FIELD OF THE INVENTION

The present invention concerns a method for rolling a section bar with a substantially "U" or "C" shaped section, also called "channel" section, as well as a section bar similar to it.

The present invention also concerns the corresponding apparatus consisting of the combination of a rolling stand and a guide and rolling device which allows to obtain a section bar of the type described above.

BACKGROUND OF THE INVENTION

Hot rolling methods are known, to obtain section bars with a substantially U- shaped cross section, that is, having at least two parallel and adjacent segments, also called wings, and reciprocally connected at the ends by a connection segment, or intermediate segment.

The rolling method provides that, starting from a rolled product with a substantially rectangular section, by passing the rolled product through successive rolling stands, the shape of the definitive section bar is determined.

More specifically, each rolling stand, by means of successive passes, provides to determine the shape and size of the wings of the section bar, and also their inclination with respect to the intermediate segment. In fact, starting from a condition in which they are substantially aligned with the intermediate segment, the wings are gradually inclined and shaped until they are taken to the desired shape and inclination.

In particular, for reasons connected to the subsequent cooling and straightening, with respect to the axis of symmetry of the cross section of the bar that passes through the center line of the intermediate segment, in conventional methods the wings exit from the last rolling stand inclined by an angle of about 3° toward the outside of the concave part of the section itself.

One disadvantage of providing such a restricted angle of inclination of the wings is that inevitably a rapid and intense wear is generated on the rolling rolls, at least in the last rolling stand. The wear on the roll affects both the circumferential surface and also the two base lateral surfaces.

The wear is due mainly to the fact that the rolling rolls also exert a rolling action on the wings, which is translated into an action of wear on the base lateral surfaces. The smaller the above-mentioned angle of inclination, the more accentuated the difference in speed will be between the innermost diameter and the outermost diameter of the rolling roll considered. Consequently, there will be a different wear along the radius of the rolling roll that increases with an at least quadratic proportion of the speed, from the center of the roll toward the periphery.

Therefore, a very different wear occurs along the profile of the rolling roll which is accentuated in proximity to the outermost radius and is reduced toward the internal part.

It is also known that worn rolling rolls are suitably reground using operations to remove material so as to redefine the actual and optimal profile that the section of the bar being rolled is desired to assume.

Given the different development of the wear along the profile of the roll, during the above-mentioned regrinding operations it is necessary to remove a considerable amount of material so as to redefine the definitive profile. This means that the roll is soon put in a condition where it cannot be used, given that in order to maintain an adequate rolling action it is possible to regrind the diameter of the roll only by about 15% of the original diameter.

It is also known that, downstream of the last rolling stand and after it has been cooled, the section bar is sent to the straightening line, which provides to take the section bar to within the geometric tolerances required by the regulations.

To prevent disadvantages caused by modifications in the geometry of the section of the bar in the straightening line, such as for example damage to the edges, the angle of inclination of the wings of the profile, when entering the straightening line, must be at most 7°. This contributes to creating the problems of wear described above, in particular on the rolls of the last rolling roll.

A rolling method is also known, from the British patent GB 1 ,054,507, to produce section bars with a U-shaped cross section, in which at exit from the rolling line the angle of inclination of the wings of the section bar is comprised between 30° and 45°. In this known method there is therefore the disadvantage of having to straighten the wings of the section bar, zeroing the angle of inclination completely in the straightening station. One purpose of the present invention is to perfect a rolling method that allows to considerably reduce the wear that affects the rolls, in particular but not only, of the last rolling stand, increasing their working life.

Another purpose of the present invention is to perfect a rolling method that allows to increase the working life of the rolling roll.

Another purpose of the present invention is to obtain a section bar, downstream of the last rolling stand, with a geometry suitable for entrance into the straightening line, and such that no damage is caused to the shape of the section.

Another purpose of the present invention is to obtain a combination of a rolling stand and a corresponding guide and rolling device for rolling a section bar which allows to reduce the wear exerted on the rolls of the rolling stand, and which also allows them to be restored by means of operations to remove material.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a method for rolling a product to be rolled in order to obtain a "U" shaped section bar, according to the present invention, comprises at least a first rolling step in which the product to be rolled is rolled by means of a rolling line with a plurality of rolling stands to define the section bar having at least two lateral segments connected to each other by an intermediate segment, and a straightening step in which, by means of a straightening station, said section bar is taken to its finished shape.

