EP0100743B1 - Method of cold-rolling tubes by way of a pilper mill and device for carrying out the method - Google Patents

Abstract

The process and the device which are the object of the invention relate to the cold rolling of tubes by means of a Pilger mill. The tube blank is made to advance near each of the upstream and downstream dead centers reached by the roll stand during its forward and return cyclical movement and backward movement of the rear part of the blank is made possible during a return pass of the roll stand. This process makes possible a doubling of production without changing the operating rate of the roll stand.

Description

The present invention relates to a cold rolling process for the manufacture of tubes by means of a pilgrim step rolling mill. This rolling mill comprises, in a known manner, fluted rolls mounted in a movable roll-carrying cage which performs a reciprocating movement along the axis of the tube blank which is periodically advanced, the rolls being driven in rotation by a known means. A mandrel is arranged in the axis of the blank which is thus laminated between the cylinders and the mandrel.

Modern pilgrim step rolling mills of this type operate at high rolling rates which require moving the blank of the tube to be laminated for relatively short times, at very precise times when the cage reaches the end of its travel and where the rolls release the draft.

French patent n ° 1 602 013 describes a pilgrim step rolling mill comprising devices which imprint on the preform periodic movements of advance along its axis and of rotation about this same axis, this when the rolls are in neutral and release the draft at the end of their alternative back-and-forth journey.

The rotational movements are printed on the blank by tube clamps arranged on either side of the cylinder holder cage. The periodic and discontinuous movements of advance are printed on the blank by an articulated pusher, mounted on a carriage which supports the rear of the blank and advances continuously towards the cage.

As described in patent FR 1 602 013, this lever, in the form of a lever, is articulated about an axis. A cam controls the axial advance movement of the blank by imparting to the pusher a periodic tilting movement synchronized with the reciprocating movement of the cylinder carrier cage, this when the cage is in the vicinity of the dead center. end of travel of one of its outward or return movements and the cylinders release the blank.

For the sake of clarity, hereinafter, the upstream side designates the inlet side of the blank to be laminated in the cylinder cage, and the downstream side, the outlet side of the tube of the cage after reduction of its section by rolling between the rolls. The upstream-downstream movement of the cage and the cylinders is designated by the forward path and by the return path, the downstream-upstream movement along the axis of the blank.

Laminating, according to the technique described in patent FR 1 602 013, is usually carried out only during the outward journey, either from upstream to downstream of the cylinders, the grooves of the cylinders being designed to allow the free passage of the blank to be laminated for a short time near the upstream dead center.

Thus, according to this implementation of the rolling mill, the rolls efficiently work the metal by deforming it only during the outward journey of the cage. During the return journey, the cylinders only pass over an already rolled product, without performing any deformation work.

FR 2 442 674 teaches, however, that it is advantageous to advance and rotate the blank only when it is released from the grip of the two cylinders, while they are at the end of the race in the vicinity of the downstream dead center. This patent further teaches that the deformation of the blank is distributed between the outward and return paths of the cylinders although the blank is not advanced in the vicinity of the upstream dead center.

FR 2 463 646 teaches that, in order to obtain the highest possible yield, the blank is advanced and rotated in the vicinity of each of the two dead centers upstream and downstream of the back and forth movement of the cylinders, the advance upstream being different from the downstream advance. This patent teaches that the maximum advance of the blank can, depending on the circumstances, be done either upstream or downstream. This document does not, however, teach the criteria on which one must base oneself to define the upstream advance and the downstream advance. It also does not teach the means of achieving these advances, nor does it teach the means making it possible to ensure, under satisfactory conditions, rolling during the return journey. On the other hand, it is clearly stated in FR 2 463 646 that, taking into account the design of the rolling mill described in this patent, the advance of the tube carried out on the downstream side leads to a forming work which is distributed between the rolling phase of the 'downstream to upstream and the rolling phase from upstream to downstream (see page 1 lines 32-45). Thus an advance of the tube at the downstream dead center has the consequence of disturbing the rolling phase from upstream to downstream.

Furthermore, given the large masses to be moved cyclically and which include not only the cylinder holder cage, but also the blank and its pusher, it is important to have control means having at the same time a minimum of inertia, a great speed of intervention and a great precision. In the absence of these various means, it does not seem that cold rolling methods by a pilgrim step rolling mill comprising a double advance of the blank have developed so far.

We therefore sought the possibility of carrying out a cold rolling process of the tubes by means of a pilgrim step rolling mill in which we can adjust each of the rolling phases - from upstream to downstream and downstream upstream - without any reaction from one phase to the other.

