JP2003138315A - Induction heater for steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heater which can reliably raise the temperature of a center part of a steel member to the temperature immediately below the liquidus, maintain a surface layer part in a non-molten condition, and feed the steel member to the next hot working in a most favorable condition. SOLUTION: In this induction heater to pass the steel member through an induction heating coil in the heater and heat the steel member, a cooling device 4 to allow a cooling medium to flow into a space between the heater body and the steel member 3 is disposed on an end part of the heater body. Preferably, a steel member surface temperature detecting means is provided on the outlet side of the heater body, and a means to control the heating quantity, the cooling medium quantity and the moving speed in a single or combined manner based on the detected temperature is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency induction heating apparatus for steel materials, and more particularly to heating steel materials supplied to hot working such as hot forging, hot rolling and hot rolling to a considerably high temperature. The present invention relates to an induction heating device that can be used.

[0002]

2. Description of the Related Art For example, an induction heating apparatus for steel materials is used as a means for heating a processing material to a predetermined temperature when supplying the processing material to hot working such as hot forging, hot rolling and hot rolling. Widely used. In particular, hot forging has been adopted as a means for forging various large mechanical parts with relatively complicated shapes, but recently, for the purpose of reducing deformation resistance and increasing formability, processing materials should be made as hot as possible. There is a demand for heating and forging.

Conventionally, when hot forging is performed after heating the surface layer of the material to a temperature in the vicinity of the liquidus line of the material to be processed in a non-oxidizing atmosphere, the hot workability is very good and the workability is excellent. It is disclosed that energy can also be reduced (Japanese Patent No. 2505999 and Japanese Patent No. 255593).
19). In heating the material using this high-frequency induction heating device, when trying to raise the temperature to just below the liquidus line to the center of the material, induction heating heats the surface layer of the material and conducts heat conduction from the surface layer to the inside. It is necessary to heat to a temperature above the liquidus, and the surface layer portion will be melted. The melting of the material causes the conveyance failure of the feed roller and the weight reduction of the material, resulting in the interruption of the forging work and the occurrence of the wall thickness of the forged product.

As a method for reducing the temperature difference between the surface layer and the inside of the processed material, two methods of (1) low frequency induction heating and (2) extension of induction heating soaking can be considered. The heating device (power supply, control panel, heating coil body) needs to be modified and the heating time is extended, and the latter requires modification of the equipment before and after the heating device extension. Remodeling and lowering productivity have become problems. In addition, Japanese Patent No. 2559319 also describes that when heating the steel material surface layer portion, the steel material surface layer portion is heated while being cooled by a non-oxidizing gas such as argon or nitrogen, but how is it specifically cooled? Or, because the equipment configuration is not disclosed explicitly, the feasibility is poor.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and reliably raises the temperature of the central portion of the steel material to a temperature just below the liquidus line, and the surface layer portion is in a non-melted state. An object of the present invention is to provide a high-frequency induction heating device that can be maintained and can supply the steel material to the next hot working in the most suitable state.

[0006]

The gist of the present invention for solving the above problems is as follows. (1) In an induction heating device that heats steel material through a high-frequency heating coil in the heating device body, a cooling device that causes a cooling medium to flow between the heating device body and the steel material is arranged at an end of the heating device body. A high frequency induction heating device characterized by the above. (2) The steel material and the heating device main body are relatively movable, and the cooling device is configured to allow the cooling medium to flow from the high temperature side to the low temperature side of the steel material (1)
Induction heating device as described. (3) The cooling medium is any one of air, nitrogen gas, argon gas, or a mixture thereof (1)
Alternatively, the induction heating device according to (2). (4) A steel material surface temperature detecting means is provided on the outlet side of the heating device main body, and means for controlling any one of a heating amount, a cooling medium amount, and a moving speed based on the detected temperature is provided. The induction heating device according to any one of (1) to (3).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a high-frequency induction heating device for heating a hot forging material. In the drawing, three heating device bodies are arranged on a line at intervals. The device itself is no different from the one normally used. That is, as shown in the drawing, three first to third heating device bodies 1a, 1b, 1c each having a high-frequency heating coil 2a, 2b, 2c inside are arranged in series at regular intervals, and the coil center is made of steel material in the arrow direction. (Steel billets) 3 are continuously conveyed and loaded in contact with each other. The conveyance of the steel material 3 is appropriately performed by a plurality of conveyance rollers 10 and a conveyance belt arranged on the inlet side of the heating device, between the heating device bodies, and on the outlet side. On the outlet side of the third heating device body 1c, there is provided a cooling device 4 for blowing a cooling medium (here, air) toward the surface of the steel material 3 that is heated to a predetermined temperature and extracted to cool the surface layer portion. is set up. Although not shown, a chute portion for feeding the steel material to the working tool (die) of the hot forging machine is installed behind the cooling device 4.

