JP2795516B2 - Liquid level detection device for molten metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid surface position detecting device for detecting a liquid surface level of a molten metal, and a liquid of the molten metal in a pot, a tundish, etc. of a metal melting furnace. It can be used for detecting and monitoring the surface position.

(Prior Art) In the fields of nonferrous metal smelting and melting casting, molten metal is handled. In particular, in the field of melt casting, computerization of a continuous casting process has been promoted in order to improve work efficiency. For that purpose, it is important to accurately grasp information on the entire continuous casting process. One of the ways to grasp this information is to detect the liquid level of the molten metal. FIG. 9 shows a conventional sensor for molten metal.
There is something like Figure 10.

9 sensors figure is composed of a detector A and the circuit part B, the detector A housing primary coil D ₁ wound with high MI cable heat resistance in the guide tube C and the secondary coil D ₂ is the is, current flows to the primary coil D ₁ when the induced voltage in the secondary coil D ₂ is generated, induced current flows in that there is a molten metal E around the detector a same molten metal E, the upper surface of the melt E according to the level variation of G in which the output of the secondary coil D ₂ was made to change.

In the sensor shown in FIG. 10, a pair of coils F ₁ and F ₂ are arranged above the upper surface G of the molten metal E. When a high-frequency current of ₁₀₀ KHz flows through the primary coil F ₁ , the position of the upper surface G of the molten metal E (liquid level) The voltage induced in the secondary coil F ₂ changes in accordance with
The position of the upper surface G of the molten metal E is detected from this change amount.

(Problems to be Solved by the Invention) Among the above-mentioned prior arts, the sensor for molten metal shown in FIG. 9 has the following problems.

. If the probe H is not inserted 200 to 500 mm deep into the metal melt E, the position of the upper surface G of the metal melt E cannot be measured. An accurate measurement could not be made.

. Although the coils D ₁ and D ₂ are accommodated in the guide tube C, the portion of the coils D ₁ and D ₂ inserted in the molten metal E will increase in temperature, and the inductance of the coils will be increased by the temperature. , The fluctuation of the zero point due to the temperature of the sensor itself is large.

. Since the maximum operating temperature is 800 ° C, the high temperature resistance is poor.

 The sensor of FIG. 10 has the following problems.

. Although the coils F ₁ and F ₂ are of a non-contact type separated from the upper surface G of the molten metal E, since the heat resistance temperature is as low as 120 ° C., the coils F ₁ and F ₂ must be cooled at all times or as necessary. In addition, a cooling device is required for this, and the entire liquid level detection device becomes large-scale and the cost increases.

Also, in some cases, a chemical was sprayed on the upper surface of the molten metal E to suppress the radiant heat from the molten metal E and to prevent the coils F ₁ and F ₂ from rising in temperature. In addition to adversely affecting the quality of the molten metal by being mixed as impurities into the molten metal E, the operation of dispersing the chemical is troublesome and troublesome, and the operation is complicated.

. Since the measurable separation distance L between the coils F ₁ and F ₂ and the upper surface F of the molten metal E is as narrow as 20 to 120 mm, accurate measurement is difficult when the amount of the molten metal E changes and the separation distance L increases. Become.

. As the temperature of the two coils F ₁ and F ₂ rises, the inductance of the coils greatly fluctuates depending on the temperature, and the fluctuation of the zero point due to the temperature of the sensor itself is large.

As described above, a sensor capable of meeting the above-mentioned requirements has not been realized, and therefore, the control of the conventional high-temperature molten metal process depends on the experience of the operator. However, this requires a large number of workers, and when the number of workers increases, the control varies depending on the worker. In addition, since a skilled worker is required, labor costs are increased and costs are increased.

(Object of the Invention) An object of the present invention is to detect the liquid level of a molten metal as the buoyancy of the molten metal, thereby to have excellent high temperature resistance characteristics, a small temperature drift, a simple structure, and the effect of the heat of the molten metal. It is an object of the present invention to provide an apparatus for detecting a liquid surface position of a molten metal having a small (thermal expansion and contraction) and high detection accuracy.

