JPH0237984B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the concentration of hydrogen gas in molten metal, and more particularly to an improvement in an apparatus that can directly measure the concentration of dissolved hydrogen in molten metal, especially aluminum or its alloy. It is something.

Conventionally, hydrogen gas dissolved or dissolved in molten metals such as aluminum or aluminum alloys generates pores inside the metal when the molten metal solidifies, and these pores have various harmful effects on the metal as a product. It is known. In the past, the harmful effects of these pores were not considered to be much of a problem, but as product quality has become higher in recent years, for example, minute "bulges" that occur on the surface of an aluminum plate during hot processing have become a problem. However, since it has been pointed out that problems such as the occurrence of pit-like defects and loss of quality in the surface treatment process of alumite, etc. when commercialized as panel materials for building materials, metal The so-called dehydrogenation operation, which removes dissolved hydrogen from molten metal, is becoming a more important step in casting operations than ever before.

By the way, such a dehydrogenation operation takes a long time, and dehydrogenation operations longer than necessary will increase the cost of the product, so the concentration of dissolved hydrogen in the molten metal is usually measured beforehand. It is said that it is best to perform only the minimum necessary dehydrogenation operation based on the measurement results.

Therefore, the method for measuring the dissolved hydrogen concentration in molten metal is based on the same reason as above, that is, the time required for the measurement is short.
British Patent No. 684865, US Patent No. 2861450
It is considered desirable to employ the so-called Telegas method, which uses a device such as that shown in the specification of the above patent.

The hydrogen gas concentration measuring device used in the telegas method, the so-called telegas device, has an immersion head that has two holes immersed in the molten metal. An inert gas such as nitrogen is sent into the molten metal through one hole, while the other is immersed in the molten metal. By repeating the process of recovering the inert gas through the holes and sending the recovered inert gas back into the molten metal via a pump, a hydrogen gas concentration detector, and an immersion head, the dissolved hydrogen concentration in the molten metal can be determined. The structure is such that hydrogen gas at a partial pressure balanced with the inert gas is introduced into the inert gas. The thermal conductivity of the mixed gas containing hydrogen gas formed by such recirculation of the inert gas is measured by one of the two detection cells (detection cell) provided in the hydrogen gas concentration detector. On the other hand, the resistance change value of the filament-type detection element (metallic resistance wire) is extracted in the other cell (on the control side), while air whose thermal conductivity is almost equal to that of the inert gas (nitrogen in this case) is always kept in the other cell (control side). The resistance value of the hot wire type detection element in the cell is maintained at a constant value, and this value is taken out as a reference value. The change in thermal conductivity based on the magnitude of the hydrogen partial pressure, and thus the magnitude of the equilibrium partial pressure of hydrogen gas, is extracted as a nonequilibrium current by the bridge circuit. Then, the hydrogen gas concentration is calculated by comparing the current value with a graph called a calibration curve that shows the relationship between the nonequilibrium current and the hydrogen gas concentration in the molten metal, which has been created in advance according to the temperature of the molten metal. The dissolved hydrogen concentration in the molten metal is determined by multiplying the value by a correction constant determined by the type of each metal.

According to the conventional telegas device with this configuration, the dissolved hydrogen concentration (hydrogen gas concentration) can be directly measured from the molten metal, so the measurement time is shorter than that of other methods that measure the hydrogen gas concentration using solidified metal as a sample. However, from the point of view of work efficiency, it could not be said that the time was sufficiently shortened.

That is, in the conventional telegas device described above, the detection cell of the hydrogen gas concentration detector is configured to directly use a hole drilled in a metal block such as brass as a cell container. It takes a considerable amount of time for the hot-wire detection elements that make up the bridge circuit, the metal block that houses these elements, and the atmosphere surrounding this metal block to reach a state of thermal equilibrium, and therefore the bridge circuit ammeter It took a relatively long time until the indicated value became stable and the hydrogen gas concentration in the molten metal was calculated.

In addition, in such a device, when the metal block is subjected to a temperature change in the surrounding atmosphere, the thermal equilibrium state between the metal block and the hot wire type detection element housed therein is disrupted, and the bridge is damaged. The problem is that not only does it take a considerable amount of time to stabilize the circuit, but the ammeter must be zero-calibrated each time because the value indicated by the ammeter in the circuit changes gradually. It also contained within it.

