LU88110A1 - DEVICE FOR CONTINUOUSLY MEASURING THE TEMPERATURE OF A METAL BATH - Google Patents

Description

DEVICE FOR THE CONTINUOUS MEASUREMENT OF THE TEMPERATURE OF A

METAL BATH

The present invention relates to a device for the continuous measurement of the temperature of a molten material, in particular of a metal bath and more particularly of the liquid steel contained in a continuous casting distributor. Such a device comprises a probe with a thermocouple and a suspension device installed above said metal bath.

During the continuous casting process it is extremely important for the operator to know at all times the exact temperature of the metal bath contained in the continuous casting distributor. An optimal casting temperature is important both for the productivity of the installation and for the quality of the product.

Indeed if the bath temperature becomes too low, there is poor flowability and the steel may freeze in the distributor. On the other hand, too high a temperature of the bath in the distributor can cause breakthroughs of the strand in or under the mold and moreover it increases the segregation of certain elements (eg C, Mn, S, P, ... ) towards the core of the casting strand.

Depending on the quality of the cast steel, the difference between the upper limit temperature and the lower acceptable limit temperature can be of the order of 10 ° C, for an average bath temperature of around 1500 ° C. Consequently, the temperature measurement must be made with sufficient precision, since an absolute error on the measured temperature of 1.0 ° C already means a relative error of 10% compared to the measurement range which interests the operator. of continuous casting. In addition, it is a matter of continuously monitoring the dynamic evolution of the temperature over time while keeping sufficient precision within this fairly narrow range. This requires, among other things, a rapid and reliable response from the measurement probes used.

There are currently several temperature probes based on thermocouples which are used to monitor the temperature of the metal bath in the continuous flow distributor.

A measurement device commonly used to determine the temperature of the steel in the tundish includes for example a lance provided at its head with a replaceable thermal sensor. This sensor consists of a hot weld of a thermocouple, mounted on a cardboard support. It is possible to obtain spot measurements with such a device, but it is not possible to continuously monitor the evolution of the temperature of the metal bath in the distributor, since the unprotected sensor is consumed in the metal bath and must be replaced after each measurement.

A more recent temperature probe consists of a thermocouple which is integrated in a cavity drilled in a solid body made of a refractory ceramic material, generally of ΙΆΙ2Ο3. This body is then either immersed in the steel bath, or left floating in a given place on the steel bath. It is thus possible to make continuous temperature measurements, but the precision and the dynamic behavior of the sensor leave something to be desired. Indeed, to ensure a suitable lifetime for the sensor, the refractory ceramic body must be fairly solid and consist of a ceramic material which is characterized above all by excellent resistance to wear by the metal bath and especially by the layer of slag floating on this bath. These requirements in relation to wear resistance unfortunately do not always favor the precision and the dynamic behavior of the probe. In addition, it should be noted that the simple introduction of the hot weld into a cavity in the refractory body can also distort the measurements. In fact, this mounting method necessarily entails a layer of air between the hot weld and the refractory body, which increases the thermal resistance of the probe. In addition, one is never sure of the exact location of the hot weld in the channel arranged in the refractory body. Thus, the measurements obtained by two different probes are not necessarily comparable and it must always be feared that the measurements obtained are distorted because the hot weld has moved in said channel.

The object of the present invention is to provide a device for the continuous measurement of the temperature of a molten material, in particular of a metal bath, comprising a probe with a thermocouple and a suspension device installed above said metal bath. , this assembly not having the aforementioned faults.

This object is achieved by a device comprising the characteristic elements of the first claim.

The dependent claims describe advantageous embodiments.

According to a main characteristic, the hot weld of the thermocouple provided with connection wires is intimately integrated, in particular molded, in a first ceramic material to form an oblong cartridge from which said connection wires emerge from a first end. This characteristic firstly allows good transmission of heat from said first ceramic material to the hot weld, since there is no longer any air seal between the two. The sensor and the ceramic material are intimately in contact and these cartridges can be produced in series so as to have strictly the same thermal characteristics.

According to another main characteristic, said oblong cartridge is embedded with said first end in a solid body made of a second refractory material so that the second end of the cartridge projects from said solid body.

This method of assembly allows a division of tasks between the oblong cartridge containing the hot weld and the solid body. Indeed, said massive body no longer fulfills any function in the measurement chain. It essentially serves as a connection between said cartridge and a device for suspending the probe and it protects the connection wires of said thermocouple. Thus it can be sized according to wear criteria without taking into consideration thermal requirements. Said second refractory material must therefore have excellent resistance to the metal bath and especially to the layer of slag covering the latter in the continuous casting distributor. Its thermal conductivity and its specific heat, on the other hand, are only incidental.

