Synthetic Lubricants or Conventional Mineral Oils?

 8th Jun 2012

Mobil SHC synthetic lubricantsSynthetic lubricants continue to gain market share, thanks to higher performance properties that, for many uses, trump the higher product 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 regularly. Sometimes, it’s part of an overall demand planning exercise. Other times it is simply to ensure the facility is getting the best possible life cycle value.  We encourage this and are glad to help customers with cost-saving calculations bespoke to their business, allowing them to make the right choices.   

Mineral oils differ substantially from synthetic lubricants in what they can achieve, what is required to make them work efficiently and their technical composition.

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

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

In contrast, synthetic lubricants are specially 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, resulting in an end product which is a pure compound - far less vulnerable to oxidation, highly resistant to break-down and almost completely uniform in molecular size.  This molecular size uniformity keeps synthetics from jellifying when it is cold, or thinning when it is hot, making the lubricant’s protective characteristics 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, as suggested 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 have an up to 30% advantage over mineral oils for traction coefficient, meaning the less force is needed to move a load. Less force means less horsepower and therefore increased energy efficiency.

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 realised 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”) 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 an added bonus. Food grade synthetics are sometimes believed to be inferior in performance to mineral oil lubricants; a belief that 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,” 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 vast.

Related to change interval are the issues of product loss through evaporation and disposal. Evaporative losses are without doubt 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. In addition, both sludge and residue form much 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.

This is not to say that synthetic lubricants do not have disadvantages. They can present material compatibility issues with certain metals, coatings and plastics, for example.  And they often cost more on a per-drum basis, (though not necessarily on a life cycle basis).

Where they are clearly superior is in the “extreme zone” where temperatures, high loads or flammability are driving factors and where needs are specific and complex. Synthetics are engineered to meet targeted performance benchmarks and a synthetic formula can (and probably has been) engineered for every combination of properties you can imagine.

For information on Mobil SHC lubricants from WP Industrial, please contact the Sales Team or call us on 0800 980 6172.

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Notes For Editors

The WP Group, headquartered near Southampton in Hampshire, is a leading independent distributor of fuels and lubricants, with a £160m annual turnover and employing 70 people.

Based at Wessex House, Cadland Road, Hardley, Hythe, WP offers a complete portfolio of products and bespoke service solutions across each of its eight trading divisions - ­ Industrial, Aviation, Agricultural, Heating, Automotive, Commercial, Motorsport and Marine.

WP, located by Fawley Oil Refinery, has a 50-year heritage and is the supplier and support specialist of choice to thousands of businesses.

Wessex House
Cadland Road
SO45 3NY
Telephone: 023 8089 7841
Freefone: 0800 980 6172
Fax: 023 8089 8876

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