The present invention was developed against the background of the above circumstances, and its purpose is to shorten the measurement time and to prevent the indicated value from changing easily due to changes in the temperature of the surrounding atmosphere. An object of the present invention is to provide an apparatus for measuring hydrogen gas concentration in molten metal that does not require so much zero point calibration.

In order to achieve this objective, the present invention involves blowing the inert gas into the molten metal, which brings the molten metal into contact with an inert gas that is immersed in the molten metal and circulated. an immersion head comprising an injection hole, a filter for separating an inert gas blown through the injection hole from the molten metal, and a recovery hole for recovering the inert gas separated by the filter; It has an inert gas flow path connected to the filling hole and the recovery hole to form a closed circuit,
an inert gas circulation mechanism that repeatedly circulates and flows an inert gas through the flow path to the immersion head by means of a pump means; a detection means that uses a hot wire type detection element whose resistance value changes to detect an electrical resistance that changes depending on the hydrogen gas concentration contained in the inert gas flowing through the flow path; In the measuring device, the detection means is connected to the inert gas flow path.
The measuring cell is provided with a measuring cell containing the hot wire type detection element that is exposed to the circulating hydrogen-containing inert gas, and a vacuum layer is provided around the measuring cell so as to surround it.

According to the present invention having such a configuration, by providing a vacuum layer around the measurement cell housing the hot wire type detection element exposed to the hydrogen-containing inert gas, the heat capacity of the cell itself can be effectively reduced. , the measuring cell can be thermally isolated from the atmosphere surrounding the detection means, so that the measuring cell is almost unaffected by temperature changes in the surrounding atmosphere and quickly stabilizes at a predetermined temperature value. As a result, it has become possible to obtain a hydrogen gas concentration measuring device that requires almost no zero point calibration and that can significantly shorten the measurement time. This reduction in measurement time further improves work efficiency, making it possible to reduce product costs.

Hereinafter, in order to clarify the present invention more specifically, two or three embodiments thereof will be described in detail based on the drawings.

First, FIG. 1 is a system diagram showing an embodiment of the hydrogen gas concentration measuring device according to the present invention. In the figure, 2 is a two-hole probe immersed in a molten metal 4 of aluminum or aluminum alloy. (immersion head), which has a first hole (blow hole) 6 that extends deeply into the molten metal 4, and nitrogen, argon, etc. that are provided above the first hole and are blown out from the first hole 6. A skirt 8 configured to collect inert gas bubbles, a second hole (collection hole) 10 opened upward inside the skirt 8; It is equipped with a filter 11 made of ceramics or the like that is less wetted by the molten metal and removes the molten metal from the guided inert gas bubbles. Each hole 6 of this two-hole probe 2
and 10 are connected to a diaphragm pump 16 via tubes 12 and 14, respectively,
the diaphragm pump 16 and tube 12,
14 and the like and the molten metal 4 form a closed flow path for inert gas.

That is, check valves 18 and 20 are provided on the tubes 12 and 14, respectively, and the check valves 18 and 20 allow the inert gas to pass through the flow path to the first side of the two-hole probe 2. The inert gas is made to flow in the direction of blowing out into the molten metal 4 from the hole 6, and the inert gas is repeatedly circulated within the closed flow path by the operation of the diaphragm pump 16 by the motor 22. .

During this inert gas circulation, the inert gas blown into the molten metal 4 from the first hole 6 of the probe 2 becomes bubbles in the molten metal 4 and reaches the skirt 8. Hydrogen dissolved in the molten metal 4 diffuses into the bubbles,
As the inert gas is repeatedly circulated within the closed flow path, the partial pressure of hydrogen diffusing into the inert gas bubbles gradually increases, and finally the concentration of hydrogen dissolved in the molten metal 4 increases. The partial pressure is increased to equilibrium. Note that hydrogen does not diffuse into the inert gas above the above equilibrium partial pressure.

Inert gas containing hydrogen gas that is below the equilibrium partial pressure, so-called hydrogen-containing inert gas, has thermal conductivity that increases according to the partial pressure of hydrogen gas contained therein. The hydrogen gas concentration detector 24 installed on the tube 14
This is how it is detected.