In order to obtain maximum efficiency, efforts have also been made to distribute the deformation work of the tube blank between the outward path and the return path of the cylinder holder cage substantially equally. We also looked for the possibility of moving the blank downstream cyclically, in the vicinity of the dead points upstream and downstream of the back and forth movement of the cylinder holder cage, with speed and precision, while allowing its elongation towards upstream during rolling during the return path of the roll cage. Finally, we sought to define the relationship to preferably carry out between the feeds which should be made in the vicinity of the upstream dead center and the downstream dead center in order to obtain, during rolling, during the outward journey, more or less, the same work of deformation as during rolling during the return journey.

We have also looked into the possibility of producing a simple device capable of being implemented on a pilgrim step rolling mill, in which the rolling phases - from upstream to downstream and from downstream to upstream - do not react to each other, a device making it possible to make different advances in the vicinity of the upstream and downstream dead centers, the values of which are in a determined ratio and are reproducible in a precise manner.

The cold rolling process of tubes, which is the subject of the present invention, relates to a pilgrim step rolling mill, comprising a cylinder-carrying cage driven in a cyclic movement back and forth, in which one advances the tube blank in the vicinity of each of the upstream and downstream dead centers. It is characterized in that the recoil of the upstream part of the blank is allowed for the entire duration of the rolling carried out during the return path of the cylinder holder cage.

Preferably, the ratio between the downstream advance and the upstream advance is substantially equal to a, a being the coefficient of elongation of the blank produced by means of the rolling mill.

The invention also relates to a device for controlling the advance of a tube blank on a cold rolling mill with pilgrim steps in which this advance is achieved by means of a cam which makes a revolution while the cage is carrying cylinders back and forth, this cam comprising two bosses of diametrically opposite unequal thicknesses which act on the blank by means of a transmission means, one of the bosses being wedged to act on the blank when the cylinder holder cage is in the vicinity of the upstream dead center and the other boss being wedged to act on the blank when the cylinder holder cage is in the vicinity of the downstream dead center, the gripper device tubes allowing the backward movement of the upstream part of the blank for the entire duration of the return path of the cylinder holder cage. The thinner boss is preferably wedged to act on the rear of the blank in the vicinity of the upstream dead center of the cylinder holder cage.

A number of advantageous features of the method and the device also form part of the invention.

We will now describe, in more detail, the characteristics of the method according to the invention as well as those of a device for the implementation of this method. Next, a particular embodiment of the invention will be described.

It is well known that during a rolling pass, any blank undergoes, in the rolling direction, an elongation proportional to its thinning. In a pilgrim-type rolling mill of the type under consideration, the outward path of the roll cage does not pose any problem. In the vicinity of the dead center upstream of the cage, a pusher such as, for example, that described in FR 1 602 013, or any other pusher of known type, advances the whole of the blank by an optimal length that 'is designated by "Δ1". Then, during the outward journey of the cage, the blank itself lengthens by a length (a-1) 01 a being the coefficient of elongation. This coefficient a is defined as being the ratio of the length of the tube after rolling to the length of the blank before rolling. Thus, during the first rolling phase, which includes moving the blank to the upstream dead center, then the outward path of the roll cage, the rear of the blank advances by A1, and l 'before dawns on aA1. The front part of the blank being free, its movement downstream poses no problem.

With regard to the second rolling phase, which comprises moving the blank to the downstream dead center, then the return path of the roll cage, it appeared that, in order to obtain an optimal yield from the rolling mill, it was desirable to do substantially the same rolling job as in the first phase. This means that the blank must lengthen by approximately the same length (a-1) A1 during the return journey from the cage and the same quantity of additional metal must come to engage in the grip of the cylinders, which corresponds to the same effective advance A1 from the rear of the blank during the second phase.

• a) de permettre un allongement de l'ébauche d'environ (a-1 )A1 au cours deu trajet retour de la cage, l'extrémité arrière de l'ébauche ne devant pas venir en butée contre un poussoir ou contre tout autre obstacle susceptible de bloquer son déplacement vers l'amont de façon directe ou indirecte,
• b) d'obtenir, à la fin de la deuxième phase, un déplacement effectif de l'ébauche de environ A1 vers l'aval par rapport à la fin de la première phase.

However, during the return journey from the cage, the blank lengthens not downstream, but upstream. Also, if one wishes to have an optimal rolling yield during the second rolling phase, it is important:

• a) to allow an elongation of the blank by approximately (a-1) A1 during the return path of the cage, the rear end of the blank not having to abut against a pusher or any other obstacle likely to block its movement upstream directly or indirectly,
• b) to obtain, at the end of the second phase, an effective displacement of the blank by approximately A1 downstream relative to the end of the first phase.

