EP0379420B1 - Device and method for feeding with molten metal for pressure die casting metallic products - Google Patents

Abstract

PCT No. PCT/FR90/00033 Sec. 371 Date Sep. 10, 1991 Sec. 102(e) Date Sep. 10, 1991 PCT Filed Jan. 16, 1990 PCT Pub. No. WO90/08002 PCT Pub. Date Jul. 26, 1990.Device and method for feeding molten metal for the pressure casting of metal products. The device for feeding molten metal to a mould 1 of a continuous pressure-casting installation comprises a vessel 2 equipped with a cover 7 carrying a spout 3, the said vessel resting on a frame 4 and comprising a framework 9 for supporting a ladle 10 of molten metal, means for weighing the said ladle and means 20 for raising the said framework. The casting method implementing this device is characterized in that, during the cast, when the quantity of metal in the ladle 10 is greater than a specific quantity, the ladle is held in a low position (position according to reference 32) and, when the quantity of metal becomes less than the said specific quantity, the ladle is raised (position 32') so as to hold the lower end 31 of the spout below the level of the metal contained in the ladle.

Description

The present invention relates to an installation for the pressure casting of metal products, in particular steel slabs. It relates more precisely to the device for supplying liquid metal to the mold according to the preamble of claim 1 and a method according to the preamble of claim 15. Such a device and such a method result from the knowledge of a person skilled in the art.

The well-known principle of die casting consists in supplying liquid metal to the mold at its lower part by means of a table of refractory material immersed in a pocket containing the molten metal, which is subjected to a pressure higher than that prevailing in the mold, the latter being generally atmospheric pressure. To this end, the bag is enclosed in a sealed tank supplied with pressurized gas. The tube passes through a removable cover of the pocket and its upper end is connected to the mold by means of a shutter itself fixed to the mold at its lower part. Under the effect of the gas pressure, the liquid metal of the ladle is pushed into the tube, then into the mold which it gradually fills. When the mold is filled, the shutter is closed, thus preventing the metal contained in the mold from flowing when, after the casting, the pressure of the tank is brought back to atmospheric pressure. The tank can then be moved on a trolley to another mold or to a waiting area where the cover of the tank is removed to allow the bag to be removed for its subsequent filling with liquid metal.

Installations of this type are known in particular in which a mobile carriage constitutes the carrying frame of the tank. The bag is held in the tank on a frame resting on the bottom of the tank, load cells being placed between the frame and the tank, in order to permanently measure the weight of the pocket and therefore of the liquid metal it contains . This measurement is used in particular to control during and at the end of casting the quantity of liquid metal remaining in the pocket. It is indeed necessary to know this quantity at the end of filling a mold, to ensure that it is sufficient to completely fill the next. It is especially necessary to control it during casting to prevent the metal level in the ladle from falling below the lower end of the pouring tube, which would allow gas under pressure to enter the tube at the expense the quality of the cast product, and especially the safety, this gas may cause dangerous projections of liquid metal out of the mold.

Therefore, and also because the lower end of the tube is necessarily at a certain distance from the bottom of the pocket to allow the passage of the liquid metal, it follows that a significant amount of liquid metal remains in the pocket in end of casting, which greatly reduces the efficiency of the installation. It is therefore desirable to reduce this bottom of the pocket as much as possible. A known solution consists in providing in the bottom of the pocket a bowl with a section slightly larger than that of the tube, but much smaller than that of the pocket, and in extending the tube so that its lower end penetrates into the bowl. Thus the quantity of metal which must remain at the bottom of the pocket is notably reduced.

However, this solution has the disadvantage of limiting the passage section between the tube and the bowl, which leads to increased erosion of the latter and of the lower end of the tube. In addition, the impurities in the metal bath and those produced by the erosion of the refractory material of the bowl and of the tube therefore tend to be entrained in the mold, which is detrimental to the quality of the cast product.

Another disadvantage is that to bring the lower end of the tube closer to the bottom of the bag, the length of the latter must be increased. The fragility of the tube is then increased, and the fact that it is only held at its upper part in the tank cover, the risk of breaking it is all the greater, especially when moving the carriage tank, or during the various handling of the cover carrying the tube, when it is placed on the tank.

In known die-casting installations, the bag rests on a bag-carrying frame bearing on the bottom of the tank, the latter being fixed by its ferrule to the chassis of the carriage. This arrangement has the disadvantage that the entire weight of the bag, in particular when it is full of liquid metal, is supported by the tank, the shell of which is then subjected to high stresses and which must therefore be strong enough to support this charge. It follows that the constituent elements of the tank must be largely dimensioned, which increases the weight of the tank and complicates its manufacture.

Yet another disadvantage is that in installations of the type described above, the devices for measuring the weight of the bag are located in the tank, under the said bag, and risk being easily damaged in the event that molten metal would overflow from it.

The object of the present invention is to solve the various problems mentioned above and in particular to limit as much as possible the quantity of liquid metal remaining in the pocket after the pouring (s).

Another object is to reduce the wear of the pocket bottom and the tube.

With these objectives in view, the object of the present invention is a device for supplying liquid metal to a mold of a die-casting installation, comprising a tank provided with a cover carrying a pouring tube, said tank resting on a frame and comprising a support frame for a liquid metal pocket, and means for weighing said pocket.

According to the invention, the device is characterized in that it comprises means for lifting said frame relative to said tank. These lifting means are provided for lifting the bag when the quantity of metal it contains is reduced so as to bring the lower end of the pouring tube closer to the bottom of the bag.

