WO2014076554A2

WO2014076554A2 - Crystallizer for continuous casting and method for the manufacture

Info

Publication number: WO2014076554A2
Application number: PCT/IB2013/002565
Authority: WO
Inventors: Alfredo Poloni
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2012-11-16
Filing date: 2013-11-15
Publication date: 2014-05-22
Anticipated expiration: 2015-05-16
Also published as: ITUD20120193A1; WO2014076554A3

Abstract

Crystallizer for continuous casting comprising a tubular body (11) with an oblong development, and a plurality of plates (19) associated to the external peripheral surface (12) of the tubular body (11). The tubular body (11) is made in a single body and is provided, in its external peripheral surface (12), with a plurality of longitudinal grooves (16) open toward the outside, and the plates (19) are intimately and permanently coupled to the external peripheral surface (12) of the tubular body (11) in order to close the longitudinal grooves (16) and to define channels (20) for the passage of a cooling liquid, the plates (19), when coupled to the tubular body (11), being detached from each other and defining a reciprocal separation gap (G) between adjacent plates (19).

Description

"CRYSTALLIZER FOR CONTINUOUS CASTING AND METHOD FOR THE MANUFACTURE"

FIELD OF THE INVENTION

The present invention concerns a crystallizer for continuous casting provided with a plurality of channels made in its walls and through which a cooling liquid is made to pass.

In particular, the crystallizer is used in the steel-making field to cast billets or blooms of any type and section, preferably square or rectangular, but also polygonal in general, or round.

BACKGROUND OF THE INVENTION

Crystallizers are known for casting billets or blooms, having a tubular body inside which the liquid metal is cooled. It is also known to provide that the tubular body is provided, in the thickness of its walls and for at least part of the longitudinal development, with a plurality of channels having a shape and sizes suitable for the passage of a cooling liquid. The channels can be reciprocally interconnected to define a closed cooling circuit.

The operations to make the cooling channels along the length of the tubular crystallizer are particularly complex and costly in terms of time and the equipment used. They require complex operations of holing and finishing so as to define passage channels that optimize the flow of the cooling liquid. Consequently, the costs and times of making the crystallizer are very high.

Crystallizers are also known that comprise a first component, with an oblong development and a tubular shape, and a second component, also tubular and associated externally and in contact with the external surface of the first component

The first component, on its external peripheral surface, is provided with a plurality of grooves, open toward the outside and made along at least part of its length.

The second component is associated to the first component by mechanical connection means, for example bolts, pins, nuts, tie rods or suchlike, to maintain a close contact between the external surface of the first component and the internal surface of the second component. The grooves are therefore closed by the internal wall of the second component to define closed channels through which the cooling liquid is made to circulate during use.

In this known solution, the second component comprises a plurality of plates, each of which is associated by means of said connection means to an external surface portion of the first component.

In this solution, the operations to assemble the first and second component are particularly complex and long. In fact, to guarantee the correct hydraulic seal of the cooling channels in every surface zone affected by the grooves, it is necessary to provide a high number of connection means and peripheral seals with O-rings to guarantee a watertight seal of the cooling water from the grooves. This is also necessary so as to take into account the different thermal dilations to which the first component is subjected with respect to the second component.

A crystallizer for continuous casting is also known from document WO-A- 00/41830, comprising a first tubular component provided on its external surface with a plurality of longitudinal grooves. The crystallizer also comprises a plurality of plates that are applied on the external surface of the first component to close the grooves and define, together with the latter, channels for the passage of a cooling liquid.

The first tubular component, in cross section, has a polygonal shape with rounded edges, both on the internal surface and on the external surface. The rounded configuration of the edges of the first tubular component entails a uniform thickness of the whole first tubular component. This condition of uniform thickness confers on the crystallizer a considerable rigidity which, during use, due to the thermal dilation and mechanical stresses, entails an accumulation of plastic deformation and hence a state of internal tension. In fact, as the casting cycles follow one another, in known crystallizers and in the internal surface where the molten metal passes, the internal tensions exceed the resistance limit of the material, thus leading to the formation of cracks, generally in correspondence with the center line of the faces. This phenomenon is even more accentuated in the zone astride the meniscus. This disadvantage is even more serious when a crack formed on the surface is propagated to one of the holes or cooling channels. In this case, the cooling liquid comes into contact with the molten metal passing through the crystallizer and generates dangerous explosions.

