JPH04122848A - Detecting apparatus of time point of complete melting of metal in induction melting furnace - Google Patents

Abstract

PURPOSE:To conduct detection quickly and accurately by determining the time point of complete melting of a metal to be melted by detecting an operating frequency of an induction melting furnace. CONSTITUTION:Numeral 8 denotes a feed power energy monitoring device, which has a function of outputting a melting power reach signal when an estimated power energy required for melting on the conditions of the material and the melting amount of a metal to be melted is reached. Therefore the feed power energy monitoring device 8 comprises a watt-hour meter with a pulse output and a preset counter in combination, and it is so designed that a supply power is integrated by the watt-hour meter with pulse output, that an integrated value thus obtained is compared with a reference preset power energy in the preset counter and that the melting power reach signal is delivered when a comparison value reaches the estimated power energy for melting. The value of a reference preset power of this preset counter is set in such a manner that several times of trial melting is executed beforehand for the metal to be melted and that the power with which the metal is melted and the temperature of the molten metal does not rise any more is calculated as the reference preset power.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an induction melting furnace suitable for smoothly melting various metals such as super alloys, and particularly to a metal melting furnace necessary for controlling a vacuum induction melting furnace. It is connected to a fall point detection device.

[Prior Art] The power supply in conventional general vacuum furnaces is controlled visually by the operator, and no special consideration is given to the control of metal melting, resulting in the following problems. There was a point.

[Problems to be Solved by the Invention] In other words, in such a vacuum induction furnace, evacuation, inert gas replacement, metal melting, etc., take one hour (because such processes take less than one worker's working time). The current situation is that the waiting time is longer.

For this reason, in order to improve work efficiency, there is a demand for automatic operation from the start of evacuation to the point at which the metal melts and reaches the holding state.

In this case, it is absolutely necessary to know the point at which the metal burns off, but conventionally this point has been detected visually by an operator, so there is a need for a means to automatically detect this point.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for detecting the point of metal burn-off in an induction melting furnace to solve the above-mentioned problems of the conventional apparatus.

[Means for Solving the Problems] The basic principle of the present invention is to detect the point of metal burn-through by monitoring the operating frequency or cycle of a power supply.

As shown in FIG. 1, physically speaking, the induction melting furnace can be considered to be composed of an inductance L and a resistance R.

On the other hand, if the capacitance of a capacitor provided on the power source side to obtain resonance is C, then the power source is supplied from these sources so as to be approximately tuned to the resonance frequency due to C, and the power source is adjusted according to changes in L. We will melt metal by changing the operating frequency.

Qualitative supplementary information regarding this change in relation to the melting furnace is as follows.

That is, before melting, the metal to be melted into the melting furnace 1 is stored in the furnace with gaps between each metal piece, as shown in FIG. 2(A).

However, when the molten metal K is in a molten state due to induction heating by the electric power supplied to the coil 1a, it adheres to the furnace wall and is housed in the furnace without any gaps, as shown in the figure (b). state.

Comparing the states in (a) and (b) in the same figure, in (a) the magnetic flux path exists over a wider area, so the inductance in the furnace 1 part is larger, and the metal melts more quickly. As time progresses, molten metal accumulates from below, reaching the state shown in FIG.

On the other hand, if the operating frequency of the power supply is f, then the equation f = 1/(2πF) holds true, so the inductance L of the melting furnace 1 is
As f decreases from before melting to the point of burn-through, one frequency f increases.

By the way, when all the metal in the furnace 1 is in a molten state, the temperature will rise due to heating by electric power, but since the shape is constant, the inductance will hardly change, and therefore the operating frequency will also be as shown in Figure 3. As shown, the frequency is constant.

Note that in the figure, the 100% time point on the horizontal axis is, for example, 50 minutes. Furthermore, since the frequency and the period have a reciprocal relationship with each other, the period can be used instead of the frequency as a detection element.

