JPS61127657A - Manufacture of ceramic tube for induction heating furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 a steel material for forging such as a round steel piece for forging.

For heating steel materials for forging such as round steel pieces for forging, for example, the first
Induction heating furnaces like the one shown in the figure are often used. This device usually consists of a refractory structure (3) constructed from a monolithic refractory (7) having a hollow part (2) in which a heating coil (1) is embedded, and a round steel piece ( 4) is adapted to pass over a skid rail formed by a metal tube (5) laid in parallel inside the hollow part (2). The round steel piece (4) being passed through is heated by the induced current generated by the current flowing through the coil (1). Round steel piece (
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 metal tube (5) to prevent the metal tube from melting or wearing out. In a device configured in this manner, the amount of 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 and are made only of ceramic tubes have come into use. In this case, the interior 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 from meandering while being transferred inside the ceramic tube and from causing an uneven load on the ceramic tube, the inside of the tube is made polygonal or provided with protrusions.

Figure 2 shows a ceramic tube made of hard refractory material with a hexagonal inner surface, an insulating sheet (9) wrapped around the outer periphery of the tube (3), and a monolithic refractory material (7) with a coil (1) embedded therein. ) constitutes the surrounding fireproof structure (3). Figure 3 also shows protrusions (10) and (1) that are almost parallel to the inner surface.
An example of a ceramic tube provided with...0) is shown below.

In the case of a polygon, lines (10') and (10') parallel to each other on the inclined planes that sandwich one corner are the lines that touch and support the round steel piece (4), and the protrusions are provided. In this case, the protrusions (10), (10) are lines that touch and support the round steel piece (4).

In each case a reservoir (6) is formed. Since the round steel piece passes over many contact points (10), (10″), etc., those places will wear out in a relatively short period of time and become unusable. During transport, oxidized scales are deposited or adhered to the inner surface of the ceramic tube (3) in flaky or molten state due to friction with the ceramic tube (or pushed).These deposits interfere with the transport of the round steel pieces. Not only that, but it also causes interference such as uneven heating temperature of the round steel piece.When the oxide scale is in the form of flakes, it is pushed out as the round steel piece is transferred and is discharged to the outside, but It is deposited in the concave groove [reservoir (6)] in the tube (3), but when the oxide scale reaches a high temperature and becomes molten, the molten substance sticks to the inner surface of the ceramic tube (3), It becomes an obstacle to the transfer of the round steel piece (4).In addition, when the molten material penetrates into the weave of the ceramic tube, it deteriorates the material of the ceramic tube, causing corrosion of the ceramic tube. When solidified, the solid material is in close contact with the ceramic tube, so when the round steel piece is transferred, the round steel piece gets caught on this solid material and meandering, giving the ceramic tube abnormal stress such as leakage load. Therefore, in order to eliminate the above-mentioned problem, it is necessary to frequently remove the oxide scale that accumulates inside the ceramic tube, but if the oxide scale is in a molten state or When solidified after being melted, the viscosity is high or the solids are stuck to the surface of the refractory material, making removal extremely difficult, resulting in significant waste of labor and time in removal work.

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

The method for manufacturing a ceramic tube of the present invention will be described in detail below. The aggregate is corundum, which has relatively high hardness.
Mullite, zircon, silica glass, spinel (MgO
- Refractory materials containing one or more of A1□03) are suitable. Corundum-based refractory materials such as sintered alumina can also be used as aggregates.

Commercially available water-sieved Kibushi clay is suitable for the kaolin clay.

Kaolin clay is used in an amount of 5 to 15 parts by weight based on the aggregate. If the amount is less than 5 parts, high pressure is required to obtain a dense molded product, and there is a drawback that sintering will not occur unless fired at a high temperature of 1.300°C or higher. On the other hand, if the amount of kaolin clay is 15 parts by weight or more, defects such as cracks will occur in the structure during the heat treatment.

