GB2178353A

GB2178353A - Rolling seamless tubes

Info

Publication number: GB2178353A
Application number: GB08616907A
Authority: GB
Inventors: Karlhans Staat
Original assignee: Kocks Technik GmbH and Co KG
Current assignee: Kocks Technik GmbH and Co KG
Priority date: 1985-07-12
Filing date: 1986-07-11
Publication date: 1987-02-11
Also published as: GB2178353B; SE8603091L; IT1235759B; GB8616907D0; DE3622678A1; SE8603091D0; IT8621103A0

Abstract

Tubular blooms 5 are rolled onto a mandrel rod 2 lying in their longitudinal bore and retained at the entry side. The mandrel rod has longitudinal sections 2a having different outer diameters and is displaced in the axial direction during the rolling process so that different outer diameters are located within the sizing pass as required. It is thus possible to change the internal diameter of the blooms 5 during rolling and to produce blooms having different internal diameters and wall thickness at various points along their length and also with constant wall-thickness to close tolerances. If known radial adjustment of the skew rolls 1 is also carried out during rolling, both the internal and the external diameters of the blooms can be changed within broad limits. <IMAGE>

Description

SPECIFICATION Rolling seamless tubes The invention relates to the transverse rolling of seamless tubular blanks, in which the seamless tubular blanks are rolled down by a mandrel rod lying in their longitudinal bore and held back at the entry end.

In a known method of this type (USA Patent Specification No. 2 006 336), a hollow block having a mandrel rod lying inside it is inserted into the sizing pass formed by rolls and is then rolled out by skew but substantially transversely operating rolls down from the mandrel rod into a tubular blank. The rear end section of the substantially cylindrical mandrel rod remote from the rolls is held back, so that the mandrel rod cannot pass through the sizing pass with the tubular blank being formed to the delivery end of the rolling stand. In this way, a tubular blank is produced with a substantially uniform wall thickness along its length.

Furthermore, a method of transverse rolling is known (German Patent Specification (Offenlegungsschrift) No. 33 09 797) in which the wall thickness can be altered over a short longitudinal section by means of radially adjusting the rolls by enlarging the outer diameter of the tubular blank.

These known methods produce either tubular blanks with uniform wall thickness or a wall thickening only through enlarging the outer diameter. The latter is, in practice, only suitable for the purpose set forth in German Offenlegungsschrift No. 33 09 797, but is otherwise useless. What are in demand, however, are tubular blanks having uniform outer diameters and having at first a uniform wall thickness to very close tolerances and, in the second place, an increase in wall thickness reflected by a reducing internal diameter.

This type of tubular blank cannot be produced using the known transverse rolling methods, such as the Assel or Diescher methods. This is due in the first place to an inability of the process to compensate for irregularities in the wall thickness in order to produce close tolerances and, in the second place, to the substantially cylindrical mandrel rod used, which is either moved through the sizing pass during rolling or which is held in a predetermined position from the entry side of the rolling stand.

Tubular blooms having close tolerances facilitate wall thickness compensation during finish-rolling and improve the quality of the finished tubes.

Tubes which only have an increased wall thickness at the two end sections but which are cylindrical on the outside are required, for example, for drill pipes in order, for example, to be able to tap threads. At present, this type of tube is produced by reheating and compressing the tube ends. Another method of dimensioning this type of tube comprises welding specially prepared short tube ends to conventionally manufactured tubes. Furthermore, in the case of tubes which have to be drawn, it is necessary that a tube end section which has a relatively thick wall be available for the tongs in order to be able to absorb and transmit the high tensile forces. Such a draw-fishing device is manufactured separately by cold or hot forming after transverse rolling. All these methods are unsatisfactory as they are complicated, time-consuming and uneconomic.

It is an object of the invention to provide a method and apparatus with which it is possible, during transverse rolling of seamless tubular blooms, to provide blooms which are uniform to close tolerances over their lengths or which have wall thicknesses which vary along their length with varying internal diameters, and, as may be required, uniform external diameters.

One aspect of the present invention is a method of transverse rolling seamless tubular blanks, in which a tubular blank is rolled over a mandrel rod lying in its longitudinal bore and held back at the entry end, and in which, in order to change its wall thickness, the tubular blank is rolled using a mandrel rod having a varying outer diameter and being displaced in the axial direction during rolling.

