JPH03110380A - Vertical induction heating furnace - Google Patents

Abstract

PURPOSE:To prevent heat dissipation from the lower surface of a steel piece of a support beam and to uniformly heat the piece by disposing heat generators for generating heat by induction heating near the upper layer surface of a refractory heat insulator between the piece placing surface of the beam and the beam lower in height than the placing surface. CONSTITUTION:In a lower part charge type vertical induction heating furnace in which a steel piece 1 is erected laterally to heat in a state that the piece 1 is placed on an elevation beam 4, a heat generator 6 for generating heat by induction heating is disposed in the vicinity of the upper layer surface of a refractory heat insulator 4-3 between a steel piece placing surface of a support beam 4 in direct contact with the piece 1 and the beam lower in level than the placing surface of the beam. A heat generating substance 6 withstands against such temperature as being exhibited by the temperature rise of the refractory heat insulator through heating and heat supply from the steel piece. Refractory metal used for a support metal 4-1 is suitable therefor, and a material except the metal such as carbon brick can be sufficiently used. The size of the generator may be determined according to the required withstand temperature of the refractory heat insulator.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a vertical induction heating furnace for steel billets, and in particular, the present invention relates to a vertical induction heating furnace for steel billets, and in particular, to effectively prevent heat dissipation from the bottom surface of the billet during induction heating. This is intended to enable uniform heating of the pieces.

(Prior art) For example, as a heat treatment for steel slabs that require heating at high temperatures, such as slabs for grain-oriented silicon steel sheets, so-called vertical induction heating has been recently developed in which the steel slab is heated while standing upright in its width direction. A heating furnace is used.

In such a vertical induction heating furnace, charging and extraction of steel billets into the furnace is generally performed from below the furnace by lifting and lowering a lifting beam on which the steel billets are placed.

FIG. 3 shows the entire vertical induction heating furnace, and FIG. 4 shows details of the support structure.

In the figure, number 1 is a steel piece, 2 is a furnace wall, and 3 is an induction coil.
4 is a support beam. This support beam 4 is
It consists of a support hardware 4-1, a water cooling pipe 4-2, and a fireproof heat insulating material 4-3. Note that steel piece 1 is support hardware 4
-1, and is loaded into the furnace from the bottom using a lifting device (not shown).

Now, as shown in FIG. 4, support fittings 4-1 made of heat-resistant metal are arranged at appropriate intervals in the longitudinal direction of the steel piece.
It directly contacts and supports the steel piece 1. This heat-resistant metal support 4-1 is supported by a water-cooled vibe 4-2. Furthermore, this pipe 4-2, including a part of the support hardware 4-1, is lined with a fireproof heat insulating material 4-3, and has a structure to prevent heat transfer to the cooling water as much as possible.

However, such a support structure has the following problems.

In other words, in an induction heating furnace, the steel billet itself, which is the object to be heated, is the heating element, so if there is a low temperature area around it, heat transfer from the steel billet occurs, and the temperature of the steel billet itself decreases. .

Here, considering the transfer of heat based on FIG. 5, it is as follows. When the temperature of the steel slab 1 rises due to self-heating, heat transfer Q1 to the fireproof insulation material 4-3 occurs,
Then, heat diffusion Q2 into the inside of the heat insulating material, and further heat transfer Q to the cooling water via the water-cooled vibe 4-2, occur, and over time a steady state is reached and each part has a certain balanced temperature. What should be noted here is that since the heat source is the steel billet itself, the steel billet itself must generate heat by compensating for this amount of heat transfer.

On the other hand, in a portion of the steel billet where such heat transfer does not occur, such as the upper portion of the steel billet, the heat generated by the steel billet directly leads to an increase in the temperature of the steel billet. Therefore, depending on the location of the steel piece,
A non-negligible imbalance occurs in the temperature rise of the steel billet,
The temperature of the steel billet becomes uneven.

To prevent this, there has been an attempt to achieve uniform heating in the width direction by dividing the induction coil in the width direction of the steel billet and controlling each coil 5 individually, as shown in FIG. As long as there is a large heat transfer as described above in the lower part of the steel slab, it is inevitable that the steel slab will have a temperature distribution, and it was only possible to ensure the lowest temperature limit.

(Problem to be solved by the invention) Therefore, in order to prevent uneven temperature distribution, it is necessary to maintain the temperature at the bottom of the steel billet, in other words, at the top of the heating beam, by using another method instead of relying on heat transfer from the steel billet. It is necessary to compensate for heat transfer by the heat source.

