WO2011083101A2

WO2011083101A2 - Hot rolling of metal tubes without welded joints on a continuous mill with a fixed mandrel

Info

Publication number: WO2011083101A2
Application number: PCT/EP2011/050018
Authority: WO
Inventors: Roger Bossoney; Raimo Peltoniemi
Original assignee: New Seamless Tube Technology Corp.
Priority date: 2010-01-07
Filing date: 2011-01-03
Publication date: 2011-07-14
Also published as: WO2011083101A3

Abstract

The invention relates to a rolling system for producing tubes without welded joints, comprising: a drill (7) for drilling a billet and obtaining a blank (2); a continuous mill (8) for rolling the blank (2), said mill (8) comprising a plurality of roll housings (20), each roll housing (20) comprising at least two rolls (5); and a mandrel (21) that is fixed during the rolling, said mandrel (21) comprising a plurality of profiled rings (22) interconnected by intermediate tubes (23), the profiled rings (22) having an outside diameter larger than the diameter of the intermediate tubes (23) and increasing cage-by-cage in the direction of rolling. The system is characterised in that each of the at least two roll (5) comprises a channel having a curvature radius for forming an essentially round gauge for producing an essentially round section of the blank (2). The rolling system is simple and light, incurs less production, installation and maintenance costs than conventional rolling systems, ensures better quality and reduces pollution.

Description

Hot rolling of seamless metal tubes on a fixed mandrel rolling mill

Technical area

The present invention relates to a hot rolling process of seamless steel tubes, more energy-efficient, tooling costs, machinery equipment costs, building costs in installation costs and costs. of processing, with a quality of products superior to that currently produced on continuous mills with free mandrel or mandrel retained.

State of the art

The basic idea, hot rolling steel tubes in successive cages of a continuous rolling mill, on fixed mandrel, has already been the subject of several patents, the oldest dating to our knowledge, from 1883 All these patents have not been applied or their application has been quickly abandoned. None of these patents could be industrially applied sustainably. The main cause of these failures was that the mandrel did not support the very high thermal loads added to the mechanical loads due to fixed mandrel rolling.

To solve this problem, we developed continuous rolling mills where the mandrel moves in the axial direction of rolling, either with a free mandrel, or with a retained mandrel. The heat energy produced between blank and mandrel is thus distributed over a sufficient length of mandrel so that the temperature and the heat load on this mandrel are acceptable. The free or retained mandrel is threaded into the blank to be rolled in front of the rolling mill.

In the case of the free mandrel, the blank and the mandrel are introduced together in the rolling mill. Whenever the draft enters in a new cage, the chuck is accelerated. When the blank is engaged in all the cages, the chuck takes an equilibrium speed, intermediate between the speeds of the blank, at the inlet and the outlet of the rolling mill. The speed of the mandrel can not be controlled and depends inter alia on the distribution of elongations between the cages and the friction between mandrel and blank, so lubrication. Continuous mills with free mandrel, are gradually abandoned and to our knowledge, it has not been built in recent years.

In the case of the chuck retained at controlled speed, the blank is introduced into the rolling mill by a pair of small rolls (pinch-rolls). Under the effect of rolling, the blank drives the mandrel at a preset speed, controlled by a group of electric motors working as a brake, thus generators. These motors are connected to the chuck by a long rack. The retainer system is also used to thread the mandrel into the blank before rolling. The useful length of the rack is therefore the length of the mandrel, plus the length of the blank, plus the length of the mill, plus the length of displacement of the mandrel during the output of the roll tube. The length of the rack is about 30 meters or more. The electric restraining motors must be fast to thread the mandrel into the blank, slow during rolling and working with high torque in the brake. Several variants of retained mandrel mills exist around the world.

Currently, continuous rolling mills for seamless tubes of the latest generation, are equipped with 3-cylinder cages. Compared with 2-roll continuous rolling mills per cage, 3-roll mills with cages have the following advantages: improved yield, better tolerances, reduced rolling defects and better stability of the mill. rolling.

