EP1877211A1

EP1877211A1 - Method for continuous casting of blanks of metal sections

Info

Publication number: EP1877211A1
Application number: EP06725757A
Authority: EP
Inventors: Jean-Marc Jolivet; Yann Le Papillon; Cosimo Salaris
Original assignee: Arcelor Profil Luxembourg SA
Current assignee: ArcelorMittal Belval and Differdange SA
Priority date: 2005-04-13
Filing date: 2006-04-13
Publication date: 2008-01-16
Also published as: WO2006108874A1; EP1712314A1

Abstract

The invention concerns a method for continuous casting of blanks of metal sections, in particular blanks of small steel H-, I-, L- or T-shaped sections, which consists in casting, in accordance with the continuous feed casting technique, into a continuous casting ingot mold (10) comprising an ingot mold body (12) supporting a funnel-shaped refractory preheater (14), said preheater (14) having an output cross-section which corresponds to the cross-section of the blank of the section to be cast. The liquid metal is poured into the preheater (14) upstream of a baffle (26), using a feeding nozzle (22) immersed in the liquid metal contained in the preheater (14), the baffle (26) being designed to dissipate the main part of the kinetic energy of the metal jet exiting from the feeding nozzle (22).

Description

PROCESS FOR THE CONTINUOUS CASTING OF METAL PROFILES OF METAL PROFILES

Technical area

The present invention relates to a method for the continuous casting of blanks of metal profiles, in particular steel sections, in particular H-sections, having a small cross-section.

State of the art

The continuous casting operation generally involves pouring a molten metal into a bottomless mold essentially consisting of a metal mold body, usually a tubular member, made of copper or copper alloy, defining a passage for the cast metal and whose walls are vigorously cooled by circulation of water; and to extract continuously from this mold a product already solidified externally over several millimeters thick. The solidification then progresses towards the axis of the product and is completed during the descent thereof downstream of the mold in the so-called "secondary cooling" zone under the effect of watering ramps. The resulting product is then cut to length and then rolled before shipment to customers or processed on site in bars, wires, profiles, plates, sheets, etc. In the technique of continuous casting under load, a rigid riser of refractory material is placed on the top of the tubular mold body to extend upward the inner passage of the metal tubular body in which the molten metal is cast. During casting, the level of the free surface of the molten metal (also called meniscus) is maintained in the riser, generally at a distance of 10 to 15 cm above the tubular body where solidification begins. This makes it possible to raise the meniscus upstream of the solidification zone, and thus to avoid the appearance of surface or subcutaneous defects related to the variation of the meniscus level in the upper part of the mold body. In addition, the volume of molten metal in the riser acts as a buffer, damping the flow turbulence that inevitably develops under the effect of the arrival of metal. The use of the riser thus makes it possible to obtain a relatively calm flow at the point where mold solidification begins, which contributes to a better quality of the solidified product and in particular to the regularity of its surface and / or to a productivity increased casting facility due to higher permitted casting speed.

In order to reduce the number of rolling operations required to obtain the final product, the continuous casting of blanks having a cross-section close to that of the product to be manufactured (near-net-shape casting) has already been proposed and performed. Thus, for example, profiles blanks resembling the profile to be manufactured are now cast continuously. Such blanks are then subjected to rolling to arrive at the final product with a much lower number of rolling operations, which substantially reduces production costs. The minimum size of blanks thus cast is about 300x700x50 mm, which corresponds to a weight of about 500 kg / m.

To date, however, it has not yet been possible to obtain, by a continuous casting process of the "near-net-shape casting" type, blanks of metal profiles of small sectional size, having, for example, a approximately 110x70x12 mm, which corresponds to a linear weight of approximately

25 kg / m.

