Papers by Keyword: Rubbing

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.

Abstract: An abnormal journal vibration occurred when a 660MW turbo generator unit was in daily operation. It was identified that rubbing vibration had taken place based on the behavior of the journal vibration and the temperature change of lubricating oil. The rubbing was located inside the bearing box between the HIP rotor and the LP rotor. However, no elimination measures had been taken in time because the damage caused by rubbing was underestimated. Few months later a full inspection revealed that the LP rotor shaft had been worn out with a 70mm wide and 28mm deep groove, which greatly weakened the strength of the LP rotor. The analysis presented here may help in diagnosing and understanding rubbing-vibration-related problems in similar situations.

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.

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.

Abstract: Analyze the origins of the vibration according to the expressions during aero-engine running. Study the vibration principle. Create the fault tree of the aero-engine vibrating failure. And with the fault tree analyze the common vibrating failure during production process. Generalize the diagnosing and debugging-aid methods for aero-engine vibrating failure.

Abstract: Rubbing is one of the most common faults that occurs in rotating machinery. This paper studies the vibration responses of a rotor system under the influence of blade induced rubbing. An experimental study was undertaken to simulate various conditions of rubbing in rotor system caused by rotating blades and its corresponding vibration responses are measured and analyzed. Experimental results showed that the effect and vibration responses caused by blade rubbing is enormous and therefore can be easily detected based on vibration spectrum analysis. Besides this, the severity of rubbing caused by different conditions of blades could also be estimated based on the magnitudes and patterns of vibration spectrum.

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.

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.

Abstract: The general aim of this study was to develop materials of the type: Y zeolite (hydrothermal synthesis), ceramic support (forming of powder) and zeolite membrane (rubbing). The preparation of the Y zeolite was conducted in accordance with the hydrothermal synthesis method, the time of crystallization was one day. The ceramic support was prepared by means of the forming of powder technique and subsequently subjected to sintering at a temperature of 1400°C/1h. The zeolite membrane (Y/α-alumina) was prepared by secondary growth method (rubbing). These materials were characterized by XRD and SEM. Obtaining Y zeolite could be confirmed by X ray diffractograms. From the images obtained by SEM, it was possible to derive from analysis that the Y zeolite is composed of a homogeneous morphology, where the particles are crowded, with uniform size. The results obtained for the ceramic support (α-alumina) showed that it displays characteristics peaks of aluminum oxide. By using micrographs it was possible to observe a heterogeneous microstructure with a compact form, without cracks upon the layers. According to the XRD, for the methodof secondary growth (rubbing), it was observed that the Y zeolite wich had been synthesized on the ceramic support displayed a crystalline structure. The micrography of the zeolite membrane (Y/α-alumina) showed the formation of a layer of zeolite on the ceramic support.

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.