JPH05264508A - Method and apparatus for nondestructive measurement of quenched and hardened range - Google Patents

Abstract

PURPOSE:To measure the quenched and hardened range of a ferromagnetic-substance material with good sensitivity, clearly and in a nondestructive manner by a method wherein the average signal level of a Barkhausen effect noise in a quenched part and a non-quenched part at a partially quenched material is compared with a reference voltage. CONSTITUTION:A secondary-voltage signal which is generated across both ends of a detection coil 2 is passed through a bypass amplifier 6. Only a BN signal as a high- frequency component is amplified (a voltage V1); after that, it is inputted to a detection and rectification circuit 7; the positive component of the BN signal is smoothed. The obtained signal level (a voltage signal V2) of the BN signal is compared with a reference voltage VS by means of a comparison circuit 8. When the signal V2 is larger than the voltage VS, the output voltage signal V3 of the circuit 8 is set to a high level. In the opposite case, the signal is set to a low level. When the signal V3 is at the low level, a quenched part (a) is detected. When it is at the high level, a non- quenched part (b) is detected. A position where the V2 is changed from the low level to the high level or in an opposite case indicates the quenching boundary between the quenched part (a) and the non-quenched part (b).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-destructive method for measuring a quench-hardening range and a device therefor capable of non-destructively measuring the quench-hardening range of a partially hardened ferromagnetic material.

[0002]

2. Description of the Related Art Heretofore, there has been no efficient measuring method and apparatus capable of measuring the quench-hardening range of a partially quenched ferromagnetic material. However, an eddy current method is known in which an eddy current is induced on the surface of a ferromagnetic material by an electromagnet that generates an alternating magnetic field, and the magnetic field induced by this eddy current is measured by a detection coil. It is not impossible to detect the quenching situation by utilizing the different eddy current generation situations. However, in this eddy current method, the difference between the signals measured in the hardened part and the non-hardened part is not so large, so the quench hardening range is clearly identified,
It is impossible to specify that boundary as well.

On the other hand, in induction hardening or beam hardening in which only the surface is hardened, there are many demands for nondestructive measurement of the hardening range (surface range and hardening depth) in order to study the hardening effect.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned situation, the present invention is to solve the problem by measuring the quench-hardening range of a partially hardened ferromagnetic material with high sensitivity and clearly and nondestructively. It is another object of the present invention to provide a nondestructive measurement method and an apparatus for the possible quench hardening range.

[0005]

In order to solve the above-mentioned problems, the present invention is to measure the quench-hardening range of a ferromagnetic material, and the Barkhausen effect noise generated when the material is subjected to alternating magnetization. Using the fact that changes due to quenching,
A non-destructive measurement method for the quench-hardening range was established by measuring the quenching boundary by comparing the average signal level of Barkhausen effect noise of the quenched and non-quenched parts of the partially quenched material with the reference voltage.

Further, it is intended to measure the quench-hardening range of a ferromagnetic material, which is a yoke type electromagnet for alternately magnetizing the material, and is arranged between the electromagnets, and the surface of the material is relative to the electromagnet. A quench-hardening range including a movable detection coil, a detection rectification circuit that extracts only a Barkhausen effect noise signal from a secondary voltage signal generated in the detection coil, and a comparison circuit that compares the signal from the detection rectification circuit with a reference voltage. A non-destructive measuring device was constructed.

[0007]

The nondestructive measurement method and apparatus for the quench-hardening range of the present invention having the above-mentioned contents are such that when a ferromagnetic material is quenched, the quench-hardened range causes a compressive residual stress,
A tensile residual stress is generated in the periphery of the material, and the characteristics of the Barkhausen effect noise generated when the material in this state is subjected to alternating magnetization are small in compressive stress and large in tensile stress. Then, the ferromagnetic material is alternately magnetized so as to cover the measurement range with an electromagnet, the Barkhausen effect noise signal is detected while moving the detection coil relative to the electromagnet, and the tensile stress is changed to the compressive stress. A comparison circuit detects that the average signal level of a part changes from a certain reference voltage to a value smaller than a certain reference voltage, accurately detects the boundary between the hardened part and the non-hardened part of the measurement range, and measures the quench-hardened range accordingly. To do.

[0008]

The present invention will be further described in detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 is a simplified layout diagram of a probe portion showing a measurement state of a quench hardening range, FIG. 2 shows a measurement circuit thereof, and W in the figure is a partially quenched ferromagnetic material,
Reference numeral 1 is an electromagnet, and 2 is a detection coil. Here, on the surface of the material W, a indicates a quenched portion and b indicates a non-quenched portion, and the quenched portion a is formed by induction hardening or laser beam hardening.

