Li Qin Wang

Friction and Wear Behaviors of Si3N4 Sliding against M50 Bearing Steel in Vacuum

The friction and wear performances of Si3N4 ceramics sliding against bearing steel and to find optimal operating condition against M50 bearing steel couples under high vacuum surroundings were investigated. The tests were studied on the ball-disk machine under different loads and steady sliding velocity. The worn surfaces of tested samples were examined using optical microscope，SEM and XPS. The results showed that the friction coefficient of Si3N4 was decided by the applied load, the critical load of Si3N4’ friction coefficient was 10N applied load; The critical load of Si3N4’ specific wear rate was 5N applied load, the specific wear rate of Si3N4 drop rapidly as the applied load exceeded the critical load; The dominant wear mechanisms of Si3N4 ceramics were adhesion wear, brittle facture and furrow wear in vacuum.

The Effect of Roller Profile Modification on Roller Bearing Performance

According to roller profile modification method, several commonly used modified rollers were selected into the bearing dynamic analysis combined with dynamic model of bearing. As the three types of modified roller an example, simulation program was established to analyze the load distribution of loaded roller under the working conditions of upright loading and offset loading of bearing, respectively. The effects of modified roller on bearing dynamic parameters were discussed. The results provided optimal direction for bearing selection and design under different working conditions.

Cage Instabilities in High-Speed Ball Bearings

The dynamic model of the cage in high-speed ball bearing was developed according to the geometry and force relationship between bearing elements. Based on this dynamic model, cage instability was researched through mass center whirl. The effect of clearance ratio, load and bearing rotation speed on cage instability were studied by taking type 7004 angular ball bearing as an example. The results shown that the increase of clearance ratio and radial load makes cage stability lowered, and the cage stability could be enhanced by increasing the axial load and bearing rotation speed.

Temperature Variables Selection for Thermal Error Modeling of Heavy-Duty CNC Milling-Boring Machine Tools

One of the difficult issues in thermal error modeling is to select appropriate temperature variables. In this paper, two selection strategies are introduced to overcome this difficulty. After measuring the temperatures and thermal errors of a heavy-duty CNC milling-boring machine tool by a laser tracker, four temperature variables which are the foundation of thermal error modeling are selected for each feed axis from fifteen temperature variables according to major factor strategy and non-interrelated strategy.

Wettability of Polymeric Bionic Surface Replicated from Ginkgo Leaves

Ginkgo is one of the oldest extant seed plants through hundreds of millions of years of evolution. Ginkgo biloba has many unique properties and applications such as drug development and drinking tea. In recent years hydrophobic surfaces with bionic structures have attracted increasing interest for fundamental research and practical applications. As we all know, the Ginkgo leaf has remarkable texturing surface. In this manuscript, wettability of the bionic surface replicated from Ginkgo leaves was explored. The Ginkgo leaves were used as the original mold, from which microstructures were replicated into the surface of polydimethylsiloxane (PDMS). Compared with the topography of Ginkgo leaves, the topographical surface of PDMS was investigated by optical microscopy and scanning electron microscopy. By measuring the contact angle of polymeric bionic surfaces, there is the increase of ~20 degree than flat PDMS surfaces. Mechanical compression was applied on the polymeric bionic surfaces in one dimension, with the real-time measurement of the contact angle. The experimental results reveal that the wetting behavior of the surface can be reversibly tuned by applied mechanical stress, which induces the change in micro-scale topography. This research provides a guide for fabricating and tuning hydrophobic surfaces for various surface engineering applications.

