EP0088980B1 - Casting apparatus and tubular mould for the continuous casting of thin-walled iron tubes - Google Patents

Abstract

The die (6) comprises a thick cylindrical body (7) which is surrounded by a cooling jacket (15) clamped against the pouring basin (2) and in contact with the latter in a plane (P). The body (7) is extended in the casting orifice (4) by a composite head (17) comprising a thin inner annular lip (22), whereof the inner surface extends that of the body (7) and a ring (24) of refractory material fitted between the lip, the body and the casting orifice. The (hot) lip (22) is connected to the body (7) in the plane (P), so that the ring (24) rejoins it also in this plane and that the flow of heat (f1) passing from the casting orifice to the cooling jacket must skirt around this ring.

Description

The present invention relates to a vertical downward continuous casting installation with tubular die for obtaining a thin cast iron tube, that is to say a tube whose thickness / diameter ratio is low, less than 10%, the thickness itself not exceeding 5 mm.

A continuous casting installation of such a tube comprises, according to a previous patent filed in France on January 27, 1978 under No. 7 802 277 and published under No. 2,415,501, below a casting basin provided with '' a lower orifice, a substantially cylindrical die which is surrounded by a cooling jacket and delimits, with a core which crosses the basin, a tubular space for pouring the tube, an extractor device pulling the solidified tube step by step as measure of its formation.

In the case of the casting of a thin-walled tube, and more particularly of a cast iron tube, the entrance to the casting space being narrow, the risk of obstruction by premature partial solidification is great.

It has therefore been proposed in patent FR-A-2 415 501 to provide the die with a head penetrating inside the pouring orifice and thus to postpone the entry of the tubular space into a more hot. In some cases, the head is a simple extension of the cylindrical body of the die. In others, in a more advantageous form, it is formed by a frustoconical projection thinner upward, which is immersed in the liquid iron inside the pouring orifice.

However, it can be seen that if the obstruction of the entry is thus practically removed, it nevertheless forms at certain longitudinal intervals, more or less regular, corresponding to multiples of the extraction pitch of the solidified tube, of the superficial inlay rings. solidified cast iron, not amalgamated, not welded with the rest of the cast iron poured into the annular space. Although of shallow depth, these rings can however reach half the total width of the annular space between the core and the die and, consequently, half the thickness of the cast tube. They are therefore intolerable in the production of a long, thin cast iron tube, since these are weakening zones which must be removed by cutting off the cast tube. Sometimes, too, there is a total blockage of the cast iron supply and a cessation of casting.

We also know from European patent applications 00 7581-A and 00 42995-A1 a vertical continuous casting installation descending from a solid bar made of copper alloy, with a diameter of the order of 6.5 mm to 8 mm. This installation comprises a die with a lower part immersed in the bath, an insulating refractory sleeve above this submerged part, and a cooling jacket, the combination of which produces a solidification front which would not make it possible to manufacture a cast iron tube and would not would not solve the problem of inlay rings.

The problem is therefore to remove these incrustation rings by modifying the die head of the continuous casting installation while maintaining perfect homogeneity and continuity of the die inner wall between this head and the body.

The present invention relates to a continuous casting installation with a die according to claim 1, which solves this problem.

Patent FR-A-2 415 501 describes a continuous casting installation with a tubular die which has all the characteristics of the first part of claim 1.

In this continuous casting installation according to claim 1, the die comprises a composite head with a narrow annular lip surrounded by an insulating ring which fills the space between the lip and the internal wall of the casting opening of the installation.

This arrangement significantly reduces the cooling flow, transfers it above said composite die head, and prevents any start of solidification on the internal wall of said composite head.

The description below of embodiments given by way of nonlimiting examples, and represented in the appended drawings, will moreover highlight the advantages and characteristics of the invention.

• la fig. 1 est une vue schématique en coupe d'une partie d'une installation de coulée continue verticale avec filière tubulaire suivant l'invention, au cours de la coulée d'un tube;
• la fig. 2 est une vue schématique partielle en coupe, à plus grande échelle que la fig. 1, de la partie supérieure de l'installation suivant l'invention;
• les fig. 3, 4 et 5 sont des vues partielles en coupe, à même échelle que la fig. 2, de variantes de l'installation suivant l'invention;
• la fig. 6 est une vue schématique partielle de détail, en coupe, analogue aux figures 3 à 5, montrant à titre comparatif une tête de filière suivant une technique connue.

