JPH08261813A - Metal molten level sensor - Google Patents

Abstract

PURPOSE: To improve anticorrosion against molten metal by building a dip electrode of a composite ceramics (SNC) comprising amorphous carbon ass dispersed into a matrix mainly composed of silica carbide and silica nitride. CONSTITUTION: A stick-shaped dipping electrode 2 is built up of an SNC which contains silicon carbide 15-80wt.%, silicon nitride 10-7wt.% and amorphous carbon 3-20wt.% while comprising the amorphous carbon as dispersed into a matrix mainly composed of the silicon carbide and silicon nitride. The dipping electrode 2 is so set to be turned to a furnace bottom C through a mounting metal 1 from the ceiling part B within a melting furnace A and adjusted to the height of a liquid surface when it is filled with a metal molten 3 upto a specified quantity. An earth 4 is set at a position lower than a measuring part of the liquid surface. When the furnace A is filled with the metal molten and the liquid surface reaches a specified position, a current flows through the metal molten 3 and is detected by a current detector D. This information is transmitted to a supply device of the metal molten 3 and the filling is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level sensor for detecting the amount of molten metal in a metal material melting furnace.

[0002]

2. Description of the Related Art The above-mentioned level sensor which has been conventionally used is a tip of a rod-shaped electrode which is vertically installed from a ceiling portion in a melting furnace for metal such as aluminum to a furnace bottom through a mounting bracket. Is adjusted to the liquid level height when the metal melt is filled up to a predetermined amount, and separately from this, a ground is installed at a position lower than the liquid level measurement site (hereinafter, abbreviated as metal melt). When the molten metal is filled in the furnace and the liquid level reaches a predetermined position, the liquid level contacts the tip of the electrode and the current flows through the molten metal. Is started to flow, and this current is detected by a current detector and the information is transmitted to a molten metal supply device to stop the filling, whereby the amount of molten metal in the melting furnace is kept constant.

In such a level sensor, the material forming the electrodes is a metal material such as stainless steel, hastelloy, titanium, cast steel, or a material obtained by plating these metals with chromium or the like, and more recently, JP-A-2-
As disclosed in Japanese Patent No. 44212, one using a ceramic sintered body containing silicon carbide and at least one of titanium diboride, titanium carbide, titanium nitride, zirconium diboride, and chromium silicide is proposed. Has been done.

[0004]

However, the above-mentioned prior art has the following problems. That is, the electrode made of the above metal material has good wettability with respect to the molten metal, so that when the molten metal is discharged, the molten metal at the electrode tip is poorly drained, and the residue of the molten metal adheres to the electrode tip. . When the molten metal is filled and discharged many times, the deposits on the tip of the electrode grow like ice columns. As a result, even when the molten metal is filled, the liquid surface does not rise to a predetermined position and contacts the deposits extending from the electrode tip portion, causing a current to flow,
Stop filling. For this reason, it is not possible to accurately control the liquid level, and it is impossible to keep the filling amount of the molten metal in the melting furnace constant.

Further, since the metal electrode has a small corrosion resistance to the molten metal, if it is immersed in the molten metal for a long time,
Erosion due to chemical reaction gradually occurs, and eventually it is consumed. For this reason, the life of the electrode material is only several tens to several hundreds of hours, and there has been a concern that the metal melt may be contaminated by the eluted metal or the like and impurities may be mixed.

On the other hand, in the conventional level sensor in which the electrodes are made of the ceramic sintered body, although the problem of the corrosion resistance is improved, the consumption of the electrodes cannot be completely suppressed. Therefore, the electrode life is short and there is a problem in strength. Furthermore, when the molten metal is discharged, the molten metal at the tip of the electrode is poorly drained, and deposits are formed on the electrode tip, making it impossible to accurately control the liquid level and keeping the amount of molten metal in the melting furnace constant. Can't keep,
In that respect, there is a problem in common with the level sensor of the metal electrode.

[0007]

In order to solve the above-mentioned problems, the level sensor of the present invention comprises 15-80 wt% of silicon carbide.
%, Silicon nitride 15 to 70 wt%, amorphous carbon 3 to 20 wt%
The immersion electrode is composed of a composite ceramics (hereinafter, abbreviated as SNC) in which amorphous carbon is dispersed in a matrix containing and containing silicon carbide and silicon nitride as main components.

