SU868563A1 - Method of non-destructive testing of ferromagnetic articles - Google Patents

Description

(54; HEP A3 METHOD FOR DECOMING CONTROL OF FERROMAGNETIC PRODUCTS

The invention relates to a control and measuring technique and can be used for flaw detection of products made of ferromagnetic materials. There is a method of nondestructive control, which consists in magnetizing the product and recording the magnetic fields of the defects 1. This method provides high performance of the control, but is not sensitive enough to internal defects. The closest to the present invention is a method of non-destructive control of ferromagnetic products, namely, that the material of the product magnetizes, excites in it an elastic oscillation by converting electrical oscillations using the magnetostrictive effect, register these oscillations after passing them through the product and determine him the quality of the product. In this method, the transducer is magnetically magnified by the defect's defect, and the presence of the defect is determined by the change in the amplitude of the direct oscillations (.23. The method allows for the detection of internal defects, but has insufficient sensitivity and reliability of control due to the amplitude method of signal evaluation. of the invention is to increase the sensitivity and reliability of the control. This goal is achieved by measuring the frequency of the received oscillations and judging the presence of a defect by its change. In addition, in order to increase the accuracy and the control, the product is magnetized in the excitation zone of elastic oscillations by an additional field, varying its value to the extent necessary to change the frequency of elastic oscillations twice, determine the magnitude of the field corresponding to this change and judge the dimensions of the defect. showing the operation of the magnetostrictive converter in the absence of a defect in Fig. 2 — vro g in the presence of a defect, where it is indicated: A is the curve of the magnetostrictive effect, showing the dependence of the yn arising in materials ugih stresses (vertical axis) of magnetization applied to the material or it proportional electric voltage in. - time dependence of this voltage}

c is the time-dependent elastic oscillation.

FIG. Figure 3 shows a block diagram of the device implementing the proposed method.

The device consists of a magnetizing system 2 located near the monitored product 1, an excitation winding 3, an oscillation generator 4, an elastic oscillation receiver 5, an amplifier 6, a frequency comparison unit 7, a delay line 8, a bias winding 9, a sawtooth voltage generator 10, a line 11 delays, a block 12 for determining the defect parameters, a block 13 for marking and indicating defects, a synchronizer 14. The winding 3 together with the product covered by it 1 forms a magnetostrictive transducer.

The essence of the method is as follows. When a ferromagnetic product is magnetized, but there is no defect, the magnetic field does not extend beyond the surface of the product. In this case, the exciting magnetostrictive transducer works without external biasing and due to the parity of the magnetostrictive effect, the elastic oscillations will be excited at the double frequency relative to the frequency of the exciting electric oscillations, as shown in FIG. 1. If there is a defect in the area of the exciting transducer, then the scattering field created by it reaches the surface of the product and magnetizes the transducer. The working point (according to Fig. 2) goes to the side branch of the A curve of the magnetostrictive effect, in this case the elastic oscillations are excited at the electrical frequency of the Fixator by the fact that the frequency of elastic oscillations changes from double frequency to single frequency, the presence of a defect is established. Since magnetostriction materials have a very high sensitivity to magnetic fields, it is possible to detect small defects as well as defects that are located at a considerable depth. The use of the frequency as an informative parameter allows one to drastically reduce the influence of various interfering factors, and therefore, to increase the reliability of the control. To determine the parameters of the defect, the magnetocurrent transducer is attenuated by an additional, varying constant magnetic field. The vector of the amplitude of this additional magnetizing field should be oppositely directed to the vector of the magnetic field strength of the defect. When a magnetostrictive transducer hits a magnetic field, the defect. The magnitude of the additional field at some moment becomes equal to the magnitude of the field.

defect. In view of the opposite direction, the fields compensate for each other, and the converter goes into operation at double frequency. Knowing the law of the change of the additional field, measuring the value of the additional half h the moment of changing the frequency of the excited elastic oscillations, judge both the presence and the size of the defect, which increases the accuracy of control.

The method is carried out .. the following © Braz.

According to FIG. 3 the controlled product 1 is magnetized with a magnetizing system 2, with magnetic field causing magnetic fields on defects. The generator 4 excites electrical oscillations of ultrasonic frequency in the winding 3 and thereby creates a variable magnetization in publish 1. As a result of the magnetostrictive effect, elastic oscillations occur in product 1, which are received by receiver 5 and amplified by amplifier 6. In the case of measuring the frequency of elastic oscillations by comparing it with the frequency of electrical oscillations being converted, the signal from the amplifier is fed to frequency comparison unit 7, to the same unit oscillations from generator 4 are brought through delay line 8.

A varying constant magnetic field, the intensity vector of which is opposite to the magnetic intensity vector, is created by winding 9 magnetically connected to generator 10 of the sawtooth voltage. When a magnetostrictive transducer hits the field of the defect, the latter is compensated by the bias field, the Transducer switches to the dual frequency mode at this moment, and a signal is generated at the output of the frequency comparison unit 7 that arrives at the defect param eter 12. On the same block signal from the generator 10 through line 11 delay. With the defect parameters exceeding the set rejection level, from 1 12 the signal is transmitted to the input of the block 13 and the defect indication.

The coordinated operation of all electronic circuits is provided by the synchronizer 14. The delay time of lines 8 and 11 is chosen equal to the propagation time of elastic oscillations from the location of winding 3 to receiver 5.

Claims (2)

1. A method of non-destructive testing of ferromagnetic products, which consists in magnetizing the material of the product, exciting elastic oscillations in it by converting electrical oscillations using a magnetostrictive effect, registering these oscillations after passing them through the product and determining the quality of the products, o T- In order to increase the sensitivity and reliability of the control, the frequency of the received oscillations is measured and, due to its change, a defect is doubly judged. 2. A method according to claim 1, characterized in that, in order to increase the accuracy of control, the product is magnetized in the excitation zone of the elastic oscillations by an additional field, its value varies within the limits required for a twofold change in the frequency of elastic oscillations, the value corresponding to this change is determined the floor and judge about the size of the defect. Sources of information taken into account during the examination 1. Defectoscopy, 1966, No. 5, p. 59-65. 2. The patent of France 2344937, cl. G01N 29/00, 07.24.70 (prototype