SU1727003A1 - Method of determining mechanical stresses in ferromagnetic products - Google Patents

Abstract

The invention relates to instrumentation engineering and makes it possible to increase the accuracy of measuring mechanical stresses in ferromagnetic products. The sample from the material of the controlled product removes the calibration dependence of losses in the material on the magnitude of mechanical stresses, the dependence of losses in the material and reactive power on the size of the gap between the sensor and the sample and determine the value of reactive power when the sensor is installed without a gap. When the sensor is mounted on a monitored product, losses and reactive power are measured. The magnitude of mechanical stresses is determined taking into account the calibration dependence by the magnitude of the losses determined from the equation: ДР (cr) - (Р-Р0) - (Q-Qo), where К2 А Р (о) is the calibration dependence of losses on mechanical stress life; P is the amount of loss measured in the controlled product; P0 is the loss value of the unloaded sample when the sensor is installed on it without a gap; Q is the amount of reactive power measured in a controlled product; Qo is the reactive power of the unloaded sample when the sensor is installed on it without a gap; Ki is the proportionality coefficient of linearized dependence of losses on the gap; “2 - proportionality coefficient of linearized dependence of reactive power on the gap. sl C

Description

The invention relates to non-destructive electromagnetic testing of metal products and can be used to determine mechanical stresses in various areas of the national economy,

The known method of measuring mechanical stresses in metal products, which consists in the fact that the pre eddy current transducer is placed above the sample with a given gap, its signal is compensated.

the compensating voltage is chosen to coincide in phase with the maximum voltage on the converter, the amplitude of the compensating voltage is chosen so that when the compensation voltage and voltage on the converter is minimum, a calibration value of the difference signal from the value of mechanical stresses in the sample is obtained, the transducer over the product with a given gap, while measuring, the phase matching is compensatedXI

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The magnitude of the mechanical stresses in the product is judged by the difference of the difference signal and the voltage of the converter.

The disadvantage of the method is that in order to achieve the required accuracy in the measurement and calibration of the need for active monitoring of the gap between the sensor and the surface to be monitored.

The closest to the present invention is a method for measuring the main voltage in magnetic materials, which consists in the fact that after removing a calibration dependence of material loss on a material on the magnitude of mechanical stresses on a sample, several magnetic sensors have radially arranged so that the axial lines of each sensor intersected at one point, with the intersection point of the axial lines aligned with the measured point on the surface of the magnetic material. Magnetic sensors are excited with alternating current and rotated around the measured point. Then, the loss in steel measured by each sensor is compared, and the direction of the axial lines of at least two sensors, in which the difference of losses has become zero, is determined. As a result, the magnitude and direction of the main voltage are obtained at the measured point.

A disadvantage of the known method is the low measurement accuracy due to the influence of the gap. When measuring on a real metal surface, the gap size is a random value and the loss in steel depends not only on the magnitude of the mechanical stresses, but also on the size of the air gap, since part of the scattering flows is closed along the core steel, and the effect of the gap on change in losses is commensurate with the effect of mechanical stresses on the change in losses. Thus, when determining the magnitude of mechanical stresses, it is necessary to take into account the real size of the gap and the scattered fluxes, otherwise the error can reach a large value.

The purpose of the invention is to improve the accuracy of the method of determining mechanical stresses by taking into account the influence of the gap on the measured losses.

This goal is achieved by the fact that in the method of determining mechanical stresses in ferromagnetic products, namely, that a sensor is installed on the surface of a sample from the material of the tested product without a gap, a new one is that the reactive power is measured. The sensor is excited with an alternating current, the sample is loaded with given voltages, the calibration dependence of material loss is removed.

on the magnitude of mechanical stresses, the new one is that when the sensor is installed on the surface of an unloaded sample with a gap, the dependence of losses in the material and reactive power on the gap size is removed, the dependences are linearized, and the proportionality coefficients are determined from them. Then the material loss and reactive power measured by the sensor can be expressed

,

fP P0 + Kih + AP (o)

| Q Q0 + K2 -h

0)

where А Р (о) is the calibration dependence of losses on mechanical stresses, in general, this dependence is non-linear and is expressed graphically;

Р is the amount of losses measured in the controlled product;

Ro is the loss of the unloaded sample when the sensor is installed on it without a gap;

Q is the magnitude of reactive power measured in a controlled product;

QO is the reactive power value of the unloaded sample when the sensor is mounted on it without a gap;

Ki is the proportionality coefficient of linearized dependence of losses on the gap;

K2 - proportionality coefficient of linearized dependence of reactive power on the gap; h is the size of the air gap.

