Tilting oxygen converter

A converter comprising a container (2) defining a first axis X; a support ring (3), coaxial to the container and spaced therefrom, provided with two diametrically opposed supporting pins (6), defining a second axis Y orthogonal to the first axis X, adapted to allow a rotation of the converter about the axis Y; suspension elements, connecting said container to said support ring, clamped at a first end to the container and at a second end to the support ring so as to not require any maintenance as compared to traditional systems which use spherical joints and pins which are subject to wear, thus saving hours of maintenance and plant standstill.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to PCT International Application No. PCT/IB2012/053463 filed on Jul. 6, 2012, which application claims priority to Italian Patent Application No. MI20111A001277 filed Jul. 8, 2011.

Not Applicable.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tilting oxygen converter provided with a suspension system for the converter container, said system connecting said container to a support ring.

State of the Art

The main object of an oxygen converter is to convert the cast iron produced in the blast furnace into raw liquid steel, which can be then refined in the secondary steel production department.

The principal functions of the oxygen converter, also known as a B.O.F. (Basic Oxygen Furnace), are to decarbonize and remove the phosphorus from the cast iron and optimize the temperature of the steel so that further treatments can be carried out before casting with minimum heating and cooling of the steel.

The exothermic oxidation reactions which are generated in the converter produce a lot of thermal energy, more than the energy needed for reaching the determined temperature of the steel. This extra heat is used to melt the scrap metal and/or the added ferrous mineral. As the B.O.F. substantially is a furnace, it is also subject to thermal dilatations.

As example of as oxygen converter, belonging to the state of the art, is described in the document U.S. Pat. No. 5,364,079.

Said converter consists of a container, defining the reactor and having a substantially cylindrical shape, supported by a support ring (“trunnion ring”), surrounding the container and suitably spaced therefrom, provided with two diametrically opposed supporting pins (“trunnions”), the assembly supported by two supports anchored to the ground. The container relation control is keyed onto one of the two supporting pins.

Said converter is supported by means of an external support ring and a suspension consisting of a plurality of articulated braces and related supports, arranged on the lower side of the support ring when the converter is in a vertical position. Each support, articulated by means of ball joints, is designed to be fixed to the support ring on one side and to the container on the other side.

Thereby, the converter is supported by a series of articulated supports which allow the container dilatations and self-alignment between the external support ring and said container.

Although the described system allows self-alignment between the two units, the presence of numerous ball joints disadvantageously determines considerable maintenance of the latter over time, constant greasing and preventive replacement of the joints given the heavy operating conditions to which they are subjected.

Centring the container and the support ring is also important in order to conveniently allow the thermal deformations or expansions of the container due to the high temperatures reached during the conversion process.

The need is therefore felt to provide an oxygen converter which allows the aforementioned drawbacks to be overcome.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide as oxygen converter provided with a suspension system for the container, connecting said container to its own support ring, which does not require maintenance, allowing scheduled and unscheduled operations to be eliminated and reducing to zero the replacement of elements subject to wear. Another object of the invention is to provide an oxygen converter, in which the container suspension system is capable of maintaining a precise centring between container and support ring during all the operating steps of the converter.

Another object of the present invention is to provide a converter, the suspension system of which is capable of absorbing the thermal dilatations of the container with respect to the support ring thereof.

A further object of the present invention is to provide a converter, the suspension system of which is capable of absorbing the vibrations induced by the melting process.

Therefore, the present invention suggests to achieve the above-discussed objects by providing a tilting converter which, in accordance with claim1, comprises a container defining a first axis X; a support ring, coaxial to the container and spaced from said container, provided with two diametrically opposed supporting pins, defining a second axis Y orthogonal to the first axis X, adapted to allow a rotation of the converter about said second axis; suspension elements, connecting said container to said support ring, restrained at a first end to the container and at a second end to the support ring; wherein said suspension elements are a plurality of elastic bars clamped at said first end and at said second end; and wherein said plurality of elastic bars comprisesthree groups of first elastic bars arranged parallel to the first axis X, said groups of first bars being arranged substantially equally spaced apart from each other along said support ring;at least two pairs of second elastic bars, each pair of said second bars being arranged on a respective plane parallel to a first plane Y-Z orthogonal to the first axis X, where Z is an axis orthogonal to a second plane X-Y and passing through the point of intersection between first axis X and second axis Y;wherein each pair of second bars is symmetrically arranged with respect to a third plane X-Z;and wherein the second elastic bars of each pair are arranged with the respective longitudinal axes converging to each other.

In an advantageous embodiment, there are provided a total of ten or twelve clamped elastic bars, i.e. clamped against rotation; six first bars arranged for a support in a vertical position and four or six second bars arranged for the horizontal support of the converter. The vertical support solution is considered isostatic and includes a number of three supports at 120°, each with a double tie-rod.

