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Field of the invention

The field of the invention is the manufacture of seamless rolled pipes using a cross-rolling rolling stand.

Background art

A rolling operation of seamless pipes is carried out in several steps, comprising the perforation step, the rolling step, also defined as the finishing step, and the calibration step to the final diameter required.

Some or all of these steps are carried out by means of rolling stands having working rolls with skew axes, which are also simply called oblique rolling mills. The working rolls in these rolling stands generate the feed of the body being rolled with a helical motion. Oblique rolling mills, also called cross rolling mills, are generally of the single stand type with two or three working rolls.

The piece to be rolled entering the rolling mill may be solid, i.e. it may be a billet, and in this case the rolling mill is a perforator, or the material to be processed is a hollow body, which was previously perforated, and in this case the rolling stand is called elongator.

In the case of rolling stands with two rolls with skew axes, the preferred arrangement over the last 20 years is the one in which the rolls are substantially arranged vertically one above the other. In this case, two lateral guide devices are always horizontally provided, which are apt to contain the expansion of the body being rolled, i.e. the variation in outer diameter between the inlet and the outlet of the rolling stand.

The most common lateral guide devices in the past were of the fixed kind, called shoe guides, which are shaped slides on which the material to be rolled slides. More recently, lateral guide devices have been made using motorized disc guides with a significant volume, due to their large diameter. Solutions of this type of lateral guides are described for example in publications US3845646 and US4387584.

In both types of lateral guides, the function is always provided of approaching and moving away the guide devices to/from the rolling axis in radial direction. In certain cases of rolling stands, the adjustment is likewise provided of the lateral guides also in the longitudinal direction parallel to the rolling axis, and in the vertical direction.

Rolling stands are known with fixed lateral guides mounted on a turret, which is rotatable by 180 °, so as to allow the fixed guide, once it is worn, to reach a substitution position and to simultaneously bring a new guide into the working position.

None of these solutions of stands with fixed lateral guides or consisting of rotatable disc guides, described among others in GB1441472A, has truly met all the requirements of the market, hence the need is felt to improve the versatility of rolling stands with working rolls with skew axes.

Summary of the invention

It is the primary object of the present invention to provide a rolling stand with two rolls with skew axes, which is versatile and flexible in its operations and has reduced maintenance costs.

This object is achieved by means of a rolling stand for rolling seamless pipes which, according to claim 1 ,

defines a horizontal rolling axis R and comprises

two working rolls with skew axes and arranged one above the other,

two lateral guides for the piece to be rolled, which in specific first rolling operations are two fixed shoe guides and in specific second rolling operations are two rotatable disc guides which are rotatable about a vertical axis, each of the two lateral guides being arranged at a side of the rolling axis R,

two motors for generating a rotation motion of the two rotatable disc guides, two rotatable turrets which are rotatable about a vertical axis thereof, for positioning the lateral guides, comprising couplings for fastening the fixed shoe guides and alternatively for fastening the rotatable disc guides, and transmission means for transmitting the rotary motion generated by the motors to the two rotatable disc guides,

at least two fastening blocks for fastening the fixed shoe guides in the working position, so as to allow rolling operations both with the fixed shoe guides and with the rotatable disc guides in various periods of the operating life of the rolling stand. According to another aspect of the invention, the aforesaid object is achieved by means of a method for substituting the lateral guides of a rolling stand, wherein there is provided a rolling stand of the invention on which two shoe guide-holders with one or more respective fixed shoe guides are mounted, comprising the following steps

- moving the two rotatable turrets together with the two shoe guide-holders and the fixed shoe guides away from the working position,

- automatically uncoupling the cooling circuit conduits of the shoe guide- holders from the rotatable turrets and removing the shoe guide-holders from the rolling stand,

- transporting two rotatable disc guides toward the rolling stand,

- hooking the rotatable disc guides on the rotatable turrets, releasing the locking brakes against the rotation of the rotatable turrets, engaging the transmission of the motion from the motors,

approaching the rotatable disc guides to the rolling position.

By virtue of the combination of the features of the invention, the advantage results of mounting the rotatable turret so as to substitute the shoe guides more easily and quickly, and to cool down, by means of a closed circuit, the shoe guide-holder assembly to which the shoe guides themselves are fastened in removable manner. The continuous, or otherwise controlled, cooling of the shoe guide-holders improves the duration of the shoe guide which, in the absence of cooling, normally lasts a few hundreds of pieces before showing significant wear, fire cracks or breaks.

