Page 40 - MetalForming Magazine May 2023

THE PATH TOWARD
OIL-FREE METALWORKING FLUIDS
on additives to provide lubricity and water to act as coolant.
sifiers, sulfonates and corrosion inhibitors—generally simple for bacteria to break down. Because fully synthetic fluids contain fewer or none of these ingredients, they prove less prone to microbial con- tamination.
Brunker explains that more of his manufacturing customers ask about naturally derived products such as bioderived complex esters. About 15 yr. ago, he notes, began a push to use more vegetable oil- based emulsions, and some of these products still exist. However, vegetable oils are prone to bacterial attack. In addition, vegetable oils oxidize, which degrades the MWF and can produce varnish on metal tools and workpieces in high-tem- perature applications.
Oil-free fluids excel in resist-
ance to microbial growth, notes Dubbert, with additives used in oil-free, synthetic MWFs pro- viding far fewer nutrients than additives historically used in traditional soluble and semi- synthetic fluids. This, in turn, reduces the level of biocides needed to protect the fluids. Reducing biocide usage repre-
sents a common concern, both
for worker safety and for health
and environmental considera-
tions. In addition to direct haz-
ards, concern exists over sec- ondary hazards associated with biocides that release formalde-
hyde as they break down. How-
ever, Dubbert offers, these concerns are balanced by a need to keep fluids and machines free from microbial con- tamination, which also presents a worker hazard.
Semisynthetics, especially those with biobased components, require biocides. Vegetable-based fluids break down faster—good for disposal, but a disadvantage for operations. Because fully synthetic fluids run cleaner and act more biologically stable, fluid life runs longer, which reduces the amount of used fluid to be disposed. However, even “green” fluids can present disposal issues because used MWFs contain metal fines, tramp oil and everything else that finds its way into a sump.
Metals and alloys such as Inconel, titanium, compacted graphite iron, stainless steel, superalloy steels, 2000- or 7000-series aluminum and magne- sium, as well as some composite mate- rials, still require the lubricity of semi- synthetics and soluble oils, according to Kook-Wha Koh, founder of Chrysan Industries, and difficult operations such as high-speed machining, deep draw- ing, broaching, roll tapping, stamping and fineblanking need oils.
Semisynthetic fluids and soluble oils may contain the same formulation components as fluids using mineral oils, offers Koh, thus if the cost differ-
38 MetalForming/May 2023
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Difficult operations such as deep drawing require the use of oils, but fluid providers continue working on alternatives.
ence is not prohibitive, semisynthetics can be substituted for mineral-oil for- mulations in many applications.
Environmental Considerations
Regulations on environmental pro- tection and health and safety influence MWF ingredients, as do corporate ini- tiatives geared toward sustainability and environmentally friendly practices. Brunker notes that over the past 10 to 15 yr., as the European Union (EU) banned several fluid additives com- monly used for semisynthetics—some biocides and chlorinated lubricity addi- tives in particular—it drove numerous operations back to using straight oils. Though less stringent than the EU, the United States is moving in this direc- tion, with a focus more on versatility of applications, which tilts the balance toward semisynthetics.
One driver of greener formulations: what happens to an MWF after removal from service. Biodegradability repre- sents a plus for fluid disposal, but “biodegradability goes both ways,” Brunker says.
A fluid that degrades while in serv- ice, resulting in a shorter service life, can drive up costs related to defective parts and higher volumes of fluid requiring disposal. Semisynthetic fluids contain soluble oils with anionic emul-
“It’s very difficult to formulate a product both biostable and biodegrad- able,” Brunker says.
Despite a trend toward more sus- tainability and fewer petroleum prod- ucts in many industries, MWFs con- taining mineral oils provide performance and cost effectiveness, Dubbert says. When used and disposed of properly, these MWFs generally prove safe. With the rise of semisyn- thetic formulations, oil no longer rep- resents 85 percent of the formulation. Instead, many concentrates include 10 to 20 percent oil, then diluted with water at 10:1 to 15:1.
More work is needed on waste treat- ment for oil-free fluids, according to Dubbert. The components that make these MWFs so stable also make them difficult to break down in a waste-treat- ment facility. Traditional waste-treat- ment methods (splitting or separating the MWF into water, oil and solids) do not effectively treat synthetic MWF solutions. Semisynthetics present sim- ilar problems. In addition, used MWF contains metal fines, machine oil and anything else that entered the system during operations, which means that dumping used fluid down the sewer is not an option without treatment, regardless of what a supplier implies, Dubbert says.