To separate the tube from its mandrel, these mills are followed by an in-line extractor generally consisting of three to six cages with two or three cylinders per cage, which pulls the tube forward while the mandrel is retained. The most modern modern rolling mills are called PQF or FQM according to the manufacturer.

Compared to the mandrel retained speed controlled, other improvements with many advantages can be made by the possibility of rolling the tubes on a fixed mandrel.

Brief summary of the invention

An object of the present invention is to provide a simpler rolling system than known rolling systems.

According to the invention, a rolling system for the manufacture of seamless tubes comprising: a piercer for piercing a billet and obtaining a blank, a continuous rolling mill for the rolling of the blank, the rolling mill comprising a plurality of rolling stands each rolling stand comprising at least two rolls; and a fixed mandrel during rolling, the mandrel comprising a plurality of profiled rings interconnected by intermediate tubes, the profiled rings having an outer diameter larger than the diameter of the intermediate tubes and growing cage-cage in the rolling direction; characterized in that each of said at least two cylinders has a groove having a radius of curvature capable of forming a substantially round gauge adapted to produce a substantially round section of the blank. According to one embodiment, each of said at least two cylinders has a substantially circular profile groove.

According to another embodiment, the rolling mill (8) is adapted to produce an aspect ratio of between 1.5 and 1.0 for each of the rolling stands. According to another embodiment, the rolling system also comprises a heat insulated channel comprising at least one induction heating ring capable of heating the ends of the blank and equalize the temperature of the blank over its entire length. . According to another embodiment, the piercer is adapted to inject an inert gas inside the blank during drilling.

According to another embodiment, the rolling system also comprises a deoxidizer injection device adapted to inject a deoxidant inside the blank. The invention also relates to a method comprising:

piercing the billet using the piercer;

equalizing the temperature of the blank with the insulated channel and said at least one heating ring; and

the rolling of the blank in the rolling mill, said rolling producing a substantially round section of the blank at each of the rolling stands.

The rolling system disclosed herein is simpler and lighter than conventional rolling systems, resulting in lower manufacturing, installation and maintenance costs than conventional rolling systems.

Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: Figure 1 illustrates a rolling system according to embodiments; Figure 2 shows profiles of a blank for a conventional mandrel-retained mill; Figure 3 shows profiles of the blank for a rolling mill according to one embodiment; Figure 4 shows a sectional view of the rolling mill according to one embodiment; Figure 5 is a sectional view of a mandrel according to one embodiment; Figure 5a shows a sectional view of the mandrel and an injector; Figure 6a illustrates deformations of the blank for a conventional mandrel-retained mill with two-roll stands; Figure 6b illustrates deformations of the blank for a conventional mandrel-retained mill with three-roll stands; Figure 6c illustrates deformations of the blank for an elongation device according to the embodiments; FIG. 7 shows an example of distribution of the elongations between the stands for a conventional retained mandrel and for the fixed mandrel according to the invention; FIG. 8 illustrates the reduction in the coefficient of friction between the blank and the fixed mandrel according to the invention as a function of the relative speed between the blank and the mandrel; and Figure 9 shows a detail of the rolling system according to embodiments. Example (s) of embodiment of the invention

A rolling system according to an embodiment is shown in Figure 1. The rolling system comprises a heating furnace 1, longitudinal or rotary, for heating the continuous casting billets. The billets can be cut to a given length by a saw 6. A piercer 7, having a rod 37 supporting a piercing bulb (not shown), pierces the billet, thus forming a hollow body, called the blank 2 below. The rolling system also comprises a rolling mill 8 for rolling the blank 2. The rolling system may also comprise a chuck cooling device 27, located next to an exit roller track 32 of the rolling mill 8.

In one embodiment, an inert gas such as nitrogen is injected into the blank 2 during the piercing operation, so as to prevent or limit oxide formation. The injection can be carried out through the stem 37.