In these drawings:

• fig. 1 is a schematic sectional view of part of a vertical continuous casting installation with tubular die according to the invention, during the casting of a tube;
• fig. 2 is a partial schematic view in section, on a larger scale than FIG. 1, of the upper part of the installation according to the invention;
• fig. 3, 4 and 5 are partial sectional views, on the same scale as FIG. 2, variants of the installation according to the invention;
• fig. 6 is a partial schematic detail view, in section, similar to FIGS. 3 to 5, showing for comparison a die head according to a known technique.

According to the embodiment of FIGS. 1 and 2, the invention is applied to an installation for continuous vertical downward casting of a thin-walled tube, made of cast iron, T, the thickness / diameter ratio of which is low, that is to say less than 10%, the thickness itself not exceeding 5 mm and possibly being of the order of 3 mm.

For the sake of simplification, there is shown in FIG. 1 that part of the casting basin 1 supplying the die of the invention, in liquid iron F. The casting basin 1 is contained in a metal case or casing 2 internally coated with a thick refractory lining 3, for example of silico-aluminous type, and it has at its lower part, which is, moreover, the only one shown in FIG. 1, a vertical pouring orifice 4, of cylindrical shape and axis XX, inside which is mounted the upper end or head of the die 6, as well as a core 8 which defines with this die a tubular space casting 10.

The core 8, which is made of graphite and is coaxial with the pouring orifice, passes right through the pouring basin 1 and is suspended at its upper part, bearing on the body 2, by known means, not shown, for example those described in patent FR No. 2,415,501. Preferably, this core 8 is hollow and internally comprises a heating device, for example an inductor 12 in the form of coil, copper, helically wound and internally cooled by water, or a heating resistor.

The die 6 is also made of graphite. It is tubular and coaxial with the core 8, that is to say with an axis XX, and it surrounds the core 8 by delimiting with it the narrow tubular space 10 whose width corresponds to the thickness of the wall of the tube T to flow. The die 6, the height of which is for example 25 cm for the casting of a cast iron tube T, with an external diameter of 170 mm and a thickness of 5 mm, is supported at its lower end by a flange 9 suspended from the body 2 of the casting basin by tie rods 14.

The flange 9 also supports a cooling jacket 15, coaxial with the die 6 and the core 8, which is in close contact with the outer wall of this die between the body 2 of the tapping basin, that is to say the outlet from the pouring orifice 4, and the flange 9. This cooling jacket 15 is shown diagrammatically in the form of a water circulation sleeve with pipes 16 and 13 for entering and leaving the water , but it is obvious that it can comprise, in accordance with patent FR 2 415 501, between the water circulation sleeve and the die 6, a coolant metal jacket with low melting point in order to ensure contact better thermal and, therefore, a perfect evacuation of calories.

The installation further comprises a device for extracting, or extracting, the cast T-tube, consisting for example of two pairs of rollers 18 and 20 with horizontal axes, applied to the outer wall of the cast T-tube, symmetrically with respect to axis XX. Two of these rollers, located on the same side of the axis XX, are connected by a transmission chain 19 and driven in rotation, step by step, that is to say with stopping times, by a gear unit 21.

Thanks to this known extraction system, the exit of the solidified tube T from the tubular space 10 is carried out step by step.

According to the invention, the casting installation is provided with a die 6 which comprises at its upper part a composite head 17 extending a hollow cylindrical body 7 which may be of constant wall thickness, said head 17 being adjusted in the orifice 4.

According to the embodiment shown in Figures 1 and 2, the composite head 17 has a thin or narrow annular lip 22, connected by a wide rounded 23, with the thick body 7, but in one piece with it, in graphite. This connection takes place exactly at the mouth of the pouring orifice 4, that is to say in the plane of the contact P (drawn in phantom) between the outer face of the metal case 2 and the upper end of the cooling jacket 15. Consequently, over its entire height, the thin annular lip 22 has, inside the pouring orifice 4, a thickness substantially less than that of the body 7 of the die 6, at the outside this orifice. At its upper part, the lip 22 has a thickness which is a fraction of that of the cooled part 7 of the die 6. In the embodiment shown, the lip 22 is frustoconical but, as its conicity is very small, it is almost over its entire height that its thickness is a fraction of that of the cooled body 7. For example, the lip 22 has a thickness at most equal to 1/3 of the thickness of the body 7, just before the rounded from its connection with this body, and an axial dimension at least equal to the thickness of the body 7 of the die and currently equal to 1.5 times this thickness.

