WO2012175822A1

WO2012175822A1 - Method and device for continuously casting a profile member blank

Info

Publication number: WO2012175822A1
Application number: PCT/FR2011/051453
Authority: WO
Inventors: Jean-Marc Jolivet; Martin Beauvais; Christophe HEMMER; Michel GAUGUE
Original assignee: Arcelormittal Investigacion Y Desarrollo, S.L.
Priority date: 2011-06-23
Filing date: 2011-06-23
Publication date: 2012-12-27
Also published as: EP2723520B1; ES2545748T3; EP2723520A1; PL2723520T3

Abstract

The invention relates to a method for continuously casting a metal profile member blank, the cross-section of which comprises at least one portion (4), the concavity of which is oriented toward the outside of the profile member, wherein according to said method liquid metal is poured into a ingot mold (10) for continuous casting, said mold including a cooled ingot-mold body (11) that defines a runner (12), the cross-section of which corresponds to the cross-section of the blank, wherein the cross-section of the runner includes at least two adjacent portions (110; 111A, 111B) connected via a concave portion (112A, 112B), the concavity of which is oriented toward the outside of the runner. The runner of the ingot mold has a taper C, a length L_c, and a minimum transverse thickness Emin, and the core of the blank has a solidification time t_s, characterized in that, once the priming is carried out, the extraction speed is maintained above a minimum extraction speed Vmin = (L_c / t_s) x A/(A + L_c CE_min). The invention also relates to a dummy head.

Description

Method and apparatus for continuous casting of a profile blank

The present invention relates to the continuous casting of a blank of a metal profile whose cross section comprises at least one concavity portion facing outwardly of the section, and in particular of a section steel section. H especially having a small cross section locally.

Typically, H, U, L, I or T section steel sections are made from square or rectangular section products which are hot rolled in suitable rolling mills. This rolling generally comprises a number of roughing passes which make it possible to obtain blanks, which then undergo a plurality of finishing passes intended to give the final shape to the profile. This manufacturing process has the disadvantage of requiring a large number of expensive rolling passes and consuming energy.

In order to reduce the production cost of these profiles and the corresponding energy consumption, it has been proposed to directly manufacture by continuous casting blanks of sections whose section has a shape close to the desired final shape. The use of such blanks has the advantage of avoiding having to make roughing rolling passes and thus reduce both the number of rolling passes and the heating energy that is required when starting. a semi-finished product such as a billet of square section. By way of example, the manufacture of a profile of the IPE100 type having a section of 100/50 / 5mm requires six poaching passes and ten finishing passes. If it was possible to manufacture directly by continuous casting a generally I-shaped section blank of dimension 1 10/70 / 12mm (having a metric weight of 25kg / m), it would be possible to manufacture ΓΙΡΕ100 by rolling simply comprising six finishing passes.

The direct production process by continuous profile blank casting has been implemented to manufacture profiles of relatively large size, the blanks having minimum dimensions of about 300/700 / 50mm, which corresponds to a linear weight of 500 kg / m.

The production of profiles having smaller dimensions encounters difficulties during the transient periods which correspond, for example, to pocket changes during the sequential casting of successive pockets or to casting incident management periods.

In general, during such periods, it is necessary to slow down considerably or stop the casting for a sufficient time. When the profiles are large, this is possible without difficulty. On the other hand, when the profiles are smaller and especially when they have a linear weight of less than 500 kg / m, there are significant difficulties in restarting such as jamming.

These difficulties also exist at the start of the casting which is a particular transitional phase.

Furthermore, the casting of small products presents difficulties in introducing into the mold of continuous casting of the liquid metal with flow conditions to obtain a good surface quality of the blanks.

To solve the problem of the flow of the liquid metal, it has been proposed, particularly in the patent application WO 2006/108874, to use a continuous casting process, said continuous casting under load. In this method, a cooled metal mold body having a section corresponding to the section of the profile blank to be obtained is used, surmounted by a connecting ring having an opening corresponding to the shape of the opening. the casting channel of the mold, on which is disposed a riser of refractory material having a shape adapted to form a funnel. This arrangement makes it possible to introduce the liquid metal into the mold with a little turbulent flow. The mold may for example be that described in patent application WO 2006/108872.

