JPS609991B2 - Firing method for graphite or silicon carbide refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for firing a graphite or silicon carbide refractory by forming a uniform and dense molten coating layer on the surface of an object to be fired.

Conventionally, when firing graphite or silicon carbide refractories, a molded product obtained by pressing a raw material mixture is filled into a pod (pot) with coke breeze, or
Alternatively, it is well known that oxidative wear and tear on the surface of the object to be fired is prevented by firing in a non-oxidizing atmosphere using C₂, Ar, N2 gas, or the like.

However, in such conventional firing methods, the working environment deteriorates due to the scattering of the coke breeze used, the consumption of non-oxidizing gas, the equipment costs required for manufacturing the shavings, special electric furnaces, etc., and the kiln filling due to the use of the sashes. Restrictions on quantity and other factors are reducing productivity. In the present invention, the drawbacks of such conventional firing methods are solved, and two layers with different compositions are laminated on the surface of the molded body to form a uniform and dense molten coating layer upon heating and firing. The purpose of the present invention is to provide a method for firing graphite or silicon carbide refractories that enables firing in an atmosphere, and the gist of this is to provide a method for firing graphite or silicon carbide refractories in advance. First, a coating thin layer with a Si02 content of 95% or more, and a thin coating layer with a Si02 content of 95% or more, and a coating layer with a Si0250 to 80% and AI203 on the surface.
5~30%, K20 and Na203~15%, &033~
15%, and Fe203, SIC, Zn○, P205
Alternatively, a thin coating layer containing 1 to 15% of a mixture of Pb○ is laminated, and this is heated in the air rather than in a reducing or inert gas atmosphere, so that the laminated layer has a high viscosity and high density in a high temperature range. A molten glass phase is formed and fired. As a result of various studies on conventional firing methods, the inventor of the present invention found that when firing a graphite or silicon carbide refractory molded article (hereinafter referred to as the matrix), the surface of the matrix has a certain degree of refractory resistance during high-temperature heating. The oxidation reaction of the graphite or silicon carbide component of the matrix becomes active on the thin coating layer (hereinafter referred to as the lower layer) with a large Si02 composition that is large and does not penetrate into the matrix or flow down the surface, and on its surface. A thin coating layer with a low Si02 composition (hereinafter referred to as the upper layer) that melts in a temperature range of 700°C or higher and reacts with the lower layer to form a dense molten glass phase is laminated, and two layers with different compositions are laminated. They discovered that by coating the material with , it became possible to perform firing even in the air, i.e., in an oxidizing atmosphere, and that all the problems with conventional firing methods could be solved.

The progress of the inventor's investigation into the optimum composition range of the upper and lower layers will be detailed below. First of all, the composition of the lower layer component Si02 is that it has a high degree of fire resistance in a high purity range of 95% or more, and has a high melting point and high density, so it exhibits an extremely stable coating effect when heated at high temperatures. Furthermore, a high viscosity, high density molten glass phase is produced by the reaction with the upper layer components described below, but if this is less than 95%, the effect of the coating layer as a base layer is reduced.

Regarding the composition of the upper coating material, the optimum composition differs depending on the composition and firing conditions of the graphite or cinnamon carbide refractory, but according to the results of various studies on these refractories, the composition of Si02 is as follows. In the range of 80% or more, the melting point of the upper layer material becomes relatively high, so 1000qo
Below this, it is not in a molten state and therefore glass is difficult to be produced by reaction with the lower layer components, and below 50%, the melting point will be low, but the glass produced will have a low viscosity and a stable coating layer will be obtained. There is no AI20
Regarding No. 3, if it is less than 5%, the viscosity of the melt of the upper layer material becomes high, and if it is more than 30%, the viscosity decreases and it becomes easy to flow off the surface of the base material.

Next, regarding the amount of the mixture of K20 and Na20, if it is less than 3%, the amount of melt will be insufficient and it will be difficult to form a uniform molten glass phase, and if it is more than 15%, the melt will be excessive and the upper layer material will flow off the surface. Not only that, but the reaction with the lower layer components becomes more intense, which penetrates into the matrix and deteriorates its properties.Therefore, the composition of the mixture must be in the range of 3 to 15%. Furthermore, regarding &03, if the composition is less than 3%, the viscosity of the melt of the upper layer material becomes large, and a uniform and dense molten glass phase cannot be formed by reaction with the lower layer component, and if the composition is less than 15% Conversely, the viscosity of the melt decreases, making it easier to flow down the surface. Furthermore, Fe208
, SIC, Zn○, P2Q or a mixture of P
If it is mixed at 5%, it has the effect of improving properties such as adhesion with the lower layer component and density, but outside this range, the effect becomes small. In this way, the upper layer of the coating material contains 95% or more of Si02, and the lower layer contains Si0250.
~80%, River 2035~30%'' K20 and Na20 3
~15%, B033~15% and Fe203, SIC
``By coating a slip prepared by suitably mixing a mixture of Zn○, P2Q, or P within a composition range of 1 to 15%, the melt will neither run off nor penetrate into the matrix during high-temperature heating. Moreover, a uniform and delicate molten glass phase with high viscosity and high density is formed, which exhibits an excellent antioxidant effect.
To explain in detail the raw materials used for the coating material of each lower layer and their preparation method, the lower layer contains Si0
2. Use a single or a mixture of silica slips with a composition of 95% or more, but if necessary, use a small amount of viscosity, chamotte,
Add 20 to 35 parts by weight of water to 100 parts by weight of a mixture containing alumina, etc. together with a binder, and wet-pulverize the mixture in a ball mill or the like to obtain a slip containing 85% or more of particles with a particle size of 100 mesh or less, preferably 325 mesh or less. It is easy to apply the coating. Furthermore, the raw materials for the upper layer are frogstone,
Rouseki, chamotte, clay or glass powder SIC, Si,
A powder mixture of PbtZn○ is mixed with sodium carbonate, sodium citrate, sand sand, dextrin, P.V.A, or rubber as a binder within the above self-composition range and under firing conditions, regardless of the base material composition. Its melting point is 700-1400q
However, depending on its components, the upper layer material may shrink in volume or generate thermal decomposition gas when heated, causing it to peel off from the surface of the lower layer, or create a large number of pores. A frit obtained by pre-calcining the material should be used. The particle size is desirably 50% or more of 48 mesh or more and 200 mesh or less from the viewpoint of coating construction and antioxidant effect, and 40 to 8 parts by weight of water is added to 10 parts by weight of the mixture. It is mixed with rice bran and made into a slip. The work of coating the base with the slip prepared in this way is to first coat the lower layer slip by brush coating, spray coating, bonding coating, or bonding current coating method, but the moisture content of the slip at this time is 25-40% for coating, 30-50% for counterfeit and bonded coatings, and 50-90% for bonded energized coatings.
If the slip is adjusted within this range, adhesion to the base surface and workability will be good, and when applying with a brush, using hydrochloric acid to adjust the pH value of the slip to 1 to 3 will improve brush spread and adhesion. It is easy to apply the coating, and if the pH value of the bonded current-carrying coating is adjusted to 5 to 8, the base body (becomes an anode) is immersed in this and becomes an anode when energized (DC).
An even and dense underlayer can be formed on the surface.