It is indeed quite different in the case of blanks of small profiles for which the casting space in its largest dimension, namely at the triple point at the location of the leave at the intersection between soul and wings, presents a diameter of just 20 mm, maximum 30 mm. This smallness is incompatible with the introduction of a casting nozzle as fine as it is. Moreover, even if it were successful, the turbulence accompanying the release of a jet of molten metal in such a confined area of the casting space between the cooled walls of the mold would be such that any attempt to solidify homogeneous and regular cast metal would certainly be doomed. For the sake of clarity, it is specified that these blanks of small cross-section blanks (generally of H, I, L or T shape) of the largest dimension - here the triple point at soul-wing intersection - hardly exceeds 30 mm and in any case never more than 50 mm, that is to say blanks whose casting space defined by the ingot mold which flows continuously is of size too small to receive a submerged nozzle, in the current state of knowledge.

Object of the invention

The object of the present invention is to provide an improved method for the continuous casting of blanks of metal profiles, including blanks of small steel profiles, according to the definition given in claim 1 below.

General description of the invention

The present invention therefore relates to a process for the continuous casting of blanks of metal profiles, in particular blanks of small steel sections, according to the technique of continuous casting under load in a continuous casting mold comprising a mold body supporting a refractory funnel-shaped extension. The liquid metal is poured into the riser upstream of a baffle, the liquid metal being poured through a feed nozzle immersed in the liquid metal contained in the riser and the baffle being advantageously designed to dissipate most of the liquid. kinetic energy of the metal jet leaving the supply nozzle.

One merit of the present invention is to have realized that the continuous casting "near-net-shape" of blanks of small profiles can be carried out by applying the continuous casting known as "in vertical load" and that the calm flow of the metal melting at the level where its solidification begins is particularly important with regard to the continuous casting of small sections.

According to the process of the present invention, the liquid metal is poured from a distributor (or "tundish") in the refractory riser of the mold using a nozzle. The level of liquid metal in the riser reaches a height such that the feed nozzle is immersed in the liquid metal in the riser. Thanks to the riser associated with the baffle, the free surface of the molten metal can be maintained at a distance from the ingot mold body where the solidification begins. In addition, the flow of metal at the level where the solidification begins is laminar or quasi laminar, in any case very little agitated, after passing through the baffle whose role, by deviating abruptly the trajectory of the metal stream from the nozzle, is to mitigate the turbulence. By its funnel shape, the riser makes it possible to direct the flow of the liquid metal progressively towards the ingot mold body.

This baffle, arranged between the outlet of the feed nozzle and the inlet of the mold body, makes it possible to dissipate the kinetic energy of the metal jet coming out of the feed nozzle, before the flow of metal reaches the region where the solidification begins, to allow the continuous casting of small sections. The homogeneity of the flow of liquid metal in the region where the solidification begins also helps to avoid surface defects of the product to be poured. The method according to the invention therefore allows the manufacture of metal profiles of better quality and above all allows the manufacture of small metal profiles by a continuous casting process of blanks which hitherto was not possible.

Advantageously, the funnel-shaped riser has an outlet cross section that corresponds to the cross section of the profile to be cast. Such an extension makes it possible to shape the flow of metal upstream of the ingot mold body where the solidification of the metal begins.

The sections to be cast may for example be H, I, L or T profiles and may have a minimum cross-sectional dimension of less than 50 mm. An example of a small profile is a profile having dimensions of 110x70x12 mm, which corresponds to a linear weight of about 25 kg / m. According to a first preferred embodiment, the baffle is formed by a riser base pierced by a plurality of holes. The flow of liquid metal leaving the feed nozzle is braked by the riser bottom and passes through the bottom of the riser through the holes. The riser bottom makes it possible to receive and brake the liquid metal inlet and to prevent its direct flow in the ingot mold body. The plurality of holes allows the liquid metal to flow through the riser bottom to the mold body. These holes are arranged so as to ensure a homogeneous flow downstream of the raising base. Equi-distribution of the liquid metal flow velocity downstream of the riser bottom helps to avoid surface defects in the cast product. The flow of metal in the mold body can be controlled by the number of holes, their arrangement and their size. Preferably, the diameter of a hole substantially corresponds to the minimum cross-sectional dimension of the channel to be cast and the holes are spaced from each other by about 5 mm edge-to-edge.

