EP1764167B1 - Method and rolling mill for manufacturing a seamless tube - Google Patents

Abstract

Production of seamless pipes comprises forming a hollow block (2) using a perforated roll system (1). A mandrel bar (4) is inserted into this, after which it is passed through a mandrel mill (3) where it is formed into a pipe (5). This is then passed directly to a reducing mill (6) where it is calibrated. The mandrel bar is removed before the pipe before entering the mill. An independent claim is included for a rolling mill system for use in the production method.

Description

The invention relates to a method for producing a seamless tube, in which first material is formed in a piercing mill to form a hollow block, in which then in a continuous rolling of the recorded on a mandrel hollow block is rolled into a billet and wherein subsequently after the removal of the mandrel bar the billet is calibrated in a sizing mill to the desired outer diameter, the billet is moved directly from the continuous rolling mill in the sizing mill without the interposition of another rolling mill, wherein the mandrel bar is removed from the billet before the entry of the billet in the sizing mill. Furthermore, the invention relates to a rolling mill for producing a seamless tube.

Such working according to the classic free-floating Konti rolling mill mills are by the JP 58119416 A and DE 24 09 870 A1 have become known and require no extractor mill. It is rather threaded in the inlet of the continuous rolling mill in the hollow block to be rolled a mandrel whose length corresponds approximately to the maximum length of the produced billet. The calibration of the rolling stands is designed so that a match between the billet and mandrel is maintained, which is evenly distributed over the circumference in the last approximately calibrated framework. This game is necessary in order to pull the mandrel out of the bowl after rolling.

Today, seamless tubes are often produced in the so-called continuous roll process (continuous tube rolling process), as is known from US Pat EP 0 601 932 known. The previously known method is in FIG. 1 shown. The raw material used is usually rolled round steel, mainly as round casting up to 350 millimeters Diameter, which is brought in lengths up to 5 meters in a rotary hearth furnace 12 to a rolling temperature of about 1280 ° C. Subsequently, the solid block is punched on a piercing mill 1 to form a thin-walled hollow block 2. In this case, a cross-rolling mill is usually used as the piercing mill. The rollers are inclined to achieve a sufficient throughput by an angle between 10 ° and 12 ° to the rolling stock. The hollow block 2 produced in the piercing mill 1 is then rolled in the same heat in the continuous rolling mill 3 via a mandrel bar 4 to the billet 5. It is achieved up to a fourfold extension, ie it comes to a reduction in cross section up to 75%. The continuous rolling mill is also referred to as MPM (Multistand Plug Mill).

The continuous rolling mill 3 consists mostly of six to nine closely spaced rolling stands, of which three are provided with the reference numerals 9, 10 and 11. The individual rolling stands are each rotated against each other, for example by 90 °. The roller circumferential speeds are coordinated according to the cross-sectional decreases, so that between the stands no significant tensile or compressive forces act on the rolling stock.

Before the start of the rolling process in the continuous rolling mill 3, the mandrel rod 4 is inserted or threaded into the hollow block 2 with the retainer arranged on the inlet side. After reaching a certain position hollow block 2 and mandrel 4 are then pushed into the continuous rolling mill 3. The rolling stock is detected by the rollers and rolled by the rolling from stand to frame smaller rolling caliber on the mandrel 4. The mandrel 4 is moved by means of a retainer at a constant speed.
If the intended for the continuous rolling 3 degree of deformation for the billet 5 is reached, the Luppenspitze runs into a continuous rolling mill 13 downstream of the continuous rolling mill 3 a. In this, the removal of the mandrel bar 4 from the finished doll so far 5. By an oval calibration of most Duo-rolls used here can be achieved a game between the mandrel 4 and the rolling stock, which is evenly distributed in the last round caliber around the circumference, so that the mandrel bar 4 can be solved more easily. Then, by means of the retainer, the withdrawal of the mandrel rod into the starting position, an ejection of the rod and the insertion of a new rod. Before a rod can be used again, it must be cooled so that a mandrel bar circuit is required. Usually, about five to ten mandrel bars of the same dimensions are in circulation.

After removal of the mandrel bar 4 from the rolled billet 5, the billet 5 is conveyed to a furnace 7 where the billet is given a uniform temperature before being rolled in a further downstream sizing mill 6 to the final, desired outside diameter.

The previously known solutions are preferably designed for high annual capacities in pipe production and go hand in hand with high investment costs. Therefore, the known systems are from an economic point of view bad for low capacity.