According to a characteristic feature of the method according to the invention, the first rolling step provides that, at exit from the last rolling stand of the rolling line, the two lateral segments of the section bar are facing toward the outside with an angle of inclination comprised between 7° and 12° with respect to an axis of symmetry of the section bar passing through the center line of the intermediate segment. Moreover, between the first rolling step and the straightening step a second rolling or compression step is provided in which, by means of a guide and rolling device, the intermediate segment of the section bar, and advantageously only that one, is compressed so that the angle of inclination of the lateral segments is taken to a reduced angle of inclination, suitable to send to the next straightening step, in this case comprised between 3° and 7°.

Since the angle of aperture of the lateral segments of the section bar, in the last rolling stand, is kept greater than that provided in the state of the art, the wear to which the rolling rolls is subjected is considerably reduced at least in the last rolling stand. In fact, with a bigger angle of inclination according to the present invention, the lateral surface of the rolls which acts on the lateral segments of the section bar is much less stressed, given that the difference of speed to which it is subjected is considerably reduced. The Applicant has estimated that, assuming an angle of inclination equal to 7° up to 12°, it is possible to increase the duration of the rolling rolls by four times compared to the state of the art.

According to another characteristic feature of the present invention, the intermediate segment of the section bar at exit from the rolling stands has at least one of its portions arched with the convexity facing toward the lateral segments.

For this purpose, the rolling rolls of the last rolling stand respectively have a first profile and a second profile each provided with at least an intermediate portion shaped to define said arched portion of the intermediate segment of the section bar.

In accordance with another characteristic feature of the present invention, the guide and rolling device comprises compression means which, at exit from the last rolling stand, exert a compression action on the intermediate segment to straighten the arched portion, consequently reducing the angle of inclination of the lateral segments with respect to the intermediate segment.

In this way, the guide device returns the lateral segments of the section bar to a suitable condition for the subsequent operations provided, for example straightening.

According to one form of embodiment, the compression means of the guide and rolling device comprise a pair of rollers disposed opposite with respect to the plane of feed of the rolled product and with the respective axes of rotation parallel and both lying on a common lying plane disposed orthogonal with respect to the direction of feed of the section bar. It is advantageous to provide that the rollers act only in proximity to the intermediate segment of the section bar. In this condition the rollers are subject to uniform wear which does not therefore alter the final geometry of the section bar to be obtained. The gap between the rollers can possibly be suitably adjusted by adjustment means, in order to also adjust the entity of the compression action which is exerted.

The wear to which the rollers of the guide and rolling device are subjected is much less than the wear to which the rolling rolls are subjected in the rolling stands, in conventional rolling methods. Moreover, the production and maintenance costs of the rollers of the guide and rolling device are also considerably less than those required for the rolling rolls of the rolling stand. This justifies the fact of giving the guide and rolling device the task of reducing the angle of inclination of the lateral segments of the section bar rather than to the rolling rolls in which there would be a much higher wear.

In some forms of embodiment it is advantageous to provide that the angle of inclination of the lateral segments of the section bar exiting from the last rolling stand is preferably comprised between 8° and 1 1°, and even more preferably 10°.

According to another form of embodiment, in the second rolling or compression step, the angle of inclination of the lateral segments is reduced to an amplitude preferably comprised between 4° and 6°, and more preferably about 5°.

DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a schematic representation of a rolling plant in accordance with a method for rolling section bars according to the present invention;

- fig. 2 is a schematic representation of the rolling cycle of a section bar;

- fig. 3 is a section view of a section bar obtained with the method according to the present invention;

- fig. 4 is an enlarged view of rolling rolls of the rolling line in fig. 1, in accordance with the method according to the present invention;

- fig. 5 is an enlarged view of rolling rolls of the rolling line in fig. 1, in accordance with the method according to the state of the art;

- fig. 6 is a schematic representation of a part of two rolling rolls with highlighted, by means of section lining, the material which is removed during restoration steps of the rolling rolls in fig. 4, in accordance with the method according to the present invention;

- fig. 7 is a schematic representation of a part of two rolling rolls with highlighted, by means of section lining, the material which is removed during restoration steps of the rolling rolls in fig. 5, in accordance with the method according to the state of the art;

- fig. 8 is a schematic representation of a detail of a combination of a rolling stand and a guide and rolling device according to the present invention.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings.