According to a particular arrangement of the invention, the pocket support frame comprises arms, extending radially and bearing on the weighing and lifting means distributed around the periphery of the tank and supported by the chassis.

Thanks to this particular arrangement, the weight of the bag is directly supported by the chassis, and the stresses applied to the tank are therefore greatly reduced, the latter being no longer subject to its own weight, and to the stresses due to the pressure of the gas which is injected there for the casting.

Another advantage of the device according to the invention is that, when the pocket contains sufficient liquid metal, the end of the tube can be kept relatively far from the bottom of the pocket, thus limiting the problems of erosion and the risks of pollution of the metal mentioned above. When the metal level in the pocket arrives near the bottom of the pocket, this is raised by the lifting means, which allows maximum use of the metal remaining in the bottom of the pocket, and it is therefore only at the end of emptying of the pocket that the passage section between tube and pocket bottom is reduced.

Yet another advantage is to shield the weighing and lifting means from the risks of deterioration by an overflow of liquid metal, by placing them at a sufficient distance from the pocket.

According to a particular arrangement of the invention, said lifting and weighing means are three in number, which ensures the isostatism of the pocket support frame and they are placed in cavities formed in the wall of the tank, s' extending beyond the perimeter thereof and closed by removable caps. As a result, said lifting and weighing means are protected from possible metal overflows, and are more easily accessible for maintenance from the outside of the tank. Sealing means are provided, at the weighing and lifting means, between the tank and the chassis, to seal the tank.

The invention also relates to a method for supplying liquid metal to a die-casting mold, using in particular the device according to the invention, this method being characterized in that, when the quantity of metal contained in the bag is greater at a predetermined quantity, the pocket is held in a low position, where the lower end of the pouring tube is far from the bottom of the pocket, and when the quantity of metal contained in the pocket becomes less than said predetermined quantity, one raises said bag without modifying the position of the tube, the lifting height being determined as a function of the level of liquid metal in the bag, this level being determined from the weight of the bag measured by the weighing means, so as to maintain the lower end of the tube below said metal level.

In addition, the lifting speed is determined so that the residence time of the tube at the bottom of the bowl is reduced in order to avoid too rapid erosion of the end of the tube and of the refractories of the bowl.

Other characteristics and advantages will appear in the description which will be given by way of example of an installation and of a pressure casting method according to the invention.

• la figure 1 est une vue schématique partielle en coupe d'une installation de coulée sous pression montrant la disposition générale de la cuve, de la poche et des moyens de levage de cette dernière,
• la figure 2 est une vue de dessus du cadre support de poche montrant la localisation des moyens de levage de celui-ci,
• la figure 3 est une vue en coupe d'un des moyens de levage et de pesage,
• la figure 3a est une vue schématique du même moyen de levage et de pesage montrant son principe fonctionnel,
• la figure 4 est une vue en coupe axiale des moyens de fixation du tube sur le couvercle de cuve, montrant deux variantes de ces moyens de fixation,
• la figure 5 est une vue de dessus de ces moyens,
• la figure 6 est une vue de dessus partielle de la cuve montrant la disposition des mécanismes de verrouillage du couvercle,
• la figure 6a est une vue agrandie d'un ensemble de deux de ces mécanismes,
• la figure 7 est une vue schématique en coupe d'un des mécanismes de verrouillage du couvercle,
• la figure 8 est une vue de détail d'une autre variante des systèmes d'amortissement de pose et de dépose du couvercle de cuve.

Reference is made to the appended drawings in which:

• FIG. 1 is a partial schematic view in section of a pressure casting installation showing the general arrangement of the tank, the bag and the means for lifting the latter,
• FIG. 2 is a top view of the pocket support frame showing the location of the lifting means of the latter,
• FIG. 3 is a sectional view of one of the lifting and weighing means,
• FIG. 3a is a schematic view of the same lifting and weighing means showing its functional principle,
• FIG. 4 is a view in axial section of the means for fixing the tube to the tank cover, showing two variants of these fixing means,
• FIG. 5 is a top view of these means,
• FIG. 6 is a partial top view of the tank showing the arrangement of the lid locking mechanisms,
• FIG. 6a is an enlarged view of a set of two of these mechanisms,
• FIG. 7 is a schematic sectional view of one of the mechanisms for locking the cover,
• Figure 8 is a detail view of another variant of the damping systems of installation and removal of the tank cover.

In Figure 1, we see the tank and the mold in the casting position. The mold 1, of which only the lower front part, comprising the supply orifice 11 in liquid metal, is shown, comprises two large walls 12 arranged face to face. These walls 12 are separated by spacers 13, 14, 15 forming the small walls of width corresponding to the thickness of the cast product. The substantially horizontal lower spacer 13 is supported by a chassis 16 which can tilt slightly around a horizontal axis, not shown, located substantially at half the total length of the mold, so as to bring the opening of the supply 11 to the tank 2. The substantially vertical front spacer 15 closes the mold at its front part and the upper spacer 14 closes it at its upper part. A fourth spacer, not shown, closes it at its rear. The assembly of walls 12 and the spacers thus forms a generally rectangular cavity of dimensions corresponding to the dimensions of the casting, here a steel slab.

The supply orifice 11 is provided in a conventional manner with a shutter shown diagrammatically at 17, the underside of which comes into sealing abutment, during casting, on the upper end of the pouring tube 3.