[0008]

However, in the level sensor according to the present invention having such a structure, the presence of the amorphous carbon makes it possible to achieve good drainage with the molten metal (for example, carbon has low wettability with the molten aluminum). The molten metal is prevented from adhering to the metal parts, and the matrix containing silicon carbide and silicon nitride, which carry the amorphous carbon, as a main component, together with the corrosion resistance of the amorphous carbon, is very large against the molten metal. Shows corrosion resistance.

Further, due to the presence of amorphous carbon, it has sufficient conductivity as an electrode of the level sensor.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic diagram of a molten metal level sensor of the present embodiment, in which the rod-shaped immersion electrode 2 is
It is composed of an SNC in which amorphous carbon is dispersed in a matrix containing silicon carbide 15 to 80 wt%, silicon nitride 10 to 70 wt% and amorphous carbon 3 to 20 wt% and containing silicon carbide and silicon nitride as main components. The immersion electrode 2 is installed so as to face the furnace bottom C from the ceiling portion B in the melting furnace A for metals through the mounting metal fitting 1, and further the liquid when the molten metal 3 is filled to a predetermined amount. In addition to adjusting the surface height, a ground 4 was installed at a position lower than the liquid surface measurement site so that the metal melt 3 could be energized. Thereby, when the molten metal is filled in the furnace A and the liquid surface reaches a predetermined position, that is, when the liquid surface and the tip of the electrode come into contact with each other, an electric current flows through the molten metal 3 and The amount of the molten metal in the melting furnace A is kept constant by detecting the information with the current detector D and transmitting the information to the supply device of the molten metal 3 to stop the filling.

In the immersion electrode 2 constituting such a level sensor, a compact of a silicon carbide raw material is fired in a nitrogen atmosphere at a high temperature and a high pressure, whereby carbon in the silicon carbide is replaced with nitrogen to obtain silicon nitride. It can be obtained by producing amorphous carbon. The ratio of each component in the material depends on the degree of progress of the substitution reaction, but the amorphous carbon is an element responsible for the conductivity of SNC and is particularly important. That is, if the amorphous carbon is less than 3 wt%, the specific resistance value required for the electrode cannot be obtained.

Further, in the immersion electrode 2, the presence of the amorphous carbon makes it possible to prevent the molten metal from running out of the molten metal and to prevent the molten metal from adhering to the tip of the electrode. The matrix containing silicon nitride as a main component, together with the corrosion resistance of amorphous carbon, shows a very large corrosion resistance to molten metal.

If the amorphous carbon content is less than 3%,
There is a problem that sufficient conduction cannot be obtained, and furthermore, metal adhesion and elution due to erosion occur. On the other hand, if it is more than 20 wt%, there is a problem that elution due to metal adhesion and erosion occurs.

If the silicon nitride content is more than 70% by weight,
Silicon nitride, for example, is very easily attacked by molten aluminum, and therefore has a problem that metal adhesion and elution due to corrosion occur.

Experimental Example 1 Composition: SNC containing 70 wt% of silicon carbide, 25 wt% of silicon nitride and 5 wt% of amorphous carbon and having a conical tip and a length of about 10 cm.
1 was processed into a rod-shaped electrode, the immersion electrode 2 was fixed to the fitting 1 as shown in FIG. 1, the molten aluminum was filled in the furnace, and a practical test was performed for about 2000 hours.

The molten metal temperature is 720 to 780 ° C. and is 24
A voltage of V was used.

As a result, a slight amount of aluminum adhered, but the amount thereof was 1 mm or less in thickness and did not affect the liquid level measurement. Before the test, the resistance from the end of the mounting bracket to the tip of the electrode is 2-3 Ω.
However, the resistance value after the test also showed the same value, the resistance value did not increase, and it functions as an electrode until the end. Corrosion was not observed and the life was 10 times or more that of the conventional metal electrode. .
Changes in the electrodes during this period were as follows.

