JPS6236996B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-resistant material that is immersed and used when melting low-melting point metals such as aluminum, lead, and zinc.

For example, silicon carbide or silicon nitride have long been attracting attention as materials that are difficult to wet as immersion protection tubes for molten aluminum, but due to their characteristics, it is impossible to obtain porosity-free materials, and even though the materials themselves are corrosion resistant, However, due to the occurrence of microcracks caused by pores, long-life products have not been obtained.

For this reason, attempts have been made to suppress the infiltration of molten aluminum into the pores by covering the outer surface with a coating material, but the coating material is easily attacked by the slag, and in the end it is not durable enough. I wasn't getting anything sexual. Furthermore, a method of forming a dense coating film using the same material as silicon carbide or silicon nitride using the CVD method has been considered, but this method has drawbacks such as being prone to peeling due to thermal shock, etc., and being expensive. Ta.

The present invention impregnates and fills the pores of a silicon carbide body or silicon nitride body with fine powder made of a material that does not easily react with molten metal, that is, one or more of alumina, silicon carbide, and silicon nitride, and further nitrides the fine powder. It is coated with a boron-based coating material and has a much longer life than conventional silicon carbide or silicon nitride corrosion-resistant materials.

That is, alumina, silicon carbide, and
Silicon nitride is relatively corrosion resistant to molten metal, and its thermal expansion is relatively close to the silicon carbide body or silicon nitride body, which is the body, so it is stable in the pores of the body. It is becoming.

In the present invention, since this filling body is further coated with a boron nitride-based coating material, this coating material partially vitrifies and not only improves the compatibility with the main body, but also aggregates of fine powder filled in the pores. It was possible to improve the bonding strength both to the pore walls and to the pore walls.

The silicon carbide body or silicon nitride body that forms the main body may be obtained by a normal molding method, and is generally made of 20
% of pores. For example, in the case of a silicon carbide body, it may be a recrystallized body in which silicon carbide powder is bonded with carbon and silicon vapor, or it may be a silicon carbide body bonded with silicon nitride. Also, in the case of a silicon nitride body, one obtained by a conventional method may be used.

The filler to be impregnated into the pores of these silicon carbide bodies or silicon nitride bodies is a fine powder made of a mixed powder of one or more of alumina, silicon carbide, and silicon nitride. That is, for the above-mentioned reason, it is preferable that it has corrosion resistance against molten metal, and that its thermal expansion is in close proximity to the silicon carbide body or silicon nitride body. The particle size may be such that it can be easily impregnated into the pores of the main body, and is usually 5 μm or less. In this case, the filler may be fired once to sinter the filler.

In the present invention, by coating the above-mentioned filling body with a boron nitride-based coating material, it not only protects the main body from slag etc. but also protects the fine powder portion filled in the pores, but the composition is It was selected to meet the above objective by having boron nitride as the main component. For example, aluminum phosphate may be blended with boron nitride powder and an aqueous dispersion of the mixture may be applied, or a portion of the boron nitride may be replaced with other components such as boron or alumina.

An embodiment of the present invention will be described below. Silicon carbide tube with one end sealed obtained by recrystallization method (porosity
20%) was impregnated with a suspension in water of a mixed powder consisting of 20% by weight of alumina powder of 5μ or less, 40% by weight of alumina powder of 1μ or less, and 40% by weight of silicon carbide powder of 5μ or less. After drying, a coating material consisting of silicon nitride powder and aluminum phosphate was applied to a thickness of 2 mm to obtain a protective tube for immersion in molten aluminum.
The obtained protective tube was immersed in molten aluminum heated to 730° C., and the corrosion resistance of the slag line in particular was measured, and almost no change was observed even after 6 months of continuous immersion.

At the same time, for comparison, we compared a recrystallized silicon carbide protection tube of the same size (using a coating material made of a mixed powder of mica powder and soda glass), which cracked after 40 days and melted inside the protection tube. Aluminum has penetrated.

In this way, the present invention utilizes the features possessed by conventional silicon carbide bodies or silicon nitride bodies,
Moreover, by eliminating these drawbacks, it had remarkable effects not found in conventional products.

Claims (1)

[Claims] 1 Molten metal made by coating a boron nitride-based coating material on the surface of a porous silicon carbide body or silicon nitride body whose pores are impregnated with fine powder consisting of one or more of alumina, silicon carbide, and silicon nitride. Corrosion resistant material for immersion.