The lip 22 is surrounded by a refractory ring 24, for example made of silico-aluminex material, having good thermal insulation characteristics. The ring 24 is adjusted on the lip 22 of which it matches the external profile and constitutes, with this lip, the composite head 17 of the die 6. The shape and the width of the ring 24 allow this head to be adjusted on the internal wall of the orifice 4 and thus of authorizing the flow of the liquid iron only between the lip 22 and the core 8.

In use, the thin annular lip has its upper end in direct contact with the liquid iron F contained in the casting basin 1 and is connected with the thick body 7 of the die 6, just at the upper limit of the energetic cooling of this die 6 through the cooling jacket 15.

The horizontal and flat upper edge 25 of the ring 24, which is flush with the upper end of the lip 22, is also in contact with the liquid iron F of the basin 1. On the other hand, its lower edge is in contact with the cylindrical body 7 and with the rounding 23 connecting the lip to this body in the plane P.

From the start of the casting, and during all the time that it lasts and that, consequently, the annular space 10 is filled with cast iron, the whole of the composite head 17 of die is therefore kept in a hot zone , since it is in contact with liquid iron by its upper horizontal edge and by the inner cylindrical face of the lip 22.

Cooling can only come from the cooling jacket 15. A cooling flow passes through the conductive graphite of the lip 22 and of the body 7, but cannot pass through the refractory material of the ring 24. As a result, the flow of cooling created between the liquid iron and the cooling jacket follow the paths indicated by the arrow lines f ₁ in dotted lines and f ₂ in broken lines in FIG. 2.

The calories of the liquid iron located above the head 17 of the die and that which is contained in the annular space 10, inside the lip 22, go to the cooling jacket 11, according to the dotted line f ₁ . This flow f ₁ ι corresponds in fact to a small escape of calories, due to the fact that the graphite lip 22 (coefficient of conductivity: 70 to 100 kCal / h / m ² / ° C). therefore a good heat conductor, has, on the one hand a small cross-section which offers a small section for the passage of calories, and on the other hand a significant length or height which slows down the heat flow f _{1 accordingly} , while the ring 24, which is made of refractory silico-aluminous material (conductivity coefficient: 0.5 to 3 kCal / h / m ² / ° C), opposes the passage of calories and must therefore be bypassed.

Thus, thanks to the composite head 17, or hot head, the liquid iron contained in the annular space 10, inside the lip 22 and the orifice casting 4, above the plane P, is relatively little cooled. We can even consider that it undergoes practically no cooling.

Below the horizontal plane P which is that of the connection of the thin lip 22 in graphite, as well as of the refractory ring 24, with the body of constant thickness of the die 7, that is to say with the part located below the upper limit of the cooling envelope 15, it is on the other hand fluxl2 much larger than the flux il which cause calories from the annular space 10 towards the cooling envelope 15. In fact, the passage section offered to the calories taken from the cast iron is much larger below the plane P since the body 7 of the graphite die, which conducts heat, has a thickness substantially greater than that of the lip 22.

The real and appreciable cooling of the cast iron therefore begins below this plane P, that is to say in the zone of the annular space 10 which is surrounded by the cooling envelope 15, and it is only below the plane P the cast iron will begin to solidify, as illustrated in Figures 1 and 2.

The lip 22 is not only in one piece with the body 7, but also its internal surface is exactly in the extension of the internal cylindrical wall 26 of this body 7 (and therefore carries the same reference numeral 26 ), so that the die has a continuous wall over its entire height and in particular between the hot zone located in the pouring orifice 4, above the plane P, and the zone cooled by the casing 11, below the plane P. This graphite wall continuity 26 offered to liquid cast iron is particularly advantageous since it exists at the start of the casting and is maintained during this, while the graphite die 6 heats up in contact with the cast iron liquid and therefore expands uniformly. As a result, the molding walls offered to liquid iron in the annular space 10, between the lip 22 and the thick body 7 on the one hand, and the core 8 on the other hand, remain continuous, which facilitates the downward flow of the cast iron and obtaining a tube T having a beautiful smooth and healthy outer wall, as well as a beautiful internal wall.

Any obstruction of the upper part of the tubular space 10 by at least partial solidification of the cast iron is thus avoided. Solidification begins on the contrary at the upper limit P of influence of the cooling jacket 15 to be complete at the lower end of the die 6, that is to say near the outlet thereof.

The solidification front is regular and continuous. There is no longer any risk of forming an inlay ring due to a difference in thickness such as that indicated at 28 in FIG. 6. In this figure, a die 36 of the prior art comprises a head 37 of frustoconical shape which , to the right of the body 2, has the same width as the body of the die and thins in the direction of the casting basin.

