Article citation information:
Wieczorek, A.N. Analysis of the possibility of integrating a mining
right-angle planetary gearbox with technical diagnostics systems. Scientific Journal of Silesian University of
Technology. Series Transport. 2016, 93, 149-163. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2016.93.16.
Andrzej N. WIECZOREK[1]
ANALYSIS OF THE POSSIBILITY OF
INTEGRATING A MINING RIGHT-ANGLE PLANETARY GEARBOX WITH TECHNICAL DIAGNOSTICS
SYSTEMS
Summary. A
key factor enabling the achievement of the required capacity by longwall mining
systems is to obtain a satisfactory service life for individual components of
such systems. Such components include right-angle planetary gearboxes for
armoured face conveyors. An increase in the service life of such equipment can
be achieved by ensuring adequacy in terms of design, materials and
organization. As a part of organizational changes, the use of individual
diagnostics systems may have the greatest impact on the service life of mining
gearboxes; however, their widespread implementation is limited by economic and
operational barriers. This paper presents an analysis of the possibility of
integrating mining gearboxes with electronic systems of technical diagnostics,
as well as expanding the scope of the technical condition monitoring by the machines
operating together with these gearboxes. As a result of the calculation and
design work performed, it has been demonstrated that it is possible to
integrate technical diagnostics systems with advanced data transmission
capabilities inside gearboxes.
Keywords:
mining, gear, vibration
1. INTRODUCTION
Currently, mining gearboxes working
often under harsh operating conditions must be characterized by a high level of
reliability and availability, which is associated with a long service life of
such equipment. This applies particularly to drive units in armoured face
conveyors in mechanized longwall mining systems. The service life of this
equipment can be significantly extended through complex changes in the design,
organization and materials. The issue of improving the service life of
gearboxes with the use of design methods is very complex and requires
specialist engineering knowledge (this problem is described in a number of
publications, e.g., [1,2,4,5]).
One of the most optimal
organizational solutions increasing the service life is the use of systems
monitoring and diagnosing with regard to the technical condition of machines
and equipment. In the scope of the technical diagnostics of gearboxes, there are
many studies concerning the methods of forecasting their condition. While the
problems of predicting technical conditions have been solved to a large extent,
in the case of mining gearboxes, there are operating issues preventing the
widespread use of technical diagnostics methods. These issues first of all
include the susceptibility of electronic circuits to mechanical damage. This
paper presents a concept of solving the problem of premature damage to
diagnostic components by installing them inside gearboxes. An analysis of the
possibility of the practical implementation of the concept was also performed.
2. ANALYSIS OF THE PROBLEM
The current level of technological
and organizational advancement allows for diagnosing the condition of gearboxes
with a high reliability, but the operating factors do not always enable this.
In underground mining, there is a technical infrastructure that enables the implementation
of diagnostics systems. In this context, it is worth mentioning dispatching
systems supervising the processes of haulage, monitoring and controlling
conveyors, as the presentation of data from sensors of process parameters.
The most important operating
problems hindering a widespread use of monitoring systems include:
-
- the need to meet the requirements of ATEX Directive
2014/34/EU; in order to satisfy this requirement, intrinsically safe solutions
should be used, which reduce the functionality of electronic devices or force
the use of heavy explosion-proof enclosures,
-
- the susceptibility of sensors, electronics and
signal cables to damage, which may occur in particular when moving the
components of a longwall mining system.
A factor that hinders the widespread
use of diagnostics systems in underground mining involves the relatively high
ratio of the cost of intrinsically safe diagnostic equipment to the cost
of gearboxes.
At present, gearboxes equipped with
systems for measuring the operating parameters are used in industry. They
include sensors installed primarily on the external part of the gearbox housing,
which operate together with processing systems. An example of such a solution
of a right-angle planetary gearbox of the drive unit in a longwall
armoured face conveyor, with a test diagnostics system installed on the
gearbox housing, is shown in Figure 1. Based on this drawing, the
susceptibility of the presented solution to mechanical damage can easily be
seen.
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(a) |
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(b) |
Fig. 1. Solution involving a
monitoring system installed on the gearbox housing: (a) view of an armoured
face conveyor equipped with gearboxes with a monitoring system and
(b) a detail of the solution
An increase in the resistance to
mechanical damage can be achieved by:
-
making cable covers and installing sensors in places
prepared especially for this purpose in the housing,
-
installing a diagnostics system inside the gearbox
-
using Internet transmission for transferring the
processed measurement data to the dispatching system.
While the implementation of the
first of these tasks is not complicated and is relatively simple (although it
requires an MES simulation to be performed in order to check whether or not the
milling leads to an undesired increase in stresses in the gearbox housing), the
solution of the latter two problems requires significant changes in the design.