The liquid metal supply device comprises a tank 2 carried by a chassis 4 of a carriage 5, making it possible to move the entire device to bring it into the pouring position or remove it from this position. The tank 2 rests on the chassis 4 by means of support pieces 6 welded to the shell 21 of the tank.

The tank has a cover 7 and locking means 8 for this cover on the tank.

Inside the tank is deposited a pocket holder frame 9 on which the pocket 10 containing the liquid metal rests. The pocket holder frame 9 is carried by arms 91 which are linked to it in a removable or eclipsable manner. The arms 91 extend towards the outside of the tank, beyond the ferrule 21 forming the vertical wall of the tank and determining the perimeter, and are supported on the chassis 4 by means of weighing means 20 ′ and lifting 20.

The bottom of the tank is covered with a refractory lining 22, and the space 23, determined by this bottom and located below the pocket holder frame 9, is provided so as to have a sufficient volume to collect practically all of the liquid metal which the pocket 10 can contain, in case the latter accidentally leaks from the latter.

The carriage 25 also carries in 5 ′ and 5˝ the equipment necessary for supplying the tank with compressed air and the equipment for the weighing and lifting systems of the bag.

The pouring tube 3, made of refractory material, dips into the pocket 10 up to a level close to the bottom of the latter, but leaving, when the pocket 10 is in a low position (shown in solid lines in FIG. 1) a passage section largely dimensioned between the lower end 31 of the tube and said bottom 32, so that the liquid metal contained in the pocket can, during casting, penetrate into the casting tube 11 with a reduced speed at this level. passage.

The bottom of the bag 10 comprises a bowl 33 of section slightly greater than that of the pouring tube 3, so that in a high position of the bag (shown in phantom 32 ′) the lower end 31 of the tube enters the bowl 33, a short distance from the bottom of this bowl. The purpose of this arrangement will be explained in more detail below, in conjunction with the description of the means for lifting the bag.

In Figure 2 is shown a top view of the pocket holder frame 9. This comprises three legs 92 extending radially outward and on which are welded gussets 92 parallel vertical. Between the gussets 93 of the same leg 92, is inserted the vertical part of an arm 91 in swan neck whose horizontal part 91 ′ extends radially outwards, beyond the ferrule 21 of the tank 2 , an opening 24 being provided for this purpose in the shell. The arm 91 is held on the gussets 93 by means of two pins 94, 95 of horizontal axis arranged one above the other.

The arms are thus removable from the frame 9, by simple disassembly of the pins, which allows, if necessary, to extract upwards the frame 9 from the tank 2 without this extraction being hampered by the horizontal parts 91 ′ Protruding arms 91. If this operation proves necessary, it is even more advantageous to deposit only the upper pin 94, the arm 91 then being able to pivot inwards, as shown in phantom lines marked 91˝ in FIG. 3, by rotation around the lower pin 95. The arms 91 can then slip away in a position inscribed inside the perimeter of the tank while remaining integral with the pocket-carrying frame 9, without interfering with the wall of the ferrule 21 during the extraction of said frame.

The weighing and lifting means of the bag will now be described in detail, in conjunction with FIGS. 3 and 3a.

As indicated above, the horizontal part 91 ′ of the arms 91 extends towards the outside of the tank through the opening 24 made in the shell 21, beyond the perimeter of the latter. The end of this horizontal part rests on the weighing means 20 ′ and lifting 20, which rest on one of the parts 6 for supporting the tank on the chassis 4 of the carriage.

Each of the lifting means 20 comprises a screw jack 25 placed in abutment on the support piece 6, and a force transmission device 50. This force transmission device comprises a guide column 52 which can slide in a sheath 51 welded to a support 51 'rigidly held on the support piece 6. A seal 53 is interposed between the column 52 and the sheath 51.

The column 52 has at its upper part a shoulder 54 capable of coming to bear on the upper end of the sheath 51.

The column 52 has a blind vertical lower bore 55 in which is placed, with play, a lower push rod 56. An upper ball 56 ′ is interposed between the rod 56 and the bottom of the bore 55, and a lower ball 56 ˝ likewise interposed between the link 56 and the movable rod 25 ′ of the jack 25.

An upper thrust link 57 is mounted in an equivalent manner in an upper blind bore 58 of the column 52. This link 57 is held in the bore 58 by an elastic sleeve 59 allowing the respective free expansion of these two parts, as well as a certain horizontal displacement of one relative to the other. A ball 57 ′ is interposed between the link 57 and the bottom of the bore 58. Another ball 57˝ is interposed between the upper end of the rod 57 and a support rod 60 of a load cell 61 placed in a recess 96 at the end of the horizontal part 91 ′ of the arm 91. The load cell is also held in abutment by its upper end opposite the support rod 60, in the bottom of the recess 96 in the arm 91.

The support rod 60 of the load cell is held fixed horizontally relative to the arm 91, by means of a double stabilization membrane system 62, which leaves the support rod 60 free to move slightly vertically under the effect of the load, while holding it horizontally and guiding it vertically.

To ensure the tightness of the tank at the level of the passage of the arms 91, a sheet metal casing 26 is welded to the shell 21 of the tank around the orifice 24. This casing is provided with an inspection cover 27 allowing a easy access to the weighing means 20 ′, after pivoting of the arm 91.

The casing 26 has at its lower part an opening 28 through which the guide sleeve 51 passes freely, a clearance being made between these two parts. The tightness of the tank is ensured by a bellows seal 63 interposed between the casing 26, at the periphery of the opening 28, and the support 51 ′ of the sheath 51.