After the drilling operation, during the withdrawal of the rod 37 and the evacuation of the blank 2, an oxide is formed on the surface of the blank 2. This oxide is particularly harmful on the inner surface of the blank 2. In order to eliminate or limit this oxide, the rolling system may comprise a deoxidant injection device 29 for injecting on the inner surface of the blank 2 a deoxidizing, liquid or powder, such as borax, salts, potassium silicate or other silicate, graphite, oil, mineral products, with additives and binders for high temperatures. The deoxidant injection device 29 produces a spiral fan movement of the deoxidizing product during the injection. Rotational movement is also imparted to the axial displacement of the blank 2, so that the deoxidant product wets the entire inner surface of the blank 2. The injection conditions of the deoxidizer injection device 29, such as the pressure of application, the flow rate, the quantity injected, the injection time and the adjustment of the spiral movement in fan, can be controlled by computer and can be adjusted automatically according to the inside diameter and the length of the blank 2. The rolling system may also include a surplus deoxidant recovery device, shown in 30 in the figure 1.

A lubricant is used to reduce the friction between the mandrel 21 and the blank 2 during rolling. The lubricant, liquid or powder, such as graphite, oil, borax, salts, potassium silicate or other silicate, mineral products, with additives and binders for high temperatures, can be injected into the blank 2 using of a lubricant injection device shown at 33 in Fig. 1. A lubricant recovery device may also be disposed at 34. The lubricant injection device 33 may include the features of the deoxidizer injection device 29 [0023] Still after the drilling operation, after the injection of the deoxidizing product, the blank 2 is transferred to the lubricant injection device 33, located before the input table of the rolling mill 8. transfer, the ends of the blank 2 cool faster than its middle. The colder ends may be responsible for heavy wear of the mandrel 21 and its decommissioning.

In one embodiment, this disadvantage is remedied by moving the blank 2 in a heat-insulated channel 36 and placing on the channel 36, between the piercer 7 and the rolling mill 8, one or two induction heating rings. 35, to slightly overheat the ends of the blank 2 and equalize the temperature of the blank 2 over its entire length. During the passage of the blank 2 in the insulated channel 36 and the induction heating ring or rings 35, the blank 2 is, in addition to the axial displacement, animated by a rotary movement printed by oblique rollers (not shown ). The temperature of the blank 2 is controlled as it passes through the heating rings 35 and the speed of the blank 2 is adjusted accordingly. In a preferred embodiment, the rolling mill 8 comprises six rolling stands 20, each cage 20 comprising at least two cylinders 5 (see Figure 4). The cylinders 5 comprise a groove (not shown) in contact with the blank 2 and exert pressure on the blank 2 against the mandrel 21 so as to perform the rolling process. In mill 8 of the invention, the mandrel 21 is fixed during rolling. The rolling is typically carried out at elevated temperature, generally at about 1100 to 1200 ° C.

Figure 4 shows a sectional view of the rolling mill 8 according to one embodiment. More particularly, FIG. 4 shows three rolling stands 20 each comprising two, three or four cylinders 5, the hollow blank 2, and the mandrel 21. The mandrel 21 comprises working parts formed by profiled rings 22, and tubes

intermediates 23 which connect the rings 22 to each other. The profiled rings 22 have an outside diameter greater than the diameter of the intermediate tubes 23, so that only the profiled rings 22 participate in the deformation of the blank 2 against the cylinders 5. The outer diameter of the profiled rings 22 increases cage in cage in the direction of rolling, to the right in Figure 4, to maintain a mean diameter of the blank 2 constant in all cages 20. It is understood that this ideal theoretical condition, can not always be achieved in convenient.

The profiled rings 22 may be made of one or more metals, metal alloys, composite materials or formed of several layers of different materials, and / or a metal base covered with a thin metal layer or non-metallic. The rings 22 are preferably made of a hard material such as ceramics. Alternatively, the rings 22 may be surface treated or deep. Figure 5 shows a sectional view of the mandrel 21 in one embodiment. In the example of Figure 5, the inside of the mandrel 21 comprises a first concentric pipe 9 for transporting a cooling medium, such as a liquid of

