EP0183118B1 - Feeding device for liquid metal with temperature control in the continiuous casting of tubes - Google Patents

Abstract

In a continuous vertical ascending casting installation for iron pipes T, graphite elements 3 defining a molten metal feed chimney 28, a die and coaxial core arrangement 13, 14 and an expansion vessel 16 are mounted under a cover 2 of an electric furnace 1. In use these graphite elements are immersed in a bath of molten metal contained in the hearth area 7 of the furnace, to thus enable precise temperature regulation and control. The outer surface of the die 13 is surrounded by a water cooling jacket 18, and the level of molten iron in the hollow cavity 25 of the core 14 is varied by the expansion vessel 16, to provide even finer control of the temperature gradient within the annular casting space. The overall arrangement is thus similar to a double boiler.

Description

The present invention relates to the continuous casting of ferrous alloy tubes and more particularly of cast iron tubes of small thickness compared to the diameter.

More particularly, the present invention relates to the continuous vertical casting of a cast iron tube from a tubular die and from a heated core coaxial with the tubular die, providing with the latter an annular section for the casting of the pipe.

A continuous casting installation of a cast iron tube with a low thickness / diameter ratio, using a tubular die and a heated coaxial core has been described in the French patent published 2 415 501. In this patent, it is acts of a descending vertical continuous casting, the liquid iron entering from the top into the annular space comprised between the die and the core.

Due to the narrowness of the annular passage reserved for liquid cast iron to form the pipe, the risk of obstruction of this annular passage by prematurely solidified cast iron in contact with the wall of the tubular die cooled externally by water jacket, is a high risk if the solidification front of the cast iron, that is to say the limit between the liquid phase and the solid phase of the cast iron, is not the object of a control that is difficult to carry out. The object of patent FR-A-2 415 501 was to define this solidification front as well as the external cooling means of the tubular die in order to control this solidification front, in particular at the beginning of the casting.

The Applicant also knows a continuous casting installation according to the preamble of claim 1, but no device for controlling and regulating the temperature of the liquid iron is provided.

The present invention poses the problem of controlling and ensuring the regulation of the temperature of the liquid iron itself, that is to say of acting on the liquid phase rather than on the solid phase in an installation. vertical ascending supply, at source, by a siphon block system in order also to avoid the risks of obstruction by premature solidification of the cast iron in said narrow annular space.

This problem is solved by the present invention which relates to an installation for supplying liquid cast iron for the continuous casting of a pipe, with a view to controlling and regulating the temperature of the cast iron, this installation, of the casting type. upward vertical continuous with source supply of an annular space between a cooled tubular die and a heated coaxial core, being characterized in that it comprises an electric furnace for maintaining the melting temperature containing liquid cast iron enveloping a device for supply of liquid iron to the annular space between die and core of the die-core molding assembly, said device of liquid iron supply which comprises the die-core molding assembly as well as a means of control and regulation of the temperature of the core, being produced in a set of graphite blocks carried by a refractory upper cover of the electric furnace, said cover being removable so as to to lift the supply device out of the temperature-maintaining cast iron bath contained in the oven, and said cover being sealable at the top of the oven, so as to immerse the supply device in the cast iron bath temperature maintenance.

According to a characteristic of this installation, the means for controlling and regulating the temperature of the core of the die-core molding assembly is constituted by a so-called expansion vessel communicating with the cavity of the hollow core of the die-core assembly in view. feeding said core cavity in liquid iron at a variable level.

Other characteristics and advantages will appear during the description which follows.

• la Fig. 1 est une vue schématique en coupe de l'installation de l'invention pendant la coulée continue d'un tube en fonte,
• la Fig. 2 est une vue schématique en coupe correspondant à la Fig. 1 de l'installation au repos, le couvercle du four électrique étant ouvert et le dipositif d'alimentation en fonte liquide suspendu au-dessus du four électrique,
• la Fig. 3 est une vue en plan suivant la ligne 3-3 de la Fig. 1.

In the accompanying drawing, given only by way of example,

• Fig. 1 is a schematic sectional view of the installation of the invention during the continuous casting of a cast iron tube,
• Fig. 2 is a schematic sectional view corresponding to FIG. 1 of the installation at rest, the cover of the electric oven being open and the liquid iron supply device suspended above the electric oven,
• Fig. 3 is a plan view along line 3-3 of FIG. 1.

