JP2626672B2 - Immersion tube for non-ferrous molten metal - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic immersion tube used by being immersed in a melt of a non-ferrous metal such as aluminum, zinc, copper, and lead. The ceramic immersion pipe referred to in the present invention means a ceramic protection pipe such as a thermocouple and a heater immersed in these molten metals, and a ceramic transport pipe for transporting these molten metals.

In this specification, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

Prior art and its problems In a furnace for melting or holding a non-ferrous metal such as aluminum (hereinafter, aluminum will be described as a representative example, the object of the present invention is not limited to aluminum), the molten metal is heated. In order to protect the heater and a thermocouple for measuring the temperature of the molten metal, a ceramic protective tube (also called a dip tube) is used. Taking a protective tube (hereinafter referred to as a heater tube) of a heater used in a state of being immersed in a molten metal as an example, a function of transmitting heat generated by an internal heater to an external molten metal is required. Therefore, in general, the inner surface of the heater tube is relatively hotter than the outer surface that comes into contact with the molten metal, so that a small gap is formed on the outer surface due to a difference in thermal stress between the inner and outer surfaces, and the molten metal reaches the inner surface. It tends to penetrate easily, and the erosion of the entire heater tube tends to progress rapidly. In particular, when the molten metal is aluminum, the activity itself is extremely high, and the reactivity with the heater tube is extremely strong. In addition, the permeability and erosion increase as the temperature rises. Easily eroded. For this reason, in the heater tube for aluminum, the above-mentioned 2
These factors combine to make damage particularly rapid,
Its service life is shortened, which is an obstacle to operation. Conventionally, as a heater tube for aluminum, silicon carbide has been used because of its low wettability to molten aluminum, excellent heat resistance, and high resistance to thermal stress destruction due to repeated heating and cooling (hereinafter referred to as spall resistance). A silicon nitride-bonded silicon carbide material in which material particles or aggregates are combined with silicon nitride is mainly used. However, even with a heater tube made of such a material, the reaction with the aluminum melt on the outer surface thereof cannot be sufficiently suppressed, so that the following causes of damage progress.

(A) Aluminum penetrates into the heater tube.

(B) The heater tube cracks due to a large expansion difference between the permeated aluminum and the material of the heater tube.

(C) Since the level of the molten aluminum fluctuates, aluminum and its oxides begin to adhere to the level fluctuation portion on the surface of the heater tube based on the infiltrated aluminum, and the deposit grows and grows soon.

By accelerating the penetration of aluminum in this way,
The function as a heater tube for performing uniform heating is reduced, and the enlarged growth of attached matter makes it impossible to continue the melting operation under certain conditions.

Means for Solving the Problems The present inventor has made various studies in view of the current state of such a technique, and as a result, formed a B ₂ O ₃ -based glass layer on the surface of the heater tube, and further formed a BN thereon. It has been found that when particles are attached, a heater tube which is hardly wetted by a molten metal such as aluminum and has excellent heat resistance and spall resistance can be obtained.

That is, the present invention provides the following dip tube for molten ceramic non-ferrous metal: "A glass coating layer containing 2% or more of B ₂ O ₃ and a BN particle adhesion layer are sequentially provided on the surface of the dip tube body. Immersion pipe for non-ferrous molten metal characterized by the following "Each material used in the present invention will be described below.

The main body of the immersion tube used in the present invention is not particularly limited, and any known immersion tube can be used. Specific examples include a molded sintered body or a melt molded body of silicon carbide, silicon nitride, silicon nitride-bonded silicon carbide, carbon-containing silicon carbide, zirconium boride, alumina, mullite, spinel, silica, titanium aluminate, or the like. .

In the present invention, as the glass coating layer formed on the surface of the immersion tube main body, it is necessary to use a glass coating layer containing 2% or more of B ₂ O ₃ . When the content of B ₂ O ₃ is less than 2%, it becomes difficult to hold the BN particle layer formed on the glass coating layer when the immersion tube is immersed in the non-ferrous metal.

The glass containing B ₂ O ₃ more than 2% is not particularly limited, and melted by heating boric acid compound is essentially composed of B ₂ O _3, as was glassy: Na to B ₂ O ₃ A compound containing an alkali metal oxide such as ₂ O is heated and melted to form a glass: borosilicate glass: soda glass containing B ₂ O ₃ ;
Phosphate glass is exemplified. As the content of B ₂ O _{3 in} the glass increases, the glass component easily enters and reacts with the pores of the main body of the immersion tube, and the adhesion between the glass coating layer and the main body is improved. However, when the content of B ₂ O ₃ is 70
%, White powder may be generated on the surface of the glass coating layer due to moisture absorption, and the uniformity of the coating may be impaired. In such a case, the product should be stored in a low humidity atmosphere or manufactured. Care must be taken to use it within a short time afterwards. The thickness of the glass coating layer can vary depending on the material of the dip tube, the type of glass, the type of non-ferrous metal, etc.
Usually, it is about 0.1 to 1.0 mm.