(Means for Solving the Problems) The apparatus for detecting the liquid level of a molten metal of the present invention uses the principle of Archimedes, that is, the principle that the buoyancy received by an object in a liquid is equal to the product of the volume of the object and the specific gravity of the liquid. It was developed based on.

FIG. 3 shows a liquid surface position detecting device for molten metal of the present invention.
As shown in FIG. 4, a probe 3 which is inserted into a molten metal 2 in a molten metal bath 1 and receives buoyancy according to the liquid level of the molten metal 2
An arm 4 for supporting the probe 3; a fulcrum 5 for supporting the arm 4 so as to be rotatable; and a buoyancy received by the probe 3 disposed below one end 4a of the arm 4. A buoyancy detector 6 for detecting via the arm 4;
In the apparatus for detecting a liquid level of a molten metal, a signal processor 7 for calculating an electric output signal of the buoyancy detector 6 and obtaining a liquid level of the molten metal 2 corresponding to the output is provided. As shown in the figure, a compensator 20 having a different coefficient of thermal expansion from the arm 4 is arranged along the arm 4, and the compensator 20 has a fixed end 20a on the probe 3 side fixed to the arm 4, and a compensator 20 on the opposite side. The weight 21 is attached to the free end 20b.

Considering only the stationary state in the molten metal level detecting device of FIG. 3, the outer diameter of the lower portion 3a of the probe 3 (portion inserted in the molten metal) is D, the specific gravity of the molten metal is ρ, When the change in the insertion depth of the buoyancy detector 6 into the molten metal 2 is ΔS, the change ΔF in the force received by the buoyancy detector 6 is obtained by the following equation.

ΔF = (L ₁ / L ₂ ) (π / 4) D ² ρΔS (1) Here, if it is assumed that D, ρ, L ₁ and L ₂ are always constant, ΔF is proportional to ΔS. It is clear that. Therefore, if ΔF can be measured accurately, ΔS (change in insertion depth =
(The liquid level change due to the increase and decrease of the molten metal).

In this case, the temperature of the molten metal is stable but extremely high at about 1200 ° C., so that D, ρ, L ₁ , and L ₂ actually change due to thermal expansion and contraction. Of these, the outer diameter D of the probe 3 increases as the temperature increases, and the specific gravity ρ of the molten metal decreases as the temperature increases. Therefore, the change in the outer diameter D of the probe 3 and the change in the specific gravity ρ of the molten metal due to the temperature change are caused by ΔF in the above equation (1).
The effects on the nation will cancel each other out. Therefore, it is considered that the influence of the temperature fluctuation is negligibly small.

Also, from the fulcrum 0 of the arm 4 in FIG.
The length L ₂ of the part up 4b, since a significant distance from the molten metal temperature change is small, it is considered negligible the influence of the variation.

The largest of the impact is the variation with temperature of the length L ₁ from the end portion 4a of the arm 4 to pivot 0.

This variation will be considered based on the system shown in FIG. 2 to simplify the explanation. Here, it is assumed that the temperature change of the arm 4 is the same everywhere in the longitudinal direction. At room temperature, the moment M due to the gravity of the system with respect to the fulcrum 0 is obtained by the following equation (2).

_{M = 1 / 2L · W 2} + LW 1 = L (W 1 + W 2/2) ... (2) L 1 = L (1 + ΔΤλ) a is for (λ is the coefficient of thermal expansion),
Moment M ₁ after the temperature rises by ΔΤ the following formula (3)
Required by

M ₁ = L (1 + ΔΤλ) (W ₁ + 1/2 · W ₂ ) (3) When (3) − (2), the difference ΔM in the generated moment
Is obtained by the following equation (4).