An electromagnet 1 for alternately magnetizing a ferromagnetic material W has an excitation coil 4 at both ends of a U-shaped yoke core 3.
Is wound and a current is supplied from a power source (not shown) to generate an alternating magnetic field. The distance between the two exciting coils 4 and 4 is set so as to sufficiently cover the measurement range of the material W. Here, the frequency of the alternating magnetic field (frequency of the power supply) can be used in the range of about 10 Hz to 1 kHz.
As the frequency increases and the current increases, the Barkhausen effect noise signal (hereinafter referred to as “BN
Signal ”. ) Tends to increase, but it is not preferable because the BN signal is saturated and the amount of heat generated by the electromagnet 1 increases even if the current is increased too much. Further, when the frequency is 10 Hz or less, the BN signal is small, and when the frequency is 1 kHz or more, the alternating magnetic field does not penetrate much into the material W,
It is preferable to stay within the aforementioned frequency range. In this embodiment, the frequency of the alternating magnetic field is set to 150 Hz.

The detection coil 2 arranged between the excitation coils 4 and 4 of the electromagnet 1 is wound around the ferrite core 5 in order to improve the detection efficiency of the BN signal, and the tip of the ferrite core 5 is made of the material W. The scanning is performed while contacting the surface. Here, the exciting coils 4 of the electromagnet 1 are
Assuming that the direction connecting the four is the X axis and the direction along the surface of the material W orthogonal to the X axis is the Y axis, the detection coil 2 can freely move the XY plane relative to the electromagnet 1 by an appropriate jig. It is said that it can be moved. Further, if the ferrite core 5 of the detection coil 2 is made thin, an accuracy of about 0.5 mm can be easily obtained.

FIG. 2 shows a measuring circuit, in which a secondary voltage signal including a BN signal generated between both ends of the detection coil 2 is passed through a high-pass amplifier 6 to amplify only a BN signal which is a high frequency component (about 100 kHz) (voltage signal). V ₁ ), the positive component of the BN signal is smoothed by inputting to the detection rectification circuit 7, and the average signal level (voltage signal V ₂ ) of the BN signal obtained thereby is compared with the reference voltage Vs by the comparison circuit 8. If the voltage signal V ₂ is larger than the reference voltage Vs, the comparison circuit 8
Of the output voltage signal V ₃ becomes high level, and in the opposite case, the voltage signal V ₃ becomes low level. Here, the high-pass amplifier 6 is composed of a high-pass filter and a high-frequency amplifier of about 1000 times, the detection rectification circuit 7 is composed of a diode D and a capacitor C, and the comparison circuit 8 is composed of a comparator. .. Since the BN signal of the non-quenched portion b has a larger amplitude than the BN signal of the quenched portion a, the voltage signal V
_{When 3} is at a low level, the hardened portion a is detected, and when it is at a high level, the non-hardened portion b is detected. The position where the voltage signal V ₃ changes from the low level to the high level or the position where the voltage signal V ₃ changes from the high level to the low level indicates the hardening boundary between the hardened part a and the non-hardened part b. Since the non-quenched part b has a tensile residual stress and the hardened part a has a compressive residual stress, the boundary can be clearly seen.

Next, the mechanism by which the Barkhausen effect noise is generated when the ferromagnetic material is alternately magnetized will be briefly described. In transition metals such as iron and nickel, which are ferromagnetic materials, the electrons in the 3d orbit located outside the electron cloud are excessive, and each atom acts as a magnet, and the magnets are arranged in the same direction. Form a macroscopic magnet. This magnet forms a fairly large magnetic domain called spontaneous magnetization, and the direction of magnetization is different for each magnetic domain, and the magnetization directions of adjacent magnetic domains are closed in series so as to be as low as possible in terms of energy. .. Under these circumstances, magnetic neutrality is maintained with respect to the outside. Here, when a magnetic field is applied from the outside, the area of the magnetic domain that is spontaneously magnetized in the same direction as the magnetic field or a direction close to the magnetic field is widened, and is magnetized as a whole, and most of the magnetic domains are oriented in the direction close to the magnetic field, and then further. When the magnetic field is strengthened, the magnetic domain rotates so that the direction of spontaneous magnetization faces the direction of the magnetic field. During this magnetization process, the domain wall at the boundary between magnetic domains moves. If the domain wall moves smoothly, the magnetization should also proceed smoothly and an irregular signal voltage should not occur, but the impurities or defects in the crystal of the material cause the domain wall to move smoothly, or the polycrystalline Since the orientation is irregular, the timing of starting the magnetization (movement of the domain wall) (the strength of the magnetic field) is different for each crystal grain, and the magnetization is discontinuous or abrupt, which causes an irregular signal, that is, BN.
A signal is generated. The BN signal is obtained by capturing the leakage magnetic flux generated between the adjacent magnetic domain across the domain wall in the vicinity of the surface of the material. As described above, the magnitude of the BN signal changes depending on the amount of impurities and defects in the material, and the BN signal also has the property of changing depending on the stress. When the tensile stress is applied, the magnetization is facilitated and the movement of the domain wall is accelerated, resulting in the BN signal. Grows. On the other hand, with compressive stress, on the contrary, the magnetization becomes difficult (the magnetic susceptibility is small), the domain wall moves slowly, and the BN signal becomes small. Quenching generally produces a compressive residual stress, which reduces the BN signal. Further, the BN signal is also greatly generated when the change in the alternating magnetic field is large.