In other advantageous embodiments, there are provided three groups of first bars for a support in a vertical position, arranged at 120° to one another, each group being formed by the same number of bars, variable between three and five. Therefore, the total number of pairs of second bars for the horizontal support, symmetrically arranged with respect to the plane X-Z, also increases from a minimum of four pairs to a maximum of seven pairs.

In all the embodiments, the second bars of each pair are arranged with the respective longitudinal axes converging to each other.

Furthermore, all the embodiments can be provided with a third elastic bar, arranged so as to be diametrically opposite (180°) to the group of first bars arranged close to the plane X-Z.

In particular, the suspension system for the converter, object of the present invention, by means of the elastic bars clamped at the ends, has the following advantages:it allows the thermal dilatations of the container to be easily absorbed, taking advantage solely of the elasticity of said bars;it efficiently absorbs the vibrations which are generated during the insufflation of oxygen into the container;it efficiently absorbs the forces generated by the inertia of the container when starting and ending its rotation;it does not require any maintenance as compared to traditional systems which use ball joints and pins which are subject to wear, saving hours of maintenance and plant standstill;it keeps the container centred with respect to the support ring with high precision in all inclination conditions;the absence of members and joints which are subject to slipping, with a sliding between coupled surfaces, prevents problems in re-positioning the converter when it returns to working condition, with axis X in vertical arrangement and loading mouth facing upwards;the slight bending stiffness of the elastic bars allows to limit the bending load on the bars generated by the container dilatations;the fixed beam configuration allows heavy loads to be supported, even with a strut configuration of the tie-rods;it requires extremely simple assembly;they are suitable for all sizes of converters, with the diameter thereof varying, for example, from about 5 m to about 8 m and the height varying from about 7 m to about 11 m.

The excellent precision of the centring between container and support ring allows the thermal expansions of the container, caused by the high temperatures reached during the conversion process, without any interference between container and support ring.

All the suspension elements present in the converter of the invention are long-limbed elastic bars, in which two dimensions are negligible as compared to the third dimension which is the length or longitudinal extension; all of said long-limbed elastic bars having the two ends integrally fixed to the container and the support ring, respectively.

Furthermore, with all the elastic bars preferably being of equal dimensions (both length and diameter, in the case of circular section bars), there is also a greater economic advantage and a smaller number of spare parts to keep in stock.

A further advantage is that the whole structure of the converter, protuberances included, is configured so as to be inserted within a sphere, the radius of which is determined by the layout requirements of the plant comprising the converter.

The dependent claims describe preferred embodiments of the invention.

The reference numbers in the figures identify the same elements or components.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, a preferred embodiment of an oxygen converter is represented, globally indicated with the reference number1.

Said converter1comprises:a container or tank2, defining an axis X, provided with a loading month4for scrap metal and liquid cast iron and provided with a lateral tapping hole5for the liquid steel obtained at the end of the conversion process;a support ring3for supporting container2, said ring3being arranged coaxial to container2and suitably spaced therefrom;two supporting pins or tilting pins6of said support ring3, or “trunnions”, diametrically opposed to each other and defining an axis Y, orthogonal to axis X, with at least one of said supporting pins6connected to a tilting mechanism (not shown);suspension elements, which connect container2to support ring3and which also carry out a centring function between container and ring.

Defining a further axis Z as the axis orthogonal to the plane X-Y and passing through the point of intersection of axes X and Y, a plane Y-Z, which can be considered an “equatorial” plane of the converter, and a plane X-Z, both the planes orthogonal to the plane X-Y, are identified.

Container2comprises a cylindrical central area20and two truncated cone areas21,22, each truncated cone area being arranged laterally to said cylindrical central area. A first truncated cone area21is welded at one end to said cylindrical central area20while at the other end if comprises the loading mouth4of the container. A second truncated cone area22is welded at one end to said cylindrical central area20, on the opposite side with respect to the first truncated cone area21, while at the other end it comprises the bottom2′ of container2.

Support ring3, arranged at central area20of container2, is hollow and preferably has a rectangular cross-section. Ring3has a first surface10facing the part of the container comprising loading month4; a second surface11, opposite the surface10, facing the part of container2comprising the bottom2′ thereof; a third internal surface lacing the central part of the container; a fourth external surface opposite the internal surface.

The suspension elements are advantageously bars which are clamped, at a first end to container2and at a second end to support ring3. The bars are locked at the ends to prevent parts from relatively moving and, with no parts subject to wear, maintenance activity is eliminated or at least notably reduced. The bars, acting as tie-rods or struts, are adjustable in order to compensate possible non-uniformity of the length of the bars, thus ensuring the correct positioning thereof.