ΔM = LΔΤλ (W ₁ + 1/2 · W ₂ ) (4)

When the liquid level of the molten metal fluctuates by ΔS, the fluctuation ΔM of the moment with respect to the fulcrum is calculated by the following equation.

ΔM = ΔS · (π / 4) D ² · ρ · L (4-1) Using (4) and (4-1), the moment variation ΔM due to thermal expansion is converted into the liquid level variation ΔS. Can be calculated by the following equation.

LΔΤλ (W ₁ + 1/2 · W ₂ ) = ΔS · (π / 4) D ² · ρ · L (4-2) ΔS = ΔΤ · λ (2W ₁ + W ₂ ) · 2 / (πD ² ρ) (5) The following was found from the equation (5).

. Although the coefficient of thermal expansion λ of the material is usually quite small, the weight (2W ₁ + W ₂ ) of the probe 3 and the arm 4 is much larger than the buoyancy. Moreover, since the temperature fluctuation ΔΤ is very large,
The detection error ΔS due to the change in the liquid level of the molten metal is quite large and cannot be ignored.

. The detection error ΔS is made smaller as the outer diameter D of the probe 3 is large, W ₁ must be considered that Kengo also becomes heavy.

. In order to reduce the detection error ΔS, W ₁ and W ₂ should be reduced as much as possible.

In the present invention, an automatic temperature compensating means as shown in FIG. 1 is applied to compensate for the above-mentioned detection error. That is, as shown in FIG.
A rod-shaped compensator 20 having a larger coefficient of thermal expansion is arranged, the fixed end 20a of the compensator 20 is fixed to the arm 4, and the free end 20b opposite to the end 20a is not fixed. is there.

In this case, since the rod-shaped compensator 20 is attached so as to be in close contact with the arm 4, it can be considered that both have the same temperature distribution. Assuming that the coefficient of thermal expansion of the compensator 20 is λ ₂ and the coefficient of thermal expansion of the arm 4 is λ ₁ , the condition for temperature compensation is λ ₂ > λ ₁ .

Here, consider only the moment of the vertical force, the position of the center of gravity of clamping member 9 which supports it and the probe 3 a, the weight of the center of gravity position as W _1, several, such as: Make assumptions.

. Since the arm 4 and the compensator 20 are sufficiently thin and sufficiently long, the vertical temperature distributions are all uniform.

. Since the thermal conductivity of the arm 4 and the compensator 20 is very good,
Their temperatures change in response to environmental temperature changes,
The temperature distribution in the lateral direction (left-right direction) is uniform over the entire length.

. It is assumed that the thermal conductivity of the material of each member such as the probe 3 and the arm 4 does not change within the temperature change range.

Center-of-gravity position of b compensator 20 in FIG. 1, W ₂ is the weight of the compensator 20 in the position of the center of gravity, c is the center of gravity of the arm 4, W ₃ is the weight of the arm 4 at its center of gravity position, d is the weight 21 the center of gravity of, W ₄ is the weight at its center of gravity position.

Here, assuming that the center of gravity of the system at a certain temperature T ₀ is J, S ₁ , S ₂ , S ₃ , and S _{4 in} FIG. ₁ are the center of gravity of the system from the positions of a, b, c, and d, respectively. This is the horizontal distance to J. The following equation is established by these relations.

W ₁ S ₁ + W ₂ S ₂ + W ₃ S ₃ = W ₄ S ₄ (6) Here, the temperature of the system changes from T ₀ to T _{1 due} to a change in the temperature of the environment.
Consider the case of rising to The change in length of the arm 4 and the compensator 20 in this case each [Delta] L, and [Delta] L _1. In order that the distance from the center of gravity J (FIG. 5) of the system to the reference plane X does not change, the following equation (7) must be satisfied.

