EP1616643A2 - Installation for pouring molten metal in a mould, device to detect the level of the molten metal and process for using this installation - Google Patents

Abstract

The mould (2) has an inlet (10) for pouring molten metal (6) into the mould impression (14) through a feed channel (12), and a detector (16, 18, 20, 22, 24, 30) to measure the level of molten metal in the mould. The detector is preferably electromagnetic in form, creating force lines (24, 24') that are disturbed by the molten metal level as it rises inside the mould, transmitting a signal through emitting (16) and receiving (22) coils to a processor (30) and flow controller (32).

Description

The present invention relates to a filling installation of a mold with liquid metal, as well as a method for the implementation of this installation.

In the technical field of the foundry, it is known to use a succession of molds, also called clods, which are made of sand. Conventionally, each mold comprises a casting bowl, intended to receive the molten metal, and at least one cavity connected to this bowl via a feed channel. In service, it involves moving each mold towards a casting machine, suitable for pouring molten metal.

This casting operation is accompanied by several requirements.

First of all, it is important to quickly flood the tundish, and keep it in the filled state while the metal is spreading towards the footprints. This makes it possible to ensure flows of high quality, free of voids, defects and gas trapping.

It is also necessary that the flow rate of metal swallowed by the mold is permanently equal to the flow rate delivered by the casting machine, in order to avoid overflow, as well as any underfeed. Finally, at the end of the casting, the level of metal in the bowl must be controlled, so that it exactly fills the mold, without causing overflow.

It is firstly known how to fill these molds manually, namely that this operation is provided by an operator. It is also possible to implement this filling automatically, so that it is controlled by a programmable equipment.

Thus, there are known optical systems, which take advantage of a beam directed to the casting bowl to determine the filling level of the casting bowl while throughout the casting. This known solution, however, involves a disadvantage, related in particular to its lack of knowledge of the actual level of filling of the mold during the casting process.

That said, the invention aims to provide an installation for controlling, reliably and accurately, the filling of a mold by means of liquid metal.

• au moins un moule comportant un bol de coulée, un canal d'alimentation, ainsi qu'au moins une empreinte reliée audit bol par ledit canal ;
• une cuve destinée à recevoir le métal liquide devant être coulé dans le moule ; et
• des moyens propres à déterminer de manière directe l'évolution du niveau de métal fondu dans l'empreinte, ces moyens de détermination comportant des moyens de détection de la présence de ce métal liquide dans l'empreinte, ces moyens de détection étant propres à pénétrer au moins partiellement dans le volume intérieur de cette empreinte.

For this purpose, it relates to an installation for filling a mold with liquid metal, comprising:

• at least one mold comprising a pouring bowl, a feed channel, and at least one cavity connected to said bowl by said channel;
• a tank for receiving the liquid metal to be poured into the mold; and
• means capable of directly determining the evolution of the level of molten metal in the cavity, these determination means comprising means for detecting the presence of this liquid metal in the cavity, these detection means being adapted to penetrate at least partially in the interior volume of this footprint.

• les moyens de détection sont de nature électromagnétique ;
• les moyens de détermination comprennent des moyens de création d'un champ électromagnétique, dont des lignes de champ forment lesdits moyens de détection, ces lignes de champ étant propres à être perturbées par le métal liquide présent dans l'empreinte ;
• les moyens de création du champ électromagnétique comprennent au moins une bobine émettrice, un générateur électrique propre à exciter cette bobine émettrice, ainsi qu'au moins une bobine réceptrice propre à coopérer avec ladite bobine émettrice ;
• il est prévu deux bobines réceptrices, une première bobine réceptrice étant placée entre la bobine émettrice et le moule, alors que l'autre bobine réceptrice est placée à l'opposé de la bobine émettrice par rapport au moule ;
• les moyens de détermination comprennent également des moyens propres à transformer l'intensité de la perturbation subie par lesdites lignes de champ en un signal analogique représentatif de l'évolution du niveau de métal liquide dans l'empreinte, ce signal analogique correspondant par exemple à l'évolution d'une tension en fonction du niveau de remplissage du moule ;
• les moyens de détermination comprennent également des moyens d'obtention d'une courbe instantanée, à partir dudit signal analogique, représentative de l'évolution du niveau de métal fondu dans l'empreinte, ainsi que des moyens de comparaison de cette courbe instantanée avec une courbe de référence, alors qu'il est en outre prévu des moyens, propres à commander le débit de métal fondu déversé à partir de la cuve, dans le cas où la courbe instantanée diffère de la courbe de référence dans une mesure inadmissible ;
• les moyens de commande sont propres à actionner un obturateur mobile, dont est équipée la cuve.

