Better coolant and chip management leads to more productive plants, higher quality parts
Poor coolant management often results in sump problems, with bacterial growth and metallic fines in coolant that can reduce machining quality. By implementing a comprehensive preventative maintenance (PM) program, manufacturers can substantially extend coolant life,reduce new coolant purchases and cut coolant disposal costs, notes Tim Hanna, managing director, Prab Fluid Filtration (Kalamazoo, MI). A good coolant recycling program can extend the life of expensive machine tools, improve overall part quality and extend coolant life two to five times over typical change-out periods.
However, with the machine tool industry running high-speed machining on harder metals, the demand for reliable, stable coolant management systems has grown.
“The machine tool industry is pushing the limits. At JK, we really believe a stable system is critical,” says Dustin Ondovcsik, manager, global sales and marketing, JK Industries LLC (Warren, MI). “The current paradigm in coolant and filtration is that variation is normal. But coolant should be a foundation, and coolant filtration systems are an integral part of the manufacturing system—it’s kind of like the blood in your body.”
Coolant Recycling Boosts Quality
Studies show that tool life can be significantly extended, from 25% up to 209%, with effective coolant recycling equipment designed to remove contaminants including tramp oils, which are usually a combination of hydraulic oils, way lubricants, greases, etc., solids and particulates. “Remember that this tramp oil is free-floating, from leaks on machines, spindles, and other places, and tramp oil or fines will hurt your surface finish,” Hanna states. “When you walk through a shop with a variety of machines, they’re various ages and quality of build—for instance, a newer Mazak might be better at holding tolerances than an older system. But a preventative maintenance program, if you do it regularly, will result in less problems.”
The life cycle of coolants can vary dramatically depending on factors including the amount of tramp oil in the sump, temperatures, and the types of machining applications at a shop, he adds. Regular maintenance can be every four to six weeks, or as much as 10 weeks, depending on the application. During hot summer months, the interval can be much shorter.
“Coolant life is very application-specific,” Hanna says, noting that it depends on the amount of tramp oils that are present. “We can’t bring it back if it’s gone rancid.”
However, many new coolants last longer than they once did. “The coolants are becoming more ‘green’ or bio-stable, such as Houghton 795,” he adds. In addition, new additives also help metalworking fluids last longer, although some of these can adversely alter chemistry. For more details on coolants, see the article “Green Coolant Technologies Advance” in the January 2012 issue of Manufacturing Engineering at http://tinyurl.com/greencoolants.
With Prab’s fluid filtration systems, a sump containing up to 15,000 gallons (56,781 L) of coolant is used along with tramp oil separators to filter the liquids of harmful oils and metallic chip fines, notes Hanna. The company offers its Guardian coolant recycling systems, tramp oil separators, and mobile sump systems for fluid processing. Inside the sump, a weir containing a sharp edge traps these elements during the filtration process, and the tramp oil separators employ polyethylene tellerettes and pall rings to help pull tramp oil and sludge from the coolant before it goes into the main sump. “In one pass, we’ve removed 96% of the tramp oil,” Hanna says, “and we keep passing it through maybe three or four times, and it’s 98% clean.”
Extending Coolant Life
Manufacturing operations need to employ methods that will allow metalworking fluids to last indefinitely, adds Barry L. Nehls, general manager, Eriez Hydroflow Filtration (Maumee, OH). “Removing contaminants from the coolants that are the result of the metalworking operations is probably the most important,” Nehls said. “These contaminants include chips, metallic fines, abrasive breakdown, lubricants, hydraulic and spindle oils, as well as foreign contamination. With the rising costs of both the oil-based chemicals as well as disposal costs, managing coolants has become more important than ever.”
The keys to effective coolant management systems, Nehls notes, include consistent removal of metallic contaminants and fines; continuous removal of tramp oils; employing procedures and methods to maintain consistent coolant concentration in use; and keeping sump volumes at consistent levels to assist in temperature control. Many facilities today use on-site coolant management professionals to coordinate the activities of a coolant management program, adds Nehls.
This year, Eriez launched a new coolant recycling machine. The Hydroflow SumpDoc is a portable in-line fluid reclamation machine on wheels. “SumpDoc is a cost-effective alternative to a central fluid recycling system or batch processing,” Nehls says. “The economic advantages stem from the elimination of downtime and savings from reuse of fluids. The SumpDoc is like a crash cart for sumps.”
The SumpDoc’s portable design and ability to function with little operator interaction allows it to work with no stops in production. The system includes a Sump Vac mode, where it traps solids in a 50-µm polyester bag; a Filtration Mode selectable from the dashboard controls for cleaning coolant; and a Coolant Makeup Mode used to check coolant concentration levels with an on-board digital refractometer, adjusting the mix as needed.
Taking a New Approach
A relative newcomer, JK Industries LLC has developed its newly patented HydroClean coolant filtration system that is said to offer a simplified, relatively compact design aimed at improving coolant recycling quality over current offerings. A unit of BAE Industries Inc. (Warren, MI), JK Industries was started three years ago by BAE Industries President Jesse Lopez and Keith Urban, JK Industries president, with the goal of offering a better coolant management system.
The HydroClean Standalone Coolant Filtration System is said to dramatically improve tool life and eliminate tank cleaning. The system’s process filters solids before removing oil, regulates temperature, and then circulates/aerates the sump.
