Water has a remarkable ability to remove heat without transitioning to its gaseous state. It’s also cheap. These characteristics make it a fantastic candidate for a cutting fluid.
Of course, water is also considered the “universal solvent,” making it an equally excellent candidate for promoting rust. For that reason, cutting fluids are trending toward an emulsion of water with high-performance semi-synthetics, says Brent Morgan, an application engineer for Castrol Ltd., Wayne, N.J.
But it takes clever chemistry to create the optimum mix.
The ideal coolant would remove heat from machining, extend tool life, inhibit rust, leave the machine gleaming, drain immediately from the chips and finished parts, and last forever. Oh, and it absolutely would not foam, even with today’s 1,000-psi coolant delivery systems. As Troy Harrison, Castrol’s senior area sales manager for New England and New York put it, “Foam will shut a shop down. … If a coolant foams, it doesn’t matter how good it is.”
Harrison will be the first to say that you can’t create a coolant mix that maximizes all these deliverables, but advanced formulations come close. If your focus is on maximizing tool life, a full synthetic would do it, according to Harrison. But other compromises would have to be made.
“Once you go to oil, you really need fire suppression, you need part washing and you create a more challenging environment for your staff,” Harrison explains. “And the cost is much higher, say $20 a gallon for a good quality straight oil that’s not diluted, versus a soluble product that costs $25 a gallon diluted 10 times.”
Full synthetics can often cause a machine’s paint to peel and are harsher on electronics. “Even straight oils in machining can cause issues with electronics,” Morgan says. “And you always have a concern with misting when using straight oils, so worker health is normally an issue.”
Conversely, semi-synthetics mixed with water generally perform very well at low concentrations, Morgan adds. “Our most popular product has between 45% and 50% mineral oil in it. But when it’s diluted with water, it’s used at 5% to 7%.”
As Harrison summarizes, “For machining, when you can, you want to run water.”
Concerns about worker health and happiness are key reasons for choosing a largely water-based coolant. “A lot of people think that uptime is the biggest concern of facilities— but it’s not,” Morgan asserts. “The biggest concern is keeping good workers in these facilities. … With higher performance semi-synthetics, you don’t get a lot of misting. There’s no odor like older technology,” he continues. “They’re more worker friendly. So that’s why there’s a major push to these things. Because it helps retain workers.”
Thin staffing also means asking operators to take over the burden of coolant management. With the majority of shops running standalone sumps for each machine, and each operator running multiple machines, this is no small problem.
One approach is to subcontract the task to Melville, N.Y.-headquartered MSC Industrial Supply Co. The company can help manufacturers in a wide variety of ways—from routine cleanouts and metalworking fluid services to recycling and waste disposal.
“We can provide sales associates or metalworking specialists to do follow-ups for skimming,” says Dan Arenella, the company’s category strategy manager for machine center optimization. “They can also perform refractometer and pH tests of the coolant for you. ... We can provide any service you need at any level, from a simple test to cleaning out and refilling an entire shop with dozens of machines.”
Arenella also stresses the value of working with a distributor in choosing a coolant, which he describes as a complex purchasing decision. “We see MSC’s metalworking fluids as solving a problem for a customer. It’s about addressing the problem with a solution, not necessarily leading with a specific product or formula.”
Making a smart decision requires the consideration of many factors, and “often requires testing a product, which may require cleaning out your machine, and having a site survey team come in to make sure there’s an advantage in productivity or cost savings,” Arenella adds.
Reducing the total cost of ownership doesn’t necessarily mean sourcing the cheapest metalworking fluid for the job. Noting that coolant accounts for less than 1%—and probably under .05%—of the overall cost of a part, Arenella says any change in coolant has “a huge impact downstream on the total cost of ownership.”
Justin Geach, global director of marketing for Master Fluid Solutions, Perrysburg, Ohio, echoes the point: “Coolant is a very small percentage of a shop’s budget, but it’s the one thing in a facility that touches every operation, machine, tool, part, operator, etc. Next-generation metalworking fluids can significantly lower total cost of ownership.”
