JPS5838483A - Resistance heating method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance heating method for heating an object to be heated by applying electricity thereto.

In the case of total resistance heating of an object to be heated, such as spring steel, conventionally the heating was controlled in stages according to the elapse of the applied voltage Vi waiting time, as shown in FIG. Initial (tg-tt
) is set to a low voltage (v+) in order to completely prevent the generation of sparks due to the low temperature of the heated object and its low resistance.
V3) in order to reduce the variation in heating temperature by 1-1.

However, if the applied voltage v'1 is controlled stepwise as described above, as the resistance of the heated object increases with the rise in temperature, the heating power P decreases as shown in FIG.
The time required to reach the predetermined temperature To (ts-to) becomes longer.

If you increase the level of the applied voltage V to prevent this and increase production speed, will it cause damage to the heated material or current-carrying electrodes due to generation of sparks, uneven heating temperature, or other problems? There is a risk that this may occur. Further, as described above, since the heating power P is significantly reduced from the maximum of one shift PO, there are drawbacks such as low usage efficiency of the heating power supply device.

The present invention was made under the above circumstances, and its purpose is to shorten the heating time without causing the above-mentioned problems, thereby increasing the productivity as well as improving the efficiency of the power supply device. Another object of the present invention is to provide a resistance heating method that can be used as described above.

Hereinafter, the present invention will be explained with reference to the drawings. In FIG. 3, the heated body a is formed into a rod shape with a constant cross-sectional area S, for example, from spring steel having a specific resistance of ρ. A pair of electrodes 1 and 2 are attached to the heated body a via a desired heating region (the effective length is L). If desired, tension in the longitudinal direction may be applied with or without the electrodes 1 and 2 so that the heated body a does not sag.

The electrodes 1 and 2 are connected to the output end of a heating power supply device 3 including a transformer, etc., and variably control the voltage applied between the electric signs 1 and 2. Also, the temperature of the heated object a A radiation thermometer 5 is provided oppositely located substantially in the center of the desired heating area to detect the temperature, and the output signal of the radiation thermometer 5 is guided to the voltage control device 4. The voltage control device 4 includes, for example, a microcomputer, etc., and is capable of determining the relationship between the temperature T of the heated body a and the specific resistance ρ (see FIG. 4), the cross-sectional area S, the effective length, and the maximum input voltage allowed. The Po level is set in advance, and the applied voltage is controlled so that the input P is always maintained at [Po] in relation to the output signal of the radiation thermometer 5. That is, since the resistance of the heated body a corresponding to the effective length is ρL/S, the input P and the applied pressure are
,! : Itip = v2/(,oL/S) (
There is a relationship D, and it becomes V-(PoρL/S)1/2 depending on the variation of the specific resistance ρ due to the variation of the temperature T. , control similar to Takekore is performed.

Then, the temperature of the heated object a is the desired heating temperature T.

When the temperature reaches the temperature, control is performed in accordance with the output signal from the radiation temperature side 5 so that the voltage applied to the voltage control device JFi becomes zero, that is, the current supply to the heated body a is cut off.

If heat loss during heating is ignored, it can be considered that the amount of heat that contributes to the temperature rise of the heated object a is proportional to the total amount of electric power input. Therefore, compared to the conventional method in which the input P gradually decreases during time t3-to, the input P is reduced to the maximum allowable value P.

As shown in FIG. 5, the heating time to reach the desired temperature To (t&-to
) is shorter than the conventional time (ts to),
Moreover, the usage efficiency of the power supply device 3 is improved.

According to the inventor's experiments, the diameter is 12.5m+, and the effective length is 1.
When heating an object made of round bar-shaped spring steel of 0.000 mm to 900° C., the required heating time was about 33 sec when the total voltage applied between the electrodes was maintained at a constant value of 64 volts. In addition, the required heating time is approximately 17 kV when the input is controlled to a constant input that is approximately equal to the maximum input (approximately 42 kV).
sec, which was approximately A as described above. in this case,
Since there is still some margin up to the maximum allowable input value, the required heating time can be further shortened.

It should be noted that the present invention is not limited to the box of the above embodiment, and for example, the material, shape, dimensions, etc. of the heated object a can be appropriately set as necessary. Further, the voltage control device 4 may be of a type that controls the power supply device #3 to fully variable control its output voltage, and in any case, it is configured to perform full current control instead of voltage control. Good too. Furthermore, in place of the radiation thermometer 5, other appropriate thermometers may be used. In addition, various modifications and applications are possible within the scope of the gist of the present invention.

In the present invention, as described above, the input is variably controlled in relation to the temperature of the heated object so that the heating power in the heated object is almost constant, so that the resistance of the heated object increases as the temperature rises. Even if the input power increases, the input power does not decrease, and the power can be maintained at the maximum power within a range that does not cause problems due to the generation of starch and motherboard. Therefore, the heating time can be shortened to improve productivity, and the margin of the power supply device can be set small to increase usage efficiency.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figures 1 and 2 are explanatory diagrams showing the characteristics of the conventional method, Figure 3 is a system diagram showing an example of the entire device to which the present invention is applied, and Figure 4 is a diagram showing the temperature and temperature of the heated object. FIG. 5 is an explanatory diagram illustrating the operating characteristics of the present invention. 1.2... Electrode, 3... Power source device, 4... Voltage control device, 5... Radiation thermometer, a... Heated object, P
...input, t...time, T...temperature. Applicant's representative Patent attorney Takehiko Suzue 7- Procedural amendment 1956, A0°3q, Commissioner of the Patent Office Shima 1) Haruki Tono], Patent Application No. 136265/1988 2, Title of the invention Resistance heating method 3, relationship with the Nagisa case to be amended Patent applicant (464) NHK Spring Co., Ltd. 4, agent 6, amendment paste] Specification 7, Contents of amendment (1) Specification box 5 Page i o Row No. 1fVJ WorkV
Correct AJ.

Claims (1)

[Claims] When a heated object is heated to a predetermined temperature by supplying electricity to the heated object, the input is fully variable controlled in relation to the temperature of the heated object so that the heating power in the heated object is approximately constant. Characteristic resistance heating method.