Elastohydrodynamic Lubrication With O/W Emulsions
Elastohydrodynamic Lubrication With O/W Emulsions
复制标题
DOI：
10.1115/1.2927216
复制
发表时间：
1994-04
影响因子：
2.5
通讯作者：
D. Zhu;G. Biresaw;S. J. Clark;T. J. Kasun
中科院分区：
文献类型：
--
作者：
D. Zhu;G. Biresaw;S. J. Clark;T. J. Kasun
本文介绍了在较宽的轧制速度范围内，不同油液浓度和pH值的水包油（O/W）乳状液弹流润滑膜厚度的实验结果。O/W型乳化液在金属成形、机械加工和液压系统中有着广泛的应用。然而，它们的润滑机制非常复杂，尚未完全了解。利用自行研制的高速光学弹流实验装置，对点接触和线接触的油膜厚度和两相流进行了测量和观察。实验观察表明，入口区周围的相转化/油池形成机制仅在非常低的速度下发生，这很可能远低于主要工业应用的实际速度范围。低速时，油膜厚度主要由油相的体积性质决定，可以用传统的弹流理论并考虑饥饿效应来估算。当转速超过某一极限（称为第一临界转速）后，存在一个过渡区，在该过渡区中没有观察到稳定的油池，油膜厚度开始减小，或稍有增加然后减小。据信，在该过渡区域中，仍有相当数量的油集中在入口区中，并且该局部油浓度随着速度增加而减小。油膜厚度似乎是由进口区的富油两相润滑剂的夹带占主导地位。油膜厚度的增加主要是由于夹带作用，油膜厚度的减小主要是由于油相饥饿程度的增加。如果速度进一步增加超过第二临界速度，膜厚将停止减少并再次开始增加。在该高速区域中，入口区域中夹带的润滑剂的局部油浓度被认为变得相当恒定并且接近于大量润滑剂供应的油浓度。因此，对于所有测试的线接触和点接触情况，随着速度的增加，膜厚度不断增加，并且总是显著小于纯油的膜厚度，但大于纯水的膜厚度。pH值较低的乳状液失稳后，形成的油池较稳定，油膜较厚。这是因为这些低pH乳液中的油滴可以更容易地被固体表面捕获和接触。然而，对于所测试的乳液，油池仍然不能经受合理的高速。
This paper presents a set of experimental results of the EHL film thickness with oil-in-water (O/W) emulsions in a wide range of rolling speed for different oil concentrations and pH values. The O/W emulsions have wide applications in metal-forming and machining processes as well as hydraulic systems. However, their lubrication mechanisms are very complex and have not been fully understood. A newly developed high speed optical EHL rig was used to measure the film thickness and observe the two-phase flow around the EHL point and line contacts. Experimental observations indicate that phase inversion/oil pool formation mechanism around the inlet zone takes place only at very low speeds, which are most likely far below practical speed ranges for major industrial applications. When the speed is low, the lubricant film thickness is dominated by the bulk properties of oil phase, and can be estimated by the conventional EHL theory together with the consideration of starvation effect. After the speed exceeds a certain limit, called first critical speed, there is a transition region, where no stable oil pool is observed and the film thickness starts to decrease, or increases slightly then decreases. It is believed that in this transition region there is still a considerable amount of oil concentrated in the inlet zone, and this local oil concentration decreases as the speed increases. The film thickness appears to be dominated by the entrainment of oil-enriched two-phase lubricant in the inlet zone. The increase of film thickness is due to entraining effect and the decrease due to the increased oil phase starvation. If the speed is further increased exceeding a second critical speed, the film thickness will stop decreasing and start to increase again. In this high speed region the local oil concentration of entrained lubricant in the inlet zone is believed to become quite constant and close to that of the bulk lubricant supply. The film thickness, therefore, continuously increases for all of the tested line and point contact cases as the speed goes up, and is always significantly smaller than that of neat oil but larger than that of pure water. The destabilized emulsions with lower pH values can form more stable oil pools and considerably thicker films. This is because the oil droplets in these low pH emulsions can be more easily trapped and brought into the contact by the solid surfaces. However, for the tested emulsions, the oil pools still cannot survive reasonably high speeds.