RU2390012C1 - Method of analysing ferromagnetic particles in oil - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed method of analysing ferromagnetic particles in oil involves successive exposure of the analysed sample to a magnetic field in different directions. The said magnetic field is constant. An alternating magnetic field whose parametres depend on differential magnetic permeability averaged in the volume of the oil is additionally applied in a fixed direction. Concentration of particles is determined from the difference between these parametres measured for different directions of the constant magnetic field.

EFFECT: selective analysis of irregularly shaped particles formed only as a result of friction.

3 cl, 2 dwg

Description

The invention is intended to measure the concentration of microparticles of iron and its alloys in lubricants in order to determine the degree of wear of friction pairs and can be used both for periodic analysis of the state of machine components and mechanisms, and for continuous monitoring during their operation.

Analysis of the content of ferromagnetic particles in oil, as a means of indicating the technical condition of friction units, has been known for a very long time. In most cases, the ferromagnetic properties of particles are used to increase their local concentration due to the attraction of an inhomogeneous constant magnetic field to the source. Further analysis is usually carried out by optical methods or by changing the capacitance of the capacitor covering the oil flow [1]. A long exposure is required here, and it is difficult to establish the number of particles responsible directly for the wear of friction pairs, since the change in the optical properties or capacitance of the capacitor is also caused by non-metallic impurities in the oil.

There are technical solutions that directly use their ferromagnetic properties for particle analysis. The latter affect the inductance of the electric coil covering the oil volume, which is an integral part of the oscillatory circuit. However, a direct indication of its natural frequency gives poor results due to strong drift, and one has to look for methods that use a frequency shift provoked by a controlled external action, for example, by cyclic inclusion of a constant magnetic field [2]. Another analysis method based on monitoring the average magnetic permeability of oil is to use the test volume as the core of the transformer [3]. In this case, the secondary alternating voltage depends on the concentration of particles. Although these methods directly measure the content of a particle of iron and its alloys, they do not distinguish their shape. The fact is that in addition to the process of wear of friction pairs, the supplier of metal particles is pitting corrosion. Numerous studies have established that in this case spherical particles are formed, while microparticles obtained by friction always have elongation. The ratio of the maximum and minimum sizes is in the range of 3-10.

The closest to the essence of the proposed application can be considered an analysis method that is sensitive to differences in particle shape [4]. Outwardly, the measurement circuit resembles a transformer version. There is a primary winding fed by alternating voltage and a secondary winding used to measure voltage. In order to compensate for the background signal, the latter is divided into two sections, one of which surrounds the volume under study, the second is parallel. The sensitivity of the method to the shape of the particles follows from the fact that the measurements are carried out with a frequency variation in the range of 1-100 Hz. In this case, the signal from the low-frequency edge of the spectrum is higher. Obviously, this effect is due to torsional vibrations or even complete rotation of nonspherical particles under the influence of an alternating magnetic field and, as the authors correctly noted, carries information about the viscosity of the sample. In the second measurement variant, the results obtained by alternately applying a magnetic field in mutually perpendicular directions are compared.

The main disadvantage of this method is the dependence of the information received on too many factors, which makes its interpretation very difficult.

Proposed in the prototype method of exposure to the sample by alternating cross magnetic field can be transformed so that it only responds to the presence of elongated particles. This is exactly what was done in the claimed method. The essence of the analysis is to use for such an effect not a variable, but a constant magnetic field. To completely eliminate the effect of viscosity, the direction switching is carried out with a period sufficient to orient all elongated particles along the lines of force. Studies have shown that for the vast majority of particles formed during friction, this time is about a second. The method is based on the fact that the effective magnetic permeability of any nonspherical ferromagnetic body depends on its orientation with respect to the measurement direction, taking the maximum and minimum values in the directions of maximum and minimum sizes, respectively. This is also true for microparticles. The control of the averaged differential magnetic permeability is carried out on the basis of measuring the frequency of the natural oscillations of the circuit containing the coil covering the test volume of the sample. The first measurement is made with the orientation of a constant magnetic field along the axis of the coil, the second in the transverse direction. The difference shows the level of elongated ferromagnetic particles. The specific concentration of these particles in "ppm" is found by the calibration function, pre-built according to the measurement results of standard samples.

The implementation scheme of the described method is shown in figure 1. A test tube with an oil sample 1 is passed into the winding 2, which is included in the oscillating circuit, which sets the frequency of the generator 3. The alternating voltage excited in the circuit is supplied to the control and processing unit 4, which also alternately turns on the windings, which create a constant magnetic field in the sample volume: along the circuit A - in the vertical direction, along the chain B - in the horizontal. The oscillation frequency of the circuit is about 80 kHz.

The operation algorithm of the installation is shown in figure 2. At some point in time t ₀ , a rectangular pulse of 2 s duration is supplied along circuit A. After one second, required to calm the transients and to completely rotate the microparticles in the direction of the field, at time t ₁ , the measurement of the frequency of the circuit f ₁ starts, which also lasts 1 second, and ends at time t ₂ simultaneously with the end of the pulse of circuit A .At the same moment, a rectangular pulse of 2 s duration is supplied along circuit B. Also, with a second delay at time t _{3, the} second exposure of the frequency measurement f _{2 is} switched _on , which ends at time t ₄ simultaneously with the end of the circuit pulse B. Then everything repeats again. Each time at the end of the described cycle, the difference is automatically calculated: f ₂ -f ₁ , on the basis of which the desired particle concentration is immediately calculated by the calibration function, displayed with a period of 4 s on the indicator. Thus, the measurement process can be observed in dynamics. All procedures are controlled by an integrated processor.

The described method is implemented in a portable analyzer prepared for serial production. The sensitivity of determining the concentrations turned out to be very high, comparable with x-ray spectral analysis: the detection threshold was a few ppm.

Information sources

1. RF patent No. 2150696 dated 10.26.95.

2. US patent No. 4841244 from 09/18/1989.

3. US Patent No. 5001424 of 03/19/1991.

4. US patent No. 4651092 from 03/17/1987.

Claims (3)

1. The method of analysis of ferromagnetic particles in oil, which includes alternating exposure to the test sample with a magnetic field in different directions, characterized in that said magnetic field is constant, and additionally a variable magnetic field is applied in a fixed direction, the parameters of which depend on the volume averaged differential magnetic permeability oils, and the particle concentration is determined based on the difference of these parameters, measured for different directions of the constant magnetic field . 2. The method according to claim 1, characterized in that of the options for the directions of the constant magnetic field there are perpendicular to each other, of which one coincides with the direction of the alternating magnetic field. 3. The method according to claim 1 or 2, characterized in that the frequency of the alternating magnetic field excited by the surrounding electrical sample, which is part of the oscillating circuit operating in the resonant mode, is used as the measured parameter.

Images