A disadvantage of this known method that a relatively large investment is required. There must be a sufficient distance between the last MPM mill stand and the first extractor rolling stand, which results from the need to extract the billet from the mandrel bar with the extractor mill. The extractor mill represents a hitherto necessary additional forming unit. Furthermore, a corresponding tool storage (mandrel bars) for the required rod cycle is required, which also requires a correspondingly complex monitoring and maintenance of the tools.
For bar cooling, an extensive mandrel bar cooling system with several cooling stations and transport facilities over the rack bed of the retainer is necessary. Overall, there is a large and therefore expensive rod park. Particularly disadvantageous are thus the elaborate rod park and the high effort that must be operated in connection with the extractor mill. The disadvantages mentioned are particularly significant when only small annual production quantities of seamless pipes are to be produced.

The invention is therefore based on the object to provide a method for producing seamless pipes and an associated rolling mill, with or with which the mentioned disadvantages are avoided. In particular, a reduction of the rod park and thus a more cost-effective production of seamless pipes are possible, especially in plants with relatively low production capacity. Furthermore, a simpler and thus cheaper construction of the rolling mill is to be made possible.

The solution of this problem by the invention according to the method is characterized in that the introduction of the billet without the interposition of another rolling mill, in particular an extraction mill, directly from the continuous rolling mill, optionally through an oven, into the sizing mill, wherein before entering the billet in the sizer Mandrel is removed from the billet, further provided that the mandrel is controlled during rolling in the continuous rolling mill moves against the rolling direction, so that it is at least largely, preferably completely, moved out of the billet after completion of the rolling process of the billet in the continuous rolling mill.

According to an alternative possible approach, the mandrel is kept largely stationary during rolling in Kontiwalzwerk so that the billet is at least largely, preferably completely, pushed over the mandrel bar after completion of the rolling process of the billet in the continuous rolling mill.

It is preferably provided that the mandrel is moved during rolling in the continuous rolling with a small movement in the rolling direction.

For all solutions, preferably the mandrel bar is cooled during the rolling process in the continuous rolling mill.

The rolling mill for producing a seamless tube has a piercing mill, with the starting material can be converted into a hollow block, also a continuous rolling mill, in which the recorded on a mandrel hollow block can be rolled into a billet, and finally a sizing mill, on the after Removal of the mandrel bar from the billet this can be calibrated to the desired outer diameter, with the sizing mill followed without the interposition of another rolling mill, in the rolling direction of the continuous rolling mill. According to the invention, it is provided that the movement means are suitable for the oscillating movement of the mandrel bar in the rolling direction.

To compensate for temperature irregularities in the billet, a furnace, in particular an induction furnace, is advantageously arranged between the continuous rolling mill and the sizing mill for tempering the billet. Alternatively, a chain cross transport can be used to compensate for the lupine temperature over the circumference and length.

Furthermore, movement means can be provided, with which the mandrel rod can be moved during rolling in the continuous rolling mill in or counter to the rolling direction.

Furthermore, a retaining device can be arranged between the continuous rolling mill and the sizing mill with which the billet can be retained against the rolling direction.

The said movement means may be suitable for oscillating movement of the mandrel bar in the rolling direction.

It is particularly advantageous if there are coolant with which the mandrel rod can be cooled. The cooling means may comprise line elements with which a cooling medium can be conducted into an inner bore extending over a predetermined axial extension in the mandrel rod.

The outer surface of the mandrel bar can be provided with a layer of wear-resistant material, in particular of ceramic material.

Furthermore, it is preferably provided that the individual rolling stands of the continuous rolling mill are designed as 3-roll stands.

Finally, the mandrel bar may have a slightly conical shape over its axial course, which favors the withdrawal of the mandrel bar from the finished billet.

By the proposed measures, the rod park can be minimized, with a reduction of the rod park can be achieved by at least two-thirds. Furthermore, significantly lower investment costs compared to conventional methods are needed. The extractor mill can be omitted. As a result, a hall length of about 10 meters can be saved. Even a mandrel bar cycle can be omitted. Another advantage is the associated reduced personnel costs due to the omission of an aggregate. Furthermore, it is due to less disturbances of the rolling mill. It is finally an improved monitoring of the wall thickness tolerances of the tube and the tube quality possible because only one mandrel per dimension must be checked for wear and surface defects.

Fig. 1

schematisch die Seitenansicht eines Walzwerks zur Herstellung nachtloser Rohre gemäß dem Stand der Technik;

Fig. 2

die zu Fig. 1 analoge Darstellung eines Walzwerks gemäß der Erfindung;

Fig. 3

für vier aufeinander folgende Zeitpunkte die Lage der Dornstange, des Hohlblocks bzw. der Luppe beim Walzen in einem Kontiwalzwerk nach einer ersten Ausgestaltung der Erfindung;

Fig. 4

für drei aufeinander folgende Zeitpunkte die Lage der Dornstange, des Hohlblocks bzw. der Luppe beim Walzen in einem Kontiwalzwerk nach einer zweiten Ausgestaltung der Erfindung; und

Fig. 5

für drei aufeinander folgende Zeitpunkte die Lage der Dornstange, des Hohlblocks bzw. der Luppe beim Walzen in einem Kontiwalzwerk nach einer dritten Ausgestaltung der Erfindung.