cooling, as well as a concentric sedan 13

allowing the return of the coolant. Figure 5a shows a sectional view of the mandrel 21 in a variant of the embodiment where the mandrel 21 also comprises a second concentric pipe 12. In this configuration, the first pipe 9 can be used to transport the coolant , the concentric inner pipe 13 allowing the return of the coolant so that the cooling liquid circulates continuously. The coolant makes it possible to limit the heating of the mandrel 21 during the rolling operation. The second pipe 12 is used to transport a lubrication medium, liquid or powder. The mandrel 21 may also comprise injectors, one of which is shown by the number 14 in FIG. 5bis, preferably arranged on the intermediate tubes 23, in fluid communication with the second conduit 12 via a valve 1 5. The injectors 14 pass through the wall of the mandrel 21 and eject the medium of lubrication of the second conduit 12 between the mandrel 21 and the blank 2. The injectors can be controlled by computer. In the example of Figure 5a, the valve 1 5 is formed of a piston 16 sliding in a bore 18. In the absence of the blank 2, the piston 16 is held in a raised position by a spring 17 obstructing the fluidic communication between the second pipe 12 and the outside of the mandrel 21.

When the blank 2 is placed on the mandrel 21, the latter drives the piston 16, establishing a fluid connection between the second pipe 12 and the outside of the mandrel 21, so as to allow the medium of lubrication to penetrate between the mandrel 21 and the sketch 2.

Figures 4 and 5 show that the contact between the blank 2 and the mandrel 21 is only in the cages 20. Only the rings 22 located in the cages perform the deformation. The rings 22 are connected by the intermediate tubes 23 whose diameter is smaller than the inside diameter of the blank 2. There is therefore no friction between the blank and the mandrel 21 between the cages 20. The friction between

the blank and the mandrel 21 is therefore greatly reduced compared with a conventional controlled speed controlled chuck. When all the cages 20 of the mill 8 are engaged on the blank 2, the friction length between the blank 2 and the mandrel 21 is, with the fixed mandrel 21, 25 to 30 times smaller than with a retained mandrel conventional. The traction on the fixed mandrel 21 will be significantly reduced. Similarly, the thermal energy produced by friction and conduction between the blank 2 and the mandrel 21 will be reduced considerably. The decrease in the traction on the mandrel 21 as well as the sharp decrease in friction contributes to reducing the total energy required for rolling.

By maintaining the fixed mandrel 21, the relative speed is increased between the blank 2 and the mandrel 21. It is known that all other things remaining equal, the coefficient of friction decreases as the relative velocity between the friction surfaces increases. Figure 8 illustrates this phenomenon. The friction energy and thus also the induced thermal energy will be reduced accordingly.

During the rolling operation in the rolling mill 8, the blank 2 undergoes an elongation when it passes through each of the cages 20. In one embodiment, the maximum elongation per cage 20 is limited. in order to reduce the thermal load on the mandrel 21 or on the rings 22 which constitutes it. For example, the rolling may be carried out with an elongation corresponding to an aspect ratio of less than 2, for example between 2 and 1. Preferably, the aspect ratio is between 1.5 and 1.0. The thermal load can also be decreased by distributing the elongation over a larger number of cages 20. For example, the rolling mill 8 may comprise one or two cages 20 in addition to a continuous rolling mill of last generation, that is, that is to say comprise more than four cages 20. FIG. 7 shows an example of distribution of the elongations between the cages 20. In conventional continuous chuck mills retained, to avoid too much pressure on the entire circumference of the mandrel and to prevent the advance of the blank on the mandrel, the profile of the groove of the cylinders is such it causes ovalization of the section of the blank as it passes through the cage. In Figure 2 corresponding to a conventional continuous rolling mill with three cylinders cage, it is easily seen that part of the deformation is transversely. Outside, only the axial deformation, in the rolling direction, contributes to the elongation of the blank 2. The transverse deformation is therefore a redundant parasitic deformation.

