Rolling plant, rolling mill and rolling method

Abstract

The invention relates to a pipe rolling plant 10 comprising a rotary piercer 20, a treatment station 30 and a main rolling mill 40. The rotary piercer and the treatment station are arranged so that the pierced blank 51 leaving them is arranged with the irregular tail 511 facing the main rolling mill 40 and with the regular head 510 facing the mandrel 41. The invention also relates to a rolling mill 40 comprising a plurality of rolling stations 43, each station comprising a plurality of rolling rolls 42, the radial position h of which is adjustable. The rolling mill also comprises a control circuit for calculating and/or measuring the distance d between the axes of rotation r of the rolls and the trailing edge 520 of the pipe 52. The control circuit is also designed to displace the rolling rolls radially towards the outside of the pipe in each rolling station 43.sub.n when the distance d assumes a predetermined value d.sub.0.

Claims

1. A plant (10) for rolling long hollow objects (51, 52) on a mandrel (41), comprising: a rotary piercer (20) that receives at its inlet a billet (50) and pierces the billet (50) longitudinally so as to obtain a pierced blank (51) having a regular head (510) and an irregular tail (511); a station (30) for treating the pierced blank (51) to a deoxidation treatment; a main rolling mill (40) comprising a plurality of rolling stations (43) that receives at its inlet the pierced blank (51) and rolls the pierced blank (51) on a mandrel so as to obtain a semifinished pipe (52); wherein the rotary piercer (20) and the treatment station (30) are arranged so that the pierced blank (51) leaving them: is arranged with a longitudinal axis of the pierced blank substantially parallel to the rolling axis X of the main rolling mill (40); and is arranged between the tip of the mandrel (41) and the first station (43.sub.1) of the main rolling mill (40); and the rotary piercer (20) and the treatment station (30) are furthermore arranged so that the pierced blank (51) leaving them is arranged with the irregular tail (511) facing the first station (43.sub.1) of the main rolling mill (40) and with the regular head (510) facing the tip of the mandrel (41).

2. The rolling plant (10) according to claim 1, wherein the plurality of rolling stations (43.sub.1-6) are arranged along a rolling axis X, each rolling station (43.sub.n) comprising a plurality of rolling rolls (42) rotatable about respective axes of rotation (r), the radial position h of which is adjustable by means of actuators; the rolling mill (40) also comprises a control circuit for controlling the radial position h of the rolling rolls (42) so as to obtain for the wall of the semifinished pipe (52) a substantially constant thickness (s) along the rolling axis X; wherein said control circuit comprises means suitable for calculating and/or measuring, projected along the rolling axis X, the distance d between the axes of rotation r of the rolls (42) and the trailing edge (520) of the pipe (52); and said control circuit is designed to displace the rolling rolls (42) radially towards the outside of the semifinished pipe (52) in each rolling station (43.sub.n) when the distance d assumes a predetermined value d.sub.0.

3. A method for rolling long hollow objects (51, 52) comprising the steps of: providing a billet (50); piercing the billet (50) longitudinally by means of a rotary piercer (20) so as to obtain a pierced blank (51) having a regular head (510) and an irregular tail (511); subjecting the pierced blank (51) to a deoxidization treatment; inserting a mandrel (41) into the pierced blank (51); rolling the pierced blank (51) on a mandrel in a main rolling mill (40) so as to obtain a semifinished pipe (52); wherein the mandrel (41) is inserted inside the pierced blank (51) via the regular head (510), and the irregular tail (511) of the pierced blank (51) is introduced firstly into the main rolling mill (40).

4. The rolling method according to claim 3, wherein the main rolling mill (40) comprises a plurality of rolling stations (43.sub.1-6), each rolling station (43.sub.n) comprises a plurality of rolling rolls (42) which are rotatable about respective axes of rotation r, the radial position h of which is adjustable by means of actuators; and the radial position h of the rolling rolls (42) is controlled so as to obtain for the wall of the semifinished pipe (52) a substantially constant thickness (s) along the rolling axis X; the method further comprises the steps of: calculating and/or measuring the distance d, projected along the rolling axis X, between the axes of rotation r of the rolls (42) of each rolling station (43.sub.n) and the trailing edge (520) of the pipe (52); and displacing the rolling rolls (42) radially towards the outside of the semifinished pipe (52) in each rolling station (43.sub.n) when the distance d assumes a predetermined value d.sub.0.