Attempts have been made to use the process just described to produce profile blanks having a linear weight of the order of 25 kg / m 2. For this, before pouring, a mannequin head has been placed in the body of the mold, as is conventionally done in continuous casting, then the liquid metal has been poured into the mold and the manikin has been moved towards the mold. down to extract the cast product. These tests have shown that the process does not make it possible to start the casting under satisfactory conditions. Indeed, when the acceleration is too great, there are breaks in the cast product shortly after the start of the casting, which does not sink the product. When the acceleration at startup is too low, there is a blockage of the blank in the mold which forces to stop the casting. It was therefore not possible to obtain small profile blanks by direct continuous casting.

The object of the present invention is to remedy these drawbacks by proposing a means for carrying out the continuous casting of profile blank having a section of shape close to the desired final section, having small dimensions corresponding to linear weights substantially less than 500kg / linear m can even be of the order of twenty kilos per linear meter, without leading to incidents of casting or damage to equipment. To this end, the subject of the invention is a process for the continuous casting of a blank of a metal profile whose cross section comprises at least one portion whose concavity is oriented towards the outside of the profile, according to which a liquid metal in a continuous casting mold comprising a cooled mold body, the mold body defining a cross section casting channel corresponding to the cross section of the blank, the casting channel cross section comprising at least two adjacent portions connected by a concave portion whose concavity is oriented towards the outside of the casting channel, the casting channel of the mold having a conicity C, a length L _c , a minimum transverse thickness E _min , the core of the blank having a solidification time t _s . According to this method, as soon as the priming is carried out, the extraction rate is maintained above a minimum extraction rate Vmin equal to: Vmin = (L _c / t _s ) x A / (A + L _c CE _min ).

To ensure startup, before pouring liquid metal, is placed in the mold a mannequin head having a base and a refractory separation blade secured to the base and adapted to obstruct one of said adjacent portions of the cross section of the channel. casting on at least a portion of the length of the casting channel of the mold body extending from the base towards the inside of the casting channel of the mold body, then the liquid metal is started to flow and set in motion the mannequin head towards the outside of the mold.

The casting mold may further comprise a connecting ring and a refractory riser. The refractory separation blade is then adapted to extend at least to the junction between the riser and the connecting ring.

The profile may comprise a core connected to at least one wing and the portion of the cross section of the pouring channel obstructed by the refractory separation blade is the portion of the cross section of the casting channel corresponding to the core of the profile.

The profile is for example an H, U, I, L or T profile with a linear density of less than 500 kg / m.

When moving the manikin head, the speed of the manikin head is changed from 0 m / s to a start speed Vd greater than the minimum extraction speed Vmin, in a start time Ta for example between 0.5 s and 1.5 s, the starting speed is maintained during a start-up time Td, preferably between 5 s and 20 s, and the speed of the manikin head is gradually increased to a casting speed Vc preferably between 4 m / min and 12 m / min. The liquid metal is, for example, steel. In this case, the temperature of the liquid metal is adjusted so that the superheat in the booster is preferably between 10 ^ and 60 ^.

The subject of the invention is also a mannequin head for implementing the method according to the invention, comprising a base of a shape adapted to slide by obstructing it in the casting channel of a continuous casting mold of a draft of a profile whose cross section comprises at least two adjacent portions connected by a concave portion whose concavity is oriented towards the outside of the blank, at least one mooring means of the solidified metal and at least one means for sealing of the base one. The manikin head further comprises a refractory separation blade extending above the upper face of the base, the cross section of the separator being adapted to obstruct one of said portions of the cross section of the casting channel. leaving free the other portion (s).

Preferably, the separation blade comprises a metal plate of generally rectangular shape and a coating of flexible refractory material.

Preferably, the metal plate has a plurality of holes and the coating is for example made of a refractory fiber foam sock slipped onto the metal plate and sewn with refractory metal son.

The coating of refractory material may also consist of a braid of refractory fibers, wound around the metal plate.

Preferably, the metal plate of the separator is integral with the clamping plate of the refractory joint.

Preferably, the clamping plate of the refractory gasket comprises at least one hole and a solid metal mooring means which is a fixing pin of the clamping plate comprising a head for mooring the cast metal and a rod comprising a thread extending through the hole of the clamping plate and screwed into a threaded hole in the base.

The base and the clamping plate have a shape adapted to the casting of profile blanks, for example in the form of H, U, I, T or L, profiles whose smallest dimension is included, for example, between 10 and 25 mm.

