Search

the formation mechanism of micro-pitting had been described in this paper,the action relationships of various influencing factors had also been analyzed,and the three main action mechanisms of local contact stress,film thickness ratio of lubricating oil and micro mechanical properties for materials had been regularized.Based on elastohydrodynamic lubrication theory and previous test results for Newtonian fluids,the reasonable calculation method of film thickness for lubricating oils had been determined.Through comparative calculations,the specific effects of oil types,lubricating oil temperatures,transmission torques and gear speeds on the oil film thickness had been analyzed.Combined with the micro-pitting design of gear transmission,feasible ideas and operational methods for lubrication improvements and optimizations had also been given.Finally,through the experimental designs,the correctness of the theoretical analysis had been verified,and the basic data for the anti micro-pitting design of the combination for gears of 18 CrNiMo7-6（material）+ISO-VG220（Lubricating oil） had been goted.

Compared with ISO 6336:1996 edition，there are great changes in the latest edition of ISO/FDIS 6336-1 to 3：2019, in particular, the calculation of the helix angle factor for helical gear has a subversive change. In order to facilitate the reader to understand the changes of the new ISO 6336, the main changes in the content of different editions of ISO 6336 are introduced, the influences of the helix angle factors and single pair tooth contact factor on safety factor before and after modification are analyzed, and the influence of helix angle on the calculation results of contact strength and bending strength are discussed here with examples.

The effect of scientific training on course learning in undergraduates is still controversial. In this study, we investigated the academic performance of undergraduate students with and without scientific training. The results show that scientific training improves students' test scores in general medical courses, such as biochemistry and molecular biology, cell biology, physiology, and even English. We classified scientific training into four levels. We found that literature reading could significantly improve students' test scores in general courses. Students who received scientific training carried out experiments more effectively and published articles performed better than their untrained counterparts in biochemistry and molecular biology examinations. The questionnaire survey demonstrated that the trained students were more confident of their course learning, and displayed more interest, motivation and capability in course learning. In summary, undergraduate academic performance is improved by scientific training. Our findings shed light on the novel strategies in the management of undergraduate education in the medical school.

The rack test device for the Three Gorges ship lift is mainly composed of four parts: driving gearbox,driving gear-rack,loading gear-rack and loading gearbox. In order to better calculate and analyze the transmission efficiency of the rack test device,through the establishing gearbox transmission efficiency calculation model,transmission efficiencies of the four parts and the transmission efficiency and the power consumption of the total whole unit are calculated respectively,the calculation results are contrastive analyzed by the input speed and torque,output speed and torque of the test data,the accuracy of calculation model and test data is verified,the research basis of transmission efficiency of gearbox and gear rack for low speed and load duty is established.

The calculation method of equivalent load for crane reducer under variable load condition is analyzed. Application factor formulas for the calculation of gear fatigue strength and bearing fatigue life are deduced,and the index value of the fatigue strength calculation of gear is recalculated based on the life coefficient. In addition,the differences of load spectral coefficients in gear and bearing fatigue calculations are pointed out. The calculation method has a guiding significance for the design and calculation of crane reducer.

According to the forming process principle,the influence of the tooth profile modification,helix modification and tooth profile deviation,helix deviation and eccentricity tolerance of radial run-out of the involute helical gear on tooth profile shape is analyzed. The curve equations of the involute transverse tooth profile are derived step by step. By using the software,the curve equation of deviation is fitted,and the theoretical curve is replaced by the deviation curve. Then,the actual tooth profile model and solid model including modification and deviation of gear are generated.

Taking one new type crane reducer with two supporting points as the research object,the three-dimensional model of reducer is established by using SolidWorks,and the virtual prototype is established by importing the 3D model into the mechanical dynamics simulation software ADAMS. In order to ensure the accuracy of the simulation model,the virtual prototype model is analyzed by the contact force constraint,the angular velocity characteristic curve and the gear meshing force variation curve of each drive shaft are obtained. The simulation of the actual value and the theoretical calculation results are compared and found that the transmission shaft angular velocity and the actual the transmission error value in 0. 17%,engaging in 4% errors are very small,so the simulation model is correct. The research results provide data support for calculate gear strength and fatigue life more accurately.

The gearbox of rack test for the Three Gorges ship lift is low speed heavy duty four stages transmission,and need frequent fast reversing operation in the process of test,due to the influence of the gear meshing backlash,elastic torsional deformation of shaft and elastic deformation of gear tooth and other factors,the operation performance of gearbox will be changed during reversing process,especially the output speed and torque. In order to analyze the influence on the transmission performance of gearbox,the calculation models of the influence of the gear meshing backlash and the elastic torsional deformation of the shaft on the rotational speed are setup respectively,the output speed of the gearbox in the reversing process is calculated and compared with the output speed of gearbox measured by experiment,which verifies the accuracy of the calculation model and the test data.