Description

(1) In order to understand more fully the invention and appreciate its advantages, a non-limiting example of embodiment thereof is described below with reference to the accompanying drawings in which:

(2) FIG. 1 shows a schematic plan view of a rolling plant according to the prior art;

(3) FIG. 2 shows a schematic plan view of a rolling plant according to the invention;

(4) FIGS. 3.a, 3.b and 3.c show schematically three rolling steps according to a known method;

(5) FIGS. 4.a, 4.b and 4.c show schematically three rolling steps according to a known method;

(6) FIGS. 5.a, 5.b and 5.c show schematically three rolling steps according to a method of the invention.

(7) In the accompanying figures, the reference number 10 denotes in its entirety a plant for rolling long hollow objects, typically seamless pipes.

(8) The plant 10 according to the invention, as shown in FIG. 2, comprises: a rotary piercer 20, a station 30 for treating the pierced blank 51 and a main rolling mill 40.

(9) The rotary piercer 20 is designed to receive a billet 50 at its inlet and to pierce it longitudinally so as to obtain a pierced blank 51 with a regular head 510 and a (frequently) irregular tail 511.

(10) The station 30 is designed to carry out a deoxidization treatment of the pierced blank 51.

(11) The main rolling mill 40 comprises a plurality of rolling stations 43 and is designed to receive at its inlet the pierced blank 51 and to roll the pierced blank 51 on the mandrel so as to obtain a semifinished pipe 52.

(12) The rotary piercer 20 and the treatment station 30 are arranged so that the pierced blank 51 leaving them: is arranged with its longitudinal axis substantially parallel to the rolling axis X of the main rolling mill 40; and is arranged between the tip of the mandrel 41 and the first station 43.sub.1 of the main rolling mill 40.

(13) In the plant 10 according to the invention, the rotary piercer 20 and the treatment station 30 are also arranged so that the pierced blank 51 leaving them is arranged with the irregular tail 511 facing the first station 43.sub.1 of the main rolling mill 40 and with the regular head 510 facing the tip of the mandrel 41.

(14) As mentioned above, the tail 511 of the pierced blank 51 often (but not always) has an irregular form. It should be noted however that with the plant according to the invention it is possible to roll any pierced blank, irrespective of the conditions of the tail 511. In other words, with the plant 10 according to the invention it is possible to achieve significant advantages compared to a conventional plant, in the frequent case where the tail 511 is irregular or even ragged. At the same time, however, the plant 10 according to the invention does not give rise to any disadvantage in those rare cases where the tail 511 has a regular form.

(15) According to another aspect, the invention also relates to a method for rolling long hollow objects. The method according to the invention comprises the steps of:

(16) providing a billet 50;

(17) piercing the billet 50 longitudinally by means of a rotary piercer 20 so as to obtain a pierced blank 51 with a regular head 510 and a tail 511 which is often irregular;

(18) subjecting the pierced blank 51 to a deoxidization treatment;

(19) inserting a mandrel 41 into the pierced blank 51;

(20) rolling the pierced blank 51 on the mandrel in a main rolling mill 40 so as to obtain a semifinished pipe 52.

(21) In the method according to the invention, moreover, the mandrel 41 is inserted inside the pierced blank 51 via the regular head 510, and the irregular tail 511 of the pierced blank 51 is introduced firstly into the main rolling mill 40.

(22) As the person skilled in the art will appreciate, with the plant 10 and the rolling method according to the invention it is possible to overcome some of the drawbacks mentioned above with reference to the prior art. In particular, the fact of introducing the mandrel 41 inside the pierced blank 51 via the head 510, which is always regular, involves the significant advantage of eliminating any risk associated with the possibility of a cold fragment being inserted between the mandrel 41 and the inner wall of the pipe 52 being rolled.

(23) Moreover, the particular orientation of the pierced blank 51 is such that the irregular and/or ragged zones caused by the rolling process are not combined with those arising previously from the rotary piercing operation. In fact, the irregular zones due to rotary piercing are located on the tail of the pierced blank 51 which subsequently forms the front end of the pipe 52. On the other hand, the tail end of the pipe is obtained from the head of the pierced blank which is always regular. The final effect is therefore that of drastically reducing the possibility that pipe fragments may become detached during rolling, thereby adversely affecting correct operation of the entire plant.

(24) According to a further aspect, the invention also relates to a rolling mill 40 for rolling a semifinished pipe 52.

