FR2651160A1 - METHOD AND DEVICE FOR CASTING METAL BARS OR THE LIKE. - Google Patents

Abstract

The invention relates to a method and a device for casting metal bars or the like using a shell (1) which can be lowered into a liquid bath (5) when it is filled with molten metal. The shell tube (1) is filled with molten metal by means of a filling tube (11), which is first introduced from above into the shell tube through its lower end provided with a discharge port. (12); the shell tube is kept floating approximately to the termination of this filling so that its lower end is located approximately at or above the surface of the liquid in the bath (5), the molten metal entering the shell tube (1) through this discharge port (12) of the filling tube (11); simultaneously, the rate of descent of the shell tube in the liquid bath (5) is made to be in a predetermined relation with the rate of rise of the molten metal in the shell (1).

Description

The present invention relates to a method and a device for pouring in

  shell of metal bars or the like using a tube closed at its lower end and serving as a shell which, when filled with molten metal, is engaged in a bath of liquid to descend into it. Such methods and devices can be used to make samples of as homogeneous a composition as possible,

  necessary for the spectrometric analysis of metals or alloys.

  In particular, severe requirements are imposed on the quality of standard samples used for the calibration of spectrometers, with regard to the homogeneity, the fineness of possible intermetallic connections.

  and the absence of casting defects (pores, segregations, oxide inclusions).

  Samples for the examination of a specific melt are generally cast in the form of flat disks or cylinders in steel molds, with a size sufficient to allow the examination to be carried out at one time. When making standard samples, however, it is necessary to carry out an initial sample of as large and uniform a volume as possible, so that after its complicated chemical analysis has been carried out, as many as possible reference samples

  identical that can be sold.

  To this end, bars of circular section having a diameter of 30 to 10 mm are advantageously poured by means of the method known up to now and already mentioned, said bars of circular section being turned externally and being sectioned to obtain individual shaped samples. discs. The above-mentioned method used until now is a shell casting process under the effect of gravity, where the shell produced in the form of a thin-walled steel cylinder closed at the bottom is filled with the molten metal is then down

  in a water bath to accelerate the solidification of the molten metal.

  While low-alloyed molten metals can be cast at relatively low cost in the form of satisfactory sample bars, there are often encountered, when casting metals having high levels of alloying additives, significant difficulties in obtaining a sufficiently homogeneous and uniform composition of the sample bars over their diameter and over their entire length. A typical example of alloys posing such difficulties relates to aluminum alloys for pistons, having a silicon content of Il at 25%, a copper content up to 4%, a magnesium content up to 2% and various other alloying elements. An alloy of this kind tends to form silicon segregations and coarse intermetallic phases. A problem encountered in all cases consists in filling the cavities, which are cylindrical most of the time and relatively long, so as to avoid foaming and

oxide turbulence.

  A use of the bar casting process, also suitable for this purpose, is generally prohibited because of the too small volume of the cast parts, for which the expenditure on equipment and operational orders, in relation to the bar casting process,

would be too large.

  The invention therefore aims to create a method and a device of the type defined above, which allow, with expenditure on equipment as small as possible, to achieve correct metal bars also from metal alloys difficult to flow, the shape and the surface quality of said bars having to be such that no, or only a small machining by removal of chips, is necessary on their outer surface because it is precisely in the rapidly solidified outer areas of the bars that the most favorable crystal structures are obtained. Furthermore, the process should not depend

  the degree of professional skill of the operator.

  This problem is solved in accordance with the invention, for a method of the type defined above, in that, for filling the shell-forming tube with molten metal, a filling tube is used, open or to be opened at its end. lower and closable at its upper end, this filling tube being immersed by its lower end in a bath of metal to be poured which then enters the filling tube, in that afterwards the full filling tube is closed at its upper end and is taken out of the metal bath with its contents then is introduced from above and through its lower end into the shell-forming tube, and then, by opening the upper end of the filling tube, the molten metal flows out of the tube filling through its lower end open or brought into the open condition in order to penetrate the tube forming the shell and simultaneously leaving nt the latter go down into the liquid bath under

  the effect of the weight of the metal filling the shell. In this regard, advantageous-

  The filling tube is inserted up to, or almost up to, the closed lower end of the shell tube and is kept in this position regardless of the height arrangement of the shell tube. With this procedure, it is possible to fill the shell with a considerable reduction in foaming or turbulence of oxides, which was not possible.

  with the aforementioned known casting process due to the complicated filling.