The background and significance of gear test detection platform and basic database construction are introduced,and a structural scheme of bevel gear closed power flow durability test bench including the composition and system function is proposed. The 3 D model of constant speed cylindrical gearbox is established by using Solid Works 3 D software,the statics and modal of the box are analyzed according to the actual working load of the test bench by finite element method. The maximum stress,deformation and natural frequency of the box and the corresponding vibration mode are obtained,and the result of the strength check of meshing gears verify the constant speed cylindrical gearbox meeting design requirement.

To improve the mechanical properties of hemicellulose hydrogel, a green, adjustable mechanical property, high swelling ratio (SR) composite hydrogel was successfully prepared by using modified lignin as a reinforcing agent. The structure and characteristics of the composite hydrogels were investigated by TGA, FTIR, SEM, rheological analysis, and SR. It can be found that the modified lignin could significantly improve the mechanical properties of the composite hydrogels. The maximum compressive stress of unmodified lignin hydrogel was 61.72 kPa and the compressive deformation was 75%. Compared with the unmodified lignin hydrogel, the mechanical properties were significantly improved, with the maximum compressive stress of the modified lignin hydrogel was 145.2 kPa and the compressive deformation was up to 90%. After adding modified lignin, the SR of the as‐prepared hydrogel was up to 155.17 g/g, which was much higher than that of unmodified lignin hydrogel (105.79 g/g). The composite hydrogel had good antioxidant properties, and the free radical removal rate can reach 85.3%, which is twice as much as that without the modified lignin. With cost‐effective lignin as a reinforcing agent, the as‐prepared hemicellulose hydrogel with adjustable mechanical properties is favorable for great application potential. [ABSTRACT FROM AUTHOR]

Taking a high- speed motor train unit transmission gear system as an example,by using gear analysis software KISSsoft,the deformation of gear supporting axial in the transmission process is calculated.Through the method of modification to compensate the influence of the shaft deformation on the gear meshing performance. Then,the difference between before and after the modification of gear meshing contact spot,tooth surface line load distribution and the transmission error,etc are compared to ensure the motor train unit gear transmission system working more stable and reliable. The work of the research has important reference value to the design of the motor train unit gear pair.

Taking designed labyrinth seal of a high speed EMU gearbox as the research object. The numerical simulation of the internal flow field of labyrinth seal is carried out by using the Fluent software,the pressure,speed,velocity vector and turbulence distribution cloud of the internal flow field of the labyrinth seal are obtained. The sealing mechanism and process of the gearbox labyrinth seal is analyzed. The results show that the fluid flows through the sealing gap when the pressure is reduced,the pressure is reduced very little.When the fluid flows out of the sealing gap into the cavity is the pressure equalizing process. After entering the cavity,the turbulivity of the cavity is the largest and the pressure is the smallest. As the distance from the center of the cavity increases,the speed increases and the pressure increases. The distribution characteristics of the flow field in the labyrinth seal under different pressure ratios are analyzed,which indicated that the leakage increases with the increase of the inlet/outlet pressure ratio,and the pressure ratio is not linearly related to the leakage. The simulation results can be used as reference for the design of gearbox labyrinth seal.

Reducer is the key component of hoisting equipment,and the case is the carrier of the gear system and plays the role of support and fixation. The three-dimensional finite element model of the gearbox is established by Solid Works software and imported it into ANSYS Workbench. The statics analysis is accomplished for each actual loading condition,the changing curve of the maximum stress and the deformation is obtained,the analysis results can provide the data support for the subsequent structure improvement and light-weight design. The natural frequency and vibration type is obtained by completing the modal analysis of the case,and whether the resonance phenomenon happens can be determined by comparing the natural frequency of the reducer with the meshing frequency and the rotational frequency.

Through the analysis of the influence factors on transmission efficiency of gearbox,a theoretical analysis model of gearbox transmission efficiency is set up from the power consumption,and the influences of gear meshing loss,bearing friction loss,oil loss,oil seal friction loss and windage loss on gearbox transmission efficiency are considered. The analysis model is validated according to the test data of a low speed and heavy duty gearbox,and the influences of speed and torque on the transmission efficiency of gearbox are discussed,the changing curves of gear efficiency with the rotational speed and torque are obtained,the foundation for further research on the efficiency of the gearbox is laid.

Based on the relationship between shear stress and Hardness,using the linear regression method,the calculation formula of effective case depth of carburized gear was derived,and it was verified by example. The results show that the accuracy of the derived simple computational formula can meet the requirements for gear design. Using this formula,the effective case depth of gear was obtained,and the model for the distribution of effective case depth of gear was established.