RU2399870C1 - Method for continuous control of thickness and continuity of bimetal layer joints - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: bimetal is exposed to an alternating magnetic field of an inductor coil with a flat-topped core piece. A measuring inductor coil is placed with clearance on the side of the ferromagnetic layer of the bimetal and a standard inductor coil is placed on the side of the ferromagnetic layer of the standard. Secondary windings of the inductor coils are connected in series - anti-parallel. Primary windings of the inductor coils are powered by alternating current with frequency at which the effective depth of penetration of eddy-currents is less than the thickness of the measured bimetal layer. Two double-winding hand probe windings are used, which are placed with clearance on the opposite side of the bimetal and standard sample respectively. Secondary windings of the coils are connected in series - anti-parallel , and primary windings are powered by alternating current on at least two frequencies. The first frequency is selected such that penetration depth of eddy currents is less than thickness of the controlled bimetal layer and the second is such that the said depth is greater than the said thickness. Deviation of thickness of the second layer and continuity of the joint of bimetal layers from the standard are determined at the first and second frequencies respectively from change in voltage across the secondary winding of the measuring coil relative voltage of the secondary winding of the coil lying above the standard.

EFFECT: higher accuracy and broader functional capabilities.

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Description

The invention relates to a control and measuring technique and can be used for continuous monitoring of the thickness and continuity of the connection of the bimetal layers in the manufacturing process of manufacturing multilayer products.

A known method of controlling the thickness of metal surface layers (AS USSR No. 1758413, G01B 7/00, G01N 27/90, 1990), which consists in the fact that the material is exposed to an alternating magnetic field, measured by an inductive transducer on the surface of this material the normal and tangential components of this field are determined by the ratio of the signals of this transducer, an alternating magnetic field is excited at least at two frequencies by an indicator with a U-shaped magnetic circuit, the poles in contact with the material being controlled, normal th field component measured on the axis of symmetry between said poles tangential component measured under a magnetic pole and said determined ratio relationship at each of the frequencies of the magnetic field on which is fixed the thickness of the surface layer material.

The disadvantages of this method are the determination of the thickness of only one layer of two-layer products, as well as the inability to use this method for contactless control, which significantly reduces the scope and functionality.

There is also known a method for continuously monitoring the thickness of the layers of bimetal with a ferromagnetic base (RF Patent No. 220058, G01B 7/06, G01N 27/90, 08/10/2003, Bull. No. 22), which consists in the fact that bimetal is exposed to an alternating magnetic field, which excited by an inductor with a U-shaped magnetic circuit, the measuring inductor is positioned with a gap on the side of the ferromagnetic layer of the bimetal, the reference on the side of the ferromagnetic layer of the standard, and the secondary windings of the inductor are connected in series with each other, the deviation of the thickness of the ferromagnetic layer is bimetal lla from the reference is determined by the voltage change of the secondary winding of the inductor relative to the measuring reference voltage secondary winding inductor.

This method is more effective than the previous one and allows you to expand the scope while maintaining the accuracy of measuring the thickness of the layers of bimetal, however, it has a number of significant disadvantages, namely:

- insufficient accuracy of measuring the thickness of the layers of bimetal in the manufacturing process of manufacturing multilayer products;

- the inability to control the continuity of the connection of the bimetal layers.

EFFECT: increased accuracy of measurement of bimetal layers in the rolling process and expansion of functionality by controlling the continuity of the connection of the bimetal layers.

The technical result is achieved by the fact that in the method consisting in the fact that the bimetal is exposed to an alternating magnetic field, which is excited by an inductor with a U-shaped magnetic circuit, the measuring inductor is placed with a gap on the side of the ferromagnetic layer of the bimetal, the reference on the side of the ferromagnetic layer of the reference, the secondary windings of the inductor are connected in series-counter, the deviation of the thickness of the ferromagnetic layer of the bimetal from the standard is determined by the change in the voltage of the secondary winding of the measuring ind ctor relative to the voltage of the secondary winding of the reference inductor, the primary windings of the electromagnets are supplied with alternating current from a generator of such a frequency when the effective penetration depth of the eddy currents is less than the thickness of the measured bimetal layer, and two double-winding patch coils are used, which have a bimetal with a gap on the opposite side and a reference sample, while the secondary windings are connected sequentially in the opposite direction, and the primary windings of the coils are powered by an alternating t com at least at two frequencies, and the first frequency is chosen so that the penetration depth of the eddy currents is less than the thickness of the controlled bimetal layer, and the second is greater, the deviation of the thickness of the second layer and the continuity of the connection of the bimetal layers from the reference are determined respectively at the first and second frequencies voltage change on the second winding of the measuring coil relative to the voltage of the secondary winding of the coil located above the standard.

