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Less friction, more speed
December 3, 2001
7 Min Read
In motor sports, where fractions of a second can separate the winners from the losers, racers will take a bit of extra speed wherever they can find it. And one place to find it is in the sliding friction between the moving parts of the engine and driveline. "The guy who doesn't care about friction is the guy I want to race on Sunday," says Richard Maskin, whose company, Dart Machinery Ltd. (Troy, MI), builds drag racing engines. Reducing friction helps performance by increasing engine efficiency, freeing up horsepower that would otherwise go to waste. In drivelines, it can diminish rolling drag. And it can boost overall reliability by making all sorts of components last longer and avoid failure on the track. For these reasons, a growing number of engine and transmission builders have started to drive away friction with a tough, thin coating from Material Technologies Inc. (Rockford, IL).
Called MicroBlue(R), the coating consists of a modified tungsten disulphide compound applied in a high-velocity impingement process. Nothing too unusual there. But Material Technologies (MTI) has come up with a patent-pending way to match the surface profile of the substrate to the size of the tungsten disulphide platelets, enhancing the mechanical interlock between coating and substrate. According to MTI president Craig LeClaire, the resulting coating outperforms traditional friction-reducing coatings on several scores. "It's considerably more slippery than graphite, moly, or Teflon(R)," LeClaire says, citing the coefficient of friction as 0.30 when applied to surfaces of 15 RMS or better. And at less than one micron thick, MicroBlue doesn't cause any significant dimensional change in coated parts. Finally, this hardwearing coating holds up to point loads as high as 350,000 psi. "It won't chip, flake or peel like the other coatings," he says.
Sealing performance. In the engine, MicroBlue has mostly seen use in eliminating a design trade-off that affects the effectiveness of piston rings. Today's engine builders like to run thin top and compression rings-often around 0.042-inch thick-in order to minimize the sliding friction and inertia that result in drag between the rings and the cylinder lining. But the thinner the ring, the more it tends to flutter at high rpm, forcing builders to tighten up ring-groove clearances in order to avoid blowby of combustion gases into the crankcase. Make the clearances too tight, however, and the ring tends to microweld to the piston. Engine builders spend no small amount of time balancing engine performance against this possibility of microwelding. "It's a classic Catch-22," notes Todd Patterson, vice president of Patterson Racing (Wichita, KS) and driver of the company's NHRA trucks.
Thanks to its ability to cut friction, MicroBlue has reduced the chances for microwelding in even the thinnest grooves. Patterson reports that the coating helped him decrease groove clearances from 0.0012 to 0.0009 inch. "The piston guys recommend 0.0015 inch," he says. "But racers always want to push things to the edge." Maskin likewise says the coating has helped him close up the groove dimensions.
MicroBlue's thinness and wear resistance make it particularly well suited to piston ring applications. Together these two characteristics result in more predictable dimensioning of ring grooves than the moly or graphite coatings of the past, according to Maskin, who runs a coating operation at Dart Machinery. "All the other coatings added thickness-as much as 0.001 inch-so we'd have to juggle sizes." And coating wear would make the dimensional difficulties worse over time. "Before we started using the new coating, 0.0006 might open up to 0.0008 as the coating wore off," says Maskin. "Now when we cut 0.0006, it stays 0.0006," Maskin says.
Beyond easy sizing, the coating's real contribution shows up on the track. "Ring seal is all about power and acceleration," says Maskin, who explains the blowby allowed by a poor ring seal in essence robs energy from the crankshaft and lets it go to waste in the crankcase. In dyno testing, his coated piston rings have so far resulted in a 3 or 5 hp gain in a 500 cubic inch, 1,300 hp engine. "That may be less than a half percent, but I've worked for thirty years looking for pennies," he says. In vacuum tests, which indicate the engine's pumping efficiency and correlate well with power, the numbers have improved by 1-1.5 inches. "Coating the rings has been a big help," he says. And these gains may just be a starting point.