One purpose of the present invention is to manufacture a crystallizer for continuous casting that guarantees that high quality cast products are obtained, and that the products are cast with high productivity and in total safety.

Another purpose is to manufacture a crystallizer for continuous casting which has high heat exchange efficiency and long working life.

Another purpose of the present invention is to perfect a method for manufacturing a crystallizer for continuous casting of the type indicated above that is simple, quick to make and that allows to reduce the costs of manufacturing the crystallizer.

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 crystallizer for continuous casting comprises a tubular body with an oblong development through which, during use, the molten metal to be cast passes, and a plurality of plates associated with the external peripheral surface of the tubular body.

According to one feature of the present invention, the tubular body is made in a single body, that is, in a single monolithic piece, and is provided in its external peripheral surface with a plurality of longitudinal grooves open toward the outside. The plates are intimately and permanently coupled to the external peripheral surface of the tubular body in order to close the longitudinal grooves and to define channels for the passage of a cooling liquid. Moreover, when coupled to the tubular body, the plates are detached from each other, that is, reciprocally distanced from each other, and define a reciprocal separation gap between adj acent plates .

Providing a tubular body in a single body not only increases the mechanical resistance against deformations, but also allows to obtain a continuous heat exchange in the whole cross section of the crystallizer. In fact, in this case, possible discontinuities are prevented, which alter the heat transfer capacity and which generate zones with differentiated cooling in the crystallizer. Such zones would be particularly harmful with regard to the final quality of the metal product cast.

Making grooves on the external surface of the tubular body is particularly easy and quick, compared with making the cooling channels in the thickness of the tubular body.

The intimate and permanent coupling of the plates to the tubular body prevents having to use and apply dedicated connection means, such as for example threaded connections which not only increase the number of components that make up the crystallizer, but also increase the production times and costs. Furthermore, the intimate and permanent coupling guarantees a watertight seal between the channels even if, in the latter, cooling liquids are made to circulate with high working pressures.

Providing the plates reciprocally detached, or also angularly distanced with respect to each other, allows to prevent possible non-uniform thermal dilations during casting from inducing tensions on the plates and on the tubular body.

Some forms of embodiment provide that, in cross section, the tubular body has a polygonal section shape, with beveled edges made on the external surface of the tubular body and with mating and opposite rounded edges on the internal peripheral surface of the tubular body. The rounded edges and the beveled edges define a reduction in thickness of the material in correspondence to the connection edges between the walls.

The combined effect of the configuration of the plates detached from each other, the beveled edges and the rounded edges of the tubular body means that the edges act as hinges around which the walls of the tubular body can rotate, so that the stresses and zones where the tensions accumulate, as the casting cycles follow each other, remain localized in the edges, reducing the possibility of creating cracks in the central zone of the walls, as happens in state-of-the-art crystallizers.

The solution according to the present invention therefore allows to make the crystallizer more yielding in the zone in correspondence with the edges where there are no cooling channels. The central zone of the walls of the crystallizer, where there are the cooling channels, are without tensions, and hence less subject to the formation of cracks.

Possible cracks that might form in the edges would not compromise the functionality and safety of the crystallizer since in this zone the cooling fluid can never enter into contact with the molten metal.

The elastic yielding of the crystallizer around the edges is particularly advantageous especially at high casting speeds.

Some forms of embodiment provide that the reciprocal separation gap between adjacent plates is defined by the thickness of the adjacent plates and by the beveled edge.

According to one form of embodiment, the intimate and permanent coupling is achieved using the brazing technique. In this way a perfect union of the two components is obtained and a suitable mechanical resistance distributed equally over the whole coupling zone between the two components, which practically become a single structure.

