JPH0261433B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ceramic tube suitable for an induction heating furnace for heating steel materials for forging such as round steel pieces for forging.

For example, an induction heating furnace as shown in FIG. 1 is often used to heat steel materials for forging such as round steel pieces for forging. This device usually consists of a fireproof structure 3 constructed of monolithic refractory material 7, which has a hollow part 2 in which a heating coil 1 is buried, and a round steel piece 4 is parallel to the hollow part 2. Metal pipe 5 laid by
It is designed to pass over skid rails formed by The round steel piece 4 is heated by the induced current generated by the current flowing through the coil 1. The space 6 formed by the round steel piece 4 and the metal tube 5 becomes a reservoir for oxidized scale generated by heating the round steel piece 4. Cooling water is passed through the inside of the metal tube 5 to prevent the metal tube from melting or wearing out. In a device configured in this manner, heat is taken away by the cooling water, which poses a problem in terms of energy conservation. To improve this, devices that do not use water-cooled metal tubes at all, but instead consist only of ceramic tubes, have come into use. In this case, the inside of the ceramic tube must be shaped so that the skid rail and reservoir are formed therein. In order to prevent the round steel piece being transferred inside the ceramic tube from meandering and from causing unbalanced loads on the ceramic tube, the inside of the tube is made polygonal or provided with protrusions. FIG. 2 shows a ceramic tube made of hard refractory material with a hexagonal inner surface. An insulating sheet 9 is wrapped around the outer periphery of the tube 8, and a coil 1 is surrounded by a monolithic refractory material 7 in which a refractory structure 3 is constructed. It consists of Further, FIG. 3 shows an example of a ceramic tube provided with substantially parallel protrusions 10, 10, . . . on its inner surface. In the case of a polygon, lines 10' and 10' parallel to each other on the inclined planes sandwiching one corner are the lines that touch and support the round steel piece 4, and if a protrusion is provided, the protrusion The strips 10, 10 are lines that contact the round steel piece 4 and support it. In each case a reservoir 6 is formed. Since the round steel piece passes over many contact points 10, 10', etc., these places become worn out in a relatively short period of time and become unusable. Further, the oxidized scale generated on the surface of the hot round steel piece is deposited or adhered to the inner surface of the ceramic tube 8 in a flaky or molten state due to friction with the ceramic tube (or being pushed) during transportation. These deposits not only obstruct the transportation of the round steel pieces, but also cause unevenness in the heating temperature of the round steel pieces. When the oxide scale is flaky,
As the round steel piece is transferred, it is extruded and either discharged to the outside or deposited in the grooves [reservoir 6] in the ceramic tube 8, but when the oxide scale reaches a high temperature and becomes molten. , the molten material adheres to the inner surface of the ceramic tube 8 and becomes an obstacle to the transfer of the round steel piece 4. Furthermore, when the melt penetrates into the structure of the ceramic tube, it deteriorates the material of the ceramic tube, causing erosion of the ceramic tube. Furthermore, when the molten material solidifies, the solid material is in close contact with the ceramic tube, so when the round steel piece is transferred, the round steel piece will be attracted to this solid material or will meander.
Since abnormal stress such as leakage load is applied to the ceramic tube, there is a problem that the ceramic tube may be destroyed. Therefore, in order to eliminate the above-mentioned problems, it is necessary to frequently remove the oxide scale that accumulates inside the ceramic tube. has high viscosity,
Since the solid matter is stuck to the surface of the refractory material and is extremely difficult to remove, the effort and time required to remove it is significant.

This invention was made to solve the above-mentioned problems with conventional refractories, and it has a smooth surface that has low permeability to molten oxide scale and has no depressions, cavities, pinholes, or pits on the surface. It is a refractory with high resistance to wear caused by sliding of steel materials such as round steel pieces.
The present invention also provides a ceramic tube with high thermal shock resistance.

The method for manufacturing the ceramic tube of the present invention will be explained in detail below. As the aggregate, a fireproof material containing one or more of corundum, mullite, zircon, silica glass, and spinel (MgO.Al ₂ O ₃ ), which have relatively high hardness, is suitable. Corundum-based refractory materials such as sintered alumina can also be used as aggregates.

As for the kaolin clay, commercially available water elutriated Kibushi clay is suitable.
Kaolin clay is used in an amount of 5 to 15 parts by weight based on the aggregate. If it is less than 5 parts, high pressure is required to obtain a dense molded body, and there is a drawback that sintering will not occur unless it is fired at a high temperature of 1300° C. or higher. On the other hand, if the amount of kaolin clay exceeds 15 parts by weight, defects such as cracks will occur in the structure during the heat treatment stage.

Aluminum phosphate is used in an amount of 1.5 to 6.5 parts by weight in solid terms. By using aluminum phosphate in combination with kaolin clay, heat treatment at a relatively low temperature increases the strength of the molded product, reduces the porosity of the molded product,
In addition, it is possible to create a structure with a permeability of the order of 10 ^-4 cm ² . Therefore, since penetration of oxide scale can be reduced, corrosion resistance can be significantly improved. If aluminum phosphate is less than 1.5 parts by weight, the above effect will be small, and if it is more than 6.5 parts by weight, lamination will occur during molding and cracks will occur during firing, making it unfavorable in terms of manufacturing.

