JP3479217B2 - Steel heating apparatus and steel heating method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material such as a billet material, which is a material to be heated, when manufacturing various parts such as automobiles, construction machines, electric appliances, and agricultural machines by forging (plasticity) processing. The present invention relates to a steel material heating device and a steel material heating method used for heating.

[0002]

2. Description of the Related Art When manufacturing various mechanical parts by hot forging, the billet material to be heated is
After being heated by a heating furnace, it is forged. As a heating furnace that heats the billet material for forging, a combustion-type heating furnace was generally used, but it cannot be efficiently heated to a high temperature and the heating temperature is not easy to control. Induction heating furnaces that heat billet materials by electromagnetic induction heating have become widespread. The induction heating furnace is configured by winding a coil around a core tube in which the billet material is transported, and by energizing the coil, the billet material transported in the core tube is heated by electromagnetic induction. ing. The heated billet material is
Sequentially conveyed to the pressing step, and forged and pressed.

In the induction heating furnace, the billet material which is continuously conveyed is usually heated in order so that the billet material is heated to a high temperature of, for example, about 1200 ° C. at the outlet of the induction heating furnace. In this case, the low-temperature billet material carried into the induction heating furnace is rapidly heated by being carried into the induction heating furnace, and then sequentially heated to a predetermined temperature near the outlet of the induction heating furnace. To be done.

In a heating furnace for plastic working, it is necessary to uniformly heat the billet material to be conveyed to a predetermined temperature not only on the surface but also in the central portion. In an induction heating furnace that heats the billet material by electromagnetic induction, the higher the frequency,
There is a problem that the inside cannot be sufficiently heated because the eddy current concentrates on the surface of the billet material. Therefore, in the induction heating furnace, the billet material is heated in each heating block by dividing the billet material into a plurality of heating blocks along the conveying direction and setting the input energy density for each heating block. As an optimum mode, finally, the surface and the central portion of the billet material are configured to be soaked to a predetermined temperature.

FIG. 3 is a graph showing the input energy density pattern in the conventional induction heating furnace together with the temperature of the billet material. The induction heating furnace shown in FIG. 3 is divided into five heating blocks along the billet transport direction, and the input energy density is set in each heating block. The input energy density in each heating block is such that the billet material is rapidly heated to raise the surface to a predetermined temperature in the three heating blocks located on the upstream side in the carrying direction, and the energy density is set to the downstream side in the carrying direction. The two heating blocks located are set so that the heated billet material is soaked. As a result, the input energy density is set to the maximum in the heating block located on the most upstream side in the transport direction, and the input energy density gradually decreases as the heating block is located on the downstream side in the transport direction.

[0006] In the three heating blocks located on the upstream side, the total input energy density of 65 to the entire induction heating furnace is set so that the surface of the billet material is heated to a predetermined temperature in a relatively short time. About 75% is input, and in the two heating blocks located on the downstream side in the transport direction, the heat loss from the surface of the billet material is large, so the total energy required to soak the billet material is high. 9 to 22% of the total energy and 6 to 6% of the total energy required to supplement the radiation loss of heat on the billet material surface.
About 25 to 35% of energy, which is the total of about 13% of energy, is input.

In the induction heating furnace, in the press process for forging and pressing the heated billet material, it may be necessary to interrupt the supply of the heated billet material due to trial punching, the start of work, mechanical trouble, or the like. . In this case, if the heating work by the induction heating furnace is completely stopped, it takes a long time to bring the inside of the furnace to a predetermined heating temperature when the heating work is restarted. It is possible to switch to a heat retention mode in which the input energy density to the induction heating furnace is reduced and the billet material conveying speed is reduced without stopping. In the induction heating furnace that has entered the heat retention mode, the billet material is heat-treated in a decelerated state,
There is no fear that a large amount of billet material is unnecessarily heated before the work in the pressing process is restarted, and the input energy density is also reduced, so energy saving is achieved.

[0008]

In the heat retention mode, the total input energy density of the induction heating furnace is about 30 to 40% of the total input energy density during normal continuous operation. The pattern (ratio) of input energy density in the heating block is not changed. In this case, the radiation loss of heat from the surface of the billet material in the induction heating furnace does not change significantly even if the billet material transportation speed is reduced, so that the billet material is transported at a low speed. The radiation loss of heat from the surface becomes large. For this reason, in the heating block on the downstream side of the induction heating furnace in the transport direction, the radiant loss energy of the billet material cannot be sufficiently supplemented with the input energy density in the heat retention mode, so the billet material is heated to a predetermined temperature. There is a risk that heating will not be completed and heating will be insufficient.

In this case, if the total input energy density in the induction heating furnace is increased so that the billet material carried out from the induction heating furnace does not become insufficiently heated, the billet material is discharged in the heating block located on the upstream side in the conveying direction. The billet material that is excessively heated and is discharged from the induction heating furnace is excessively heated.

