandrel rod. An expandable and retractable 
stripping member can be provided in a roll line behind the rolls at an 
outlet side. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
methods and constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
method of and roll stand for diagonal rolling of tubes, it is not intended 
to be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.