Papers by Keyword: Rubbing

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Authors: Lim Meng Hee, M. Salman Leong, K.H. Hui
Abstract: Blade faults are ranked among the most frequent causes for gas turbine failures. This paper provides a review on the types of blade faults as well as its pertinent detection methods. In this paper, blade faults are categorized into five major groups according to their nature and characteristics namely, blade rubbing, blade fatigue failures, blade deformation, blade fouling, and blade root related problems such as cracked root and loose blade. This paper aims to provide an overview on the characteristics of each type of blade fault as well as its best detection methods available to date.
Authors: Said Larbi, Said Djebali, Ali Bilek
Abstract: The aim of the present work is the investigation of the influence of graphite powder addition to an unsaturated polyester type polymer (32% styrene content in mass) on the mechanical and tribological properties. For this purpose, we conducted bending tests and wear tests with a combination of four loads and three speeds for three different compositions (0, 1 and 2% graphite). The wear tests are carried out on a dry type pin on disk tribometer. The disk is made of quenched and annealed C48 steel (540 Hv hardness). Before the rubbing process, the discs are subjected to polishing in order to obtain approximately the same initial surface roughness. The results show that the addition of graphite powder improves the tribological properties; a noticeable decrease of the coefficient of friction, the mass loss and the wear rate are achieved with the increase of the graphite powder percentage for all sliding speeds and loads. A 2% graphite content causes a drop of the friction coefficient from 0.4 to 0.2. The results of bending tests showed a significant decrease of the stress and strain at failure and a slight increase in Young's modulus. In addition, for the three compositions, the results show a clear preponderance of the influence of the load on the tribological properties.
Authors: Gui Zhen Liu, Ya Zhe Chen, Yang Liu, Bang Chun Wen
Abstract: Established a single-disc rubbing rotor system test-bench ,and can simulate the design of a single point of rubbing and rubbing of the rotor part. In the case of constant speed to ensure that observed in the rubbing rotor vibration under different conditions, the use of waveform, frequency spectrum, Orbit and other detailed analysis of the system before and after rubbing and chaotic properties of nonlinear response the experimental. results show that the occurrence rub rotor system, the system will stimulate a high frequency and fractional-octave, when there will be a serious rub chaos.
Authors: Yong Yong He, Xin Yun Yin
Abstract: Rubbing between the rotor and the stator is the frequent fault and will cause very serious accident, even catastrophe, to rotating machinery. Therefore, timely detection of such rubbing is very important avoid severe consequences. Vibration based methods are very mature and traditional methods but not effective to detect incipient rubbing in rotating machinery. Rubbing between the rotor and the stator will cause elastic strain in the rubbing location and thus can produce acoustic emission (AE). Apparently, such AE contains direct and abundant information about the rubbing and can be used to detect and diagnose such fault effectively. In this paper, the AE based method is proposed for detecting and identifying the rubbing of the rotor-bearing system. An experimental study is presented to investigate the characteristics and features of rubbing AE using parameter analysis method. The results show that AE is very sensitive to the rubbing and AE parameters can reveal the characteristics and features of rubbing AE. Parameter analysis demonstrates that rubbing AE contains multiple modals, which will attenuate with propagation by negative exponent manner.
Authors: Wen Xiu Lu, Fu Lei Chu, Dan Guo
Abstract: The rubbing fault is a very serious and frequent malfunction in rotating machinery, and the determination of the rubbing location is very important in actual fault diagnosis. In this paper, a method based on genetic algorithms to detect the rubbing location is presented. The finite element model of the rubbing rotor is established with the rubbing location, the stator stiffness, the clearance between stator and rotor, the damping coefficient and the friction coefficient as the fault parameters, and the rubbing location determination is transferred into the parameter identification problem. The genetic algorithm is then utilized to search the solution. Using genetic algorithms avoids some of the weaknesses of traditional parameter identification methods such as local minimum problem in nonlinear system identification. The experimental results suggest that the rubbing location can be effectively determined when the rubbing occurs.
