Test methods for evaluating wear, extreme pressure and friction (in lubrication)
Lubricant testing is undergoing an evolution. In the years during and after World War 2, a lot of problems occurred due to catastrophic failure of lubricants under high pressures. Around that time, the magical ZDDP was developed and it remains one of the most effective extreme pressure additives for lubricants today. Other additives were also developed, all of them designed to help avoid catastrophic seizures, adhesive wear, welding in equipment and components.
Already in the 1930s, additives based on phosphorus and sulphur had started to appear and the increase in EP additives is clearly illustrated by the evolution of the number of patents, filed between 1930 and 1950: it grew from 9 per year in 1935 to an average of 40-50 per year in the post war years.
The backbone of lubricant specifications has become: risk reduction! Many of these original test methods are still around and still used today. The most common ones are shortly described next.
Falex Pin&Vee block method, aka ‘the Falex’ method The Pin&Vee block test was invented by Frederic Faville, founder of today’s Falex Corporation in the 1930s. ‘Fritz’ Faville – an additive salesman – wanted to demonstrate the quality of his additives and needed a ‘portable’ machine that could measure both extreme pressure and anti-wear properties of lubricants. His clever design of a mechanical loading system, applying an increasing pressure on the line contacts between a rotating pin and two blocks with a Vee-notch, resulted in a repeatable test method that could not easily be influenced by the operator. Thanks to that quality, it culminated in ASTM standard methods (D3233 and D2570) and remains one of the most common EP and anti-wear quality control methods for (solid) lubricants today.
The Timken test
This method and test machine were originally developed by the Timken Steel company for the selection of bearing greases. A standardised block is pressed against a rotating ring through a lever arm, while the grease or oil are fed into the contact. The highest load at which no scoring takes place is defined as Timken OK load, simple visual inspection of the test block confirms the scoring load. This method became ASTM D2509 and D2782 for greases and oils respectively. As the test became an industry standard, production and further ASTM development were licensed to Falex Corporation who supply and support the equipment and standard test pieces ever since.
NOTE: ASTM methods should not be confused with some commonly known salesman’s demonstrators that can be found particularly on YouTube adverts. These little cylinder-on-ring tests are sometimes called Timken, Timpken, but also Falex test, lubricity test, etc. They are in no way a standard test method and their results are highly operator dependent.
With the explosion of these products, came the need to test their quality. As manufacturers started to produce these additives or blend them in their greases and oils, the need for objective comparison – and thus for standardisation – became more and more important. Also at the same time, anti-wear additives came into the market and they too needed standardised quality tests. In the USA, the ASTM has played and still plays a key role in the development and publication of consensus-based test standards for materials.
The Four Ball methods
The Pin&Vee block principle : two lubricated Vee- blocks are pressed against a rotating Pin by a set of lever arms at a set (wear test) or increasing (e.p. test) load.
Shell developed a lubricant EP test, based on a Four Ball configuration in the 1940s. 3 steel balls in a cup are pressed against a fourth spinning ball with increasing and high load (up to 1000kg). Due to the self aligning configuration, 3 contact points are created on the lower balls, where either wear or fatal damage (welding) takes place, depending on speed, increasing load and temperature. The critical loads where seizure (the onset of adhesive wear) and welding (fatal collapse of the lubricant causes severe adhesive wear) take place, are
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LUBE MAGAZINE NO.123 OCTOBER 2014
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