3 and 4 show examples of actually measured BN signals. FIG. 3 shows a signal obtained by measuring the hardened portion a, the high frequency signal is a BN signal, and the low frequency signal is an exciting current of the electromagnet 1. FIG. 4 shows a similar signal obtained by measuring the non-quenched portion b. These BN signals are the voltage signal V ₁ after passing through the high pass amplifier 6.

In FIG. 5, the electromagnet 1 is arranged at a position sandwiching the quench-hardened boundary of the partially hardened ferromagnetic material W, and the detection coil 2 is reciprocally moved between the exciting coils 4 and 4 of the electromagnet 1. The voltage signal V ₂ is shown when the voltage signal is applied. As a result, the average signal level rapidly changes to 1/2 or less at the quench-hardened boundary, and the rising or falling of this signal changing portion is about 1 mm when the scanning speed and time scale of the detection coil 2 are taken into consideration. is there. According to the present invention, it is possible to measure the quench-hardened boundary with high accuracy within about 1 mm.

The chart shown in FIG. 6 shows the voltage signal of each part of the measurement circuit when the detection coil 2 is moved in the arrangement shown in FIG. Average signal level V
_By comparing ₂ with the reference voltage Vs, the boundary between the hardened portion a and the non-hardened portion b can be sharply detected, and when the voltage signal V ₃ is at a low level, the measurement point is the hardened portion a. It can be seen that there is some, and conversely, at a high level, the measurement point is the non-quenched portion b. Furthermore, while the position of the electromagnet 1 is specified, the output voltage signal V ₃ is monitored while measuring the displacement of the detection coil 2 with an encoder, and the output voltage signal V ₃ is binarized and input to a storage device, and data is processed by a microcomputer. It is also possible to create a map that specifies the range of the hardened portion a and the non-hardened portion b of the material surface.

In the present embodiment, the quench hardening range of the partially hardened ferromagnetic material W as described above can be measured accurately and nondestructively. However, in parts such as gears whose outer peripheral portion is hardened. By measuring the quench-hardening range on the side surface, the quenching depth can be measured very accurately and nondestructively. Further, by comparing the BN signal with the BN signal of the completely hardened same material, it is possible to judge the quality of the hardening.

[0017]

According to the nondestructive measurement method and apparatus for the quench hardening range of the present invention as described above, the boundary between the quenching portion and the non-quenching portion of the partially quenched ferromagnetic material, that is, the quenching hardening range. Can be easily measured with high accuracy of about 1 mm or less and non-destructively. In the measurement, the electromagnet and the detection coil are 0.2 to 0.
Since it can be floated for about 3 mm for measurement, the electromagnet and the detection coil can be integrated to perform 100% / sec or higher high-speed 100% inspection (1 piece / 30 seconds or less), and it can also be used for automatic inspection in a production line.

[Brief description of drawings]

FIG. 1 is a simplified cross-sectional view showing a probe unit of an apparatus according to the present invention.

FIG. 2 is a simplified circuit diagram showing the measuring circuit.

FIG. 3 is an oscillograph showing a BN signal of a hardened part.

FIG. 4 is an oscillograph showing a BN signal of a non-quenched portion.

FIG. 5 is an oscillograph of the average signal level of the BN signal measured by reciprocating the detection coil across the boundary between the hardened part and the non-hardened part.

FIG. 6 is a simplified chart showing voltage signals of respective parts of the measurement circuit shown in FIG.

[Explanation of symbols]

 W Material a Hardened part b Non-hardened part 1 Electromagnet 2 Detection coil 3 Yoke core 4 Excitation coil 5 Ferrite core 6 High-pass amplifier 7 Detection rectifier circuit 8 Comparison circuit

Claims (2)

[Claims] 1. A method for measuring the quench-hardening range of a ferromagnetic material, wherein the Barkhausen effect noise generated when the material is subjected to alternating magnetization changes by quenching. A non-destructive measurement method for a quench hardening range, which comprises measuring a quenching boundary by comparing an average signal level of Barkhausen effect noise of a quenching portion and a non-quenching portion with a reference voltage. 2. A method for measuring a quench-hardening range of a ferromagnetic material, comprising a yoke-type electromagnet for alternately magnetizing the material, and a yoke-shaped electromagnet disposed between the electromagnets and having a surface of the material relatively to the electromagnet. A movable detection coil, a detection rectification circuit for extracting only a Barkhausen effect noise signal from a secondary voltage signal generated in the detection coil, and a comparison circuit for comparing the signal by the detection rectification circuit with a reference voltage. Non-destructive measuring device for quench hardening range.