As a concrete example of the cooling device 4, as shown in FIG. 2, an annular shape (not a perfect annular shape, which is connected to the cooling main pipe 5) is used.
The cooling header 6 is formed by cutting away parts, and a plurality (six in the figure) of cooling nozzles 7 are arranged at equal intervals on the inner diameter side of the cooling header 6. The cooling nozzle 7 is shown in FIG.
As shown in (a), on the inlet side of the steel material 3, it is installed toward the center of the cooling header 6 and at a certain angle with respect to the surface of the steel material, and is fed along the center line of the annular cooling header 6. A cooling medium (air) is caused to flow so as to face the feeding direction of the coming steel material 3 to cool the surface of the steel material. The cooling device 4 is preferably installed as close to the end of the heating device body as possible, but it is necessary to prevent it from being heated by the heating coil. Also, the cooling header 6
The diameter or shape may be appropriately changed according to the cross-sectional size or shape of the steel material, and the number of cooling nozzles can be arbitrarily changed. Therefore, it is convenient if the entire cooling device is of a cassette type and can be replaced by the heating device side.

In addition, in the induction heating apparatus of FIG. 1, between the first heating apparatus main body 1a and the second heating apparatus main body 1b, the second heating apparatus main body 1a is provided.
Between the heating device main body 1b and the third heating device main body 1c, and on the outlet side of the cooling device 4, thermometers 8a, 8b, 8c for measuring the surface temperature of the steel material 3 are installed, respectively. A thermometer 9 for measuring the temperature of the center of the steel material that has been heated on the line is installed on the outlet side.
As the thermometer, a radiation thermometer that can measure temperature without contact is used. In addition, the thermometer 8 for measuring the intermediate surface temperature
It is also possible to omit a and 8b.

In actual operation, in the apparatus shown in FIG. 1, for example, a steel material (billet) 3 having a circular cross section is sequentially supplied from the inlet side of the first heating device body 1a at room temperature (room temperature), and is conveyed by the conveying roller 10. The high-frequency heating coils 2a, 2b passing through the trailing material while being conveyed while pushing the preceding material,
The surface layer portion is induction-heated stepwise by 2c. By heating the surface layer of the material, the entire cross section of the material is heated by heat conduction from the surface layer to the inside. In such a heating process, in order to heat the center of the steel to a temperature just below the liquidus line, it is necessary to heat the surface layer to a temperature higher than that, and particularly in hot forging, the material diameter is relatively large. Since it is usually (φ 40 mm or more), there is a problem that the heat energy does not reach the inside unless the surface layer portion is heated to a temperature exceeding the liquidus due to the heat conduction characteristic.

Therefore, in the present invention, as shown in FIG. 1 and FIG. 2, the surface layer cooling device 4 (cooling nozzle 7) installed on the outlet side of the heating device moves from the outlet side of heating toward the inlet side (high temperature of steel material). The cooling medium (air) was injected from the side toward the low temperature side to cool the steel surface layer. The air blown from the nozzle 7 to the surface layer of the steel material collides with the steel material and then flows along the surface layer of the steel material in a direction opposite to the traveling direction of the steel material while weakening the cooling capacity. FIG. 3 conceptually shows the heating process and the surface layer cooling process of the present invention. Although the material surface temperature and the central temperature largely deviate in the intermediate process of heating once, the surface cooling by air injection from the cooling device is effective. As, the difference between the surface temperature and the central temperature begins to decrease, and finally the central temperature rises to a temperature just below the liquidus line. At this time, the surface temperature does not exceed the liquidus temperature. If the surface layer is not cooled, the surface temperature becomes the temperature shown by the broken line, and the center temperature exceeds the liquidus temperature before reaching the position just below the liquidus line.

