RU2113699C1 - Device for diagnostics of rolling bearings - Google Patents

Abstract

FIELD: measurement technology, mechanical engineering. SUBSTANCE: device is intended for test and prediction of state of rolling bearings under conditions of known type of wear-out. It has driving shaft, two current collectors, registering equipment and source of electric voltage which one pole is coupled via first current collector to driving shaft and which second current collector can be connected to outer race of bearing. Device is also fitted with integrator and degree converter which one input is connected to second pole of source of voltage, which second input is connected to second current collector and output is coupled to input of integrator. Registering equipment is connected to its output. Values of index of conversion function can be adjusted in degree converter which increases accuracy of diagnosis. EFFECT: increased accuracy of diagnosis. 1 cl, 1 dwg

Description

 The invention relates to the field of measuring equipment and can be used mainly in various branches of mechanical engineering for monitoring and predicting the state of rolling bearings under conditions where the dominant type of wear is known.

 Known devices in which the rings of a controlled bearing are included in an electric circuit in series with a voltage source and a measuring device that determines the parameters of the electric current through the bearing. As a diagnostic parameter, for example, the normalized integral contact time of parts, defined as the relative total duration of the current pulses, is used.

 However, the wear rate is affected not only by the time during which the metal contact of the bearing parts occurs, but also by the forces in the contact zones. At the same time, the force in the contact determines the actual area, and therefore the electrical resistance of the contact and the amplitude of the current through the bearing. The known device does not take into account the amplitude of the current, therefore, the accuracy of assessing the condition of the bearing is limited.

 The closest in technical essence to the proposed one can be considered a device containing a drive shaft made with the possibility of installing and fixing the inner ring of a monitored bearing, two current collectors, recording equipment and an electric voltage source, one pole of which is connected to the drive shaft through the first current collector and the other through the recording equipment is connected to a second current collector, which is configured to be connected to the outer ring of a monitored bearing. This device is taken as a prototype.

 The recording equipment responds to current values in a circuit formed by series-connected voltage sources, a first current collector with a drive shaft, a bearing, a second current collector and recording equipment. In this case, both the microcontact time in the bearing and the forces in the contact zones are taken into account.

 However, the functional relationship between the wear rate and the current through the bearing, shown below, is non-linear, and the known device responds to the current value in the first degree, which limits the accuracy and reliability of assessing the condition of the bearing.

 The invention solves the problem of improving the accuracy of diagnosis.

 This is achieved by the fact that the known device comprising a drive shaft configured to mount and fasten the inner ring of a controlled bearing, two current collectors, recording equipment and a voltage source, one pole of which is connected to the drive shaft through the first current collector and the second current collector is connected to the outer ring of the monitored bearing, according to the invention is additionally equipped with an integrator and a power converter, one input of which is is dined with the second pole of the voltage source, the second input is connected to the second current collector, and the output is connected to the integrator input, to the output of which the recording equipment is connected. Moreover, the power converter is configured to control the value of the exponent N of the conversion function.

 The drawing shows a diagram of the device.

 The inner ring of the monitored bearing 1 is mounted and fixed on the drive shaft 2, one pole of the voltage source 3 through a current collector 4 is connected to the drive shaft 2, the second pole is connected to the first input of the power converter 5, the second input of which is connected through the current collector 6 to the outer ring of the monitored bearing 1, and the output is connected to the input of the integrator 7, to the output of which the recording equipment is connected 8. The power converter 5 may contain, for example, a series-connected converter 9 Vatel current - voltage, a logarithmic circuit 10, an amplifier 11 with adjustable gain and N antilogarifmiruyuschy converter 12.

 The device operates as follows. The inner ring of the monitored bearing 1 is rotated by means of the drive shaft 2. During the operation of the bearing, due to the hydrodynamic effect, a stable film of lubricant appears between its rolling bodies and rings, which prevents metal contact of the parts. The film thickness in the friction zones continuously fluctuates, short-term local destruction of the film in the contacts of the highest microroughnesses is possible - microcontacts. As a rule, a lubricant has a low electrical resistivity, therefore, when microcontacting in a bearing, the electrical resistance between its rings sharply decreases (by several orders of magnitude), and the current in a circuit containing a series-connected bearing 1, shaft 2, current collector 4, voltage source 3 , power converter 5 and current collector 6, respectively, increases.

 Thus, the metal contacting of the bearing parts corresponds to current pulses in the circuit, the duration of which is equal to the time of microcontacting, and the amplitude is determined by the contacting conditions, in particular, the value of the actual contact area.

Power converter 5 converts the instantaneous current value into a signal proportional to the current in the selected degree N. Moreover, the conversion is as follows. The current value in the circuit i (t) is converted by block 9 into a voltage proportional to the current U ₉ (t) ~ i (t), and at the output of the logarithmic circuit 10, the voltage U ₁₀ (t) ~ lnU ₉ (t) ~ lni (t ) After amplifying the signal by the amplifier 11 N times and performing an exponential conversion by the anti-logarithmic converter 12, a voltage is generated at the output of the power converter 5
U ₅ (t) = U ₁₂ (t) ~ exp [N • U ₁₀ (t)] ~ exp [N • lni (t)] ~ i ^N (t).

 By changing the gain N of the amplifier 11, it is thus possible to adjust the value of the exponent of the conversion function of block 5. The circuit implementation of blocks 9-12 of the power converter 5 can be carried out, for example, in accordance with the recommendations.

 After integrating the voltage from the output of the power converter 5 by the integrator 7, it enters the recording equipment 8. The integrator 7 can be made, for example, in the form of an integrating RC circuit, and as recording equipment 8, for example, an N-388-1P recording recorder can be used .

