BY LISA TOCCI

What might be gained by replacing mineral oil with biodegradable, vegetable-based lubricants?

Swedish truck and bus manufacturer Scania AB was willing to find out. In the late 199Os, at its transmission plant in Sibbhult, Sweden, Scania was experiencing problems with dermati- tis, respiratory irritation and oil mist, all causes for complaint by the workers there. At the same time, it was hoping to see longer lubricant life and a cleaner environment.

Working with technical oil supplier Binol AB (part of Sweden’s Karlshamns Group), the com- pany agreed to try out a vegetable oil grinding fluid in its CBN (cubic boron nitride) grinding machine, made by Germany’s Junker Maschinen. This high-speed machine produces retarder shafts

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and power takeoff shafts, plus planet gears, for assembly into the gearboxes that are shipped to other Scania plants worldwide. They transformed the grinder into a “green machine tool,” switching to a biodegradable grinding fluid derived from plant esters, and gauged its performance during a year of operation.

Binol’s director of environment, Ulrika Ti-ulsson Messer, was closely involved with the effort, and based her 1999 master’s thesis on the environ- mental impact of the exchange. Since then, she has focused on the technical performance, working environment and operational acceptability of such lubricants.

The Junker machine at Sibbhult tends to be used for long runs of the same part, so it made a good basis for comparison, she notes. (During the time of the test, it was making an average of 11,000 parts per month.) This machine originally was purchased and installed in March 1996, and from start-up through mid-1998 used a grinding oil

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based on severely refined paraffinic white oil. This was replaced with a plant based product: largely a highly refined rapeseed oil, combined with some synthetic ester based on natural fatty acids (included for viscosity purposes).

A CHEMISTRY LESSON As Trulsson Messer explained to last year’s Tribology Colloquium at Germany’s Technische Akademie Esslingen, vegetable oils are triesters, built from glycerol (which contains carbon, hydrogen and oxygen) and three fatty acids. The selection of the fatty acids determines many char- acteristics, such as the evaporation loss rate and low-temperature behaviors. For example, the more saturated the fatty acid, the higher the freez-

ing point and the more resistant to oxidation. Likewise, a vegetable oil’s oxygen content has a dramatic effect on its behavior as a lubricant, especially its susceptibility to oxidation and poly- merization.

Just as with mineral oils, she stressed, the art of formulating with vegetable oils means compro- mise and a need to select the best total combina- tion of properties for the particular application.

As part of the $350 million Karlshamns Group, one of the world‘s largest suppliers of vegetable fats, Binol is certainly well-fixed to develop these products. Its unusual name actually is derived from the Swedish words for “biodegradable tech- nical oils.” Binol believes that the market in the European Union for such products will grow 10 to 15 percent in the next five years; meanwhile, it says, the market for conventional mineral oils will shrink. Its products today include metalworking fluids and lubricants for metalworking; hydraulic oils and chainsaw oils for the forestry

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and construction indus- tries; thermal fluids for radiators and cooling sys- tems; and specialty agricul- tural applications. It typi- cally spends 25 percent of its resources on R&D, so the Scania plant clearly offered a high-profile opportunity to put its expertise to work.

G T Q ~ ~ T Q ~ T Q ~ Before making the switch to the vegetable oil, Binol closely weighed it against the mineral oil product it was replacing. “We saw some differences in fluid properties,” said Trulsson Messer. ‘A big difference between the mineral oil and vegetable oil was their pour points [-20 C versus -10 C, respectively]. The mineral oil had the advantage here, but since the machine was running indoors that wasn’t as important,’’ she said. (Of course, this might be a fac- tor when storing the fluid, especially in icy climates like Northern Europe, she cautioned.)

In the case of flash point, the advantage was awarded to the vegetable oil (206 degrees C, versus 170 C for the mineral oil).

Most surprisingly, “there was no significant difference between the two oils in oxidative stability.” Both oils endured greater than 1,500 hours without breakdown in a modified ASTM test.

Once the basic physical properties were estab- lished, the question then arose, how to measure the fluids’ technical perfor- mance? “One way might have been to compare the useful life of the machine tool,” she pointed out.

However, because the machine was so new, there was not enough data yet to support this. However, Scania does set limits on surface roughness - might the vegetable oil do a better job? Actually, both oils were able to satisfy Scania’s needs. Even so, the surface roughness dropped when using the vegetable oil. “The machine operators said they actually could see the difference,” Trulsson Messer added. “I” not sure if that’s so, but that’s what they claimed.”