W ₁ (S ₁ + ΔL) + W ₂ (S ₂ + 1 / 2ΔL−1 / 2ΔL ₁ ) + W ₃ (S ₂
+ 1 / 2ΔL) = W ₄ (S ₄ + ΔL ₁ −ΔL) (7) Since the relationship between ΔL and ΔL ₁ is ΔL ₁ = (λ ₂ / λ ₁ ) ΔL (8), (6) (8) ) Into equation (7), W ₄ = [λ ₁ / (λ ₂ −λ ₁ )] × [W ₁ −W ₂ (λ ₂ −λ ₁ ) / 2
λ ₁ + 1/2 · W ₃ ] (9) holds.

That weight W ₄ of the compensation of the weight 21 is satisfied (9) (9-2) equation, the gravity center position J of the system will be unaffected by the ambient temperature.

 The following equation can be derived from equation (9).

W ₄ + 1/2 · W ₂ = λ ₁ / λ ₂ −λ ₁ [W ₁ + 1/2 · W ₃ ] (9-1) According to equation (9-1), even when W ₄ = 0, 1/2. If W ₂ = λ ₁ / λ ₂ −λ ₁ [W ₁ + 1/2 · W ₃ (9-2) holds, the same compensation effect is obtained. Actually, since the temperature distribution of the system is not uniform, the position of the center of gravity J of the system slightly changes due to the non-uniform temperature, but it is considered that the influence on the liquid level measurement of the molten metal is greatly suppressed. .

In this case, the weight 21 is not used for the free end 20b of the compensator 20, but the free end 20b is made thicker than the fixed end 20a to substitute for the weight 21, and the free end 20b is used. May satisfy the expression (9).

(Operation) In the liquid level detecting device of the present invention, the probe 3 inserted in the molten metal tank 1 receives the buoyancy of the molten metal 2 in the molten metal tank 1, and the buoyancy is transmitted to the arm 4. Is transmitted to the buoyancy detector 6 from the other end 4b. In this case, since the other end 4b of the arm 4 is in contact with the buoyancy detector (for example, a load cell) 6, the arm 4 rotates only a small angle that cannot be seen even if it receives buoyancy. The buoyancy is transmitted to the buoyancy detector 6, and the buoyancy detector 6 detects the buoyancy. The detected buoyancy is output as an electric signal, and extraneous noise (noise due to mechanical vibration at the place where the molten metal bath 1 is set) contained in the signal is removed by the filter 8, and furthermore, the calculation shown in FIG. The arithmetic processing is performed by the processor 7, and the liquid level of the molten metal corresponding to the buoyancy detected by the buoyancy detector 6 is calculated.

Moreover, in the present invention, as shown in FIG.
When the temperature of the arm 4 is raised by the heat of the molten metal, the arm 4 extends to the left (left side of the fulcrum 5) in FIG. 1 due to thermal expansion. It is fixed, and the free end 20b is unfixed, so that when thermally expanded, the right side of FIG. 1 (the side opposite to the expansion direction of the arm 4)
Extend to. For this reason, the extension of the two is canceled, and the thermal expansion and contraction of the arm 4 is automatically compensated, and the influence on the liquid level measurement of the molten metal is largely suppressed.

Further, since the thermal expansion coefficient λ ₂ of the compensator 20 is larger than the thermal expansion and contraction λ ₁ of the arm 4 (λ ₂ > λ ₁ ), the change in elongation due to the thermal expansion of the arm 4 causes the thermal expansion of the compensator 20. The change in elongation due to expansion is reliably compensated.

(Embodiment) FIGS. 1 to 4 show an embodiment of the apparatus for detecting the liquid level of molten metal of the present invention.

In these figures, 1 is a molten metal tank, 2 is a molten metal in the molten metal tank, 3 is a probe in which the lower part 3a is inserted in the molten metal, 4 is an arm, and 5 is an arm that can rotate in the direction of an arrow. And 6 is a buoyancy detector.

The probe 3 is formed of ceramics having excellent heat resistance and a relatively small coefficient of thermal expansion. Its shape is a round bar. The lower part 3a is inserted into the molten metal 2 and the upper part 3b is supported by the arm 4, as shown in FIGS.

