EP0029786B1 - Process and device for producing a steel tube without welding joint by hot-rolling on a mandrel - Google Patents

Abstract

In the manufacture of seamless steel tube by hot-rolling a tube blank on a mandrel in a continuous rolling mill, the tube is withdrawn from the mandrel and reduced by reducing roll stands downstream of and in alignment with the rolling mill which operate on the part of the tube withdrawn from the mandrel. The mandrel is advanced through the rolling mill at a controlled speed and is not released until the reduction of the tube has been completed. The reducing roll stands are then opened and the released mandrel follows the tube through the stands but without contacting the rolls.

Description

The invention relates to the manufacture of a seamless steel tube by hot rolling on a mandrel.

In certain hot rolling processes on a long mandrel of tubular blanks by a continuous rolling mill or the like, where the mandrel is retained during rolling, it has been possible to have downstream of the rolling mill and along the same pass axis one or more so-called cages "extraction" in which the tube engages towards the end of the rolling operation, which has the effect of extracting it from the mandrel while the latter remains maintained upstream of the rolling mill (FR-A-2419776).

Although in this type of installation, the mandrel is then retracted upstream of the rolling mill for interleaving the next stool as soon as the blank which has just been laminated is released, it is not immune to a rupture of the mandrel or of the attachment device which has the consequence that a part of the shrouded tube passes through the extractor. However, it should be noted that to develop a sufficient extraction effect, the extraction cages must exert a radial force such that it normally follows a slight reduction in diameter of the tube whose thickness is not altered. But, if a part of the tube comes to be presented with the mandrel still inside, the extraction rollers no longer working in the hollow have to exert such considerable forces that one arrives at rupture. There are well-known safety devices in rolling mills which allow the cylinders of the extraction cages to be erased as soon as the forces become too large, but experience shows that these, taking into account the speeds of passage of the product and masses involved, only work properly if the opening to be provided remains small, and just compatible with the small diameter reductions necessary to ensure extraction.

In view of the above, it has always been considered industrially impossible to achieve significant diameter reductions on the extractor itself; if the laminated tube has to undergo a significant reduction in diameter, it can therefore only be done on a reducer sufficiently distant from the extractor mill assembly so that the laminated tubes which still contain all or part of the mandrel can be stopped and put out of circuit . The distances and times required for this possible verification and sorting operation are such that, for tubes rolled under normal conditions, the temperature is no longer sufficient on arrival at the reducer. The laminated tubes are therefore systematically reheated before reduction, resulting in significant energy loss.

In other processes (continuous rolling mill) using a free or speed-controlled mandrel with letting go of the mandrel at the end of rolling, it is known to extract the mandrel from the laminated tube outside the pass axis of the rolling mill, the mandrel being sent to the cooling and recycling devices while the laminated tube is sent to a reducing rolling mill.

However, the succession of operations (braking and stopping of the mandrel tube, transfer in the axis of the chucker, chuck) is such that the blank cools and is no longer able to undergo a reduction in diameter without prior reheating, where an appreciable loss of energy.

The invention relates to a method for manufacturing a seamless steel tube, in which a tube blank fitted on a mandrel is hot rolled in a continuous rolling mill, the mandrel is subjected to a controlled speed during rolling, the mandrel tube and the mandrel is released at the end of the rolling so that it leaves the continuous rolling mill following the tube (FR-A-2 198797); it aims to avoid the above drawbacks.

The method of the invention is characterized by the characterizing part of claim 1.

This process makes it possible to obtain significant reductions in diameter and, optionally, in thickness of the tube, these latter being made possible by the very importance of the reduction in diameter, this in the axis of the continuous rolling mill a very small distance and without any handling of the product, so that the time which elapses between the passage of a considered section of product in the rolling mill and its passage in the reducer is very small and does not require intermediate reheating, hence a significant energy saving and a great simplification of the installation, the investment as well as the cost of operation and maintenance are reduced very substantially.