In a preferred embodiment, the cylinders 5 comprise a circular groove having a radius of curvature defining a substantially round caliber to all the cages 20, adapted to produce a section of the blank 2 substantially round. FIG. 3 shows the outside inlet profile 3 and the outside outlet profile 4 of the blank 2, for such a circular groove. As seen in FIG. 3, the deformation of the blank 2 is only axial, and the redundant parasitic deformations are essentially eliminated. Given the suppression of the redundant parasitic deformation, for the same elongation of the same blank 2, the necessary deformation energy is therefore lower with the rolling mill 8 according to this embodiment. In Figure 3, are also visible the inner inlet profile 10 of the blank 2 and the inner output profile 1 1 at the inlet and outlet of the cage 20, respectively. The inner output profile 1 1 is larger than the inner inlet profile 10 due to the action of the profiled rings 22.

The caliber round all cages 20 causes a constant radial deformation over the entire periphery of the caliber, so the axial speed is almost constant throughout the section of the blank 2, resulting in a near zero tangential deformation of the profiles 3 , 4, 10, 1 1 of the blank 2. The defects induced by axial tensions are substantially eliminated, which contributes to the increase of the setting (the yield). The reduction of the maximum elongation by cage 20 and the strong reduction of the friction between the blank 2 and the mandrel 21 as discussed above, allow to predict the round caliber at all the cages 20.

The elongations and the profiles of the blank 2 determine the more or less significant deformations of the ends of the blank 2. FIGS. 6a to 6c show schematically the shape of one of the ends of the blank 2 after the rolling, or hot tube 19, in different types of rolling mills. More particularly, FIG. 6a relates to a conventional mandrel mill retained with two-roll stands, FIG. 6b relates to another conventional mandrel rolling mill retained with three-roll stands, and FIG. 6c relates to rolling mill 8 comprising the cages 20 with three cylinders 5, according to the embodiments for obtaining a round caliber at all the cages 20.

Figures 6a to 6c show that with limited elongations and round gauges to all cages as advocated by the present invention, it avoids the cutting of the ends. In addition, the feathering is considerably improved by the ends of the hot tube 19 requiring no cutting after the hot rolling step. This deletion of hot cuts, allows to roll in single length without altering the setting to the mile. In this case, it is possible to remove the hot saws.

In conventional processes, the thin blanks are laminated as far as possible in double length, which makes it possible to improve the setting by the mile by limiting, for two finished tubes, two cuts at the ends of the tube instead of four. According to the embodiments making it possible to obtain a round gauge, the cuts at the ends of the hot tube 19 are no longer necessary and a single-length rolling can be performed without penalizing the setting. It is understood that the present invention can also be applied to double-length rolling. Figure 9 shows in more detail the rolling mill 8. In Figure 9, the mandrel 21 is retained by an extension 24 which is fixed during the rolling operation, to a cross member 25, which is supported against the first of the rolling stands 20 via longitudinal members 26. Once the rolling is complete, the mandrel 21 can be moved by a mechanical crane 28.

The rolling system also comprises a deposition and cooling device 27 of the mandrel 21, the device 27 being placed laterally to the roller track 32 of the output of the rolling mill 8. This arrangement and the suppression of the lubrication of the mandrels and the significant decrease in length of these, significantly simplifies the circulation of mandrels 21. With short cycles, the ability to

production is not affected by rolling in single length.

The rolling system according to the embodiments has several advantages, including, on the one hand, the simplification of the rolling device by:

removing a mobile chuck holding system consisting of a long rack used in conventional rolling systems, including electric motors for retaining and moving the rack;

the important simplification of the circulation of the mandrels 21, due to the suppression of the lubrication of these mandrels 21 and the significant decrease in length thereof;

the removal of an in-line extractor mill or the removal of an off-line chuck extraction device, required in conventional rolling systems;

the round calibration at all the cages 20, avoiding the irregular ends of the hot tube 19 at the exit of the rolling mill 8, making it possible to remove the cuts at the ends of the tube 19; and the removal of the cuts at the ends of the tube 19 allowing, for a rolling tubes 19 in single length, the removal of hot saws.