Said bars are suitably dimensioned in order to operate as elastic support means to absorb the dilations.

Said bars preferably have a circular section. However, other section shapes can be provided according to the designed longitudinal extension of the bars.

The bars are advantageously made from high-alloyed steels, such as steel for springs with high yield stress values or other suitable steel with similar characteristics of elasticity. Furthermore, the bars can be thermally treated (for example by means of hardening and tempering or solution heat-treatment according to the type of steel used) and can be provided with a surface coating, e.g. consisting of nickel, chrome or another appropriate element. The fine material used allows very high resistance not only to mechanical stress but also to the phenomena of oxidation, of notable importance in the context of oxygen converters.

With reference toFIGS. 7aand 7b, which show the converter of the invention in its upright position with loading mouth4facing upwards, a first advantageous variant of the invention includes:three pairs of first elastic bars7arranged parallel to axis X and at an equal angular distance between one pair and the next (120°);two pairs of second elastic bars8,8′ each pair of said second bars being symmetrically arranged with respect to the plane X-Z on a respective plane parallel to the plane Y-Z.

Therefore, considering the converter in a vertical position (FIG. 7a), the first bars7are in a vertical position while the second bars8,8′ are in a horizontal position. The first bars7pass orthogonally through the plane Y-Z. The second bars8,8′, on the other hand, are parallel to the plane Y-Z and pass, at an end thereof, through the plane X-Y.

In particular, a pair of second bars8is arranged at a first side of the plane Y-Z, i.e. above the plane Y-Z and support ring3when the converter is in the upright position (FIG. 2); while a pair of second elastic bars8′ is arranged at a second side of the plane Y-Z, i.e. underneath the plane Y-Z and support ring3when the converter is in the upright position (FIG. 2).

In particular, said pair of bars8is arranged close to the first surface10of the ring, while said pair of bars8′ is arranged close to the second surface11of the ring.

With reference toFIGS. 1 and 3, which schematically show the converter of the invention in its upright position, a second advantageous variant of the invention includes;three pairs of first elastic bars7arranged parallel to axis X and at an equal angular distance between one pair and the next (120°);and three pairs of second elastic bars8,8′, each pair of said second bars being symmetrically arranged with respect to the plane X-Z on a respective plane parallel to the plane Y-Z.

This second variant, in addition to the characteristics described above in the first variant inFIGS. 7aand 7b, includes a further pair of second bars8′, arranged underneath the pair of bars8′ already provided in the first variant close to the second surface11of the ring, so that on each side of the plane X-Z, the three second bars8,8′ are arranged on the same vertical plane.

In particular, a pair of second bars8is arranged at a first side of the plane Y-Z, i.e. above the plane Y-Z and support ring3when the converter is in the upright position (FIG. 2); while two pairs of second elastic bars8′ are arranged at a second side of the plane Y-Z, i.e. underneath the plane Y-Z and support ring3when the converter is in the upright position (FIG. 2).

In particular, said pair of bars8is arranged close to the first surface10of the ring, while said pairs of bars8′ are arranged close to the second surface11of the ring. In particular, a pair of second bars8′ is proximal to said second surface11, while the other pair of second bars8′ is distal from said second surface11.

Other variants of the converter of the invention, on the other hand, include a suspension system comprising a greater number of first elastic bars7, arranged parallel to the axis X. The number of said first elastic bars can be advantageously increased as a function of the load to be supported. With the increase of the load to be supported, it is preferable to minimize the variation of section or keep the section of the first bars7constant, increasing, on the other hand, the number thereof in order to allow them to deform freely by bending.

In the variants inFIGS. 1 and 7b, the three pairs of first elastic bars7are arranged at 120° to each other in order to have isostatic equilibrium, i.e. a balanced load distribution for each group of elastic bars. This configuration allows excellent results to be obtained for an overall weight of the container of around 340 tons.

In the case of greater loads, rather than to design thicker first elastic bars which would have less elasticity, it is preferable to increase the number of first bars, advantageously including three groups of said first bars7. These groups of first bars7are substantially arranged at 120° to each other in order to continue to have isostatic equilibrium. A greater number of thin bars allows the load to be distributed in an optimal manner, maintaining a suitable elasticity of the bars. Therefore, these other variants of the converter also include a greater number of second elastic bars.

For example, a third advantageous variant of the converter, schematically shown inFIGS. 7eand 7din its upright position, includes three groups30,31,32of first bars7, each group consisting of three first bars7. This third variant further includes four pairs of second elastic bars; a pair of second bars8is arranged at a first side of the first plane Y-Z, above support ring3when the converter is in a vertical position; three pairs of second bars8′,8″ are arranged at a second side of the first plane Y-Z, underneath support ring3when the converter is in a vertical position.

