JPH05192753A - Instrument for measuring powder film thickness in continuous casting - Google Patents

Abstract

PURPOSE:To enable the measurement of thickness of powder film in high accuracy based on the variations of intensity and phase difference of output signal from a receiving coil in magnetic field. CONSTITUTION:A transmitting coil 11 and the receiving coil 12 are embedded into a mold 1 for continuous casting in a prescribed interval in the shifting direction of a cast slab 6 and an occilation 13 connected to the transmitting coil 11 are alternately oscillated with low frequency and high frequency at a prescribed timing to form the magnetic field with the transmitting coil 11. Then the magnetic field is detected with the receiving coil 12, and the difference between the phase of the induction current as the output signal of the receiving coil 12 and the phase of the low frequency and high frequency currents at the time of exciting, the transmitting coil 11 is detected with a phase difference detector 15 and arithmetic processing is executed with an arithmetic part 16 and the thickness of the powder film executing a mold temp. correction can be calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the thickness of a powder film formed between a mold and a slab in a continuous casting process of steel, aluminum or the like.

[0002]

2. Description of the Related Art FIG. 3 is a schematic view showing a continuous casting mode of steel, in which a dipping nozzle 2 is placed in a mold 1 whose upper and lower ends are open.
The molten steel 3 is poured into the mold 1 to contact the water-cooled inner wall of the mold 1 to solidify the outer periphery, and the cast piece 6 covered with the solidified shell 5 formed by this solidification is sequentially obtained while the mold 1 is obtained.
The powder 4 in the molten state at the upper part of the molten steel 3 enters into the gap between the mold 1 and the solidified shell 5 in this process, and the friction between the mold 1 and the solidified shell 5 is reduced. It plays a role of reducing and improving heat conduction, and is solidified by contact with the mold 1 and adhered to the outer peripheral surface of the solidified shell 5 and is withdrawn along with the cast piece 6 downward from the mold 1. ing.

The powder 4 existing between the mold 1 and the solidified shell 5 is generally referred to as a powder film 4a, and the thickness of the powder film 4a is closely related to the development of the solidified shell 5 and the solidified shell 5 In order to prevent the so-called breakout in which the molten steel 3 is broken and the molten steel 3 inside is ejected to the outside, an accurate thickness measuring technique is desired. In the conventional thickness measurement of the powder film 4a, a method is proposed in which the thermal energy transmitted through the solidified powder film 4a is measured by an infrared detector or the like at the position where the slab 6 is pulled out from the mold 1. Has been done.

[0004]

By the way, the conventional method for measuring the thickness of the powder film as described above is an indirect method for obtaining the thickness of the powder film between the mold 1 and the slab 6 by the indirect method. It is not a thing that shows the degree, and errors are likely to occur due to changes in operating conditions, and since the energy transmittance changes when the type of powder used further changes, the thermal energy of the slab that passes through the powder film also changes, There was a defect that the measurement value had to be corrected every time the type of powder was changed.

The present inventor conducted experiments and researches to measure the powder film thickness more directly, and as a result, embedded a transmitter coil and a receiver coil in a mold at predetermined intervals, and set the transmitter coil in a predetermined manner. A magnetic field is generated by oscillating toward the slab side at a frequency, while the receiving coil receives this and the phase and strength of the magnetic field detected by analysis of this received data correlatively changes depending on the powder film thickness. I found out. The present invention has been made on the basis of such findings, and the purpose thereof is to provide a powder film thickness in continuous casting that enables accurate detection by the phase difference of the magnetic field that changes with the powder film thickness and the change in strength. To provide a measuring device.

[0006]

A powder film thickness measuring device in continuous casting according to the present invention has a high frequency for measuring the powder film thickness at a predetermined interval in a mold for continuous casting having a water cooling structure. And a transmission coil oscillated at a low frequency that compensates for the influence of the mold temperature,
A receiver coil for capturing a magnetic field formed by the oscillation of the transmitter coil at each of the high frequency and the low frequency; and an arithmetic unit for obtaining a powder film thickness based on a detection value of the receiver coil. Is characterized by.

[0007]

In the present invention, the transmitter coil is oscillated by a high frequency current and a low frequency current, the magnetic field formed by this is detected by the receiver coil, and the phase difference and strength of the receiver coil output are obtained in advance. Since the powder film thickness is calculated based on the relationship between these values and the powder film thickness, it is possible to obtain an accurate powder film thickness that compensates for changes in the mold temperature without being affected by the type of powder. .