The invention will now be described in a more precise but nonlimiting manner with reference to the appended figures in which:

FIG. 1 is a schematic view of the section of a profile blank in

H.

- Figure 2 is a schematic longitudinal sectional view of a continuous casting mold of a profile blank, during casting. FIG. 3 is a cross-sectional view of the continuous casting mold of FIG.

- Figure 4 is a diagram highlighting the taper of an ingot mold.

- Figure 5 is a diagram of variation of casting speed during a transitional period.

- Figure 6 is a schematic longitudinal sectional view of the mold of Figure 2, equipped with a casting manikin at the stage of starting the casting.

FIG. 7 is a cross-sectional view of the mold of FIG.

- Figure 8 is a schematic perspective view of the metal frame of a manikin head separator for starting the continuous casting of a small profile.

FIG. 9 is a perspective view of a first embodiment of a mannequin head with separator for starting the continuous casting of profile blanks of small dimensions.

FIG. 10 is a perspective view of a second embodiment of a continuous casting mannequin head of a small profile blank.

- Figure 1 1 is a schematic longitudinal sectional view of a mannequin head of continuous profile blank casting attached to a mannequin body.

FIG. 12 is a diagram of the increase in extraction speed of a manikin head for the continuous casting of a small profile blank.

In general, the invention applies to the casting of profile blanks whose section has a shape comprising at least one concavity facing outwards so that there is at least one line joining two points of contact. solid skin forming during casting and coming out of the casting section.

In Figure 1 there is shown the section of a blank of a profile that corresponds to this definition. This is the blank of an H profile which comprises a core blank 1 connecting two wing blanks 2 and 3. As can be seen in the figure, at the junction between the core 1 and wings 2 and 3, the cross section of the profile comprises a portion 4 whose concavity is oriented outwards. In the particular case of a section section H or I as shown, the cross section has four portions having concavities oriented outwardly of the profile. This figure shows the characteristic dimensions of a profile which are the height H, the width of the wings L and the thickness of the core E. These dimensions identify the profile and define its linear weight. The figure also shows the circle of diameter D corresponding to the junction between the soul and the wing and which allows to determine the maximum massivity of section elements of the section.

By way of example, if the profile that one wishes to manufacture is an IPE100 whose height H is 100mm, the width L of the wings is 50mm and the thickness of the core E is 5mm, the resulting blank directly by continuous casting to manufacture in satisfactory conditions the profile considered, has a height H of 1 10mm, a wing width L of 70mm and a thickness of the soul E of 12mm. Such a blank has a linear weight of 25kg / m.

To continuously pour such a blank, one can use a continuous casting machine which is shown in Figure 2 the ingot mold during casting.

The continuous casting mold generally marked 10 comprises a copper mold body 1 1 cooled by a circulation of water in a plurality of channels 13. This mold body delimits a pouring channel 12 whose cross section has substantially the shape of the section of the draft of the product that one wishes to manufacture. As can be seen in FIG. 3, the H-shaped casting channel 12 comprises a first portion 1 10 intended to form the core of the blank, and two portions 1 1 1 A and 1 1 1 B intended to form the core of the blank, and to form the wings of the blank. Portions 1 1 1 A and 1 1 1 B are not in the extension of the portion 1 10 to which they are connected by leaves defining portions 1 12A and 1 12B having an outwardly oriented concavity of the casting channel . The entire casting channel is surrounded by a plurality of channels 13 for circulating a cooling fluid such as water to cool the mold and thus ensure the solidification of the metal as is known to those skilled in the art in continuous casting.

In the longitudinal direction, the casting channel 12, has a shape having a draft adapted to be able to continuously flow the profile. This clearance corresponds to the conicity of the mold which results from an evolution of the profile between the inlet and the outlet of the casting channel intended to absorb the effects of solidification on the geometry of the blank during its passage in the mold. In FIG. 4, the inlet and outlet profiles 12A and 12B of the casting channel of an ingot mold for casting an H profile are shown. As can be seen in this figure, the casting channel comprises a central portion connecting two side wings. The profiles of the central parts 1 A input and 1 B output, have substantially identical thicknesses. On the other hand, the length of the central outlet portion is slightly smaller than that of the central entrance portion, so that the profiles of the outlet wings 2B and 2'B are brought closer to each other relative to each other. to the wings of entries 2A and 2Ά. It is the same fillet connection of the wings with the core 4A, 4Ά and 4B, 4'B inlet and outlet ingotière respectively. Of In this case, the distance d _A of the points A and A 'of the connection leaves 4A and 4A' of the input profile is greater than the distance d _B of the corresponding points B and B 'of the connection leaves of the output profile.