In particular, in addition to the characteristics described above in the second variant inFIGS. 1 and 2, the third variant includes a further pair of second bars8″ arranged close to surface11of support ring3facing the bottom2′ of the converter. This further pair of bars8″ is arranged on the same plane parallel to the plane Y-Z containing the pair of bars8′ proximal to said surface11, the bars8″ being arranged externally to the bars8′.

This configuration allows excellent results to be obtained for an overall weight of the container of around 750 tons.

A fourth advantageous variant of the converter, schematically shown inFIGS. 7eand 7fin its upright position, includes three groups30,31,32of first bars7, each group consisting of four first bars7.

This fourth variant further includes six pairs of second elastic bars: two pairs of second bars8,80′″ are arranged at a first side of the first plane Y-Z, above support ring3when the converter is in a vertical position; four pairs of second bars8′,8″ are arranged at a second side of the first plane Y-Z, underneath support ring3when the converter is in a vertical position.

In particular, in addition to the characteristics described above in the second variant inFIGS. 1 and 2, the fourth variant includes:a further pair of second bars8′″ arranged close to the surface10of ring3. This further pair of bars8′″ arranged on the same plane parallel to the plane Y-Z containing the pair of bars8, the bars8″′ being arranged externally to the bars8;two further pairs of second bars8′ arranged close to the surface11of support ring3facing the bottom2′ of the converter. Each of these further two pairs of bars8″ is arranged on a respective plane parallel to the plane Y-Z and containing a respective pair of bars8′, the bars8″ being arranged externally to the bars8′.

This configuration allows excellent results to be obtained for an overall weight of the container of around 1100 tons.

A fifth advantageous variant of the converter, schematically shown inFIGS. 7gand 7hin its upright position, includes three groups30,31,32of first bars7, each group consisting of five first bars7.

This fifth variant further includes seven pairs of second elastic bars: three pairs of second bars8,8″′,8ivare arranged at a first side of the first plane Y-Z, above support ring3when the converter is in a vertical position; four pairs of second bars8′,8″ are arranged at a second side of the first plane Y-Z, underneath support ring3when the converter is in a vertical position.

In particular, in addition to the characteristics described above in the second variant inFIGS. 1 and 2, the fifth variant includes:two further pairs of second bars8″′,8ivarranged close to the surface10of ring3.

The further pair of bars8″′ is arranged on the same plane parallel to the plane Y-Z containing the pair of bars8, the bars8″′ being arranged externally to the bars8; while the further pair of bars8ivis arranged above the pair of bars8so that, on each side of the plane X-Z, the bars8iv,8and8′ are arranged on a same vertical plane (FIG. 7g);and two further pairs of second bars8″ arranged close to the surface11of support ring3facing the bottom2′ of the converter. Each of these further two pairs of bars8″ is arranged on a respective plane parallel to the plane Y-Z and containing a respective pair of bars8′, the bars8″ being arranged externally to the bars8′.

On each side of the plane X-Z, the bars8″′ and8″ are also arranged on a same vertical plane (FIG. 7g).

This configuration allows excellent results to be obtained for an overall weight of the container of around 1350 tons.

Advantageously, in the case of groups of three or five bars7, the axis of the bar7at the centre of group30lies on the plane X-Z (FIGS. 7dand 7h).

In all the variants of the invention all the first bars7are arranged, in plan view, along a circumference. The first group30of first elastic bars7is arranged close to the plane X-Z. The second group31and the third group32of the first bars7are arranged symmetrically to each other with respect to the plane X-Z. The second elastic bars are arranged at an angular distance γ of ±50÷90°, preferably ±60÷80°, from the plane X-Z.

The second bars8,8′,8″,8″′,8ivarranged on one side with respect to the plane X-Z are parallel to each other and are also parallel to said first surface10and second surface11of ring3. The same goes for the second bars8,8′,8″,8″′,8ivarranged on the other side with respect to the plane X-Z.

The pairs of bars8′,8″, underneath support ring3when the converter is in a vertical position, are advantageously arranged closer to the barycenter of the converter in order to support the loads where there is a greater load and a tendency by the converter to rotate.

In order to ensure perfect vertical centring of the converter, the second elastic bars8,8′,8″,8″′,8ivof each pair are advantageously arranged on a same plane, parallel to the plane Y-Z, with the respective axes converging to each other in a preferred variant.