• L'implantation du mécanisme de levage 20 à l'extérieur de la cuve évite tous les éventuels problèmes de protection de celui-ci contre la chaleur, les projections d'acier et les éventuelles percées de poche.
• Le supportage de la poche en trois points est parfaitement isostatique, ceci se traduit par un supportage stable et fiable de la poche.
• Le cadre support de poche 9 est constitué d'un simple caisson circulaire sans mécanismes compliqués. Les seuls éléments quelque peu mécaniques sont les bras 91 en col de cygne amovibles qui permettent de placer le cadre à l'intérieur de la cuve aussi bien que de le démonter.
• Les trois points de supportage sont pourvus de pesons 61 avec membranes de stabilisation 62 et biellettes flottantes 57 destinées à compenser les déplacements horizontaux dûs soit à la flexion mécanique sous charge du cadre, soit aux dilations thermiques inévitables dues à la température régnant à l'intérieur de la cuve.
• Les vérins à vis de levage 25 sont à la fois extérieurs à la cuve et solidaires de celle-ci sans pour autant faire reposer le poids de la poche sur la virole de cuve elle-même. Cette disposition permet d'éviter de solliciter la virole par les charges dues à la poche et à l'acier qu'elle contient tout en conservant les positions relatives des points de levage et de la virole, même après dilation thermique.
• Les carters 26 de la cuve dans lesquels sont logés les mécanismes de pesage sont munis de couvercles amovibles qui en facilitent l'inspection et l'entretien.
• Les rotules des biellettes de poussée et de support du cadre porte-poche permettent d'éviter de créer dans les colonnes de levage des efforts horizontaux néfastes car incontrôlables, ainsi la durée de vie des éléments en est nettement améliorée.
• Les biellettes de poussée supérieures 57 sont centrées par les manchons élastiques 59 qui laissent libre les déformations thermiques ou flexions mécaniques tout en maintenant centré l'ensemble porte-poche.
• Les joints à soufflet 63 entre les carters de cuve et les supports des fourreaux de guidage permettent d'éviter les usinages délicats de la cuve et autorisent un positionnement précis des colonnes par rapport au support de poche sans pour autant imposer des tolérances de fabrication difficiles à obtenir. De plus ces soufflets absorbent les dilations différentielles entre la virole 21 de la cuve et les appuis 6 des vérins de levage.

The various advantages resulting from the arrangement which has just been described are listed below:

• The installation of the lifting mechanism 20 outside the tank avoids all possible problems of protection of the latter against heat, steel projections and possible pocket breakthroughs.
• The support of the pocket in three points is perfectly isostatic, this results in a stable and reliable support of the pocket.
• The pocket support frame 9 consists of a simple circular box without complicated mechanisms. The only somewhat mechanical elements are the removable gooseneck arms 91 which allow the frame to be placed inside the tank as well as to be disassembled.
• The three support points are provided with load cells 61 with stabilization membranes 62 and floating rods 57 intended to compensate for the horizontal displacements due either to the mechanical bending under load of the frame, or to the inevitable thermal dilations due to the prevailing temperature inside of the tank.
• The lifting screw jacks 25 are both external to the tank and integral with the latter without however resting the weight of the pocket on the tank shell itself. This arrangement makes it possible to avoid stressing the shell by the loads due to the pocket and to the steel which it contains while retaining the relative positions of the lifting points and of the shell, even after thermal expansion.
• The casings 26 of the tank in which the weighing mechanisms are housed are provided with removable covers which facilitate inspection and maintenance.
• The ball joints of the push rods and of the support for the pocket holder frame make it possible to avoid creating in the lifting columns harmful horizontal forces since they are uncontrollable, thus the lifetime of the elements is clearly improved.
• The upper push rods 57 are centered by the elastic sleeves 59 which allow free thermal deformations or mechanical flexions while keeping the pocket holder assembly centered.
• The bellows seals 63 between the tank casings and the supports of the guide sleeves make it possible to avoid delicate machining of the tank and allow precise positioning of the columns relative to the pocket support without imposing manufacturing tolerances which are difficult to get. In addition, these bellows absorb the differential expansions between the shell 21 of the tank and the supports 6 of the lifting cylinders.

It will be noted that, in the low position of the pocket-carrying frame, its weight and that of the pocket are transmitted to the chassis via the shoulders 54 of the columns 52 which bear directly on the sheath 51. In this position a clearance , clearly visible in Figure 3, is formed between the upper ball 56 'of the lower thrust link 56 and the bottom of the bore 55 of the corresponding column. Thus in this position, the lifting cylinders are not stressed. This arrangement is particularly advantageous because, as will be explained below, the bag is kept in the low position as long as the quantity of liquid metal it contains is large, and it is only lifted at the end of draining. In this way, the lifting cylinders are only used when the weight of the pocket holder and pocket frame assembly is the lowest, which allows the use of lifting cylinders of lower capacity.

We will describe in connection with Figures 4 and 5 the means of fixing the pouring tube on the cover of the tank.

To this end, the cover is provided in its central upper part with a reinforcement 71 comprising a central bore 72 for the passage of a collar 73 which encloses the pouring tube 3, a refractory joint 74 cast between the collar 73 and the tube 3 ensuring their tight connection.

A frustoconical machining is carried out in the cover reinforcement 71, constituting a frustoconical seat 75, 75 ′ for a spherical bearing 76, 76 ′ of an annular part or ring 77, 77 ′ supporting the collar 73. This arrangement constitutes a system with ball joint which allows a certain clearance in the positioning of the ring on its seat, while maintaining the tightness of the connection.

