Waste not, spend not: Turning Performance

Courtesy of Eriez

A technician cleans a machine sump with an Eriez Hydroflow sump cleaner.

Recycling coolant pays big dividends for job shops.

When machine shops start recycling, one material often leads to another. For example, many discover coolant recycling after they establish a chip recycling program. Once they do, shops find out that coolant recycling not only makes economic sense, but can improve part quality, extend tool life and help maintain a cleaner working environment. Shops also have a choice between investing in recycling equipment and having a service provider do the job.

PNM Co. is an example of a shop that began recycling on the chip side. About a decade ago, the Fresno, Calif., job shop began briquetting chips, targeting aluminum ones because more than 90 percent of its work involves machining that material, noted Dave Counts, company president. He added that the briquetting machine eliminated several hours of labor each day from loading and transporting two to three chip bins, but the shop then needed to deal with the coolant squeezed from the chips.

“We were holding onto the coolant and skimming some oil off of it and having a lot of it trucked away,” Counts said. “It was very time-consuming. The cost was way up there to do all that stuff.”

PNM conducted an online search to find a coolant recycling system that suited its price and performance requirements and located the SmartSkim centralized system from Universal Separators Inc. After installation, the shop saw its coolant consumption drop by a third and an even larger reduction in its cost to have used oils hauled away. That’s because, with the coolant and contaminants removed from the way and hydraulic oils, the recycling company charges less per gallon to remove it. “We fill up a 55-gal. drum every 3 or 4 months. Before, we were filling four or five drums a month,” Counts said, adding that payback was less than a year.

PNM purchased the coolant recycler when it had 15 CNC machines. The 50-worker shop now has 20 CNC machines and the system still has remaining capacity, according to Counts. Most of those machines have oil skimmers to enhance coolant cleanliness.

Cutting Costs

PNM is not alone in its motivation to purchase coolant recycling equipment. Bill Gimbel, vice president of sales and an owner of Universal Separators, Verona, Wis., noted that many shops consider coolant removal bills a cost of doing business and only after they obtain a device to extract coolant from chips do they realize the benefits of coolant recycling. “We get a lot of leads that way,” Gimbel said. “They might save the coolant but if they’re not reusing it, they’re paying to get rid of it.”

Although coolant isn’t cheap and prices continue to rise, the larger expense is paying to have dirty coolant hauled off-site, according to Mark Kluis, general manager for Universal Separators. “Customers tell us that’s the bigger savings.”

Courtesy of Sanborn Technologies

The Turbo-Separator Model T10-3-315 from Sanborn Technologies is a centrifuge recycling system that removes solids and tramp oil from coolant.

Others, however, say recovered coolant represents the biggest savings. According to Steve Friedman, president of coolant recycling system manufacturer Sanborn Technologies, Walpole, Mass., the rule-of-thumb cost analysis of a coolant recovery system includes the cost of buying new coolant at $1.00 per gal. ($20 per gal. of concentrate diluted to a 20:1 ratio) and the cost of disposing of used coolant at $0.50 per gal. Therefore, every gallon of recovered coolant saves a facility $1.50. “Over the years, many localities have found the cost of coolant disposal has remained somewhat constant as treatment technologies have improved for waste haulers and treaters, but the costs for coolant concentrate have risen dramatically as the cost of base stock has increased,” he said.

Friedman noted that many coolant recycling systems somewhat extend the life of coolant but only an integrated coolant recovery system will return like-new fluid of the highest quality back to the machine tools.

Recycling Equipment

The role of coolant recycling equipment is to remove the tramp oil, particulates and bacteria, returning the coolant to like-new condition and enabling it to have a long life. The tramp oil resides in the rag, or cream, layer at the top of the coolant. “The rag layer kills the useful life of the coolant, creates bacteria, causes dermatitis and ruins tool life,” said Tim Hanna, managing director of PRAB Fluid Filtration Div., Kalamazoo, Mich., a manufacturer of fluid filtration equipment. He added that minimizing tramp oil in a machine sump reportedly extends tool life by at least 15 to 20 percent. “I’ve heard of as much as doubling the life of tooling.”

Courtesy of Universal Separators

Coolant flows from the clean side to the dirty side in a SmartSkim batch recycling/filtration system from Universal Separators.

In addition to a bag filter that removes suspended solids, Hanna explained that the company’s Guardian coolant recycling system has a barrel skimmer that sits below the coolant surface and a double-diaphragm air pump that pulls the coolant and rag layer into the tramp oil separator. In the separator’s first chamber, the layer of tramp oil rises to the top and is extracted through a weir.

