JP2002372382A - Temperature control method in high frequency heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance temperature control accuracy of a work, i.e., a steel band sprayed with powder, when the temperature of the work is controlled by the atmospheric temperature at the time of high frequency heating. SOLUTION: When an work 7 including a steel band is subjected to high frequency heating with an output controlled not lower than the Curie point of the steel band while traveling in a heating furnace at a controlled speed, light radiated from the work 7 is received by a radation thermometer 12 and the temperature is measured. The measured temperature is compared with a reference temperature (3) and the high frequency output is corrected depending on the temperature difference (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling temperature in induction sintering, tempering, annealing, quenching and the like.

[0002]

2. Description of the Related Art The most common method of producing a bimetallic sintered bearing alloy comprising a backing metal substantially made of steel and a bearing alloy sintered layer bonded to the backing metal is based on the fact that the entire sintering is performed by electric resistance. This is a method performed in a heating furnace. The powder having the composition of the copper alloy sintered layer is laminated on the backing metal, the copper alloy powder and the backing metal are induction-heated by a high frequency induction by a solenoid coil, and preheated to the vicinity of the Curie point of the steel of the backing metal in a reducing atmosphere, followed by firing. A sintering method by raising the temperature to a sintering temperature in a reducing atmosphere of an electric resistance furnace to form a copper alloy sintered layer and joining this layer to the back metal is known from Japanese Patent Publication No. Hei 7-26125. . In this method, it is stated that the entire length of the sintering line is expected to be shortened by rapid temperature rise by high-frequency induction heating, and that production efficiency is expected to be increased. A similar method has also been proposed in Japanese Patent Publication No. 1-503150, which states that the lead phase, which is the secondary phase of the copper alloy, is finely divided. In a sintering example using a back metal having a thickness of 0.075 inches, the sintering time in the electric furnace is 5.1 minutes.

The present inventors have tried various methods of measuring the temperature in high-frequency sintering. (1) In high-frequency induction heating, the steel sheet temperature is different from the ambient temperature because the steel sheet is directly heated, and the ambient temperature is measured with a thermocouple. Even though the temperature of the steel plate (work) cannot be controlled, the light emitted from the work (ro) physically indicates the apparent temperature, but to correct this to the actual temperature, the emissivity or emissivity ratio Can be used;
(2) Focusing on the fact that the synchrotron radiation sensor is of a non-contact type with the workpiece and can be installed at a position that is not affected by high-frequency induction, the temperature measurement method shown in FIG. 1 was devised (February 2000). Japanese Patent Application No. 2000-25136 (hereinafter referred to as “first application”)
Say). That is, in FIG. 1 in which the illustration of the sintering furnace body and the coil is omitted, reference numeral 12 denotes a radiation thermometer.
A radiation thermometer (trade name: IRC) manufactured by Company O can be used. The radiation thermometer is provided with a total of four radiation thermometers 12a for measuring the front surface of the work 7, 12b and 12d for measuring the edge of the rear surface, and 12c for measuring the center of the rear surface. Backside measurement radiation thermometer 12b, 12c, 1
2d can directly measure the temperature of the back metal, and the work surface measurement radiation thermometer 12a can measure the temperature of the powder through a heat-resistant glass 15a such as quartz glass provided as a window of the protective tube 22. Radiation thermometers 12b, c, d
Receives radiated light from the work 7 through a heat-resistant glass 15d such as quartz glass.

In normal electric resistance heating, the temperature of a work is controlled by controlling the ambient temperature. On the other hand, in the high-frequency heating, the present applicant performs a method of performing heating by setting high-frequency power in advance according to physical properties such as dimensions, specific gravity, specific heat, and electrical conductivity of the object to be heated, a sintering temperature, and the like. Have been.
In the conventional method, an empirical method of accumulating and correcting such setting and temperature measurement data was performed.

On the other hand, the temperature of the work is also affected by factors other than the above, such as the latent heat of the atmosphere protective tube stored during processing and the gas flow in the furnace subject to seasonal fluctuation, and is ± 40 ° C.
The above temperature fluctuation occurred. The conventional control method could not cope with the temperature fluctuation of the work due to these factors.

[0006]

SUMMARY OF THE INVENTION In the high-frequency heating method which has been conventionally performed by the present applicant, high-frequency power is set based on accumulated data. Therefore, when there is a disturbance, the temperature of the work greatly fluctuates.

[0007]

According to the method of the present invention, an object to be heated comprising a steel strip is controlled at a temperature above the Curie point of the steel strip while traveling through a heating furnace at a controlled speed. When performing high-frequency sintering at the output, infrared radiation radiated from the object to be heated is received by a radiation thermometer and measured for temperature.The measured temperature is compared with a reference temperature, and the high-frequency power is corrected according to the temperature difference. This is a temperature control method in high-frequency heating characterized by performing.

[0008]

First, as a method of high-frequency induction heating, a method of constantly controlling the temperature irrespective of product number information is also possible. For example, the temperature rises rapidly at 100% of the output of the heating device specification, and after reaching a predetermined heating temperature, the output is reduced.
This is a method of on-off control. This method is effective in the case of large disturbance or heating control in a temperature range below the Curie point where the temperature rise rate is high. However, in sintering such as bimetallic plain bearings, the temperature rise rate is about 10 ° C / sec, not high speed, and high-frequency induction heating directly heats the work, and high-frequency induction is applied to objects other than the object to be heated. And there is relatively little disturbance. Therefore, in the present invention, high-frequency induction heating with a constant output is performed in a temperature range equal to or higher than the Curie point temperature. Under these heating conditions, if the protection tube accumulates heat by successively applying high-frequency induction heating to a long coil or a large number of coils, the protection tube becomes a heat source, causing a change with time that gives the work an unspecified amount of heat. Need to be controlled.