A first embodiment is shown in the right part of FIG. 4 and in FIG. 5, in which the right part represents the fixing of the ring 77, and the left part the fixing of the upper flange 83. In this mode embodiment, the ring 77 ′ is held in abutment on the frustoconical seat 75 ′ by fixing members 78 called toads. These toads are bolted to a support wedge 79 welded to the reinforcement 71 and comprising a groove 80 receiving the head of the bolt 81. Shims of adjustable thickness 82 are interposed between the toads 78 and the support wedges 79. changing the thickness of these shims, it is possible to slightly modify the seat of the ring 77 ′ on its seat and thus adjust the verticality of the pouring tube 3. The collar 73 is kept pressed against the ring 77 ′ By a flange 83 fixed to the reinforcement 71 by bolts 85, the head of which engages under hooking pieces 84 welded to the reinforcement 71.

In the second embodiment shown on the left-hand side of FIG. 4, the annular part or ring 77 has at least three circumferentially distributed legs 86, under which springs 87 are placed which hold the tube 3 suspended in a flexible manner. absence of effort exerted vertically on the upper end thereof. In this case, a vertical clearance remains between the spherical bearing surface 76 of the ring, and the seat 75 of the cover reinforcement 71. When the mold 1 of the casting installation is tilted into the casting position (as shown in FIG. Figure 1) the lower part of the closure device 17 presses on the upper end of the tube 3. The springs 87 are compressed and the ring 77 rests on reference blocks 88 which determine the attitude of the ring and consequently the position of the tube. The thickness of the reference shims 88 is preset so that the spherical bearing surface 76 of the ring 77 is pressed with sufficient force on the seat 75 to ensure the tightness of the contact, when the tabs 86 are supported on the shims of reference 88. In this variant, the tube and the collar 73 are preferably rigidly held relative to the ring 77 by clamping the flange 83 on said ring.

The two embodiments which have just been described essentially have the aim of facilitating the adjustment of the position of the tube 3, so that its lower end 31 is in perfect match with bowl 33 in the pocket. The difficulty of this positioning stems from the fact that numerous causes of eccentricity exist, originating from defects in concentricity and parallelism of the various elements present, in particular deviations in positioning of the pocket 10 in the tank 2, of the cover 7 relative to to the tank 2, and the tube 3 relative to the collar 73, as well as possible deformations of the cover and the tube. All of these causes can result in an eccentricity of the lower end of the tube 3 relative to the bowl 33 of the pocket bottom, of the order of 80 to 100 mm.

It is therefore necessary to regularly check and adjust this positioning to prevent the lower end of the tube from hitting the bottom of the bag when the latter is brought into the high position. In installations according to the prior art, in which the tube is clamped directly on the cover, this adjustment could only be made by remanufacturing the bearing surface of the flange on the cover, or by insertion of an annular wedge wedge between the cover and flange.

Thanks to the fixing system according to the invention, this adjustment is greatly facilitated due to the spherical bearing of the intermediate annular part 77, 77 ′ which can swivel on the conical seat 75, 75 ′, while retaining the tightness of the tank at this connection.

In the first variant described above, it suffices to make this adjustment to modify the thickness of the adjusting shims 82 in order to adjust the seat of the ring 77 ′ on its seat 75 ′, and therefore the position of the tube 3.

In the second variant, it is the reference shims 88 which determine the seat of the ring 77, when the mold is tilted in the casting position and presses on the upper end of the tube. In addition, in the absence of force on this end of the tube, the assembly of the tube 3, of the collar 73 and of the ring 77 are slightly raised relative to the cover by the springs 87, which ensures a certain freedom of movement of this assembly relative to the cover. This avoids, for example during the movement of the carriage 5, creating significant stresses in this fixing assembly, subjected to the effects of the inertia of the tube and possible jolts during movement, constraints which would risk causing breakage. of tube if it was linked to the cover by a rigid fitting.

In connection with FIGS. 6 to 8, a description will now be given of the means for locking the cover 7 on the tank 2.

Generally known, in order to ensure the tight closure of the tank 2 by the cover 7, these are respectively provided with flanges 101, 102, designed to come into tight contact with one another. In the particular arrangement of the lid locking means on the tank according to the invention, these means comprise a plurality of C-shaped locking pieces, hereinafter called "cés" 103, distributed circumferentially at the periphery of the tank and the upper 104 and lower 105 branches of which enclose the flanges 101, 102 in the locked position. Ces 103 are pivotally mounted on the tank by means of pivots 106 of vertical axis fixed on the flange 102 of the tank beyond the outer perimeter thereof. The lower branch 105 of the block 103 carries a stop 107 directed towards the inside of the block provided for resting, in the locked position, on a support plate 108 fixed under the underside of the tank flange 102.

The upper branch 104 of the cé has a bore 109 of vertical axis in which is placed a hydraulic cylinder 110 whose head of the movable rod 111 is supported, in the locking position and when the cylinder is pressurized, on a second support plate 112 fixed on the upper face of the cover flange 101.

Thus, in the locking position, the tank flange 102 and the cover flange 101 are pressed one on the other, between the stops 107 and the heads 111 of the jacks, the latter ensuring the clamping pressure. As the cylinders are supplied from the same source, the clamping pressure is uniform over the entire periphery of the tank.