When the sensor is installed on a monitored surface with an unknown gap, the material loss is measured and the reactive power is additionally measured, which is also new. By transforming system (1), the magnitude of the mechanical stresses is determined from the equation

50

AP (o) (P-Po) (Q-Qo) - (2)

FIG. 1 shows the dependence of losses on mechanical stresses for St 20 steel; in fig. 2 is a block diagram of a device that implements a method for determining mechanical stresses in ferromagnetic products.

The device contains an auto-oscillator 1, a sensor 2, a wattmeter 3 and a varmeter 4. The auto-oscillator 1 supplies a sinusoidal voltage to the sensor 2. A wattmeter 3 and a varmeter 4 connected by inputs to sensor 2 measure the material loss and the reactive power consumed by the sensor from the oscillator, respectively.

The method is carried out as follows.

Install the sensor on the surface of the sample from the material of the controlled product without a gap and excite an alternating current with a frequency of 1 kHz. Measured reactive power (Qo) and loss (Ro) in the unloaded material. The dependencies of reactive power and material losses on the gap between the sensor and the unloaded sample are removed. Linearize these dependencies. The proportionality coefficients are determined from them. The sample is loaded with known stresses from 0 to 0.8 yield strength and removes the calibration dependence of the increments of losses in the material on the magnitude of mechanical stresses DG (a). Since the reactive power in the steel is several orders of magnitude less than the reactive power in the gap (at h 0.05 mm), and its change from the effect of mechanical stresses is even smaller, changes in reactive power from the magnitude of the mechanical stresses can be neglected. Then the material loss and the amount of reactive power measured by the sensor can be expressed as follows.

h + L P (o) h

0)

Transform system 1 get the expression

LR (with $ (P-Ro) - - | (Q-Qo). (2)

The sensor is installed on a controlled surface in an unknown air gap, the material loss and the amount of reactive power are measured, substituting these values in expression 2 determine the increment of material loss D P and the calibration dependence of the loss on mechanical stresses shown in the drawing for steel .20, mechanical stresses are found.

All measurements are carried out at a constant induction in the core of the sensor.

Claims (1)

Invention Formula The method of determining the mechanical stresses in ferromagnetic products, which means that the sensor is installed without a gap on the surface of the unloaded material sample the controlled product, excite with alternating current, load the sample with predetermined voltages and remove the calibration dependence of the loss in the material on the magnitude of the mechanical stresses, install the sensor on the monitored surface and measure the losses in the monitored product, according to which, taking into account the calibration dependence, they determine the mechanical stresses that are required and, in order to improve the accuracy, when installing the sensor reactive power is additionally measured on the surface of the unloaded sample, after which the sensor is installed in the same place with gap and additionally remove the dependence of losses in the material and reactive power on the gap, linearize these dependencies and determine the proportionality coefficients for them, and when installing the sensor on a controlled product, reactive power is additionally measured, and the loss is determined from the equation: DR (o) (P-Ro) -C (Q-Qo). where Д Р (о) is the calibration dependence of losses on mechanical stresses: p is the amount of loss measured in the controlled product; PO is the loss of the unloaded sample when the sensor is installed on it without a gap; Q is the amount of reactive power measured in a controlled product; Qo value of reactive power of the unloaded sample when the sensor is mounted on it without a gap; Ki is the proportionality coefficient of linearized dependence of losses on the gap; K2 - proportionality coefficient of linearized dependence of reactive power from the gap. -zoo -is® -6 ° so foo so zoo r & @ -mls) Fi. Jets & F 9ui.2 - / i -l -h g bammvemp 5 bo / e # e / p / e t