JPH07120440A - Crack detection device - Google Patents

Abstract

PURPOSE:To provide a crack detection device having the capability of properly detecting a crack occurring in a workpiece under application to an induction hardening device of travel hardening type. CONSTITUTION:A digital filter 11 adjustable in passband is laid between an acoustic emission (AE) detecting means 8 for detecting acoustic emission from a workpiece 1 and outputting a signal after the conversion of the emission into a digital AE signal, and a periodic degree calculation means 9 for calculating the degree of the periodicity of the acoustic emission on the basis of the AE signal. In this case, the passband of the filter 11 is set so as to exclude a band containing the frequency of a heating noise signal due to a heating process, thereby allowing the passage of only an AE signal excluding the heating noise signal for output to the means 9. As a result, even if the workpiece 1 is subjected to heating and cooling treatment concurrently and a crack occurs therein, the periodicity of the acoustic emission can be detected with high accuracy for the proper detection of the crack.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack detecting device used in an induction hardening apparatus for detecting whether or not a crack has occurred in a work.

[0002]

2. Description of the Related Art As an example of a crack detecting device used in an induction hardening apparatus, there is a crack detecting device disclosed in JP-A-3-91859. The crack detection device, of detecting the acoustic emission (140 ~180 KH _Z) which is generated from the workpiece disposed in the induction hardening apparatus Digital A
The AE detection means for converting to an E signal and outputting it, the periodicity calculation means for performing self-calculation processing on the AE signal from the AE detection means to calculate the degree of periodicity of acoustic emission, and the periodicity calculation means A crack occurrence determination unit that determines whether or not a crack has occurred in the work by comparing the calculated periodicity with a preset reference value of the periodicity is provided.

If the work is heated by an induction hardening apparatus and then cooled, cracks may occur in the work. If no crack is generated in the work, A
While the degree of periodicity (periodicity) of the acoustic emission detected by the E detection means is low, the acoustic emission has a characteristic that the periodicity of the acoustic emission is high when a crack is generated. The emission, and by extension, the periodicity of the corresponding AE signal is compared with the periodicity reference value to determine whether or not a crack has occurred in the work.

[0004]

The induction hardening apparatus is roughly classified into a stationary hardening method and a moving hardening method.
As shown in FIG. 3 and FIG. 4, the stationary quenching type induction hardening apparatus is provided with the hardening coil 2 fixed to the work 1 and cooling the work 1 after the heat treatment of the work 1 is completed. The heating area and the cooling area are displaced from each other in time (there is a time lag L).

On the other hand, the induction hardening apparatus of the moving hardening type has a long work 1 as shown in FIGS.
The quenching coil 2 is configured to move relative to the work 1. In this induction hardening apparatus, at the same time as the heat treatment by the quenching coil 2, the already heat-treated portion is cooled, so that the heating area and the cooling area are temporally overlapped. In any of the induction hardening apparatuses, cracks are generated in the work 1 during the cooling process after the heating process.

By the way, in the induction hardening apparatus, a high frequency current is passed through the hardening coil 2 to generate an eddy current in the work 1 to heat the work 1.
A signal having a high periodicity (hereinafter referred to as a heating noise signal) is generated from the work 1 corresponding to the high frequency current. Therefore, in the crack detection device described above, when it is intended to be used in the induction hardening device of the moving quenching system, not only the acoustic emission but also the heating noise signal having high periodicity as well as the acoustic emission are simultaneously detected,
Even for this data, there is a possibility that the autocorrelation function R (k) shown on the abscissa of the delay number k as shown in FIG. 7 may not be obtained and proper crack detection may not be achieved. The fact is that the crack detection cannot be performed on the long work 1 which is limited to the induction hardening apparatus of the system and is processed by the moving hardening method.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a crack detection device which can be applied to a moving quenching type induction hardening device to appropriately detect a crack generated in a work.

[0008]

In order to achieve the above-mentioned object, the present invention provides an AE detecting means for detecting acoustic emission generated from a work arranged in an induction hardening apparatus, converting it into a digital AE signal, and outputting it. And a periodicity calculating means for calculating the degree of periodicity of acoustic emission based on the AE signal from the AE detecting means, and comparing the periodicity calculated by the periodicity calculating means with a preset periodicity reference value. In the crack detection device provided with a crack occurrence determination means for determining the presence or absence of a crack in the work piece, a passband adjustable digital filter is interposed between the AE detection means and the cycle degree calculation means. And

[0009]

With this configuration, the digital filter removes the heating noise signal by setting the pass band of the digital filter so as to exclude the band including the frequency of the heating noise signal associated with the heating process. Since only the AE signal excluding the heating noise signal is passed and output to the periodicity calculating means, even if the workpiece 1 is subjected to the heating treatment and the cooling treatment at the same time, if the workpiece is cracked, It is possible to accurately detect the frequency of acoustic emission that occurs.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A crack detecting device according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an induction hardening apparatus 3 and a crack detection apparatus 4 used in the induction hardening apparatus 3. The induction hardening apparatus 3 is provided with first and second chucks 5 and 6 which are vertically movable relative to each other.
The long work 1 made of a steel member can be supported and released. Work 1 is wound,
A quenching coil 2 is arranged so as to be movable in the vertical direction (longitudinal direction of the work 1). The quenching coil 2 is connected to a high-frequency generator (not shown).
Supply high frequency current to the. The quenching coil 2 generates an eddy current in the work 1 by applying a high-frequency current to heat the corresponding part of the work 1, and moves in the vertical direction to heat the work 1 over its entire length. It has become.

