[0001] The present invention relates to a method for controlling the level of steel in continuous
casting in an ingot mold, in particular for small sized billets.
[0002] It is known that the method for producing steel in continuous casting, first created
for producing basic steels, has progressively developed to a more advanced quality.
[0003] For example, billets currently produced with this method are required to exhibit
almost absolute surface and sub-surface integrity, which can only be obtained by non-linear
(parabolic and derivative) taper ingot molds and with the precise control of functional
parameters.
[0004] Among these essential parameters, the control of steel level in an ingot mold is
certainly important. This applies to both what relates to the absolute value (that
is, the exact detection of the meniscus position) and to what relates to the stability
of such value, the first one since it determines the initial size of the skin being
moulded and the consequent conditions of cooling of the billet, and the second one
since it is a potential cause of inclusions caused by covering dust in the steel thus
produced.
[0005] To this purpose, a number of methods for detecting the steel level in an ingot mold
have been produced so far, but each of them exhibits a series of inaccuracies that
makes them not sufficiently reliable. Gross errors even occur in known methods, above
all if applied to small sized ingot molds (that is, having a side up to 160 mm).
[0006] With reference to the above prior art, it can be noted that the methods used so far
can be summarised as radioactive, optical, magnetic and thermal methods.
[0007] The method based on a radioactive level measurement is the most widespread. This
method reads the variation in a radioactive flow darkened by the level of steel present
in the ingot mold.
[0008] It must be underlined that a recent survey conducted on a continuous casting machine
for billets has shown a considerable inaccuracy in the determination of the absolute
value of the steel level. This occurs due to the uneven formation of solidified slag
between the steel meniscus and the same ingot mold wall. Such slag screen radioactive
rays and alter the actual value of steel level even by 30/40 mm.
[0009] Moreover, it should not be forgotten that this method exhibits a high speed of detection
of the variations in the steel level, which is associated to the low accuracy in the
determination of such level value.
[0010] The second method, of the optical type, acts by reading the level of light emitted
by the meniscus surface or the light of a luminous beam reflected by the covering
dust.
[0011] This method is almost exclusively used in free casting since it detects the upper
portion of what is present in the ingot mold and is not capable of distinguishing
between steel, slag or covering dust.
[0012] Moreover, such behaviour turns dust thickness errors into coarse errors of evaluation
of the level of the same steel.
[0013] In any case, it should not be forgotten that the optical method maintains a high
speed of detection of variations in the steel level. However, it should also be underlined
that there is an absolute inaccuracy in the level determination due to the above difficulties.
[0014] The third method, of the magnetic type, essentially consists in a sensor (a coil)
detecting the variations of magnetic "resonance" surrounding it. This method is mainly
used for controlling the steel level in continuous casting for thick slabs or blooms
since it is much affected by the variations of magnetic permeability of the ingot
mold copper as temperature changes.
[0015] This type of problem requires the sensor to be arranged at a considerable distance
from the ingot mold walls; this particular prediction is not feasible in continuous
casting for billets, for reasons of size, due to their very small size.
[0016] In any case, it can be said that the magnetic method exhibits a high speed of detection
of variations in the steel level, beside a good accuracy in the level determination.
On the other hand, the magnetic detection method cannot be used for producing small
sections (for example, smaller than 160 mm) and has a very high purchase cost.
[0017] Finally, the fourth known measurement method is that called thermal method, and is
based on the fact that the thermal spectrum on the ingot mold wall is function of
the steel level. Thus, in this detection method, the level of the same steel is read
in an indirect manner through the detection of the ingot mold wall temperature.
[0018] Such temperature measurement occurs through the use of micro-thermocouples inserted
into the copper wall of the ingot mold, or through the detection of the magnetic permeability
variation induced in copper by the different temperature.
[0019] Unfortunately, the thermal nature of the method causes a response delay and the resulting
hysteresis is the reasons why the same method is generally not used in particular
cases.
[0020] In any case, the thermal method exhibits an excellent accuracy in the determination
of the level (if read in precise conditions) but exhibits the defect of having absolute
unreliability in the dynamic detection of level variations.
[0021] All of the above causes serious problems to obtain a measurement of steel level meeting
all requirements to have an optimum control over the continuous casting method. This
is even more felt in particular for the production of small section billets mentioned
above.
[0022] US-A-4 770 230 relates to an apparatus for starting a continuous casting plant having
an arrangement for controlling the level if molten metal in a continuous casting mould.
[0023] GB-A-1 463 624 refers to a method and an apparatus for controlling the pouring of
molten metal in a continuous casting process.
[0024] Thus, a general object of the present invention is to find a different solution to
the technical problem mentioned above.