Given that the mineral oil outperformed the vegetable oil in areas like extreme pressure and antiwear capa- bilities, this improvement is hard to explain. Surface roughness is influenced by many factors, not just EP and antiwear, Trulsson Messer pointed out. The vegetable oil may have done a better job of carrying heat away from the tool/work piece interface, she conjec- tured. Other factors affect- ing surface roughness can include the stiffness of the work piece, the material being worked, the condition of the machine and tool or wheel, the uniformity of the preceding process, the amount of stock to be removed, the time allowed for appropriately gentle cut- ting or grinding, and the care given to every detail of the process.

The final two factors - time and care - reveal the economic limits of a process. In the case of the Scania’s Junker grinding machine, all these factors came into play, but the major parameter affecting

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surface roughness was the time allowed for machining each part. Scania allots 165 sec- onds per work piece, to reach the desired roughness. But Binol’s researchers theorized: If you can get better roughness in the same time using vegetable oil, it should be possi- ble to speed the time to reach the targeted roughness, right?

Binol calculated that the vegetable oil grind- ing fluid would make it possible to reduce the relative time for machining by 71 per- cent - and still remain within Scania’s requirement of 0.80 microns surface roughness. Actually, it conceded, even the mineral oil would allow a shorter machining time - about 66 percent. But the plant based fluid‘s 5 percent advantage would add up quickly over the course of a year, amounting to thou- sands more parts produced.

Currently, Scania isn’t striving to increase its parts output - but now it knows that it has the capacity at standby, and at reasonable cost, if it wants to tap into it. The shortened machine times could be achieved simply by increasing the cutting feed (the relative movement of the abrasive grinding wheel to the work piece), and not the speed of the wheel itself, Trulsson Messer surmised.

wo ACC~PTANCE Another big plus for the vegetable oil grinding fluid

28 FEBRUARY 2 0 ~ 1

Less residue and oil mist meant a cleaner work enwironment at the Scania plant.

was in the working envi- ronment, she pointed out. Acute disorders can be associated with metalwork- ing fluid exposure - including skin irritation, contact dermatitis, sensiti- zation and respiratory irri- tation. And workers are concerned about chronic health problems, as well, including a fear of cancer.

Although the machining process on the Junker machine is enclosed, which reduces the opportunity for exposure, some operations still require parts to be manually unloaded. Also, changing the tools involves manual manipulation - and offers another occasion for hands and arms to come into direct contact with the grinding oil. When the machine ran on the mineral oil fluid, half the operators said they experienced eczema, defatting and dry- ing of the skin, irritation and contact dermatitis. Others described respiratory

problems. Some were affect- ed so severely they were considering changing to other work tasks.

After the equipment was switched to the vegetable oil fluid, Binol interviewed the machine operators. They said all skin disorders virtually disappeared, and their skin appeared “refat- ted.” They noted no irritat- ing smoke or fumes, and even the operators who experienced skin reactions noticed a lessening of symptoms; all were able to continue to work. All the workers agreed that the respiratory irritation they had experienced no longer occurred with the vegetable oil grinding fluid. And they were glad to find that the work surfaces in the shop no longer were covered with condensed oil mist. Some workers even felt that the odor of the veg- etable oil product was a plus, less noticeable and more pleasant than the

mineral oil smell, Trulsson Messer reported.

thy improvements were seen at the Sibbhult plant. First, as with nearly every machining process, this one almost con- tinually loses some circulating lubricant due to splashing, misting and carrying away of the lubricant on machined parts. The swarf and turn- ings also account for some of the losses. Regular topping off of the Junker’s oil tank is needed - but the top-off volume

dropped 66 percent in the first year using the veg- etable oil. It had lower evaporative losses, left less residue on the work pieces, and also had a lower ten- dency to form oil mist.

Finally, the machine also has an oil mist col- lector (electrostatic pre- cipitator type) mounted on top. When its filters become covered with cap- tured oil, they must be removed and cleaned. The frequency of cleaning and the maintenance needed fell significantly after the vegetable oil product was introduced - undoubted- ly due to the lower mist- ing effect, declared Trulsson Messer. With the mineral oil product, the mist filters needed servic- - ing 35 times over a year - every 10 days on aver- age. Using the vegetable oil product reduced the frequency by 85 percent, to intervals averaging longer than 10 weeks. I

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