EP0187609B1 - Apparatus for the rotating feeding of a cast to a vertical continuous-casting plant for spheroidal graphite cast iron tubes - Google Patents

Abstract

Installation comprising a reservoir crucible 11, 12 for molten cast-iron F with step-by-step extraction of a pipe T produced from the crucible comprising a cooled die. To obtain a cast-iron pipe of uniform thickness over its entire circular periphery, despite the absence of a core, the molten cast-iron F is set in slow rotation in the crucible by the tangential supply of molten cast-iron with a low rate of flow through a tangential orifice 18, by the rotation of a magnet 36 disposed in a hollow central relief 17 upstanding from the base of the crucible, by the rotation of paddle arms 44 disposed in the molten iron, or by the tangential injection of an inert gas.

Description

The present invention relates to the vertical upward continuous casting of a spheroidal graphite cast iron pipe, without the use of a core to form the pipe cavity.

The invention relates more particularly to a device for supplying liquid iron to a tubular die giving the external shape of the pipe, either from a siphon block (source supply), or from a ladle. under low gas pressure.

The rotary supply of a device for casting liquid metal, for example of cast iron, has been known for a long time for example by patent FR-493,449, with a view to centrifuging the liquid metal and obtaining a hollow body, and, a little more recently, by patent FR-1,122,833, with a view to homogenizing, that is to say uniformly distributing the liquid metal inside the mold or of the mold for continuous casting. However, this rotary supply does not cause the bath to rotate, in particular because the cast iron falls vertically, with no horizontal component of rotational speed.

More recently still, in patent FR-A-2 352 612, an installation for rotating liquid iron has been described at a centrifugation speed using a rotating magnetic field around a crucible containing liquid iron, in view of obtaining a cast iron tube by continuous ascending casting, without the use of a core.

However, the problem is posed of rotating a mass of liquid cast iron, at a speed lower than the centrifugation speed, with the aim of homogenizing and regulating the supply, inside a cooled tubular die. and fixed, giving the external shape of the tube to be generated, without the use of a core. The problem is to maintain a permanent movement of rotation of the liquid iron in the fixed and cooled tubular die in order to regularize the thickness of the iron tube obtained on each circular section of this tube and thus obtain inner walls and completely concentric exterior.

The invention relates to a device for feeding a fixed tubular die, which solves this problem.

This rotary liquid iron supply device for a vertical continuous casting installation of a spheroidal graphite cast iron pipe, comprising a cooled die constituting a crucible-reservoir for liquid cast iron, crucible from which a cast iron pipe to spheroidal graphite must be generated, and means for rotating the mass of liquid iron contained in said crucible-reservoir, is characterized in that the crucible-reservoir of liquid iron has a central refractory relief of the same vertical axis as the crucible -tank to reduce the mass of liquid iron to an annular mass.

According to an embodiment of the device of the invention, said impulse or rotation means are hydraulic means. The device of the invention is then characterized in that it comprises at the base of the crucible-reservoir at least one tangential inlet conduit for liquid iron which opens into the crucible-reservoir for liquid iron.

This tangential supply of liquid iron can be subjected to rhythmic pulsations which favor a slow rotation of the liquid iron.

These means for rotating may also be gaseous, with the use of a gaseous fluid chemically inert with respect to the cast iron (argon, nitrogen).

According to another embodiment, said means are magnetic. In this case, the supply device of the invention is characterized in that it comprises magnetic means housed inside the hollow central relief providing, with the cooled die, an annular chamber of liquid iron, over a higher height. to that of the annular volume of liquid cast iron, in order to create a magnetic field rotating around the axis of the die and of the central relief over the entire height of the annular mass of liquid cast iron.

In another embodiment, the impulse or rotary drive means are mechanical. In this case, the rotary feeding device of the invention is characterized in that it internally has a hollow central relief, in the axis and through the cavity thereof, a vertical rotating shaft carrying at its part upper of the vertical arms of refractory material immersed in the annular mass of liquid cast iron in order to cause it to rotate.

