EP3096901B1

EP3096901B1 - Crystallizer for continuous casting and method for its production

Info

Publication number: EP3096901B1
Application number: EP15707790.0A
Authority: EP
Inventors: Alfredo Poloni; Gianbruno LUVARÀ; Nicola SARTORI; Valentina ZAMMATTIO
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2014-01-20
Filing date: 2015-01-20
Publication date: 2018-03-14
Anticipated expiration: 2035-01-20
Also published as: ES2671472T3; WO2015107511A1; EP3096901A1

Description

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 can be used in the steel-making field to cast metal products of any type and section such as billets or blooms, preferably with a square or rectangular section, but also polygonal in general, such as beam-blanks, or round. However, applications of the crystallizer to cast thin, medium or thick slabs are not excluded.
The crystallizer to which the present invention is applied can be either the tubular type or the plate type.

BACKGROUND OF THE INVENTION

Crystallizers for casting billets or blooms are known, having a tubular body inside which the liquid metal is cooled. It is also known to provide the tubular body, in the thickness of its walls and for at least part of its longitudinal development, with a plurality of channels, of adequate shape and size for the passage of a cooling fluid. The channels can be interconnected with each other to define a closed cooling circuit.
The operations to make the cooling channels on the length of the crystallizer, whether it is tubular or with plates, are particularly complex and uneconomical in terms of time and equipment used. In fact, they require complex holing and finishing operations to define passage channels that optimize the flow of the cooling fluid. The result is high costs and long times to produce the crystallizer.
Crystallizers are also known that comprise one or more plates defining the casting channel through which the molten metal to be cast is made to pass.
Solutions are also known in which the plates, on the surface that is external during use, are provided with a plurality of grooves that develop, open toward the outside, along the longitudinal extension of the crystallizer.
One known solution provides that a longitudinal bar is associated with each groove to define a channel for the passage of a cooling fluid.
Each longitudinal bar has a height of its cross section which is less than the depth of the groove. In this way, when the longitudinal bar is inserted into the groove, the thickness of the longitudinal bar, together with the bottom wall of the groove, defines a transit section for the cooling fluid.
The longitudinal bars can be attached to the plate either by mechanical interference or by positioning another plate on top of the first plate, to contain the longitudinal bars.
These attachment solutions are not only rather complex to obtain, but are also not very reliable in terms of the mechanical and hydraulic seal of the cooling fluid that is made to pass in the channels.
Furthermore, the operations to close the grooves are particularly uneconomical in terms of times and costs of production.
The cooling fluid can reach a pressure of about 20bar which, if the longitudinal bars are not correctly attached, can cause leakages.
GB 2055644 A describes a solution in which inserts are inserted, made of a plastic material such as silicone resin or suchlike, into a plate of the crystallizer that has grooves open toward the outside. The function of the inserts, with a shape mating with the shape of the grooves, is to divide up the stream of cooling liquid, defining a U-shaped channel facing toward the casting cavity of the molten metal. The plastic insert is closed from the outside by a first metal closing strip and then by casting a low melting point metal alloy which, once solidified, seals the insert.
The stable position of the plastic insert is guaranteed by the fact that the free edges of the groove made in the plate deform above the corresponding edges of the metal strip, generating a partial mechanical interference.
One purpose of the present invention is to simplify and reduce the production times of a crystallizer for continuous casting.
Another purpose of the present invention is to prevent leakages of the cooling fluid through the crystallizer.
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 and quick to produce, and which allows to reduce the 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 according to the present invention, used to cast molten metal, comprises at least a wall provided, in its surface that is external during use, with a plurality of grooves, each of which made open toward the outside and having a mainly longitudinal development.
By mainly longitudinal development we mean that the groove extends for a substantial part, equal to at least 50%, of the overall length of the crystallizer.
A longitudinal metal bar is inserted into each of said grooves and develops for at least part of the length of the respective groove, which closes the groove toward the outside and which defines therewith, on the side facing toward the casting cavity of the molten metal, a channel for the passage of a cooling fluid.
In accordance with one aspect of the present invention, the longitudinal metal bars are made integral with the wall of the crystallizer by welding them onto at least part of the internal edges of said grooves.
In particular, one formulation of the invention provides that the welding is made in correspondence to the end part facing toward the outside of the internal edges of each groove.
In another formulation of the invention, each welding is defined by a corresponding welding bead, there advantageously being two welding beads provided opposite, and advantageously of equal length, on each opposite internal edge of each groove.
In one formulation of the invention, the longitudinal bars are made of a metal chosen from copper, copper-silver, or bronze.
In another formulation of the invention, the longitudinal metal bars are obtained using a process of either rolling or drawing.
In another formulation of the invention, the welding of the longitudinal metal bars and corresponding portions of the walls of the crystallizer is a laser type welding.
With the present invention, it is possible to define an intimate and permanent coupling of the wall and the longitudinal bars that guarantees adequate mechanical resistance, equally distributed over the entire coupling zone of the two components, which practically become a single structure.
In other words, thanks to the integration, substantially in a single body, of the longitudinal metal bars with the walls of the crystallizer, and thanks to the fact that the longitudinal metal bars occupy all the space of the grooves, except for that provided for the passage of the cooling liquid, at the end of the production process the crystallizer has a degree of rigidity that is substantially comparable to that it had before the grooves were made upon it.
The welding of the wall and the longitudinal bars, in correspondence with the grooves, guarantees the mechanical and air-tight seal of the channels, even where the working pressures to which the cooling fluid is subjected during use are very high.
The present invention also concerns a method to make a crystallizer for continuous casting comprising:

making, on at least one wall of a crystallizer, a plurality of grooves each of which made open toward the outside and having a mainly longitudinal development, and
inserting into each of the grooves a longitudinal metal bar that develops for at least part of the length of the respective groove, which closes the groove toward the outside and which defines therewith a channel for the passage of a cooling fluid.

According to some forms of embodiment of the invention, the method comprises integrating the longitudinal metal bars in a single body with the walls of the crystallizer by welding the longitudinal metal bars onto portions of the internal edges of the grooves

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 cross section view of a tubular crystallizer according to the present invention, in accordance with a first form of embodiment;
fig. 2 is a cross section view of a crystallizer according to the present invention, in accordance with a second form of embodiment;
fig. 3 is an application of the invention to a plate type crystallizer, in accordance with a second form of embodiment;
fig. 4 is an enlarged view of detail "D" in fig. 1;
fig. 5 is a section view of a variant of fig. 3.

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, crystallizers for continuous casting according to the present invention are described by way of example.
More precisely, figs. 1 and 2 refer to tubular crystallizers for the continuous casting of metal products with a respectively square and round section, while fig. 3 refers to a crystallizer with plates for the continuous casting of metal products with a rectangular section.
In particular, the crystallizers 10 comprise at least one wall 11 defining at least part of a casting channel 12 through which the molten metal is made to pass during use.
With reference to fig. 1, the crystallizer 10 is provided with four walls 11 made in a single body with each other to define a tubular body 13 with a rectangular cross section, in this case square. However, it is not excluded that in other forms of embodiment the walls 11 are separate components reciprocally connected to each other by suitable connection means and/or are different in number, for example to define desired sections of the metal product to be obtained.
With reference to fig. 2, the crystallizer 10 comprises a single wall 11, cylindrical in shape, to define the tubular body 13 with a circular cross section shape.
With reference to fig. 3, the crystallizer 10 is the type with plates, for the production for example of thick, conventional, or thin slabs, and comprises pairs of at least two walls 11 like the one shown, disposed facing each other to define the casting channel for the molten metal.
Each wall 11 can be made of copper or its alloys, such as a copper-silver alloy, or a copper-chrome-zircon alloy or copper-nickel-beryllium.
Merely by way of non-restrictive example of the present invention, the wall 11 has a thickness comprised between 15mm and 35mm.
According to some forms of embodiment of the present invention, which can be combined with the forms of embodiment described here, the at least one wall 11 of the crystallizer 10 is provided with a surface that is internal during use 14, defining part of the casting channel 12, and a surface that is external during use 15, opposite the surface that is internal during use 14.
Some forms of embodiment provide that the surface that is internal during use 14 of the wall 11 can be lined with a covering layer with the function of increasing resistance to wear, and also to allow a low-friction sliding of the molten metal. Merely by way of example, the covering layer is made of material comprising an alloy of chrome or nickel-chrome.
Each wall 11 is provided, in its surface that is external during use 15, with a plurality of grooves 16, each of which is made open toward the outside and having a mainly longitudinal development. The longitudinal development of the grooves 16, according to possible forms of embodiment, substantially coincides with the direction in which, during use, the metal material is cast.
The grooves 16 are separated from each other by protruding portions 17, each of which defines the lateral walls of two adjacent grooves 16.
According to possible forms of embodiment, the grooves 16 can have a cross section shape chosen from a group comprising rectangular, circular, polygonal, curved or a combination thereof.
A longitudinal metal bar 18 is inserted into each of the grooves 16 and develops for at least part of the length of the respective groove 16, which closes the groove 16 toward the outside and defines therewith a channel 19 for the passage of a cooling fluid.
Merely by way of example, the channels 19 can be configured to resist pressure stresses exerted by the cooling liquid of about 20bar.
According to possible forms of embodiment, the longitudinal metal bars 18 have a cross section shape and sizes at least partly mating with part of the cross section of the grooves 16.
