RU2191167C1 - Charge for refractory article making - Google Patents

Abstract

FIELD: production of refractory articles. SUBSTANCE: invention relates to composites used for making ammunition (saggers, boxes, shells, sleeves and others) in calcinations of ceramic articles, among them, ceramic long- measured rods of the complex configuration that are necessary in casting by melting models made of heat- resistant alloys, for example, buckets for aviation engines. The charge composition involves components taken in the following ratio, wt.-%: melted mullite or mullite-corundum articles crushed material of fractions, mm: 3.0-0.8, 12-20; 0.8-0.2, 8-16; synthetic corundum = 80 - = 50 , 20-32; = 10, 10-18; alumina, 27.5-32.7; silicon carbide = 10 - = 14, 0.5-1.0; dispersed aluminum, 0.8-1.6. EFFECT: decreased calcination temperature, retained thermal stability of large-scale articles. 3 cl, 2 tbl

Description

 The invention relates to the production of refractory products, and in particular to compositions used for the manufacture of refractory products (capsules, baskets, glasses, boats, etc.) during the firing of ceramic products, including ceramic lengthy rods of complex configuration, necessary when casting on investment casting from heat-resistant alloys, such as blades for aircraft engines.

Known high alumina charge for the manufacture of refractory products, containing, wt.%:
Electrocorundum with grain sizes, mm: 0.8-1.0 - 45-55
0.12-0.16 - 8-12
Calcined industrial alumina with a specific surface of about 7500 cm ² / g - 22-28
Refractory clay - 12-17
(See A.S. USSR 166895, class C 04 B 35/10, publ. 06/30/69).

However, to obtain refractory products made from this mixture, a high firing temperature of 1650 ^o C. is required.

 A mixture is also known for the manufacture of extruded refractories, including, by weight. %: corundum - 23-38, mullite-alumina chamotte - 15-50, refractory clay or kaolin - 7-12, fused mullite - 20-35 (See A.S. USSR 628135, IPC С 04 В 35/10, publ. 10/15/78).

The disadvantage of products from this mixture is also a high firing temperature - 1550-1600 ^o C.

 The closest to the composition of the proposed is a mixture for the manufacture of refractory products using fused mullite, corundum and alumina, containing, wt.%: Fused mullite - 15-30, corundum - 35-60, alumina - 25-35 (See a. S. USSR 607822, IPC S 04 B 35/10, publ. 25.05.78).

The refractory material on the basis of this mixture has a sufficiently high strength and heat resistance, but to obtain it requires a high firing temperature of 1580-1750 ^o C.

 The technical task of the proposed composition of the mixture for the manufacture of refractories is to reduce the firing temperature while maintaining the heat resistance of large products. The dimensions of work products, for example, boxes - 320 x 245 x 125 mm, glasses - ⌀ 200 mm, height - 260 mm with a product wall thickness of 12-15 mm, are due to the dimensions of the ceramic rods required for investment casting.

 It should be noted that, as a rule, in the manufacture of refractory products such as refractory products in order to reduce economic costs (especially associated with the consumption of electricity and fuel gas), it is required that the conditions of their firing coincide with the conditions of their operation. For the same purposes, use the battle of refractory products. Therefore, the firing temperature of refractory products should be brought closer to the temperature of their operation.

The problem is solved in that the mixture for the manufacture of refractory products, including mullite-containing material, corundum and alumina, additionally contains dispersed aluminum and silicon carbide, and as the mullite-containing material, mullite-corundum products are additionally used as corundum, and electrocorundum is used as corundum, in the following ratio of components , wt.%:
Processed mullite or mullite-corundum products battle, fractions, mm: 3-0.8 - 12-20
0.8-0.2 - 8-16
Electrocorundum 80-50 - 20-32
10 - 10-18
Alumina - 27.5-32.7
Silicon Carbide 10-14 - 0.5-1.0
Dispersed aluminum - 0.8-1.6
The problem is also solved by the fact that:
1. Use alumina G _to ;
2. The specific surface of alumina G _to is 6500-7200 cm ² / g.

The manufacture of the molding mixture and products is carried out according to the following technology: preparation of the starting components — crushing and sieving of the battle, the preferred content of mullite in which is at least 15%; grinding alumina, for example, grade G _k (the content of α-AL ₂ O ₃ in which it is desirable to have at least 93%) until it reaches a specific surface of 6500-7200 cm ² / g; mixing components with water; vibration casting; drying and firing.

 All components of the refractory mixture are mixed dry in a paddle mixer. Then add water in an amount of 6.5-9 wt.%, In excess of 100% and further mixed. Products are molded on a vibrating stand. After hardening, the masses of the mold are disassembled, and the preforms are dried and fired.