The position of the axis of the pivots 106 is such that, by pivoting the ces 103 around this axis, the upper branch 104 can be brought into a release position 104 ′ (shown in phantom in Figure 6a) in which the cover 7 can be lifted without its flange 101 interfering with said upper branch 104. To this end the cé 104 has a tab 113 located at the height of the cover flange 101, and forming a lateral projection of the cé. The pivot 106 passes through a bore produced in this lug 113, which can thus pivot on this pivot. A washer 114 aimed at the upper end of the pivot prevents release accidental from the cé upwards. A vertical clearance is provided between the tab 113 on the one hand of the washer 114 and the upper surface of the fixing piece 115 of the pivot on the flange 102 on the other hand, so that the web 103 has a certain latitude of movement vertical, when the tightening force applied by the jack 110 tends to move the block upwards to press its stop 107 against the support plate 108 of the tank flange.

To ensure the pivoting of these, these are grouped functionally in pairs. The two ribs 103, 103 ′ of the same pair are adjacent and connected to their rear part 117 opposite the branches 104, 105, by a double-acting hydraulic cylinder 116. Each of the pivots 106, 106 ′ of the two ribs 103, 103 ′ of a pair, is offset laterally with respect to the vertical median plane of the block, in the direction of the other block, respectively 103 ′, 103, of the same pair. In other words, the ces 103, 103 ′ are symmetrical with respect to a median vertical plane equidistant from the two ces of the same pair.

In the lid locking position, the jack 116 is in the extended rod position. To unlock the cover, the pressure of the clamping cylinders 110 is first removed, then the pivoting control cylinders 116 are supplied to retract their rod, which causes the pivoting of the two sides of the same pair in opposite directions until 'to bring their branches into their release position 104 ′, 104˝.

The advantages of the lid locking means which have just been described reside in particular in the uniformity of the tightening over the entire circumference of the tank, and in the absence of the need for a determined orientation of the cover relative to the tank. , since the support points of the clamping cylinders 110 do not necessarily have a precise circumferential location on the cover flange. In addition, even in the event of a hydraulic leak on these clamping cylinders or on their supply circuit, the cover is retained by the upper branches of the cés, and cannot therefore be lifted under the effect of the internal pressure of the tank. only slightly, thus limiting the leakage of pressurized gas contained in the tank, and also avoiding the ejection of the cover.

To guarantee sealing at the level of the tank-lid connection, and also to ensure the centering of one with respect to the other, a circumferential groove 117 can be machined in one flanges, the other comprising a rib 118 which penetrates into said groove 117. A seal 125 is interposed in the bottom of the groove 117 and compressed by the rib 118 when the cover is tightened on the tank.

To avoid shocks during the fitting of the cover on the tank, dampers in the form of elastic elements 119, such as springs, are placed in blind bores made in the cover flange 101. When the cover is in pressing on the tank, these elastic elements are compressed, as shown in FIG. 7, and are flush with the joint plane of the two flanges 101, 102. When the cover is lifted, these elastic elements are relaxed and protrude below the underside of the cover flange 101. When the cover is put in place, it is these elastic elements which first come into contact with the tank flange 102, thus damping the contacting of the cover on the tank.

FIG. 8 shows another variant of these shock absorbers, placed here outside the flanges. In this variant, a shock absorber housing 120 is fixed to the cover 7. This housing contains a spring 121 compressed by a shoulder of a shock absorber rod 122 which carries a shoe 123, which is supported when the cover is positioned on the tank, on a support plate 124 fixed on the tank flange 102. In this variant, it is necessary to position the cover relative to the tank during its installation, so that the pads 123 are opposite the plates support 124.

We will now describe the different stages of a pressure casting process for a slab using the various mechanisms described above.

Before casting, the carriage 5 is in the standby position remote from the mold 1, the cover being removed and the bag removed. The cover 7, provided with the tube 3, rests by its flange 101 on a nearby oven in which the pouring tube 3 enters to heat it and keep it at temperature.

The ladle, containing the molten steel from the steelworks, is deposited in the tank 2 on the ladle-holder frame 9 kept in the low position.

The cover with the pouring tube is then lifted and moved to place it on the tank. During this manipulation, the risks of deterioration and breakage of the tube 3 are considerably reduced thanks to the means for fixing the tube to the cover, previously described in their second variant, which allow a certain freedom of movement of the tube relative to the cover. The fitting of the cover on the tank is done smoothly thanks to the shock absorbers 119. When the cover is lowered, the slag floating on the liquid metal is moved away from the zone of penetration of the tube so as to avoid its introduction into this one. This can be done by blowing argon or nitrogen into the tube from its upper end, or by scraping the central part of the metal surface to remove the slag, or by bubbling, that is ie by introduction of a neutral gas through the bottom of the pocket. One can also provide a fusible cap temporarily closing the lower end of the tube during the period of fitting the cover.

Once the cover 7 deposited and centered on the tank 2, the latter is locked by means of the locking means 8 of the cover previously described.

The carriage carrying the assembly thus formed is then moved to put it in the casting position under the mold 1.

The mold is then tilted and the closure device 17, previously open, comes to bear on the upper end of the pouring tube, thereby pressing the ring 77 of the means for fixing the tube on the cover, on its seat 75. The pressure exerted by the mold, associated with plastic seals inserted between the closure device and the tube provides the seal of the connection.