According to other features of the invention:

• the detection means are of electromagnetic nature;
• the determination means comprise means for creating an electromagnetic field, whose field lines form said detection means, these field lines being adapted to be disturbed by the liquid metal present in the cavity;
• the means for creating the electromagnetic field comprise at least one transmitting coil, an electric generator capable of exciting this transmitter coil, and at least one receiver coil adapted to cooperate with said transmitter coil;
• two receiver coils are provided, a first receiver coil being placed between the transmitter coil and the mold, while the other receiver coil is placed opposite the transmitter coil with respect to the mold;
• the determination means also comprise means capable of transforming the intensity of the disturbance undergone by said field lines into an analog signal representative of the evolution of the level of liquid metal in the cavity, this analog signal corresponding for example to the evolution of a voltage as a function of the filling level of the mold;
• 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 cavity, as well as means for comparing this instantaneous curve with a reference curve, while there is further provided means for controlling the flow of molten metal discharged from the tank, in the case where the instantaneous curve differs from the reference curve to an inadmissible extent;
• the control means are adapted to actuate a movable shutter, which is equipped with the tank.

• on actionne les moyens de création du champ électromagnétique, de manière à générer des lignes de champ pénétrant au moins partiellement dans le volume intérieur de l'empreinte ; et
• on détermine l'évolution du niveau de métal liquide dans l'empreinte, en fonction de l'intensité de la perturbation subie par ces lignes de champ.

The subject of the invention is also a method for implementing the installation as defined above, comprising the following steps:

• the means for creating the electromagnetic field are actuated so as to generate field lines penetrating at least partially into the interior volume of the cavity; and
• the evolution of the level of liquid metal in the imprint is determined as a function of the intensity of the disturbance undergone by these field lines.

• on compare ladite courbe instantanée et ladite courbe de référence, et on modifie le débit de métal liquide déversé à partir de la cuve, si la différence entre cette courbe instantanée et cette courbe de référence est inadmissible ;
• on modifie le débit de métal liquide en déplaçant ledit obturateur ;
• on choisit un seuil prédéterminé de l'empreinte, on détecte l'instant auquel le niveau de métal liquide atteint ce seuil, on laisse s'écouler un intervalle de latence, dépendant notamment de la valeur instantanée du débit de métal fondu déversé à partir de la cuve, et on arrête l'admission de métal liquide dans le moule au terme de cet intervalle de latence.

According to other features of the invention:

• comparing said instantaneous curve and said reference curve, and modifying the flow rate of liquid metal poured from the tank, if the difference between this instantaneous curve and this reference curve is inadmissible;
• the flow rate of liquid metal is changed by moving said shutter;
• a predetermined threshold of the cavity is selected, the moment at which the level of liquid metal reaches this threshold is detected, a latency interval is allowed to run, depending in particular on the instantaneous value of the flow of molten metal discharged from the tank, and the admission of liquid metal into the mold is stopped at the end of this latency interval.

• la figure 1 est une vue générale, illustrant une installation de remplissage d'un moule à sable avec du métal liquide, qui est conforme à l'invention ;
• la figure 2 est une vue analogue à la figure 1, illustrant l'installation de la figure 1 durant la phase de remplissage proprement dite et
• la figure 3 est un graphe représentant l'évolution du niveau de métal fondu en fonction du temps, à l'intérieur d'une empreinte dont est pourvu un moule équipant l'installation des figures 1 et 2.

The invention will be described below, with reference to the accompanying drawings, given solely by way of non-limiting example, in which:

• Figure 1 is a general view, illustrating a filling plant of a sand mold with liquid metal, which is according to the invention;
• FIG. 2 is a view similar to FIG. 1, illustrating the installation of FIG. 1 during the actual filling phase and
• FIG. 3 is a graph showing the evolution of the level of molten metal as a function of time, within a cavity provided with a mold equipping the installation of FIGS. 1 and 2.

The installation of Figures 1 and 2 comprises different molds, only one is shown, while being assigned the reference 2. In service, this mold runs below a tank 4, which is filled with a liquid molten metal 6, which is for example cast iron or steel. This metal was poured into the tank 4 in a conventional manner, through a pocket not shown.

The bottom of the tank 4 is closed, in known manner, by a shutter 8, also called stopper. The latter can be operated along its main axis, namely vertically in Figure 1, through an actuator 9 of conventional type.

Each mold, which is of generally parallelepipedic shape, usually comprises a pouring bowl 10, of frustoconical shape, in which flows the molten metal 6 poured from the tank 4. This bowl 10 is extended by a feed channel 12, which opens into at least one cavity 14. In the example described and shown, there are two such impressions 14, shown schematically.

