JPS6232152B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a high alumina unfired powder composition used for lining a melting furnace for non-ferrous metals having a melting point of 1200°C or less, and particularly suitable for use in a melting furnace for copper alloys. The present invention relates to an unfired powder composition. [Prior Art] High alumina refractory materials are used for furnace materials, such as lining materials, in furnaces for melting nonferrous metals such as copper, brass, zinc, and aluminum. High alumina refractories consist of particles of high alumina aggregate and a binder. High alumina aggregate has aluminum oxide of 60%
% by weight or more, and the remainder mainly consists of silicon dioxide. However, the high alumina refractory material has drawbacks in that it is weak against thermal shock and generates reactants when it comes into contact with molten aluminum. Since the refractory material is susceptible to thermal shock, when used in a furnace for melting copper or copper alloys, cracks occur on the inner surface of the furnace when the furnace is cooled, and molten metal permeates into the interior of the furnace from there during the next melting process. As the molten metal permeates into the furnace, a difference in coefficient of thermal expansion occurs between the permeated part and the unpermeated part, and the permeated part peels off when the furnace is cooled. In induction melting furnaces, coil short circuit accidents may occur due to penetration of molten copper. In the case of melting aluminum or an aluminum alloy, the molten metal and the refractory material react, and reaction products adhere to the furnace wall, reducing the area inside the furnace. Furthermore, depending on the composition of the molten aluminum alloy, some of the reaction products may penetrate into the interior of the furnace, resulting in peeling of the furnace wall. The present inventors have previously discovered that by incorporating silicon nitride into the above-mentioned high alumina refractory material, the thermal shock resistance of the refractory material can be improved and the reaction with molten aluminum can be prevented. For example, see Japanese Patent Application Laid-Open No. 56-22675. [Object of the Invention] The object of the present invention is to provide a high alumina unfired powder composition for lining a nonferrous metal melting furnace that is more resistant to erosion by slag during copper alloy melting than the silicon nitride-containing high alumina refractory material described above. It is on offer. [Summary of the Invention] The present invention contains graphite particles in an unfired powder composition consisting of a mixture of high alumina aggregate particles and silicon nitride particles, or a mixture further containing a binder. The high alumina unfired powder composition of the present invention is composed of high alumina aggregate containing 60% by weight or more of aluminum oxide, silicon nitride, and graphite, and coarse particles with a particle size of 1.2 mm or more and coarse particles with a particle size of 1.2 mm or more. A powder composition consisting of a mixture of intermediate grains with a diameter of 0.15 to less than 1.2 mm and fine grains with a grain size of less than 0.15 mm, and contains 5 to 25% by weight of silicon nitride and 3 to 12% by weight of graphite. The alumina aggregate consists of 40 to 70% by weight of coarse particles, 10 to 30% by weight of medium particles, and 10 to 40% by weight of fine particles. Silicon nitride and graphite consist of intermediate grains and fine grains. The high alumina unfired powder composition of the present invention is
Used as a refractory material for the lining of melting furnaces for nonferrous metals with a melting point of 1200°C or less. The refractory material of the present invention exhibits a significantly longer service life than previously developed refractory materials when used in a melting furnace for copper-zirconium alloys such as copper-zirconium alloys or copper-zirconium-phosphorus alloys. The refractory material of the present invention is resistant to thermal shock, similar to the previously developed silicon nitride-containing refractory material. Moreover, when used for melting aluminum alloy, it does not generate any reactants with the molten metal. The present inventor discovered the following while melting several types of copper alloys using a melting furnace made of a refractory material made of a mixture of high alumina aggregate particles and silicon nitride particles. discovered. Copper such as copper-zirconium alloy or copper-zirconium-phosphorus alloy
When a zirconium alloy is melted, the furnace wall is eroded by the slag on the surface of the molten metal, and the refractory material near the slag melts away. This corrosion is caused by the formation of slag containing CuO as the main component when copper-zirconium alloys are melted, and this slag reacts with silicon dioxide, which is mainly present in the refractory material, to produce low-melting-point reactants. I found out that this happens by blending in. Therefore, high alumina refractory materials containing silicon nitride are