Preferably, the angle β, which the longitudinal axis of each elastic bar8,8′,8″,8′″,8ivof each pair forms with the plane X-Z on the sheet inFIG. 1, is around 0-40°. Excellent results of self-centring of the converter were obtained with the angle β preferably in the range 10÷30°, limit values included. In the example inFIG. 1, the angle β is equal to around 20°.

All the elastic bars7,8,8′,8″,8″′,8ivare arranged, in plan view, substantially along a circumference (FIGS. 1 and 7). Therefore, they are arranged substantially along the lateral surface of a cylinder.

The second elastic bars are restrained at one end to container2and at the other end to support ring3by means of locking on respective fixing brackets12,13and12′,13′ (see, for example,FIGS. 1 and 2): hence the constraint is a fixed joint (fixed beam). The fixing brackets12,13,12′,13′, welded or bolted to container2and ring13, have through holes into which the bars are inserted; the ends of such bars are threaded and the locking thereof onto the brackets takes plane by means of a self-aligning locking system and nuts. Advantageously, a single fixing bracket12′ and a single fixing bracket13′ can be provided, at each side of the plane X-Z, in order to fix the ends of the elastic bars provided underneath or above support ring3. The fixing brackets12,12′ and13,13′ are provided at the cylindrical central area20of container2. In particular, the fixing brackets12,12″ are arranged close to the rotating pins6. In a variant, the second bars8,8′ are fixed so as to be substantially tangent to a cylindrical surface containing the internal surface of support ring3(see, for example,FIG. 1).

The first elastic bars7are restrained at one end of container2by means of locking on the fixing brackets14. On the other hand, they are restrained at the other end by means of locking directly onto the first surface10of support ring3. Also in this case, the constraint is a fixed joint (fixed beam). Both the fixing brackets14, welded or bolted to container2, and the first surface10of ring3have through holes into which the elastic bars7are inserted; the ends of such bars are threaded and the locking thereof onto the brackets14and the first surface10of the ring takes place by means of a self-aligning locking system and nuts. The elastic bars7pass, at least with one end thereof, through the cavity of ring3, optionally within a respective sleeve having the function of delimiting the passage channel of the respective bar7. A single fixing bracket14can be advantageously included for each pair or group of elastic bars7.

With reference to the FIGS. from1to3and from7ato7g(converter in a vertical position), the first elastic bars7are fixed to container2in a position underneath support ring3, i.e. underneath the plane Y-Z; while they are fixed to ring3directly on the first surface10of the latter, i.e. above the plane Y-Z.

The fixing brackets14are advantageously fixed to both the lateral surface of the second truncated cone area22of container2and to the bottom2′ of the container, delimiting said second truncated cone area. Thereby, it is possible to take advantage of the greater stiffness of bottom2′ having a circular closed structure, without the need of reinforcing the cylindrical area of the container.

In all the variants, the first elastic bars7advantageously have a length equal to the length of the second elastic bars8,8′,8″,8″′,8iv. The thickness or diameter can also be equal for all the bars7,8,8′,8″,8″′,8iv. The elastic bars therefore define tie-rods of equal dimension which are perfectly interchangeable with one another.

As an alternative, however, the length of the first elastic bars7is different from the length of the second elastic bars8,8′,8″,8″′,8iv. The thickness or diameter can also be different between the bars7and the bars8,8′,8″,8″′,8iv.

In any case, all the bars7,8,8′,8″,8″′,8ivare dimensioned so as to have a suitable length and thickness or diameter to operate in the elastic field with infinite duration.

The two supporting pins6, actuated by at least one tilting mechanism, allow the rotation of the converter about axis Y.

The converter usually moves from a first position in which it is in a vertical position with the loading mouth4facing upwards (FIG. 2) to a second position inclined by around 30° with respect to the vertical40(FIG. 4), by means of rotation of the supporting pins6in a first direction of rotation. In the position inFIG. 4, loading of the liquid cast iron and scrap metal takes place through mouth4.

After loading, the converter returns to the first position inFIG. 2. One or more lances, introduced into the container by means of mouth4, provide for insufflation of oxygen for a predetermined period of time so as to drastically lower the content of carbon and reduce the concentration of imparities such as sulphur and phosphorus.

Once the conversion into raw liquid steel has been completed, the converter moves from the first position inFIG. 2to a third position (FIG. 5) inclined by around 90° with respect to the vertical40, by means of rotation of the supporting pins6in a second direction of rotation, opposite to the first one. In this third position, the tapping of the liquid steel takes place by means of tapping hole5.

In all the variants of the invention, shown in the FIGS. the load, determined by the sum of the weights of container2, liquid cast iron and scrap metal, is unloaded to the ground by means of support ring3, the elastic bars7,8,8′,8″,8″′ e8ivthe tilting pins6and the related supports.