The drawing shows a diagram of a device that implements a method for continuously monitoring the thickness and continuity of the connection of the layers of bimetal.

The device consists of a bimetallic strip 1, reference 2, two inductors, one of which is measuring 3, and the other is reference 4. The secondary windings of the inductors 3 and 4 are connected in series and opposite, and the primary are powered by alternating current from the generator 5 of such a frequency, when the effective depth the penetration of eddy currents is less than the thickness of the measured layer of bimetal. The structure of the device includes a rectifier 6, a deviation indicator of thickness 7, and double-winding overhead coils - measuring 8 and reference 9. The secondary windings of coils 8 and 9 are connected in series and opposite, and the primary windings of coils 8 and 9 are supplied with alternating current at least at two frequencies from generator 10, while the first frequency is chosen such that the penetration depth of the eddy currents is less than the thickness of the controlled bimetal layer, and the second is greater. The device also uses a demodulator 11, an amplifier 12, and a microprocessor device 13 to register deviations in the thickness and continuity of the connection of the layers of the bimetallic strip.

The method is as follows.

The bimetallic strip 1 and the reference 2 are magnetized using the U-shaped electromagnets of the measuring 3 and the reference inductors 4 at a fixed frequency by the generator 5. The electromagnets are mounted on the side of the ferromagnetic layers of the bimetallic strip and the reference. In an electromagnet, the magnetic circuit is closed by a measured strip, in the reference - by the standard. The primary windings of electromagnets are supplied with alternating current from a generator of such a frequency when the effective penetration depth of the eddy currents is less than the thickness of the measured strip. In the secondary windings of electromagnets, voltages occur that are proportional to the thicknesses of the measured ferromagnetic base of the bimetal and the standard. The secondary windings are connected so that their voltage in the comparison circuit is directed towards one another. Since the voltage coming from the secondary winding of the reference electromagnet is constant, and the voltage from the secondary winding of the measuring electromagnet, which controls the thickness of the ferromagnetic layer of the rolled bimetallic strip, varies depending on the change in this thickness, the resulting voltage will be proportional to the deviation of the thickness from the specified reference. The rectified current flows to the pointer 7 deviations of the thickness of the ferromagnetic layer of the bimetallic strip from a given thickness.

The inductance of the electromagnetic system is equal to:

where n is the number of turns;

l _W and l _in - respectively, the length of the magnetic circuit and the air gap;

S _W and S _in - section of the magnetic circuit and the air gap;

µ _W and µ _in - magnetic permeability of iron and air;

R _f - losses in the magnetic circuit penetrated by the magnetic flux _f ;

ω is the angular frequency.

Since for the radical expression in the above formula, the following holds:

then with a slight error, we can assume that the inductance of the system is equal to:

Given that the magnetic permeability of iron is µ _W = 7000-7500, and air µ _in = 1, i.e.

can take

The total resistance of the winding is calculated by the well-known formula:

where R is the active resistance of the coil winding.

In practice, the active resistance of the winding R is much less than the inductive ωL, therefore, the active resistance is not taken into account in the calculations. Based on the measured values of voltage U and current I, the impedance is calculated

and then inductance

from here we obtain the dependence of the thickness of the air gap on the change in voltage occurring on the coil:

Double-winding overhead coils - measuring 8 and reference 9 are positioned with a gap on the opposite side of the strip of bimetal 1 and reference sample 2 respectively. The secondary windings of the coils 8, 9 are connected in series and opposite, and the primary windings of the coils are supplied with alternating current from the generator, at least two frequencies, and the first frequency is chosen so that the penetration depth of the eddy currents is less than the thickness of the controlled bimetal layer, and the second is greater.

The sinusoidal current of the first frequency, acting in the exciting (primary) windings of the measuring and reference overhead coils, creates an electromagnetic field that excites eddy currents in the electrically conductive upper layer of the bimetallic strip. These eddy currents decay as they penetrate deep into the investigated object. The electromagnetic field of eddy currents acts on the secondary windings of the measuring 8 and reference 9 coils, inducing emfs in them, which are proportional to the thicknesses of the measured upper layer of bimetal and reference. The voltage of the reference coil is also constant, and the voltage of the measuring coil, which controls the thickness of the upper layer of the bimetallic strip, varies depending on the change in this thickness. The resulting signal is fed to the demodulator 11, the output of which creates a rectified voltage proportional to the deviation of the thickness of the bimetal layer from the specified standard. The rectified and amplified signal by the amplifier 12 is fed to the input of the microprocessor device 13, where the thickness deviation is recorded.