A discharge nozzle 7 connected to a cooling water supply device (not shown) is provided on the first chuck 5 side of the quenching coil 2, and the cooling water is jetted to the heat treatment portion of the work 1 to cause the relevant portion. Is to be cooled rapidly. The quenching process in the heat treatment section is performed after the delay time t _{2 has} elapsed from the heat treatment by the quenching coil 2.

The crack detection device 4 is roughly composed of an AE detection means 8, a cycle degree calculation means 9, a crack occurrence determination means 10, a digital filter 11, and a pass band setting means 12. The AE detection means 8 is an AE sensor 13 which is embedded in the second chuck 6 and detects a signal (including acoustic emission generated by the work 1) transmitted from the work 1 to the second chuck 6, and the AE sensor 13. A preamplifier 14, a main amplifier 15, a sample-hold circuit 16 and an A / D converter 17 which are sequentially connected in series to the subsequent stage of 13
And a first setting unit 18 connected to the sample and hold circuit 16 and the A / D converter 17. AE sensor
The signal detected by 13 is the preamplifier 14 and the main amplifier 15
The signal is amplified by and input to the sample hold circuit 16.
The sample hold circuit 16 samples and maintains the input signal at a preset sampling period. The signal (analog signal) maintained in the sample hold circuit 16 is converted into a digital AE signal (discretized waveform data) by the A / D converter 17 and output.

On the output side of the A / D converter 17, a digital filter 11 whose pass band can be adjusted is provided. Digital filter 11, the pass band width that can be set is the ± 10KH _Z, pass bandwidth analog filters can be set ± 50KH
_The pass band can be set narrower (higher accuracy) than _Z. Passband setting means connected to the digital filter 11
Twelve are provided. The pass band setting means 12 comprises a heat treatment signal generator 19, a first gate circuit 20, a frequency measuring section 21, and a second setting section 22, which are sequentially connected in series. The output side is connected to the digital filter 11. In addition, the frequency measuring unit 21,
In addition to the signal from the first gate circuit 20, a main amplifier
15 output signals can be input.

The heat treatment signal generator 19 generates a heat treatment signal simultaneously with the heat treatment for the work 1. The first gate circuit 20 is turned on when a heat treatment signal is input, outputs a gate signal, and stops the output of the gate signal by inputting a cooling treatment signal from a cooling treatment signal generator 23 described later. To do. The time from the generation of the heating processing signal to the generation of the cooling processing signal, and by extension, the time from the output of the gate signal to the stop thereof is set to be equal to the delay time t ₂ described above by the synchronization setting or the like.

The frequency measuring section 21 measures the frequency of the output signal of the main amplifier 15 (which is a heating noise signal at this point) by inputting the gate signal, and outputs the frequency signal indicating the measurement content as the second frequency signal. Output to the setting unit 22. Second
The setting unit 22 determines the pass band so as to exclude the frequency indicated by the frequency signal, and sets the pass band of the digital filter 11.

The periodicity calculating means 9 comprises a memory 24 and an autocorrelation calculating section 25. The memory 24 stores the AE signal that passes through the digital filter 11 (this AE signal is acoustic emission due to the pass band setting of the digital filter 11). Autocorrelation calculator 25
Is the following equation (1) for the AE signal stored in the memory 24:
Is calculated and the data showing the autocorrelation is output.

[0017]

[Equation 1]

In the equation (1), N is the total number of samplings, and x (n) is the discretized waveform data sampled at the (n + 1) th time series. x (n + k) is x
It is the discretized waveform data sampled by the kth later than in (n) in chronological order, and the k is called the delay number.

In general, when the autocorrelation function R (k) is displayed in a graph with the number of delays k on the horizontal axis and the value of the autocorrelation function R (k) on the vertical axis, the autocorrelation function R ( A characteristic is shown in which the absolute value of the value of k) gradually decreases (see FIG. 7). When the periodicity of the AE signal is high, the absolute value of the value of the autocorrelation function R (k) does not reach 0 even if the delay number k is large (that is, the autocorrelation is high), and the AE
When the periodicity of the signal is low, the delay number k is small and 0
It is known to converge to (i.e., the autocorrelation is low).

The autocorrelation calculation unit 25 executes the calculation of the autocorrelation function R (k) as described above, and the maximum value (may be an average value) of the values in a predetermined section (hereinafter, the autocorrelation). Sex data)) is output.

The crack generation determining means 10 comprises a cooling processing signal generator 23, a second gate circuit 26, a section setting section 27, a reference setting section 28, and a determination section 29. The section setting unit 27 sets a delay number k for specifying a calculation range of the autocorrelation data that is set as appropriate. Standard setting section 28
Sets a periodicity reference value for comparing the autocorrelation data.

