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.
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.
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:
- Switch off the centrifuge and remove the housing and rotor cover by disengaging the quick locks.
- Remove the filled sludge basket and clean the basket by removing the compacted sludge.
- Reinstall the cleaned sludge basket.
- 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.
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.
Once they’ve decided to recycle coolant, shops needs to decide between purchasing equipment or using a service provider. For shops using the latter option, Coolant Management Services provides coolant recycling services at the customer’s facility. CMS, which services Southern California, travels to the machine shop, evacuates coolant from machine sumps, brings it to its truck, runs it through a centrifuge to remove particles to 5µm and up to 99.5 percent of the tramp oil and brings the filtered product back to the machines.
Arnold explained that the company is a full-line distributor that also sells coolant recycling equipment, but it’s frequently less expensive for shops to use a service. CMS also helps companies manage their coolant and can provide an on-site laboratory for coolant testing.
“Our burden rate [indirect costs associated with employees, over and above gross compensation or payroll costs] is considerably less than the rate for most customers,” Arnold said. He noted that a shop needs to use a total of about 700 gal. of coolant in their machines to make the service feasible, and most customers have their coolant recycled every 6 to 8 weeks.
Another service CMS provides is machine tool cleaning, which complements coolant recycling, Arnold added.
Many shops don’t effectively clean their machines, according to Bill Shaver, owner of Fluid Management Inc., a coolant recycling and machine cleaning service with locations in Minneapolis and Greenville, S.C. “That’s one of the reasons they use more coolant than they should,” he said. “They leave the particulate and bacteria in the machine and then the clean coolant is inoculated with bacteria and fungus right away.”
Even when shops do thoroughly clean equipment, it requires operators taking time away from production or maintenance personnel with multiple demands. “What’s more important, cleaning out a tank or repairing a machine that has electrical faults and is nonproductive?” Shaver asked rhetorically. For customers that don’t run 24/7, Fluid Management performs recycles and cleans during off-hours, he noted.
Shaver added that cleaning a machine involves removing the swarf and scrubbing the sump tanks, pumps, screens and conveyors—“anything that has contact with the coolant.” After cleaning, the machines are thoroughly dried with clean shop towels so no soap residue remains.
Courtesy of Eriez
The Eriez Hydroflow Vacuum Filter is an automatic system that does not use air for backwash or to dry the solids, eliminating the need for additional air compressors, accumulators and mist collectors.
Regardless of who performs the recycling, recovered coolant lasts virtually forever. Shaver pointed out that of Fluid Management’s seven original customers from when it started in 1993, five out of the remaining six have not disposed of their coolant and the one that did needed a different coolant because the shop’s product mix changed. After checking coolant concentration at the start of each shift, Shaver recommends adding coolant at the correct mixture level to maintain the proper concentration level in the sump.
And a high level of recycling, obviously, significantly reduces coolant consumption. For example, Shaver noted that one customer in South Carolina was dumping 150,000 gal. of coolant annually prior to beginning recycling. “When we finished our first year, they dumped zero gallons of coolant and reduced their coolant purchases from about 26 totes a year to nine,” he said.
While setting up a coolant recycling program requires an investment, it typically pays for itself in a matter of months or at most a year. If investing in a system is not an option, using a service can achieve the goal with less upfront cost. In either case, any shop that is not recycling its coolant may be seeing some of its profits—as well as most of its coolant—going right down the drain. CTE
About the Author: Alan Richter is editor of CTE, having joined the publication in 2000. Contact him at (847) 714-0175 or firstname.lastname@example.org.
Recovering a 'precious' metal
Recycling tungsten carbide not only helps with “greening” the environment, but generates greenbacks as well. The latter benefit has become more pronounced as the price of carbide has increased, according to Irvin Kaage, president of Transor Filter USA, Elk Grove Village, Ill. Transor sells filtration systems to toolmakers and other carbide part manufacturers to remove oil-suspended particles down to 1µm. Kaage noted that the price of recovered carbide is near $15 a pound.
“So you can imagine one person’s dirt is another person’s gold,” he said.
The Transor’s filter element is composed of a stack of thousands of 1½ "-dia. paper discs with a center hole. The discs are assembled on a rigid, fluted rod about 36 " long and are compressed tightly together. “They look a little bit like oversized Lifesavers,” Kaage commented.
The oil flows from the OD to the ID of the filter and debris is deposited on the outer edges of the discs, he explained. Periodically, such as after an 8-hour shift, back flushing takes place to clean the filter by forcing compressed air through the ID to the OD. The debris, which consists of tungsten carbide, cobalt and abrasive fines from grinding wheels, is deposited in a cloth-lined bag. The procedure takes about 6 minutes. The vast majority of the debris is carbide, Kaage noted.