 Thus, the recording equipment 8 responds to the value of the diagnostic parameter, which is proportional to the average for the time corresponding to the integration constant of block 7, to the value of the instantaneous currents through the monitored bearing raised to the power N.

 The value of the exponent N is selected taking into account the type of bearing and the dominant type of wear. For example, when diagnosing ball bearings under conditions where frictional wear is dominant, N = 3 is assumed. The required value of N is set by adjusting the power converter 5 before performing the diagnosis.

 The proposed device compares favorably with the prototype with a higher accuracy in determining the technical condition of bearings. It was established that the wear rate and current in the circuit are in a functional relationship, however, this possibility is nonlinear. In addition, the contact conditions are constantly changing, therefore the amplitude, shape, duration of an individual pulse, as well as the repetition rate of current pulses in the measuring circuit are random values. The known device responds to the current value in the first degree and, therefore, has a methodological error.

 The proposed device is devoid of this drawback. The technical condition of the bearing is determined by a parameter proportional to the average current value to a degree other than unity, and the exponent is selected in accordance with the dependence of the intensity of the dominant type of wear on the current in the circuit. So, for example, if the intensity of frictional wear of a ball bearing is proportional to the cube of the current, then when diagnosing with the purpose of subsequent monitoring and predicting the technical condition of ball bearings by frictional wear, the device measures a parameter with an exponent of three.

 Thus, the proposed device evaluates the condition of the bearing by a parameter functionally related to the intensity of the dominant type of wear, which increases the accuracy of diagnosis.

 The following is a definition of the functional relationship between the friction wear rate and the current through the ball bearing.

 Frictional wear of the ball bearing occurs due to slipping when contacting on microprotrusions of the working surfaces of the bearing parts. In the presence of an indissoluble lubricating film between the contacted surfaces, frictional wear is not observed.

 Consider the case when the friction mode in the bearing is mixed, close to hydrodynamic. In this mode, most bearings work, it is characterized by the fact that the main load is absorbed by a stable layer of hydrodynamic lubricating film, while at the same time short-term metal contacts of parts are possible.

It is known that the frictional wear of ball bearings is proportional to the pressure in the contact zone to a degree other than unity. For elastic contact [1]
I _h ~ p $\genfrac{}{}{0ex}{}{\text{(26 + t) / 13}}{\text{c}}$ , (one)
where I _n is the intensity of linear wear;
p _c - circuit pressure in the contact zone;
t is the parameter of the friction fatigue curve (in the general case, t = 3 ... 12).

Тогда ток через подшипник определится [3]
i ~ (A_r•n)^1/2 ~ ε^11/2 (6)
С учетом (6) и (3) интенсивность изнашивания
I_h~ i^(26+t)/11 (7)
Значение параметра кривой фрикционной усталости может быть в пределах от 3 до 12. При этом показатель степени тока может иметь значение от 2,64 до 3,45. С учетом случайного характера контактирования различных деталей в подшипнике при отсутствии дополнительных сведений о значениях t для материалов деталей целесообразно принять среднее значение показателя степени. Тогда
I_n ~ i³ (8)
Выражение (8) показывает, что интенсивность фрикционного изнашивания шарикоподшипников пропорциональная кубу тока через подшипник.In accordance with the theory of elasticity, the contact pressure is interrelated with the relative approximation of ε of the surfaces during contact [2]
ε ~ p $\genfrac{}{}{0ex}{}{\text{2/13}}{\text{c}}$ (2)
Then the relative approach of ε surfaces corresponds to the wear rate
I _h ~ ε ^{(26 + t) / 2} (3)
At the same time, the relative proximity ε corresponds to the actual contact area A _r , consisting of n conductive contact spots [2]

Then the current through the bearing is determined [3]
i ~ (Ar _r • n) ^1/2 ~ ε ^11/2 (6)
Taking into account (6) and (3), the wear rate
I _h ~ i ^{(26 + t) / 11} (7)
The value of the parameter of the frictional fatigue curve can be in the range from 3 to 12. Moreover, the degree of current can have a value from 2.64 to 3.45. Given the random nature of the contact of various parts in the bearing in the absence of additional information about the values of t for the materials of the parts, it is advisable to take the average value of the exponent. Then
I _n ~ i ³ (8)
Expression (8) shows that the intensity of frictional wear of ball bearings is proportional to the cube of current through the bearing.

 During operation of the bearing, the contact conditions are constantly changing, therefore, to assess the performance of bearings by frictional wear, it is advisable to measure a parameter defined as the average value of the current cube.

Literature
1. Kragelsky I.V., Dobychin M.N., Kombalov V.S. Basics of friction and wear calculations. -M.: Engineering, 1977.

 2. Demkin N. B. Contacting of rough surfaces. -M.: Science, 1970.

 3. Holm R. Electrical contacts. -M .: Foreign literature, 1961.

Claims (2)

 1. A device for diagnosing rolling bearings, comprising a drive shaft configured to mount and fix the inner ring of a monitored bearing, two current collectors, recording equipment and an electric voltage source, one pole of which is connected to the drive shaft through the first current collector and the second current collector to the outer ring of the monitored bearing, characterized in that it is equipped with an integrator and a power converter, one input of which is connected a second pole of the source voltage, a second input connected to a second current collector, and an output connected to the input of the integrator, the output of which is connected to the recording apparatus.  2. The device according to claim 1, characterized in that the power converter is configured to control the value of the exponent of the conversion function.