| SUN Nan-nan,CHAO Shen,ZHU Gui-xiang,WANG Yong-qiang,LIU Cheng-long,GUO Feng.Effect of Wettability Gradient on Oil Film Lubrication under Reciprocating Motion with Limited Lubricant Supply[J],52(7):130-138 |
| Effect of Wettability Gradient on Oil Film Lubrication under Reciprocating Motion with Limited Lubricant Supply |
| |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2023.07.010 |
| KeyWord:limited oil supply reciprocating motion oil film thickness self-collecting oil wettability gradient surface load effect |
| Author | Institution |
| SUN Nan-nan |
State Key Laboratory of Engine Reliability, Shandong Weifang , China;Weichai Power Co., Ltd., Shandong Weifang , China |
| CHAO Shen |
State Key Laboratory of Engine Reliability, Shandong Weifang , China;Weichai Power Co., Ltd., Shandong Weifang , China |
| ZHU Gui-xiang |
State Key Laboratory of Engine Reliability, Shandong Weifang , China;Weichai Power Co., Ltd., Shandong Weifang , China |
| WANG Yong-qiang |
School of Mechanical and Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| LIU Cheng-long |
School of Mechanical and Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| GUO Feng |
School of Mechanical and Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
|
| Hits: |
| Download times: |
| Abstract: |
| Starvation can usually be found in lubrication of machine elements due to insufficient oil replenishment, and the present study is to explore the role of wettability gradient on the lubrication film building under reciprocating motion with limited oil supply. On the glass block specimens, oleophilic lubrication tracks with oleophobic side regions were prepared. Oleophobic AF (anti-fingerprint) layers were fabricated on the glass block surface. With masks by femtosecond laser, oxygen plasma etching was used to remove prescribed strip area of the oleophobic AF layer on the glass block surface in such a way that oleophilic track with different width were obtained. A custom-made optical EHL (elastohydrodynamic lubrication) test rig, which was capable of reciprocating motion with pure rolling, was used to measure the film thickness and oil pools in the present study. Lubricated point contact was formed between the steel ball and the prepared glass block surface. PAO4 base oil was employed in the test with a limited supply of 0.04 μL. AFM measurement showed that there was typical nanoscale papillae structure on the AF layer, which contributed as well to the oleophobic behaviours of the low surface energy surface of the glass block. The wettability gradient was justified by the movement of a PAO4 droplet to the glass region when it was placed on the boundary of the AF region and the glass region due to the high surface energy of the original glass block. Measurements of film thickness and oil pools showed that the wettability gradient, which was created at the two sides of the oleophilic tracks, generally demonstrated better oil replenishment performance when the track width was 0.2 mm and 0.4 mm, and then the film thickness was higher. On the contrary, the film thickness with a full AF layer (the oleophilic track width was 0 mm) was even lower than that with the original glass block due to its weak affinity to the lubricant. Moreover, it was observed that the film thickness was mostly increased at the center of the stroke, and the film thickness may be up to 3 times as much as that by the original surface. At the two stroke ends only slight film thickness increase was obtained. For film thickness enhancement, wettability gradient worked more efficiently under high frequency or at high speed. When the oleophilic track width was 0.8 mm, which was much larger than the diameter of the contact area, the film thickness was similar to that of the original glass surface, indicating that the induced oil replenishment did not work. It can be understood that when the oleophilic track width and the contact region were of the similar size, the lubricating performance can be improved. A steel ball-on-steel block test was also used to assess the role of wettability gradient, and it was observed that the friction with wettability gradient lubrication track was always lower than that without wettability gradient, and the friction difference between the two increased with running time, and a friction decrease of 30% could be realized. In addition, it was displayed that at low speed, the load had no obvious influences on the film thickness with limited lubricant supply. At high speed, more starvation was observed for heavy loads, thus the wettability gradient worked better for such conditions. At last, the enhanced oil transportation by wettability gradient was numerically investigated with computational fluid dynamics. The simulation results show that the wettability gradient surface can effectively confine the lubricating oil in the track, which is beneficial to the oil replenishment during the reciprocating motion. The proposed wettability gradient is proved to be an effective way to enhance oil replenishment on the lubricated surface, and consequently the oil supply and lubrication state with reciprocating motion can be significantly improved. |
| Close |
|
|
|