SU916068A1 - Device for measuring liquid metal level in mould - Google Patents

Description

The invention relates to metallurgy? more precisely to the measurement of the liquid metal level in the molds of small cross-sectional area (up to ~ 200 cm / vertical and radial continuous casting machines with metal filing from ^prome-! diate bucket open stream.

A device for contactless measurement of the level of liquid metals is known, which contains a capacitive sensor with a sensitive element made in the form of a "metal plate placed parallel to the metal surface, and a measuring transducer in the form of a motor [1].

However, the device cannot be used to measure the level of liquid metal in small-section molds, since the sensitive element of the sensor (plate), blocking the cross-section of the mold, prevents the metal from flowing from the tundish into the mold, and reducing the size of the plate leads to a significant2

decrease the measurement range and ACCURACY.

The closest to the proposed technical essence is a device for contactless measurement of the level of liquid metal in the mold, containing a level sensor in the form of a whip antenna mounted in the upper part of the mold perpendicular to the wide face and parallel to the surface of the metal in the mold. The antenna is connected via a cable line to a high-frequency bridge, to the input of which the energy of high-frequency oscillations is supplied from the generator. A level recorder is connected to the second input of the bridge.

A hollow mold is considered as a segment of a rectangular waveguide, open from the entrance side, in which oscillations of the main type of CCO are excited. The input impedance of such a waveguide, and hence the input impedance of the antenna, depends on the position of the metal level in the mold. Measure3. 916068 4

The impedance of the whip antenna from the position of the metal level is ensured by the inclusion of a high-frequency bridge in the power supply of the whip antenna [2]. five

Not the balance of the device is the low reliability of the sensor when used for crystallizers of small cross section. Due to the small cross-section of the crystallizer, it is difficult to exclude 10 the probability of a metal jet entering the antenna, which leads to a loss in operation. sensor properties. To prevent the metal jet from hitting the antenna, an accurate installation of the tilting of the crystallizer is required.

The purpose of the invention is to improve the reliability and accuracy of measuring the level of a liquid metal in molds of small section with the flow of metal open 20

jet.

This goal is achieved by the fact that a device for continuous measurement of the level of a liquid metal contains a sensor, a high-frequency generator of modulated electromagnetic oscillations, a directional coupler and a high-frequency matched detector, the level sensor is made in the form of two closed metal conductors arranged one in the other. mounted between the tundish and the mold (so that the jet of metal from the tundish passes through the inner conductor) ₃₅ and connected to metal a second pipe arranged coaxially inside a metal rod, wherein one end of the rod .elektricheski connected with the inner conductor, the other end through a coupler lenny direction ₄₀ - to the generator and the detector, and the tube is electrically connected to the outer conductor and the total mass. Also around the bottling

the cup of the tundish through ₄₅ [metal liners are inserted in the lining.

FIG. 1 shows the device

(his working position on the object), general view; in fig. 2 is a diagram of the installation of 50 metal rods in a tundish; in fig. 3 is a circuit diagram of the device, ’in FIG. 4 is an electrical diagram of a set of elements of a casting installation (crystallizer - 55

metal jet - tundish (in Fig. 5, the experimental output characteristic of the sensor device.

Metal closed, located one in another, internal 1 and external 2 device sensor conductors are small-height thin-walled cylinders, in general, of arbitrary configuration.

In the particular case, the conductors may have the shape of a round cylinder and be aligned with each other. The transverse dimensions of the inner conductor are commensurate with the dimensions of the section of the mold 3. Pipe 4 with the inner core 5 is a constructive segment of the high-frequency coaxial communication line. One of the arms of the main channel of directional coupler 6 is connected to it. A high-frequency generator 7 of frequency-modulated oscillations is connected to the second shoulder of the main channel of the coupler, and a high-frequency matched detector 8 is connected to the shoulder of the additional channel. radio frequency cables.

To measure the level of the liquid metal in the mold, a sensor is installed between the mold 3 and the intermediate bucket 9 so that the jet 10 of the metal, coming from the tundrum into the mold, passes through the cavity of the internal closed conductor of the sensor. The generator 7, the detector 8 and the right foam coupler 6 can be removed from the sensor outside the control object using radio frequency cables.