Next, the slip for the upper layer is coated on the surface of the lower layer by forming an even thin layer by brushing, spraying, or dipping, and after that, the coating layer consisting of the upper and lower layers is sufficiently dried. This is then fired. Specific examples of graphite refractories to which the firing method of the present invention can be applied include alumina-graphite enrichment nozzles, sliding nozzles or stoppers, magnesia-graphite nozzles, and graphite bricks for blast furnaces. Examples of quality refractories include lining refractories for blast furnaces, refractories for general use in iron tapping, etc. Examples of the manufacturing method of the present invention applied to some of these refractories will be described below.

Example 1 30% carbon, 60% alumina, 7% silica, 3% other
A mixture with a composition consisting of
On the surface of the molded body (length: 80 m), add 25 parts by weight of fused silica containing 99% Si0 to 25 parts by weight of water, and use a pole mill to grind the green-type silica slip to 200 mesh or less using a brush. Apply it evenly to the thickness, and then mix 50% of Rouseki of 200 mesh or less, 40% of glass powder of 100 mesh or less, 5% of clay, and 5% of side sand of 48 mesh or less on the surface to make Si0264.8%. AI203
14.5%, K20 and Na208.0%, &034.7
% and other 8.0% mixture, 7 parts by weight of a 3% dextrin aqueous solution as a binder was added, and the slip was kneaded with a brush to a thickness of 0.5 skin*, and further dried. The sample obtained was heated to a temperature of 1
It was fired for 4 days at 150 qo.

The fired product taken out of the kiln was no inferior to the reduction-fired product made by conventional sac filling, and the product had a uniformly graced surface. Example 2 80% silicon carbide, 15% metallic silicon, and 5% carbon
The specimen was a molded body of silicon carbide bricks (20 sides x 35 sides x 50 sides) with a Si02 content of 95%.
A lower layer of 0.7 side thickness was coated on the surface of the specimen by immersing it in katsite slip (1), which was then dried, and further mixed with 60% anite stone and 40% glass powder. teSj0266.
0%, mountain 20314.1% "K20 and Na208.3
%, B034・7% and other 6.9% mixture 10
3% dextrin aqueous solution was added and kneaded in the weight part of the sample (2) and the upper layer of 0.5 side thickness was laminated.The sample was soaked in the slip (0) and then dried. and soaked it again in the slip (0) to make each 0
．． Sample B in which a coating layer consisting of two upper layers was formed under 7 legs and 0.5 Yanagi thickness, and the above specimen was further added to Sj027
45 parts by weight of water was added to 10 parts by weight of Rouseki powder consisting of 1.7%, Yama 20324.1%, Na 200.9%, and K20 1.7%, and immersed in a kneaded slip (m) to obtain 0.7% The lower layer of skin thickness was coated and then dried, and this was soaked in a slip (B) to cover the upper layer of 0.5 skin. Sample 'C} and the blood sample of the above specimen without surface coating were dried respectively. After that, these were heated and fired in a silicon carbide heating element electric furnace at 140,000 ℃ for 3 hours, and the results of measuring the oxidation state of each obtained fired body showed that the sample failure related to the present invention was as shown below. The amount of oxidation loss is 1' of the sample Tsukuda.
5. A remarkable antioxidant effect was observed in 1/4 of sample (C} and 1/3 of sample [D}.

Furthermore, as mentioned above, in the present invention, the coating layer on the surface of the base material is made of two layers, an upper layer and a lower layer, but by laminating the upper and lower layers multiple times, a more complete antioxidant effect can be exerted. Of course.

Claims (1)

[Claims] 1 S on the surface of the graphite or silicon carbide refractory molded product.
A thin coating layer with an iO_2 content of 95% or more, and a layer of SiO_250-80% and Al_2O_35-30% on its surface.
, K_2O and Na_2O_3~15%, B_2O_33
~15% and Fe_2O_3, SiC, ZnO, P_
A thin covering layer containing 1 to 15% of a mixture of 2O_5 or PbO is laminated and then dried, and this is heated in the air, that is, in an oxidizing atmosphere, to coat the formed body on the laminated layer in an appropriately high temperature range. A method for firing a graphite or silicon carbide refractory, which comprises forming a molten glass phase with high viscosity and density before firing.