May 2012 / Volume 64 / Issue 5|
By Alan Richter, Editor
| Applying ‘green’ coolant to maintain machining performance while being friendly to workers and the environment.
Green chemistry applies according the life cycle of a chemical product, including its design, manufacture and use.
The definitions of “green” coolant chemistry are as diverse as New Zealand’s flora and fauna. “A green coolant chemistry can be defined many different ways,” said Daryl Adams, metalworking lead product manager for Quaker Chemical Corp., Conshocken, Pa., “but it is something that will have a positive impact on the environment, whether it’s reducing energy consumption, increasing the longevity of the bath, reducing chemical usage or recycling and reusing the product.”
Some definitions, however, carry more weight than others. The U.S. Environmental Protection Agency defines green, or sustainable, chemistry as the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies according the life cycle of a chemical product, including its design, manufacture and use, the agency states on its Web site (www.epa.gov/greenchemistry).
Hank Limper, market development manager, metal removal, metal cleaning and metal protecting for Houghton International Inc., Valley Forge, Pa., emphasized that although a green metalworking coolant can be vegetable oil-based, it’s not a requirement.
“A vegetable oil-based coolant isn’t necessarily going to last any longer in your machine tool or central system than an oil-based coolant,” he said. “Green means environmentally friendly, operator friendly, sustainable and made with renewable resources—raw materials that can be recycled and reused in other metalworking products. You opt for a product with a small environmental footprint.”
One step toward going green is determining which raw materials are biologically neutral, according to Limper.Changing Requirements
Not surprisingly, Limper has seen a significant change in coolant formulations since he joined Houghton more than 3 decades ago, with the first 15 to 20 years focused on traditional amine borate-type coolants.
“They were the industry standard at the time, but everybody in the industry accepted the fact they were going to go rancid,” he said. “They were treated with a biocide or fungicide as needed.”
Courtesy of Chemetall
However, even early in his career the state of California was legislating what a formulation couldn’t contain, such as chlorine and boron. California continues to play a significant role is establishing restrictions for metalworking fluids.
For example, in 2011, the South Coast Air Quality Management District adopted Rule 1144, which placed restrictions on volatile organic compound (VOC) emissions from metalworking fluids and direct-contact lubricants at industrial facilities, with more stringent restrictions added in 2012 that significantly impact the region’s metalworking industry. The rule applies to four counties in Southern California: Los Angeles, Orange, Riverside and San Bernardino. (Many VOCs harm human health at high exposure concentrations.)
According to Quaker Chemical, its direct participation in validating and developing the test method to accurately measure VOC content resulted in a deep understanding of the rule’s impact on the metalworking industry, as well as the insight needed to develop compliant, high-performance metalworking fluids. The new VOC test method is based on an EPA-developed method for testing paint. “Paint chemistry is a different chemistry than what is used in metalworking fluids,” Adams said.
As a result, Adams noted that Quaker formulated cutting and grinding fluids and corrosion preventives to address the new restrictions, which can be applied without dilution. These products preserve the effective performance characteristics of traditional coolants while maintaining VOC levels lower than the specific maximum allowed, a requirement of Rule 1144 for this type of product application, he added.
The company added those cutting and grinding fluids and corrosion preventives to its existing product line, which have VOC levels within the acceptable limits of the new rule.
“Our goal is to develop, modify or identify existing products that meet the performance and quality standards of customers affected by the new rule,” said Wayne McVey, Quaker’s technical manager–cleaning, forming and corrosion.
“Even manufacturers not directly impacted are inquiring about the new requirements and how it may affect their operations in the future,” Adams said.Formaldehyde-Releasing Biocides a Problem
Limper noted that global requirements are playing an expanded role in the market as global manufacturers establish more U.S.-based metalworking facilities and become U.S. customers.
“When global companies build plants in the U.S., they want either the same products, typically because they were an approved part of their manufacturing process, or products that would perform the same but would not contain things like boron and formaldehyde donors,” he said.
Courtesy of Chemetall
Formaldehyde, which the U.S. Department of Health and Human services listed as a known human carcinogen last June, isn’t added to coolants. However, some biocides, such a triazine, release formaldehyde as a chemical trigger in the presence of acidic byproducts from microbes living in a fluid, Limper explained. The formaldehyde kills bacteria.
Chemetall is another coolant manufacturer that doesn’t formulate its products with registered bactericides and secondary amines, such as dicyclohexylamine (DCHA), according to Dr. Yixing “Philip” Zhao, senior scientist for the New Providence, N.J.-based company.
“DCHA has very high bioresistant properties,” he said. “Its toxicity may not be as high as a biocide, but it is high enough to be a concern.”
Zhao pointed out that triazine, also known as hexahydrotriazine, or HHT, is popular because it’s efficient and inexpensive, and the most economical and efficient bactericides release formaldehyde. There are bactericides that don’t release formaldehyde, but they’re not as efficient at killing bacteria and cost more, he added. “In a metalworking fluid, you’re always concerned about performance versus cost.”