The versatility of the rolling stand of the invention allows an increased variety of rolled products to be obtained with the same stand, as it can be used in various operating conditions. The advantage of the fixed shoe guide with respect to the rotating one is an improved containment of the material being rolled and an improved cylindrical shape of the rolled body at the rolling mill outlet. On the other hand, the disadvantage of using the fixed shoe guide is the shorter duration with respect to the rotatable disc guide and the need to compensate for the wear by periodically approaching the shoe guide to the rolling axis, and therefore it is preferable to use lateral rotatable disc guides in certain operating conditions by substituting the fixed ones with a quick and simple operation.

It is apparent that such a system is very versatile and therefore allows the solution to be optimized for each type of product to be rolled. Moreover, it is a solution of rolling stand which can be applied to the rolling of both holed pieces and solid pieces, i.e. as a perforating stand and as an elongator or finishing stand.

Furthermore, since it is not needed to put cooling water onto the shoe guide, as is rather common practice, the cooling of the material being rolled is reduced, by keeping it at temperatures exceeding 1000 °C, which is to the complete benefit of the successive rolling operations.

The dependent claims refer to preferred embodiments of the invention.

Brief description of the drawings

Further features and advantages of the invention will become more apparent in the light of the detailed description of a preferred, but not exclusive, embodiment of a rolling stand according to the invention, shown by way of non-limiting example, with the aid of the accompanying drawings in which:

figure 1 depicts a front view, in the direction of the rolling axis, of a rolling stand according to the invention in a first operating configuration;

figure 2 depicts a front view of a detail of the rolling stand in figure 1 ;

figure 3 depicts a top view of a detail of the rolling stand in figure 1 , in a first operating position;

figure 4 depicts a top view of another detail of the rolling stand in figure 1 , in a second operating position;

figure 5 depicts a plan view of a detail of the rolling stand in figure 1 ;

figure 6 depicts a front view of an enlarged, exploded detail of the rolling stand in figure 1 ;

figure 7 depicts a sectional view on a vertical plane parallel to the rolling axis, of the rolling stand in figure 1 ;

figure 8 depicts the axial section, along a vertical plane, of a detail of the rolling stand in figure 1 ;

figure 9 depicts a side view of the detail in figure 8; figure 10 depicts the axial section along a vertical plane, of another detail of the rolling stand in figure 1 ;

figure 11 depicts a front view in the direction of the rolling axis, of a rolling stand according to the invention in a second operating configuration;

figure 12 depicts a side view of the stand in figure 11 ;

figure 13 depicts a plan view of the stand in figure 11 ;

figure 14 depicts a front view, in the direction of the rolling axis, of a rolling stand according to the invention in a configuration of preparing to change the rotatable disc lateral guides;

figure 15 depicts a plan view of the stand in figure 14;

figure 16 depicts a front view in the direction of the rolling axis, of a rolling stand according to the invention in a configuration where the rotatable disc lateral guides are substituted by fixed lateral guides;

figure 17 depicts a plan view of the stand in figure 16;

figure 18 depicts a front view in the direction of the rolling axis, of a rolling stand according to the invention in a configuration where fixed lateral guides are inserted, and before reaching the operating position;

figure 19 depicts a plan view of the stand in figure 18.

The same numbers in the figures correspond to the same elements or components.

Detailed description of embodiments of the invention

With particular reference to the drawings, the rolling stand 1 according to the invention defines the rolling line R, which coincides with the axis Y of the Cartesian system of spatial coordinates X, Y, Z. The rolling stand comprises a frame 2, which incorporates two vertical working rolls 3, 4, i.e. arranged above and below the rolling axis R, between which the element to be rolled 5 passes, two fixed lateral guides also called shoe guides 6, 7. The two shoe guides 6, 7 are fastened on two respective shoe guide-holders 8, 9, which are mounted on the rotatable turrets 10, 11 , respectively. Figure 3 shows the rotatable turret 10 which allows the rotation of the shoe guide-holder 8 about a vertical axis, to which shoe guide-holder 8 the two shoe guides 6 and 6' are fastened in intermediate position toward the substituting position. In order to substitute the shoe guide 6 subsequent to its wear, it is provided to remove it from its operating position where it contains the element to be rolled 5, and to substitute it with a second spare shoe guide 6' by bringing it into a change and substitution position. This occurs by causing the shoe guide-holder 8 to be rotated by 180 ° so as to position the shoe guide 6' in the operating position against the element to be rolled 5 after having radially moved the rotatable turret 10 away from its operating position.