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

• la Fig. 1 est une vue schématique en coupe du dispositif d'alimentation suivant l'invention avec alimentation tangentielle en métal liquide, en complément d'une alimentation axiale,
• la Fig. 2 est une vue en coupe suivant la ligne 2-2 de la Fig. 1,
• la Fig. 3 est une vue schématique en perspective illustrant l'alimentation tangentielle en complément de l'alimentation axiale du dispositif de la Fig. 1,
• les Fig. 4-5-6 sont des vues schématiques en coupe analogues à la Fig. 1, de variantes de dispositif de l'invention avec moyens respectivement magnétiques, mécaniques et gazeux de mise en rotation de la fonte,
• la Fig. 7 est une vue en coupe suivant la ligne 7-7 de la Fig. 6.

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

• Fig. 1 is a schematic sectional view of the supply device according to the invention with tangential supply of liquid metal, in addition to an axial supply,
• Fig. 2 is a sectional view along line 2-2 of FIG. 1,
• Fig. 3 is a schematic perspective view illustrating the tangential supply in addition to the axial supply of the device of FIG. 1,
• Figs. 4-5-6 are schematic sectional views similar to FIG. 1, variant devices of the invention with respectively magnetic, mechanical and gaseous means for rotating the cast iron,
• Fig. 7 is a sectional view along line 7-7 of FIG. 6.

According to the embodiment of FIG. 1, the invention is applied to the continuous upward casting of a cast iron pipe T, said pipe being thin because the thickness / diameter ratio is low, less than 10%. The thickness of the barrel, i.e. of the tubular part already centering at nesting does not exceed 15 mm for a diameter of 1000 mm, 8 mm for a diameter of 300 mm and 5 mm for a diameter of 80 mm.

• - une alimentation en fonte liquide sous basse pression gazeuse,
• - un bloc-siphon pour alimentation tangentielle d'un creuset-réservoir de fonte liquide qui constitue les moyens hydrauliques précités d'impulsion ou de mise en rotation de la fonte liquide, et d'entretien de cette rotation,
• - un creuset-réservoir constitué par une filière tubulaire refroidie,
• - un extracteur non représenté du tuyau T formé.

The installation includes:

• - a supply of liquid cast iron under low gas pressure,
• - a siphon block for tangential supply of a crucible-reservoir of liquid iron which constitutes the aforementioned hydraulic means of impulse or of rotation of the liquid iron, and of maintenance of this rotation,
• - a crucible-reservoir constituted by a cooled tubular die,
• - an extractor not shown from the pipe T formed.

1. Axial supply of liquid iron under low gas pressure.

A teapot-type pressure casting ladle with a filler neck 2, oblique, closed by a cover 3 contains liquid iron F. A vertical pouring tube 4 made of refractory material passes through the upper wall of the closed teapot pocket 1. The tube 4 plunges almost to the bottom of the pocket 1 and rises well above the upper wall of the pocket to lead into the crucible-reservoir of the cooled die, described below, below which is placed the ladle 1. The ascending pouring tube 4 is tightly connected with the upper wall of the teapot ladle by a frustoconical nozzle 5 with flange, of axis XX like the tube 4. The frustoconical nozzle 5 is also used for the connection of the ascending flow 4 of axis XX with the siphon block described below.

2. Tangential feed in liquid iron by siphon block.

A base 6, made of refractory material, for example of the silico-aluminous type, internally comprises the lower part of an L-shaped casting duct 7 with horizontal or slightly oblique leg and with tangential orifice 18 vertical for a tangential supply at source. of the crucible-reservoir described below. The tangential orifice 18 has a smaller cross-sectional area than that of the ascending pouring tube 4. The base 6 serves as a support for the vertical casting conduit constituted by a vertical chimney 9 of axis YY parallel to the axis XX of the tube of vertical pouring 4. The vertical chimney 9 communicates at its lower part with the horizontal leg of the pouring duct 7 and ends at its upper part with a pouring funnel 10 of axis YY. The height of the chimney 9 is equal to that of the crucible-reservoir or of the die which is discussed below. The chimney 9 and the crucible-tank form communicating vessels. The horizontal duct 7 for casting has a diameter smaller than that of the tube 4. This supply assembly 6-7-9-10 is called blocksiphon.

