JPH0693379B2 - Reheating method of continuous feed type induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a continuous feed type induction heating apparatus mainly used for forging, which has not been heated to a predetermined temperature when restarted after being stopped due to a trouble. The present invention relates to a reheating method for a continuous feed type induction heating device that minimizes the generation of a heated product.

[Conventional technology]

A conventional continuous feed type induction heating device is shown in JP-B-63-10875. The operation in the conventional example in the case where the subsequent process is stopped due to a trouble employs the slow-speed feed heat retention. Slow feed heat retention is a transfer speed of 50-60% at a specified transfer speed. In other words, it was intended to reduce the amount of waste material at the time of waiting until the subsequent process is started at a low speed.

[Problems to be Solved by the Invention]

The reheating method of the conventional continuous feed type induction heating device has kept the heat at a very low speed, so that the heat retention time is long,
When the heating coil is long in a large-scale device, a large amount of waste material (heated material that is bypassed without being sent to the subsequent process) is generated, and it is difficult to process the bypassed waste material.

The present invention provides a reheating method for a continuous feed type induction heating device in which the generation of waste materials is reduced.

[Means for Solving the Problems]

The reheating method of the continuous feed type induction heating device according to the present invention includes a heating coil divided into a front stage and a rear stage, and a heating power supply device that supplies power to each of the front and rear heating coils. In a continuous feed type induction heating device that conducts induction heating to a predetermined temperature while continuously transporting the heating target at a steady speed S _D , when the induction heating device is restarted after being stopped, the heating target is in a stationary state. At, the electric power is supplied only to the heating coil in the latter stage, and after a certain time, the object to be heated is conveyed at the speed S _L equal to or lower than the S _D , and the electric power supplied to the heating coil in the preceding stage is the constant power S _L. A value P close to / S _D
Set to _L , the power supplied to the latter heating coil to a value P _R2 higher than the steady-state power, and the latter stage as the temperature of the heated object at the outlet side of the latter heating coil approaches a predetermined temperature. The power supplied to the heating coil is gradually lowered from P _R2, and when the temperature of the heated object on the heating coil inlet side of the latter stage approaches a predetermined temperature, the conveyance speed of the heated object, the The power supplied to the heating coils at the front and rear stages is returned to a steady value.

[Action]

In the present invention, at the time of reheating, the material is conveyed at a speed slower than the steady state, and while reheating in the former stage, the shortage is reheated in the latter stage to heat at least the material to be heated in the former stage to a predetermined temperature.

〔Example〕

FIG. 1 is a block diagram for carrying out an embodiment of the present invention. In the figure, (1a) is a pre-stage heating coil, (1b) is a post-stage heating coil, (2) is a pinch roller, (3) is a skid rail, (4a) and (4b) are power supply devices including inverter devices, and (5). Is a free roller, (6) is a proximity switch, (7) is a metal blade facing the proximity switch (6),
(8) is a feeding conveyor, (10) is an object to be heated, and (20) is a control device. Here, the object to be heated (10) is a plurality of cylindrical steel materials, and is continuously conveyed from the inlet of the front heating coil (1a) to the outlet of the rear heating coil (1b).

Pre-heating coil (1a) during steady operation of this induction heating device
And the temperature curve of the object to be heated (10) in the latter heating coil (1b) is shown in FIG. 2 (1), and as shown in the upper figure, the object to be heated (10) in the latter heating coil (1b) ( The temperature of 10) is soaked at a predetermined temperature (about 1250 ° C).

As shown in FIG. 1, the object to be heated (10) is a pinch roller (2).
Being transported in. The speed is S _D in the steady state in FIG. The free roller (5) in contact with the heated object (10) rotates with the movement of the heated object (10),
The metal blade (7) attached to the shaft also rotates. If a proximity switch (6) that detects when the metal blade (7) approaches is arranged, a pulse is periodically output as the object to be heated (10) moves. Therefore, the distance traveled by the object to be heated (10) can be grasped by counting the pulses. The output signal of the proximity switch (6) shown in FIG. 1 is shown by the name of the position of the object to be heated in FIG. Now, it is assumed that the induction heating device is stopped due to a failure in the subsequent process. In FIG. 3 (d), the timer in the control device (20) starts operating,
Start measuring the stop time. The temperature of the object to be heated (10) begins to decrease over the entire area of the heating coil (1). And
The temperature change is, for example, the curve (2) in FIG.
As an example, the temperature drops to about 700 ° C after 10 minutes stoppage.

Here, the following operation is performed when the induction heating device is restarted.
When the operation restart signal is input, first, electric power is applied only to the latter-stage heating power source (4b), and the object to be heated (10) is not fed, but static heating is performed. This period is called a static heating period. During this period, the object to be heated (10) in the post-stage heating coil (1b)
Bring the temperature to the specified temperature as close as possible. The temperature of the object to be heated (10) at the time of starting the static heating depends on the period of time during which the induction heating device is stopped (ascertained by the timer above) and the object to be heated (1).
It can be calculated by the heat radiation loss of 0) and heat transfer with air. The table shows the constants for the calculation. The purpose of this static heating is to first raise the temperature in the range where the temperature cannot be raised in the low-speed feeding period described below.

The stationary heating period ends when the temperature of the object to be heated approaches the steady temperature. Here, the temperature rise value is (applied power x
Heating efficiency x static heating time / specific heat of heated object). Therefore, since the temperature rise value can be estimated by calculation or a preliminary experiment, the time when the temperature approaches the steady temperature can be determined. As for the temperature curve of the object to be heated (10) at the end of the stationary heating period, only the rear heating coil (1b) is heated as shown in (3) of FIG.