The installation of electronic
circuits inside the gearbox is associated with solving the basic problem
connected with the operation of the gearbox, i.e., the problem of an increase
in the temperature in the gearbox housing, which has a significant impact on
the reliability of the operation of electronic components [3]. The
examples of thermograms in mining gearboxes (Fig. 2) clearly show the areas
with a higher temperature (areas of the contact zone between the sealing and
the shaft, as well as areas affected by heat from the bevel gear stage). As the
figure shows, the operating temperature may exceed the recommended operating
temperature of the electronic circuits (-70°C).
Fig. 2. Examples of thermograms
obtained for the mining right-angle spur planetary gearbox
The easiest way to solve the problem
of the impact of a high temperature in the gearbox is to create a system for
cooling the electronic circuit, but this requires modifications to the lubricating
and cooling systems of the gearbox, which must be performed in a way that does
not disturb the flow of oil inside the gearbox.
Another of the aforementioned
problems is to enable wireless transmission of the measuring signal
between the electronic circuit and the elements of the mining automation system.
The electronic circuits must meet the requirements of the ATEX Directive,
while, in the case of Wi-Fi signal transmission circuits, it will be
relatively difficult to achieve their intrinsic safety.
3. METHOD OF
IMPLEMENTING THE INTEGRATION OF A GEARBOX WITH TECHNICAL DIAGNOSTICS SYSTEMS
When analysing possible solutions to the
technical and economic problems mentioned in the previous section, it has been
found that the development of a completely new gearbox, which is suitable for
an internal installation of diagnostics systems, was necessary. A diagram
showing the measures that must be taken in order to implement the design of a
gearbox integrated with technical diagnostics systems is shown in Figure 3.
3.1. Lubrication and cooling system
of the gear suitable for the installation of a diagnostics system inside
the unit
In order to integrate the gearbox
with the internal technical diagnostics system, it was necessary to develop a
new lubrication system, taking into account the possibility of creating an
additional chamber in the gearbox housing for electronic circuits, as well as
install sensors. The lubrication and cooling system of the gearbox is composed
of coolers for lowering the oil temperature during the operation. Considering
the need to implement the integration of the technical diagnostics system
with the gearbox, as well as the relationship between the reliability of
the electronic circuits and the operating temperature, it has been assumed that
the allowable temperature of the lubricating oil is 70°C. The solution to the
problem of obtaining a temperature of the diagnostics system that is lower than
the allowable temperature is to place a water jacket within a separate
technical diagnostics chamber and incorporate it into the cycle of cooling with
water from the firefighting system. A solution involving the lubrication
and cooling system of a mining gearbox is shown in Figure 4. Details of the solution
have been presented in the patent descriptions [6,7,8,9].
Fig. 3. Diagram
of measures associated with integrating a gearbox with technical diagnostics
systems
The
location and overall dimensions of the additional instrumentation chamber
depend on the size of the gearbox and the planned functionalities of the new
system for technical condition prediction. Figure 5 shows the chamber for
simple diagnostics systems for a right-angle spur planetary gearbox with a
transmitted power up to 400 kW. The chamber for a complex diagnostics
system for the designed gearbox is discussed in Section 3.4 of this paper.
3.2. Power transmission elements of a mining gearbox
In order to perform an analysis of the possibility
of integrating the mining gearbox with a technical diagnostics system, it
was necessary to design the gearbox components (such as the teeth, shafts and
bearings) and perform strength calculations for them. For the needs of the analysis,
it was assumed that the teeth and bearing enabling the transfer of 560 kW for
the 39:1 gear ratio would be designed. For the purpose of implementing
this task, a functional model of the gearbox was created using KISSsys software
(Fig. 6A), which allowed for the determination of geometric parameters of
the teeth in a parameterized manner and the selection of bearings, which
meet the strength requirements. In addition, efficiencies of the teeth of the
gearbox were determined.
Fig. 4. Diagram of the
lubrication system suitable for the installation of the diagnostics system
inside the gearbox: 1 = gearbox housing; 2 = cooler coil; 3 = cover; 4 = inlet
of coolant;
5 = outlet of coolant; 6 = coolant distributor; 7 = oil cooling tank; 8 =
direction of oil flow;
9 = shaft of the bevel gear; 10 = bearing; 11 = instrumentation chamber; 20 =
measurement and transmission system; 22 = output from the electronic measurement
and transmission system; C3 = oil temperature sensor; C6 = oil quality sensor;
C7 = oil temperature sensor;
C8 = protection sensor
As part of the
strength calculations, the power losses in the bearings of the gearbox using
Bearinx software from Schäffler (the computational model adopted is shown in
Fig. 6B) were also determined.
