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Assessment of the state of a lubricator by the size of the acoustic signal
in a loaded pair of friction of a mining machine transmission
To cite this article: V I Knyazkina et al 2020 J. Phys.: Conf. Ser. 1515 052037
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ICMSIT 2020
Journal of Physics: Conference Series 1515 (2020) 052037
IOP Publishing
doi:10.1088/1742-6596/1515/5/052037
1
Assessment of the state of a lubricator by the size of the
acoustic signal in a loaded pair of friction of a mining machine
transmission
V I Knyazkina, K A Safronchuk, S L Ivanov and E V Pumpur
Saint-Petersburg Mining University, 2, 21st line, Saint-Petersburg, 199106, Russia
E-mail: knyazkina.valeriya.94@mail.ru
Abstract. As a result of the studies, the possibility of assessing the state of the working surfaces
of mining machines, in particular bearing assemblies as a whole without disassembling the
gearbox, is confirmed. An innovative solution in this matter is to ensure the delivery of the
lubricator to tribolcoupling through the channels of the lubrication system, according to its state,
determined by the size of the acoustic signal of the ultrasonic range in the friction pair.
1. Introduction
Today, the development of the mining industry cannot be imagined without the operation and use of
mining machines of increased reliability and power of mining equipment. It is possible to increase its
reliability by preventing the identified causes of failures of mining equipment operating in difficult
geological conditions of open cuts under adverse weather conditions, against the background of high
dynamic and stationary loads in the transmissions of mining machines, and timely and high-quality
maintenance and repair.
The time to eliminate the consequences of unscheduled shutdowns, depending on the severity of the
consequences of failures in the current situation, is determined by the complexity of the work to restore
the working condition, the repair manufacturability of a failed unit or element, and the mechanization
of repair and maintenance work. Moreover, in the systematization of failures, they are divided into three
groups: failures associated with the mechanical system of the mining machine, electrical or hydraulic
system, and work on setting up the drives.
2. Systematization of the causes of mining machines failures
Figure 1 shows the Poreto diagram for the failures of the mechanical part of the excavator. The diagram
shows that one third of failures is associated with failures of the excavator's running mechanism. Such
failures should be classified as constructive. Approximately the same level of reliability has a lifting
mechanism, slewing ring, pressure mechanism. Failures of these elements of the system are caused by
the action in excess of normative loads during excavator operation, associated with difficult mining and
geological conditions, poor preparation of the face and operator control of the excavator, insufficient
lubrication of moving parts of mechanisms and transmissions. As a result, intense degradation processes
take place in the drive elements, a break in the teeth of the gear wheels [4].
The wear process is the leading degradation process for excavator drives. Approximately 79% of all
failures in mining equipment are associated with the wear of elements of electromechanical equipment.
ICMSIT 2020
Journal of Physics: Conference Series 1515 (2020) 052037
IOP Publishing
doi:10.1088/1742-6596/1515/5/052037
2
Figure 1. Analysis of breakdown time
of excavators due to failures of
elements of the mechanical system.
The process of wear of the elements in contact with each other is accompanied by an increased level
of vibration , which further activates this degradation process, exacerbated by the growing imbalance of
the rotors; alignment of shafts of aggregates and mechanisms; weakening of landings, changing the
shape and size of the elements of the movable joints, and in particular gears, accompanied by distortions
of the supports; increased wear of other resource-determining tribocouplings - transmissions and other
kinematic pairs of mining machines as a whole.
In order to ensure a high level of reliability and maintainability of mining equipment, statistics were
collected on the failure of components and assemblies of mining machines, from 2016 to 2019. It was
established that the transmission system is the weakest point of the mining machine, and in particular
their bearing assemblies. The service life of the bearing assemblies depends on many reasons, but the
most common causes of damage are the drawbacks and defects of the lubricating composition (figure
2).
Figure 2. Failure analysis of bearing assemblies.
3. The need to assess the lubricant in the transmission of the mining machine
To ensure the normal operation of mining machines, in severe operating conditions, the grease must
guarantee the separation of the contacting surfaces, prevent scuffing and seizing, and reduce the wear
rate. The selection of the appropriate type of grease for the bearing assemblies is critical. A reasonable
choice of lubricants plays an extremely important role in ensuring a high level of operational reliability
of mining equipment. Therefore, the lubricating medium should be considered an equal element of the
tribological system [2, 5]. At the same time, if the attitude to the selection of the composition and grades
of steels for the manufacture of parts of mining machines, as well as the technological processes to
improve their mechanical properties is serious , the choice of a lubricant is not always the same.
ICMSIT 2020
Journal of Physics: Conference Series 1515 (2020) 052037
IOP Publishing
doi:10.1088/1742-6596/1515/5/052037
3
Since the main cause of failure of mining machines is the increased wear of resource-determining
tribological couplings [2, 3], therefore, the lubricating medium should be considered an equal element
of the tribological system.