For example, as shown in FIG. 2, this hydrogen gas concentration detector 24 includes a detector block 26 made of aluminum or brass, and a detector block 26 for measuring the respective thermal conductivities of hydrogen-containing inert gas and air. It has a pair structure in which two detection parts 27, 27 are formed, and each detection part 27 has a double structure in which a measurement cell 30 is further housed in a cylinder 28 formed in the detector block 26. .

That is, in FIG. 2, 32 is a cylindrical first sealing member made of a heat insulating material, and the opening of a bottomed cylindrical cell container 34 made of a metal material such as stainless steel is located in the lower part of the inner space. A second sealing member 3 made of a heat insulating material is also fitted and bonded, and is also made of a heat insulating material at the upper part of the inner space.
6 is fitted into the first seal member 3.
2 is hermetically fitted into the opening of each cylinder 28 to form a gas diffusion chamber 38 and a vacuum chamber 40, which are mutually airtight spaces, inside and outside the cell container 34 within the cylinder 28.

The gas diffusion chamber 38 of one of the detection parts 27 includes through holes 42, 42a, 4 formed in the first sealing member 32.
2b to tubes 14, 14a, and 14b, which are flow paths for hydrogen-containing inert gas, and the hydrogen-containing inert gas flows through one tube 14a.
The gas passes through the through-hole portion 42a, passes through the upper part of the gas diffusion chamber 38, and flows out into the tube 14b through the other through-hole portion 42b. Further, the gas diffusion chamber 38 of the other detection section 27 is connected to the outside air through tubes 44, 44a, and 44b, and the measurement cell 30 is filled with air having approximately the same thermal conductivity as the inert gas. It's becoming like that.

Inside these diffusion chambers 38, that is, inside the measurement cells 30, there is a hot wire type detection device made of a wire made of platinum or the like whose temperature, or resistance value, changes depending on the change in thermal conductivity of the gas being diffused. An element (electrical resistance wire) 46 is provided to detect the thermal conductivity of the hydrogen-containing inert gas or air as a resistance value. At this time, the higher the partial pressure of hydrogen gas, the higher the thermal conductivity of the hydrogen gas-containing inert gas, and the hot wire type resistance element 46 is cooled more and its resistance value is lowered. More current will flow through it.

Further, in this embodiment, the hot wire type detection element 46 is connected to the cell container 34 from the second sealing member 36.
A hollow pipe (supporting body) 48 made of a non-conductive material such as alumina or ceramics is bent at the lower end, extending (hanging) inward, and one side passes through the inside of the pipe 48, and the other end is bent. The other end is wrapped upwardly around the outer surface of the pipe 48,
Both are connected to platinum wire stems 46a and 46b provided through the second seal member 36, and these platinum wire stems 46a and 46b are further connected to conductors 51a and 51a from a Wheatstone bridge circuit 50, which will be described later.
51b, 51c, and 51d, respectively.

If the electrical resistance wires 46 are held by being wound around the support in this way, problems such as the electrical resistance wires coming into contact with each other in the middle or colliding with the cell wall due to vibration and being damaged can be avoided. This has the advantage that a measurement cell with a long service life and little error in detected values can be obtained.

On the other hand, the vacuum chambers 40 of each of the detection units 27, 27 are communicated with each other within the detector block 26, and a vacuum pump (not shown) connected to a pipe 52 communicating with the vacuum chambers 40 is used to generate a vacuum. After this state, it is sealed by known means such as vacuum fasteners or brazing (not shown).

The thermal conductivities of the hydrogen-containing inert gas and air, each converted into a resistance value by the hydrogen gas concentration detector 24 having such a structure, are compared in a Wheatstone bridge circuit 50 as shown in FIG. This non-balanced current is extracted as an unbalanced current corresponding to the difference in thermal conductivity (resistance value) of The hydrogen gas concentration (dissolved hydrogen concentration) in the measured molten metal is calculated and displayed using the formula.
can now be grasped instantly. In addition, 5
6 is a thermocouple immersed in the molten metal 4, which provides temperature data of the molten metal 4 to the arithmetic processing circuit 54; and 58, which supplies current to the Wheatstone bridge circuit 50 and the arithmetic processing circuit 54. This is a constant voltage (constant current) power supply circuit.

Further, in FIG. 1, reference numeral 60 denotes an inert gas cylinder, from which a predetermined inert gas such as nitrogen gas is supplied between the hydrogen gas concentration detector 24 and the check valve 20 via a tube 62. It is designed to be introduced into the tube 14 portion of the tube. Note that the supply of inert gas from the cylinder 60 is controlled by a stopper valve 64 provided on the tube 62.

