Menasri Noureddine and Bouchoucha Ali
Rotating machines play a strategic role in the process; it is the case of a gear unit of a cement mill. These machines are composed of tribo-pairs (bearings and gears, etc.…
Abstract
Purpose
Rotating machines play a strategic role in the process; it is the case of a gear unit of a cement mill. These machines are composed of tribo-pairs (bearings and gears, etc.) subjected to mechanical stress and harsh industrial environments. This study aims to make an experimental investigation of bearing wear of a gear unit DMGH 25.4 of a horizontal cement mill.
Design/methodology/approach
Several tests were carried out in collaboration with industrial Algerian companies, for example, spectroscopy, micro hardness, X-Ray diffraction analysis and microscopic examination of wear-characterized QJ1244 N2MA bearing.
Findings
Experimental results reveal that there are two types of bearing wear: the first is a continuous mode of damage. The second mode is the wear by a third body (wear debris in suspension in oil). The spalling results from the propagation of cracks through the thickness of the material generally give rise to cracks in the sub-layer depth hertz. An unusual hardening observed suggests that the damage was caused by the dissipation of a large surge of frictional energy lasting several milliseconds. It is found also that heating due to insufficient lubrication of the bearing led to the formation of high-density fine carbides in the microstructure of 100Cr6, which tends to decelerate the movement of dislocations during plastic deformation.
Practical implications
This study allowed the characterization of bearings wear in industrial mechanical systems.
Originality/value
Characterization of the bearings showed that the unusual hardening observed suggests that the damage was caused by the dissipation of a large surge of frictional energy lasting several milliseconds. The microhardness of the worn bearing is very high compared to the beginning wear bearing, which is due to the quantity of carbides formed. The thermo-mechanical stresses do not affect the main phases such as martensite, but they accelerate the fracture propagation at the surface.
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N. Menasri, M. Zaoui and A. Bouchoucha
Rotating machines play a strategic role in a manufacturing process, and it is the case of a cement mill. These machines are composed of fragile bodies (bearings and gears, etc.…
Abstract
Rotating machines play a strategic role in a manufacturing process, and it is the case of a cement mill. These machines are composed of fragile bodies (bearings and gears, etc.) subjected to mechanical stress and harsh industrial environment.
Sources of failure are many; the wear and the spalling of bearing, the wear and fracture of a tooth of a gear, the misalignment of the axes, etc. To avoid unexpected downtime and costly, those bodies must be monitored continuously. There are several ways to do that; vibration analysis, lubricant analysis, infrared thermography and acoustic analysis. Vibration analysis (frequency) is most often used by operating a signal from an accelerometer. Whenever a fault participated in a contact, it changed the vibration characteristics of the system. By analyzing the acceleration measurements from an accelerometer, we can identify and quantify these changes in order to establish a relationship between the measures and the type of defect, which will be used as signatures for fault diagnosis system. In a system of power transmission (gear unit of a cement mill) the frequency of occurrences of faults can be known from the geometry and kinematics of the system.
This article deals with the detection of bearing defects isolated in a gear unit of a cement mill by spectral analysis of vibration; which based on a systematic analysis spectral and envelope spectrum of vibration signal for the presence of images of all vibrational defects may affect the body in question.
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D. Necib, A. Bouchoucha, H. Zaidi, M. Amirat and D. Eyidi
This study concerns tests carried out without lubrication on a universal lathe to study the influence of the magnetic field on the wear of a cutting tool made of metallic carbide…
Abstract
This study concerns tests carried out without lubrication on a universal lathe to study the influence of the magnetic field on the wear of a cutting tool made of metallic carbide. The tests parameters are: the intensity of the magnetic field (from 0 to 28.5 kA.m-1), the cutting speed (from 6 to 136 m.min-1), the advance speed and the cut depth (pass). Both of the previous parameters are fixed respectively at 0.125 mm.rev-1 and 0.5 mm. The material being cut is made of XC38 steel. The tool wear is evaluated by weighing method (before and after each test). The results showed that the magnetic field has an influence on wear and that there is a critical value (H = 16.5 kA.m-1) for which wear is minimum. Also, the scanning electron microscope (SEM) and optical microscope observations revealed the existence of three types of wear that are: flank wear, crater wear and wear by plastic deformation. Moreover, we concluded that, the increase of the magnetic field modifies the shape and the morphology of chips and rises the contact temperature.