(25) The rolling mill 40 according to the invention comprises a plurality of rolling stations 43.sub.1-6 arranged along a rolling axis X, wherein each rolling station 43.sub.n comprises a plurality of rolling rolls 42 which are rotatable about respective axes of rotation r, the radial position of which is adjustable by means of actuators.

(26) The rolling mill 40 also comprises a control circuit suitable for controlling the radial position h of the rolling rolls 42 so as to obtain for the wall of the semifinished pipe 52 a thickness s which is as constant as possible along the rolling axis X and is as similar as possible to a desired thickness.

(27) In the rolling mill 40 according to the invention, the control circuit comprises means suitable for calculating and/or measuring, projected along the rolling axis X, the distance d between the axes of rotation r of the rolls 42 of each rolling station 43.sub.n and the trailing edge 520 of the pipe 52.

(28) In the rolling mill 40 according to the invention moreover the control circuit is designed to displace the rolling rolls 42 radially towards the outside of the semifinished pipe 52 in each rolling station 43.sub.n when the distance d assumes a predetermined value d.sub.0. This is shown in FIGS. 5.b and 5.c, where the distance between the axis r of the roll and the mandrel 41 is reduced from h.sub.0 to h.sub.1 as for normal tapering, but upon reaching the distance d.sub.0 immediately changes from h.sub.1 to h.sub.2>h.sub.0.

(29) According to yet another aspect, the invention also relates to a second method for rolling long hollow objects 51, 52 comprising the steps of:

(30) providing a pierced blank 51;

(31) inserting a mandrel 41 into the pierced blank 51;

(32) providing a main rolling mill 40 comprising a plurality of rolling stations 43.sub.1-6, each rolling station 43.sub.n comprising a plurality of rolling rolls 42 which are rotatable about respective axes of rotation r, the radial position h of which is adjustable by means of actuators;

(33) rolling the pierced blank 51 on the mandrel in the main rolling mill 40 so as to obtain a semifinished pipe 52.

(34) The radial position h of the rolling rolls 42 is controlled so as to obtain for the wall of the semifinished pipe 52 a thickness s which is as constant as possible along the rolling axis X and is as similar as possible to a desired thickness.

(35) The second method according to the invention also comprises the steps of:

(36) calculating and/or measuring the distance d, projected along the rolling axis X, between the axes of rotation r of the rolls 42 of each rolling station 43.sub.n and the trailing edge 520 of the pipe 52; and

(37) displacing the rolling rolls 42 radially towards the outside of the semifinished pipe 52 in each rolling station 43.sub.n when the distance d assumes a predetermined value d.sub.0.

(38) The means designed to calculate and/or to measure the distance d between the axes r and the trailing edge 520 may comprise sensors, of the type known per se, able to recognize and track the position of the trailing edge 520 during its movement along the rolling axis X.

(39) Instead of or in addition to the sensors, the means designed to calculate and/or to measure the distance d may comprise sensors, of the type known per se, able to recognize the pressure peak which is recorded in each station 53 when the trailing edge 520 of the pipe 52 passes underneath the rolling rolls 42. It should also be noted here that, in addition to the interaxial distance between two successive stations which is obviously precisely known, the speed of feeding of the pipe 52 along the plant is also known. This speed may in fact be detected by special sensors or may also be calculated by the ratio between the length of the pipe 52 (which increases by a known factor in each station 43) and the rolling time (which is instead constant for all the stations 43). Knowing therefore the moment when the trailing edge 520 leaves the station 43.sub.n-1 as well as the interaxial distance and the speed of the pipe, it is possible to calculate in real time the distance d between the trailing edge 520 and the axis r of the rolls of the following station 43.sub.n.

(40) As the person skilled in the art will have been able to readily appreciate from the above description, with the rolling mill 40 and the second rolling method according to the invention significant advantages may be achieved compared to the prior art.

(41) The interruption of tapering in the vicinity of the trailing edge 520 of the pipe 52 allows in fact to protect the mandrel from the precocious wear which occurs with the conventional tapering method. The method according to the invention in any case produces an end section of the pipe which must be cut and discarded because it has a thickness which exceeds the permitted tolerance. This section, however, would have to be removed in any case owing to the irregularities arising from rolling; moreover the length of the thicker section is not determined by spontaneous and therefore random phenomena, but is determined by the control circuit and is therefore equal to about d.sub.0.

(42) Obviously, a person skilled in the art, in order to satisfy any specific requirements which might arise, may make to the plant 10, the rolling mill 40 and the methods according to the present invention further modifications and variations, all of which being moreover contained within the scope of protection of the invention, as defined by the following claims.