When measuring the hydrogen concentration in the molten metal 4 with the hydrogen gas concentration measuring device having such a configuration, the stopper valve 64 is opened while the constant voltage power supply circuit 58 is operated, and the inert gas in the cylinder 60 is discharged from the above-mentioned closed state. After filling the flow path, the two-hole probe 2 is gently immersed in the molten metal 4, and then the stopper valve 64 is closed to stop the supply of inert gas into the flow path. At this time, the thermocouple 56 is also immersed in the molten metal 4, and it is confirmed that the indicated value of the arithmetic processing circuit 54 is 0. After confirming that the indicated value is 0,
The diaphragm pump 16 is operated by the motor 22, and the inert gas is repeatedly circulated and distributed within the closed flow path. Then, the arithmetic processing circuit 54
After confirming that the indicated value has stabilized, the final stable value is read as the measured value.

According to this embodiment as described above, the vacuum chamber 40 provided around the measurement cell 30 insulates the cell container 34 from the outside air and effectively reduces the heat capacity of the cell container 34 itself. As a result, the measured values stabilized quickly, and the measurement time was thereby shortened.

Incidentally, according to the results of experiments conducted by the present inventors,
Unbalanced output by conventional telegas equipment: (mV)
The state of change over time of is shown in FIG.
This was shown by the solid line in FIG. As is clear from the experimental results shown in Figure 3, in the case of conventional telegas equipment, even after 24 minutes have passed after the start of measurement (after turning on the power switch for the detector and its attached circuits), the indicated value still remains. On the other hand, in the case of the device of this example, the indicated value becomes stable (thermal equilibrium state) approximately 10 minutes after the start of measurement, and as a result, the temperature in the molten metal by the device of this example becomes stable. It can be seen that the measurement time for the hydrogen gas concentration was significantly shortened compared to that of the conventional device.

Note that the above non-equilibrium output is a value expressed by the following equation assuming that heat radiation and convection can be ignored.

=1/2I・Rf・a(tf−tc)/1+atf・δ・γ
/1+γ Here, I is the DC current supplied to the Wheatstone bridge circuit, R _f is the resistance value of the electrical resistance wire on the hydrogen-containing inert gas inflow side, α is the temperature coefficient of the electrical resistance wire, and tf is the electrical resistance wire. The temperature of the resistance wire, tc is the inner wall temperature of the measurement cell, δ is the ratio of the amount of change in thermal conductivity Δλ (due to hydrogen gas inflow) to the thermal conductivity λm of only inert gas at the average temperature in the measurement cell, and γ is Rr, the ratio of the resistance value R of the electrical resistance wire on the air inflow side to Rf, is the input impedance of the recorder. However, it is assumed that there is a relationship of 2Rr≫R _f +R.

Further, in this embodiment, the hydrogen gas concentration detector 24 has a configuration as shown in FIG. 2, but is not limited to this, and may have a configuration as shown in FIGS. 4 and 5. It doesn't make any difference.

That is, the measurement cell 67 of the hydrogen gas concentration detector 66 shown in FIG.
0, tubes 14a, 14b and tube 72
a, 72b are hermetically inserted and bonded from the inside and outside, respectively, and the other ends of the tubes 72a, 72b are connected to the gas diffusion chamber 38 at the lower end of the cell container 34.
The diffusion chamber 38 is configured such that hydrogen gas is diffused upward from the lower part of the diffusion chamber 38. Note that since the configuration of other parts is the same as in the previous embodiment, the same reference numerals are used and detailed explanations are omitted.

In addition, in the case shown in FIG. 5, each measurement cell 74 has a cylinder 2 whose outer cylinder is a metal tube 76.
8 and each metal tube 76 is directly attached to the pipe 52 by welding.
Each tube 14a, 14b is a metal tube 76.
It is connected to the upper part of the gas diffusion chamber 38 through a hole provided in the side wall of the gas diffusion chamber 38 and a through hole 80 formed in the first seal member 78 . Note that the upper end of the hollow pipe 48 is closed with a plug member to keep the internal space airtight from the external atmosphere.

The hydrogen gas concentration detector 82 configured as shown in FIG.
It can be used as a compact structure, and is more effective when placed in a constant temperature bath.

