EP1981666A1

EP1981666A1 - Method of controlling the flow of adjuvant for the casting of a molten metal

Info

Publication number: EP1981666A1
Application number: EP07730910A
Authority: EP
Inventors: Nicolas Mocellin; Patrick Simonnin
Original assignee: D'etudes Et De Realisations Techniques Sert Ste
Current assignee: D'etudes Et De Realisations Techniques Sert Ste
Priority date: 2006-02-03
Filing date: 2007-02-02
Publication date: 2008-10-22
Also published as: US20090016569A1; WO2007088285A1; FR2897003B1; FR2897003A1; CN101378863A

Abstract

According to this method, the adjuvant is delivered from a supply means (12) placed above the casting bowl (4), a target zone (Z) for the theoretical passage of this adjuvant is chosen, said zone lying downstream of the supply means (12), and the actual passage of the adjuvant in the target zone (Z) is detected optically, by means of at least one camera (14). At least one image of the target zone (Z) is taken by means of the or each camera (14), this image being taken with an exposure time short enough to identify the density of particles of this adjuvant that are present in the or each image, and a warning signal is generated if the measured particle density is below a predetermined value.

Description

METHOD FOR CONTROLLING THE FLOW OF A CASTING ADJUVANT OF A MOLTEN METAL

The present invention relates to a method for controlling the flow of a casting aid of a molten metal.

In the field of foundry, it is known to make, by means of a mold cavity, a succession of molds, or clods, moving axially in the direction of a casting machine suitable for pouring molten metal. A pouring bowl, intended to receive this molten metal, is connected by a feed channel to the footprint to be filled.

Depending on the nature that it is desired to confer on the final material, it is sometimes necessary to pour into the pouring bowl, together with the molten metal, an adjuvant intended to give the cast metal particular metallurgical characteristics, when solidification. By way of example, if it is desired to limit the formation of carbides, it is known to use an adjuvant called inoculant, based on ferro-silicon. This process is known as "late inoculation".

For this purpose, there is provided a device for dispensing this adjuvant above the casting bowl. This is for example a worm for dosing the adjuvant and then conveyed to an inclined feed tube, the downstream end is placed above the casting bowl and in the vicinity of the jet of molten metal.

According to a first known solution, this adjuvant is continuously dispensed, so that the latter discharges not only into the casting bowl, but also to the surface of the clumps, during the displacement of the latter. In addition to the cost associated with high consumption of adjuvant, this solution also causes pollution constitutive sand clods as well as mechanical elements of the entire installation.

It is also known to pour the adjuvant discontinuously. For this purpose, when the casting bowl stops at the plumb with the casting machine, initiating the action of the screw, so as to cause the flow of the adjuvant. Then we proceed to the actual casting. Once this is done, the adjuvant supply is stopped. During the process described above, there are risks of clogging of the feed tube, which may be due to projections of molten metal at the downstream end of this tube. It is therefore necessary to control that the adjuvant is actually admitted into the casting bowl, in order to give the molten metal the required properties.

For this purpose, FR-A-2 820 063 describes a method for controlling the flow of this adjuvant, in which a target zone, theoretical passage of this adjuvant, which is disposed downstream of the device, is first chosen. allowing the feeding of this adjuvant. It is then necessary to detect by optical means, in particular by means of a CCD-type camera, the actual passage of this adjuvant into the aforementioned target zone. Finally, in the case where this camera does not detect the adjuvant theoretically present in this target zone, an alert signal is generated so as to warn the operator.

This known solution proves, in a global way, quite satisfactory. The object of the invention is however to improve the accuracy of this prior control method, in particular for certain values of the flow rate of the casting aid.

For this purpose, it relates to a method for controlling the flow of a casting aid, intended to be distributed during the casting of a molten metal in a casting bowl, in which method the adjuvant is dispensed from a supply means, in particular tubular, disposed above the pouring bowl, a target passage zone is chosen theoretical of this adjuvant, disposed downstream of the supply means, is detected optically, by means of at least one camera, the actual passage of the adjuvant in the target area and if necessary generates a signal of alert, characterized in that at least one image of the target area is made by means of the or each camera, assigning to this image a sufficiently low exposure time to identify the particle density of this adjuvant present on the or each image, and the alert signal is generated if the identified particle density is less than a predetermined value.

According to other features of the invention:

an exposure duration of each image of between 0.1 and 0.5 milliseconds is assigned; a duration of exposure of each image of about 0.2 milliseconds is assigned;

the adjuvant is dispensed at a flow rate of less than 10 grams / second, preferably less than 9 grams / second; - the or each camera is CMOS type;

several images are made during the entire casting of the molten metal in the pouring bowl and the warning signal is generated if, for at least one of said images, the density of the adjuvant particles identified is less than said value; predetermined; two successive images are separated by an interval whose duration is between 40 and 80 milliseconds; the adjuvant is directly poured into a jet of said molten metal;

at least one first camera whose beam extends parallel to a main axis of the adjuvant particle stream, seen from above, and at least one second camera, the beam of which is angularly shifted relative to the beam the first camera;

- The beam of the first camera and the beam of the second camera are mutually offset at an angle of between 10 and 30 °, especially close to 20 °.