3. The crucible-reservoir constituted by the cooled die.

In the axis XX of the axial ascending pouring tube, the base 6 of the siphon block carries a crucible constituted by a tubular die 11 in graphite of axis XX and by the base 6 itself constituting an uncooled bottom of the tank 12 .

The die 11 is cooled externally by a jacket 13, for example made of copper, with circulation of cooling water which enters via a pipe 14 and leaves via a pipe 15.

The jacket 13, in contact with the die 11, is arranged so as to wrap the die 11 over almost its entire height with the exception, however, of its lower part which remains uncooled. To this end, an annular support plate 16 of the liner 13, made of refractory material, for example of the silico-aluminous type, therefore thermally insulating, is interposed between the liner 13 and the base 6, in order to avoid cooling of the base 6 by the cooling jacket 13.

In this example, but not necessarily, the volume of the crucible-reservoir 11-6 constituted by the die 11 and the base 6 is substantially reduced and reduced to an annular volume by a central relief 17 of axis XX, coaxial with the pouring tube ascending 4, and crossed by it. The use of the central relief 17 is particularly advantageous for the casting of a tube T of large diameter. The central relief 17 is an integral part of the siphon block 6-7-9-10 and of the crucible-reservoir constituted by the combination of the base 6 and the cooled tubular die 11. The central frustoconical relief 17 has a large base, au- below the support constituted by the base 6, of diameter substantially less than the internal diameter that one wants to obtain for the tube T to be formed. A fortiori, the small upper base of the frustoconical central relief 17 has a diameter substantially smaller than that of the cavity of the pipe T to be obtained.

It is advantageous for the relief 17 to be higher than the die 11 because this makes it possible to limit the volume of liquid iron to an annular space over the entire height of the die 11 whereas if the central relief 17 was significantly lower than the die 11 there would be liquid iron above the top of the relief 17 and therefore an unnecessary excess of liquid iron.

The central relief 17 is hollowed right through, from its upper face to the lower face of the base 6 by a cylindrical cavity for the passage of the complementary pouring tube of the frustoconical nozzle 5 which adjusts in this interlocking. The tangential orifice 18 of the pouring duct 7 in L opens at the bottom, that is to say near the bottom of the annular volume of the crucible-reservoir 6-11, tangentially. Preferably, while the section for the passage of liquid iron through the vertical pouring tube 4 is as large as possible (axial supply of liquid iron under gas pressure), the section for the passage of liquid iron through the horizontal duct flow 7 in L to the tangential orifice 18, which is limited by the width of the annular space between the cooled die 11 and the central relief 17, at the base of the crucible-reservoir 6-11, is substantially less lower than that of the upward axial casting tube 4.

4. The extractor of the cast iron pipe being formed is not shown. It comprises a means for gripping the nascent cast iron pipe, for example a tubular mannequin or steel sleeve as described in patent application 84 00 382, said gripping means or mannequin M being caught between rollers or rollers E of guidance and drive up. For attaching or securing the nascent tube T to the mannequin M, the latter comprises a dovetail notch M1.

Operation

The description of the operation of the device of the invention is limited below to the rotation of the liquid pig iron inside the crucible-reservoir 6 - 11, that is to say in the annular space included. between the die 11 and the central relief 17, given that, once the liquid iron has started to rotate, the maintenance of this rotation continues in the same way and that the processes of step-by-step rise and solidification of the barrel T pipe in formation are the same as those already described in the patent application in France No. 8,400,382.

5. Liquid iron supply: this supply takes place in two phases,

a) Non-rotating main supply, under gas pressure, to fill the crucible-tank with die 11 and bottom 12 with cast iron F: pressurized fluid is introduced through the conduit 32 into the teapot pocket 3. The cast iron F rises to- above the central relief 17, pours into the annular space between the central relief 17 and the die 11 and rises in the vertical chimney 9 where the liquid iron is introduced from the orifice 18 and the horizontal leg of the conduit of casting 7.