In particular, the configuration of the elastic bars7,8,8′,8″,8″′,8ivallows the weight to be absorbed for any inclination of container2.

The first elastic bars7act substantially as tie-rods for inclination angles of the converter with respect to the vertical from 0° (position inFIG. 2) to 90° (FIG. 5) and from 270° to 360° (position inFIG. 2); on the other hand, they act substantially as struts for inclination angles of the converter with respect to the vertical from 90° (position inFIG. 5) to 270°.

The position with inclination angle equal to 180°, shown inFIG. 6, with loading mouth4facing downwards, is provided for cleaning the container, once emptied.

The pairs of second elastic bars8,8′,8″,8″′,8ivensure optimal support, stability and rigidity of the container. Said pairs of second bars8,8′,8″,8″′,8ivserve principally to support the weight of the container in a direction transverse to axis Y when this is inclined by 90° (tapping position—seeFIG. 5). The convergence of the second elastic bars of each pair, in a preferred configuration thereof, also contributes towards absorbing possible loads in the direction of the axis Y. They act substantially as struts for inclination angles of the converter with respect to the vertical from 0° (position inFIG. 2) to 90° (FIG. 5) and from 270° to 360° (position inFIG. 2); on the other hand, they act substantially as tie-rods for inclination angles of the converter with respect to the vertical from 90° (position inFIG. 5) to 270°.

The pairs of second bars8,8′,8″,8″′,8ivalso carry out the function of preventing possible movements/oscillations on the horizontal plane when the converter is inclined by 90° for the step of tapping the liquid steel. With the bars8,8′,8″,8″′,8ivof each pair being inclined and opposite to each other on a same plane, i.e. converging, they self-centre the container.

In general, therefore, the load on the first elastic bars7gradually gees from a maximum value with converter in the vertical position to a zero value with converter in the horizontal position, while the load on the second elastic bars8,8′,8″,8″′,8ivgradually goes from zero to a maximum value when the converter moves from the horizontal position to the vertical position.

The moments which are generated with the rotation of the converter about axis Y are perfectly absorbed by the configurations of elastic bars of the variants described above.

All the variations described above can be further provided with at least a third elastic bar9, arranged so as to be diametrically opposite (180°) to the first group30of first bars7arranged close to the plane X-Z.FIGS. 1aand 2ashow, by way of example, a top view and a side view, respectively, of the converter of the second variant provided with a single third elastic bar9.

The third bar9is advantageously positioned underneath the plane Y-Z, i.e. underneath support ring3when the converter is in the vertical position (FIG. 2a), in such a way that it is not exposed to an excessive thermal load during the tapping step (seeFIG. 5).

Preferably, but not necessarily, the third bar9is positioned equally spaced apart from the second bars8,8′,8″,8″′,8ivprovided at both sides of the plane X-Z, preferably at 120° from said second bars, and the angle β, which the longitudinal axis of each second elastic bar of every pair forms with the plane X-Z, is preferably 30°.

The third elastic bar is restrained at one end to container2and at the other end to support ring3by means of locking on respective fixing brackets16and15(see, for example,FIG. 1a): hence the constraint is a fixed joint (fixed beam). The fixing brackets15and16, welded or bolted to container2and ring13, have through holes into which bar9is inserted; the ends of bar9are threaded and the locking thereof onto the brackets15,16takes place by means of a self-aligning locking system and nuts.

The task of said at least one third elastic bar9is to prevent/block possible lateral movements due to the low frequency vibrations of the container which are generated during the melting step in the vertical position, following the injection of oxygen.

Preferably, the at least one third bar9also has the same dimensions as all the other elastic bars present in the converter of the invention. As an alternative, the dimensions of the third bar9can be different with respect to the first bars and/or the second bars.

According to a preferred embodiment, in all the above-described variants there is provided only one third elastic bar9. However, the number of third elastic bars can be greater than one according to the container size. In any case, the third bats9are positioned underneath the plane Y-Z when the converter is in the vertical position.

A former advantage is that all the elastic bars7,8,8′,8″,8″′,8ivare fixed-end bars, provided with an innovative self-aligning locking system, at the two end supports, for the axial closure and compensation of misalignments.

Since both the fixing brackets12,12′,13,13′,14and the internal and external surfaces of support ring3are generally provided fey means of low precision machine tools, they present machining errors which entail very rough parallelism tolerances and/or shape irregularities.

For this reason, the end supports of the bars7,8,8′,8″,8″′,8iv,9can have support planes which are not perfectly parallel therefore converging.

