WO2014118744A1

WO2014118744A1 - Crystallize r for continuous casting and method for obtaining the same

Info

Publication number: WO2014118744A1
Application number: PCT/IB2014/058707
Authority: WO
Inventors: Andrea De Luca
Original assignee: Danieli & C. Officine Meccaniche Spa
Priority date: 2013-02-01
Filing date: 2014-01-31
Publication date: 2014-08-07
Also published as: EP2950947B1; EP2950947A1; ITUD20130013A1

Abstract

Crystallizer for the continuous casting of metal material in a liquid state, the crystallizer comprising at least a base body (13) defining at least part of a passage cavity (12) for the liquid metal material being cast and being provided with an internal surface (14) facing, during use, toward said passage cavity (12) and with a surface that is external during use (15), opposite to the surface that is internal during use (14). The surface that is external during use (15) is provided with a plurality of longitudinal grooves (16) open toward the outside. The longitudinal grooves (16) are closed by an external layer (17) made using electrolytic deposition techniques, in order to define cooling channels (18) through which a cooling liquid is made to pass.

Description

CRYSTALLIZE R FOR CONTINUOUS CASTING AND METHOD FOR OBTAINING THE SAME

FIELD OF THE INVENTION

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

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

The present invention also concerns the method to produce a crystallizer for continuous casting.

BACKGROUND OF THE INVENTION

Crystallizers for billets or blooms are known, having a tubular body or plates associated with each other to define a closed section inside which the liquid metal is cast and progressively cooled. It is also known to provide that, in the thickness of the walls, starting from the external face and for at least part of the longitudinal development, the tubular body or plates are provided with a plurality of channels of a shape and sizes suitable for the passage of a cooling liquid. The channels can be interconnected with each other to define a closed cooling circuit.

The operations for making the cooling channels on the length of the tubular crystallizer are particularly complex and expensive in terms of time and equipment used. Making the channels requires complex holing and finishing operations to define channels that optimize the flow of the cooling liquid, with consequent high costs and long production times of the crystallizer.

To this purpose various solutions have been studied to reduce the production times of crystallizers and to reduce the quantity of material used.

One example of a known solution is described in documents US-A-5.716.510, US-A-4.949.773 and JP-A-H02.121752, which describe a method for making a crystallizer of the type with plates, comprising a base body made of steel, conformed as a plate, on which a plurality of longitudinal grooves are made, by mechanical removal of material. In particular, the longitudinal grooves are made on the side of the plate that, during use, faces toward the cast metal. Subsequently, the longitudinal grooves are filled with disposable material, in this specific case wax, to define a substantially continuous surface. The surface is subsequently covered with a thin, electrically conductive layer and, above it, one or more layers of pure copper are deposited until the desired thickness is reached, for example from about 5 mm, 8 mm, which defines the heat-removal layer which, during use, faces toward the cast metal and is substantially in contact therewith so as to transmit the cooling action.

These documents provide that the copper is deposited on the steel base body by means of electrolytic deposition techniques.

Above the layer of copper thus obtained a layer of anti-wear lining is then deposited, made of nickel and chromium, with the function of increasing the working life of the crystallizer.

It is then provided to discharge the wax from the grooves by melting it, so as to free the cooling channels of the crystallizer.

One disadvantage of the solution described above is that the layer of copper, put to cover the base body, is located, during use and after the crystallizer has been assembled, substantially in direct contact with the molten metal being cast. The layer of copper can reach rather high temperatures during use, even near to about 250°C, and in high-speed casting processes can reach and exceed 300°C. Such a high processing temperature can entail a deterioration in the properties of mechanical and thermal resistance of the added material.

Merely by way of example, the material that the added layer of copper is made of has a yield point of less than lOOMPa, that is, comprised between 40MPa and 70MPa.

The electrolytic copper that makes up the layer substantially in contact with the cast metal, is therefore not suitable for casting processes in general, and in particular for high-speed processes, due to the high thermo-mechanical stresses.