According to the embodiment of FIG. 1, the installation of the invention essentially comprises an electric oven 1 or liquid iron container or heating crucible-tank, and a refractory upper cover 2 capable of sealingly closing the upper part of the electric oven 1.

The electric oven 1 containing liquid iron F therefore serves as a container for the bath or in the envelope of liquid iron for maintaining the temperature of the liquid iron supply device proper which, according to the invention, is carried by the cover 2 and is constituted by a set 3 of graphite blocks.

1 ° The electric oven 1 -

Placed on an openwork platform 4 in order to have access to the lower part or to the bottom of the electric oven 1, with a view to emptying this oven through a closable lower orifice not shown, the electric oven 1 comprises at inside a thick sheet metal casing 5 a thick refractory lining 6, for example of the silico-aluminous type, providing a capacity 7 for receiving liquid iron. The electric oven 1 is provided with electric heating means constituted for example by an inductor 8 enveloping the vertical wall of its refractory lining 6. The electric oven 1 also has at its upper part a chute 9 for outward flow of a possible overflow of liquid iron. The electric oven 1 is closed at its upper part by the upper cover 2 also comprising an outer sheet metal casing and a thick refractory lining, of the silico-aluminous type for example. The upper cover 2 is provided with a fixing flange or ears 10 cooperating with fixing bolts 11, the lower end of which is secured to the perforated platform 4, so that that, by tightening the bolts 11, the cover 2 is applied in leaktight manner to the upper part of the oven 1, by means of a seal, not shown, which is crushed between the oven 1 and the cover 2, but without covering an overflow hole formed by a chute 9.

2 ° The cover 2-

According to the invention, the cover 2 serves as a suspended support for a set of graphite blocks 3 constituting a molding assembly 13-14 with cooled die 13 and heated hollow core 14 coaxial with the die, around an axis XX vertical, also constituting a device 15 for supplying liquid iron to the molding assembly 13-14, around a vertical axis YY and finally constituting a means 16 for regulating and controlling the temperature of the hollow core 14, said means constituting a vase 16 called "expansion".

In the closed position of the cover 2, the set 3 of graphite blocks with the capacity 7 of the furnace 1 provides a liquid iron housing space in which the part of the set 3 located below the cover 2 is immersed.

3 ° The molding assembly 13-14 of axis XX-

In more detail, the molding assembly comprises a tubular die 13 of axis XX, made of graphite, housed in a cavity provided on the assembly 3 of graphite blocks at the bottom of which it rests by an outer flange 17 of circular shape . The die 13, passing through the refractory lining of the cover 2, is enveloped by a cooling sleeve 18 over a part of its height corresponding approximately to the thickness of the refractory lining of the cover 2, the hollow sleeve 18 being traversed by a fluid such as water or a liquid metal with a low melting point, such as lead or tin.

The internal wall of the die 13 is machined with precision in cylindrical form. However, at the lower part, the die 13 is flared in a frustoconical manner at 21 to facilitate the entry of liquid metal, that is to say liquid cast iron. At its upper part, the die 13 is flared, above the cover 2, along a frustoconical surface 22 of clearance out of contact with the cast iron tube in formation.

The hollow core 14 of external shape carefully machined in cylindrical form, is made of graphite like the die 13 with respect to which it is well centered coaxially (axis XX) and rests on the graphite assembly 3 by a lower flange 23 of support located substantially below the die 13 so as to provide with the lower flaring 21 of the liquid metal inlet an annular space which is largely dimensioned, substantially greater than the annular space comprised between the die 13 and the core 14 to form the barrel of a cast iron pipe T. The hollow core 14 forms a circular lower chamber 24 for communication with the graphite block which it supports in assembly 3. The hollow core 14 has a cylindrical cavity or interior chamber 25 communicating with the chamber 24 and communicating at its upper part with the open air by a cylindrical-conical orifice 26 passing through the upper wall of the graphite core 14 and closed by a flap graphite ball 27 resting by gravity on the orifice 26 which serves as its seat.