According to possible forms of embodiment, see for example fig. 4, the longitudinal metal bars 18 have a height H of their cross section that is less than the overall depth P of the grooves 16. This allows to define, between the thickness of the longitudinal metal bar 18 and the bottom of the groove 16, the useful passage section for the cooling fluid in the channels 19.
According to possible forms of embodiment, the longitudinal metal bars 18 can have a substantially rectangular cross section shape, although it is not excluded that in other forms of embodiment it can be different, for example triangular, polygonal, curved or a combination of the above.
According to possible forms of embodiment, the longitudinal metal bars 18 can be inserted into the grooves 16 with interference.
In other forms of embodiment, the longitudinal metal bars 18 can be inserted into the grooves 16 with play.
According to possible formulations of the present invention, the longitudinal metal bars 18 can be made of a material chosen from the group comprising copper, copper-silver or bronze.
The longitudinal metal bars 18 can be made by rolling or drawing.
According to possible forms of embodiment, the longitudinal metal bars 18 are attached to or made integral with the walls 11 by means of welding in correspondence with portions of the internal edges of the grooves 16. In this way the longitudinal metal bars 18 are solidly joined with the walls 11.
According to a possible form of embodiment of the present invention, for example shown in fig. 4, the longitudinal metal bars 18 are attached to the walls 11 by means of welding beads 20 made in correspondence to at least part of the interface zone between the longitudinal metal bars 18 and the grooves 16.
The welding beads 20 are made in correspondence to the sides or lateral edges of the grooves 16 and extend from the surface which is external during use 15 toward the inside. This guarantees the hydraulic seal of the cooling fluid which is made to circulate in the channels 19.
According to possible forms of embodiment, it can be provided that the welding beads 20 are made parallel on both opposite lateral edges of each of the grooves 16; they can also have a welding penetration depth comprised between 3mm and 10mm, preferably between 4mm and 7mm, even more preferably between 5mm and 6mm.
In possible implementations of the present invention, the welding beads 20 have a width comprised between 2mm and 8mm, preferably between 2mm and 6mm, more preferably between 3mm and 5mm.
In some forms of embodiment, the welding beads 20 extend for a good part of the overall length of the longitudinal metal bars 18, for example for a length comprised between 60% and 100% of the overall length of the longitudinal metal bars 18.
A preferred form of embodiment of the present invention provides that the welding beads 20 extend continuously for the whole length of the crystallizer 10, that is, the whole length of the wall 11. In this way it is possible to increase the efficiency of the mechanical and hydraulic seal of the longitudinal metal bars 18.
The longitudinal metal bars 18 become an integrating part or single body of the wall 11. This gives the crystallizer 10 great mechanical rigidity which can become substantially comparable to that of a known crystallizer as described above, having holes made directly in the thickness of the crystallizer 10.
The welding operations of the welding beads 20 can be carried out automatically, for example, using numerical control techniques that guarantee precision and speed of production. During the welding operations of the welding beads 20 it is possible to use a protection gas to protect the welding bath, so that it does not come into contact with the oxygen and thus oxidation is prevented. Alternatively, the welding can be carried out in a controlled atmosphere environment.
Possible forms of embodiment of the present invention can provide that the wall 11 is preheated before welding is carried out. Preheating can take place up to a maximum temperature of about 300°C, preferably comprised between 150°C and 250°C. It is quite evident that the intensity of heating must be such that it does not modify the micro-crystalline structure of the materials and their mechanical properties.
The welding beads 20 can be made using one of the welding techniques chosen from a group comprising laser beam welding or fiber laser and electronic beam welding.
Fiber laser welding can allow to reach wavelengths less than or equal to 1 µm, particularly efficacious for making welding beads 20 on materials made of copper or alloys thereof.
From experiments carried out, Applicant has seen that it is possible to obtain welding beads 20 with a depth sufficient for the purpose, for example 5mm, already with somewhat limited powers, for example in the order of 6-10 kW, and hence relatively inexpensive, by suitably setting the speed of advance.