The value of the penetration depth δ of eddy currents of the used frequency in the layer material is calculated by the well-known formula:

. Так при

только 0,7% возбуждаемых вихревых токов проникают через исследуемый слой, а 99,3% - нет. При таком исполнении увеличивается чувствительность устройства и появляется возможность измерения толщины слоя биметалла в сотые доли мкм, что повышает точность измерения, а также возможность измерения сплошности соединения слоев биметалла на второй частоте.where ω is the circular frequency of the excitation current; µ _a is the absolute magnetic permeability of the material layer; σ is the electrical conductivity of the material. Calculations show that, for example, at an excitation current frequency of 10 MHz at a material depth h = 1δ, eddy currents decay ~ up to 37%, at h = 2δ up to 13.5%, and at h = 3δ up to 5%. This means that with a strip thickness h <δ, more than 37% of eddy currents will penetrate through the strip, thereby reducing the sensitivity of the device, which will lead to the impossibility of measuring coatings in tenths of a micron, as well as to the impossibility of measuring the continuity of the connections of the bimetal layers at the second frequency. To increase the sensitivity of the device, a frequency of the supply current is chosen such that the penetration depth of the eddy currents δ does not exceed

. So with

only 0.7% of the excited eddy currents penetrate the studied layer, while 99.3% do not. With this design, the sensitivity of the device increases and it becomes possible to measure the thickness of the bimetal layer in hundredths of a micron, which increases the accuracy of the measurement, as well as the ability to measure the continuity of the connection of the bimetal layers at the second frequency.

To measure the continuity of the bimetal layers, the penetration depth of the eddy currents is chosen greater than the layer thickness, i.e. δ> h. A sinusoidal current of the second frequency, acting in the exciting (primary) windings of the measuring 8 and reference 9 coils, creates an electromagnetic field that excites eddy currents in the electrically conductive upper layer of the bimetallic strip. These eddy currents decay as they penetrate deep into the investigated object. The electromagnetic field of eddy currents acts on the secondary windings of the measuring 8 and reference 9 coils, inducing emfs in them, which are proportional to the change in the continuity of the connection of the bimetal and reference layers. The voltage of the reference coil is also constant, and the voltage of the measuring coil, which controls the continuity of the connection of the layers of the bimetal strip, varies depending on changes in the continuity of the connection of the layers and the thickness of the bimetal layer. The resulting signal is supplied to the demodulator 11, the output of which creates a rectified voltage proportional to the change in the continuity of the connection of the layers and the thickness of the bimetal from a given standard. The rectified and amplified signal by the amplifier 12 is fed to the input of the microprocessor device 13, where the signals at the first and second frequencies are compared, and the change in the continuity of the connection of the bimetal layers is judged by the voltage difference.

Thus, the deviation of the thickness of the second layer and the continuity of the connection of the bimetal layers from the reference are determined, respectively, at the first and second frequencies by the voltage change at the second winding of the measuring coil relative to the voltage of the secondary winding of the coil located above the reference.

To test the operability of the proposed technical solution at ZPS AO (Tambov), on a roll production line of a bimetallic strip with dimensions of thickness (1.9-4.5) mm with an antifriction layer AO-10, AO-20-1, thickness measurements were carried out and continuity of the connection of the bimetal layers during the rolling process, the measurement error in this case did not exceed 3.0%.

Claims (1)

A method for continuously monitoring the thickness and continuity of the connection of the bimetal layers, namely, that the bimetal is exposed to an alternating magnetic field, which is excited by an inductor with a U-shaped magnetic circuit, the measuring inductor is positioned with a gap on the side of the ferromagnetic layer of the bimetal, the reference on the side of the ferromagnetic layer of the reference, moreover, the secondary windings of the inductors are connected in series - counter, the deviation of the thickness of the ferromagnetic layer of the bimetal from the standard is determined by the change in voltage of the secondary windings of the measuring inductor relative to the voltage of the secondary winding of the reference inductor, characterized in that the primary windings of the inductors are supplied with alternating current from the generator of such a frequency, when the effective penetration depth of the eddy currents is less than the thickness of the measured layer of bimetal, and they also use two double-winding patch coils, which are located with the gap on the opposite side, respectively, of the bimetal and the reference sample, while the secondary windings are connected in series - counter, and The egg windings of the coils are supplied with alternating current at least at two frequencies, the first frequency being chosen such that the penetration depth of the eddy currents is less than the thickness of the bimetal layer being monitored, and the second is larger, the deviation of the thickness of the second layer and the continuity of the connection of the bimetal layers from the standard are determined respectively, at the first and second frequencies according to the voltage change at the second winding of the measuring coil relative to the voltage of the secondary winding of the coil located above the standard.