The mandrel is then sent to the cooling, possible control and recycling circuits towards the entrance to the rolling mill.

A device for implementing the method comprises a continuous rolling mill, means for accompanying the mandrel at a controlled speed during the rolling of the blank, reduction cages downstream of the continuous rolling mill and in line with it, means for supporting the mandrel during its passage through the reduction cages without contact with the cages and means for controlling the opening of the cages before the passage of the mandrel.

This device can be considered as the combination of a continuous rolling mill working on a long mandrel at a controlled speed during rolling and released at the end of rolling, with a particular reducing rolling mill.

• La Figure 1 est un schéma d'une installation conforme à l'invention;
• La Figure 2 et la Figure 3 sont des coupes transversales schématiques de deux réalisations d'une cage du laminoir extracteur;
• La Figure 4 est un diagramme espace/temps des vitesses du tube et du mandrin dans l'installation; et
• La Figure 5 représente schématiquement les cages du laminoir lors de différentes phases du procédé.

An example of implementation of the invention will be described below, with reference to the attached drawing figures in which:

• Figure 1 is a diagram of an installation according to the invention;
• Figure 2 and Figure 3 are schematic cross sections of two embodiments of a cage of the extractor mill;
• Figure 4 is a space / time diagram of the tube and mandrel speeds in the installation; and
• Figure 5 shows schematically the stands of the rolling mill during different stages of the process.

The Figures relate to the rolling on a long mandrel and the reduction in the same hot, that is to say without intermediate reheating, of a thin tube obtained in a reproducible process with controlled mandrel retention.

By "thin" tube is meant a tube in the range 100 x 4 (mm) to 250 x 7 (mm), the first and second values respectively designating the outside diameter and the thickness of the wall of the tube.

By significant reduction is meant values of the outgoing diameter / incoming diameter ratio up to 3 and even more.

The installation essentially comprises (FIG. 1) a continuous rolling mill 1 and a reducing-extracting rolling mill 2 (to reduce the tube and separate it from the mandrel) in line with the continuous rolling mill. The distance L between the last stand of the continuous rolling mill and the first stand of the reducer-extractor rolling mill, as small as possible, is of the order of a length of tube, or for example a distance of the order of 10 meters.

The two rolling mills are in synchronous speed, the output speed of the continuous rolling mill being for example 2 to 5 m / s, so that the time interval between rolling and reduction is generally less than one minute.

The numbers of stands of the rolling mills are chosen according to the needs, in a manner known per se.

A person skilled in the art knows the continuous rolling mill and the reducing rolling mill, so we will only describe the modifications made by the present invention to the reducing rolling mill for the implementation of the new process.

• - des dispositifs de commande 3 pour écarter complètement et rapidement les cylindres des cages de réduction à une section de passage entre les cylindres nettement supérieure au diamètre du mandrin;
• - des dispositifs mécanisés 5 de soutien du mandrin, situés entre les cages de réductions, susceptibles de venir se placer autour ou simplement au-dessous de l'axe de passe pour y maintenir le mandrin lors de son passage de telle sorte que le mandrin ne puisse à aucun moment venir au contact avec les cylindres de réduction en position ouverte, ce qui entraînerait une détérioration des surfaces de travail de mandrin et des cylindres, les rendant rapidement inaptes à un laminage correct;
• - des dispositifs de détection 6 de l'arrivée du tube et du mandrin devant le laminoir réducteur 2 commandant les mécanismes 3 au moment opportun pour l'ouverture des cages 4 à la grandeur qui convient;
• - des dispositifs de régulation pour régler la vitesse des cages du laminoir réducteur en relation précise avec la vitesse de celles du laminoir continu, évitant tout défaut sur le produit qui pourrait résulter d'une différence de vitesse inadéquate entre le laminoir continu et le laminoir réducteur lorsque les laminoirs sont simultanément en prise sur le tube.

