Abstract:
The installation according to the invention comprises at least one mould, a vessel intended to receive the liquid metal and means for directly determining the evolution of the level of molten metal in the impression of the mould. These determination means comprise means for detecting the presence of this liquid metal in the impression, particularly of electromagnetic nature, which are adapted to penetrate at least partially in the interior volume of this impression.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an installation for filling a mould with liquid metal, as well as to a process allowing this installation to be employed.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the technical domain of foundrywork, it is known to employ a succession of moulds, also called boxless moulds, which are made of sand. Each mould conventionally comprises a casting bowl intended to receive the molten metal, as well as at least one impression connected to this bowl via a feed channel. In service, it is question of displacing each mould in the direction of a casting machine adapted to pour molten metal.  
         [0003]     This casting operation is subjected to several requirements.  
         [0004]     Firstly, it is important to flood the casting bowl rapidly and to maintain it in the full state while the metal is propagating in the direction of the impressions. In effect, this ensures high-quality casting, bereft of voids, defects and trapped gas.  
         [0005]     It is also necessary that the flowrate of metal swallowed by the mould be permanently equal to the flowrate delivered by the casting machine, in order to avoid any overflow, as well as any under-feed. Finally, at the end of casting, the level of metal in the bowl must be controlled in order that it fills the mould exactly, without, however, provoking any overflow.  
         [0006]     It is firstly known to proceed with filling these moulds manually, namely this operation is carried out by an operator. It is also possible to carry out this filling automatically, so that it is piloted by programmable equipment.  
         [0007]     For example, optical systems are known which employ a beam directed towards the casting bowl in order to determine the level of filling of the bowl during the casting. However, this known solution presents a drawback, connected in particular with its lack of knowledge of the real level of filling of the mould in the course of the casting process.  
         [0008]     This being specified, the invention aims at proposing an installation for controlling the filling of a mould with liquid metal, reliably and precisely.  
       SUMMARY OF THE INVENTION  
       [0009]     To that end, the invention relates to an installation for filling a mould with liquid metal, comprising: 
        at least one mould comprising a casting bowl, a feed channel, as well as at least one impression connected to said bowl by said channel,     a vessel intended to receive the liquid metal having to be cast into the mould; and     means for directly determining the evolution of the level of molten metal in the impression, these determination means comprising means for detecting the presence of this liquid metal in the impression, these detection means being adapted to penetrate at least partially in the interior volume of this impression.        
 
         [0013]     According to other characteristics of the invention: 
        the detection means are of electromagnetic nature;     the determination means comprise means for creating an electromagnetic field, of which lines of field form said detection means, these lines of field being able to be disturbed by the liquid metal present in the impression;     the means for creating the electromagnetic field comprise at least one emitter coil, an electric generator adapted to excite this emitter coil, as well as at least one receiver coil adapted to cooperate with said emitter coil;     two receiver coils are provided, a first receiver coil being placed between the emitter coil and the mould, while the other receiver coil is placed opposite the emitter coil with respect to the mould;     the determination means also comprise means adapted to transform the intensity of the disturbance undergone by said lines of field into an analog signal representative of the evolution of the level of liquid metal in the impression, this analog signal corresponding for example to the evolution of a voltage as a function of the level of filling of the mould;     the determination means also comprise means for obtaining an instantaneous curve, from said analog signal, representative of the evolution of the level of molten metal in the impression, as well as means for comparing this instantaneous curve with a reference curve, while means are, in addition, provided for controlling the flowrate of molten metal poured from the vessel, in the event of the instantaneous curve differing from the reference curve to an inadmissible extent;     the control means are adapted to actuate a mobile stopper with which the vessel is equipped.        
 
         [0021]     The invention also relates to a process for employing the installation as defined hereinabove, comprising the following steps of: 
        actuating the means for creating the electromagnetic field so as to generate lines of field penetrating at least partially in the interior volume of the impression; and     determining the evolution of the level of liquid metal in the impression, as a function of the intensity of the disturbance undergone by these lines of field.        