Other forms of embodiment provide that the coupling of the external surface of the internal component and the internal surface of the external component is obtained by gluing, using suitable glues resistant to high temperatures and pressures.

The present invention also concerns the method for manufacturing a crystallizer for continuous casting as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

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

- fig. 1 is a view of a longitudinal section of a crystallizer for continuous casting according to the present invention;

- fig. 2 is a section view from II to II of fig. 1 ;

- fig. 3 is an enlarged view of a detail of fig. 2 according to a variant;

- fig. 4 is an enlarged view of a detail of fig. 3 according to another variant form of embodiment.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications.

DETAILED DESCRIPTION OF SOME FORMS OF EMBODIMENT

With reference to fig. 1, a crystallizer for continuous casting is indicated in its entirety by the reference number 10 and comprises a tubular body 11 with a longitudinal development along a longitudinal axis Z, and is provided with an external peripheral surface 12 and an internal peripheral surface 13 defining a through cavity which, during use, is in contact with the metal material cast.

The tubular body 11 is defined in this case by four walls 15 reciprocally connected with each other in a single body to define a substantially tubular rectangular section shape, in this case square.

The tubular body 11 is provided in its external peripheral surface 12 with beveled edges 14 that connect the adjacent walls 15 to each other.

According to some forms of embodiment, for example shown in fig. 3, the beveled edges 14 have a rectilinear development.

Some forms of embodiment provide that the beveled edges 14 have a bevel angle a, estimated with respect to the plan development of one of the walls 15 between which the beveled edge 14 is interposed, comprised between 30° and 60°, preferably between 40° and 50°, in this case about 45°.

In possible forms of embodiment, the internal peripheral surface 13 of the tubular body 11 is provided with rounded edges 27 which internally connect the walls 15 of the tubular body 11 with each other, and disposed opposite the mating beveled edges 14.

According to other forms of embodiment, for example shown in fig. 4, the beveled edges 14 have a curved development with a less accentuated curvature than the rounded edges 27.

The presence of beveled edges 14 on the external peripheral surface 12 and of rounded edges 27 on the internal peripheral surface 13 determines a reduction in the thickness of the material present in correspondence with the edges or corners of the tubular body 1 1 with respect to the thickness of the walls 15. This confers greater flexibility on the tubular body 11, as will be described hereafter.

The external peripheral surface 12 of the tubular body 11 is provided with a plurality of longitudinal grooves 16 made along the longitudinal development of the tubular body 1 1.

The longitudinal grooves 16 are closed by plates 19, each of which is connected to the external peripheral surface 12 of the tubular body 1 1, to define cooling channels 20 in which a cooling fluid is made to circulate, as will be described hereafter.

Some forms of embodiment provide that the longitudinal grooves 16 are made substantially parallel to the longitudinal axis Z.

In the form of embodiment shown in fig. 2, the longitudinal grooves 16 have a substantially rectangular section shape, with rounded tops, although other section shapes are not excluded.

For example, with reference to the form of embodiment in fig. 3, the longitudinal grooves 16 have a trapezoidal section shape, that is, dovetailed. In particular, the longitudinal grooves 16 are disposed with a larger base 17 of the trapezoidal section facing toward the internal part of the tubular body 1 1, and a smaller base 18 of the trapezoidal section facing toward the external peripheral surface 12. In this way the heat exchange capacity toward the internal part of the tubular body 1 1 is increased, given the greater heat exchange surface and the greater quantity of cooling liquid in circulation. Furthermore, the overall extension of the contact surface between the tubular body 1 1 and the plates 19 is kept unchanged.

The internal peripheral surface 13 of the tubular body 1 1 has suitably rounded peripheral edges to prevent, in said zones, any intensification of the cooling action on the metal cast.

In other forms of embodiment, the tubular body 11 has a polygonal section shape, also chosen according to the type of metal product that the crystallizer 10 has to obtain. In this case too, the edges between adjacent walls are suitably beveled.

