WO2007128834A1

WO2007128834A1 - Bearing and guide roller assembly for rolling plants and respective guiding box

Info

Publication number: WO2007128834A1
Application number: PCT/EP2007/054499
Authority: WO
Inventors: Andrea De Luca; Alfredo Poloni; Roberto Boschin
Original assignee: Danieli & C. Officine Meccaniche S.P.A.; Caiffa, Michaela; Boschin, Mauro; Boschin, Max
Priority date: 2006-05-10
Filing date: 2007-05-09
Publication date: 2007-11-15
Also published as: ITMI20060919A1

Abstract

A bearing and guide roller assembly for rolling mill systems comprises a roller- holder lever (9) having two protruding parts (10' and 10') with two coaxial holes, two bushings (5, 7) inserted in the holes, a bronze bushing (2) formed by two frusto-conical axially perforated half bronze bushings (2', 2'), fixed one to the other on the respective smaller bases, forming an external annular surface with V section, a pin (1), on which two half bronze bushing (2', 2') are fixed, various fluid feeding conduits (8, 16', 16', 17', 17', 17''), a ring (3) having an internal surface (15) whose shape mates with the V groove. Between the bronze bushing (2) and the inner surface of the ring (3) a thin gap (4) exists where a fluid gap is formed during relative rotation.

Description

BEARING AND GUIDE ROLLER ASSEMBLY FOR ROLLING PLANTS AND RESPECTIVE GUIDING BOX Field of the invention

The present invention relates to a bearing and guide roller assembly, in particular for finishing rolling systems for long metal products, e.g. wire rod, in fast calibration blocks, so-called BGV, and also a guiding box which comprises at least one pair thereof. State of the art In rolling mills used for hot rolling of long products, shaped idle roller or roller pairs, between rolling stands, are used to correctly and accurately guide and direct the rolled product coming from an upstream stand with respect to the rolling direction within the rolling channel of the stand arranged downstream. These guide rollers are usually mounted in counterpoised arrangement so as to form a pair which defines an adjustable gap according to the geometric and structural features of the product being machined, thus forming what is commonly named as guiding box or tray of the rolled product.

Normally, these rolled product guiding boxes are mounted on transversally sliding supports, both in the direction of the rolling axis and in the opposite direction, in the inlet zone of the respective rolling stand. Sliding supports allow millimethc centring of the box in relation to the rolling channel with their movement.

The roller guides turn at very high speed and are subjected to high mechanical and thermal stress. Indeed, the lamination speed at a BGV block outlet reaches values higher than 100 m/sec and consequently the rotation speed of the guides of the last two or three rolling steps exceeds 50,000 rpm. Since the guide rollers are idly mounted, i.e. without motor means or autonomous rotational motion, they are subject to very high speed variations, going from zero to rolling speed in a few fractions of a second at each rolled product lead-in, i.e. after the inter-billet time. The violent acceleration of the roller which is determined by contact friction with the roller product generates high wear due to the physical-chemical effect and to abrasion consequent to initial slipping. Furthermore, in guide rollers, the members connecting the rollers themselves to their rotation axes and allowing rotation of the same are highly stressed. In the prior art, members generally consisting of mechanic rolling bearings are known, such as those for example provided by US-4295356, which poorly withstand the aforementioned violent accelerations because, by inertia, they cannot accelerate their weight and, at high revolutions, are subject to rapid wear of the rollers or balls. Such bearings are also subject to penetration of dirt from the environment in which they work, such as for example the introduction of scaling, water spray, oil spray, dust or other debris, which may cause incrustations. Rapid wear, malfunctioning and breakage of the bearings is determined in this context and consequently rolling faults or, in the worst cases, rolled product jams in the strip mill are produced on the end product. In all cases, frequent stops are necessary to replace components and also for normal maintenance. This causes high costs for downtime and spare parts.

Hydrodynamic oil bearings have been proposed instead of mechanical bearings in order to overcome these drawbacks. An example of hydrodynamic bearing for guide roller is described in US-6280087. This document describes, in a variant, a single body guide roller rotationally fixed onto two separate half pins, in turn fixed to a supporting structure constituted by two jaws. The high speed rotation is ensured by the creation of two hydrodynamic oil film bearings about the two half pins. Assembly of the roller is rather difficult and manufacturing of the two-jaw supporting structure requires very accurate machining to ensure the necessary coupling precision. Furthermore, an adjustment system for the distance of the jaws must be provided to establish the necessary stability of the hydrodynamic film between the half pins and the roller. Indeed, since the diameter of the roller is much higher than the transversal dimension of the pins, the stability of the roller itself is negatively effected by the bias of external disturbing forces.