4 ° Y-Y axis liquid iron supply device

This source supply device 15 has the form of a graphite siphon block forming part of the assembly 3 externally covered with a thick refractory lining 6. The device 15 comprises a vertical chimney 28 with an upper funnel, axis YY surmounting the cover 2 by a height H substantially greater than the height h of the die 13 exceeding the cover 2. The vertical chimney 28 extends to the bottom wall of the assembly 3 of graphite block so as to open out outside the graphite block above the capacity 7 of the oven 2. But at its lower part, the chimney 28 is closed for example by a transverse drawer 29, or by any other equivalent means, the opening of which controls emptying the chimney 28 into the capacity 7. Above the shutter drawer 29, the chimney 28 is extended following a right angle bend by a horizontal conduit 30 which opens below the flare taper 21 inlet of liquid iron into the annular space of the molding assembly 13-14, at the lower part thereof so as to supply it at source. The graphite block containing the chimney 28 is enveloped by a tubular electric heating resistor of a height corresponding to almost the entire height of the chimney 28, that is to say to the chimney part 28 included above the oven. (height H + thickness of cover 2).

5 ° The expansion tank 16 of axis Z-Z

According to the invention, it is a graphite vase or container 16 with a vertical axis ZZ, also carried by the cover 2 and passing through it, of height roughly corresponding to that of the assembly of molding 13-14. The expansion tank 16 comprises a cavity or a cylindrical chamber 31 almost closed with the exception of a lower opening 32 opening into a lower circular communication chamber 33, and with the exception of an upper orifice 34 connected by a conduit 35 under the control of a valve 36 to a source of pressurized gas such as air or nitrogen or argon.

The vase 16 is closed at its upper part by a graphite cover 16 a which is screwed. The lower communication chamber 33 communicates on the one hand with the lower communication chamber 24 of the molding assembly 13-14 by a horizontal conduit 37 hollowed out in the graphite assembly 3, on the other hand with the capacity 7 of the electric oven 1 by a vertical extension of the lower opening 32, this extension which opens onto the lower face of the assembly 3 of graphite blocks, being closed for example by a transverse drawer 38 whose opening allows the emptying of the cavity 31 in the capacity 7 of the oven 1. The expansion vessel 16 is the means of controlling and regulating the temperature of the core 14.

Operation

The capacity 7 of the electric oven 1 is initially empty or else contains a remainder of liquid iron F or foot of bath.

The electric oven 1 being closed in a leaktight manner by its cover 2 with tightened bolts 11, and the set of graphite blocks 3 thus being sus hanged above the capacity 7 of the furnace, liquid cast iron is introduced through the filling hole 12 of axis WM (Fig. 3) to a level slightly lower than the height of the overflow chute 9 If this level is exceeded, the excess liquid iron flows outwards through the chute 9. The inductor 8 is energized. The oven 1 is therefore heated.

The cover 16a of the expansion vessel 16 of axis ZZ being removed (unscrewed), liquid iron F is introduced into the cavity 31 of the vessel 16. As the cavity 31 of the vessel 16 communicates with the cavity 25 of the core 14 d axis XX, the level of the liquid iron rises at the same time and to the same height in the cavities 25 and 31.

The filling in liquid iron of the cavities 25 and 31 is stopped well below the orifices 26 and 34, at the highest halfway up the cavity 25, so that, the cover 16a being screwed again, and the fluid under pressure (compressed air or inert gas under pressure such as nitrogen or argon) being introduced via line 35, or on the contrary the line 35 being connected to a suction source, the level of liquid iron in the cavity 25 may vary between a lower level in solid line located at the level of the flared entry 21 of the die 13 (FIG. 1), a little below the lower part of the cooling sleeve 18, and an upper level, in line interrupted, located just below the ball valve 27.

In addition, the vertical chimney 28 is heated over its entire height located above the capacity 7 of the oven, by the electric heating resistor 28a energized. In addition, a cooling fluid, for example cold water, is brought into circulation by the conduit 19, the sleeve 18 and the conduit 20. Before starting the casting of a cast iron tube T, the core is heated 14 by bringing pressurized fluid into the conduit 35 so as to cause liquid iron to rise from the cavity 31 of the expansion vessel 16 towards the cavity 25 of the core 14 up to the upper part thereof.

Only the upper part of the core 14 which is traversed by the cylindrical-conical orifice 26 serving as a seat for the ball valve 27, is not heated. It corresponds to the upper part of the annular space between the die 13 and the core 14, through which the cast iron tube T to be formed must exit, therefore to the part where the tube T in formation must be cooled externally without being heated internally .

