JPS61209960A - Manufacture of electrocasted refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention (1) relates to a method for producing alumina, zirconia, and siliceous electroformed refractories.

[To L11 Alumina, zirconia, and siliceous electrocast refractories are called AZS refractories and are widely used as refractories for the glass industry. AZS refractories are manufactured by melting a predetermined blended raw material in an electric arc furnace, casting the melt into a mold mainly bonded with silica sand, and then slowly cooling the melt. When forming this mold,
Water glass is sometimes used as a binder to bind silica sand, but silica sand may seize on the product, strength may decrease due to lack of mold strength or absorption of moisture from the air, and absorbed moisture may enter the casting. There are disadvantages such as the generation of pores.

In addition, when water glass is used as a binder, used silica sand
Since the temperature of the molten metal during casting reaches as high as 1900°C, it is exposed to high temperatures for quite a long time, making it difficult to sinter and reuse.

Furthermore, even if re-pulverized, the alkali derived from water glass remains, resulting in a decrease in fire resistance and the drawback that it cannot be reused alone.

On the other hand, organic binders such as phenol and furan have high bond strength and are unlikely to deteriorate over time, but they may cause carburization from the organic binder to the surface of the cast product or gas generated from the binder to the cast product. There are negative effects on product quality, such as intrusion and the resulting formation of pores. Particularly in recent years, when manufacturing high-quality glass, such as glass for electronics such as cathode ray tubes for televisions and photomasks, the quality of refractories for glass melting furnaces is extremely important. Refractories that generate this cannot withstand use. Many theories and empirical rules are known about the causes of bubble formation in molten glass. Based on these theories, it is said that the following requirements are required for refractories for glass melting furnaces.

(1) The refractory has a dense structure without pores.

(2) Contains no iron or other metals, and contains very little oxide thereof.

(3) The refractory composition maintains a high degree of oxidation.

However, the method for measuring the degree of oxidation is not clear, and in reality, the highest possible oxidation state is melted, cast, or
It is the only thing that must be maintained during each step of slow cooling.

In order to prevent the adverse effects on product quality caused by organic binders when using organic binders, the present applicant proposed the invention of Japanese Patent Application No. 57-61105, in which an oxidizing agent is added to the mold mixture in advance. We succeeded in eliminating the negative effects on the castings by oxidizing carbon and reducing gases.

However, oxidizing agents are expensive, chemicals must be handled with care, and there are problems such as NOx emissions.

The present invention improves the conventional manufacturing method of alumina, zirconia, and siliceous electrocast refractories, and provides a method for manufacturing electrocast refractories that can supply AZS refractories of superior quality to the glass industry. is intended to provide.

In a method for producing electroformed refractories made of alumina, zirconia, and silica for use in refractories, a mold is formed by maintaining negative pressure in mold sand via a thermoplastic film without using a binder, A method for producing electrocast refractories, which comprises maintaining a negative pressure even after casting and bringing outside air or an oxidizing gas into contact with the casting to maintain the casting in an oxidized state.

Production - As mentioned above (because the molding method does not use a binder, it is possible to solve all the problems that occur when using organic or inorganic binders as described above at once. After the thermoplastic film melts and disappears by casting,
By contacting with outside air or the like, the surface of the casting can be maintained in a sufficiently oxidized state for a desired period of time. Furthermore, if necessary, the entire casting frame can be inserted into a suitably sized closed chamber containing an oxidizing atmosphere such as oxygen, and the outside air drawn into the chamber can be made into a highly oxidizing gas.

The AZS refractory obtained by the method of the present invention has a bright yellow appearance and has extremely low foamability against glass. In particular, the presence of a highly foamable area close to the casting surface (which is believed to be due to carburization or partial reduction caused by the mold binder), which has often occurred in the past, is not observed.

support Next, embodiments will be described with reference to the drawings.

First, a wooden model 5 with predetermined dimensions as shown in FIG.
Manufacture.

In FIG. 1(A), a stand 6 having an exhaust lower and a ventilation hole 14 is prepared. The exhaust lower and the ventilation hole 14 communicate within the platform 6. A wooden model 5 with a hole 4 drilled therein is placed on this stand 6.