DESCRIPTION OF ONE FORM OF EMBODIMENT

With reference to fig. 1, a rolling plant 12 to which the rolling method according to the present invention is applied comprises a guide and rolling device 10 disposed downstream of a finishing rolling line 11 which in its turn comprises a plurality of rolling stands; in this case ten rolling stands respectively 13a, 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, 13m.

Moreover, the rolling plant 12 comprises a heating furnace 15 to heat the products to be rolled, a descaler 16 disposed immediately downstream of the heating furnace 15 and a roughing rolling line 17.

Between the roughing rolling line 17 and the finishing rolling line 1 1, and also downstream of the latter, shearing means 19 are provided to shear the product to be rolled and respectively a section bar 25.

The section bar 25 at exit from the finishing rolling line 1 1 is conveyed toward a cooling apparatus 20 for its subsequent passage toward a straightening station 21.

The straightening station 21 has the function of bringing the shape and the size of the cross section of the section bar 25 inside the range of tolerance provided for that type of product and thus give it its definitive shape.

The rolling stands 13a, 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, 13m are each provided with a pair of rolls 22 (figs. 4, 6 and 8), each of which has the shape of the shaped profile as shown in fig. 2.

In particular (fig. 2), starting from the first stand 13a in which the product to be rolled has a substantially rectangular section, the subsequent rolling stands have a profile shape which allows to define a substantially U-shaped section bar 25 (fig. 3), that is, provided with two lateral segments, also called wings 26, connected to each other by an intermediate segment 27.

The section bar 25 has an axis of symmetry Z disposed in proximity to the center line of the intermediate segment 27.

The last rolling stand 13m (fig. 2) has corresponding rolling rolls 22 with respectively a first profile 29 (fig. 4) and a second profile 30 which respectively define the external surface and the internal surface of the section bar 25.

Specifically, at exit from the last rolling stand 13m the section bar 25 has the wings 26 inclined by an angle of inclination a, facing toward the external part of the section bar itself, with respect to the axis of symmetry Z. The angle of inclination a is comprised between 7° and 12°, preferably between 8° and 1 1 °, even more preferably 10°.

Moreover, the first profile 29 of the roll 22 of the last rolling stand 13m has an intermediate portion 31 shaped like an arc of a circle, or in any case arched, and two lateral portions 32 which respectively define the external surface of the intermediate segment 27 and the external surfaces of the wings 26. It is advantageous to provide that the end segments of the intermediate portion 31 are substantially orthogonal with respect to the two lateral portions 32. This causes a consequent curve radius of the arched portion of the intermediate segment 27. The section shape of the section bar 25 at exit from the last rolling stand 13m is substantially identical to the shape defined by the gap between the rolls 22, except for its elastic returns.

As can be seen in fig. 5, in the state of the art the angle of inclination a is about 3°, that is much smaller than that provided by the method according to the present invention. In fact, an angle a of only 3°, as in the state of the art, implies a very limited aperture of the wings 26 of the section bar 25 and thus determines an increase in wear to which the rolls 22, and in particular the lateral portions 32, are subjected, as described above. Moreover, also in this case of the state of the art, the intermediate portion 31 is substantially orthogonal to the lateral portions 32 and therefore, given that the aperture of the wings 26 is very small, the profile is much less arched.

The guide and rolling device 10 (fig. 8), according to the present invention, is disposed immediately downstream of the last rolling stand 13m and comprises a support structure 35 on which two guide elements are mounted, respectively lower 36a and upper 36b, defining a guide channel 37 between them.

In proximity to the end part of the guide elements 36a, 36b, compression means 39 e.g. two rollers 39, are disposed with respective axes of rotation Y substantially orthogonal to the direction of feed of the section bar 25 which is rolled, and parallel to the intermediate segment 27 of the latter.

The lower guide element 36a is suitable to support and allow the sliding with respect to it of the external surface of the intermediate segment 27 of the section bar 25.

The upper guide element 36b is conformed identical to the concave internal surface of the section bar 25.

Both the guide elements 36a, 36b are each provided with an entrance end 40 which is tapered to facilitate the entrance of the section bar 25 exiting from the pair of rolls 22.