These thermal precautions being taken, we proceed to the casting of the T tube in cast iron.

Liquid cast iron is poured through the vertical chimney 28. The latter descends to the horizontal duct 30 which it fills, then rises in the flared inlet 21 of the die 13 and continues its rise under a pressure corresponding to the height of the chimney 28, in the annular space between the die 13 and the core 14.

Thanks to the heating of the core 14, over almost its entire height, with the exception of its upper part (outlet end of the tube T), the cast iron which is in contact with the core 14 remains liquid while the cast iron which is in contact with the die 13 cooled by the mancon 18, is cooled and tends to solidify along a solidification front delimiting a solid phase which progresses in thickness from the bottom up, according to the solidification front described in patent FR 24 15 501, but in opposite direction since the casting is rising instead of being falling in this patent.

The solidification of the cast iron is complete at the upper level of the core 14 and at the base of the clearance 22 which allows the pipe T to freely exit (Fig. 1).

By pulling on the pipe T in the direction of the arrow with the aid of a known extractor, not shown, and continuing the supply of liquid iron from the source by the vertical chimney 28 and the clearance 21 from the die 13 , we produce a cast iron tube T.

External heating of the cast iron supplying the die 13 with a core 14: it is provided by the liquid cast iron F contained in the capacity 7 and heated, kept liquid by the inductor 8. The temperature of this cast iron F can be increased by increasing (if possible) the heating power of the inductor 8. It is also possible to renew the liquid iron contained in the capacity 7 if its temperature is considered to be insufficiently high. It is therefore possible to introduce liquid iron at an even higher temperature through the filling hole 12 (FIG. 3) so as to replace at least part of the insufficiently hot iron which flows through the overflow chute 9.

Ansi all the blocks 3 of graphite is maintained at the right temperature by a kind of water bath constituted by the cast iron contained in the capacity 7 of the furnace 1.

Core temperature control and regulation 14.

This control and this regulation are carried out so as to continuously obtain a solid tube T made of cast iron at the outlet of the annular space between die 13 and core 14, that is to say at the level of the upper end edge of the core 14.

a) if the cast iron still comes out in the liquid state of this space and forms flow burrs on the outer edge of the core 14, this is because the core 14 is too hot at its upper part and the cooling sleeve 18 is not effective enough.

The level of the cast iron F is then lowered in the cavity 25 of the core 14 by reducing the pressure of the gaseous fluid in the cavity 31 of the expansion vessel 16, and, simultaneously, the cooling of the sleeve 18 is made more energetic by accelerating the refrigerant fluid flow which flows through the conduits 19 and 20 and, if possible, decreasing its temperature.

These two measures together or at least one of the two must restore a solidification front as described in patent FR-A-2,415,501
that is to say with an entirely solid melting phase at the outlet of the annular space between the die 13 and the core 14.

b) on the contrary, if the cast iron solidifies inside the annular space between the die 13 and the core 14, which obliges to stop the casting and to dismantle the whole of the die 13 and of the core 14 for put back at least one new core 14 if the solid cast iron has not adhered to the die 13, this means that the upper part of the core 14 is too cold and / or that the die 13 is too vigorously cooled.

By restarting the casting with a new core 14 and perhaps a new die 13, or make sure to make the upper part of the part warmer core 14 by raising the level of cast iron, for example in N in broken lines in the cavity 25 of the core 14, by increasing the pressure of gaseous fluid in the cavity 31 of the expansion vessel 16. The level then decreases correlatively in N1 in broken lines in the cavity 31 of the expansion vessel 16. This measurement makes it possible to obtain a correct solidification front as defined in patent FR 2 415 501 in order to obtain a cast iron tube T.

The temperature control of the walls of the die 13 and of the core 14 is carried out using thermocouples not shown and suitably placed in particular on the core 14.

Thus, the annular space between the die 13 and the core 14 benefiting from a control and a temperature regulation, it is possible to pour a tube T of very thin cast iron since it prevents the cast iron from freezing prematurely or on the contrary that it remains liquid up to the upper part of the annular space between the die 13 and the core 14.