When molten aluminum is filled in the furnace and the temperature in the furnace rises up to around 500 ° C to 600 ° C, the free carbon in the electrode superficial layer part is slightly oxidized and burned off, but immediately after that, several tens of μm are left on the electrode surface. A thick silica film is formed and free carbon burnout ceases. In this state, there is almost no conduction on the surface. However, the part that is in contact with the mounting metal is not in contact with the atmosphere, so that electrical continuity is maintained. Further, when the molten aluminum was filled and the liquid surface came into contact with the tip of the electrode, the silica film on the surface only at the tip of the electrode was destroyed, and the conductivity of only that portion was restored. Then, the current flowed at the moment of contact with the molten aluminum, and the filling of the molten aluminum was stopped.

Although the SNC and aluminum are in contact with each other at the tip of the electrode, the wettability is poor due to the presence of the amorphous carbon contained therein. Therefore, when the liquid level is lowered, the aluminum is well drained and has an ice column shape. Almost no adhesion occurs. Therefore, accurate measurement was possible even when the liquid level rose again.

Experimental Example 2 In accordance with the method for producing the SNC, the immersion electrodes 2 having the compositions shown in Table 1 were produced, and each was attached to the level sensor shown in FIG. 1 and tested in the same environment as in the above Experimental Example 1. Then, the electric resistance value before and after the test and the adhesion thickness of aluminum were measured. Table 1 shows the results.

[0021]

[Table 1]

Since the SNC is obtained by substituting carbon in silicon carbide with nitrogen to generate silicon nitride and amorphous carbon, when the content of a certain element is determined, the content of other elements is also generally determined. .

As is apparent from Table 1, the test piece 1 has a small amount of amorphous carbon, and it is considered that the test piece 1 is slightly conducted by silicon carbide which is a skeleton component rather than amorphous carbon. The test piece 2 also has a large electric resistance due to lack of amorphous carbon. The test pieces 3 to 5 have a good composition balance, a low resistance value, and no problem such as adhesion. In the test piece 6, the composition ratio of silicon nitride was too large, and aluminum was slightly attached after the test.

From the above, when the amount of amorphous carbon is small, a sufficient resistance value cannot be obtained, and elution due to metal adhesion and erosion occurs, so it can be said that it is not suitable for a level sensor. On the contrary, when the amount of amorphous carbon is sufficient to obtain conduction, but the amount of silicon nitride is too large, silicon nitride is particularly apt to be corroded by molten aluminum, which is also unsuitable for a level sensor. From this, silicon carbide 15-
80 wt%, silicon nitride 15-70 wt%, amorphous carbon 3-2
It was confirmed that the range of 0 wt% is preferable.

Within this range, it is more preferable that the content of silicon carbide is 50 to 70 wt% and the content of silicon nitride is 25 to 40 wt%.
The range of amorphous carbon 5 to 10 wt% was favorable.

[0026]

As described above, in the level sensor of the present invention, the immersion electrode is made of 15 to 80 wt% of silicon carbide and 15 to 80% of silicon nitride.
70 wt%, 3 to 20 wt% of amorphous carbon, and a composite ceramic in which amorphous carbon is dispersed in a matrix containing silicon carbide and silicon nitride as main components. Since the cutting is good and the adhesion of the molten metal can be prevented, it is possible to guarantee accurate liquid level management, that is, to keep the amount of molten metal in the melting furnace constant.

Further, since the immersion electrode has a very high corrosion resistance to the molten metal, it has a long life and there is no risk of the molten metal being contaminated by the leached substances.

Further, the presence of the amorphous carbon in the immersion electrode has an excellent effect that it has sufficient conductivity as an electrode of the level sensor.

[Brief description of drawings]

FIG. 1 is a schematic view of a molten metal level sensor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Mounting bracket 2 Immersion electrode 3 Molten metal 4 Earth A Metal melting furnace B Ceiling C Bottom

Claims (1)

[Claims] 1. Silicon carbide 15 to 80 wt%, silicon nitride 15
A molten metal level sensor provided with a dipping electrode made of a composite ceramic in which amorphous carbon is dispersed in a matrix mainly containing silicon carbide and silicon nitride and containing 70 to 70 wt% of amorphous carbon and 3 to 20 wt% of amorphous carbon.