DD147467A3 - METHOD FOR PRODUCING MELT TILES - Google Patents

Abstract

The invention relates to a process for the production of crucibles from carbon-bonded silicon carbide for use temperatures of 850 to 1500 degrees C with the aim to increase the utility of the crucible by an improved structure by the recipe for the production of crucibles is to change. Here, of the known basic components of the basic component silicon carbide is partially replaced by a special silicon carbide, the surface of which is predominantly covered with beta-silicon carbide and silicon dioxide. The proportion of the particular silicon carbide is 15 to 45 mass% of the total silicon carbide amount. The alpha silicon carbide contains 8 to 35 mass% of beta silicon carbide, 2 to 12 mass% of silicon dioxide has a grain size up to 0.25 mm as well as a high specific surface area and high proportion of spiked grains. Crucibles of this kind can be used e.g. used as crucible for heavy metal casting or under special conditions in induction furnaces.

Description

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Process for the preparation of crucibles

Field of application of the invention

The invention relates to a method for the production of crucibles from carbon-bonded silicon carbide for use temperatures of 850 to 1500 ⁰ C.

Characteristic of the known technical solutions

Carbon-bonded silicon carbide crucibles with a high silicon carbide content are known. These crucibles may contain self-icing ingredients tailored to the application temperature, which glaze during use and thus ensure a largely constant thermal conductivity. The formation of a new glaze prevents the burn-out and thus the reduction of thermal conductivity and strength during use. "These types of crucibles consist mainly of the basic components silicon carbide, graphite and coked binders such as tar, pitch or synthetic resin. It is known that glazes adhere poorly to carbon-bonded silicon carbide products and continuous glazes are achieved by applying intermediate carriers. Furthermore, from DD-PS 48 157 a process for the preparation of a self-glaze is known in which one adds solid fluxes to the basic constituents in addition to metallic powders, ie that 1-40 % readily oxidizable metals or alloys such as SiMn, FeSi, FeCr, FeMn,

fife

Sl, Mn, Fe and 1 - 40 % solid flux, such as solid. Sodium water glass, various. Adding glaze frits, inter alia, to the offset and applying the offset flux in a liquid or liquefied solution to the surface of the corresponding product. " For certain applications, the achieved by this method self-glaze is sufficient, but has in their uniformity but lack.

DE-AS 1186387 also describes a process for the preparation of refractory materials in which the shaped mixture heated to a temperature of preferably 1200 to 1300 ⁰ C, held at this temperature for 24 h, then again very quickly to 1245 to 1500 ⁰ C. heated and then again for 5 to 30 min. is kept at this temperature.

This process is complex and subject to high technological risk.

At the same time, the known processes for the production of crucibles have the disadvantage that 'the structure due to the surface properties and the possible grain shapes commercially available SiC varieties undesirable inhomogeneities.

Object of the invention:

The aim of the invention is to increase the usage temperature of the crucibles by an improved microstructure.

Explanation of the essence of the invention;

The invention has for its object to change the recipe for the production of crucibles so that the use value is increased.

According to the invention the object is achieved in that of the known basic components of the basic component silicon carbide is partially replaced by a particular kind of oC-SiC.

This ac -silicon carbide is obtainable as a by-product in the production of proprietary silicon carbide heating rods and characterized in that its surface is predominantly covered with Si-silicon carbide and silicon dioxide. The proportion of the particular silicon carbide is 15-45 mass% of the total silicon carbide amount. It has been determined analytically that the particular silicon carbide contains 8-35 mass% / - silicon carbide and 2-12 mass% silicon dioxide. The special silicon carbide has a grain size of up to 0.25 mm as well as a high specific surface area and a high proportion of spiked grains.

embodiment

From carbonizable binder and dry components in heatable mixers a moldable mass is produced. It should be noted that the dry component silicon carbide consists of 15-45 mass% of xT silicon carbide, the surface of this ^ C silicon carbide being covered with 8-35 Maase% / ^ silicon carbide and 2-12 mass% silicon dioxide is. The * "C-silicon carbide is used in a grain size up to 0.25 mm This mass is pressed into the crucible blanks and two stages, first verkokend then in Koksschüttpulver at 1200 ⁰ C flue gas temperature and oxidizing in electric furnaces from 800 -.. Burned 1,200 ⁰ C to achieve the For oxidation protection, the crucibles are coated with glaze before the oxidizing fire, for example an onglaze with the main constituent ceramic frit.

Example: Goat crucible for heavy metal casting

22% pitch, at least EP 70 ⁰ C

2% tar 25% crucible graphif

22% silicon carbide commercially available 0 - 0.1 mm 18% "^ silicon carbide 0 - 0.25 mm 8% metal alloys, minimum content 50% Mn

3% ceramic frit

Another advantage in the application of the described method for producing silicon carbide crucibles is that the particular silicon carbide recoverable in the manufacture of inherently bonded silicon carbide heating rods is optimally used economically and thus a substantial reduction in the cost of self-consumption is achieved. In addition, the crucible described by the method according to the invention showed improved application results under special conditions, such. B. when used in induction furnaces. In addition, due to the altered microstructure, the resistance to teppiperaturation improves.

Finally, all crucibles produced show a perfect glaze.

Claims (2)

09054 Erfindungsanspriiche Crude crucible molding compound consisting of silicon carbide, graphite, easily oxidizable metals or alloys, solid fluxes and carbonizable binders, characterized in that 15-45% by mass of the silicon carbide is composed of ° G silicon carbide, the surface of which predominantly comprises / ^ silicon carbide and silicon dioxide is covered. 2. Molding composition according to item 1, characterized in that this ^ -Siliziumkarbid 8-35% by mass / ^ - contains silicon carbide and 2-12% by mass of silica. Molding composition according to item 1, characterized in that this silicon carbide is used with a grain size of up to 0.25 mm.