Reducing lubricant waste
A proactive approach for stampers
The best strategy for waste reduction is to reduce waste generation. Stampers have several strategies available, such as switching to metalworking fluids formulated for long life and instituting a fluid management and maintenance program.
All metal forming facilities that use chemicals ultimately produce wastes, and these facilities then have to deal with them, usually in two steps: treatment and disposal. Treatment and disposal are reactions to the processes that generate waste, so it's obvious that one way to ease the waste treatment and disposal burden is to minimize waste generation in the first place.
For stamping operations in particular, many options can help to reduce waste generation at the outset and help ensure that the facility fully complies with environmental regulations. Two of these options are using fluids formulated for long life and developing a sound fluid management and maintenance program.
Most stamping operations were not designed with wastewater treatment in mind, but regulations are clear regarding waste disposal responsibility. Because most process wastes generated in stamping operations largely are composed of water, the most pertinent governing federal environmental regulation is the Clean Water Act (CWA). This law addresses the disposal of nonhazardous material directly into open waterways or its application on land.
Stampers generally send their waste to a publicly owned treatment works (POTW), which then treats it and discharges the treated waste into an open waterway. The creation of the National Pollutant Discharge Elimination System (NPDES) gave POTWs the authority to regulate influent arriving at their facilities by issuing facility-specific permits.
Compliance is best controlled at the front end, so it can be helpful to understand the chemistry and role of metalworking fluids used in the manufacturing process as they relate to waste generation, treatment, and disposal.
In general, stampers use three types of fluids:
- Soluble oils. These fluids combine oil, emulsifiers, and performance additives.
- Semisynthetic fluids. These solutions have oil concentrations of 2 percent to 30 percent, compared to 60 to 90 percent for soluble oils. In semisynthetic fluids, the emulsion has already formed in the concentrate. The resulting emulsifier content results in smaller oil globule formation.
- Synthetic fluids. These fluids contain no mineral oil. Simple synthetics contain organic and inorganic salts dissolved in water. Complex synthetics also contain salts, as well as water-soluble chemical lubricants.
While many variations of each type exist, the types of waste generated from these fluids must be treated by physical or chemical methods or a combination of the two. The fluid's oil content is the main factor in determining the treatment method. In general, soluble oils lend themselves to chemical treatment, while synthetics usually require a combination of chemical and physical approaches.
Physical treatment can include evaporation, which is best for small volumes; filtration; or settling. Chemical treatment usually involves using one or more of the following:
- Inorganic salts (A1SO4)
- Polymers (polyamines and diallyldimethylammonium chlorides)
- pH adjustment (acids and bases)
Both treatment courses operate on the principle of volume reduction that leads to dischargeable water. They also result in a waste fraction, or nonwater components. Although this material commonly is hauled off-site, an increasing number of facilities are attempting to reuse or recycle it. Stamping operations should evaluate treatment technologies in terms of their own specific waste streams in a carefully controlled mix-and-match fashion to determine the most effective approach.
POTWs generally dictate several parameters. Those that manufacturers should monitor and the levels they need to achieve differ for every POTW, but the parameters that are likely to require constant monitoring include:
- Biochemical oxygen demand (BOD). This is an aggregate property measured by the depletion of oxygen by standard bacteria under set conditions. Any substance that acts as a food source for bacteria increases the BOD; in a stamping operation, these sources include emulsified oils, glycols, and cleaners. The threat of BOD lies in the impact of wastes on natural waterways. Waste with large amounts of BOD provides a large food source for microorganisms, which then multiply and use the dissolved oxygen in the water more quickly. Oxygen-depleted water can harm organisms higher up the food chain, thereby upsetting the ecological balance.
- Chemical oxygen demand (COD). This has a similar effect after discharge as BOD, but the method of measurement is different. Because organics are completely oxidized in testing for COD, this test is generally more accurate. Once again, the goal is to minimize COD in discharged waste to help minimize negative environmental impacts.
- Suspended solids. These are particulate materials that remain in solution while a solution is in motion. The solids can be measured by drawing a known volume of fluid through a preweighed filter. The filter is then dried, cooled, and weighed again. The weight difference is then calculated to determine the extent of contamination.