Because graphite is a good conductor of heat and that the section of the die head 37, above the plane P, is large (much larger than that of the composite head 17), the calories of the liquid iron F are taken by the cooling jacket 15 through the wide passage section offered by the die head above the plane P according to a flow f ₃ shown in broken lines. This flow f ₃ is much greater than the flow i _i because it crosses a much larger graphite passage section. As a result, solidification of the cast iron, although slow, begins in FS above the plane P.

At the level of the plane P the thickness of solidified cast iron FS can reach half the width of the annular space 10 and even the whole of this space, until it is blocked. Below the plane P, the cooling of the liquid iron is much more vigorous since the path of the flow of calories f ₂ to the cooling jacket 15 is much more direct, much shorter.

The plane P of separation between these two cooling zones therefore marks a clear difference in thickness of solidified cast iron, which at 28 presents a breakthrough at each extraction pass.

On the contrary, the composite head 17 of the die 6 of FIGS. 1 and 2 remains hot and avoids the cooling of the cast iron in this zone of the die, so that no solidification begins above the plane P. It is only below the plane P that solidification begins. The aforementioned serious defect is therefore avoided.

Furthermore, by virtue of its composite structure and the thickness of the refractory ring 24, the head 17 of the die is robust, offers no mechanical fragility because the ring 24 protects and externally strengthens the thinned lip 22, and thus ensures the continuity of the thickness of the die, including in the zone contained inside the pouring orifice 4.

Although the embodiment of FIGS. 1 and 2 is particularly advantageous, it is possible to produce in other ways a composite hot head of die comprising, on the one hand a graphite part of small section, providing a continuity of cylindrical wall to the flow of the cast iron in the annular space 10 and offering a small section for the passage of calories in the direction of the cooling jacket 15, and on the other hand an insulating refractory part, for example silico-aluminous.

Whatever the embodiment, however, the limit between the composite head and the body 7 of the die must remain the horizontal plane P, the body 7 having the same height as the envelope 15.

In fig. 3, the die head comprises, above the plane P, two thin concentric annular lips, respectively outer 32 and inner 22. The lips 22 and 32 are made of graphite since they are the continuity of the thick tubular body 7 of the die. The outer surface of the outer lip 32 is cylindrical to be applied exactly against the wall of the pouring orifice, while the facing surfaces of the two lips are slightly frustoconical and are separated by an insulating refractory ring 34, made of silico material -aluminous, in close contact with each of them, which of course is flush with their upper ends, in the same horizontal plane. These ends are in contact with the liquid cast iron of the casting basin when, as shown in solid lines, the refractory lining 3 is connected with the outer wall of the outer lip 32 of the composite die head. In this case, a double flow f _i of transfer of calories is established between the liquid iron contained in the pouring orifice 4 and the cooling jacket 15. These two flows i _i each pass through an annular lip 32 and 22. However, since these lips are thin, the loss of calories by these two fluxes remains very low and is not likely to cause a start of solidification of the melt above the plane P, that is to say in line with lips 22 and 32.

According to a variant, indicated in phantom, the refractory lining extends above the head and is connected with the internal wall of the internal lip 22.

As in the previous embodiment, the refractory ring 34 constitutes an obstacle preventing the passage of calories while ensuring mechanical reinforcement of the hot die head.

According to another embodiment, shown in FIG. 4, the composite die head comprises, above the plane P, a lip 42, the hollowed out external face 43 of which is concave in an obviously semitoric profile, which forms an upper rim or widening 44 joining the internal wall of the orifice. casting and a housing for a refractory ring, silico-aluminous, 45 with semi-toroidal conjugate profile and cylindrical external profile adjusted to the cylindrical internal profile of the pouring orifice 4. The flange 44 occupies the same annular width as the body 7 located below the plane P. But this upper rim 44 of large width, in contact with the liquid iron contained in the casting basin 1, is substantially thinned. In addition, it is reinforced and supported by the semi-toric refractory ring 45 located just below, so that the flow f _i of heat entrainment towards the cooling jacket 15 cannot spread over the entire annular width of this upper rim nor go directly towards the cooling jacket 15. On the contrary, the flow i ₁ must bypass the refractory ring 45 and cross a narrow annular section ab, between the refractory ring 45 and the tubular space 10 Therefore, the entrainment of calories by the flow f _i is weak.