If L _c is the length of the casting channel of the mold, the taper is, by definition, equal to (d _A -d _B ) / (d _A ^* L _c ) and is expressed in m ^"1 .

The ingot mold body 1 1 is surmounted by a connecting ring 14 made of resistant refractory, separated from the upper face of the ingot mold body 11 by a gap 15 through which a neutral gas such as argon can be blown. The connecting ring 14 has a central passage 14A of shape corresponding to the shape of the casting channel of the body of the mold. The connecting ring 14 is surmounted by a refractory riser 16 whose hollow central portion 16A is in the form of an upwardly flared funnel and whose bottom has an outlet opening of shape corresponding to the shape of the central passage 14A of the connecting ring 14.

FIG. 2 also shows the nozzle 24 through which liquid steel is poured into the casting mold to feed the liquid steel bath 25 which begins to solidify in the zone corresponding to the casting channel 12 of the body of copper mold 1 1. This beginning of solidification creates an outer shell 26 and a central portion 27 corresponding to the core of the blank whose apex 28 corresponds to the beginning of total solidification of the core. While the length of the casting channel of the mold body is L _c , the solidified top 28 of the core is at a distance L _s below the start of the casting channel of the mold body. The length L _s is lower than L _c which means that the soul is fully solidified before the exit of the mold, while on both sides of the soul, the end of solidification is further.

Indeed, the central core and the two lateral wings have different thicknesses (or massivities) and, as a result, have different solidification times. Indeed, those skilled in the art know that the thickness e solidified after a time t can be expressed by a relation of the type e = k t. It follows from this formula that the time required to achieve complete solidification of a portion of a profile is shorter as this part is thin.

In general, the thinnest part of the profile is the central part of the blank.

This therefore has a lower solidification time than the other parts of the profile. The person skilled in the art knows how to determine this minimum solidification time as a function, in particular, of the geometry of the blank to be produced, and of the composition of the metal which is cast and the intensity of the cooling.

In order for the continuous casting of such profiles to proceed satisfactorily, the inventors have found in a new way that, at the outlet of the mold, at least the parts the most massive of the blank should not be completely solidified and secondly, that complete solidification of the thinnest part of the blank should not take place too far upstream of the exit of the mold. For this, the rate of extraction of the blank must always remain greater than a minimum extraction speed to ensure that there is not too much solidification of the blank at the outlet of the mold to avoid blocking the blank. This minimum extraction rate is a function of the length of the casting channel of the mold, the minimum thickness of the blank and the nature of the cast metal. In addition, the inventors have found that this minimum speed also depends on the conicity of the mold.

As seen in Figure 2, the thinnest part, that is to say the web of the profile is fully solidified at a distance L _s of the beginning of the mold 1 1 itself whose length of the channel is L _c . This distance L _s of end of solidification of the core of the profile corresponds to the distance traveled by a slice of liquid steel in the mold during the solidification time t _s of the soul, proportional to the square of half of the minimum thickness E _min of it. If V is the extraction rate, the solidification end length of the core L _s is equal to V xt _s .

The inventors have found that for the casting to be done under good conditions, that is to say without jamming, it is necessary to prevent the cooling of the thinnest part of the blank, after solidification in the mold, to lead to a contraction stronger than that allowed by the conicity of the mold. This leads to imposing an extraction speed greater than a minimum extraction speed Vmin, which is calculated as follows:

Vmin = (The yx [2 K φ t _s / (2 K φ t _s + L _c CE _min )]

with:

L _c = length of the casting channel of the mold.

t _s = time of solidification of the thinnest part of the soul.

φ = average heat flux extracted in the lower part of the mold, between the end zone of solidification of the thinnest part of the blank and the outlet of the mold.

E _min = minimum thickness of the part of the pouring channel corresponding to the core of the profile.

C = Conicity of the mold.

K = Coefficient depending on the nature of the metal = a x (1 / pCp)

with:

a = average coefficient of expansion of the metal,

p = Density of the metal. Cp = Heat capacity of the metal.