The actual casting operation can then begin. For this, compressed air at a pressure of 1 to 8 bars or more is injected into the tank, which causes the liquid metal to rise in the tube and then in the mold. The pressure is adjusted according to a program which permanently takes into account the quantity of metal introduced into the mold and the variations in the horizontal sections of the mold encountered by the metal during its rise in the mold. When the mold is filled, the closure device is closed and the internal pressure of the tank brought back to ambient pressure.

The carriage can then be moved to another mold where the operations described above are repeated.

As long as the level of metal in the pocket is greater than a predetermined level, and therefore as long as the quantity of metal in the pocket is greater than a corresponding predetermined quantity, the pocket is kept in the low position.

When the metal in the pocket reaches this predetermined level, close to and above the lower end 31 of the tube, the lifting operation of the pocket is started. The level of metal in the pocket is calculated from the measurement of the weight of the pocket-metal assembly by integrating the dimensional characteristics of the pocket and of the tube.

When the weight corresponding to the desired predetermined level of the metal is reached, the lifting is triggered. The total lift stroke is determined so as to obtain at the end of the stroke a minimum distance between the bottom of the bowl 33 and the lower end 31 of the tube 3 so as to leave as little metal as possible in the bottom of the pocket.

, qui représente les variations de pression P en fonction du temps t, permet le contrôle de la vitesse de montée du métal dans le moule.As has been said, the pressure of the tank is regulated during the casting. The rise of the steel in the mold is obtained by an increase in the pressure in the tank. It is therefore necessary to permanently check on the one hand the value of the pressure and on the other hand the instantaneous value of the variation of the pressure as a function of time. Checking the deposit $$\frac{\text{dP}}{\text{dt}}$$

, which represents the pressure variations P as a function of time t, allows the control of the rate of rise of the metal in the mold.

When lifting the bag, this lifting would tend to cause a corresponding rise of the liquid metal in the mold.

qui détermine la pression qui doit être créée à tout instant dans la cuve. L'objectif étant de maîtriser la vitesse de montée du métal dans le moule, une correction de consigne est nécessaire. En outre la mesure de pression n'est représentative de la hauteur d'acier dans le moule qu'à condition d'effectuer la correction correspondant à la hauteur de levage de la poche puisque le levage de la poche créant une variation correspondante du niveau de métal dans la poche par rapport au niveau de métal dans le moule, il s'ensuit une variation de la hauteur ferrostatique entre ces deux niveaux.In the absence of additional regulation, the speed of this rise would be added to the speed resulting from the setpoint $$\frac{\text{dP}}{\text{dt}}$$

which determines the pressure that must be created at all times in the tank. The objective being to control the rate of rise of the metal in the mold, a setpoint correction is necessary. Furthermore, the pressure measurement is representative of the height of steel in the mold only on condition that the correction corresponding to the lifting height of the pocket is effected since the lifting of the pocket creating a corresponding variation in the level of metal in the pocket compared to the level of metal in the mold, it follows a variation of the ferrostatic height between these two levels.

• a) Correction de la consigne $$\frac{\text{dP}}{\text{dt}}$$
  
  : pendant la durée du levage de la poche, la consigne $$\frac{\text{dP}}{\text{dt}}$$
  
  devient $$\frac{\text{dP1}}{\text{dt}}$$
  
  - V, où dP1 est la consigne avant correction, et V est la vitesse de montée de la poche.
• b) Correction des pressions P (I) de changement de consigne : les changements de consigne $$\frac{\text{dP}}{\text{dt}}$$
  
  doivent être effectués pour une nouvelle pression de consigne P′(I) = P (I) - DPC où P(I) est la pression de changement de consigne avant correction et DPC est la valeur du déplacement vertical de la poche à l'instant t, les valeurs de pression étant ramenées, dans ces formules, à des hauteurs d'acier correspondantes.

Additional regulation should therefore be made by making the following corrections:

• a) Correction of the setpoint $$\frac{\text{dP}}{\text{dt}}$$
  
  : during the bag lifting period, the setpoint $$\frac{\text{dP}}{\text{dt}}$$
  
  bECOMES $$\frac{\text{dP1}}{\text{dt}}$$
  
  - V, where dP1 is the setpoint before correction, and V is the speed of rise of the bag.
• b) Correction of the setpoint change pressures P (I): the setpoint changes $$\frac{\text{dP}}{\text{dt}}$$
  
  must be performed for a new setpoint pressure P ′ (I) = P (I) - DPC where P (I) is the setpoint change pressure before correction and DPC is the value of the vertical displacement of the pocket at the moment t, the pressure values being reduced, in these formulas, to corresponding steel heights.

At the end of the emptying of the tank, it is moreover necessary to take care to avoid the passage of slag, or of air in the tube, which would risk causing steel projections out of the mold. The objective is to stop the flow when only the bowl of the ladle contains liquid metal, the lower end of the tube then being still immersed in this metal.

et $$\frac{\text{Δm}}{\text{Δt}}$$

où Δ P représente la variation de la pression dans la cuve, et Δ m la variation de poids du métal contenu dans la poche, en fonction du temps Δ t. En effet, lorsque le niveau d'acier dans la poche atteint la partie supérieure de la cuvette, lesdites variables $$\frac{\text{Δm}}{\text{ΔP}}$$

et $$\frac{\text{Δm}}{\text{Δt}}$$

décroissent rapidement. Typiquement, on arrêtera la coulée lorsqu'on obtiendra des variations de $$\frac{\text{Δm}}{\text{ΔP}}$$

et de $$\frac{\text{Δm}}{\text{Δt}}$$

prédéterminée selon des valeurs de consigne.To do this, we analyze the variations over time of two variables: $$\frac{\text{Δm}}{\text{ΔP}}$$

and $$\frac{\text{Δm}}{\text{Δt}}$$

where Δ P represents the variation of the pressure in the tank, and Δ m the variation in weight of the metal contained in the pocket, as a function of time Δ t. When the level of steel in the pocket reaches the upper part of the bowl, said variables $$\frac{\text{Δm}}{\text{ΔP}}$$

and $$\frac{\text{Δm}}{\text{Δt}}$$

decrease rapidly. Typically, we will stop casting when we obtain variations in $$\frac{\text{Δm}}{\text{ΔP}}$$

and of $$\frac{\text{Δm}}{\text{Δt}}$$

predetermined according to set values.