According to a second preferred embodiment, the baffle is formed by a bottom of raising and a helical channel formed in the bottom of raiser. The liquid metal exiting the supply nozzle is braked by the riser bottom and passes through the helical channel. The riser bottom makes it possible to receive and brake the liquid metal inlet and to prevent its direct flow in the ingot mold body. The helical channel, preferably peripheral, allows the liquid metal to flow through the riser bottom to the mold body. The metal flow downstream of the riser bottom can be controlled by the helical channel arrangement and its size. Preferably, the passage section of the helical channel is between 1 and 4 times the passage section of the supply nozzle.

According to a third preferred embodiment, the riser comprises a main tray and an auxiliary receiving tray receiving the feed nozzle and being arranged laterally to the main tray. The baffle is formed by a passage threshold disposed between the main tray and the receiving tray so as to allow the flow of liquid metal from the receiving tray to the main tray communicating with the mold. The liquid metal coming out of the nozzle feed is poured into the receiving tray, and flows from the receiving tray to the main tray overflow over the threshold. The receiving tray thus makes it possible to receive the metal jet of the feed nozzle and to prevent its direct flow in the ingot mold body. The liquid metal in the main tank thus has a calm flow with respect to the flow in the receiving tank, thanks to the barrier effect provided by the passage threshold.

In addition, the liquid metal can meet an auxiliary baffle before reaching the inlet of the mold body. Such auxiliary baffle may for example be arranged between the passage threshold and the inlet of the mold body and may further calm the flow of metal in the mold body. The auxiliary baffle may take the form of one of the baffles described above.

The riser advantageously comprises a refractory body preferably having a low thermal conductivity and a compact refractory seal providing the sealed mechanical connection between the riser and the mold body placed underneath. The compact refractory seal has good mechanical strength and is preferably a SiAION seal. Such a refractory seal supports the friction against the skin of metal, especially steel, during the oscillation of the mold and is very useful to ensure somehow the transition between a highly insulating refractory which is constituted by the riser and the cooled copper of the mold against which the solidification of the cast metal takes place.

A gas under pressure is advantageously injected into the mold between the riser and the mold body. This gas, preferably argon, can be injected through a slot of for example 0.15 mm. The injection of gas through a slot, homogeneous on the perimeter of the mold, makes it possible to avoid parasitic premature starts of the solidification on the compact refractory joint by forming a real mechanical screen between the riser and the mold body.

The flow velocity of the metal at the outlet of the feed nozzle can be located between 50 and 180 m / min, while the flow rate of the metal at the inlet of the mold body between 5 and 10 m / min.

Description of the drawings

Other features and characteristics of the invention will become apparent from the detailed description of some advantageous embodiments presented below, by way of illustration, with reference to the accompanying drawings. These show:

FIG. 1: a schematic sectional view of an ingot mold according to a first embodiment;

FIG. 2: a schematic sectional view of an ingot mold according to a second embodiment;

FIG. 3: a cross-sectional view according to section A-A of FIG. and FIG. 4: a schematic sectional view of an ingot mold according to a third embodiment.

In the figures, the same reference signs designate identical or similar elements.

Detailed description of some preferred embodiments

During continuous casting under load, the liquid metal, for example liquid steel, is poured into a mold 10 comprising an ingot mold body 12 supporting a refractory riser 14. The mold body 12 comprises a passage 16 for the metal, the passage 16 defining a section similar to the section of the product to be cast. The mold body 12 further comprises, near the passage 16, cooling means (not shown) for cooling the steel in the passage 16. The refractory riser 14 comprises a refractory body 18 having a low thermal conductivity and a Compact refractory seal 20, preferably a SiAION seal, having good mechanical strength.