In such a heat insulation mode induction heating furnace, when the billet material is underheated or overheated, when the normal operation of continuously supplying the billet material to the pressing step is restarted, the pressing step is performed. The billet material that is not in a predetermined heating state is discharged as something that cannot be forged and pressed. As a result, even though the induction heating furnace is in the heat retention mode, waste billet material that cannot be pressed is generated in the pressing process, and energy is wasted by heating the waste billet material. However, there is a problem that economic efficiency is significantly impaired.

Further, when the billet material is continuously heated in the induction heating furnace, the billet material conveying speed may be greatly reduced depending on the type of billet material and the work of the pressing step in the subsequent stage. However, if the deceleration speed of the billet material is increased, the billet material is overheated in the midstream region in the transport direction of the induction heating furnace. Therefore, the transport speed of the billet material can be set only to about 50 to 60% of the transport speed in the normal continuous operation, and as a result, the billet material can be adapted to the type of the billet material, the work of the pressing process, and the like. There is also a possibility that the billet material cannot be heated.

The present invention is intended to solve such a problem, and its object is to have excellent energy efficiency, and moreover, to ensure uniform heating of a steel material to a predetermined temperature even in a heat retention mode. A steel material heating device and a steel material heating method capable of heating are provided.

[0013]

The steel material heating apparatus of the present invention is an induction heating furnace for sequentially heating a plurality of steel materials that are continuously conveyed by electromagnetic induction heating, and each steel material heated in the induction heating furnace. And an electric heating furnace that continuously heats by electric resistance heating.

The input energy density in the induction heating furnace is set to a pattern corresponding to the radiation loss energy density pattern of the heat of the steel material in the induction heating furnace.

The steel material heating method of the present invention is characterized in that the steel material is rapidly heated by electromagnetic induction heating so that the surface thereof has a predetermined temperature, and then is heated by electric resistance heating to equalize the temperature.

The input energy density in the electromagnetic induction heating is set in a pattern corresponding to the pattern of the heat radiation loss energy density of the steel material in the electromagnetic induction heating.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a steel material heating apparatus of the present invention. The steel material heating device is used, for example, to sequentially heat the billet material 30 which is a bar material having a circular cross section as a steel material which is a material to be forged. The induction heating furnace 10 is arranged on the upstream side in the direction, and the electric heating furnace 20 is continuously arranged on the downstream side in the conveying direction of the billet material 30 with respect to the induction heating furnace 10.

The induction heating furnace 10 is provided with three heating blocks 11 along the conveying direction of the billet material 30, and in each heating block 11, the central portion thereof is constituted by a silicon carbide refractory ceramic tube. The respective core tubes 13 are inserted in a horizontal state. A coil 14 is wound around the core tube 13 of each heating block 11.

A pinch roller 40 for carrying the billet material 30 into the furnace core tube 13 of the heating block 11 is provided further upstream of the heating block 11 in the carrying direction of the billet material 30 in the carrying direction of the billet material 30. It is provided. Billet material 30 by pinch roller 40
Are sequentially pushed into the core tube 13 of the heating block 11. Billet material 30 pressed into the core tube 12
Are sequentially and continuously conveyed in the core tube 13 of each heating block 11.

A conveyance detection roller 41 for monitoring the conveyance of the billet material 30 is provided between the pinch roller 40 and the induction heating furnace 10. The conveyance detection roller 41 allows the billet in the induction heating furnace 10 to be conveyed. Material 30 Congestion or stoppage is detected. When the conveyance detection roller 41 detects congestion of the billet material 30 or the like, the heating in the induction heating furnace 10 is stopped, whereby the billet material 3 is
0 is prevented from overheating.

Billet material 30 conveyed in the core tube 13
The coils 14 wound around the core tube 13 in each heating block 11 are energized to be electromagnetically induction heated while passing through the core tube 13 of each heating block 11.

In the electric heating furnace 20 which is continuously provided with the induction heating furnace 10, a conveying path 22 for conveying the billet material 30 is horizontally provided at the center of a furnace body 21.
A ceramic heater 23 is provided around the area 2.

In the induction heating furnace 10, each heating block 11
The energy density applied to the coil 14 is patterned and set in advance for each case. Further, in the electric heating furnace 20, the ceramic heater 23 is controlled so that the inside of the furnace has a predetermined temperature.

FIG. 2 shows an induction heating furnace 10 and an electric heating furnace 20.
3 is a graph showing the input energy density pattern and the radiation loss energy density pattern of the billet material in FIG. In the steel material heating device, the billet material 30 carried into the induction heating furnace 10 by the pinch rollers 40 is sequentially heated by electromagnetic induction heating in each heating block 11 in the induction heating furnace 10 and then heated to an electric heating furnace. It is soaked at 20. In this way, the billet material 30 is soaked in the electric heating furnace 20 in the latter stage, so that it is not necessary to soak the billet material 30 in the induction heating furnace 10 provided in the former stage. In the heating furnace 10, the surface of the billet material 30 is, for example, 1200
The input energy density may be set so that the surface temperature of the billet material 30 sequentially rises in the three heating blocks 11 so that the temperature becomes ℃. Therefore, in the induction heating furnace 10 having a large input energy density, the pattern of the input energy density required for heating the billet material 30 is the radiation loss energy density of the heat from the billet material 30 in each heating block 11. It is set to correspond to the pattern.