For example, taking into consideration the ends of the bars7(FIGS. 8 and 9), the first end support60(FIG. 8), part of support ring3, may have the external support surface10and the internal support surface10′ not perfectly parallel to each other, causing discontinuous support of the locking elements and consequent clearances which are harmful to the wear resistance and stability of the tie-rod. Taking into consideration also the second end support60′ (FIG. 9), part of fixing bracket14, the external40and internal support surfaces40′ thereof may present machining errors or shape irregularities. Furthermore, there may also be distance errors between the external surface10of end support60and the external surface40of end support60′.

Each tie-rod or strut of the converter of the invention comprises (FIG. 15):an elastic bar provided with threaded ends47,48;locking elements to lock the ends of the bar to respective end supports60,60′;a pair of support flanges or thicknesses44,45which, in the configuration with tie-rod locked at the ends, are arranged at end support60′, said end support60′ being interposed between the two flanges44,45.

Bar7(FIG. 15) comprises a central portion46, delimited on one side by a shoulder52and on the other by an intermediate threaded portion49, and two lateral portions50,51having longitudinal extension along axis X which differ from each other.

Lateral portion50is arranged between threaded end47and the corresponding shoulder52and has a longitudinal extension along axis X which is substantially equal to the longitudinal extension of the hole70provided its the end support60(FIG. 8). The lateral portion50has a diameter which is smaller than the diameter of the adjacent threaded end47.

The lateral portion51, on the other hand, is arranged between threaded end48and said intermediate threaded portion49, and has a longitudinal extension along axis X which is greater than the longitudinal extension of lateral portion50and slightly longer than the sum of the longitudinal extensions of the three holes80,90,90′ (FIG. 9), provided in the respective end support60′ and in the two flanges44,45, respectively. Lateral portion51has a diameter which is smaller than the diameter of the adjacent threaded end48and intermediate threaded portion49.

The locking elements comprise at each end of the bar:two pairs of spacers42,43and42′,43′, each pair of spacers advantageously having surfaces joined to each other53,54e53′,54′ substantially in the shape of an annular portion of a spherical cap (FIGS. 14aand 14b);and at least two tightening nuts41.

In the configuration with tie-rod locked at the ends, at each end support there are provided;a first pair of spacers42,43arranged at an external side of the respective end support,a second pair of spacers42′,43′ arranged at an internal side of the respective end support.

The first pair of spacers and the corresponding second pair of spacers are advantageously symmetrically arranged with respect to the interposed end support, and the pair of joined surfaces53,54of the first pair of spacers has a spherical cap radius which is equal to the spherical cap radius of the pair of joined surfaces53′,54′ of the second pair of spacers, said pair of joined surfaces, however, being arranged on different spherical surfaces. Each elastic bar is therefore clamped (non-spherical joint) by means of an innovative looking system at the two end supports for the axial closure and compensation of misalignments.

Said at least two tightening nuts41are externally tightened onto the first pair of spacers42,43, i.e. the external pair of spacers.

In particular, with reference toFIGS. 8, 11 and 12, the clamping locking system of elastic bar7provides at the threaded end47of the bar (FIG. 8):external tightening nuts41, e.g. in a minimum number of two, to be tightened on threaded end47of bar7;a first external pair of spacers or washers42,43, to be arranged between said two tightening nuts41and external surface10of end support60; each spacer42,43being provided with a respective hole61,62for passing threaded end47of the bar, the spacer43having an surface of annular portion of spherical cap53joined to a corresponding surface54provided in spacer42(FIGS. 14aand 14b);a second internal pair of spacers or washers42′,43′, to be arranged between shoulder52of bar7and internal surface10′ of end support60; each spacer42′,43′ being provided with a respective hole61′,62′ for passing threaded end47of the bar, the spacer43having an surface of annular portion of spherical cap53′ joined to a corresponding surface54′ provided in spacer42′ (FIGS. 14aand 14b);

First end support60is provided with a hole70for passing a respective end of the bar (FIG. 8).

With reference toFIGS. 8, 12 and 14, spacer42′ rests with a flat surface55′ thereof against shoulder52, while spacer43′ rests with a flat surface56′ thereof against internal surface10′ of end support60. Spacer43, on the other hand, rests with a flat surface56thereof against external surface10of end support60, while flat surface55of spacer42is pressed by the tightening bolts41.

By tightening the bolts41on threaded end47of bar7, the joined surfaces53′,54′ of the spacers43′,42′ and the joined surfaces53,54of the spacers43,42, respectively, will come into complete contact with each other, while the flat surfaces56,56′ will adapt to the shape of the respective surfaces10,10′ of end support60.