- Oil and grease. POTWs are required to produce effluent of a certain minimum quality, so they are authorized to set limitations on wastewater parameters. Oil and grease are measured by the extraction of material in water with Freon® or a Freon substitute. Oil and grease also can be measured analytically. Any material with higher affinity for Freon is measured as oil and grease.
In terms of chemistry as a potential contributor to wastewater, stamping fluids with a low pH cause product separation, with free oil floating to the top; glycols and organics in water contribute to BOD and COD; and oils and amines contribute to BOD, COD, and oil and grease.
Minimizing Waste Production
Managing and treating waste often can be difficult and expensive. While the most effective way to treat waste is not to generate it in the first place, no stamping operation today can operate waste-free. However, stampers can use a handful of strategies to minimize the amount of waste they generate. One way is to develop a waste minimization plan (WMP).
A WMP is a site-specific plan that takes into account the facility as a whole and introduces procedures that reduce waste generation. Redesigning processes with waste in mind, properly maintaining fluids, and preventing wastes from mixing can lead to significant waste reductions. The best WMPs track the life of a product from purchase to disposal.
Prevention. Every stamper should take a critical look at the facility's physical layout and every manufacturing process. Manufacturing facilities develop over time, and many become a hodgepodge of systems that were tacked on without considering waste generation. Updating equipment, altering processes, and scrutinizing operating procedures can greatly reduce waste generation. Stampers should review all procedures developed before waste generation became a primary concern.
Cure. Developing a good fluid maintenance program for all water-dilutable products is essential. Samples of products in use should be sent to a laboratory for analysis, which should perform at the least general testing and specific determination of concentration, pH, and emulsion stability.
Facilities also should use in-house fluid-monitoring systems to ensure the integrity of the soluble oils and semisynthetics they use. Manufacturing facilities have many potential contaminants, so any given waste is likely to be a mixture of several chemistries that can change from day to day. A product that was purchased as a coolant is not likely to possess the same chemical composition by the time it is waste.
Understanding the flows, leaks, and the sump life of chemicals used at a facility is crucial before choosing and embarking on a wastewater treatment system. A knowledgeable supplier can assist in this process.
Dealing With Changing Waste Streams
The most effective way to ensure consistent waste treatment is to provide a consistent waste stream. The best way to do that is to control the products entering the facility with waste treatment in mind. If a product is not ordered, it cannot become waste.
As a matter of course during the manufacturing process, most stamping operations vary the constituents or volume of their waste streams. This has led many to adopt a "treatment train" approach—a strategy that uses several steps in sequence. The entire volume of the waste is treated with specific technologies for specific waste constituents.
If the waste stream is not closely controlled, other methods to ensure waste-discharge compliance are available.
One method is to use a gross screening, followed by a batch chemical treatment, and then evaporation and discharge.
A typical plant produces a mixed waste stream that includes synthetics, semisynthetics, soluble oils, wash water, cleaners, and rust preventives. A typical treatment procedure is a set, established approach that calls for adding a consistent dose of chemicals to the facility's treatment tank, regardless of the composition of the waste present at the time. A bench testing program is an alternative that can improve both accuracy and results. Such a program involves evaluating a sample of each batch to determine the optimal dosages of chemicals needed to treat the waste.
In addition, the bench testing program can evaluate fluids before they are used in the plant, which facilitates greater control of the waste stream at the outset.
Three trends are worth noting. The first is a growing interest in recycling as part of the waste minimization process. Oil and water are the most likely targets for recycling. Oil can be re-refined or sold for fuel value, and water can be used on-site for cooling or washing. Establishing a viable recycling program depends on the treatment capabilities at a facility, which is perhaps the biggest hurdle.
The second trend is a movement away from oil-based products, which can be beneficial from a waste treatment perspective.
Third, more and more stampers are turning to their suppliers for assistance in developing sound fluid maintenance programs. Technologies for the treatment of waste at stamping facilities are advancing rapidly, as are partnerships between operations and their suppliers. In the not-too-distant future, as outsourcing continues to gain ground, the day may come when suppliers will shoulder responsibility for care of a fluid from maintenance to disposal. If handled properly, this increases efficiency and reduces waste.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.