It is therefore felt the need to make a bearing and guide roller unit which is simple and cost-effective to make and which allows to overcome said drawbacks, presenting high reliability. Summary of the invention Therefore, the present invention reaches the aforementioned objects being by means of a bearing and guide roller assembly for rolling mills comprising: - a roller-holder structure having a first protruding part provided with at least one hole and a second protruding part provided with at least one second hole, in which the first and second holes are coaxial,

- at least one bronze bushing comprising two half bodies having frusto-conical shape, a respective axial hole, each defining a respective smaller base, arranged in contact with each other by means of the respective smaller bases, forming an external annular shaped surface,

- means for fastening at least one bronze bushing to said roller-holder structure between said first and second protruding parts through said axial hole of the bearing and said first and second holes of the roller-holder structure;

- fluid feeding conduits, - a ring whose internal surface is complementary to the shape of said external annular surface arranged externally and coaxially to said bronze bushing;

- the shape and dimensions of the internal surface and the annular external surface being such that they create a gap between said ring and said bronze bushing to allow a reciprocal relative rotation and create a fluid gap during the relative rotation.

It is also the object of the present invention a guiding box for rolled products comprising one or more pairs of bearing and guide roller assembly. It is the particular object of the present invention a bearing and guide roller assembly for rolling mills and respective guiding box, as better described in the claims, which form an integral part of the present description.

Thanks to the listed features, the lifespan of the bearing-roller guide assembly according to the invention is considerably increased and this allows to reduce stop cycles of the rolling mill for maintenance, with considerably saving of costs, without effecting the roller product quality. Brief description of the Figures

Further features and advantages of the present invention will be more apparent in the light of the detailed description of a preferred, but not exclusive, embodiment of the same and variants, illustrated by way of non-limitative example, with reference to the accompanying drawings, in which: Fig. 1 is a side sectional view according to an axial plane of a bearing-roller guide assembly according to the invention;

Fig. 2 is a front sectional view according to an axial plane of a pair of guide rollers according to the invention; Fig. 3 shows views of a first embodiment of a half bronze bushing according to the invention;

Fig. 4 is a partial sectional view of a guide roller detail according to a variant of the invention. The same reference numbers in the figures identify the same elements. Detailed description of a preferred embodiment of the invention Figure 1 shows a bearing and guide roller assembly according to the invention, inserted in a guiding box of the rolling mill comprising a roller-holder lever 9 pivoted to a first end of a structure (not shown) and having a second essentially C- shaped end with two essentially but not necessarily wedge-shaped protuberances or arm elements 10', 10". A respective hole is made in the end part of each of said arm elements 10', 10" and the two holes have common axis. A respective bushing 5, 7 is inserted in each hole. The upper bushing 7 is internally threaded and its external surface is smooth. Both the internal and external surfaces of the lower bushing 5 are smooth, not threaded, and the upper edge is folded outwards to form a lip 1 1.

A cylindrical pin 1 is arranged in the two bushings 5 and 7. One end 6 is threaded to keep it fastened inside the bushing 7. There exists a bronze bushing 2, consisting of two frusto-conical half bodies 2', 2" with a central hole which are fixed to pin 1. The two half bodies 2', 2" interface in contact at the smaller faces. The coupling and the centring of the two half bodies or half bronze bushings is achieved by means of pin 1 , while axial securing is obtained by securing the threaded head of pin 1 in bushing 7. A flexible pin 12 is inserted between the half bodies to stop reciprocal rotation. The union of the two half bodies 2' and 2" forms the body of the bronze bushing 2 having an annular substantially triangular or "V"-shaped external surface. As seen in section, said side surface comprises two slanted planes which reciprocally form an angle between 90° and 150°. There also exists an external ring, or roller, 3, arranged coaxially to the bronze bushing, which has the function of guiding the rolled product, and the external surface whose shape depends on the diameter of the rolled product and of the rolling diagrams (oval-round sequences), presenting for example a semicircular section groove 14 (see figure 2 and 4), in the case of wire rod rolling, and has an internal surface mating with the shape of the external "V"-shaped groove of the bronze bushing 2. Ring 3 can turn idle and is rotated either by the passage of the rolled product or, if necessary, may be provided with a rotation speed of its own by means of appropriate means. This construction method of the bearing and guide roller assembly is simple and rational and allows to obtain a perfect centring of the roller on the bronze bushing body, thanks to the inclined planes of the "V" groove.