  With the process according to the invention, advantageously, the shell tube is lowered into the liquid bath at a speed which is approximately equal to the rate of rise of the molten metal in the shell tube, so that the level of the molten metal filling the shell tube remains constantly at about the same height. When the filling tube is introduced up to, or approximately up to, the closed bottom end of the shell tube and held in this position, a drop height of the molten metal is assured which is as small as possible and which remains constant, which practically entirely prevents foaming and turbulence of oxides. Due to the controlled descent of the shell tube into the liquid bath, immediate cooling is also obtained, and progressing with the filling level, of the molten metal introduced, so that a fine crystal structure and free of segregation is created in the finally solidified casting. According to German Patent No. 750,673, a method is known for casting metal blocks formed of aluminum alloys containing copper in a shell which is placed on a casting table which can be lowered into a water bath . The filling of the shell is however carried out, in this process, by means of a pouring chute and not by means of a filling tube which rises, as in the process according to the invention, while the movement of the casting table is produced by means of a type of lowering device

hydraulic or the like.

  In addition, in this known method, the shell used for the casting of metal blocks is adapted in height during its progressive filling and during the simultaneous descent movement of the casting table in the water bath, so that the chute casting, directed laterally towards the shell, can be maintained by its outlet end at a height as small as possible above the upper level of the molten metal introduced into the shell. This obviously makes it possible to reduce the formation of foam and the turbulence of oxides in the metal block being cast. However, this filling method is too complicated to be used in a method of casting metal bars or the like in a process of casting in a shell and in

  therefore it cannot be used in practice.

  The invention also relates to a shell casting device for implementing the method according to the invention, this device comprising a shell tube, which is closed at the bottom by a bottom and which can be lowered into a liquid bath. . This device is arranged, in accordance with the invention, so that the shell tube is mounted in a floating body and is guided with it, in and above the container receiving the liquid bath, upwards and towards the bottom by immersing in the bath, said float body being arranged so that it keeps floating in the liquid bath the shell tube before it is filled with molten metal in such a way that its lower end is located approximately near or above the upper level of the liquid bath and then, during filling, it allows the tube forming the shell to descend into the liquid bath; in addition, it is possible to introduce into the shell tube a filling tube for filling molten metal in the shell tube, said filling tube being provided with an opening allowing the discharge of molten metal into the tube forming shell. In this regard, it is advantageous to arrange and size the float body so that it allows the shell tube, when it is filled, to descend into the liquid bath at a speed which is in a desired relationship. with the rate of rise of the molten metal in the shell tube. To adapt to metallurgical requirements, the float body can also be arranged so that the speed of descent of the shell tube decreases or

  increases as its filling increases.

  In order to be able to remove the solidified molded part from the shell tube as easily as possible and without damaging the latter, this shell tube can be produced in two foldable parts or in a widening part with a conical profile towards

the top.

  The float body can be made of a light material, such as styropore or cork, or it can be formed by a hollow body of thin-walled sheet metal or the like. It can surround the shell tube completely or only partially and it can be guided up and down on a vertical guide in the container receiving the liquid bath and above it. This guide must be arranged so that it guides the tube forming the shell, during its downward movement, in a vertical position, which can be achieved in a fairly simple manner with annular ears movable on cables. of tension, but however also with any other type

known guide mechanism.

  The shell tube can also be balanced with respect to its self-weight by means of deflection rollers and by means of counterweights, so that the float body can have correspondingly reduced dimensions and be designed only to counterbalance the ascending forces varying during the

  filling the shell tube.

  The filling tube is advantageously placed in a support independent of the height position of the shell-forming tube or it can be fixed in a height position independent of the tube

forming a shell.

  The device according to the invention can be used, because of its arrangement, in particular for the production of sample bodies in the form of bars which involve relatively large quantities of metals.

small, around 10 to 15kg.

  The method and the device according to the invention are however applicable not only to the casting of such sample bodies in the form of bars described above, but also to the manufacture of other cast parts of elongated profile. Thus, it is possible, for example, to envisage an advantageous application to the casting of profiled bars formed of metallic substances which react strongly with air, such as for example alloys based on titanium or magnesium or also aluminum alloys with a high content of reactive elements, for example lithium. The method and the device according to the invention allow, under such conditions, for example the removal of the casting material below a closed protective saline cover and the casting under a protective gaseous atmosphere, or alternatively by - below a saline recovery bath, without major additional expenses. Molten metal can be transferred, almost completely excluding contact with air, from a hot-holding oven

  into a casting mold where rapid solidification takes place.