It became necessary to prevent corrosion by slag whose main component is CuO, and this led to the discovery of the refractory material of the present invention. The following phenomenon occurs when a refractory material containing high alumina aggregate and silicon nitride contains a solid substance, such as graphite, which reacts with molten nonferrous metal to generate carbon monoxide. This results in
The amount of CuO is reduced and the erosion of the refractory material by slag is suppressed. (i) A portion of CuO in the slag and molten metal is reduced by the graphite in the refractory material as shown in equation (1). CuO+C→Cu+CO ……(1) (ii) CO generated by oxidation of graphite in the refractory material is (2)
Part of the remaining CuO in the slag and molten metal is reduced as shown in the formula. CuO＋CO→Cu＋CO ₂ ……(2) (iii) CO generated by oxidation of graphite is deposited on the furnace wall surface.
Alternatively, a gas film consisting of CO ₂ is formed, which prevents wetting of the molten metal and the refractory material. Each component of the present invention will be explained. (b) Alumina aggregate Aggregates containing at least 60% by weight of aluminum oxide should be used. As the aluminum oxide content in the aggregate increases, the amount of silicon dioxide decreases, and therefore the amount of products from the reaction between CuO-based slag and refractory material decreases. Therefore, the erosion effect of the refractory material is weakened. Figure 1 is a graph showing how the rate of erosion of refractory materials by slag containing CuO as the main component changes when the amount of aluminum oxide in high alumina aggregate is changed. It is clear that the higher the amount of aluminum oxide in the aggregate, the lower the erosion rate. It is clear that the amount of aluminum oxide in the aggregate is preferably 70% by weight or more. The experiment was conducted using a refractory material consisting of 12% by weight silicon nitride, 5% by weight graphite, 10% by weight clay, and the remainder high alumina aggregate. High alumina aggregate has coarse grains from 4.7 to 1.2 mm and less than 1.2 mm to 0.15
It consists of medium grains of mm and fine grains of less than 0.15 mm, with coarse grains accounting for 60% by weight of the total aggregate, and medium grains accounting for approximately 25% by weight. Due to the fireproof material, the outer diameter is 50mmφ and the height is 50mm.
A crucible with a cylindrical shape and a hole with a diameter of 20 mmφ and a height of 30 mm in the center is molded, this crucible is placed in a graphite crucible, the surrounding area is sealed to prevent it from being affected by the atmosphere, and the crucible is fired at 1200℃. did. The reason for firing at 1200℃ was to simulate the condition after long-term use as a melting furnace lining material. Using this refractory crucible, a copper-0.01% by weight zirconium-0.01% by weight phosphorus alloy was melted, held for 2 hours, the molten metal was removed, and the crucible was cut lengthwise into two to reduce the corrosion rate due to slag. It was calculated using the following formula. Note that all measurements of the erosion rate described below were performed in this manner. Erosion rate (%) = (Cross-sectional area of the hole increased by erosion) - (Cross-sectional area of the original hole) / (Cross-sectional area of the original hole) x 100 High alumina aggregate is It can be obtained by a calcination method or the like. Aggregates obtained by the firing method have better thermal shock resistance and sinterability than aggregates obtained by the electrofusion method. Aggregates obtained by the electrofusion method have superior erosion resistance due to slag containing CuO as a main component, compared to aggregates obtained by the sintering method. Therefore, it is desirable to use a mixture of both. Examples of aggregates containing 70% by weight or more of aluminum oxide include mullite and corundum. When using chamotu with a small amount of aluminum oxide, it is desirable to mix it with corundum or mullite to make the amount of aluminum oxide 60% by weight or more. The particle size structure of high alumina aggregate affects the thermal shock resistance, strength, permeability by molten metal, erosion resistance, etc. of the refractory material. High alumina aggregate has a particle size of
It is desirable to consist of coarse particles of 1.2 mm or more, intermediate particles of less than 1.2 mm to 0.15 mm, and fine particles of less than 0.15 mm in diameter. In order to increase the strength of the refractory material, such as compressive strength, it is necessary to use coarse particles. Coarse particles are also necessary to improve thermal shock resistance. However, if only coarse particles are used, there will be many voids and a dense product cannot be obtained, so the strength is low and the molten metal easily penetrates, and there is a strong tendency to be physically eroded by the molten metal. By mixing fine particles, it is possible to strengthen the structure of the refractory material, increase its strength, and prevent penetration and erosion of molten metal. but,
