Concerns about the environmental impact of fluids and lubricants have resulted in new eco solutions. But choosing the best option is not that simple.
Worldwide, more than 50% of lubricants are discharged into the environment, according to the Baden-Württemberg State Environmental Protection Agency.
Germany’s RWTH Aachen University estimates that global lubricant consumption to be around 37.3 million tons per year. Of this total, more than 18 million tons find their way into the ecosystem without any safeguards.
For Dr. Fu Zhao, associate professor at Purdue University’s School of Mechanical Engineering, the use of metalworking fluids and lubricants raises several issues.
First, there’s the high waste-handling cost. These fluids are not biodegradable and may contain hazardous substances such as heavy metals. Then, there are the occupational health risks due to their chemical composition and contaminants, including bacteria and fungi. Finally, they are made from non-renewable resources.
Diverse eco-solutions have been proposed in recent years.
Minimum quantity lubrication (MQL) is one. Kuroda Jena Tec specializes in linear and rotary motion products, and has seen increasing demand for its MQL system, particularly from companies manufacturing large batches of identical automotive components. Precise delivery of lubricating oil in the form of finely dispersed droplets reduces consumption by using the exact amount of lubricant required for the cutting process.
The oil mist is generated via the Venturi effect. Compressed air is then used to deliver a precise quantity of mist to the cutting edge of the tool through a nozzle with a small hole the exact diameter of the droplets.
Stuart Vere, engineering manager at Kuroda Jena Tec UK, stated:
MQL is slowly being delivered for users looking to reduce consumption costs, as it can be applied to different industry types and chip forming processes.
Vegetable oil-based lubricants also have gained market share. U.S.-based Renewable Lubricants manufactures bio-based lubricants derived from soy, corn or canola.
Vice president William Garmier explains that the company’s bio-based formulas are a combination of patented antioxidants and pour point depressant (PPD) technology. PPDs are polymers designed to control wax crystal formation, which inhibits lubricant flow at low temperatures.
This low-cost method improves cold temperature performance and stabilizes oxidation of vegetable oil-based lubricants for high- and low-temperature applications. It provides products that perform as well or better than synthetic lubricants at a lower cost. They are compatible with the same system materials that operate on mineral oil-based and most synthetic-based fluids.
U.S.-based 5ME focuses on increasing manufacturing efficiency. Its cryogenic machining technology uses through-tool liquid nitrogen delivery to mitigate the heat produced during metal cutting. This offers environmental benefits. Executive vice president Pete Tecos explained:
This process enables higher cutting speeds for increased material removal and longer tool life by transmitting liquid nitrogen at -321°F (-196°C) through the spindle/turret and tool body, directly to the cutting edge. This increases throughput and part quality while reducing energy consumption. It is particularly suited for tough materials like stainless or alloy steels, Inconel, and titanium, commonly used in aerospace part production.
The company has recently joined forces with Okuma, a leader in CNC machine tools, to establish two cryo demonstration facilities, including one at Okuma’s Aerospace Center of Excellence in North Carolina.
Discussing the Options
For David Wright, director general of the UK Lubricants Association, the sector is keen to embrace new eco-technology if it makes economic sense.
Consumers and end users of lubricants will not accept lower-performing products over time and expect any new innovation to guarantee the same performance.
Dr. Zhao agrees: “Less lubrication is possible, but keep in mind we don’t want to sacrifice technical performance or energy efficiency. I don’t think we can eliminate lubrication completely.”
He reckons MQL is a viable option, “except for hard materials and difficult processes.”
Cryogenic machining also has limits:
Low temperature tends to make materials more brittle, which may shorten tool life and increase surface roughness. And liquid N2 is produced via an energy-intensive process.
Watch our video report on Cryogenic Machining posted online in October 2015
Variants of MQL have been explored, such as using liquid CO2 as the coolant and carrier. “But it is likely there will be no single solution for all applications.”
Replacing petroleum products with those derived from biomass or vegetable oils has attracted lots of interest, he points out. But he does not believe that any of the new fluids are completely neutral to the environment:
Vegetable oil production leads to more land use and may release nutrients to water bodies.
He suggests industry should place more emphasis on the in-process reuse and recycling of oil:
This is always the best option and the reuse of oil for less demanding applications is the next. Burning the oil to recover energy is still better than landfill. The challenge is how to remove contaminants from waste oil and separate useful ingredients.
And if the end goal was new materials and processes that require less cutting fluid?
3D printing is replacing traditional machining in many applications. In the future we can expect more eco-friendly processes and products to be developed, where we are not sacrificing either technical performance or energy efficiency.