Furthermore, with electrolytic deposition techniques, the deposition thicknesses of the added layer of copper are low, and therefore the distance between the cooling channels and the surface in contact with the cast material will be limited, and not necessarily constrained to the thickness of the added layer itself. This is particularly dangerous especially if, due to the stresses that the crystallizer may be subject to, cracks are caused that propagate from the cooling channels to the internal surface in contact with the molten metal or viceversa. In this case, the cooling liquid can come into contact with the molten metal passing through the crystallizer and, in this case can generate dangerous explosions.

Another disadvantage is that electrolytic deposition techniques do not allow to precisely control the entity and distribution of the thicknesses of the material deposited. In this case, the crystallizer may have unacceptable geometric tolerances which can cause it to be discarded, with consequent repercussions on production costs.

This also determines uncontrolled variations in the characteristics of heat transmission through the wall of the crystallizer. Furthermore, even very small dimensional defects in the added layer of copper, present on the face in contact with the cast metal and due to the electrolytic deposition process, can affect as surface defects the skin of the product solidifying inside the crystallizer.

To satisfy the requirements of mechanical resistance, known crystallizers comprise a structure, generally made of stainless steel, which confers rigidity and contains the cooling channels. This structure constitutes the part which conveys the water, while the crystallizer proper consists of the layer of added electrolytic material.

One purpose of the present invention is to produce a crystallizer for continuous casting that guarantees to obtain high quality cast products and to cast the products at high productivity and in total safety.

Another purpose is to produce a crystallizer for continuous casting that has a highly efficient heat exchange and long working life.

Another purpose of the present invention is to perfect a method to produce a crystallizer for continuous casting of the type indicated above which is simple, quick and which allows to reduce production costs of 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 at least a base body defining at least part of a cavity for the passage of the liquid metal material that is to be cast.

The base body is provided with an internal surface, facing toward the cavity during use, and an external surface, opposite the internal surface.

Some forms of embodiment may provide that the base body has a tubular shape with an internal section mating with that of the product to be cast.

In other forms of embodiment, the base body is configured as a plate, to define at least one of the walls of the crystallizer. In this last case, a plurality of base bodies obtained with the method according to the invention are then associated with each other so as to define the cavity for the passage of the liquid metal material, having a section equal to that of the product to be obtained.

According to one aspect of the present invention, a plurality of longitudinal grooves, open toward the outside, are made on the surface that is external during use and therefore that is not in contact during use with the liquid metal material being cast. The longitudinal grooves are closed by an external layer, which is deposited on the surface of the base body that is external during use, and made using electrolytic deposition techniques, in order to define cooling channels through which a cooling liquid is made to pass, during use.

This technique of making the longitudinal grooves on the face of the base body that is external during use allows to avoid complex operations for making the cooling channels, since they are made, simply and quickly, by closing the longitudinal grooves. Furthermore, the external layer which has the function of closing the longitudinal grooves faces toward the outside during use, that is, toward the opposite side with respect to the casting cavity of the liquid metal, and its only function is to contain the cooling liquid passing through the cooling channels. The external layer in this case has the function of resisting only the pressure of the cooling liquid inside the cooling channels and therefore it is sufficient that it is sized for this purpose. Moreover, it has no function or effect on the characteristics of heat transmission between cooling liquid and cast metal.

The external layer, not being in direct contact with the liquid metal, is maintained due to the cooling effect at a rather low temperature, less than 100°C. This temperature is such that it does not alter the performance of mechanical resistance required of the external layer during use.

The surface that is internal during use, that is, the one facing toward the liquid metal material, is instead defined by the base body which can have any desired thickness whatsoever, required mechanical properties, internal surface having the desired optimum planarity and surface quality, and no longer obligated by technological requirements of material deposition.

In this way, depending on the sizes and the shape of the finished crystallizer, the types of metal to be cast and the product to be obtained etc., it is possible to choose the thickness of the base body most suitable for specific requirements.

In particular, during the design step it is possible to determine the thickness of the material which on each occasion faces toward the liquid metal material, allowing to obtain a crystallizer that respects the safety and heat transmission requirements.

Some forms of embodiment of the present invention provide that the base body is made of copper or its alloys. Copper or its alloys have high heat conductivity, giving the advantage of a more efficient heat exchange with the cooling liquid.

In another form of embodiment, the base body is made of copper obtained by press-forging.

Press-forged copper allows to obtain a base body having suitable mechanical resistance, such as to resist the thermo-mechanical stresses to which it will be subjected during use.

