Research & Innovation
Gear Oils of the Future
The most severe applications in industry today are often not satisfied by synthetic gear oil. The ideal gear oil should last for many years without needing to be changed, thus saving a significant amo...
February 1, 2004 By Pulp & Paper Canada
The most severe applications in industry today are often not satisfied by synthetic gear oil. The ideal gear oil should last for many years without needing to be changed, thus saving a significant amount in downtime and labour and waste disposal costs.
After years of use it should still have only the slightest traces of wear metals (50 ppm). It should reduce friction, lower operating temperatures and reduce electrical power consumption, saving money in electricity. It should separate readily from water to eliminate emulsification and foaming.
Impossible? Taking gear oils to the next level of performance, to go beyond the performance of synthetic gear oils, is now a reality.
Synthetic gear oils will still be needed for extremes of temperatures, hot or cold. But for most indoor industrial applications where shock loading, overheating, wear and contamination with water are the worst enemies, there is a different solution that actually outperforms synthetics in these conditions.
This revolutionary gear oil technology separates from water. This demulsibility allows water to be drained off the bottom of the gearbox, even while the gearbox is still running. Since there is no emulsion, there is no foaming. The water is also prevented from reaching the gear teeth and causing corrosion.
Many industrial plants have gearboxes that get contaminated with water, necessitating changing the oil on a monthly or even weekly basis to remove the milky white emulsion. Now imagine the money that can be saved by simply draining off the water without changing the oil. Since this advanced technology gear oil separates almost instantly from water, if the water is drained off, the oil will last for many years, instead of weeks or months.
Synthetic gear oils are not as tolerant of water. Synthetic PAOs (polyalphaolefins) have limited additive solubility and in order to get the additives to dissolve, ester is added to the formulation. Unfortunately the esters are subject to hydrolysis by water, limiting the useful life of synthetic gear oil in the presence of water.
For example, a gear oil developed by Lubrication Engineers, Almasol, avoids problems with water by using a very specific type of petroleum base oil. The paraffinic structure of this oil is non-polar and therefore remains separate from polar water molecules, thus avoiding the emulsification seen with regular gear oil.
The next problem is achieving lower friction and wear. Regular and synthetic gear oils offer two layers of protection to keep metal surfaces apart. The first layer of protection is the oil film itself. At low speeds and/or high loads this protective film becomes very thin and ruptures.
The second layer of protection now come in to play. The extreme pressure (EP) additives are activated by the friction of metal-to-metal contact and react with the surface to form a chemical film, which prevents the surfaces from welding together. Sulphur-phosphorus compounds are the most common type of extreme pressure additive, but regardless of the type, these EP additives become depleted over time — they simply get used up.
The addition of a third layer of protection, a solid lubricant suspended in the oil, dramatically improves performance. When the oil film ruptures, the solid lubricant physically separates the metal surfaces, acting like miniature ball bearings. This extra layer provides so much extra protection that the EP additives are often not activated at all and therefore last for years longer than EP additives in gear oils without solid lubricants. A solid lubricant also provides a smooth, low drag surface to reduce friction and reduce consumption of electrical energy.
The choice of solid lubricant technology has a huge influence on performance and should not be taken lightly. Materials used as solid lubricants include molybdenum disulfide (MoS2), graphite (C), fluorocarbon polymers such as polytetrafluoroethylene (PTFE, commercially known as Teflon), metallic oxides and a ceramic material commercially known as Almasol. Table 1 shows a comparison of these technologies.
Note that on a microscopic level all metal surfaces are uneven and have high and low spots. The high points, called asperities, on opposing working surfaces meet under heavily loaded conditions and the instantaneous contact temperatures of these asperities often exceed 1000F. Pressures in the contact zone can also exceed the 175,000 psi yield strength of steel.
This dry film technology has been used on every manned U.S. space flight. The results of this technology are impressive: much longer life for the equipment, less downtime and lost production, lower maintenance costs (parts and labour), long lubricant life (years between oil changes), and increased energy savings as less amperage is required to perform the same work.
The energy savings alone are often enough to pay back the higher cost of the lubricant within months, giving years of savings before the oil needs to be changed again.