The introduction of liquid iron F into the annular volume of the crucible-reservoir 11-12 and the vertical chimney 9 is continued until the level of liquid iron F is at N at the top of the die 11, just below the upper edge of the die 11 and the top of the central relief 17. In comparison with the following tangential feed, the axial feed is at high speed.

b) Tangential auxiliary supply in liquid iron, at low flow rate (hydraulic means of impulse in rotation): this supply for the renewal and rotation of the liquid iron does not take place immediately after the previous high flow supply since the upper level N is reached before starting to pour a pipe T, but at a time indicated below. This tangential, renewal, low-flow supply, which takes place along arrow f through the vertical chimney 9, and through the tangential orifice 18 will be described later. In comparison with the previous axial feed, the tangential feed is at low flow but at high speed.

2. Molding of the barrel of the cast iron pipe, and extraction of the pipe as it is formed:

The mannequin M is introduced into the die 11 from above. While the die 11 is not cooled at its lower end, it is instead cooled over most of its height, to its upper end, by the cooling jacket 13. The cast iron therefore solidifies at contact of the die in increasing thickness up to the mannequin M in contact with which it solidifies and on which it is hooked by the notch M1. The mannequin M is then pulled upwards by rollers or rollers E for driving and guiding. The rollers E driven by a stepping motor, cause the dummy M to rise in spurts. The mannequin M drives the solidified part of the iron upwards, step by step. When the manikin M has pulled upwards a primer of cast iron pipes T of sufficient height to be caught in turn by the rollers or drive rollers E, the manikin M becomes useless and can be separated at any time from the pipe T During the formation of this pipe leader T, it was necessary to pour liquid cast iron into the funnel 10 to replace or renew the quantity of cast iron which served to form said pipe leader T. We thus take care to keep constant the level M of the liquid iron during extraction, a little below the upper part of the die 11, at a height where the iron is still cooled by the casing 13.

This tangential supply takes place according to the diagram in FIG. 3. The liquid iron entering tangentially through the orifice 18 at the bottom of the annular volume comprised between the die 11 and the central relief 17, has a horizontal speed sufficient to rotate, gradually, at low speed, the entire annular mass of cast iron liquid F and to maintain this rotation of the liquid iron. Care is thus taken to keep the level N of liquid iron constant during the extraction of the pipe T, a little below the upper part of the jacket 11, at a height where the iron is still cooled by the cooling jacket 13 , while slowly rotating the cast iron F around the axis XX.

By thus rotating the cast iron slowly around the axis XX, the temperature of the liquid cast iron contained in the crucible-reservoir 11-12 is homogenized and the thickness of the pipe T is regulated on the circular section of the barrel of the pipe T in training. Said circular section therefore has perfectly concentric inner and outer walls.

The upward extraction of the solidified T pipe is carried out discontinuously, step by step, as described in patent application 8 400 382. The barrel primer of the T pipe lengthens at each climb stroke printed by the rollers or rollers E according to a constant thickness over the entire circular section of the barrel, thanks to the slow rotation due to the tangential supply of liquid iron by the vertical chimney 9 and the orifice tangential 18.

It will be recalled that the homogenization of the bath temperature is to a certain extent linked to the regularization of the thickness of the barrel formed with slow rotation of the liquid iron due to the solidification process of the liquid iron. The iron is a eutectic liquid, the solidification is very different from that of steels during solidification, the cast iron does not undergo the phenomenon of segregation and does not comprise a solid and liquid mixture. Cast iron is a eutectic liquid which suddenly passes from the liquid phase to the solid phase, without mixing the two phases and without dendrite. The Applicant has found that smaller thicknesses were obtained where the bath was warmer and greater thicknesses by homogenizing and regulating the temperature of the bath by rotation of the liquid iron. By this rotation it also obtains a more regular thickness on a circular section.