Laser beam welding allows to localize the welding heat energy only in the interface zones between the wall 11 and the longitudinal metal bars 18, limiting the extent of the super-heated zones. By suitably regulating the power supplied and the focal point of the laser welding beam, it is possible to control the welding depth or penetration.
With this welding technique it is possible to reach high working speeds, for example comprised between 100 mm/s and 200 mm/s, guaranteeing that the crystallizer 10 can be obtained quickly.
According to a variant described using fig. 4, in correspondence to at least part of the interface zone between the longitudinal metal bars 18 and the grooves 16, that is, in correspondence to portions of the internal lateral edges of the grooves 16, it is provided to apply a brazing material 24, suitable to make the longitudinal metal bars 18 integral with the sides of the grooves 16.
The brazing material 24 can be applied on at least some of the interface zones between the longitudinal metal bars 18 and the grooves 16. In particular, it can be provided that the brazing material 24 is applied on at least one of the external surfaces of the longitudinal metal bars 18 and/or on the lateral sides of at least part of the grooves 16.
According to possible implementations of the invention, the brazing material 24 can be applied using spraying techniques.
Once the brazing material 24 has been applied on at least some of the interface zones between the grooves 16 and the longitudinal metal bars 18, the latter are inserted into the grooves 16 in the position that they will assume during normal use.
Subsequently, at least the interface zones between the grooves 16 and the longitudinal metal bars 18 are heated to melt the brazing material 24 and to perform the welding.
According to possible forms of embodiment, it can be provided that during the heating step the whole wall 11 on which the longitudinal metal bars 18 are provided can be heated. In other forms of embodiment, it can be provided that during the heating step the crystallizer 10 is heated.
Some forms of embodiment provide that heating is carried out at a temperature comprised between 200°C and 650°C. It is quite evident that the intensity of the heating must be such that it does not modify the micro-crystalline structure of the materials and their mechanical properties.
For the brazing operation, the heating can be carried out in a heating furnace.
The brazing material 24 can be chosen from a group comprising alloys with a base of tin, lead, copper, silver, zinc or combinations thereof.
In possible forms of embodiment, the grooves 16 have a substantially rectangular cross section shape, possibly with rounded tops, although other section shapes are not excluded.
Merely by way of non-restrictive example of the present invention, if the grooves 16 are rectangular, they can have a width comprised between 5mm and 12mm and a depth comprised between 7mm and 15mm.
According to other forms of embodiment, for example described with reference to fig. 3, at least some of the grooves 16, on at least one lateral wall thereof, have an abutment shoulder 21 against which the longitudinal metal bar 18 rests during use.
According to a possible form of embodiment, the abutment shoulder 21 can protrude with respect to the lateral walls that define the grooves 16 by a distance S comprised between about 0.3mm and 2mm, preferably between 0.3mm and 1mm, even more preferably between about 0.3mm and 0.7 mm.
According to possible solutions, the abutment shoulder 21 can be made directly when the groove 16 is made, with a single operation of material removal.
Merely by way of example, it can be provided that the abutment shoulder 21 is made by milling using a milling tool that has shaped teeth to define the abutment shoulder 21.
Some forms of embodiment provide that the grooves 16 can be made by means of chip removal operations, for example using a multi-tooth milling tool to reduce performance times.
In particular, the groove 16 is defined by a first portion 22, more internal during use in the thickness of the wall 11, and a second portion 23, wider than the first portion 22, which opens directly toward the outside and with a shape and size substantially mating with those of the longitudinal metal bar 18.
The limited width of the first portion 22 allows to define the abutment shoulder 21 on which the longitudinal metal bar 18 rests.
The first portion 22 of the groove 16 defines the usable passage section of the cooling fluid.
The presence of the abutment shoulder 21 allows to define an abutment for the precise and univocally determined positioning of the longitudinal metal bars 18. This allows to position all the longitudinal metal bars 18 in the same position inside the groove 16, guaranteeing that channels 19 are obtained that all have the same passage section for the cooling fluid.
It is clear that modifications and/or additions of parts may be made to the crystallizer 10 for continuous casting and the method to make the crystallizer 10 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