At temperatures above the Curie point of steel, the heating efficiency is lower than at temperatures below the Curie point, making it difficult to control the temperature at a constant output. The range allows the control to follow temperature changes and allow for temperature compensation. On the other hand, if the temperature is lower than the Curie point, the temperature of the work is saturated at the Curie point, and thus the necessity of control is small. Next, for example, in a situation where two phenomena occur at the same time when the high-frequency output increases and the line speed decreases, since the temperature of the work rises above the set temperature increase, in the present invention, by keeping the line speed constant, Temperature fluctuation due to control can be suppressed. Alternatively, when it is desirable to make the line speed variable, the work can be maintained at the set temperature by detecting the line speed and adjusting the high-frequency power.

The method of high-frequency induction heating above the Curie point in the present invention is not particularly limited, but it is preferable to employ the transverse coils 10 and 20 shown in FIG. Hereinafter, an embodiment of the present invention will be described with reference to FIG.

The output of high-frequency induction heating depends on the thickness of the work,
The part number information such as sheet width, sintered powder thickness, processing temperature, sheet passing speed, etc.
The heating control device 2 calculates the high-frequency power to be applied to the transverse coil 10 by using a programmed calculation formula. The output signal sets the high-frequency current of the transformer 4 and passes through the matching coil 5 to the transverse coil 20.
Flows as the output (Pc) current calculated. That is, the high frequency current of the set output is always supplied to the work 7. When the passing speed is variable, the passing speed is detected by a passing speed sensor such as an encoder, and the detected speed is compared with a setting signal by the setup computer 1.
Output correction is performed using the obtained comparison signal. Normally, high-frequency power at a rate of 60 to 80% of the set output of the heating device is constantly guided to the work 7. The temperature of the work 7 is measured by the radiation thermometer 12 at a predetermined position ahead of the transverse coil 10 in the work feeding direction, and the measured temperature signal is transmitted to the temperature controller 8. After the leading edge of the steel strip has passed, the correction control system is activated.

The temperature controller 8 calculates a difference between the set temperature and the actually measured temperature, and transmits a PID-controlled temperature control signal to the heating control device 2. In the heating control device 2, the temperature control signal (Pd) (−50 to
50%) is multiplied by a set ratio da (for example, da = 0.05) to correct the set output Pc. Correction output Pa is, for example, Pa = da × P
d × Pc + Pc. In terms of output specifications, there is a margin of 20 to 80%, so Pd × Pc + Pd = Pa can also be set. However, in this case, thermal fluctuations that cannot be calculated by heat may reach the work. As described above, the correction output is kept low.

By performing high-frequency induction heating with the corrected output, and subsequently performing temperature measurement and control, the temperature of the work can be controlled with high accuracy.

[0014]

According to the present invention, it is possible to maintain a work at a set temperature with a high degree of accuracy with respect to aging. For example, 1.5 for a target temperature in the range of 900 to 1000 ° C.
The temperature change of the ton coil can be kept within a range of ± 5 ° C. As long as there is no disturbance, the high-frequency output is kept constant, and high-frequency induction heating is performed under conditions that match the specific heat and mass of the work. Any disturbance occurring in the furnace is detected by the temperature change and the control system is activated, so that stable production is realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method of measuring a temperature with a radiation thermometer in a high-frequency induction heating furnace.

FIG. 2 is an explanatory diagram of a transverse coil.

FIG. 3 is an explanatory view of one embodiment of the method of the present invention.

[Explanation of symbols]

 1 Setup computer 2 Heating control device 4 Transformer 7 Work 10 Transverse coil 12 Radiation thermometer 20 Transverse coil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidetomo Sato 3-65 Midorigaoka, Toyota-shi, Aichi Prefecture Inside Daitoyo Kogyo Co., Ltd. (72) Inventor Tsuneya Tsuzuki 3-65, Midorigaoka, Toyota-shi, Aichi Pref. (72) Inventor Hiroaki Kobayashi 3-65 Midorigaoka, Toyota City, Aichi Prefecture Inside Daitoyo Kogyo Co., Ltd. (72) Inventor Akio Ota 13-4 Kodenma-cho, Nihonbashi, Chuo-ku, Tokyo Japan Ajax Magnesamic Co., Ltd. F term (reference) 3K059 AA01 AB19 AB26 AB28 AC33 AD03 AD15 BD01 CD02 CD14 CD18 CD40 CD64 CD73 CD75 4K018 DA26 4K034 AA09 DA06 DB02 4K056 BB07 CA02 FA12

Claims (2)

[Claims] 1. A method for heating an object to be heated comprising a steel strip in a heating furnace at a controlled speed while performing high-frequency heating at a controlled output above the Curie point of the steel strip. Temperature control in high-frequency heating, characterized by receiving radiation emitted from an object with a radiation thermometer, measuring the temperature, comparing the measured temperature with a reference temperature, and correcting the high-frequency power according to the temperature difference Method. 2. The temperature control method according to claim 1, wherein the emitted light is infrared light.