This section was edited by Associate Editor Alan S. Brown

DIAMONDLIKE PERFORMANCE

A SUPPLIER TO FORMULA 1 AND NASCAR RACERS, BEKAERT (SOREVI), HAS INSTALLED A MACHINE TO APPLY DIAMONDLIKE COATINGS TO RACING ENGINE PARTS AT ITS RESEARCH TRIANGLE PARK, N.C., FACILITY. The company has been supplying racing teams with coatings for tappets and other valvetrain components for years. Now, it is shooting for a more difficult target: aluminum pistons.

Diamondlike coatings are thin, 0.002 to 0.004 millimeter, chemically similar to diamond (but with added hydrogen), and with similar properties. Like diamonds, they rank among the hardest and most lubricious of materials. When applied to a valvetrain, the coating’s low coefficient of friction lets racers run at higher revs for more power while the hardness protects engine components from wear.

Pistons are the next frontier. Especially under the high loads found in racing, pistons tend to tilt and rub against their cylinders. The resulting friction robs power. Rubbing also erodes soft aluminum, degrading piston efficiency and shortening lifespan.

Aluminum pistons are prone to wear, but hard diamondlike
coatings can protect their surface while reducing sliding friction.

Diamondlike coatings attack both problems, but they are not easy to apply. They are usually deposited by breaking down a mist of hydrocarbons at high temperatures (close to 2,000°C) under vacuum. This is hot enough to melt aluminum. Now, Bekaert says it has a system that can apply the coating at less than 200°C.

To apply the coating, Bekaert had to redesign the typical aluminum piston, which has a rough finish to entrain oil (to reduce friction) as it moves. It takes a very flat surface, however, to accept diamondlike coatings. Machining a smoother surface is relatively simple, and it turns out that diamondlike-coated pistons generate so little friction, they do not need to entrain much oil for smooth operation.

Coating very soft aluminum with much harder diamondlike coatings is like putting a plywood sheet over a box spring mattress. Hit the plywood enough and it will eventually pop off the mattress. On the piston, repeated bumps against the cylinder wall will cause the coating to flake and fail. Bekaert solves the problem by applying a layer of intermediate hardness between the aluminum and diamondlike coating to cushion the transition.

In addition to pistons, Bekaert coats piston pins (eliminating the need for bushings), valves, and suspension components. It also applies diamondlike coatings to such high-volume automotive parts as valvetrain tappets and diesel injection components. Nonautomotive applications include coats for optical disc molds, plastic molds, electronics, and textile machinery parts.

KEEPING THE LEAD IN

When Edward Buiel discusses rechargeable lead-acid batteries, he speaks with the passion of a convert. Buiel is vice president and chief technical officer of Axion Power International Inc. in New Castle, Pa. After 12 years of developing large-scale lithium-ion batteries for electric cars, he thinks he has an alternative: a high-tech version of the car’s lead-acid battery. It charges faster than other lead-acid batteries and costs a quarter of the price of a comparable lithium-ion battery.

Lithium-ion batteries are the dominant power source for cell phones, laptops, and portable electronics. The problem comes when scaling them up to run a car for 50 to 90 miles on a single charge. “The battery materials have very high energy densities, pretty close to TNT, and they are very unstable,” Buiel said. “If they are exposed to air or heat, they can go into a spontaneous exothermic reaction and explode. You can make them safer, but that makes them less efficient.”

Fast-recharging lead-acid batteries may power electric vehicles.

Buiel pointed out that lithium-ion batteries are also expensive, about $800 to $1,000 per kilowatt-hour. That puts the cost of a 20 kilowatt-hour battery, large enough to drive an electric car 50 to 90 miles, at $16,000 to $20,000. “That’s why the Chevrolet Volt electric car costs $40,000,” he said. “But not every American can afford that.” A similarly sized lead-acid battery would cost $4,000, or $200 per kilowatt-hour.

The Volt, a plug-in electric hybrid, runs on lithium-ion batteries with a range of 40 miles on a charge. The car has a one-liter engine that runs a generator to power the vehicle beyond that. Comments published in 2008 said the Volt is expected to have a list price of at least $35,000 when it becomes available later this year. (General Motors was shut down when we called to confirm. A security officer who answered the phone said the company would not reopen until February.)

In the past, fast recharges were a stumbling block for lead-acid batteries, because they produce electricity by a chemical reaction that forms hydrogen sulfide on the negative electrode. The coating causes the electrode to fail, especially when recharged at high currents. It also causes swings in acidity that shorten battery life. Axion avoids the problem by making its negative electrode from activated carbon, a porous material used in ultracapacitors. The electrode absorbs and releases protons from the battery electrolyte without a chemical reaction.

This not only prolongs electrode life, but enables the batteries to charge four times faster than typical car batteries. Lead-capacitor batteries don’t have the energy density of their lithium-ion cousins, but they discharge more of the energy they store and survive more charge/discharge cycles.

The world already has an infrastructure to mine lead, manufacture lead-acid batteries, and reclaim and recycle lead from spent batteries, Buiel said. It would be relatively easy to sell improved products into the $330 billion global market for lead-acid batteries.

Axion has converted one pickup truck into a dual-mode vehicle that uses a 40-kilowatt electric motor for the front transaxle and a truck’s internal combustion engine for the rear axle. “The battery gives it a 50-mile range, and if you need to tow something, you turn the internal combustion engine on,” Buiel said. He estimated that he could produce a kit to convert pickups to battery power for less than $10,000.