Since the life of the probe 3 which comes into direct contact with the hot metal melt 2 is limited, it must be replaced after a certain period. Therefore, it is desirable to attach the probe 3 to the arm 4 so that it can be easily replaced. For this purpose, for example, as shown in FIGS. 4 and 7, the probe 3 is sandwiched between two clamps 9 attached to the tip of the arm 4,
The probe 3 is fixed when the clamps 9 are tightened with the screws 10, and when the screws 10 are loosened, the fixation is released and the probe 3 can be removed. In addition, the measurement range of the liquid level detection device can be adjusted to be large.

The center of gravity of the arm 4 is held substantially horizontally by a fulcrum 5 so that the load of the arm 4 is applied to the buoyancy detector 6 as little as possible. Further, the fulcrum 5 of the arm 4 is set to the same height as the liquid level of the molten metal 2 as much as possible.
It is desirable that the moment due to the force applied by the flow of the molten metal 2 to the probe 3 be as small as possible.
Further, the arm 4 is formed of a material having excellent rigidity or has a shape having excellent rigidity so that the arm 4 does not bend or bend even if it is long, so that the buoyancy received at the end 4a of the arm 4 is reduced. It is desirable that the signal be transmitted from the other end 4b to the buoyancy detector 6 as accurately as possible.

Further, in the present invention, as shown in FIG. 1, a bar-shaped compensator 20 made of a material having a higher coefficient of thermal expansion than the arm 4 is mounted on the arm 4. Moreover, the compensator 20 is attached so as to be in close contact with the arm 4, and only the fixed end 20 a of the compensator 20 on the probe 3 side is fixed to the arm 4, and the free end 20 b on the opposite side is fixed to the arm 4. It is not fixed.

A weight 21 is attached to the free end 20b. The weight of the weight 21 is the length of the arm 4, the length of the compensator 20,
Determined in relation to their coefficients of thermal expansion, etc., but the weight 21 in any event is formed so that the weight W ₄ of the center of gravity position d satisfies the equation (9).

In the present invention, the weight 21 may be used instead of the weight 21 by using the free end 20b side of the compensator 20 without using the weight 21.

The material of the arm 4 is, for example, SUS430, the coefficient of thermal expansion λ ₁ = 13.1 × 10 ⁻⁶ , and the material of the compensator 20 is, for example, S
US304, thermal expansion coefficient λ ₂ = 20.1 × 10 ⁻⁶ , and carbon steel, for example, is suitable as the weight 21.

A load cell is used for the buoyancy detector 6.
As shown in FIG. 5, the force F applied to the load cell can be decomposed to the vertical component force F ₁ to the horizontal force F _2. Vertical component of these
F ₁ can be calculated level change if accurately measured. Absolutely no relation with the buoyancy of the horizontal force F ₂ is the probe 3, since only adversely affect the load cell and do not take appropriate measures, the measurement error of the liquid level of the molten metal occurs in some cases. This in order to prevent the influence of the horizontal force F ₂ is the load cell load losses that of the commercially available 13
A bearing 14 is preferably provided rotatably at the force receiving point above (FIG. 5), as shown in FIGS. Thus it becomes extremely small horizontal component of force F ₂ if, the smaller the error caused by it can be ignored.

The signal processor 7 processes the output of the electric signal from the buoyancy detector 6 to calculate the liquid level of the molten metal 2 in the molten metal tank 1 and to display the detected liquid level.

Since the environment of the factory such as metal melting and casting is quite severe, it is almost impossible to completely suppress mechanical vibration. Such mechanical vibration (external vibration) is transmitted to the molten metal detecting device, and large noise is generated. When the output waveform of the load cell was examined by artificially applying vibration to the molten metal detector, the result was as shown by signal a in FIG. As is apparent from this figure, the noise due to the external vibration is not only very large but also its frequency is random and irregular.