In another form of embodiment, the base body is made by means of hot extrusion and subsequently cold drawn. In this form of embodiment too, the base body maintains a suitable mechanical resistance.

The press- forging method allows to obtain a base body with good characteristics that allow it to resist the thermo-mechanical stresses to which it will be subjected during normal use, ensuring a longer working life.

According to another aspect of the present invention, a layer of anti-wear lining is applied on the surface of the base body that is internal during use, with the function of increasing resistance to wear during the casting steps.

The present invention also concerns the method for producing a crystallizer for continuous casting as described above. In particular, the method comprises at least a first step of making the base body as defined above, a second step of making, on the surface of the base body that is external during use, a plurality of longitudinal grooves open toward the outside, and a third step of making an external layer on the surface that is external during use, by means of electrolytic deposition techniques, in order to close the longitudinal grooves and to define cooling channels through which the cooling liquid is made to pass.

According to another aspect of the present invention, between the second and third step a step is provided to fill the longitudinal grooves with a filling material which, after the third step, is removed so as to define the cooling channels.

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 cross section of a crystallizer according to the present invention;

- fig. 2 is a view of a variant of fig. 1 ;

- fig. 3 is a view of another variant of fig. 1 ;

- fig. 4 is a longitudinal section view of the crystallizer in fig. 2 from III to III;

- figs. 5 to 10 show schematically steps of the method for making a crystallizer according to the present invention.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. 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 figs. 1, 2 and 3, a crystallizer for continuous casting is indicated in its entirety by the reference number 10, 1 10 and 210 respectively.

The crystallizer 10, 1 10, 210 can be made substantially in a single body, as shown in figs. 1 and 2, or comprise a plurality of walls 1 1 (fig. 3) reciprocally coupled with each other. In both cases (figs. 1, 2, 3) the crystallizer 10, 1 10, 210 has a substantially oblong development along a longitudinal axis Z and defines a cavity 12 for the passage of liquid metal material being cast.

The crystallizer 10, 110, 210 can have a substantially annular cross section (fig. 1), rectangular (fig. 3), polygonal or mixed.

The crystallizer 10, 1 10, 210 comprises at least a base body 13 provided with a surface 14 that is internal during use, hereafter internal surface 14, which during use is substantially in contact with the liquid metal material being cast, and a surface 15 that is external during use, hereafter external surface 15, opposite the internal surface 14 and provided with a plurality of longitudinal grooves 16 open toward the outside.

According to possible forms of embodiment, the longitudinal grooves 16 extend for the entire length of the base body 13, although it is not excluded that, in other forms of embodiment, the longitudinal grooves 16 extend only for a part of the overall length of the base body 13.

In the form of embodiment shown in figs. 1 and 2, the base body 13 is tubular, in a single body, to define the cavity 12 for the passage of the liquid metal material. In the form of embodiment in fig. 3, a base body 13 is provided substantially formed by a plate for each wall 1 1, defining a part of the cavity 12. In this case, the base bodies 13 of each wall 11 are reciprocally connected with substantially known attachment means, not shown in the drawings.

As shown in fig. 4, the longitudinal grooves 16 are made substantially parallel to the longitudinal axis Z.

In the form of embodiment shown in figs. 1, 2 or 3, the longitudinal grooves 16 have a substantially rectangular section shape with rounded tops, although other section shapes are not excluded, such as for example trapezoid or swallow- tailed, with the larger base of the trapezoid section facing toward the internal surface 14.

In other forms of embodiment, the section size of the longitudinal grooves 16 can be variable longitudinally so as to suitably vary the speeds at which the cooling liquid passes through, and to set, for example, a higher speed in the zones where the heat exchange is to be increased.

By way of example only, not restrictive of the present invention, in the case of rectangular longitudinal grooves 16, these have a width comprised between 5mm and 20 mm and a depth comprised between 10 mm and 20 mm. The longitudinal grooves 16 provided on the external surface 15 of the base body 13 are closed by an external layer 17 to define cooling channels 18 through which to make a cooling liquid pass.

By way of example only, the cooling channels 18 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 thickness of the external closing layer 17 of the longitudinal grooves 16 is also evaluated.