When a sufficient barrel length has thus been obtained for the pipe T, the pouring of liquid iron is stopped in the funnel 10 and the annular space between the die 11 and the central relief 17, for example by a lower orifice not shown from which the shutter is removed. It then suffices to completely lift the pipe T formed above the die 11.

To slowly rotate the liquid iron in order to homogenize the temperature of the bath and to regularize the thickness of the pipe T on its circular section, it is possible to use other means called "hydraulic" than those of FIG. 1 to 3.

Variant of Fig. 4.

In an example of execution similar to that of FIG. 1 but having certain differences, the so-called “hydraulic” means for slowly rotating the liquid iron are replaced by magnetic means.

Due to the space occupied by these magnetic means, as will be seen below, the aforementioned double supply in liquid iron is replaced by a single supply, by vertical chimney 9, after removal of the supply by pressurized teapot pocket. carbonated.

A central relief 34 blind at its upper part replaces the central relief 17 of FIG. 1. It comprises a cavity 35 for housing electromagnets or magnets 36 carried by a rotary shaft 37 of vertical axis XX which is that of the central relief 34 and of the crucible and reservoir 11-12. Inside the cavity 35, the magnets 36 and the shaft 37 are protected from any contact with the liquid iron. The magnets 36 extend over the entire height of the mass of liquid cast iron F. The rotary shaft 37 is rotated by a geared motor group 38. The rotation is carried out at slow speed as in the previous case , that is to say at a speed of the order of a few revolutions per minute while the centrifugation speed is much higher (for example from 10 times higher for large diameters to 100 times higher for diameters the weakest). Liquid cast iron is supplied by siphon block with vertical chimney 9, horizontal duct 7, opening at the lower part of the annular volume of liquid cast iron comprised between the central relief 34 and the die 11, possibly by a tangential orifice 18 as in fig. 1. But, in this case, due to the use of magnetic means such as electromagnets or rotary magnets 36, tangential orifice 18 is optional. The liquid iron supply duct can simply open out at the bottom 12 of the crucible-reservoir 11-12.

The barrel of the pipe T is formed in the same way as in the previous example of FIGS. to 2 with the only difference that the liquid iron, from the start only comes from the siphon block with vertical chimney 9 and that the slow rotation of the liquid iron takes place either only by the rotation of the electromagnets 36 or by the combined action of driving the electromagnets in rotation 36 and the tangential arrival of the liquid iron through a tangential orifice 18 if one is provided, as in FIG. 4.

Other means for slowly rotating the liquid iron can also be used:

Variant of Fig. 5:

In this example, a central relief 39 of axis XX, tubular, replaces the reliefs 17 and 34 above. The relief 39 is traversed right through by a cylindrical cavity 40 of axis XX, itself crossed with clearance by a rotary shaft 41 of axis XX driven in rotation by a geared motor group 42. The rotary shaft 41 carries to its upper part is a horizontal plate 43, or horizontal arms 42 at the peripheral edge from which or at the peripheral ends from which hang vertical graphite bars 44, for example two, three or four or more depending on the dimensions of the tray or arms 43 and the height of which is sufficient for their lower end to be immersed in the liquid iron of the crucible-reservoir 11-12 near the bottom 12 of the crucible-reservoir 11-12.

The liquid cast iron is supplied only by siphon block as in the example in FIG. 4, optionally with tangential orifice 18 at the bottom 12 of the crucible-reservoir 11-12. Inside this cavity 40, the shaft 41 is protected from any contact with liquid iron.

The formation of a pipe T which can be seen in FIG. 5 a solidified primer, attached to the mannequin M, is carried out as in the two previous examples, with the only difference that the slow rotation drive of the liquid iron takes place by the slow rotation of the drive bars 44 which make turn the bath around the XX axis

In all the previous examples, we note that the barrel of the pipe (Fig. 5) is obtained without a core, hence the usefulness of the slow rotation of the cast iron in order to regularize the thickness of the barrel on any which circular section of said barrel.