The tubular body 1 1 is made of copper or alloys thereof, such as a copper- silver alloy, or a copper-chromium-zirconium alloy.

Some forms of embodiment provide that the internal peripheral surface 13 of the tubular body 1 1 is covered with a covering layer, with the function of increasing resistance to wear, and also to allow the molten metal to flow with low friction. Merely by way of example, the covering layer is made of material comprising an alloy of chromium or nickel-chromium.

The plates 19 are made of a material that can be an alloy of copper-silver or steel.

Each plate 19 is substantially flat, with an overall length equal to or less than the longitudinal extension of the longitudinal grooves 16, and a width L less than the width B of the wall 15, or rather the surface portion of the wall 15 affected by the longitudinal grooves 16. In the assembled condition of the plates 19 with the tubular body 11, a reciprocal separation gap G is defined between the plates 19. In particular, the reciprocal separation gap G between the plates 19 is defined by the thickness of the adjacent plates 19 and the beveled edge 14.

In other words, each plate 19 is connected to the tubular body 11 so as to prevent any reciprocal contact with the other plates 19 adjacent to it, even when the crystallizer 10 is thermally dilated.

The particular configuration of the beveled edges 14 and the rounded edges 27, and of the plates 19 coupled with the tubular body 11, with a break in continuity, that is, so as to prevent any reciprocal contact between them, makes the crystallizer 10 more yielding in the zone of the edges, each of which can be compared to a hinge around which two adjacent walls can mutually rotate following the stresses, both thermal and mechanical, to which the crystallizer 10 is subjected during use.

In this way it is possible to de-stress the central part of the walls of the crystallizer 10, where there are the cooling channels 20, thus preventing any possible formation of cracks on the internal surface of the crystallizer 10, which cracks could propagate toward the cooling channels 20.

The plates 19, in this case four plates 19, one for each wall 15, are connected to the tubular body 1 1 by means of a connection material 21.

Some forms of embodiment provide that the connection material 21 consists of a brazing material.

Other forms of embodiment provide that the brazing material is chosen from a group comprising alloys based on tin, lead, copper, silver, zinc or combinations thereof.

Although hereafter in the description we shall refer only to the solution which provides to use a brazing material, it cannot be excluded that, in other forms of embodiment, the connection between the tubular body 11 and the plates 19 is obtained by gluing, or rather using a gluing material.

Some forms of embodiment provide that the connection material 21 is a gluing material chosen from a group comprising at least epoxy resins, chinoacrylates or similar or comparable glues, suitable for the particular use.

Merely by way of example, the cooling channels 20 are configured to resist pressure stresses exerted by the cooling liquid of about 20 bar. Depending on the working pressure of the cooling liquid, the type of connection material 21 to be used is also evaluated.

The cooling fluid allows to obtain a uniform cooling of the whole cross section of the crystallizer 10.

Merely by way of example, it is provided that the internal peripheral surface 13 of the tubular body 11 is kept at a temperature of about 350°C, the surface of the cooling channels 20 disposed nearest the internal peripheral surface 13 is kept at a temperature of about 160°C, the interface zone between the tubular body 1 1 and each of the plates 19 is kept at a temperature of about 60°C and the external surface of the plates 19 is kept at a temperature of about 30°C.

It should be noted that the interface zone between tubular body 1 1 and each of the plates 19, that is, the zone where there is the connection material 21, is at a relatively low temperature, so as to preserve the capacity for sealing and connecting of the connection material 21. This cooling action is even more accentuated if it is provided to make longitudinal grooves 16 with a trapezoidal conformation as shown in fig. 3.

Merely by way of example, not restrictive of the present invention, and with reference to the form of embodiment shown in figs. 2 and 3, the tubular body 1 1 has a thickness comprised between 15 mm and 25 mm, while the plates 19 have a thickness comprised between 5 mm and 15 mm.

Merely by way of example, not restrictive of the present invention, in the case of longitudinal grooves 16 that are rectangular in shape, these have a width comprised between 5 mm and 12 mm and a depth comprised between 10 mm and 15 mm.