 
         [0024]     According to other characteristics of the invention: 
        said instantaneous curve and said reference curve are compared and the flowrate of liquid metal poured from the vessel is modified if the difference between this instantaneous curve and this reference curve is inadmissible;     the flowrate of liquid metal is modified by displacing said stopper;     a predetermined threshold of the impression is chosen, the instant is detected at which the level of liquid metal reaches this threshold, a latent period is allowed to lapse, depending in particular on the instantaneous value of the flowrate of molten metal poured from the vessel, and the admission of liquid metal in the mould is stopped at the end of this latent period.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The invention will be described hereinafter with reference to the accompanying drawings, given solely by way of non-limiting example and in which:  
         [0029]      FIG. 1  is a general view illustrating an installation for filling a sand mould with liquid metal, according to the invention.  
         [0030]      FIG. 2  is a view similar to  FIG. 1 , illustrating the installation of  FIG. 1  during the phase of filling proper, and  
         [0031]      FIG. 3  is a graph representing the evolution of the level of molten metal as a function of time, inside an impression with which a mould equipping the installation of  FIGS. 1 and 2  is provided. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0032]     Referring now to the drawings, the installation of  FIGS. 1 and 2  comprises different moulds, of which only one has been shown, given reference  2 . In service, this mould circulates beneath a vessel  4  which is filled with a liquid molten metal  6  which is for example cast-iron or steel. This metal was poured in the vessel  4  in conventional manner via a ladle (not shown).  
         [0033]     The bottom of the vessel  4  is closed, in known manner, by a stopper  8 , also called stopple. The latter may be manoeuvred along its principal axis, namely vertically in  FIG. 1 , via an actuator  9  of conventional type.  
         [0034]     Each mould, which is of globally parallelepipedic shape, conventionally comprises a casting bowl  10 , of truncated shape, into which flows the molten metal  6  poured from the vessel  4 . This bowl  10  extends in a feed channel  12  which opens out into at least one impression  14 . In the example described and shown, two such impressions  14  are provided, which have been illustrated schematically.  
         [0035]     The installation of  FIGS. 1 and 2  also comprises means for determining the evolution of the level of molten metal, inside the impression  14 . It is firstly question of three electromagnetic coils, mounted on the same axis, horizontal in the present case.  
         [0036]     More precisely, a central emitter coil  16  is provided, adapted to be excited by a sinusoidal electric signal whose frequency is some kilohertz. To that end, the coil  16  is placed in relation with an appropriate generator  18 , of type known per se.  
         [0037]     The emitter coil is associated with two lateral, so-called receiver coils, of which one,  20 , is placed in the vicinity of the mould  2 . On the other hand, the other receiver coil  22  is placed opposite this mould  2 , with respect to the central emitter coil  16 .  
         [0038]     A single set of three coils has been shown in  FIGS. 1 and 2 , to the right of the mould. It should be noted that another set of coils may optionally be provided in the vicinity of the other impression, namely to the left in these Figures.  
         [0039]     By way of additional variant, the coils may be placed above the mould, or in the vicinity of a corner thereof. In that case, the axis of these coils is respectively either vertical or oblique.  
         [0040]     When the generator  18  feeds the emitter coil  16 , an electromagnetic field is created, which circulates between the receiver coils  20  and  22 . The lines of field thus created are illustrated in  FIGS. 1 and 2  where they are represented by broken lines.  
         [0041]     More precisely,  24  denotes the lines of field which circulate in the vicinity of the first receiver coil  20 . As  FIGS. 1 and 2  show, these lines  24  extend in part in a zone noted  24 ′, within the interior volume of the impression  14 . On the other hand, the lines of field  26 , extending in the vicinity of the other receiver coil  22 , namely opposite the coil  20 , do not interfere with the impression  14 .  
         [0042]     The three coils  16 ,  20  and  22  are, furthermore, connected, via a line  28 , to an electronic unit  30  whose functions will be described hereinbelow. Finally, this unit  30  is connected, via a control line  32 , with the actuator  9 .  
         [0043]     Functioning of the filling installation described hereinabove will now be explained in the following:  
         [0044]     The actuator  9  must firstly be manoeuvred in order to open the stopper  8  so as to admit molten metal into the casting bowl  10 . This molten metal then progressively fills the feed channel  12 , then penetrates inside the impressions  14 , as illustrated in  FIG. 2 .  