In the previous example, the present invention was explained only when applied to a diffusion type hydrogen gas concentration detector, but the present invention can also be applied to a semi-diffusion type or flow type hydrogen gas concentration detector. It is.

In addition, in the above example, the measurement cell side, which is the standard for comparison, was all open to the atmosphere.
Of course, this is not limited to this, and instead of the atmosphere, the same inert gas as the inert gas for hydrogen gas concentration measurement is passed through the measurement cell through a closed circuit flow path different from the closed circuit flow path for hydrogen concentration measurement. It may also be supplied internally. In short, it is sufficient that a gas having the same thermal conductivity as the inert gas for hydrogen gas concentration measurement is supplied to the reference measurement cell.
It is only necessary that the thermal conductivity, which serves as a reference, be detected in this way.

In addition, the hydrogen gas concentration measuring device according to the present invention can be implemented with various modifications and modifications without departing from the spirit of the present invention as set forth in the claims. be. For example, without using the arithmetic processing circuit 54, the hydrogen gas concentration in the molten metal may be calculated by comparing the conventionally measured unbalanced current with a calibration curve. Instead of the motor 22, inert gas may be controlled and driven using a valve mechanism.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of a hydrogen gas concentration measuring device according to the present invention, and FIG. 2 is a sectional view of essential parts showing an example of a hydrogen gas concentration detector used in the device. Figure 3 shows the experimental results of measuring hydrogen gas in molten metal using the hydrogen gas concentration detector shown in Figure 2 and a conventional telegas device as a change over time in the nonequilibrium output. It is. FIGS. 4 and 5 are sectional views of main parts showing other examples of hydrogen gas concentration detectors used in the apparatus of the present invention, respectively. 2: 2-hole probe, 4: Molten metal, 16: Diaphragm pump, 22: Motor, 24, 66, 8
2: Hydrogen gas concentration detector, 26: Detector block, 27: Detector, 28: Cylinder, 30, 6
7, 74: measurement cell, 32, 68, 78: first seal member, 34: cell container, 36: second seal member, 38: gas diffusion chamber, 40: vacuum chamber, 46: hot wire type detection element, 48: Hollow pipe, 50: Wheatstone bridge circuit, 54: Arithmetic processing circuit, 5
6: Thermocouple, 76: Metal tube.

Claims (1)

[Scope of Claims] 1. An inert gas immersed in the molten metal 4 and brought into contact with the circulated inert gas and the molten metal, through a blowing hole 6 for the inert gas into the molten metal and the blowing hole. An immersion head 2 equipped with a filter 11 for separating the blown inert gas from the molten metal and a recovery hole 10 for recovering the inert gas separated by the filter; an injection hole and a recovery hole of the immersion head; It has inert gas passages 12 and 14 connected to it to constitute a closed circuit, and by means of a pump means 16,
an inert gas circulation mechanism that repeatedly circulates and flows inert gas to the immersion head through the flow path;
Hydrogen contained in the inert gas flowing through the inert gas flow path is detected using a hot wire type detection element 46 which is provided on the inert gas flow path and whose resistance value changes depending on the change in thermal conductivity of the gas. A hydrogen gas concentration measuring device including a detection means 24 for detecting electrical resistance that changes depending on the gas concentration, wherein the detection means 24 is a hydrogen-containing inert gas that is connected to the inert gas flow path and is circulated. It has measurement cells 30, 67, 74 that house the hot wire type detection element 46 exposed to gas, and a vacuum layer 4 surrounding the measurement cell.
1. An apparatus for measuring hydrogen gas concentration in molten metal, characterized in that a 0 is provided. 2. The device according to claim 1, wherein the hot wire type detection element 46 is held by being wound around a support 48 inserted into the measurement cell. 3 The measurement cells 30, 67 are in a predetermined block 2
By the vacuum action of vacuum means fitted and connected to the hole 28 provided in the hole 6, said vacuum layer 40 is formed between the inner wall surface of said hole and the outer surface of said measuring cell. An apparatus according to claim 1 or 2. 4. Claim 1, wherein the measurement cell 74 constitutes an inner cylinder member with a double cylinder structure, and the space between the inner cylinder member and the outer cylinder member 76 located outside thereof is the vacuum layer. 2. The device according to item 2 or item 2.