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Hongjuan Yang, Lin Fu, Yanhua Liu, Weiji Qian and Bo Hu
This paper aims to investigate the delamination wear properties of a carbon strip in a carbon strip rubbing against a copper wire at the high-sliding speed (380 km/h) with or…
Abstract
Purpose
This paper aims to investigate the delamination wear properties of a carbon strip in a carbon strip rubbing against a copper wire at the high-sliding speed (380 km/h) with or without electrical current.
Design/methodology/approach
The friction and wear properties of a carbon strip in a carbon strip rubbing against a copper wire are tested on the high-speed wear tester whose speed can reach up to 400 km/h. The test data have been collected by the high-speed data collector. The worn surfaces of the carbon strip are observed by the scanning electron microscope.
Findings
It was found that there was a significant increase of the delamination wear with the decrease of the normal load when the electric current is applied. The size of the flake-like peeling also increases with the decrease of normal load. The delamination wear extends gradually from the edge of the erosion pits to the surrounding area with the decrease of the normal load. However, the delamination wear never appears in the absence of electric current. It is proposed that the decreased normal load and the big electrical current are the major causes of the delamination wear of the carbon strip.
Originality value
The experimental test at high-sliding speed of 380 km/h was performed for the first time, and the major cause of the delamination was discovered in this paper.
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Dongwei Wang, Faqiang Li, Yang Zhao, Fanyu Wang and Wei Jiang
This paper aims to study the tribological characteristics of the electrical contact system under different displacement amplitudes.
Abstract
Purpose
This paper aims to study the tribological characteristics of the electrical contact system under different displacement amplitudes.
Design/methodology/approach
First, the risk frequency of real nuclear safety distributed control system (DCS) equipment is evaluated. Subsequently, a reciprocating friction test device which is characterized by a ball-on-flat configuration is established, and a series of current-carrying tribological tests are carried out at this risk frequency.
Findings
At risk frequency and larger displacement amplitude, the friction coefficient visibly rises. The reliability of the electrical contact system declines as amplitude increases. The wear morphology analysis shows that the wear rate increases significantly and the degree of interface wear intensifies at a larger amplitude. The wear area occupied by the third body layer increases sharply, and the appearance of plateaus on the surface leads to the increase of friction coefficient and contact resistance. EDS analysis suggests that oxygen elements progressively arise in the third layer as a result of increased air exposure brought on by larger displacement amplitude.
Originality/value
Results are significant for recognizing the tribological properties of electrical connectors in nuclear power control systems.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0098/
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Song Xiao, Yuanpei Luo, Jingchi Wu, Can Zhang, Yang Rao, Guangning Wu and Jan Sykulski
In high-speed trains, the energy is supplied from a high voltage catenary to the vehicle via a pantograph catenary system (PCS). Carbon pantograph strips must maintain continuous…
Abstract
Purpose
In high-speed trains, the energy is supplied from a high voltage catenary to the vehicle via a pantograph catenary system (PCS). Carbon pantograph strips must maintain continuous contact with the wire to ensure safety and reliability. The contact is often confined to a particular spot, resulting in excessive wear due to mechanical and thermal damage, exacerbated by the presence of an electric arc and associated electrochemical corrosion. The effectiveness and reliability of the PCS impacts on the performance and safety of HSTs, especially under high-speed conditions. To alleviate some of these adverse effects, this paper aims to propose a configuration where a circular PCS replaces the currently used pantograph strips.
Design/methodology/approach
Two dynamic multi-physics models of a traditional PCS with a carbon strip and a novel PCS with a circular pantograph strip catenary system are established, and the electrical and mechanical characteristics of these two systems are compared. Moreover, a PCS experimental platform is designed to verify the validity and accuracy of the multi-physics model.
Findings
A novel circular pantograph system is proposed in this paper to alleviate some of the shortcomings of the traditional PCS. Comparing with a traditional PCS, the circular PCS exhibits superior performance in both electromagnetic and thermal aspects.
Originality/value
The paper offers a new technical solution to the PCS and develops a dedicated multi-physics model for analysis and performance prediction with the aim to improve the performance of the PCS. The new system offers numerous benefits, such as less friction heat, better heat dispersion and improved catenary-tracking performance.
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Xianchen Yang, Xinmei Li and Songchen Wang
Conventional wear models cannot satisfy the requirements of electrical contact wear simulation. Therefore, this study aims to establish a novel wear simulation model that…
Abstract
Purpose
Conventional wear models cannot satisfy the requirements of electrical contact wear simulation. Therefore, this study aims to establish a novel wear simulation model that considered the influence of thermal-stress-wear interaction to achieve high accuracy under various current conditions, especially high current.