At present, physical and mechanical laboratory tests of materials is of great importance, since they
allow to get the most accurate forecast with a minimum of material costs 3 ,5. The current level of
development of friction and wear tests is characterized by a wide variety of test designs. Laboratory
tests are reduced to obtaining the necessary information about the object using its model 3. In this case,
the adequacy of the results obtained to real processes is possible when there is a unified physical nature
of the phenomena occurring in the studied object and in the model accepted as the basis by the researcher
2, 3.
In the gears of mining machines, the contact in the gearing of the transmissions occurs along the line,
while the temperature in the contact can reach 150 ... 600 ºС. Under these operating conditions, the
grease should guarantee separation of the contacting surfaces, prevent scuffing and seizing, and help
reduce the wear rate. In addition, the lubricant should have a stable viscosity, low pour point, good
anticorrosion properties [2].
When assessing the lubricity of oils, it is necessary to reliably determine the nature of the friction in
the contact, which in turn can be estimated by the value of the coefficient of friction. The acoustic signal
of the ultrasonic frequency range in the friction pair allows us to fully evaluate the nature of the friction.
It also says a lot about the state of the lubricator, the friction pair where it is located [3].
4. The experimental part
A stand was developed to identify the patterns of change in the acoustic signal of the ultrasonic range
from the specific load and speed in the contact, the friction pair according to the “counterbody-plate”
scheme. A detailed description of it is given in the paper 1. As an artificial medium, TAD-17 and
Mobil ATF 3309 grease were used. The counterbody pressure on the plate was in the range from 0.773
MPa to 9.01 MPa at a counterbody rotation speed of 30.89 rad / s to 60.2 rad / s.
Changes of the size of the acoustic emission signal of external friction in the kinematic pair were
carried out by device METKATOM ARP-11. In the course of the experiments, the parameter D was
estimated, which is proportional to the value of the acoustic signal in the ultrasonic frequency band that
occurs in the contact during friction in the “counterbody-plate” pair.
Figure 3 shows the changes in the value of the acoustic signal, expressed by indicator D, for a
sequential series of angular velocities at constant vapor pressures for the TAD-17 lubricant. The
experimental data were processed to obtain the average harmonic estimate of three measurements,
followed by approximation by a power function. As can be seen from the figure, there is a stable
tendency for indicator D to increase with increasing angular velocity, and the higher the pressure in the
friction pair, the more rapidly the D increases, which indicates the deterioration of the friction conditions
in the pair, squeezing the grease out of the contact and switching to dry friction.
Figure 3. The change in the size of indicator D
because of the speed in pair of friction with
grease "TAD-17".
Similarly figure 4 shows the changes in the value of the acoustic signal, expressed in terms of D, for
a series of angular velocities at constant pressures in a pair for grease Mobil ATF 3309.
ICMSIT 2020
Journal of Physics: Conference Series 1515 (2020) 052037
IOP Publishing
doi:10.1088/1742-6596/1515/5/052037
4
Figure 4. The change in the value of
indicator D from the speed in the
friction pair with the lubricant
"Mobil ATF 3309".
Figure 5 and figure 6 show the changes in the size of the acoustic signal, expressed in terms of
indicator D, for a sequential series of pressures in the friction pair at constant angular velocities for
lubricants TAD-17 and Mobil ATF 3309.
Bearing in mind the presented trends, according to the results of laboratory experiments, it was
possible to identify areas of boundary friction below 6 MPa. Friction conditions with TAD-17 and Mobil
ATF 3309 lubricants generally have a common trend. In case of high loads and speeds when applying
TAD-17 grease, the indicator of the acoustic emission signal of friction increases sharply, which
indicates that at high loads and speeds this type of gear oil should not be used for transmission elements
of mining machines in similar operating conditions . Based on previous studies presented in [1], it was
also revealed that this region of boundary friction is the limit for the type of industrial oil I-20 lubricant
during the copper-coating process, and such friction will be the most preferred as a result, even in
comparison with Mobil ATF 3309 greasing.
Figure 5. The change in the sizeof indicator D
from the pressure in the pair of friction with
lubricant "TAD-17".
Figure 6. The change in the size of indicator D
from the pressure in the friction pair with grease
"Mobil ATF 3309".
As a result of the studies, the possibility of assessing the condition of the working surfaces of mining
machines, in particular bearing assemblies in general, without disassembling the gearbox has been
confirmed. An innovative solution in this matter is to ensure the delivery of the lubricator to tribological
coupling through the channels of the lubrication system, upon receiving the acoustic signal of the
ultrasonic range in the friction pair, the value of which is above the permissible limit. As a part of the
maintenance and repair strategy for the actual condition, implementing the technology of routine
maintenance of mining equipment and identifying defects in resource-defining mates, it is possible to
effectively replace, recycle, clean and restore the properties of oils, lubricants, and working fluids for
mining machines.
ICMSIT 2020
Journal of Physics: Conference Series 1515 (2020) 052037
IOP Publishing
doi:10.1088/1742-6596/1515/5/052037
5
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