Coarse particles and fine particles alone do not provide sufficient thermal shock resistance or corrosion resistance. These drawbacks can be compensated for by mixing intermediate grains. The amounts of coarse grains, medium grains, and fine grains in the high alumina aggregate are preferably 40 to 70% by weight of coarse grains, 10 to 30% by weight of medium grains, and 10 to 40% by weight of fine grains, respectively. The size of coarse particles is preferably 4.7 mm or less. (b) Silicon nitride By containing silicon nitride, the thermal shock resistance of the refractory material increases, making it difficult for cracks to occur during cooling of the furnace. Furthermore, it becomes difficult for aluminum or molten aluminum alloy to react with the refractory material. As silicon nitride, it is desirable to use Si ₃ N ₄ . It is desirable that the size of the silicon nitride particles be as small as possible in order to obtain a dense refractory material with few voids. It is desirable to use fine particles with a particle size of less than 0.15 mm. It is desirable that the particle size of silicon nitride is less than 1.2 mm at most;
It is desirable that particles smaller than 0.15 mm account for 80% by weight or more of the total amount of silicon nitride. The graphs in Figures 2 to 7 show how the penetration rate of molten metal, the rate of erosion of the refractory material by slag, the compressive strength and thermal shock resistance of the refractory material change depending on the amount of silicon nitride in the refractory material. This is what is shown. The composition of the refractory material consists of high alumina aggregate, silicon nitride, graphite and clay. The amount of clay is 10% by weight
The amount of graphite was kept constant and varied to 3, 5, and 10% by weight. The ratio of coarse grains, medium grains, and fine grains in high alumina aggregate is approximately 60% by weight for coarse grains and approximately 60% by weight for medium grains.
25% by weight, the rest being fine particles. For silicon nitride
Fine particles made of Si ₃ N ₄ and having a particle size of less than 0.15 mm were used.
Fine particles with a particle size of less than 0.15 mm were also used for graphite. Molten metal components: Copper - 0.01% by weight Zirconium - 0.01% by weight
It is a phosphorus alloy. The permeation rate of molten metal is determined by measuring the cross-sectional area of the permeated layer when the crucible is cut lengthwise, and dividing this by the cross-sectional area of the original hole in the crucible, since a layer of molten metal and slag permeates around the hole in the crucible. demand. All subsequent measurements of permeability were performed in this manner. FIG. 2 shows the molten metal penetration rate of a refractory material containing 5% by weight of graphite. When the amount of silicon nitride is 5 to 20% by weight, the permeability is the lowest, and when it exceeds 20% by weight, the permeability tends to increase. The amount of silicon nitride is desirably 25% by weight at most. Figure 3 shows how the molten metal penetration rate changes when the amount of graphite is 3, 5, and 10% by weight and the amount of silicon nitride is changed. It has been confirmed that for any amount of graphite, if the amount of silicon nitride is 5 to 20% by weight, a remarkable effect is exhibited in preventing penetration of molten metal. FIG. 4 shows the relationship between the amount of silicon nitride and the rate of erosion by slag for a refractory material containing 5% by weight of graphite. Figure 5 shows the relationship between the amount of silicon nitride and the rate of erosion by slag for refractory materials with varying amounts of graphite of 3, 5, and 10% by weight. In order to prevent erosion by slag containing CuO as a main component, it is preferable that the amount of silicon nitride be around 10% by weight, specifically 7 to 12% by weight. Figure 6 shows the relationship between the compressive strength after firing and the amount of silicon nitride of a refractory material with a graphite content of 5% by weight, and Figure 7 shows the impact that leads to cracking when such a refractory material is subjected to a thermal shock test. The relationship between the number of times and the amount of silicon nitride is shown. The shape of the test piece is 50mm in diameter.
It is a round bar with a diameter of 50 mm and a length of 50 mm. The melting furnace lining was fired in advance assuming that it would be exposed to the molten metal, and the firing temperatures were set at 1000°C, 1200°C, and 1400°C. Thermal shock tests were conducted on round bars fired at 1200°C. In the thermal shock test, a round bar is placed in a heating furnace and heated to 1200℃.
This was carried out by repeatedly heating and maintaining the temperature for 15 minutes, then taking it out of the furnace and putting it into water. From the viewpoint of compressive strength and thermal shock resistance, it has become clear that the amount of silicon nitride is desirably 7 to 15% by weight. (c) Graphite By including graphite in the refractory lining of the furnace, the amount of CuO in the molten copper-zirconium alloy decreases, and the amount of slag that is mainly composed of CuO is reduced, resulting in a refractory material. erosion is suppressed. Graphite forms a gas film between the refractory material and the molten metal, making it difficult for the refractory material to wet the molten metal. As is clear from Figure 8, the amount of graphite is 3 to 12
