JPH01158352A - Method and apparatus for measuring content of hydrogen in molten bath of aluminum base metal - Google Patents

Abstract

PURPOSE:To simplify measurement, by receiving a definite amount of an aluminum base metal in a hermetically closed container having a definite volume and solidifying the same by gradual cooling to discharge the gas in the molten metal bath and subsequently measuring the concn. of the hydrogen gas in the container. CONSTITUTION:A definite amount of an aluminum base metal molten bath 1 is held in the cast 2 received in a metal container 7 having a hermetically closed structure. Next, the temp. of the cast is made constant and a definite amount of the metal molten bath is injected in the cast 2 and the container 7 is hermetically closed to be held for a definite time and the molten bath is solidified by gradual cooling to discharge hydrogen gas. Subsequently, the container 7 is refluxed by a suction pump 5 to absorb steam through a drying box 8 and the gas in the container 7 is sucked by an extraction pump 3 to be reacted with the reagent in a hydrogen detector 4. On the basis of a calibration curve preliminarily drawn from the amount of the hydrogen gas in the metal molten bath and the discharge amount of the hydrogen gas by gradual cooling, the amount of hydrogen is calculated from the reading of the detector 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method and apparatus for measuring hydrogen content contained in molten aluminum-based metal.

[Prior Art] In the present invention, the aluminum-based metal refers to aluminum or an aluminum alloy. The molten aluminum-based metal contains a gas whose main component is hydrogen, and the presence of this gas causes defects such as pinholes and blowholes in cast products, resulting in poor aluminum moldings. making it difficult to cast. Therefore, measures are taken to reduce the gas content as much as possible, such as degassing treatment using flux, holding, and molten metal temperature control. In order to control the gas content in molten metal, it is necessary to measure the gas content, and various measurement methods have been implemented, but a simple and highly accurate measurement method has not yet been developed.

A simple measurement method in front of a melting furnace is the pinhole test method using an isolite brick mold.
It has been implemented. In this method, a small amount of molten metal taken from a melting furnace is poured into an isolite brick mold, and when the molten metal solidifies, the amount of hydrogen gas contained in the molten metal is determined by the number of pinholes created by air bubbles rising to the surface. It is. However, this method has drawbacks such as the degree of preheating of the isolite bricks has a large effect on the occurrence of pinholes, and the judgment is based on the naked eye observation of the measurer, so there is variation due to individual differences among the measurers.

Typical methods for quantitatively measuring the amount of hydrogen gas contained in molten metal include the so-called initial bubble method and the telegas method.

For example, the initial bubble method is disclosed in Japanese Patent Application Laid-Open No. 51118492.
As shown in Figure 2, the molten metal is placed in a vacuum tank, the pressure is reduced, and the amount of hydrogen gas in the molten metal is determined from the temperature and pressure at the time of the first bubble generation. In this method, the first bubbles generated during decompression are observed and judged with the naked eye of the measurer, so the measurer's skill level is required, and the pressure at the time of bubble generation varies depending on the presence or absence of bubble generation nuclei. There are drawbacks to measurement accuracy, such as: Furthermore, a measuring device using this principle requires a vacuum system and is expensive.

The telegas method, as shown in British Patent No. 884885 and British Patent No. 1510957, involves injecting and circulating an inert gas such as argon-nitrogen into a molten metal, and then discharging the gas when it reaches equilibrium with the molten metal. The concentration of hydrogen gas contained in the molten metal is determined by measuring the thermal conductivity of the gas, and the hydrogen content in the molten metal is calculated from this value. Although this method is said to have low data variation and high measurement accuracy, there are limitations on the length and shape of the measurement probe due to the principles of injecting and circulating inert gas and measuring its thermal conductivity. Therefore, there is a drawback that the range of movement of the object to be measured to the molten metal is limited. Furthermore, since an inert gas is handled and a measuring device for determining the thermal conductivity of the gas is required, the measuring device based on this principle is quite expensive.

Other methods include vacuum extraction method and electron impact method.

Vacuum extraction is a method in which hydrogen is extracted by heating a sample in a vacuum, and is broadly divided into melt extraction and solid phase extraction. Although this method can measure hydrogen concentration with high accuracy, it is not suitable for on-site measurement because it requires surface processing of the sample and the measurement time is long. The electron impact method uses the metal sample as a cathode and applies the principle of extracting hydrogen from the sample by bombarding it with ions accelerated at high voltage. Gas extraction is completed in a short time, but the blank value is large and fluctuates, so the measurement accuracy is not high.

[Problems to be Solved by the Invention] The present invention is directed to the following problems: conventional measurement methods are inferior in measurement accuracy when using a simple method, and when using a high-precision method, the measuring device is large and expensive; In view of the current situation where there are problems such as the need for a long time, in order to develop a measurement method and n1 constant device that is a simple measurement that can be effectively used in pre-furnace inspections, etc., and that also satisfies the necessary measurement accuracy. This is what was done.

