A metalworking fluid system with no sump, no splash, no water, no biocides — maybe even no additives? Researchers at the University of Michigan in Ann Arbor have developed a new technique to lubricate, cool and evacuate chips in metalworking operations using a simple, two-component solution of carbon dioxide and vegetable oil.
To address the health, safety and environmental issues surrounding conventional metalworking fluids and their disposal, Steven J. Skerlos, assistant professor of mechanical engineering, and his colleagues dissolved vegetable oil in supercritical carbon dioxide – CO2 under 1,000 pounds per square inch of pressure – and found that it performed well in tests compared to conventional fluids.
Our core idea was to carry oil without water, said Skerlos. We knew that oil is soluble in supercritical CO2 so no emulsifier is needed, and you can use less oil. Other industries, including pharmaceutical, dry cleaning and food, use the technology as an alternative solvent, but no one had looked at it for metalworking.
The components of the system, Skerlos explained, are a CO2 tank, with a line and valve to a compressor, which feeds to a pressure vessel. Vegetable oil is injected into the pressure vessel, where it is solubilized. This dispersion is sprayed out of a nozzle at high speed and pressure to deliver oil and form dry ice near the cutting zone.
The rapid expansion of the CO2 leads to cooling at cryogenic temperatures, and because the supercritical CO2 system has high pressure and improves the lubricant wetting properties, it readily penetrates into the cutting zone. The high pressure at the exit nozzle also clears chips from the work area.
In their completed tests, Skerlos and his colleagues, Andres F. Clarens and Kim F. Hayes of Michigans civil and environmental engineering department, used soybean oil, and they are now testing canola oil.
This is the early stage, and the process isnt optimized yet, Skerlos said. The next steps include exploring the use of mineral oil, quantifying the improvements, and building a business case for the technology.
This is a new class of metalworking fluid with potential break-through characteristics. We need to work with industry, to test this system at scale, Skerlos continued. We want to find a machining challenge – speed, material or application – that conventional metalworking fluids have a tough time with, and show that we can do it.
Because she is unfamiliar with its details, Health & Safety Specialist Carol Poole, Quaker Chemical Corp., Conshohocken, Pa., could not comment on the University of Michigan work. But, she said, the metalworking fluid industry is definitely open to new technologies, particularly with the current EHS [environmental, health and safety] concerns and the prices of raw materials rising. Any new fluid technology must meet certain criteria. Is there a market? Is it feasible to manufacture as well as to use? What is needed up- and downstream from the new technology? But it all starts with a good idea, Poole said.
The metalworking fluid industry is very conservative, noted Fred Passman, president of BCA Inc. in Princeton, N.J. While the global [fluid suppliers] are always willing to try to innovate, what are the economics?
More information about the University of Michigan researchers study of the feasibility of delivering metalworking fluids in scCO2 is available at http://www.engin.umich.edu/labs/EAST/cryolube.html.