Aluminum phosphate is used in an amount of 1.5 to 6.5 parts by weight in solid terms. When aluminum phosphate is used in combination with kaolin clay, it increases the strength of the molded product through heat treatment at a relatively low temperature, reduces the porosity of the molded product, and increases the air permeability to 10-'
It is possible to form a cJ-order tissue. Therefore, since penetration of oxide scale can be reduced, corrosion resistance can be significantly improved. If the aluminum phosphate is less than 1.5 parts by weight, the above effects will be small, and if it is more than 6.5 parts by weight, it will not be suitable for manufacturing, such as lamination during molding and cracking during firing.

The above-mentioned materials are mixed, kneaded with water, and then pressure-molded using a rubber press. In the conventional mold-insertion 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 such as those 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 obtained by the rubber press method has no difference in density between the inside and the outer edge, and the molded product is dense throughout and has no cracks or laminations. Therefore, the thermal shock resistance is high, and the effect is particularly great for long ceramic tubes, such as the absence of cavities at the boundary between the particles and the matrix. After rubber press molding,
300-1, heat-treated at 200°C.

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. Also, 1, 2
If fired at temperatures above 00°C, thermal decomposition of the kaolin clay will generate a mullite liquid phase inside the brick, which, when solidified, increases the elastic modulus of the brick and therefore reduces thermal shock resistance, which is not preferable.

Next, embodiments of the invention will be described.

Example 100 parts by weight of sintered alumina, 10 parts by weight of kaolin clay and aluminum phosphate (50% aqueous solution - solid equivalent) 4
Part by weight of the mixed powder was added with water and kneaded.

The kneaded product was rubber press molded. Molding pressure 1,000kg
/cIA for 1 minute. The shape is length 7oowm x outer diameter? On, the inner surface is a regular hexagon and the distance between opposing surfaces is 40
It was a fraud. (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 1.200°C. The fired product had a bulk specific gravity of 2.85, an apparent porosity of 18.8%, and a compressive strength of 900 kg/aJ. 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. Ultrafine silicon carbide is a mixture of β-type silicon carbide with a particle size of 5 μM or less with clay, a binder, and water, and contains approximately 50% silicon carbide. After coating, it was dried and used. The coating material has the effect of closing pinholes, pinholes, 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 thus produced ceramic tube was used as a ceramic tube in a high-frequency induction heating furnace for forging. Round steel piece is approximately 30-36Mφ, length 150, weight 1.5
kg/item in a ceramic tube about 1
It passed at a speed of 70 mm/sec and was heated by high frequency induction. The three ceramic tubes described above were arranged in series, with a gap of 51 degrees between each tube. The oxide scale generated inside the tube is pushed by the round steel piece,
A portion of the liquid was made to be able to be discharged to the outside through this gap. The round steel piece is heated while passing through these three ceramic tubes, and at the exit the round steel piece is heated to about 1.200℃.
is heated to. 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,
The ceramic tube was used for about two months without any occurrence of the above-mentioned unbalanced load or buckling, and there was little wear on the sliding surfaces. 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, pull out the ceramic tube (3) from the fireproof structure (3), rotate it by a predetermined angle, and put it back into the fireproof structure (3).
3) Fitted inside.

[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, (3) ... Ceramic tube, (9) ... Insulating sheet, (10) ... Projection. Patent applicant Nippon Crucible Co., Ltd. Same as above Chuo Ceramics Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) 5 to 15 parts by weight of relatively hard fire-resistant aggregate
Parts by weight of kaolin clay and 1.5 to 6.5 parts by weight of aluminum phosphate in solid terms are added, kneaded with water, rubber press molded, and then heated at 300 to 1,200°C. A method for manufacturing ceramic tubes for induction heating furnaces. (2) Production of 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. Method. (3) The method for manufacturing a ceramic tube for an induction heating furnace according to claim 1 or 2, characterized in that the inner surface of the tube is coated with a coating material containing ultrafine silicon carbide as a main component.