This enables a different outer diameter of the mandrel rod to be brought into the sizing pass during rolling. If this outer diameter is smaller than the previous one, the larger gap between the outer surface of the mandrel rod and the working surfaces of the rolls results in a larger wall thickness, as long as the section of mandrel rod having this outer diameter is located within the sizing pass. If the mandrel rod is again longitudinally displaced, and hence a different longitudinal section of the mandrel rod having a different outer diameter is brought into the sizing pass, the wall thickness of the tube blank is again changed. In this way, irregularities in wall thickness can be equalized down to the range of very close tolerances or the most diverse wall thicknesses can be rolled in the region of different longitudinal sections.In both cases, this takes place with the external diameter remaining constant and with the internal diameter of the bloom varying.

Given a suitable mandrel rod design lubrication, friction on the surface of the mandrel rod during transverse rolling is thus relatively low and it is possible to displace the mandrel rod in the longitudinal direction during the rolling process and so alter the external diameter of the mandrel rod in the region of the deformation zone, which in turn alters the internal diameter of the tubular bloom and therewith the wall thickness, with the external diameter remaining constant.

It is advantageous if, furthermore, the tubular blanks are rolled in a known manner with radially displaceable rolls. Thus it is possible not only to alter the inner diamter of the tubes during rolling in the region of different longitudinal sections, but also the outer diameter too. Hence tubular blanks can be produced having very different diameters at various points, as appropriate and suitable.

Apparatus for transverse rolling seamless tubular blanks having a mandrel rod projecting through the sizing pass from the entry end and whose trailing end section remote from the sizing pass is held in the axial direction are known, for example, as Assel, Diescher or skew-rolling stands.

In accordance with another aspect of the present invention, apparatus for rolling seamless tubular blanks comprises a sizing pass defined by rolls and a mandrel rod projecting through the sizing pass from the entry end, the rear end section of the mandrel rod remote from the sizing pass being held in the axial direction, and the mandrel rod being infinitely displaceable in the longitudinal direction during rolling and having an outer diameter which varies at different points.

Axial displacement of the mandrel rod on insertion of a new hollow block is know, but the infinite displacement referred to here along a relatively short path during the actual rolling process is not. On displacement, other mandrel rod diameters enter the cross-sectional plane of the sizing pass so that the external diameter of the inner tool effective in the sizing pass is changed, and hence also the internal diameter of the tubular blank being formed. If, at the same time, the position of the rolls is not changed, the wall thickness of the tubular blanks change accordingly. In the case of this type of transverse rolling stand, it is, however, usually possible to displace the rolls radially in order to alter also the outer diameter of the tubular blank being formed, which also correspondingly applies to any existing guides or additional discs.If simultaneous use is made of this and of the axial displacement of the mandrel rod, a tubular blank of almost any desired cross section can be rolled within broad limits, wherein the cross section can be changed as often as required along the length of the tubular blank.

In one advantageous embodiment of the invention, the mandrel rod has at least one conical longitudinal section. With one such longitudinal section, the inner diameter effective in the sizing pass, and hence also the internal diameter being formed in the tubular blank, can be infinitely altered by only a small axial displacement of the mandrel rod.

Particularly in the case of weak conicity of the mandrel rod, the internal diameter of the tubular bloom and hence, in the case of fixed rolls, the wall thickness can be extremely precisely adjusted by axial displacement of the mandrel rod, so that changes in wall thickness can be compensated for and close wall tolerances achieved.

In certain cases, it is recommended that the middle longitudinal section of the rolls used for smoothing and calibrating have a conical shape corresponding to the conicity of the associated longitudinal section of the mandrel rod. Corresponding conicity is to be understood in this case as meaning that the slopes of the surface of the mandrel rod and of the abovementioned longitudinal section of of the rolls are the same, so that when viewed in the longitudinal section, they are parallel to one another. This prevents unwanted spiral-shaped tracks on the surface of the tubular bloom.

It is important that the desired longitudinal position of the mandrel rod is accurately adjusted or maintained in the longitudinal direction. This can be done by means of longitudinal measurement, preferably in the region of the trailing end section. As a result of the mechanical and thermal stresses on the mandrel rod and in view of its relatively large length, it must be assumed that changes in the length of the mandrel rod will occur during rolling so that, when rolling with a conical longitudinal section of the mandrel rod, unintended changes to the internal diameter can occur in the tubular blank being formed because this change in length causes the conical longitudinal section to be displaced within the sizing pass. This would, however, lead to a change in the tensile or compressive stress on the mandrel rod in the axial direction.It is thus recommended to maintain the position of the mandrel rod by means of measuring tension or compression. It is advisable to carry out this measurement of tension or compression at the rear end of the mandrel rod using known means.

If it is desired to keep the wall thickness of the tubular bloom within close tolerances by axial displacement of a conical longitudinal section of the mandrel rod, it is advantageous to adjust the axial position of the mandrel rod in dependence on the measured wall thickness of the rolled tubular bloom.