Said cartridge coating the hot weld can be dimensioned essentially according to thermal criteria. Of course said first refractory material constituting this cartridge must still have good resistance to high temperatures and to wear by the metal bath, but this character has become incidental. Indeed, this cartridge is only slightly exposed to the metal bath and, thanks to an assembly of its projecting end downward, it is not at all in contact with the slag floating on the surface. In addition, the life of this cartridge may be different from the. lifetime of the solid refractory body, since these elements can be exchanged at low cost and without modifying the characteristics of the measuring assembly.

As a result, the first refractory material, in which the hot weld is integrated to form an oblong cartridge, is preferably a material which has a very good thermal conductivity and a high electrical resistance, in comparison with said second material which has rather better characteristics from the point of view of wear.

It should also be noted that the location of the hot solder in the probe according to the present invention is exactly defined by a studied seat of said oblong cartridge in said solid body. This seat guarantees a very good reproducibility of the measurements in case of replacement of said cartridge. In addition, sealing of said cartridge in said solid body guarantees that the location of the hot solder in the probe can no longer vary during its use. It is also easy to check if this location is exactly the same for two different probes. To do this, simply compare the length of the projecting end of their cartridge.

In a first embodiment of a measuring device according to the present invention, said solid body has the shape of an elongated body, for example a straight cylinder, and said cartridge is integrated in one of its two ends. The hot solder can then be immersed deep in the metal bath if desired.

In a second embodiment, said solid body has the shape of a truncated cone and said cartridge is embedded on the side of the small base of said truncated cone. This execution of the probe is designed to float on the surface of the metal bath. The solid body serves as a float which, while being able to be retained and guided by a suspension device, follows the variations in the level of the metal bath in the tundish. This gives measurements at a strictly constant immersion depth, although the level of steel in the tundish is essentially variable. It will be appreciated that the frustoconical shape of the solid body allows good buoyancy in a stable position and at the same time ensures a maximum wear layer at the level of the particularly aggressive slag layer.

It remains to be noted that said oblong cartridge is advantageously made of boron nitride which is an excellent electrical insulator and which has a high thermal conductivity and good resistance to high temperatures and thermal shocks. Said solid body is however advantageously made of a refractory material based on AI2O3. These refractory materials have long proven themselves in similar applications in metallurgy. Other advantages and characteristics of the invention will appear in the description, by way of illustration, of preferred embodiments, represented by the appended drawings, of which: - Figure 1 shows a section through a probe. frustoconical; - Figure 2 shows a cylindrical probe attached to a suspension device.

Figure 1 shows a longitudinal section of a frustoconical probe 10 according to the present invention. It comprises a solid body 12 made of a refractory material based on AI2O3, which has substantially the shape of a straight truncated cone having a small base 13 and a large base 15. From the small base 13 protrudes a cartridge 14. This cartridge 14 is made of boron nitride which is one of the rare materials which have a very good thermal conductivity at the same time as a high electrical resistivity. These characteristics make it possible to incorporate a hot weld of a thermocouple directly into the cartridge in intimate contact with the boron nitride. Boron nitride has, moreover, the properties of being practically insensitive to thermal shocks, of exhibiting good resistance to oxidation and of not having wettability by steel and slag. In addition, boron nitride can be worked on by means of traditional tools. All these properties mean that the protection of the hot solder can be made durable and reliable. However, care should be taken to provide the .thermocouple with a protective coating to avoid, among other things, possible nitriding.

The cartridge 14 containing the hot weld of the thermocouple is housed, in this example, over approximately two thirds of its length in a bore axially passing through said solid body 12, while the other third is projecting relative to the small base 13 of the body 12. Near the small base 13 the axial bore, in which the cartridge 14 is housed, is widened so that the latter can be securely sealed in the body 12 using a refractory cement 16. In order to provide the cartridge 14 in said axial bore with an impeccable seat, which guarantees a precise definition of its position in this bore, the end of the cartridge 14 is housed in a sleeve 18, which is embedded in said solid body 12. This sleeve 18 has an internal diameter which corresponds to the diameter of the cartridge 14 and is closed by a ring 20 which constitutes an axial stop for the cartridge 14. The sleeve 20 consequently defines exactly the pos ition of the cartridge 14 relative to the body 12 during assembly and sealing of the latter using said cement 16.