The coolant then travels through a baffle into the second compartment, or media section, where coalescing occurs, turning small droplets of tramp oil into larger droplets. That’s achieved by flowing the coolant through plastic tellerettes and pall rings, which grab the small droplets and form larger ones. The droplets then rise to the top of the surface with the assistance of an air sparger and are extracted through a second weir. The separator keeps removing contaminants as gravity overflows coolant from the clean side of the system to its dirty side in a continuous processing cycle before the clean coolant is fed back to the machine sump.

“If you’re doing a 200-gal. sump, it’s fair to say in 3 to 4 hours you remove 98 percent of all tramp oils,” Hanna said. The company’s standard systems process up to 1,500 gal. per hour.

He noted that system options include an ozone generator to kill bacteria, a polishing filter for particle filtration down to 5µm and hose reels. For example, while an installation might feature a fully automatic, closed-loop, central recycling system, such as one used by NASA, other customers use hose reels to top off sumps or recharge coolant after cleaning. “The hose reels are filled with clean coolant and, as a sump is evacuated, they just pull the handle, like when filling a car’s gas tank, to fill up the coolant sump,” Hanna said.

Courtesy of Sanborn Technologies

There are four basic steps to removing separated sludge from the Sanborn T10-3-315:

1. Switch off the centrifuge and remove the housing and rotor cover by disengaging the quick locks.
2. Remove the filled sludge basket and clean the basket by removing the compacted sludge.
3. Reinstall the cleaned sludge basket.
4. Reinstall the rotor and housing cover and switch on the centrifuge.

The recycling system reduces new fluid purchase costs by 45 to 75 percent and reduces hazardous waste disposal costs by 50 to 90 percent, according to PRAB. Nonetheless, the removed tramp oil must be hauled away because various oils, such as way lubrication, hydraulic and mold release oils, are mixed together and can’t be effectively separated. However, tramp oil becomes an energy source, such as for a heater that burns used oil, and suitable for sale to oil reclaimers, according to Barry Nehls, general manager of Eriez Hydroflow, Erie, Pa., a manufacturer of fluid recycling and filtration equipment.

Coolant Consistency

When using recycled coolant from a central system involving multiple machines producing the same component, Nehls emphasized that it’s critical that the fluid delivered to each machine is at the same pressure, level of cleanliness, concentration and temperature to achieve application consistency.

That’s the case at one manufacturer that applies water-soluble coolant to creep-feed grind Inconel parts for power transmission turbine engines, where maintaining a constant temperature is particularly critical, he noted. The coolant is filtered to remove particles down to 5µm, and the system includes an optional coalescer to continuously remove tramp oil. “They keep the fluid in as good shape as it can be kept,” he said.

Nehls added that it’s also important to establish and adhere to a coolant recycling schedule, with higher-quality coolant lasting longer. “If you wait until you have odors, you’ve waited too long,” he said, noting shops will then start experiencing surface finish problems and significantly shorter tool life.

Another problem with having too long of a coolant recycling interval is microbiological infestation. That can become particularly prevalent when a sump is down for an extended time, allowing tramp oil to seal the sump surface, Nehls explained.

Courtesy of PRAB

PRAB reports that its Guardian coolant recycling system reduces new fluid purchase costs by 45 to 75 percent and hazardous waste disposal costs by 50 to 90 percent.

Before adding fresh or recovered coolant to the mix, equipment must be thoroughly cleaned with a bactericide to remove any biological growth, such as fungus, which can hang under a machine like Spanish moss. “If you dump clean coolant back in and the microbial activity hasn’t gone away, you just gave it fresh food,” Nehls said. “You just rang the dinner bell.”

He pointed out that two types of bacteria grow in metalcutting fluids: aerobic and anaerobic. Aerobic bacteria need oxygen to live and although they will deplete a fluid of its oxygen and eventually break it down, the process isn’t as quick as the work of anaerobic bacteria. “They’re not that serious,” he said about aerobic bacteria.

Anaerobic bacteria, however, break down coolant emulsifiers, which hold the water and oil together. The byproducts of that are two-carbon acid and usually sulfur dioxide, known by its rotten egg odor. “Once that happens your emulsion is in serious trouble,” Nehls said. “If the coolant goes into a high-speed centrifuge, it’ll usually tear the emulsion apart.”

Although the vast majority of new coolants are suitable for recycling in a high-speed centrifuge, which rotates at about 9,800 rpm, there are products in which the emulsifying package is not strong enough, and some of the concentrate is stripped out during centrifugation, according to Miles Arnold, vice president for Coolant Management Services, Los Alamitos, Calif.