In the drawings, embodiments of the invention are shown. Show it:

Fig. 1

schematically the side view of a rolling mill for producing no-dumbbells according to the prior art;

Fig. 2

the too Fig. 1 analogous representation of a rolling mill according to the invention;

Fig. 3

for four consecutive times the position of the mandrel bar, the hollow block or the billet during rolling in a Konti-rolling mill according to a first embodiment of the invention;

Fig. 4

for three consecutive times the position of the mandrel, the hollow block or the billet during rolling in a continuous rolling mill according to a second embodiment of the invention; and

Fig. 5

for three successive times the position of the mandrel, the hollow block or the billet during rolling in a continuous rolling mill according to a third embodiment of the invention.

In Fig. 1 an embodiment is shown as known in the art; Reference is made to the explanations made at the outset. Opposite shows Fig. 2 the embodiment according to the invention, wherein otherwise the constant elements of the rolling mill are constructed accordingly, so that in this respect reference is made to the above explanations.

The difference between the solution according to the prior art and the invention is that in the rolling mill according to the invention no extractor rolling mill (see position 13 in FIG Fig. 1 ) is provided more. The rolled in the continuous rolling mill 3 billet 5 passes directly through the trained as Induktionserwärmvorrichtung furnace 7 in the sizing mill 6, in which the tube is rolled to the final desired outer diameter.

A first possibility of rolling the hollow block 2 to the billet 5 in the continuous rolling mill 3 is in Fig. 3 schematically indicated, wherein the position of the hollow block 2, the mandrel 4 and the billet 5 is shown at four consecutive times, namely at an initial time t _A , at a later time t ₁ , at an even later time t ₂ and the still later end time t _E.

At the initial time t _A , the mandrel bar 4 is inserted into the hollow block 2, wherein the tip of the mandrel bar 4 as viewed in the rolling direction W is located within the continuous rolling mill 3. The hollow block is still in front of the roll stand 9. Then the mandrel 4 together with the hollow block 2 is pushed in the rolling direction W in the continuous rolling mill 3. The mandrel 4 thereby moves preferably at a constant speed v _mandrel in the rolling direction W, s. Times t ₁ and t ₂ . The billet 5 moves as a result of the decrease in cross-section with a higher speed V _Luppe by the continuous rolling mill 3 in the rolling direction. The controlled movement of the mandrel 4 is caused by moving means, which are not shown in the figure. When the end of the Luppen has left the Kontiwalzwerk, the mandrel 4 is still moved a short distance. Subsequently, a restraint device 8 is raised in the form of a fork between the last stand and the end of the roll, which tightly encloses the mandrel bar 4 except for a small gap. Then, the mandrel 4 is retracted by the retainer (not shown) against the rolling direction W and the billet 5 thus deducted from the rod.

The lubrication of the mandrel is done before threading the rod in the hollow block in the rolling line.

Subsequently, the billet runs over the furnace 7 directly into the sizing mill 6 (reducing mill) to produce the finished pipe dimensions. In the oven a thermal compensation in that over the circumference and the length of the billet a uniform temperature is generated.

An alternative solution works Fig. 4 out. Shown are the layers of hollow block, mandrel bar and billet at three consecutive times t _A , t ₁ and t _E.

Here it is provided that also first the mandrel 4 is threaded into the hollow block 2. Then, the hollow block 2 together with mandrel 4 is positioned as it is in the upper part of Fig. 4 at the time t _A to see, so with great template in the continuous rolling mill 3. The cavity block 2 is then rolled to the billet 5, wherein the billet is conveyed in the rolling direction W 5 due to the movement of the rolls of the stands 9, 10,. 11 Meanwhile, the mandrel 4 is moved counter to the rolling direction W; it is preferably withdrawn at a constant speed v _mandrel . At the end of rolling, the remaining length of the mandrel bar 4 in the billet 5 is minimized, and the necessary residual pull-out force can be applied by the following conveyor roller bar (not shown).

Another alternative solution is in Fig. 5 outlined. Again, the layers of hollow block, mandrel and billet are shown at three consecutive times t _A , t ₁ and t _E.

In the embodiment, it is provided that the mandrel 4 together with threaded hollow block 2 are first positioned according to the upper partial figure before the rolling process begins. The hollow block 2 is pushed in the inlet of the continuous rolling mill 3 on the fixedly positioned mandrel 4, which is then locked with a pivotable abutment, not shown. The mandrel 4 is not or almost not moved, so that the hollow block 2 is rolled off during the transformation to the billet 5 of the mandrel bar 4. At the end of the rolling process, the billet 5 has no contact with the mandrel 4.

The mandrel bar 4 is provided in the region of the forming zones under the rolls of the rolling stands with a wear-resistant material, for example with ceramic inserts.

