Research on Life Loss of Generator Retainer Caused by Negative Sequence Current

With a large number of wind and solar power sources connected to the power grid, higher requirements are put forward for the power generation equipment to respond to the power grid imbalance. The safety research of generator rotor retaining ring under the impact of negative sequence current is of great significance. For 300MW turbogenerator, the two-dimensional and three-dimensional eddy current, temperature rise, stress and life of generator rotor under the impact of negative sequence current are analyzed and studied. The two-dimensional calculation models of stator and rotor are established, and the distribution of negative sequence eddy current field in rotor section is analyzed; considering the contact resistance between rotor and retaining ring and the end effect of magnetic field, a three-dimensional analysis model is established, and the calculation results of three-dimensional eddy current field, temperature field and stress field are obtained. The analysis shows that after considering the contact resistance between rotor and retaining ring and end effect, the current density at the contact between retaining ring and rotor big tooth edge is 17.6 times of the two-dimensional calculation result of rotor section, and the maximum temperature of rotor retaining ring reaches 170.36°C.

The Impact of Vibration Operational Reliability of Turning Mechanism of Gantry and Tower Cranes

Impacts of vibration on operational reliability of turning mechanisms of gantry and rower cranes are considered. Besides that, the structural features of kinematic chain of drive, including gear transmission with internal large module teeth, roller bearing without retaining ring, excitement of torsional, bending low-frequency vibrations at operation in nominal mode of cargo lifting that causes the origination of of increasing friction moment and stop of turning mechanism are researched in this article. Moreover, the technological and structural solutions aimed on decreasing of excited vibrations are proposed, and the supporting-rotating rolling bearings without retaining ring with improved technical-economic indicators are considered.

Development of disc spring stack containment methods for vibration isolation

Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations. However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement. A method to contain the isolator stack then becomes critical for practical uses. Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance. In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design. Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks. Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve. However, significant differences in isolation performance are observed in vibration testing and found to depend on characteristics such as lateral stability, lateral strength, and degrees of freedom. Lastly, advantages, disadvantages, and appropriate applications for each containment method are summarized. The conclusions of this work are that containment method is an important variable in the application of disc spring isolators and robust, versatile containment designs have been demonstrated.

Improved simple T-cannula technique to facilitate surgery and daily skin care of growing pigs

In order to further increase the stability of the cannula behind the ribs and to facilitate cannula exteriorization in growing pigs, the present study aimed to evaluate whether elongation of the cannula flange could increase the stability of the cannula behind the ribs and to develop a tool to improve the exteriorization of the cannula through the ribs. Moreover, it was assessed whether a special skin protection paste and soft polyurethane foam material used in daily skin care could prevent erythema around the fistula. The feasibility of both, the modified simple T-cannula and daily skin care procedure, was evaluated in a digestibility experiment. Simple T-cannulae were made of high-molecular-weight polyethylene and inserted into the distal ileum of eight growing pigs (average body weight at surgery 30 kg). Modifications in the cannula design included a longer flange (11 cm) that was narrowed from the center to the ends and a bending of the flange to adapt it to the curve of the costal arch. In order to reduce the damage to the thread on the outer cannula barrel during surgery, a special surgical plug in conjunction with a screw thread on the inside of the barrel was developed. With respect to the daily cleaning of the fistula, a special skin protection paste was applied on the skin around the fistula to create a waterproof film that entirely sealed the skin. Additionally, foam material was inserted between the retaining ring and the skin to absorb the leaking digesta. Monitoring of the pigs throughout the trial showed that modifications in cannula design proved to be useful as they facilitated exteriorization of the cannula through the ribs and stability of the cannula behind the ribs. Moreover, the use of the skin protection paste and foam material during postsurgical treatment of growing pigs effectively prevented skin irritation around the flank area.

Contact stress analysis of disc cutter peg-hole with interference fit

To study the relation of the interference fit between cutter body and cutter ring, a theoretical design of interference fit of the cutter peg-hole is carried out according to the theory of thick-walled cylinders. The finite element method is used to analyzed the mapping relationship between the contact stress of cutter ring and cutter body. Thermal expansion assembly of the cutter ring is simulated, and the temperature of the thermal expansion assembly of the cutter ring is determined. The result shows that the contact length between the cutter body and the cutter ring has little influence on the contact stress of the cutter ring, but with increasing contact length the stress concentration of the retaining ring will increase. The contact stress of the cutter ring is basically the same at the same amount of interference and temperature, but the contact stress of the ring decreases with increasing contact length at high temperature. When the contact length is the same, the contact stress and the radial force of the mating surface increase with increasing amount of interference. The reasonable temperature for thermal expansion assembly of the cutter ring is 160 °C.

Cavitation Erosion Resistance of Laser Beam Nitride Layers of X5CrNi18-10 Stainless Steel

The use of nitration in technical applications, as thermochemical treatment, regardless of the used method (ionic, gas or laser beam nitration) is realized to obtain a nitrogen rich layer, which increase the resistance to shock or abrasion, as a result of the high hardness obtained. All the previous cavitation researches showed that hardness is an important mechanical properties, for cavitation erosion resistance increase. The present paper show some results regarding the cavitation erosion behavior of laser beam nitrated layers. As basic material was used the austenitic stainless steel X5CrNi18-10. This material is frequently used for manufacturing details subjected to cavitation, such as valves, drawers of hydraulic distribution and regulation devices, or the retaining ring for butterfly valves. There were used three power regimes of the laser beams: 120 W, 180 W and 240 W. To obtain cavitation erosion was used the standard device with piezo-ceramic crystals of Timisoara Polytechnic University Cavitation Laboratory. The cavitation erosion comparisons, both with the basic material subjected only to the common thermochemical treatments and with the laboratory cavitation standard steel (OH12NDL), show that the nitrated surfaces presents increased cavitation erosion behavior, the principal factor being the important hardness increase of the nitrated layer. We mention also, that for higher laser beam powers the thickness of the nitrated layer increases. All the images obtained at the end of tests show that the cavitation exposure was stopped before overtaking the nitrated layer. So, all our results concern only the hardened layers.