These changes include:

• - Control devices 3 for completely and quickly removing the cylinders from the reduction cages to a passage section between the cylinders clearly greater than the diameter of the mandrel;
• - Mechanized devices 5 for supporting the mandrel, situated between the reduction cages, capable of being placed around or simply below the pass axis to hold the mandrel there during its passage so that the mandrel does not may at no time come into contact with the reduction cylinders in the open position, which would cause deterioration of the working surfaces of the mandrel and of the cylinders, rendering them rapidly unsuitable for correct rolling;
• - Detection devices 6 for the arrival of the tube and the mandrel in front of the reducing rolling mill 2 controlling the mechanisms 3 at the appropriate time for the opening of the cages 4 to the appropriate size;
• - regulating devices to adjust the speed of the cages of the reducing rolling mill in precise relation with the speed of those of the continuous rolling mill, avoiding any defect on the product which could result from an inadequate speed difference between the continuous rolling mill and the reducing rolling mill when the rolling mills are simultaneously engaged on the tube.

It is not necessary to describe in detail these devices which are known per se. However, by way of examples, two embodiments of a cage of the reducer-extractor rolling mill will be described below, with reference to FIGS. 2 and 3.

Figures 2 and 3 show different embodiments of a cage of the extractor mill.

FIG. 2 illustrates a cage 4 of the type with two cylinders 8 and 9. The four chocks 10 slide in openings made in the cage.

A double corner 11 and a similar part 12 respectively for the upper and lower part of the cage allow the cylinders 8 and 9 to be brought closer or apart under the action of jacks 13 and 14. The close position corresponds to the reduction and to the subsequent mandrel, the position spread when the mandrel passes through the extractor mill.

In the event that the mandrel is "swallowed", the abnormal force would cause a pressure increase in the jacks 13 and 14 and a relief valve would open. For double security, break boxes 15 are interposed between the clamping screws 16 and the bearing face.

Figure 3 shows a cage 4 of the three-cylinder type 17, 18, 19.

The cylinder bearings are housed in sliding chocks.

Three double sloping corners 21, 22, 23 allow the cylinders 17, 18, 19 to be brought closer or further apart respectively.

The close position corresponds to the reduction and mandrel operation which follows while the separated position corresponds to the passage of the mandrel in the extractor mill.

Three cylinders 24, 25, 26 provide the movements in question.

In the event that the mandrel is swallowed, the abnormal force would cause a rise in pressure in the cylinders and the opening of a relief valve.

It will be noted that the cages open automatically if the rear of the mandrel accidentally exceeds a certain position.

The graph in FIG. 4 makes it possible to compare the relative displacements of the mandrel and the blank E (which will become the tube T) during rolling and then reduction of the tube.

For everything relating to the rolling of the blank in the continuous rolling mill, reference may be made to FR-A-2 198 797 which describes a process for manufacturing a seamless metal tube, in a continuous rolling mill, on a mandrel. In this process, as in the present case, the mandrel M is first retained so as to advance with a controlled speed, for example at constant speed, then it is released, when the rolling operation is finished, to exit the continuous rolling mill after the blank has become a T tube.

• Al axe première cage du laminoir continu
• A2 axe dernière cage du laminoir continu
• A3 : axe première cage du réducteur-extracteur
• A4 : axe dernière cage du réducteur-extracteur
• TA : durée d'approche et de remplissage du laminoir continu
• TV : durée de sortie du tube du laminoir continu
• TE durée d'extraction du mandrin hors du tube
• VM : vitesse du mandrin durant le laminage
• VSLC : vitesse de sortie du tube du laminoir continu
• VSLR : vitesse de sortie du tube du laminoir réducteur-extracteur
• VEM : vitesse d'évacuation du mandrin.

In Figure 4, the references have the following meanings:

• Al axis first stand of the continuous rolling mill
• A2 axis of the last stand of the continuous rolling mill
• A3: axis of the first cage of the reducer-extractor
• A4: last cage axis of the reducer-extractor
• TA: duration of approach and filling of the continuous rolling mill
• TV: exit time from the tube of the continuous rolling mill
• TE extraction time of the mandrel out of the tube
• VM: speed of the mandrel during rolling
• VSLC: exit speed of the continuous rolling mill tube
• VSLR: exit speed of the tube from the reducer-extractor rolling mill
• VEM: evacuation speed of the mandrel.

