Market Pull

Andy Michael, technical manager at Clariant Corp. in Mount Holly, North Carolina, highlighted new test results regarding application benefits of polyalkylene glycol base stocks in industrial gear oils.

Presenting at the Society of Tribologists and Lubrication Engineers May meeting in Atlanta, he began with a perspective on the global market. Citing market research firm IndustryARC in Hyderabad, India, Michael noted that in 2014, the Asia-Pacific region was responsible for 46 percent of global industrial gear oil demand by value, while the Americas accounted for 22 percent, Europe for 21 percent and the Middle East and Africa a combined 11 percent. Globally, the oils were used primarily in general manufacturing (27 percent by weight), the steel industry (21 percent), mining applications (19 percent), and construction, agriculture and energy applications (10 percent each).

According to IndustryARCs research, the 2016 global gear oil market totaled 859,000 metric tons valued at $5.56 billion, compared to 891,500 tons at $5.3 billion in 2014. In 2014, the analysts stated that traditional API Group I and Group II mineral oils were used to blend 607,000 tons of industrial gear oils ($2.5 billion); Group III oils were used in 26,000 tons ($153 million); Group IV polyalphaolefins in 139,000 tons ($1.45 billion), Group V PAGs in 71,000 tons ($912 million); and esters in 48,000 tons ($307 million).

Global volume growth of industrial gear oil demand is expected to be 1.6 percent, calculated as a compound annual rate, from 2016 to 2021. At these rates, this will be a more than 930,000 ton, $6 billion market in 2021. The IndustryARC forecast anticipated increasing demand for gear oils formulated primarily from premium-priced PAO, PAG and ester base stocks for demanding applications. PAGs are formulated in food grade lubes, worm gear oils and extreme pressure gear oils.

Oil-solubles for Gears

Many believe that PAGs can only be used in water based lubricant formulations. Michael explained that some hydrophilic PAGs are used in water based hydraulic fluids and metalworking fluids, but oil-soluble PAGs are more hydrophobic and are stable in oil based formulations. PAGs are commercially available with ISO viscosity grades between 32 and 1,000.

He reminded attendees that PAGs are produced by polymerizing ethylene oxide and propylene oxide or their derivatives, in varying ratios. Raw materials and reaction conditions are controlled in order to synthesize polymers with various structures, such as homopolymers, random and block copolymers; chemical functionality, such as oxygen atoms in the backbone, butanol or ethanediol terminal groups; branching; and physical properties.

According to Michael, It is becoming more important for gear oils to cope with higher speeds, extremely high loads and high temperatures. These application conditions are the logical consequence of continuous productivity increases required by end users. At the same time, end users are looking to reduce maintenance costs through reduced downtime, lower energy consumption and extended oil change intervals.

He continued: Although these trends are general knowledge, there are very few facts and figures in the scientific literature about the influence of specific base stocks on gear oil performance.

Thus, Clariant conducted a study comparing mineral, ester, PAO and PAG base stocks, all ISO VG 220, which is commonly used for industrial gear oils. Michael noted that PAGs can excel in terms of viscosity index, rust prevention and water tolerance (table 1).

We made the observation that PAGs offer extraordinary wear protection even without additives, Michael reported. The higher the ethylene oxide content and the higher viscosity of the PAG, the better the anti-scuffing performance in lubrication tests.

Clariants B11 PAGs, with terminal chemistry of butanol and an EO/PO ratio of 1:1, and its D21 PAGs, with terminal chemistry of ethanediol and EO/PO ratio of 2:1, passed the highest load defined (stage 12) in the FZG gear oil test A/8.3/90, according to the DIN ISO 14635-1 method, without any additives. In contrast, a PAO blend with the same viscosity failed by load stage 9, and a mineral oil blend failed at load stage 7.

This superior lubrication by PAGs, he emphasized, was achieved without using additives that can contribute to foaming, corrosion and other undesirable side effects.

Perfect PAGs?

Are PAGs perfect on their own, or can additives improve their performance?

Michael explained that an extreme pressure additive package can enhance industrial gear oils formulated with PAGs. As an example, he pointed to Clariants 1655N. Four percent of the additive boosted the load carrying capacity of the companys PAG B01/150, ISO VG 150 base stock from load stage 12 up to load stage 14 in the FZG test.

In PAG D21/150 at ISO VG 150, a 4 percent mixture of the same additive reduced wear scars from 0.5 to 0.34 millimeters in four-ball wear tests (DIN 51350-3) and increased seizure and weld loads by 300 pounds in four-ball extreme pressure tests (DIN 51350-4).

Additionally, the additive package reduced foaming at 4 percent treat rate and prevented foaming at 20 percent treat rate in the PAG D21/150 base stock using the ISO 6247 foam test. In the Turbine Oil Stability Test (DIN EN ISO 4263-4) and in-house tests, 4 percent additive prevented thermo-oxidative degradation of this base stock at temperatures up to 120 degrees Celsius. Increasing the treat rate to 8 percent extended protection up to 150 C.

In Clariants in-house oxidation stability test-using 15 grams of oil in an open glass bottle with copper and iron wires as oxidation catalysts at 120 C-PAGs darkened in color, but remained clear and free of sludge after four weeks because decomposition products were soluble in these oils.

Michael noted that in the field, PAG based formulations have outperformed mineral oil formulations in terms of service life and energy efficiency for spur, bevel and especially worm gears. He concluded that this head-to-head comparison study of additive-free ISO VG 220 base stocks clearly showed that PAGs were a primary factor in the superior performance of gear oils.

Energy Efficiency

Additional work on PAGs and energy efficiency was performed by Steffen Fleischer, global application development manager for industrial lubricants at the Clariant Innovation Center in Frankfurt, Germany. His work was presented at the UNITI Mineral Oil Technology Congress in Stuttgart, Germany, in April.

Fleischer used a modified FZG two-disc test apparatus with a torque loss meter to calculate load-dependent energy losses. These inefficiencies are caused by friction between gear teeth and influenced by the type of base stock. The coefficient of friction and oil temperature were lower for PAG D21 than for B01 and B11, all ISO VG 150.

He compared three model gear oils over a range of conditions (see table 2). In every case, energy losses were smallest for the PAG product, followed by PAO and then mineral oils. Load-dependent energy losses increased with load for all three base stocks. PAG D21/150 was approximately 50 percent more efficient than mineral base stock at stages 5, 7 and 9 (torques of 94, 183 and 302 Newton meters, respectively). Energy efficiency of the PAG D21/150 relative to mineral and PAO base stocks was greater at slower pinion shaft speeds and higher temperatures.

Fleischer also reported results from an energy efficiency case study. An extruder for polymer compounding was operated with average engine power of 200 kilowatts-63 percent of the machines maximum power-and 70 liters of lubricant. When the mineral oil based lubricant was replaced with one formulated with a D21 PAG, energy consumption was reduced by 0.5 percent.

Estimated annual savings were calculated to be 1,005 euros ($1,200 U.S. dollars). The savings corresponded to a gear oil price difference of 14 euros per liter. Another advantage of the PAG based gear oil was lower operating temperature, leading to longer service lifetime and less need for cooling.

Mary Moon, Ph.D., is a chemist with hands-on R&D and management experience formulating, testing and manufacturing lubricating oils and greases and specialty chemicals. She is skilled in industrial applications of tribology, electrochemistry and spectroscopy. Contact her at mmmoon@ix.netcom.com or (267) 567-7234.