By way of example only, not restrictive of the present invention, the base body 13 has a thickness comprised between 15 mm and 40 mm, while the external layer 17 has a thickness comprised between 3 mm and 10 mm.

The base body 13 is made of copper or its alloys, such as a copper-silver alloy, or a copper-chromium-zirconium alloy.

The base body 13 is configured to resist mechanical and thermal stresses to which the crystallizer 10 is subjected during use. According to a possible form of embodiment of the present invention, the base body 13 can be made of material having a yield point of even more than 400MPa, by way of example only, about 415MPa.

The external layer 17 is made using electrolytic deposition techniques with copper, nickel or their alloys.

The external layer 17 can be made of a material having a yield point lower than lOOMPa, typically comprised between 40MPa and 70MPa.

In some forms of embodiment the material that the external layer 17 is made of can have a yield point that is at least five times lower than that of the material that the base body 13 is made of.

Some forms of embodiment provide that the internal surface 14 of the base body 13 can be lined with a covering layer 19 with the function of increasing resistance to wear, and to allow low-friction sliding of the liquid metal material during casting. Merely by way of example, the covering layer is made of a layer of chromium or with two adjacent layers, one nickel and one chromium.

In some forms of embodiment, for example the one shown in fig.4, each of the ends of the base body 13 is in turn connected to support and oscillation means 20 of the crystallizer 1 10.

The support and oscillation means 20 connected to one of the ends of the base body 13 comprise a first flange 21 and a second flange 22 disposed one above the other and reciprocally connected with each other.

Between the first 21 and the second flange 22 hydraulic sealing means 23 are interposed, in this case an "O-ring".

The longitudinal grooves 16 extend for a determinate length that is less than the entire longitudinal development of the base body 13.

The ends of each longitudinal groove 16 are in turn connected to respective connection channels 24 made in the second flange 22. The connection channels 24 are in turn connected to the cooling circuit to determine the circulation of the cooling liquid.

We shall now describe the method for making the crystallizer 10, 1 10, 210 for continuous casting in figs. 1-4.

In particular, with reference to figs. 5-10, we shall describe the method for making one of the walls 1 1 of the crystallizer 210 in fig. 3, although a similar description can be given for the crystallizers in figs. 1 and 2 having the base body 13 in a single piece.

As shown in fig. 5, one of the base bodies 13 is in the form of a plate with a substantially rectangular section. The base body 13, whether it is tubular or plates, is obtained by press-forging to confer good mechanical properties on the material, adequate for the thermo-mechanical stresses that it will have to support during use.

At least the internal surface 14 of the base body 13 can be suitably finished mechanically, by means of mechanical working by removing material, or by broaching.

The particular surface finishing of the internal surface 14, which during use is substantially in contact with the metal being cast, allows to reduce the phenomena of wear to which the crystallizer 1 10 is subjected, and to increase its working life.

Some forms of embodiment can provide that the base body 13 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 with the aid of a mold and/or press.

The longitudinal grooves 16 are subsequently made on the external surface 15 (fig. 6) of the base body 13, for example by means of chip removal operations.

A subsequent step is provided in which the longitudinal grooves 16 are filled with filling material 25 (fig. 7).

Some forms of embodiment of the invention provide that the filling material 25 is a low-melting conductive material, which melts for example at less than 200°C, such as lead, tin or bismuth alloys.

In other forms of embodiment, the filling material 25 is a non-conductive material, such as for example wax or polymer materials.

In this latter case, it may be provided that above the filling material 25 a binding layer of conductive material is applied, not shown in the drawings, such as zinc or copper, for example using cold spray deposition techniques, metalization or other techniques.

The function of the binding layer of conductive material is to obtain a layer through which electric current can circulate so as to allow the subsequent electrolytic deposition. In fact, it is provided that after filling the longitudinal grooves 16, the external layer 17 is made on the external surface 15 (fig. 8).

The external layer 17 can be made using one of the techniques of electrolytic deposition, such as coppering or nickeling, which are carried out at temperatures comprised between 20°C and 50°C, thus keeping unchanged the filling material 25 in the longitudinal grooves 16.

Some forms of embodiment provide that the base body 13 is immersed in an electrolytic bath of copper or nickel, which bonds chemically with the material of the base body 13 to form a layer with a thickness proportional to the time it remains in the bath.