Instead of being semi-toric, the hollowed out outer surface of the lip and the refractory ring may have a rectangular recess profile. Fig. 5 shows an embodiment of this type. In this figure, in fact, a graphite composite head has a thin internal lip 46, the hollowed out outer surface of which delimits two housings of rectangular section, which are filled by two refractory rings 48 and 49, concentric and of the same cylindrical shape (rectangular profile nearly). The two rings 48 and 49 are separated by a horizontal partition 50 made of graphite, formed by a circumferential fin of the lip 46 in contact with the refractory lining 3 and, consequently, not capable of providing a passage for calories. In addition, as in the embodiment of FIG. 4, the lip 46 has an upper rim or planar partition 52, which gives the graphite head a meridian profile at F. The upper section of this meridian profile at F can be either covered with refractory lining 3, if the latter is connected by a rounding (in solid lines) with the internal wall of the graphite lip 46, or in contact with liquid cast iron if the rounded connection is made along the line in broken lines, in the extension of the peripheral edges of the partitions 50, 52.

According to a variant, the lip 46 can be devoid of an upper rim 52; the upper insulating ring 49 is then, at its upper part, in contact with the lining 3, which gives the graphite lip a T-meridian profile.

As in the example in fig. 4, the passage section offered to the flow 1 ₁ for discharging calories to the cooling jacket 15 remains limited to the thinned vertical tubular lip 46 of the head.

Of course, the composite head may also include other arrangements of graphite lip and of ring opposing the passage of calories, depending on the installations.

In cases where the insulating ring 45 (fig. 4), 48, 49 (fig. 5), is not in direct contact with the cast iron, it is advantageous to choose for this ring a material having better qualities insulating, without needing the refractory properties required by contact with liquid iron. Thus, the rings 45, 48, 49 can be made of alumina fibers while the ring 24 can be made of silico-alumina concrete, the latter being much less insulating than the alumina fibers.

In these different variants, the height of a lip 32, 42, 46 above the plane P, and its average radial width, are similar to those of the lip 22 in FIGS. 1 and 2.

Finally, although the invention has been described for a vertical downward continuous casting installation comprising a tubular die, it also applies to an upward continuous casting installation with tubular die, the die head becoming the "foot" of the die and being immersed in the cast iron bath located at the bottom of the installation; it also applies to a horizontal continuous casting installation (the X-X axis being horizontal) or to an inclined continuous casting installation (the X-X axis being oblique).

Claims (9)

1. Continuous casting installation with a tubular die comprising a pouring basin (1) provided with a lower orifice (4), a jacket (15) for cooling the die mounted below the basin, along the extension of the inner wall of the casting orifice (4) and a heated core (8) which with the die (6) defines a narrow tubular casting space (10), which is coaxial with respect to the casting orifice (4), the die (6) comprising a thick cylindrical body (7) surrounded by the cooling jacket (15) and a head (17) projecting into the casting orifice (4), comprising a narrow annular lip (22, 32, 42, 46) with an inner surface (26) forming a continuous extension of the inner surface (26) of the body (7) of the die, which is connected to the latter opposite the plane of contact (P) between the basin and the cooling jacket the said installation being characterised in that the head (17) of the die (6) is composite and comprises at least one ring (23, 24, 45, 48, 49) of insulating material, which opposes the passage of heat, which surroundsthe lip (22, 32,42,46) and which is in contact with the body (7).

2. Continuous casting installation with a die according to Claim 1, characterised in that it comprises a second outer lip (32) which is coaxial with respect to the inner lip (22), separated from the latter by an annular space and is externally cylindrical in order to bear against the wall of the casting orifice, the refractory ring (34) filling the space between the two lips.

3. Continuous casting installation with a die according to one of Claims 1 and 2, characterised in that the lip (42, 46) comprises an upper rim (44, 52) and is recessed externally by at least one annular cavity for housing an insulating ring (45, 48, 49).

4. Continuous casting installation with a die according to Claim 3, characterised in that the recessed outer surface (43) of the lip (42) is concave and semi- annular.

5. Continuous casting installation with a die according to Claim 3, characterised in that the lip (46) comprises a lateral rib (50) forming a partition for the separation of two superimposed concentric rings (48, 49).

6. Continuous casting installation with a die according to one of Claims 1 and 2, characterised in that the radial width of the lip (22, 46) is approximately one third of that of the body (7) of the die.

7. Continuous casting installation with a die according to Claim 3, characterised in that the ring (48, 49) consists of insulating materials such as alumina fibres.

8. Continuous casting installation with a die according to Claim 1, characterised in that the lip (22, 32, 42, 46) has an axial height at least equal to the thickness of the body (7) and preferably one and a half times this thickness.

9. Continuous casting installation with a die according to Claim 1, characterised in that the insulating ring (24, 34) is flush with the upper end of the lip (22, 32).

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