Around the tundish 11 of the tundish through the lining 12 metal rods 13 are inserted in such a way that the liquid metal 14 in the tundish is electrically contacted with the tal body. The rods (at least 4 pieces) are arranged around the nozzle evenly.

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The device works only when there is a continuous stream of metal passing through the inner conductor of the sensor.

The principle of operation of the device is illustrated by its electrical circuit, shown in FIG. 3

The diagram with dashed lines shows the electrical circuit of the actual device for measuring the level of the liquid metal and the electrical circuit of the aggregate

elements (mold - metal jet - tundish) foundry.

A collection of elements crystallizer - metal stream - tundish considered as an electromagnetic system as chas- ⁵ cal neekranirovainogo segment two-wire line with a long squirrel lower and upper end. One of the conductors of the line segment formed · liquid metal jet flowing out prome- ⁰ diate bucket, the second conductor is formed by the mold walls and the space between the tundish and the mold - closed outer sensor conductor ¹⁵ partially shielding jet. The short-circuited lower end of the segment is formed by electrically closing the jet of metal and the walls of the mold (mass) with a liquid metal in the mold. For high frequencies of ²⁰ (MHz), characteristic of the operating frequencies of the line segment, the currents in the short circuit run in a thin surface layer of the liquid metal, so that the position of the short line segment coincides with the position of the metal level in the crystallizer.

The upper short-circuited end of the line segment is formed by electrically closing the metal jet through a thin layer ^{30 of} liquid metal adjacent to the lining of the tundish base and metal rods on the tundish body (mass).

It is known that the input impedance of a piece of line as an electromagnetic system with distributed parameters, measured at any point of the segment (with the exception of the short-circuited end), contains a reactive component, which, depending on the frequency of the protector — ^{40 of} the currents in the line, periodically inductive and capacitive. character The value of equivalent reactivity (inductance or capacitance) of the input impedance of the ⁴ 5 line segment depends on the length of the segment. Since the change in the position of the H level of the metal in the mold is equivalent to the displacement of a short-circuit line segment, i.e., a change in the length of the segment, ^50, the magnitude of the reactivity depends on the position of the H level of the metal. Thus, by measuring the magnitude of the equivalent reactivity, one can judge the position of the metal level in the crystallizer.

To measure the equivalent reactivity to the line segment at the measuring point, it is necessary to connect a gauge 916068

nyu chain. In the proposed device, the connection of the measuring circuit to the segment is carried out in a contactless manner, through capacitive coupling, as the direct electrical contact of the measuring circuit with the metal stream (with one of the conductors of the line segment) is technologically impossible. The internal closed conductor (Fig. 1) of the sensor of the measuring device, covering the metal stream, forms with the latter the electrical capacitance (communication capacitance) C _b , through which non-contact supply of high-frequency energy from the generator to the segment takes place.

Measurement of the reactivity of the segment is implemented in the device indirectly by measuring the resonant frequency of the oscillating circuit.

With the inductive nature of the input complex resistance of the line segment, capacitance _Cw forms, with the equivalent inductance of the segment, a series oscillatory circuit connected as a load to the communication line with the excitation generator. The resonant frequency of the circuit is a function of the magnitude of the equivalent inductance and, consequently, the position of the H level of the metal in the mold.

The high-frequency signal from the generator of frequency-modulated oscillations of constant amplitude, acting on the communication line through the main channel (coordinated with the communication line) of the directional coupler to the load (oscillatory circuit), is reflected from it.

Since the amplitude of the reflected signal отражστρ, as is well known, depends on the magnitude of the line load resistance

, ^AT + \ l / ^?

where - the amplitude of the signal from the generator (assuming no loss in the communication line), '

P is the reflection coefficient;

2n ~ load resistance at the end of the communication line;

V / is the characteristic impedance of the communication line,

then, when the oscillator frequency changes in the region of the resonant frequency of the oscillating circuit (load), the amplitude of the reflected signal, like the load impedance, varies according to the law after 7 U1Y.

final resonance, taking the minimum value at resonance.

A directional coupler, included in the communication line, provides the selection from the communication line of the reflected signal 5 in the form of a resonant radio pulse, which is removed from the additional arm of the coupler and goes to the detector.