  Other characteristics and advantages of the invention will be

  highlighted in the following description, given by way of example

  nonlimiting, with reference to the accompanying drawings in which: - Figure I shows in vertical section the temperature maintenance container as well as the shell tube, which can be lowered into a water bath, the figure showing the tube filling before its introduction into the shell tube, - Figure 2 shows the shell tube in the same way

  immersed in the liquid bath during its filling by means of

  diary of the filling tube, - Figure 3 shows on a larger scale a perspective view and cut away of the shell tube in which is introduced the filling tube. In the embodiment shown, the shell is constituted by a thin-walled tube I which is closed at its lower end by a bottom 2. This tube 1 forming a shell is mounted in a straight body forming a float, which remotely surrounds the shell-forming tube which is dimensioned so that it keeps the shell-tube empty with its closed inner bottom 2 a short distance above the surface of the water bath 5 and that it makes it descend into the water bath 5 when filling with molten metal. For this purpose, the float body 3 is guided by means of annular ears 6 on tension cables 7, which are fixed by their lower end to the bottom 8 of the container 4 and by their upper end to a cross member 9 connecting two supports 10, being kept stretched in a

  vertical direction between these fixings.

  The tube-shell can be formed by a section of a tube of

  precision commercial steel, on which a bottom plate is welded.

  When the shell tube has a constant section, as in the example of

  shown embodiment, it may be necessary to cut mechanical-

  ment the shell tube for demolding the molded part which is poured into this tube. It is however also possible, as has already been specified, to use a shell tube in two foldable parts or in a widening part with an upward conical profile, in order to allow

  to use the shell tube several times.

  For filling the shell tube with molten metal, a filling tube 11 is used, which can be formed from a ceramic material or from another suitable material, resistant to molten metal, for example a metal tube protected from appropriately by coatings. The outside diameter of the filling tube It is a little smaller than the inside diameter of the shell tube I. The lower end of the filling tube It is closed by a bottom which is provided with a discharge orifice 12 through which the molten metal in the filling tube can enter the shell tube 1. The upper end of the filling tube It is provided with a tight-closing lid in which there is provided a valve 13 for opening and closing the 'upper end of the filling tube relative to the atmosphere. The valve 13 is held in the closed position by a pressure spring 14 and it can be brought into the open position by means of a traction lever 15 operating in opposition to the force of the

pressure spring 14.

  At its upper end, the filling tube is provided with a pendulum 16 with the aid of which it can be maintained, in a position of introduction into the shell tube 1, in a support 17 provided at the upper end of the uprights 10. In this position, the filling tube II located in the shell tube 1 is maintained independently

  from the height position of the shell tube.

  To facilitate the centered introduction of the filling tube II into the upper opening end of the shell tube 1, there is provided a

  tubular centering piece 18, which is fixed to the cross-member 9.

  When the valve 13 of the cover is open, the filling tube 11 can be lowered, through its discharge orifice 12, sufficiently far into the bath of molten metal 20 located in the temperature-maintaining container 19. Consequently, it plunges to a great depth below the surface of the molten metal bath and as a result clean molten metal, because it is removed from the impurities floating on the surface of the bath, has entered the tube

  filling via the orifice 12 in the form of a drain

  calm and corresponding to the diving depth of this filling tube. Then, the cover valve 13 is closed and the filling tube 11 is taken out of the molten metal bath 20, the molten metal located in the filling tube remaining therein because the cover valve is closed and being driven with this tube. The filling tube is now engaged by its open lower end and by means of the tubular centering piece 18 in the

  tube-shell 1 and it is suspended by its pendulum 16 in the support 17.

  In this position, the lower end, comprising the discharge orifice 12, of the filling tube 1 is located a very short distance above the bottom 2 of the shell tube I. Now the valve 13 of the cover is open and consequently the upper end of the filling tube It is connected to the atmosphere. As a result, the lifting effect exerted by the filling tube 11 on the molten metal located inside it is suppressed so that the molten metal can exit the filling tube through its discharge orifice 12 to penetrate in the shell tube 3. Under the effect of the increase in the weight of the quantity of metal introduced, the float body 3 and the shell tube 1 descend into the water bath 5 and in this respect, by a corresponding dimensioning of the float body 3, the lowering speed must be roughly equal to the rising speed of the molten metal in the shell tube 1. The discharge orifice 12 of the filling tube 11 is thus obtained, during the entire penetration of the molten metal into the shell tube 1, constantly in direct contact or else in close proximity to the surface of the molten metal introduced into the shell tube. The metal leaving the filling tube 11 enters the shell tube without free fall or only with a small free fall, and therefore with as little turbulence as possible. On the other hand, it is avoided that the filling tube plunges into the molten metal introduced into the shell tube because it would risk being blocked in the molten metal during solidification. Thanks to the downward movement of this tube in the liquid bath, which is carried out in correspondence with the increase in the filling height of the shell-tube, it is possible to obtain immediate cooling, and progressing with the filling level , molten metal and therefore the establishment of a fine and free crystal structure

  segregation in the solidified casting.