The following operations are performed in the next slow feed period. Stationary heating period the heated object of the previous heating coil end (1a) and subsequent heating coils (1b) becomes to compensate the temperature of (10) at a later stage heating power source (4b), the speed S _L, subsequent heating power The output of (4b) (P _{R2 in} Fig. 3) is determined as follows.
Assuming that the temperature of the object to be heated (10) at the start of low-speed feeding is T _L , the predetermined heating temperature is T _S , and the weight of the object to be heated (10) in the post-stage heating coil (1b) per unit time is M, T _S −T _L is the temperature rise value for raising the temperature in the latter heating power supply (4b), and the required power is (T _S −
T _L ) × (specific heat of heated object) × M / Calculated with a value proportional to heating efficiency. Since the specific heat, passing weight M, and heating efficiency can be known in advance, the required power can also be calculated, and this power becomes the set output (P _R2 ) of the post-stage heating power supply (4b). The temperature T _L is selected to be the object to be heated (10) at the inlet of the post-stage heating coil (1b) at the start of low-speed feeding. Here, since the passing weight M per time is proportional to the speed S _L , if S _L is too large, the required power, that is, the output of the post-stage heating power supply (4b) will exceed the rated value. Further, generally, the induction heating current flowing inside the object to be heated flows only to the surface, so that heating over time increases the heat conduction to the inside of the object to be heated, which facilitates uniform heating of the object to be heated. . Therefore, it is preferable that S _L has a value considerably lower than the steady speed S _D , for example, a value of 1/2.

Output of the preceding heating power supply (4a) during the low-speed feeding period (see Fig. 3
P _L ) is determined as follows. Generally, the electric power required for heating is almost proportional to the feed rate. Therefore, the output P _L of the pre-stage heating power supply (1a) is set to the value obtained by the steady output × S _L / S _D. This is to obtain a temperature curve for steady operation in the pre-stage heating coil (1a).
During this low-speed feeding period, the temperature of the low-temperature object (10) that enters the post-stage heating coil (1a) and the post-stage heating coil (1b) is compensated and raised by the post-stage heating coil (1b). .

When this low-speed feeding period starts, the article to be heated (10) is sequentially discharged from the outlet of the post-stage heating coil (1b). At the beginning of this low-speed feeding period, the temperature curve of the object to be heated (10) becomes as shown in (4) of FIG. The temperature of the article to be heated (10) in the post-stage heating coil (1b) gradually rises, and when the article to be heated (10) located at the inlet of the post-stage heating coil (1b) is discharged at the start of the low-speed feed period. Shows a temperature curve as shown in (5) of FIG. 2, and the temperature of the object to be heated (10) has risen to a predetermined temperature.

The object to be heated (10), which was in the pre-stage heating coil (1a) at the start of the low-speed feeding period, has been heated by the pre-stage heating power source (4a) and is therefore heated to the post-stage heating coil (1b). As shown in (5) of FIG. 2, the temperature curve is higher than the temperature curve at the start of the low-speed feed period ((3) in FIG. 2). Therefore, the post-stage heating power source (4b) gradually lowers the output to restore the predetermined output as shown in FIG. This output change timing (T in FIG. 3) is determined by the moving pulse (FIG. 3 (b)) of the object to be heated (10) and the counter (FIG. 3 (c)) in the controller (20). ). The point at which the object to be heated (10), which was at the inlet of the preceding heating coil (1a) at the start of the low-speed feed, reached the inlet of the subsequent heating coil (1b), was the above-mentioned predetermined output, that is, the timing for returning to steady operation. Become.

As described above, the object to be heated (10) in the pre-stage heating coil (1a) and the post-stage heating coil (1b) at the time of starting the static heating, that is, at the time of starting the reheating is heated to a predetermined heating temperature from a low temperature. To go. After that, it goes without saying that the temperature has risen to the predetermined temperature after returning to the steady operation.

The control function (configured by the control device (20)) for performing the above operation can be inexpensively configured by a commercially available program controller or the like.

〔The invention's effect〕

As described above, according to the present invention, even in the continuous feed type induction heating device, it is possible to reduce the amount of waste material that does not reach the predetermined temperature during the re-operation after the operation is stopped.

Therefore, since no high temperature waste material is produced, workability is greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an induction heating apparatus for carrying out the present invention, and FIG.
FIG. 4 is an explanatory diagram showing the temperature change of the object to be heated in the coil, FIG. 3 is an explanatory diagram showing one embodiment of the operating method according to the present invention,
The figure is an explanatory view showing an example of a cooling curve calculation. In the figure,
(1a) is the former heating coil, (1b) is the latter heating coil,
(4a) is the former heating power source, (4b) is the latter heating power source, (10)
Is an object to be heated, and (20) is a control device. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A heating coil divided into a front stage and a rear stage, and a heating power supply device for supplying electric power to the heating coils in the front stage and the rear stage, respectively, to continuously heat an object to be heated at a constant power and a constant speed S _D. In a continuous feed type induction heating device that performs induction heating to a predetermined temperature while being conveyed, when the induction heating device is restarted after being stopped, the object to be heated is stationary and power is supplied only to the latter heating coil. Is supplied, and after a certain period of time, the object to be heated is conveyed at a speed S _L that is equal to or lower than the S _D , and the power supplied to the heating coil in the preceding stage is S _L of steady power.
Set a value P _L close to / S _D , set the power supplied to the latter heating coil to a value P _R2 higher than the steady power, and set the temperature of the heated object on the outlet side of the latter heating coil to As the temperature approaches the specified temperature, the power supplied to the latter heating coil will be reduced.
Gradually lower from P _R2 , when the temperature of the heated object on the inlet side of the latter heating coil approaches a predetermined temperature, the conveying speed of the heated object, the heating coil of the front stage and the latter stage A reheating method for a continuous feed induction heating device, characterized in that the supplied power is returned to a steady value.