This formula can also be written:

Vmin = (The yx A / (A + L _c CE _min )]

With: A = 2 K φ t _s

Note that if the conicity is zero, the minimum extraction speed is that which leads to the end of solidification of the soul just out of the mold (V _min xt _s = L _c ).

By way of example, for steel sections of weakly or unalloyed construction, the minimum extraction speeds Vmin (in m / min) as a function of the length of the casting channel of the mold L _c (in meters) and the thickness Emin of the portion of the pouring channel corresponding to the thinnest core of the profile (in mm) are reported in Table I for a mold of zero conicity.

Table I

Null conicity

When the conicity is significant, the minimum extraction rate is substantially reduced. For example, for a thickness of 14mm Emin, a runner length L _c of 0.5 m, a taper of 20.10 m ³ ^"1, and an average flux Φ 1, 8 MW / m ^2, the speed minimum extraction is 2.48m / min instead of 5.9m / min for zero taper.

This need not to lower the speed of extraction below a speed limit has the consequence that, to cast blanks sections of small section, facilities and / or operating methods must be adapted accordingly .

For example, to allow sequential flow sequential pockets, the distributors must have sufficient capacity to power casting at minimum speed during the change of pocket. As shown in FIG. 5, during the casting of the contents of a first bag (period p1), the extraction rate is high in order to obtain good productivity. During the pocket change, period P _t , the extraction speed is gradually reduced to a low speed which, contrary to what is possible with products of large section, must not be zero and must stay above the minimum speed as defined above. This minimum speed is maintained for a time Al necessary to replace the empty bag with a full bag. When the replacement is completed, it is possible to speed up the extraction to reach a high extraction speed V ₂ which can be lower, equal to or greater than the speed V _! , depending on the circumstances.

During the transition period, the amount of liquid steel consumed is proportional to the product of the minimum speed Vmin by the duration Al of the deceleration, taking into account the number of pouring lines. This quantity must remain less than the quantity available in the distributor.

As indicated in the formula for calculating the minimum speed plus the high conicity, the lower the speed limit and therefore the less severe the operating constraints.

Given the various other constraints that the skilled person knows, he will be able to adapt the sizing of his equipment, the taper and / or the length of the casting channel of the mold, since this factor is involved in the calculation of the limiting speed of extraction, to determine the satisfactory operating conditions to flow in good conditions drafts profile small section he wants to achieve.

However, at the start of the casting, the extraction speed is initially zero, which is not compatible with the condition indicated above. Also, the inventors have devised a particular starting procedure for progressively moving from zero speed to a starting speed Vd greater than or equal to the minimum extraction speed defined above, but less than a maximum starting speed Vdmax at above which there may be rupture of the solidified shell of the product because it is too thin. The person skilled in the art knows how to determine this maximum starting speed as a function of the characteristics of the casting machine, the geometry of the product and the casting parameters.

During this casting initiation phase, the liquid metal poured into the mold must partially solidify, in particular in contact with the dummy disposed in the ingot mold to start the casting, in order to anchor the blank on the mold. dummy. As is known to those skilled in the art, this anchoring makes it possible to start the extraction of the solidified product and thus start the casting.

However, the inventors have found that in order to be able to speed up without blocking the blank during this priming period, it is necessary to avoid solidification of the thinnest parts of the blank. Also, they have imagined to dispose above the head of the pouring manikin, a refractory separator inserted in the part of the mold intended to mold the thinnest part of the blank, in order to prevent solidification in this zone. during the priming phase. During the initiation of the casting, the separator is gradually extracted from the mold. In order for the initiation of the casting to take place under satisfactory conditions, it is necessary that at the moment when the upper end of the separator leaves the mold, the state of solidification of the blank at the outlet of the mold is compatible with the conditions indicated above to avoid jamming. For this, the length of the separator and the process parameters must be adapted accordingly. Those skilled in the art will be able to determine the minimum length necessary according to the characteristics of the mold, the cast metal and the kinetics of extraction of the manikins during the priming phase.

This procedure is suitable for continuous casting both with a straight mold and with a curved mold, the mold being of conventional type or having a refractory riser as is known for the so-called continuous casting "in charge".