Spending an extra couple of hours cleaning a machine properly reduces the need to do it as often, Geach points out. “We have seen customers get only a few months of sump life with their standard procedure, but with proper education, effort and equipment they see well over a year.
“Chip conveyors and tool changes are often overlooked during machine cleaning,” he adds. “There can be a lot of sludge and contamination in the conveyor. And tool changers often have drains that go back into the coolant tank. Also, customers should clean screens, pump inlets, change filters, etc. They will also want to flush and thoroughly clean high-pressure systems if they have any.”
Running a rinse and using a proper machine sump cleaner are simple steps to improve coolant health. “A small amount of additional time to clean a machine properly can significantly extend coolant life, lowering costs and reducing fluid waste,” Geach says.
Thankfully, there are several options to automate the monitoring of a coolant condition. For example, Blaser Swisslube AG’s Liquidtool Manager tracks coolant temperature and concentration in real time, according to Chris Porsch, the U.S. national sales director for the Bern, Switzerland-based company. And, he says, Liquidtool stores data in the cloud for easy access on demand via a smartphone or PC.
Built by sister company Liquidtool Systems AG, the system includes the hardware sensor that goes into the coolant tank, plus the software that compiles and graphs the data. And the upper and lower limits for coolant concentration can be set to alert the user if the mix strays from the norm.
“The problem is, once that concentration gets too low, or the sump level goes down, all the normal calculations to keep your fluid at the proper level are out the door,” Porsch notes. While an expert could calculate a correction to such a mess, he explains, “no machine operator is going to go back there and try and guess how much fluids he’s lost, and then do a mathematical equation to put in the right amount of fluid to bring the concentration back to the ideal.”
It’s more likely the operator will follow standard operating procedures for topping off the fluid, and the problem will worsen. Conversely, Liquidtool Manager provides a warning without operators having to check. Blaser even has an autofill system coming soon, Porsch adds.
Meanwhile, Castrol’s SmartControl attaches to the sump and measures concentration, pH, temperature, flow rate and conductivity. Why conductivity? “Because if your conductivity starts increasing, but your concentration doesn’t, that indicates that foreign material is coming into the sump without being properly filtered out,” Morgan explains. “If it’s dramatically increasing, you need to check your filtration system.”
Acidity also plays an important role in corrosion protection. “For instance, if you’re machining cast iron, you should be running with a product that has a pH of 9.3 to 9.4 and a lot of reserve alkalinity for corrosion protection,” Morgan says.
SmartControl features alarms, self-calibration and even cleans itself. As with Liquidtool Manager, the Castrol tool stores and communicates the data it gathers, which Harrison says is particularly valued by quality control personnel at aerospace and automotive accounts. “If a quality issue ever pops up, they go in and pull all the data to check if the coolant was in proper condition, and therefore not a cause.”
But perhaps the most appreciated features of SmartControl is one of its simplest: It has the same red-yellow-green stack light used on machines throughout industry. “Management always makes the comment, ‘all I have do is glance over, and if I see a green light, I know I’m good to go,’” Morgan says. And if they don’t, it’s obvious they need to take action. “They’ll call us and ask what they need to do, and we can give them the proper adjustments to make to save their coolant,” Morgan continues. “If it had gone on for a few weeks, we probably would have to tell them they need to dump and recharge, with all the associated downtime costs and waste disposal problems.”
Blaser’s Vasco Skytec H 600 was created specifically for hard milling titanium “and those types of machining processes that require high lubricity to continue to ensure good tool life and good surface finish,” according to Porsch. The high lubricity allows for a consistent application of the coolant, he explains, which in turn yields a better surface finish. “And that’s what gives you longer tool life. Because the water cools, but the lubricity from the additive also allows for a reduced amount of heat being generated right off the bat.”
The coolant is suitable for both high-pressure delivery and high-pressure machining. The latter refers to the pressure put into the workpiece from a deep cut, which generates more heat. Skytec H 600 includes “extreme pressure additives,” Porsch adds. “The machining pressure will generate heat, and that will activate those ingredients within the fluid itself.”