Therefore, the point at which the operating frequency or cycle of the power supply becomes constant is the point at which it melts, so the technology of the present invention monitors the transition of this operating frequency or cycle and attempts to detect the point at which it becomes constant. It is a thought.

[Examples] The present invention will be specifically described below with reference to two examples shown in the drawings. In addition, in the embodiment shown below, explanation will be made using the frequency detection means, but between the frequency f and the period T, f = 1 /
Because of the relationship T, the two-frequency detection means can be replaced by the period detection means.

a. First embodiment FIG. 4 shows a block diagram of the configuration of the first embodiment.

In the figure, 1 is an induction melting furnace, and 2 is an AC power source.

A power source includes an inverter, etc., and 3 is a frequency detector.

The frequency detector 3 extracts the current or voltage signal of the power supply 2 and compares the periods of these current or voltage signals within a predetermined time to determine the output frequency (operating frequency) of the power supply.
Detect.

4 is a data storage device 9 which stores the ever-changing frequency signal as data.

Reference numeral 5 denotes a change determiner, which selects one of the frequency data stored in the data storage device 4, for example, data after a certain point in time, respectively, f (n), f (n-1), f (n-2), etc.
・The deviation ε3. which is obtained by comparing these sequentially with the immediately preceding pig. ε2. ε,・ε,=f (n) −f (n-1)e2=f(
n 1) f(n 2>ε, = f (n
-2), -f (n-3), and when comparing each of these deviations with the judgment standard deviation △ε, ε1〈△
When ε, ε2 △ε, or even ε3〈△ε become small twice or three times in a row, it is determined that the two frequencies have become constant, and 1 judge number is output.

Reference numeral 6 denotes a signal generation circuit, which outputs an output based on the judgment signal from the change judgment device 5, notifies the power supply 2 through the voltage switch 7 that burn-through has occurred, and switches the power supplied to the furnace to the holding power.

b. Second Embodiment Although the metal burn-off can be detected practically enough in the first embodiment described above, in reality, some of the metal that is being melted on the furnace wall is left behind, or Solidified matter that adheres to the wall for cooling may cause a so-called "dansling" phenomenon, and in such a case, there is a risk that the inductance, and therefore the frequency, will not be constant.

Furthermore, the furnace wall may be melted by the heated molten metal, and in such a case, there is a possibility that the single frequency will not be constant after melting.

Therefore, if burn-through is detected only at one fixed frequency, a dangerous situation may occur in such a case.

The second embodiment shown in FIG. 5 is an improvement on the first embodiment in consideration of this point.

In the figure, parts corresponding to those in the first embodiment are designated by the same reference numerals as in FIG. 4.

Reference numeral 8 denotes a supply power amount monitoring device, which has a function of outputting a burn-through time arrival signal when the amount of melted material of the metal to be melted reaches the expected amount of power required for melting.

For this purpose, the power supply amount monitoring device 8 is used, for example.

It consists of a combination of an integrating wattmeter with pulse output and a preset counter.The power supply power is integrated by the integrating wattmeter with pulse output, and this integrated value is sent to the preset counter.
It is compared with the reference preset electric energy, and when the comparison value reaches the expected melting electric energy, a burn-through time arrival signal is output.

The reference preset power value of this preset counter is
Trial melting of the metal to be melted is performed several times in advance, and the power at which the metal melts and the temperature of the molten metal does not rise any further is calculated and set as the standard preset power.

9 is an energization time monitoring device, which also calculates the standard time required to reach burn-through when trial melting the metal material concerned, sets this as the standard burn-through time, and calculates the time after melting starts. When this time has been reached, a melt-down time reached signal is output.

In the second embodiment, the total amount of electricity and the total energization time after the start of metal melting in the induction melting furnace 1 are monitored by the supplied power amount monitoring device 8 and the energization time monitoring device 9, and the supplied power amount monitoring device When an arrival signal is generated from either 8 or the energization time monitoring device 9, it is assumed that metal has burnt through.

The supplied power is switched to holding power via the OR element 10 and the voltage switch 7 to prevent dangerous excessive melting.