The cooling processing signal generator 23 generates the cooling processing signal. This cooling processing signal is sent to the first gate circuit 20.
Is input to the second gate circuit 26. When the cooling processing signal is input to the second gate circuit 26, the second gate circuit 26
Is turned on, whereby the AE signal is output from the memory 24 to the autocorrelation calculator 25 so that the above-described calculation of the autocorrelation calculator 25 can be performed.

The determination unit 29 compares the autocorrelation data from the autocorrelation calculation unit 25 with the periodicity reference value to determine whether the autocorrelation is low, and thus whether the periodicity is low or high. Then, based on this result, it is determined whether or not the work 1 is cracked, and the determination result is output. That is, it is known that the acoustic emission generated when the work 1 is cracked has a high periodicity as described above. When the autocorrelation data is larger than the periodicity reference value, the absolute value of the value of the autocorrelation function R (k) does not easily converge to 0 regardless of the increase in the delay number k, that is, the autocorrelation Is high, and eventually work 1
It is determined that cracks have occurred in the. On the contrary, when the autocorrelation data is smaller than the periodicity reference value, the absolute value of the value of the autocorrelation function R (k) easily converges as the delay number k increases, that is, The correlation is low, and it is determined that the work 1 is not cracked.

In the crack detecting device 4 configured as described above, when the work 1 is supported by the first and second chucks 5 and 6 and the induction hardening process is started, the heat treatment signal indicates the first
Is output to the gate circuit 20 and the cooling processing signal is output after the delay time t ₂ . Then, this delay time t ₂
During this period, the frequency measuring unit 21 measures the frequency of the heating noise signal associated with the heating process. Further, the second setting unit 22 sets the pass band of the digital filter 11 so as to exclude the band including this frequency. When the heat treatment and the cooling treatment are simultaneously performed on the work 1 in the state where the pass band is set as described above (the moving quenching treatment is performed), the heating noise signal generated by the heat treatment is excluded by the digital filter 11. The AE signal from which the heating noise signal is removed passes through the digital filter 11.

The periodicity calculation means 9 and the crack occurrence determination means 10 cooperate as described above to compare the periodicity of the acoustic emission with the periodicity reference value to determine whether or not the workpiece 1 is cracked. To determine.

As described above, since the digital filter 11 removes the heating noise signal and passes only the AE signal excluding the heating noise signal, when the work 1 is cracked, the acoustic emission of the acoustic emission generated from the work 1 is generated. Reliably detect the periodicity. Therefore, work 1
Can properly detect cracks. Since the digital filter 11 is used, the pass band width can be set to be narrow as described above, so that the heating noise signal can be excluded with high accuracy.

In the present embodiment, the second setting unit 22 is configured to set the pass band of the digital filter 11 by determining the pass band so as to exclude the frequency indicated by the frequency signal from the frequency measuring unit 21. If the was the case, when the heating frequency when moving quenching example 100H _Z or 200H _Z as determined in advance as is the passband of the digital filter 11 to exclude 100H _Z or 200H _Z The second setting unit 22 and the frequency measuring unit that are set in advance
21 may be omitted.

[0028]

Since the present invention is the crack detecting device constructed as described above, the pass band of the digital filter is set so as to exclude the band including the frequency of the heating noise signal associated with the heating process. As a result, the digital filter removes the heating noise signal, passes only the AE signal excluding the heating noise signal, and outputs the AE signal to the periodicity calculating means, and the workpiece is subjected to the heating process and the cooling process at the same time. However, when a crack is generated in the work, the periodicity of the acoustic emission generated from the work is accurately detected, so that the crack can be properly detected in the work. Further, since the pass band width can be set narrow by using the digital filter, the heating noise signal can be reliably excluded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a crack detection device according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram of the crack detection device.

FIG. 3 is a diagram showing an example of a stationary quenching type induction hardening apparatus.

FIG. 4 is a view showing a heating region and a cooling region of the same induction hardening apparatus.

FIG. 5 is a diagram showing an example of an induction hardening apparatus of a moving hardening type.

FIG. 6 is a view showing a heating region and a cooling region of the same induction hardening apparatus.

FIG. 7 is a diagram showing an autocorrelation calculation result for a heating noise signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work 3 Induction hardening device 4 Crack detection device 8 AE detection means 9 Period degree calculation means 10 Crack occurrence determination means 11 Digital filter 12 Pass band setting means

Claims (1)

[Claims] 1. An AE detecting means for detecting acoustic emission generated from a work arranged in an induction hardening device, converting the acoustic emission into a digital AE signal and outputting the digital AE signal, and an acoustic emission of the acoustic emission based on the AE signal from the AE detecting means. A cycle degree calculating means for calculating the degree of periodicity, and a crack occurrence determining means for comparing the cycle degree calculated by the cycle degree calculating means with a preset cycle degree reference value to determine the presence or absence of a crack in the work. A crack detection device comprising: a crack detection device, characterized in that a digital filter capable of adjusting a pass band is interposed between the AE detection means and the periodicity calculation means.