Cool solution

University of Michigan researchers have developed a new class of lubrication technology that could save industry billions of dollars in metalworking operations, while reducing pollution and wear and tear on cutting machines and tools.

The lubricant is a solution of vegetable oil in carbon dioxide, said Steven Skerlos, University of Michigan assistant professor of mechanical engineering.

Today, companies around the world spend billions on metalworking fluids which are used as coolants and lubricants to control heat build up during metal cutting. These metalworking fluids are typically emulsions of oil and water, where the oil is used to reduce heat generation and the water is used to conduct heat away from the cutting zone.

But industry is looking for alternatives. Since oil and water don’t mix, current metalworking fluid systems are inherently unstable. They are also corrosive and, because they are fluids with similarities to milk, metalworking fluids can breed bacteria unhealthy to machinists.

To solve these problems, the U-M research team substituted supercritical carbon dioxide (scCO2) for water, mixed it with soybean oil to make a metal working lubricant, and saw a level of performance that was much higher than they had ever observed. "Supercritical" means the carbon dioxide is pressurised to a state where it becomes a solvent to vegetable oil.

"The level of success was somewhat surprising," Skerlos said. "For example, we found that soybean oil dissolved in supercritical carbon dioxide performs much better than straight soybean oil, even if the amount of soybean oil applied is ten times less in the supercritical carbon dioxide system."

The scCO2 system is also a much more effective coolant. This is because as the pressure is released as a spray, dry ice is formed which can be thought of as a cryogenic spray. Skerlos explained that this is the same phenomenon that makes your finger cold when you release the air through the valve on a bike tyre.

The patent-pending technology is generating a buzz in the industry, particularly in the aerospace sector, which is currently trying to achieve high speed machining rates on titanium parts.

However, Skerlos says the technology will have applicability anywhere that metalworking fluid is used now, including automotive steel and aluminium machining.

Discussions regarding license agreements are active among metalworking fluid companies and companies that can supply the scCO2-based cooling and lubrication system.