The company recently received a $1.2 million grant to develop lightweight batteries for U.S. Marine Corps vehicles. “They’re not that interested in hybrids, but like that our batteries work in very cold weather,” Buiel said.

Axion can expect competition from Furukawa Battery of Yokohama, Japan, which is making a similar battery under a license from Australia’s Commonwealth Scientific and Industrial Research Organization. However, Buiel said that Axion holds the key patents on its technology.

BEARINGS FOR BACK PAIN

AT SOME POINT, 80 PERCENT OF ALL PEOPLE WILL IDENTIFY BACK PAIN AS A SERIOUS PROBLEM. For those with back pain caused by a compressive injury of the spine, one approach to relief is spinal decompression, and at least one provider uses precision ball bearings to bring comfort.

In the past, physicians used traction to alleviate pain associated with herniated and bulging discs, facet joint pain, and sciatica. This involved attaching limbs to weights and stretching patients for prolonged periods of time (think days at a time). Decompression uses a regimen of 20 to 30 half-hour treatments to stretch the spine, reducing pressure so that discs, joints, and muscles can heal.

The DRX9000 from Axiom Worldwide of Tampa, Fla., is a decompression system that consists of a two-part mattress: a top half that holds the upper body in a stationary position and a bottom half that moves up to 3.5 inches to stretch the lower body.

“One major advantage of our device is that we utilize steel bearing and shafting technology in our floating lower mattress,” said Scot Johnson, engineering director for Axiom. Some competitive decompression systems use a similar two-part design that moves on plastic or composite slides, which can slip or stick.

The DRX9000’s lower mattress floats on linear bearings with precision ground shafts. In addition, each bearing’s load plate is precision-ground rather than stamped and checked for consistency when it is manufactured. The load plates have ends that are thinner than their centers, making the center a fulcrum for self-alignment. Because wiper seals on the bearings are floating, they don’t restrict self-alignment and the floating load plate adjusts the clearance automatically.

NB Corp. of Hanover Park, Ill., developed the bearings, which it calls its Topball line. Axiom uses both the single and double-wide block-housed Topball bearings identified as TWA 12 UU.

According to Johnson, a recent prospective pilot study showed that a regimen of 20 28-minute treatments spread over six weeks on the DRX system reduced back pain for 89 percent of patients. “For a lot of people, that is the difference between forced immobility and being able to walk again,” he said. 

WINDMILL MAINTENANCE ISSUES

The growth of wind energy—about 30 percent per year since 2005—is well documented. Less well known are wind’s maintenance headaches. Wind turbines are big, complex mechanical systems. A typical 3 megawatt unit’s gearbox can weigh up to 15 tons. Its blades, each one-third as long as a city block, make it taller than the Statue of Liberty. A technician making a maintenance call cannot just disassemble parts and lay them out on the floor.

Wind components also operate under demanding conditions. The gearbox must convert rotor speeds of 20 to 25 rpm into 1,200 to 1,800 rpm to drive the generator. It must do this while subject to enormous stress as winds gust and change direction. Even routine maintenance is trying, and it is easy to miss problems until they become serious.

As a result, according to SKF Group’s national wind energy accounts manager, Kevin George, “We don’t have large turbines running 20 years without a problem. We’re getting gearbox failures in five years, and generator failures in three years.” The cost of system failure is high. Just renting a crane to replace a generator or gearbox can cost $250,000. So repair cost degrades wind’s ability to compete with other power sources.

SKF, which makes bearings, seals, and lubrication and predictive maintenance systems, sees this as an opportunity to upgrade turbine components and develop new designs with inherently better reliability.

Ceramic balls prevent arcing from degrading grease in wind turbine bearing raceways.

According to George, wind produces variable speeds, sudden stops and starts, and sometimes extreme loads that lead to transient misalignments that reduce gearbox life. SKF has developed a high-capacity cylindrical roller bearing that uses a low-friction cage to eliminate roller-to-roller contact found in the full complement bearings ordinarily used in gearboxes. “This provides more load capacity in the same envelope,” George said.

The variable speed drives used with generators sometimes create arcing, which degrades grease and bearing raceways, and leads to misalignment. SKF’s solution is a larger version of the hybrid deep groove ball bearing that it pioneered for smaller motors. The bearing uses silicon nitride ceramic balls, which do not conduct electricity. This keeps electrical discharges out of the raceway. Silicon nitride is lighter than steel, which reduces rolling mass, and it tests three to five times as hard as steel, which improves lifespan.

SKF has also developed an automated lubricating system to serve the entire turbine. It is not simple because the hub, mainshaft, yaw bearing, mainbox, and other components all require different grease formulations. In addition, SKF has released its third version of a remote condition monitoring system that identifies potential problems so engineers can plan maintenance. That helps utilities address more than one issue at a time, so they can reduce labor and crane rental costs.

The company says its new Nautilus double-row tapered roller bearing is designed for heavy, complex radial and axial loads. Vestas Wind Systems A/S, one of the world’s top turbine manufacturers, has used it to connect the gearbox directly to the hub and eliminate the entire mainshaft in its new V-90 turbine. The result is a significantly smaller and lighter wind turbine with no sacrifice in capacity.