US3459949A

US3459949A - Detection of the level of the metal bath in the moulds for continuous casting

Info

Publication number: US3459949A
Application number: US415100A
Authority: US
Inventors: Pierre Poncet
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-12-01
Filing date: 1964-12-01
Publication date: 1969-08-05
Anticipated expiration: 1986-08-05

Description

Aug. 5, 1969 p, PONCET 3,459,949

DETECTION OF THE LEVEL OF THE METAL BATH IN THE MOULDS FOR CONTINUOUS CASTING Filed Dec. 1, 1964 2. Sheets-Sheet 1 ATTORNEY Aug. 5, 1969 P PQNCET 3,459,949

DETECTION OF THE LEVEL OF THE METAL BATH IN THE MOULDS FOR CONTINUOUS CASTING Filed Dec. 1. 1964 1 2 Sheets-Sheet 2 l M01. raw LEVEL H IGHT I flea-H126 CELL RESPOAASE Gm, 913? BY vm M A I :1 ORNEB ABSTRACT OF THE DISCLOSURE In the photo-electric detection of level variations within the mould of a continuous casting machine, there is formed an optical image of the upper surface of the molten bath within the mould, as for instance by means of an objective lens, and the cell is disposed on a spot of this image, as far as possible from the image of the jetof molten metal flowing into the mould, so as to be exclusively influenced by level variations ahd not by the jet itself.

This invention relates to the continuous casting of metals by means of a generally water-cooled mould into one end of which the molten metal is poured, while the solidified bar thus obtained is continuously withdrawn from the other end thereof.

One of the problems with which such a process is com cerned consists in maintaining the molten metal at a sub stantially constant level in .the mould by acting either on the rate of flow of the molten metal into the mould, or on the linear velocity of the solidified bar issuing therefrom. This adjustment is generally effected manually and it therefore requires the presence of a skilled operator in the vicinity of themould for detecting any substantial variation of the liquid level therein.

Several methods have been proposed for detecting these variations and for automatically effecting the corrections required. In one known embodiment a radiation pyrometer is disposed obliquely with respect to the mould in such manner that the intensity of heat energy which it receives depend upon the height of the level in the mould, the signal from the said pyrometer being used to actuate the correcting or regulating mechanism. The disadvantage of this known arrangement is that the pyrometer is in fiuenced not only by the surface of the bath of molten liquid in the mould, but also by a number of other heatemitting bodies, and primarily by the jet or stream which flows into the mould from the tundish or other liquid metal container. Since this jet or stream is at a substan tially higher temperature than the bath which is cooled by the mould wall, its undesirable influence is considerable. It is the object of the present invention to avoid this disadvantage.

In accordance with the present invention a method for the detection of the variation of the level of the bath of. molten metal in the mould of a continuous casting unit consists in forming an optical image of the surface of the bath within the mould by means of an objective lens or the like having its axis disposed obliquely with respect to the vertical axis of the mould inlet, and in so disposing at least one detecting photo-electric cell on a small sur=- face of the said image situated far from the image of the liquid jet which flows into the mould, that the said detecting cell be responsive to the variations of the said level above and below an average level corresponding to the desired normal level without being substantially influenced. by the jet itself.

In a first embodiment of the invention a single detect ing cell is disposed on the line which delimits the surface, of the bath within the mould in the optical image when a. mg a the level of the said bath corresponds to the normal levelv desired.

Alternatively a plurality of detecting cells are disposed on the line which delimits the surface of the bath within the mould in the optical image when the level of the said bath corresponds to the normal level. desired, the response of the said detecting cells being additive.

According to another feature of this invention a first group of at least one detecting cell is disposed on a line which delimits the surface of the bath within the mould in the optical image when the level of the bath is below the normal level desired, while a'second group of at least one detecting cell is disposed on a line which delimits the said surface in the said image When the level is above the normal level desired, the responses of all these de tecting cells being additive.

An auxiliary reference cell map further be so arranged as to detect the variations of external conditions, such as the temperature of the molten metal poured into the mould, which could influence the detecting cell or cells, without being itself influenced by the level variations in the mould, the response of the said reference cell, or a fraction thereof, being substracted from the response of the detecting cell or cells.

The auxiliary reference cell may be so disposed as to see the jet of high temperature liquid metal which flows into the mould, substantially where this jet issues from the pouring tundish and it may for this purpose be dis posed behind an auxiliary objective lens.

In the accompanying drawings:

FIG. 1 is "a diagrammatical illustration of a continu ous casting unit equipped with a detecting arrangement: according to this invention.

FIG. 2 shows the optical image formed by the objective lens of this arrangement.

FIG. 3 is; the graphic representation cell response versus molten level height in the arrangement of FIGS. 1 and 2.