[0025] Another object is to realise a method for controlling the level of steel in continuous
casting in an ingot mold, in particular for small sized billets, which should be adapted
for carrying out the above task, even though being easy to operate.
[0026] These objects according to the present invention are achieved by realising a method
for controlling the level of steel in continuous casting in an ingot mold, in particular
for small sized billets, as illustrated in the attached independent claim.
[0027] Further important features and details of the present invention are illustrated in
the dependent claims.
[0028] The features and advantages of a method for controlling the level of steel in continuous
casting in an ingot mold, in particular for small sized billets, according to the
present invention, will appear more clearly from the following detailed description
of an embodiment made by way of a nonlimiting example with reference to the attached
drawings. In such drawings:
- figure 1 is a first side elevation section view of an ingot mold for billets to which
a device for controlling the level of steel is attached;
- figure 2 is a second side elevation section view of the device of figure 1;
- figure 3 is a top plan view of the device shown in figures 1 and 2.
[0029] With general reference to the various figures, there is shown a schematic view of
a device for controlling the level of steel in continuous casting in an ingot mold,
in particular for small sized billets, indicated with reference numeral 11. Such device
11 is arranged in the proximity of an outside wall 12 of a copper ingot mold 13 with
square section, around which a water conveyor 14 is arranged for cooling it during
the steel continuous casting operations. Steel is fed through a casting duct 15 directly
connected to a tundish (not shown) that allows realising a series of sequences in
the desired number.
[0030] Moreover, for example, such water conveyor 14 is provided with a flanging 16 at which
device 11 according to the present invention is arranged.
[0031] Device 11 comprises a radioactive detector and a thermal detector. In particular,
it can be noted that the radioactive detector comprises a radioactive source 17, for
example realised with cobalt 60, and a scintillator 18, among which a radioactive
flow sets up. Such flow remains constant until it is darkened by a level 19 of steel
present in the ingot mold entering from the casting duct 15. Thereby, there occurs
a variation of a radioactive flow that indicates the variation of position of level
19 of steel into the ingot mold 13.
[0032] A special connection line 20 is connected to a central processor 21 that receives
the variation signal and commands a limitation or an increase of steel feeding from
the casting duct 15 to maintain the level 19 of steel constant.
[0033] Device 11 for controlling the level of steel in continuous casting in an ingot mold
also comprises a thermal detector, globally indicated with reference numeral 22, also
connected to the central processor 21 through its own connection line 23.
[0034] Such thermal detector 22 checks the thermal spectrum on wall 12 of ingot mold 13
based on the level 19 of steel. Such measurement of temperature is carried out, for
example, through the detection - by the thermal detector 22 - of the variation of
magnetic permeability induced in the copper wall 12 of ingot mold 13.
[0035] Such combination of radioactive detectors 17, 18 and thermal detector 22 allows correcting
all technical problems of the prior art.
[0036] In fact, by using the two radioactive detectors 17, 18 and the thermal detector 22
at the same time, the resulting assembly exhibits much better features than those
of known devices.
[0037] Such device allows realising a new and original method for controlling the level
of steel in continuous casting ion an ingot mold, in particular for small sized billets.
[0038] In fact, after a first initial step for regulating the continuous casting method
in an ingot mold 13 for billets, the radioactive detector 17, 18 is actuated at a
high speed of detection of changes in the level 19 of steel. In fact, in this first
step a broad detection of the level that sets up is sufficient since, among the other
things, the solidified slag is minimal.
[0039] This type of detection allows a quick, effective and quite precise start up of the
casting operation.
[0040] In a second step at steady condition, as soon as the start up transient has finished,
the thermal detector 22 is actuated, which signals the steel level 19 to processor
21.
[0041] Such thermal detector 22 detects with the utmost accuracy the steel level 19, once
the temperature of copper of wall 12 of ingot mold 13 has reached the predetermined
level.
[0042] In this way, the control of the level of steel in an ingot mold for small sized billets
is optimised.
[0043] In fact, the first detector 17, 18 exhibits a high dynamic response capability (about
0,10 seconds) whereas the second detector 22 is highly accurate when reading the level
(excluding the transients).
[0044] It is thus confirmed that the new method for controlling the level consists of the
radioactive system, which operates in a traditional manner during the automatic start
up step and during the initial regulation step. Afterwards, the level value detected
by the thermal system (suitably filtered in time to ensure the utmost accuracy) corrects
the value assumed by the radioactive system according to its priority, adjusting it
to the new condition. In this way, the correction of quick variations of the level
relies on the quick response of the radioactive system, which starts the regulation
based on the reference determined by the thermal system as absolute value.