This clamping locking solution advantageously allows misalignment errors of the surfaces10,10′ to be compensated for by means of sliding between the joined surfaces with spherical cap shape. The radius of the spherical cap is the same for both pairs of joined surfaces but the centres are different, i.e. the two spherical cap surfaces are not part of the same spherical surface (see curved dotted lines100inFIG. 7). Therefore, this configuration of the spacers represents a self-aligning “locked joint”, i.e. a joint which cannot work as a ball joint, but when the bar is tightened, necessarily works as a fixed joint.

The joined surfaces with spherical cap shape allow rotation in the assembly step, whereby these surfaces always fit together with each other. The flat surfaces56,56′ of the spacers43,43′ will deform following tightening, whereby the contact between said flat surfaces56,56′ and the support surfaces10,10′ is maximized so as to obtain a continuous support.

The use of this locking system allows the use of high-precision processing machines to be avoided, and therefore higher production and management costs. Furthermore, this locking system advantageously allows the use of a support ring without any openings in the external lateral surface thereof, which is necessary for accessing the tightening area in the case of state-of-the-art spherically jointed tie-rods, determining a greater mechanical resistance of the ring structure.

Instead, with reference toFIGS. 9, 11 and 13, the clamping locking system of the elastic bar includes, at threaded end48of the bar (FIGS. 9 and 10):external tightening nuts41, e.g. in a minimum number of two, to be tightened on threaded end48;two flanges44,45, or support thicknesses, to be arranged so that end support60′ is arranged between said two flanges;a first external pair of spacers or washers42,43, to be arranged between said tightening nuts41and external flange45; each spacer42,43being provided with a respective hole61,62for passing threaded end48of bar7, the spacer43having a an annular portion surface53of spherical cap joined to a corresponding surface54provided in spacer42(FIGS. 14aand 14b);a second infernal pair of spacers or washers42′,43′, to be arranged between internal flange44and internal nut41′; each spacer42′,43′ being provided with a respective hole61′,62′ for passing threaded end48of bar7, the spacer43′ having a an annular portion surface53′ of spherical cap joined to a corresponding surface54′ provided in spacer42′;an internal nut41′ to be tightened on intermediate threaded portion49until resting on the internal pair of spacers42′,43′.

The first flange45is arranged between the external pair of spacers42,43and the respective external surface40of end support60′ and a second flange44is arranged between the internal pair of spacers42′,43′ and the respective internal surface40′ of end support60′.

Hole80of end support60′ has a greater diameter than hole70of end support60. The flanges44,45are provided with respective holes90,90′ with a smaller diameter than the diameter of hole80. The flanges44and45may consist of half flanges (FIG. 13a) held integral with each other by means of fixing means, such as stud bolts with nut and lock nut; as an alternative, the external flange is instead provided as an integral component (FIG. 13b—flange45′).

With reference toFIGS. 9, 13 and 14, spacer42′ rests with a flat surface55′ thereof against internal nut41′, while spacer43′ rests with a flat surface56′ thereof against a flat surface of internal flange44. Spacer43, on the other hand, rests with a flat surface56thereof against a flat surface of external flange45, while flat surface55of spacer42is pressed by the tightening bolts41.

By tightening the bolts41on threaded end48of bar7and tightening internal bolt41′ on intermediate threaded portion49, the joined surfaces53′,54′ of the spacers43′,42′ and the joined surfaces53,54of the spacers43,42, respectively, will come into complete contact with each other, while the flat surfaces56,56′ will put pressure on the flanges44,45which will adapt to the shape of the surfaces40,40′ of support60′.

Internal tightening bolt41′ is advantageously configured to be, in the condition of end-locked tie-rod, longer than the length L of the useful part200of thread of intermediate threaded portion49protruding from spacer42′ towards the inside of bar7. This allows the prevention of notching stress concentrations due to exposed threads of the part subjected to bending of the bar itself. Once tightened, therefore, internal nut41′ will have exposed threads at area91(FIG. 15) into which bar7tapers inwardly.

In addition to the advantages derived from the use of pairs of spacers with spherical joined surfaces, already discussed above, the fact of providing internal nut41′, which is completely accessible inasmuch as it is provided on the exterior of support ring3, allows distance errors to be compensated between the support surfaces, those integral with the container and those integral with the support ring. Internal nut41′ is therefore an adjustment nut in order to compensate these distance errors and adapt the structure to all the variable distances which there may be in the design.

The presence of flanges44and45, defining further spacers, advantageously allows hole80to be kept considerably larger than the diameter or thickness of the bar, thus facilitating the passing of the bar and the corresponding assembly of end supports. Thereby, in addition to compensating planarity distance errors, alignment errors between the hole70of end support60and the hole80of end support60′ are also compensated.

Therefore, the above-described locking system for locking the bar to the end supports globally allows remarkable ease of assembly and centring simplicity.