[0008]

Principle of the Invention Next, the principle of measuring the powder film thickness in the apparatus of the present invention will be described. FIG. 1 is an explanatory view of the principle of the powder film thickness measuring device according to the present invention. In FIG. 1, 1 is a mold, 6 is a slab, 4a is a powder film, 11,
Reference numeral 12 denotes a transmitter coil and a receiver coil which are embedded in the mold 1 at a predetermined interval. 100Hz to transmitter coil 11
The energy of the magnetic field generated by passing a high-frequency current of a certain degree is, as indicated by the arrow in FIG. 1, the first path that directly propagates in the mold 1, the powder between the mold 1 and the slab 6. Reaching the receiving coil 12 through a second path propagating in the film 4a and a third path propagating in the cast piece 6, an induced current is induced in the receiving coil 12.

By the way, the inner wall of the mold 1 is usually a copper plate,
Since the slab 6 has higher conductivity than the slab 6, the degree of attenuation of the magnetic field energy propagating through the first path is large, and when the separation distance between the transmission coil 11 and the reception coil 12 exceeds a predetermined length,
The magnetic field energy reaching the receiving coil 12 in the first path is at a level that can be ignored. Therefore, the magnetic field around the receiving coil 12 is dominated by the magnetic field energy propagating through the second and third paths.

On the other hand, the magnetic field energy propagating through the third path is constant unless the amount of molten steel on the path through which the magnetic field energy passes changes. Therefore, the change in the magnetic field energy captured by the receiving coil 12 changes according to the thickness of the powder film 4a forming the second path.

Since the magnetic field energy propagating through the second path passes through the powder film 4a, which is a defective conductor,
Compared with the magnetic field energy propagating through the third path, there is less attenuation and phase delay, and the magnetic field energy propagating through the second path has a larger passage amount as the powder film 4a becomes thicker, and the receiving coil The output signal strength from 12 also increases, and the phase delay of the output signal also decreases.
On the contrary, as the powder film thickness becomes smaller, the intensity of the output signal becomes smaller and the phase delay of the output signal becomes larger. Therefore, the powder film thickness can be measured by detecting the intensity or phase of the output signal from the receiving coil 12.
However, a part of the magnetic field energy propagating through the second path passes through the side wall of the mold, but if the temperature of the mold 1 fluctuates, the phase and the intensity of the detection signal fluctuate, so that correction is necessary. Becomes

That is, the above description has been made on the case where the frequency for exciting the transmitter coil 11 is 100 Hz, which is relatively high.
For example, when a low frequency of about 20 Hz is used, the magnetic field energy mainly propagates in the mold 1, which is the shortest distance. Therefore, at this time, the fluctuation of the phase and the strength due to the fluctuation of the powder film thickness in the output signal of the receiving coil 12 is relatively small, and the change of the phase and the strength due to the change of the conductivity due to the temperature fluctuation of the mold 1 is dominant. The changes in phase and intensity obtained at low frequencies correspond to temperature fluctuations in the mold.

When this is expressed by a mathematical expression, the change in the phase and intensity of the output signal from the receiving coil 12 when the transmitting coil 11 is excited at a high frequency corresponds to the change in the powder film thickness. The relationship between the two is expressed by the following equation (1), and the phase difference and the fluctuation of the reception intensity correspond to the fluctuation of the powder film thickness. On the other hand, changes in the phase and intensity of the output signal from the receiving coil 12 when the transmitting coil 11 is excited at a low frequency correspond to changes in the temperature of the mold 1. For example, the relationship between the two is shown below regarding the phase difference ( It can be expressed by the equation (2), and the phase difference and the received intensity fluctuation correspond to the temperature fluctuation of the mold.

Θ ₁ = f ₁ (T) + g ₁ (F) + C ₂ (1) θ ₂ = f ₂ (T) + g ₂ (F) + C ₁ (2) where θ ₁ is obtained at a high frequency Phase difference θ ₂ : Phase difference obtained at a low frequency T: Mold temperature F: Powder film thickness f ₁ , f ₂ , g ₁ , g ₂ : Known function (however, the value of g ₂ is smaller than g ₁ ) C ₁ and C ₂ : known constants Therefore, based on the output signal of the receiving coil 12 when the transmitting coil 11 is excited at a low frequency, the change amount of the phase and the intensity with the temperature change of the mold 1 is obtained, and it is high. By removing the change due to the change in the mold temperature from the change in the phase and intensity of the output signal of the receiver coil 12 when the transmitter coil 11 is excited at a frequency, the powder film thickness that compensates for the influence of the mold temperature can be obtained. Measurement becomes possible.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing a powder film thickness measuring device in continuous casting according to the present invention. In the figure, reference numeral 1 denotes a mold for continuous casting, which has a rectangular tubular shape with open upper and lower ends, and has a water cooling structure. Molten steel 3 is injected into the mold 1 from a dipping nozzle 2 which has penetrated into the mold 1 through an upper opening for a proper length, and at the same time, a powder 4 is supplied to the surface of the molten steel 3 from a nozzle (not shown).