That is, in each heating block 11 of the induction heating furnace 10, the radiation loss of heat of the billet material 30 increases sequentially from the upstream side to the downstream side in the carrying direction, so that from the upstream side to the downstream side in the carrying direction. The heating blocks 11 arranged in order are patterned and set so that the input energy density of the heating blocks 11 sequentially increases. Therefore, the input energy density pattern (see FIG. 3) of the conventional induction heating furnace in which the billet material 30 is uniformly heated on the outlet side is a pattern of the input energy density which is completely opposite.

In this manner, when the billet material 30 is sequentially subjected to electromagnetic induction heating in the induction heating furnace 10, when the billet material 30 is charged from the induction heating furnace 10 into the electric heating furnace 20, the billet material 30 is charged. The surface of the sample has a high temperature of about 1200 ° C., while the central part has a temperature of about 700 ° C., which is lower than that. When the billet material 30 is put into the electric heating furnace 20 in such a state, the electric heating furnace 20 heats the central portion of the billet material 30 to a high temperature of 1200 ° C. similar to the surface, and the billet material 30 is heated. Heat soak 30. In this case, in the electric heating furnace 20, since the billet material 30 is electrically resistance-heated from the surroundings, radiation loss of heat from the surface of the billet material 30 is suppressed, and the billet material 30 is efficiently soaked. .

In such a steel material heating apparatus, when the supply of the billet material 30 is interrupted due to a trouble in the pressing process or the like, the induction heating furnace 10 and the electric heating furnace 20.
In, the feeding speed of the billet material is reduced, and the input energy density to the induction heating furnace 10 and the electric heating furnace 20 is reduced throughout. Therefore, the pattern (ratio) of the input energy density in each heating block 11 of the induction heating furnace 10 is not changed, and therefore the input energy of a size substantially proportional to the energy density of the radiation loss of the billet material 30. The billet material 30 is sequentially heated in each heating block 11 having a high density, so that the billet material 30 is not likely to be excessively heated on the upstream side in the transport direction, and is insufficiently heated on the downstream side in the transport direction. There is no fear.

Moreover, even when the billet material conveying speed is reduced during the continuous operation, excessive heating and insufficient heating of the billet material 30 are prevented in the same manner, whereby uneven heating of the billet material 30 occurs. Will be suppressed. In the steel material heating device of the present invention, even if the billet material 30 is conveyed at a normal speed of about 30%, the billet material 30
Can be heated to a predetermined temperature for uniform heating without causing excessive heating and insufficient heating.

[0030]

As described above, the steel material heating apparatus and the steel material heating method of the present invention are designed so that after heating the steel material in the induction heating furnace, it is soaked in the electric heating furnace. As compared with the case where the steel material is heated to a predetermined temperature in the induction heating furnace, the energy efficiency required for heating is improved. Moreover, even when the transportation of the steel material is slowed down or stopped, the steel material can be soaked to a predetermined temperature without overheating and insufficient heating. As a result, the amount of steel material wasted due to poor heating is significantly reduced, and economic efficiency is significantly improved. Further, since the inside of the electric heating furnace can be heated to a predetermined temperature in advance with a relatively small amount of power output at the start of operation, the amount of steel material wasted due to heating failure from the beginning of heating can be reduced. It is also possible to reduce the wasted power.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a steel material heating device of the present invention.

FIG. 2 is a graph showing the input energy density pattern and the radiation loss energy density pattern of the billet material in the steel material heating device together with the temperature of the billet material.

FIG. 3 is a graph showing a pattern of input energy density and a pattern of radiation energy density of a billet material in a conventional induction heating furnace together with the temperature of the billet material.

[Explanation of symbols]

10 induction heating furnace 11 heating block 13 core tube 14 coils 20 Electric heating furnace 21 furnace body 22 Transport path 23 heater 30 billet material

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F27B 9/36 F27B 9/36 H05B 3/00 375 H05B 3/00 375 6/10 341 6/10 341

Claims (4)

(57) [Claims] 1. An induction heating furnace for sequentially heating a plurality of steel materials conveyed by electromagnetic induction heating, and an electric heating furnace for continuously heating each steel material heated by the induction heating furnace by electric resistance heating. A steel material heating device comprising: 2. The steel material heating device according to claim 1, wherein the input energy density in the induction heating furnace is set to a pattern corresponding to a pattern of radiation loss energy density of heat of the steel material in the induction heating furnace. 3. A method for heating a steel material, which comprises rapidly heating the steel material to a predetermined temperature by electromagnetic induction heating and then heating the steel material by electric resistance heating to equalize the temperature. 4. The steel material heating method according to claim 3, wherein the input energy density in the electromagnetic induction heating is set in a pattern corresponding to the pattern of the heat radiation loss energy density of the steel material in the electromagnetic induction heating.