Crystallizer for continuous casting comprising at least one wall (11) provided, in its surface that is external during use (15), with a plurality of grooves (16) each of which made open toward the outside and having a mainly longitudinal development, a longitudinal metal bar (18) being inserted into each of said grooves (16) and developing for at least part of the length of the respective groove (16), which closes said groove (16) toward the outside and which defines therewith a channel (19) for the passage of a cooling fluid, characterized in that said longitudinal metal bars (18) are made integral with said wall (11) of the crystallizer by welding them onto at least part of the internal edges of said grooves (16).
Crystallizer as in claim 1, characterized in that welding beads (20) are provided in correspondence to said parts of the internal edges of said grooves (16).
Crystallizer as in claim 2, characterized in that said welding beads (20) extend from the surface which is external during use (15) toward the inside of said wall (11) and are present in pairs on facing internal sides of each groove (16).
Crystallizer as in claim 2 or 3, characterized in that said welding beads (20) extend for at least a part of the overall length of said longitudinal bars (18).
Crystallizer as in claim 1, characterized in that a brazing material (24) is provided in correspondence to at least part of the internal edges of said grooves (16).
Crystallizer as in any claim hereinbefore, characterized in that, on at least one of their lateral walls, at least some of said grooves (16) have an abutment shoulder (21) against which said metal longitudinal bar (18) rests during use.
Crystallizer as in any claim hereinbefore, characterized in the each of said grooves (16) is defined by a first portion (22), which during use is more internal within the thickness of the wall (11), and by a second portion (23) with a greater width than the first portion (22), which opens directly toward the outside and has a shape and sizes substantially mating with those of said longitudinal metal bar (18).
Crystallizer as in any claim hereinbefore, characterized in that said longitudinal metal bars (18) have a cross section shape and sizes at least partly mating with part of the cross section of said grooves (16).
Method to make a crystallizer for continuous casting which comprises making, on at least one wall (11) of a crystallizer (10), a plurality of grooves (16) each of which made open toward the outside and having a mainly longitudinal development, and inserting into each of said grooves (16) a longitudinal metal bar (18) that develops substantially for at least part of the length of the respective groove (16), which closes said groove (16) toward the outside and which defines therewith a channel (19) for the passage of a cooling fluid, characterized in that it provides to make said longitudinal metal bars (18) integral with said walls (11) by welding them in correspondence with portions of the internal edges of said grooves (16).
Method as in claim 9, characterized in that said integration provides to make welding beads (20) using one of the welding techniques chosen from a group comprising laser beam welding and fiber laser welding and electronic beam welding.
Method as in claim 9, characterized in that said integration provides to apply a brazing material (24) on at least part of the internal edges of said grooves (16), and to subsequently heat at least interface zones in order to carry out the welding.
Method as in any of the claims from 9 to 11, characterized in that during the making of said grooves (16), an abutment shoulder (21) is made in at least some of said grooves (16), and in that during the insertion of one of said longitudinal metal bars (18) into one of said grooves (16), said longitudinal metal bar (18) is positioned resting against said abutment shoulder (21).