In the heating / cooling process described above, heating control is performed in comparison with the target temperature while constantly measuring the material surface temperature and the central temperature with the thermometers 8a, 8b, 8c and 9. . The flow of temperature control of steel is shown in FIG. In FIG. 4, since the physical properties of steel materials differ depending on their components, the liquidus temperature T ₀ is confirmed in advance from the physical property values of the steel materials. Next, based on this liquidus temperature and the predicted operation fluctuation, the upper limit temperature T ₁ of the material surface layer and the minimum required temperature T _{2 of the} material center portion (generally T ₀ −
After setting artificially about 20 ° C), the standard heating temperature pattern of the steel material is calculated and set in consideration of the capability of the heating device used. That is, here, the surface temperature between each heating coil, the surface temperature of the final heating coil outlet side, and the cross-sectional center temperature on the final heating coil outlet side are set, the heating pattern corresponding to this is determined, and the heating device and the cooling device are set. Determine the output value of. The definition of each temperature in FIG. 4 is as follows. T _1: the third heating device out surface configuration in side temperature T _2: the third center setting of the heating device delivery temperature T _3: the second heating device - the surface layer measured temperature T ₄ of between the third heating device: the 3 surface temperature measured on the outlet side of the heating device T ₅ : center measured temperature on the outlet side of the third heating device T ₆ : surface temperature measured between the first heating device and the second heating device actual measurement value T _{5 of the} cross-section center temperature Is the minimum required temperature T _{2 at the} center and the measured value T _{4 of the} surface temperature on the outlet side of the final heating coil is compared with the upper limit temperature T _{1 at the} surface, which is T ₄ ≦ T ₁ and T ₅ ≧
If the condition of T ₂ is satisfied, the heating pattern of the steel material is considered to be satisfactory, and the steel product is directly sent to the next step (for example, forging step).

However, the measured value is T_Four≤T₁And T_Five≧ T
₂If the conditions of are not met, the temperature control is
I need to change my mind. That is, the case where the conditions are not met
As T_Four> T₁And T_Five≧ T₂, T_Four> T₁
And T_Five<T₂, T_Four<T ₁And T_Five<T₂I thought
In addition, the respective insufficient temperature or excessive temperature is calculated.
Will be issued. On the other hand, in the present invention, the material heating device
Transport speed, heating coil voltage and surface cooling air volume
This may be a single item or a combination of two or more of these items.
Perform heating control by selecting the desired heating pattern.
Controls the temperature of steel. For example, the case
Then, increase the transfer speed or change the voltage of the induction heating coil.
Lower, or any combination of these, the steel surface
This is dealt with by lowering the temperature of the layer and the center,
In this case, increase the transfer speed or increase the voltage of the induction heating coil.
Lower it, increase the airflow of the cooling system, or these
Surface temperature T of the steel with any combination of_FourLowering steel
Material center temperature T_FiveDeal by raising. The case
In this case, slow down the transfer speed or reduce the voltage of the induction heating coil.
Increase the air volume, reduce the air flow in the cooling device, or
With any combination of these, to raise the surface temperature of steel
Deal more. Adopting such a control method of the present invention,
Change in heating rate of steel, change in steel size, and liquidus line for each steel
Capable of coping with temperature changes without changing equipment
Makes it possible.

Further, although the intermediate surface temperature measurement values T ₃ and T ₆ are not particularly used in the above control flow, finer temperature control may be performed in some cases if these measured values are also controlled. It is possible. In this case, it is preferable that cooling devices are arranged on the outlet sides of the first and second heating device bodies 1a and 1b, respectively, and the steel material surface layer is cooled for each heating device. By doing so, the surface layer of the steel material can be gently heated, which is effective for steel materials having a large cross-sectional size.

In the illustrated example, three heating device bodies are installed in series, but the present invention is not limited to this, and a single, two, or more arrangement may be used. The number of heating device bodies may be selected in consideration of the type of subsequent hot working, the type and size of steel material (particularly, the cross-sectional size), and the productivity. For example, when a billet having a small cross section is made of steel, the purpose can be sufficiently achieved by heating with a single or two heating device main bodies.

Further, in the above description, an example of heating the material used for hot forging is described, but the present invention is not limited to this.
Hot rolling of steel bars and wire rods at temperatures just below the liquidus line by high frequency induction heating and combustion burner heating in rolling, and hot rolling of gears at temperatures just below the liquidus line by high frequency induction heating and combustion burner heating in rolling Similarly in
When heating a steel material shape having a distance from the surface layer to the center, it can be applied to equipment for heating to the temperature just below the liquidus line to the center of the steel material without melting the surface layer.