For his part, Patterson doesn't go so far as to attribute specific wins to the coating, but he does say it played a role in his victories over the course of this racing season. He's also seen the coating's effects on sealing efficiency during dyno and vacuum testing. "At high rpm, the horsepower has gone up at least a few percent," he says, pointing to a 20 hp gain in the 9,000 to 9,500 rpm range on a 358 cubic-inch, V8 engine that makes 950 hp at 9,300 rpm. And the vacuum numbers rose from 17 to 21 inches on the same engine. Speed wise, Patterson believes the coated pistons have helped him pick up two to three hundredths of a second over a 1,320-ft track, thanks to the power gain at high rpm.
Looking beyond piston rings, the use of MicroBlue inside the engine components remains in its infancy. "It could be used wherever you have metal-to-metal contact," Maskin says, citing engine bearings and oil pumps other components that could benefit from the coating. And LeClaire hints that his coating has already been applied to more than just piston rings. "We've done a lot more engine work than people realize," he says.
Drag down. MicroBlue's popularity is growing in racing drivelines. In these applications it addresses friction's contribution to rolling drag, according to Steve Eppard, a principal of SWE Racing Transmissions (Indianapolis, IN). "In auto racing the whole point is "come up with ways to make the car as free-rolling as possible," says Eppard, whose company supplies driveline components to 17 Indy teams and serves as a transmission consultant for three teams. A year ago, Eppard began using MicroBlue "everywhere there's metal to metal contact," including upright bearings, gears, hubs, dog rings, and forks.
Without dynamometer testing aimed solely at that coating's contribution, Eppard can't really say how much speed gain comes from MicroBlue. Anecdotally, his customers tell him they've realized improvements as large as 2 mph-improvement that Eppard attributes to the rolling drag reduction. Among those customers is Treadway Racing, whose team manager Skip Faul says he has seen some faster results after applying MicroBlue(R). What's more, he reports that "temperatures have come down a bit," indicating a possible gain in driveline efficiency. "Heat comes at the expense of horsepower," Eppard points out.
As with engine components, the coating's thinness and wear characteristics come into play on driveline components, and Eppard expects he'll tighten some dimensional tolerances. But in drivelines, the coating's big benefit has come from longevity. Critical parts are replaced on a stringent mileage schedule to avoid any catastrophic failures on the track. "With some of these parts, you can't have a failure at 225 mph or someone's going to hit the wall pretty hard," says Eppard. Coating the parts helps extend that schedule. Eppard estimates that coated parts last about 30% longer than uncoated ones on average. "Parts that went to 2,000 miles now go to 3,000," Eppard says. Some parts do even better. Drop gear, drop gear shaft and input shafts that had to be replaced every 700 miles untreated now go to 2,000 miles.
Whether used in driveline or engine components, friction reduction hasn't only paid off in terms of extra power or longevity. It's delivered these benefits in just the right way-without the need for major engine rework. As Patterson puts it, "The best improvements are the ones that don't require any mechanical changes."
Applications in the slow lane, too
So you don't build racing engines for a living? No matter, MicroBlue(r) has its roots in a variety of industrial friction-reduction applications. The coating got its start on DC-driven hydrostatic spindle assemblies for a major machine tool maker, where its contribution to friction reduction translated to a lower current draw and lower temperature rise, says MTI president Craig LeClaire. MicroBlue also recently served as an alternative to a hard chrome coating in a new hydraulic manifold. "It has glass-filled seals that are abrasive and have the nasty habit of galling and welding to the contact surfaces," he says. And MTI has lately been investigating the coating's influence on gear noise. MTI applies MicroBlue coating to a wide range of both ferrous and non-ferrous metals, including aluminum, tool steels, and ductile iron to name just a few. It also goes on engineering thermoplastics.
For more information about Friction-reducing coating from MTI: Enter 547
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