If the base body 13 is tubular, it may be provided that before it is immersed in the electrolytic bath, its ends are protected to prevent the deposition of material on the internal surface 14 of the cavity 12 as well.

A step is then provided to deposit the covering layer 19 (fig. 9) on the internal surface 14 of the base body 13.

Subsequently, a step is provided to remove the filling material 25 from the longitudinal grooves 16 to define the cooling channels 18 (fig. 10).

The removal of the filling material 25 may include inserting the base body 13 thus obtained in a furnace, to melt the filling material 25 and make it flow through the longitudinal grooves 16.

Merely by way of example, the base body 13 is taken to a temperature of about 200°C, so as not to modify the mechanical characteristics of the material that makes up the initial, monolithic base body 13.

In a variant form of embodiment, it may be provided that the step of removing the filling material 25 is carried out before the step of depositing the covering layer 19.

It is clear that modifications and/or additions of parts may be made to the crystallizer 10, 1 10, 210 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, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Crystallizer for the continuous casting of metal material in a liquid state, the crystallizer comprising at least a base body (13) defining at least part of a passage cavity (12) for the liquid metal material being cast and being provided with an internal surface (14) facing, during use, toward said passage cavity (12) and with a surface that is external during use (15), opposite to the surface that is internal during use (14), characterized in that the surface that is external during use (15), and not in contact with said liquid metal material of said base body (13), is provided with a plurality of longitudinal grooves (16) open toward the outside, and in that said longitudinal grooves (16) are closed by an external layer (17) made using electrolytic deposition techniques, in order to define cooling channels (18) through which a cooling liquid is made to pass.

2. Crystallizer as in claim 1, characterized in that said base body (13) is made of copper or its alloys.

3. Crystallizer as in claim 1 or 2, characterized in that said base body (13) is made of copper made by press-forging.

4. Crystallizer as in any claim hereinbefore, characterized in that said external layer (17) is made of a material chosen from copper, nickel or alloys thereof.

5. Crystallizer as in any claim hereinbefore, characterized in that the material of which said external layer (17) is made has a yield point at least five times lower than that of which said base body (13) is made.

6. Crystallizer as in any claim hereinbefore, characterized in that said base body (13) is made in a single piece and has a tubular shape with an internal section which defines the shape of the cast metal product.

7. Crystallizer as in any claim from 1 to 5, characterized in that it comprises a plurality of said base bodies (13) substantially conformed as a plate and defining together said passage cavity (12).

8. Crystallizer as in any claim hereinbefore, characterized in that an anti-wear covering layer (19) is applied on said surface that is internal during use (14).

9. Method to obtain a crystallizer (10, 1 10, 210) for the continuous casting of metal material in a liquid state, said method comprising at least a first step of making a base body (13) defining at least part of a passage cavity (12) for the liquid metal material being cast, said base body (13) being provided with an internal surface (14) facing, during use, toward said passage cavity (12) and a surface that is external during use (15), opposite the surface that is internal during use (14), characterized in that it comprises a second step of making, on the surface that is external during use (15) of said base body (13), a plurality of longitudinal grooves ( 16) open toward the outside, and a third step of making an external layer (17) on said surface that is external during use (15), by means of electrolytic deposition techniques, in order to close said longitudinal grooves (16) and to define cooling channels (18) through which a cooling liquid is made to pass.

10. Method as in claim 9, characterized in that between said second and third step it provides a step of filling said longitudinal grooves (16) with a filling material (25), and in that after said third step it provides to remove said filling material (25) in order to define said cooling channels (18).

1 1. Method as in claim 10, characterized in that the removal of said filling material (25) provides to heat said crystallizer (10, 1 10, 210) to melt the filling material (25).

12. Method as in claim 10 or 1 1, characterized in that said filling material (25) is chosen from a group comprising wax, a polymer material, a low-melting conductive material.

13. Method as in claim 10, 1 1 or 12, characterized in that after said filling step and before said third step it provides to apply, on said filling material (25), a binding layer made of conductive material.

14. Method as in any claim from 9 to 13, characterized in that it comprises a step of depositing a covering layer (19) on said surface that is internal during use