The hole 4 is made to overlap the position of the ventilation hole 14. Place Soubreu model 3 on top of this wooden model 5. A thermoplastic film 2 and a heater 1 for heating the film are provided above the wooden model 5.

Next, in FIG. 1(b), the exhaust lower is connected to a vacuum pump (not shown), and while the exhaust is being exhausted, the thermoplastic film 2 is heated by the heater 1 to soften it and placed on the wooden model 5.

Since the soft thermoplastic film 2 is vacuumed through the holes 4, it tightly adheres to the wooden model 5.

In FIG. 1(c), a casting frame 15 is placed on a stand 6, and silica sand 8 is densely filled around the wooden model 5 (1.1-).

While exhausting the air through the exhaust port 10, a soft, weeping thermoplastic film 9 is placed over the silica sand 8. As a result, the thermoplastic film 9 tightly adheres to the silica sand 8, and the interior of the silica sand 8 is under reduced pressure, losing all fluidity. In this state, the exhaust from the exhaust lower is stopped, the stand 6 is removed, and the wooden mold 5 and the Souvreux model 3 are also removed.

Since the exhaust from the exhaust port 10 continues, the silica sand 8 does not collapse and becomes the mold 17 which has a cavity in the same shape as the wooden model 5. In FIG. Another mold 18 is made in almost the same process as steps a) to (c), and as shown in Fig. 1 (e), when the previously made mold 17 is placed on top of this, a thermoplastic film is formed inside. A cavity 16 surrounded by 2 and a thermoplastic film 13 is formed.

Note that the reference numeral 19 in FIG. 1(A) indicates a film holder, the reference numeral 20 in FIG. 1(D) indicates a casting frame 20, and the reference numeral 12 indicates an exhaust port.

To explain one experimental example, for example, using a thermoplastic film 2.9.13 with a thickness of 100 microns and using Australian Fremantle silica sand as the silica sand 8, a cavity 16 with dimensions i oox 300 x 450 ms was formed, and a mold was formed. And so. While continuing the exhaust state, fill the cavity 16 with AZS melt (trade name: Monoflux O8).
-3) was injected from the injection path 21 and cast. 3 after casting
The exhaust pump continued to be driven for 0 minutes, and suction was continued from the exhaust ports 10 and 12. Thereafter, the suction was stopped, and the cast product was buried in sand and left to cool for 3 days. When the casting was taken out from the sand after cooling, the outer surface was bright yellow, there was almost no burning of the molding sand, and no cracks were observed. Furthermore, the foamability against glass, which indicates the degree of oxidation, was also low. Furthermore, the used silica sand did not contain any impurities and could withstand repeated reuse.

Table 1 shows the results of comparative experiments on foaming properties against glass.

[Brief explanation of the drawing]

It is. 1... Heater 2.9.13... Thermoplastic film 3.5...
・・・Model 6・・・・・・・・・Table 8・・・・・・ Silica sand 16・・・・・・Cavity - Table - 2 Glass used: Soda lime glass manufacturing temperature : 1200℃ Number of ponds (pieces/cm2) Surface part Internal normal (7) AZS refractory 120 150 (Patent application 1973)
AZS refractory according to the present invention (according to the method of No. 7-61105) 87 Alumina electrocast refractory with extremely low foamability O~1 0~1 (trade name Monoflux M) Note: Refractory sample (diameter 40 mm length) 7 mm) was calcined at 1200° C. for 1 hour, a glass sample (diameter 20 mm, length 5 mm) was placed on top of the sample, held for 1 hour, and then allowed to cool outside the furnace. The number of ponds was counted using a microscope, and the number of ponds per unit area was calculated. ! Q ψ

Claims (1)

[Claims] (1) In a method for manufacturing alumina, zirconia, and siliceous electroformed refractories, a mold is formed by maintaining negative pressure in mold sand through a thermoplastic film without using a binder, and the mold remains under negative pressure after casting. A method for manufacturing an electrocast refractory, which comprises maintaining the casting in an oxidized state by maintaining pressure and bringing outside air or an oxidizing gas into contact with the casting.