When the pouring is finished and the empty pocket it is lowered to the low position, and the carriage 2 is returned to its standby position, where the cover is unlocked, removed, and placed on the furnace where the tube is kept at temperature for a next casting cycle.

The description which has just been made of the casting process is not exhaustive in all of its phases. We have limited ourselves to describing the essential and specific phases of the process according to the invention, which could moreover be adapted to the characteristics specific to each die-casting installation.

Claims (16)

1. Apparatus for supplying liquid metal to a mould of a pressurised casting installation, comprising a vat (2) provided with a lid (7) supporting a casting tube (3), said vat resting on a chassis (4) and comprising a frame (9) for supporting a liquid metal ladle (10) and means (20′) for weighing said ladle, characterised in that it comprises means (20) for lifting said frame with respect to said vat.
2. Apparatus according to Claim 1, characterised in that the ladle support frame comprised arms (91) extending radially and resting on the lifting means (20) distributed on the periphery of the vat and supported by the frame.
3. Apparatus according to Claim 2, characterised in that said lifting means (20) and weighing means (20′) are disposed outside the perimeter of the vat, and sealing means (53, 63) are disposed at the level of said lifting and weighing means between the vat and the chassis.
4. Apparatus according to Claim 3, characterised in that the arms (91) which extend radially beyond the perimeter of the vat are fixed to the ladle-support frame (9) in an eclipsable manner in order to be able to be moved into a position inscribed inside the perimeter of the vat.
5. Apparatus according to Claim 3, characterised in that each of the weighing and lifting means comprises, in a substantially vertical alignment, a balance (61) on which the arm (91) rest, a guide column (52) and a jack (25), small rods (56, 57) provided with swivels (56′, 57′, 56˝, 57˝) being disposed between the guide column and on the one hand the balance and on the other hand the movable rod (25′) of the jack, said column being guided in a sleeve (51) fixed to the chassis.
6. Apparatus according to Claim 5, characterised in that the guide column comprises a shoulder (54) able to come to rest on the sleeve.
7. Apparatus according to Claim 1, characterised in that the casting tube (3) is fixed to the lid (7) by means of a swivel device (75, 76).
8. Apparatus according to Claim 7, characterised in that the swivel device comprises a collar (73) surrounding the casting tube in a tight manner and connected to a ring (77, 77′) comprising a spherical bearing surface (76, 76′) resting on a frustoconinal seat (75, 75′) of the lid.
9. Apparatus according to Claim 8, characterised in that the ring (77′) is retained on the lid by clips (78), wedges (79, 82) of adjustable thickness being disposed between the clips and the lid in order to adjust the position of the ring with respect to the lid.
10. Apparatus according to Claim 8, characterised in that the ring (77) comprises at least three lugs (86) distributed circumferentially, reference wedges (88) and compression springs (87) are interposed between said lugs and the lid, the thickness of said wedges being such that when the lugs (86) rest on the latter, the spherical bearing surface (76) of the ring is in close contact with the frustoconical seat (75) of the lid, and said springs being such that in the absence of the thrust exerted on the tube in the downwards direction, a clearance exists between the ring and the lid.
11. Apparatus according to Claim 1, comprising means (8) for locking the lid on the vat, the lid and the vat being provided with flanges (101, 102) provided to come into close contact one with the other, characterised in that said locking means comprise a plurality of C's (103) distributed over the periphery of the vat, pivotally mounted on the latter and whereof the sides (104, 105) enclose said flanges in the locking position.
12. Apparatus according to Claim 11, characterised in that two adjacent C's are connected by the same jack (116) for controlling the pivoting.
13. Apparatus according to Claim 11, characterised in that each C comprises on one side (105), an abutment (107) for bearing against a flange (102), and on the other side (104), a tightening jack (110) pressing on the other flange (101).
14. Apparatus according to Claim 11, characterised in that shock absorbers (119) for fitting the lid are placed between the flange on the lid (101) and the flange on the vat (102).
15. Pressurised casting method using the vat according to Claim 1, according to which a mould (1) is supplied with liquid metal by injecting the liquid metal into said mould by means of a casting tube (3) fixed to the lid of the vat and immersed in a ladle (10) containing said metal, the metal being pushed into the tube under the effect of the internal pressure created in the vat, characterised in that when the quantity of metal in the ladle is greater than a predetermined quantity, said ladle is retained in a lower position, and when the quantity of metal in the ladle becomes less than the said predetermined quantity, the ladle is raised in order to keep the lower end of the tube (31) below the level of the metal contained in said ladle.
16. Method according to Claim 15, characterised in that at the time of lifting of the ladle, the internal pressure in the vat is regulated in order to maintain a predetermined ascending speed of the metal in the mould.

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