Analysis on Dynamic Contact Force in High Power Density Gear Transmission Based on Flexible Model

Recently, most of researchers pay more attention to the flexible model for solving dynamic contact force in high power density gear transmission. But, the detailed formula of the contact force parameters is not given. Therefore, in this paper the detailed calculation of coefficient of restitution (COR) is proposed, which can solve the elastoplastic contact deformation problems compared with other method. To improve the simulation efficiency, a flexible model based on ADAMS and Hertzian theory is presented. According to the simulation results, the normal contact force of the flexible model is much higher than that of the rigid model in plastic contact deformation. Meanwhile, the normal contact force delay exists in flexible model compared with rigid model. At last, the flexible model simulation results are close to the theoretical result in steady state. Consequently, the flexible model can be applied to analyze dynamic characteristic in reasonable time and many revolutions of the high power density gear transmission.

Modeling and Simulation of Wear in PTFE Lip Seals

Radial lip seals made from PTFE composites are used more frequently for sealing of crank shafts in automotive and aerospace industries. Due to the seal loses materials and finally fails. Through experiment on a test rig, the tribology performance of seal can be predicted. Because of the non-linear elasto-viscoplastc material properties of PTFE composites, the finite element analysis (FEA) is adopted. A modified iterative remeshing method is adopted in wear process. The lip wears out according to the contact pressure of the node on the contact surface. Comparisons between numerical simulation and short-term service are made. The results show that the maximum of contact pressure decreased and width increased with wear time added, and the maximum of contact pressure moves toward the lip tip. Finally, it reaches lip tip, the phenomenon of uneven contact pressure was disappeared.

Friction and Wear Behavior of Structural Ceramics Sliding against Bearing Steel under Vacuum Condition

The friction and wear behavior of Si3N4, SiC and ZrO2 sliding against M50 bearing steel under vacuum condition at various applied load were investigated. The results showed that the properties of different ceramic materials cause the difference in wear behaviors. The coefficient of friction was lowest in SiC and M50 bearing steel couple than other cases for graphitic carbon replaced carbidic carbon at the worn layer of SiC. The specific wear rate of ZrO2 was highest and the lowest was Si3N4. The ceramic ball materials have transferred on M50 bearing steel surfaces and tribofilm consistently formed on the ceramic balls wearing surfaces. Dominant wear behaviors for three structural ceramics were adhesion abrasion, plastic deformation and brittle fracture. The couple with Si3N4 and M50 showed the best operating conditions for friction and wear resistance under higher applied load.

Friction and Wear Behaviors of PTFE Composites Reinforced with Different Fillers

The tribological performances of mixed PTFE-based composites were evaluated on the MM-200 block-on-ring test rig under dry friction condition. The following filler contents: carbon fiber (CF), flake graphite (FG) and spherical graphite (SG) were adopted to investigate their effects on the tribological performances of the composites. The experiments were carried out by a four levels orthogonal table-L16（43）, and the experiment data were deal with the methods of range and variance analysis. The results shown that all the filler contents could reduce wear, and the wear rate was stable when the content of fillers were more than 10 wt.%. The degrees of three fillers affecting the wear of composites were CF>FG>SG, and that affecting the friction coefficient were SG>CF>FG. The friction coefficient decreased with increasing the contents of SG, increased with that of CF, first decreased and then increased with that of FG. When the contents of FG is 15 wt.%, the friction coefficient is the lowest. The main worn form was adhesion wear.

Tribological Performance of PTFE Composites Filled with Spherical-Graphite

The tribologcial performance of PTFE composites filled with different contents of spherical-graphite and Flake-graphite were comparatively evaluated on MM-200 test rig in block-on-ring configuration under dry condition. The microstructures of worn surfaces of PTFE composites were examined with SEM, and wear mechanisms was also analyzed. The changes of notched impact strength with the content changed were also considered. The results show that the tribological performance of spherical-graphite was better than flake-graphite with same weight filled: The friction coefficient of spherical-graphite, about 0.10~0.15, was under flake-graphite, about 0.12~0.18; the wear rate of spherical-graphite was lower than flake-graphite at each content. Notched impact strength of spherical-graphite was from 7.0kJ/m2 to 8.7 kJ/m2 with the content increased, while flake-graphite was fall rapidly from 8.5kJ/m2 to 3.0kJ/m2 with the content added more than 5wt. %.