The installation of FIGS. 1 and 2 also comprises means for determining the evolution of the level of molten metal inside the cavity 14. These are first of all three electromagnetic coils, mounted on a same axis, in this case horizontal.

More specifically, there is provided a central transmitting coil 16, adapted to be excited by a sinusoidal electrical signal, whose frequency is a few kilohertz. For this purpose, the coil 16 is connected to a suitable generator 18, of a type known per se.

The transmitting coil is associated with two lateral coils, said receivers, one of which is placed in the vicinity of the mold 2. On the other hand, the other receiver coil 22 is placed opposite this mold 2, with respect to the transmitter central coil 16.

In Figures 1 and 2, there is shown a single set of three coils, right of the mold. It should be noted that Another set of coils may optionally be provided in the vicinity of the other imprint, namely to the left of these figures.

As a further alternative, the coils may be placed above the mold, or near an angle thereof. In this respect, the axis of these coils is then respectively vertical or oblique.

When the generator 18 supplies the transmitter coil 16, an electromagnetic field is created, which flows between the receiver coils 20 and 22. The field lines thus created are illustrated in FIGS. 1 and 2, where they are represented in FIG. dashed lines.

More precisely, the field lines circulating in the vicinity of the first receiver coil 20 are noted. As shown in FIGS. 1 and 2, these lines 24 extend in part, in an area marked 24 ', to the In contrast, the field lines 26, extending in the vicinity of the other receiver coil 22, ie opposite the coil 20, do not interfere with the coil. footprint 14.

The three coils 16, 20 and 22 are also connected, via a line 28, to an electronic unit 30, the functions of which will be described in the following. This unit 30 is finally connected, via a control line 32, with the actuator 9.

The implementation of the filling installation, described above, will now be explained in the following.

It is first of all to operate the actuator 9, 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 indentations 14, as illustrated in FIG. 2.

It is conceivable that, as it is mounted in the cavity 14, the liquid metal is likely to disturb the electromagnetic field generated by the coils 16, 20 and 22, in particular in the zone 24 'of the field lines 24. Under these conditions, these field lines, which penetrate in part into the interior volume of the cavity, are able to detect the presence of the molten metal in this cavity.

Furthermore, it should be noted that the intensity of the aforesaid disturbance increases as the cavity 14 is filled. Under these conditions, the electronic unit 30 is able to transform the value of the disturbance undergone by the field lines 24 into an analog signal, which corresponds, for example, to a variation of the voltage as a function of the actual filling level of the cavity 14. The value of this voltage is therefore representative, at each instant, of the level of metal in the footprint.

FIG. 3 is a graph illustrating this evolution of the voltage, thus determined by the electronic unit 30, as a function of time. First of all, there is a zone, denoted I, in which this voltage is zero, which corresponds to the absence of interference of the molten metal with the field lines 24. Then, from the moment at which this interference begins to occur, the voltage increases with increasing time as the impression 14 is filled by the molten metal. This phase of rising of the level of this molten metal corresponds to zone II of this graph.

It is then a question of verifying that the rise of the level of molten metal in the cavity 14 takes place at an acceptable speed. For this purpose, a preliminary phase is carried out learning, allowing access to a curve not shown, showing the evolution of the voltage as a function of the actual filling level of the cavity 14, during a filling said reference.

Then, if the electronic unit 30 finds that the instantaneous evolution of the voltage differs unacceptably 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 moment, it is a question of reducing the flow of molten metal discharged from the tank 4, by lowering or even closing the stopper 8. On the other hand, if this voltage instant is significantly lower than the reference voltage, it is to raise the stopper 8, to increase the flow of molten metal administered from the tank 4.

Furthermore, the final phase of the casting of molten metal is carried out as follows. It is first of all to detect the moment at which the level of molten metal reaches a predetermined threshold of the imprint, which is materialized by the reference S, visible in FIG. 2. It can be seen that, at this moment, the voltage shown in FIG. 3 reaches a corresponding value, denoted V _s .

Then, a latency interval is allowed, which depends on the instantaneous value of the flow of molten metal discharged from the tank 4. Finally, at the end of this interval, the electronic unit 30 controls the actuator 9, so that to cause the closure of the stopper 8, which causes the stop of the supply of molten metal.

It should be noted that the range and the sensitivity of the sensor, which constitute the three coils 16, 20 and 22, can be adapted according to the characteristics of the mold. Thus, in the case where each of these coils is formed of 200 turns, which have a section Rectangular 140 mm by 110 mm and separated from each other by a distance of 210 mm, the corresponding measuring range inside the mold has a depth of 300 mm on a surface of about 200 mm by 250 mm , centered on the coils.

