SU49437A1 - Method of magnetic testing materials - Google Patents

Description

Already known are devices for magnetic analysis of materials in which the sample under investigation is used as the core of a transformer, the primary winding of which is fed with sinusoidal alternating current.

The magnitude and shape of the current and voltage curve in the secondary winding of a transformer can be judged on a number of sample properties, such as: microstructure, carburizing depth, austenite content or other non-magnetic components, etc.

Such devices are widely used in practice. In particular, it was proposed to use for this purpose a cathode oscilloscope, by which the Lissajous figures obtained from samples with different structures are compared.

The main disadvantage of existing instruments is that they hardly allow separating the effect of a parameter that is interested in production from the influence of other less significant factors, for example, separating the effect of the cementation depth from the effect of fluctuations in the chemical composition within a given steel grade. .

A feature of the device proposed in accordance with the invention, which also uses a cathode oscilloscope, is the use of a phase regulator included in the circuit of the auxiliary plates of the oscilloscope and designed to arbitrarily change the shape of the Lissajous figures obtained on the oscilloscope screen so that they can be selected most sensitive to changes in certain parameters characterizing the test specimen.

In FIG. Figures 1 and 2 show the connection schemes: a magnetizing sample device and a cathode oscilloscope with a phase regulator; FIG. Figures 3–7 depict various forms of Lissajous figures obtained on the oscilloscope screen during testing.

FIG. 1 there are the following designations: / and 2 - two identical magnetizing solenoids in which two identical secondary coils 3 and 4 are placed. The solenoids are supplied with alternating current supplied to terminals 5 ,. as a result, alternating electromotive forces are induced in the secondary coils. The secondary coils are interconnected by a tan so that the electromotive forces are subtracted and no voltage is produced at their common ends led to the plug sockets 6.

In the coil 5 put the test sample 7; In the coil 4, however, there is a compensating constant sample W. In view of the fact that during long-term stay of this sample in the alternating magnetic field of solenoid 2, it heats up strongly — it must be cooled with a small stream of running water, which is supplied with a rubber hose through a tube and through channel in the sample.

The alternating current magnetizing the samples is set by ammeter 9 using a rheostat 8. If both samples are placed in coils, then the voltage across the terminals b will not be zero at all, but will depend on the properties of the test sample. The test method is based on the analysis of the indicated (variable) voltage using a cathode oscilloscope.

The oscilloscope switching circuit is shown in FIG. 2. The main part of it is a cathode tube, the contacts of which are shown in the diagram. She, as usual, is enclosed in an iron case that serves as a magnetic screen. Contacts 72 are connected to the sockets (5 magnetizing devices (Fig. 1), the resulting secondary voltage of which is applied to one of the tube capacitors. The sinusoidal voltage from the phase regulator 13 is supplied to the second capacitor according to the form of which it is possible to judge the heat treatment of the test sample. The voltage from the phase regulator is supplied through an adjustable potentiometer 25. The phase regulator is powered by an alternating current from a three-phase network. The oscillograph circuit is also implemented from the AC mains through transformers 14 and 15. The first one is equipped with two secondary windings, one of which feeds the oscilloscope tube heat and the other serves to heat the Kenotron 16 in the anode circuit of the Brown tube. from transformer / 5,

A filter consisting of a reactive coil and two / 7 capacitors is used to smooth the pulsations. The negative potential for focusing the electron beam is given by the variable resistance T8 in the anode circuit.

The action of the device is as follows. When the phase shifter is turned on, a horizontal line-trace of harmonic spot oscillations is obtained on the screen. After switching on the second pair of capacitor plates of the oscilloscope, the voltage of the secondary windings of the device b, if there is a sample in the coil, the Lissajous figures are displayed on the screen.

If you wish to test samples of other dimensions (other details), you must put another compensating sample 10.

The shape of the figures on the screen depends, other things being equal, on the heat treatment of the sample. This can be seen at least from FIG. 3, which shows various figures for high-speed steel. Tempering and tempering temperatures are indicated in the drawing.

In order to control the heat treatment, it is necessary to have pre-arranged tables (passports) of the kind shown in FIG. 3. Then, by comparing i the figure observed on the screen with the figures of the table, it is possible to determine both the quenching temperature and the tempering temperature of the test specimen. As for the tables, they must be made in advance. To do this, a sufficient number of samples must be subjected to very carefully various heat treatments and Lissajous figures should be removed from these reference samples. Heat treatment of standards must be checked by metallographic and other tests.

When you turn the knob of the phasoregulator, the view of the Lissajous figures changes. This circumstance can be used to significantly increase the sensitivity of the method. FIG. 4 shows two Lissajous figures obtained at the same position of the rotor of the phasoregulator; FIG. The 5 figures, taken from the same samples, but with a different rotor position, are again common to both samples. The difference between the samples is noticeable in both cases, but in the second case, it appears with greater clarity. Consequently, during the second phase shift, the setting is more sensitive. FIG. Figures 6 and 7 show figures taken in exactly the same way, but from a different pair of samples. Obtained in this case

the results are directly opposite to the first. The position of the phasoregulator, beneficial to the first pair of samples, is unfavorable to the second and vice versa. Thus, by rotating the rotor of the phasoregulator, it is possible to translate the highest sensitivity of the installation from one region of structural states to another. In the same way, it is possible to choose a phase so as to obtain the best conditions for sorting the tested parts according to any particular feature (for example, by grouting depth, etc.).

The subject matter of the invention.

A method for magnetic testing ferromagnetic materials based on

study of the shape of Lissajous figures;

obtained using a cathode oscilloscope, for one pair of plastics which is supplied the differential voltage of two differential transformers, the cores of which are tested and reference samples of compared materials, and on the other pair of plates there is an alternating network voltage, different in that method of obtaining the shape of the Lissajous figures, which are most sensitive to changes in those other properties of the sample under investigation, applied to the oscilloscope plates the auxiliary voltage shifted in phase by with respect to the voltage of the sample magnetizing circuit, for example, using a phase regulator.

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