In the present invention, it is essential to form an adhesion layer of BN particles on a glass coating layer containing 2% or more of B ₂ O ₃ .
The purity of the BN particles is preferably 99% or more, since the use of low-purity BN particles may result in insufficient corrosion resistance. The BN particles generally have a particle size of 200 mesh or less, more preferably 350 mesh or less. In the heater tube before use, the BN particles do not necessarily cover the entire surface of the glass coating layer without any gaps, but react with B ₂ O ₃ in the glass coating due to contact with the non-ferrous molten metal during use. It is necessary to cover the entire surface of the glass coating. Therefore, it is preferable to provide about 0.5 to 1.0 mm to the glass coating layer. In the present invention, a part (up to about 20%) of BN is converted to B ₂ O ₃
It may be replaced by a powder. However, in this case, B ₂ O ₃
Since the powder is hygroscopic, care must be taken in the storage and management of the product.

The method for producing the heater tube of the present invention is not particularly limited, but one row thereof is as follows.

First, about 100 parts or less of borate glass fine powder or 100 parts of glass fine powder mixed with borax or boric acid as a source of B ₂ O ₃ is added with about 1 to 3 parts of an organic binder such as dextrin, sodium alginate, and sodium acrylate. And further add 30-40 parts of water to prepare a slurry. Alternatively, in preparing the slurry, 30 to 40 parts of an inorganic binder such as water glass or silica sol may be used instead of the organic binder. Next, the immersion tube main body is dipped in the obtained slurry, or the slurry is applied to the immersion tube main body by a spray gun, a brush or the like, and dried at a temperature of about 150 ° C. to remove moisture, and then 650 to 1000 ° C. The glass coating layer is formed on the outer surface of the main body of the immersion tube by heating at an appropriate temperature. Alternatively, a slurry is prepared by adding an organic binder to a saturated aqueous solution of borax and / or boric acid, applied to the main body of the dip tube, dried, and heated at about 650 to 1000 ° C. to form a borate glass coating layer on the outer surface of the main body of the dip tube. May be directly formed.

The formation of the BN particle layer on the gas coating layer can be performed by various means. For example, a commercially available paint containing BN particles can be applied by a dip dipping method or by using a spray gun or a brush. Alternatively, dextrin, sodium alginate, about 1 to 10 parts of an organic binder such as sodium acrylate or about 20 to 60 parts of silica sol is added to 100 parts of BN fine powder having a mesh passing of 200 mesh or less,
Further, if necessary, water may be added to prepare a slurry, and the slurry may be applied in the same manner as described above. Furthermore, an organic slurry obtained by adding about 10 to 80 parts of a silicone resin and about 50 to 150 parts of an organic solvent such as toluene and xylene to 100 parts of BN fine powder passing 200 mesh or less, in the same manner as described above, good. Next, the glass coating layer forming immersion tube coated with the BN-containing slurry is dried at about 150 ° C., and then heat-treated at a temperature of about 250 to 650 ° C. When the heating temperature is lower than 250 ° C., the adhesion of the BN particles to the glass coating layer tends to be insufficient. When the heating temperature is higher than 650 ° C., there is a risk that the BN particles are oxidized.

The reason why the combination of the B ₂ O ₃ -containing glass coating layer and the BN particle adhesion layer used in the present invention can exert a particularly remarkable effect has not yet been completely elucidated,
It is presumed to be due to the following mechanism. That is, BN
Has a high affinity for B ₂ O ₃ among boron compounds, and therefore, when a heater tube is used, B ₂ in the glass coating layer
Combined with O ₃ , the integration with the surface layer of the glass coating layer is eventually completed. In this state, since the entire surface of the glass coating layer is covered with BN, excellent corrosion resistance can be obtained.
On the other hand, when a glass containing no B ₂ O ₃ is used, the BN particles are not sufficiently bonded to the glass coating layer, so that the BN particles are eluted in the non-ferrous molten metal and are lost, and the corrosion resistance is not improved. Will be. When particles of other boron compounds such as B ₄ C and ZrB ₂ are used instead of BN, the particles also have a lower affinity for B ₂ O ₃ because these compounds have lower affinity for B ₂ O _3. It does not bond sufficiently strongly to the containing glass, elutes into the non-ferrous metal and is lost, and no improvement in corrosion resistance is achieved.

Effect of the Invention The heater tube according to the present invention is excellent not only in chemical corrosion resistance to non-ferrous molten metal but also in durability against mechanical spalling caused by rapid thermal stress.
Therefore, it is extremely useful as a member used while immersed in a non-ferrous molten metal.

EXAMPLES Examples are given below to clarify features of the present invention.

Example 1 (a) Ceramic material From a commercially available heater tube for dipping molten aluminum of the following two compositions and physical properties, 8 mm × 8 mm ×
Specimens (a) and (b) of 100 mm were cut out.

Specimen (a): Heater tube made of silicon nitride bonded silicon carbide of about 85% SiC and about 15% Si ₃ N ₄ , porosity = 16%, bending strength = 440 kg / cm ² Specimen (b): about 85% SiC %, C = about 15%, B ₄ C = about 3%, S
iO ₂ + Al ₂ O ₃ = approximately 2% carbon-containing silicon carbide heater tube, porosity = 20%, flexural strength = 230 kg / cm ² , since the antioxidant glass layer is formed on the surface ,
It was processed so as not to include this part.