The life of regular and synthetic gear oils is often limited to just a few months (usually less than two years) due to wear metals levels exceeding 50 ppm and a drop in EP additive levels. With this technology, the oil life is prolonged to many years, even decades, with dramatically lower wear levels.
The reduction in friction and wear has been documented by many, including FAG Bearings (see the English translation at www.lubeng.com/download/FAG1.jpg and the original document at www.lubeng.com/download/FAG2.jpg). The bearing manufacturer found a reduction of 23% in friction compared to regular gear oil.
Higher protection against shock loading is also shown by the achievement of 13 stages on the FZG Test (ASTM 2266) vs. 12 stages for most other gear oils. In the FZG test, commercial gear oils tested had 138% to 263% more wear than the tested Almasol Vari-Purpose gear lubricant.
Another characteristic of this technologically advanced gear oil is much stronger adhesiveness, cohesiveness and tackiness. These factors are often overlooked in gear oils but are vital in reducing wear.
Tacky gear oil will stick to the gear surfaces and the walls of the reservoir even when the unit is not in operation. This seals out water, which prevents corrosion. It also means that the gear oil stays on the gear teeth, giving full protection at startup. Conventional gear oils will drain to the bottom of the reservoir and not stay on the teeth. The gear oil will also climb up gears that are only slightly submerged, giving full protection should the gear oil level drop below normal levels.
Seal compatibility is another neglected area. Cheap base oils are high in aromatics, which attack rubber hoses and seals. The same carefully chosen paraffinic base oils which separate readily from water also don’t attack rubber, and therefore extend the life of oil seals and hoses, meaning fewer leaks and spills and less top-up oil.
Why is oil changed? Usually because of contamination with water, wear metals or because it has turned black due to oxidation. If a gear oil can separate from water, produce far less wear metals and have very high oxidation resistance, it can last for many years before needing change, thus outlasting regular and synthetic gear oils. Fewer oil changes save money on labour, new oil and used oil disposal. Using less oil is also better for the environment.
Despite the significant return on investment of advanced lubricants, many companies focus on the price per litre and miss out on the real savings: electricity, downtime, labour, and the capital cost of replacing expensive equipment sooner.
These savings have been documented by many companies and are published on-line at www.lubeng.com under the Customer Feedback link.
At Smurfit Stone in Montreal, this solid lubricant was tested in an overheating gearbox that was running conventional gear oil. Operating temperature dropped gradua
lly from175F to 143F, says maintenance manager Gilles Hache. Based on this result, a second gearbox was converted and demonstrated an equally significant reduction in temperature. Eventually all the equipment in the plant was converted. The oil in the gearboxes was used for seven years, from 1995 to 2002, without any oil change.
The ability of the new gear oil to separate from water also prevented a major failure at Smurfit Stone when 15 gal of water flooded a large gearbox. The 40 gal of oil in the gearbox did not emulsify and a detailed examination of the equipment showed that the gear teeth and other mechanical components had not sustained any damage.
With companies focusing on the bottom line and increasing efficiency, it is clear that the proactive maintenance provided by this lubrication technology can play a vital role in ensuring the profitability of Canadian companies in the future.
|Almasol||Molybdenum Disulfide||Graphite||Fluorocarbon (PTFE)|
|Maximum Service Temperature|
|Load Carrying Capacity, psi2|
|Comments||Has a natural affinity to metal as a result of surface attraction. Will not build on itself or affect machine tolerances||Oxidizes in air above 343C (650F) to form molybdenum trioxide which is abrasive. Tendency to build on itself and affect close tolerances. Cannot tolerate hydrochloric acid and nitric acid, which are often present in lubricant environments especially where heat, water and air are present.||Galvanic corrosion problems. Tendency to build on itself.||No load-carrying capacity. Tendency to build on itself.|
Christopher Barnes is with Lubrication Engineers of Canada Ltd., Oakville, Ont., the Canadian distributor for Lubrication Engineers Inc. of Fort Worth, Tex. He can be reached at 905-829-3833 or at email@example.com.
Print this page