The rolling system according to the embodiments further comprises advantages such that:

the suppression of redundant deformations, the reduction of cage elongations and a significant reduction in friction, resulting in a sharp reduction in mechanical loads, torques and powers;

the reduction of cage elongations and the reduction of the mechanical loads making it possible to reduce the diameter of the rolls 5;

reducing the loads and decreasing the diameter of the rolls 5 to reduce the weight and the volume of the cages 20, resulting in ease of handling in the manufacture and operation of the rolling system; and

reducing the weight of the cages 20 for lightening the building structures, reduce the loads of a traveling crane and lighten the foundations supporting the rolling system.

In addition, the removal of the extractor, the great simplification of the circulation of the mandrels 21, the removal of the rack, cause a reduction in the area occupied by the equipment. Indeed, in a conventional continuous rolling mill installation, the distance between the rear of the rack and the outlet of the extractor is of the order of 70 to 80 meters whereas with the fixed mandrel rolling system of

the invention, the length of equivalent equipment is about 40 meters.

The rolling system according to the embodiments also reduces fixed costs, such as: the reduction in equipment costs due to the simplification of the installation, the removal of the mobile chuck retainer and the removal of the extractor;

the decrease in the cost of buildings, due to the reduction of surfaces, structures such as overhead cranes, foundations and installation of production equipment.

Advantages of the rolling system also include a reduction in the variable costs of transformation, such as:

a reduction in the costs of the tooling, in particular the mandrels 21, where only the rings 22 located in the cages 20 are subject to wear, unlike the long mandrels of conventional rolling mills with a working length of 10 to 14 meters, whose costs are very important; but also due to a lower wear of the cylinders 5 as the forces, couples, energies and powers being lower than with conventional rolling;

reducing the quantities of consumables by eliminating the lubrication of the mandrels 21 and by recovering excess deoxidizer and lubricant;

the reduction of the energy consumed by the suppression of the redundant deformations, by the reduction of the friction energy and by the control of the temperature;

the significant improvement in the development by the hot suppression of the cuts at the ends of the tube 19, the reduction of rejects, the reduction of defects and the decrease in production stops due to the simplification of the rolling system; and

the reduction in operating costs due to the simplification of the production equipment operation, the reduction of

maintenance and downsizing of the necessary manpower.

The rolling system according to the embodiments makes it possible to obtain a better quality of the tubes 19. In fact, the round calibration at all the cages 20 induces an approximately constant axial speed in the entire section of the blank 2 and a mean diameter of the blank 2 almost constant during the rolling, resulting in an almost constant axial speed throughout the section of the blank 2. This almost constant axial speed greatly reduces the deformation tensions , particularly the axial and tangential tensions which are very low, while the radial deformation is carried out almost solely under compression. In addition, the reduction of cage elongations is added to this significant reduction in strain tensions. On the other hand, the suppression of the friction between the cages 20, also contributes to the reduction of the tensions. This significant reduction in voltages results in a significant reduction in both external and internal defects on the tubes 19. In addition, round calibration to all the cages 20, the maintenance of a constant average diameter during rolling and the reduction of elongation by cage 20, ensure excellent geometric quality, tolerances and rotundity of the tubes 19.

The suppression of the lubrication of the mandrels 21, the injection of the lubricant as the deoxidizer directly into the blank 2, as well as the recovery of the excess of deoxidizer and lubricant, decreases.

noticeably the ambient pollution.

Reference numbers used on heating oven figures

draft

external entrance profiles

outside exit profiles

cylinder

saw

piercer

continuous rolling mill

first conduct

interior entrance profile

inner exit profile

second conduct

sedan

injector

valve

piston

spring

bore

Hot tube

rolling cage

mandrel

profiled rings

intermediate tube

extended

crossbeam

rails

deposition and cooling device

magnetic crane

deoxidant injection device

surplus deoxidant recovery device

roller exit lane

lubricant injection device

lubricant recovery device

induction heating ring

insulated channel

rod supporting a piercing pear

Claims

claims

1. Rolling system for the manufacture of seamless tubes comprising:

a piercer (7) for piercing a billet and obtaining a blank (2);

a continuous rolling mill (8) comprising a plurality of rolling stands (20), each rolling stand (20) comprising at least two rolls (5); and

a mandrel (21) comprising a plurality of profiled rings (22) interconnected by intermediate tubes (23), the profiled rings (22) having an outer diameter larger than the diameter of the intermediate tubes (23) and growing cage cage in the direction of rolling; characterized in that

each of said at least two cylinders (5) has a groove having a radius of curvature capable of forming a substantially round gauge adapted to produce a substantially round section of the blank (2).