He pointed out that, in addition to fines and chips, the bag contains some oil that remains in the sludge, and, as the dirt and debris settle, the oil drains from the bag and back into the system. After collecting about 3 " of debris in the bag, an end user deposits it into a 55-gal. drum.
“If not working around the clock, we normally suggest the customer schedule the replacement of that filter bag on a Monday morning before they start work so the particulate is as dry as possible,” Kaage said.
According to Transor, 1µm filtration extends grinder wheel life by as much as 400 percent while reducing cycle time up to 25 percent. In addition, setup time is reportedly reduced because there is less buildup of dirty oil on the fixtures and workpiece surface.
Transor partners with Tungco Inc., Madisonville, Ky., to recover and recycle reclaimed carbide. Shops send it to Tungco and receive up to $15 per pound. Kaage estimated that customers generate, on average, about 300 lbs. of carbide monthly, with quantities varying based on whether a company manufactures or regrinds tools and the size and quantity of tools produced.
Although the published filter life is 15,000 operating hours, many customers report significantly longer life, Kaage noted. He indicated that SGS Tool Co., Munroe Falls, Ohio, is Transor’s largest U.S. customer, owning about 50 filtration systems. SGS has 2 million hours of operation on those systems combined. “When you look at the frequency of filter element replacement, the operating cost is less than 2 cents an hour,” Kaage said, noting that system payback is typically 12 to 14 months.
Coolant Management Services
Fluid Management Inc.
Nowak Machined Products
PRAB Fluid Filtration Div.
Transor Filter USA
Universal Separators Inc.
Shop saves big through waste minimization
Nowak Machined Products understands the financial drain of paying to have tramp oil-saturated coolant hauled away. Haulage actually costs more than replacing the shop’s semisynthetic coolant, according to Mike Orchard, maintenance coordinator for Muskegon, Mich.-based Nowak. The company produces aluminum, gray iron and steel parts, primarily for motorcycles.
When tramp oil, such hydraulic oil from spills and machine oils used on the parts, caused the coolant to lose some lubricity and when the sight and smell of a machine sump became too offensive because of bacteria and fungus growth, the company disposed of the fluid. “We had no way to clean that coolant,” Orchard said, “so we just put it in a big container and had someone from a waste hauling company come and pick it up.”
The shop, which has about 50 machine tools with 20- to 300-gal. coolant sumps, tried removing tramp oil with belt skimmers, but found they weren’t effective when machines were running. While searching for a solution, Nowak found PRAB, Kalamazoo, Mich., which installed a centralized coolant recycling system for the parts manufacturer to use on a 2-month trial basis.
Because the system effectively recovered the contaminated coolant, Nowak purchased a coolant recycler that holds up to 400 gal. of clean coolant and 400 gal. of dirty coolant based on PRAB’s sizing recommendation. That was about 2½ years ago, and the equipment has required little maintenance other than routine cleaning and filter changes since then, according to Orchard. “We replaced the seals on the pump once, but it wasn’t a major issue,” he said. “The system runs around-the-clock except when we’re not here on the weekends.”
In addition to coolant from the sumps being recycled, Nowak also recycles the coolant the shop drains from chips before selling them.
Since installing the coolant recycling system, Orchard noted that the waste hauler infrequently visits to remove the collected tramp oil.
Related Glossary Terms
Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.
Additive to cutting fluids to inhibit bacterial growth. See fungicide.
Filtering device that uses a spinning bowl and the differences in specific gravities of materials to separate one from another. A centrifuge can be used to separate loosely emulsified and free oils from water-diluted metalworking fluid mixes and to remove metalworking fluids from chips.
- computer numerical control ( CNC)
computer numerical control ( CNC)
Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
Suspension of one liquid in another, such as oil in water.
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- inner diameter ( ID)
inner diameter ( ID)
Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.
Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.
- metalcutting ( material cutting)
metalcutting ( material cutting)
Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.
- outer diameter ( OD)
outer diameter ( OD)
Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.
Abrasive process that improves surface finish and blends contours. Abrasive particles attached to a flexible backing abrade the workpiece.
Reduction or removal of workhardening effects, without motion of large-angle grain boundaries.
- sawing machine ( saw)
sawing machine ( saw)
Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).
Metal fines and grinding wheel particles generated during grinding.
- tramp oil
Oil that is present in a metalworking fluid mix that is not from the product concentrate. The usual sources are machine tool lubrication system leaks.
- tungsten carbide ( WC)
tungsten carbide ( WC)
Intermetallic compound consisting of equal parts, by atomic weight, of tungsten and carbon. Sometimes tungsten carbide is used in reference to the cemented tungsten carbide material with cobalt added and/or with titanium carbide or tantalum carbide added. Thus, the tungsten carbide may be used to refer to pure tungsten carbide as well as co-bonded tungsten carbide, which may or may not contain added titanium carbide and/or tantalum carbide.
Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.