% by weight is preferred, particularly 5 to 10% by weight. Figure 8 shows that using a refractory crucible in which the amount of silicon nitride was 10% by weight, the amount of clay as a binder was 10% by weight, and the amount of graphite was varied, copper - 0.01% by weight, zirconium - 0.01%. This figure shows the corrosion rate due to slag when a weight percent phosphorus alloy is melted. It is clear that if the amount of graphite is too small or too large, the erosion rate will increase. For graphite, it is desirable to use particles with a particle size of less than 1.2 mm, and it is particularly desirable to use a mixture of particles with a particle size of less than 1.2 to 0.15 mm and particles with a particle size of less than 0.15 mm. The mixing ratio is 40 to 40 particles less than 0.15mm
It is preferable to set it to 80% by weight. Graphite reacts with the molten metal, oxidizes, and disappears. As a result, the areas where graphite particles were present remain as voids. Therefore, when the size of the voids is large, the strength of the refractory material decreases. Furthermore, since the contact area with the molten metal increases, the molten metal can more easily penetrate. On the other hand, if the graphite is too small, it is likely to react with oxygen in the atmosphere and disappear before reacting with the molten metal. Therefore, it is desirable to use intermediate particles and fine particles with a particle size of less than 1.2 mm, and to use a mixture of intermediate particles and fine particles. Graphite includes earthy graphite and flaky graphite, both of which can be used. (d) Binder High alumina refractory materials can be molded without the use of a binder, as fine aggregate particles act as a kind of binder. However, adding a binder makes it easier to mold and provides greater strength after molding. Binding agents include inorganic clay, sodium silicate,
Organic substances such as aluminum monophosphate or pulp waste liquid can be used. Clay is most preferred. The amount of binder is 0.05-15% by weight
is desirable, and when using clay, it is 7 to 12% by weight.
is particularly desirable. When using a binder such as sodium silicate, aluminum monophosphate, or pulp waste liquid, the amount is preferably 0.05 to 5% by weight. The clay particle size is
In order to exhibit sufficient caking power, it is desirable to use fine particles less than 0.15 mm. (e) How to use the refractory material The refractory material of the present invention is used without being fired. As a method for using the material without firing, for example, there is a method in which a small amount of water is added to a mixture of particles of the refractory material in order to increase the caking property, and the mixture is loaded into a predetermined place in a melting furnace and compacted with an air rammer or the like. The mixture may be formed into a predetermined shape in advance, dried, and then fitted into a predetermined position in the melting furnace. The refractory material of the present invention is applied to a melting furnace for non-ferrous metals having a melting point of 1200°C or lower. When a melting furnace made of the refractory material of the present invention is used at a temperature of 1200°C or higher, the silicon nitride in the refractory material is rapidly oxidized and converted to silicon dioxide _SiO2 . The converted silicon dioxide reacts with the molten metal, causing peeling of the furnace wall and penetration of the molten metal. If used at a temperature of 1200° C. or lower, peeling of the furnace wall due to oxidation of silicon nitride will not occur, and the effect of improving thermal shock resistance and preventing reaction with molten aluminum by silicon nitride will be effectively exhibited. The non-ferrous alloy melted in the melting furnace made of the refractory material of the present invention may contain iron as an alloy component. The amounts of coarse particles, intermediate particles, and fine particles in the entire refractory material are preferably 40 to 50% by weight of coarse particles, 15 to 25% by weight of intermediate particles, and 30 to 45% by weight of fine particles, respectively. [Embodiments of the Invention] As shown in Table 1, crucibles and round bars were made from 10 types of refractory materials. A mixture of fused mullite and fused corundum was used as the high alumina aggregate. The chemical compositions of the alumina aggregate, silicon nitride, and clay are shown in Table 2. The coarse grain size of the high alumina aggregate was 4.7 to 1.2 mm. Examples of the present invention are samples Nos. 1-9. Among these, Samples Nos. 1 to 6 contain clay as a binder.
Nos. 7 and 8 contain aluminum monophosphate as a binder. No. 9 does not contain a binder. No. 10 is a conventional example and does not contain graphite.