As a numerical example, the tube T has an outside diameter of 118 mm and a thickness of 3 mm. Although the application of the invention is not limited to such numerical values, but on the contrary extends to greater values, both in diameters and in thicknesses, it is for small diameters and small thicknesses, and low thickness / diameter ratios, for example of the order of 3/100, that it is the most advantageous.

Any accidental leakage coming from the die-core 13-core assembly 14 or from the supply device 15 or from the expansion tank 16 is collected by the capacity 7 of the furnace 1.

Any excess liquid iron drains through the overflow chute 5.

At the end of a casting period, the set 3 of the graphite blocks is drained of the liquid iron F which it contains by detaching the cover 2 from the oven 1, by lifting it well above the oven 1 (Fig. 2) and by opening the drawers 29 and 38 as soon as they are released from the oven 1.

The liquid iron then falls into the capacity 7 of the furnace 1.

To drain the capacity 7 of the oven 1, it is necessary to open the drain holes located at the bottom of the oven (for example in the axes XX, YY and ZZ), and not shown.

Benefits

Thanks to the electric furnace 1 containing the envelope of liquid cast iron F in its capacity 7, all of the graphite blocks 3 are kept at high temperature in its part immersed in the furnace 1, throughout the casting. Thus, by controlling only the power supply of the inductor 8 of the electric oven 1, that is to say the heating power of the electric oven 1, we simultaneously control, simultaneously, the outside temperatures of the submerged parts graphite blocks constituting the device 15 for supplying liquid iron, those of the graphite blocks constituting the die 13 and constituting the core 14, and those of the graphite blocks containing the expansion vessel 16.

Thanks to the communicating vessels 31 and 25 constituted by the expansion vessel 16 in combination with the cavity of the core 14, and thanks to the control of the levels of liquid iron in the cavity of the core 14 under the gas pressure supplied by the conduit 35, it is possible to ensures the temperature regulation of the core 14 in a simple, safe and easily reproducible and safe manner since the ball valve 27 in combination with the cylindrical-conical orifice 26 acts as a safety valve in the event of excess liquid iron in the cavity 25.

By filling the capacity 7 of the furnace 1 with liquid iron and by partially filling the capacities 31 and 25 with the same liquid iron, that is to say with the same ferrous metal alloy as that of the iron cast in the supply device. 15 to obtain a pipe T, and by virtue of the introduction of this liquid cast iron at about the same time into the tank 7, into the cavity 31 of the expansion tank 16 and into the chimney 28 of the supply device 15, temperature uniformity is obtained which is beneficial to the mechanical strength of all the graphite blocks 3 because thermal stresses are avoided by avoiding differences in expansion.

Thanks to the presence of the cooling sleeve 18 essentially on the outer part of the die 13 corresponding to the crossing of the refractory lining of the cover 2, therefore essentially outside the set of graphite blocks 3, and due to the thermal barrier constituted by said refractory lubrication, no temperature heterogeneity is provided on all of the graphite blocks 3 due to the location of this cooling away from the assembly 3 of the graphite blocks.

Finally, for reasons of ease of construction, the assembly 3 of the graphite blocks can advantageously be produced in a certain number of cylindrical parts capable of being attached and screwed onto the parallelepipedic block 3 (FIG. 3).

Claims (17)

1. Installation for the continuous casting of ferrous alloy tubes, in particular cast-iron tubes, of the vertical ascending type with a bottom feed to an annular space between a cooled tubular die (13) and a heated coaxial core (14), characterised in that it comprises an electrical furnace (1) for maintaining the melting temperature containing molten cast-iron (F) surrounding a device (15) for the feed of molten iron to the annular space between the die (13) and core (14) of the casting arrangement (die 13 - core 14), the said device (15) for the feed of molten iron which comprises the casting arrangement (die 13 - core 14) as well as means (16) for checking and regulating the temperature of the core (14), being provided in an arrangement (3) of graphite blocks carried by an upper refractory cover (2) of the electrical furnace (1 the said cover (2) being removable in order to raise the feed device (15) from the bath of iron (F) for maintaining the temperature contained in the furnace (1) and the said cover (2) being able to be closed off hermetically at the upper part of the furnace (1) in order to immerse the feed device (15) in the bath of iron (F) for maintaining the temperature.