[0045] It has thus been noted that a method for controlling the level of steel in continuous
casting in an ingot mold, in particular for small sized billets, according to the
present invention, achieves the objects mentioned above.
[0046] The method for controlling the level of steel in continuous casting in an ingot mold,
in particular for small sized billets, of the present invention thus conceived, can
be subject to several changes and variants, all falling within the scope of the same
invention.
[0047] Moreover, in the practice, the materials and units used, as well as their size and
components, can be of any type according to the technical requirements.
1. Method for controlling the level of steel in continuous casting in an ingot mold,
wherein there are provided a radioactive detector (17, 18) and a thermal detector
(22) in the proximity of a level (19) of the steel fed to an ingot mold (13) by a
casting duct (15) characterised in that in a first initial step for regulating the continuous casting method, said radioactive
detector (17, 18) is actuated at a high speed of detection of changes in the level
(19) of steel, and in a second step at steady condition, as soon as the start up transient
has finished, said high-precision steel level (19) thermal detector (22) is actuated.
2. Method according to claim 1, characterised in that said radioactive detector (17, 18) detects a variation of a radioactive flow for
signalling the variation of position of said steel level (19) into said ingot mold
(13).
3. Method according to claim 1, characterised in that said thermal detector (22) detects the variation of temperature of the copper of
a wall (12) of said ingot mold (13).
4. Method according to claims 1-3, characterised in that a central processor (21) receives variation signals from said detectors (17, 18;
22) and commands a limitation or an increase of steel feeding from said casting duct
(15) to maintain said level (19) of steel constant.
1. Verfahren zum Regeln der Füllstandhöhe von Stahl beim Stranggießen in einer Kokille,
wobei ein Radioaktivitätsdetektor (17, 18) und ein thermischer Detektor (22) in der
Nähe eines Füllstands (19) des mittels eines Gießkanals (15) der Kokille (13) zugeführten
Stahls vorgesehen sind, dadurch gekennzeichnet, dass in einem ersten, anfänglichen Schritt zum Regulieren des Stranggießverfahrens der
Radioaktivitätsdetektor (17, 18) mit einer hohen Erfassungsgexhwindigkeit bezüglich
Änderungen der Füllstandshöhe (19) von Stahl betrieben wird und in einem zweiten Schritt
im Beharrungszustand, sobald die anfänglichen Schwankungen geendet haben, der hochpräzise
thermische Detektor (22) für die Füllstandhöhe des Stahles betrieben wird.
2. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, dass der Radioaktivitätsdetektor (17, 18) eine Änderung eines radioaktiven Flusses erfasst,
um die Änderung der Lage der Füllstandhöhe (19) des Stahles in der Kokille (13) zu
signalisieren.
3. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, dass der thermische Detektor (22) eine Temperaturänderung des Kupfers einer Wand (12)
der Kokille (13) erfasst.
4. Verfahren gemäß den Ansprüchen 1 bis 3, dadurch gekennzeichnet, dass ein zentraler Prozessor (21) Änderungssignale von den Detektoren (17, 18; 22) empfängt
und eine Begrenzung oder eine Erhöhung der Stahlzufuhr aus dem Gießkanal (15) anweist,
um die Füllstandhöhe (19) des Stahles konstant zu halten.
1. Procédé de contrôle du niveau d'acier dans une lingotière, lors d'un procédé de coulée
continue, un détecteur radioactif (17, 18) et un détecteur thermique (22) étant prévus
à proximité d'un niveau (19) de l'acier qui est introduit dans une lingotière (13)
par une conduite de coulée (15), caractérisé en ce que, dans une première étape initiale de régulation du procédé de coulée continue, le
détecteur radioactif (17, 18) est actionné à une vitesse élevée de détection des modifications
du niveau (19) d'acier et, dans une deuxième étape, à l'état stabilisé, dès que l'état
transitoire de démarrage est passé, le détecteur thermique (22) haute précision du
niveau (19) d'acier est actionné.
2. Procédé selon la revendication 1, caractérisé en ce que le détecteur radioactif (17, 18) détecte une variation de flux radioactif pour signaler
la variation de la position du niveau d'acier (19) dans la lingotière (13).
3. Procédé selon la revendication 1, caractérisé en ce que le détecteur thermique (22) détecte la variation de température du cuivre d'une paroi
(12) de la lingotière (13).
4. Procédé selon les revendications 1-3, caractérisé en ce qu'un processeur central (21) reçoit des signaux de variation en provenance des détecteurs
(17, 18 ; 22) et commande une limitation ou une augmentation de l'alimentation en
acier en provenance de la conduite de coulée (15), afin que le niveau (19) d'acier
reste constant.