C Means for Solving Problem] The present invention has been made to solve the above problems, and its gist is to store a certain amount of molten aluminum-based metal in a sealed container with a certain volume. , an aluminum group characterized in that the hydrogen gas content in the molten metal is determined by solidifying it while slowly cooling and releasing the gas dissolved in the molten metal, and then measuring the hydrogen gas concentration in the container. A method for measuring hydrogen content in a molten metal; a closed container with a fixed volume that houses a crucible for holding a molten aluminum metal and has a slow cooling function for the molten metal; and a hydrogen gas concentration detection device connected to the closed container. The present invention provides an apparatus for measuring hydrogen gas content in a molten aluminum-based metal, which is characterized by:

Here, the slow cooling function may be provided for the entire closed container system including the crucible. Moreover, the crucible means a molten metal holding container in general including a mold.

When a molten aluminum-based metal is rapidly solidified, the hydrogen dissolved in the molten metal remains retained in the solidified metal and is hardly released into the atmosphere.

Here, slow cooling refers to cooling the molten metal at a solidification rate that releases hydrogen necessary for measurement into the atmosphere.

The amount of hydrogen gas dissolved in aluminum or aluminum alloy molten metal is shown in a model in Figure 5. The amount of hydrogen gas dissolved is
The higher the temperature of the molten metal, the more it decreases as the temperature decreases, and becomes almost zero when it reaches the freezing point. When the molten metal is gradually cooled, a certain proportion of dissolved gas is released into the atmosphere as the temperature decreases. However, when the molten metal is rapidly solidified, most of the contained gas remains trapped in the aluminum and solidifies.

The principle of the present invention is that if the cooling conditions are kept constant when the molten metal is gradually cooled to the freezing point and the hydrogen gas contained in it is released, for example by using a mold with good insulation or by heating the mold,
The amount of hydrogen gas released from the molten metal has a good correlation with the amount of hydrogen contained in the molten metal, so by determining the hydrogen gas concentration in the container, the amount of hydrogen gas contained in the molten metal can be determined. This means that the amount can be calculated.

For this purpose, it is necessary to keep the container tightly closed, and it is also desirable to take measures to mix the hydrogen gas and the atmospheric gas so that the gas has a uniform composition. Moisture in the atmospheric gas reacts with metal elution to generate hydrogen atoms, which are activated and adsorbed on the aluminum surface, and further move into the metal lattice and dissolve therein. Therefore, since the presence of this moisture causes measurement errors, dehumidification of the atmospheric gas is recommended from the standpoint of improving measurement accuracy.

In addition to the above methods, methods for slowly cooling the molten metal include controlling the mold temperature with an electric heater, or using an electromagnetic field or pressurized gas to slowly cool the mold and the molten aluminum in a non-contact state. Can be adopted as appropriate.

In addition, even if it is cooled in a crucible made of ceramics with relatively good thermal conductivity (for example, Sialon ■ manufactured by Hitachi Metals ■), the hydrogen gas necessary for measurement can be released. In this case, if the cooling from the bottom is increased, directional solidification will occur, and more hydrogen will be released from the top of the molten metal. This method is effective as a method for shortening the all fixed time.

The concentration of hydrogen gas in the container can be measured using simple methods such as using a commercially available hydrogen detection tube (such as the Kita side type) to distinguish by color reaction, or reading the length of the discolored part. . In addition, depending on the purpose, you can use a hydrogen gas measuring device that uses principles such as catalytic combustion type, infrared type, thermal conductivity calculation type, etc.! IP1 constant accuracy is improved.

[Example] The method and apparatus of the present invention will be specifically and detailedly explained based on Examples, but the technical scope of the present invention is not limited thereto.

FIG. 1 shows a schematic diagram of a measuring device that is an embodiment of the present invention. A predetermined amount of molten aluminum-based metal 1 is held in a mold 2 housed in a metal container 7 having a closed structure to prevent release gas from escaping, and is slowly cooled. metal container 7
has a sealed structure with an O-ring 9 or the like. The inside of the container is heated by the held molten metal and the air expands, so it becomes pressurized. This pressurized state is maintained by the sealed structure.

For slow cooling, for example, a mold with low thermal conductivity (for example, a mold made of fireproof and insulating brick with high porosity such as isolite brick) or heating with a heater 6 to control the temperature can be used. method is adopted.

The released hydrogen gas has a high diffusion rate and is easily made uniform, but it is circulated within the container by the pump 5 as necessary so that it is mixed more uniformly within the container. Furthermore, as mentioned above, since water vapor in the atmosphere gives errors to measurements, a desiccant box 8 made of silica gel or the like is placed in the middle of the reflux pipe IO.

A piping 11 is provided as an inlet for gas collection from a metal container, and a detection tube 4 and an extraction pump 3 are connected thereto.

It is effective to reduce the pressure inside the container in order to increase the amount of released hydrogen. For example, if a reserve tank is provided, the pressure inside the tank is reduced, a mold into which molten aluminum-based metal is poured is stored in a metal container, and the mold is sealed, the reduced pressure reserve tank is electrically connected to the metal container. There is a constant reduced pressure inside.