The above-mentioned materials are mixed, kneaded with water, and then pressure-molded using a rubber press. In the conventional mold-filling method, the kneaded material is put into a mold or wooden mold of a certain shape and then pressure-formed, but in this case lamination occurs and variations in density and porosity distribution occur. This can cause cracks to occur during use. Particularly in the case of long ceramic tubes as in the examples below, a homogeneous and dense molded body cannot be obtained by molding. On the other hand, according to the rubber press method, the kneaded material is filled into a rubber mold and loaded into a rubber press device, and static pressure is applied while degassing the air in the clay, resulting in a molded product with a uniform structure. easily obtained. In other words, the molded product produced by the rubber press method has no difference in density between the inside and the outer edge, and the molded product is entirely dense without cracks or laminations. Therefore, it has high thermal shock resistance and is particularly effective for long ceramic tubes, such as the formation of cavities at the boundary between the particles and the matrix. After rubber press molding, heat treatment is performed at 300-1200℃.
At temperatures below 300°C, the heat-treated body may be deformed or deteriorated due to moisture absorption, water absorption, etc., which is not preferable. Additionally, if fired at temperatures above 1200℃, a mullite liquid phase will be generated inside the brick due to thermal decomposition of the kaolin clay, which is undesirable because when it solidifies, the elastic modulus of the brick will increase, resulting in a decrease in thermal shock resistance. .

Next, embodiments of the invention will be described.

Example A mixed powder of 100 parts by weight of sintered alumina, 10 parts by weight of kaolin clay and 4 parts by weight of aluminum phosphate (50% aqueous solution - solid equivalent) was added with water and kneaded.
The kneaded product was rubber press molded. Molding pressure 1000Kg/
^cm2 and held for 1 minute. Shape is length 700mm x outer diameter 70
mm, the inner surface is a regular hexagon, and the distance between opposing surfaces is 40 mm.
It was hot. (See Figure 2). In the rubber press molding, the core metal was made to have a regular hexagonal cross section, the rubber of the outer pressurizing part was cylindrical, and the outer side of the cylinder was pressurized with liquid.

After drying, the molded product was fired in a tunnel kiln at 1200°C. The fired product has a bulk specific gravity of 2.85 and an apparent porosity of 18.8.
%, and the compressive strength was 900Kg/cm ² . After firing, a coating material mainly composed of ultrafine silicon carbide was applied to the inner surface to a thickness of approximately 0.2 mm. Ultra-fine silicon carbide is a mixture of β-type silicon carbide with a particle size of 5 μm or less, clay, a binder, and water, and it is a mixture of β-type silicon carbide with a particle size of 5 μm or less.
It contains 50%. After coating, it was dried and used. The coating material has the effect of closing pinholes, pits, etc. on the inner surface, preventing penetration of oxide scale, and facilitating the removal of oxide scale. The coating material may be used without being reapplied as it is initially applied, or may be reapplied during use, after cleaning, etc.

The ceramic tube thus produced was used as a ceramic tube in a high-frequency induction heating furnace for forging. Round steel piece is approximately 30-36mmφ length 150mm,
A piece weighing 1.5 kg/piece was passed through a ceramic tube at a speed of about 170 mm/sec and heated by high frequency induction. The three ceramic tubes described above were arranged in series, with a gap of about 5 mm between each tube. The oxidized scale generated inside the tube was pushed by the round steel piece, allowing some of it to be discharged to the outside through this gap. The round steel piece is heated while passing through these three ceramic tubes, and the round steel piece at the exit is heated to approximately 1200°C. The round steel piece slides while being supported by two surfaces sandwiching one corner of the regular hexagon on the inner surface of the ceramic tube, and the ceramic tube does not suffer from the aforementioned unbalanced load or buckling, and there is no wear on the sliding surfaces. I used it for about 2 months. Next, the other two sides were used for two months each, and one ceramic tube could be used for about six months. In this case, the ceramic tube 8 was extracted from the refractory structure 3, rotated by a predetermined angle, and then fitted into the refractory structure 3 again.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional induction heating device, FIG. 2 is a sectional view of an induction heating device using a ceramic tube according to the method of the present invention, and FIG. 3 is a sectional view showing another example of a ceramic tube. . 1... Coil, 2... Hollow part, 3... Fireproof structure, 4
... Round steel piece, 5... Metal pipe, 6... Reservoir (concave groove),
7... Monolithic refractory, 8... Ceramic tube, 9
...Insulating sheet, 10...Protrusion.

Claims (1)

[Claims] 1. 5 to 15 parts by weight of relatively hard fire-resistant aggregate.
Ceramic for induction heating furnaces, which is characterized by adding parts by weight of kaolin clay and 1.5 to 6.5 parts by weight of aluminum phosphate on a solid basis, kneading with water, rubber press molding, and then heating at 300 to 1200°C. How to make tubes. 2. The method for manufacturing a ceramic tube for an induction heating furnace according to claim 1, wherein the refractory aggregate contains one or more of corundum, mullite, silica glass, zircon, and spinel. 3. The method of manufacturing a ceramic tube for an induction heating furnace according to claim 1 or 2, wherein a coating material containing ultrafine silicon carbide as a main component is applied to the inner surface of the tube.