2. The rolling system according to claim 1, wherein each of said at least two cylinders (5) has a substantially circular profile groove.

3. The rolling system according to claims 1 or 2, wherein

the rolling mill (8) is adapted to produce an aspect ratio of between 1.5 and 1.0 for each of the rolling stands (20).

4. The rolling system according to one of claims 1 to 3, comprising at least four rolling stands (20).

5. The rolling system according to one of claims 1 to 4, wherein

each of said plurality of rolling stands (20) comprises three or four cylinders (5).

6. The rolling system according to one of claims 1 to 5, also comprising a heat insulated channel (36) comprising at least one induction heating ring (35) adapted to heat the ends of the blank (2) and equalize the temperature of the blank (2) along its entire length.

7. The rolling system according to one of claims 1 to 6, wherein

the piercer (7) is adapted to inject an inert gas into the interior of the blank (2) during drilling.

8. The rolling system according to claim 7, wherein the piercer (7) comprises a pear rod (37) through which the inert gas is injected.

9. The rolling system according to one of claims 1 to 8, also comprising a deoxidant injection device (29) adapted to inject a deoxidant inside the blank (2) and a device recovering any excess of deoxidant (30).

10. The rolling system according to one of claims 1 to 9, also comprising a lubricant injection device (33) adapted to inject a lubricant inside the blank (2) and a device recovering any excess lubricant (34).

1 1. The rolling system according to one of claims 1 to 10, wherein

the mandrel (21) comprises a first pipe (9) allowing carrying a cooling medium and a concentric inner pipe (13) allowing the return of the cooling medium.

12. The rolling system of claim 1 1, wherein the mandrel (21) also comprises a second concentric pipe (12) for transporting a lubricating medium, and a plurality of injectors (14) in fluid communication with the second pipe ( 12), said injectors (14) for ejecting said medium of lubrication between the mandrel (21) and the blank (2) when the latter is on the mandrel (21).

13. The rolling system according to the preceding claim, wherein

each of said injectors (14) comprises a valve (1 5) comprising a piston (16) adapted to establish a fluid connection between the second pipe (12) and the outside of the mandrel (21) when the blank (2) is placed on the mandrel (21).

14. The rolling system according to one of claims 1 to 13, wherein

the profiled rings (22) are made of a ceramic material.

5. Rolling method using a rolling system comprising a piercer (7); an insulated channel (36) comprising at least one heating ring (35); a continuous rolling mill (8) comprising a plurality of rolling stands (20), each rolling stand (20) comprising at least two rolls (5); a mandrel (21) fixed, the mandrel (21) comprising a plurality of profiled rings (22) interconnected by intermediate tubes (23), the profiled rings (22) having an outer diameter greater than the diameter of the intermediate tubes (23). ) and caged cage in the direction of rolling; each of said at least two cylinders (5) having a substantially circular profile groove;

comprising: drilling a billet with the piercer (7) to obtain a blank (2);

equalizing the temperature of the blank (2) with the insulated channel (36) and said at least one heating ring (35); and

rolling the blank (2) into the continuous rolling mill (8), said rolling producing a substantially round section of the blank (2) at each of the rolling stands (20).

16. The rolling method according to claim 15, wherein

the piercer (7) is adapted to inject a gas, and wherein an inert gas is injected into the blank (2) during said piercing.

17. The rolling method according to claims 1 5 or 16, wherein

the rolling system also comprises a deoxidizer injection device (29), and wherein a deoxidant is injected into the blank (2) after said drilling.

18. The rolling method according to claim 1, wherein

during said rolling, the elongation ratio is between 1.5 and 1.0 for each of the cages (20).