[Working core a, the working power source 2 of the first embodiment is turned on, and the metal in the furnace is melted. During this time, the operating frequency is detected by the frequency detector 3 and the data storage 4
Based on the stored data, the change determiner 5 makes a determination one by one.

In this case, if 311 (or even two) in the data to be compared are consecutively smaller than the judgment standard deviation,
A determination signal is output from the change determiner 5 to determine the point of burn-through, and based on this signal, the signal generating circuit 6. Voltage switch 7
The power supply is switched to the holding power via the power supply.

b. Effect of the second embodiment: In a normal case, the change determiner 5 determines that one frequency has become a constant value.) The same detection operation as in the first embodiment is performed.

However, in abnormal situation 1, for example, due to the presence of solidified material adhering to the furnace wall or melting of the furnace wall due to rising temperature of the molten metal, the operating frequency becomes unstable even after the metal bath has dropped. When an attempt is made, the following protective action is performed.

That is, in such a case, due to the existence of the supplied power amount monitoring device 8 and the energization time monitoring device 9 as described above, either the total amount of power or the total energization time after the start of melting will reach the respective reference values. When the voltage reaches the point, a signal is output from the power supply amount monitoring device W8 or the energization time monitoring device 9, respectively, and based on this signal, it is assumed that the melting point has been reached, and the voltage switch 7 is forcibly activated. The supplied power is switched to the holding power.

[Effects of the Invention] As described above, the present invention is based on determining the melting point of the metal to be melted by detecting the operating frequency of the induction melting furnace. Since this is a detection device for detecting the point of metal burn-through in an induction melting furnace, which makes a determination based on the total energization time, it has an excellent first-order effect.

(2) Since the point at which metal burns through is detected using an electrical signal called a frequency signal, the detection can be performed quickly and accurately.

■If the results of the determination based on the frequency signal are supplemented by the total electric energy or the total melting time as in the second embodiment, the situation of abnormal temperature rise due to detection failure at the time of melting can be completely prevented. .

■Thus, using the detection of the burn-through point according to the present invention,
It is possible to configure an automatic operation device for an induction melting furnace. This makes it possible to automate the entire process from the start of vacuuming to melting the metal and transitioning to the holding state, compared to conventionally time-consuming processes such as vacuuming, inert gas replacement, and metal melting, resulting in greater work efficiency. can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a connection diagram for explaining the present invention in detail. Figures 2 (a) and (b) are longitudinal sectional front views showing the states of the induction melting furnace before and after metal melting, respectively, and Figure 3 shows the frequency -
The time characteristic diagrams, FIGS. 4 and 5 are block diagrams showing the first and second embodiments of the present invention, respectively. 1: Induction melting furnace 2: Power source 3: Frequency detector 4: Data storage device 5: Change judger 8: Supply power amount monitoring device 9: Energization time monitoring device

Claims (1)

[Claims] 1. An induction device in which power is supplied to an induction melting furnace via a resonance capacitor, and the metal to be melted into the melting furnace is melted in approximately synchronization with the LC resonance frequency. The melting furnace includes means for detecting the frequency or period of the power supply, and change determining means for sequentially comparing the frequency or period detected by the frequency or period detecting means, The point of metal burn-off in an induction melting furnace is characterized in that the point of burn-off of the metal to be melted is detected by the value of one or more deviations being continuously smaller than the value of a predetermined standard deviation. detection device. 2. A power supply monitoring device that detects the cumulative amount of power supplied after the start of metal melting and outputs a melting power arrival signal when the expected melting power amount for the metal is reached, and a power supply monitoring device that counts the total amount of time after the start of metal melting. , is equipped with at least one monitoring device of an energization time monitoring device that outputs a burn-through time arrival signal when the counting time reaches the standard burn-through time at which the metal is expected to be melted, and the frequency of the supplied power is When the metal burn-off point in the induction melting furnace according to claim 1 is determined to have reached the metal burn-off point by generation of an arrival signal from at least one of the monitoring devices, when Detection device.