         [0045]     It will be appreciated that, as it rises in the impression  14 , the liquid metal is such as to disturb the electromagnetic field generated by the coils  16 ,  20  and  22 , in particular in zone  24 ′ of the lines of field  24 . Under these conditions, these lines of field, which penetrate in part in the interior volume of the impression, are adapted to detect the presence of the molten metal in this impression.  
         [0046]     Furthermore, it is to be noted that the intensity of the aforementioned disturbance increases as the impression  14  is filled. Under these conditions, the electronic unit  30  is adapted to transform the value of the disturbance undergone by the lines of field  24  into an analog signal which corresponds for example to a variation of the voltage as a function of the real level of filling of the impression  14 . The value of this voltage is consequently representative, at each instant, of the level of metal in the impression.  
         [0047]      FIG. 3  is a graph illustrating this evolution of the voltage thus determined by the electronic unit  30 , as a function of time. A zone noted I is firstly observed, in which this voltage is zero, this corresponding to the absence of interference of the molten metal with the lines of field  24 . Then, from the instant when this interference begins to occur, the voltage increases with time, as the impression  14  is filled with the molten metal. This phase of rise of the level of this molten metal corresponds to zone II of this graph.  
         [0048]     It should then be verified that the rise of the level of molten metal in the impression  14  occurs at an acceptable speed. To that end, a previous phase of apprenticeship is effected, allowing access to a curve (not shown) figuring the evolution of the voltage as a function of the real level of filling of the impression  14 , during a so-called reference filling.  
         [0049]     Then, if the electronic unit  30  ascertains that the instantaneous evolution of the voltage differs in inacceptable manner from this reference curve, this unit  30  controls the actuator  9 , via the line  32 . More precisely, if the instantaneous voltage is clearly greater than the reference voltage, at a given instant, the flowrate of molten metal poured from the vessel  4  must be reduced by lowering and even closing the stopper  8 . On the other hand, if this instantaneous voltage is clearly lower than the reference voltage, the stopper  8  should be raised in order to increase the flowrate of molten metal administered from this vessel  4 .  
         [0050]     Furthermore, the final phase of the casting of molten metal is effected in the following manner. The instant at which the level of molten metal reaches a predetermined threshold of the impression, which is materialized by reference S visible in  FIG. 2 , should firstly be detected. It is appreciated that, at that instant, the voltage plotted on  FIG. 3  attains a corresponding value, noted V s .  
         [0051]     Then a latent period is allowed to lapse, which depends on the instantaneous value of the flowrate of molten metal poured from the vessel  4 . Finally, at the end of this period, the electronic unit  30  controls the actuator  9  so as to provoke closure of the stopper  8 , this stopping feed of molten metal.  
         [0052]     It should be noted that the range and sensitivity of the sensor constituted by the three coils  16 ,  20  and  22 , may be adapted as a function of the characteristics of the mould. For example, if each of these coils is formed by 200 turns, which present a rectangular section of 140 mm by 110 mm and are separated from one another by a distance of 210 mm, the corresponding range of measurement inside the mould presents a depth of 300 mm over a surface of about 200 mm by 250 mm, centred on the coils.  
         [0053]     In addition, it will be noted that the arrangement of the three coils  16 ,  20  and  22  is advantageous, since the receiver coils  20  and  22  are mounted in opposition, namely the coil  20  is adjacent the mould, while the coil  22  is thereopposite. In this way, only the lines of field  24  are disturbed when the metal rises, while those,  26 , do not undergo such a disturbance. Consequently, the electronic unit  30  benefits in manner known per se, from a regime of differential signals, thus allowing the sensitivity of the measurement to be increased.  
         [0054]     The invention makes it possible to attain the objects set forth hereinabove.  
         [0055]     In effect, the prior art employs an optical measurement in the casting bowl, which proves to be very poor in data since it is not representative of the level of molten metal in the impression. Such a measurement thus corresponds solely to the image of the difference between, on the one hand, the feed flowrate of the molten metal from the vessel  4  and, on the other hand, the instantaneous flowrate swallowed by the mould.  
         [0056]     On the other hand, the invention takes advantage of a means for detecting the level of the molten metal which is adapted to penetrate in the impression itself. Consequently, the invention gives a direct character to the measurement thus effected, this guaranteeing a possibility of monitoring the level of filling, during a large part of the filling process.