  The valve 13 of the filling tube cover can be a valve simply producing an opening and a closing but it is however also possible to combine it with a fine regulating valve, which allows a precise metering of the quantity of metal leaving by the discharge port 12 of the filling tube II. It is thus possible to obtain a precise adaptation of the casting speed to the solidification speed in the molded part, conditioned by cooling in the water bath 5, in any suitable manner and according to the

metallurgical imperatives.

R E V E ND IC A T I ON S

  1. Method for casting metal bars or the like in a shell casting process using a shell (1) consisting of a tube closed at its lower end and which, when filled with molten metal, is lowered in a liquid bath (5), process characterized in that, for filling the shell tube with molten metal, an open or openable filling tube (11) is used, at its lower end and closable at its upper end , which is initially immersed by its lower end in a bath (20) of the molten metal, so that the molten metal is introduced into the filling tube, in which afterwards the full filling tube is closed at its end upper and is taken out, with its contents, out of the molten bath to be then introduced from above, by its inner end, into the tube forming a shell, in that later, by opening the extr upper part of the filling tube, the molten metal is discharged from the filling tube via its open lower end, or which has been opened, with a view to its introduction into the shell tube, and in that the movement downward movement of the shell tube is produced only by the weight of the metal introduced into

this tube.

  2. Method according to claim 1, characterized in that the shell tube (1) is lowered into the liquid bath (5) with a speed which is approximately equal to the rate of rise of the molten metal in

the tube forming a shell.

  3. Method according to claim 1, characterized in that the filling tube (11) is introduced up to, or approximately until the closed lower end of the shell tube (1) and is maintained in this position independently of the descent of the tube forming

shell in the liquid bath.

  4. Shell casting device for the implementation of the

  method according to one of claims 1 to 4, comprising a tube forming

  shell which is closed at the bottom by a bottom and which can be lowered into a liquid bath, device characterized in that the shell tube (1) It is arranged in a float body (3) and is guided with it ci, in and above the container (4) receiving the liquid bath (5), upwards and downwards while immersing in the bath, said float body (3) being arranged so that it maintains , floating the shell tube (1) before filling with molten metal, with its lower end located approximately at the height of the upper level of liquid in the bath (5) or above and allow it to move lowering into the liquid bath during filling, and in that a filling tube (11), serving for the introduction of molten metal into the shell tube, can be introduced into the shell tube (1), this filling tube being provided with an orifice (12) allowing discharge

  molten metal in the shell tube.

  5. Shell casting device according to claim 4, characterized in that the float body (3) is arranged and dimensioned so that it allows the shell tube (1), during filling, to descend into the liquid bath (5) at a speed which is in a desired relationship with the rate of rise of the molten metal

in the shell tube.

  6. Shell casting device according to one of the claims

  tions 4 or 5, characterized in that the float body (3) has, in its lower region, a different lift volume, for example more

  large (larger lift section) than in its upper area.

  7. Device according to claim 4, characterized in that the float body (3) is arranged being spaced laterally from the tube

forming a shell (1).

  8. Device according to claim 4, characterized in that the filling tube (11) can be introduced into the tube forming a shell

  (1), from its open upper end, up to, or approximately

  until its lower closed end.

  9. Device according to Claim 4, characterized in that the filling tube (11) comprises, at its lower end by which it can be introduced beforehand into the tube forming the shell (1), a

  bottom provided with a hole (12) for discharging molten metal.

  10. Device according to claim 4, characterized in that the filling tube (l) is provided, at its upper end, with a tightly closed cover, which comprises a valve (13) for connecting

  the interior volume of the filling tube with the atmosphere.

  11. Device according to claim 4, characterized in that the filling tube (11) can be fixed relative to the container (4) of the liquid bath (5) in a support (16, 17) regardless of the height position of the shell tube (1), in its engagement position in the

shell tube.