The molten steel 3 poured into the mold 1 is gradually pulled up below the mold 1 in a state where the surrounding solidifies by contact with the inner wall of the water-cooled mold 1 and a solidified shell 5 is formed. . On the other hand, the powder 4 supplied to the surface of the molten steel 3 becomes a molten state by the heat of the molten steel 3 and covers the surface of the molten steel 3,
When the molten steel 3 is cooled by the contact with the water-cooled inner wall of the mold 1 to form a solidified shell 5 and a gap is formed between the mold 1 and the solidified shell 5, this oxidization is prevented. The solidified shell 5 also penetrates inside and solidifies in the state of the powder film 4a to function as a lubricant for reducing the friction caused by the direct sliding contact between the solidified shell 5 and the mold 1.
Promotes heat conduction between the mold and the mold 1.

When the molten steel 3 becomes a slab 6 whose outside is covered with the solidification shell 5, and is continuously drawn downward from the lower opening of the mold 1, the powder film 4a also becomes solidified. It is pulled out together with the cast piece 6 while being attached to the outer peripheral surface. On the lower side of the mold 1, a large number of cooling water nozzles (not shown) are arranged along the drawing path of the slab 6.
Is further cooled by water sprayed from these cooling water nozzles, solidified to the inside, and then cut into a desired length, and fed as a raw material to a post-process such as rolling.

The casting coil 11 faces the inner side of the casting mold 1 and
Also, the receiving coil 12 is required to move upwards and downwards at a required distance (70mm).
It is buried by separating them. The transmission coil 11 is connected to the oscillation circuit 13 and is excited by the output of the oscillation circuit 13 to form a magnetic field in the mold 1, the powder film 4a, and the slab 6 around it. The oscillator circuit 13 is configured to alternately oscillate a high frequency of about 100 Hz and a low frequency of about 20 Hz at a predetermined timing. On the other hand, the receiving coil 12 is embedded below the transmitting coil 11 at a position separated by an appropriate length in a plane substantially parallel to the outer surface of the slab 6 to be detected, and a magnetic field generated by the excitation of the transmitting coil 11 is generated. The induced current induced in the receiving coil 12 by the action of energy is input to the phase difference detector 15 via the amplifier 14.

The output of the oscillation circuit 13 is also given to the phase difference detector 15, so that the phase difference between the phase difference detector 15 and the exciting current given to the transmitter coil 11 is obtained and outputted to the arithmetic unit 16. It has become. The calculation unit 16 subtracts the phase difference when it is excited at a low frequency from the phase difference when the transmission coil 11 is excited at a high frequency, and then the powder obtained based on the test results performed in advance. The correspondence between the thickness dimension of the film 4a and the phase difference is applied to the input from the phase difference detector 15 to calculate the thickness dimension of the powder film 4a, and for example, a CRT display connected to the calculation unit 16 Indicators such as
17 Display on top. The result is used for the operation management by the operator, for example, for controlling the drawing speed (casting speed) of the slab 6.

Although the powder film thickness is obtained based on the phase difference in the above-described embodiment, the powder film thickness may be obtained based on the change in the intensity of the output signal from the receiving coil 12. In this case, the output of the amplifier 14 is directly taken into the calculation unit 16, the intensity change is obtained, and the powder film thickness is calculated from the previously input correspondence between the intensity change and the powder film thickness.

[0021]

As described above in detail, in the apparatus of the present invention, a pair of coils are embedded in a mold for continuous casting with a proper distance from each other, and one of these coils is subjected to a magnetic field by energizing low-frequency and high-frequency exciting currents. As a transmitting coil for generating, and the other as a receiving coil, since the powder film thickness is measured based on the phase change or intensity change of the detection signal of the magnetic field captured by the receiving coil, for stable operation of continuous casting equipment. It is possible to detect the powder film thickness, which is extremely useful information, with high accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the method of the present invention.

FIG. 2 is a block diagram of an apparatus of the present invention for measuring the powder film thickness between a continuous casting mold and a slab.

FIG. 3 is a schematic view showing an implementation state of a conventional measuring device.

[Explanation of symbols]

 1 Mold 4a Powder film 5 Solidification shell 6 Cast piece 11 Transmission coil 12 Reception coil 15 Phase difference detector 16 Arithmetic unit

Claims (1)

[Claims] 1. A transmitter coil oscillated at a high frequency for measuring a powder film thickness and at a low frequency for compensating the influence of the mold temperature at a predetermined interval in a mold for continuous casting having a water cooling structure. A receiving coil for capturing a magnetic field formed by the oscillation of the transmitting coil at the high frequency and a low frequency of the transmitting coil, and an arithmetic unit for obtaining a powder film thickness based on a detection value of the receiving coil. A powder film thickness measuring device in continuous casting characterized by the above.