As is known to those skilled in the art, once the casting is started, it is possible to increase the extraction speed to increase productivity without exceeding a steady state extraction limit speed, in particular the length of the machine. The person skilled in the art knows how to determine this maximum steady-state extraction speed which is greater than or equal to the maximum starting speed. Note that in steady state, the end of solidification of the thinnest part of the blank can very well take place substantially after the exit of the mold. During this casting phase, it may be desirable to reduce the extraction rate. But this must never become less than the minimum speed defined above.

We will now describe in more detail a preferred embodiment of the start of the continuous casting in charge of a profile blank.

For this, we consider Figures 6 and 7 which are distinguished from Figures 2 and 3 only by the stage of the casting to which they correspond. Also, we will describe only the parts of these figures that correspond to the start of the casting. Inside the casting channel 12 of the mold body, is disposed a mannequin head 17 having a base 18 connected to the mannequin body 19 for pulling the mannequin head down to extract it from the mold

The base 18 of the manikin head is surmounted by a separator 20 having a base 21 conforming to the shape of the pouring channel and a separating blade 22 extending upwards. In the arrangement shown, which corresponds to the very beginning of the casting, the upper end 22A of the separation blade 22 is located above the connecting ring 14. The head of the manikin comprises for example also two dowels. mooring 23 fixed in the base on either side of the separation plate and whose heads extend above the base, inside the casting channel.

The refractory separation blade 22 is disposed inside the central portion 1 10 of the casting channel. This refractory separation blade comprises a central frame 220 surrounded by a refractory coating 240 made of refractory fibers having a certain flexibility so that the separation blade completely obstructs the portion 1 10 by preventing the continuous infiltration of liquid metal between the wall of the ingot mold body and the surface of the separating blade which would be likely to create a junction between the two wings of the profile, and adapts to the width variations of the portion 1 10 resulting from the body. The solid shell corresponding to the beginning of the solidification of the blank extends over the entire periphery of the end portions 1 1 1 A and 1 1 1 B, in particular in the portions 1 12 A and 1 12 B having turned concavities out of the pouring channel.

As shown in Figures 8 and 9, the manikin head has a base 18 having a shape adapted to slide inside a casting channel. On it is reported the separator 20 which comprises a base 21 and a separating blade 22. The separator 20 consists of a metal frame generally marked 200 in Figure 4 and which comprises a lower clamping plate 210 and a central frame. The clamping plate 210 is of identical shape to the shape of the base 18 of the manikin head and has holes 21 1 for the passage of the anchor pins 23 which are screwed into threaded holes 23A provided in the The central armature is constituted by a rectangular metal plate 220 extending above the base clamping plate 210 and having a plurality of holes 221. The clamping plate 210 is disposed above the base 18 of the manikin head on which is disposed a fibrous refractory seal 230 held in place by clamping the clamping plate 210 which itself is covered with refractory fibrous material. The central armature 220 for arming the separating blade is wrapped by a fiber sock refractory 240 held in position by platinum son 241 which pass through the holes 221 provided in the central frame.

In a particular embodiment, the refractory fiber sock was obtained from a strip of 25mm thick SWB607 / 128 plies which was cut in half thickness like a sandwich, so as to be inserted around the metal plate. Then, after being moored to the metal plate by the platinum wires, the part having undergone the cutting was glued along the junction line 242 by a very thin layer of Refracol No. 3 so that the liquid steel does not reach the plate during casting. The refractory SW607-128 (Surperwool ™ 607 ™ Blanket) manufactured by Morgan Thermal Ceramics. It consists of about 62 to 68% SiO _2, 26 to 32% CaO and 3 to 7% MgO. It is in the form of sheets of refractory wool density of about 128kg / m ³ and has a classification temperature of 1100 ° C (EN 1094-3 standard). Refracol ™ # 3 Adhesive is a Class B Class PRE grout refractory cement consisting of approximately 12 to 14% Al ₂ O ₃ , 82 to 87% SiO ₂ and 0.35% Fe ₂ O ₃ . .

In a second embodiment shown in FIG. 10, which differs from the previous one solely by refractory coating of the armature of the separating blade, it does not consist of a sock made from a sheet of refractory material but is obtained by wrapping around the central reinforcing plate a braid 440 made of refractory fiber, for example of the alkaline earth silicate type consisting of 60 to 70% SiO ₂ and 30 to 40% CaO + MgO . Such refractory braids are known in themselves to those skilled in the art.

With such an arrangement, inventors have found that it is possible to start the continuous casting of blanks of small dimensions provided that the particular conditions of starting speed and temperature of the liquid metal are met.