• a) lors du temps de manoeuvre au point mort aval Δθ₂, de faire tourner l'ébauche autour de son axe, de façon connue, par exemple du même angle que lors du temps de manoeuvre au point mort amont et de la faire avancer d'une longueur d'environ αΔ1, c'est-à-dire d'une longueur Δ1 égale à l'avance effectuée au point mort amont multipliée par le coefficient a.
• b) pendant le trajet retour de la cage l'ébauche s'allonger vers l'amont d'une longueur d'environ (α-1)Δ1.

To obtain maximum yield from the rolling mill, the operating times Δθ ₁ and Aθ ₂ which are available in the vicinity of the upstream and downstream dead centers for advancing and freely turning the blank, have substantially the same duration Δθ. Similarly, the durations of the outward and return journeys of the cage are substantially equal. The total duration of the second rolling phase Δt2, including the duration Δθ ₂ of the maneuvering time at downstream dead center, is thus equal to the total duration Δt ₁ , including the duration Δθ ₁ , of maneuvering at upstream dead center. We can admit that Δt ₁ = Δt ₂ = Δt. It follows from these observations that, in order to have an optimal yield from the back rolling phase, it is important:

• a) during the downstream maneuvering time Δθ ₂ , to rotate the blank around its axis, in a known manner, for example by the same angle as during the neutral operating time upstream and advancing it by a length of about αΔ1, that is to say a length Δ1 equal to the advance made at the upstream dead center multiplied by the coefficient a.
• b) during the return journey from the cage, the blank is extended upstream by a length of approximately (α-1) Δ1.

Thus, at the end of the second phase, the rear of the blank is effectively advanced by a residual length of approximately Δ1 substantially equal to its advance during the first rolling phase.

The invention also relates to a device for controlling the advance of the blank for implementing the method which has just been described. This device makes it possible, under particularly favorable conditions, to carry out the periodic advance of the blank according to the laws which have just been established. It comprises, in known manner, a pusher in the form of a tilting lever, similar to a rocker arm, which is advantageously mounted on a carriage such as, for example, that described in FR 1 602 013. This carriage supports the rear of the draft while advancing at a practically constant speed in the direction of the cylinder holder cage. The tilting of the pusher is controlled by a cam which rotates one complete revolution while the cylinder holder cage goes back and forth. The particularity of the device according to the invention consists in that the cam comprises two diametrically opposite bosses, which each control a rocking movement of the pusher and, consequently, a movement in advance of the blank. The cam is calibrated so that the advances of the blank occur when the cylinder cage is located in the vicinity of each of the two upstream and downstream dead centers.

The thickness of the first boss is such that the corresponding tilting of the pusher transmits to the blank an optimal advance of Δ1 in the vicinity of the upstream dead center, before the outward journey of the cylinder holder cage. This value Δ1 is determined in a known manner as a function of various parameters such as: quality of the metal, dimensions of the blank and of the tube to be produced, characteristics of the grooves of the cylinders and of the mandrel, or others.

Preferably, the second boss, diametrically opposite on the cam, is substantially as thick as that which allows the pusher to transmit to the blank an advance substantially equal to αΔ1 in the vicinity of the downstream dead center, before the return path of the carrier cage. -cylinders. To take into account the constant advance speed ^Δ1 _Δt of the carriage and the multiplying coefficient k of the lever-shaped pusher, the thickness, e ₁ of the first boss is substantially k Δ1 (1- ^Δθ _Δt ) and the thickness e ₂ of the second boss of k Δ1 (α- ^Δθ _Δt ).

• La figure 1 représente, en vue cavalière, un laminoir à froid à pas de pèlerin, qui permet la mise en oeuvre du procédé suivant l'invention.
• La figure 2 représente, en coupe selon son plan de symétrie vertical, un chariot qui supporte l'arrière de l'ébauche et qui est équipé du dispositif de commande d'avance de l'ébauche suivant l'invention.
• La figure 3 représente plus en détail, en coupe, selon le même plan, la came suivant l'invention qui commande le basculement du poussoir.
• Les figures 4a, 4b, 4c, 4d, 4e représentent schématiquement chacune une demi-coupe axiale de l'ébauche au début et en fin de chacune des deux phases de laminage consécutives, aller et retour, correspondant à un cycle complet de laminage aller-retour de la cage porte-cylindres dans le procédé suivant l'invention.
• La figure 5 est un diagramme où sont représentés schématiquement en ordonnées, les déplacements successifs de la partie arrière de l'ébauche en fonction du temps au cours du cycle décrit dans les figures 4a à 4c.