The invention will be described below, with reference to the accompanying drawings, given solely by way of non-limiting examples and in which: - Figure 1 is a side view illustrating a first embodiment of the method of the invention ;

- Figures 2 and 3 are front views, illustrating two images obtained through the implementation of the method of the invention; and FIG. 4 is a view from above illustrating a second embodiment of the method of the invention.

FIG. 1 represents the general context in which the method according to the invention is implemented. There are shown several juxtaposed clods, which are each designated by the reference 2. Each pair of clumps defines, at its joint plane, a casting bowl 4.

The latter is suitable for receiving a stream of molten metal

6, discharged from a casting machine 8. The flow of metal flowing from the machine 8 is controlled, in a known manner, by a stopper not shown, or any other system. During the casting operation, it is sometimes necessary to add to the molten metal 6 an adjuvant, such as an inoculant. For this purpose, there are provided means for dispensing this adjuvant, which comprise a metering and conveying means, for example an Archimedean screw 10, extended by a feed tube 12 extending obliquely with respect to the horizontal. The theoretical course of the adjuvant between the downstream end of the tube 12 and the pouring bowl 4 is indicated by the arrow F.

According to the teaching of FR-A-2 820 063, a target zone, designated as a whole by the reference Z, is chosen which extends from the downstream end of the feed tube 12 to the vicinity of the region. where the metal jet 6 flows. This zone Z corresponds to the theoretical passage of the adjuvant, towards the pouring bowl 4.

Figure 1 also illustrates an optical device for implementing the method of the invention. This device firstly comprises a camera 14, for example of the CMOS (Complementary Metal Oxide Semiconductor) type. This camera 14 is connected to an image analysis system 16 associated with an alarm 18, for example of the visual type. This camera 14 is disposed on the same side of the metal jet 6 as the distribution means 10, 12, substantially in line with the latter. The beam 20 of the camera 14 is directed towards the target zone Z of theoretical passage of the adjuvant. The casting process is carried out as follows.

Once the seed train immobilized, so that the casting bowl 4 is in line with the casting machine 8, the screw 10 is actuated, so as to initiate the distribution of the adjuvant in the direction of the casting bowl 4. Concomitantly, the molten metal 6 is discharged from the casting machine 8, it being understood that the first particles of adjuvant must reach the pouring bowl 4 before the latter receives the metal jet. melted 6, which confers the required properties to all the molten metal admitted into the bowl.

The supply tube 12 is arranged so that, as soon as the molten metal 6 flows, the adjuvant is poured directly into the jet of this molten metal. This measure is advantageous since it allows the jet to entrain the adjuvant, so that the latter is instantly melted. On the other hand, if the adjuvant is dispensed directly into the tundish, it then floats for a certain time before being melted, which leads to the formation of agglomerated adjuvant plates that may remain above the bolus until 'at the end of the casting.

In order to check that the adjuvant is actually admitted into the pouring bowl 4, the camera 14 is able to detect the contrast caused by the adjuvant particles interposed between this camera and the molten metal jet 6, which constitutes a brilliant background United. This detection, known as shadows, is carried out in a manner known per se. According to the invention, it is a matter of implementing on this camera 14 a technique known per se, called "shutterization", by means of an electronic shutter. Under these conditions, the exposure time of each image, which can be achieved by this camera, is significantly reduced compared to conventional exposure times. Thus, if the usual duration is of the order of 40 milliseconds, the duration of exposure according to the invention has a value between 0.1 and 0.5 milliseconds, or 100 to 500 microseconds. By way of example, mention will be made of 200 microseconds as a typical value of this duration of exposure according to the invention.

FIGS. 2 and 3 illustrate two images produced by the camera 14, according to the procedure according to the invention explained above. In these figures, we find the target zone Z and the jet 6 of molten metal flowing in this zone Z. Given the very short exposure time, the position of the adjuvant particles in the space is is fixed, so that it is possible to distinguish these particles in the images of Figures 2 and 3.

In these figures, the adjuvant particles, which are assigned P references, are schematically represented in the form of a cross. It is then possible to identify, in a simple and precise manner, the density of these particles P in the target zone Z, namely the surface of this zone Z, in which particles P are present, which surface therefore forms a contrast with the jet 6 of molten metal. It is of course conceivable that this particle density, which is thus identified by means of the camera 14 and the analysis system 16, is representative of the amount of adjuvant actually present at a given instant in the target zone Z. In order to achieve a satisfactory control of the flow, it is necessary to determine beforehand a threshold value of the particle density P, as defined above. For this purpose, a standard type casting is carried out, for which it is visually ascertained that the adjuvant is actually present in the molten metal jet. As has been seen above, it is then possible, during this standard casting, to identify the density of particles P present in zone Z, which leads to obtaining the aforementioned threshold value, by means of the where appropriate the application of a certain tolerance.