Furthermore, it is possible to adjust the axial position of the mandrel rod in dependence on the measured rolling pressure acting radially on the rolls.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 3 show half of a sizing pass in longitudinal section with the mandrel rod in various longitudinal positions during rolling; Figures 4 and 5 show half a sizing pass in longitudinal section during rolling with a different mandrel rod shape; Figures 6 to 14 show various tube blanks manufactured according to the invention; and Figure 15 is a plan view of the apparatus according to the invention.

Figure 1 shows part of a roll 1 belonging to a skew rolling stand having guide discs. For the purposes of simplification, guide discs and the second identical roll 1 are not shown. The middle longitudinal region 1 a of each roll 1 and the guide discs together form the actual sizing pass with the narrowest run-through cross section. A mandrel rod 2 projects into this sizing pass and has conically shaped sharply tapering front end section 3. The mandrel rod 2 is infinitely displaceable in the longitudinal direction according to the arrow X during rolling. A hollow block 4 is rolled and thereby is shaped into a tubular blank 5 beyond the sizing pass.

Figures 2 and 3 show the same sizing pass as Figure 1, but at different times in the course of a rolling operation. In Figure 1, the leading end section of the tube blank 5 is being produced with a relatively small inner diameter and a relatively thick wall. Immediately after rolling the leading end of the tube blank, the mandrel rod 2 is advanced in the direction of rolling designated Y, so that the longitudinal section 2a of the mandrel rod 2 is located in the region of the sizing pass. The tube blank 5 is thus given a larger diameter and a smaller wall thickness, as the position of the rolls 1 is not changed in this embodiment. Fig. 3 shows that, during rolling of the trailing end section of the tube blank 5, the mandrel rod 2 has been retracted into the position according to Fig. 1, so that the trailing end section of the tube blank 5 is also given a greater wall thickness and a smaller inner diameter. The result is a tube blank as shown in Figure 6. The reduced inner diameter can be varied by displacing the mandrel rod, if it is essentially in the position shown in Figs. 1 and 3, by a relatively small amount either in or against the direction of rolling.

If the longitudinal section 2a of the mandrel rod 2 is given a slightly conical shape and the longitudinal section la of the rolls 1 is correspondingly slightly conical, so that their surfaces are parallel to one another as seen in the longitudinal section in Figure 2, deviations in the wall thickness of the hollow block 4 or the tubular bloom 5 being produced can be compensated for by suitable axial displacement of the mandrel rod 2.

Figures 4 and 5 correspond essentially to Figures 1 to 3, but show a mandrel rod 2 of a different form. It has not just one, but two sharply tapered conical longitudinal sections 3 and 6 as well as an additional cylindrical or slightly tapering longitudinal section 7 with a smaller outer diameter than the remaining length 7a of the mandrel rod 2. In Figure 4, the mandrel rod 2 has been moved into a position in which the longitudinal section 7 having the smaller diameter is in the region of the sizing pass and functions therein as an effective internal tool. The tube blank 5 is given a cylindrical internal diameter which, due to the usual expansion, is somewhat larger that the outer diameter of the longitudinal section 7 of the mandrel rod 2.Figure 5 shows that the tube blank 5 can also be rolled with the longitudinal section 7a of the mandrel rod 2 having the largest diameter by advancing the mandrel rod in the direction of rolling Y until this section of the mandrel rod 2 is in the region of the sizing pass. This can also take place during rolling, so that the inner diameter varies for different longitudinal sections of the tube blank 5. Of course, it is also possible to displace the mandrel rod 2 in such a way that one of the conical longitudinal sections 3 or 6 is located in the region of the sizing pass, so that tubular blooms having numerous different internal diameters can be rolled with the mandrel rod 2 shown in Figures 4 and 5. If the radial adjustment of the rolls 1 marked Z is also used, the outer diameter of the tube blank 5 can be altered too, which can also take place, if required, during rolling.

It is thus possible to manufacture extremely varied tubular blooms 5 which can be given very different internal and external diameters along their lengths.

Some of the numerous possibilities are shown in Figures 6 to 14. They can serve a variety of purposes which cannot all be listed here. For example, the tubular blooms 5 in Figures 8 and 9 are suitable for having internal threads tapped into one or both end sections and the tube blank in Figure 11 is suitable for the manufacture of conical tubes. Figure 12 shows a tube blank which is suitable above all for drawing, as it has a strong end section having a smaller diameter for grasping by the tongs. Whereas the tube blanks in Figures 6 to 11 have been rolled without radial adjustment of the rolls 1, in the case of rolling the tube blanks 5 in Figures 12 to 14, it is necessary to adjust the rolls 1 in the radial direction.