(B) Glass coating layer A predetermined ratio of the crushed plate glass having the composition shown in Table 1 and the inside of the crushed borosilicate glass having the composition shown in Table 2 are blended.
60 parts of methyl alcohol was added to 100 parts, and the mixture was pulverized with an alumina ball mill for 6 hours to reduce the particle size of the powder to 150 mesh or less, and then dried.

Table 1 SiO ₂ 72% Al ₂ O ₃ 1% CaO + MgO 14% Na ₂ O 13% Table ₂ SiO ₂ 66% B ₂ O ₃ 25.6% Na ₂ O 4.3% K ₂ O 2% Al ₂ O ₃ 1.9% CaO 0.4% 2 parts of dextrin are added to 100 parts of each of these powders (Nos. 2, 3, 7, 8) and a mixed powder (No. 4, 5, 6) of sheet glass and boric anhydride having the composition shown in Table 1. And 30% silica sol 50
After a uniform slurry is formed, the slurry is applied to the specimen (a) or (b) with a brush, dried at 110 ° C, rapidly heated to 1000 ° C, and held for 1 hour. A coating layer was provided. For powder No. 9, while boiling, 35
After immersing the specimen (b) in a 20% aqueous boric acid solution for 20 minutes,
C., rapidly heated to 1000.degree. C., and maintained for 1 hour to provide a glass coating layer.

(C) BN particle adhesion layer The glass coating layer forming specimens Nos. 3 to 9 obtained above include BN
Alternatively, a slurry containing B ₄ C was brushed. That is, 325 by adding 2 parts of 30% silica sol 120 parts dextrin B ₄ C 100 parts of 98.5% pure with a purity of 99.8% BN or 325 mesh pass mesh pass, the slurry was prepared, subjected to this piece No. Apply 3 to 9 to a thickness of about 0.5mm,
It was dried at about 110 ° C, and heated to 350 ° C.

Incidentally, the glass coating layer formed specimen No.2 is, BN or B ₄
C was not applied. Specimen No.1 was about 85% SiC,
As-cut as cut from a commercially available silicon nitride bonded silicon carbide heater tube of about 15% Si ₃ N ₄ .

(D) Corrosion resistance test A 2 mm diameter platinum wire was wound around each test piece, hung on the tip of a 10 mm diameter stainless steel rod, and the test piece was completely immersed in JIS ADC12 molten aluminum alloy (750 ° C).
Hold for 20 hours.

(E) Test results Appearance: The state of adhesion of the molten metal on the surface of the specimen taken out of the molten metal was observed, and the ease of removing the adhered substances with tweezers was examined.

Erosion: The central part of the specimen taken out of the molten metal was cut with a diamond cutter to check the permeation state of the molten metal.

 Table 3 shows the results of the corrosion resistance test.

 From the results shown in Table 3, the following is clear.

Specimen No. 1 was significantly eroded, and it is clear that the commercially available heater tube made of silicon nitride-bonded silicon carbide lacks corrosion resistance.

Specimen No. 2 provided with a glass coating layer containing no B ₂ O ₃
Has better corrosion resistance than Specimen No. 1. This is presumed to be because the glass coating layer itself hardly has corrosion resistance, but carbon-containing silicon carbide itself has better corrosion resistance than silicon nitride-bonded silicon carbide.

Specimens Nos. 3 and 4 had a 2% glass coating layer.
The results show that when B ₂ O ₃ is not contained, the corrosion resistance of the heater tube is hardly improved even if the BN particle adhesion layer is formed.

On the other hand, specimens Nos. 5 to 7 and 9 contained 2% B ₂ O _3.
It shows that when the coating layer of glass and the BN particle adhesion layer are contained, the heater tube is provided with extremely high corrosion resistance.

Further, Sample No. 8 shows that when other boron compounds are used instead of the BN particles, improvement in corrosion resistance cannot be achieved.

 In addition, the evaluation in Table 3 was performed based on the following criteria.

×: poor △: slightly poor ○: good ◎: very good

Continued on the front page (72) Inventor Shigenobu Manki 5-1-1, Hirano-cho, Higashi-ku, Osaka-shi, Osaka Prefecture Inside (72) Inventor Koji 5-1-1, Hirano-cho, Higashi-ku, Osaka-shi, Osaka Osaka Gas Co., Ltd. (72) Inventor Yoshitaka Hayashi 5-1-1, Hirano-cho, Higashi-ku, Osaka-shi, Osaka, Japan Inside Osaka Gas Co., Ltd. (72) Inventor Hisao Yokoyama 5-1-1, Hirano-cho, Higashi-ku, Osaka, Osaka, Japan (72) Inventor Kakei Nishihira 24-501 Kawanakashinmachi, Daito City, Osaka Prefecture References JP-A-62-21778 (JP, A)

Claims (1)

(57) [Claims] An immersion tube for a non-ferrous molten metal, wherein a glass coating layer containing 2% or more of B ₂ O ₃ and a BN particle adhesion layer are sequentially provided on the surface of the immersion tube main body.