The description and the figures below present, in a nonlimiting manner, a particular mode of implementation of the invention.

• Figure 1 shows, in perspective view, a cold rolling mill with pilgrim's step, which allows the implementation of the method according to the invention.
• FIG. 2 represents, in section along its vertical plane of symmetry, a carriage which supports the rear of the blank and which is equipped with the device for controlling the advance of the blank according to the invention.
• Figure 3 shows in more detail, in section, along the same plane, the cam according to the invention which controls the tilting of the pusher.
• FIGS. 4a, 4b, 4c, 4d, 4e each diagrammatically represent an axial half-section of the blank at the beginning and at the end of each of the two consecutive rolling phases, back and forth, corresponding to a complete round rolling cycle. return of the cylinder holder cage in the process according to the invention.
• Figure 5 is a diagram where are shown schematically on the ordinate, the successive displacements of the rear part of the blank as a function of time during the cycle described in Figures 4a to 4c.

In FIG. 1, a cold rolling mill with pilgrim steps is shown, of a design similar to that which is, for example, described in FR 1 602 013. The cylinder holder cage (1) is shown in phantom. The connecting rods (2-2 ') give it an alternating back and forth movement along the axis (XX') of the blank (3). A carriage (4) comprising a pusher (5) shown in more detail in FIG. 2, supports the rear of the blank (3). This carriage (4) is driven by a screw (6) which makes it move continuously and regularly at the speed Δ1 / At in the direction of the cage (1), that is to say in the direction of the arrow (F) defining the upstream-downstream direction. Tube clamps (7-7 ') hold the blank (3) upstream and downstream of the cage (1). As in the prior art, these tube clamps (7-7 ') periodically rotate the blank (3) around its axis (XX') by an angle of, for example, 60 °, this when the cage ( 1) arrives at one of its dead centers at the end of the outward or return journey. The blank (3) slides in the clamps (7-7 ') when the pusher (5) advances it relative to the carriage (4).

A rod clamp (8), located at the rear of the rolling mill, maintains an internal mandrel (9) and periodically rotates it in synchronism with the rotations of the blank (3). This mandrel does not undergo any axial displacement.

In Figure 2, the section of the carriage (4) by the vertical plane passing through the axis (XX ') of the blank, allows to better see the details. This carriage (4) supports the rear of the blank (3) by means of a sleeve (10) and a hollow rotating sheath (11). The blank (3) is pushed from behind via a spring stop (12) integral with the sheath (11). As shown in the figure, the sleeve (10) can move relative to the carriage along the axis (XX ') by sliding on spans (P-P'). A heliocoidal spring (13) is compressed when the sleeve (10) moves by relation to the carriage upstream. The pusher (5) is articulated around a horizontal axis (15) integral with the carriage (4). The lower part of the pusher (5) is divided into two fingers (14) symmetrical with the cutting plane to allow the fixed internal mandrel (not shown here) to pass in the axis of the blank (3) as well as to allow changes rough (3).

Thus the blank (3) is pushed forward by the combination on the one hand, of the continuous movement of the carriage (4) driven by the screw (6) at constant speed A1 / Δt and, on the other hand , periodic thrust of the fingers (14) of the plunger (5) which oscillates around the axis (15). The pusher (5) is controlled by a roller rod (16) and a cam (17) acting in opposition to the sleeve (10).

According to the invention, the cam (17) has two diametrically opposite bosses (18-19), as shown in FIG. 3.

The thickness (e ₁ ) of the boss (18) measured beyond the minimum radius (r) of the cam, is determined so that, when this boss acts on the pusher (5) via the rod to roller (16), this pusher moves the blank (3) upstream via the sleeve (10) and the sleeve (11) of length Δ1 when the cage is in the vicinity of the upstream dead center . Likewise, and preferably, the thickness (e ₂ ) of the boss (19) measured beyond this same radius (r), is determined so that, via the pusher (5), this boss causes an advance of the blank by αΔ1, when the cylinder carrier cage is in the vicinity of the downstream dead center.

