JPS593083A - Graphite crucible - 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 This invention is applicable to non-ferrous metals (especially aluminum alloys), such as carbon-pond graphite crucibles whose main raw materials are graphite and silicon carbide, and clay-bond graphite crucibles whose main raw materials are graphite and clay. Regarding graphite crucibles, which are widely used for melting metals, flux, etc., sprinkled on the upper layer of molten metal contained in the crucible body may penetrate into the crucible body due to repeated use of the crucible body. The purpose is to prevent this and improve its useful life.

When using a graphite crucible for melting nonferrous metals (especially aluminum alloys), the crucible is used to cover the surface of the molten metal within the main body (to prevent oxidation of the molten metal), to remove slag, to degas, and to provide crystal structure. Flux is usually used for miniaturization. The flux includes alkali metals (No, K, etc.), alkaline earth metals (Ca.

The main components are chlorides and fluorides of At, Si, etc.). These component mixtures have a low melting point and low viscosity at the melting temperature of the metal, and during their use, they penetrate into the pores of the crucible body and react with the components of the crucible body, resulting in One deteriorates the characteristics of the main body. As a result, the crucible body undergoes large thermal expansion and is prone to cracking, resulting in a significant reduction in service life. Although it is possible to improve the durability of carbon bonded graphite crucibles to some extent by making the body more dense, increasing the amount of silicon carbide, and adding highly corrosion-resistant aggregate raw materials, this will reduce the spalling resistance. The extent to which durability can be improved is limited.

Therefore, this invention was made to solve the above problems, and contains silicon nitride (Si3N4): 10 to 85%, and further contains corundum (At20.) and zircon (Zr203.5IO2) as necessary. , and mullite (3
A graphite crucible with a coating layer formed on the inner surface of the graphite crucible body containing one or more of At203''2Si02) and the remainder consisting of silicon carbide (SiC) and impurities. It is characterized by being a melting pot.

The reason why the numerical values are limited as described above in this invention will be explained below.

(1) Silicon nitride Silicon nitride, along with silicon carbide, has no reactivity with molten nonferrous metals, is difficult to wet, is chemically stable, and has a high flux (
It has excellent slag properties, good thermal conductivity, and low thermal expansion. Therefore, by containing silicon nitride as a component of the coating layer, the thermal expansion of the coating layer can be approximated to that of the graphite crucible body, and furthermore, the adhesion between the coating layer and the graphite crucible body can be improved. As a result, the crucible has significantly improved spalling resistance, high volume stability, and improved oxidation resistance. If the silicon nitride content is less than 10 parts, there is no effect of addition, and therefore, spalling resistance is insufficient, and cracks caused by peeling of the coating layer are likely to occur. On the other hand, if the silicon nitride content exceeds 85%, the corrosion resistance will deteriorate on the contrary. In addition, the sintering strength can be maintained high by making the particle size of 10 to 20 pieces of silicon nitride contained in the coating layer 5 microns or less.

(2) Corundum, zircon, and mullite Corundum, zircon, and mullite are added to make it possible to reduce the content of expensive silicon nitride without reducing corrosion resistance to flux, but if it exceeds 40%, high heat It is undesirable because it becomes expandable, has poor thermal conductivity, and reduces spalling resistance.
If it is less than 3%, the above-mentioned effect of addition cannot be obtained.

If the thickness of the coating layer is less than 2 Trrrn, the effect of extending the corrosion resistance (durability) will be small, while if it exceeds 10 mm, the corrosion resistance will be good, but cracks and peeling will occur during repeated use (long-term use). This is not desirable because it easily occurs, the coating lacks stability, and it impairs thermal conductivity. In addition, when forming the coating layer, in order to improve the workability on the inner surface of the graphite crucible body, a sticky organic binder such as starch paste or CMC is added to the above ingredients to form a well-kneaded clay. Coat this on the inner surface of the graphite crucible body using a trowel or the like. After the graphite melt is coated with a coating layer on the inner surface of the main body in this way, it is sufficiently dried, for example,
It is fired and sintered at around 00°C.

[Example 1] Prepare the required number of +30 graphite crucible bodies (wall thickness: 15 pus),
Crucibles 1 to 8 of the present invention were prepared by separately forming coating layers having the components shown in Table 1 on the inner surfaces of the required number of graphite crucible bodies and having the thicknesses shown in Table 1. For comparison purposes, +30 graphite crucible body without coating layer (wall thickness 15 mm)
was prepared as a comparative crucible 1, and a comparative crucible 2 was prepared in which a coating layer consisting solely of Si3N4 was formed on the inner surface of the +30 graphite crucible body (thickness: 15 mm) with a thickness of 3 wLl.

And in these crucibles, 10kg of aluminum
was melted and maintained at a temperature of 800°C, and the molten aluminum surface was heated with a flux of 450f (3
The time required for the flux to penetrate into the graphite crucible body and reach its outer surface was investigated.

The results are shown in Table 1 as arrival times. Table 1
Therefore, all of Rutsu 1 to 8 of the present invention are compared to Rupo 1,
It is clear that the corrosion resistance is extremely high compared to No. 2.

[Example 2] Crucibles 9 to 12 of the present invention were created by forming a coating layer containing the ingredients shown in Table 2 and having the thickness shown in Table 2 on various graphite crucible bodies for actual factories. .

These were used to melt aluminum of the weight shown in Table 2, and their service life was investigated.

The results are shown in Table 2. In addition, for the purpose of comparison, the service life of only the graphite crucible body used in each of the crucibles 9 to 12 of the present invention was investigated, and this is also shown in Table 2.

From Table 2, it is clear that all of the crucibles of the present invention have a significantly longer service life than the graphite crucible body alone.

By the way, when the crucible is first used, a mixture of molten metal oxide and flux adheres to the inner surface of the crucible, and if this thickly adheres, it impairs thermal conductivity, and due to its thermal expansion, the crucible may break (break). ), so it is normal to perform work to remove these in a timely manner, but in the crucible of the present invention, the removability of the deposits was good and the removal work was easy. On the other hand, in a normal graphite crucible (without a coating layer), the mixture of molten metal oxide and flux reacts and adheres to the inner surface, making it difficult to completely remove it.

In addition, even when melting copper alloys, etc., the coating layer according to the present invention is graphite-free, so that the accelerating effect of erosion due to oxidation of graphite in the crucible body is suppressed, and therefore the service life is extended. .

As explained above, the present invention can provide a graphite crucible with an extremely long service life.

Applicant: Akechi Firebrick Co., Ltd. Agent: Tsutsumi, Keitabe, and 1 other person

Claims (1)

[Claims] (11) A coating layer consisting of 10 to 85% silicon nitride, and the remainder of silicon carbide and unavoidable impurities (at least % by weight) is formed on the inner surface of the graphite crucible body. (2) Silicon nitride (10 to 85%), one or more of corundum, zircon, and mullite: 3 to 40%, and silicon carbide and unavoidable impurities (by weight) %) is formed on the inner surface of the graphite crucible body.