The structure comprising the rotatable turret 10, the shoe guide-holder 8 and other accessory elements is supported by a base 12 which has three degrees of freedom required to allow the shoe guide-holder 8 and the operating shoe guide 6 to carry out movements along the directions X, Y, Z in order to be positioned on the proper resting zone.

Similarly, the base 13 allows the movements along the directions X, Y, Z of the second structure comprising the rotatable turret 11 and the shoe guide-holder 9. The rotatable turret 11 allows the shoe guide-holder 9 to perform the same functions described above for the shoe guide-holder 8. Figure 4 shows the shoe guide-holder 9 in its working position. A further description in greater detail of the shoe guide-holder 9 is not required as it is entirely equal to the one of the shoe guide-holder 8 and is apparent to those skilled in the art.

With particular reference to figure 7, the movement of base 13 along the three axes X, Y, Z occurs due to the two sliding guides 14 and 15, which are arranged in a "V" configuration like opposite inclined planes. By controlling the mutual position of the planes of the guides 14 and 15, the shoe guide 7 can carry out the movements required in the three spatial directions. The sliding of base 13 along axis X, i.e. the axis perpendicular to the plane in figure 7, is achieved by causing the surfaces of the guides 14 and 15 to slide in direction X. The stroke along axis X which the base 13 can perform is rather large, in the range of 150 mm. This stroke is the operating one during the rolling, while base 13 and all the components carried thereby can slide by a much greater stroke which allows the shoe guide-holder 9 to be moved away from the rolling line R by the amount required to detach it from the stand, as explained below in the description of the process of substituting the lateral guides.

The two locks 16, 17, or blocks, which have two inclined sides which carry the guides 14 and 15, can be approached or moved away to/from each other parallel to axis Y by means of the action of two respective jacks 18, 19. Thereby, it is possible to cause the structure which comprises the shoe guide-holder 9 and the rotatable turret 11 to carry out a movement both in direction Z, i.e. upward in the figure, and in direction Y, i.e. along the rolling direction. The resulting movement of the shoe guide 7 along direction Z has a limited stroke, i.e. of about +/- 12 mm. This upward vertical movement is achieved by pushing the two locks 16, 17 in convergent direction toward each other using the jacks 18, 19, while the downward vertical movement occurs by moving the two locks 16, 17 away from each other. The movement of the structure which carries the shoe guide-holder 9 and the rotatable turret 11 in the direction parallel to axis Y is achieved by means of an actuation of the jacks 18 and 19 in the same direction. The stroke allowed in the direction parallel to axis Y is about +/- 50 mm.

Since the second base 12 with the components it carries is perfectly equal and symmetrical to base 13, the movement thereof is achieved in the same manner as described above.

Advantageously, the two shoe guide-holders 8, 9 are provided with a forced liquid circulation circuit for cooling the shoe guides 6, 6' and 7, T which is now described only for the shoe guide-holder 8, the other shoe guide-holder 9 being of perfectly equal and symmetrical make-up with respect to the rolling axis R. Each shoe guide 6, 6' is provided with a delivery pipe of the cooling liquid and a discharge pipe of the cooling liquid, typically water, although other liquids used in this field of the art are not excluded. Thus, there are at least two pipes on the shoe guide-holder 8 for all shoe guides mounted thereon. In the present case, the shoe guide-holder 8 has four pipes 20, 21 , 22, 23, there being two shoe guides 6, 6' mounted thereon. Obviously, if the shoe guide-holder had more than two shoe guides, e.g. three shoe guides, the number of conduits would be six. In this case for example, for the shoe guide 6, there is pipe 20, which brings the cold water, and pipe 23, which discharges the hot water after it has cooled down the shoe guide 6.

The shoe guide-holder 8 includes two fastening units 24, 25, or blocks, one of which is shown in figures 1 and 2, while the first fastening unit is hidden in these drawings. Similarly, the shoe guide-holder 9 has two anti-rotation units 26, 27, of which unit 26 is shown in figure 7, while the second anti-rotation unit is shown in figures 1 , 2 and 7. The anti-rotation units 26, 27 are shown in greater detail in figures 8, 9, 10. These anti-rotation units serve the function of holding the shoe guide 7, which is operational in a given moment, in contact position with element 5 during the rolling, and of generating reaction forces against the rotation torque which the pressure contact of the shoe guide 7 on element 5 being laminated generates during the rolling.