More precisely, to take into account, on the one hand, the proper advance A ^Δθ _Δt of the carriage (4) during the upstream and downstream dead times, and, on the other hand, the coefficient "k" equal to the length ratio upper and lower arms of the pusher (5) relative to the axis (15), the thickness (e1) of the boss (18) is substantially k Δ1 (1 - ^Δθ _Δt ) and the thickness (e ₂ ) of the boss (19) is substantially k Δ1 (a ^Δθ _Δt ). The profile of the cam (17) corresponds substantially to the profile of the staircase curve (0 C ₂ C ₃ C ₄ C ₅ ...) of Figure 5, which represents the displacement of the rear part of the blank in function time. The cam (17) can be traced by giving it, for the thickness of the bosses, the difference between the ordinates of the curve (OC ₂ C ₃ C ₄ C ₅ ...) and the ordinates of the straight line (OY) representing the displacement of the carriage (4) along the axis (XX ') at a constant speed ^Δθ _Δt . To take account of the inertia of the mechanical parts and to avoid jolts, the angular points of the curve (0 C ₂ C ₃ C ₄ C ₅ ...) are obviously rounded on the cam (17).

To better understand the preferred mode of implementing the process, there is shown schematically, and without taking account of a scale, in Figures 4a, 4b, 4c, 4d, 4th, in section, the successive positions of the blank (3) relative to the mandrel (9), before and after each of the two phases of a complete rolling cycle with a back and forth movement of the cage (1).

As is well known by practitioners, the mandrel (9) is rotated around the axis (XX ') during the neutral time θθ before each rolling pass back or forth, this at the same time as the blank (3) but is never moved along the axis (XX ').

Like the mandrels of the prior art, this mandrel (9) has a cylindrical rear part and a front part which tapers in accordance with a profile known per se to best conform to the deformation of the blank (3) during of a rolling pass.

The plane orthogonal to the axis XX ', along which the cylindrical part and the thinned front part of the mandrel (9) are connected is here marked at (AA').

For the sake of clarity, a fixed orthogonal plane, further back, has been identified by (BB '). A mark (C) has also been shown on the rear of the blank (3) which advances step by step between each rolling pass, both back and forth. This mark (C) successively occupies the positions (C ₁ , C ₂ , C ₃ , C ₄ , C ₅ ...) with respect to the plane (BB '). These references (C ₁ , C ₂ , C ₃ , C ₄ , C _5, etc.) have also been shown on the corresponding points of the diagram in FIG. 5, as well as on the cam in FIG. 3.

In Figure 5, the starting point (0) of the curves corresponds to point (C ₁ ). A mark (D) has been shown on the already laminated part of the blank in line with the end (20) of the mandrel (9).

At the end of a complete rolling operation by back-and-forth movement of the cage (1), the blank (3) is pressed against the mandrel (9) by the last return phase as shown in FIG. 4a. The reference (C ₁ ) is in the marked plane (BB ').

In order to allow rolling work during the next rolling cycle and, more particularly, during the next forward phase of the cage (1), the blank (3) is advanced by the carriage (4) and the pusher. (5) of length Δ1, this for the time available at the upstream dead center Δθ ₁ of the cylinder holder cage (1). The reference (C ₁ ) comes at (C ₂ ) at a distance Δ1 downstream from the plane (BB '), as shown in FIG. 4b.

The blank (3) detaches from the mandrel (9) as is particularly apparent near the plane (AA ') in Figure 4b. The point (D) of the laminated part which was in (D ₁ ) plumb with the front end (20) of the blank (3) advanced by Δ1 in (D ₂ ), as shown in Figure 4b.

The outward path, either in the direction (F) of the cage (1), then thins the blank by lengthening it and pressing it against the mandrel (9), as shown in FIG. 4c. The reference (C) remained in (C ₃ ) at the same distance Δ1 from the plane (BB '). The point (D) of the blank (3) advanced in (D ₃ ) at a distance aA1 from the front end (20) of the mandrel (9).

While the cage (1) is in neutral downstream, under the action of the carriage (4) and the pusher (5), the blank (3) is again advanced but this time, not of a length Δ1, but of approximately αΔ1, as shown in FIG. 4d where the mark (C) comes at (C ₄ ) at a distance approximately αΔ1 downstream of its anterior position (C ₃ ), that is to say at a distance of approximately (1 + a) Δ1 from the plane (BB '). The mark (D) is simultaneously advanced beyond its previous position (D ₃ ) by the same distance of approximately αΔ1. It is thus located in (D ₄ ) at a distance of approximately 2 αΔ1 from said end (20). During the return path of the cage (1), the blank is pressed against the mandrel (9). The front end of the blank does not move, as shown by the reference (D5) which does not move relative to (D ₄ ). The metal of the blank is however forced backwards and the mark (C) comes at (C ₅ ) at a distance 2 Δ1 downstream from the plane (BB '), as shown in FIG. 4e. We can then start a new round-trip rolling cycle which will start with a new advance from the rear of the blank (materialized by point C) with a new length Δl.

