The main use of lubricants is to minimize tribiological wear and friction between surfaces in contact. Lubricants remove the debris from the contact zones, thus minimizing further erosion of bearing surfaces due to abrasion.
基于目前的2.5％的增长率，全球润滑剂市场的价值将在几年内超过1600亿美元，而汽车和运输部门是增长的主要领域。
Manufacturers of lubricants who are looking to cash in on the market rate, need to concentrate on quality control, research and development activities. Customers would prefer dealing with lubricant suppliers who provide reliable products which improve the performance and bring down the overall costs at the same time.
Evaluating and testing lubricants for suitable applications based on the Stribeck curve is a reliable and straightforward procedure. The main challenge in using this procedure is finding a single tool which can cover all areas of the curve. The UMT TriboLab™ from Bruker is a universal tribometer that overcomes this challenge.
Stribeck曲线
The Stribeck curve is obtained by plotting the coefficient of friction (COF) as a function of the Stribeck parameter – ηV/Fz, where V is the sliding velocity, η is the viscosity of the lubricant, and Fz我们的正常负载。
Figure 1 depicts the schematic of a Stribeck curve. There are three well-defined regimes in the figure-boundary, intermediate or mixed, and hydrodynamic. The surface asperities in the boundary lubrication condition carry the load. In the hydrodynamic lubrication regime, the load is completely supported by the lubricating film between the two surfaces in contact. In the intermediate lubrication regime, the elastic deformation of the asperity and viscous resistance of the lubricant together support the load.
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Figure 1.Schematic of a lubricant Stribeck curve showing three lubrication regimes
The direct asperities contact existing between the two surfaces is based on the boundary and extreme pressure lubrication. At this condition, the COF is the ratio between the effective shear stress and the plastic flow stress of the contact materials.
Friction can be minimized by using additives with the lubricant that help in generating a low-shear strength interface on hard metal contacts. By using adsorbed mono-molecular and low-shear layer to cover the surfaces in contact, friction can be reduced at low temperatures ranging from 100-150oC and high pressures up to 1GPa.
At high temperatures, the inorganic sacrificial films that are formed due to reactions between the metal surface and lubricant additives that contain chlorine, sulphur or phosphorus protect the metallic contact from extreme wear. Under such conditions, the lubrication is determined by a working temperature at which such protective films are rapidly formed for protecting the contacts from wear.
The mixed and boundary lubrication regimes are caused when the lubricant film does not separate the bearing surfaces completely, and a certain amount of solid-to-solid contact is experienced, particularly in low velocity and/or high load conditions.
By subjecting a lubricant to different force, temperature and velocity conditions, the Stribeck curve that spans all the three lubrication regimes is obtained. A useful Stribeck curve can be plotted with a tribometer that can operate over a wide range of test parameters.
布鲁克的UMT Tribolab
UMT Tribolab系统基于通用机械测试（UMT）平台及其对速度，负载和定位的精确控制。由于其模块化设计，Tribolab的测试能力跨越了广泛的速度，力和温度。Tribolab具有众多创新功能，可促进任何类型的部落测试的快速简便配置。
The TriboLab can be made user- friendly, productive and versatile by using intuitive integrated hardware and software interfaces like Tribo ID™ and TriboScript™. Tribo ID automatically detects and configures the components attached to the main system to ensure that the system works properly.
TriboScript提供了一个安全的高级脚本接口，可促进从先前创建的测试块中轻松汇编测试序列。Tribolab系统在实时控制和数据分析软件的帮助下提供了高可重复性和准确性。
Evaluating Lubricants for Potential Applications
Stribeck测试是在SAE 52100球和Tribolab上进行的。在每个测试集的开头引入了一个闯入步骤。对四种不同的润滑剂（A，B，C和D）进行了测试，以绘制Stribeck曲线。根据Stribeck曲线，确定了润滑剂的合适应用及其在每个润滑方面的基于性能的排名。
With the TriboLab, the velocity and normal force can be altered simultaneously in order to maintain a specific V/Fzratio. Stribeck tests were performed on the four lubricants by varying the V/Fzfrom 0.01 to 20,000, covering all three lubrication regimes. The normal force and the friction force (Fx) were also measured during these tests. The value of electrical contact resistance (ECR) between the disk and the ball were determined and recorded. The ECR data that is measured gives a qualitative indication of the lubricant film thickness between the disk and the ball.
