JPH024551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ceramics for sleeves in non-melting induction heating furnaces for steel materials. Furthermore, the present invention relates to ceramics for sleeves of groove-type non-melting induction heating furnaces for steel materials. High-frequency or low-frequency induction heating furnaces are often used to heat metal or steel materials for metal processing such as forging or extrusion. This induction heating furnace has been widely used as a simple heating device for heating relatively small metals or steel materials, but in recent years, conventional induction heating furnaces have required special coils to be prepared for different sizes of steel materials. The loss of replacement and adjustment time for the dedicated coil and the initial cost of the dedicated coil are large. Moreover, problems such as large energy loss have become apparent. That is, in a typical conventional induction heating furnace, a steel material to be heated is placed on the central axis of a spirally wound induction coil, and skid rails are provided to allow movement. The steel material to be heated is pushed through the coil from behind by a pusher and is heated while sliding on the skid rail. However, in this type of induction heating furnace, the steel to be heated moves while contacting the skid rail, and the skid rail may wear out due to sparks generated between the steel to be heated and the skid rail, and the steel to be heated in contact with the skid rail may be damaged. There are various disadvantages such as uneven heating due to cooling by heat conduction, the need to make the coil larger only in the area where skid rails are installed, and large heat loss from the steel surface. It was something that had. The present invention provides ceramics for induction heating furnaces that can be suitably used in new induction furnaces that do not have skid rails and eliminate the drawbacks of conventional induction furnaces. This is a ceramic for a sleeve of a non-melting induction heating furnace for steel material, which is made by adding an auxiliary agent and baking it after forming. As mentioned above, in conventional induction furnaces, the steel material to be heated moves on skid rails.
In extreme cases, the ceramic sleeve provided inside the coil would not suffer wear and tear even if it were made of castable material, as long as it could thermally withstand the heating by radiation from the steel to be heated. However, in an induction furnace that eliminates the drawbacks of conventional induction furnaces, in which the steel to be heated moves while contacting the inner surface of a ceramic sleeve without using skid rails, It must be resistant to abrasion, and must also withstand thermal radiation from the heated steel material, rapid heating due to this radiant heat, rapid cooling after the heated steel material has passed, that is, thermal shock; Since it is necessary to withstand the high temperature oxidizing atmosphere in the furnace, it is generally a severe requirement for ceramics to provide ceramics that satisfy all of these requirements. The present inventors solved this problem while applying it to an actual induction furnace, and were able to arrive at the present invention. In particular, this problem is particularly difficult for ceramics because in order to improve wear resistance, ceramics must be made denser, and if ceramics are made denser, their thermal shock resistance will be poorer. It relies on the antinomic characteristics common to ceramics. From the above points of view, we first selected a ceramic material with high hardness, increased its density to raise its wear resistance to a satisfactory level, and then worked on improving its thermal shock resistance as the next step, making it possible to use an actual induction furnace. As a result of our efforts to obtain the most suitable ceramics, we have obtained the present invention as summarized above.The ceramics of the present invention will be further described in detail. Silicon nitride and silicon carbide are known to be hard materials with relatively small coefficients of thermal expansion. Although various methods have been proposed for making this material into a dense molded body, there have been no reports yet on silicon nitride ceramics or silicon carbide ceramics that can be suitably used in the above-mentioned induction furnace. The present inventors have found that silicon nitride ceramics or silicon carbide ceramics that are fired under atmospheric pressure, that is, added with an appropriate sintering aid, molded, and then fired in an atmospheric pressure atmosphere, can be suitably used in induction furnaces. As we have discovered, these ceramics preferably have a bulk density of 90% or more of the theoretical density from the viewpoint of abrasion resistance, and from the viewpoint of thermal shock resistance, a bending strength of 20 kg/mm ² or more and an expansion coefficient of 50 x 10. It is preferable that the temperature is ^-7 °C ^-1 or less. In order to satisfy the above characteristics, Ca, Fe, Cr, Mn must be added as impurities in silicon nitride or silicon carbide raw materials.
may exist in trace amounts, but if the amount
If Fe 3, Ca 0.5, Mn and Cr exceed 0.1% by weight, low melting point compounds will be generated at the grain boundaries and the strength at high temperatures will deteriorate, so Fe 3, Ca 0.5, Mn
and Cr should be kept at 0.1% by weight or less. The method for manufacturing the ceramics of the present invention using the above raw materials does not need to be specified, and in the case of silicon nitride ceramics, known sintering accelerators such as magnesia, spinel, ittria, etc. 0.5 to 10 for one or more selected types
In the case of silicon carbide ceramics, one or more selected from alumina, carbon, boron carbide, and boron oxide are added in an appropriate amount of 0.1 to 20% by weight, and cast molding, extrusion molding, etc. It may be formed into a desired shape and size, such as a sleeve shape or a circular half-groove shape, by a conventional molding method, and then fired. Example 1 Silicon nitride powder with an average particle size of 2μ (Ca as an impurity)
(containing 0.3, Fe 1.5, Cr 0.07wt%) and magnesia as a sintering aid in the proportions shown in Table 1.
A sleeve was molded using a rubber press method. This sleeve was heated at 1700° C. for 10 hours in a nitrogen atmosphere to obtain a fired ceramic sleeve having an inner diameter of 100 mm, a wall thickness of 9 mm, and a length of 500 mm. The coefficient of thermal expansion of this material is also listed in Table 1. Next, these sleeves were placed inside a coil with an outer diameter of 129 mm, and while a current was applied to the coil, the outer diameter of the sleeve was 80 mm.
A round steel plate with a length of 300 mm was moved while being in contact with the inner surface of the sleeve, and heated from room temperature to 125°C.
The above-mentioned round steel was operated for 3 months on a basis of heating 100 rounds per day. Afterwards, as a result of investigating the tested ceramic sleeve, no cracks were found, and only the wear and tear shown in Table 1 was observed in the part that was in contact with the round steel, so it is still reusable. It was in a state of Example 2 Silicon carbide powder with an average particle size of 2μ (Al as an impurity)
0.9, Fe 1.5, C 1wt%) was mixed with alumina as a sintering aid in the proportions shown in Table 1.
A sleeve was molded using a rubber press method. This sleeve was heated at 2000° C. for 5 hours in a nitrogen atmosphere to obtain a fired ceramic sleeve having an inner diameter of 100 mm, a wall thickness of 9 mm, and a length of 500 mm. The coefficient of thermal expansion of this material is also listed in Table 1. The sleeve thus obtained was tested in the same manner as described in Example 1. After the test, no cracks were observed in the sleeve.
The parts that were in contact with the round steel showed wear and tear as shown in Table 1, and could still be reused. 【table】

Claims (1)

[Claims] 1. Adding a sintering aid to silicon nitride or silicon carbide,
Ceramics for sleeves in non-melting induction heating furnaces for steel materials, which are formed and fired after forming. 2 The sintering aid for silicon nitride is one or two selected from the group of magnesia, spinel, and ittria.
The ceramic for a sleeve of a non-melting induction heating furnace for steel material according to claim 1, which is a type or more. 3. The ceramic for a sleeve of a non-melting induction heating furnace for steel materials according to claim 1, wherein the sintering aid for silicon carbide is one or more selected from the group of alumina, carbon, boron carbide, and boron oxide.