The backward movement of the rear of the blank (3) during the return path of the cage (1) is made possible by the control of the pusher (5) by the descending part (C ₄ C ₅ ) of the boss (19) of the cam (17). The shape of the descending part (C ₄ C ₅ ) of this boss (19) corresponds to a recoil of the fingers (14) of the pusher (5) which allows the recoil of the sleeve (10) and of the sleeve (11) pushed by the rear end of the blank.

The shape of the cam (17) can easily be deduced from the diagram of FIG. 5 where, on the abscissa (OT), is plotted the time and, on the ordinate (OL), the advance from the rear of the blank materialized by the mark C. The continuous advance of the carriage (4) along the axis (XX ') is materialized by the right (OY). The slope of this line is Δ1 / Δt.

The equal time intervals "t" taken to carry out each round-trip or return rolling phase are indicated by the marks (t ₁ , t ₂ , t ₃ , t ₄ ) on the time axis. The actual advances made by the back of the blank (or point C) during each phase, are materialized by the ordinates of the curve (0 C ₂ C ₃ C ₄ C ₅ ). The point (C ₁ ) is confused with the origin (O). This curve then repeats itself. On the time axis, we notice the intervals Δθ ₁ and Δθ ₂ corresponding to the duration of the maneuver times available at the neutral points upstream and downstream of the movement of the cage (1).

It is during these time intervals Δθ = Δθ ₁ = Δθ ₂ that the blank (3) is released from the grip of the cylinders and can be advanced under the combined effect of the advance of the carriage (4) and the fingers (14) of the pusher (5).

Likewise, FIG. 6 represents the displacements of the front part of the blank as a function of time. The scales used are the same as in FIG. 5. The point (D ₁ ) is confused with the origin 0. The points (D ₂ , D ₃ , D ₄ and D ₅ ) correspond to the same instants as the points (C ₂ , C ₃ , C ₄ , C ₅ ) of FIG. 5. It can be seen that, during a complete cycle, the front (D) advances by 2 αΔ1, while the rear (C) advances by 2 Δ1.

During the first dead time Δθ ₁ , the rear of the blank (C) as well as the front (D) advance simultaneously by a length Δ1 of (C ₁ ) in (C ₂ ) and of (D ₁ ) in (D ₂ ). This advance results, on the one hand, from a displacement Δ1 ^Δθ _Δt due to the advance of the carriage (4) as a whole and, on the other hand, from a displacement Δ1 (1 - ^Δθ _Δt ) under the pushing of the fingers (14) of the pusher (5) actuated by the rising part (C ₁ C ₂ ) of the boss (18) of the cam (17). During the forward rolling path, the point (C) remains substantially stationary at (C ₂ ), because the fingers (14) of the pusher (5) do not exert pressure on the sleeve (10). Indeed, the advance Δ1 (1- ^Δθ _Δt ) of the carriage (4) is compensated by the recoil of the fingers (14) corresponding to the descending part (C ₂ C ₃ ) of the boss (18). Simultaneously, point (D) advances from (D ₂ to D ₃ ) by a length (α-1) Δ1.

During the second dead time Δθ ₂ , the front as well as the rear of the blank (3) advance approximately αΔ1. The marks (C) and (D) come respectively in (C ₄ ) and (D ₄ ). This advance is the result, on the one hand, of the advance of the carriage (4) by Δ1 ^Δθ _Δt and, on the other hand, of the advance of approximately Δ1 (α- ^Δθ _Δt of the fingers (14) actuated by the rising part C ₃ C ₄ of the boss (19). The rising parts of the bosses (18-19) each correspond to the same angle β = π ^Δθ _Δt ·

During the return journey, the front of the blank (D) remains stationary at (D5) while the rear recedes by about (a-1) Δ1, point C moving from C ₄ to C ₅ .

The backward movement of the rear (C) of the blank (3) is permitted because, in advance of the carriage (4) by Δ1 (1 - ^Δθ _Δt ), there is a greater recoil equal to Δ1 (α - ^Δθ _Δt ) of the fingers (14) of the pusher (5) actuated by the descending part (C ₄ C ₅ ) of the boss (19) of the cam (17).