FIG. 4 is a view similar to FIG. 2 but corresponding to an embodiment comprising a pair of cells responsive to the same level line in the optical image.

FIG. 5 is a view similar to FIG. 1, but corresponding to the embodiment illustrated in FIG. 2.

FIG. 6 illustrates the optical image in an embodiment comprising two pairs of cells, each pair being responsive to a predetermined level line,

FIG. 7 is the corresponding graphic representation response versus level height.

FIG. 8 shows the optical image in the case of three pairs of cells responsive to three different level lines.

FIG. 9 is the block diagram of a regulating device.

FIG. 10 diagrammatically shows a continuous casting unit with a detecting arrangement comprising a reference cell.

FIG. 11 shows a possible mode of connection of the reference cell in the regulating device.

In. FIG. 1 the molten metal 1 from a tundish 2 flows in the form of a jet or stream 3 into the upper end of a vertical water-cooled tubular mould 4 where it forms a liquid bath 5, while the solidified bar 6 is pulled from the lower end of the mould at a substantially uniform velocity. The flow rate is controlled by a conical refrac tory block or valve 7 actuated by a rod and lever gearing 8, 9, in order to maintain a substantially constant level in the mould. Alternatively the block or valve 7 may be dispensed with the control of the level in the mould being affected by variation of the linear velocity of the solidi tied bar 6.

An objective lens 10 is laterally disposed at an angle to the vertical axis of the mould, so as to form an. inverted optical image of the upper end thereof together with the low r portion of the liquid. iet and the upper surface. oi":

the molten metal bath 5, the whole as clearly shown FIG. 2. This image could be observed for instance on a ground glass disposed in a plane 11 transverse to the .axis of the lens. A photo-electric cell 12 is situated in the plane 11, in-the optical image of the bath '5, at a dis= tance from the image of the jet 3 and substantially on the line A, or normal level line, which limits the surface of the moten metal bath in the optical image of'FIG. 2 when the level is normal in the mould.

Considering FIG. '3 in which the adscissae represent the height of the molten metal level in the mould while the ordinates correspond to the response of the cell, when the level is low (line A in FIG. 2) the energy received by the cell is reduced and consequently its response (vo1tage, intensity or resistance) is small. When the level rises, the corresponding level line moves downwardly in FIG. 2 and when it approaches position A, the cell begins be ing illuminated. lts response rises rapidly until it is fully illuminated, the said response thereafter remaining substantially constant. It is seen that the gradient of the cell response is quite substantial between abscissae a and b. The response of the cell may thus be used for the auto matic actuation of the block or valve 7 in order to maintain the molten metal level at a substantially constant height close to the normal level. line A.

The cell is small with respect to the optical image and owing to its eccentric position therein, as indicated in FIG. 2., the said cell is substantially unaffected by the image of the bright jet 3 which it does not see. Even if this jet moves somewhat to and fro, as this most frequently occurs, its image will generally not reach the cell and cause a false response thereof.

The photo-electric cell 12.- is preferably selectively sen sitive to infra-red. It is thus practically unaffected by the flames of the gas burners which are generally used to protect the molten metal from oxidation.

In FIG. 4 the cell has been duplicated, in this sense that two individual cells 12a, 12b are disposed on the normal, level line A, one on each side of the image of the jet 3. These cells are so mounted electrically with re spect to each other (as for instance in series or in parallel according to their characteristics) that their responses be additive. If one of them is incidentally influenced by the jet during an abnormally large lateral displacement thereof, the undesirable effect on the final response will only be one half of what would have been the case with the arrangement of FIG. 2.

In FIGS. 5 and 6 the level detecting arrangement comprises two pairs of cells, each pair being arranged as in FIG. 4, apart from the fact that one pair 112a, 112b is substantially disposed on a low level line A and the

other pair

212a, 212b on a high level line A". FIG. 7 shows the graphic representation response versus level height respectively for the set 112a-112b and for the set 212a 21%. The curve in dash line represents the total or addi tive response, as for instance if both pairs are connected in series in the case of voltage emitting cells. It will be observed that the response gradient extends through a distance or height c-d which is much greater than in the case of FIG. 3. The automatic detection is therefore more progressive. It is obvious that one cell could be omitted in each pair. More particularly the arrangement could only comprise two cells, such as 112a and 212a, disposed on the same side of the jet. In such a case if the latter deviates towards the said side it influences both cells and therefore the resulting disturbance may he re duced to a minimum.

FIG. 8 illustrates an arrangement comprising three pairs of cells Ina-112b, 212a-212b and 312a-312b, the latter being disposed on the normal level line A. The response of the detecting unit is still more progressive than in the case of FIG. 5.