Gaseous fluidic means for rotating the liquid iron at low speed in rotation can also be used according to different exemplary embodiments illustrated in FIGS. 6 to 11:

Variant of Figs. 6 and 7:

The liquid cast iron is supplied by siphon block 7-9-10. The duct 7 opens out at the bottom 12 of the annular volume comprised between the central relief 17 and the die 11 by a non-tangential orifice 8.

In this example, an inert gaseous fluid such as for example nitrogen or argon is brought tangentially near the bottom of the annular volume of liquid iron comprised between the die 11 and the central relief 17.

The gaseous fluid for rotating the liquid iron is brought for example by two horizontal nozzles 45 mounted tangentially to the cylindrical cavity of the crucible-reservoir and to the cylindrical cavity 46 of the die 11, in the extension of the cylindrical internal wall of the die 11, in the mass of the base 6 and in the vicinity of the bottom 12. Each of the two nozzles 45 comprises a plug or a porous frustoconical nozzle 47 mounted at the bottom of an orifice also frustoconical which opens tangentially into the cavity 46, the nozzle porous 47 being of refractory material, for example silicoaluminous, (a sort of rammed earth with a large particle size to have a suitable porosity), a cylindrical sleeve 48 of the same diameter as the large base of the porous nozzle 47, the sleeve 48 being of material refractory and passing through the wall thickness of the base 6, coaxial with the nozzle 47, and, in the axis of the cylindrical sleeve 48, a duct 49 for supplying gaseous fluid to the porous nozzle 47, the duct 49 being connected to a source of gaseous fluid under pressure, not shown. A closure plate 50 is applied on the outer end edge of the cylindrical sleeve 48 and on a boss 51 coming from the body with the base 6 or else attached to the latter. The closing plate 50 is crossed by the conduit 49. There are therefore in this example two nozzles 45, two bosses 51, two conduits 49.

For the rotational drive at slow speed of the liquid iron supplied only by the ascending pouring tube 4, under gas pressure introduced into the teapot pocket 1, the insufflation of inert gaseous fluid such as nitrogen or argon by the two tangential nozzles 45 gradually pushes the liquid iron contained in the crucible-reservoir in a slow rotation movement according to the arrows f2 (Fig. 7). By simply varying the pressure of the gaseous fluid, the speed of rotation of the liquid iron is adjusted. This inert gas blowing is carried out in the form of fine bubbles distributed in the liquid iron thanks to the porous nozzles 47 interposed between the conduits 49 and the liquid iron.

It should be noted that in the absence of central relief 17, the energy of slow rotation of a greater mass of liquid iron than when the volume of iron is annular, is also greater, which results in a increase in pressure and flow rate of inert gaseous fluid through the nozzles 45.

There is yet another way of causing the cast iron to rotate slowly by gaseous fluid supplied tangentially:

Variant of Figs. 9, 10 and 11: instead of introducing the gaseous fluid by tangential nozzles 45 with porous plug 47, tangential injection nozzles are used directly blowing the inert gaseous fluid into the liquid iron contained in the crucible-reservoir 11-12 . Each injection nozzle is constituted by a frustoconical nozzle made of refractory material and is traversed by a conduit 53 and opening tangentially in a mouth 54 which is flush with the bottom 12 of the tank of the crucible-reservoir 11-12 devoid of central relief. In this example, the tangential injection nozzles 52 are eight in number. Each supply pipe 53 for supplying an injection nozzle 52 opens into a circular groove 55 serving as a distributor of inert gas under pressure. A single external conduit 56 controlled by a valve 57 brings the inert gaseous fluid under pressure to the circular groove 55. The circular groove for distributing and distributing inert gaseous fluid 55 is provided in the base 6, at the lower part thereof. . The liquid cast iron is supplied as in the example in FIG. 8 by teapot pocket and ascending pouring tube 4 emerging at the bottom 12 of the crucible-reservoir 11-12 in the axis XX of said crucible-reservoir.