The ends of the tubular body 1 1 are in turn connected to support and oscillation means 22 of the crystallizer 10. Each of the support and oscillation means 22 connected to one of the ends of the tubular body 1 1 comprises a first flange 23 and a second flange 24 disposed one above the other and reciprocally connected with each other. Between the first 23 and the second flange 24 hydraulic sealing means 25 are interposed, in this case an O-ring.

In the form of embodiment shown in fig. 1, the longitudinal grooves 16 extend for a determinate length which is less than the whole longitudinal development of the tubular body 11.

The ends of each longitudinal groove 16 are in turn connected to respective connection channels 26 made in the second flange 24. The connection channels 26 in turn are connected to the cooling circuit to determine the circulation of the cooling liquid.

The ends of the longitudinal grooves 16 terminate at the upper part rounded toward the connection channels 26, to reduce the losses of load due to the flow of the cooling liquid.

The method to manufacture the crystallizer 10 for continuous casting in figs. 1 and 2 provides a first step of making the tubular body 11, a second step of making the plates 19, and a third step in which the plates 19 are connected to the tubular body 1 1.

The first step of making the tubular body 11 provides that, starting from a tubular section bar, already shaped and with the desired shape and sizes, the longitudinal grooves 16 are made on its external peripheral surface 12.

Some forms of embodiment provide that the longitudinal grooves 16 are made by chip-removal operations, for example using a multi-tooth miller to reduce the operating times.

An operation is also provided to make the beveled edges 14, for example by operations to remove material.

Some forms of embodiment can provide that the tubular body 11 is curved with respect to its longitudinal axis Z, with a radius of curvature substantially equal to that of the continuous casting line. The curving operation is obtained by plastic deformation using a mold and/or press.

The second step of the method provides to make the plates 19.

The plates 19 are obtained by cutting to size a flat sheet. In particular, a first pair of plates 19, which during use are disposed opposite each other, is cut with a substantially rectangular plan shape, while the other pair of plates 19 is cut so as to follow the curvature conferred on the tubular body 11 in the first step.

The third step provides to couple the plates 19 with the tubular body 11.

In particular, during the third step the connection material 21 is applied, in this case a brazing material, on at least one of either the external peripheral surface 12 of the tubular body 11 or the surfaces of the plates 19.

In order to simplify the operation to apply the brazing material, it is advantageous to apply the latter only on the external peripheral surface 12 of the tubular body 11.

Some forms of embodiment of the method provide that the operation to apply the brazing material is done using spraying or spreading of brazing pastes.

A subsequent sub-step is then provided, in which the plates 19 are associated on the external peripheral surface 12 of the tubular body 11.

In particular, the plates 19 are scarfed to the tubular body 11 to allow their subsequent solidarization and to achieve the intimate and permanent connection. During the solidarization operation both the tubular body 11 and the plates 19 are heated, in order to activate the brazing material which is interposed between them. Some forms of embodiment provide that the heating is done at a temperature comprised between 250°C and 650°C. It is quite obvious that the intensity of the heating must be such that the microcrystalline structure of the materials and their mechanical properties are not modified.

The heating to perform the brazing can be carried out in a heating furnace.

Once the reciprocal coupling of the tubular body 11 and the plates 19 has been obtained, subsequent operations necessary for the final use can be provided.