In Figure 12 is shown the evolution in time of the extraction speed of the product or manikin at the beginning of the casting to obtain a satisfactory casting start. In this diagram, before the moment t ₀ , the manikin head is disposed inside the mold so that the separating blade extends in the pouring channel opening out above the connecting ring and the mold does not contain liquid steel. A fraction of a second before time t ₀ , liquid steel is introduced into the mold so that at time t ₀ , the latter is full of liquid steel. The extraction of the manikin head is then started by an accelerated movement so that at time t 1, a speed V d is reached which is the starting speed. This first phase is a priming phase during which a solid steel shell is formed in areas of the mold which are not obstructed. This Shell covers the heads of the anchor studs which ensures its anchoring to the mannequin head. Once the startup speed is reached, this speed is maintained until time t ₂ for a time sufficient to ensure a good start. The period between time ti and time t ₂ is the start-up period. It makes it possible to constitute a solidified roughing start extending all around the casting channel which, at the latest at time t ₂ , is sufficient to continue the continuous casting of the blank. From time t ₂ , when casting is well initiated, the extraction speed is accelerated until time t ₃ so as to reach the casting speed Vc that is maintained throughout the remainder of the casting of the blank. This speed Vc is the speed of steady-state casting. The inventors have found that for the initiation of the rough casting having a linear weight of less than 500 kg / m, or even less than 300 kg / m, or even less than 100 kg / m and even less than 50 kg / m, under good conditions, it was necessary that only one of the two parts of the pour channel located on either side of a concave zone is filled with liquid metal and that the other is well obstructed. Indeed, at the beginning of the casting, if the solidified shell extends on either side of a concave portion whose concavity is oriented towards the outside of the blank, there is jamming of the primer solidified in the mold. This is not the case when only one of the two portions surrounding the concave portion is filled with metal. Of course, when the profile is H-shaped, the core is surrounded by two separate portions of the core by concave portions. Clogging the soul, it avoids two portions located on either side of a concave portion are filled with metal.

The inventors have also found that the ignition time Ta which flows between the instant t ₀ and the instant t i must be between 0.5 s and 1 s, and the starting speed V d. is greater than the minimum extraction speed corresponding to the profile considered. They also found that the starting speed Vd should be maintained during a start time Td preferably between 5s and 20s. With these conditions, it is possible to progressively change the extraction speed of the manikin to a casting speed Vc included, in steady state, between 4m / min and 12m / min, for example.

The inventors have found, finally, that when the metal is steel, the overheating of the liquid metal in the booster, that is to say the difference between the temperature of the liquid metal and the temperature of the solidus should preferably be between 10 ° C and 40 ° C.

By way of example, the inventors have been able to start and flow in good conditions the continuous casting of profile blanks whose nominal dimensions are 1 10 mm, 70 mm and 12 mm, which corresponds to a linear weight of approximately 25 kg / m, with the following parameters: start-up speed 3m / min, start-up time 1 s, start-up time between 5 and 15s and casting speed of order 10m / min. This blank makes it possible to manufacture a profile of the type IPE 100 with just six passes to finishing with hot rolling. In this example, the extraction rate should not fall below 2.84 m / min for a length of mold of 390 mm and a conicity of 20 for 1000.

The inventors have noted that with this profile, when the extraction rate drops below 2.84 m / min, the blank could be jammed in the ingot mold.

In addition, the inventors performed IPE 100 blank casting startup tests without using a separator. These tests have always led to failures by jamming of the blank, in particular because it was not possible to reach an extraction rate greater than 2.84 m / min at the end of priming.

The casting and starting process which has just been described for blanks of sections in H or I, can be adapted to any section whose section comprises two non-aligned portions delimiting a concave portion whose concavity is oriented towards the outside of the profile. Those skilled in the art will be able to determine the appropriate parameters, the essential point being that at the very beginning of the start of the casting, it is not possible to form a solidified shell by clamping a connected part of the wall of the pouring channel.