Then, once this threshold value is determined, different images, similar to those of FIGS. 2 and 3, are made during the entire casting phase, the duration is typically between 5 and 20 seconds. These different images are taken at regular intervals, whose value is typically between 40 and 80 milliseconds. This allows access to a few hundred images, each of which is representative of the presence of adjuvant in the target area at a given time.

In the case where, for a significant number of these images, the measured particle density P is less than the threshold value determined above, the image analysis system 16 activates the alarm 18, so as to warn the user of the 'operator. In concrete terms, the image of FIG. 2 does not lead to the activation of the alarm, since the density of particles P present in the target zone Z is sufficiently high. On the other hand, this density of particles P measured in the image of FIG. 3 is smaller, so that it is lower than the threshold value and thus leads to the triggering of the alarm.

The invention achieves the previously mentioned objectives. Indeed, the Applicant has found that for relatively low adjuvant flow rates, the solution described in FR-A-2 820 063 shows some limitations in terms of accuracy.

Thus, by using the CCD camera mentioned in this state of the art, whose typical exposure time of each image is 40 milliseconds, the adjuvant particles form black lines, which are difficult to identify in the images produced using this method. camera. Under these conditions, for the aforementioned low flow rates, especially less than about 10 grams / second, the presence of these features is likely to distort the assessment of the amount of adjuvant actually present in the target area. On the other hand, thanks to the invention, the fact of very substantially lowering the exposure time of each image allows a very clear visualization of the various particles of adjuvant, in particular for low flow rates of the latter. Under these conditions, the density of these particles in the target zone can be precisely identified and then compared with a threshold value. This ensures a particularly reliable appreciation of the amount of adjuvant actually present in the molten metal stream.

The invention is not limited to the example described and shown.

In this regard, Figure 4 illustrates an alternative embodiment where there is, in addition to the camera 14 described with reference to the previous figures, an additional camera 14 '. In this figure 4, which is a view from above, there is found the molten metal jet 6, the feed tube 12, and the particle flow P of adjuvant. According to this embodiment, the beam 20 of the first camera 14 extends parallel to the main axis A of the feed tube 12, which also corresponds to the axis of the adjuvant flow, the latter being seen from above. In contrast, the beam 20 'of the second camera 14', while being directed towards the molten metal jet 6, is offset angularly with respect to the first beam 20 at an angle α. This angle α is typically between 10 and 30 degrees, especially close to 20 degrees. The arrangement of this FIG. 4 is advantageous insofar as the second camera 14 'provides access to another viewing angle, offset from that conferred by the first camera 14. The operator is then able to 'to access to an in-depth vision of the entire casting operation.

With the embodiment of Figure 4, it is possible to determine certain cases where the adjuvant is not poured into the jet, but directly into the casting bowl, or next to the latter, that is to say say on the sand of the mold where it is then totally inoperative.

In this case, the image produced by the first camera 14 shows a density of adjuvant particles present which is not lower than the threshold value. The possible anomaly may, however, be detected by the second camera 14 ', which produces an image from which the adjuvant particles are absent, which makes it possible to alert the operator.

Claims

A method of controlling the flow of a casting aid, to be dispensed when pouring molten metal into a casting bowl (4), wherein the adjuvant is dispensed from a casting means supply (12), in particular tubular, disposed above the casting bowl (4), a target zone (Z) for the theoretical passage of this adjuvant, disposed downstream of the supply means (12), is selected, and by means of optical means, by means of at least one camera (14, 14 '), the effective passage of the adjuvant in the target zone (Z) and, where appropriate, an alert signal is generated, characterized in that performing at least one image of the target area (Z) by means of the or each camera (14, 14 '), assigning to this image a sufficiently low exposure time to identify the particle density (P) of this adjuvant present on the or each image, and the warning signal is generated if the identified particle density is less than one val predetermined.

2. Method according to claim 1, characterized in that affects an exposure time of each image between 0.1 and 0.5 milliseconds.

3. Method according to claim 2, characterized in that affects an exposure time of each image of about 0.2 milliseconds.

4. Method according to any one of the preceding claims, characterized in that distributes the adjuvant at a rate less than 10 grams / second, preferably less than 9 grams / second.

5. Method according to any one of the preceding claims, characterized in that the or each camera (14, 14 ') is of the CMOS type.

6. Method according to any one of the preceding claims, characterized in that several images are made during the entire casting of the molten metal in the casting bowl (4) and the warning signal is generated if, for at least one of said images, the identified adjuvant particle density is less than said predetermined value.

7. Method according to the preceding claim, characterized in that two successive images are separated by an interval whose duration is between 40 and 80 milliseconds.

8. Process according to any one of the preceding claims, characterized in that the adjuvant is poured directly into a jet (6) of said molten metal.

9. Method according to any one of the preceding claims, characterized in that at least a first camera (14) is used whose beam (20) extends parallel to a main axis (A) of the particle stream. adjuvant, viewed from above, and at least a second camera (14 '), the beam (20') is angularly offset from the beam of the first camera.

Method according to one of the preceding claims, characterized in that the beam (20) of the first camera (14) and the beam (20 ') of the second camera (14') are mutually offset at an angle ( α) between 10 and 30 °, especially close to 20 °.