It is clear that modifications and/or additions of parts may be made to the crystallizer 10 for continuous casting 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 crystallizer 10 for continuous casting, and the method to make the crystallizer 10, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Crystallizer for continuous casting comprising a tubular body (11) with an oblong development, and, in cross section, a polygonal shape defined by a plurality of walls (15), and a plurality of plates (19) associated to the external peripheral surface (12) of said tubular body (11), said tubular body (11) being made in a single body and being provided, in its external peripheral surface (12), with a plurality of longitudinal grooves (16) open toward the outside, characterized in that said plates (19) are intimately and permanently coupled to the external peripheral surface (12) of said tubular body (11) in order to close said longitudinal grooves (16) and to define channels (20) for the passage of a cooling liquid, said plates (19), when coupled to said tubular body (11), being detached from each other and defining a reciprocal separation gap (G) between adjacent plates (19), in correspondence to the edges of the tubular body (1 1), and in that said tubular body (11) is provided, in correspondence to said reciprocal separation gap (G) and on the external peripheral surface (12) of said tubular body (11), with beveled edges (14) opposite to mating rounded edges (27), present on the internal peripheral surface (13) of said tubular body (11), to define a reduction in thickness of the material in correspondence to the connection edges between said walls (15).

2. Crystallizer as in claim 1, characterized in that said beveled edges (14) have a rectilinear development.

3. Crystallizer as in claim 1, characterized in that said beveled edges (14) have a curved development with a less accentuated curvature with respect to said rounded edges (27).

4. Crystallizer as in claim 1, 2 or 3, characterized in that said reciprocal separation gap (G) is defined by the thickness of the adjacent plates (19) and by said beveled edge (14).

5. Crystallizer as in any claim hereinbefore, characterized in that said tubular body (11) is defined by a plurality of walls (15), and in that each of said plates (19) has a width (L) less than the width (B) of the wall (15).

6. Crystallizer as in any claim hereinbefore, characterized in that a connection material (21), chosen from a brazing material and a gluing material, provides to couple said plates (19) to said tubular body (11).

7. Crystallizer as in claim 6, characterized in that said gluing material is chosen from a group comprising at least epoxy resins and chinoacrylates.

8. Crystallizer as in any claim hereinbefore, characterized in that said longitudinal grooves (16) have a trapezoidal section shape.

9. Crystallizer as in claim 8, characterized in that said longitudinal grooves (16) with a trapezoidal section are disposed so that a larger base (17) of said trapezoidal section faces toward the internal part of the tubular body (11), and a smaller base (18) of said trapezoidal section faces toward the external peripheral surface (12).

10. Method to make a crystallizer (10) for continuous casting, comprising a first step of making a tubular body (11) in a single body with an oblong development, in cross section, a polygonal shape defined by a plurality of walls (15), and on the external peripheral surface (12) of which a plurality of longitudinal grooves (16) are made, open toward the outside; a second step of making a plurality of plates (19); and a third step in which the plates (19) are connected to the tubular body (11), characterized in that during said first step it is provided to make beveled edges (14) on the external peripheral surface (12) of said tubular body (11) and, on the internal peripheral surface (13) of said tubular body (11), rounded edges (27) mating with and opposite to said beveled edges (14), to define a reduction in thickness of material in correspondence to the connection edges between said walls (15), and in that in said third step said plates (19) are intimately and permanently coupled to the external peripheral surface (12) of said tubular body (11) in order to close said longitudinal grooves (16) and to define channels (20) for the passage of a cooling liquid, said plates (19) being disposed detached from each other and defining, between adjacent plates (19), a reciprocal separation gap (G) located in correspondence to said beveled edges (14).

1 1. Method as in claim 10, characterized in that said beveled edges (14) are made with a rectilinear development.

12. Method as in claim 10, characterized in that said beveled edges (14) are made with a curved development and with a less accentuated curvature with respect to said rounded edges (27).

13. Method as in claim 10, 11 or 12, characterized in that said tubular body (11) is defined by a plurality of walls (15), and in that during said second step it is provided to define a width (L) of said plates (19) which is less than the width (B) of said walls (15).

14. Method as in any claim from 10 to 13, characterized in that during said third step it is provided to apply a layer of brazing material on at least one of either the external peripheral surface (12) of the tubular body (11) or on the contact surface of said plates (19) with said tubular body (1 1).

15. Method as in any claim from 10 to 13, characterized in that during said third step it is provided to apply a layer of gluing material on at least one of either the external peripheral surface (12) of the tubular body (11) or on the contact surface of said plates (19) with said tubular body (11).