Synthetic Lubricants or Conventional Oils: Making the Best Choice

Synthetic lubricants continue to gain market share, thanks to higher performance properties that, for many uses,
trump higher per-drum costs. Growth in US demand, now $2.2 billion per year, also benefits from tightening
environmental and worker safety requirements.

Virtually every customer (and prospect) we serve re-visits the “mineral oil vs. synthetic lubricants” debate on
a regular basis.  Sometimes, it’s part of an overall demand planning exercise; other times it’s simply to assure the
facility is getting the best possible life cycle value.  We encourage this, and are glad to help customers “do the math”
based on their specific situation, so they can make the best choices.  Processes change, products change, and the
price volatility of crude at the producer level substantially impacts the equation, so a fresh look, at least annually,
is well worth doing.   

Mineral oils differ substantially from synthetic lubricants in what they can accomplish, what’s required to make
them function efficiently, and their composition.

Naturally-occurring crude is a cocktail of hydrocarbons.  Even after aggressive solvent-based refining, thousands
of inorganic compounds -  as well as organic compounds of oxygen, sulfur and nitrogen -  remain.  These three in
particular are problematic, because they enable oxidation and acid development, and facilitate the formation of sludge,
particularly in high-temperatures applications. 

The varying molecules of refined lubricants also have differing shapes, which makes lubricant surfaces irregular at
the molecular level.  These irregularities generate friction which increases power requirements, increases wear,
and reduces efficiency.   More on this in a minute.

In contrast, synthetic lubricants are engineered products, created by chemical reaction through the precise application
of pressure and temperature to a specific recipe of components.  All of the components are high-purity, with strong
molecular bonds.  As a result, the end product is a pure compound, far less vulnerable to oxidation, highly resistant to
break-down, and very uniform in molecular size.  This molecular size uniformity keeps synthetics from jellifying when
it’s cold, or thinning-out when it’s hot, so the lubricant’s protective characteristics are more predictable.   The saturated
molecules created from the synthetic process are also non-hydrophilic, so they won’t emulsify, or produce undesirable
by-products, in high-humidity environments.

Molecular size is also key to one of synthetic lubricants great operational virtues – its traction coefficient, which was
alluded to earlier.  Traction coefficient is the force required to move a load, divided by the load.  The coefficient number
expresses the ease with which the lubricant film is sheared. 

Compared to mineral oil molecules, Mobil synthetic lubricants, for example, have an up to 30% advantage over
mineral oils for traction coefficient.  This means the force needed to move a load is less. Less force means less
horsepower to do the work.

In a gear reducer, the lubricant in the tooth mesh is sheared, and the lower the traction coefficient, the lower the
energy dissipated due to lubricant shearing.  The difference is realized by low amperage draw on the motor, and
reduced lubricant /gear temperature. 

Changing to a low traction synthetic will reduce power consumption in a spur / helical gear by 0.5% for each reduction,
and up to 8% for high reduction worm gears.   

The issue of gear wear is also a consideration.  A study cited in Machinery Lubrication Magazine (Dennis Lauer,
“Synthetic Gear Oil Selection,” May 2001) showed synthetic lubricants make gears more efficient than mineral oils. 
A polyglycol showed the highest efficiency:  18% more than the high performing mineral oil.  SHC gear oil also
made the best gears 8-9% more efficient.  The performance of synthetic lubricants in food grade applications in
accordance with USDA-H11 is also a plus.  Food grade synthetics are sometimes believed to be inferior in
performance to mineral oil lubes,  a belief the study dispels.

Perhaps the most-discussed difference between mineral oils and synthetic lubricants is service life. 
Synthetic lubricants as a class don’t “show their age,” so to speak, particularly at high temperatures, and
have a longer service life.  Often, the change interval is three to five times longer for synthetics at identical
operating temperatures; the exact number depends on whether the base is PAG or SHC. 

Synthetic lubricants have a lower friction coefficient in a gearbox and a better relationship between viscosity and
temperature.  This means synthetic lubricants can be used at lower viscosity grades, and lower temperatures. 
When this is the case, the gap between the service lives of minerals and synthetics becomes a canyon. 

Related to change interval are the issues of product loss, through evaporation and disposal.  Evaporative losses
are definitively lower for synthetics.  Disposal is more costly with synthetics, but nowhere near enough to compensate
for change-out intervals that are 3 to 5 times more frequent.  And both sludge and residue form more readily with
mineral oil products. 

In regard to safety and insurance risks, the flash point for synthetics as a class is always higher, and reduced
flammability is a key driver for synthetic’s growing popularity in high-temperature applications.

Synthetics, to be sure, can have disadvantages.  They can present material compatibility issues with certain metals,
coatings and plastics, for example.  And, they can cost more on a per-drum basis, (though not necessarily on
a life cycle basis.)

Story #1: Synthetic Lubricants or Conventional Oils: Making the Best Choice

Story #2: "Store Lubricant Oils and Greases Properly to Avoid Contamination, Deterioration,
and Poor Lubricant Performance – and to Save Time and Money."

Story #3: "Castrol Recognizes Provider of Value-Added Products and Services" (Acrobat file)

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