The liquid steel is poured from a distributor (or "tundish", not shown) into the refractory riser 14 through a feed nozzle 22. The flow of the molten steel through the nozzle 22 is generally regulated by a shutter (not shown) which adjusts the opening between the distributor and the nozzle 22.

At the outlet of the feed nozzle 22, the flow of liquid steel may have a speed in the range of 50 to 180 m / min. The liquid steel leaving the supply nozzle 22 is received in the refractory riser 14. Typically, the level of liquid steel in the riser 14 is greater than the outlet opening of the supply nozzle 22. The nozzle supply 22 is therefore immersed in the liquid steel 24 contained in the riser 14.

According to an important aspect of the invention, the riser 14 comprises a baffle element 26 between the outlet of the feed nozzle 22 and the inlet of the ingot mold body 12. This baffle 26 forms an obstacle to the flow of liquid steel from the nozzle 22 and thus calms the flow of steel entering the mold body 12. The flow of liquid steel at the inlet of the mold body can have a speed in the range of from 5 to 10 m / min.

According to a first embodiment, illustrated in Fig.1, the baffle 26 is disposed near the outlet opening of the riser 14 and is formed by a riser base 28 provided with a plurality of holes 30 drilled. Thanks to the riser bottom 28, the impact energy of the jet of liquid acid from the nozzle 22 is broken. The holes 30 drilled in the riser bottom 28 are arranged and dimensioned so as to allow the liquid steel to pass through the bottom of the riser 28 and to be distributed throughout the entire section of the mold body 12. The holes 30 are disposed of so as to produce a homogeneous dispersion of the molten steel in the mold body 12. For the casting of profiles of size 110x70x12 mm, the diameter of the holes is for example about 12 mm. These holes are spaced 5 mm apart.

Fig.1 also shows the funnel shape of the riser 14. The upper portion of the riser has a cross-section tapering toward the riser outlet. The lower part of the riser has a cross section corresponding to the inlet section of the passage 16 of the mold body 12. The shaping of the steel flow is therefore performed upstream of the inlet in the passage 16 of the ingot mold body 12, avoiding and turbulence at the entrance to the passage 16. An ingot mold 10 according to a second embodiment is shown on the

Fig.2. According to this embodiment, the baffle 26 is disposed near the outlet opening of the riser 14 and is made by a riser base 32 provided with a peripheral helical channel 34 in the bottom of the riser 32. The bottom The riser 32 includes an inlet section 36 facing the riser 14, configured to carry the liquid steel of the riser 18 to an inlet 38 of the helical channel 34. The riser base 32 also includes a turned outlet section 40 to the mold body 12, configured to carry the liquid steel of an outlet 42 of the helical channel 34 to the passage 16 of the mold body 12. A cut through the bottom raises 32 along the line AA of the Fig.2 is shown in Fig.3.

Thanks to the bottom enhancement 32, the impact energy of the jet of liquid acid from the nozzle 22 is broken. The peripheral helical channel 34 allows the liquid steel to pass through the riser bottom 32 and to be distributed in the passage 16 of the mold body 12. The helical channel 34 is arranged and dimensioned so as to produce a homogeneous dispersion of the liquid steel in the mold body 12. The passage section of the helical channel 34 may be 1-4 times the passage section of the supply nozzle 22.

The steel must travel in a helical path to reach the solidification start zone. It follows a tangential circulation that is favorable to solidification homogeneity having the same function as an electromagnetic stirring.