Fig. 5. View of the
cooling chamber of the bevel gear stage (1) and the technical diagnostics
chamber (2) of a right-angle spur planetary gearbox with a transmitted power up
to 400 kW
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(a) (b)
Fig. 6. Computational
models of the prototype right-angle planetary gearbox:
(a) a computational model created using KISSsys software and (b) a
computational model created using Bearinx software
3.3 Functionalities of the technical diagnostics system for mining
gearboxes
The
selection of specific
technical solutions for the diagnostics system must be adapted to its expected
functionalities. In the initial step for further considerations on the
capabilities of the system, vibrations of the gearbox housing were measured
with the use of piezoelectric accelerometers, while the temperature was
measured with the use of Pt100 sensors. Both of these types of sensor must meet
the requirements of ATEX Directive 2014/34/EU. In addition, the technical
diagnostics system for mining gearboxes should enable continuous monitoring of
their technical condition in a manner that takes into account the mining
operations conducted.
Based on
the analysis of the operating conditions of gearboxes of armoured face
conveyors, which are most exposed to damage among all the gearboxes used in
mining, it has been found that the installation of these systems inside the
gearbox will significantly increase their service life. In order to determine
the functional assumptions for the prototype diagnostics system, the following
requirements and expectations of future users in the scope of diagnostics
systems integrated with a gearbox were specified:
- possibility
of determining the velocities or accelerations of vibrations in a user-defined
frequency band (e.g., consistent with ISO 10816),
- possibility
of determining the values of the diagnostic parameters and analyses
(e.g., the spectrum of the vibration signal or the spectrum of the
envelope) suitable for the assessment of the technical condition of
individual components of gearboxes,
- possibility
of having the diagnostics system operate together with mobile devices using
an optical fibre link and the built-in Wi-Fi interface,
- possibility
of transmitting the values of diagnostic parameters via an optical fibre link
to the main dispatching system with the use of selected communication protocols
(e.g., MODBUS/TCP),
- possibility
of configuring the diagnostics system through the built-in Web server,
- possibility
of defining alarm thresholds, which, if exceeded, initiate a warning or alarm,
- possibility
of saving the values of the measured parameters and time waveforms on
the internal memory card in order to enable recovery after failure or
damage,
- possibility
of recording the measurement results in the database,
- possibility
of using at least four-channel measurement systems (two channels for
acceleration measurements and two channels for temperature measurements),
- possibility
of viewing the current values of the technical condition parameters on the
built-in OLED display or a mobile device.
In order
to achieve the planned functionalities of the diagnostics system, the use of
complex electronic circuits and advanced software is required. The fulfilment
of these requirements with the use of the existing solutions is practically impossible
in the case of an intrinsically safe solution. There are some devices that
offer these functionalities, but their integration in a relatively compact
unit, which can be installed inside the gearbox, would be very difficult to
achieve. As a part of the analysis, it has been found that placing the existing
non-intrinsically safe circuits in a flame-proof housing could solve the
problem. The development of a diagnostics system, which fulfils both the
requirements of the ATEX Directive and the requirements of prospective users,
is crucial for ensuring the integration of the electronic circuit with the
mechanical device. In order to demonstrate the capabilities of this
integration, a design of the housing of the prototype technical diagnostics
system, as a flame-proof solution, was prepared. This also allowed
for determining the required dimensions of the cooling chamber for the
electronics circuits of the gearbox. The design of the housing for the circuit
is shown in Figure 7. This housing has the ability to stop flames in the event
of an explosion. It is also equipped with an inspection port (necessary for
communication with the use of the Wi-Fi module) and with cable glands, which
meet the requirements of the standards harmonized with the ATEX Directive.
Fig. 7. View of the prototype
technical diagnostics system in a flame-proof housing
3.4. Gearbox housing
together with the chamber for the technical diagnostics system
The housing of the right-angle spur planetary
gearbox has been designed based on the load-bearing elements (gear teeth,
splines, bearings and shafts), as well as on the basis of the dimensions of the
housing for the diagnostics system. The installation of measurement sensors and
protection for the signal cables were taken into account as early as the design
stage. The calculations of power losses in the teeth and bearings allowed for
determining the required number of coolers for transferring the heat
generated, while guaranteeing that the temperature of operation of the
diagnostics system would be at a level below 70°C. An important factor
affecting the dimensions of the gearbox involves the need to take into account
the specific character of the connection of the gearbox with the armoured face
conveyor; this concerns, in particular, the dimensions of the connectors
specified in the RAG 35000 standard. The general view of the designed housing
is shown in Figure 8. In this figure, the location of the technical diagnostics
chamber is different from that shown in the gearbox depicted in Figure 3. This
results from the adopted dimensions of the diagnostics system and the need to
install a dedicated system for cooling the housing of the electronic circuit.