 The composition and quantitative ratios of the components of fused mullite or mullite-corundum products, electrocorundum and alumina components provide sintering of the mass at a lower firing temperature and provide strength and heat resistance of the fired material. The specified limits of the particle size distribution of the components are selected in order to ensure maximum mobility of the molding material in the process of vibration, which in turn ensures optimal packing of the mass in the mold.

The use of dispersed aluminum powder is due to the following factors: aluminum, absorbing most of the free water, binds it with the formation of colloidal hydrate of aluminum oxide Al (OH) ₃ , which, being a thin layer around large particles of the above components, has an additional binder effect. This is especially important at the stage of drying the preform in the mold. At this moment, most of the free water binds to dispersed aluminum, forming Al (OH) ₃ , and a small part of H ₂ O evaporates. When this occurs, an exothermic reaction occurs, with the release of a large amount of heat, the temperature of the workpiece rises to 50 ^o C and above and the volume of the workpiece increases. An optimal increase in volume with optimal heating leads to a decrease in product discontinuities due to the release of air from the mass to the surface of the product. In this case, a minimum number of shells are formed on the surface of the products from air bubbles, which do not affect the quality of the products as a whole.

 To ensure such conditions of hardening of articles in the mold, silicon carbide powder with a grain size of 10.14 in the indicated amounts is introduced into the refractory mass, which reduces the heating of the workpieces and their volume expansion.

When dispersed aluminum is introduced below the specified limit, the mass does not bind (harden) due to the formation of Al (OH) ₃ , and with an increase in the aluminum content there is a very strong heating of the mass with the appearance of water vapor, at which the molding process is difficult to carry out.

During firing, Al (OH) ₃ decomposes with the formation of active alumina (Al ₂ O ₃ ), which reinforces the glass crystal phase and strengthens it. Silicon oxide (α-cristabolite) formed during the oxidation of silicon carbide also enters the glassy-crystalline phase. Their uniform arrangement around large grains provides additional sintering of the mass, which contributes to the production of sufficiently strong and heat-resistant products at a firing temperature of 1360 ^o C.

 Boxes and glasses were made from the proposed charge.

The resulting products were used for roasting large rods in a tunnel furnace in a bed of alumina at a calcination temperature of 1360 ^o C. The heat resistance of the products is estimated by the number of walkers (heat exchange) of the products. Table 1 and 2 shows the composition of the refractory mixture and the technical characteristics of products from it.

 Table 1 shows the compositions of the proposed mixture and prototype.

 Table 2 shows the properties of the proposed composition of the charge and prototype.

From tables 1 and 2 it is seen that the products from the proposed mixture, calcined at a sufficiently low temperature (1360 ^o C), have satisfactory performance characteristics that can be used as a fire source (box, glasses) when firing large bulky ceramic rods required in the manufacture aircraft engine blades, Lost wax alloy casting.

Compared with the prototype, ceramic products from the proposed mixture have a sufficiently high heat resistance (residual strength at a temperature difference of 1250-20 ^o C air-water) at a low (1350-1360 ^o C) firing temperature.

The value of heat resistance can be estimated by the number of heat shifts and residual strength. The heat resistance of the proposed mixture, estimated by the number of heat exchangers (air-water), at a temperature difference of 1300-20 ^o C is 28-35, and its heat resistance, estimated by the residual strength at a temperature difference of 1250-20 ^o C (air-water) after 8 cycles is 100, after 35 cycles - 70-90.

 The data presented confirm the preservation of heat resistance of the material made from the proposed mixture.

In addition, experimentally obtained data on the number of walkers of products to failure also indicate the possibility of manufacturing products with high heat resistance:
for glasses (⌀ 100 mm, h = 260 mm) - 30-35 walker;
for boxes - (320 x 245 x 125 mm) - 20-25 walker.

Claims (2)

1. The mixture for the manufacture of refractory products, including mullite-containing material, corundum and alumina, characterized in that it additionally contains dispersed aluminum and silicon carbide, as mullite-containing material use fused mullite or mullite-corundum products, and as corundum - electrocorundum in the following ratio components, wt.%:
Fused mullite or mullite-corundum products fractions battle, mm:
3.0-0.8 - 12-20
0.8-0.2 - 8-16
Electrocorundum 80-50 - 20-32
10 - 10-18
Alumina - 27.5-32.7
Silicon Carbide 10-14 - 0.5-1.0
Dispersed aluminum - 0.8-1.6
2. The mixture according to claim 1, characterized in that they use alumina G _to . 3. The mixture according to claim 2, characterized in that the use of alumina G _to with a specific surface area of 6500-7200 cm ² / year

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