具紋理之滑動面潤滑摩擦模型建構與分析

Abstract

機械導軌的主要功能在於承載負荷及導向，尤其高負載移動的機械需採用面與面接觸滑動的硬式導軌，此類面接觸的導軌需潤滑以降低摩擦，文獻上雖有依據經驗於表面加工紋理再經由實驗評估其運動摩擦性能，但缺乏理論分析，亟需探討具紋理之滑動面運動時的潤滑與摩擦模型。 本研究利用CAE軟體建構滑動面之運動摩擦模型，首先以半模型類比處理空蝕課題的Half-Sommerfeld邊界條件，構築以油袋產生的承載力與負荷重量達到平衡時的等效油膜厚度之計算模型，分析其於平衡狀態時之摩擦力，並藉由量測數據比較，顯示該理論模型與量測結果具有相關性，但二者仍有明顯差距。研究進一步考量摩擦面滑動時產生的傾斜角，將滑動攻角導入摩擦模型中，亦即負荷由油袋以及滑動面之承載力共同承受，研究結果顯示在面壓4.141KPa條件下，滑動攻角在14×10^-6rad以及面壓9.886KPa條件下，滑動攻角在8×10^-6rad時所造成的液動壓力與量測結果相近，得到較水平滑動時更為合理的結果。本研究之主要貢獻在於建構一具紋理之滑動面的潤滑摩擦模型，解決長期以來難以處理摩擦面油膜極小深寬比的課題，並經量測比較其合理性。

The function of the guideway is to carry the load and guide the direction of motion. The hard rail, a surface-to-surface contact guideway, is particularly employed in the situation of motion at high loading. In such a guideway, lubrication between contacted surfaces is important. Although literatures showed texture patterns, serving as lubricant reservoir, are design and fabricated based on empirical methods, it is necessary to develop a theoretical model for analyzing lubrication and friction characteristics of sliding surface with textures. In this paper, CAE software is employed to construct the lubrication and friction model for sliding surface with simple texture. First, the half-Sommerfeld boundary condition is used to simulate the cavitation effect. The effective thickness of lubricant and the corresponding friction are then computed based on the load and the bearing capacity of the oil pocket. Experiments to measure the friction forces are then conducted for comparisons. It showed that there exists an offset between theoretical results and experimental data, though both results showed the same tendency. Considering the lubricant induces an angle of attack during sliding, the friction model with an attack angle is constructed for exploring the loading capacity, which means the load is supported by both oil pocket and sliding surface. Results showed that the hydrodynamic pressure caused by the angle of attack at 1.4×10^-5 rad under 4.141 KPa surface pressure and at 8×10^-6 rad under 9.886 KPa surface pressure are close to experimental results. This research work provided a method to solve the problem in analyzing the loading and friction of sliding surfaces with textures due to tiny aspect ratio of lubricant film. The friction model for sliding surface with textures is constructed and verified its reasonability through experiments.