[0017]

EXAMPLE A case where the present invention is applied will be described below as an example taking the case of heating a hot forging material as an example. [Implementation conditions] Hot forging material: Steel type S48, diameter 67.5φ x length 19
7 mm, liquidus temperature 1280 ° C., target material center minimum temperature (T ₂ ) 1260 ° C. Heating device: 3 division type high frequency induction heating shown in FIG. 1,
The specifications are shown in Table 1, and the operating conditions are shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

[Results of Implementation] When the steel material was heated under the above conditions, the temperature transition of the steel material was as shown in FIG. For comparison, FIG. 5 also shows an example in which the surface layer of the material is not cooled at all. As can be seen from the figure, when the surface layer of the steel material is cooled by air spray (wind speed is 10 m / s), the temperature of the surface layer is suppressed to 1275 ° C.
The temperature is 0 ° C, whereas the center is 125 without cooling.
Even at 0 ° C, the surface layer reached 1370 ° C, and melting was recognized. Therefore, when air spray cooling is used, uniform cooling is possible while preventing melting of the surface layer of the steel material, and the temperature difference between the surface layer and the center of the steel material is 120 ° C in the example in which cooling is not performed, but in the present invention, up to 25 ° C It is shrinking. In the present invention, as shown in Table 2, the material cycle time (the time required to process one material in the forging process) is 11.
Although it is 6 seconds, the cycle time without conventional cooling is about 15 to 16 seconds, which is shortened, and it is also confirmed that it contributes to the improvement of productivity in the forging process as a result. It was

[0021]

According to the high-frequency induction heating apparatus of the present invention described above, it is possible to reliably raise the temperature of the central portion of the steel material to a temperature just below the liquidus line while maintaining the surface layer portion of the steel material in a non-molten state. This makes it possible to supply the steel material to the next hot working in the most suitable state, and contributes to the improvement of operability, yield and productivity in the next hot working. Moreover, in terms of equipment, there is also an advantage that the cooling device can be arranged without significantly modifying the conventional heating device.

[Brief description of drawings]

FIG. 1 is an overall schematic view showing an embodiment of an induction heating device according to the present invention.

FIG. 2 is a diagram showing a specific example of the cooling device in FIG.
(A) is a partial cross-sectional side view and (b) is a front view.

FIG. 3 is a schematic diagram showing a relationship between a material temperature and a heating time when a steel material is heated by applying the present invention.

FIG. 4 is a control flow chart when heating and controlling a steel material using the apparatus of the present invention.

FIG. 5 is a diagram simulating the relationship between temperature and time from the start of heating to the end of heating of the steel material (S48) in the example of the present invention.

[Explanation of symbols]

1a-1c Heating device main body 2a-2c High-frequency heating coil 3 Steel material 4 Cooling device 5 Cooling main 6 Cooling header 7 Cooling nozzle 8a-8c Surface layer thermometer 9 Center part thermometer 10 Conveying roller

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuru Nakamura             12 Nakamachi, Muroran City, Hokkaido Nippon Steel Corporation Stock             Muroran Works (72) Inventor Osamu Kada             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Masahiro Toda             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Koichi Morishita             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Haruhiko Segawa             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Motohide Mori             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Kohei Segawa             1 Wano Wari, Arao-cho, Tokai-shi, Aichi Made in Aichi             Within Steel Co., Ltd. (72) Inventor Yasuo Hirose             1 Wano Wari, Arao-cho, Tokai-shi, Aichi Made in Aichi             Within Steel Co., Ltd. (72) Inventor Shoji Iwaki             1 Wano Wari, Arao-cho, Tokai-shi, Aichi Made in Aichi             Within Steel Co., Ltd. F term (reference) 3K059 AA09 AB04 AB19 AB20 AB26                       AC33 AD03                 4K034 AA03 BA08 CA01 CA03 DA06                       DB02 DB03 DB04 FA01 FB03

Claims (4)

[Claims] 1. An induction heating apparatus for heating a steel material through a high-frequency heating coil in a heating apparatus main body, wherein a cooling device is provided at an end of the heating apparatus main body for introducing a cooling medium between the heating apparatus main body and the steel material. A high-frequency induction heating device characterized by being arranged. 2. The steel material and the heating device body are relatively movable, and the cooling device is configured to allow the cooling medium to flow from the high temperature side to the low temperature side of the steel material. High frequency induction heating device. 3. The high frequency induction heating device according to claim 1, wherein the cooling medium is any one of air, nitrogen gas, argon gas, or a mixture thereof. 4. A steel material surface temperature detecting means is provided on the outlet side of the heating device main body, and means for controlling any one of a heating amount, a cooling medium amount and a moving speed based on the detected temperature is provided. The high frequency induction heating device according to any one of claims 1 to 3, which is characterized in that.