The Effects of Temperature on Lubricants

Jim Fitch, Noria Corporation
Tags: industrial lubricants

This column is about the many strange effects temperature has on lubricant states, performance and condition. The idea was triggered by a clever analogy about an egg I heard at an ASTM conference a couple years back. It goes like this:

   Put an egg in the refrigerator and it remains unchanged.

   Place it in very hot water and you get a hard-boiled egg.

   Leave one out at room temperature and you get a rotten egg.

   Put an egg under a mother hen and you get a live chick.

Jims_frying_egg_on_oil_drum.jpgLike many things in life, when it comes to lubricant temperature, there's a need for control and moderation. In other words, you can expect problems if you have too little or too much. Find the temperature sweet spot and the performance and service life of your lubricant can be extended manyfold. Of course it's all so easy to say, but in practice can be oh so difficult to do.

Where's My Cardigan?
On a cold winter morning like today, I like to wear my cardigan, which I always keep in a drawer next to my desk. It's just the added warmth I need to stave off the polar conditions that seem to penetrate my office walls.

Cold temperature can stress our lubricants as well. Unlike food, or our egg, which seems to benefit from cold temperatures, lubricants can chemically degrade, separate into phases and exhibit altered physical states. Let me give you a few examples of the consequences of cold lubricants:

Neither Oil nor Wine Like the Mercury to Rise
Hot oil has gotten the most press, even in this publication. After all, oil is not like some fine wines that get better over time. In fact, even the very best Boudreaux will stress-out when exposed to too much heat. For instance, most wines will age roughly twice as fast at 77°F compared to 55°F, which of course is why connoisseurs and collectors prefer cellar temperature to store their liquid assets.

In 1903, Svante Arrhenius won a Nobel Prize when he figured out the relationship between temperature and most chemical reaction rates. Often called the Arrhenius Rate Rule, it relates to the fact that lubricants, once they've exceeded their base activation temperature, will degrade (oxidize) twice as fast for every 10°C (18°F) increase in temperature. In fact, there are a range of problems associated with too much heat. Let's start another list on the consequences of high temperature:

Taking Your Oil's Temperature
The table below illustrates the use of thermal lubrication charts. These can be easily designed with software found on most computers today. They can be printed and laminated for posting on those machines exposed to dynamic temperature changes.

Of course, temperature plays a vital role in machine condition monitoring which is why heat guns are found in most PdM tool boxes these days. Just like we need to take our temperature to know if we are running a fever, most problems with lubrication, friction and wear will have a temperature profile or signature. So in that sense, temperature change is good.

When viewed together, the entire subject of temperature is definitely no trivial matter… so keep that thermometer handy.

Develop Thermal Lubrication Charts (TLC) for Critical Machines

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