Authors: Jun Shimizu, Li Bo Zhou, Takeyuki Yamamoto, Han Huang
Abstract: This study aims to clarify the friction and wear phenomena, which are of great importance in abrasive machining with atomic-scale material removal, such as polishing of magnetic disk substrates and CMP of semiconductor substrates. Various phenomena that occurred when a well-defined copper surface rubbed by an extremely fine rigid diamond abrasive, such asthe sliding without removal and the atomic-scale wear, were analyzed using a molecular dynamics model, in which the abrasive grain was connected to a three-dimensional spring and the holding rigidity of the abrasive grain was taken into account. A series of simulations using different indentation depths clarified that the one- or two-dimensional atomic-scale stick-slip phenomenon in proportion to the period of atomic arrays of workpiece surface occurred in the sliding processes without atomic removal. The results also demonstrated that the period and amplitude of the fundamental stick-slip wave varied when accompanied with atomic removal due to the increase in normal load.
Authors: Li Sze Lai, Yin Fong Yeong, Kok Keong Lau, Mohd Shariff Azmi
Abstract: In this work, synthesis of ZIF-8 membranes via in situ and secondary seeded growth methods was conducted at the preliminary stage. Synthesis durations were varied at 4 h and 36 h using in situ growth method. For secondary growth, the seeding procedure was applied through rubbing and dip-coating of the seeds on the support. The resultant membranes were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Subsequently, the defects of the resultant membranes were determined using nitrogen gas permeation test. The results showed that, ZIF-8 membrane synthesized using in situ growth method for 4 h exhibited highest crystallinity and lower defects with the nitrogen gas permeance of 5.09 × 10-7 mol/m2·s·Pa. Besides, in situ growth method has shown its potential in synthesizing high quality ZIF-8 membrane through an easy and faster route.
Authors: V.H. Flores Sánchez, R.A. Vázquez García, O. Coreño Alonso, J. Coreño Alonso, Ma.I. Reyes Valderrama, Eduardo Arias, Ivana Moggio, M. Martínez García
Abstract: Oligo(phenylimines) hereafter named PI6, PI8 and PI9 were synthesized by condensation reaction between the terephtalaldehyde and diamines of different length size (diaminohexane, diaminooctane and diaminononane) via mechanochemistry. The reactions were carried out without solvent or catalyst and completed after only 90 minutes. The products were characterized by 1H-NMR, UV-Vis, FT-IR spectroscopy, GPC, DSC and Small angle X-ray diffraction. Thin films were prepared by spin coating from concentrated solutions on glass and quartz substrates and mechanically rubbed with a polyacrylonitrile tissue. The oriented films were studied by both Laser Scanning Confocal Microscopy (LSCM) and UV-Vis spectroscopy. With this last technique, the higher optical dichroism was observed for PI6. The oriented films of this oligo(phenylimine) were thus used as patterns to induce molecular orientation of a fluorescent phenyleneethynylene polymer in order to obtain polarized light emission.
Authors: Chang Qing Su, Yi Min Zhang
Abstract: The rubbing phenomenon occurs when a rotating element eventually hits a stationary part of the rotating machinery. Increasing the rotor speed and decreasing the radial clearance between the rotating and the non-rotating parts can enhance the performance of the rotating machinery. This leads to an increased risk of rubbing contact. Rotor rubbing is the source of numerous different phenomena, for example sub- and super-harmonic vibrations, amplitude jumps and rotor instability. So the reliability analysis and sensitivity analysis of rotor system with rubbing is important for design purposes. Reliability analysis can help the designer to establish acceptable tolerance on rotor system. Sensitivity analysis can help the designer to know which problem in rotor system with rubbing is being solved and how the solution may affect the design of rotor system for system correction and reanalysis. On the basis of the dynamic equations of the cracked rotor system model and with consideration of the random parameters including shaft stiffness and damping, disk damping, radial clearance and stator radial stiffness, the random responses of cracked rotor system are researched. The reliability and sensitivity analysis of the cracked rotor system with rubbing are studied. According to the discretization of random process and stress-strength interference theory, the transient reliability model of cracked rotor system with rubbing is proposed. The reliability for rubbing in cracked rotor system is obtained by way of statistical fourth moment method, Edgeworth series technique and first passage theory. Numerical results are also presented and discussed.
Authors: Ke Zhang, Yu Hou Wu, Shi Hong Li
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