FIG. 9 illustratesin the form of a block diagram a possible embodiment of a regulating device in which. the

signal from a. single detecting cell 12 may be used for ill regulating the rate of flow of the molten metal or the linear velocity of the solidified bar. The cell 12 has one of its terminals grounded while the other one is connected by a wire 13 with the slider 14 of a potentiometer 15 the latter being connected across an electric cell 16. The resulting voltage (signal from the photo-electric cell minus adjustable voltage supplied by the potentiometer 15) is applied through a wire 17 to a synchronous chopper 18 actuated by the AC network. The alternating voltage thus obtained is amplified in an amplifier 19 and the am plified voltage is applied to the controlling phase of a main two-phase motor 20, the other phase of which is permanently energized by the AC network. By properly adjusting the setting of the potentiometer 15 it may be obtained that the voltage or potential of the wire 17 be zero when the level is normal, of one polarity when the level is high and of the other polarity when it is low. The chopper 18 energizes the main two-phase motor 20 in accordance for rotation in one direction or in the other, as this is well-known in the art, and the shaft 21 of this motor may directly actuate the controlling member, as for instance the rod and lever gearing 89 of FIG. 1.

It is finally to be observed that in the case of a plurality of cells (as for instance two), one could be used as a reference for modifying the conditions of the automatic regulation in accordance with external influences, and more particularly with the variations in the temperature of the molten metal. The reference cell may be arranged to see either the bath Seven at its lowest level, or the jet- 3 itself, and the resulting signal may be added to or substracted from the signal from the detecting cells. The reference cell may be disposed either in the optical image, or behind another objective lens, as diagrammatically indicated in FIG. 10 wherein the reference cell 412 behind the auxiliary lens 21 is arranged to see the jet 3 as it issues from the tundish 2.

FIG. 11 shows a possible electric diagram in which the reference cell 412 is connected across the above described potentiometer 15 of FIG. 9 in lieu of the cell 16. It will be appreciated'that the counter-voltage applied between the

wires

13 and 17 thus varies in accordance with the temperature of the jet and that it may be obtained that zero potential on the wire 17 may always correspond exactly to the normal level line A of FIG. 2 in spite of temperature variations.

It is to be understood that the term photo-electric cell should be understood lato sensu and that it should include any light-responsive device capable of emitting a signal in proportion to the intensity of the light received I claim:

1. A device to detect level variations with respect to a normal level of the upper surface of the liquid bath with in a mould for continuous casting having an inlet with a substantially vertical axis to continuously receive a jet of molten metal and an outlet from which a solidified bar is continuously extracted, said device comprising optical means completely exterior to said mould to form a optical image of the upper surface of said bath with an optical image of said jet flowing thereinto; and at least one de= tecting photo-electric cell. which is small relative to the size of the image of the upper surface disposed at a small portion of said optical image of said surface, said photo electric cell being situated far from the image of said jet, in such manner that said cell is responsive to level variations of the upper surface of said bath within said mould above and below said normal level without being sub stantially influenced by said jet itself.

2. In a device as claimed in claim 1, said optical means comprising an objective lens having its axis obliquely disposed with respect to the vertical axis of the inlet of said mould.

3.. A device to detect level variations with respect to a normal level of the upper surface of the liquid bath within av mould for continuous casting having an inlet with a substantially vertical axis to continuously receive a jet of molten metal and an outlet from which a solidi= fied bar is continuously extracted, said device compris= ing optical means completely exterior to said mould to form an optical image of :the upper surface of said bath with an optical image of said jet flowing thereinto; at least one detecting photo-electric cell which is small rela= tive to the size of the image of the upper surafce disposed at a small portion of said optical image of said surface, said photo-electric cell being situated far from the image of said jet, in such manner that said cell is responsive to level variations of the upper surface of said bath within said mould above and below said normal level without being substantially influenced by said jet itself; at least one reference photo-electric cell so disposed that it is influenced by the general environment of said mould, but not by the variations of the liquid bath level therein; and means to subtract an aliquot portion of the rep sonse of said reference cell from the response of said detecting cell to reduce the influence of said environment on said detecting cell:

5 4. In a device as claimed in claim 1, said optical means comprising an objective lens having its axis obliquely dis posed with respect to the vertical. axis of the inlet of said mouldl References Cited UNITED STATES PATENTS 2,246,907 6/1941 Webster Normand- 22-473 23,306,073 12/1942 Metcalf Wmmwmmwr, 250-238 10 $045,125 7/ 1962 Mason -s 250-238 3,293,705 12/1966 Lenz et al, n s.. ..r 22--79 OTHER REFERENCES Athens: Temperature Compensation of Silicon Solar 15 Cells, IBM Technical Diclosure Bulletin, vol, 3, No. 10, March 1965, p. 65,

WALTER. STOLWEIN, Primary Examiner CL XR 20 73 290