The entrance ends 40 are also shaped so as to bring the guide and rolling device 10 as close as possible to the rolls 22, but avoiding problems of interference with them.

Each of the rollers 39 has a substantially cylindrical shape and a width such as to affect only the intermediate segment 27 of the section bar 25 in transit, preventing any reciprocal contact between the upper roller 39 and the wings 26 of the section bar 25.

The rollers 39 have their respective axes of rotation Y parallel to each other and both lying on the same common lying plane P which is substantially orthogonal with respect to the direction of feed of the section bar.

Specifically, the two rollers 39 are disposed distanced from each other so that a gap is defined between them such as to compress the intermediate segment 27. In fact, the gap defined between the rollers 39 is smaller than the thickness of the intermediate segment 27 which exits from the last rolling stand 13m. There is thus a compression of the section bar 25 of the intermediate segment 27, which as well as causing a lengthening thereof (albeit limited), also generates a straightening of the curvature of the intermediate segment 27, determined by the rolls 22 of the last rolling stand 13m.

The straightening of the intermediate segment 27 takes the wings 26 of the section bar 25 from a condition inclined by said angle a, to a condition in which they are inclined at a reduced angle of inclination α' (not shown in the drawings but easily comprehensible to a person of skill in the art), which is suitable for the insertion of the section bar 25 into the straightening station 21.

In particular, it is advantageous to provide that the reduced angle of inclination a' is comprised between 3° and 7°, preferably between 4° and 6°, more preferably around 5°, with respect to the axis of symmetry Z.

The section bar 25, at exit from the guide and rolling device 10, can therefore be cooled and then sent to the straightening station 21 with a reduced angle of inclination α' of the wings 26 suitable for the workings to which it will be subjected, without problems of damaging the shape of the profile.

The guide and rolling device 10 also comprises adjustment means 42 to adjust the gap between the rollers 39, to allow to restore the wear to which they are subjected.

The adjustment of the gap between the rollers 39 can be carried out either manually, as provided in the form of embodiment shown in fig. 8, or in an automated manner.

The rollers 39 are subjected to a substantially uniform wear along their circumferential surface which does not modify the shape of their external profile. Consequently, it is not necessary to subject the rollers 39 to frequent operations to remove material as happens for the rolls 22, but only to adjust their gap, and then possibly to replace them when they are worn.

Merely by way of example, the Applicant has seen that the rollers 39 can process up to 12,000 tons of section bars before they have to be replaced.

The Applicant has also found that with the method according to the present invention, it is possible to considerably reduce the wear to which the rolls 22 of the last rolling stand 13m are subjected, allowing to increase the duration thereof even up to four times compared with the rolls used with a method of the state of the art. Merely by way of example, in figs. 6 and 7 the volumes of material which are removed during the regrinding of the rolls are highlighted, with section lining. As can be seen, the volume of material removed from the rolls 22 which use the method according to the present invention (fig. 6) is much less than the volume removed from the rolls which use the rolling method of the state of the art (fig.7).

The rolling method according to the present invention provides to heat the product to be rolled in the heating furnace 15, to a suitable temperature for rolling. Subsequently the heated product to be rolled is sent to a descaler 16 to remove the scale, and to a roughing rolling line 17 which carries out a first rolling operation.

At exit from the roughing rolling line 17 the product to be rolled has a substantially rectangular shape and is sent to the finishing rolling line 1 1.

The rolling stands 13a, 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, 13m provide to roll the product to be rolled until it achieves the shape of the section bar 25 described above.

At exit from the last rolling stand 13m, the section bar 25 is conveyed by means of guide elements 36a, 36b of the guide and rolling device 10, toward the rollers 39 of the latter.

In this step the rollers 39 provide to exert a compression action only on the intermediate segment 27, which determines a suitable geometry for the entrance of the cooled section bar 25 into the straightening station 21.

At exit from the guide and rolling device 10 the section bar 25 is cooled by a cooling apparatus 20, in order to then pass to the straightening station 21 in which it is calibrated to achieve the tolerances of shape and size provided by regulations.

It is clear that modifications and/or additions of parts may be made to the method for rolling section bars, the combination of rolling stand and guide and rolling device as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of method for rolling section bars, the combination of rolling stand and guide and rolling device, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.