The anti-rotation unit 26, shown in detail with a section on a vertical plane in figure 8 and with a side view in figure 9, comprises an outer cylinder 28 which contains therein a hydraulically-controlled sliding piston 29. Piston 29 contains a conduit for the passage of the cooling liquid therein. When it is in the operating position where it engages the shoe guide-holder 9, the anti-rotation unit 26 has piston 29 raised to engage a conduit connected with one of the conduits, which are entirely similar to the conduits 20, 21 , 22, 23 described above for the shoe guide-holder 9. On-off valves are provided on cooling liquid delivery in the anti-rotation units 24, 25, 26, 27 to avoid the water from leaking during the movement of the shoe guide-holders 8 and 9 for substituting a worn shoe guide with the other new one mounted on the same shoe guide or for substituting the shoe guide-holders with the lateral rotating guides 50, 51 as described below. Clearly, the on-off valves are open only when the shoe guide-holders 8, 9 are blocked in operating position, while the on-off valves are in closed position in the other cases.

When the substituting operation of one of the shoe guides is to be performed, e.g. substituting the shoe guide 7 with the spare shoe guide T which is mounted on the shoe guide-holder 9, piston 29 of the anti-rotation unit 26 and piston 29' of the anti- rotation unit 27 are lowered by actuating the hydraulic control circuit to disengage the cooling liquid conduit and to free the passage to the shoe guide-holder 9, which thereby can rotate about the vertical axis of the rotatable turret 11 and invert the position of the worn shoe guide 7 with the one of the new shoe guide 7'.

When the shoe guide-holder 9 has performed its rotation of 180 ° and the shoe guide T has reached its operating position at element 5, the pistons 29 and 29' are raised up to blocking the shoe guide-holder 9 in its new position, and to engage the cooling liquid conduits in the corresponding support blocks 38' and 38" of the shoe guide-holder 9.

The anti-rotation unit 26, which is arranged on the side of the shoe guide-holder 9 which does not generate a reaction force to the torque created by the rolling, i.e. the anti-rotation unit arranged on the side downstream of the shoe guide-holder considering the rolling direction has, at the end of piston 29, a flat face 30 which is inclined with respect to the vertical in order to compensate for the clearances created between piston 29 and the shoe guide-holder 9, since the torque acting on the shoe guide-holder on such a side tends to generate a distancing. The inclined face 30 matches with a corresponding inclined face arranged on the support block 38' of the shoe guide-holder 9. If a detachment is created between the contacting faces during the rolling due to an increase in the clearances, piston 29 is raised and the contact between the inclined faces is restored.

In order to ensure that piston 29 does not rotate about the axis thereof, and therefore that face 30 does not lose its coplanarity with the corresponding inclined face on the body of the shoe guide-holder, an anti-rotation device of piston 29 is provided, made with a locking screw 39 which prevents the rotation thereof about its axis, while allowing the axial sliding of piston 29.

The anti-rotation unit 27, which is arranged upstream of the shoe guide-holder, is entirely similar to unit 26, with a cylinder 28' which comprises a hydraulic piston 29' in which however the end does not have an inclined contact plane, such a unit being the one that creates the reaction force against the torque generated by the contact of the shoe guide 7 with the object 5 to be rolled.

Also in this case, an anti-rotation device of piston 29' is provided, which is made with a locking screw 39' which prevents piston 29' from rotating about the axis thereof inside cylinder 28'.

What has been described hereto is the rolling stand 1 when the fixed shoe guides are mounted thereon. In accordance with the invention, the rolling stand 1 can perform rolling operations also with lateral guides consisting of rotatable disc guides, hence other components are also provided in the rolling stand 1 , which contribute to the operation thereof in this different mode.

The rolling stand 1 comprises a motor 40 and a reduction unit 41 for reducing the motion transmitted by motor 40 to the rotatable turret 10. When fixed lateral guides or shoe guides are installed on the rolling stand 1 , motor 40 does not supply power and the reduction unit 41 is blocked to contribute to contrasting the torque discharged onto the rotatable turret 10 due to the forces acting on the shoe guide- holder 8 during the rolling.

There is no need to repeat the description of the second structure which comprises the shoe guide-holder 9 and the rotatable turret 11 , because it is perfectly similar in its components and functions and is symmetrical with respect to the rolling axis R, to the first above-described structure on which the rotatable turret 10 is present.

