Archive for the ‘Lubricants and Fuels’ Category

Lubricant Testing: Evaluating Tribological Behavior of lubricating oils and greases

January 10, 2012 1 comment

Lubricants form an important part of most mechanical systems. The right lubricant can enhance system life, enhance efficiency, cool and remove debris. Lubrication is an interesting and an innovative field where the choice of an appropriate lubricating media is made based on the application. The term lubricant brings to mind oils and greases. These are the most popular lubricating media in use currently. However, many applications now use solid lubricants like Graphite, Molybdenum Di Sulfide (MoS2), Boron Nitride and  Polytetrafluroethylene (PTFE) where use of oils and greases is not desirable.

Coming back to the lubricating oils and greases – oils typically comprise of “Base Oil” and “Additives”. Additives are added to base oil to give the lubricating oil its end performance characteristics. Similarly, greases also use additives to achieve the desired performance characteristics. It is important to evaluate these additives themselves as well as the end product to verify how well the lubricant does its job. To aid development and quality check, there are a variety of tribological tests for lubricants in the market. Some popular tribometers for lubrication evaluation are:

  1. Four Ball Tester:This is an excellent development and quality check method. The unique sample configuration of three bottom balls and one top ball makes a very stable and a repeatable contact allowing tests to be very repeatable.  It can be used to determine Wear Preventive properties (WP), Extreme Pressure properties (EP) and friction behavior of lubricants. The drawback of the Four Ball Tester is that its contact geometry creates a point contact – this is great to create a very repeatable test geometry, but a point contact is usually not encountered in real life applications. However, the wide acceptance of its test results make it an excellent choice to benchmark products. It is a good choice for R&D due to its relatively inexpensive samples and quick results. Its can be a great marketing tool for lubricant manufacturers wanting to showcase lube performance as its tests are widely accepted.You can read more about the four ball tester here:
  2. “Timken” OK Load Tester: This tribometer is a great tool for lube testing. It was originally developed Timken and was used to determine the load carrying capacity of lubricants. It uses a bearing race pressed against a steel block creating a line contact. This line contact is a lot more representative of real life contacts when compared to the point contact as in the Four Ball Tester. The Timken “OK” Load test requires the test load to be increased until the lubricating film between the ring and the block is broken. Scoring is observed as a result of this broken lubricant film and this load value is then reported as the Timken OK Load. This tribometer is a good choice for R&D and quality control. Easily available samples and quick set up make it a good choice for lubricant evaluation. You can read more about the Timken OK Load Tester here:—32.php

There are more instruments for lube evaluation which I will cover in future posts.