Tests have shown that, depending on the types of grooves and mandrels used, one can observe a slight recoil from the rear part of the blank during the forward rolling path. This setback depends, in particular, on the position of the neutral radius of the rolling cylinder relative to the depth of the groove. The neutral radius is the radius of the circle for which the circumferential speed is equal and opposite to the speed of translation of the cage. It is easy to understand that, when the tube comes into contact with the groove in its deepest zone, that is to say of radius smaller than the neutral radius, the cylinder tends to entrain the metal in the direction of movement of the cage because the circumferential speed at throat depth is less than the speed of translation in the direction of movement.

On the contrary, at the end of the groove, in the shallow zone thereof, the circumferential speed at the bottom of the groove is greater than the translation speed and the cylinder tends, on the contrary, to drive the metal in the opposite direction from the direction of movement of the cage.

A very great advantage of the method and of the device according to the invention is that they make it possible to give the cam bosses the desired shape to accompany relative displacement of the rear of the blank relative to the carriage during travel paths. rolling.

It is generally not necessary for the profile of the cam in the descending zone (C ₂ -C ₃ ) to be such that the fingers (14) in their recoil movement remain in contact with the rear part of the bush (10) integral with the blank (3) in its movement of relative movement upstream relative to the carriage (14). This means that the slope of descent of the cam profile beyond the top of the boss (18) can be, if desired, much faster than the minimum slope which ensures the retraction of the fingers (14) at a speed of each instant equal to the relative speed of recoil from the rear of the blank (3) relative to the carriage (4).

On the other hand, during the return rolling path, it is very important to control the recoil movement of the blank by means of an adapted profile of the cam in the descending zone (C ₄ -C ₅ ) beyond the top of the boss (19).

In fact, due to the advance αΔ1 of the blank which was produced at the level of the downstream dead center, the blank is detached from the thinned part of the mandrel over a considerable length and risks sliding upstream while escaping. partly in the grip of the cylinder grooves during the return path of the cylinder cage. The cam profile in the area (C ₄ -C ₅ ) must therefore be studied in order to allow the recoil without sliding of the blank relative to the carriage. This recoil speed without slippage of the blank during the back rolling phase depends on many factors such as the physical characteristics of the metal to be rolled, the section of the blank, the elongation coefficient "α" which is imposed, the shape of the mandrel in the rolling zone, and the corresponding shape of the grooves of the rolls.

In practice, it is generally attempted to give the cam in the area (C47-C5) a profile such that the speed of recoil of the fingers (14) is substantially equal at all times to the speed of recoil of the blank without slipping.

In order to avoid the risks of breakage of the pusher or of the cam, it is useful to provide a force limiting means such as a calibrated spring which can be inserted at a suitable point in the mechanical transmission between the rear of the and the cam. This device can also be accommodated at the level of the drive means of the cam-carrying carriage.

It is possible to have between the cam (17) and the pusher (5) not a roller rod (16) rolling directly on the cam, but a transmission means comprising an amplitude adjustment making it possible to modify the coefficient “k »Transmission to the fingers (14) of the displacements caused by the bosses (18) and (19). One can, for example, use a connection between cam (17) and pusher (5) produced by means of a lever having at least one adjustable arm such as that described in FR 2 379 326. Thanks to such a device , the advance can be modified as a function of the deformability characteristics of the metals or alloys to be transformed, “α” remaining constant for a given cam.

It is also possible to envisage placing the cam and the pusher not on a mobile carriage, but at a fixed location, the pusher (5) then driving the blank (3) by means of a direct transmission.

It is also possible, instead of a single cam, to use two synchronized cams, one comprising the boss (18) and the other, the boss (19). These two cams can each actuate directly or indirectly, a pusher whose fingers come to bear on the rear of the blank, generally by means of a socket.

Tests have shown that the process and the device according to the invention make it possible to remarkably increase the productivity of cold rolling mills with pilgrim steps thanks to the balanced distribution of the rolling works over the entire operating cycle, without modifying the rate of operation of the cylinder holder cage. Furthermore, taking into account the high rates of walking of the cage, it is particularly advantageous to mount the advance device on a mobile carriage such as that described in FIGS. 1 and 2. Advance changes can be made easily by changing cam or using a transmission with amplitude adjustment.

Such an arrangement makes it possible to reduce the importance of the masses in movement, to shorten the mechanical transmissions and to reduce the clearances for the advance of the blank, compared to an arrangement according to which the cam system is mounted at a fixed station. In all cases, the advance modifications can be carried out easily by changing the cam or even by using a transmission comprising an amplitude adjustment.

The nonlimiting example below describes, without limitation, an embodiment of the device and the method according to the invention.