【table】

[Table] Refractory materials No. 7 and No. 8 were made by blending specified amounts of raw materials excluding a binder, adding an aluminum monophosphate solution, mixing, and molding. Therefore, the composition without a binder is expressed as 100%. Table 3 shows the compressive strength and thermal shock test results of the refractory materials. The test was conducted on a molded round bar that had been fired in advance, assuming that it would be exposed to molten metal. In Table 3, 0 flaking after 20 times indicates that the refractory material did not flake off even though the thermal shock was repeated 20 times.

【table】

[Table] Products containing a binder have higher compressive strength than those without. Compressive strength is hardly affected by the presence or absence of graphite. Using crucibles made of refractory materials of samples No. 1 to 10, copper oxide, copper-0.01% by weight zirconium alloy,
Copper - 0.01% by weight zirconium - 0.01% by weight phosphorus alloy and brass (zinc content: 28% by weight) were melted, and the erosion rate by slag and the penetration rate of the molten metal were determined. The results are shown in Table 4. The purpose of dissolving copper oxide (CuO) was to examine the extent to which refractory materials are eroded by CuO.

【table】

〔Effect of the invention〕

As is clear from the above description, the refractory material of the present invention has the effect of being less likely to be corroded by slag during melting of the copper alloy.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of aluminum oxide in high alumina aggregate and the erosion rate, Figures 2 and 3 are graphs showing the relationship between the amount of silicon nitride and the molten metal penetration rate, and Figures 4 and Figure 5 is a graph showing the relationship between the amount of silicon nitride and the erosion rate, Figure 6 is a graph showing the relationship between the amount of silicon nitride and compressive strength, and Figure 7 is the impact required to generate a crack in a thermal shock test. A graph showing the relationship between the number of times and the amount of silicon nitride, and FIG. 8 is a graph showing the relationship between the amount of graphite and the erosion rate.

Claims (1)

[Claims] 1. Consisting of high alumina aggregate containing 60% by weight or more of aluminum oxide, silicon nitride, and graphite, coarse particles with a particle size of 1.2 mm or more and particles with a particle size of 0.15 to less than 1.2 mm. It is a powder composition consisting of a mixture of medium grains and fine grains with a particle size of less than 0.15 mm, and the alumina aggregate contains 40 to 70% by weight of coarse grains, 10 to 30% by weight of medium grains, and 10 to 10% by weight of fine grains. Silicon nitride and graphite consist of intermediate grains and fine grains, silicon nitride is 5-25% by weight of the entire mixture, and graphite is 3-12% by weight of the entire mixture.
A high alumina unfired powder composition for lining a non-ferrous metal melting furnace, characterized in that it is used for lining a non-ferrous metal melting furnace having a melting point of 1200° C. or lower. 2. The high alumina unfired powder composition for lining a nonferrous metal melting furnace according to claim 1, wherein the silicon nitride contains 80% by weight or more of fine particles. 3. The high alumina unfired powder composition for lining a nonferrous metal melting furnace according to claim 1, wherein the graphite contains 40 to 80% by weight of fine particles. 4. The high alumina unfired powder composition for lining a nonferrous metal melting furnace according to claim 1, wherein the powder composition contains 0.05 to 15% by weight of a binder.