Unlike the nozzles 45 with porous plugs 47 which inject numerous small gas bubbles, the injection nozzles 52 inject large gas bubbles into the liquid iron. But as the nozzles 52 open at the bottom 12 of the crucible-reservoir 11-12, instead of opening on the cylindrical wall of the crucible-reservoir 11-12, they reduce the friction of the liquid cast iron in rotation on the bottom 12. In addition , if the gas bubbles are injected at high speed, the kinetic energy for rotating the liquid iron is higher.

Finally, another means that can be described as hydraulic and pulsating has been devised to drive the slow-melting liquid iron in the crucible-reservoir 11-12:

Variant of Figs. 12 to 14: this variant uses as in FIG. 1 a tangential feed means. In this example, the central relief 17 creating a volume of annular liquid iron in the crucible-reservoir 11-12 has disappeared, but it could just as easily exist. The existence or the absence of the central relief 17 depends on the diameter of the pipe T to be formed. In this exemplary embodiment, the tangential supply of liquid iron near the bottom 12 of the crucible-reservoir 11-12 is carried out by a particular device of siphon block with pocket 58 under gas pressure. The pocket 58 of liquid iron F is of the skimmer type, comprising a vertical partition 59, a chamber 60 with a closed vault, receiving at its upper part at gas pressure by a conduit 32 controlled by a tap 33 from a well 61 open to its upper part by a funnel 62 for filling with liquid iron following an arrow f. The chamber 60 and the filling well 61 communicate through an orifice 63 formed in the lower part of the partition 59. The skimmer pocket 58 comprises at the lower part of the chamber 60 a horizontal or nearly horizontal pouring chute 64, of which the pouring duct is connected to the base 6 and opens tangentially into the cylindrical cavity 46 of the crucible-reservoir 11-12, near the bottom 12 of said crucible-reservoir by a tangential orifice 65.

The level of liquid pig iron in the crucible-reservoir 11-12 can vary between an upper level N situated at the upper part of the die 11 and a lower level N1 situated below the level N, not far from the top of the die 11 ; these upper N and lower N1 levels in the die 11 correspond to the same upper N and lower N1 levels in the well 61 of the skimmer bag 58, by effect of communicating vessels through the orifice 63 and the pouring chute 64. On the other hand, these upper N and lower N1 levels in the die 11 correspond to a lower level N2 in the chamber 60 and an upper level N3 which are different from N and N1. To obtain the upper level N corresponding to the lower level N2 in the chamber 60 under gas pressure, a maximum gas pressure P1 is required while to obtain the lower level N1 in the die 11, corresponding to the upper level N3 in the chamber 60 of pocket 58 requires minimum gas pressure P2.

To make a pipe, we proceed as described in the first example, using at the start a mannequin M not shown: we admit a maximum gas pressure P1 in a chamber 60 of a skimmer pocket 58, without pulsation of this pressure, to raise the cast iron in contact with the dummy M for good attachment, which causes a drop in the level of liquid cast iron from N to N2.

Then, to replace by liquid iron that which had solidified in contact with the mannequin M, the level of N2 to N is raised in the crucible tank 11-12, by introducing liquid iron following the arrow f into the well 61 of the skimmer pocket 58. Then the gas pressure in the chamber 60, through the conduit 32, is varied periodically and regularly between the maximum value P1 and a minimum value P2 while continuing to renew the liquid iron in the well 61 during step-by-step extraction. A gas pressure pulse is made according to the sinusoidal curve of FIG. 14 which is a diagram of the variation in gas pressure P admitted by the conduit 32 into the chamber 60 as a function of time t. At the maximum pressure P1 correspond respectively the levels N in the die and N2 in the chamber 60, and at the minimum pressure P2 correspond respectively the levels N3 in the chamber 60 and N1 in the die 11. This gas pressure pulsation which s' accompanied by a pulsation of liquid iron level in the crucible-reservoir 11-12 creates a pumping system for liquid pig iron arriving tangentially through the orifice 65. This pumping or pulsation or periodic gas pressure variation system for the tangential supply of the liquid iron creates a slow rotation of the liquid iron along the arrow f2 in the crucible-reservoir 11-12. By adjusting the pulse frequency and the pulse amplitude, i.e. the values of the pressures P1 and P2 (Fig. 14), therefore the levels N, N2 and N1, N3, the speed of the rotation of the liquid iron and a very regular thickness of formed tube is obtained.