Chemically, “it’s an ester base product, so it’s mineral oil free, and consists of plant-based synthetic materials,” explains Randy Templin, Blaser’s technical director for the Americas. That explains most of its performance characteristics, but “there are other proprietary additives that really make a difference.”
Blaser developed Skytec in part through extensive testing against the best titanium machining products recommended by customers and machine tool builders. Every test was conducted on identical material, using identical tooling from the same lot. “We gathered all the tool life data and then tried numerous formulations to see how we could exceed the best out there and we did so,” Templin says.
Makino subsequently conducted its own test, roughing titanium on a T2 machine (Vc 60 m/min; fz 0.18; ae 10 mm; ap 60 mm), and found that Vasco Skytec H 600 delivered 38.9% longer tool life than the coolant it previously considered the industry benchmark, according to Blaser. And even at that tool change, wear on the inserts was 16% less than what they experienced with the other coolant.
In another example, Porsch says a customer in Utah that used H 600 doubled its tool life over a “staunch competitor.” Plus, “the lack of foaming is exceptional, especially when it comes to high pressure. It’s also stable in the sump,” he says, noting this isn’t always the case with a high-lubricity coolant.
Templin agrees that customers have so far experienced good sump life with Vasco Skytec H 600, with no foul odors, though Blaser offer products that last longer, if that’s the requirement. Likewise, “if you machine a lot of aluminum, in addition to titanium and stainless steel, and tool life is important, but not the most important consideration, then our new B-Cool Skytec 500 would be a better product.”
B-Cool Skytec 500 performs “extremely well” with titanium, according to Templin, just not quite as good as H 600. “It’s more cost effective, especially for high-volume aluminum machining. The H 600 could do it, but from a price performance standpoint, you’re better off with Skytec 500. Also, the B-Cool Skytec 500 is ideal for recycling the coolant from the chips,” due to its superior microbial stability, according to the company.
The hot topic at Castrol is its XBB technology, in which XBB is shorthand for “excludes boron and biocides.” The latter has been used since the early days of metalworking fluids. Boron is added to enhance product stability, though it’s use is limited in Europe and often curtailed completely by some companies in the U.S.
Eliminating both chemicals is a “great improvement in health and safety,” Castrol asserts. And the company has developed unique chemistry to resist biological growth without them, Morgan says, while also providing “a good pH balance. XBB contains higher alkalinity and we can stabilize these formulas to make them last long in the sump.”
Aerospace companies have embraced XBB coolants as the best choice for many applications, Harrison says, even though they generally do not restrict the use of biocides or boron, focusing instead on achieving good throughput with difficult materials. “A leading OEM with one of the most stringent approval processes in aerospace, and their Tier-1 suppliers, have found success with Hysol SL 45 XBB, mainly running parts made with the harder nickel alloys and titanium. They found that its performance was better than anything (the manufacturer) had previously approved.”
Morgan adds that the wetting properties and low viscosity of Hysol SL 45 XBB enable it to flow easily into a hole, making it suitable for drilling as well as milling, turning, reaming, tapping, broaching and even grinding. It also covers a range of materials, spanning aluminum and titanium alloys, plus ferrous alloys. But there are eight variations on the XBB technology, and Harrison suggests that the Alusol XBB SL series, with “lots of aerospace approvals,” would perhaps be better.
Alusol XBB SL is designed to cling to the part long enough to be machined, then flows off. “That’s especially important with aluminum,” Morgan says. “If you don’t wet that surface properly, you get poor machining performance. So when we create aluminum machining fluids we take care to deliver the right surface tension to properly wet out on aluminum.”
At the same time, “this product, like a lot of the technology that we’ve built over the years, has extra detergency,” Morgan says. “The fluid doesn’t cling to the chips or the parts as much as other coolants, so it stays in your sump longer. That’s one of the reasons we sell a lot of the coolant, because it gives you a major reduction in usage. We have a lot of studies going against competition where customers report significant reductions in usage just by switching to our products.”
If it sounds like magic, it kind of is. So shops need to work with a broad-minded expert to pick the right mix for their needs.
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