In addition, it will be noted that the arrangement of the three coils 16, 20 and 22 is advantageous, since the receiving coils 20 and 22 are mounted in opposition, namely that the coil 20 is adjacent to the mold, while the coil 22 is opposed thereto. . Thus, only the field lines 24 are disturbed during the rise of the metal, while those 26 do not undergo such a disturbance. Consequently, in a manner known per se, the electronic unit 30 benefits from a differential signal regime, thus making it possible to increase the sensitivity of the measurement.

The invention achieves the previously mentioned objectives.

Indeed, the prior art uses an optical measurement in the casting bowl, which is very poor in information since it is not representative of the level of the molten metal in the cavity. Thus, such a measurement corresponds only to the image of the difference between, on the one hand, the feed rate of the molten metal from the tank 4 and, on the other hand, the instantaneous flow rate swallowed by the mold.

In contrast, the invention takes advantage of a means for detecting the level of the molten metal, able to penetrate into the cavity itself. Therefore, the invention gives a direct character to the measurement thus made, which guarantees a possibility of control of the filling level during a large part of the filling process.

Claims (12)

Filling plant of a mold (2) with liquid metal (6), comprising: - At least one mold (2) comprising a casting bowl (10), a feed channel (12), and at least one cavity (14) connected to said bowl by said channel; - a tank (4) for receiving the liquid metal (6) to be poured into the mold (2); and means (16, 18, 20, 22, 24, 30) capable of directly determining the evolution of the level of molten metal in the cavity (14), said determination means comprising detection means (24) the presence of this liquid metal in the cavity, these detection means being adapted to penetrate at least partially into the interior volume of this footprint. Installation according to claim 1, characterized in that the detection means (24) are of electromagnetic nature. Installation according to claim 2, characterized in that the determining means comprise means (16, 18, 20, 22) for creating an electromagnetic field, whose field lines (24) form said detection means, these lines field being adapted to be disturbed by the liquid metal present in the cavity (14). Installation according to Claim 3, characterized in that the means for creating the electromagnetic field comprise at least one transmitting coil (16), an electric generator (18) able to excite this transmitting coil, and at least one receiver coil (20). 22) adapted to cooperate with said transmitting coil. Installation according to Claim 4, characterized in that two receiving coils (20, 22) are provided, a first receiver coil (20) being placed between the transmitting coil (16) and the mold (2), while the another receiver coil (22) is placed opposite the transmitter coil (16) with respect to the mold (2). Installation according to any one of claims 3 to 5, characterized in that the determination means also comprise means (30) capable of transforming the intensity of the disturbance undergone by said field lines (24) into a representative analog signal the evolution of the level of liquid metal in the cavity (14), this analog signal corresponding for example to the evolution of a voltage as a function of the filling level of the mold. Installation according to claim 6, characterized in that the determination means also comprise means (30) for obtaining an instantaneous curve, from said analog signal, representative of the evolution of the level of molten metal in the imprint , as well as means (30) for comparing this instantaneous curve with a reference curve, while means (32) are furthermore provided for controlling the flow of molten metal discharged from the tank (4). ), in the case where the instantaneous curve differs from the reference curve to an inadmissible extent. Installation according to claim 7, characterized in that the control means (32) are adapted to actuate a movable shutter (8), which is equipped with the vessel (4). Method of implementing the installation according to any one of Claims 3 to 8, comprising the following steps: the means (16, 18, 20, 22) for creating the electromagnetic field are actuated so as to generate field lines that penetrate at least partially into the interior volume of the cavity (14); and the evolution of the level of liquid metal in the cavity (14) is determined as a function of the intensity of the disturbance undergone by these field lines. Process according to Claim 9, for the implementation of the installation according to one of Claims 7 or 8, characterized in that said instantaneous curve and said reference curve are compared, and in that the flow rate is modified. of liquid metal spilled from the tank (4), if the difference between this instantaneous curve and this reference curve is inadmissible. Process according to Claim 10, for the implementation of the installation of Claim 8, characterized in that the flow rate of liquid metal is changed by moving said shutter (8). Process according to any one of Claims 9 to 11, characterized in that a predetermined threshold (S) of the cavity (14) is chosen, the moment at which the level of liquid metal reaches this threshold is detected, it is left a latency interval, depending in particular on the instantaneous value of the flow rate of molten metal discharged from the tank (4), is stopped and the admission of liquid metal into the mold (2) is stopped at the end of this interval of latency.

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