Figure 15 shows a rotating hearth furnace 10 which is charged by way of a charging device 12 with blocks (not shown) of, for example, 500 kg and approximately 3 metres long. Heated to rolling temperature, these blocks leave the rotating hearth furnace 10 by way of a roller table 13, pass through a descaling device 14 and, by way of a transverse conveyor 15, into a reception channel 16 of a skew-rolling stand 17, where each block is pierced to make a hollow block 4 in accordance with the known skew-rolling method.

The hollow block 4 produced in this way passes, after the mandrel rod has been withdrawn, by way of a further transverse conveyor 1 8 onto a reception table 19. A pair of initially stationary drive rolls 20 is moved in the radial direction against the hollow block 4 and retains it, while a mandrel rod 2, which may be internally cooled, is pushed into the hollow block 4 by means of a second pair of drive rolls 21. The mandrel rod 2 is inserted until its leading end projects into the pass of a second skew-rolling stand 22. This skewrolling stand may be a conventional one, such as an Assel or Diescher skew rolling stand. Using the first drive roll pair 20, which is now running, the hollow block 4 is pushed into the skew-rolling stand 22, with the mandrel rod 2 being held at the entry side.In the skew-rolling stand 22 a hollow block 4 approximately, for example, 8 metres long is rolled out into, for example, a tubular bloom 5 20 metres in length, wherein the tubular bloom 5 is rolled down by the mandrel rod 2 which is still held at the entry side.

Following rolling in the skew-rolling stand 22, the leading end section of the tubular bloom 4 produced in this way moves into a finish-rolling line 23 connected at a sufficient distance downstream thereof, which is, for example, in the form of a stretch-reducing rolling line. Using a separating device 24, the finished tube, which can be over 100 metres long depending on the finished diameter, is divided into sections as required before passing by way of a roller table 25 to a cooling bed 26.

A wall thickness measuring device 27 is disposed beyond the skew-rolling stand 22 and controls the drive of the second drive roll pair 21 by way of a computer 28. The mandrel rod 2 is displaced in the axial direction or retained by these drive rolls 21.

Claims

1. A method of transverse rolling seamless tubular blanks, in which a tubular blank is rolled over a mandrel rod lying in its longitudinal bore and held back at the entry end, and in which, in order to change its wall thickness, the tubular blank is rolled using a mandrel rod having a varying outer diameter and being displaced in the axial direction during rolling.

2. A method as claimed in claim 1, in which the tubular blank is rolled using radially adjustable transverse rolls.

3. A method as claimed in claim 1 or 2, in which the longitudinal position of the mandrel rod is adjusted by means of measurement of length.

4. A method as claimed in claim 1 or 2, in which the longitudinal position of the mandrel rod is adjusted by means of measurement of tension or compression.

5. Apparatus for transverse rolling seamless tubular blanks comprising a sizing pass defined by rolls and a mandrel rod projecting through the sizing pass from the entry end, the rear end section of the mandrel rod remote from the sizing pass being held in the axial direction, and the mandrel rod being infinitely displaceable in the longitudinal direction during rolling and having an outer diameter which varies at different points.

6. Apparatus as claimed in claim 5, in which the mandrel rod has at least one conical longitudinal section.

7. Apparatus as claimed in claim 6, in which the middle longitudinal section of the rolls used for smoothing and calibrating is of conical shape corresponding to the conicity of the associated longitudinal section of the mandrel rod.

8. Apparatus as claimed in claim 6 or 7, having means for measuring the wall thickness of the rolled tubular bloom and for adjusting the axial position of the mandrel rod accordingly.

9. Apparatus as claimed in claim 6 or 7, having means for measuring the rolling pressure acting radially on the rolls and for adjusting the axial position of the mandrel rod accordingly.

10. Apparatus as claimed in claim 5, 6 or 7, in which a device is provided for measuring the length of the mandrel rod and for adjusting its support longitudinally in accordance therewith to maintain the leading end section of the mandrel rod in a constant position at the sizing pass.

11. Apparatus as claimed in claim 5, 6 or 7, in which a device is provided for measuring the tension or compression in the mandrel rod to provide an estimate of the actual length thereof and for adjusting its support longitudinally in accordance with the measured tension or compression to maintain the leading end section of the mandrel rod in a substantially constant position at the sizing pass.

12. A method of transverse rolling seamless tubes substantially as herein described with reference to the accompanying drawings.

1 3. Apparatus for transverse rolling seamless tubes, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.