The rotatable turret 10 is capable of carrying the shoe guide-holder 8, preventing the rotation in the above-described operating mode, and is also capable of operating in a second operating mode where a rotatable disc guide 50 is mounted thereon, which is put into rotation by motor 40, through the reduction unit 41 . A significant rotation value is involved since the tangential speed of the outer surface of the disc guide may be about double the feed speed of the piece being rolled. Also in this case, the part in which the rotatable turret 11 and the rotatable disc lateral guide 51 are arranged being formed in a perfectly similar manner as the one described above, the description thereof is not repeated.

The operation of substituting the lateral rotatable disc guides with the fixed lateral guides occurs as described below, with the aid of figures 11 to 19, which only include the numerals of the elements required to understand the substitution operations.

The working position of the rolling stand 1 with the lateral rotatable disc guides 50, 51 mounted is illustrated by the three views in figures 11 , 12, 13. The two motors 40, 40' are engaged and the motion is transmitted to the two respective disc guides 50, 51 by means of the reduction units 41 , 42. When the two disc guides 50, 51 are to be substituted with the fixed shoe guides 6, 7 mounted on the shoe guide-holders 8 and 9, they must be stopped and, if needed, cooled. During the operation of stand 1 with the rotatable disc guides 50, 51 mounted above, the four anti-rotation units 24, 25, 26, 27 have the pistons 29, 29' - in addition to the other two not shown in the figures- lowered, in a position which does not interfere with the volume of the rotatable disc guides. As can be seen in figures 14 and 15, the bases 12 and 13 with the rotatable disc guides 50, 51 and the other components which are integral with the bases 12 and 13, are caused to slide in the direction of the arrows X1 , X2, thus positioning the two disc guides 50, 51 in free position in order to grasp them with suitable means, e.g. a crane, and in order to transport them to the maintenance zone or to another appropriate zone.

The position of the rolling stand 1 shown in figures 16 and 17 shows the extracting position of the disc guides 50, 51 and the step of transporting the two shoe guide- holders 8, 9 toward the stand. The anti-rotation units 24, 25, 26, 27 still remain in the lowered position. The shoe guide-holders 8, 9 are transported toward the stand and inserted in the respective turret, while the rotatable disc guides 50, 51 are taken away by means of suitable means, such as a bridge crane. The reduction units 41 , 42 are blocked, since there is no movement to be transmitted from the motors 40, 40', in this configuration. The anti-rotation units 24, 25, 26, 27 are raised into the locking position of the two shoe guide-holders 8, 9 and the cooling circuits are connected as described above.

Figures 18 and 19 show the rolling stand 1 with the shoe guide-holders 8, 9 inserted on the respective rotatable turrets 10, 11 before the shoe guides 6, 7 are approached to the rolling position, which is shown in figure 1 .

It is apparent that the operation of substituting the fixed shoe guides 6, 7, which are mounted on the shoe guide-holders 8 and 9, with the rotatable disc guides 50, 51 occurs with a substitution operation which is perfectly similar to the one described above.

There is a need to substitute the worn disc guides with other new rotatable disc guides also in the operating mode of the rolling stand with the rotatable disc guides 50, 51 only. In this case, the substitution of the rotatable disc guides occurs in similar manner as the one described above, but in this case the anti-rotation units 24, 25, 26, 27 remain in the position with the piston lowered, the use thereof not being required in this substitution operation.

One advantageous variant of the stand of the invention includes the presence of only two anti-rotation units in the rolling stand, one for each of the two shoe guide- holders 8, 9. In the case of the shoe guide-holder 9, the anti-rotation unit 27 is kept and the anti-rotation unit 26 is eliminated. Similarly, in the case of the shoe guide- holder 8, the anti-rotation unit 25 is kept and the anti-rotation unit 24 is eliminated, it being strictly required to create a reaction to the torque generated during the rolling, which is generally kept in the same direction.

In the light of the above-described description, the advantages of the rolling stand of the invention are apparent.

The stand is more versatile because, depending on the needs dictated by the product to be rolled, it can mount both fixed lateral guides and rotatable disc lateral guides, one substituting the other, and the substitution occurs in shorter times. The guides have means for adjusting the movement thereof along the axes X, Y, Z both when the stand mounts the fixed lateral guides and the motorized rotatable disc guides.

The operating life of the fixed shoe guides is also extended by the improved cooling ability with which the rolling stand is provided.