More Metals Keep Quiet

Farmington Hills, MI-The engineers at Material Sciences Corp. have been busy lately. They have already chalked up some success with Quiet Steel(TM) and Sound Trap(TM), increasingly popular sheet metal composites used to control noise, vibration, and harshness (NVH) in automotive and industrial applications. Now they're putting the finishing touches on three kinds of new noise-fighting material systems. One offers an entirely new way to apply Quiet Steel technology. Another allows it to work in higher temperature environments. And the third will combine the technology with alternatives to conventional automotive steels.

All the new materials build on MSC's core technology for creating constrained-layer damping composites from laminations of sheet metal and various core materials that provide the damping. Matt Murphy, MSC's strategic accounts manager, points out that MSC tunes its composites to specific applications. The number and thickness of the layers can vary, depending on the application's structural, thermal, and frequency-response requirements. So can the type of core material. The company currently draws from more than 75 different cores-usually viscoelastic materials such as acrylics or silicones but occasionally other organic materials, wovens, or fibers. "There is a long list of materials we can work with," says Mark Gresser, MSC's automotive director.

Add-on damping

And that list now includes magnets. The newest material from the company is a line of magnetic NVH products that stick to ferrous metal surfaces. Called MagnaDamp(TM), it can help silence metal products that don't otherwise incorporate Quiet Steel. And it does so without the use of pressure-sensitive adhesives used in some of the company's earlier add-on products. As with its other composites, MSC tailors the magnetic, damping, and sheet metal layers to different applications. One early product, for example, surrounds the viscoelastic core with one thin layer of cold rolled stainless and another of flexible magnetic sheet.

As far as NVH performance goes, MagnaDamp won't likely be quite as efficient as Quiet Steel. Part of that shortfall has to do with limited coverage of an applied material compared to components made entirely from Quiet Steel. "There will usually be some surfaces you wouldn't be able to cover with a magnet," says Gresser. What's more, he adds, the flexible magnetic product inherently lacks some of Quiet Steel's stiffness-and loss of stiffness translates to diminished NVH performance.

Still, MagnaDamp doesn't really compete against Quiet Steel as much as against other applied NVH treatments-what Gresser collectively calls "soft stuff." And here it may have an edge. "MagnaDamp isn't as efficient as Quiet Steel, but it provides much better damping than peel-and-stick mastics," Gresser claims (see chart). And at thicknesses down to 1.25 mm, MagnaDamp saves packaging space compared to thicker add-on damping materials.

MagnaDamp probably won't see much use in automotive applications, but there are plenty of industrial and consumer product applications where it could make a difference. Gresser says noisy office furniture might be a good fit for the technology. Put it on a metal file cabinet, for instance, and drawer rattling weakens. "It also makes a lot of sense for appliance applications," he says.

More heat

MSC has also been working to develop higher temperature damping materials for use as brake shims. The company has years of experience when it comes to controlling brake noise in cars. Yet a 350C maximum temperature has kept Quiet Steel out of the hottest brake systems, such as those found on heavy-duty trucks and buses. "Have you ever heard a school bus that didn't have noisy brakes?" Gresser asks. The answer may soon be a resounding "yes." A new Quiet Steel product slated for release this month bumps the maximum temperature up to 400C, while another developmental material system is targeted at maximum temperatures up to 450C.

Alternative metals

Though it got its start in brake insulators and then moved into powertrain components, MSC has over the past few years seen more activity in automotive body structures. The Ford F-150, for example, has been a well-publicized example in which Quiet Steel went into the dash to combat noise radiating through the firewall. New Cadillac vehicles incorporate Quiet Steel in their dashes too. More recently, DaimlerChrysler employed Quiet Steel for the tubs that form part of the floor and hold flat-folding rear seats in 2005 Chrysler mini-vans. "We had never done a floor before," Murphy says. The seat tubs are also remarkable for their size. Formed from a blank measuring more than 60 x 60 inches, the roughly foot-deep tub "is the largest we've done when you consider its size and draw depth together," Murphy says. He adds that Quiet Steel got the nod from Chrysler in this application not just because of its damping performance but also because it took up far less packaging space and weighed less than spray on damping solutions.

To support these structural applications, MSC has started working with some of the same kinds of alternative metals that the auto industry has begun to adopt. Gresser says the company has done some initial work with Advanced High Strength Steels, such as the DP and TRIP steels. To take a recent example, the company participated in developing a roof panel that would fight road-and rain-noise. Because of its position on the vehicle, this panel uses Quiet Steel made from high-strength, dent-resistant steel (DR-210).

Not all of the company's efforts for alternative materials involve steel at all. MSC has applied its damping technology to 5000 Series aluminum. Gresser says these new Quiet Aluminum(TM) products are already under consideration for an upcoming aluminum bodied vehicle and will be commercially available later this year.