• a) on impose au mandrin une vitesse contrôlée (ici constante) VM pendant le laminage;
• b) on commence la réduction de l'ébauche du tube avant la fin du laminage (point X);
• c) on achève la réduction du tube (point Y) avant de lâcher le mandrin (point Z).

We see in the Figure that:

• a) a controlled speed (here constant) VM is imposed on the mandrel during rolling;
• b) the reduction of the blank of the tube is started before the end of rolling (point X);
• c) the reduction of the tube (point Y) is completed before releasing the mandrel (point Z).

• schéma (a): laminage de l'ébauche sur le mandrin et, simultanément, réduction du tube,
• schéma (b): extraction et réduction du tube,
• schéma (c): passage du mandrin dans le laminoir réducteur-extracteur.

FIG. 5 represents diagrams (a), (b), and (c) of the relative arrangements of the rolls of the cages of the reducer-extractor mill (assumed to be three cages), of the tube T and of the mandrel M, respectively during the phases 1, II and III of Figure 4:

• diagram (a): rolling of the blank on the mandrel and, simultaneously, reduction of the tube,
• diagram (b): extraction and reduction of the tube,
• diagram (c): passage of the mandrel in the reducer-extractor rolling mill.

The extractor mill preferably comprises a high number of cages and, for example, at least five cages, as shown in Figure 1. In Figure 5, only the two end cages and the central cage of this are shown. rolling mill for the convenience of the figure but it will be understood that it is indeed a rolling mill with five stands as in the case of Figure 1.

Claims (7)

1. A process for the production of a seamless steel tube, in which a tube billet carried onto a mandrel is hot-rolled in a continuous rolling mill, a controlled speed is imposed on the mandrel during rolling, the tube is separated from the mandrel and the mandrel is released at the end of the rolling operation so that it exists from the continuous rolling mill following the tube, characterized in that the operation of reducing the tube (T) is commenced in a reducing rolling mill located on the extension of the axis of the rolling mill (1), this reduction being carried out in a zone of the tube in which the mandrel (M) is no longer present, before the end of the rolling of the billet, by the passage through this zone of the tube between cylinders (8,9; 17, 18, 19) of reduction stands (4) situated downstream of and aligned with the continuous rolling mill (1), and the tube is reduced before the mandrel is released and before the mandrel which follows the tube arrives in front of these cages (4), and the opening of the cages (4) is caused to occur before the mandrel is passed through said cylinders to avoid any contact between the mandrel and the working surfaces of said cylinders.

2. A process according to claim 1, characterized in that the opening of the stands (4) is caused to occur before the mandrel is released.

3. A device for effecting a process according to claim 1 or 2, which comprises a continuous rolling mill and means for accompanying the mandrel at a controlled speed while the tube billet is rolled, characterized in that it comprises stands (4) for reducing the tube (T) downstream of the continuous rolling mill (1) and aligned therewith, means (5) for supporting the mandrel (M) during its passage into the reduction stands (4) without contact with the middle cylinders (8,9; 17, 18, 19) of these stands and means (3) for causing the opening of the stands (4) to occur before the passage of the mandrel (M).

4. A device according to claim 3, characterized in that it comprises devices (6) for detecting the arrival of the tube and of the mandrel in front of the reduction stands (4) to operate the means (3) which cause the stands (4) to open.

5. Seamless steel tubes which are produced by a process according to claim 1 or 2 are produced by means of a device according to claim 3 or 4.

6. Seamless steel tubes according to claim 5, characterized in that their dimensions range from 100 x 4 to 250 x 7 mm.

7. Seamless steel tubes according to one of claims 5 and 6, characterized in that the reduction ratio (exiting diameter/entering diameter) is 3 or more.

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