According to a third embodiment, illustrated in FIG. 4, the baffle 26 is formed by a passage threshold 44 disposed between a main tray 46 of the riser 14 and a receiving tray 48 of the riser 14. The receiving tray 48 is arranged laterally to the main tank 46 and receives the incident liquid steel jet from the immersed feed nozzle 22. The bottom 50 of the reception 48 breaks the energy of the incident jet. The liquid steel passes above the threshold of passage 44 of the receiving tray 48 to the main tray 46, where it directly feeds the passage 16 into the mold body 12. The level of the liquid steel 24 in the riser 14 is maintained at a level above the threshold of passage 44 so as to allow the passage of the liquid steel from the receiving tray 48 to the main tray 46. With the receiving tray 48 and the passage threshold 44, the flow liquid steel entering the main tray 46 of the riser 14 is quiet. The turbulence in the liquid steel flow in the main tray 46 is minimized. In addition, the main tray 46 of the riser 14 has a funnel-shaped thinner towards the extension output. The riser outlet has a cross section corresponding to the inlet section of the passage 16 of the mold body 12. The shaping of the steel flow is therefore carried out upstream of the inlet in the passage 16 of the mold body 12, thus avoiding turbulence at the entrance to the passage 16.

An auxiliary baffle 52 may be arranged between the baffle 26 and the inlet of the mold body 12, thus further calming the flow of the steel entering the passage 16 of the mold body 12. Such auxiliary baffle 52 is schematically represented in dashed lines in FIG. 4 and may for example take the form of one of the baffles 26 described above.

It goes without saying that the invention may have many other alternative embodiments to the extent that the definition given in the appended claims are respected. Thus, the term "baffle" used previously and which, in combination with the refractory riser, together constitute the essential characteristic elements of the invention, must be understood generically as describing any means constituting an obstacle deviating from the trajectory of the invention. a fluid stream placed on the path of the fresh metal stream between the outlet of the casting nozzle and the entry into the casting space in the mold and having as a first effect the hydrodynamic separation of a volume in two contiguous volumes upstream and downstream in the flow direction of the molten metal to be cast.

Claims

claims

1. Process for the vertical continuous casting of blanks of small sections of metal, in particular steel, having an H, I, L or T shape, in which said vertical continuous casting is done, according to the technique of continuous casting in charge, in a continuous casting mold (10) comprising an ingot mold body (12) supporting a funnel-shaped refractory riser (14) above, said funnel-shaped riser (14) having a cross-section of outlet which corresponds to the cross-section of said casting blank to pour cast molten metal is poured into said riser (14) through a feed nozzle (22) immersed upstream of a baffle (26) designed to dissipate most of the kinetic energy of the metal jet leaving the said feed nozzle (22), before entering the ingot mold (12).

2. The method of claim 1, wherein said blanks of small sections have their largest dimension in cross-section less than 50 mm.

The method of claim 1 or 2, wherein: said baffle (26) is formed by a riser base (28) and a plurality of holes (30) drilled in said riser base (28).

The method of claim 1 or 2, wherein: said baffle (26) is formed by a riser base (32) and a helical channel (34) in said riser base (32).

The method of claim 1 or 2, wherein: said riser (14) comprises a main tray (46) and an auxiliary receiving tray (48) laterally arranged to said main tray (46); said baffle (26) is formed by a through threshold (44) disposed between said main tray (46) and said receiving pan (48); said molten metal leaving said feed nozzle (22) is poured in said receiving pan (48), and flowing from said receiving pan (48) to said main pan (46) overflow over said passage threshold (44).

The method of claim 5, wherein said molten metal meets an auxiliary baffle (52) before reaching the inlet of said mold body

(12).

7. Method according to any one of the preceding claims, wherein the riser (14) comprises a refractory body (18) and a compact refractory seal (20) for sealing connection with the mold body (12) having good mechanical strength. .

The method of claim 7, wherein pressurized gas is injected into said mold (10) between said riser (14) and said mold body (12).

The method of any one of the preceding claims, wherein the flow rate of the metal at the outlet of said feed nozzle (22) is between 50 and 180 m / min.

The method of any of the preceding claims, wherein the flow rate of the metal at the inlet of said mold body (12) is between 5 and 10 m / min.