In order to prevent this, an anti-vibration rubber may be laid below the molten metal detector, but the anti-vibration rubber has problems such as poor heat resistance and burning. Therefore, in the present invention, a low-pass filter 8 is provided between the buoyancy detector 6 and the signal processor 7 as shown in FIG. Noise was removed electrically. As a result, almost no external noise was removed as shown by the signal b in FIG.

In FIG. 4, reference numeral 14 denotes a Z stage which can be moved up and down in the directions of arrows ab so as to be adjustable in height, 15 is a linear steel for accurately measuring the vertical movement distance of the Z stage, and 16 is a shield case. .

(Effect of the Invention) The liquid level detecting device for molten metal of the present invention has the following effects.

. Since the liquid level of the molten metal is detected as buoyancy, the liquid level of the molten metal can be accurately detected regardless of whether the amount of the molten metal is large or small. Is more accurate than a sensor that detects

. Since the liquid level of the molten metal is detected as buoyancy, if the probe 3 is inserted deeper into the molten metal, even if the amount of the molten metal is slightly reduced, as long as the molten metal receives the buoyancy of the molten metal, the metal can be received. Since the liquid level can be detected, there is no need to adjust the measurable separation distance L according to the increase or decrease of the amount of the molten metal as in the sensor shown in FIG. 7, and the measurement becomes easy.

. Since the fixed end 20a of the compensator 20 is fixed to the arm 4 and the free end 20b is fixed to the arm 4, the thermal expansion and contraction of the arm 4 due to the heat of the molten metal is automatically performed by the compensator 20. And the arm 4 is hardly affected by the thermal expansion and contraction of the arm 4, and the accuracy of detecting the liquid level of the molten metal hardly decreases.

. If the free end portion 20b of the compensator 20 is made thicker or the weight 21 is attached and made heavier, the influence of the thermal expansion and contraction is further reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the thermal expansion and contraction of an arm in the molten metal liquid level detecting device of the present invention, FIG. 2 is a principle diagram of thermal expansion and contraction of the arm, and FIG. 3 is a liquid of the molten metal of the present invention. FIG. 4 is an explanatory diagram showing an embodiment of the liquid level detecting device, FIG. 5 is an explanatory diagram of a force applied to a load cell, FIG. 6 is an explanatory diagram of an improved load cell, FIG. FIG. 8 is an explanatory view of a probe mounting structure, FIG. 8 is an explanatory view of extraneous noise, and FIGS. 9 and 10 are explanatory views of different examples of the conventional liquid level detection sensor. 1 is a molten metal tank 2 is a molten metal 3 is a probe 3a is a lower part of a probe 3b is an upper part of a probe 4 is an arm 4a is one end of an arm 4b is one end of an arm 5 is a fulcrum 6 is a buoyancy detector 7 is a buoyancy detector 7 Signal processor 8 is filter 9 is both clamps 10 is screw 14 is bearing 20 is compensator 20 a is fixed end of compensator 20 b is free end of compensator 21 is weight

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Claims (1)

(57) [Claims] A probe (3) inserted into a molten metal (2) in a molten metal tank (1) and receiving buoyancy according to the liquid level of the molten metal (2).
An arm 4 for supporting the probe 3; a fulcrum 5 for supporting the arm 4 so as to be rotatable; and a buoyancy that is disposed below one end 4a of the arm 4 and receives the probe 3. A buoyancy detector 6 for detecting via the arm 4;
A signal processor 7 for calculating an electric output signal of the buoyancy detector 6 and obtaining a liquid level of the molten metal 2 corresponding to the output; A compensator 20 having a larger coefficient of thermal expansion than the arm 4 is disposed along the arm 4. The compensator 20 has a fixed end portion 20a of the arm 4 closer to the probe 3 than the fulcrum, and is fixed to the arm 4.
A liquid surface position detecting device for molten metal, wherein a free end portion 20b opposite to the same end portion 20a is not fixed.