Claims

1. - Continuous casting process of a blank of a metal section whose cross section comprises at least a portion (4) whose concavity is oriented towards the outside of the section, in which a liquid metal is cast in a casting mold continuous flow (10) comprising a cooled mold body (11), the mold body defining a casting channel (12) of cross-section corresponding to the cross-section of the blank, the cross section of the casting channel comprising at least two adjacent portions (1 10; 1 1 1 A, 1 1 1 B) connected by a concave portion (1 12A, 1 12B) whose concavity is oriented towards the outside of the casting channel, the casting channel of the mold having a conicity C, a length L _c , a minimum transverse thickness E _min , the core of the blank having a solidification time t _s , characterized in that, as soon as the priming is performed, the speed of extraction above a minimum extraction speed Vmin = (L _c / t _s ) x A / (A + L _c CE _min ).

2. - Method according to claim 1, characterized in that before pouring liquid metal in the mold, is disposed in the mold a mannequin head (17) having a base (18) and a refractory separation blade (22). ) integral with the base and adapted to obstruct one of said adjacent portions (1 10) of the cross section of the casting channel over at least a portion of the length of the casting channel of the mold body extending from the base towards the inside of the casting channel of the mold body, then the liquid metal is started to flow and the mannequin head is moved in the direction of the outside of the mold.

3. - Method according to claim 2, wherein the casting mold further comprises a connecting ring (14) and a refractory riser (26) and in that the refractory separation blade (22) is adapted to extend at least until the junction between the riser and the connecting ring.

4. - Method according to claim 2 or claim 3, wherein the profile comprises a core (1) connected to at least one wing (2; 3) and in that the portion (1 10) of the cross section of the channel of casting obstructed by the refractory separation blade is the portion of the cross section of the pouring channel corresponding to the core (1) of the profile.

5. - Method according to claim 4, wherein the profile is a section H, U, I, L or T, the smallest dimension is between 10 and 25 mm.

6. - Process according to any one of claims 2 to 5, wherein the liquid metal is steel and in that the temperature of the liquid metal is adjusted so that the superheat in the riser is between 10 ° C and 60 ° C.

7. - Method according to claim 6, wherein, when the manikin head is set in motion, the speed of the manikin head is changed from 0 m / s to a starting speed Vd greater than the speed of the mannequin head. minimum extraction in a starting time Ta between 0.5 s and 1.5 s, the speed is maintained at the starting speed during a starting time Td, preferably between 5 s and 20 s, and the speed of the manikin head is progressively brought to a casting speed Vc, preferably between 4 m / min and 12 m / min.

8. Manikin head (17) for carrying out the method according to any one of claims 1 to 5, comprising a base (18) of a shape adapted to slide, by obstructing it, in the pouring channel ( 12) of a mold (1 1) of continuous casting of a blank of a profile whose cross section comprises at least two portions (1, 2, 3) adjacent connected by a concave portion (4) whose concavity is oriented towards the outside of the blank, at least one means (23) for anchoring the solidified metal, at least one sealing means of the base (230; 210), characterized in that it comprises, in in addition, a refractory separation blade (22) extending above the upper face of the base, the cross section of the separating blade being adapted to obstruct one of said portions (1 10) of the cross-section of the channel pouring leaving free the other portion or portions (1 1 1 A, 1 1 1 B).

9. A manikin head according to claim 8, wherein the separating blade (22) comprises a central frame consisting of a metal plate of generally rectangular shape (220) and a coating (240, 440) of flexible refractory material.

10. Manikin head according to claim 9, wherein the metal plate (220) has a plurality of holes (221) and in that the coating consists of a sock (240) made of refractory fibers threaded onto the plate. rectangular metal (220) and stitched with the refractory metal wire (241).

1 1. - Manikin head according to claim 9, wherein the refractory material coating consists of a refractory fiber braid 440, wrapped around the metal plate (220).

12. Manikin head according to any one of claims 9 to 11, for which said means of sealing the base comprises a refractory seal (230) on the upper face of the base and a clamping plate ( 210) of the refractory seal.

13. - Manikin head according to claim 12, wherein the metal plate (220) is integral with the clamping plate (210) of the refractory joint.

14. - Manikin head according to any one of claims 12 or 13, wherein the clamping plate (210) of the refractory seal comprises at least one hole (21 1) and in that a metal mooring means solid is a stud (23) for fixing the clamping plate, comprising a head for mooring the cast metal and a rod (23A) having a thread extending through the hole of the clamping plate and screwed into a threaded hole of the base (18).

15. - Manikin head according to any one of claims 8 to 14, wherein the base (18) has a shape adapted to the casting of blanks H, U, I, T or L, whose smallest dimension is between 10 and 25 mm.