Advantageously, the maximum diameter of the two half bodies 2', 2", and therefore of the bronze bushing body 2, is from 0,5 to 0,9 times the diameter of the ring 3. This allows to have a wider side surface of the ring 3 which allows to reduce the specific pressures, support higher axis and radial loads, and give higher stability to the guide roller under the bias of external disturbing forces. The machining tolerances of the side and internal structures of the two half bronze bushings are calculated so that when the ring 3 and half bronze bushing 2', 2" assembly is "sandwiched", by fastening pin 1 in bushing 7, there is a gap or clearance 4 between the inclined surfaces of the ring itself and those mating with the body of the bronze bushing 2. Said gap has an average height preferably from 0,01 to 0,07 mm. The bronze bushing body 2 is kept still on one side by the shoulder of pin 1 and on the other by the lip 1 1 of the bushing 5; ring 3 is instead rotationally fed by the passage of rolled product to reach high rotation speeds which may reach and exceed 50.000 rpm.

A fluid, preferably pressurised water, is sent in gap 4 to form a fluid gap or film to support ring 3. Feed of water, or other appropriate fluid, is performed through specific channels or ducts made in the supporting structure 9, in the arm element 10, in the lower bushing 5 and in the pin 1. The circuit is open, and therefore the water is let out through the inclined planes and is collected in the base of the machine. Advantageously, the invention may use the same water which is used in the cooling circuit of the rolling mill system which is then appropriately recovered, filtered and recirculated. This also allows to obtain considerable advantages with respect to the traditional use of oil for bearings in terms of system layout simplification and relative reduction of investment costs because fewer pumps and dedicated circuits are required, and of running costs because water or other fluid which costs less and pollutes less than oil is used.

Water in the bearing and guide roller assembly according to the invention not only supports the roller but advantageously also performs lubricating and cooling functions.

The flow rate and the pressure of the water conveyed to the rollers depend on the position of the guiding box in the finishing mill and on the rotation speed set by the rolled product in said position; at the first stands high flow rates and high pressures are used to favour cooling of the roller, while lower pressures are used at the last stands. Preferably, the pressures used along the mill vary from 2 to 6 bars.

Figure 2 shows a preferred embodiment of the guiding box object of the invention, comprising a pair of bearing and guide roller assemblies arranged side by side and aligned so that the respective external surfaces present grooves 14 side by side, at a certain reciprocal distance depending on the shape and dimensions of the rolled product 25 which slides between them.

According to further embodiments of the invention, a guiding box may comprise several pairs of bearing and guide roller assemblies. According to a first advantageous embodiment, with reference to figure 3, a first set of radial grooves is made on the smaller base of one or both of the half bodies 2', 2" of the bronze bushing to create a channel which carries water inside the gap or clearance (4).

More specifically, three radial grooves are preferably and reciprocally arranged at 120°, which comprise a first part indicated respectively by 17', 17", 17'", which originates from the internal hole where pin 1 is inserted (fig. 1 ) and ends on the external edge 13 of the smaller base.

Optionally, a second series of said grooves may be present which, departing essentially from where the first series ends, on the external edge 13, extends on the side external surface of the half body of the bronze bushing, respectively indicated with 18', 18", 18'", to a distance "d" from the external edge 13".

The presence of this second set of grooves 18', 18", 18'", advantageously allows to carry water to the loading zones and prevent the water itself from being distributed to the zones where less passage resistance is found. In this way, it is guaranteed a uniform fluid gap in gap 4 along the entire circular crown between bronze bushing 2 and ring 3 and therefore more efficient operation of the bearing. According to a second advantageous embodiment, with particular reference to figure 4, a third set of inclined grooves 16', 16" is provided on the internal surface 15 of ring 3 so that the passage of pressurised water in gap 4, and therefore in grooves 16, can impart a rotation to the roller itself, thanks to a side component of the speed. In this way, the roller may be provided with a rotary motion also when there is no passage of rolled product. Advantageously, the pressure of the water can be controlled so as to adjust the speed of rotation of ring 3 so as to be close to that caused by the subsequent passage of the rolled product.

Multiple advantages can be imparted by a pre-rotation of the roller. Sliding is drastically reduced during rolled product lead-in and therefore roller wear is decreased which increases their operative life. The water gap or film in gap 4 is already completely formed also during idle operation, i.e. in the so-called inter- billet stage, and therefore the bearings always work in hydrodynamically supported conditions.

According to a variant not shown in the figures, in order to pre-rotate the rollers, there are provided fins, or similar shaped millings, instead of a third set of internally inclined grooves, on the side surface of the rollers themselves like the impeller structure of a hydraulic turbine; specific channels carry the pressurised water to strike against said fins thus imparting the rotational movement to ring 3. Ring 3 may be preferably made of titanium carbide, but some of the following materials may also be selected: tungsten carbide, ceramics, sintered, stellite. Special inserts or surface treatments on all or part of the surfaces may also be made.