As the hydrogen detection tube, for example, Kitagawa gas detection tube, Model 37 and 137U, etc. are used. Model 37 measures hydrogen concentration by color change due to color reaction. The reaction principle is that hydrogen reacts with palladium sulfate, and then with ammonium molybdate to produce molybdenum blue.

H2+P d S Qa+ (NH4)a Mo O4
+H2S O4 → Mo308 Changes from pale yellow to green to blue depending on the hydrogen concentration. still,
Model 1870, which measures reaction length, utilizes a reaction in which hydrogen reacts with palladium sulfate and magnesium perchlorate, causing the color to change from yellow to green.

Note that this reaction is accelerated at high temperatures, so cooling by the pipe 11 is required.

The measurement procedure using the measuring device shown in FIG. 1 is shown below.

(1) Keep the mold temperature constant.

(2) Pour a certain amount of molten metal into the mold.

(3) The container is sealed and held for a certain period of time to slowly cool and solidify the molten metal and release hydrogen gas.

(4) Aspirate the gas in the metal container with a suction pump and react with the reagent in the detection tube.

(5) Calculate the amount of hydrogen gas in the molten metal from the reading of the detection tube. Note that the relationship between the amount of hydrogen gas in the molten metal and the amount of hydrogen gas released by slow cooling is measured in advance, and a calibration curve is created. If the scale on the detection tube is converted to the amount of hydrogen gas in the molten metal, the amount of hydrogen gas can be read directly.

The amount of hydrogen gas released from the molten aluminum-based metal was measured using the measuring device shown in FIG. 1 (a catalytic combustion type hydrogen detector was used in implementation N3).

Example 1 A metal container with a volume of 1200cI11 (of which the space is 42cm)
A crucible of isolite bricks was placed in a molten metal of high-silicon aluminum A 390 alloy taken from the furnace.
For 500 g, the amount of hydrogen gas released by slow cooling during the process of (1) dissolution (2) retention (3) insertion of hydrogen-based material into the molten metal (4) degassing treatment (5) holding for 80 minutes after treatment is as follows: Measurement was performed using a general-purpose hydrogen gas detection tube (model 37). Further, the hydrogen gas content of the same sample was measured using a vacuum melt extraction method. The measurement results are shown in Table 1 and Figure 2.

Example 2 JIS aluminum alloy AC as aluminum-based alloy
Measurement was carried out in the same manner as in Example 1, except that 4C was used and Model 137U was used as the detection tube. The measurement results are shown in Table 2 and Figure 3.

Example 3 A metal container with a volume of 700 cd (of which the space is 365 cj
) inside the bottom of the cylinder of Sialon made by Hitachi Metals.
A crucible sealed with a 304 cooling plate was housed, and 600 g of JIS aluminum alloy AC4C molten metal in various states was poured into the crucible, and the amount of hydrogen gas released by slow cooling was measured. Samples Nα2 and Na7 are samples in which isolite bricks soaked in water are poured into molten aluminum to intentionally increase the hydrogen gas content. The hydrogen detector used to measure the amount of hydrogen gas released by slow cooling was XP-316 manufactured by Shin Cosmos Electric. This detector is of the catalytic combustion type and uses a gas sensor that measures the temperature rise of the platinum wire fill due to catalytic combustion of gas on the catalyst surface by changes in resistance value. Hydrogen gas content ffi measurements on the same samples were performed in the same manner as in Example 1. The measurement results are shown in Table 3 and Figure 4.

Table 1 (cc/loOg aluminum) Table 2 m3 Tables 2, 3, and 4 show that there is a good correlation between the amount of hydrogen gas released by slow cooling and the hydrogen gas content. It can be seen that the hydrogen gas content in the aluminum-based alloy melt can be measured by the method.

[Effects of the Invention] As specifically explained above, the present invention provides a method and apparatus for extremely simply and quantitatively measuring the hydrogen content in a molten aluminum-based metal.

[Brief Description of the Drawings] Fig. 1 is a schematic diagram of an example of a measuring device according to the present invention, and Figs. 2, 3, and 4 show the amount of hydrogen gas released by slow cooling and the amount of hydrogen gas released in the metal molten fluid. It is a diagram showing the relationship with hydrogen content,
FIG. 5 is a diagram showing the relationship between the amount of hydrogen gas dissolved in the molten aluminum metal and the temperature. 1... Aluminum-based metal molten metal 2... Mold 4... Hydrogen gas detection tube 7... Metal container Fig. 1

Claims (1)

[Scope of Claims] 1. A certain amount of molten aluminum-based metal is stored in a sealed container with a certain volume, solidified while slowly cooling, and the gas dissolved in the molten metal is released. 1. A method for measuring hydrogen content in an aluminum-based metal molten metal, the method comprising determining the hydrogen gas content in the molten metal by measuring the hydrogen gas concentration in the molten metal. 2. Store the crucible for holding molten aluminum-based metal,
1. An apparatus for measuring hydrogen gas content in an aluminum-based molten metal, comprising a sealed container having a constant volume and equipped with a molten metal slow cooling function, and a hydrogen gas concentration detecting device connected to the sealed container.