A pilgrim pitch rolling mill is used for cold rolling capable of blanks with an outside diameter of between 70 and 140 mm, equipped with working rolls of 500 mm in diameter working at the rate of 120 round-trip cycles per minute.

A blank tube 80 mm in outside diameter and 8 mm thick is used.

This rolling mill is equipped with a feed system by means of a pusher controlled by a cam which performs one turn while the cylinder holder cage makes a round trip. Given the characteristics of the rolling mill and the blank metal, the working parameters are chosen to be a feed of the blank Δ1 of 10 mm and an elongation coefficient a of 4.

This rolling mill is first used in a conventional manner, the cam comprising a single boss, and a single advance Δ1 per cycle is thus produced at the upstream dead center.

The blank therefore advances by 1.2 m / min and 4.8 m / min of laminated tube is obtained. The cam with a single boss is then replaced by a cam according to the invention comprising two bosses whose thickness ratios and profiles are determined in accordance with the invention, so as to allow an advance of the blank equal to Δ1 at upstream neutral and equal to αΔ1 at downstream neutral. It is found, under these conditions, that by operating at the same rate of 120 cycles per minute, the blank advances by 2.4 m / min and we obtain 9.6 m / min of laminated tube. The invention therefore makes it possible to double production without modifying the rate of operation of the cylinder holder cage.

Claims (14)

1. A process for the cold rolling of tubes in which a pilger rolling mill comprising a roll-bearing housing (1) actuated with a cyclic to-and-fro movement is used, in which the tube blank (3) is advanced in the vicinity of each of the upstream and downstream dead points, characterised in that the return of the upstream portion of the blank is permitted throughout the duration of rolling carried out during the return travel of the roll-bearing housing (1).

2. A process according to claim 1, characterised in that the ratio between the downstream advance and the upstream advance is substantially equal to a, a being the coefficient of elongation of the blank.

3. A process according to claim 1, characterised in that the return of the rear portion of the tube blank relative to a fixed reference point is substantially equal to the effective advance at the upstream dead point multiplied by (a-1).

4. A process according to one of claims 1 to 3, characterised in that the return of the rear portion of the blank is monitored.

5. A device for carrying out a process for the cold rolling of tubes in which a pilger rolling mill comprising a roll-bearing housing (1) actuated with a cyclic to-and-fro movement is used, said device allowing the advance of the tube blank (3) to be controlled in the vicinity of each of the upstream and downstream dead points, characterised in that this advance is controlled by means of at least one cam (17) which performs one turn while the roll-bearing housing (1) performs a to-and-fro movement this cam comprising two diametrally opposed humps (18-19) of unequal thickness which act axially on the blank via a transmission means, one of the humps being set to act on the blank at the moment when the roll-bearing housing is located in the vicinity of the upstream dead point and the other being set to act on the blank at the moment when the roll-bearing housing is located in the vicinity of the downstream dead point and in that the tube- gripping device (7, 7') allows the return of the upstream portion of the blank throughout the duration of the return travel of the roll-bearing housing (1).

6. A device according to claim 5, characterised in that the hump of least thickness (18) is set to act on the blank in the vicinity of the upstream dead point of the roll-bearing housing.

7. A device according to claim 5 or 6, characterised in that the cam (17) is integral with a carriage (4) which travels at a constant speed in a downstream direction during rolling.

8. A device according to claim 5, 6 or 7, characterised in that the cam (17) acts on the blank (3) via a pushing device (5).

9. A device according to claim 8, characterised in that a transmission means (16) is placed between the cam (17) and the pushing device (5).

10. A device according to claim 8 or 9, characterised in that the pushing device (5) or the transmission means (16) comprise amplitude adjustment means.

11. A device according to one of claime 6 to 10, characterised in that the ratio between the thicknesses of the two humps e2/e, is approximately a.

12. A device according to one of claims 6 to 11, characterised in that the thickness (e_l) of the hump (18) is substantially equal to k Δ1 (1- ^ΔθΔt ) and that the thickness (e₂) of the hump (19) is substantially equal to k Δ1 (a- ^Δθ _Δt ), expressions in which k is the multiplying coefficient of the pushing device, Δθ is the manipulation time available at the upstream and downstream dead points for advancing and turning the blank freely and At is the duration of a turning phase including Δθ.

13. A device according to one of claims 5 to 12, characterised in that a stress-limiting means is interposed in the region of the mechanical transmission between the rear of the blank and the cam or in the region of the carriage driving means.

14. A device according to claim 13, characterised in that this stress-limiting means is a calibrated spring.

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