The bronze bushing 2 is preferably made of alloyed or sintered steel with very hard coatings, i.e. Vickers hardness higher than or equal to 1000 HV, or with lead and self-lubricating metal inserts. According to the invention, it is possible to restore the bronze bushing when worn simply by grinding the contact surfaces, i.e. the smaller bases of the two half bronze bushings 2' and 2" and therefore returning gap 4 to its original value. A considerable cost saving is thus obtained by reusing the same bronze bushing for another rolling campaign. The bearing and guide roller assembly of the invention thus presents a series of advantages, as described below.

A hydrodynamic support bearing is made in which water can be used as supporting, lubricating and cooling fluid. Furthermore, water is no polluting and its use does not require sophisticated recovery and recirculation systems. The rotating inertia of the guide roller is lower, given the light weight of the rotating parts. The particular shape of the bronze bushing 2, presenting inclined plane peripheral surfaces, creates a radial and axial support of the external rotating ring 3. The bronze bushing consists of two half bodies, whose assembly is particularly simple.

Globally, the working life of the bearing is increased from the current 3-4 shifts to at least 30-40 shifts, i.e. ten-fold. Construction is simpler because no seals are required.

Claims

1. A bearing and guide roller assembly for rolling mill systems comprising:

- a roller-holder structure (9) having a first protruding part (10') provided with at least one hole and a second protruding part (10") provided with at least one second hole, in which the first and second holes are coaxial,

- at least one bronze bushing (2) comprising two half bodies (2', 2") having frusto- conical shape, a respective axial hole, each defining a respective smaller base, arranged in contact with each other by means of the respective smaller bases, forming an external annular shaped surface, - means (1 , 5, 6, 7) for fastening at least one bronze bushing (2) to said roller- holder structure (9) between said first and second protruding parts (10', 10") through said axial hole of the bearing and said first and second holes of the roller- holder structure (9);

- fluid feeding conduits (8, 16', 16", 17', 17", 17'"), - a ring (3) having an internal surface (15) whose shape is complementary to the shape of said external annular surface arranged externally and coaxially to said bronze bushing;

- the shape and dimensions of the internal surface (15) and the annular external surface being such that they create a gap (4) between said ring (3) and said bronze bushing (2) so as to allow a reciprocal relative rotation and to create a fluid gap during the relative rotation.

2. A bearing and guide roller assembly according to claim 1 , wherein said means for fastening comprise:

- a pin (1 ) to which the bronze bushing (2) is fixed, - a first (5) bushing inserted in the first hole and a second bushing (7) inserted in the second hole of said roller-holder structure (9) interposed between the pin (1 ) and the holes themselves.

3. A bearing and guide roller assembly according to claim 1 , wherein the two half bodies (2', 2") have an external shape which mirrors that of the contact surface, and are removably fixed together by means of a flexible pin (12).

4. A bearing and guide roller assembly according to claim 1 or 3, wherein the annular shaped external surface has a triangular section or "V" shape, on a plane laying on the axis of the roller, having a vertex angle from 90° to 150°.

5. A bearing and guide roller assembly according to claim 1 , wherein the fluid feeding conduits comprise radial grooves (17', 17", 17'") made on the smaller base of one or both the half bodies (2', 2").

6. A bearing and guide roller assembly according to claim 1 , wherein the fluid feeding conduits comprise radial grooves (17', 17", 17'", 18', 18", 18'") made on the smaller base and on the external side surface of one or both the half bodies (2', 2").

7. A bearing and guide roller assembly according to claim 1 , wherein the fluid feeding conduits comprise inclined grooves (16', 16") made on the internal surface of the ring (3).

8. A bearing and guide roller assembly according to claim 1 , wherein the fluid feeding conduits comprise fins or millings on the side surface of the ring (3).

9. A bearing and guide roller assembly according to claim 1 , wherein the fluid feeding conduits comprise conduits made in said roller-holder structure (9), and in said means for fastening (1 , 5).

10. A bearing and guide roller assembly according to claim 1 , wherein said gap (4) has an average height from 0,01 mm to 0,07 mm during said rotation.

11. A bearing and guide roller assembly according to one of the preceeding claims, wherein the maximum width of the bronze bushing (2) is from 0,5 to 0,9 times the external diameter of the ring (3).

12. Rolled product guiding box comprising one or more pairs of bearing and guide roller assemblies according to one or more of the preceding claims, in which the bearing and guide roller assemblies of each pair are side by side, aligned, and arranged with respective axes parallel.