When the generator operates in a periodic saw-tooth mode (symmetry ^{, zero} saw), the frequency changes according to a linear law over the entire operating frequency range of the oscillatory circuit (device), determined by the measuring range of the liquid level H, of the metal in the crystallizer, a periodic time sequence of video pulses is removed from the detector in the form of a resonant curve with a time interval between the vertices of adjacent pulses, proportional to the value of the level of the liquid metal in the mold, which is further converted into Continuous output signal.

The external closed conductor 2 of the device’s sensor acts as an electromagnetic shield from the influence of external electromagnetic fields and foreign objects in the mold area on the parameters of the oscillating circuit, and also reduces the losses of the circuit to radiation, which increases the quality factor of the oscillatory system and, as a result, the measurement accuracy.

The constructive segment of the sensor's communication line, being a part of the generator's communication line with the Szd capacity, serves to increase the reliability of the device, eliminating the negative effect of high temperature in the area of the measurement object on the performance of a standard line (radio frequency cable). The length of a constructive segment is determined from the condition of ensuring the normal temperature mode of operation of a standard communication link and is, as follows from __ practice, 25-30 cm.

I. .

The introduction of the rods 13 into the lining around the tundish pouring nozzle eliminates the influence of the position of the H level of the liquid metal in the tundish on the operation of the device. In the absence of rods, the electric circuit of the set of elements (mold - metal stream - tundish) of the casting installation takes the form shown in FIG. 4. In this case, the upper part of the line segment is not short-circuited, but loaded on

38 8

some capacity C _o formed by the liquid metal in the tundish and the tundish metal case, separated by a dielectric - lined from an electrical insulating material.

The change in the level of the metal in the tundish affects the capacitance C &, and, consequently, the equivalent inductance of the line segment, and, accordingly, the resonant frequency of the oscillating circuit, which leads to measurement error.

In addition, the active losses of high-frequency energy 15 in the tundish lining material significantly reduce the quality factor of the circuit, creating an additional error. The introduction of rods also eliminates this error due to a decrease in the volume of the dielectric (lining), in which energy losses are possible, as well as due to the smallness of the intensity electric field on a short-circuited portion of the line segment.

25 Experimental output characteristic of the device sensor (dependence of the resonant frequency of the sensor on the position of the liquid metal level in the mold), obtained on the model

30 of the mold section 150x70 mm, shown in FIG. 5. Imitation of the metal level was carried out by a short-circuiting metal piston moved in the cavity of the mold of the mold.

35 Experimental results confirmed on real object.

The device can perform its function without the introduction of rods in the tundish. However, in this case, reliable

40 and high-precision control of the level of the metal in the mold is possible either on condition that the level in the tundish is stabilized, or on the condition that more information is obtained on the position of the metal in the tundish and

subsequent use of it to correct the readings of the main meter. Execution <. Both conditions require the use of an additional level sensor

50 metal in tundish and the complexity of the conversion devices.

Technical and economic effect of the present invention is that it provides the speed ^{55 of the} automatic control system (ASR) of the metal level. This is particularly important in the continuous casting of medium and small sections,

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where the delay in the operation of the ASR can "swing" the system to the overflow of metal through the top of the mold, or lead to an emergency level drop? the effect of radiation factors harmful to personnel when using radioisotope sensors is excluded; blocking of the crystallizer with radioisotope block counters and especially with sensor containers is prevented, which slows down the maintenance of the crystallizer, complicates its design and prevents uniform cooling of its working walls; It is not necessary to mix the injection point of the jet into the crystallizer from the stream axis, which causes the appearance of the diamond shape and related ingot defects in the varietal and bloom blanks.

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Claims (1)

Claim A device for measuring the level of liquid metal in the mold of a continuous casting machine with metal feed through a pouring glass prom916068 ten bucket with open jet, containing a sensor, a high-frequency generator, a directional coupler and a high-frequency matched detector, distinguished by 5 ¹ in that, in order to increase the reliability and accuracy of measurement, the level sensor is made in the form of two closed metal, coaxially arranged electrodes installed between the tundish and the mold and connected with a metal pipe with a metal rod coaxially located inside it, with one end of the rod electrically connected to the inner The electrode, the other end through a directional coupler with the generator and detector, and the waveguide is electrically connected to the external electrode, with metal rods inserted into the tins lining around the nozzle.