In the large base 15 of the body 12 is embedded a tube 22 whose end, which projects from the large base 15, can be coupled to a probe suspension device which is installed above the metal bath . This tube 22 and the sleeve 18 are connected coaxially by a second tube 24 of smaller diameter. The sleeve 18, the tube 22 and the tube 24, thus constitute a metal pipe which is firmly anchored in the refractory material of said solid body 12. Through this pipe are routed the connection wires of the hot weld which emerge axially from the end of the cartridge 14 which is contained in the sleeve 18.

This probe 10 is placed with the small base 13 facing downwards in the continuous casting distributor which contains the molten steel. In view of the difference between the relative densities of the refractory body 12 and of the steel, this probe 10 can float on the surface of the metal bath. The cartridge 14 is thus immersed at a strictly constant depth in the metal bath. It should be noted that this depth of immersion of the hot weld is not affected by the level variations in the distributor, since the probe 10 floating on the liquid steel follows all these level variations.

Figure 2 shows a cylindrical probe 10 'suspended from a suspension device 11. The probe 10' differs from the probe 10 of Figure 1 only in that the body 12 'is an oblong body of cylindrical shape having a lower base 13 'and an upper base 15'.

A cartridge 14 ′ containing the hot weld of a thermocouple protrudes relative to said lower base 13 ′. From the upper base 15 'comes a metal tube 22' which is coupled to a pipe 28 via a coupling 26. In this coupling 26 is inter alia housed the cold junction, which is preferably cooled by a flow of air or other gas passing through line 28.

Line 28, which serves both as a protective sheath for electrical lines and as a line for cooling gas for the cold junction, has a gantry shape; that is to say, it is composed of a first vertical tube 29 extending the coupling 26 upwards, a second tube 30 extending horizontally to the edge of the continuous casting distributor and a third tube 31 descending vertically in a fourth tube 34, in which it can slide vertically.

The horizontal tube 30 is supported by a support 32 which can be moved vertically in a vertical support 33. By moving the support 32 in height, it is known to descend the probe 10 'more or less deeply into the metal bath. On the other hand, by allowing the support 32 to slide freely in the vertical support 33, a probe of the kind shown in FIG. 1 can freely follow the variations in the level of the metal bath.

It will be appreciated that the present invention provides a device for the continuous measurement of the temperature of a molten material, in particular of a metal bath and more particularly of the liquid steel contained in a continuous casting distributor, which is distinguished by greater durability of the probe and which at the same time makes more precise continuous measurements than thermocouple devices used until now.

Claims (7)

1. Device for continuous measurement of the temperature of a molten material, in particular a metal bath, comprising a probe with a thermocouple provided with connection wires and a device for suspending the probe installed above said metal bath , characterized in that the hot weld of the thermocouple is integrated in a first ceramic material to form an oblong cartridge. (14) from which the connection wires emerge from a first end, in that this cartridge is embedded with this first end in a solid body (12), made of a second refractory ceramic material, so that the second end of the cartridge (14) projects relative to said solid body (12), and in that the latter is integral with said suspension device (11) so that the projecting end of said cartridge (14) faces downwards. 2. Device according to claim 1, characterized in that said solid body (12 ') has the shape of an elongated body, in that said cartridge (14') is integrated in one of its two ends (13 ') and that the other end (15 ') is integral with said suspension device (11) above the metal bath. 3. Device according to claim 1 or 2, characterized in that said solid body (12) has the shape of a truncated cone, in that said cartridge (14) is embedded on the side of the small base (13) of said cone truncates and that the other base (15) is integral with said suspension device (11). 4. Device according to any one of claims 1 to 3, characterized in that said solid body (12) acts as a float swimming on the bath and that said suspension device (11) allows said solid body to follow variations in level of the liquid bath, the cartridge (14) being permanently immersed in the metallic phase of the bath. 5. Device according to any one of claims 1 to 4, characterized in that the first ceramic material is boron nitride. 6. Device according to any one of claims 1 to 5, characterized in that the second ceramic material is a refractory material based on AI2O3. 7. Device according to any one of claims 1 to 6, characterized in that said first end of the cartridge (14) is introduced into a metal sleeve (18) which is embedded in the solid body (12) and defines exactly the position of the cartridge (14) relative to the body (12), during assembly and sealing of the cartridge (14) with refractory cement.