Design/methodology/approach
The proposed electrical contact wear model was established by combining oxidation theory and the modified Archard wear model. The wear subroutine was written in FORTRAN, and adaptive mesh technology was used to update the wear depth. The simulation results were compared with the experimental results and the typically used stress-wear model. The temperature of the contact surface, distribution of the wear depth and evolution of the wear rate were analyzed.
Findings
With the increase in the current flow, the linear relationship between the wear depth and time changed to the parabola. Electrical contact wear occurred in two stages, namely, acceleration and stability stages. In the acceleration stage, the wear rate increased continuously because of the influence of material hardness reduction and oxidation loss.
Originality/value
In previous wear simulation models, the influence of multiple physical fields in friction and wear has been typically ignored. In this study, the oxidation loss during electrical contact wear was considered, and the thermo-stress-wear complete coupling method was used to analyze the wear process.
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This paper aims to improve the reliability of numerical methods for predicting the transient heat transfers in combustion chambers heated internally by moving heat sources.
Abstract
Purpose
This paper aims to improve the reliability of numerical methods for predicting the transient heat transfers in combustion chambers heated internally by moving heat sources.
Design/methodology/approach
A two-phase fluid dynamic model was used to govern the non-uniformly distributed moving heat sources. A Riemann-problem-based numerical scheme was provided to update the fluid field and provide convective boundary conditions for the heat transfer. The heat conduction in the solids was investigated by using a thermo-mechanical coupled model to obtain a reliable expanding velocity of the heat sources. The coupling between the combustion and the heat transfer is realized based on user subroutines VDFLUX and VUAMP in the commercial software ABAQUS.
Findings
The capability of the numerical scheme in capturing discontinuities in initial conditions and source terms was validated by comparing the predicted results of commonly used verification cases with the corresponding analytical solutions. The coupled model and the numerical methods are capable of investigating heat transfer problems accompanied by extreme conditions such as transient effects, high-temperature and high-pressure working conditions.
Originality/value
The work provides a reliable numerical method to obtain boundary conditions for predicting the heat transfers in solids heated by expanding multiphase reactive flows.
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M. Zaoui and N. Menasri
The welds are the site of high residual stresses, localized in the vicinity of the weld cracks. Their presence caused many type of damage mode as stress corrosion, fatigue, sudden…
Abstract
The welds are the site of high residual stresses, localized in the vicinity of the weld cracks. Their presence caused many type of damage mode as stress corrosion, fatigue, sudden failure and increasing the temperature of ductile/brittle transition. Residual stresses in restrained welds and weld repairs are very complex. The heat treatment affects the value and distribution of residual stress in the specimen. This peak stress in all three samples occurred not at the toe, but in the middle of the weld bead, where the yield stress is higher. The use of the neutron diffraction (ND) technique for residual stress measurements is described. In addition, studies of macrostructure and hardness were conducted. The results of different tests conclude the influence of heat treatment on Residual stresses in welds.
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Gabriela Capurro and Josh Greenberg
Purpose – The authors examine framing and narrativization in news coverage of health threats to assess variations in news discourse for known, emerging and novel health risks…
Abstract
Purpose – The authors examine framing and narrativization in news coverage of health threats to assess variations in news discourse for known, emerging and novel health risks. Methodology/Approach – Using the analytical categories of known, emerging, and novel risks the authors discuss media analyses of anti-vaccination, antimicrobial resistance (AMR), and Covid-19. Findings – Known risks are framed within a biomedical discourse in which scientific evidence underpins public health guidelines, and following these directives prevent risk exposure while non-compliance is characterized as immoral and risky. News coverage of emerging risks highlights public health guidelines but fails to convey their importance as the risks seem too distant or abstract. Media coverage of novel risks is characterized by the ubiquity of uncertainty, which emerges as a “master frame” under which all incidents and events are subsumed. Stories about novel risks highlight the fluid and changing nature of scientific knowledge, which has the unintended effect of fueling uncertainty as studies and experts contradict each other. Originality/Value – This chapter introduces a new analytical framework for examining how media stories represent public health risks, along with previously unpublished analysis of media coverage about AMR and Covid-19. This chapter provides insight about the nature of risk discourses involving media, public health officials, activists, and citizens.