Furthermore, in the upper part of the heating beam, if an induction coil is placed so that an induced current flows through the support hardware around the heat-resistant metal support hardware that is in direct contact with the steel piece, it will be possible to Since the temperature rises due to self-heating, the occurrence of heat transfer can be suppressed, but such heat transfer cannot be expected in the refractory insulation material between the support hardware, so the transfer of heat is particularly significant.

(Means for solving the problem) As mentioned above, in order to prevent heat transfer from the bottom surface of the steel slab, it is necessary to rely on heat input from the steel slab to maintain the temperature at the top of the lifting device. (It is necessary to rely on the equipment to generate its own heat. However, most of the materials that make up the lifting and lowering equipment are fireproof and insulating materials, and because no induced current flows through them, they do not generate heat on their own.

As a result of intensive research to solve the above problem, the inventors found that in order to compensate for the heat, it is sufficient to place something that generates heat by itself due to an induced current near the upper surface of the fireproof insulation material. Especially in this case, if you combine it with the thermal resistance of the fireproof insulation material, the heat transfer (heat loss) to the pipe cooling water can be reduced.
At the same time, it is possible to maintain the temperature of the part of the fireproof insulation material facing the steel billet high, suppressing heat transfer from the steel billet to the fireproof insulation material, and effectively preventing a drop in the temperature of the steel billet. I gained a lot of knowledge.

This invention is based on the above knowledge.

In other words, the present invention provides a bottom-charging vertical induction heating furnace in which the steel billet is placed upright in its width direction and heated while placed on a lifting beam, and the steel billet of the support beam is in direct contact with the steel billet. A vertical induction heating furnace in which a heating element that generates heat by induction heating is arranged near the upper surface of the refractory insulation material between the support beams, which has a lower height level than the R face and the steel piece mounting surface of the support beam. It is.

This invention will be specifically explained below.

FIG. 1 shows the structure of a steel billet support lifting device according to the present invention, and number 6 in the figure is a heat-generating substance embedded in the upper layer of the fireproof heat insulating material 4-3. The exothermic substance 6 may be any substance that raises the temperature of the fireproof insulation material when heated and can withstand the temperature reached in combination with the heat input from the steel slab, and is generally used for support hardware. Although heat-resistant metals such as those described above are suitable, other materials other than metals such as bricks can also be used.

The size of the heating element may be determined according to the required temperature of the fireproof/insulating material, and the required temperature can be easily determined experimentally or empirically.

(Example) In the place shown in Figure 1, the thickness of the heating element:
A 30ma+ cobalt-based heat-resistant metal was used, and the steel slab was heated at a target temperature of 1300°C.

After the heat treatment, the temperature distribution in the cross section AA' in the direction of arrows was investigated and the results are shown in FIG. The figure also shows the results of a study on temperature distribution when heat treatment was performed according to a conventional method that does not use a heating element.

Note that the amount of power input to the steel slab is the same.

As is clear from the figure, when a heating element is disposed, the temperature drop in the fireproof heat insulating material portion is significantly reduced compared to when a heating element is not disposed.

In terms of the amount of power input, the amount of power input to the steel slab is the same, but the amount of heat generated by the heating element, that is, the amount of heat consumed to maintain the fireproof insulation material at a high temperature, naturally leads to an increase in power consumption. There is. However, if you consider the improvement in quality and yield by eliminating the low-temperature part of the steel billet, there is a sufficient effect.

(Effects of the Invention) Thus, according to the present invention, uniform heating of the steel slab can be achieved by effectively preventing heat dissipation from the lower surface of the steel slab during induction heating of the steel slab.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the structure of a steel billet support lifting device according to the present invention, Fig. 2 is a temperature distribution diagram after heat treatment on the cross section AA' in Fig. 1, and Fig. 3 is: An overall view of the vertical induction heating furnace, Figure 4 is a detailed view of the support structure, Figure 5 is a diagram showing the transfer of heat from the bottom of the steel billet in a conventional vertical induction heating furnace, and Figure 6 is , is a longitudinal sectional view of a vertical induction heating furnace equipped with a split induction coil. 1... Steel piece 2... Furnace wall 3... Induction coil 4... Support beam 4-1... Support hardware 4-3... Fireproof insulation material 6... Heating element 4-2 ...Water cooling pipe 5...Split coil patent applicant

Claims (1)

[Claims] 1. In a bottom-loading vertical induction heating furnace in which the steel billet is heated while standing upright in its width direction and placed on a lifting beam, the support beam is in direct contact with the steel billet. A heating element that generates heat by induction heating is arranged near the steel billet mounting surface of the support beam and the upper surface of the fireproof insulation material between the support beams, which is lower in height than the steel billet mounting surface of the support beam. Vertical induction heating furnace.