2. Installation according to Claim 1, characterised in that the means for checking and regulating the temperature of the core (14) of the casting arrangement consisting of the die (13) core (14) is constituted by a so-called expansion vessel (16) communicating with the cavity (25) of the hollow core (14) with a view to supplying the said cavity (25) of the core (14) with molten iron at a variable level.

3. Installation according to Claim 1, characterised in that the cavity (25) of the hollow core (14) communicates at its upper end with the atmosphere through a cylindrico-conical orifice (26) closed off by a ball valve (27) resting on the orifice (26) which serves it as a seat.

4. Installation according to Claim 2, characterised in that the expansion vessel (16) comprises a cavity (31) which is almost closed with the exception of a lower opening (32) connected to the cavity (25) of the hollow core (14) and with the exception of an upper orifice (34) connected by a conduit (35) controlled by a valve (36) to a source of pressurised gas.

5. Installation according to Claims 3 and 4, characterised in that the cavity (25) of the hollow core (14) communicates at its lower end with a circular chamber (24) whereas the cavity (31) of the expansion vessel (16) communicates at its lower end with a circular chamber (33), the circular chambers (24-33) being connected to each other by a horizontal conduit (37).

6. Installation according to Claim 1, characterised in that the die (13) is flared at its upper end along a frustoconical surface (22) for the disengagement of the tube (T) to be formed and comprises at its lower end a frustoconical flare (21) for facilitating the entry of molten metal.

7. Installation according to Claim 1, characterised in that the die (13) rests on the bottom of a cylindrical cavity in the arrangement (3) of graphite blocks by an external circular flange (17).

8. Installation according to Claim 1, characterised in that the hollow core (14) coaxial ont the axis (X-X) with the die (13) rests on the arragement (3) of blocks of graphite by a lower support flange (23) situated substantially below the die (13) in order to provide with the lower flare (21) of the die (13) a wide annular space forthe entry of molten metal, this space being substantially greater than the annular space comprised between the die (13) and the core (14) in order to form the body of the iron pipe (T).

9. Installation according to Claim 1, characterised in that the die (13) is surrounded by a cooling sleeve (18) over part of its height corresponding approximately to the thickness of the refractory lining of the cover (2).

10. Installation according to Claim 1, characterised in that the device (15) for feeding molten metal to the casting arrangement (13-14) comprises a chimney (28) having a height (H) above the cover (2) which is substantially greater than the height (h) of the die (13) above the cover (2).

11. Installation according to Claims 1 and 10, characterised in that the feed device (15) is provided with a tubular electrical heating resistor (28a) surrounding virtually the entire chimney (28), that is to say the part of the chimney located above the furnace (1) over a height corresponding to the sum of the height (H) and the thickness of the cover (2).

12. Installation according to Claim 5, characterised in that the lower opening (32) of the cavity (31) of the expansion vessel (16) is extended by a vertical extension which opens into the lower surface of the arrangement (3) of graphite blocks and which is blocked by a transverse gate (38) whose opening allows drainage of the cavity (31) into the space (7) of the furnace (1 ).

13. Installation according to Claim 10, characterised in that the vertical chimney (28) of the feed device (15) opens at its lower end into the lower surface of the arrangement (3) of graphite blocks, but is blocked by a transverse gate (29) whose opening controls the drainage of the chimney (28) into the space (7) of the furnace (1) and the chimney (28) is extended at right angles above the transverse gate (29) by a horizontal conduit (30) which opens below the frustoconical flare (21) for the entry of molten metal into the annular space of the casting arrangement (13-14) in order to feed it from the bottom.

14. Installation according to Claim 1, characterised in that the furnace (1) for maintaining temperature comprises at its upper end an overflow (9) for excess molten metal.

15. Installation according to Claim 1, characterised in that, in the closed position of the cover (2), the arrangement (3) of blocks of graphite provides with the space (7) of the furnace (1) a space for holding molten iron in which the part of arrangement (3) situated below the cover (2) is immersed.

16. Installation according to Claim 1, characterised in that, the arrangement (3) of blocks of graphite is formed from a certain number of cylindrical parts able to be joined and screwed on a parallelepipedal block (3).

17. Installation according to Claim 1, characterised in that the casting arrangement (13-14), its feed device (15) and the expansion vessel (16) have parallel vertical axes respectively (X-X, Y-Y and Z-Z).

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