TIMKEN OK LOAD #OilChat 93

Posted by Q8OilsMarketing on

Timken OK Load is a measurement that indicates the possible performance of extreme pressure (EP) additives in lubricants. In the Timken EP Test a standardized bearing race is rotated against a steel test block, as shown on the left. The contact area is flooded with the grease or oil that is being tested. Increasing loads are placed on the test block until a score mark is made on the test block. The load immediately before the score mark is made, is reported as the Timken OK load.  The units of measurement are pounds-force or kilograms-force.

When reviewing the technical data sheet for a lubricant or the lubricant specifications for a piece of equipment, you will often see reference to the Timken OK Load Test. So what does it mean when one lubricant has a 35 pound Timken OK Load rating and another has a 40 kg Timken OK Load rating? The truth is … it may have very little relevance to the amount of EP protection you are getting.

There are basically three reasons for this:

  1. The Timken Test Machine was designed by the Timken Bearing Company in 1935 and manufactured until 1972. Timken used the machine to confirm that extreme pressure chemistry in the cutting oils they were using (to manufacture bearings) was still working. It was never designed to quantify performance in any terms other than pass or fail with a 35 pound load applied. Large wear scars or scoring represented a fail and smooth scars were a pass. The test was later adopted by the lubricants industry when Timken began selling the machines. The American Society for Testing and Materials published the ASTM D-2509 procedure for testing greases and ASTM D-2782 for testing oils. From that point on manufacturers started competing for bragging rights to the highest Timken OK Load rating. The Timken test became a marketing tool rather than a simple indicator of the presence of EP additives. The Timken Bearing Company attempted to clarify the misunderstanding about the test with the following statement,“It was generally assumed that the higher the O.K. value, the more load the lube could hold without the film strength being compromised. However, this is not necessarily the case, and the primary purpose of the test is to determine whether or not the lube has an EP additive. Values higher than 35 lbs. indicate the presence of an EP additive.”
  2. There are certain EP additives that can be added to lubricants to give very high Timken results. However, no correlation has ever been established between these extraordinarily high Timken OK Loads and actual field performance. In fact, some of the additives that produce such high Timken OK Loads can be corrosive and/or hazardous and may damage the equipment they are formulated to protect.
  3. In terms of scientific testing, the Timken OK Load test has very poor repeatability and thus a wide margin of error. In fact, the official ASTM D-2509 Timken test procedure states that the results from one test to the next of the same lubricant on the same Timken machine can vary as much as plus or minus 23%. This means a lubricant that gets a pass rating at 60 pounds could actually be anywhere from a 46 pound load to a 74 pound load. If the same product is tested on a different machine, the rating can be off by plus or minus 59%, which means it could actually be anywhere from a 25 pound load to a 95 pound load. The poor repeatability of the test makes it possible for a lubricant manufacturer to repeat the test until the highest result is found and claimed. There are also many modified versions of the Timken machine used by some marketers to “demonstrate” load carrying properties. These are not accepted tests for determining EP properties as the results can easily be manipulated.

Most lubrication engineers and industry professionals agree that the Timken Test should only be used to indicate whether EP agents are present without implying anything about relative performance levels. Most equipment manufacturers now specify more relevant tests that have proven direct correlation to actual field experience (such as the Four Ball EP Weld Test, the  FZG Gear Tests and others) to indicate precisely how much EP and anti-wear performance they require of a lubricant.

So, how much EP is enough? What if grease “A” quotes a 100 pound Timken OK Load pass rating and a 400 kg 4-Ball Weld Load and Grease “B” quotes a 60 pound Timken OK Load pass rating and a 800 kg 4-Ball Weld Load. Which one would perform better in extreme pressure applications? The Timken OK Load ratings tell you that both greases have EP chemistry, but the 4-Ball Weld tells you grease “B” (even with the lower Timken OK Load rating) has the more effective EP chemistry.

In summary, do not let extreme Timken OK Load ratings over-influence the selection of lubricants. Actual field performance, other EP and performance tests (such as corrosion protection and oxidation resistance) may have far greater relevance in many applications.

Q8 offers a comprehensive range of extreme pressure lubricants for a wide variety of automotive, construction, industrial, mining, agricultural and other applications. For more information about the complete range of Q8 lubricants, phone 011 462 1829, email us at info@bcl.co.za or visit www.bcl.q8oils.co.za.