JK Industries was granted five patents in July by the US Patent Office for the HydroClean system, which is installed at Mazak, Caterpillar, and GE. The system features a primary chip conveyance with hinged, magnetic or drag-type belts, an automatic self-cleaning 80-μm filter, a coolant tank “sweeper” package that continuously agitates the solids to be pumped into the next filtration, a centrifugal separator that eliminates solids 60 μm and larger, and a high-capacity, absolute-rated canister filter element guaranteed to protect tooling and remove all sludge from the system.
Haberman Machine (Oakdale, MN), a nearly 30-year-old family-owned precision machining shop, produces parts for the medical, environmental, oil and gas industries, as well as for military applications including assault rifles, laser-guided missiles, tank parts and armament systems. The company has Kitamura CNC systems and Fanuc Robodrills that require fast removal of high volumes of aluminum chips.
Haberman’s cleaning process involved two men to pump out the dirty coolant and then shovel out the aluminum sludge. This time-consuming, messy process lead to lost production, waste disposal, and expensive coolant replacement. Additionally, the coolant concentration was very difficult to stabilize since the individual sumps would lose as much as 50% of their capacity from water evaporation during the cutting operation in a single shift, causing concentrations to vary greatly.
In its new state-of-the-art facility, Haberman Machine installed the HydroClean filtration systems and JK Industries’ central mix and makeup (CMM) system. With the HydroClean systems, the CNC machines have been able to sustain over six months of continuous operation without any buildup of aluminum sludge in the reservoirs, and the CMM has been able to successfully maintain coolant concentrations at the target set point with less than 2% variation.
Matching Chip Removal to the Process
It’s critical that the method of removing chips and chip particulate from the coolant in a CNC machining process be specifically matched to the machining process, notes John D’Amico, co-principal and director of sales and marketing, Jorgensen Conveyors Inc. (Mequon, WI). “The critical factors are coolant type, maximum coolant flow rate, type of material being machined, chip geometry, chip volume per function of time and how the coolant is delivered back to the machine cutting zone, such as through the tool, through the spindle, external nozzles, and coolant pressure,” he says. “The chip system also needs to perform effectively in discharging dry coolant-free chips as the regulations associated with transport of chips in the recycling stream have become more stringent.”
Some of the trends in metalworking manufacturing are definitely driving requirements in coolant management and chip handling, D’Amico adds. “The green/environmental push is requiring us to again provide chip and coolant management systems that focus to the specific process on the machine more than ever. Chips need to be dry before they leave the shop for recycling. Conveyors and filters need to be designed and controlled with a higher sensitivity to energy consumption than ever before. Coolant life and coolant quality must be maximized as spent coolant is a hazardous waste stream item.”
Jorgensen has developed its UVS EcoLogic conveyor control with patented technology addressing green, energy-efficient operation of conveyor systems in untended machine operation environment.\
The current high-speed machining environment, coupled with new cutting tool technology enabling the machining of harder materials, creates the need for the chip removal conveyor systems which are more durable and wear-resistant as conveyors see more chips that are more abrasive to the conveyor, D’Amico notes. “The increase in the use of composite materials such as titanium or nickel alloys for parts across the various metalworking manufacturing segments is driving the need for high-wear systems capable of handling a full array of larger tougher chips as well as finer lighter particulate. Higher-speed machining of ‘near-net’ shaped parts creates a higher percentage of finer chip particulate in the mix,” he observes, “which coupled with the use of high-pressure coolant, creates an increasing need for chip removal systems that can perform to get this difficult finer particulate out of the system before it reaches the machine supply pumps.”
Squeezing Coolant from Chips
Chip-handling practices vary widely. Manufacturers employ chip wringers, shredders and crushers in a variety of methods, from manual to automated. A newer trend toward cellular-oriented systems follows the general industry trend toward more cell-focused manufacturing, notes Carl Baker, Prab vice president, engineering. “When we go into a shop, it’s basically creating a custom solution from standard products, like an engineered solution,” notes Baker. “Chips of all types cause different problems in handling—they can be long and stringy, or they can be other shapes for which we’ll use crushers and shredders. We’re constantly refining.”
The new generation of machining centers and the flexibility that’s required mandates that chip-handling systems follow, he notes. “Chip-handling systems must adapt to those manufacturing cells. We do some preprocessing at the cell. If a machine is producing a long stringy chip, we’ll crush it with a small horizontal crusher. It depends on the requirements of a customer.”
Chips are often moved throughout manufacturing plants with trucks or rollouts that allow getting chips or turnings where needed to enhance the value of the scrap, Baker says. “Moving of the chips really is a big operation. You can use one of several methods—you can blow them away or use a pump-back system, with central filtration.” Chip moving typically is done in three ways, he adds, with pneumatic methods or liquid pumps, or just manually in old-fashioned chip carts.
The decision to go with a briquetter is based largely on the relationship between the machine tool customer and the recycler, notes Baker, and using a briquetting system allows compressing chips into blocks that are 83% solid. “It’s very, very common with aluminum, but it’s less so with other materials,” Baker says. “There’s been a little bit of a movement toward wringers and the briquetters. It’s very application-specific.”
A builder of briquetting systems, John Hart USA (Centerville, MN) produces strictly briquetting units but offers full systems for coolant management, including auger boxes, shredders and other related equipment for coolant and chip handling, notes Josh Gabrick, sales representative. “The fluid recovery out of the chips is quite significant,” he observes. “With briquetting, you basically handle the chips once.”
Briquetting systems from John Hart compress chips into a cylinder that has a face pressure on the cylinder of about 30,000 psi, but the pressure on the entire briquette is much higher, Gabrick notes. “Our systems essentially squeeze out the fluid and we have certain design features that help it exit the chamber, and maximizes your coolant recovery out of the chips.”