The mandrel 4 can perform a small oscillating movement during the rolling process to avoid partial overheating in the working zone.

In all solutions can be provided that the mandrel 4 is subjected to continuous cooling during the rolling process in the continuous rolling mill 3. This is also possible with the displaceable arrangement of the mandrel bar 4 if, for example, via a cable towing device, a cooling channel running inside the mandrel bar 4 is supplied with coolant.

A further development provides a conical mandrel 4, which facilitates the removal or rolling of the billet 5 of the mandrel bar 4. Preferably, instead of the rolling mills with two rolls usually provided, three-roll mills are also provided.

LIST OF REFERENCE NUMBERS

1

Piercer

2

hollow block

3

continuous rolling mill

4

mandrel

5

Luppe

6

sizing mill

7

oven

8th

Restraint

9

rolling mill

10

rolling mill

11

rolling mill

12

Rotary hearth furnace

13

Extraktorwalzwerk

W

rolling direction

t _A

Start time

t ₁

time

t ₂

time

t _E

end time

v _{thorn rod}

Speed of the mandrel

v _Luppe

Speed of the doll

Claims (13)

1. A method for producing a seamless tube, where a primary material is initially recast in a piercer (1) into a hollow block (2), where the hollow block (2) accommodated on a mandrel bar (4) is then rolled in a continuous rolling mill (3) to form a hollow (5) and wherein subsequently, after the removal of the mandrel bar (4) from the hollow (5), said mandrel bar (4) is calibrated in a sizing mill (6) to the desired outer diameter, wherein the hollow (5) is passed directly from the continuous rolling mill (3) into the sizing mill (6) without interconnecting a further rolling mill, wherein the mandrel bar (4) is removed from the hollow (5) before the hollow (5) enters into the sizing mill (6),
   characterized in
   that the mandrel bar (4) is displaced in the continuous rolling mill (3) in a controlled manner opposite to the rolling direction (W) or is held so as to be stationary for the most part during the rolling so that, after the rolling process of the hollow (5) in the continuous rolling mill (3) has ended, said mandrel bar (4) is moved out of the hollow (5) at least to a large extent, preferably completely, or the hollow (5) is pushed off via the mandrel bar (4).
2. The method according to claim 1,
   characterized in
   that the mandrel bar (4) is displaced with a small displacement path in rolling direction (W) during the rolling in the continuous rolling mill (3).
3. The method according to claim 2,
   characterized in
   that the small displacement path is carried out by means of an oscillation motion.
4. The method according to one of claims 1 to 3,
   characterized in
   that the mandrel bar (4) is cooled during the rolling process in the continuous rolling mill (3).
5. A rolling mill for producing a seamless tube, which encompasses a piercer (1), by means of which primary material can be recast into a hollow block (2), which furthermore encompasses a continuous rolling mill (3), in which the hollow block (2) accommodated on a mandrel bar (4) can be rolled to form a hollow (5) and encompasses a sizing mill (6), in which the mandrel bar (4), after being removed from the hollow (5), can be calibrated to the desired outer diameter, wherein the sizing mill (6) connects in rolling direction (W) to the continuous rolling mill (3) without interconnecting a further rolling mill, in particular for carrying out the method according to one of claims 1 to 4,
   characterized in
   that provision is made for suitable displacement means for the oscillating motion of the mandrel bar (4) in rolling direction (W).
6. The rolling mill according to claim 5,
   characterized in
   that a furnace (7) for maintaining the temperature of the hollow (5) is arranged between the continuous rolling mill (3) and the sizing mill (6).
7. The rolling mill according to claim 5 or 6,
   characterized by
   displacement means, by means of which the mandrel bar (4) can be displaced in the continuous rolling mill (3) in a controlled manner or opposite to the rolling direction (W) during the rolling.
8. The rolling mill according to one of claims 5 to 7,
   characterized in
   that a retaining device (8), which retains the hollow (5) opposite to the rolling direction (W), is arranged between the continuous rolling mill (3) and the sizing mill (6).
9. The rolling mill according to one of claims 5 to 8,
   characterized by
   coolants, which are assigned to the mandrel bar (4).
10. The rolling mill according to claim 9,
    characterized in
    that the coolants comprise line segments, by means of which a coolant can be introduced into an internal bore in the mandrel bar (4), which expands across a predetermined axial extension.
11. The rolling mill according to one of claims 5 to 10,
    characterized in
    that the outer surface of the mandrel bar (4) is provided with a layer consisting of wear-resistant material.
12. The rolling mill according to one of claims 5 to 11,
    characterized in
    that the individual roll stands (9, 10, 11) of the continuous rolling mill (3) are embodied as 3-roller stands.
13. The rolling mill according to one of claims 5 to 12,
    characterized in
    that the mandrel bar (4) encompasses a slightly conical shape across its axial course.

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