Claims (10)

1. Apparatus for the rotary supply of molten cast iron to an installation for the continuous vertical casting of a pipe from spheroidal graphite cast iron, comprising a cooled die (11) constituting a reservoir crucible (11-12) for the molten cast iron, from which crucible a pipe (T) of spheroidal graphite cast iron is to be produced and means for causing the mass of molten cast iron in the said reservoir crucible (11-12) to rotate, characterized in that the reservoir crucible (11-12) for molten cast iron (F) has a refractory central relief (17-34-39) on the same vertical axis (X-X) as the reservoir crucible (11-12), in order to reduce the mass of molten cast iron (F) to an annular mass.

2. Apparatus according to Claim 1, characterized in that the said means for producing slow rotation are hydraulic means (7-18) consisting of a pipe (7) for the tangential inlet of molten cast iron which opens into the lower part of the reservoir crucible (11-12), in the vicinity of the bottom (12) of the latter through a tangential orifice (18).

3. Apparatus according to Claim 1, characterized in that the means for setting the mass of molten cast iron (F) in rotation are gaseous and consist of horizontal nozzles (45) which are tangential with respect to the reservoir crucible (11-12), in the vicinity of the bottom (12), the said nozzles (45) being intended to blow an inert gas into the mass of molten cast iron (F).

4. Apparatus according to Claim 3, characterized in that each nozzle (45) comprises a porous jet (47) of refractory material interposed between a blowing-in pipe (49) and the molten cast iron (F) in order to distribute the inert gas in the cast iron (F) in fine bubbles.

5. Apparatus according to Claim 4, characterized in that each nozzle (45) comprises a porous jet (47) opening tangentially into the cylindrical cavity (11-46) of the reservoir crucible (11-12).

6. Apparatus according to Claim 1, characterized in that the means (36-37-38) for setting the molten cast iron (F) in slow rotation are magnetic means consisting of magnets (36) supported by a rotary vertical shaft (37) driven by a speed-reducer unit (38), the magnets (36) being housed in a blind cavity (35) of the central relief (34) on the axis (X-X) coaxial with respect to the reservoir crucible (11-12), in the same way as the shaft (37) and the magnets (36) extending over the entire height of the mass of molten cast iron (F).

7. Apparatus according to Claim 1, characterized in that the means (44) for setting the molten cast iron in slow rotation are mechanical means consisting of vertical graphite bars (44) suspended from the peripheral edge of a horizontal plate (43) or from the ends of horizontal arms (43), the said bars (44) being set in rotation by a shaft (41) passing coaxially with clearance through a cylindrical cavity (40) in the central relief (39) on the vertical axis (X-X), the said shaft (41) being set in rotation by a speed-reducer unit (42) and the height of the bars (44) being sufficient for their lower end to be immersed in the molten cast iron (F) in the vicinity of the bottom (12) of the reservoir crucible (11-12).

8. Apparatus according to Claim 2, characterized in that provided in addition to a pipe (7) and a tangential orifice (18) opening into the lower part of the reservoir crucible (11-12) for setting the molten cast iron (9) hydraulically in slow rotation is a vertical tube (4) on the axis (X-X) for the axial and bottom supply of molten cast iron coming from a casting ladle under gas pressure (2) located below the reservoir crucible (11-12), the said vertical tube (4) having a section of passage greater than that of the tangential orifice (18).

9. Apparatus according to Claim 1, characterized in that the supply of molten cast iron is achieved by a siphon unit comprising a bottom pipe (7-8-9-10) opening into the lower part of the reservoir crucible (11-12).

10. Apparatus according to Claim 1, characterized in that the supply of molten cast iron is achieved by a casting ladle (1) under gas pressure comprising a bottom casting tube (4) on the same axis (X-X) as the reservoir crucible (11-12).

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