图2表示Lube-A和ECR图的Stribeck曲线。边界，混合和流体动力区域也显示在图中。由于润滑剂的粘度，流体动力区域的COF高得多。与直接金属接触导致的混合区相比，COF倾向于在边界区增加。在流体动力区域的开头，COF的值非常低。
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Figure 2.Lube-A的Stribeck曲线以及一个ECR图，显示了三个润滑方案。
The electrical contact resistance data, shown in Figure 2, is also segregated into three regions, confirming the friction results. The ECR signal in the hydrodynamic regime was considerably high, and showed a declining trend at the initiation of the mixed region corresponding to a V/Fz大约200个。
At the initiation of the boundary regime, and at a V/Fzratio of 1.3, a steep decrease in ECR value was observed, which can be attributed to the metal-to-metal contact. Out of the four lubricants, Lube-A exhibited best performance at the mixed and boundary regimes, and hence, it was used as a reference for other lubricants.
图3中显示了润滑剂和润滑油B的骨曲线曲线的比较。可以看出，在混合区域和边界区域，润滑油B的COF值比Lube-A更高。
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Figure 3.Comparative Stribeck curves of Lube-A and Lube-B.
图4显示了Lube-A和Lube-C Stribeck曲线的比较。可以看出，Lube-C在中间润滑方案中表现出更高的COF值。两种润滑剂的摩擦行为在边界区域都相似，但是在流体动力区域，由于粘度贡献的差异，润滑剂-C的COF值远低于润滑剂-A。
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图4。Comparative Stribeck curves of Lube-A and Lube-C
The Stribeck curves of Lube-A and–D are compared in Figure 5. It is seen that Lube-D exhibited lower COF values than Lube-A only in the hydrodynamic regions.
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图5。Comparative Stribeck curves of Lube-A and Lube-D
It is a general notion that lubricants with lower COF exhibit better performance. The four lubricants were ranked from 1-4 based on their COF data in each regime, where 1 represents the highest performance and 4 represents the lowest. Table 1 shows the ranking of the lubricants.
表格1。Ranking of the lubes in three lubrication regimes
| Lubricant |
边界 |
混合 |
流体动力学 |
| Lube-A |
1 |
1 |
3 |
| Lube-B |
2 |
2 |
3 |
| Lube-C |
1 |
3 |
1 |
| Lube-D |
3 |
4 |
2 |
根据表中的数据，Lube-A和Lube-C在边界区显示出最佳性能，而Lube-D在该区域中排名最低。Lube-A在混合区域表现出最佳性能，而Lube-D显示出最差的表现。Lube-B在混合区域和边界区域排名第二。
Lube-D在流体动力区域排名第一，润滑剂C排名第二。在流体动力区域中，润滑油A和润滑油B均为4（较差）。ECR的测量值与Stribeck测试期间的测量摩擦值一致。
结论
为了使润滑剂的完整部落学表征，必须在所有三个方案中进行测试和比较，以在广泛的测试参数（例如速度，力和温度）上进行。
UMT Tribolab启用了全面的Stribeck测试，以识别润滑剂的特定应用，并根据其在所有三个制度中的性能进行对。为了深入探索润滑剂的应用潜力，至关重要的是在涵盖所有三个润滑方案的条件下进行测试。
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This information has been sourced, reviewed and adapted from materials provided by Bruker Nano Surfaces.
For more information on this source, please visit布鲁克纳米表面。