Courtesy of Houghton International
When a bactericide releases formaldehyde, it becomes airborne with the coolant mist and vapor. The National Toxicology Program has listed formaldehyde exposure as a known cause of human cancers of the nose, nasal cavity and upper throat.
The EPA has proposed a maximum triazine level of 500 ppm in solutions of metalworking fluids to minimize exposure, but it’s an open issue as to what level of formaldehyde exposure is safe for workers, according to David Enright, Chemetall’s industry manager for metalworking fluids. “It’s sometimes hard for a user to even be aware that the fluids have formaldehyde because it hasn’t been released,” he said.
However, even if 500 ppm is safe for workers, an effective kill dose is 1,500 to 2,000 ppm, rendering triazine moot at a lower level, noted David M. Gotoff, Chemetall’s product manager.Out with the Old
The challenge, then, is to formulate a coolant that is safe for the environment and workers while still being biostable, bioresistant and robust. In contrast, conventional coolant chemistry relies on the addition of bactericides to keep bacteria in check. Otherwise, the coolant experiences an explosion of bacteria growth after a certain number of hours.
“That’s why they have to use bactericides,” Zhao said. “It’s old chemistry, old knowledge and the old way people achieved coolant stability.”
Conversely, the new bioresistant coolant chemistries in the figure don’t contain bactericides, only one has DCHA as a reference in the biochallenge tests, and the amount of bacteria stays very low over time.
“This demonstrates Chemetall’s principle approach to green product development,” Zhao said. “We’re moving into the new chemistry, new esters and vegetable-based additives.”
That level of coolant performance is achievable without adding cost, according to Gotoff. “In the majority of cases, we’re not more expensive per se than our competitors that use an older product,” he said. “We experiment to achieve optimal results.”
End users calculating coolant cost should consider the entire metalworking operation. A stable and robust coolant emulsion lowers equipment maintenance costs, reduces the frequency of replacing worn cutting tools and extends sump life, according to Enright.
Nonetheless, a stable and robust coolant only stays that way with effective process control. That requires testing for and maintaining coolant concentration, alkalinity, conductivity, tramp oil and bacteria and fungus count, Enright noted.
“Among these factors, concentration is probably the most important one to be controlled tightly because a decreased concentration will not only provide less lubricity, but also fewer emulsifiers and alkalinity agents, such as amines,” stated Zhao in a white paper about process monitoring and controlling coolant sump longevity. “Therefore, the stability of the emulsion will be greatly decreased. Subsequently, an unstable emulsion will also facilitate bacteria growth and this will deteriorate emulsions.”
Houghton’s Limper concurred that maintaining coolant concentration is the optimal way to achieve coolant longevity. “If you run your coolant too low, you welcome corrosion and biological activity,” he said. “If you run it too high, you invite dermatological issues and mucous membrane issues, such as nose, throat and lung irritation. We preach that as gospel, and that hasn’t changed since long before I was born and won’t change after I’m out of this industry.”
Depending on the application, the upper coolant-concentration limit is generally from about 9 to 12 percent because levels higher than that expose workers to too high a pH and potential dermatological issues. The lower limit is about 4 percent because levels lower than that might promote rust and corrosion on machine tools and toolholders and make it more difficult to control bacteria, fungi and their associated odors, Limper explained.Water Wars?
However, even at the correct concentration level, water-soluble coolant application can have an additional environmental impact. Limper noted that many countries prefer manufacturers to machine with straight oil because water is a scarce commodity that’s reserved for human rather than industrial consumption. These countries typically have strict waste-treatment regulations.
Although the U.S. has numerous fresh water sources, such as the Great Lakes, droughts are not uncommon and states are more apt to ration water for manufacturing parts than for raising livestock and growing produce if a severe drought were to occur.
“That’s another definition of being green and more environmentally friendly: using a coolant that will last indefinitely in the sump leads to a greatly reduced waste stream and far fewer recharges, thereby using less of this precious resource called water,” Limper said.
Courtesy of Houghton International
In the event that manufacturers don’t have the resources or time, Quaker Chemical also offers services to check, monitor and control the quality of metalworking fluids in addition to its products. “Under our Chemical Management Services program, we typically put a number of part- or full-time individuals on-site,” Adams said, noting the scope of service may require only one part-time position or as many as 25 full-time people, depending on the facility size and program level.
Typically, customers look for an average savings of 10 percent each year as a result of the implementation of such a program; however, the program focus is more than monitoring chemical usage and process efficiencies. Services can range from simple evaluations of how much material is used in a packaging process to chemical-procurement management if a customer is looking to consolidate vendors and buy larger quantities to achieve volume discounts. “There are a number of creative and innovative ways to save customers money and improve efficiencies,” Adams said.
Within the manufacturing “ecosystem,” coolant plays a critical role. When looking just at the world of coolant, a green chemistry continually provides benefits similar to a life-sustaining object perpetually rotating on its axis. CTEAbout the Author: Alan Richter is editor of CTE. He joined the publication in 2000. Contact him at (847) 714-0175 or firstname.lastname@example.org.
Lubricating properties of minimum-quantity lubrication
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