The changes made (milling of the
housing to install the sensors, additional diagnostics chamber) could have a significant impact on the stress
distribution in the housing due to reactive forces. In order to check for the
possibility of the occurrence of excessive stress concentrations, a numerical
simulation, with the use of Autodesk Mechanical Simulation software, was
performed. A view of the finite element mesh and the manner of applying the forces
on the gearbox housing are shown in Figure 9, while Figure 10 presents the
areas of concentrations obtained on the basis of MES calculations. The
concentrations are visible not only in the places where bearings are mounted on
the housing, but also near the technical diagnostics chamber. However, the
value of reduced stresses is small and does not exceed 33 MPa, which was
considered to be a safe level.
Fig. 8. Gearbox housing enabling the integration of the technical
diagnostics systems (designations: 1 = chamber of the diagnostics system; 2 =
cooler; 3 = additional chamber of the cooler)
Fig. 9. View of the finite element
mesh and the manner of applying the forces on the gearbox housing
Fig. 10. Areas of the
stress concentrations in the housing caused by reactive forces
The final view of the visual model
of the prototype gearbox, integrated with diagnostics systems (taking into
account the results of the numerical simulation), the housing of the technical
diagnostics system, and the technical condition sensors is shown in Figure 11.
Fig. 11. Gearbox integrated with technical diagnostics systems
(designations: 1 = upper part of the housing of the diagnostics system with
visible cable glands; 2 = piezoelectric sensors;
3 = sensor of the lubricating oil level)
3.5. Diagnosing the technical condition of the armoured face conveyor
The diagnostics system installed
inside the gearbox will be equipped with two to four channels for the
measurement of vibrations and the same number of channels for the measurement
of temperature. This will also allow for monitoring of the technical condition
of the drive shaft in the armoured face conveyor. This capability is shown in
an illustrative manner in Figure 12. In order to extend the scope of the
technical diagnostics, it is necessary to mill an opening for signal
cables and sensors in the housing of the conveyor drive (Fig. 13).
The functionalities of the
diagnostics system mentioned in Section 3.3, in particular, those implemented
in the MODBUS or PROFIBUS communication system and in the Wi-Fi wireless
transmission modules, allow for transmitting the signals from the system
monitoring the technical condition of the entire power unit to the mining
dispatching system, thereby enabling the visualization of the operation of the
machines in association with their technical condition. A diagram of this
complex solution is shown in Figure 14. It should be added at this point that
the extension of the range of machines covered by the diagnostic monitoring
significantly reduces the relative cost of the investment in the diagnostics
system. A relatively high purchase cost of the diagnostics system in relation
to the cost of the gearbox will be reduced significantly, if it is compared
with the cost of the entire longwall armoured face conveyor.
4.
CONCLUSION
This paper presents the results of
an analysis of the possibility of integrating a mining right-angle spur
planetary gearbox with technical diagnostics systems. The multistage design and
conceptual work has shown that it is possible to install electronic circuits
for processing the signals from sensors inside the gearbox. The solution
presented has a number of features and functionalities, the lack of which has
been so far regarded as the main obstacle to the widespread use of
diagnostics systems in mining machines and equipment, including gearboxes.
These features and functionalities
include:
- reduction
of the susceptibility to damage caused by operating factors,
- meeting
the requirements of ATEX Directive,
- the
possibility of covering both the gearbox and the machine driven by it
with diagnostic monitoring,
- installation
of special modules in the diagnostics systems to enable the transmission of
the measurement signals with the use of the industrial automation system
existing in the mines or wireless transmission systems,
- relatively
low cost of the diagnostics system in relation to the cost of the entire
armoured face conveyor.
Acknowledgement
The study was carried out as a part of the “Development of an innovative
pro-ecological specialized gear transmission integrated with a diagnostic system”
project (no. POIG.01.04.00-24-094/11).
(a)
(a)
Fig. 12. Possibilities of using a
technical diagnostics system integrated with the mining gearbox for monitoring
the technical condition of the drive shaft bearings in the armoured face
conveyor: (a) the view from the side of the gearbox and (b) the view from the
side of the conveyor
Fig. 13. View of the housed armoured
face conveyor adapted for diagnosing the technical condition of the drive shaft
bearing (designations: 1 = milled mounting for the piezoelectric sensor; 2 =
milled channel for signal cables)
Fig. 14.
Diagram of a comprehensive diagnostics system for the drive unit of an armoured
face conveyor
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Received 12.05.2016;
accepted in revised form 19.08.2016
Scientific Journal of Silesian University of Technology. Series Transport is licensed under a Creative Commons Attribution 4.0 International License